Yocto Project Development Manual

Scott Rifenbark

Scotty's Documentation Services, Inc.

Permission is granted to copy, distribute and/or modify this document under the terms of the Creative Commons Attribution-Share Alike 2.0 UK: England & Wales as published by Creative Commons.

Manual Notes

Revision History
Revision 1.16 October 2011
The initial document released with the Yocto Project 1.1 Release.
Revision 1.2April 2012
Released with the Yocto Project 1.2 Release.
Revision 1.3October 2012
Released with the Yocto Project 1.3 Release.
Revision 1.4April 2013
Released with the Yocto Project 1.4 Release.
Revision 1.5October 2013
Released with the Yocto Project 1.5 Release.
Revision 1.5.1January 2014
Released with the Yocto Project 1.5.1 Release.
Revision 1.6April 2014
Released with the Yocto Project 1.6 Release.
Revision 1.7October 2014
Released with the Yocto Project 1.7 Release.
Revision 1.8April 2015
Released with the Yocto Project 1.8 Release.
Revision 2.0October 2015
Released with the Yocto Project 2.0 Release.
Revision 2.1April 2016
Released with the Yocto Project 2.1 Release.
Revision 2.2October 2016
Released with the Yocto Project 2.2 Release.
Revision 2.3May 2017
Released with the Yocto Project 2.3 Release.
Revision 2.4Usually October
Released with the Yocto Project 2.4 Release.

Table of Contents

1. The Yocto Project Development Manual
1.1. Welcome
1.2. Other Information
2. Getting Started with the Yocto Project
2.1. Setting Up the Development Host to Use the Yocto Project
2.1.1. Setting Up a Native Linux Host
2.1.2. Setting Up to Use CROss PlatformS (CROPS)
2.2. Working With Yocto Project Source Files
2.2.1. Accessing Source Repositories
2.2.2. Accessing Index of Releases
2.2.3. Using the Downloads Page
2.2.4. Cloning the poky Repository
2.2.5. Checking Out by Branch in Poky
2.2.6. Checking Out by Tag in Poky
2.3. Performing a Simple Build
3. The Yocto Project Open Source Development Environment
3.1. Setting Up a Team Yocto Project Development Environment
3.2. Submitting a Defect Against the Yocto Project
3.3. Submitting a Change to the Yocto Project
3.3.1. Using Scripts to Push a Change Upstream and Request a Pull
3.3.2. Using Email to Submit a Patch
4. Common Tasks
4.1. Understanding and Creating Layers
4.1.1. Layers
4.1.2. Creating Your Own Layer
4.1.3. Following Best Practices When Creating Layers
4.1.4. Making Sure Your Layer is Compatible With Yocto Project
4.1.5. Enabling Your Layer
4.1.6. Using .bbappend Files in Your Layer
4.1.7. Prioritizing Your Layer
4.1.8. Managing Layers
4.1.9. Creating a General Layer Using the yocto-layer Script
4.2. Customizing Images
4.2.1. Customizing Images Using local.conf
4.2.2. Customizing Images Using Custom IMAGE_FEATURES and EXTRA_IMAGE_FEATURES
4.2.3. Customizing Images Using Custom .bb Files
4.2.4. Customizing Images Using Custom Package Groups
4.2.5. Customizing an Image Hostname
4.3. Writing a New Recipe
4.3.1. Overview
4.3.2. Locate or Automatically Create a Base Recipe
4.3.3. Storing and Naming the Recipe
4.3.4. Running a Build on the Recipe
4.3.5. Fetching Code
4.3.6. Unpacking Code
4.3.7. Patching Code
4.3.8. Licensing
4.3.9. Dependencies
4.3.10. Configuring the Recipe
4.3.11. Using Headers to Interface with Devices
4.3.12. Compilation
4.3.13. Installing
4.3.14. Enabling System Services
4.3.15. Packaging
4.3.16. Sharing Files Between Recipes
4.3.17. Properly Versioning Pre-Release Recipes
4.3.18. Post-Installation Scripts
4.3.19. Testing
4.3.20. Examples
4.3.21. Following Recipe Style Guidelines
4.4. Adding a New Machine
4.4.1. Adding the Machine Configuration File
4.4.2. Adding a Kernel for the Machine
4.4.3. Adding a Formfactor Configuration File
4.5. Finding Temporary Source Code
4.6. Using Quilt in Your Workflow
4.7. Using a Development Shell
4.8. Using a Development Python Shell
4.9. Building Targets with Multiple Configurations
4.10. Working With Libraries
4.10.1. Including Static Library Files
4.10.2. Combining Multiple Versions of Library Files into One Image
4.10.3. Installing Multiple Versions of the Same Library
4.11. Enabling GObject Introspection Support
4.11.1. Enabling the Generation of Introspection Data
4.11.2. Disabling the Generation of Introspection Data
4.11.3. Testing that Introspection Works in an Image
4.11.4. Known Issues
4.12. Optionally Using an External Toolchain
4.13. Creating Partitioned Images
4.13.1. Creating Partitioned Images
4.13.2. Using OpenEmbedded Image Creator Wic to Generate Partitioned Images
4.14. Building an Initial RAM Filesystem (initramfs) Image
4.15. Flashing Images Using bmaptool
4.16. Making Images More Secure
4.16.1. General Considerations
4.16.2. Security Flags
4.16.3. Considerations Specific to the OpenEmbedded Build System
4.16.4. Tools for Hardening Your Image
4.17. Creating Your Own Distribution
4.18. Creating a Custom Template Configuration Directory
4.19. Building a Tiny System
4.19.1. Overview
4.19.2. Goals and Guiding Principles
4.19.3. Understand What Contributes to Your Image Size
4.19.4. Trim the Root Filesystem
4.19.5. Trim the Kernel
4.19.6. Remove Package Management Requirements
4.19.7. Look for Other Ways to Minimize Size
4.19.8. Iterate on the Process
4.20. Building Images for More than One Machine
4.21. Working with Packages
4.21.1. Excluding Packages from an Image
4.21.2. Incrementing a Package Version
4.21.3. Handling Optional Module Packaging
4.21.4. Using Runtime Package Management
4.21.5. Generating and Using Signed Packages
4.21.6. Testing Packages With ptest
4.22. Working with Source Files
4.22.1. Setting up Effective Mirrors
4.22.2. Getting Source Files and Suppressing the Build
4.23. Building Software from an External Source
4.24. Selecting an Initialization Manager
4.24.1. Using systemd Exclusively
4.24.2. Using systemd for the Main Image and Using SysVinit for the Rescue Image
4.25. Selecting a Device Manager
4.25.1. Using Persistent and Pre-Populated/dev
4.25.2. Using devtmpfs and a Device Manager
4.26. Using an External SCM
4.27. Creating a Read-Only Root Filesystem
4.27.1. Creating the Root Filesystem
4.27.2. Post-Installation Scripts
4.27.3. Areas With Write Access
4.28. Performing Automated Runtime Testing
4.28.1. Enabling Tests
4.28.2. Running Tests
4.28.3. Exporting Tests
4.28.4. Writing New Tests
4.28.5. Installing Packages in the DUT Without the Package Manager
4.29. Debugging With the GNU Project Debugger (GDB) Remotely
4.30. Debugging with the GNU Project Debugger (GDB) on the Target
4.31. Debugging Parallel Make Races
4.31.1. The Failure
4.31.2. Reproducing the Error
4.31.3. Creating a Patch for the Fix
4.31.4. Testing the Build
4.32. Maintaining Open Source License Compliance During Your Product's Lifecycle
4.32.1. Providing the Source Code
4.32.2. Providing License Text
4.32.3. Providing Compilation Scripts and Source Code Modifications
4.33. Using the Error Reporting Tool
4.33.1. Enabling and Using the Tool
4.33.2. Disabling the Tool
4.33.3. Setting Up Your Own Error Reporting Server
5. Using the Quick EMUlator (QEMU)
5.1. Running QEMU
5.2. Switching Between Consoles
5.3. Removing the Splash Screen
5.4. Disabling the Cursor Grab
5.5. Running Under a Network File System (NFS) Server

Chapter 1. The Yocto Project Development Manual

1.1. Welcome

Welcome to the Yocto Project Development Manual! This manual provides relevant procedures necessary for developing in the Yocto Project environment (i.e. developing embedded Linux images and user-space applications that run on targeted devices). The manual groups related procedures into higher-level sections. Procedures can consist of high-level steps or low-level steps depending on the topic. You can find conceptual information related to a procedure by following appropriate links to the Yocto Project Reference Manual.

The following list describes what you can get from this manual:

  • Setup Procedures: Procedures that show you how to set up a Yocto Project Development environment and how to accomplish the change workflow through logging defects and submitting changes.

  • Emulation Procedures: Procedures that show you how to use the Yocto Project integrated QuickEMUlator (QEMU), which lets you simulate running on hardware an image you have built using the OpenEmbedded build system.

  • Common Procedures: Procedures related to "everyday" tasks you perform while developing images and applications using the Yocto Project.

This manual will not give you the following:

  • Redundant Step-by-step Instructions: For example, the Yocto Project Software Development Kit (SDK) Developer's Guide contains detailed instructions on how to install an SDK, which is used to develop applications for target hardware.

  • Reference or Conceptual Material: This type of material resides in an appropriate reference manual. For example, system variables are documented in the Yocto Project Reference Manual.

  • Detailed Public Information Not Specific to the Yocto Project: For example, exhaustive information on how to use the Source Control Manager Git is better covered with Internet searches and official Git Documentation than through the Yocto Project documentation.

1.2. Other Information

Because this manual presents information for many different topics, supplemental information is recommended for full comprehension. For introductory information on the Yocto Project, see the Yocto Project Backgrounders on the Yocto Project Website. You can find an introductory to using the Yocto Project by working through the Yocto Project Quick Start.

For a comprehensive list of links and other documentation, see the "Links and Related Documentation" section in the Yocto Project Reference Manual.

Chapter 2. Getting Started with the Yocto Project

This chapter provides procedures related to getting set up to use the Yocto Project. For a more front-to-end process that takes you from minimally preparing a build host through building an image, see the Yocto Project Quick Start.

2.1. Setting Up the Development Host to Use the Yocto Project

This section provides procedures to set up your development host to use the Yocto Project. You can use the Yocto Project on a native Linux development host or you can use CROPS, which leverages Docker Containers, to prepare any Linux, Mac, or Windows development host.

Once your development host is set up to use the Yocto Project, further steps are necessary depending on what you want to accomplish. See the following references for information on how to prepare for Board Support Package (BSP) development, kernel development, and development using the Eclipse™ IDE:

2.1.1. Setting Up a Native Linux Host

Follow these steps to prepare a native Linux machine as your Yocto Project development host:

  1. Use a Supported Linux Distribution: You should have a reasonably current Linux-based host system. You will have the best results with a recent release of Fedora, openSUSE, Debian, Ubuntu, or CentOS as these releases are frequently tested against the Yocto Project and officially supported. For a list of the distributions under validation and their status, see the "Supported Linux Distributions" section in the Yocto Project Reference Manual and the wiki page at Distribution Support.

  2. Have Enough Free Memory: You should have at least 50 Gbytes of free disk space for building images.

  3. Meet Minimal Version Requirements: The OpenEmbedded build system should be able to run on any modern distribution that has the following versions for Git, tar, and Python.

    • Git 1.8.3.1 or greater

    • tar 1.27 or greater

    • Python 3.4.0 or greater.

    If your build host does not meet any of these three listed version requirements, you can take steps to prepare the system so that you can still use the Yocto Project. See the "Required Git, tar, and Python Versions" section in the Yocto Project Reference Manual for information.

  4. Install Development Host Packages: Required development host packages vary depending on your build machine and what you want to do with the Yocto Project. Collectively, the number of required packages is large if you want to be able to cover all cases.

    For lists of required packages for all scenarios, see the "Required Packages for the Host Development System" section in the Yocto Project Reference Manual.

Once you have completed the previous steps, you are ready to continue using a given development path on your native Linux machine. If you are going to use BitBake, see the "Cloning the poky Repository" section. If you are going to use the Extensible SDK, see the "Using the Extensible SDK" Chapter in the Yocto Project Software Development Kit (SDK) Developer's Guide. If you want to work on the kernel, see the Yocto Project Linux Kernel Development Manual. If you are going to use Toaster, see the "Setting Up and Using Toaster" section in the Toaster User Manual.

2.1.2. Setting Up to Use CROss PlatformS (CROPS)

With CROPS, which leverages Docker Containers, you can create a Yocto Project development environment that is operating system agnostic. You can set up a container in which you can develop using the Yocto Project on a Windows, Mac, or Linux machine.

Follow these general steps to prepare a Windows, Mac, or Linux machine as your Yocto Project development host:

  1. Go to the Docker Installation Site: Docker is a software container platform that you need to install on the host development machine. To start the installation process, see the Docker Installation site.

  2. Choose Your Docker Edition: Docker comes in several editions. For the Yocto Project, the stable community edition (i.e. "Docker CE Stable") is adequate. You can learn more about the Docker editions from the site.

  3. Go the Install Site for Your Platform: Click the link for the Docker edition associated with your development host machine's native software. For example, if your machine is running Microsoft Windows Version 10 and you want the Docker CE Stable edition, click that link under "Supported Platforms".

  4. Understand What You Need: The install page has pre-requisites your machine must meet. Be sure you read through this page and make sure your machine meets the requirements to run Docker. If your machine does not meet the requirements, the page has instructions to handle exceptions. For example, to run Docker on Windows 10, you must have the pro version of the operating system. If you have the home version, you need to install the Docker Toolbox.

    Another example is that a Windows machine needs to have Microsoft Hyper-V. If you have a legacy version of the the Microsoft operating system or for any other reason you do not have Microsoft Hyper-V, you would have to enter the BIOS and enable virtualization.

  5. Install the Software: Once you have understood all the pre-requisites, you can download and install the appropriate software. Follow the instructions for your specific machine and the type of the software you need to install.

  6. Optionally Orient Yourself With Dockers: If you are unfamiliar with Dockers and the container concept, you can learn more here - https://docs.docker.com/get-started/. You should be able to launch Docker or the Docker Toolbox and have a terminal shell on your development host.

  7. Set Up the Containers to Use the Yocto Project: Go to https://github.com/crops/docker-win-mac-docs/wiki and follow the directions for your particular development host (i.e. Linux, Mac, or Windows).

    Once you complete the setup instructions for your machine, you have the Poky, Extensible SDK, and Toaster containers available. You can click those links from the page and learn more about using each of those containers.

Once you have a container set up, everything is in place to develop just as if you were running on a native Linux machine. If you are going to use the Poky container, see the "Cloning the poky Repository" section. If you are going to use the Extensible SDK container, see the "Using the Extensible SDK" Chapter in the Yocto Project Software Development Kit (SDK) Developer's Guide. If you are going to use the Toaster container, see the "Setting Up and Using Toaster" section in the Toaster User Manual.

2.2. Working With Yocto Project Source Files

This section contains procedures related to locating and securing Yocto Project files. You establish and use these local files to work on projects.

Notes

  • For concepts and introductory information about Git as it is used in the Yocto Project, see the "Git" section in the Yocto Project Reference Manual.

  • For concepts on Yocto Project source repositories, see the "Yocto Project Source Repositories" section in the Yocto Project Reference Manual."

2.2.1. Accessing Source Repositories

Yocto Project maintains upstream Git Source Repositories that you can examine and access using a browser-based UI:

  1. Access Repositories: Open a browser and go to http://git.yoctoproject.org to access the GUI-based interface into the Yocto Project source repositories.

  2. Select a Repository: Click on any repository in which you are interested (e.g. poky).

  3. Find the URL Used to Clone the Repository: At the bottom of the page, note the URL used to clone that repository (e.g. http://git.yoctoproject.org/poky).

  4. Examine Change History of the Repository: At the top of the page, click on any branch in which you might be interested (e.g. rocko). You can then view the commit log or tree view for that development branch.

2.2.2. Accessing Index of Releases

Yocto Project maintains an Index of Releases area that contains related files that contribute to the Yocto Project. Rather than Git repositories, these files represent snapshot tarballs.

Tip

The recommended method for accessing Yocto Project components is to use Git to clone a repository and work from within that local repository. The procedure in this section exists should you desire a tarball snapshot of any given component.

  1. Access the Index of Releases: Open a browser and go to http://downloads.yoctoproject.org/releases to access the Index of Releases. The list represents released components (e.g. eclipse-plugin, sato, and so on).

    Note

    The yocto directory contains the full array of released Poky tarballs. The poky directory in the Index of Releases was historically used for very early releases and exists for retroactive completeness only.

  2. Select a Component: Click on any released component in which you are interested (e.g. yocto).

  3. Find the Tarball: Drill down to find the associated tarball. For example, click on yocto-2.4 to view files associated with the Yocto Project 2.4 release (e.g. poky-rocko-19.0.0.tar.bz2, which is the released Poky tarball).

  4. Download the Tarball: Click a tarball to download and save a snapshot of a given component.

2.2.3. Using the Downloads Page

The Yocto Project Website uses a "Downloads" area from which you can locate and download tarballs of any Yocto Project release. Rather than Git repositories, these files represent snapshot tarballs.

Tip

The recommended method for accessing Yocto Project components is to use Git to clone a repository and work from within that local repository. The procedure in this section exists should you desire a tarball snapshot of any given component.

  1. Go to the Yocto Project Website: Open The Yocto Project Website in your browser.

  2. Get to the Downloads Area: Click the "Downloads" tab.

  3. Select the Type of Files: Click the type of files you want (i.e "Build System", "Tools", or "Board Support Packages (BSPs)".

  4. Locate and Download the Tarball: From the list of releases, locate the appropriate download link and download the files.

2.2.4. Cloning the poky Repository

To use the Yocto Project, you need a release of the Yocto Project locally installed on your development system. The locally installed set of files is referred to as the Source Directory in the Yocto Project documentation.

You create your Source Directory by using Git to clone a local copy of the upstream poky repository.

Tip

The preferred method of getting the Yocto Project Source Directory set up is to clone the repository.

Working from a copy of the upstream repository allows you to contribute back into the Yocto Project or simply work with the latest software on a development branch. Because Git maintains and creates an upstream repository with a complete history of changes and you are working with a local clone of that repository, you have access to all the Yocto Project development branches and tag names used in the upstream repository.

Follow these steps to create a local version of the upstream poky Git repository.

  1. Set Your Directory: Be in the directory where you want to create your local copy of poky.

  2. Clone the Repository: The following command clones the repository and uses the default name "poky" for your local repository:

         $ git clone git://git.yoctoproject.org/poky
         Cloning into 'poky'...
         remote: Counting objects: 367178, done.
         remote: Compressing objects: 100% (88161/88161), done.
         remote: Total 367178 (delta 272761), reused 366942 (delta 272525)
         Receiving objects: 100% (367178/367178), 133.26 MiB | 6.40 MiB/s, done.
         Resolving deltas: 100% (272761/272761), done.
         Checking connectivity... done.
                        

    Unless you specify a specific development branch or tag name, Git clones the "master" branch, which results in a snapshot of the latest development changes for "master". For information on how to check out a specific development branch or on how to check out a local branch based on a tag name, see the "Checking Out By Branch in Poky" and Checking Out By Tag in Poky", respectively.

    Once the repository is created, you can change to that directory and check its status. Here, the single "master" branch exists on your system and by default, it is checked out:

         $ cd ~/poky
         $ git status
         On branch master
         Your branch is up-to-date with 'origin/master'.
         nothing to commit, working directory clean
         $ git branch
         * master
                        

    Your local repository of poky is identical to the upstream poky repository at the time from which it was cloned.

2.2.5. Checking Out by Branch in Poky

When you clone the upstream poky repository, you have access to all its development branches. Each development branch in a repository is unique as it forks off the "master" branch. To see and use the files of a particular development branch locally, you need to know the branch name and then specifically check out that development branch.

Note

Checking out an active development branch by branch name gives you a snapshot of that particular branch at the time you check it out. Further development on top of the branch that occurs after check it out can occur.

  1. Switch to the Poky Directory: If you have a local poky Git repository, switch to that directory. If you do not have the local copy of poky, see the "Cloning the poky Repository" section.

  2. Determine Existing Branch Names:

         $ git branch -a
         * master
           remotes/origin/1.1_M1
           remotes/origin/1.1_M2
           remotes/origin/1.1_M3
           remotes/origin/1.1_M4
           remotes/origin/1.2_M1
           remotes/origin/1.2_M2
           remotes/origin/1.2_M3
               .
               .
               .
           remotes/origin/master-next
           remotes/origin/master-next2
           remotes/origin/morty
           remotes/origin/pinky
           remotes/origin/purple
           remotes/origin/pyro
           remotes/origin/rocko
                        

  3. Checkout the Branch: Checkout the development branch in which you want to work. For example, to access the files for the Yocto Project 2.4 Release (Rocko), use the following command:

         $ git checkout -b rocko origin/rocko
         Branch rocko set up to track remote branch rocko from origin.
         Switched to a new branch 'rocko'
                        

    The previous command checks out the "rocko" development branch and reports that the branch is tracking the upstream "origin/rocko" branch.

    The following command displays the branches that are now part of your local poky repository. The asterisk character indicates the branch that is currently checked out for work:

         $ git branch
           master
         * rocko
                        

2.2.6. Checking Out by Tag in Poky

Similar to branches, the upstream repository uses tags to mark specific commits associated with significant points in a development branch (i.e. a release point or stage of a release). You might want to set up a local branch based on one of those points in the repository. The process is similar to checking out by branch name except you use tag names.

Note

Checking out a branch based on a tag gives you a stable set of files not affected by development on the branch above the tag.

  1. Switch to the Poky Directory: If you have a local poky Git repository, switch to that directory. If you do not have the local copy of poky, see the "Cloning the poky Repository" section.

  2. Fetch the Tag Names: To checkout the branch based on a tag name, you need to fetch the upstream tags into your local repository:

         $ git fetch --tags
         $
                        

  3. List the Tag Names: You can list the tag names now:

         $ git tag
         1.1_M1.final
         1.1_M1.rc1
         1.1_M1.rc2
         1.1_M2.final
         1.1_M2.rc1
            .
            .
            .
         yocto-2.2
         yocto-2.2.1
         yocto-2.3
         yocto-2.3.1
         yocto-2.4
         yocto_1.5_M5.rc8
                        

  4. Checkout the Branch:

         $ git checkout tags/2.4 -b my_yocto_2.4
         Switched to a new branch 'my_yocto_2.4'
         $ git branch
           master
         * my_yocto_2.4
                        

    The previous command creates and checks out a local branch named "my_yocto_2.4", which is based on the commit in the upstream poky repository that has the same tag. In this example, the files you have available locally as a result of the checkout command are a snapshot of the "rocko" development branch at the point where Yocto Project 2.4 was released.

2.3. Performing a Simple Build

Several methods exist that allow you to build an image within the Yocto Project. This procedure shows how to build an image using BitBake from a Linux host.

Notes

The build process creates an entire Linux distribution from source and places it in your Build Directory under tmp/deploy/images. For detailed information on the build process using BitBake, see the "Images" section in the Yocto Project Reference Manual. You can also reference the "Building Images" section in the Yocto Project Quick Start.

The following figure and list overviews the build process:

  1. Set up Your Host Development System to Support Development Using the Yocto Project: See the "Setting Up to Use the Yocto Project" section in the Yocto Project Quick Start for options on how to get a build host ready to use the Yocto Project.

  2. Initialize the Build Environment: Initialize the build environment by sourcing the build environment script (i.e. oe-init-build-env).

  3. Make Sure Your local.conf File is Correct: Ensure the conf/local.conf configuration file, which is found in the Build Directory, is set up how you want it. This file defines many aspects of the build environment including the target machine architecture through the MACHINE variable, the packaging format used during the build (PACKAGE_CLASSES), and a centralized tarball download directory through the DL_DIR variable.

  4. Build the Image: Build the image using the bitbake command. For example, the following command builds the core-image-minimal image:

         $ bitbake core-image-minimal
                    

    For information on BitBake, see the BitBake User Manual.

Chapter 3. The Yocto Project Open Source Development Environment

3.1. Setting Up a Team Yocto Project Development Environment

It might not be immediately clear how you can use the Yocto Project in a team development environment, or scale it for a large team of developers. One of the strengths of the Yocto Project is that it is extremely flexible. Thus, you can adapt it to many different use cases and scenarios. However, these characteristics can cause a struggle if you are trying to create a working setup that scales across a large team.

To help you understand how to set up this type of environment, this section presents a procedure that gives you the information to learn how to get the results you want. The procedure is high-level and presents some of the project's most successful experiences, practices, solutions, and available technologies that work well. Keep in mind, the procedure here is a starting point. You can build off it and customize it to fit any particular working environment and set of practices.

  1. Determine Who is Going to be Developing: You need to understand who is going to be doing anything related to the Yocto Project and what their roles would be. Making this determination is essential to completing the steps two and three, which are to get your equipment together and set up your development environment's hardware topology.

    The following roles exist:

    • Application Development: These types of developers do application level work on top of an existing software stack.

    • Core System Development: These types of developers work on the contents of the operating system image itself.

    • Build Engineer: This type of developer manages Autobuilders and releases. Not all environments need a Build Engineer.

    • Test Engineer: This type of developer creates and manages automated tests needed to ensure all application and core system development meets desired quality standards.

  2. Gather the Hardware: Based on the size and make-up of the team, get the hardware together. Any development, build, or test engineer should be using a system that is running a supported Linux distribution. Systems, in general, should be high performance (e.g. dual, six-core Xeons with 24 Gbytes of RAM and plenty of disk space). You can help ensure efficiency by having any machines used for testing or that run Autobuilders be as high performance as possible.

  3. Understand the Hardware Topology of the Environment: Now that you know how many developers and support engineers are required, you can understand the topology of the hardware environment. The following figure shows a moderately sized Yocto Project development environment.

    Need figure.

  4. Use Git as Your Source Control Manager (SCM): Keeping your Metadata and any software you are developing under the control of an SCM system that is compatible with the OpenEmbedded build system is advisable. Of the SCMs BitBake supports, the Yocto Project team strongly recommends using Git. Git is a distributed system that is easy to backup, allows you to work remotely, and then connects back to the infrastructure.

    Note

    For information about BitBake, see the BitBake User Manual.

    It is relatively easy to set up Git services and create infrastructure like http://git.yoctoproject.org, which is based on server software called gitolite with cgit being used to generate the web interface that lets you view the repositories. The gitolite software identifies users using SSH keys and allows branch-based access controls to repositories that you can control as little or as much as necessary.

    Note

    The setup of these services is beyond the scope of this manual. However, sites such as these exist that describe how to perform setup:

  5. Set up the Application Development Machines: As mentioned earlier, application developers are creating applications on top of existing software stacks. Following are some best practices for setting up machines that do application development:

    • Use a pre-built toolchain that contains the software stack itself. Then, develop the application code on top of the stack. This method works well for small numbers of relatively isolated applications.

    • When possible, use the Yocto Project plug-in for the Eclipse™ IDE and SDK development practices. For more information, see the "Yocto Project Software Development Kit (SDK) Developer's Guide".

    • Keep your cross-development toolchains updated. You can do this through provisioning either as new toolchain downloads or as updates through a package update mechanism using opkg to provide updates to an existing toolchain. The exact mechanics of how and when to do this are a question for local policy.

    • Use multiple toolchains installed locally into different locations to allow development across versions.

  6. Set up the Core Development Machines: As mentioned earlier, these types of developers work on the contents of the operating system itself. Following are some best practices for setting up machines used for developing images:

    • Have the Yocto Project build system itself available on the developer workstations so developers can run their own builds and directly rebuild the software stack.

    • Keep the core system unchanged as much as possible and do your work in layers on top of the core system. Doing so gives you a greater level of portability when upgrading to new versions of the core system or Board Support Packages (BSPs).

    • Share layers amongst the developers of a particular project and contain the policy configuration that defines the project.

  7. Set up an Autobuilder: Autobuilders are often the core of the development environment. It is here that changes from individual developers are brought together and centrally tested and subsequent decisions about releases can be made. Autobuilders also allow for "continuous integration" style testing of software components and regression identification and tracking.

    See "Yocto Project Autobuilder" for more information and links to buildbot. The Yocto Project team has found this implementation works well in this role. A public example of this is the Yocto Project Autobuilders, which we use to test the overall health of the project.

    The features of this system are:

    • Highlights when commits break the build.

    • Populates an sstate cache from which developers can pull rather than requiring local builds.

    • Allows commit hook triggers, which trigger builds when commits are made.

    • Allows triggering of automated image booting and testing under the QuickEMUlator (QEMU).

    • Supports incremental build testing and from-scratch builds.

    • Shares output that allows developer testing and historical regression investigation.

    • Creates output that can be used for releases.

    • Allows scheduling of builds so that resources can be used efficiently.

  8. Set up Test Machines: Use a small number of shared, high performance systems for testing purposes. Developers can use these systems for wider, more extensive testing while they continue to develop locally using their primary development system.

  9. Document Policies and Change Flow: The Yocto Project itself uses a hierarchical structure and a pull model. Scripts exist to create and send pull requests (i.e. create-pull-request and send-pull-request). This model is in line with other open source projects where maintainers are responsible for specific areas of the project and a single maintainer handles the final "top-of-tree" merges.

    Note

    You can also use a more collective push model. The gitolite software supports both the push and pull models quite easily.

    As with any development environment, it is important to document the policy used as well as any main project guidelines so they are understood by everyone. It is also a good idea to have well structured commit messages, which are usually a part of a project's guidelines. Good commit messages are essential when looking back in time and trying to understand why changes were made.

    If you discover that changes are needed to the core layer of the project, it is worth sharing those with the community as soon as possible. Chances are if you have discovered the need for changes, someone else in the community needs them also.

  10. Development Environment Summary: Aside from the previous steps, some best practices exist within the Yocto Project development environment. Consider the following:

    • Use Git as the source control system.

    • Maintain your Metadata in layers that make sense for your situation. See the "Understanding and Creating Layers" section for more information on layers.

    • Separate the project's Metadata and code by using separate Git repositories. See the "Yocto Project Source Repositories" section for information on these repositories. See the "Working With Yocto Project Source Files" section for information on how to set up local Git repositories for related upstream Yocto Project Git repositories.

    • Set up the directory for the shared state cache (SSTATE_DIR) where it makes sense. For example, set up the sstate cache on a system used by developers in the same organization and share the same source directories on their machines.

    • Set up an Autobuilder and have it populate the sstate cache and source directories.

    • The Yocto Project community encourages you to send patches to the project to fix bugs or add features. If you do submit patches, follow the project commit guidelines for writing good commit messages. See the "Submitting a Change to the Yocto Project" section.

    • Send changes to the core sooner than later as others are likely to run into the same issues. For some guidance on mailing lists to use, see the list in the "Submitting a Change to the Yocto Project" section. For a description of the available mailing lists, see the "Mailing Lists" section in the Yocto Project Reference Manual.

3.2. Submitting a Defect Against the Yocto Project

Use the Yocto Project implementation of Bugzilla to submit a defect (bug) against the Yocto Project. For additional information on this implementation of Bugzilla see the "Yocto Project Bugzilla" section in the Yocto Project Reference Manual. For more detail on any of the following steps, see the Yocto Project Bugzilla wiki page.

Use the following general steps to submit a bug"

  1. Open the Yocto Project implementation of Bugzilla.

  2. Click "File a Bug" to enter a new bug.

  3. Choose the appropriate "Classification", "Product", and "Component" for which the bug was found. Bugs for the Yocto Project fall into one of several classifications, which in turn break down into several products and components. For example, for a bug against the meta-intel layer, you would choose "Build System, Metadata & Runtime", "BSPs", and "bsps-meta-intel", respectively.

  4. Choose the "Version" of the Yocto Project for which you found the bug (e.g. 2.4).

  5. Determine and select the "Severity" of the bug. The severity indicates how the bug impacted your work.

  6. Choose the "Hardware" that the bug impacts.

  7. Choose the "Architecture" that the bug impacts.

  8. Choose a "Documentation change" item for the bug. Fixing a bug might or might not affect the Yocto Project documentation. If you are unsure of the impact to the documentation, select "Don't Know".

  9. Provide a brief "Summary" of the bug. Try to limit your summary to just a line or two and be sure to capture the essence of the bug.

  10. Provide a detailed "Description" of the bug. You should provide as much detail as you can about the context, behavior, output, and so forth that surrounds the bug. You can even attach supporting files for output from logs by using the "Add an attachment" button.

  11. Click the "Submit Bug" button submit the bug. A new Bugzilla number is assigned to the bug and the defect is logged in the bug tracking system.

Once you file a bug, the bug is processed by the Yocto Project Bug Triage Team and further details concerning the bug are assigned (e.g. priority and owner). You are the "Submitter" of the bug and any further categorization, progress, or comments on the bug result in Bugzilla sending you an automated email concerning the particular change or progress to the bug.

3.3. Submitting a Change to the Yocto Project

Contributions to the Yocto Project and OpenEmbedded are very welcome. Because the system is extremely configurable and flexible, we recognize that developers will want to extend, configure or optimize it for their specific uses.

The Yocto Project uses a mailing list and a patch-based workflow that is similar to the Linux kernel but contains important differences. In general, a mailing list exists through which you can submit patches. You should send patches to the appropriate mailing list so that they can be reviewed and merged by the appropriate maintainer. The specific mailing list you need to use depends on the location of the code you are changing. Each component (e.g. layer) should have a README file that indicates where to send the changes and which process to follow.

You can send the patch to the mailing list using whichever approach you feel comfortable with to generate the patch. Once sent, the patch is usually reviewed by the community at large. If somebody has concerns with the patch, they will usually voice their concern over the mailing list. If a patch does not receive any negative reviews, the maintainer of the affected layer typically takes the patch, tests it, and then based on successful testing, merges the patch.

The "poky" repository, which is the Yocto Project's reference build environment, is a hybrid repository that contains several individual pieces (e.g. BitBake, OpenEmbedded-Core, meta-yocto, documentation, and so forth) built using the combo-layer tool. The upstream location used for submitting changes varies by component:

  • Core Metadata: Send your patch to the openembedded-core mailing list. For example, a change to anything under the meta or scripts directories should be sent to this mailing list.

  • BitBake: For changes to BitBake (i.e. anything under the bitbake directory), send your patch to the bitbake-devel mailing list.

  • "meta-yocto-bsp" and "meta-poky" trees: These trees are part of the "meta-yocto" repository in the Yocto Project source repositories. Use the poky mailing list.

For changes to other layers hosted in the Yocto Project source repositories (i.e. yoctoproject.org), tools, and the Yocto Project documentation, use the Yocto Project general mailing list.

Note

Sometimes a layer's documentation specifies to use a particular mailing list. If so, use that list.

For additional recipes that do not fit into the core Metadata, you should determine which layer the recipe should go into and submit the change in the manner recommended by the documentation (e.g. the README file) supplied with the layer. If in doubt, please ask on the Yocto general mailing list or on the openembedded-devel mailing list.

You can also push a change upstream and request a maintainer to pull the change into the component's upstream repository. You do this by pushing to a contribution repository that is upstream. See the "Workflows" section in the Yocto Project Reference Manual for additional concepts on working in the Yocto Project development environment.

Two commonly used testing repositories exist for OpenEmbedded-Core:

  • "ross/mut" branch: The "mut" (master-under-test) tree exists in the poky-contrib repository in the Yocto Project source repositories.

  • "master-next" branch: This branch is part of the main "poky" repository in the Yocto Project source repositories.

Maintainers use these branches to test submissions prior to merging patches. Thus, you can get an idea of the status of a patch based on whether the patch has been merged into one of these branches.

Note

This system is imperfect and changes can sometimes get lost in the flow. Asking about the status of a patch or change is reasonable if the change has been idle for a while with no feedback. The Yocto Project does have plans to use Patchwork to track the status of patches and also to automatically preview patches.

The following sections provide procedures for submitting a change.

3.3.1. Using Scripts to Push a Change Upstream and Request a Pull

Follow this procedure to push a change to an upstream "contrib" Git repository:

Note

You can find general Git information on how to push a change upstream in the Git Community Book.

  1. Make Your Changes Locally: Make your changes in your local Git repository. You should make small, controlled, isolated changes. Keeping changes small and isolated aids review, makes merging/rebasing easier and keeps the change history clean should anyone need to refer to it in future.

  2. Stage Your Changes: Stage your changes by using the git add command on each file you changed.

  3. Commit Your Changes: Commit the change by using the git commit command. Make sure your commit information follows standards by following these accepted conventions:

    • Be sure to include a "Signed-off-by:" line in the same style as required by the Linux kernel. Adding this line signifies that you, the submitter, have agreed to the Developer's Certificate of Origin 1.1 as follows:

           Developer's Certificate of Origin 1.1
      
           By making a contribution to this project, I certify that:
      
           (a) The contribution was created in whole or in part by me and I
               have the right to submit it under the open source license
               indicated in the file; or
      
           (b) The contribution is based upon previous work that, to the best
               of my knowledge, is covered under an appropriate open source
               license and I have the right under that license to submit that
               work with modifications, whether created in whole or in part
               by me, under the same open source license (unless I am
               permitted to submit under a different license), as indicated
               in the file; or
      
           (c) The contribution was provided directly to me by some other
               person who certified (a), (b) or (c) and I have not modified
               it.
      
           (d) I understand and agree that this project and the contribution
               are public and that a record of the contribution (including all
               personal information I submit with it, including my sign-off) is
               maintained indefinitely and may be redistributed consistent with
               this project or the open source license(s) involved.
                                  

    • Provide a single-line summary of the change. and, if more explanation is needed, provide more detail in the body of the commit. This summary is typically viewable in the "shortlist" of changes. Thus, providing something short and descriptive that gives the reader a summary of the change is useful when viewing a list of many commits. You should prefix this short description with the recipe name (if changing a recipe), or else with the short form path to the file being changed.

    • For the body of the commit message, provide detailed information that describes what you changed, why you made the change, and the approach you used. It might also be helpful if you mention how you tested the change. Provide as much detail as you can in the body of the commit message.

      Note

      You do not need to provide a more detailed explanation of a change if the change is minor to the point of the single line summary providing all the information.

    • If the change addresses a specific bug or issue that is associated with a bug-tracking ID, include a reference to that ID in your detailed description. For example, the Yocto Project uses a specific convention for bug references - any commit that addresses a specific bug should use the following form for the detailed description. Be sure to use the actual bug-tracking ID from Bugzilla for bug-id:

           Fixes [YOCTO #bug-id]
      
           detailed description of change
                                  

  4. Push Your Commits to a "Contrib" Upstream: If you have arranged for permissions to push to an upstream contrib repository, push the change to that repository:

         $ git push upstream_remote_repo local_branch_name
                        

    For example, suppose you have permissions to push into the upstream meta-intel-contrib repository and you are working in a local branch named your_name/README. The following command pushes your local commits to the meta-intel-contrib upstream repository and puts the commit in a branch named your_name/README:

         $ git push meta-intel-contrib your_name/README
                        

  5. Determine Who to Notify: Determine the maintainer or the mailing list that you need to notify for the change.

    Before submitting any change, you need to be sure who the maintainer is or what mailing list that you need to notify. Use either these methods to find out:

    • Maintenance File: Examine the maintainers.inc file, which is located in the Source Directory at meta-poky/conf/distro/include, to see who is responsible for code.

    • Search by File: Using Git, you can enter the following command to bring up a short list of all commits against a specific file:

           git shortlog -- filename
                                  

      Just provide the name of the file for which you are interested. The information returned is not ordered by history but does include a list of everyone who has committed grouped by name. From the list, you can see who is responsible for the bulk of the changes against the file.

    • Examine the List of Mailing Lists: For a list of the Yocto Project and related mailing lists, see the "Mailing lists" section in the Yocto Project Reference Manual.

  6. Make a Pull Request: Notify the maintainer or the mailing list that you have pushed a change by making a pull request.

    The Yocto Project provides two scripts that conveniently let you generate and send pull requests to the Yocto Project. These scripts are create-pull-request and send-pull-request. You can find these scripts in the scripts directory within the Source Directory (e.g. ~/poky/scripts).

    Using these scripts correctly formats the requests without introducing any whitespace or HTML formatting. The maintainer that receives your patches either directly or through the mailing list needs to be able to save and apply them directly from your emails. Using these scripts is the preferred method for sending patches.

    First, create the pull request. For example, the following command runs the script, specifies the upstream repository in the contrib directory into which you pushed the change, and provides a subject line in the created patch files:

         $ ~/poky/scripts/create-pull-request -u meta-intel-contrib -s "Updated Manual Section Reference in README"
                        

    Running this script forms *.patch files in a folder named pull-PID in the current directory. One of the patch files is a cover letter.

    Before running the send-pull-request script, you must edit the cover letter patch to insert information about your change. After editing the cover letter, send the pull request. For example, the following command runs the script and specifies the patch directory and email address. In this example, the email address is a mailing list:

         $ ~/poky/scripts/send-pull-request -p ~/meta-intel/pull-10565 -t meta-intel@yoctoproject.org
                        

    You need to follow the prompts as the script is interactive.

    Note

    For help on using these scripts, simply provide the -h argument as follows:
         $ poky/scripts/create-pull-request -h
         $ poky/scripts/send-pull-request -h
                            

3.3.2. Using Email to Submit a Patch

You can submit patches without using the create-pull-request and send-pull-request scripts described in the previous section. However, keep in mind, the preferred method is to use the scripts.

Depending on the components changed, you need to submit the email to a specific mailing list. For some guidance on which mailing list to use, see the beginning of this section. For a description of all the available mailing lists, see the "Mailing Lists" section in the Yocto Project Reference Manual.

Here is the general procedure on how to submit a patch through email without using the scripts:

  1. Make Your Changes Locally: Make your changes in your local Git repository. You should make small, controlled, isolated changes. Keeping changes small and isolated aids review, makes merging/rebasing easier and keeps the change history clean should anyone need to refer to it in future.

  2. Stage Your Changes: Stage your changes by using the git add command on each file you changed.

  3. Commit Your Changes: Commit the change by using the git commit --signoff command. Using the --signoff option identifies you as the person making the change and also satisfies the Developer's Certificate of Origin (DCO) shown earlier.

    When you form a commit, you must follow certain standards established by the Yocto Project development team. See Step 3 in the previous section for information on how to provide commit information that meets Yocto Project commit message standards.

  4. Format the Commit: Format the commit into an email message. To format commits, use the git format-patch command. When you provide the command, you must include a revision list or a number of patches as part of the command. For example, either of these two commands takes your most recent single commit and formats it as an email message in the current directory:

         $ git format-patch -1
                        

    or

         $ git format-patch HEAD~
                        

    After the command is run, the current directory contains a numbered .patch file for the commit.

    If you provide several commits as part of the command, the git format-patch command produces a series of numbered files in the current directory – one for each commit. If you have more than one patch, you should also use the --cover option with the command, which generates a cover letter as the first "patch" in the series. You can then edit the cover letter to provide a description for the series of patches. For information on the git format-patch command, see GIT_FORMAT_PATCH(1) displayed using the man git-format-patch command.

    Note

    If you are or will be a frequent contributor to the Yocto Project or to OpenEmbedded, you might consider requesting a contrib area and the necessary associated rights.

  5. Import the Files Into Your Mail Client: Import the files into your mail client by using the git send-email command.

    Note

    In order to use git send-email, you must have the proper Git packages installed on your host. For Ubuntu, Debian, and Fedora the package is git-email.

    The git send-email command sends email by using a local or remote Mail Transport Agent (MTA) such as msmtp, sendmail, or through a direct smtp configuration in your Git ~/.gitconfig file. If you are submitting patches through email only, it is very important that you submit them without any whitespace or HTML formatting that either you or your mailer introduces. The maintainer that receives your patches needs to be able to save and apply them directly from your emails. A good way to verify that what you are sending will be applicable by the maintainer is to do a dry run and send them to yourself and then save and apply them as the maintainer would.

    The git send-email command is the preferred method for sending your patches using email since there is no risk of compromising whitespace in the body of the message, which can occur when you use your own mail client. The command also has several options that let you specify recipients and perform further editing of the email message. For information on how to use the git send-email command, see GIT-SEND-EMAIL(1) displayed using the man git-send-email command.

Chapter 4. Common Tasks

Table of Contents

4.1. Understanding and Creating Layers
4.1.1. Layers
4.1.2. Creating Your Own Layer
4.1.3. Following Best Practices When Creating Layers
4.1.4. Making Sure Your Layer is Compatible With Yocto Project
4.1.5. Enabling Your Layer
4.1.6. Using .bbappend Files in Your Layer
4.1.7. Prioritizing Your Layer
4.1.8. Managing Layers
4.1.9. Creating a General Layer Using the yocto-layer Script
4.2. Customizing Images
4.2.1. Customizing Images Using local.conf
4.2.2. Customizing Images Using Custom IMAGE_FEATURES and EXTRA_IMAGE_FEATURES
4.2.3. Customizing Images Using Custom .bb Files
4.2.4. Customizing Images Using Custom Package Groups
4.2.5. Customizing an Image Hostname
4.3. Writing a New Recipe
4.3.1. Overview
4.3.2. Locate or Automatically Create a Base Recipe
4.3.3. Storing and Naming the Recipe
4.3.4. Running a Build on the Recipe
4.3.5. Fetching Code
4.3.6. Unpacking Code
4.3.7. Patching Code
4.3.8. Licensing
4.3.9. Dependencies
4.3.10. Configuring the Recipe
4.3.11. Using Headers to Interface with Devices
4.3.12. Compilation
4.3.13. Installing
4.3.14. Enabling System Services
4.3.15. Packaging
4.3.16. Sharing Files Between Recipes
4.3.17. Properly Versioning Pre-Release Recipes
4.3.18. Post-Installation Scripts
4.3.19. Testing
4.3.20. Examples
4.3.21. Following Recipe Style Guidelines
4.4. Adding a New Machine
4.4.1. Adding the Machine Configuration File
4.4.2. Adding a Kernel for the Machine
4.4.3. Adding a Formfactor Configuration File
4.5. Finding Temporary Source Code
4.6. Using Quilt in Your Workflow
4.7. Using a Development Shell
4.8. Using a Development Python Shell
4.9. Building Targets with Multiple Configurations
4.10. Working With Libraries
4.10.1. Including Static Library Files
4.10.2. Combining Multiple Versions of Library Files into One Image
4.10.3. Installing Multiple Versions of the Same Library
4.11. Enabling GObject Introspection Support
4.11.1. Enabling the Generation of Introspection Data
4.11.2. Disabling the Generation of Introspection Data
4.11.3. Testing that Introspection Works in an Image
4.11.4. Known Issues
4.12. Optionally Using an External Toolchain
4.13. Creating Partitioned Images
4.13.1. Creating Partitioned Images
4.13.2. Using OpenEmbedded Image Creator Wic to Generate Partitioned Images
4.14. Building an Initial RAM Filesystem (initramfs) Image
4.15. Flashing Images Using bmaptool
4.16. Making Images More Secure
4.16.1. General Considerations
4.16.2. Security Flags
4.16.3. Considerations Specific to the OpenEmbedded Build System
4.16.4. Tools for Hardening Your Image
4.17. Creating Your Own Distribution
4.18. Creating a Custom Template Configuration Directory
4.19. Building a Tiny System
4.19.1. Overview
4.19.2. Goals and Guiding Principles
4.19.3. Understand What Contributes to Your Image Size
4.19.4. Trim the Root Filesystem
4.19.5. Trim the Kernel
4.19.6. Remove Package Management Requirements
4.19.7. Look for Other Ways to Minimize Size
4.19.8. Iterate on the Process
4.20. Building Images for More than One Machine
4.21. Working with Packages
4.21.1. Excluding Packages from an Image
4.21.2. Incrementing a Package Version
4.21.3. Handling Optional Module Packaging
4.21.4. Using Runtime Package Management
4.21.5. Generating and Using Signed Packages
4.21.6. Testing Packages With ptest
4.22. Working with Source Files
4.22.1. Setting up Effective Mirrors
4.22.2. Getting Source Files and Suppressing the Build
4.23. Building Software from an External Source
4.24. Selecting an Initialization Manager
4.24.1. Using systemd Exclusively
4.24.2. Using systemd for the Main Image and Using SysVinit for the Rescue Image
4.25. Selecting a Device Manager
4.25.1. Using Persistent and Pre-Populated/dev
4.25.2. Using devtmpfs and a Device Manager
4.26. Using an External SCM
4.27. Creating a Read-Only Root Filesystem
4.27.1. Creating the Root Filesystem
4.27.2. Post-Installation Scripts
4.27.3. Areas With Write Access
4.28. Performing Automated Runtime Testing
4.28.1. Enabling Tests
4.28.2. Running Tests
4.28.3. Exporting Tests
4.28.4. Writing New Tests
4.28.5. Installing Packages in the DUT Without the Package Manager
4.29. Debugging With the GNU Project Debugger (GDB) Remotely
4.30. Debugging with the GNU Project Debugger (GDB) on the Target
4.31. Debugging Parallel Make Races
4.31.1. The Failure
4.31.2. Reproducing the Error
4.31.3. Creating a Patch for the Fix
4.31.4. Testing the Build
4.32. Maintaining Open Source License Compliance During Your Product's Lifecycle
4.32.1. Providing the Source Code
4.32.2. Providing License Text
4.32.3. Providing Compilation Scripts and Source Code Modifications
4.33. Using the Error Reporting Tool
4.33.1. Enabling and Using the Tool
4.33.2. Disabling the Tool
4.33.3. Setting Up Your Own Error Reporting Server

This chapter describes fundamental procedures such as creating layers, adding new software packages, extending or customizing images, porting work to new hardware (adding a new machine), and so forth. You will find that the procedures documented here occur often in the development cycle using the Yocto Project.

4.1. Understanding and Creating Layers

The OpenEmbedded build system supports organizing Metadata into multiple layers. Layers allow you to isolate different types of customizations from each other. You might find it tempting to keep everything in one layer when working on a single project. However, the more modular your Metadata, the easier it is to cope with future changes.

To illustrate how layers are used to keep things modular, consider machine customizations. These types of customizations typically reside in a special layer, rather than a general layer, called a Board Support Package (BSP) Layer. Furthermore, the machine customizations should be isolated from recipes and Metadata that support a new GUI environment, for example. This situation gives you a couple of layers: one for the machine configurations, and one for the GUI environment. It is important to understand, however, that the BSP layer can still make machine-specific additions to recipes within the GUI environment layer without polluting the GUI layer itself with those machine-specific changes. You can accomplish this through a recipe that is a BitBake append (.bbappend) file, which is described later in this section.

Note

For general information on BSP layer structure, see the Board Support Packages (BSP) - Developer's Guide.

4.1.1. Layers

The Source Directory contains both general layers and BSP layers right out of the box. You can easily identify layers that ship with a Yocto Project release in the Source Directory by their folder names. Folders that represent layers typically have names that begin with the string meta-.

Note

It is not a requirement that a layer name begin with the prefix meta-, but it is a commonly accepted standard in the Yocto Project community.

For example, when you set up the Source Directory structure, you will see several layers: meta, meta-skeleton, meta-selftest, meta-poky, and meta-yocto-bsp. Each of these folders represents a distinct layer.

As another example, if you set up a local copy of the meta-intel Git repository and then explore the folder of that general layer, you will discover many Intel-specific BSP layers inside. For more information on BSP layers, see the "BSP Layers" section in the Yocto Project Board Support Package (BSP) Developer's Guide.

4.1.2. Creating Your Own Layer

It is very easy to create your own layers to use with the OpenEmbedded build system. The Yocto Project ships with scripts that speed up creating general layers and BSP layers. This section describes the steps you perform by hand to create a layer so that you can better understand them. For information about the layer-creation scripts, see the "Creating a New BSP Layer Using the yocto-bsp Script" section in the Yocto Project Board Support Package (BSP) Developer's Guide and the "Creating a General Layer Using the yocto-layer Script" section further down in this manual.

Follow these general steps to create your layer without the aid of a script:

  1. Check Existing Layers: Before creating a new layer, you should be sure someone has not already created a layer containing the Metadata you need. You can see the OpenEmbedded Metadata Index for a list of layers from the OpenEmbedded community that can be used in the Yocto Project.

  2. Create a Directory: Create the directory for your layer. While not strictly required, prepend the name of the folder with the string meta-. For example:

         meta-mylayer
         meta-GUI_xyz
         meta-mymachine
                            

  3. Create a Layer Configuration File: Inside your new layer folder, you need to create a conf/layer.conf file. It is easiest to take an existing layer configuration file and copy that to your layer's conf directory and then modify the file as needed.

    The meta-yocto-bsp/conf/layer.conf file demonstrates the required syntax:

         # We have a conf and classes directory, add to BBPATH
         BBPATH .= ":${LAYERDIR}"
    
         # We have recipes-* directories, add to BBFILES
         BBFILES += "${LAYERDIR}/recipes-*/*/*.bb \
                     ${LAYERDIR}/recipes-*/*/*.bbappend"
    
         BBFILE_COLLECTIONS += "yoctobsp"
         BBFILE_PATTERN_yoctobsp = "^${LAYERDIR}/"
         BBFILE_PRIORITY_yoctobsp = "5"
         LAYERVERSION_yoctobsp = "3"
                            

    Here is an explanation of the example:

    • The configuration and classes directory is appended to BBPATH.

      Note

      All non-distro layers, which include all BSP layers, are expected to append the layer directory to the BBPATH. On the other hand, distro layers, such as meta-poky, can choose to enforce their own precedence over BBPATH. For an example of that syntax, see the layer.conf file for the meta-poky layer.
    • The recipes for the layers are appended to BBFILES.

    • The BBFILE_COLLECTIONS variable is then appended with the layer name.

    • The BBFILE_PATTERN variable is set to a regular expression and is used to match files from BBFILES into a particular layer. In this case, LAYERDIR is used to make BBFILE_PATTERN match within the layer's path.

    • The BBFILE_PRIORITY variable then assigns a priority to the layer. Applying priorities is useful in situations where the same recipe might appear in multiple layers and allows you to choose the layer that takes precedence.

    • The LAYERVERSION variable optionally specifies the version of a layer as a single number.

    Note the use of the LAYERDIR variable, which expands to the directory of the current layer.

    Through the use of the BBPATH variable, BitBake locates class files (.bbclass), configuration files, and files that are included with include and require statements. For these cases, BitBake uses the first file that matches the name found in BBPATH. This is similar to the way the PATH variable is used for binaries. It is recommended, therefore, that you use unique class and configuration filenames in your custom layer.

  4. Add Content: Depending on the type of layer, add the content. If the layer adds support for a machine, add the machine configuration in a conf/machine/ file within the layer. If the layer adds distro policy, add the distro configuration in a conf/distro/ file within the layer. If the layer introduces new recipes, put the recipes you need in recipes-* subdirectories within the layer.

    Note

    In order to be compliant with the Yocto Project, a layer must contain a README file.

  5. Optionally Test for Compatibility: If you want permission to use the Yocto Project Compatibility logo with your layer or application that uses your layer, perform the steps to apply for compatibility. See the "Making Sure Your Layer is Compatible With Yocto Project" section for more information.

4.1.3. Following Best Practices When Creating Layers

To create layers that are easier to maintain and that will not impact builds for other machines, you should consider the information in the following list:

  • Avoid "Overlaying" Entire Recipes from Other Layers in Your Configuration: In other words, do not copy an entire recipe into your layer and then modify it. Rather, use an append file (.bbappend) to override only those parts of the original recipe you need to modify.

  • Avoid Duplicating Include Files: Use append files (.bbappend) for each recipe that uses an include file. Or, if you are introducing a new recipe that requires the included file, use the path relative to the original layer directory to refer to the file. For example, use require recipes-core/package/file.inc instead of require file.inc. If you're finding you have to overlay the include file, it could indicate a deficiency in the include file in the layer to which it originally belongs. If this is the case, you should try to address that deficiency instead of overlaying the include file. For example, you could address this by getting the maintainer of the include file to add a variable or variables to make it easy to override the parts needing to be overridden.

  • Structure Your Layers: Proper use of overrides within append files and placement of machine-specific files within your layer can ensure that a build is not using the wrong Metadata and negatively impacting a build for a different machine. Following are some examples:

    • Modify Variables to Support a Different Machine: Suppose you have a layer named meta-one that adds support for building machine "one". To do so, you use an append file named base-files.bbappend and create a dependency on "foo" by altering the DEPENDS variable:

           DEPENDS = "foo"
                                      

      The dependency is created during any build that includes the layer meta-one. However, you might not want this dependency for all machines. For example, suppose you are building for machine "two" but your bblayers.conf file has the meta-one layer included. During the build, the base-files for machine "two" will also have the dependency on foo.

      To make sure your changes apply only when building machine "one", use a machine override with the DEPENDS statement:

           DEPENDS_one = "foo"
                                      

      You should follow the same strategy when using _append and _prepend operations:

           DEPENDS_append_one = " foo"
           DEPENDS_prepend_one = "foo "
                                      

      As an actual example, here's a line from the recipe for gnutls, which adds dependencies on "argp-standalone" when building with the musl C library:

           DEPENDS_append_libc-musl = " argp-standalone"
                                      

      Note

      Avoiding "+=" and "=+" and using machine-specific _append and _prepend operations is recommended as well.

    • Place Machine-Specific Files in Machine-Specific Locations: When you have a base recipe, such as base-files.bb, that contains a SRC_URI statement to a file, you can use an append file to cause the build to use your own version of the file. For example, an append file in your layer at meta-one/recipes-core/base-files/base-files.bbappend could extend FILESPATH using FILESEXTRAPATHS as follows:

           FILESEXTRAPATHS_prepend := "${THISDIR}/${BPN}:"
                                      

      The build for machine "one" will pick up your machine-specific file as long as you have the file in meta-one/recipes-core/base-files/base-files/. However, if you are building for a different machine and the bblayers.conf file includes the meta-one layer and the location of your machine-specific file is the first location where that file is found according to FILESPATH, builds for all machines will also use that machine-specific file.

      You can make sure that a machine-specific file is used for a particular machine by putting the file in a subdirectory specific to the machine. For example, rather than placing the file in meta-one/recipes-core/base-files/base-files/ as shown above, put it in meta-one/recipes-core/base-files/base-files/one/. Not only does this make sure the file is used only when building for machine "one", but the build process locates the file more quickly.

      In summary, you need to place all files referenced from SRC_URI in a machine-specific subdirectory within the layer in order to restrict those files to machine-specific builds.

  • Perform Steps to Apply for Yocto Project Compatibility: If you want permission to use the Yocto Project Compatibility logo with your layer or application that uses your layer, perform the steps to apply for compatibility. See the "Making Sure Your Layer is Compatible With Yocto Project" section for more information.

  • Follow the Layer Naming Convention: Store custom layers in a Git repository that use the meta-layer_name format.

  • Group Your Layers Locally: Clone your repository alongside other cloned meta directories from the Source Directory.

4.1.4. Making Sure Your Layer is Compatible With Yocto Project

When you create a layer used with the Yocto Project, it is advantageous to make sure that the layer interacts well with existing Yocto Project layers (i.e. the layer is compatible with the Yocto Project). Ensuring compatibility makes the layer easy to be consumed by others in the Yocto Project community and could allow you permission to use the Yocto Project Compatible Logo.

Note

Only Yocto Project member organizations are permitted to use the Yocto Project Compatible Logo. The logo is not available for general use. For information on how to become a Yocto Project member organization, see the Member Organizations page of the Yocto Project website.

The Yocto Project Compatibility Program consists of a layer application process that requests permission to use the Yocto Project Compatibility Logo for your layer and application. The process consists of two parts:

  1. Successfully passing a script (yocto-check-layer) that when run against your layer, tests it against constraints based on experiences of how layers have worked in the real world and where pitfalls have been found. Getting a "PASS" result from the script is required for successful compatibility registration.

  2. Completion of an application acceptance form, which you can find at https://www.yoctoproject.org/webform/yocto-project-compatible-registration.

To be granted permission to use the logo, you need to satisfy the following:

  • Be able to check the box indicating that you got a "PASS" when running the script against your layer.

  • Answer "Yes" to the questions on the form or have an acceptable explanation for any questions answered "No".

  • You need to be a Yocto Project Member Organization.

The remainder of this section presents information on the registration form and on the yocto-check-layer script.

4.1.4.1. Yocto Project Compatible Program Application

Use the form to apply for your layer's approval. Upon successful application, you can use the Yocto Project Compatibility Logo with your layer and the application that uses your layer.

To access the form, use this link: https://www.yoctoproject.org/webform/yocto-project-compatible-registration. Follow the instructions on the form to complete your application.

The application consists of the following sections:

  • Contact Information: Provide your contact information as the fields require. Along with your information, provide the released versions of the Yocto Project for which your layer is compatible.

  • Acceptance Criteria: Provide "Yes" or "No" answers for each of the items in the checklist. Space exists at the bottom of the form for any explanations for items for which you answered "No".

  • Recommendations: Provide answers for the questions regarding Linux kernel use and build success.

4.1.4.2. yocto-check-layer Script

The yocto-check-layer script provides you a way to assess how compatible your layer is with the Yocto Project. You should run this script prior to using the form to apply for compatibility as described in the previous section. You need to achieve a "PASS" result in order to have your application form successfully processed.

The script divides tests into three areas: COMMON, BSD, and DISTRO. For example, given a distribution layer (DISTRO), the layer must pass both the COMMON and DISTRO related tests. Furthermore, if your layer is a BSP layer, the layer must pass the COMMON and BSP set of tests.

To execute the script, enter the following commands from your build directory:

     $ source oe-init-build-env
     $ yocto-check-layer your_layer_directory
                    

Be sure to provide the actual directory for your layer as part of the command.

Entering the command causes the script to determine the type of layer and then to execute a set of specific tests against the layer. The following list overviews the test:

  • common.test_readme: Tests if a README file exists in the layer and the file is not empty.

  • common.test_parse: Tests to make sure that BitBake can parse the files without error (i.e. bitbake -p).

  • common.test_show_environment: Tests that the global or per-recipe environment is in order without errors (i.e. bitbake -e).

  • common.test_signatures: Tests to be sure that BSP and DISTRO layers do not come with recipes that change signatures.

  • bsp.test_bsp_defines_machines: Tests if a BSP layer has machine configurations.

  • bsp.test_bsp_no_set_machine: Tests to ensure a BSP layer does not set the machine when the layer is added.

  • distro.test_distro_defines_distros: Tests if a DISTRO layer has distro configurations.

  • distro.test_distro_no_set_distro: Tests to ensure a DISTRO layer does not set the distribution when the layer is added.

4.1.5. Enabling Your Layer

Before the OpenEmbedded build system can use your new layer, you need to enable it. To enable your layer, simply add your layer's path to the BBLAYERS variable in your conf/bblayers.conf file, which is found in the Build Directory. The following example shows how to enable a layer named meta-mylayer:

     LCONF_VERSION = "6"

     BBPATH = "${TOPDIR}"
     BBFILES ?= ""

     BBLAYERS ?= " \
       $HOME/poky/meta \
       $HOME/poky/meta-poky \
       $HOME/poky/meta-yocto-bsp \
       $HOME/poky/meta-mylayer \
       "
                

BitBake parses each conf/layer.conf file as specified in the BBLAYERS variable within the conf/bblayers.conf file. During the processing of each conf/layer.conf file, BitBake adds the recipes, classes and configurations contained within the particular layer to the source directory.

4.1.6. Using .bbappend Files in Your Layer

A recipe that appends Metadata to another recipe is called a BitBake append file. A BitBake append file uses the .bbappend file type suffix, while the corresponding recipe to which Metadata is being appended uses the .bb file type suffix.

You can use a .bbappend file in your layer to make additions or changes to the content of another layer's recipe without having to copy the other layer's recipe into your layer. Your .bbappend file resides in your layer, while the main .bb recipe file to which you are appending Metadata resides in a different layer.

Being able to append information to an existing recipe not only avoids duplication, but also automatically applies recipe changes from a different layer into your layer. If you were copying recipes, you would have to manually merge changes as they occur.

When you create an append file, you must use the same root name as the corresponding recipe file. For example, the append file someapp_2.4.bbappend must apply to someapp_2.4.bb. This means the original recipe and append file names are version number-specific. If the corresponding recipe is renamed to update to a newer version, you must also rename and possibly update the corresponding .bbappend as well. During the build process, BitBake displays an error on starting if it detects a .bbappend file that does not have a corresponding recipe with a matching name. See the BB_DANGLINGAPPENDS_WARNONLY variable for information on how to handle this error.

As an example, consider the main formfactor recipe and a corresponding formfactor append file both from the Source Directory. Here is the main formfactor recipe, which is named formfactor_0.0.bb and located in the "meta" layer at meta/recipes-bsp/formfactor:

     SUMMARY = "Device formfactor information"
     SECTION = "base"
     LICENSE = "MIT"
     LIC_FILES_CHKSUM = "file://${COREBASE}/meta/COPYING.MIT;md5=3da9cfbcb788c80a0384361b4de20420"
     PR = "r45"

     SRC_URI = "file://config file://machconfig"
     S = "${WORKDIR}"

     PACKAGE_ARCH = "${MACHINE_ARCH}"
     INHIBIT_DEFAULT_DEPS = "1"

     do_install() {
	     # Install file only if it has contents
             install -d ${D}${sysconfdir}/formfactor/
             install -m 0644 ${S}/config ${D}${sysconfdir}/formfactor/
	     if [ -s "${S}/machconfig" ]; then
	             install -m 0644 ${S}/machconfig ${D}${sysconfdir}/formfactor/
	     fi
     }                

In the main recipe, note the SRC_URI variable, which tells the OpenEmbedded build system where to find files during the build.

Following is the append file, which is named formfactor_0.0.bbappend and is from the Raspberry Pi BSP Layer named meta-raspberrypi. The file is in the layer at recipes-bsp/formfactor:

     FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
                

By default, the build system uses the FILESPATH variable to locate files. This append file extends the locations by setting the FILESEXTRAPATHS variable. Setting this variable in the .bbappend file is the most reliable and recommended method for adding directories to the search path used by the build system to find files.

The statement in this example extends the directories to include ${THISDIR}/${PN}, which resolves to a directory named formfactor in the same directory in which the append file resides (i.e. meta-raspberrypi/recipes-bsp/formfactor. This implies that you must have the supporting directory structure set up that will contain any files or patches you will be including from the layer.

Using the immediate expansion assignment operator := is important because of the reference to THISDIR. The trailing colon character is important as it ensures that items in the list remain colon-separated.

Note

BitBake automatically defines the THISDIR variable. You should never set this variable yourself. Using "_prepend" as part of the FILESEXTRAPATHS ensures your path will be searched prior to other paths in the final list.

Also, not all append files add extra files. Many append files simply exist to add build options (e.g. systemd). For these cases, your append file would not even use the FILESEXTRAPATHS statement.

4.1.7. Prioritizing Your Layer

Each layer is assigned a priority value. Priority values control which layer takes precedence if there are recipe files with the same name in multiple layers. For these cases, the recipe file from the layer with a higher priority number takes precedence. Priority values also affect the order in which multiple .bbappend files for the same recipe are applied. You can either specify the priority manually, or allow the build system to calculate it based on the layer's dependencies.

To specify the layer's priority manually, use the BBFILE_PRIORITY variable. For example:

     BBFILE_PRIORITY_mylayer = "1"
                

Note

It is possible for a recipe with a lower version number PV in a layer that has a higher priority to take precedence.

Also, the layer priority does not currently affect the precedence order of .conf or .bbclass files. Future versions of BitBake might address this.

4.1.8. Managing Layers

You can use the BitBake layer management tool to provide a view into the structure of recipes across a multi-layer project. Being able to generate output that reports on configured layers with their paths and priorities and on .bbappend files and their applicable recipes can help to reveal potential problems.

Use the following form when running the layer management tool.

     $ bitbake-layers command [arguments]
                

The following list describes the available commands:

  • help: Displays general help or help on a specified command.

  • show-layers: Shows the current configured layers.

  • show-recipes: Lists available recipes and the layers that provide them.

  • show-overlayed: Lists overlayed recipes. A recipe is overlayed when a recipe with the same name exists in another layer that has a higher layer priority.

  • show-appends: Lists .bbappend files and the recipe files to which they apply.

  • show-cross-depends: Lists dependency relationships between recipes that cross layer boundaries.

  • add-layer: Adds a layer to bblayers.conf.

  • remove-layer: Removes a layer from bblayers.conf

  • flatten: Flattens the layer configuration into a separate output directory. Flattening your layer configuration builds a "flattened" directory that contains the contents of all layers, with any overlayed recipes removed and any .bbappend files appended to the corresponding recipes. You might have to perform some manual cleanup of the flattened layer as follows:

    • Non-recipe files (such as patches) are overwritten. The flatten command shows a warning for these files.

    • Anything beyond the normal layer setup has been added to the layer.conf file. Only the lowest priority layer's layer.conf is used.

    • Overridden and appended items from .bbappend files need to be cleaned up. The contents of each .bbappend end up in the flattened recipe. However, if there are appended or changed variable values, you need to tidy these up yourself. Consider the following example. Here, the bitbake-layers command adds the line #### bbappended ... so that you know where the following lines originate:

           ...
           DESCRIPTION = "A useful utility"
           ...
           EXTRA_OECONF = "--enable-something"
           ...
      
           #### bbappended from meta-anotherlayer ####
      
           DESCRIPTION = "Customized utility"
           EXTRA_OECONF += "--enable-somethingelse"
                                      

      Ideally, you would tidy up these utilities as follows:

           ...
           DESCRIPTION = "Customized utility"
           ...
           EXTRA_OECONF = "--enable-something --enable-somethingelse"
           ...
                                      

4.1.9. Creating a General Layer Using the yocto-layer Script

The yocto-layer script simplifies creating a new general layer.

Note

For information on BSP layers, see the "BSP Layers" section in the Yocto Project Board Specific (BSP) Developer's Guide.

The default mode of the script's operation is to prompt you for information needed to generate the layer:

  • The layer priority.

  • Whether or not to create a sample recipe.

  • Whether or not to create a sample append file.

Use the yocto-layer create sub-command to create a new general layer. In its simplest form, you can create a layer as follows:

     $ yocto-layer create mylayer
                

The previous example creates a layer named meta-mylayer in the current directory.

As the yocto-layer create command runs, default values for the prompts appear in brackets. Pressing enter without supplying anything for the prompts or pressing enter and providing an invalid response causes the script to accept the default value. Once the script completes, the new layer is created in the current working directory. The script names the layer by prepending meta- to the name you provide.

Minimally, the script creates the following within the layer:

  • The conf directory: This directory contains the layer's configuration file. The root name for the file is the same as the root name your provided for the layer (e.g. layer.conf).

  • The COPYING.MIT file: The copyright and use notice for the software.

  • The README file: A file describing the contents of your new layer.

If you choose to generate a sample recipe file, the script prompts you for the name for the recipe and then creates it in layer/recipes-example/example/. The script creates a .bb file and a directory, which contains a sample helloworld.c source file, along with a sample patch file. If you do not provide a recipe name, the script uses "example".

If you choose to generate a sample append file, the script prompts you for the name for the file and then creates it in layer/recipes-example-bbappend/example-bbappend/. The script creates a .bbappend file and a directory, which contains a sample patch file. If you do not provide a recipe name, the script uses "example". The script also prompts you for the version of the append file. The version should match the recipe to which the append file is associated.

The easiest way to see how the yocto-layer script works is to experiment with the script. You can also read the usage information by entering the following:

     $ yocto-layer help
                

Once you create your general layer, you must add it to your bblayers.conf file. Here is an example where a layer named meta-mylayer is added:

     BBLAYERS = ?" \
        /usr/local/src/yocto/meta \
        /usr/local/src/yocto/meta-poky \
        /usr/local/src/yocto/meta-yocto-bsp \
        /usr/local/src/yocto/meta-mylayer \
        "
                

Adding the layer to this file enables the build system to locate the layer during the build.

4.2. Customizing Images

You can customize images to satisfy particular requirements. This section describes several methods and provides guidelines for each.

4.2.1. Customizing Images Using local.conf

Probably the easiest way to customize an image is to add a package by way of the local.conf configuration file. Because it is limited to local use, this method generally only allows you to add packages and is not as flexible as creating your own customized image. When you add packages using local variables this way, you need to realize that these variable changes are in effect for every build and consequently affect all images, which might not be what you require.

To add a package to your image using the local configuration file, use the IMAGE_INSTALL variable with the _append operator:

     IMAGE_INSTALL_append = " strace"
                

Use of the syntax is important - specifically, the space between the quote and the package name, which is strace in this example. This space is required since the _append operator does not add the space.

Furthermore, you must use _append instead of the += operator if you want to avoid ordering issues. The reason for this is because doing so unconditionally appends to the variable and avoids ordering problems due to the variable being set in image recipes and .bbclass files with operators like ?=. Using _append ensures the operation takes affect.

As shown in its simplest use, IMAGE_INSTALL_append affects all images. It is possible to extend the syntax so that the variable applies to a specific image only. Here is an example:

     IMAGE_INSTALL_append_pn-core-image-minimal = " strace"
                

This example adds strace to the core-image-minimal image only.

You can add packages using a similar approach through the CORE_IMAGE_EXTRA_INSTALL variable. If you use this variable, only core-image-* images are affected.

4.2.2. Customizing Images Using Custom IMAGE_FEATURES and EXTRA_IMAGE_FEATURES

Another method for customizing your image is to enable or disable high-level image features by using the IMAGE_FEATURES and EXTRA_IMAGE_FEATURES variables. Although the functions for both variables are nearly equivalent, best practices dictate using IMAGE_FEATURES from within a recipe and using EXTRA_IMAGE_FEATURES from within your local.conf file, which is found in the Build Directory.

To understand how these features work, the best reference is meta/classes/core-image.bbclass. This class lists out the available IMAGE_FEATURES of which most map to package groups while some, such as debug-tweaks and read-only-rootfs, resolve as general configuration settings.

In summary, the file looks at the contents of the IMAGE_FEATURES variable and then maps or configures the feature accordingly. Based on this information, the build system automatically adds the appropriate packages or configurations to the IMAGE_INSTALL variable. Effectively, you are enabling extra features by extending the class or creating a custom class for use with specialized image .bb files.

Use the EXTRA_IMAGE_FEATURES variable from within your local configuration file. Using a separate area from which to enable features with this variable helps you avoid overwriting the features in the image recipe that are enabled with IMAGE_FEATURES. The value of EXTRA_IMAGE_FEATURES is added to IMAGE_FEATURES within meta/conf/bitbake.conf.

To illustrate how you can use these variables to modify your image, consider an example that selects the SSH server. The Yocto Project ships with two SSH servers you can use with your images: Dropbear and OpenSSH. Dropbear is a minimal SSH server appropriate for resource-constrained environments, while OpenSSH is a well-known standard SSH server implementation. By default, the core-image-sato image is configured to use Dropbear. The core-image-full-cmdline and core-image-lsb images both include OpenSSH. The core-image-minimal image does not contain an SSH server.

You can customize your image and change these defaults. Edit the IMAGE_FEATURES variable in your recipe or use the EXTRA_IMAGE_FEATURES in your local.conf file so that it configures the image you are working with to include ssh-server-dropbear or ssh-server-openssh.

Note

See the "Images" section in the Yocto Project Reference Manual for a complete list of image features that ship with the Yocto Project.

4.2.3. Customizing Images Using Custom .bb Files

You can also customize an image by creating a custom recipe that defines additional software as part of the image. The following example shows the form for the two lines you need:

     IMAGE_INSTALL = "packagegroup-core-x11-base package1 package2"

     inherit core-image
                

Defining the software using a custom recipe gives you total control over the contents of the image. It is important to use the correct names of packages in the IMAGE_INSTALL variable. You must use the OpenEmbedded notation and not the Debian notation for the names (e.g. glibc-dev instead of libc6-dev).

The other method for creating a custom image is to base it on an existing image. For example, if you want to create an image based on core-image-sato but add the additional package strace to the image, copy the meta/recipes-sato/images/core-image-sato.bb to a new .bb and add the following line to the end of the copy:

     IMAGE_INSTALL += "strace"
                

4.2.4. Customizing Images Using Custom Package Groups

For complex custom images, the best approach for customizing an image is to create a custom package group recipe that is used to build the image or images. A good example of a package group recipe is meta/recipes-core/packagegroups/packagegroup-base.bb.

If you examine that recipe, you see that the PACKAGES variable lists the package group packages to produce. The inherit packagegroup statement sets appropriate default values and automatically adds -dev, -dbg, and -ptest complementary packages for each package specified in the PACKAGES statement.

Note

The inherit packages should be located near the top of the recipe, certainly before the PACKAGES statement.

For each package you specify in PACKAGES, you can use RDEPENDS and RRECOMMENDS entries to provide a list of packages the parent task package should contain. You can see examples of these further down in the packagegroup-base.bb recipe.

Here is a short, fabricated example showing the same basic pieces:

     DESCRIPTION = "My Custom Package Groups"

     inherit packagegroup

     PACKAGES = "\
         packagegroup-custom-apps \
         packagegroup-custom-tools \
         "

     RDEPENDS_packagegroup-custom-apps = "\
         dropbear \
         portmap \
         psplash"

     RDEPENDS_packagegroup-custom-tools = "\
         oprofile \
         oprofileui-server \
         lttng-tools"

     RRECOMMENDS_packagegroup-custom-tools = "\
         kernel-module-oprofile"
                

In the previous example, two package group packages are created with their dependencies and their recommended package dependencies listed: packagegroup-custom-apps, and packagegroup-custom-tools. To build an image using these package group packages, you need to add packagegroup-custom-apps and/or packagegroup-custom-tools to IMAGE_INSTALL. For other forms of image dependencies see the other areas of this section.

4.2.5. Customizing an Image Hostname

By default, the configured hostname (i.e. /etc/hostname) in an image is the same as the machine name. For example, if MACHINE equals "qemux86", the configured hostname written to /etc/hostname is "qemux86".

You can customize this name by altering the value of the "hostname" variable in the base-files recipe using either an append file or a configuration file. Use the following in an append file:

     hostname="myhostname"
                

Use the following in a configuration file:

     hostname_pn-base-files = "myhostname"
                

Changing the default value of the variable "hostname" can be useful in certain situations. For example, suppose you need to do extensive testing on an image and you would like to easily identify the image under test from existing images with typical default hostnames. In this situation, you could change the default hostname to "testme", which results in all the images using the name "testme". Once testing is complete and you do not need to rebuild the image for test any longer, you can easily reset the default hostname.

Another point of interest is that if you unset the variable, the image will have no default hostname in the filesystem. Here is an example that unsets the variable in a configuration file:

     hostname_pn-base-files = ""
                

Having no default hostname in the filesystem is suitable for environments that use dynamic hostnames such as virtual machines.

4.3. Writing a New Recipe

Recipes (.bb files) are fundamental components in the Yocto Project environment. Each software component built by the OpenEmbedded build system requires a recipe to define the component. This section describes how to create, write, and test a new recipe.

Note

For information on variables that are useful for recipes and for information about recipe naming issues, see the "Required" section of the Yocto Project Reference Manual.

4.3.1. Overview

The following figure shows the basic process for creating a new recipe. The remainder of the section provides details for the steps.

4.3.2. Locate or Automatically Create a Base Recipe

You can always write a recipe from scratch. However, three choices exist that can help you quickly get a start on a new recipe:

  • devtool add: A command that assists in creating a recipe and an environment conducive to development.

  • recipetool create: A command provided by the Yocto Project that automates creation of a base recipe based on the source files.

  • Existing Recipes: Location and modification of an existing recipe that is similar in function to the recipe you need.

Note

For information on recipe syntax, see the "Recipe Syntax" section in the Yocto Project Reference Manual.

4.3.2.1. Creating the Base Recipe Using devtool add

The devtool add command uses the same logic for auto-creating the recipe as recipetool create, which is listed below. Additionally, however, devtool add sets up an environment that makes it easy for you to patch the source and to make changes to the recipe as is often necessary when adding a recipe to build a new piece of software to be included in a build.

You can find a complete description of the devtool add command in the "A Closer Look at devtool add" section in the Yocto Project Software Development Kit (SDK) Developer's Guide.

4.3.2.2. Creating the Base Recipe Using recipetool create

recipetool create automates creation of a base recipe given a set of source code files. As long as you can extract or point to the source files, the tool will construct a recipe and automatically configure all pre-build information into the recipe. For example, suppose you have an application that builds using Autotools. Creating the base recipe using recipetool results in a recipe that has the pre-build dependencies, license requirements, and checksums configured.

To run the tool, you just need to be in your Build Directory and have sourced the build environment setup script (i.e. oe-init-build-env). Here is the basic recipetool syntax:

Note

Running recipetool -h or recipetool create -h produces the Python-generated help, which presented differently than what follows here.

     recipetool -h
     recipetool create [-h]
     recipetool [-d] [-q] [--color auto | always | never ] create -o OUTFILE [-m] [-x EXTERNALSRC] source

          -d       Enables debug output.
          -q       Outputs only errors (quiet mode).
          --color  Colorizes the output automatically, always, or never.
          -h       Displays Python generated syntax for recipetool.
          create   Causes recipetool to create a base recipe.  The create
                   command is further defined with these options:

                   -o OUTFILE      Specifies the full path and filename for the generated
                                   recipe.
                   -m              Causes the recipe to be machine-specific rather than
                                   architecture-specific (default).
                   -x EXTERNALSRC  Fetches and extracts source files from source
                                   and places them in EXTERNALSRC.
                                   source must be a URL.
                   -h              Displays Python-generated syntax for create.
                   source          Specifies the source code on which to base the
                                   recipe.
                    

Running recipetool create -o OUTFILE creates the base recipe and locates it properly in the layer that contains your source files. Following are some syntax examples:

Use this syntax to generate a recipe based on source. Once generated, the recipe resides in the existing source code layer:

     recipetool create -o OUTFILE source
                    

Use this syntax to generate a recipe using code that you extract from source. The extracted code is placed in its own layer defined by EXTERNALSRC.

     recipetool create -o OUTFILE -x EXTERNALSRC source
                    

Use this syntax to generate a recipe based on source. The options direct recipetool to generate debugging information. Once generated, the recipe resides in the existing source code layer:

     recipetool create -d -o OUTFILE source
                    

4.3.2.3. Locating and Using a Similar Recipe

Before writing a recipe from scratch, it is often useful to discover whether someone else has already written one that meets (or comes close to meeting) your needs. The Yocto Project and OpenEmbedded communities maintain many recipes that might be candidates for what you are doing. You can find a good central index of these recipes in the OpenEmbedded metadata index.

Working from an existing recipe or a skeleton recipe is the best way to get started. Here are some points on both methods:

  • Locate and modify a recipe that is close to what you want to do: This method works when you are familiar with the current recipe space. The method does not work so well for those new to the Yocto Project or writing recipes.

    Some risks associated with this method are using a recipe that has areas totally unrelated to what you are trying to accomplish with your recipe, not recognizing areas of the recipe that you might have to add from scratch, and so forth. All these risks stem from unfamiliarity with the existing recipe space.

  • Use and modify the following skeleton recipe: If for some reason you do not want to use recipetool and you cannot find an existing recipe that is close to meeting your needs, you can use the following structure to provide the fundamental areas of a new recipe.

         DESCRIPTION = ""
         HOMEPAGE = ""
         LICENSE = ""
         SECTION = ""
         DEPENDS = ""
         LIC_FILES_CHKSUM = ""
    
         SRC_URI = ""
                                

4.3.3. Storing and Naming the Recipe

Once you have your base recipe, you should put it in your own layer and name it appropriately. Locating it correctly ensures that the OpenEmbedded build system can find it when you use BitBake to process the recipe.

  • Storing Your Recipe: The OpenEmbedded build system locates your recipe through the layer's conf/layer.conf file and the BBFILES variable. This variable sets up a path from which the build system can locate recipes. Here is the typical use:

         BBFILES += "${LAYERDIR}/recipes-*/*/*.bb \
                     ${LAYERDIR}/recipes-*/*/*.bbappend"
                        

    Consequently, you need to be sure you locate your new recipe inside your layer such that it can be found.

    You can find more information on how layers are structured in the "Understanding and Creating Layers" section.

  • Naming Your Recipe: When you name your recipe, you need to follow this naming convention:

         basename_version.bb
                        

    Use lower-cased characters and do not include the reserved suffixes -native, -cross, -initial, or -dev casually (i.e. do not use them as part of your recipe name unless the string applies). Here are some examples:

         cups_1.7.0.bb
         gawk_4.0.2.bb
         irssi_0.8.16-rc1.bb
                        

4.3.4. Running a Build on the Recipe

Creating a new recipe is usually an iterative process that requires using BitBake to process the recipe multiple times in order to progressively discover and add information to the recipe file.

Assuming you have sourced the build environment setup script (i.e. oe-init-build-env) and you are in the Build Directory, use BitBake to process your recipe. All you need to provide is the basename of the recipe as described in the previous section:

     $ bitbake basename
                

During the build, the OpenEmbedded build system creates a temporary work directory for each recipe (${WORKDIR}) where it keeps extracted source files, log files, intermediate compilation and packaging files, and so forth.

The path to the per-recipe temporary work directory depends on the context in which it is being built. The quickest way to find this path is to have BitBake return it by running the following:

     $ bitbake -e basename | grep ^WORKDIR=
                

As an example, assume a Source Directory top-level folder named poky, a default Build Directory at poky/build, and a qemux86-poky-linux machine target system. Furthermore, suppose your recipe is named foo_1.3.0.bb. In this case, the work directory the build system uses to build the package would be as follows:

     poky/build/tmp/work/qemux86-poky-linux/foo/1.3.0-r0
                

Inside this directory you can find sub-directories such as image, packages-split, and temp. After the build, you can examine these to determine how well the build went.

Note

You can find log files for each task in the recipe's temp directory (e.g. poky/build/tmp/work/qemux86-poky-linux/foo/1.3.0-r0/temp). Log files are named log.taskname (e.g. log.do_configure, log.do_fetch, and log.do_compile).

You can find more information about the build process in "The Yocto Project Development Environment" chapter of the Yocto Project Reference Manual.

4.3.5. Fetching Code

The first thing your recipe must do is specify how to fetch the source files. Fetching is controlled mainly through the SRC_URI variable. Your recipe must have a SRC_URI variable that points to where the source is located. For a graphical representation of source locations, see the "Sources" section in the Yocto Project Reference Manual.

The do_fetch task uses the prefix of each entry in the SRC_URI variable value to determine which fetcher to use to get your source files. It is the SRC_URI variable that triggers the fetcher. The do_patch task uses the variable after source is fetched to apply patches. The OpenEmbedded build system uses FILESOVERRIDES for scanning directory locations for local files in SRC_URI.

The SRC_URI variable in your recipe must define each unique location for your source files. It is good practice to not hard-code pathnames in an URL used in SRC_URI. Rather than hard-code these paths, use ${PV}, which causes the fetch process to use the version specified in the recipe filename. Specifying the version in this manner means that upgrading the recipe to a future version is as simple as renaming the recipe to match the new version.

Here is a simple example from the meta/recipes-devtools/cdrtools/cdrtools-native_3.01a20.bb recipe where the source comes from a single tarball. Notice the use of the PV variable:

     SRC_URI = "ftp://ftp.berlios.de/pub/cdrecord/alpha/cdrtools-${PV}.tar.bz2"
                

Files mentioned in SRC_URI whose names end in a typical archive extension (e.g. .tar, .tar.gz, .tar.bz2, .zip, and so forth), are automatically extracted during the do_unpack task. For another example that specifies these types of files, see the "Autotooled Package" section.

Another way of specifying source is from an SCM. For Git repositories, you must specify SRCREV and you should specify PV to include the revision with SRCPV. Here is an example from the recipe meta/recipes-kernel/blktrace/blktrace_git.bb:

     SRCREV = "d6918c8832793b4205ed3bfede78c2f915c23385"

     PR = "r6"
     PV = "1.0.5+git${SRCPV}"

     SRC_URI = "git://git.kernel.dk/blktrace.git \
                file://ldflags.patch"
                

If your SRC_URI statement includes URLs pointing to individual files fetched from a remote server other than a version control system, BitBake attempts to verify the files against checksums defined in your recipe to ensure they have not been tampered with or otherwise modified since the recipe was written. Two checksums are used: SRC_URI[md5sum] and SRC_URI[sha256sum].

If your SRC_URI variable points to more than a single URL (excluding SCM URLs), you need to provide the md5 and sha256 checksums for each URL. For these cases, you provide a name for each URL as part of the SRC_URI and then reference that name in the subsequent checksum statements. Here is an example:

     SRC_URI = "${DEBIAN_MIRROR}/main/a/apmd/apmd_3.2.2.orig.tar.gz;name=tarball \
                ${DEBIAN_MIRROR}/main/a/apmd/apmd_${PV}.diff.gz;name=patch"

     SRC_URI[tarball.md5sum] = "b1e6309e8331e0f4e6efd311c2d97fa8"
     SRC_URI[tarball.sha256sum] = "7f7d9f60b7766b852881d40b8ff91d8e39fccb0d1d913102a5c75a2dbb52332d"

     SRC_URI[patch.md5sum] = "57e1b689264ea80f78353519eece0c92"
     SRC_URI[patch.sha256sum] = "7905ff96be93d725544d0040e425c42f9c05580db3c272f11cff75b9aa89d430"
                

Proper values for md5 and sha256 checksums might be available with other signatures on the download page for the upstream source (e.g. md5, sha1, sha256, GPG, and so forth). Because the OpenEmbedded build system only deals with sha256sum and md5sum, you should verify all the signatures you find by hand.

If no SRC_URI checksums are specified when you attempt to build the recipe, or you provide an incorrect checksum, the build will produce an error for each missing or incorrect checksum. As part of the error message, the build system provides the checksum string corresponding to the fetched file. Once you have the correct checksums, you can copy and paste them into your recipe and then run the build again to continue.

Note

As mentioned, if the upstream source provides signatures for verifying the downloaded source code, you should verify those manually before setting the checksum values in the recipe and continuing with the build.

This final example is a bit more complicated and is from the meta/recipes-sato/rxvt-unicode/rxvt-unicode_9.20.bb recipe. The example's SRC_URI statement identifies multiple files as the source files for the recipe: a tarball, a patch file, a desktop file, and an icon.

     SRC_URI = "http://dist.schmorp.de/rxvt-unicode/Attic/rxvt-unicode-${PV}.tar.bz2 \
                file://xwc.patch \
                file://rxvt.desktop \
                file://rxvt.png"
                

When you specify local files using the file:// URI protocol, the build system fetches files from the local machine. The path is relative to the FILESPATH variable and searches specific directories in a certain order: ${BP}, ${BPN}, and files. The directories are assumed to be subdirectories of the directory in which the recipe or append file resides. For another example that specifies these types of files, see the "Single .c File Package (Hello World!)" section.

The previous example also specifies a patch file. Patch files are files whose names usually end in .patch or .diff but can end with compressed suffixes such as diff.gz and patch.bz2, for example. The build system automatically applies patches as described in the "Patching Code" section.

4.3.6. Unpacking Code

During the build, the do_unpack task unpacks the source with ${S} pointing to where it is unpacked.

If you are fetching your source files from an upstream source archived tarball and the tarball's internal structure matches the common convention of a top-level subdirectory named ${BPN}-${PV}, then you do not need to set S. However, if SRC_URI specifies to fetch source from an archive that does not use this convention, or from an SCM like Git or Subversion, your recipe needs to define S.

If processing your recipe using BitBake successfully unpacks the source files, you need to be sure that the directory pointed to by ${S} matches the structure of the source.

4.3.7. Patching Code

Sometimes it is necessary to patch code after it has been fetched. Any files mentioned in SRC_URI whose names end in .patch or .diff or compressed versions of these suffixes (e.g. diff.gz are treated as patches. The do_patch task automatically applies these patches.

The build system should be able to apply patches with the "-p1" option (i.e. one directory level in the path will be stripped off). If your patch needs to have more directory levels stripped off, specify the number of levels using the "striplevel" option in the SRC_URI entry for the patch. Alternatively, if your patch needs to be applied in a specific subdirectory that is not specified in the patch file, use the "patchdir" option in the entry.

As with all local files referenced in SRC_URI using file://, you should place patch files in a directory next to the recipe either named the same as the base name of the recipe (BP and BPN) or "files".

4.3.8. Licensing

Your recipe needs to have both the LICENSE and LIC_FILES_CHKSUM variables:

  • LICENSE: This variable specifies the license for the software. If you do not know the license under which the software you are building is distributed, you should go to the source code and look for that information. Typical files containing this information include COPYING, LICENSE, and README files. You could also find the information near the top of a source file. For example, given a piece of software licensed under the GNU General Public License version 2, you would set LICENSE as follows:

         LICENSE = "GPLv2"
                            

    The licenses you specify within LICENSE can have any name as long as you do not use spaces, since spaces are used as separators between license names. For standard licenses, use the names of the files in meta/files/common-licenses/ or the SPDXLICENSEMAP flag names defined in meta/conf/licenses.conf.

  • LIC_FILES_CHKSUM: The OpenEmbedded build system uses this variable to make sure the license text has not changed. If it has, the build produces an error and it affords you the chance to figure it out and correct the problem.

    You need to specify all applicable licensing files for the software. At the end of the configuration step, the build process will compare the checksums of the files to be sure the text has not changed. Any differences result in an error with the message containing the current checksum. For more explanation and examples of how to set the LIC_FILES_CHKSUM variable, see the "Tracking License Changes" section in the Yocto Project Reference Manual.

    To determine the correct checksum string, you can list the appropriate files in the LIC_FILES_CHKSUM variable with incorrect md5 strings, attempt to build the software, and then note the resulting error messages that will report the correct md5 strings. See the "Fetching Code" section for additional information.

    Here is an example that assumes the software has a COPYING file:

         LIC_FILES_CHKSUM = "file://COPYING;md5=xxx"
                            

    When you try to build the software, the build system will produce an error and give you the correct string that you can substitute into the recipe file for a subsequent build.

4.3.9. Dependencies

Most software packages have a short list of other packages that they require, which are called dependencies. These dependencies fall into two main categories: build-time dependencies, which are required when the software is built; and runtime dependencies, which are required to be installed on the target in order for the software to run.

Within a recipe, you specify build-time dependencies using the DEPENDS variable. Although nuances exist, items specified in DEPENDS should be names of other recipes. It is important that you specify all build-time dependencies explicitly. If you do not, due to the parallel nature of BitBake's execution, you can end up with a race condition where the dependency is present for one task of a recipe (e.g. do_configure) and then gone when the next task runs (e.g. do_compile).

Another consideration is that configure scripts might automatically check for optional dependencies and enable corresponding functionality if those dependencies are found. This behavior means that to ensure deterministic results and thus avoid more race conditions, you need to either explicitly specify these dependencies as well, or tell the configure script explicitly to disable the functionality. If you wish to make a recipe that is more generally useful (e.g. publish the recipe in a layer for others to use), instead of hard-disabling the functionality, you can use the PACKAGECONFIG variable to allow functionality and the corresponding dependencies to be enabled and disabled easily by other users of the recipe.

Similar to build-time dependencies, you specify runtime dependencies through a variable - RDEPENDS, which is package-specific. All variables that are package-specific need to have the name of the package added to the end as an override. Since the main package for a recipe has the same name as the recipe, and the recipe's name can be found through the ${PN} variable, then you specify the dependencies for the main package by setting RDEPENDS_${PN}. If the package were named ${PN}-tools, then you would set RDEPENDS_${PN}-tools, and so forth.

Some runtime dependencies will be set automatically at packaging time. These dependencies include any shared library dependencies (i.e. if a package "example" contains "libexample" and another package "mypackage" contains a binary that links to "libexample" then the OpenEmbedded build system will automatically add a runtime dependency to "mypackage" on "example"). See the "Automatically Added Runtime Dependencies" in the Yocto Project Reference Manual for further details.

4.3.10. Configuring the Recipe

Most software provides some means of setting build-time configuration options before compilation. Typically, setting these options is accomplished by running a configure script with some options, or by modifying a build configuration file.

Note

As of Yocto Project Release 1.7, some of the core recipes that package binary configuration scripts now disable the scripts due to the scripts previously requiring error-prone path substitution. The OpenEmbedded build system uses pkg-config now, which is much more robust. You can find a list of the *-config scripts that are disabled list in the "Binary Configuration Scripts Disabled" section in the Yocto Project Reference Manual.

A major part of build-time configuration is about checking for build-time dependencies and possibly enabling optional functionality as a result. You need to specify any build-time dependencies for the software you are building in your recipe's DEPENDS value, in terms of other recipes that satisfy those dependencies. You can often find build-time or runtime dependencies described in the software's documentation.

The following list provides configuration items of note based on how your software is built:

  • Autotools: If your source files have a configure.ac file, then your software is built using Autotools. If this is the case, you just need to worry about modifying the configuration.

    When using Autotools, your recipe needs to inherit the autotools class and your recipe does not have to contain a do_configure task. However, you might still want to make some adjustments. For example, you can set EXTRA_OECONF or PACKAGECONFIG_CONFARGS to pass any needed configure options that are specific to the recipe.

  • CMake: If your source files have a CMakeLists.txt file, then your software is built using CMake. If this is the case, you just need to worry about modifying the configuration.

    When you use CMake, your recipe needs to inherit the cmake class and your recipe does not have to contain a do_configure task. You can make some adjustments by setting EXTRA_OECMAKE to pass any needed configure options that are specific to the recipe.

  • Other: If your source files do not have a configure.ac or CMakeLists.txt file, then your software is built using some method other than Autotools or CMake. If this is the case, you normally need to provide a do_configure task in your recipe unless, of course, there is nothing to configure.

    Even if your software is not being built by Autotools or CMake, you still might not need to deal with any configuration issues. You need to determine if configuration is even a required step. You might need to modify a Makefile or some configuration file used for the build to specify necessary build options. Or, perhaps you might need to run a provided, custom configure script with the appropriate options.

    For the case involving a custom configure script, you would run ./configure --help and look for the options you need to set.

Once configuration succeeds, it is always good practice to look at the log.do_configure file to ensure that the appropriate options have been enabled and no additional build-time dependencies need to be added to DEPENDS. For example, if the configure script reports that it found something not mentioned in DEPENDS, or that it did not find something that it needed for some desired optional functionality, then you would need to add those to DEPENDS. Looking at the log might also reveal items being checked for, enabled, or both that you do not want, or items not being found that are in DEPENDS, in which case you would need to look at passing extra options to the configure script as needed. For reference information on configure options specific to the software you are building, you can consult the output of the ./configure --help command within ${S} or consult the software's upstream documentation.

4.3.11. Using Headers to Interface with Devices

If your recipe builds an application that needs to communicate with some device or needs an API into a custom kernel, you will need to provide appropriate header files. Under no circumstances should you ever modify the existing meta/recipes-kernel/linux-libc-headers/linux-libc-headers.inc file. These headers are used to build libc and must not be compromised with custom or machine-specific header information. If you customize libc through modified headers all other applications that use libc thus become affected.

Warning

Never copy and customize the libc header file (i.e. meta/recipes-kernel/linux-libc-headers/linux-libc-headers.inc).

The correct way to interface to a device or custom kernel is to use a separate package that provides the additional headers for the driver or other unique interfaces. When doing so, your application also becomes responsible for creating a dependency on that specific provider.

Consider the following:

  • Never modify linux-libc-headers.inc. Consider that file to be part of the libc system, and not something you use to access the kernel directly. You should access libc through specific libc calls.

  • Applications that must talk directly to devices should either provide necessary headers themselves, or establish a dependency on a special headers package that is specific to that driver.

For example, suppose you want to modify an existing header that adds I/O control or network support. If the modifications are used by a small number programs, providing a unique version of a header is easy and has little impact. When doing so, bear in mind the guidelines in the previous list.

Note

If for some reason your changes need to modify the behavior of the libc, and subsequently all other applications on the system, use a .bbappend to modify the linux-kernel-headers.inc file. However, take care to not make the changes machine specific.

Consider a case where your kernel is older and you need an older libc ABI. The headers installed by your recipe should still be a standard mainline kernel, not your own custom one.

When you use custom kernel headers you need to get them from STAGING_KERNEL_DIR, which is the directory with kernel headers that are required to build out-of-tree modules. Your recipe will also need the following:

     do_configure[depends] += "virtual/kernel:do_shared_workdir"
                

4.3.12. Compilation

During a build, the do_compile task happens after source is fetched, unpacked, and configured. If the recipe passes through do_compile successfully, nothing needs to be done.

However, if the compile step fails, you need to diagnose the failure. Here are some common issues that cause failures.

Note

For cases where improper paths are detected for configuration files or for when libraries/headers cannot be found, be sure you are using the more robust pkg-config. See the note in section "Configuring the Recipe" for additional information.

  • Parallel build failures: These failures manifest themselves as intermittent errors, or errors reporting that a file or directory that should be created by some other part of the build process could not be found. This type of failure can occur even if, upon inspection, the file or directory does exist after the build has failed, because that part of the build process happened in the wrong order.

    To fix the problem, you need to either satisfy the missing dependency in the Makefile or whatever script produced the Makefile, or (as a workaround) set PARALLEL_MAKE to an empty string:

         PARALLEL_MAKE = ""
                            

    For information on parallel Makefile issues, see the "Debugging Parallel Make Races" section.

  • Improper host path usage: This failure applies to recipes building for the target or nativesdk only. The failure occurs when the compilation process uses improper headers, libraries, or other files from the host system when cross-compiling for the target.

    To fix the problem, examine the log.do_compile file to identify the host paths being used (e.g. /usr/include, /usr/lib, and so forth) and then either add configure options, apply a patch, or do both.

  • Failure to find required libraries/headers: If a build-time dependency is missing because it has not been declared in DEPENDS, or because the dependency exists but the path used by the build process to find the file is incorrect and the configure step did not detect it, the compilation process could fail. For either of these failures, the compilation process notes that files could not be found. In these cases, you need to go back and add additional options to the configure script as well as possibly add additional build-time dependencies to DEPENDS.

    Occasionally, it is necessary to apply a patch to the source to ensure the correct paths are used. If you need to specify paths to find files staged into the sysroot from other recipes, use the variables that the OpenEmbedded build system provides (e.g. STAGING_BINDIR, STAGING_INCDIR, STAGING_DATADIR, and so forth).

4.3.13. Installing

During do_install, the task copies the built files along with their hierarchy to locations that would mirror their locations on the target device. The installation process copies files from the ${S}, ${B}, and ${WORKDIR} directories to the ${D} directory to create the structure as it should appear on the target system.

How your software is built affects what you must do to be sure your software is installed correctly. The following list describes what you must do for installation depending on the type of build system used by the software being built:

  • Autotools and CMake: If the software your recipe is building uses Autotools or CMake, the OpenEmbedded build system understands how to install the software. Consequently, you do not have to have a do_install task as part of your recipe. You just need to make sure the install portion of the build completes with no issues. However, if you wish to install additional files not already being installed by make install, you should do this using a do_install_append function using the install command as described in the "Manual" bulleted item later in this list.

  • Other (using make install): You need to define a do_install function in your recipe. The function should call oe_runmake install and will likely need to pass in the destination directory as well. How you pass that path is dependent on how the Makefile being run is written (e.g. DESTDIR=${D}, PREFIX=${D}, INSTALLROOT=${D}, and so forth).

    For an example recipe using make install, see the "Makefile-Based Package" section.

  • Manual: You need to define a do_install function in your recipe. The function must first use install -d to create the directories under ${D}. Once the directories exist, your function can use install to manually install the built software into the directories.

    You can find more information on install at http://www.gnu.org/software/coreutils/manual/html_node/install-invocation.html.

For the scenarios that do not use Autotools or CMake, you need to track the installation and diagnose and fix any issues until everything installs correctly. You need to look in the default location of ${D}, which is ${WORKDIR}/image, to be sure your files have been installed correctly.

Notes

  • During the installation process, you might need to modify some of the installed files to suit the target layout. For example, you might need to replace hard-coded paths in an initscript with values of variables provided by the build system, such as replacing /usr/bin/ with ${bindir}. If you do perform such modifications during do_install, be sure to modify the destination file after copying rather than before copying. Modifying after copying ensures that the build system can re-execute do_install if needed.

  • oe_runmake install, which can be run directly or can be run indirectly by the autotools and cmake classes, runs make install in parallel. Sometimes, a Makefile can have missing dependencies between targets that can result in race conditions. If you experience intermittent failures during do_install, you might be able to work around them by disabling parallel Makefile installs by adding the following to the recipe:

         PARALLEL_MAKEINST = ""
                            

    See PARALLEL_MAKEINST for additional information.

4.3.14. Enabling System Services

If you want to install a service, which is a process that usually starts on boot and runs in the background, then you must include some additional definitions in your recipe.

If you are adding services and the service initialization script or the service file itself is not installed, you must provide for that installation in your recipe using a do_install_append function. If your recipe already has a do_install function, update the function near its end rather than adding an additional do_install_append function.

When you create the installation for your services, you need to accomplish what is normally done by make install. In other words, make sure your installation arranges the output similar to how it is arranged on the target system.

The OpenEmbedded build system provides support for starting services two different ways:

  • SysVinit: SysVinit is a system and service manager that manages the init system used to control the very basic functions of your system. The init program is the first program started by the Linux kernel when the system boots. Init then controls the startup, running and shutdown of all other programs.

    To enable a service using SysVinit, your recipe needs to inherit the update-rc.d class. The class helps facilitate safely installing the package on the target.

    You will need to set the INITSCRIPT_PACKAGES, INITSCRIPT_NAME, and INITSCRIPT_PARAMS variables within your recipe.

  • systemd: System Management Daemon (systemd) was designed to replace SysVinit and to provide enhanced management of services. For more information on systemd, see the systemd homepage at http://freedesktop.org/wiki/Software/systemd/.

    To enable a service using systemd, your recipe needs to inherit the systemd class. See the systemd.bbclass file located in your Source Directory. section for more information.

4.3.15. Packaging

Successful packaging is a combination of automated processes performed by the OpenEmbedded build system and some specific steps you need to take. The following list describes the process:

  • Splitting Files: The do_package task splits the files produced by the recipe into logical components. Even software that produces a single binary might still have debug symbols, documentation, and other logical components that should be split out. The do_package task ensures that files are split up and packaged correctly.

  • Running QA Checks: The insane class adds a step to the package generation process so that output quality assurance checks are generated by the OpenEmbedded build system. This step performs a range of checks to be sure the build's output is free of common problems that show up during runtime. For information on these checks, see the insane class and the "QA Error and Warning Messages" chapter in the Yocto Project Reference Manual.

  • Hand-Checking Your Packages: After you build your software, you need to be sure your packages are correct. Examine the ${WORKDIR}/packages-split directory and make sure files are where you expect them to be. If you discover problems, you can set PACKAGES, FILES, do_install(_append), and so forth as needed.

  • Splitting an Application into Multiple Packages: If you need to split an application into several packages, see the "Splitting an Application into Multiple Packages" section for an example.

  • Installing a Post-Installation Script: For an example showing how to install a post-installation script, see the "Post-Installation Scripts" section.

  • Marking Package Architecture: Depending on what your recipe is building and how it is configured, it might be important to mark the packages produced as being specific to a particular machine, or to mark them as not being specific to a particular machine or architecture at all.

    By default, packages apply to any machine with the same architecture as the target machine. When a recipe produces packages that are machine-specific (e.g. the MACHINE value is passed into the configure script or a patch is applied only for a particular machine), you should mark them as such by adding the following to the recipe:

         PACKAGE_ARCH = "${MACHINE_ARCH}"
                            

    On the other hand, if the recipe produces packages that do not contain anything specific to the target machine or architecture at all (e.g. recipes that simply package script files or configuration files), you should use the allarch class to do this for you by adding this to your recipe:

         inherit allarch
                            

    Ensuring that the package architecture is correct is not critical while you are doing the first few builds of your recipe. However, it is important in order to ensure that your recipe rebuilds (or does not rebuild) appropriately in response to changes in configuration, and to ensure that you get the appropriate packages installed on the target machine, particularly if you run separate builds for more than one target machine.

4.3.16. Sharing Files Between Recipes

Recipes often need to use files provided by other recipes on the build host. For example, an application linking to a common library needs access to the library itself and its associated headers. The way this access is accomplished is by populating a sysroot with files. Each recipe has two sysroots in its work directory, one for target files (recipe-sysroot) and one for files that are native to the build host (recipe-sysroot-native).

Note

You could find the term "staging" used within the Yocto project regarding files populating sysroots (e.g. the STAGING_DIR variable).

Recipes should never populate the sysroot directly (i.e. write files into sysroot). Instead, files should be installed into standard locations during the do_install task within the ${D} directory. The reason for this limitation is that almost all files that populate the sysroot are cataloged in manifests in order to ensure the files can be removed later when a recipe is either modified or removed. Thus, the sysroot is able to remain free from stale files.

A subset of the files installed by the do_install task are used by the do_populate_sysroot task as defined by the the SYSROOT_DIRS variable to automatically populate the sysroot. It is possible to modify the list of directories that populate the sysroot. The following example shows how you could add the /opt directory to the list of directories within a recipe:

     SYSROOT_DIRS += "/opt"
                

For a more complete description of the do_populate_sysroot task and its associated functions, see the staging class.

4.3.17. Properly Versioning Pre-Release Recipes

Sometimes the name of a recipe can lead to versioning problems when the recipe is upgraded to a final release. For example, consider the irssi_0.8.16-rc1.bb recipe file in the list of example recipes in the "Storing and Naming the Recipe" section. This recipe is at a release candidate stage (i.e. "rc1"). When the recipe is released, the recipe filename becomes irssi_0.8.16.bb. The version change from 0.8.16-rc1 to 0.8.16 is seen as a decrease by the build system and package managers, so the resulting packages will not correctly trigger an upgrade.

In order to ensure the versions compare properly, the recommended convention is to set PV within the recipe to "previous_version+current_version". You can use an additional variable so that you can use the current version elsewhere. Here is an example:

     REALPV = "0.8.16-rc1"
     PV = "0.8.15+${REALPV}"
                

4.3.18. Post-Installation Scripts

Post-installation scripts run immediately after installing a package on the target or during image creation when a package is included in an image. To add a post-installation script to a package, add a pkg_postinst_PACKAGENAME() function to the recipe file (.bb) and replace PACKAGENAME with the name of the package you want to attach to the postinst script. To apply the post-installation script to the main package for the recipe, which is usually what is required, specify ${PN} in place of PACKAGENAME.

A post-installation function has the following structure:

     pkg_postinst_PACKAGENAME() {
     # Commands to carry out
     }
                

The script defined in the post-installation function is called when the root filesystem is created. If the script succeeds, the package is marked as installed. If the script fails, the package is marked as unpacked and the script is executed when the image boots again.

Note

Any RPM post-installation script that runs on the target should return a 0 exit code. RPM does not allow non-zero exit codes for these scripts, and the RPM package manager will cause the package to fail installation on the target.

Sometimes it is necessary for the execution of a post-installation script to be delayed until the first boot. For example, the script might need to be executed on the device itself. To delay script execution until boot time, use the following structure in the post-installation script:

     pkg_postinst_PACKAGENAME() {
     if [ x"$D" = "x" ]; then
          # Actions to carry out on the device go here
     else
          exit 1
     fi
     }
                

The previous example delays execution until the image boots again because the environment variable D points to the directory containing the image when the root filesystem is created at build time but is unset when executed on the first boot.

If you have recipes that use pkg_postinst scripts and they require the use of non-standard native tools that have dependencies during rootfs construction, you need to use the PACKAGE_WRITE_DEPS variable in your recipe to list these tools. If you do not use this variable, the tools might be missing and execution of the post-installation script is deferred until first boot. Deferring the script to first boot is undesirable and for read-only rootfs impossible.

Note

Equivalent support for pre-install, pre-uninstall, and post-uninstall scripts exist by way of pkg_preinst, pkg_prerm, and pkg_postrm, respectively. These scrips work in exactly the same way as does pkg_postinst with the exception that they run at different times. Also, because of when they run, they are not applicable to being run at image creation time like pkg_postinst.

4.3.19. Testing

The final step for completing your recipe is to be sure that the software you built runs correctly. To accomplish runtime testing, add the build's output packages to your image and test them on the target.

For information on how to customize your image by adding specific packages, see the "Customizing Images" section.

4.3.20. Examples

To help summarize how to write a recipe, this section provides some examples given various scenarios:

  • Recipes that use local files

  • Using an Autotooled package

  • Using a Makefile-based package

  • Splitting an application into multiple packages

  • Adding binaries to an image

4.3.20.1. Single .c File Package (Hello World!)

Building an application from a single file that is stored locally (e.g. under files) requires a recipe that has the file listed in the SRC_URI variable. Additionally, you need to manually write the do_compile and do_install tasks. The S variable defines the directory containing the source code, which is set to WORKDIR in this case - the directory BitBake uses for the build.

     SUMMARY = "Simple helloworld application"
     SECTION = "examples"
     LICENSE = "MIT"
     LIC_FILES_CHKSUM = "file://${COMMON_LICENSE_DIR}/MIT;md5=0835ade698e0bcf8506ecda2f7b4f302"

     SRC_URI = "file://helloworld.c"

     S = "${WORKDIR}"

     do_compile() {
     	${CC} helloworld.c -o helloworld
     }

     do_install() {
     	install -d ${D}${bindir}
     	install -m 0755 helloworld ${D}${bindir}
     }
                    

By default, the helloworld, helloworld-dbg, and helloworld-dev packages are built. For information on how to customize the packaging process, see the "Splitting an Application into Multiple Packages" section.

4.3.20.2. Autotooled Package

Applications that use Autotools such as autoconf and automake require a recipe that has a source archive listed in SRC_URI and also inherit the autotools class, which contains the definitions of all the steps needed to build an Autotool-based application. The result of the build is automatically packaged. And, if the application uses NLS for localization, packages with local information are generated (one package per language). Following is one example: (hello_2.3.bb)

     SUMMARY = "GNU Helloworld application"
     SECTION = "examples"
     LICENSE = "GPLv2+"
     LIC_FILES_CHKSUM = "file://COPYING;md5=751419260aa954499f7abaabaa882bbe"

     SRC_URI = "${GNU_MIRROR}/hello/hello-${PV}.tar.gz"

     inherit autotools gettext
                     

The variable LIC_FILES_CHKSUM is used to track source license changes as described in the "Tracking License Changes" section. You can quickly create Autotool-based recipes in a manner similar to the previous example.

4.3.20.3. Makefile-Based Package

Applications that use GNU make also require a recipe that has the source archive listed in SRC_URI. You do not need to add a do_compile step since by default BitBake starts the make command to compile the application. If you need additional make options, you should store them in the EXTRA_OEMAKE or PACKAGECONFIG_CONFARGS variables. BitBake passes these options into the GNU make invocation. Note that a do_install task is still required. Otherwise, BitBake runs an empty do_install task by default.

Some applications might require extra parameters to be passed to the compiler. For example, the application might need an additional header path. You can accomplish this by adding to the CFLAGS variable. The following example shows this:

     CFLAGS_prepend = "-I ${S}/include "
                    

In the following example, mtd-utils is a makefile-based package:

     SUMMARY = "Tools for managing memory technology devices"
     SECTION = "base"
     DEPENDS = "zlib lzo e2fsprogs util-linux"
     HOMEPAGE = "http://www.linux-mtd.infradead.org/"
     LICENSE = "GPLv2+"
     LIC_FILES_CHKSUM = "file://COPYING;md5=0636e73ff0215e8d672dc4c32c317bb3 \
                         file://include/common.h;beginline=1;endline=17;md5=ba05b07912a44ea2bf81ce409380049c"

     # Use the latest version at 26 Oct, 2013
     SRCREV = "9f107132a6a073cce37434ca9cda6917dd8d866b"
     SRC_URI = "git://git.infradead.org/mtd-utils.git \
                     file://add-exclusion-to-mkfs-jffs2-git-2.patch \
     "

     PV = "1.5.1+git${SRCPV}"

     S = "${WORKDIR}/git"

     EXTRA_OEMAKE = "'CC=${CC}' 'RANLIB=${RANLIB}' 'AR=${AR}' 'CFLAGS=${CFLAGS} -I${S}/include -DWITHOUT_XATTR' 'BUILDDIR=${S}'"

     do_install () {
             oe_runmake install DESTDIR=${D} SBINDIR=${sbindir} MANDIR=${mandir} INCLUDEDIR=${includedir}
     }

     PACKAGES =+ "mtd-utils-jffs2 mtd-utils-ubifs mtd-utils-misc"

     FILES_mtd-utils-jffs2 = "${sbindir}/mkfs.jffs2 ${sbindir}/jffs2dump ${sbindir}/jffs2reader ${sbindir}/sumtool"
     FILES_mtd-utils-ubifs = "${sbindir}/mkfs.ubifs ${sbindir}/ubi*"
     FILES_mtd-utils-misc = "${sbindir}/nftl* ${sbindir}/ftl* ${sbindir}/rfd* ${sbindir}/doc* ${sbindir}/serve_image ${sbindir}/recv_image"

     PARALLEL_MAKE = ""

     BBCLASSEXTEND = "native"
                    

4.3.20.4. Splitting an Application into Multiple Packages

You can use the variables PACKAGES and FILES to split an application into multiple packages.

Following is an example that uses the libxpm recipe. By default, this recipe generates a single package that contains the library along with a few binaries. You can modify the recipe to split the binaries into separate packages:

     require xorg-lib-common.inc

     SUMMARY = "Xpm: X Pixmap extension library"
     LICENSE = "BSD"
     LIC_FILES_CHKSUM = "file://COPYING;md5=51f4270b012ecd4ab1a164f5f4ed6cf7"
     DEPENDS += "libxext libsm libxt"
     PE = "1"

     XORG_PN = "libXpm"

     PACKAGES =+ "sxpm cxpm"
     FILES_cxpm = "${bindir}/cxpm"
     FILES_sxpm = "${bindir}/sxpm"
                    

In the previous example, we want to ship the sxpm and cxpm binaries in separate packages. Since bindir would be packaged into the main PN package by default, we prepend the PACKAGES variable so additional package names are added to the start of list. This results in the extra FILES_* variables then containing information that define which files and directories go into which packages. Files included by earlier packages are skipped by latter packages. Thus, the main PN package does not include the above listed files.

4.3.20.5. Packaging Externally Produced Binaries

Sometimes, you need to add pre-compiled binaries to an image. For example, suppose that binaries for proprietary code exist, which are created by a particular division of a company. Your part of the company needs to use those binaries as part of an image that you are building using the OpenEmbedded build system. Since you only have the binaries and not the source code, you cannot use a typical recipe that expects to fetch the source specified in SRC_URI and then compile it.

One method is to package the binaries and then install them as part of the image. Generally, it is not a good idea to package binaries since, among other things, it can hinder the ability to reproduce builds and could lead to compatibility problems with ABI in the future. However, sometimes you have no choice.

The easiest solution is to create a recipe that uses the bin_package class and to be sure that you are using default locations for build artifacts. In most cases, the bin_package class handles "skipping" the configure and compile steps as well as sets things up to grab packages from the appropriate area. In particular, this class sets noexec on both the do_configure and do_compile tasks, sets FILES_${PN} to "/" so that it picks up all files, and sets up a do_install task, which effectively copies all files from ${S} to ${D}. The bin_package class works well when the files extracted into ${S} are already laid out in the way they should be laid out on the target. For more information on these variables, see the FILES, PN, S, and D variables in the Yocto Project Reference Manual's variable glossary.

Notes

  • Using DEPENDS is a good idea even for components distributed in binary form, and is often necessary for shared libraries. For a shared library, listing the library dependencies in DEPENDS makes sure that the libraries are available in the staging sysroot when other recipes link against the library, which might be necessary for successful linking.

  • Using DEPENDS also allows runtime dependencies between packages to be added automatically. See the "Automatically Added Runtime Dependencies" section in the Yocto Project Reference Manual for more information.

If you cannot use the bin_package class, you need to be sure you are doing the following:

  • Create a recipe where the do_configure and do_compile tasks do nothing: It is usually sufficient to just not define these tasks in the recipe, because the default implementations do nothing unless a Makefile is found in ${S}.

    If ${S} might contain a Makefile, or if you inherit some class that replaces do_configure and do_compile with custom versions, then you can use the [noexec] flag to turn the tasks into no-ops, as follows:

         do_configure[noexec] = "1"
         do_compile[noexec] = "1"
                                

    Unlike deleting the tasks, using the flag preserves the dependency chain from the do_fetch, do_unpack, and do_patch tasks to the do_install task.

  • Make sure your do_install task installs the binaries appropriately.

  • Ensure that you set up FILES (usually FILES_${PN}) to point to the files you have installed, which of course depends on where you have installed them and whether those files are in different locations than the defaults.

4.3.21. Following Recipe Style Guidelines

When writing recipes, it is good to conform to existing style guidelines. The OpenEmbedded Styleguide wiki page provides rough guidelines for preferred recipe style.

It is common for existing recipes to deviate a bit from this style. However, aiming for at least a consistent style is a good idea. Some practices, such as omitting spaces around = operators in assignments or ordering recipe components in an erratic way, are widely seen as poor style.

4.4. Adding a New Machine

Adding a new machine to the Yocto Project is a straightforward process. This section describes how to add machines that are similar to those that the Yocto Project already supports.

Note

Although well within the capabilities of the Yocto Project, adding a totally new architecture might require changes to gcc/glibc and to the site information, which is beyond the scope of this manual.

For a complete example that shows how to add a new machine, see the "Creating a New BSP Layer Using the yocto-bsp Script" section in the Yocto Project Board Support Package (BSP) Developer's Guide.

4.4.1. Adding the Machine Configuration File

To add a new machine, you need to add a new machine configuration file to the layer's conf/machine directory. This configuration file provides details about the device you are adding.

The OpenEmbedded build system uses the root name of the machine configuration file to reference the new machine. For example, given a machine configuration file named crownbay.conf, the build system recognizes the machine as "crownbay".

The most important variables you must set in your machine configuration file or include from a lower-level configuration file are as follows:

You might also need these variables:

You can find full details on these variables in the reference section. You can leverage existing machine .conf files from meta-yocto-bsp/conf/machine/.

4.4.2. Adding a Kernel for the Machine

The OpenEmbedded build system needs to be able to build a kernel for the machine. You need to either create a new kernel recipe for this machine, or extend an existing kernel recipe. You can find several kernel recipe examples in the Source Directory at meta/recipes-kernel/linux that you can use as references.

If you are creating a new kernel recipe, normal recipe-writing rules apply for setting up a SRC_URI. Thus, you need to specify any necessary patches and set S to point at the source code. You need to create a do_configure task that configures the unpacked kernel with a defconfig file. You can do this by using a make defconfig command or, more commonly, by copying in a suitable defconfig file and then running make oldconfig. By making use of inherit kernel and potentially some of the linux-*.inc files, most other functionality is centralized and the defaults of the class normally work well.

If you are extending an existing kernel recipe, it is usually a matter of adding a suitable defconfig file. The file needs to be added into a location similar to defconfig files used for other machines in a given kernel recipe. A possible way to do this is by listing the file in the SRC_URI and adding the machine to the expression in COMPATIBLE_MACHINE:

     COMPATIBLE_MACHINE = '(qemux86|qemumips)'
                

For more information on defconfig files, see the "Changing the Configuration" section in the Yocto Project Linux Kernel Development Manual.

4.4.3. Adding a Formfactor Configuration File

A formfactor configuration file provides information about the target hardware for which the image is being built and information that the build system cannot obtain from other sources such as the kernel. Some examples of information contained in a formfactor configuration file include framebuffer orientation, whether or not the system has a keyboard, the positioning of the keyboard in relation to the screen, and the screen resolution.

The build system uses reasonable defaults in most cases. However, if customization is necessary, you need to create a machconfig file in the meta/recipes-bsp/formfactor/files directory. This directory contains directories for specific machines such as qemuarm and qemux86. For information about the settings available and the defaults, see the meta/recipes-bsp/formfactor/files/config file found in the same area.

Following is an example for "qemuarm" machine:

     HAVE_TOUCHSCREEN=1
     HAVE_KEYBOARD=1

     DISPLAY_CAN_ROTATE=0
     DISPLAY_ORIENTATION=0
     #DISPLAY_WIDTH_PIXELS=640
     #DISPLAY_HEIGHT_PIXELS=480
     #DISPLAY_BPP=16
     DISPLAY_DPI=150
     DISPLAY_SUBPIXEL_ORDER=vrgb
                

4.5. Finding Temporary Source Code

You might find it helpful during development to modify the temporary source code used by recipes to build packages. For example, suppose you are developing a patch and you need to experiment a bit to figure out your solution. After you have initially built the package, you can iteratively tweak the source code, which is located in the Build Directory, and then you can force a re-compile and quickly test your altered code. Once you settle on a solution, you can then preserve your changes in the form of patches.

During a build, the unpacked temporary source code used by recipes to build packages is available in the Build Directory as defined by the S variable. Below is the default value for the S variable as defined in the meta/conf/bitbake.conf configuration file in the Source Directory:

     S = "${WORKDIR}/${BP}"
            

You should be aware that many recipes override the S variable. For example, recipes that fetch their source from Git usually set S to ${WORKDIR}/git.

Note

The BP represents the base recipe name, which consists of the name and version:
     BP = "${BPN}-${PV}"
                

The path to the work directory for the recipe (WORKDIR) is defined as follows:

     ${TMPDIR}/work/${MULTIMACH_TARGET_SYS}/${PN}/${EXTENDPE}${PV}-${PR}
            

The actual directory depends on several things:

  • TMPDIR: The top-level build output directory.

  • MULTIMACH_TARGET_SYS: The target system identifier.

  • PN: The recipe name.

  • EXTENDPE: The epoch - (if PE is not specified, which is usually the case for most recipes, then EXTENDPE is blank).

  • PV: The recipe version.

  • PR: The recipe revision.

As an example, assume a Source Directory top-level folder named poky, a default Build Directory at poky/build, and a qemux86-poky-linux machine target system. Furthermore, suppose your recipe is named foo_1.3.0.bb. In this case, the work directory the build system uses to build the package would be as follows:

     poky/build/tmp/work/qemux86-poky-linux/foo/1.3.0-r0
            

4.6. Using Quilt in Your Workflow

Quilt is a powerful tool that allows you to capture source code changes without having a clean source tree. This section outlines the typical workflow you can use to modify source code, test changes, and then preserve the changes in the form of a patch all using Quilt.

Tip

With regard to preserving changes to source files, if you clean a recipe or have rm_work enabled, the devtool workflow as described in the Yocto Project Software Development Kit (SDK) Developer's Guide is a safer development flow than the flow that uses Quilt.

Follow these general steps:

  1. Find the Source Code: Temporary source code used by the OpenEmbedded build system is kept in the Build Directory. See the "Finding Temporary Source Code" section to learn how to locate the directory that has the temporary source code for a particular package.

  2. Change Your Working Directory: You need to be in the directory that has the temporary source code. That directory is defined by the S variable.

  3. Create a New Patch: Before modifying source code, you need to create a new patch. To create a new patch file, use quilt new as below:

         $ quilt new my_changes.patch
                        

  4. Notify Quilt and Add Files: After creating the patch, you need to notify Quilt about the files you plan to edit. You notify Quilt by adding the files to the patch you just created:

         $ quilt add file1.c file2.c file3.c
                        

  5. Edit the Files: Make your changes in the source code to the files you added to the patch.

  6. Test Your Changes: Once you have modified the source code, the easiest way to test your changes is by calling the do_compile task as shown in the following example:

         $ bitbake -c compile -f package
                        

    The -f or --force option forces the specified task to execute. If you find problems with your code, you can just keep editing and re-testing iteratively until things work as expected.

    Note

    All the modifications you make to the temporary source code disappear once you run the do_clean or do_cleanall tasks using BitBake (i.e. bitbake -c clean package and bitbake -c cleanall package). Modifications will also disappear if you use the rm_work feature as described in the "Building Images" section of the Yocto Project Quick Start.

  7. Generate the Patch: Once your changes work as expected, you need to use Quilt to generate the final patch that contains all your modifications.

         $ quilt refresh
                        

    At this point, the my_changes.patch file has all your edits made to the file1.c, file2.c, and file3.c files.

    You can find the resulting patch file in the patches/ subdirectory of the source (S) directory.

  8. Copy the Patch File: For simplicity, copy the patch file into a directory named files, which you can create in the same directory that holds the recipe (.bb) file or the append (.bbappend) file. Placing the patch here guarantees that the OpenEmbedded build system will find the patch. Next, add the patch into the SRC_URI of the recipe. Here is an example:

         SRC_URI += "file://my_changes.patch"
                        

4.7. Using a Development Shell

When debugging certain commands or even when just editing packages, devshell can be a useful tool. When you invoke devshell, all tasks up to and including do_patch are run for the specified target. Then, a new terminal is opened and you are placed in ${S}, the source directory. In the new terminal, all the OpenEmbedded build-related environment variables are still defined so you can use commands such as configure and make. The commands execute just as if the OpenEmbedded build system were executing them. Consequently, working this way can be helpful when debugging a build or preparing software to be used with the OpenEmbedded build system.

Following is an example that uses devshell on a target named matchbox-desktop:

     $ bitbake matchbox-desktop -c devshell
            

This command spawns a terminal with a shell prompt within the OpenEmbedded build environment. The OE_TERMINAL variable controls what type of shell is opened.

For spawned terminals, the following occurs:

  • The PATH variable includes the cross-toolchain.

  • The pkgconfig variables find the correct .pc files.

  • The configure command finds the Yocto Project site files as well as any other necessary files.

Within this environment, you can run configure or compile commands as if they were being run by the OpenEmbedded build system itself. As noted earlier, the working directory also automatically changes to the Source Directory (S).

To manually run a specific task using devshell, run the corresponding run.* script in the ${WORKDIR}/temp directory (e.g., run.do_configure.pid). If a task's script does not exist, which would be the case if the task was skipped by way of the sstate cache, you can create the task by first running it outside of the devshell:

     $ bitbake -c task
            

Notes

  • Execution of a task's run.* script and BitBake's execution of a task are identical. In other words, running the script re-runs the task just as it would be run using the bitbake -c command.

  • Any run.* file that does not have a .pid extension is a symbolic link (symlink) to the most recent version of that file.

Remember, that the devshell is a mechanism that allows you to get into the BitBake task execution environment. And as such, all commands must be called just as BitBake would call them. That means you need to provide the appropriate options for cross-compilation and so forth as applicable.

When you are finished using devshell, exit the shell or close the terminal window.

Notes

  • It is worth remembering that when using devshell you need to use the full compiler name such as arm-poky-linux-gnueabi-gcc instead of just using gcc. The same applies to other applications such as binutils, libtool and so forth. BitBake sets up environment variables such as CC to assist applications, such as make to find the correct tools.

  • It is also worth noting that devshell still works over X11 forwarding and similar situations.

4.8. Using a Development Python Shell

Similar to working within a development shell as described in the previous section, you can also spawn and work within an interactive Python development shell. When debugging certain commands or even when just editing packages, devpyshell can be a useful tool. When you invoke devpyshell, all tasks up to and including do_patch are run for the specified target. Then a new terminal is opened. Additionally, key Python objects and code are available in the same way they are to BitBake tasks, in particular, the data store 'd'. So, commands such as the following are useful when exploring the data store and running functions:

     pydevshell> d.getVar("STAGING_DIR", True)
     '/media/build1/poky/build/tmp/sysroots'
     pydevshell> d.getVar("STAGING_DIR", False)
     '${TMPDIR}/sysroots'
     pydevshell> d.setVar("FOO", "bar")
     pydevshell> d.getVar("FOO", True)
     'bar'
     pydevshell> d.delVar("FOO")
     pydevshell> d.getVar("FOO", True)
     pydevshell> bb.build.exec_func("do_unpack", d)
     pydevshell>
            

The commands execute just as if the OpenEmbedded build system were executing them. Consequently, working this way can be helpful when debugging a build or preparing software to be used with the OpenEmbedded build system.

Following is an example that uses devpyshell on a target named matchbox-desktop:

     $ bitbake matchbox-desktop -c devpyshell
            

This command spawns a terminal and places you in an interactive Python interpreter within the OpenEmbedded build environment. The OE_TERMINAL variable controls what type of shell is opened.

When you are finished using devpyshell, you can exit the shell either by using Ctrl+d or closing the terminal window.

4.9. Building Targets with Multiple Configurations

Bitbake also has functionality that allows you to build multiple targets at the same time, where each target uses a different configuration.

In order to accomplish this, you setup each of the configurations you need to use in parallel by placing the configuration files in your current build directory alongside the usual local.conf file.

Follow these guidelines to create an environment that supports multiple configurations:

  • Create Configuration Files: You need to create a single configuration file for each configuration for which you want to add support. These files would contain lines such as the following:

         MACHINE = "A"
                        

    The files would contain any other variables that can be set and built in the same directory.

    Note

    You can change the TMPDIR to not conflict.

    Furthermore, the configuration file must be located in the current build directory in a directory named multiconfig under the build's conf directory where local.conf resides. The reason for this restriction is because the BBPATH variable is not constructed until the layers are parsed. Consequently, using the configuration file as a pre-configuration file is not possible unless it is located in the current working directory.

  • Add the BitBake Multi-Config Variable to you Local Configuration File: Use the BBMULTICONFIG variable in your conf/local.conf configuration file to specify each separate configuration. For example, the following line tells BitBake it should load conf/multiconfig/configA.conf, conf/multiconfig/configB.conf, and conf/multiconfig/configC.conf.

         BBMULTICONFIG = "configA configB configC"
                        

  • Launch BitBake: Use the following BitBake command form to launch the build:

         $ bitbake [multiconfig:multiconfigname:]target [[[multiconfig:multiconfigname:]target] ... ]
                        

    Following is an example that supports building a minimal image for configuration A alongside a standard core-image-sato, which takes its configuration from local.conf:

         $ bitbake multiconfig:configA:core-image-minimal core-image-sato
                        

Support for multiple configurations in this current release of the Yocto Project (Rocko 2.4) has some known issues:

  • No inter-multi-configuration dependencies exist.

  • Shared State (sstate) optimizations do not exist. Consequently, if the build uses the same object twice in, for example, two different TMPDIR directories, the build will either load from an existing sstate cache at the start or build the object twice.

4.10. Working With Libraries

Libraries are an integral part of your system. This section describes some common practices you might find helpful when working with libraries to build your system:

4.10.1. Including Static Library Files

If you are building a library and the library offers static linking, you can control which static library files (*.a files) get included in the built library.

The PACKAGES and FILES_* variables in the meta/conf/bitbake.conf configuration file define how files installed by the do_install task are packaged. By default, the PACKAGES variable includes ${PN}-staticdev, which represents all static library files.

Note

Some previously released versions of the Yocto Project defined the static library files through ${PN}-dev.

Following is part of the BitBake configuration file, where you can see how the static library files are defined:

     PACKAGE_BEFORE_PN ?= ""
     PACKAGES = "${PN}-dbg ${PN}-staticdev ${PN}-dev ${PN}-doc ${PN}-locale ${PACKAGE_BEFORE_PN} ${PN}"
     PACKAGES_DYNAMIC = "^${PN}-locale-.*"
     FILES = ""

     FILES_${PN} = "${bindir}/* ${sbindir}/* ${libexecdir}/* ${libdir}/lib*${SOLIBS} \
                 ${sysconfdir} ${sharedstatedir} ${localstatedir} \
                 ${base_bindir}/* ${base_sbindir}/* \
                 ${base_libdir}/*${SOLIBS} \
                 ${base_prefix}/lib/udev/rules.d ${prefix}/lib/udev/rules.d \
                 ${datadir}/${BPN} ${libdir}/${BPN}/* \
                 ${datadir}/pixmaps ${datadir}/applications \
                 ${datadir}/idl ${datadir}/omf ${datadir}/sounds \
                 ${libdir}/bonobo/servers"

     FILES_${PN}-bin = "${bindir}/* ${sbindir}/*"

     FILES_${PN}-doc = "${docdir} ${mandir} ${infodir} ${datadir}/gtk-doc \
                 ${datadir}/gnome/help"
     SECTION_${PN}-doc = "doc"

     FILES_SOLIBSDEV ?= "${base_libdir}/lib*${SOLIBSDEV} ${libdir}/lib*${SOLIBSDEV}"
     FILES_${PN}-dev = "${includedir} ${FILES_SOLIBSDEV} ${libdir}/*.la \
                     ${libdir}/*.o ${libdir}/pkgconfig ${datadir}/pkgconfig \
                     ${datadir}/aclocal ${base_libdir}/*.o \
                     ${libdir}/${BPN}/*.la ${base_libdir}/*.la"
     SECTION_${PN}-dev = "devel"
     ALLOW_EMPTY_${PN}-dev = "1"
     RDEPENDS_${PN}-dev = "${PN} (= ${EXTENDPKGV})"

     FILES_${PN}-staticdev = "${libdir}/*.a ${base_libdir}/*.a ${libdir}/${BPN}/*.a"
     SECTION_${PN}-staticdev = "devel"
     RDEPENDS_${PN}-staticdev = "${PN}-dev (= ${EXTENDPKGV})"
                

4.10.2. Combining Multiple Versions of Library Files into One Image

The build system offers the ability to build libraries with different target optimizations or architecture formats and combine these together into one system image. You can link different binaries in the image against the different libraries as needed for specific use cases. This feature is called "Multilib."

An example would be where you have most of a system compiled in 32-bit mode using 32-bit libraries, but you have something large, like a database engine, that needs to be a 64-bit application and uses 64-bit libraries. Multilib allows you to get the best of both 32-bit and 64-bit libraries.

While the Multilib feature is most commonly used for 32 and 64-bit differences, the approach the build system uses facilitates different target optimizations. You could compile some binaries to use one set of libraries and other binaries to use a different set of libraries. The libraries could differ in architecture, compiler options, or other optimizations.

Several examples exist in the meta-skeleton layer found in the Source Directory:

  • conf/multilib-example.conf configuration file

  • conf/multilib-example2.conf configuration file

  • recipes-multilib/images/core-image-multilib-example.bb recipe

4.10.2.1. Preparing to Use Multilib

User-specific requirements drive the Multilib feature. Consequently, there is no one "out-of-the-box" configuration that likely exists to meet your needs.

In order to enable Multilib, you first need to ensure your recipe is extended to support multiple libraries. Many standard recipes are already extended and support multiple libraries. You can check in the meta/conf/multilib.conf configuration file in the Source Directory to see how this is done using the BBCLASSEXTEND variable. Eventually, all recipes will be covered and this list will not be needed.

For the most part, the Multilib class extension works automatically to extend the package name from ${PN} to ${MLPREFIX}${PN}, where MLPREFIX is the particular multilib (e.g. "lib32-" or "lib64-"). Standard variables such as DEPENDS, RDEPENDS, RPROVIDES, RRECOMMENDS, PACKAGES, and PACKAGES_DYNAMIC are automatically extended by the system. If you are extending any manual code in the recipe, you can use the ${MLPREFIX} variable to ensure those names are extended correctly. This automatic extension code resides in multilib.bbclass.

4.10.2.2. Using Multilib

After you have set up the recipes, you need to define the actual combination of multiple libraries you want to build. You accomplish this through your local.conf configuration file in the Build Directory. An example configuration would be as follows:

     MACHINE = "qemux86-64"
     require conf/multilib.conf
     MULTILIBS = "multilib:lib32"
     DEFAULTTUNE_virtclass-multilib-lib32 = "x86"
     IMAGE_INSTALL_append = " lib32-glib-2.0"
                    

This example enables an additional library named lib32 alongside the normal target packages. When combining these "lib32" alternatives, the example uses "x86" for tuning. For information on this particular tuning, see meta/conf/machine/include/ia32/arch-ia32.inc.

The example then includes lib32-glib-2.0 in all the images, which illustrates one method of including a multiple library dependency. You can use a normal image build to include this dependency, for example:

     $ bitbake core-image-sato
                    

You can also build Multilib packages specifically with a command like this:

     $ bitbake lib32-glib-2.0
                    

4.10.2.3. Additional Implementation Details

Generic implementation details as well as details that are specific to package management systems exist. Following are implementation details that exist regardless of the package management system:

  • The typical convention used for the class extension code as used by Multilib assumes that all package names specified in PACKAGES that contain ${PN} have ${PN} at the start of the name. When that convention is not followed and ${PN} appears at the middle or the end of a name, problems occur.

  • The TARGET_VENDOR value under Multilib will be extended to "-vendormlmultilib" (e.g. "-pokymllib32" for a "lib32" Multilib with Poky). The reason for this slightly unwieldy contraction is that any "-" characters in the vendor string presently break Autoconf's config.sub, and other separators are problematic for different reasons.

For the RPM Package Management System, the following implementation details exist:

  • A unique architecture is defined for the Multilib packages, along with creating a unique deploy folder under tmp/deploy/rpm in the Build Directory. For example, consider lib32 in a qemux86-64 image. The possible architectures in the system are "all", "qemux86_64", "lib32_qemux86_64", and "lib32_x86".

  • The ${MLPREFIX} variable is stripped from ${PN} during RPM packaging. The naming for a normal RPM package and a Multilib RPM package in a qemux86-64 system resolves to something similar to bash-4.1-r2.x86_64.rpm and bash-4.1.r2.lib32_x86.rpm, respectively.

  • When installing a Multilib image, the RPM backend first installs the base image and then installs the Multilib libraries.

  • The build system relies on RPM to resolve the identical files in the two (or more) Multilib packages.

For the IPK Package Management System, the following implementation details exist:

  • The ${MLPREFIX} is not stripped from ${PN} during IPK packaging. The naming for a normal RPM package and a Multilib IPK package in a qemux86-64 system resolves to something like bash_4.1-r2.x86_64.ipk and lib32-bash_4.1-rw_x86.ipk, respectively.

  • The IPK deploy folder is not modified with ${MLPREFIX} because packages with and without the Multilib feature can exist in the same folder due to the ${PN} differences.

  • IPK defines a sanity check for Multilib installation using certain rules for file comparison, overridden, etc.

4.10.3. Installing Multiple Versions of the Same Library

Situations can exist where you need to install and use multiple versions of the same library on the same system at the same time. These situations almost always exist when a library API changes and you have multiple pieces of software that depend on the separate versions of the library. To accommodate these situations, you can install multiple versions of the same library in parallel on the same system.

The process is straightforward as long as the libraries use proper versioning. With properly versioned libraries, all you need to do to individually specify the libraries is create separate, appropriately named recipes where the PN part of the name includes a portion that differentiates each library version (e.g.the major part of the version number). Thus, instead of having a single recipe that loads one version of a library (e.g. clutter), you provide multiple recipes that result in different versions of the libraries you want. As an example, the following two recipes would allow the two separate versions of the clutter library to co-exist on the same system:

     clutter-1.6_1.6.20.bb
     clutter-1.8_1.8.4.bb
                

Additionally, if you have other recipes that depend on a given library, you need to use the DEPENDS variable to create the dependency. Continuing with the same example, if you want to have a recipe depend on the 1.8 version of the clutter library, use the following in your recipe:

     DEPENDS = "clutter-1.8"
                

4.11. Enabling GObject Introspection Support

GObject introspection is the standard mechanism for accessing GObject-based software from runtime environments. GObject is a feature of the GLib library that provides an object framework for the GNOME desktop and related software. GObject Introspection adds information to GObject that allows objects created within it to be represented across different programming languages. If you want to construct GStreamer pipelines using Python, or control UPnP infrastructure using Javascript and GUPnP, GObject introspection is the only way to do it.

This section describes the Yocto Project support for generating and packaging GObject introspection data. GObject introspection data is a description of the API provided by libraries built on top of GLib framework, and, in particular, that framework's GObject mechanism. GObject Introspection Repository (GIR) files go to -dev packages, typelib files go to main packages as they are packaged together with libraries that are introspected.

The data is generated when building such a library, by linking the library with a small executable binary that asks the library to describe itself, and then executing the binary and processing its output.

Generating this data in a cross-compilation environment is difficult because the library is produced for the target architecture, but its code needs to be executed on the build host. This problem is solved with the OpenEmbedded build system by running the code through QEMU, which allows precisely that. Unfortunately, QEMU does not always work perfectly as mentioned in the xxx section.

4.11.1. Enabling the Generation of Introspection Data

Enabling the generation of introspection data (GIR files) in your library package involves the following:

  1. Inherit the gobject-introspection class.

  2. Make sure introspection is not disabled anywhere in the recipe or from anything the recipe includes. Also, make sure that "gobject-introspection-data" is not in DISTRO_FEATURES_BACKFILL_CONSIDERED and that "qemu-usermode" is not in MACHINE_FEATURES_BACKFILL_CONSIDERED. If either of these conditions exist, nothing will happen.

  3. Try to build the recipe. If you encounter build errors that look like something is unable to find .so libraries, check where these libraries are located in the source tree and add the following to the recipe:

         GIR_EXTRA_LIBS_PATH = "${B}/something/.libs"
                            

    Note

    See recipes in the oe-core repository that use that GIR_EXTRA_LIBS_PATH variable as an example.

  4. Look for any other errors, which probably mean that introspection support in a package is not entirely standard, and thus breaks down in a cross-compilation environment. For such cases, custom-made fixes are needed. A good place to ask and receive help in these cases is the Yocto Project mailing lists.

Note

Using a library that no longer builds against the latest Yocto Project release and prints introspection related errors is a good candidate for the previous procedure.

4.11.2. Disabling the Generation of Introspection Data

You might find that you do not want to generate introspection data. Or, perhaps QEMU does not work on your build host and target architecture combination. If so, you can use either of the following methods to disable GIR file generations:

  • Add the following to your distro configuration:

         DISTRO_FEATURES_BACKFILL_CONSIDERED = "gobject-introspection-data"
                            

    Adding this statement disables generating introspection data using QEMU but will still enable building introspection tools and libraries (i.e. building them does not require the use of QEMU).

  • Add the following to your machine configuration:

         MACHINE_FEATURES_BACKFILL_CONSIDERED = "qemu-usermode"
                            

    Adding this statement disables the use of QEMU when building packages for your machine. Currently, this feature is used only by introspection recipes and has the same effect as the previously described option.

    Note

    Future releases of the Yocto Project might have other features affected by this option.

If you disable introspection data, you can still obtain it through other means such as copying the data from a suitable sysroot, or by generating it on the target hardware. The OpenEmbedded build system does not currently provide specific support for these techniques.

4.11.3. Testing that Introspection Works in an Image

Use the following procedure to test if generating introspection data is working in an image:

  1. Make sure that "gobject-introspection-data" is not in DISTRO_FEATURES_BACKFILL_CONSIDERED and that "qemu-usermode" is not in MACHINE_FEATURES_BACKFILL_CONSIDERED.

  2. Build core-image-sato.

  3. Launch a Terminal and then start Python in the terminal.

  4. Enter the following in the terminal:

         >>> from gi.repository import GLib
         >>> GLib.get_host_name()
                            

  5. For something a little more advanced, enter the following:

         http://python-gtk-3-tutorial.readthedocs.org/en/latest/introduction.html
                            

4.11.4. Known Issues

The following know issues exist for GObject Introspection Support:

  • qemu-ppc64 immediately crashes. Consequently, you cannot build introspection data on that architecture.

  • x32 is not supported by QEMU. Consequently, introspection data is disabled.

  • musl causes transient GLib binaries to crash on assertion failures. Consequently, generating introspection data is disabled.

  • Because QEMU is not able to run the binaries correctly, introspection is disabled for some specific packages under specific architectures (e.g. gcr, libsecret, and webkit).

  • QEMU usermode might not work properly when running 64-bit binaries under 32-bit host machines. In particular, "qemumips64" is known to not work under i686.

4.12. Optionally Using an External Toolchain

You might want to use an external toolchain as part of your development. If this is the case, the fundamental steps you need to accomplish are as follows:

  • Understand where the installed toolchain resides. For cases where you need to build the external toolchain, you would need to take separate steps to build and install the toolchain.

  • Make sure you add the layer that contains the toolchain to your bblayers.conf file through the BBLAYERS variable.

  • Set the EXTERNAL_TOOLCHAIN variable in your local.conf file to the location in which you installed the toolchain.

A good example of an external toolchain used with the Yocto Project is Mentor Graphics® Sourcery G++ Toolchain. You can see information on how to use that particular layer in the README file at http://github.com/MentorEmbedded/meta-sourcery/. You can find further information by reading about the TCMODE variable in the Yocto Project Reference Manual's variable glossary.

4.13. Creating Partitioned Images

Creating an image for a particular hardware target using the OpenEmbedded build system does not necessarily mean you can boot that image as is on your device. Physical devices accept and boot images in various ways depending on the specifics of the device. Usually, information about the hardware can tell you what image format the device requires. Should your device require multiple partitions on an SD card, flash, or an HDD, you can use the OpenEmbedded Image Creator, Wic, to create the properly partitioned image.

You can generate partitioned images (image.wic) two ways: using the OpenEmbedded build system and by running the OpenEmbedded Image Creator Wic directly. The former way is preferable as it is easier to use and understand.

4.13.1. Creating Partitioned Images

The OpenEmbedded build system can generate partitioned images the same way as it generates any other image type. To generate a partitioned image, you need to modify two variables.

Further steps to generate a partitioned image are the same as for any other image type. For information on image types, see the "Images" section in the Yocto Project Reference Manual.

4.13.2. Using OpenEmbedded Image Creator Wic to Generate Partitioned Images

The wic command generates partitioned images from existing OpenEmbedded build artifacts. Image generation is driven by partitioning commands contained in an Openembedded kickstart file (.wks) specified either directly on the command line or as one of a selection of canned .wks files as shown with the wic list images command in the "Using an Existing Kickstart File" section. When you apply the command to a given set of build artifacts, the result is an image or set of images that can be directly written onto media and used on a particular system.

The wic command and the infrastructure it is based on is by definition incomplete. The purpose of the command is to allow the generation of customized images, and as such, was designed to be completely extensible through a plug-in interface. See the "Plug-ins" section for information on these plug-ins.

This section provides some background information on Wic, describes what you need to have in place to run the tool, provides instruction on how to use the wic utility, and provides several examples.

4.13.2.1. Background

This section provides some background on the wic utility. While none of this information is required to use Wic, you might find it interesting.

  • The name "Wic" is derived from OpenEmbedded Image Creator (oeic). The "oe" diphthong in "oeic" was promoted to the letter "w", because "oeic" is both difficult to remember and to pronounce.

  • Wic is loosely based on the Meego Image Creator (mic) framework. The Wic implementation has been heavily modified to make direct use of OpenEmbedded build artifacts instead of package installation and configuration, which are already incorporated within the OpenEmbedded artifacts.

  • Wic is a completely independent standalone utility that initially provides easier-to-use and more flexible replacements for an existing functionality in OE Core's image-live class and mkefidisk.sh script. The difference between Wic and those examples is that with Wic the functionality of those scripts is implemented by a general-purpose partitioning language, which is based on Redhat kickstart syntax.

4.13.2.2. Requirements

In order to use the wic utility with the OpenEmbedded Build system, your system needs to meet the following requirements:

  • The Linux distribution on your development host must support the Yocto Project. See the "Supported Linux Distributions" section in the Yocto Project Reference Manual for the list of distributions that support the Yocto Project.

  • The standard system utilities, such as cp, must be installed on your development host system.

  • You need to have the build artifacts already available, which typically means that you must have already created an image using the Openembedded build system (e.g. core-image-minimal). While it might seem redundant to generate an image in order to create an image using Wic, the current version of Wic requires the artifacts in the form generated by the build system.

  • You must build several native tools, which are tools built to run on the build system:

         $ bitbake parted-native dosfstools-native mtools-native
                                

  • You must have sourced the build environment setup script (i.e. oe-init-build-env) found in the Build Directory.

4.13.2.3. Getting Help

You can get general help for the wic command by entering the wic command by itself or by entering the command with a help argument as follows:

     $ wic -h
     $ wic --help
                    

Currently, Wic supports two commands: create and list. You can get help for these commands as follows:

     $ wic help command
                    with command being either
                    create or list.
                    

You can also get detailed help on a number of topics from the help system. The output of wic --help displays a list of available help topics under a "Help topics" heading. You can have the help system display the help text for a given topic by prefacing the topic with wic help:

     $ wic help help_topic
                    

You can find out more about the images Wic creates using the existing kickstart files with the following form of the command:

     $ wic list image help
                    

with image being either directdisk or mkefidisk.

4.13.2.4. Operational Modes

You can use Wic in two different modes, depending on how much control you need for specifying the Openembedded build artifacts that are used for creating the image: Raw and Cooked:

  • Raw Mode: You explicitly specify build artifacts through command-line arguments.

  • Cooked Mode: The current MACHINE setting and image name are used to automatically locate and provide the build artifacts.

Regardless of the mode you use, you need to have the build artifacts ready and available. Additionally, the environment must be set up using the oe-init-build-env script found in the Build Directory.

4.13.2.4.1. Raw Mode

The general form of the wic command in raw mode is:

     $ wic create image_name.wks [options] [...]

       Where:

          image_name.wks
             An OpenEmbedded kickstart file.  You can provide
             your own custom file or use a file from a set of
             existing files as described by further options.

          -o OUTDIR, --outdir=OUTDIR
             The name of a directory in which to create image.

          -i PROPERTIES_FILE, --infile=PROPERTIES_FILE
             The name of a file containing the values for image
             properties as a JSON file.

          -e IMAGE_NAME, --image-name=IMAGE_NAME
             The name of the image from which to use the artifacts
             (e.g. core-image-sato).

          -r ROOTFS_DIR, --rootfs-dir=ROOTFS_DIR
             The path to the /rootfs directory to use as the
             .wks rootfs source.

          -b BOOTIMG_DIR, --bootimg-dir=BOOTIMG_DIR
             The path to the directory containing the boot artifacts
             (e.g. /EFI or /syslinux) to use as the .wks bootimg
             source.

          -k KERNEL_DIR, --kernel-dir=KERNEL_DIR
             The path to the directory containing the kernel to use
             in the .wks boot image.

          -n NATIVE_SYSROOT, --native-sysroot=NATIVE_SYSROOT
             The path to the native sysroot containing the tools to use
             to build the image.

          -s, --skip-build-check
              Skips the build check.

          -D, --debug
              Output debug information.
                        

Note

You do not need root privileges to run Wic. In fact, you should not run as root when using the utility.

4.13.2.4.2. Cooked Mode

The general form of the wic command using Cooked Mode is:

     $ wic create kickstart_file -e image_name

       Where:

           kickstart_file
               An OpenEmbedded kickstart file. You can provide your own
               custom file or a supplied file.

           image_name
               Specifies the image built using the OpenEmbedded build
               system.
                        

This form is the simplest and most user-friendly, as it does not require specifying all individual parameters. All you need to provide is your own .wks file or one provided with the release.

4.13.2.5. Using an Existing Kickstart File

If you do not want to create your own .wks file, you can use an existing file provided by the Wic installation. Use the following command to list the available files:

     $ wic list images
     directdisk Create a 'pcbios' direct disk image
     mkefidisk Create an EFI disk image
                    

When you use an existing file, you do not have to use the .wks extension. Here is an example in Raw Mode that uses the directdisk file:

     $ wic create directdisk -r rootfs_dir -b bootimg_dir \
           -k kernel_dir -n native_sysroot
                    

Here are the actual partition language commands used in the mkefidisk.wks file to generate an image:

     # short-description: Create an EFI disk image
     # long-description: Creates a partitioned EFI disk image that the user
     # can directly dd to boot media.

     part /boot --source bootimg-efi --ondisk sda --label msdos --active --align 1024

     part / --source rootfs --ondisk sda --fstype=ext3 --label platform --align 1024

     part swap --ondisk sda --size 44 --label swap1 --fstype=swap

     bootloader  --timeout=10  --append="rootwait rootfstype=ext3 console=ttyPCH0,115200 console=tty0 vmalloc=256MB snd-hda-intel.enable_msi=0"
                    

4.13.2.6. Examples

This section provides several examples that show how to use the wic utility. All the examples assume the list of requirements in the "Requirements" section have been met. The examples assume the previously generated image is core-image-minimal.

4.13.2.6.1. Generate an Image using an Existing Kickstart File

This example runs in Cooked Mode and uses the mkefidisk kickstart file:

     $ wic create mkefidisk -e core-image-minimal
     Checking basic build environment...
     Done.

     Creating image(s)...

     Info: The new image(s) can be found here:
      current_directory/build/mkefidisk-201310230946-sda.direct

     The following build artifacts were used to create the image(s):
      ROOTFS_DIR: /home/trz/yocto/yocto-image/build/tmp/work/minnow-poky-linux/core-image-minimal/1.0-r0/rootfs
      BOOTIMG_DIR: /home/trz/yocto/yocto-image/build/tmp/work/minnow-poky-linux/core-image-minimal/1.0-r0/core-image-minimal-1.0/hddimg
      KERNEL_DIR: /home/trz/yocto/yocto-image/build/tmp/sysroots/minnow/usr/src/kernel
      NATIVE_SYSROOT: /home/trz/yocto/yocto-image/build/tmp/sysroots/x86_64-linux

     The image(s) were created using OE kickstart file:
      /home/trz/yocto/yocto-image/scripts/lib/image/canned-wks/mkefidisk.wks
                        

The previous example shows the easiest way to create an image by running in Cooked Mode and using the -e option with an existing kickstart file. All that is necessary is to specify the image used to generate the artifacts. Your local.conf needs to have the MACHINE variable set to the machine you are using, which is "minnow" in this example.

The output specifies the exact image created as well as where it was created, which is in the current directory by default. The output also names the artifacts used and the exact .wks script that was used to generate the image.

Note

You should always verify the details provided in the output to make sure that the image was indeed created exactly as expected.

Continuing with the example, you can now write the image to a USB stick, or whatever media for which you built your image, and boot the resulting media. You can write the image by using bmaptool or dd:

     $ oe-run-native bmaptool copy build/mkefidisk-201310230946-sda.direct /dev/sdX
                        

or

     $ sudo dd if=build/mkefidisk-201310230946-sda.direct of=/dev/sdX
                        

Note

For more information on how to use the bmaptool to flash a device with an image, see the "Flashing Images Using bmaptool" section.

4.13.2.6.2. Using a Modified Kickstart File

Because partitioned image creation is driven by the kickstart file, it is easy to affect image creation by changing the parameters in the file. This next example demonstrates that through modification of the directdisk kickstart file.

As mentioned earlier, you can use the command wic list images to show the list of existing kickstart files. The directory in which these files reside is scripts/lib/image/canned-wks/ located in the Source Directory. Because the available files reside in this directory, you can create and add your own custom files to the directory. Subsequent use of the wic list images command would then include your kickstart files.

In this example, the existing directdisk file already does most of what is needed. However, for the hardware in this example, the image will need to boot from sdb instead of sda, which is what the directdisk kickstart file uses.

The example begins by making a copy of the directdisk.wks file in the scripts/lib/image/canned-wks directory and then by changing the lines that specify the target disk from which to boot.

     $ cp /home/trz/yocto/yocto-image/scripts/lib/image/canned-wks/directdisk.wks \
          /home/trz/yocto/yocto-image/scripts/lib/image/canned-wks/directdisksdb.wks
                        

Next, the example modifies the directdisksdb.wks file and changes all instances of "--ondisk sda" to "--ondisk sdb". The example changes the following two lines and leaves the remaining lines untouched:

     part /boot --source bootimg-pcbios --ondisk sdb --label boot --active --align 1024
     part / --source rootfs --ondisk sdb --fstype=ext3 --label platform --align 1024
                        

Once the lines are changed, the example generates the directdisksdb image. The command points the process at the core-image-minimal artifacts for the Next Unit of Computing (nuc) MACHINE the local.conf.

     $ wic create directdisksdb -e core-image-minimal
     Checking basic build environment...
     Done.

     Creating image(s)...

     Info: The new image(s) can be found here:
      current_directory/build/directdisksdb-201310231131-sdb.direct

     The following build artifacts were used to create the image(s):

      ROOTFS_DIR: /home/trz/yocto/yocto-image/build/tmp/work/nuc-poky-linux/core-image-minimal/1.0-r0/rootfs
      BOOTIMG_DIR: /home/trz/yocto/yocto-image/build/tmp/sysroots/nuc/usr/share
      KERNEL_DIR: /home/trz/yocto/yocto-image/build/tmp/sysroots/nuc/usr/src/kernel
      NATIVE_SYSROOT: /home/trz/yocto/yocto-image/build/tmp/sysroots/x86_64-linux

     The image(s) were created using OE kickstart file:
      /home/trz/yocto/yocto-image/scripts/lib/image/canned-wks/directdisksdb.wks
                        

Continuing with the example, you can now directly dd the image to a USB stick, or whatever media for which you built your image, and boot the resulting media:

     $ sudo dd if=build/directdisksdb-201310231131-sdb.direct of=/dev/sdb
     86018+0 records in
     86018+0 records out
     44041216 bytes (44 MB) copied, 13.0734 s, 3.4 MB/s
     [trz at empanada tmp]$ sudo eject /dev/sdb
                        

4.13.2.6.3. Creating an Image Based on core-image-minimal and crownbay-noemgd

This example creates an image based on core-image-minimal and a crownbay-noemgd MACHINE that works right out of the box.

     $ wic create directdisk -e core-image-minimal

     Checking basic build environment...
     Done.

     Creating image(s)...

     Info: The new image(s) can be found here:
      current_directory/build/directdisk-201309252350-sda.direct

     The following build artifacts were used to create the image(s):

     ROOTFS_DIR: /home/trz/yocto/yocto-image/build/tmp/work/crownbay_noemgd-poky-linux/core-image-minimal/1.0-r0/rootfs
     BOOTIMG_DIR: /home/trz/yocto/yocto-image/build/tmp/sysroots/crownbay-noemgd/usr/share
     KERNEL_DIR: /home/trz/yocto/yocto-image/build/tmp/sysroots/crownbay-noemgd/usr/src/kernel
     NATIVE_SYSROOT: /home/trz/yocto/yocto-image/build/tmp/sysroots/crownbay-noemgd/usr/src/kernel

     The image(s) were created using OE kickstart file:
      /home/trz/yocto/yocto-image/scripts/lib/image/canned-wks/directdisk.wks
                        

4.13.2.6.4. Using a Modified Kickstart File and Running in Raw Mode

This next example manually specifies each build artifact (runs in Raw Mode) and uses a modified kickstart file. The example also uses the -o option to cause Wic to create the output somewhere other than the default output directory, which is the current directory:

     $ wic create ~/test.wks -o /home/trz/testwic --rootfs-dir \
          /home/trz/yocto/yocto-image/build/tmp/work/crownbay_noemgd-poky-linux/core-image-minimal/1.0-r0/rootfs \
          --bootimg-dir /home/trz/yocto/yocto-image/build/tmp/sysroots/crownbay-noemgd/usr/share \
          --kernel-dir /home/trz/yocto/yocto-image/build/tmp/sysroots/crownbay-noemgd/usr/src/kernel \
          --native-sysroot /home/trz/yocto/yocto-image/build/tmp/sysroots/x86_64-linux

     Creating image(s)...

     Info: The new image(s) can be found here:
      /home/trz/testwic/build/test-201309260032-sda.direct

     The following build artifacts were used to create the image(s):

     ROOTFS_DIR: /home/trz/yocto/yocto-image/build/tmp/work/crownbay_noemgd-poky-linux/core-image-minimal/1.0-r0/rootfs
     BOOTIMG_DIR: /home/trz/yocto/yocto-image/build/tmp/sysroots/crownbay-noemgd/usr/share
     KERNEL_DIR: /home/trz/yocto/yocto-image/build/tmp/sysroots/crownbay-noemgd/usr/src/kernel
     NATIVE_SYSROOT: /home/trz/yocto/yocto-image/build/tmp/sysroots/crownbay-noemgd/usr/src/kernel

     The image(s) were created using OE kickstart file:
      /home/trz/test.wks
                        

For this example, MACHINE did not have to be specified in the local.conf file since the artifact is manually specified.

4.13.2.7. Plug-ins

Plug-ins allow Wic functionality to be extended and specialized by users. This section documents the plug-in interface, which is currently restricted to source plug-ins.

Source plug-ins provide a mechanism to customize various aspects of the image generation process in Wic, mainly the contents of partitions. The plug-ins provide a mechanism for mapping values specified in .wks files using the --source keyword to a particular plug-in implementation that populates a corresponding partition.

Note

If you use plug-ins that have build-time dependencies (e.g. native tools, bootloaders, and so forth) when building a Wic image, you need to specify those dependencies using the WKS_FILE_DEPENDS variable.

A source plug-in is created as a subclass of SourcePlugin. The plug-in file containing it is added to scripts/lib/wic/plugins/source/ to make the plug-in implementation available to the Wic implementation. For more information, see scripts/lib/wic/pluginbase.py.

Source plug-ins can also be implemented and added by external layers. As such, any plug-ins found in a scripts/lib/wic/plugins/source/ directory in an external layer are also made available.

When the Wic implementation needs to invoke a partition-specific implementation, it looks for the plug-in that has the same name as the --source parameter given to that partition. For example, if the partition is set up as follows:

     part /boot --source bootimg-pcbios   ...
                    

The methods defined as class members of the plug-in having the matching bootimg-pcbios.name class member are used.

To be more concrete, here is the plug-in definition that matches a --source bootimg-pcbios usage, along with an example method called by the Wic implementation when it needs to invoke an implementation-specific partition-preparation function:

    class BootimgPcbiosPlugin(SourcePlugin):
        name = 'bootimg-pcbios'

    @classmethod
        def do_prepare_partition(self, part, ...)
                    

If the subclass itself does not implement a function, a default version in a superclass is located and used, which is why all plug-ins must be derived from SourcePlugin.

The SourcePlugin class defines the following methods, which is the current set of methods that can be implemented or overridden by --source plug-ins. Any methods not implemented by a SourcePlugin subclass inherit the implementations present in the SourcePlugin class. For more information, see the SourcePlugin source for details:

  • do_prepare_partition(): Called to do the actual content population for a partition. In other words, the method prepares the final partition image that is incorporated into the disk image.

  • do_configure_partition(): Called before do_prepare_partition(). This method is typically used to create custom configuration files for a partition (e.g. syslinux or grub configuration files).

  • do_install_disk(): Called after all partitions have been prepared and assembled into a disk image. This method provides a hook to allow finalization of a disk image, (e.g. writing an MBR).

  • do_stage_partition(): Special content-staging hook called before do_prepare_partition(). This method is normally empty.

    Typically, a partition just uses the passed-in parameters (e.g. the unmodified value of bootimg_dir). However, in some cases things might need to be more tailored. As an example, certain files might additionally need to be taken from bootimg_dir + /boot. This hook allows those files to be staged in a customized fashion.

    Note

    get_bitbake_var() allows you to access non-standard variables that you might want to use for this.

This scheme is extensible. Adding more hooks is a simple matter of adding more plug-in methods to SourcePlugin and derived classes. The code that then needs to call the plug-in methods uses plugin.get_source_plugin_methods() to find the method or methods needed by the call. Retrieval of those methods is accomplished by filling up a dict with keys containing the method names of interest. On success, these will be filled in with the actual methods. Please see the Wic implementation for examples and details.

4.13.2.8. OpenEmbedded Kickstart (.wks) Reference

The current Wic implementation supports only the basic kickstart partitioning commands: partition (or part for short) and bootloader.

Note

Future updates will implement more commands and options. If you use anything that is not specifically supported, results can be unpredictable.

The following is a list of the commands, their syntax, and meanings. The commands are based on the Fedora kickstart versions but with modifications to reflect Wic capabilities. You can see the original documentation for those commands at the following links:

4.13.2.8.1. Command: part or partition

Either of these commands create a partition on the system and use the following syntax:

     part [mntpoint]
     partition [mntpoint]
                        

If you do not provide mntpoint, Wic creates a partition but does not mount it.

The mntpoint is where the partition will be mounted and must be of one of the following forms:

  • /path: For example, "/", "/usr", or "/home"

  • swap: The created partition is used as swap space.

Specifying a mntpoint causes the partition to automatically be mounted. Wic achieves this by adding entries to the filesystem table (fstab) during image generation. In order for wic to generate a valid fstab, you must also provide one of the --ondrive, --ondisk, or --use-uuid partition options as part of the command. Here is an example using "/" as the mountpoint. The command uses "--ondisk" to force the partition onto the sdb disk:

     part / --source rootfs --ondisk sdb --fstype=ext3 --label platform --align 1024
                        

Here is a list that describes other supported options you can use with the part and partition commands:

  • --size: The minimum partition size in MBytes. Specify an integer value such as 500. Do not append the number with "MB". You do not need this option if you use --source.

  • --source: This option is a Wic-specific option that names the source of the data that populates the partition. The most common value for this option is "rootfs", but you can use any value that maps to a valid source plug-in. For information on the source plug-ins, see the "Plug-ins" section.

    If you use --source rootfs, Wic creates a partition as large as needed and to fill it with the contents of the root filesystem pointed to by the -r command-line option or the equivalent rootfs derived from the -e command-line option. The filesystem type used to create the partition is driven by the value of the --fstype option specified for the partition. See the entry on --fstype that follows for more information.

    If you use --source plugin-name, Wic creates a partition as large as needed and fills it with the contents of the partition that is generated by the specified plug-in name using the data pointed to by the -r command-line option or the equivalent rootfs derived from the -e command-line option. Exactly what those contents and filesystem type end up being are dependent on the given plug-in implementation.

    If you do not use the --source option, the wic command creates an empty partition. Consequently, you must use the --size option to specify the size of the empty partition.

  • --ondisk or --ondrive: Forces the partition to be created on a particular disk.

  • --fstype: Sets the file system type for the partition. Valid values are:

    • ext4

    • ext3

    • ext2

    • btrfs

    • squashfs

    • swap

  • --fsoptions: Specifies a free-form string of options to be used when mounting the filesystem. This string will be copied into the /etc/fstab file of the installed system and should be enclosed in quotes. If not specified, the default string is "defaults".

  • --label label: Specifies the label to give to the filesystem to be made on the partition. If the given label is already in use by another filesystem, a new label is created for the partition.

  • --active: Marks the partition as active.

  • --align (in KBytes): This option is a Wic-specific option that says to start a partition on an x KBytes boundary.

  • --no-table: This option is a Wic-specific option. Using the option reserves space for the partition and causes it to become populated. However, the partition is not added to the partition table.

  • --extra-space: This option is a Wic-specific option that adds extra space after the space filled by the content of the partition. The final size can go beyond the size specified by the --size option. The default value is 10 Mbytes.

  • --overhead-factor: This option is a Wic-specific option that multiplies the size of the partition by the option's value. You must supply a value greater than or equal to "1". The default value is "1.3".

  • --part-type: This option is a Wic-specific option that specifies the partition type globally unique identifier (GUID) for GPT partitions. You can find the list of partition type GUIDs at http://en.wikipedia.org/wiki/GUID_Partition_Table#Partition_type_GUIDs.

  • --use-uuid: This option is a Wic-specific option that causes Wic to generate a random GUID for the partition. The generated identifier is used in the bootloader configuration to specify the root partition.

  • --uuid: This option is a Wic-specific option that specifies the partition UUID.

4.13.2.8.2. Command: bootloader

This command specifies how the bootloader should be configured and supports the following options:

Note

Bootloader functionality and boot partitions are implemented by the various --source plug-ins that implement bootloader functionality. The bootloader command essentially provides a means of modifying bootloader configuration.

  • --timeout: Specifies the number of seconds before the bootloader times out and boots the default option.

  • --append: Specifies kernel parameters. These parameters will be added to the syslinux APPEND or grub kernel command line.

  • --configfile: Specifies a user-defined configuration file for the bootloader. You can provide a full pathname for the file or a file that exists in the canned-wks folder. This option overrides all other bootloader options.

4.14. Building an Initial RAM Filesystem (initramfs) Image

An initial RAM filesystem (initramfs) image provides a temporary root filesystem used for early system initialization (e.g. loading of modules needed to locate and mount the "real" root filesystem).

Note

The initramfs image is the successor of initial RAM disk (initrd). It is a "copy in and out" (cpio) archive of the initial filesystem that gets loaded into memory during the Linux startup process. Because Linux uses the contents of the archive during initialization, the initramfs image needs to contain all of the device drivers and tools needed to mount the final root filesystem.

Follow these steps to create an initramfs image:

  1. Create the initramfs Image Recipe: You can reference the core-image-minimal-initramfs.bb recipe found in the meta/recipes-core directory of the Source Directory as an example from which to work.

  2. Decide if You Need to Bundle the initramfs Image Into the Kernel Image: If you want the initramfs image that is built to be bundled in with the kernel image, set the INITRAMFS_IMAGE_BUNDLE variable to "1" in your local.conf configuration file and set the INITRAMFS_IMAGE variable in the recipe that builds the kernel image.

    Tip

    It is recommended that you do bundle the initramfs image with the kernel image to avoid circular dependencies between the kernel recipe and the initramfs recipe should the initramfs image include kernel modules.

    Setting the INITRAMFS_IMAGE_BUNDLE flag causes the initramfs image to be unpacked into the ${B}/usr/ directory. The unpacked initramfs image is then passed to the kernel's Makefile using the CONFIG_INITRAMFS_SOURCE variable, allowing the initramfs image to be built into the kernel normally.

    Note

    If you choose to not bundle the initramfs image with the kernel image, you are essentially using an Initial RAM Disk (initrd). Creating an initrd is handled primarily through the INITRD_IMAGE, INITRD_LIVE, and INITRD_IMAGE_LIVE variables. For more information, see the image-live.bbclass file.

  3. Optionally Add Items to the initramfs Image Through the initramfs Image Recipe: If you add items to the initramfs image by way of its recipe, you should use PACKAGE_INSTALL rather than IMAGE_INSTALL. PACKAGE_INSTALL gives more direct control of what is added to the image as compared to the defaults you might not necessarily want that are set by the image or core-image classes.

  4. Build the Kernel Image and the initramfs Image: Build your kernel image using BitBake. Because the initramfs image recipe is a dependency of the kernel image, the initramfs image is built as well and bundled with the kernel image if you used the INITRAMFS_IMAGE_BUNDLE variable described earlier.

4.15. Flashing Images Using bmaptool

An easy way to flash an image to a bootable device is to use bmaptool, which is integrated into the OpenEmbedded build system.

Following, is an example that shows how to flash a Wic image.

Note

You can use bmaptool to flash any type of image.

Use these steps to flash an image using bmaptool:

Note

Unless you are able to install the bmap-tools package as mentioned in the note in the second bullet of step 3 further down, you will need to build bmaptool before using it. Build the tool using the following command:
     $ bitbake bmap-tools-native
                

  1. Update the local.conf File: Add the following to your local.conf file:

         IMAGE_FSTYPES += "wic wic.bmap"
                        

  2. Get Your Image: Either have your image ready (pre-built) or take the step build the image:

         $ bitbake image
                        

  3. Flash the Device: Flash the device with the image by using bmaptool depending on your particular setup:

    • If you have write access to the media, use this command form:

           $ oe-run-native bmap-tools-native bmaptool copy ./tmp/deploy/images/qemux86-64-core-image-minimal-machine.wic /dev/sdX
                                  

    • If you do not have write access to the media, use the following commands:

           $ sudo chmod 666 /dev/sdX
           $ oe-run-native bmap-tools-native bmaptool copy ./tmp/deploy/images/qemux86-64-core-image-minimal-machine.wic /dev/sdX
                                  

      Note

      If you are using Ubuntu or Debian distributions, you can install the bmap-tools package using the following command and then use the tool without specifying PATH even from the root account:
           $ sudo apt-get install bmap-tools
                                      

For help on the bmaptool command, use the following command:

     $ bmaptool --help
            

4.16. Making Images More Secure

Security is of increasing concern for embedded devices. Consider the issues and problems discussed in just this sampling of work found across the Internet:

When securing your image is of concern, there are steps, tools, and variables that you can consider to help you reach the security goals you need for your particular device. Not all situations are identical when it comes to making an image secure. Consequently, this section provides some guidance and suggestions for consideration when you want to make your image more secure.

Note

Because the security requirements and risks are different for every type of device, this section cannot provide a complete reference on securing your custom OS. It is strongly recommended that you also consult other sources of information on embedded Linux system hardening and on security.

4.16.1. General Considerations

General considerations exist that help you create more secure images. You should consider the following suggestions to help make your device more secure:

  • Scan additional code you are adding to the system (e.g. application code) by using static analysis tools. Look for buffer overflows and other potential security problems.

  • Pay particular attention to the security for any web-based administration interface.

    Web interfaces typically need to perform administrative functions and tend to need to run with elevated privileges. Thus, the consequences resulting from the interface's security becoming compromised can be serious. Look for common web vulnerabilities such as cross-site-scripting (XSS), unvalidated inputs, and so forth.

    As with system passwords, the default credentials for accessing a web-based interface should not be the same across all devices. This is particularly true if the interface is enabled by default as it can be assumed that many end-users will not change the credentials.

  • Ensure you can update the software on the device to mitigate vulnerabilities discovered in the future. This consideration especially applies when your device is network-enabled.

  • Ensure you remove or disable debugging functionality before producing the final image. For information on how to do this, see the "Considerations Specific to the OpenEmbedded Build System" section.

  • Ensure you have no network services listening that are not needed.

  • Remove any software from the image that is not needed.

  • Enable hardware support for secure boot functionality when your device supports this functionality.

4.16.2. Security Flags

The Yocto Project has security flags that you can enable that help make your build output more secure. The security flags are in the meta/conf/distro/include/security_flags.inc file in your Source Directory (e.g. poky).

Note

Depending on the recipe, certain security flags are enabled and disabled by default.

Use the following line in your local.conf file or in your custom distribution configuration file to enable the security compiler and linker flags for your build:

     require conf/distro/include/security_flags.inc
                

4.16.3. Considerations Specific to the OpenEmbedded Build System

You can take some steps that are specific to the OpenEmbedded build system to make your images more secure:

  • Ensure "debug-tweaks" is not one of your selected IMAGE_FEATURES. When creating a new project, the default is to provide you with an initial local.conf file that enables this feature using the EXTRA_IMAGE_FEATURES variable with the line:

         EXTRA_IMAGE_FEATURES = "debug-tweaks"
                    

    To disable that feature, simply comment out that line in your local.conf file, or make sure IMAGE_FEATURES does not contain "debug-tweaks" before producing your final image. Among other things, leaving this in place sets the root password as blank, which makes logging in for debugging or inspection easy during development but also means anyone can easily log in during production.

  • It is possible to set a root password for the image and also to set passwords for any extra users you might add (e.g. administrative or service type users). When you set up passwords for multiple images or users, you should not duplicate passwords.

    To set up passwords, use the extrausers class, which is the preferred method. For an example on how to set up both root and user passwords, see the "extrausers.bbclass" section.

    Note

    When adding extra user accounts or setting a root password, be cautious about setting the same password on every device. If you do this, and the password you have set is exposed, then every device is now potentially compromised. If you need this access but want to ensure security, consider setting a different, random password for each device. Typically, you do this as a separate step after you deploy the image onto the device.

  • Consider enabling a Mandatory Access Control (MAC) framework such as SMACK or SELinux and tuning it appropriately for your device's usage. You can find more information in the meta-selinux layer.

4.16.4. Tools for Hardening Your Image

The Yocto Project provides tools for making your image more secure. You can find these tools in the meta-security layer of the Yocto Project Source Repositories.

4.17. Creating Your Own Distribution

When you build an image using the Yocto Project and do not alter any distribution Metadata, you are creating a Poky distribution. If you wish to gain more control over package alternative selections, compile-time options, and other low-level configurations, you can create your own distribution.

To create your own distribution, the basic steps consist of creating your own distribution layer, creating your own distribution configuration file, and then adding any needed code and Metadata to the layer. The following steps provide some more detail:

  • Create a layer for your new distro: Create your distribution layer so that you can keep your Metadata and code for the distribution separate. It is strongly recommended that you create and use your own layer for configuration and code. Using your own layer as compared to just placing configurations in a local.conf configuration file makes it easier to reproduce the same build configuration when using multiple build machines. See the "Creating a General Layer Using the yocto-layer Script" section for information on how to quickly set up a layer.

  • Create the distribution configuration file: The distribution configuration file needs to be created in the conf/distro directory of your layer. You need to name it using your distribution name (e.g. mydistro.conf).

    Note

    The DISTRO variable in your local.conf file determines the name of your distribution.

    You can split out parts of your configuration file into include files and then "require" them from within your distribution configuration file. Be sure to place the include files in the conf/distro/include directory of your layer. A common example usage of include files would be to separate out the selection of desired version and revisions for individual recipes.

    Your configuration file needs to set the following required variables:

         DISTRO_NAME
         DISTRO_VERSION
                        

    These following variables are optional and you typically set them from the distribution configuration file:

         DISTRO_FEATURES
         DISTRO_EXTRA_RDEPENDS
         DISTRO_EXTRA_RRECOMMENDS
         TCLIBC
                        

    Tip

    If you want to base your distribution configuration file on the very basic configuration from OE-Core, you can use conf/distro/defaultsetup.conf as a reference and just include variables that differ as compared to defaultsetup.conf. Alternatively, you can create a distribution configuration file from scratch using the defaultsetup.conf file or configuration files from other distributions such as Poky or Angstrom as references.
  • Provide miscellaneous variables: Be sure to define any other variables for which you want to create a default or enforce as part of the distribution configuration. You can include nearly any variable from the local.conf file. The variables you use are not limited to the list in the previous bulleted item.

  • Point to Your distribution configuration file: In your local.conf file in the Build Directory, set your DISTRO variable to point to your distribution's configuration file. For example, if your distribution's configuration file is named mydistro.conf, then you point to it as follows:

         DISTRO = "mydistro"
                        
  • Add more to the layer if necessary: Use your layer to hold other information needed for the distribution:

    • Add recipes for installing distro-specific configuration files that are not already installed by another recipe. If you have distro-specific configuration files that are included by an existing recipe, you should add an append file (.bbappend) for those. For general information and recommendations on how to add recipes to your layer, see the "Creating Your Own Layer" and "Following Best Practices When Creating Layers" sections.

    • Add any image recipes that are specific to your distribution.

    • Add a psplash append file for a branded splash screen. For information on append files, see the "Using .bbappend Files in Your Layer" section.

    • Add any other append files to make custom changes that are specific to individual recipes.

4.18. Creating a Custom Template Configuration Directory

If you are producing your own customized version of the build system for use by other users, you might want to customize the message shown by the setup script or you might want to change the template configuration files (i.e. local.conf and bblayers.conf) that are created in a new build directory.

The OpenEmbedded build system uses the environment variable TEMPLATECONF to locate the directory from which it gathers configuration information that ultimately ends up in the Build Directory conf directory. By default, TEMPLATECONF is set as follows in the poky repository:

     TEMPLATECONF=${TEMPLATECONF:-meta-poky/conf}
            

This is the directory used by the build system to find templates from which to build some key configuration files. If you look at this directory, you will see the bblayers.conf.sample, local.conf.sample, and conf-notes.txt files. The build system uses these files to form the respective bblayers.conf file, local.conf file, and display the list of BitBake targets when running the setup script.

To override these default configuration files with configurations you want used within every new Build Directory, simply set the TEMPLATECONF variable to your directory. The TEMPLATECONF variable is set in the .templateconf file, which is in the top-level Source Directory folder (e.g. poky). Edit the .templateconf so that it can locate your directory.

Best practices dictate that you should keep your template configuration directory in your custom distribution layer. For example, suppose you have a layer named meta-mylayer located in your home directory and you want your template configuration directory named myconf. Changing the .templateconf as follows causes the OpenEmbedded build system to look in your directory and base its configuration files on the *.sample configuration files it finds. The final configuration files (i.e. local.conf and bblayers.conf ultimately still end up in your Build Directory, but they are based on your *.sample files.

     TEMPLATECONF=${TEMPLATECONF:-meta-mylayer/myconf}
            

Aside from the *.sample configuration files, the conf-notes.txt also resides in the default meta-poky/conf directory. The script that sets up the build environment (i.e. oe-init-build-env) uses this file to display BitBake targets as part of the script output. Customizing this conf-notes.txt file is a good way to make sure your list of custom targets appears as part of the script's output.

Here is the default list of targets displayed as a result of running either of the setup scripts:

     You can now run 'bitbake <target>'

     Common targets are:
         core-image-minimal
         core-image-sato
         meta-toolchain
         meta-ide-support
            

Changing the listed common targets is as easy as editing your version of conf-notes.txt in your custom template configuration directory and making sure you have TEMPLATECONF set to your directory.

4.19. Building a Tiny System

Very small distributions have some significant advantages such as requiring less on-die or in-package memory (cheaper), better performance through efficient cache usage, lower power requirements due to less memory, faster boot times, and reduced development overhead. Some real-world examples where a very small distribution gives you distinct advantages are digital cameras, medical devices, and small headless systems.

This section presents information that shows you how you can trim your distribution to even smaller sizes than the poky-tiny distribution, which is around 5 Mbytes, that can be built out-of-the-box using the Yocto Project.

4.19.1. Overview

The following list presents the overall steps you need to consider and perform to create distributions with smaller root filesystems, achieve faster boot times, maintain your critical functionality, and avoid initial RAM disks:

4.19.2. Goals and Guiding Principles

Before you can reach your destination, you need to know where you are going. Here is an example list that you can use as a guide when creating very small distributions:

  • Determine how much space you need (e.g. a kernel that is 1 Mbyte or less and a root filesystem that is 3 Mbytes or less).

  • Find the areas that are currently taking 90% of the space and concentrate on reducing those areas.

  • Do not create any difficult "hacks" to achieve your goals.

  • Leverage the device-specific options.

  • Work in a separate layer so that you keep changes isolated. For information on how to create layers, see the "Understanding and Creating Layers" section.

4.19.3. Understand What Contributes to Your Image Size

It is easiest to have something to start with when creating your own distribution. You can use the Yocto Project out-of-the-box to create the poky-tiny distribution. Ultimately, you will want to make changes in your own distribution that are likely modeled after poky-tiny.

Note

To use poky-tiny in your build, set the DISTRO variable in your local.conf file to "poky-tiny" as described in the "Creating Your Own Distribution" section.

Understanding some memory concepts will help you reduce the system size. Memory consists of static, dynamic, and temporary memory. Static memory is the TEXT (code), DATA (initialized data in the code), and BSS (uninitialized data) sections. Dynamic memory represents memory that is allocated at runtime: stacks, hash tables, and so forth. Temporary memory is recovered after the boot process. This memory consists of memory used for decompressing the kernel and for the __init__ functions.

To help you see where you currently are with kernel and root filesystem sizes, you can use two tools found in the Source Directory in the scripts/tiny/ directory:

  • ksize.py: Reports component sizes for the kernel build objects.

  • dirsize.py: Reports component sizes for the root filesystem.

This next tool and command help you organize configuration fragments and view file dependencies in a human-readable form:

  • merge_config.sh: Helps you manage configuration files and fragments within the kernel. With this tool, you can merge individual configuration fragments together. The tool allows you to make overrides and warns you of any missing configuration options. The tool is ideal for allowing you to iterate on configurations, create minimal configurations, and create configuration files for different machines without having to duplicate your process.

    The merge_config.sh script is part of the Linux Yocto kernel Git repositories (i.e. linux-yocto-3.14, linux-yocto-3.10, linux-yocto-3.8, and so forth) in the scripts/kconfig directory.

    For more information on configuration fragments, see the "Generating Configuration Files" section of the Yocto Project Linux Kernel Development Manual and the "Creating Configuration Fragments" section in the Yocto Project Linux Kernel Development Manual.

  • bitbake -u taskexp -g bitbake_target: Using the BitBake command with these options brings up a Dependency Explorer from which you can view file dependencies. Understanding these dependencies allows you to make informed decisions when cutting out various pieces of the kernel and root filesystem.

4.19.4. Trim the Root Filesystem

The root filesystem is made up of packages for booting, libraries, and applications. To change things, you can configure how the packaging happens, which changes the way you build them. You can also modify the filesystem itself or select a different filesystem.

First, find out what is hogging your root filesystem by running the dirsize.py script from your root directory:

     $ cd root-directory-of-image
     $ dirsize.py 100000 > dirsize-100k.log
     $ cat dirsize-100k.log
                

You can apply a filter to the script to ignore files under a certain size. The previous example filters out any files below 100 Kbytes. The sizes reported by the tool are uncompressed, and thus will be smaller by a relatively constant factor in a compressed root filesystem. When you examine your log file, you can focus on areas of the root filesystem that take up large amounts of memory.

You need to be sure that what you eliminate does not cripple the functionality you need. One way to see how packages relate to each other is by using the Dependency Explorer UI with the BitBake command:

     $ cd image-directory
     $ bitbake -u taskexp -g image
                

Use the interface to select potential packages you wish to eliminate and see their dependency relationships.

When deciding how to reduce the size, get rid of packages that result in minimal impact on the feature set. For example, you might not need a VGA display. Or, you might be able to get by with devtmpfs and mdev instead of udev.

Use your local.conf file to make changes. For example, to eliminate udev and glib, set the following in the local configuration file:

     VIRTUAL-RUNTIME_dev_manager = ""
                

Finally, you should consider exactly the type of root filesystem you need to meet your needs while also reducing its size. For example, consider cramfs, squashfs, ubifs, ext2, or an initramfs using initramfs. Be aware that ext3 requires a 1 Mbyte journal. If you are okay with running read-only, you do not need this journal.

Note

After each round of elimination, you need to rebuild your system and then use the tools to see the effects of your reductions.

4.19.5. Trim the Kernel

The kernel is built by including policies for hardware-independent aspects. What subsystems do you enable? For what architecture are you building? Which drivers do you build by default?

Note

You can modify the kernel source if you want to help with boot time.

Run the ksize.py script from the top-level Linux build directory to get an idea of what is making up the kernel:

     $ cd top-level-linux-build-directory
     $ ksize.py > ksize.log
     $ cat ksize.log
                

When you examine the log, you will see how much space is taken up with the built-in .o files for drivers, networking, core kernel files, filesystem, sound, and so forth. The sizes reported by the tool are uncompressed, and thus will be smaller by a relatively constant factor in a compressed kernel image. Look to reduce the areas that are large and taking up around the "90% rule."

To examine, or drill down, into any particular area, use the -d option with the script:

     $ ksize.py -d > ksize.log
                

Using this option breaks out the individual file information for each area of the kernel (e.g. drivers, networking, and so forth).

Use your log file to see what you can eliminate from the kernel based on features you can let go. For example, if you are not going to need sound, you do not need any drivers that support sound.

After figuring out what to eliminate, you need to reconfigure the kernel to reflect those changes during the next build. You could run menuconfig and make all your changes at once. However, that makes it difficult to see the effects of your individual eliminations and also makes it difficult to replicate the changes for perhaps another target device. A better method is to start with no configurations using allnoconfig, create configuration fragments for individual changes, and then manage the fragments into a single configuration file using merge_config.sh. The tool makes it easy for you to iterate using the configuration change and build cycle.

Each time you make configuration changes, you need to rebuild the kernel and check to see what impact your changes had on the overall size.

4.19.6. Remove Package Management Requirements

Packaging requirements add size to the image. One way to reduce the size of the image is to remove all the packaging requirements from the image. This reduction includes both removing the package manager and its unique dependencies as well as removing the package management data itself.

To eliminate all the packaging requirements for an image, be sure that "package-management" is not part of your IMAGE_FEATURES statement for the image. When you remove this feature, you are removing the package manager as well as its dependencies from the root filesystem.

4.19.7. Look for Other Ways to Minimize Size

Depending on your particular circumstances, other areas that you can trim likely exist. The key to finding these areas is through tools and methods described here combined with experimentation and iteration. Here are a couple of areas to experiment with:

  • glibc: In general, follow this process:

    1. Remove glibc features from DISTRO_FEATURES that you think you do not need.

    2. Build your distribution.

    3. If the build fails due to missing symbols in a package, determine if you can reconfigure the package to not need those features. For example, change the configuration to not support wide character support as is done for ncurses. Or, if support for those characters is needed, determine what glibc features provide the support and restore the configuration.

    4. Rebuild and repeat the process.

  • busybox: For BusyBox, use a process similar as described for glibc. A difference is you will need to boot the resulting system to see if you are able to do everything you expect from the running system. You need to be sure to integrate configuration fragments into Busybox because BusyBox handles its own core features and then allows you to add configuration fragments on top.

4.19.8. Iterate on the Process

If you have not reached your goals on system size, you need to iterate on the process. The process is the same. Use the tools and see just what is taking up 90% of the root filesystem and the kernel. Decide what you can eliminate without limiting your device beyond what you need.

Depending on your system, a good place to look might be Busybox, which provides a stripped down version of Unix tools in a single, executable file. You might be able to drop virtual terminal services or perhaps ipv6.

4.20. Building Images for More than One Machine

A common scenario developers face is creating images for several different machines that use the same software environment. In this situation, it is tempting to set the tunings and optimization flags for each build specifically for the targeted hardware (i.e. "maxing out" the tunings). Doing so can considerably add to build times and package feed maintenance collectively for the machines. For example, selecting tunes that are extremely specific to a CPU core used in a system might enable some micro optimizations in GCC for that particular system but would otherwise not gain you much of a performance difference across the other systems as compared to using a more general tuning across all the builds (e.g. setting DEFAULTTUNE specifically for each machine's build). Rather than "max out" each build's tunings, you can take steps that cause the OpenEmbedded build system to reuse software across the various machines where it makes sense.

If build speed and package feed maintenance are considerations, you should consider the points in this section that can help you optimize your tunings to best consider build times and package feed maintenance.

  • Share the Build Directory: If at all possible, share the TMPDIR across builds. The Yocto Project supports switching between different MACHINE values in the same TMPDIR. This practice is well supported and regularly used by developers when building for multiple machines. When you use the same TMPDIR for multiple machine builds, the OpenEmbedded build system can reuse the existing native and often cross-recipes for multiple machines. Thus, build time decreases.

    Note

    If DISTRO settings change or fundamental configuration settings such as the filesystem layout, you need to work with a clean TMPDIR. Sharing TMPDIR under these circumstances might work but since it is not guaranteed, you should use a clean TMPDIR.

  • Enable the Appropriate Package Architecture: By default, the OpenEmbedded build system enables three levels of package architectures: "all", "tune" or "package", and "machine". Any given recipe usually selects one of these package architectures (types) for its output. Depending for what a given recipe creates packages, making sure you enable the appropriate package architecture can directly impact the build time.

    A recipe that just generates scripts can enable "all" architecture because there are no binaries to build. To specifically enable "all" architecture, be sure your recipe inherits the allarch class. This class is useful for "all" architectures because it configures many variables so packages can be used across multiple architectures.

    If your recipe needs to generate packages that are machine-specific or when one of the build or runtime dependencies is already machine-architecture dependent, which makes your recipe also machine-architecture dependent, make sure your recipe enables the "machine" package architecture through the MACHINE_ARCH variable:

         PACKAGE_ARCH = "${MACHINE_ARCH}"
                        

    When you do not specifically enable a package architecture through the PACKAGE_ARCH, The OpenEmbedded build system defaults to the TUNE_PKGARCH setting:

         PACKAGE_ARCH = "${TUNE_PKGARCH}"
                        

  • Choose a Generic Tuning File if Possible: Some tunes are more generic and can run on multiple targets (e.g. an armv5 set of packages could run on armv6 and armv7 processors in most cases). Similarly, i486 binaries could work on i586 and higher processors. You should realize, however, that advances on newer processor versions would not be used.

    If you select the same tune for several different machines, the OpenEmbedded build system reuses software previously built, thus speeding up the overall build time. Realize that even though a new sysroot for each machine is generated, the software is not recompiled and only one package feed exists.

  • Manage Granular Level Packaging: Sometimes cases exist where injecting another level of package architecture beyond the three higher levels noted earlier can be useful. For example, consider the emgd graphics stack in the meta-intel layer. In this layer, a subset of software exists that is compiled against something different from the rest of the generic packages. You can examine the key code in the Source Repositories "daisy" branch in classes/emgd-gl.bbclass. For a specific set of packages, the code redefines PACKAGE_ARCH. PACKAGE_EXTRA_ARCHS is then appended with this extra tune name in meta-intel-emgd.inc. The result is that when searching for packages, the build system uses a four-level search and the packages in this new level are preferred as compared to the standard tune. The overall result is that the build system reuses most software from the common tune except for specific cases as needed.

  • Use Tools to Debug Issues: Sometimes you can run into situations where software is being rebuilt when you think it should not be. For example, the OpenEmbedded build system might not be using shared state between machines when you think it should be. These types of situations are usually due to references to machine-specific variables such as MACHINE, SERIAL_CONSOLE, XSERVER, MACHINE_FEATURES, and so forth in code that is supposed to only be tune-specific or when the recipe depends (DEPENDS, RDEPENDS, RRECOMMENDS, RSUGGESTS, and so forth) on some other recipe that already has PACKAGE_ARCH defined as "${MACHINE_ARCH}".

    Note

    Patches to fix any issues identified are most welcome as these issues occasionally do occur.

    For such cases, you can use some tools to help you sort out the situation:

    • sstate-diff-machines.sh: You can find this tool in the scripts directory of the Source Repositories. See the comments in the script for information on how to use the tool.

    • BitBake's "-S printdiff" Option: Using this option causes BitBake to try to establish the closest signature match it can (e.g. in the shared state cache) and then run bitbake-diffsigs over the matches to determine the stamps and delta where these two stamp trees diverge.

4.21. Working with Packages

This section describes a few tasks that involve packages:

4.21.1. Excluding Packages from an Image

You might find it necessary to prevent specific packages from being installed into an image. If so, you can use several variables to direct the build system to essentially ignore installing recommended packages or to not install a package at all.

The following list introduces variables you can use to prevent packages from being installed into your image. Each of these variables only works with IPK and RPM package types. Support for Debian packages does not exist. Also, you can use these variables from your local.conf file or attach them to a specific image recipe by using a recipe name override. For more detail on the variables, see the descriptions in the Yocto Project Reference Manual's glossary chapter.

  • BAD_RECOMMENDATIONS: Use this variable to specify "recommended-only" packages that you do not want installed.

  • NO_RECOMMENDATIONS: Use this variable to prevent all "recommended-only" packages from being installed.

  • PACKAGE_EXCLUDE: Use this variable to prevent specific packages from being installed regardless of whether they are "recommended-only" or not. You need to realize that the build process could fail with an error when you prevent the installation of a package whose presence is required by an installed package.

4.21.2. Incrementing a Package Version

This section provides some background on how binary package versioning is accomplished and presents some of the services, variables, and terminology involved.

In order to understand binary package versioning, you need to consider the following:

  • Binary Package: The binary package that is eventually built and installed into an image.

  • Binary Package Version: The binary package version is composed of two components - a version and a revision.

    Note

    Technically, a third component, the "epoch" (i.e. PE) is involved but this discussion for the most part ignores PE.

    The version and revision are taken from the PV and PR variables, respectively.

  • PV: The recipe version. PV represents the version of the software being packaged. Do not confuse PV with the binary package version.

  • PR: The recipe revision.

  • SRCPV: The OpenEmbedded build system uses this string to help define the value of PV when the source code revision needs to be included in it.

  • PR Service: A network-based service that helps automate keeping package feeds compatible with existing package manager applications such as RPM, APT, and OPKG.

Whenever the binary package content changes, the binary package version must change. Changing the binary package version is accomplished by changing or "bumping" the PR and/or PV values. Increasing these values occurs one of two ways:

  • Automatically using a Package Revision Service (PR Service).

  • Manually incrementing the PR and/or PV variables.

Given a primary challenge of any build system and its users is how to maintain a package feed that is compatible with existing package manager applications such as RPM, APT, and OPKG, using an automated system is much preferred over a manual system. In either system, the main requirement is that binary package version numbering increases in a linear fashion and that a number of version components exist that support that linear progression. For information on how to ensure package revisioning remains linear, see the "Automatically Incrementing a Binary Package Revision Number" section.

The following three sections provide related information on the PR Service, the manual method for "bumping" PR and/or PV, and on how to ensure binary package revisioning remains linear.

4.21.2.1. Working With a PR Service

As mentioned, attempting to maintain revision numbers in the Metadata is error prone, inaccurate, and causes problems for people submitting recipes. Conversely, the PR Service automatically generates increasing numbers, particularly the revision field, which removes the human element.

Note

For additional information on using a PR Service, you can see the PR Service wiki page.

The Yocto Project uses variables in order of decreasing priority to facilitate revision numbering (i.e. PE, PV, and PR for epoch, version, and revision, respectively). The values are highly dependent on the policies and procedures of a given distribution and package feed.

Because the OpenEmbedded build system uses "signatures", which are unique to a given build, the build system knows when to rebuild packages. All the inputs into a given task are represented by a signature, which can trigger a rebuild when different. Thus, the build system itself does not rely on the PR, PV, and PE numbers to trigger a rebuild. The signatures, however, can be used to generate these values.

The PR Service works with both OEBasic and OEBasicHash generators. The value of PR bumps when the checksum changes and the different generator mechanisms change signatures under different circumstances.

As implemented, the build system includes values from the PR Service into the PR field as an addition using the form ".x" so r0 becomes r0.1, r0.2 and so forth. This scheme allows existing PR values to be used for whatever reasons, which include manual PR bumps, should it be necessary.

By default, the PR Service is not enabled or running. Thus, the packages generated are just "self consistent". The build system adds and removes packages and there are no guarantees about upgrade paths but images will be consistent and correct with the latest changes.

The simplest form for a PR Service is for it to exist for a single host development system that builds the package feed (building system). For this scenario, you can enable a local PR Service by setting PRSERV_HOST in your local.conf file in the Build Directory:

     PRSERV_HOST = "localhost:0"
                    

Once the service is started, packages will automatically get increasing PR values and BitBake takes care of starting and stopping the server.

If you have a more complex setup where multiple host development systems work against a common, shared package feed, you have a single PR Service running and it is connected to each building system. For this scenario, you need to start the PR Service using the bitbake-prserv command:

     bitbake-prserv --host ip --port port --start
                    

In addition to hand-starting the service, you need to update the local.conf file of each building system as described earlier so each system points to the server and port.

It is also recommended you use build history, which adds some sanity checks to binary package versions, in conjunction with the server that is running the PR Service. To enable build history, add the following to each building system's local.conf file:

     # It is recommended to activate "buildhistory" for testing the PR service
     INHERIT += "buildhistory"
     BUILDHISTORY_COMMIT = "1"
                    

For information on build history, see the "Maintaining Build Output Quality" section in the Yocto Project Reference Manual.

Note

The OpenEmbedded build system does not maintain PR information as part of the shared state (sstate) packages. If you maintain an sstate feed, its expected that either all your building systems that contribute to the sstate feed use a shared PR Service, or you do not run a PR Service on any of your building systems. Having some systems use a PR Service while others do not leads to obvious problems.

For more information on shared state, see the "Shared State Cache" section in the Yocto Project Reference Manual.

4.21.2.2. Manually Bumping PR

The alternative to setting up a PR Service is to manually "bump" the PR variable.

If a committed change results in changing the package output, then the value of the PR variable needs to be increased (or "bumped") as part of that commit. For new recipes you should add the PR variable and set its initial value equal to "r0", which is the default. Even though the default value is "r0", the practice of adding it to a new recipe makes it harder to forget to bump the variable when you make changes to the recipe in future.

If you are sharing a common .inc file with multiple recipes, you can also use the INC_PR variable to ensure that the recipes sharing the .inc file are rebuilt when the .inc file itself is changed. The .inc file must set INC_PR (initially to "r0"), and all recipes referring to it should set PR to "${INC_PR}.0" initially, incrementing the last number when the recipe is changed. If the .inc file is changed then its INC_PR should be incremented.

When upgrading the version of a binary package, assuming the PV changes, the PR variable should be reset to "r0" (or "${INC_PR}.0" if you are using INC_PR).

Usually, version increases occur only to binary packages. However, if for some reason PV changes but does not increase, you can increase the PE variable (Package Epoch). The PE variable defaults to "0".

Binary package version numbering strives to follow the Debian Version Field Policy Guidelines. These guidelines define how versions are compared and what "increasing" a version means.

4.21.2.3. Automatically Incrementing a Package Version Number

When fetching a repository, BitBake uses the SRCREV variable to determine the specific source code revision from which to build. You set the SRCREV variable to AUTOREV to cause the OpenEmbedded build system to automatically use the latest revision of the software:

     SRCREV = "${AUTOREV}"
                    

Furthermore, you need to reference SRCPV in PV in order to automatically update the version whenever the revision of the source code changes. Here is an example:

     PV = "1.0+git${SRCPV}"
                    

The OpenEmbedded build system substitutes SRCPV with the following:

     AUTOINC+source_code_revision
                    

The build system replaces the AUTOINC with a number. The number used depends on the state of the PR Service:

  • If PR Service is enabled, the build system increments the number, which is similar to the behavior of PR. This behavior results in linearly increasing package versions, which is desirable. Here is an example:

         hello-world-git_0.0+git0+b6558dd387-r0.0_armv7a-neon.ipk
         hello-world-git_0.0+git1+dd2f5c3565-r0.0_armv7a-neon.ipk
                                

  • If PR Service is not enabled, the build system replaces the AUTOINC placeholder with zero (i.e. "0"). This results in changing the package version since the source revision is included. However, package versions are not increased linearly. Here is an example:

         hello-world-git_0.0+git0+b6558dd387-r0.0_armv7a-neon.ipk
         hello-world-git_0.0+git0+dd2f5c3565-r0.0_armv7a-neon.ipk
                                

In summary, the OpenEmbedded build system does not track the history of binary package versions for this purpose. AUTOINC, in this case, is comparable to PR. If PR server is not enabled, AUTOINC in the package version is simply replaced by "0". If PR server is enabled, the build system keeps track of the package versions and bumps the number when the package revision changes.

4.21.3. Handling Optional Module Packaging

Many pieces of software split functionality into optional modules (or plug-ins) and the plug-ins that are built might depend on configuration options. To avoid having to duplicate the logic that determines what modules are available in your recipe or to avoid having to package each module by hand, the OpenEmbedded build system provides functionality to handle module packaging dynamically.

To handle optional module packaging, you need to do two things:

  • Ensure the module packaging is actually done.

  • Ensure that any dependencies on optional modules from other recipes are satisfied by your recipe.

4.21.3.1. Making Sure the Packaging is Done

To ensure the module packaging actually gets done, you use the do_split_packages function within the populate_packages Python function in your recipe. The do_split_packages function searches for a pattern of files or directories under a specified path and creates a package for each one it finds by appending to the PACKAGES variable and setting the appropriate values for FILES_packagename, RDEPENDS_packagename, DESCRIPTION_packagename, and so forth. Here is an example from the lighttpd recipe:

     python populate_packages_prepend () {
         lighttpd_libdir = d.expand('${libdir}')
         do_split_packages(d, lighttpd_libdir, '^mod_(.*)\.so$',
                          'lighttpd-module-%s', 'Lighttpd module for %s',
                           extra_depends='')
     }
                    

The previous example specifies a number of things in the call to do_split_packages.

  • A directory within the files installed by your recipe through do_install in which to search.

  • A regular expression used to match module files in that directory. In the example, note the parentheses () that mark the part of the expression from which the module name should be derived.

  • A pattern to use for the package names.

  • A description for each package.

  • An empty string for extra_depends, which disables the default dependency on the main lighttpd package. Thus, if a file in ${libdir} called mod_alias.so is found, a package called lighttpd-module-alias is created for it and the DESCRIPTION is set to "Lighttpd module for alias".

Often, packaging modules is as simple as the previous example. However, more advanced options exist that you can use within do_split_packages to modify its behavior. And, if you need to, you can add more logic by specifying a hook function that is called for each package. It is also perfectly acceptable to call do_split_packages multiple times if you have more than one set of modules to package.

For more examples that show how to use do_split_packages, see the connman.inc file in the meta/recipes-connectivity/connman/ directory of the poky source repository. You can also find examples in meta/classes/kernel.bbclass.

Following is a reference that shows do_split_packages mandatory and optional arguments:

     Mandatory arguments

     root
        The path in which to search
     file_regex
        Regular expression to match searched files.
        Use parentheses () to mark the part of this
        expression that should be used to derive the
        module name (to be substituted where %s is
        used in other function arguments as noted below)
     output_pattern
        Pattern to use for the package names. Must
        include %s.
     description
        Description to set for each package. Must
        include %s.

     Optional arguments

     postinst
        Postinstall script to use for all packages
        (as a string)
     recursive
        True to perform a recursive search - default
        False
     hook
        A hook function to be called for every match.
        The function will be called with the following
        arguments (in the order listed):

        f
           Full path to the file/directory match
        pkg
           The package name
        file_regex
           As above
        output_pattern
           As above
        modulename
           The module name derived using file_regex

     extra_depends
        Extra runtime dependencies (RDEPENDS) to be
        set for all packages. The default value of None
        causes a dependency on the main package
        (${PN}) - if you do not want this, pass empty
        string '' for this parameter.
     aux_files_pattern
        Extra item(s) to be added to FILES for each
        package. Can be a single string item or a list
        of strings for multiple items. Must include %s.
     postrm
        postrm script to use for all packages (as a
        string)
     allow_dirs
        True to allow directories to be matched -
        default False
     prepend
        If True, prepend created packages to PACKAGES
        instead of the default False which appends them
     match_path
        match file_regex on the whole relative path to
        the root rather than just the file name
     aux_files_pattern_verbatim
        Extra item(s) to be added to FILES for each
        package, using the actual derived module name
        rather than converting it to something legal
        for a package name. Can be a single string item
        or a list of strings for multiple items. Must
        include %s.
     allow_links
        True to allow symlinks to be matched - default
        False
     summary
        Summary to set for each package. Must include %s;
        defaults to description if not set.
                     

4.21.3.2. Satisfying Dependencies

The second part for handling optional module packaging is to ensure that any dependencies on optional modules from other recipes are satisfied by your recipe. You can be sure these dependencies are satisfied by using the PACKAGES_DYNAMIC variable. Here is an example that continues with the lighttpd recipe shown earlier:

     PACKAGES_DYNAMIC = "lighttpd-module-.*"
                    

The name specified in the regular expression can of course be anything. In this example, it is lighttpd-module- and is specified as the prefix to ensure that any RDEPENDS and RRECOMMENDS on a package name starting with the prefix are satisfied during build time. If you are using do_split_packages as described in the previous section, the value you put in PACKAGES_DYNAMIC should correspond to the name pattern specified in the call to do_split_packages.

4.21.4. Using Runtime Package Management

During a build, BitBake always transforms a recipe into one or more packages. For example, BitBake takes the bash recipe and currently produces the bash-dbg, bash-staticdev, bash-dev, bash-doc, bash-locale, and bash packages. Not all generated packages are included in an image.

In several situations, you might need to update, add, remove, or query the packages on a target device at runtime (i.e. without having to generate a new image). Examples of such situations include:

  • You want to provide in-the-field updates to deployed devices (e.g. security updates).

  • You want to have a fast turn-around development cycle for one or more applications that run on your device.

  • You want to temporarily install the "debug" packages of various applications on your device so that debugging can be greatly improved by allowing access to symbols and source debugging.

  • You want to deploy a more minimal package selection of your device but allow in-the-field updates to add a larger selection for customization.

In all these situations, you have something similar to a more traditional Linux distribution in that in-field devices are able to receive pre-compiled packages from a server for installation or update. Being able to install these packages on a running, in-field device is what is termed "runtime package management".

In order to use runtime package management, you need a host/server machine that serves up the pre-compiled packages plus the required metadata. You also need package manipulation tools on the target. The build machine is a likely candidate to act as the server. However, that machine does not necessarily have to be the package server. The build machine could push its artifacts to another machine that acts as the server (e.g. Internet-facing).

A simple build that targets just one device produces more than one package database. In other words, the packages produced by a build are separated out into a couple of different package groupings based on criteria such as the target's CPU architecture, the target board, or the C library used on the target. For example, a build targeting the qemuarm device produces the following three package databases: all, armv5te, and qemuarm. If you wanted your qemuarm device to be aware of all the packages that were available to it, you would need to point it to each of these databases individually. In a similar way, a traditional Linux distribution usually is configured to be aware of a number of software repositories from which it retrieves packages.

Using runtime package management is completely optional and not required for a successful build or deployment in any way. But if you want to make use of runtime package management, you need to do a couple things above and beyond the basics. The remainder of this section describes what you need to do.

4.21.4.1. Build Considerations

This section describes build considerations of which you need to be aware in order to provide support for runtime package management.

When BitBake generates packages, it needs to know what format or formats to use. In your configuration, you use the PACKAGE_CLASSES variable to specify the format:

  1. Open the local.conf file inside your Build Directory (e.g. ~/poky/build/conf/local.conf).

  2. Select the desired package format as follows:

         PACKAGE_CLASSES ?= “package_packageformat

    where packageformat can be "ipk", "rpm", and "deb", which are the supported package formats.

    Note

    Because the Yocto Project supports three different package formats, you can set the variable with more than one argument. However, the OpenEmbedded build system only uses the first argument when creating an image or Software Development Kit (SDK).

If you would like your image to start off with a basic package database containing the packages in your current build as well as to have the relevant tools available on the target for runtime package management, you can include "package-management" in the IMAGE_FEATURES variable. Including "package-management" in this configuration variable ensures that when the image is assembled for your target, the image includes the currently-known package databases as well as the target-specific tools required for runtime package management to be performed on the target. However, this is not strictly necessary. You could start your image off without any databases but only include the required on-target package tool(s). As an example, you could include "opkg" in your IMAGE_INSTALL variable if you are using the IPK package format. You can then initialize your target's package database(s) later once your image is up and running.

Whenever you perform any sort of build step that can potentially generate a package or modify an existing package, it is always a good idea to re-generate the package index with:

    $ bitbake package-index
                    

Realize that it is not sufficient to simply do the following:

    $ bitbake some-package package-index
                    

The reason for this restriction is because BitBake does not properly schedule the package-index target fully after any other target has completed. Thus, be sure to run the package update step separately.

You can use the PACKAGE_FEED_ARCHS, PACKAGE_FEED_BASE_PATHS, and PACKAGE_FEED_URIS variables to pre-configure target images to use a package feed. If you do not define these variables, then manual steps as described in the subsequent sections are necessary to configure the target. You should set these variables before building the image in order to produce a correctly configured image.

When your build is complete, your packages reside in the ${TMPDIR}/deploy/packageformat directory. For example, if ${TMPDIR} is tmp and your selected package type is IPK, then your IPK packages are available in tmp/deploy/ipk.

4.21.4.2. Host or Server Machine Setup

Although other protocols are possible, a server using HTTP typically serves packages. If you want to use HTTP, then set up and configure a web server such as Apache 2, lighttpd, or SimpleHTTPServer on the machine serving the packages.

To keep things simple, this section describes how to set up a SimpleHTTPServer web server to share package feeds from the developer's machine. Although this server might not be the best for a production environment, the setup is simple and straight forward. Should you want to use a different server more suited for production (e.g. Apache 2, Lighttpd, or Nginx), take the appropriate steps to do so.

From within the build directory where you have built an image based on your packaging choice (i.e. the PACKAGE_CLASSES setting), simply start the server. The following example assumes a build directory of ~/poky/build/tmp/deploy/rpm and a PACKAGE_CLASSES setting of "package_rpm":

     $ cd ~/poky/build/tmp/deploy/rpm
     $ python -m SimpleHTTPServer
                    

4.21.4.3. Target Setup

Setting up the target differs depending on the package management system. This section provides information for RPM, IPK, and DEB.

4.21.4.3.1. Using RPM

The dnf application performs runtime package management of RPM packages. You must perform an initial setup for dnf on the target machine if the PACKAGE_FEED_ARCHS, PACKAGE_FEED_BASE_PATHS, and PACKAGE_FEED_URIS variables have not been set or the target image was built before the variables were set.

As an example, assume the target is able to use the following package databases: all, i586, and qemux86 from a server named my.server. You must inform dnf of the availability of these databases by creating a /etc/yum.repos.d/oe-packages.repo file with the following content:

     [oe-packages]
     baseurl=http://my.server/rpm/i586 http://my.server/rpm/qemux86 http://my.server/rpm/all
                        

From the target machine, fetch the repository:

     # dnf makecache
                        

After everything is set up, dnf is able to find, install, and upgrade packages from the specified repository.

Note

See the DNF documentation for additional information.

4.21.4.3.2. Using IPK

The opkg application performs runtime package management of IPK packages. You must perform an initial setup for opkg on the target machine if the PACKAGE_FEED_ARCHS, PACKAGE_FEED_BASE_PATHS, and PACKAGE_FEED_URIS variables have not been set or the target image was built before the variables were set.

The opkg application uses configuration files to find available package databases. Thus, you need to create a configuration file inside the /etc/opkg/ direction, which informs opkg of any repository you want to use.

As an example, suppose you are serving packages from a ipk/ directory containing the i586, all, and qemux86 databases through an HTTP server named my.server. On the target, create a configuration file (e.g. my_repo.conf) inside the /etc/opkg/ directory containing the following:

     src/gz all http://my.server/ipk/all
     src/gz i586 http://my.server/ipk/i586
     src/gz qemux86 http://my.server/ipk/qemux86
                        

Next, instruct opkg to fetch the repository information:

     # opkg update
                        

The opkg application is now able to find, install, and upgrade packages from the specified repository.

4.21.4.3.3. Using DEB

The apt application performs runtime package management of DEB packages. This application uses a source list file to find available package databases. You must perform an initial setup for apt on the target machine if the PACKAGE_FEED_ARCHS, PACKAGE_FEED_BASE_PATHS, and PACKAGE_FEED_URIS variables have not been set or the target image was built before the variables were set.

To inform apt of the repository you want to use, you might create a list file (e.g. my_repo.list) inside the /etc/apt/sources.list.d/ directory. As an example, suppose you are serving packages from a deb/ directory containing the i586, all, and qemux86 databases through an HTTP server named my.server. The list file should contain:

     deb http://my.server/deb/all ./
     deb http://my.server/deb/i586 ./
     deb http://my.server/deb/qemux86 ./
                        

Next, instruct the apt application to fetch the repository information:

     # apt-get update
                        

After this step, apt is able to find, install, and upgrade packages from the specified repository.

4.21.5. Generating and Using Signed Packages

In order to add security to RPM packages used during a build, you can take steps to securely sign them. Once a signature is verified, the OpenEmbedded build system can use the package in the build. If security fails for a signed package, the build system aborts the build.

This section describes how to sign RPM packages during a build and how to use signed package feeds (repositories) when doing a build.

4.21.5.1. Signing RPM Packages

To enable signing RPM packages, you must set up the following configurations in either your local.config or distro.config file:

     # Inherit sign_rpm.bbclass to enable signing functionality
     INHERIT += " sign_rpm"
     # Define the GPG key that will be used for signing.
     RPM_GPG_NAME = "key_name"
     # Provide passphrase for the key
     RPM_GPG_PASSPHRASE = "passphrase"
                    

Note

Be sure to supply appropriate values for both key_name and passphrase

Aside from the RPM_GPG_NAME and RPM_GPG_PASSPHRASE variables in the previous example, two optional variables related to signing exist:

  • GPG_BIN: Specifies a gpg binary/wrapper that is executed when the package is signed.

  • GPG_PATH: Specifies the gpg home directory used when the package is signed.

4.21.5.2. Processing Package Feeds

In addition to being able to sign RPM packages, you can also enable signed package feeds for IPK and RPM packages.

The steps you need to take to enable signed package feed use are similar to the steps used to sign RPM packages. You must define the following in your local.config or distro.config file:

     INHERIT += "sign_package_feed"
     PACKAGE_FEED_GPG_NAME = "key_name"
     PACKAGE_FEED_GPG_PASSPHRASE_FILE = "path_to_file_containing_passphrase"
                    

For signed package feeds, the passphrase must exist in a separate file, which is pointed to by the PACKAGE_FEED_GPG_PASSPHRASE_FILE variable. Regarding security, keeping a plain text passphrase out of the configuration is more secure.

Aside from the PACKAGE_FEED_GPG_NAME and PACKAGE_FEED_GPG_PASSPHRASE_FILE variables, three optional variables related to signed package feeds exist:

  • GPG_BIN: Specifies a gpg binary/wrapper that is executed when the package is signed.

  • GPG_PATH: Specifies the gpg home directory used when the package is signed.

  • PACKAGE_FEED_GPG_SIGNATURE_TYPE: Specifies the type of gpg signature. This variable applies only to RPM and IPK package feeds. Allowable values for the PACKAGE_FEED_GPG_SIGNATURE_TYPE are "ASC", which is the default and specifies ascii armored, and "BIN", which specifies binary.

4.21.6. Testing Packages With ptest

A Package Test (ptest) runs tests against packages built by the OpenEmbedded build system on the target machine. A ptest contains at least two items: the actual test, and a shell script (run-ptest) that starts the test. The shell script that starts the test must not contain the actual test - the script only starts the test. On the other hand, the test can be anything from a simple shell script that runs a binary and checks the output to an elaborate system of test binaries and data files.

The test generates output in the format used by Automake:

     result: testname
                

where the result can be PASS, FAIL, or SKIP, and the testname can be any identifying string.

For a list of Yocto Project recipes that are already enabled with ptest, see the Ptest wiki page.

Note

A recipe is "ptest-enabled" if it inherits the ptest class.

4.21.6.1. Adding ptest to Your Build

To add package testing to your build, add the DISTRO_FEATURES and EXTRA_IMAGE_FEATURES variables to your local.conf file, which is found in the Build Directory:

     DISTRO_FEATURES_append = " ptest"
     EXTRA_IMAGE_FEATURES += "ptest-pkgs"
                    

Once your build is complete, the ptest files are installed into the /usr/lib/package/ptest directory within the image, where package is the name of the package.

4.21.6.2. Running ptest

The ptest-runner package installs a shell script that loops through all installed ptest test suites and runs them in sequence. Consequently, you might want to add this package to your image.

4.21.6.3. Getting Your Package Ready

In order to enable a recipe to run installed ptests on target hardware, you need to prepare the recipes that build the packages you want to test. Here is what you have to do for each recipe:

  • Be sure the recipe inherits the ptest class: Include the following line in each recipe:

         inherit ptest
                                

  • Create run-ptest: This script starts your test. Locate the script where you will refer to it using SRC_URI. Here is an example that starts a test for dbus:

         #!/bin/sh
         cd test
         make -k runtest-TESTS
                                

  • Ensure dependencies are met: If the test adds build or runtime dependencies that normally do not exist for the package (such as requiring "make" to run the test suite), use the DEPENDS and RDEPENDS variables in your recipe in order for the package to meet the dependencies. Here is an example where the package has a runtime dependency on "make":

         RDEPENDS_${PN}-ptest += "make"
                                

  • Add a function to build the test suite: Not many packages support cross-compilation of their test suites. Consequently, you usually need to add a cross-compilation function to the package.

    Many packages based on Automake compile and run the test suite by using a single command such as make check. However, the host make check builds and runs on the same computer, while cross-compiling requires that the package is built on the host but executed for the target architecture (though often, as in the case for ptest, the execution occurs on the host). The built version of Automake that ships with the Yocto Project includes a patch that separates building and execution. Consequently, packages that use the unaltered, patched version of make check automatically cross-compiles.

    Regardless, you still must add a do_compile_ptest function to build the test suite. Add a function similar to the following to your recipe:

         do_compile_ptest() {
            oe_runmake buildtest-TESTS
         }
                                

  • Ensure special configurations are set: If the package requires special configurations prior to compiling the test code, you must insert a do_configure_ptest function into the recipe.

  • Install the test suite: The ptest class automatically copies the file run-ptest to the target and then runs make install-ptest to run the tests. If this is not enough, you need to create a do_install_ptest function and make sure it gets called after the "make install-ptest" completes.

4.22. Working with Source Files

The OpenEmbedded build system works with source files located through the SRC_URI variable. When you build something using BitBake, a big part of the operation is locating and downloading all the source tarballs. For images, downloading all the source for various packages can take a significant amount of time.

This section presents information for working with source files that can lead to more efficient use of resources and time.

4.22.1. Setting up Effective Mirrors

As mentioned, a good deal that goes into a Yocto Project build is simply downloading all of the source tarballs. Maybe you have been working with another build system (OpenEmbedded or Angstrom) for which you have built up a sizable directory of source tarballs. Or, perhaps someone else has such a directory for which you have read access. If so, you can save time by adding statements to your configuration file so that the build process checks local directories first for existing tarballs before checking the Internet.

Here is an efficient way to set it up in your local.conf file:

     SOURCE_MIRROR_URL ?= "file:///home/you/your-download-dir/"
     INHERIT += "own-mirrors"
     BB_GENERATE_MIRROR_TARBALLS = "1"
     # BB_NO_NETWORK = "1"
                

In the previous example, the BB_GENERATE_MIRROR_TARBALLS variable causes the OpenEmbedded build system to generate tarballs of the Git repositories and store them in the DL_DIR directory. Due to performance reasons, generating and storing these tarballs is not the build system's default behavior.

You can also use the PREMIRRORS variable. For an example, see the variable's glossary entry in the Yocto Project Reference Manual.

4.22.2. Getting Source Files and Suppressing the Build

Another technique you can use to ready yourself for a successive string of build operations, is to pre-fetch all the source files without actually starting a build. This technique lets you work through any download issues and ultimately gathers all the source files into your download directory build/downloads, which is located with DL_DIR.

Use the following BitBake command form to fetch all the necessary sources without starting the build:

     $ bitbake -c fetchall target
                

This variation of the BitBake command guarantees that you have all the sources for that BitBake target should you disconnect from the Internet and want to do the build later offline.

4.23. Building Software from an External Source

By default, the OpenEmbedded build system uses the Build Directory when building source code. The build process involves fetching the source files, unpacking them, and then patching them if necessary before the build takes place.

Situations exist where you might want to build software from source files that are external to and thus outside of the OpenEmbedded build system. For example, suppose you have a project that includes a new BSP with a heavily customized kernel. And, you want to minimize exposing the build system to the development team so that they can focus on their project and maintain everyone's workflow as much as possible. In this case, you want a kernel source directory on the development machine where the development occurs. You want the recipe's SRC_URI variable to point to the external directory and use it as is, not copy it.

To build from software that comes from an external source, all you need to do is inherit the externalsrc class and then set the EXTERNALSRC variable to point to your external source code. Here are the statements to put in your local.conf file:

     INHERIT += "externalsrc"
     EXTERNALSRC_pn-myrecipe = "path-to-your-source-tree"
            

This next example shows how to accomplish the same thing by setting EXTERNALSRC in the recipe itself or in the recipe's append file:

     EXTERNALSRC = "path"
     EXTERNALSRC_BUILD = "path"
            

Note

In order for these settings to take effect, you must globally or locally inherit the externalsrc class.

By default, externalsrc.bbclass builds the source code in a directory separate from the external source directory as specified by EXTERNALSRC. If you need to have the source built in the same directory in which it resides, or some other nominated directory, you can set EXTERNALSRC_BUILD to point to that directory:

     EXTERNALSRC_BUILD_pn-myrecipe = "path-to-your-source-tree"
            

4.24. Selecting an Initialization Manager

By default, the Yocto Project uses SysVinit as the initialization manager. However, support also exists for systemd, which is a full replacement for init with parallel starting of services, reduced shell overhead and other features that are used by many distributions.

If you want to use SysVinit, you do not have to do anything. But, if you want to use systemd, you must take some steps as described in the following sections.

4.24.1. Using systemd Exclusively

Set the these variables in your distribution configuration file as follows:

     DISTRO_FEATURES_append = " systemd"
     VIRTUAL-RUNTIME_init_manager = "systemd"
                

You can also prevent the SysVinit distribution feature from being automatically enabled as follows:

     DISTRO_FEATURES_BACKFILL_CONSIDERED = "sysvinit"
                

Doing so removes any redundant SysVinit scripts.

To remove initscripts from your image altogether, set this variable also:

     VIRTUAL-RUNTIME_initscripts = ""
                

For information on the backfill variable, see DISTRO_FEATURES_BACKFILL_CONSIDERED.

4.24.2. Using systemd for the Main Image and Using SysVinit for the Rescue Image

Set these variables in your distribution configuration file as follows:

     DISTRO_FEATURES_append = " systemd"
     VIRTUAL-RUNTIME_init_manager = "systemd"
                

Doing so causes your main image to use the packagegroup-core-boot.bb recipe and systemd. The rescue/minimal image cannot use this package group. However, it can install SysVinit and the appropriate packages will have support for both systemd and SysVinit.

4.25. Selecting a Device Manager

The Yocto Project provides multiple ways to manage the device manager (/dev):

  • Persistent and Pre-Populated/dev: For this case, the /dev directory is persistent and the required device nodes are created during the build.

  • Use devtmpfs with a Device Manager: For this case, the /dev directory is provided by the kernel as an in-memory file system and is automatically populated by the kernel at runtime. Additional configuration of device nodes is done in user space by a device manager like udev or busybox-mdev.

4.25.1. Using Persistent and Pre-Populated/dev

To use the static method for device population, you need to set the USE_DEVFS variable to "0" as follows:

     USE_DEVFS = "0"
                

The content of the resulting /dev directory is defined in a Device Table file. The IMAGE_DEVICE_TABLES variable defines the Device Table to use and should be set in the machine or distro configuration file. Alternatively, you can set this variable in your local.conf configuration file.

If you do not define the IMAGE_DEVICE_TABLES variable, the default device_table-minimal.txt is used:

     IMAGE_DEVICE_TABLES = "device_table-mymachine.txt"
                

The population is handled by the makedevs utility during image creation:

4.25.2. Using devtmpfs and a Device Manager

To use the dynamic method for device population, you need to use (or be sure to set) the USE_DEVFS variable to "1", which is the default:

     USE_DEVFS = "1"
                

With this setting, the resulting /dev directory is populated by the kernel using devtmpfs. Make sure the corresponding kernel configuration variable CONFIG_DEVTMPFS is set when building you build a Linux kernel.

All devices created by devtmpfs will be owned by root and have permissions 0600.

To have more control over the device nodes, you can use a device manager like udev or busybox-mdev. You choose the device manager by defining the VIRTUAL-RUNTIME_dev_manager variable in your machine or distro configuration file. Alternatively, you can set this variable in your local.conf configuration file:

     VIRTUAL-RUNTIME_dev_manager = "udev"

     # Some alternative values
     # VIRTUAL-RUNTIME_dev_manager = "busybox-mdev"
     # VIRTUAL-RUNTIME_dev_manager = "systemd"
                

4.26. Using an External SCM

If you're working on a recipe that pulls from an external Source Code Manager (SCM), it is possible to have the OpenEmbedded build system notice new recipe changes added to the SCM and then build the resulting packages that depend on the new recipes by using the latest versions. This only works for SCMs from which it is possible to get a sensible revision number for changes. Currently, you can do this with Apache Subversion (SVN), Git, and Bazaar (BZR) repositories.

To enable this behavior, the PV of the recipe needs to reference SRCPV. Here is an example:

     PV = "1.2.3+git${SRCPV}"
            

Then, you can add the following to your local.conf:

     SRCREV_pn-PN = "${AUTOREV}"
            

PN is the name of the recipe for which you want to enable automatic source revision updating.

If you do not want to update your local configuration file, you can add the following directly to the recipe to finish enabling the feature:

     SRCREV = "${AUTOREV}"
            

The Yocto Project provides a distribution named poky-bleeding, whose configuration file contains the line:

     require conf/distro/include/poky-floating-revisions.inc
            

This line pulls in the listed include file that contains numerous lines of exactly that form:

     #SRCREV_pn-opkg-native ?= "${AUTOREV}"
     #SRCREV_pn-opkg-sdk ?= "${AUTOREV}"
     #SRCREV_pn-opkg ?= "${AUTOREV}"
     #SRCREV_pn-opkg-utils-native ?= "${AUTOREV}"
     #SRCREV_pn-opkg-utils ?= "${AUTOREV}"
     SRCREV_pn-gconf-dbus ?= "${AUTOREV}"
     SRCREV_pn-matchbox-common ?= "${AUTOREV}"
     SRCREV_pn-matchbox-config-gtk ?= "${AUTOREV}"
     SRCREV_pn-matchbox-desktop ?= "${AUTOREV}"
     SRCREV_pn-matchbox-keyboard ?= "${AUTOREV}"
     SRCREV_pn-matchbox-panel-2 ?= "${AUTOREV}"
     SRCREV_pn-matchbox-themes-extra ?= "${AUTOREV}"
     SRCREV_pn-matchbox-terminal ?= "${AUTOREV}"
     SRCREV_pn-matchbox-wm ?= "${AUTOREV}"
     SRCREV_pn-settings-daemon ?= "${AUTOREV}"
     SRCREV_pn-screenshot ?= "${AUTOREV}"
          .
          .
          .
            

These lines allow you to experiment with building a distribution that tracks the latest development source for numerous packages.

Caution

The poky-bleeding distribution is not tested on a regular basis. Keep this in mind if you use it.

4.27. Creating a Read-Only Root Filesystem

Suppose, for security reasons, you need to disable your target device's root filesystem's write permissions (i.e. you need a read-only root filesystem). Or, perhaps you are running the device's operating system from a read-only storage device. For either case, you can customize your image for that behavior.

Note

Supporting a read-only root filesystem requires that the system and applications do not try to write to the root filesystem. You must configure all parts of the target system to write elsewhere, or to gracefully fail in the event of attempting to write to the root filesystem.

4.27.1. Creating the Root Filesystem

To create the read-only root filesystem, simply add the "read-only-rootfs" feature to your image. Using either of the following statements in your image recipe or from within the local.conf file found in the Build Directory causes the build system to create a read-only root filesystem:

     IMAGE_FEATURES = "read-only-rootfs"
                

or

     EXTRA_IMAGE_FEATURES += "read-only-rootfs"
                

For more information on how to use these variables, see the "Customizing Images Using Custom IMAGE_FEATURES and EXTRA_IMAGE_FEATURES" section. For information on the variables, see IMAGE_FEATURES and EXTRA_IMAGE_FEATURES.

4.27.2. Post-Installation Scripts

It is very important that you make sure all post-Installation (pkg_postinst) scripts for packages that are installed into the image can be run at the time when the root filesystem is created during the build on the host system. These scripts cannot attempt to run during first-boot on the target device. With the "read-only-rootfs" feature enabled, the build system checks during root filesystem creation to make sure all post-installation scripts succeed. If any of these scripts still need to be run after the root filesystem is created, the build immediately fails. These build-time checks ensure that the build fails rather than the target device fails later during its initial boot operation.

Most of the common post-installation scripts generated by the build system for the out-of-the-box Yocto Project are engineered so that they can run during root filesystem creation (e.g. post-installation scripts for caching fonts). However, if you create and add custom scripts, you need to be sure they can be run during this file system creation.

Here are some common problems that prevent post-installation scripts from running during root filesystem creation:

  • Not using $D in front of absolute paths: The build system defines $D when the root filesystem is created. Furthermore, $D is blank when the script is run on the target device. This implies two purposes for $D: ensuring paths are valid in both the host and target environments, and checking to determine which environment is being used as a method for taking appropriate actions.

  • Attempting to run processes that are specific to or dependent on the target architecture: You can work around these attempts by using native tools, which run on the host system, to accomplish the same tasks, or by alternatively running the processes under QEMU, which has the qemu_run_binary function. For more information, see the qemu class.

4.27.3. Areas With Write Access

With the "read-only-rootfs" feature enabled, any attempt by the target to write to the root filesystem at runtime fails. Consequently, you must make sure that you configure processes and applications that attempt these types of writes do so to directories with write access (e.g. /tmp or /var/run).

4.28. Performing Automated Runtime Testing

The OpenEmbedded build system makes available a series of automated tests for images to verify runtime functionality. You can run these tests on either QEMU or actual target hardware. Tests are written in Python making use of the unittest module, and the majority of them run commands on the target system over SSH. This section describes how you set up the environment to use these tests, run available tests, and write and add your own tests.

For information on the test and QA infrastructure available within the Yocto Project, see the "Testing and Quality Assurance" section in the Yocto Project Reference Manual.

4.28.1. Enabling Tests

Depending on whether you are planning to run tests using QEMU or on the hardware, you have to take different steps to enable the tests. See the following subsections for information on how to enable both types of tests.

4.28.1.1. Enabling Runtime Tests on QEMU

In order to run tests, you need to do the following:

  • Set up to avoid interaction with sudo for networking: To accomplish this, you must do one of the following:

    • Add NOPASSWD for your user in /etc/sudoers either for all commands or just for runqemu-ifup. You must provide the full path as that can change if you are using multiple clones of the source repository.

      Note

      On some distributions, you also need to comment out "Defaults requiretty" in /etc/sudoers.
    • Manually configure a tap interface for your system.

    • Run as root the script in scripts/runqemu-gen-tapdevs, which should generate a list of tap devices. This is the option typically chosen for Autobuilder-type environments.

  • Set the DISPLAY variable: You need to set this variable so that you have an X server available (e.g. start vncserver for a headless machine).

  • Be sure your host's firewall accepts incoming connections from 192.168.7.0/24: Some of the tests (in particular DNF tests) start an HTTP server on a random high number port, which is used to serve files to the target. The DNF module serves ${WORKDIR}/oe-rootfs-repo so it can run DNF channel commands. That means your host's firewall must accept incoming connections from 192.168.7.0/24, which is the default IP range used for tap devices by runqemu.

  • Be sure your host has the correct packages installed: Depending your host's distribution, you need to have the following packages installed:

    • Ubuntu and Debian: sysstat and iproute2

    • OpenSUSE: sysstat and iproute2

    • Fedora: sysstat and iproute

    • CentOS: sysstat and iproute

Once you start running the tests, the following happens:

  1. A copy of the root filesystem is written to ${WORKDIR}/testimage.

  2. The image is booted under QEMU using the standard runqemu script.

  3. A default timeout of 500 seconds occurs to allow for the boot process to reach the login prompt. You can change the timeout period by setting TEST_QEMUBOOT_TIMEOUT in the local.conf file.

  4. Once the boot process is reached and the login prompt appears, the tests run. The full boot log is written to ${WORKDIR}/testimage/qemu_boot_log.

  5. Each test module loads in the order found in TEST_SUITES. You can find the full output of the commands run over SSH in ${WORKDIR}/testimgage/ssh_target_log.

  6. If no failures occur, the task running the tests ends successfully. You can find the output from the unittest in the task log at ${WORKDIR}/temp/log.do_testimage.

4.28.1.2. Enabling Runtime Tests on Hardware

The OpenEmbedded build system can run tests on real hardware, and for certain devices it can also deploy the image to be tested onto the device beforehand.

For automated deployment, a "master image" is installed onto the hardware once as part of setup. Then, each time tests are to be run, the following occurs:

  1. The master image is booted into and used to write the image to be tested to a second partition.

  2. The device is then rebooted using an external script that you need to provide.

  3. The device boots into the image to be tested.

When running tests (independent of whether the image has been deployed automatically or not), the device is expected to be connected to a network on a pre-determined IP address. You can either use static IP addresses written into the image, or set the image to use DHCP and have your DHCP server on the test network assign a known IP address based on the MAC address of the device.

In order to run tests on hardware, you need to set TEST_TARGET to an appropriate value. For QEMU, you do not have to change anything, the default value is "QemuTarget". For running tests on hardware, the following options exist:

  • "SimpleRemoteTarget": Choose "SimpleRemoteTarget" if you are going to run tests on a target system that is already running the image to be tested and is available on the network. You can use "SimpleRemoteTarget" in conjunction with either real hardware or an image running within a separately started QEMU or any other virtual machine manager.

  • "Systemd-bootTarget": Choose "Systemd-bootTarget" if your hardware is an EFI-based machine with systemd-boot as bootloader and core-image-testmaster (or something similar) is installed. Also, your hardware under test must be in a DHCP-enabled network that gives it the same IP address for each reboot.

    If you choose "Systemd-bootTarget", there are additional requirements and considerations. See the "Selecting Systemd-bootTarget" section, which follows, for more information.

  • "BeagleBoneTarget": Choose "BeagleBoneTarget" if you are deploying images and running tests on the BeagleBone "Black" or original "White" hardware. For information on how to use these tests, see the comments at the top of the BeagleBoneTarget meta-yocto-bsp/lib/oeqa/controllers/beaglebonetarget.py file.

  • "EdgeRouterTarget": Choose "EdgeRouterTarget" is you are deploying images and running tests on the Ubiquiti Networks EdgeRouter Lite. For information on how to use these tests, see the comments at the top of the EdgeRouterTarget meta-yocto-bsp/lib/oeqa/controllers/edgeroutertarget.py file.

  • "GrubTarget": Choose the "supports deploying images and running tests on any generic PC that boots using GRUB. For information on how to use these tests, see the comments at the top of the GrubTarget meta-yocto-bsp/lib/oeqa/controllers/grubtarget.py file.

  • "your-target": Create your own custom target if you want to run tests when you are deploying images and running tests on a custom machine within your BSP layer. To do this, you need to add a Python unit that defines the target class under lib/oeqa/controllers/ within your layer. You must also provide an empty __init__.py. For examples, see files in meta-yocto-bsp/lib/oeqa/controllers/.

4.28.1.3. Selecting Systemd-bootTarget

If you did not set TEST_TARGET to "Systemd-bootTarget", then you do not need any information in this section. You can skip down to the "Running Tests" section.

If you did set TEST_TARGET to "Systemd-bootTarget", you also need to perform a one-time setup of your master image by doing the following:

  1. Set EFI_PROVIDER: Be sure that EFI_PROVIDER is as follows:

         EFI_PROVIDER = "systemd-boot"
                                

  2. Build the master image: Build the core-image-testmaster image. The core-image-testmaster recipe is provided as an example for a "master" image and you can customize the image recipe as you would any other recipe.

    Here are the image recipe requirements:

    • Inherits core-image so that kernel modules are installed.

    • Installs normal linux utilities not busybox ones (e.g. bash, coreutils, tar, gzip, and kmod).

    • Uses a custom Initial RAM Disk (initramfs) image with a custom installer. A normal image that you can install usually creates a single rootfs partition. This image uses another installer that creates a specific partition layout. Not all Board Support Packages (BSPs) can use an installer. For such cases, you need to manually create the following partition layout on the target:

      • First partition mounted under /boot, labeled "boot".

      • The main rootfs partition where this image gets installed, which is mounted under /.

      • Another partition labeled "testrootfs" where test images get deployed.

  3. Install image: Install the image that you just built on the target system.

The final thing you need to do when setting TEST_TARGET to "Systemd-bootTarget" is to set up the test image:

  1. Set up your local.conf file: Make sure you have the following statements in your local.conf file:

         IMAGE_FSTYPES += "tar.gz"
         INHERIT += "testimage"
         TEST_TARGET = "Systemd-bootTarget"
         TEST_TARGET_IP = "192.168.2.3"
                                

  2. Build your test image: Use BitBake to build the image:

         $ bitbake core-image-sato
                                

4.28.1.4. Power Control

For most hardware targets other than SimpleRemoteTarget, you can control power:

  • You can use TEST_POWERCONTROL_CMD together with TEST_POWERCONTROL_EXTRA_ARGS as a command that runs on the host and does power cycling. The test code passes one argument to that command: off, on or cycle (off then on). Here is an example that could appear in your local.conf file:

         TEST_POWERCONTROL_CMD = "powercontrol.exp test 10.11.12.1 nuc1"
                                

    In this example, the expect script does the following:

         ssh test@10.11.12.1 "pyctl nuc1 arg"
                                

    It then runs a Python script that controls power for a label called nuc1.

    Note

    You need to customize TEST_POWERCONTROL_CMD and TEST_POWERCONTROL_EXTRA_ARGS for your own setup. The one requirement is that it accepts "on", "off", and "cycle" as the last argument.

  • When no command is defined, it connects to the device over SSH and uses the classic reboot command to reboot the device. Classic reboot is fine as long as the machine actually reboots (i.e. the SSH test has not failed). It is useful for scenarios where you have a simple setup, typically with a single board, and where some manual interaction is okay from time to time.

If you have no hardware to automatically perform power control but still wish to experiment with automated hardware testing, you can use the dialog-power-control script that shows a dialog prompting you to perform the required power action. This script requires either KDialog or Zenity to be installed. To use this script, set the TEST_POWERCONTROL_CMD variable as follows:

     TEST_POWERCONTROL_CMD = "${COREBASE}/scripts/contrib/dialog-power-control"
                    

4.28.1.5. Serial Console Connection

For test target classes requiring a serial console to interact with the bootloader (e.g. BeagleBoneTarget, EdgeRouterTarget, and GrubTarget), you need to specify a command to use to connect to the serial console of the target machine by using the TEST_SERIALCONTROL_CMD variable and optionally the TEST_SERIALCONTROL_EXTRA_ARGS variable.

These cases could be a serial terminal program if the machine is connected to a local serial port, or a telnet or ssh command connecting to a remote console server. Regardless of the case, the command simply needs to connect to the serial console and forward that connection to standard input and output as any normal terminal program does. For example, to use the picocom terminal program on serial device /dev/ttyUSB0 at 115200bps, you would set the variable as follows:

     TEST_SERIALCONTROL_CMD = "picocom /dev/ttyUSB0 -b 115200"
                    

For local devices where the serial port device disappears when the device reboots, an additional "serdevtry" wrapper script is provided. To use this wrapper, simply prefix the terminal command with ${COREBASE}/scripts/contrib/serdevtry:

     TEST_SERIALCONTROL_CMD = "${COREBASE}/scripts/contrib/serdevtry picocom -b
115200 /dev/ttyUSB0"
                    

4.28.2. Running Tests

You can start the tests automatically or manually:

  • Automatically running tests: To run the tests automatically after the OpenEmbedded build system successfully creates an image, first set the TEST_IMAGE variable to "1" in your local.conf file in the Build Directory:

         TEST_IMAGE = "1"
                            

    Next, build your image. If the image successfully builds, the tests will be run:

         bitbake core-image-sato
                            
  • Manually running tests: To manually run the tests, first globally inherit the testimage class by editing your local.conf file:

        INHERIT += "testimage"
                            

    Next, use BitBake to run the tests:

         bitbake -c testimage image
                            

All test files reside in meta/lib/oeqa/runtime in the Source Directory. A test name maps directly to a Python module. Each test module may contain a number of individual tests. Tests are usually grouped together by the area tested (e.g tests for systemd reside in meta/lib/oeqa/runtime/systemd.py).

You can add tests to any layer provided you place them in the proper area and you extend BBPATH in the local.conf file as normal. Be sure that tests reside in layer/lib/oeqa/runtime.

Note

Be sure that module names do not collide with module names used in the default set of test modules in meta/lib/oeqa/runtime.

You can change the set of tests run by appending or overriding TEST_SUITES variable in local.conf. Each name in TEST_SUITES represents a required test for the image. Test modules named within TEST_SUITES cannot be skipped even if a test is not suitable for an image (e.g. running the RPM tests on an image without rpm). Appending "auto" to TEST_SUITES causes the build system to try to run all tests that are suitable for the image (i.e. each test module may elect to skip itself).

The order you list tests in TEST_SUITES is important and influences test dependencies. Consequently, tests that depend on other tests should be added after the test on which they depend. For example, since the ssh test depends on the ping test, "ssh" needs to come after "ping" in the list. The test class provides no re-ordering or dependency handling.

Note

Each module can have multiple classes with multiple test methods. And, Python unittest rules apply.

Here are some things to keep in mind when running tests:

  • The default tests for the image are defined as:

         DEFAULT_TEST_SUITES_pn-image = "ping ssh df connman syslog xorg scp vnc date rpm dnf dmesg"
                            
  • Add your own test to the list of the by using the following:

         TEST_SUITES_append = " mytest"
                            
  • Run a specific list of tests as follows:

         TEST_SUITES = "test1 test2 test3"
                            

    Remember, order is important. Be sure to place a test that is dependent on another test later in the order.

4.28.3. Exporting Tests

You can export tests so that they can run independently of the build system. Exporting tests is required if you want to be able to hand the test execution off to a scheduler. You can only export tests that are defined in TEST_SUITES.

If your image is already built, make sure the following are set in your local.conf file:

     INHERIT +="testexport"
     TEST_TARGET_IP = "IP-address-for-the-test-target"
     TEST_SERVER_IP = "IP-address-for-the-test-server"
                

You can then export the tests with the following BitBake command form:

     $ bitbake image -c testexport
                

Exporting the tests places them in the Build Directory in tmp/testexport/image, which is controlled by the TEST_EXPORT_DIR variable.

You can now run the tests outside of the build environment:

     $ cd tmp/testexport/image
     $ ./runexported.py testdata.json
                

Here is a complete example that shows IP addresses and uses the core-image-sato image:

     INHERIT +="testexport"
     TEST_TARGET_IP = "192.168.7.2"
     TEST_SERVER_IP = "192.168.7.1"
                

Use BitBake to export the tests:

     $ bitbake core-image-sato -c testexport
                

Run the tests outside of the build environment using the following:

     $ cd tmp/testexport/core-image-sato
     $ ./runexported.py testdata.json
                

4.28.4. Writing New Tests

As mentioned previously, all new test files need to be in the proper place for the build system to find them. New tests for additional functionality outside of the core should be added to the layer that adds the functionality, in layer/lib/oeqa/runtime (as long as BBPATH is extended in the layer's layer.conf file as normal). Just remember the following:

  • Filenames need to map directly to test (module) names.

  • Do not use module names that collide with existing core tests.

  • Minimally, an empty __init__.py file must exist in the runtime directory.

To create a new test, start by copying an existing module (e.g. syslog.py or gcc.py are good ones to use). Test modules can use code from meta/lib/oeqa/utils, which are helper classes.

Note

Structure shell commands such that you rely on them and they return a single code for success. Be aware that sometimes you will need to parse the output. See the df.py and date.py modules for examples.

You will notice that all test classes inherit oeRuntimeTest, which is found in meta/lib/oetest.py. This base class offers some helper attributes, which are described in the following sections:

4.28.4.1. Class Methods

Class methods are as follows:

  • hasPackage(pkg): Returns "True" if pkg is in the installed package list of the image, which is based on the manifest file that is generated during the do_rootfs task.

  • hasFeature(feature): Returns "True" if the feature is in IMAGE_FEATURES or DISTRO_FEATURES.

4.28.4.2. Class Attributes

Class attributes are as follows:

  • pscmd: Equals "ps -ef" if procps is installed in the image. Otherwise, pscmd equals "ps" (busybox).

  • tc: The called test context, which gives access to the following attributes:

    • d: The BitBake datastore, which allows you to use stuff such as oeRuntimeTest.tc.d.getVar("VIRTUAL-RUNTIME_init_manager").

    • testslist and testsrequired: Used internally. The tests do not need these.

    • filesdir: The absolute path to meta/lib/oeqa/runtime/files, which contains helper files for tests meant for copying on the target such as small files written in C for compilation.

    • target: The target controller object used to deploy and start an image on a particular target (e.g. QemuTarget, SimpleRemote, and Systemd-bootTarget). Tests usually use the following:

      • ip: The target's IP address.

      • server_ip: The host's IP address, which is usually used by the DNF test suite.

      • run(cmd, timeout=None): The single, most used method. This command is a wrapper for: ssh root@host "cmd". The command returns a tuple: (status, output), which are what their names imply - the return code of "cmd" and whatever output it produces. The optional timeout argument represents the number of seconds the test should wait for "cmd" to return. If the argument is "None", the test uses the default instance's timeout period, which is 300 seconds. If the argument is "0", the test runs until the command returns.

      • copy_to(localpath, remotepath): scp localpath root@ip:remotepath.

      • copy_from(remotepath, localpath): scp root@host:remotepath localpath.

4.28.4.3. Instance Attributes

A single instance attribute exists, which is target. The target instance attribute is identical to the class attribute of the same name, which is described in the previous section. This attribute exists as both an instance and class attribute so tests can use self.target.run(cmd) in instance methods instead of oeRuntimeTest.tc.target.run(cmd).

4.28.5. Installing Packages in the DUT Without the Package Manager

When a test requires a package built by BitBake, it is possible to install that package. Installing the package does not require a package manager be installed in the device under test (DUT). It does, however, require an SSH connection and the target must be using the sshcontrol class.

Note

This method uses scp to copy files from the host to the target, which causes permissions and special attributes to be lost.

A JSON file is used to define the packages needed by a test. This file must be in the same path as the file used to define the tests. Furthermore, the filename must map directly to the test module name with a .json extension.

The JSON file must include an object with the test name as keys of an object or an array. This object (or array of objects) uses the following data:

  • "pkg" - A mandatory string that is the name of the package to be installed.

  • "rm" - An optional boolean, which defaults to "false", that specifies to remove the package after the test.

  • "extract" - An optional boolean, which defaults to "false", that specifies if the package must be extracted from the package format. When set to "true", the package is not automatically installed into the DUT.

Following is an example JSON file that handles test "foo" installing package "bar" and test "foobar" installing packages "foo" and "bar". Once the test is complete, the packages are removed from the DUT.

     {
         "foo": {
             "pkg": "bar"
         },
         "foobar": [
             {
                 "pkg": "foo",
                 "rm": true
             },
             {
                 "pkg": "bar",
                 "rm": true
             }
         ]
     }
                

4.29. Debugging With the GNU Project Debugger (GDB) Remotely

GDB allows you to examine running programs, which in turn helps you to understand and fix problems. It also allows you to perform post-mortem style analysis of program crashes. GDB is available as a package within the Yocto Project and is installed in SDK images by default. See the "Images" chapter in the Yocto Project Reference Manual for a description of these images. You can find information on GDB at http://sourceware.org/gdb/.

Tip

For best results, install debug (-dbg) packages for the applications you are going to debug. Doing so makes extra debug symbols available that give you more meaningful output.

Sometimes, due to memory or disk space constraints, it is not possible to use GDB directly on the remote target to debug applications. These constraints arise because GDB needs to load the debugging information and the binaries of the process being debugged. Additionally, GDB needs to perform many computations to locate information such as function names, variable names and values, stack traces and so forth - even before starting the debugging process. These extra computations place more load on the target system and can alter the characteristics of the program being debugged.

To help get past the previously mentioned constraints, you can use gdbserver, which runs on the remote target and does not load any debugging information from the debugged process. Instead, a GDB instance processes the debugging information that is run on a remote computer - the host GDB. The host GDB then sends control commands to gdbserver to make it stop or start the debugged program, as well as read or write memory regions of that debugged program. All the debugging information loaded and processed as well as all the heavy debugging is done by the host GDB. Offloading these processes gives the gdbserver running on the target a chance to remain small and fast.

Because the host GDB is responsible for loading the debugging information and for doing the necessary processing to make actual debugging happen, you have to make sure the host can access the unstripped binaries complete with their debugging information and also be sure the target is compiled with no optimizations. The host GDB must also have local access to all the libraries used by the debugged program. Because gdbserver does not need any local debugging information, the binaries on the remote target can remain stripped. However, the binaries must also be compiled without optimization so they match the host's binaries.

To remain consistent with GDB documentation and terminology, the binary being debugged on the remote target machine is referred to as the "inferior" binary. For documentation on GDB see the GDB site.

The following steps show you how to debug using the GNU project debugger.

  1. Configure your build system to construct the companion debug filesystem:

    In your local.conf file, set the following:

         IMAGE_GEN_DEBUGFS = "1"
         IMAGE_FSTYPES_DEBUGFS = "tar.bz2"
                        

    These options cause the OpenEmbedded build system to generate a special companion filesystem fragment, which contains the matching source and debug symbols to your deployable filesystem. The build system does this by looking at what is in the deployed filesystem, and pulling the corresponding -dbg packages.

    The companion debug filesystem is not a complete filesystem, but only contains the debug fragments. This filesystem must be combined with the full filesystem for debugging. Subsequent steps in this procedure show how to combine the partial filesystem with the full filesystem.

  2. Configure the system to include gdbserver in the target filesystem:

    Make the following addition in either your local.conf file or in an image recipe:

         IMAGE_INSTALL_append = “ gdbserver"
                        

    The change makes sure the gdbserver package is included.

  3. Build the environment:

    Use the following command to construct the image and the companion Debug Filesystem:

         $ bitbake image
                        

    Build the cross GDB component and make it available for debugging. Build the SDK that matches the image. Building the SDK is best for a production build that can be used later for debugging, especially during long term maintenance:

         $ bitbake -c populate_sdk image
                        

    Alternatively, you can build the minimal toolchain components that match the target. Doing so creates a smaller than typical SDK and only contains a minimal set of components with which to build simple test applications, as well as run the debugger:

         $ bitbake meta-toolchain
                        

    A final method is to build Gdb itself within the build system:

         $ bitbake gdb-cross-architecture
                        

    Doing so produces a temporary copy of cross-gdb you can use for debugging during development. While this is the quickest approach, the two previous methods in this step are better when considering long-term maintenance strategies.

    Note

    If you run bitbake gdb-cross, the OpenEmbedded build system suggests the actual image (e.g. gdb-cross-i586). The suggestion is usually the actual name you want to use.

  4. Set up the debugfs

    Run the following commands to set up the debugfs:

         $ mkdir debugfs
         $ cd debugfs
         $ tar xvfj build-dir/tmp-glibc/deploy/images/machine/image.rootfs.tar.bz2
         $ tar xvfj build-dir/tmp-glibc/deploy/images/machine/image-dbg.rootfs.tar.bz2
                        

  5. Set up GDB

    Install the SDK (if you built one) and then source the correct environment file. Sourcing the environment file puts the SDK in your PATH environment variable.

    If you are using the build system, Gdb is located in build-dir/tmp/sysroots/host/usr/bin/architecture/architecture-gdb

  6. Boot the target:

    For information on how to run QEMU, see the QEMU Documentation.

    Note

    Be sure to verify that your host can access the target via TCP.

  7. Debug a program:

    Debugging a program involves running gdbserver on the target and then running Gdb on the host. The example in this step debugs gzip:

         root@qemux86:~# gdbserver localhost:1234 /bin/gzip —help
                        

    For additional gdbserver options, see the GDB Server Documentation.

    After running gdbserver on the target, you need to run Gdb on the host and configure it and connect to the target. Use these commands:

         $ cd directory-holding-the-debugfs-directory
         $ arch-gdb
    
         (gdb) set sysroot debugfs
         (gdb) set substitute-path /usr/src/debug debugfs/usr/src/debug
         (gdb) target remote IP-of-target:1234
                        

    At this point, everything should automatically load (i.e. matching binaries, symbols and headers).

    Note

    The Gdb set commands in the previous example can be placed into the users ~/.gdbinit file. Upon starting, Gdb automatically runs whatever commands are in that file.

  8. Deploying without a full image rebuild:

    In many cases, during development you want a quick method to deploy a new binary to the target and debug it, without waiting for a full image build.

    One approach to solving this situation is to just build the component you want to debug. Once you have built the component, copy the executable directly to both the target and the host debugfs.

    If the binary is processed through the debug splitting in OpenEmbedded, you should also copy the debug items (i.e. .debug contents and corresponding /usr/src/debug files) from the work directory. Here is an example:

         $ bitbake bash
         $ bitbake -c devshell bash
         $ cd ..
         $ scp packages-split/bash/bin/bash target:/bin/bash
         $ cp -a packages-split/bash-dbg/* path/debugfs
                        

4.30. Debugging with the GNU Project Debugger (GDB) on the Target

The previous section addressed using GDB remotely for debugging purposes, which is the most usual case due to the inherent hardware limitations on many embedded devices. However, debugging in the target hardware itself is also possible with more powerful devices. This section describes what you need to do in order to support using GDB to debug on the target hardware.

To support this kind of debugging, you need do the following:

  • Ensure that GDB is on the target. You can do this by adding "gdb" to IMAGE_INSTALL:

         IMAGE_INSTALL_append = " gdb"
                        

    Alternatively, you can add "tools-debug" to IMAGE_FEATURES:

         IMAGE_FEATURES_append = " tools-debug"
                        

  • Ensure that debug symbols are present. You can make sure these symbols are present by installing -dbg:

         IMAGE_INSTALL_append = " packagename-dbg"
                        

    Alternatively, you can do the following to include all the debug symbols:

         IMAGE_FEATURES_append = " dbg-pkgs"
                        

Note

To improve the debug information accuracy, you can reduce the level of optimization used by the compiler. For example, when adding the following line to your local.conf file, you will reduce optimization from FULL_OPTIMIZATION of "-O2" to DEBUG_OPTIMIZATION of "-O -fno-omit-frame-pointer":
     DEBUG_BUILD = "1"
                
Consider that this will reduce the application's performance and is recommended only for debugging purposes.

4.31. Debugging Parallel Make Races

A parallel make race occurs when the build consists of several parts that are run simultaneously and a situation occurs when the output or result of one part is not ready for use with a different part of the build that depends on that output. Parallel make races are annoying and can sometimes be difficult to reproduce and fix. However, some simple tips and tricks exist that can help you debug and fix them. This section presents a real-world example of an error encountered on the Yocto Project autobuilder and the process used to fix it.

Note

If you cannot properly fix a make race condition, you can work around it by clearing either the PARALLEL_MAKE or PARALLEL_MAKEINST variables.

4.31.1. The Failure

For this example, assume that you are building an image that depends on the "neard" package. And, during the build, BitBake runs into problems and creates the following output.

Note

This example log file has longer lines artificially broken to make the listing easier to read.

If you examine the output or the log file, you see the failure during make:

     | DEBUG: SITE files ['endian-little', 'bit-32', 'ix86-common', 'common-linux', 'common-glibc', 'i586-linux', 'common']
     | DEBUG: Executing shell function do_compile
     | NOTE: make -j 16
     | make --no-print-directory all-am
     | /bin/mkdir -p include/near
     | /bin/mkdir -p include/near
     | /bin/mkdir -p include/near
     | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
       0.14-r0/neard-0.14/include/types.h include/near/types.h
     | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
       0.14-r0/neard-0.14/include/log.h include/near/log.h
     | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
       0.14-r0/neard-0.14/include/plugin.h include/near/plugin.h
     | /bin/mkdir -p include/near
     | /bin/mkdir -p include/near
     | /bin/mkdir -p include/near
     | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
       0.14-r0/neard-0.14/include/tag.h include/near/tag.h
     | /bin/mkdir -p include/near
     | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
       0.14-r0/neard-0.14/include/adapter.h include/near/adapter.h
     | /bin/mkdir -p include/near
     | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
       0.14-r0/neard-0.14/include/ndef.h include/near/ndef.h
     | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
       0.14-r0/neard-0.14/include/tlv.h include/near/tlv.h
     | /bin/mkdir -p include/near
     | /bin/mkdir -p include/near
     | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
       0.14-r0/neard-0.14/include/setting.h include/near/setting.h
     | /bin/mkdir -p include/near
     | /bin/mkdir -p include/near
     | /bin/mkdir -p include/near
     | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
       0.14-r0/neard-0.14/include/device.h include/near/device.h
     | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
       0.14-r0/neard-0.14/include/nfc_copy.h include/near/nfc_copy.h
     | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
       0.14-r0/neard-0.14/include/snep.h include/near/snep.h
     | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
       0.14-r0/neard-0.14/include/version.h include/near/version.h
     | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
       0.14-r0/neard-0.14/include/dbus.h include/near/dbus.h
     | ./src/genbuiltin nfctype1 nfctype2 nfctype3 nfctype4 p2p > src/builtin.h
     | i586-poky-linux-gcc  -m32 -march=i586 --sysroot=/home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/
       build/build/tmp/sysroots/qemux86 -DHAVE_CONFIG_H -I. -I./include -I./src -I./gdbus  -I/home/pokybuild/
       yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/sysroots/qemux86/usr/include/glib-2.0
       -I/home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/sysroots/qemux86/usr/
       lib/glib-2.0/include  -I/home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/
       tmp/sysroots/qemux86/usr/include/dbus-1.0 -I/home/pokybuild/yocto-autobuilder/yocto-slave/
       nightly-x86/build/build/tmp/sysroots/qemux86/usr/lib/dbus-1.0/include  -I/home/pokybuild/yocto-autobuilder/
       yocto-slave/nightly-x86/build/build/tmp/sysroots/qemux86/usr/include/libnl3
       -DNEAR_PLUGIN_BUILTIN -DPLUGINDIR=\""/usr/lib/near/plugins"\"
       -DCONFIGDIR=\""/etc/neard\"" -O2 -pipe -g -feliminate-unused-debug-types -c
       -o tools/snep-send.o tools/snep-send.c
     | In file included from tools/snep-send.c:16:0:
     | tools/../src/near.h:41:23: fatal error: near/dbus.h: No such file or directory
     |  #include <near/dbus.h>
     |                        ^
     | compilation terminated.
     | make[1]: *** [tools/snep-send.o] Error 1
     | make[1]: *** Waiting for unfinished jobs....
     | make: *** [all] Error 2
     | ERROR: oe_runmake failed
                

4.31.2. Reproducing the Error

Because race conditions are intermittent, they do not manifest themselves every time you do the build. In fact, most times the build will complete without problems even though the potential race condition exists. Thus, once the error surfaces, you need a way to reproduce it.

In this example, compiling the "neard" package is causing the problem. So the first thing to do is build "neard" locally. Before you start the build, set the PARALLEL_MAKE variable in your local.conf file to a high number (e.g. "-j 20"). Using a high value for PARALLEL_MAKE increases the chances of the race condition showing up:

     $ bitbake neard
                

Once the local build for "neard" completes, start a devshell build:

     $ bitbake neard -c devshell
                

For information on how to use a devshell, see the "Using a Development Shell" section.

In the devshell, do the following:

     $ make clean
     $ make tools/snep-send.o
                

The devshell commands cause the failure to clearly be visible. In this case, a missing dependency exists for the "neard" Makefile target. Here is some abbreviated, sample output with the missing dependency clearly visible at the end:

     i586-poky-linux-gcc  -m32 -march=i586 --sysroot=/home/scott-lenovo/......
        .
        .
        .
     tools/snep-send.c
     In file included from tools/snep-send.c:16:0:
     tools/../src/near.h:41:23: fatal error: near/dbus.h: No such file or directory
      #include <near/dbus.h>
                       ^
     compilation terminated.
     make: *** [tools/snep-send.o] Error 1
     $
                

4.31.3. Creating a Patch for the Fix

Because there is a missing dependency for the Makefile target, you need to patch the Makefile.am file, which is generated from Makefile.in. You can use Quilt to create the patch:

     $ quilt new parallelmake.patch
     Patch patches/parallelmake.patch is now on top
     $ quilt add Makefile.am
     File Makefile.am added to patch patches/parallelmake.patch
                

For more information on using Quilt, see the "Using Quilt in Your Workflow" section.

At this point you need to make the edits to Makefile.am to add the missing dependency. For our example, you have to add the following line to the file:

     tools/snep-send.$(OBJEXT): include/near/dbus.h
                

Once you have edited the file, use the refresh command to create the patch:

     $ quilt refresh
     Refreshed patch patches/parallelmake.patch
                

Once the patch file exists, you need to add it back to the originating recipe folder. Here is an example assuming a top-level Source Directory named poky:

     $ cp patches/parallelmake.patch poky/meta/recipes-connectivity/neard/neard
                

The final thing you need to do to implement the fix in the build is to update the "neard" recipe (i.e. neard-0.14.bb) so that the SRC_URI statement includes the patch file. The recipe file is in the folder above the patch. Here is what the edited SRC_URI statement would look like:

     SRC_URI = "${KERNELORG_MIRROR}/linux/network/nfc/${BPN}-${PV}.tar.xz \
                file://neard.in \
                file://neard.service.in \
                file://parallelmake.patch \
               "
                

With the patch complete and moved to the correct folder and the SRC_URI statement updated, you can exit the devshell:

     $ exit
                

4.31.4. Testing the Build

With everything in place, you can get back to trying the build again locally:

     $ bitbake neard
                

This build should succeed.

Now you can open up a devshell again and repeat the clean and make operations as follows:

     $ bitbake neard -c devshell
     $ make clean
     $ make tools/snep-send.o
                

The build should work without issue.

As with all solved problems, if they originated upstream, you need to submit the fix for the recipe in OE-Core and upstream so that the problem is taken care of at its source. See the "Submitting a Change to the Yocto Project" section for more information.

4.32. Maintaining Open Source License Compliance During Your Product's Lifecycle

One of the concerns for a development organization using open source software is how to maintain compliance with various open source licensing during the lifecycle of the product. While this section does not provide legal advice or comprehensively cover all scenarios, it does present methods that you can use to assist you in meeting the compliance requirements during a software release.

With hundreds of different open source licenses that the Yocto Project tracks, it is difficult to know the requirements of each and every license. However, the requirements of the major FLOSS licenses can begin to be covered by assuming that three main areas of concern exist:

  • Source code must be provided.

  • License text for the software must be provided.

  • Compilation scripts and modifications to the source code must be provided.

There are other requirements beyond the scope of these three and the methods described in this section (e.g. the mechanism through which source code is distributed).

As different organizations have different methods of complying with open source licensing, this section is not meant to imply that there is only one single way to meet your compliance obligations, but rather to describe one method of achieving compliance. The remainder of this section describes methods supported to meet the previously mentioned three requirements. Once you take steps to meet these requirements, and prior to releasing images, sources, and the build system, you should audit all artifacts to ensure completeness.

Note

The Yocto Project generates a license manifest during image creation that is located in ${DEPLOY_DIR}/licenses/image_name-datestamp to assist with any audits.

4.32.1. Providing the Source Code

Compliance activities should begin before you generate the final image. The first thing you should look at is the requirement that tops the list for most compliance groups - providing the source. The Yocto Project has a few ways of meeting this requirement.

One of the easiest ways to meet this requirement is to provide the entire DL_DIR used by the build. This method, however, has a few issues. The most obvious is the size of the directory since it includes all sources used in the build and not just the source used in the released image. It will include toolchain source, and other artifacts, which you would not generally release. However, the more serious issue for most companies is accidental release of proprietary software. The Yocto Project provides an archiver class to help avoid some of these concerns.

Before you employ DL_DIR or the archiver class, you need to decide how you choose to provide source. The source archiver class can generate tarballs and SRPMs and can create them with various levels of compliance in mind.

One way of doing this (but certainly not the only way) is to release just the source as a tarball. You can do this by adding the following to the local.conf file found in the Build Directory:

     INHERIT += "archiver"
     ARCHIVER_MODE[src] = "original"
                

During the creation of your image, the source from all recipes that deploy packages to the image is placed within subdirectories of DEPLOY_DIR/sources based on the LICENSE for each recipe. Releasing the entire directory enables you to comply with requirements concerning providing the unmodified source. It is important to note that the size of the directory can get large.

A way to help mitigate the size issue is to only release tarballs for licenses that require the release of source. Let us assume you are only concerned with GPL code as identified by running the following script:

     # Script to archive a subset of packages matching specific license(s)
     # Source and license files are copied into sub folders of package folder
     # Must be run from build folder
     #!/bin/bash
     src_release_dir="source-release"
     mkdir -p $src_release_dir
     for a in tmp/deploy/sources/*; do
        for d in $a/*; do
           # Get package name from path
           p=`basename $d`
           p=${p%-*}
           p=${p%-*}
           # Only archive GPL packages (update *GPL* regex for your license check)
           numfiles=`ls tmp/deploy/licenses/$p/*GPL* 2> /dev/null | wc -l`
           if [ $numfiles -gt 1 ]; then
              echo Archiving $p
              mkdir -p $src_release_dir/$p/source
              cp $d/* $src_release_dir/$p/source 2> /dev/null
              mkdir -p $src_release_dir/$p/license
              cp tmp/deploy/licenses/$p/* $src_release_dir/$p/license 2> /dev/null
           fi
        done
     done                

At this point, you could create a tarball from the gpl_source_release directory and provide that to the end user. This method would be a step toward achieving compliance with section 3a of GPLv2 and with section 6 of GPLv3.

4.32.2. Providing License Text

One requirement that is often overlooked is inclusion of license text. This requirement also needs to be dealt with prior to generating the final image. Some licenses require the license text to accompany the binary. You can achieve this by adding the following to your local.conf file:

     COPY_LIC_MANIFEST = "1"
     COPY_LIC_DIRS = "1"
     LICENSE_CREATE_PACKAGE = "1"
                

Adding these statements to the configuration file ensures that the licenses collected during package generation are included on your image.

Note

Setting all three variables to "1" results in the image having two copies of the same license file. One copy resides in /usr/share/common-licenses and the other resides in /usr/share/license.

The reason for this behavior is because COPY_LIC_DIRS and COPY_LIC_MANIFEST add a copy of the license when the image is built but do not offer a path for adding licenses for newly installed packages to an image. LICENSE_CREATE_PACKAGE adds a separate package and an upgrade path for adding licenses to an image.

As the source archiver class has already archived the original unmodified source that contains the license files, you would have already met the requirements for inclusion of the license information with source as defined by the GPL and other open source licenses.

4.32.3. Providing Compilation Scripts and Source Code Modifications

At this point, we have addressed all we need to prior to generating the image. The next two requirements are addressed during the final packaging of the release.

By releasing the version of the OpenEmbedded build system and the layers used during the build, you will be providing both compilation scripts and the source code modifications in one step.

If the deployment team has a BSP layer and a distro layer, and those those layers are used to patch, compile, package, or modify (in any way) any open source software included in your released images, you might be required to release those layers under section 3 of GPLv2 or section 1 of GPLv3. One way of doing that is with a clean checkout of the version of the Yocto Project and layers used during your build. Here is an example:

     # We built using the rocko branch of the poky repo
     $ git clone -b rocko git://git.yoctoproject.org/poky
     $ cd poky
     # We built using the release_branch for our layers
     $ git clone -b release_branch git://git.mycompany.com/meta-my-bsp-layer
     $ git clone -b release_branch git://git.mycompany.com/meta-my-software-layer
     # clean up the .git repos
     $ find . -name ".git" -type d -exec rm -rf {} \;
                

One thing a development organization might want to consider for end-user convenience is to modify meta-poky/conf/bblayers.conf.sample to ensure that when the end user utilizes the released build system to build an image, the development organization's layers are included in the bblayers.conf file automatically:

     # LAYER_CONF_VERSION is increased each time build/conf/bblayers.conf
     # changes incompatibly
     LCONF_VERSION = "6"

     BBPATH = "${TOPDIR}"
     BBFILES ?= ""

     BBLAYERS ?= " \
       ##OEROOT##/meta \
       ##OEROOT##/meta-poky \
       ##OEROOT##/meta-yocto-bsp \
       ##OEROOT##/meta-mylayer \
       "
                

Creating and providing an archive of the Metadata layers (recipes, configuration files, and so forth) enables you to meet your requirements to include the scripts to control compilation as well as any modifications to the original source.

4.33. Using the Error Reporting Tool

The error reporting tool allows you to submit errors encountered during builds to a central database. Outside of the build environment, you can use a web interface to browse errors, view statistics, and query for errors. The tool works using a client-server system where the client portion is integrated with the installed Yocto Project Source Directory (e.g. poky). The server receives the information collected and saves it in a database.

A live instance of the error reporting server exists at http://errors.yoctoproject.org. This server exists so that when you want to get help with build failures, you can submit all of the information on the failure easily and then point to the URL in your bug report or send an email to the mailing list.

Note

If you send error reports to this server, the reports become publicly visible.

4.33.1. Enabling and Using the Tool

By default, the error reporting tool is disabled. You can enable it by inheriting the report-error class by adding the following statement to the end of your local.conf file in your Build Directory.

     INHERIT += "report-error"
                

By default, the error reporting feature stores information in ${LOG_DIR}/error-report. However, you can specify a directory to use by adding the following to your local.conf file:

     ERR_REPORT_DIR = "path"
                

Enabling error reporting causes the build process to collect the errors and store them in a file as previously described. When the build system encounters an error, it includes a command as part of the console output. You can run the command to send the error file to the server. For example, the following command sends the errors to an upstream server:

     $ send-error-report /home/brandusa/project/poky/build/tmp/log/error-report/error_report_201403141617.txt
                

In the previous example, the errors are sent to a public database available at http://errors.yoctoproject.org, which is used by the entire community. If you specify a particular server, you can send the errors to a different database. Use the following command for more information on available options:

     $ send-error-report --help
                

When sending the error file, you are prompted to review the data being sent as well as to provide a name and optional email address. Once you satisfy these prompts, the command returns a link from the server that corresponds to your entry in the database. For example, here is a typical link:

     http://errors.yoctoproject.org/Errors/Details/9522/
                

Following the link takes you to a web interface where you can browse, query the errors, and view statistics.

4.33.2. Disabling the Tool

To disable the error reporting feature, simply remove or comment out the following statement from the end of your local.conf file in your Build Directory.

     INHERIT += "report-error"
                

4.33.3. Setting Up Your Own Error Reporting Server

If you want to set up your own error reporting server, you can obtain the code from the Git repository at http://git.yoctoproject.org/cgit/cgit.cgi/error-report-web/. Instructions on how to set it up are in the README document.

Chapter 5. Using the Quick EMUlator (QEMU)

This chapter provides procedures that show you how to use the Quick EMUlator (QEMU), which is an Open Source project the Yocto Project uses as part of its development "tool set". For reference information on the Yocto Project implementation of QEMU, see the "Quick EMUlator (QEMU)" section in the Yocto Project Reference Manual.

5.1. Running QEMU

To use QEMU, you need to have QEMU installed and initialized as well as have the proper artifacts (i.e. image files and root filesystems) available. Follow these general steps to run QEMU:

  1. Install QEMU: See "The QEMU Emulator" section in the Yocto Project Software Development Kit (SDK) Developer's Guide for information on how to install QEMU.

  2. Setting Up the Environment: How you set up the QEMU environment depends on how you installed QEMU:

    • If you cloned the poky repository or you downloaded and unpacked a Yocto Project release tarball, you can source the build environment script (i.e. oe-init-build-env):

           $ cd ~/poky
           $ source oe-init-build-env
                                  

    • If you installed a cross-toolchain, you can run the script that initializes the toolchain. For example, the following commands run the initialization script from the default poky_sdk directory:

           . ~/poky_sdk/environment-setup-core2-64-poky-linux
                                  

  3. Ensure the Artifacts are in Place: You need to be sure you have a pre-built kernel that will boot in QEMU. You also need the target root filesystem for your target machine’s architecture:

    • If you have previously built an image for QEMU (e.g. qemux86, qemuarm, and so forth), then the artifacts are in place in your Build Directory.

    • If you have not built an image, you can go to the machines/qemu area and download a pre-built image that matches your architecture and can be run on QEMU.

    See the "Extracting the Root Filesystem" section in the Yocto Project Software Development Kit (SDK) Developer's Guide for information on how to extract a root filesystem.

  4. Run QEMU: The basic runqemu command syntax is as follows:

         $ runqemu [option ]  [...]
                        

    Based on what you provide on the command line, runqemu does a good job of figuring out what you are trying to do. For example, by default, QEMU looks for the most recently built image according to the timestamp when it needs to look for an image. Minimally, through the use of options, you must provide either a machine name, a virtual machine image (*.vmdk), or a kernel image (*.bin).

    Here are some additional examples to help illustrate further QEMU:

    • This example starts QEMU with MACHINE set to "qemux86". Assuming a standard Build Directory, runqemu automatically finds the bzImage-qemux86.bin image file and the core-image-minimal-qemux86-20140707074611.rootfs.ext3 (assuming the current build created a core-image-minimal image).

      Note

      When more than one image with the same name exists, QEMU finds and uses the most recently built image according to the timestamp.

           $ runqemu qemux86
                                  

    • This example produces the exact same results as the previous example. This command, however, specifically provides the image and root filesystem type.

           $ runqemu qemux86 core-image-minimal ext3
                                  

    • This example specifies to boot an initial RAM disk image and to enable audio in QEMU. For this case, runqemu set the internal variable FSTYPE to "cpio.gz". Also, for audio to be enabled, an appropriate driver must be installed (see the previous description for the audio option for more information).

           $ runqemu qemux86 ramfs audio
                                  

    • This example does not provide enough information for QEMU to launch. While the command does provide a root filesystem type, it must also minimally provide a MACHINE, KERNEL, or VM option.

           $ runqemu ext3
                                  

    • This example specifies to boot a virtual machine image (.wic.vmdk file). From the .wic.vmdk, runqemu determines the QEMU architecture (MACHINE) to be "qemux86" and the root filesystem type to be "vmdk".

           $ runqemu /home/scott-lenovo/vm/core-image-minimal-qemux86.wic.vmdk
                                  

5.2. Switching Between Consoles

When booting or running QEMU, you can switch between supported consoles by using Ctrl+Alt+number. For example, Ctrl+Alt+3 switches you to the serial console as long as that console is enabled. Being able to switch consoles is helpful, for example, if the main QEMU console breaks for some reason.

Note

Usually, "2" gets you to the main console and "3" gets you to the serial console.

5.3. Removing the Splash Screen

You can remove the splash screen when QEMU is booting by using Alt+left. Removing the splash screen allows you to see what is happening in the background.

5.4. Disabling the Cursor Grab

The default QEMU integration captures the cursor within the main window. It does this since standard mouse devices only provide relative input and not absolute coordinates. You then have to break out of the grab using the "Ctrl+Alt" key combination. However, the Yocto Project's integration of QEMU enables the wacom USB touch pad driver by default to allow input of absolute coordinates. This default means that the mouse can enter and leave the main window without the grab taking effect leading to a better user experience.

5.5. Running Under a Network File System (NFS) Server

One method for running QEMU is to run it on an NFS server. This is useful when you need to access the same file system from both the build and the emulated system at the same time. It is also worth noting that the system does not need root privileges to run. It uses a user space NFS server to avoid that. Follow these steps to set up for running QEMU using an NFS server.

  1. Extract a Root Filesystem: Once you are able to run QEMU in your environment, you can use the runqemu-extract-sdk script, which is located in the scripts directory along with the runqemu script.

    The runqemu-extract-sdk takes a root filesystem tarball and extracts it into a location that you specify. Here is an example that takes a file system and extracts it to a directory named test-nfs:

         runqemu-extract-sdk ./tmp/deploy/images/qemux86/core-image-sato-qemux86.tar.bz2 test-nfs
                        

  2. Start QEMU: Once you have extracted the file system, you can run runqemu normally with the additional location of the file system. You can then also make changes to the files within ./test-nfs and see those changes appear in the image in real time. Here is an example using the qemux86 image:

         runqemu qemux86 ./test-nfs
                        

Note

Should you need to start, stop, or restart the NFS share, you can use the following commands:

  • The following command starts the NFS share:

         runqemu-export-rootfs start file-system-location
                                

  • The following command stops the NFS share:

             runqemu-export-rootfs stop file-system-location
                                

  • The following command restarts the NFS share:

         runqemu-export-rootfs restart file-system-location