[yocto] Building your own UI

[Joshua Lock]

On 07/02/12 13:54, jfabernathy wrote:
> On 02/07/2012 01:54 PM, Joshua Lock wrote:
>> On 07/02/12 07:57, James Abernathy wrote:
>>> This may be a dumb question, but I'll ask anyway.
>>> Suppose you have a project where you need a very custom user interface.
>>> Not just a series of applications that appear on a desktop like you see
>>> in sato, or Gnome, or KDE. Basically your application becomes the UI.
>>> I can see 2 approaches to this:
>>>
>>> 1. Start with core-image-minimal and add the packages you need to
>>> support GFX, X11, and your application plus dependencies.
>>> 2. Take core-image-sato and change the applications to be your subtasks
>>> , and the look-and-feel of the desktop.
>>>
>>> What are the considerations of both approaches?
>>
>> A key selling point of the Yocto approach is to provide a highly
>> customised OS for your target application, rather than taking an
>> existing solution and stripping it back.
>>
>> 2. is the antithesis of the Yocto approach if you don't want/need the
>> Sato UI.
>>
>> The intention is that the core metadata should provide sufficient
>> granularity through the defined images and tasks to get people started.
>>
>> I'd recommend something like 1. only taking core-image-core (horrible
>> name I know) if you want an X based OS.
>>
> I built core-image-core and it works and is basic. So it's not a really
> small Sato???
>
>> We no doubt need more documentation in this area, and Hob is designed
>> to help here.
>>
>>
>>> Is one better, or easier than the other?
>>
>> Creating your own image is better in that you only build and ship what
>> you need. Arguably building atop a custom image is easier, but you
>> lose control.
>>
>>> How would you do this in Yocto?
>>
>> You might consider creating a custom image by starting with
>> core-image-minimal and adding IMAGE_FEATURES and IMAGE_INSTALL entries
>> to provide the core functionality you desire.
>>
>> $ less foo.bb
>> # a noddy example image, base of a NAS OS
>>
>> # start with core-image-minimal
>> require recipes-core/images/core-image-minimal.bb
>>
>> IMAGE_FEATURES += "package-management nfs-server ssh-server-dropbear"
>> IMAGE_INSTALL += "my-custom-nas-app"
>>
> I have difficulty understanding the difference in IMAGE_FEATURES and
> IMAGE_INSTALL. To me IMAGE_INSTALL is clear I've used that in a
> core-image-sato.bbappend file in an image directory in my own recipes-xx
> directory. I see how IMAGE_FEATURES is uses in the core-image-core:
>
> IMAGE_FEATURES += "apps-console-core ${X11_IMAGE_FEATURES}"
>
> But I have no idea what ${X11_IMAGE_FEATURES} is or how to find where
> it's defined. The apps-console-core is define in the Poky Refernce manual:
>
> http://www.yoctoproject.org/docs/current/poky-ref-manual/poky-ref-manual.html#ref-features-image
>
>
> However, I'm not sure were to find it's definition in the many recipes.

The features are defined in core-image.bbclass:
http://git.yoctoproject.org/cgit/cgit.cgi/poky/tree/meta/classes/core-image.bbclass

Most of them translate into one or more task recipes 
(meta/recipes-*/tasks/) except package-management which translates to 
ROOTFS_PKGMANAGE which in turn is defined in each of the package 
management rootfs construction classes (meta/classes/rootfs_*.bbclass).


Aside: I usually rely in git grep to track down where a variable is defined.

Cheers,
Joshua
-- 
Joshua Lock
         Yocto Project "Johannes factotum"
         Intel Open Source Technology Centre