[yocto] Whats the better way to maintain the Yocto project for an embedded product - git submodules or repo or using Combo-layer

[VanCutsem, Geoffroy]

> -----Original Message-----
> From: yocto-bounces at yoctoproject.org [mailto:yocto-
> bounces at yoctoproject.org] On Behalf Of Paul Barker
> Sent: Wednesday, January 18, 2017 11:09 AM
> To: yocto at yoctoproject.org; Eswaran Vinothkumar (BEG-PT/PJ-IOT1)
> <Vinothkumar.Eswaran at de.bosch.com>
> Subject: Re: [yocto] Whats the better way to maintain the Yocto project for
> an embedded product - git submodules or repo or using Combo-layer
> 
> On 18 January 2017 09:32:15 GMT+00:00, "Eswaran Vinothkumar (BEG-PT/PJ-
> IOT1)" <Vinothkumar.Eswaran at de.bosch.com> wrote:
> >Hello Yocto community members,
> >
> >Currently I am working on the task of using Yocto to build customized
> >Embedded Linux distribution for an embedded product. I have created a
> >new BSP layer for my project (meta-custommachine) and have successfully
> >created barebox, Linux Kernel and root filesystem images for my board.
> >
> >Now I wish to create an internal repository for Yocto project to track
> >and maintain the changes. I am unclear what is the better way to create
> >an repository. I googled for the same and found that the Freescale
> >community is maintaining their Yocto project using the repo tool. So I
> >tried to have a similar structure for my project. I created a repo with
> >the default.xml file which has the information about where to fetch the
> >repositories for poky, meta-ptx and meta-custommachine. I am seeing the
> >folder structures as expected and build is also fine.
> >
> >I had a discussion with one of my senior team member about this and he
> >is interested in using git submodules. So I tried to add the layers
> >meta-custommachine and meta-ptx within poky repository as sub-
> modules.
> >Is this the proper way of adding new layers within the poky repository?
> >Or may I know how can I maintain a Yocto repository using git
> >submodules. Does git submodules work better than repo tool ?
> >
> >I am newbie to create and maintain a repo, so I am not able to
> >visualize what is the future effect of choosing one over the other.
> >Currently I am using the krogoth release of Yocto and planning to
> >update this with new Yocto releases.
> >
> >Any information on the topic would be helpful.
> 
> Both of these approaches are widely used, I'd go with whichever feels most
> comfortable to you/your team. Personally I'm a fan of using repo as I can set
> it to check out the latest commits on a given branch (eg. krogoth) instead of
> always having to set an exact commit hash to use.
> 
> If using git submodules it is often advised to have a separate top level
> repository which just pulls in the submodules.

Alexander Kanevskiy (aka Sasha) touched on some of that especially in the context of delivering a Continuous Integration and Continuous Delivery mechanism in his presentation at the last ELCE in Berlin. You can view his slides here: http://events.linuxfoundation.org/sites/events/files/slides/Creating%20Continuous%20Delivery%20for%20Yocto%20Based%20IoT%20Distribution%2020161012%20LF.pdf

There is a quick summary of the pro's and con's of using combo-tool vs. git submodule on slide 20.

Geoffroy