[yocto] How to write a distro layer?

[Vincent Prince]

 You don't need to use add-layer, just create conf/bblayers.conf with
wanted layers:

LCONF_VERSION = "7"

BBPATH = "${TOPDIR}"
BSPDIR := "${@os.path.abspath(os.path.dirname(d.getVar('FILE', True)) +
'/../..')}"

BBFILES ?= ""
BBLAYERS = " \
  ${BSPDIR}/sources/poky/meta \
  ${BSPDIR}/sources/poky/meta-poky \
  ${BSPDIR}/sources/meta-openembedded/meta-oe \
  "


2018-08-03 15:43 GMT+02:00 Uwe Geuder <jrswdnan22 at snkmail.com>:

> Thanks Vincent for your quick reply!
>
> On Fri, Aug 3, 2018 at 12:44 PM, Vincent Prince <vincent.prince.fr-at-...>
> wrote:
> > 2018-08-03 10:39 GMT+02:00 Uwe Geuder <jrswdnan22 at snkmail.com>:
>
> >>    One of the few informations I could find about how to create my own
> >>    layer was something like
> >>    https://www.openembedded.org/wiki/Creating_a_new_Layer
>
> > Did you check
> > https://www.yoctoproject.org/docs/latest/mega-manual/mega-
> manual.html#creating-a-general-layer-using-the-bitbake-layers-script
>
> Yes. The template generated by that script is very minimal and
> generic. I don't see any guidance for distro layers in particular.  As
> a matter fact I believe our layer has been created by that script
> (although that was long before my time).
>
>
> >> The yocto reference manual says for many variables: "Set it in your
> >> local.conf". For me they are policy, so why shouldn't I set them in
> >> distro/<distro>.conf?
>
> > Did you also check
> > https://www.yoctoproject.org/docs/latest/mega-manual/mega-
> manual.html#creating-your-own-distribution
>
> I had read that many times before, but not recently so let's check again...
>
> | Note
> | The DISTRO variable in your local.conf file determines the name of
> | your distribution
>
> [...]
>
> | 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"
>
>
> Correct, that's what I remembered. But if I set it in local.conf
> before adding my layer the bitbake sanity check will complain that
> there is no such layer. And if I modify local.conf after adding the
> layer all recipes will be re-parsed when building the first time.
>
> I don't see any guidance in what order the steps should be carried out
> when setting up a new build area.
>
> They do indicate that you should copy another distro's conf file,
> that's why I asked whether using "require" as we do is a bad/dangerous
> idea.
>
> > You can look some Freescale example here:
> > https://github.com/Freescale/meta-freescale-distro
>
> Good, I hadn't found those. At least the distro/<name>.conf files look
> pretty much like I would expect them.
>
> But all of them (I understand the layer defines 8 different distros)
> do set the DISTRO variable. I haven't run the yocto-check-layer for a
> while, but the last time I did it complained that a distro layer MUST
> NOT set its own DISTRO variable. Do you happen to know whether
> meta-freescale-distro passes the yocto-check-layer script without
> complaints? (I know I could test myself...)
>
> > In fact, when Yocto manual refers to adding something to local.conf,
> > it is the minimal way to do it, but the cleanest is indeed to set it
> > in machine/distro config file.
>
> That has also been my thinking. If that's generally accepted we
> probably should send a patch to the manual. It's pretty misleading if
> the manual without any further explanations says "do it way A" if "way
> B" often is actually the better one.
>
>
> > 1.) DISTRO is local to build folder,
>
> By "local to build folder", do you mean that within the same build folder
> one cannot build more than 1 distro? Not relevant for me, because I
> have only one for the time being, but just to understand the message.
>
> > so it should be in local.conf, and you can use a wrapper script to help
> > creating this local.conf file,
>
> Yes, that's what we do. Without a wrapper script builds were unlikely
> to be reproducible by any measure...
>
>
> > https://github.com/Freescale/fsl-community-bsp-base/blob/
> master/setup-environment
>
> Interesting. I cannot spot how that script handles layers.
>
> My own script
>
> 1) sources oe-init-build-env
> 2) modifies the generated conf/local.conf
> 3) runs bitbake-layer add-layer for all layers we need in our distro
>
> >> In an attempt to make our code more in line with what I understand to be
> >> correct style, I tried to move all policy settings to
> >> distro/<distro>.conf and the DISTRO setting to local.conf.
> >>
> >> However that created a couple of problems:
> >>
> >> 1. If I set DISTRO in local.conf before adding all needed layers, my own
> >> distro layer last, bitbake-layers fails in a sanity check that the
> >> distro does not exist. Fair enough, it doesn't know about before it has
> >> been added.
> >>
> >> 2. If I first modify my local.conf with all my settings except DISTRO,
> >> then run all the add-layer operations and finally modify local.conf a
> >> 2nd time to set DISTRO correctly the build works. However, all recipes
> >> are reparsed when the build starts. I guess this is caused by the config
> >> change.
> >>
> >> So in the end having the DISTRO setting in layer.conf seems to work
> >> best. All add-layer commands succeed and recipes can be used from the
> >> cache when the build starts. Best, except that I don't think that's the
> >> way it's documented.
> >>
> >> Any thoughts what I might be missing?
>
> > You can use git submodule, or google repo to create Yocto environment,
>
> Yes, we have all layers as submodules in a single git repo, so we
> always can do a clean build "from a single SHA1"
>
> > you don't need to create your layer each time
>
> What do you mean by creating a layer? Of course the source is in
> git and it only changes when necessary.
>
> What I do in every new build area is run add-layer. (Currently still
> repeatedly for one layer at a time, but I think I read in the new
> release notes that bitbake-layer can now add several layers at once.)
>
> I have thought about saving the generated layers.conf file and
> restoring it by my setup script. But somehow I feel more confident if
> the parsing is done for each new build area. Otherwise one might end
> up in the situation that one day you note that a change made weeks or
> months ago has broken something and nobody noted it.
>
> > and you don't have to compile before using bitbake-layers.
>
> Not sure what you mean by that. Of course I cannot build/compile
> anything before the build area is set-up completely.
>
> Bitbake-layer parses all recipes of the layer it adds. If I do not
> modify local.conf after adding the last layer the first build
> starts immediately from cached recipes.
>
> If I modify local.conf to set DISTRO after adding the last layer, the
> first build re-parses everything. Not that it's a huge increase to the
> whole build time, but it does not feel right.
>
> Regards,
>
> Uwe
>
> ---
> Uwe Geuder
> Neuro Event Labs Oy
> Tampere, Finland
> uwe.gexder at neuroeventlabs.com (Bot check: fix one obvious typo)
> --
> _______________________________________________
> yocto mailing list
> yocto at yoctoproject.org
> https://lists.yoctoproject.org/listinfo/yocto
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.yoctoproject.org/pipermail/yocto/attachments/20180803/95effdd7/attachment-0001.html>