[oe] A new bitbake extension: .bbappend files

[Frans Meulenbroeks]

2010/7/18 Chris Larson <clarson at kergoth.com>

> On Sun, Jul 18, 2010 at 12:47 PM, Frans Meulenbroeks <
> fransmeulenbroeks at gmail.com> wrote:
>
> > 2010/7/16 Richard Purdie <rpurdie at rpsys.net>
> >
> > > Whilst our layers mechanism, is great it does have a drawback which has
> > > bugged me for a while. If you have a recipe like pointercal which has
> > > machine specific information in it and you have your new machine code
> in
> > > a layer, how do you add a pointercal file for your machine?
> > >
> > > Answer is you copy the whole pointercal recipe and files into your
> > > layer, then add the single file for your machine. To me this is ugly,
> > > ugly, ugly. We hate code duplication and as soon as you create two
> > > copies of the same information, we've failed.
> > >
> > > So how could we do this better? Somehow we need to say that a given
> > > directory X has some information which should be merged with the
> > > original recipe. I've thought through several different ways of doing
> > > this and the best solution I found was "bbappend".
> > >
> > > The idea is that if bitbake finds any X.bbappend files, when it loads
> > > X.bb, it will also include these files after it parses the base .bb
> file
> > > (but before finalise and the anonymous methods run). This means that
> > > the .bbappend file can poke around and do whatever it might want to the
> > > recipe to customise it.
> > >
> > > I went ahead and tried it out as its quite simple to code this in
> > > bitbake. I liked the result enough I've already merged this into Poky:
> > >
> > >
> > >
> >
> http://git.pokylinux.org/cgit.cgi/poky/commit/?id=63e6ba85677b8aa9f4cf9942a1fccbb8a8c72660
> > >
> > > I'm proposing to push it to bitbake master if there are no serious
> > > objections.
> > >
> > > As an example use case, for the pointercal case above in another later
> > > you could add a pointercal_0.0.bbappend file which contained something
> > > like:
> > >
> > > FILESPATH := "${FILESPATH}:${@os.path.dirname(bb.data.getVar('FILE', d,
> > > True))}"
> > >
> > > which would then cause the directory containing the bbappend file to be
> > > searched for pointercal files.
> > >
> > > There are of course many other uses this could be put to for creating
> > > customised layers, its totally generic.
> > >
> > > For the specific case of paths, I have wondered if there would be a way
> > > to leverage help from bitbake in creating a sane set of search paths
> but
> > > I'm still thinking about that. This extension is good enough in its own
> > > right in my opinion to be worthwhile.
> > >
> > > Cheers,
> > >
> > > Richard
> > >
> >
> > I've been pondering a litlte bit more about this.
> > Will the .bbappend mechanism allow me to override a file in the original
> > recipe?
> > If so how?
> >
> > Typical use case: I want to have a dedicated defconfig for my linux
> kernel.
> > Alternate use case: a dedicated busybox configuration.
> >
>
> You can do this today with FILESPATHBASE.
>
> I.e. FILESPATHBASE =. "${TOPDIR}/files:", then mkdir -p files/busybox; cp
> mybusyboxdefconfig files/busybox/defconfig
>

Ah cool, didn't know that, will give it a try.
Actually this might be mentioned somewhere in the wiki (if it is not in
yet). I can imagine especially wrt kernel that people want to do have their
own config.

Frans