[oe] A new bitbake extension: .bbappend files

[Chris Larson]

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
-- 
Christopher Larson
clarson at kergoth dot com
Founder - BitBake, OpenEmbedded, OpenZaurus
Maintainer - Tslib
Senior Software Engineer, Mentor Graphics