[oe] A new bitbake extension: .bbappend files

[Frans Meulenbroeks]

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.

Frans.