[oe] Programtically setting TMPDIR in bitbake.conf

[Alex Bennee]

Hi,

I'd like tweak the OpenEmbedded TMPDIR variable so it can optionally
build into a sub-directory of ${TOPDIR} based on the current git
status of the OE tree. The usage I envisage would be something like:

bitbake my-image
=>
builds to /path/to/build/current/[deploy/staging/etc...]

RELEASE=1 bitbake my-image
=>
builds to /path/to/build/build-12345ab/[deploy/staging/etc...]

Which would be based on the GIT commit ID. I'd probably want to
support the "dirty" semantics similar to the kernels versioning to
indicate the tree had uncommitted changes.

I know bitbake.conf can use arbitrary python to fill in the variables
but I'm unclear where these fragments can be put. A lot of python
snippets seem to refer to things like bb.data.getVar() which I assume
is part of bitbake itself. Is it possible to define some python in the
OE tree I can call from bitbake.conf? Is this functionality that has
to be added to bitbake itself?

I assume the change has to be made to bitbake.conf as other variables
are derived from TMPDIR at that point?

Basically I want to avoid writing an overly complex python one-liner
directly in bitbake.conf, that would seem to perl-ish ;-)

Cheers,

-- 
Alex, homepage: http://www.bennee.com/~alex/
http://www.half-llama.co.uk