[Buildroot] [RFC] Override source directories

Hello,

Here is a set of RFC patches that implement the basic mechanism I have
been referring to since a couple of weeks/months about allowing users
to override the source directory for packages.

From an user perspective, it allows ones to create a "local.mk" file
in the Buildroot main source directory, with variable definitions such
as :

 ZLIB_OVERRIDE_SRCDIR = /tmp/zlib
 MYAPP_OVERRIDE_SRCDIR = /home/foobar/project/myapp
 LIBGLIB2_OVERRIDE_SRCDIR = /home/foobar/git/libglib2

At build time, Buildroot would use those directories at the source for
the packages, instead of downloading, extracing and patching them in
the usual way.

Internally, this is implemented inside our package infrastructure, so
this mechanism should work for all packages that rely on the
infrastructure. The GENTARGETS macro makes sure that the package build
process bypasses the download, extract and patch step when
<pkg>_OVERRIDE_SRCDIR is defined, and instead a symlinking step is
added. It's very simple.

This series of patches also add the <pkg>-reconfigure and
<pkg>-rebuild targets, which makes it easy for users to restart the
package build process at the compilation step or at the configuration
step, without having to mess up with stamp file details.

There are still a few issues to solve and discuss, though :

 * Is local.mk inside the main source directory the good solution?
   Should we instead provide a configuration option to set the path to
   the override file? Or another solution?

 * As the mechanism is implemented today, "make clean" removes the
   symbolic link $(O)/build/<pkg>-<version>, but not the stamp files
   created inside this source directory. So next time the build is
   started, things will go wrong. To solve this, the only solution I
   see is to separate the directory with the stamp files from the
   source directory, at least in the case of overriden source
   directories.

 * Other things?

Feedback, comments and ideas welcome.

Regards,

Thomas

The following changes since commit 7234c23967fa70b760c64700e56bb1778019fbeb:

  CHANGES: update with recent changes (2011-05-18 21:02:30 +0200)

are available in the git repository at:
  http://free-electrons.com/~thomas/buildroot.git for-2011.08/sourcedir

Thomas Petazzoni (4):
      package: enhance infrastructure to support source dir override
      package: remove stamp files in <pkg>-dirclean
      package: add <pkg>-rebuild and <pkg>-reconfigure
      Include a local.mk for package overrides

 Makefile                    |    1 +
 package/Makefile.package.in |   30 ++++++++++++++++++++++++++++++
 2 files changed, 31 insertions(+), 0 deletions(-)

Thanks,
-- 
Thomas Petazzoni