Re: [Buildroot] [RFC] linux: Make CONFIG_LOCALVERSION_AUTO work with OVERRIDE_SRCDIR

["Yann E. MORIN" <yann.morin.1998@free.fr>]

Florian, Thomas, All,

On 2022-07-18 15:01 +0200, Thomas Petazzoni via buildroot spake thusly:
> On Wed,  6 Jul 2022 14:06:21 -0700
> Florian Fainelli <f.fainelli@gmail.com> wrote:
> > Linux is able to generate an automic version based upon the git tree
> > that is being used which is very useful for making sure that the kernel
> > being used is truly the one that we intend to be using.
> > 
> > When using LINUX_OVERRIDE_SRCDIR however, since we do not rsync the .git
> > folder, all of the necessary information for scripts/setlocalversion to
> > compute the exact version and git commit id is lost.
> > 
> > Add a post rsync hook that copies it over in order to allow 'git
> > rev-parse' to work and produce an usable version.
> > 
> > Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
> 
> Thanks for your patch. What bothers me is that it is a Linux-specific
> solution for a problem that isn't Linux-specific. Many other packages
> also use Git commands to generate a version string that they embed in
> their binaries. So this problem really is global and I'm not sure we
> want a Linux-specific fixup for it.

Indeed.

> To me the long term solution is to enable out of tree build of
> packages. This way, instead of rsync'ing the code, we would directly
> build it from its original location. Some initial work was done in this
> area, but it's obviously a much larger endeavor than the fixup you are
> proposing. A more immediate alternative would be to also rsync the .git
> folder instead of excluding it, but do that globally for all packages
> that use override-srcdir. The .git directory was explicitly excluded to
> reduce the amount of data to rsync.

And in any case, it is still possible to hack this for now:

  - set LINUX_OVERRIDE_SRC_DIR in your local.mk
  - define the post-rsync hook there as well

Note: it is usualy possible to add the hook in local.mk, but it is
fragile: if the package itself uses post-rsync hooks, but its first
assignment is not an append-assignment +=, then your hook in local.mk is
ignored. In practice, we have no package [*] that uses post-rsync hooks,
so it shoiuld be safe to do define one in local.mk.

[*] of course, there is one exception: uboot, and I wonder if we should
not have a better solution nowadays.

Regards,
Yann E. MORIN.

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