Re: patch-2.7.3 no longer applies relative symbolic link patches

[Linus Torvalds <torvalds@linux-foundation.org>]

On Mon, Jan 26, 2015 at 8:32 AM, Josh Boyer <jwboyer@fedoraproject.org> wrote:
>
> I went to do the Fedora 3.19-rc6 build this morning and it failed in
> our buildsystem with:
>
> + '[' '!' -f /builddir/build/SOURCES/patch-3.19-rc6.xz ']'
> + case "$patch" in
> + unxz
> + patch -p1 -F1 -s
> symbolic link target '../../../../../include/dt-bindings' is invalid
> error: Bad exit status from /var/tmp/rpm-tmp.mWE3ZL (%prep)

Ugh. I don't see anything we can do about this on the git side, and I
do kind of understand why 'patch' would be worried about '..' files.
In a perfect world, patch would parse the filename and see that it
stays within the directory structure of the project, but that is a
rather harder thing to do than just say "no dot-dot files".

The short-term fix is likely to just use "git apply" instead of "patch".

The long-term fix? I dunno. I don't see us not using symlinks, and a
quick check says that every *single* symlink we have in the kernel
source tree is one that points to a different directory using ".."
format. And while I could imagine that "patch" ends up counting the
dot-dot entries and checking that it's all inside the same tree it is
patching, I could also easily see patch *not* doing that. So using
"git apply" _might_ end up being the long-term fix too.

I suspect that if "patch" cannot apply even old-style kernel patches
due to the symlinks we have in the tree, and people end up having to
use "git apply" for them, I might end up starting to just use
rename-patches (ie using "git diff -M") for the kernel.

I've considered that for a while already, because "patch" _does_ kind
of understand them these days, although I think it gets the
cross-rename case wrong because it fundamentally works on a
file-by-file basis. But if "patch" just ends up not working at all,
the argument for trying to maintain backwards compatibility gets
really weak.

                                   Linus