Maybe this may help:
I compiled Git under Linux with NO_PREAD=1, and also _disabled_
file position save/restore in git_pread(). Now (I clone small repo to
save traffic):
moonlight:/tmp$ git-clone git://people.freedesktop.org/~keithp/parsecvs
Initialized empty Git repository in /tmp/parsecvs/.git/
remote: Generating pack...
remote: Done counting 476 objects.
remote: Deltifying 476 objects.
remote: 100% (476/476) done
Indexing 476 objects...
remote: Total 476 (delta 339), reused 0 (delta 0)
100% (476/476) done
Resolving 339 deltas...
100% (339/339) done
error: packfile /tmp/parsecvs/.git/objects/pack/pack-dda2f32249fab26059a035bd273dce9feaf6bade.pack does not match index
error: packfile /tmp/parsecvs/.git/objects/pack/pack-dda2f32249fab26059a035bd273dce9feaf6bade.pack cannot be accessed
error: packfile /tmp/parsecvs/.git/objects/pack/pack-dda2f32249fab26059a035bd273dce9feaf6bade.pack does not match index
error: packfile /tmp/parsecvs/.git/objects/pack/pack-dda2f32249fab26059a035bd273dce9feaf6bade.pack cannot be accessed
fatal: failed to unpack tree object HEAD
Errors are different, but seems Git is sensitive to pread() that messes
file position. The problem may be in index-pack.c:
static const char *open_pack_file(const char *pack_name)
{
if (from_stdin) {
...
pack_fd = output_fd;
} else {
...
pack_fd = input_fd;
}
...
}
There's no dup() call, so when we mess pack_fd (that is used in
pread() only), we also mess one more file descriptor that is used
sequentially (output_fd in my case), and so may corrupt the pack.
--
Tomash Brechko
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