The add_submodule_odb function tries to add a submodule's
object store as an "alternate". It needs the existing list
to be initialized (from the objects/info/alternates file)
for two reasons:
1. We look for duplicates with the existing alternate
stores, but obviously this doesn't work if we haven't
loaded any yet.
2. We link our new entry into the list by prepending it to
alt_odb_list. But we do _not_ modify alt_odb_tail.
This variable starts as NULL, and is a signal to the
alt_odb code that the list has not yet been
initialized.
We then call read_info_alternates on the submodule (to
recursively load its alternates), which will try to
append to that tail, assuming it has been initialized.
This causes us to segfault if it is NULL.
This rarely comes up in practice, because we will have
initialized the alt_odb any time we do an object lookup. So
you can trigger this only when:
- you try to access a submodule (e.g., a diff with
diff.submodule=log)
- the access happens before any other object has been
accessed (e.g., because the diff is between the working
tree and the index)
- the submodule contains an alternates file (so we try to
add an entry to the NULL alt_odb_tail)
To fix this, we just need to call prepare_alt_odb at the
start of the function (and if we have already initialized,
it is a noop).
Note that we can remove the prepare_alt_odb call from the
end. It is guaranteed to be a noop, since we will have
called it earlier.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
////////////////////////////////////////////////////////////////
GIT - the stupid content tracker
////////////////////////////////////////////////////////////////
"git" can mean anything, depending on your mood.
- random three-letter combination that is pronounceable, and not
actually used by any common UNIX command. The fact that it is a
mispronunciation of "get" may or may not be relevant.
- stupid. contemptible and despicable. simple. Take your pick from the
dictionary of slang.
- "global information tracker": you're in a good mood, and it actually
works for you. Angels sing, and a light suddenly fills the room.
- "goddamn idiotic truckload of sh*t": when it breaks
Git is a fast, scalable, distributed revision control system with an
unusually rich command set that provides both high-level operations
and full access to internals.
Git is an Open Source project covered by the GNU General Public License.
It was originally written by Linus Torvalds with help of a group of
hackers around the net. It is currently maintained by Junio C Hamano.
Please read the file INSTALL for installation instructions.
See Documentation/gittutorial.txt to get started, then see
Documentation/everyday.txt for a useful minimum set of commands, and
Documentation/git-commandname.txt for documentation of each command.
If git has been correctly installed, then the tutorial can also be
read with "man gittutorial" or "git help tutorial", and the
documentation of each command with "man git-commandname" or "git help
commandname".
CVS users may also want to read Documentation/gitcvs-migration.txt
("man gitcvs-migration" or "git help cvs-migration" if git is
installed).
Many Git online resources are accessible from http://git-scm.com/
including full documentation and Git related tools.
The user discussion and development of Git take place on the Git
mailing list -- everyone is welcome to post bug reports, feature
requests, comments and patches to git@vger.kernel.org (read
Documentation/SubmittingPatches for instructions on patch submission).
To subscribe to the list, send an email with just "subscribe git" in
the body to majordomo@vger.kernel.org. The mailing list archives are
available at http://marc.theaimsgroup.com/?l=git and other archival
sites.
The messages titled "A note from the maintainer", "What's in
git.git (stable)" and "What's cooking in git.git (topics)" and
the discussion following them on the mailing list give a good
reference for project status, development direction and
remaining tasks.
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