[PATCH] fix over-eager caching in sha1_file_name
- From
Jeff King <peff@peff.net>
- Date
- May 22, 2010, 06:43 UTC
- Message-ID
- <20100522064308.GA11335@coredump.intra.peff.net>
- In-Reply-To
- <20100522054852.GB29118@coredump.intra.peff.net>
On Sat, May 22, 2010 at 01:48:52AM -0400, Jeff King wrote:
Show 20 quoted lines
> I would have thought that worked, assuming you were in /some/dir. And > oddly, _some_ stuff works. I tried: > > mkdir repo && cd repo && git init > echo content >file && git add . && git commit -m file > git archive --format=tar --prefix=work/ HEAD | tar -C .. -xf - > > to create the situation. Running > > cd repo > git --work-tree=$PWD/../work diff-files > git --work-tree=$PWD/../work diff > > works as expected (the first one notices stat-dirtiness, and the second > shows an empty diff). But then I get: > > $ git --work-tree=$PWD/../work reset --hard > fatal: unable to read tree ea394696ee1f7f5b55ca0d97d37748933cf39095 > > So there is clearly a bug. I'll investigate.
Ugh. This code dates back to the first two weeks of git, but didn't become a bug until sometime in the intervening 5 years. See below for the explanation and fix.
-- >8 -- Subject: [PATCH] fix over-eager caching in sha1_file_name
This function takes a sha1 and produces a loose object filename. It caches the location of the object directory so that it can fill the sha1 information directly without allocating a new buffer (and in its original incarnation, without calling getenv(), though these days we cache that with the code in environment.c).
This cached base directory can become stale, however, if in a single process git changes the location of the object directory (e.g., by running setup_work_tree, which will chdir to the new worktree).
In most cases this isn't a problem, because we tend to set up the git repository location and do any chdir()s before actually looking up any objects, so the first lookup will cache the correct location. In the case of reset --hard, however, we do something like:
1. look up the commit object
2. notice we are doing --hard, run setup_work_tree
3. look up the tree object to reset
Step (3) fails because our cache object directory value is bogus.
This patch takes the minimalist fix. It retains the caching, but checks the validity of our object directory against the one cached in environment.c, which adds only a single function call and a pointer comparison to the fast path.
Signed-off-by: Jeff King <peff@peff.net> --- As I noted above, this is the minimal fix. I think it would be more readable, though, to simply remove this caching layer altogether and use a static buffer. I suspect the original was just trying to avoid the slow getenv() call, which is no longer an issue now. We can probably afford an snprintf. I'll post that patch shortly.
sha1_file.c | 6 ++++-- 1 files changed, 4 insertions(+), 2 deletions(-)
diff --git a/sha1_file.c b/sha1_file.c index d8e61a6..f047b3c 100644 --- a/sha1_file.c +++ b/sha1_file.c @@ -103,10 +103,12 @@ static void fill_sha1_path(char *pathbuf, const unsigned char *sha1) char *sha1_file_name(const unsigned char *sha1) { static char *name, *base; + static const char *sha1_file_directory; - if (!base) { - const char *sha1_file_directory = get_object_directory(); + if (!base || sha1_file_directory != get_object_directory()) { + sha1_file_directory = get_object_directory(); int len = strlen(sha1_file_directory); + free(base); base = xmalloc(len + 60); memcpy(base, sha1_file_directory, len); memset(base+len, 0, 60);
-- 1.7.1.352.gb63a7.dirty