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shallow: use stat_validity to check for up-to-date file

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When we are about to write the shallow file, we check that
it has not changed since we last read it. Instead of
hand-rolling this, we can use stat_validity. This is built
around the index stat-check, so it is more robust than just
checking the mtime, as we do now (it uses the same check as
we do for index files).

The new code also handles the case of a shallow file
appearing unexpectedly. With the current code, two
simultaneous processes making us shallow (e.g., two "git
fetch --depth=1" running at the same time in a non-shallow
repository) can race to overwrite each other.

As a bonus, we also remove a race in determining the stat
information of what we read (we stat and then open, leaving
a race window; instead we should open and then fstat the
descriptor).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Jeff King 2014-02-27 05:56:31 -05:00 committed by Junio C Hamano
parent 5f95c9f850
commit 0cc77c386c
1 changed files with 7 additions and 17 deletions
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24
shallow.c
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@ -10,7 +10,7 @@
#include "commit-slab.h"
static int is_shallow = -1;
static struct stat shallow_stat;
static struct stat_validity shallow_stat;
static char *alternate_shallow_file;
void set_alternate_shallow_file(const char *path, int override)
@ -52,12 +52,12 @@ int is_repository_shallow(void)
* shallow file should be used. We could just open it and it
* will likely fail. But let's do an explicit check instead.
*/
if (!*path ||
stat(path, &shallow_stat) ||
(fp = fopen(path, "r")) == NULL) {
if (!*path || (fp = fopen(path, "r")) == NULL) {
stat_validity_clear(&shallow_stat);
is_shallow = 0;
return is_shallow;
}
stat_validity_update(&shallow_stat, fileno(fp));
is_shallow = 1;
while (fgets(buf, sizeof(buf), fp)) {
@ -137,21 +137,11 @@ struct commit_list *get_shallow_commits(struct object_array *heads, int depth,
void check_shallow_file_for_update(void)
{
struct stat st;
if (!is_shallow)
return;
else if (is_shallow == -1)
if (is_shallow == -1)
die("BUG: shallow must be initialized by now");
if (stat(git_path("shallow"), &st))
die("shallow file was removed during fetch");
else if (st.st_mtime != shallow_stat.st_mtime
#ifdef USE_NSEC
|| ST_MTIME_NSEC(st) != ST_MTIME_NSEC(shallow_stat)
#endif
)
die("shallow file was changed during fetch");
if (!stat_validity_check(&shallow_stat, git_path("shallow")))
die("shallow file has changed since we read it");
}
#define SEEN_ONLY 1