On Thu, Feb 27, 2014 at 05:18:58PM +0700, Duy Nguyen wrote:
> On Thu, Feb 27, 2014 at 4:22 PM, Jeff King <p...@peff.net> wrote:
> > On Thu, Feb 27, 2014 at 04:10:12AM -0500, Jeff King wrote:
> >
> >> I also notice that check_shallow_file_for_update returns early if
> >> !is_shallow. Is that safe? Is it possible for another process to have
> >> made us shallow since the program began? In that case, we would have to
> >> stat() the file always, then complain if it exists and !is_shallow.
>
> I think it's safer to do it your way.
Yeah, I played around a bit and found that using "git fetch --depth" in
a non-shallow repo could run into this case.
> > if (stat(git_path("shallow"), &st))
> > die("shallow file was removed during fetch");
> > + else if (!is_shallow)
> > + die("shallow file appeared during fetch");
Note that this is wrong; when the file is missing (the first part of the
conditional), we need to check "is_shallow" before dying. Otherwise we
erroneously complain when creating the file for the first time.
As I was fixing it, though, I recalled that we had to write a similar
system for the packed-refs file. Fortunately, it was easy to reuse, and
I ended up with the patch below.
-- >8 --
Subject: shallow: use stat_validity to check for up-to-date file
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 <p...@peff.net>
---
shallow.c | 24 +++++++-----------------
1 file changed, 7 insertions(+), 17 deletions(-)
diff --git a/shallow.c b/shallow.c
index 75da07a..9668b39 100644
--- a/shallow.c
+++ b/shallow.c
@@ -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
--
1.8.5.2.500.g8060133
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