On Tue, 10 Jun 2008, Ben Lynn wrote:
>
> Unfortunately, the solution isn't perfect. Try this:
Heh.
That's just because our "smudge_racily_clean_entry()" uses 0 as the magic
smudging size.
You can fix this multiple ways. One would be to pick another size that is
simply less likely (eg ~0 instead), which leaves the theoretical race, and
just makes it practically impossible to hit (not that I think it's very
practical to hit already).
The other approach is to know that an empty blob always has a very
specific SHA1. Here's an trial patch.
Linus
---
read-cache.c | 16 ++++++++++++++++
1 files changed, 16 insertions(+), 0 deletions(-)
diff --git a/read-cache.c b/read-cache.c
index 8e5fbb6..f83de8c 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -138,6 +138,16 @@ static int ce_modified_check_fs(struct cache_entry *ce, struct stat *st)
return 0;
}
+static int is_empty_blob_sha1(const unsigned char *sha1)
+{
+ static const unsigned char empty_blob_sha1[20] = {
+ 0xe6,0x9d,0xe2,0x9b,0xb2,0xd1,0xd6,0x43,0x4b,0x8b,
+ 0x29,0xae,0x77,0x5a,0xd8,0xc2,0xe4,0x8c,0x53,0x91
+ };
+
+ return !hashcmp(sha1, empty_blob_sha1);
+}
+
static int ce_match_stat_basic(struct cache_entry *ce, struct stat *st)
{
unsigned int changed = 0;
@@ -193,6 +203,12 @@ static int ce_match_stat_basic(struct cache_entry *ce, struct stat *st)
if (ce->ce_size != (unsigned int) st->st_size)
changed |= DATA_CHANGED;
+ /* Racily smudged entry? */
+ if (!ce->ce_size) {
+ if (!is_empty_blob_sha1(ce->sha1))
+ changed |= DATA_CHANGED;
+ }
+
return changed;
}
--
To unsubscribe from this list: send the line "unsubscribe git" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
