read-cache: force_verify_index_checksum
Teach git to skip verification of the SHA1-1 checksum at the end of
the index file in verify_hdr() which is called from read_index()
unless the "force_verify_index_checksum" global variable is set.
Teach fsck to force this verification.
The checksum verification is for detecting disk corruption, and for
small projects, the time it takes to compute SHA-1 is not that
significant, but for gigantic repositories this calculation adds
significant time to every command.
These effect can be seen using t/perf/p0002-read-cache.sh:
Test HEAD~1 HEAD
--------------------------------------------------------------------------------------
0002.1: read_cache/discard_cache 1000 times 0.66(0.44+0.20) 0.30(0.27+0.02) -54.5%
Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin/fsck.c b/builtin/fsck.c
index f76e416..b5e13a4 100644
--- a/builtin/fsck.c
+++ b/builtin/fsck.c
@@ -771,6 +771,7 @@
}
if (keep_cache_objects) {
+ verify_index_checksum = 1;
read_cache();
for (i = 0; i < active_nr; i++) {
unsigned int mode;
diff --git a/cache.h b/cache.h
index fbdf7a8..ed3c592 100644
--- a/cache.h
+++ b/cache.h
@@ -705,6 +705,8 @@
extern int hold_locked_index(struct lock_file *, int);
extern void set_alternate_index_output(const char *);
+extern int verify_index_checksum;
+
/* Environment bits from configuration mechanism */
extern int trust_executable_bit;
extern int trust_ctime;
diff --git a/read-cache.c b/read-cache.c
index e447751..008b335 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1371,6 +1371,9 @@
ondisk_cache_entry_extended_size(ce_namelen(ce)) : \
ondisk_cache_entry_size(ce_namelen(ce)))
+/* Allow fsck to force verification of the index checksum. */
+int verify_index_checksum;
+
static int verify_hdr(struct cache_header *hdr, unsigned long size)
{
git_SHA_CTX c;
@@ -1382,6 +1385,10 @@
hdr_version = ntohl(hdr->hdr_version);
if (hdr_version < INDEX_FORMAT_LB || INDEX_FORMAT_UB < hdr_version)
return error("bad index version %d", hdr_version);
+
+ if (!verify_index_checksum)
+ return 0;
+
git_SHA1_Init(&c);
git_SHA1_Update(&c, hdr, size - 20);
git_SHA1_Final(sha1, &c);
diff --git a/t/t1450-fsck.sh b/t/t1450-fsck.sh
index 33a51c9..677e15a 100755
--- a/t/t1450-fsck.sh
+++ b/t/t1450-fsck.sh
@@ -689,4 +689,17 @@
! grep $blob out
'
+test_expect_success 'detect corrupt index file in fsck' '
+ cp .git/index .git/index.backup &&
+ test_when_finished "mv .git/index.backup .git/index" &&
+ echo zzzzzzzz >zzzzzzzz &&
+ git add zzzzzzzz &&
+ sed -e "s/zzzzzzzz/yyyyyyyy/" .git/index >.git/index.yyy &&
+ mv .git/index.yyy .git/index &&
+ # Confirm that fsck detects invalid checksum
+ test_must_fail git fsck --cache &&
+ # Confirm that status no longer complains about invalid checksum
+ git status
+'
+
test_done
