[PATCH v8] read-cache: force_verify_index_checksum
From: Jeff Hostetler <jeffhost@microsoft.com>
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>
---
builtin/fsck.c | 1 +
cache.h | 2 ++
read-cache.c | 7 +++++++
t/t1450-fsck.sh | 32 ++++++++++++++++++++++++++++++++
4 files changed, 42 insertions(+)
Show changes to 4 files +42 −0
builtin/fsck.c, cache.h, read-cache.c, t/t1450-fsck.sh
diff --git a/builtin/fsck.c b/builtin/fsck.c
index 1a5cacc..5512d06 100644
--- a/builtin/fsck.c
+++ b/builtin/fsck.c
@@ -771,6 +771,7 @@ int cmd_fsck(int argc, const char **argv, const char *prefix)
}
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 80b6372..87f13bf 100644
--- a/cache.h
+++ b/cache.h
@@ -685,6 +685,8 @@ extern void update_index_if_able(struct index_state *, struct lock_file *);
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 9054369..c4205aa 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1371,6 +1371,9 @@ struct ondisk_cache_entry_extended {
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 @@ static int verify_hdr(struct cache_header *hdr, unsigned long size)
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..eff1cd6 100755
--- a/t/t1450-fsck.sh
+++ b/t/t1450-fsck.sh
@@ -689,4 +689,36 @@ test_expect_success 'bogus head does not fallback to all heads' '
! grep $blob out
'
+# Corrupt the checksum on the index.
+# Add 1 to the last byte in the SHA.
+corrupt_index_checksum () {
+ perl -w -e '
+ use Fcntl ":seek";
+ open my $fh, "+<", ".git/index" or die "open: $!";
+ binmode $fh;
+ seek $fh, -1, SEEK_END or die "seek: $!";
+ read $fh, my $in_byte, 1 or die "read: $!";
+
+ $in_value = unpack("C", $in_byte);
+ $out_value = ($in_value + 1) & 255;
+
+ $out_byte = pack("C", $out_value);
+
+ seek $fh, -1, SEEK_END or die "seek: $!";
+ print $fh $out_byte;
+ close $fh or die "close: $!";
+ '
+}
+
+# Corrupt the checksum on the index and then
+# verify that only fsck notices.
+test_expect_success 'detect corrupt index file in fsck' '
+ cp .git/index .git/index.backup &&
+ test_when_finished "mv .git/index.backup .git/index" &&
+ corrupt_index_checksum &&
+ test_must_fail git fsck --cache 2>expect &&
+ grep "bad index file" expect &&
+ git status
+'
+
test_done
--
2.9.3
