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 f76e4163abbac825c00111504a040f8091d967d3..b5e13a45560f9338a65191c22d213f33052bf9b9 100644 (file)
--- 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 fbdf7a815a1f6b56df82877d0a5b2febe5a7d095..ed3c5927cc5a3fdb6897903433327bde88656ae8 100644 (file)
--- a/cache.h
+++ b/cache.h
@@ -705,6 +705,8 @@ 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 e44775182392c5672fd6ec84eb954db339e5a1ea..008b335844c48fad9408452c11bd921d7b9b0b44 100644 (file)
--- 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 33a51c9a67fe833e31e51099f7568b64be385d07..677e15a7a43ba774f7e54486cd8ac4c0565475ff 100755 (executable)
--- a/t/t1450-fsck.sh
+++ b/t/t1450-fsck.sh
@@ -689,4 +689,17 @@ test_expect_success 'bogus head does not fallback to all heads' '
        ! 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