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From: git@jeffhostetler.com
To: git@vger.kernel.org
Cc: gitster@pobox.com, peff@peff.net,
	Jeff Hostetler <jeffhost@microsoft.com>
Subject: [PATCH v7] read-cache: force_verify_index_checksum
Date: Fri, 14 Apr 2017 20:32:21 +0000	[thread overview]
Message-ID: <20170414203221.43015-2-git@jeffhostetler.com> (raw)
In-Reply-To: <20170414203221.43015-1-git@jeffhostetler.com>

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 | 13 +++++++++++++
 4 files changed, 23 insertions(+)

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..677e15a 100755
--- 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
-- 
2.9.3


  reply	other threads:[~2017-04-14 20:32 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-04-14 20:32 [PATCH v7] read-cache: call verify_hdr() in a background thread git
2017-04-14 20:32 ` git [this message]
2017-04-24 17:26   ` [PATCH v7] read-cache: force_verify_index_checksum Johannes Sixt
2017-04-24 18:39     ` Jeff Hostetler
2017-04-25  2:10       ` Junio C Hamano
2017-04-25 21:04         ` Johannes Schindelin
2017-04-26  3:25           ` Junio C Hamano
2017-05-08  9:45   ` Christian Couder
2017-05-08 16:50     ` Jeff Hostetler
2017-05-08 20:03       ` Christian Couder
2017-05-08 20:18         ` Jeff Hostetler
2017-05-09  2:11           ` Junio C Hamano
2017-05-09  5:27     ` Junio C Hamano

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