pack-mtimes: support reading .mtimes files

To store the individual mtimes of objects in a cruft pack, introduce a
new `.mtimes` format that can optionally accompany a single pack in the
repository.

The format is defined in Documentation/technical/pack-format.txt, and
stores a 4-byte network order timestamp for each object in name (index)
order.

This patch prepares for cruft packs by defining the `.mtimes` format,
and introducing a basic API that callers can use to read out individual
mtimes.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 9 insertions, 1 deletions

diff --git a/object-store.h b/object-store.h
index bd2322ed8c..3c98028ce6 100644
--- a/object-store.h
+++ b/object-store.h
@@ -115,12 +115,20 @@ struct packed_git {
 		 freshened:1,
 		 do_not_close:1,
 		 pack_promisor:1,
-		 multi_pack_index:1;
+		 multi_pack_index:1,
+		 is_cruft:1;
 	unsigned char hash[GIT_MAX_RAWSZ];
 	struct revindex_entry *revindex;
 	const uint32_t *revindex_data;
 	const uint32_t *revindex_map;
 	size_t revindex_size;
+	/*
+	 * mtimes_map points at the beginning of the memory mapped region of
+	 * this pack's corresponding .mtimes file, and mtimes_size is the size
+	 * of that .mtimes file
+	 */
+	const uint32_t *mtimes_map;
+	size_t mtimes_size;
 	/* something like ".git/objects/pack/xxxxx.pack" */
 	char pack_name[FLEX_ARRAY]; /* more */
 };