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, 17 insertions, 2 deletions

diff --git a/packfile.c b/packfile.c
index 835b2d2716..fc0245fbab 100644
--- a/packfile.c
+++ b/packfile.c
@@ -334,12 +334,22 @@ static void close_pack_revindex(struct packed_git *p)
 	p->revindex_data = NULL;
 }
 
+static void close_pack_mtimes(struct packed_git *p)
+{
+	if (!p->mtimes_map)
+		return;
+
+	munmap((void *)p->mtimes_map, p->mtimes_size);
+	p->mtimes_map = NULL;
+}
+
 void close_pack(struct packed_git *p)
 {
 	close_pack_windows(p);
 	close_pack_fd(p);
 	close_pack_index(p);
 	close_pack_revindex(p);
+	close_pack_mtimes(p);
 	oidset_clear(&p->bad_objects);
 }
 
@@ -363,7 +373,7 @@ void close_object_store(struct raw_object_store *o)
 
 void unlink_pack_path(const char *pack_name, int force_delete)
 {
-	static const char *exts[] = {".pack", ".idx", ".rev", ".keep", ".bitmap", ".promisor"};
+	static const char *exts[] = {".pack", ".idx", ".rev", ".keep", ".bitmap", ".promisor", ".mtimes"};
 	int i;
 	struct strbuf buf = STRBUF_INIT;
 	size_t plen;
@@ -718,6 +728,10 @@ struct packed_git *add_packed_git(const char *path, size_t path_len, int local)
 	if (!access(p->pack_name, F_OK))
 		p->pack_promisor = 1;
 
+	xsnprintf(p->pack_name + path_len, alloc - path_len, ".mtimes");
+	if (!access(p->pack_name, F_OK))
+		p->is_cruft = 1;
+
 	xsnprintf(p->pack_name + path_len, alloc - path_len, ".pack");
 	if (stat(p->pack_name, &st) || !S_ISREG(st.st_mode)) {
 		free(p);
@@ -869,7 +883,8 @@ static void prepare_pack(const char *full_name, size_t full_name_len,
 	    ends_with(file_name, ".pack") ||
 	    ends_with(file_name, ".bitmap") ||
 	    ends_with(file_name, ".keep") ||
-	    ends_with(file_name, ".promisor"))
+	    ends_with(file_name, ".promisor") ||
+	    ends_with(file_name, ".mtimes"))
 		string_list_append(data->garbage, full_name);
 	else
 		report_garbage(PACKDIR_FILE_GARBAGE, full_name);