md: skip resync for raid array with journal

If a raid array has journal, the journal can guarantee the consistency,
we can skip resync after a unclean shutdown. The exception is raid
creation or user initiated resync, which we still do a raid resync.
Signed-off-by: Shaohua Li <shli@fb.com>
Signed-off-by: NeilBrown <neilb@suse.com>

drivers/md/md.c

@@ -1647,6 +1647,8 @@ static int super_1_validate(struct mddev *mddev, struct md_rdev *rdev)
 			}
 			set_bit(Journal, &rdev->flags);
 			rdev->journal_tail = le64_to_cpu(sb->journal_tail);
+			if (mddev->recovery_cp == MaxSector)
+				set_bit(MD_JOURNAL_CLEAN, &mddev->flags);
 			break;
 		default:
 			rdev->saved_raid_disk = role;
@@ -1689,6 +1691,8 @@ static void super_1_sync(struct mddev *mddev, struct md_rdev *rdev)
 	sb->events = cpu_to_le64(mddev->events);
 	if (mddev->in_sync)
 		sb->resync_offset = cpu_to_le64(mddev->recovery_cp);
+	else if (test_bit(MD_JOURNAL_CLEAN, &mddev->flags))
+		sb->resync_offset = cpu_to_le64(MaxSector);
 	else
 		sb->resync_offset = cpu_to_le64(0);
 

drivers/md/md.h

@@ -232,6 +232,7 @@ struct mddev {
 #define MD_STILL_CLOSED	4	/* If set, then array has not been opened since
 				 * md_ioctl checked on it.
 				 */
+#define MD_JOURNAL_CLEAN 5	/* A raid with journal is already clean */
 
 	int				suspended;
 	atomic_t			active_io;