md: override md superblock recovery_offset for journal device

Journal device stores data in a log structure. We need record the log
start. Here we override md superblock recovery_offset for this purpose.
This field of a journal device is meaningless otherwise.
Signed-off-by: Shaohua Li <shli@fb.com>
Signed-off-by: NeilBrown <neilb@suse.com>

drivers/md/md.c

@@ -1646,6 +1646,7 @@ static int super_1_validate(struct mddev *mddev, struct md_rdev *rdev)
 				return -EINVAL;
 			}
 			set_bit(Journal, &rdev->flags);
+			rdev->journal_tail = le64_to_cpu(sb->journal_tail);
 			break;
 		default:
 			rdev->saved_raid_disk = role;
@@ -1721,6 +1722,9 @@ static void super_1_sync(struct mddev *mddev, struct md_rdev *rdev)
 			sb->feature_map |=
 				cpu_to_le32(MD_FEATURE_RECOVERY_BITMAP);
 	}
+	/* Note: recovery_offset and journal_tail share space  */
+	if (test_bit(Journal, &rdev->flags))
+		sb->journal_tail = cpu_to_le64(rdev->journal_tail);
 	if (test_bit(Replacement, &rdev->flags))
 		sb->feature_map |=
 			cpu_to_le32(MD_FEATURE_REPLACEMENT);
@@ -8097,6 +8101,8 @@ static int remove_and_add_spares(struct mddev *mddev,
 			continue;
 		if (test_bit(Faulty, &rdev->flags))
 			continue;
+		if (test_bit(Journal, &rdev->flags))
+			continue;
 		if (mddev->ro &&
 		    ! (rdev->saved_raid_disk >= 0 &&
 		       !test_bit(Bitmap_sync, &rdev->flags)))

drivers/md/md.h

@@ -87,10 +87,16 @@ struct md_rdev {
 					 * array and could again if we did a partial
 					 * resync from the bitmap
 					 */
+	union {
 		sector_t recovery_offset;/* If this device has been partially
 					 * recovered, this is where we were
 					 * up to.
 					 */
+		sector_t journal_tail;	/* If this device is a journal device,
+					 * this is the journal tail (journal
+					 * recovery start point)
+					 */
+	};
 
 	atomic_t	nr_pending;	/* number of pending requests.
 					 * only maintained for arrays that

include/uapi/linux/raid/md_p.h

@@ -258,7 +258,10 @@ struct mdp_superblock_1 {
 	__le64	data_offset;	/* sector start of data, often 0 */
 	__le64	data_size;	/* sectors in this device that can be used for data */
 	__le64	super_offset;	/* sector start of this superblock */
+	union {
 		__le64	recovery_offset;/* sectors before this offset (from data_offset) have been recovered */
+		__le64	journal_tail;/* journal tail of journal device (from data_offset) */
+	};
 	__le32	dev_number;	/* permanent identifier of this  device - not role in raid */
 	__le32	cnt_corrected_read; /* number of read errors that were corrected by re-writing */
 	__u8	device_uuid[16]; /* user-space setable, ignored by kernel */