Btrfs: cleanup unused latest_devid and latest_trans in fs_devices

The member variants - latest_devid and latest_trans - of fs_devices structure
are set, but no one use them to do anything. so remove them.
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>

fs/btrfs/volumes.c

@@ -475,14 +475,13 @@ static noinline int device_list_add(const char *path,
 			return PTR_ERR(fs_devices);
 
 		list_add(&fs_devices->list, &fs_uuids);
-		fs_devices->latest_devid = devid;
-		fs_devices->latest_trans = found_transid;
 
 		device = NULL;
 	} else {
 		device = __find_device(&fs_devices->devices, devid,
 				       disk_super->dev_item.uuid);
 	}
+
 	if (!device) {
 		if (fs_devices->opened)
 			return -EBUSY;
@@ -567,10 +566,6 @@ static noinline int device_list_add(const char *path,
 	if (!fs_devices->opened)
 		device->generation = found_transid;
 
-	if (found_transid > fs_devices->latest_trans) {
-		fs_devices->latest_devid = devid;
-		fs_devices->latest_trans = found_transid;
-	}
 	*fs_devices_ret = fs_devices;
 
 	return ret;
@@ -586,8 +581,6 @@ static struct btrfs_fs_devices *clone_fs_devices(struct btrfs_fs_devices *orig)
 	if (IS_ERR(fs_devices))
 		return fs_devices;
 
-	fs_devices->latest_devid = orig->latest_devid;
-	fs_devices->latest_trans = orig->latest_trans;
 	fs_devices->total_devices = orig->total_devices;
 
 	/* We have held the volume lock, it is safe to get the devices. */
@@ -626,10 +619,7 @@ void btrfs_close_extra_devices(struct btrfs_fs_info *fs_info,
 			       struct btrfs_fs_devices *fs_devices, int step)
 {
 	struct btrfs_device *device, *next;
-
-	struct block_device *latest_bdev = NULL;
-	u64 latest_devid = 0;
-	u64 latest_transid = 0;
+	struct btrfs_device *latest_dev = NULL;
 
 	mutex_lock(&uuid_mutex);
 again:
@@ -637,11 +627,9 @@ void btrfs_close_extra_devices(struct btrfs_fs_info *fs_info,
 	list_for_each_entry_safe(device, next, &fs_devices->devices, dev_list) {
 		if (device->in_fs_metadata) {
 			if (!device->is_tgtdev_for_dev_replace &&
-			    (!latest_transid ||
-			     device->generation > latest_transid)) {
-				latest_devid = device->devid;
-				latest_transid = device->generation;
-				latest_bdev = device->bdev;
+			    (!latest_dev ||
+			     device->generation > latest_dev->generation)) {
+				latest_dev = device;
 			}
 			continue;
 		}
@@ -683,9 +671,7 @@ void btrfs_close_extra_devices(struct btrfs_fs_info *fs_info,
 		goto again;
 	}
 
-	fs_devices->latest_bdev = latest_bdev;
-	fs_devices->latest_devid = latest_devid;
-	fs_devices->latest_trans = latest_transid;
+	fs_devices->latest_bdev = latest_dev->bdev;
 
 	mutex_unlock(&uuid_mutex);
 }
@@ -800,11 +786,9 @@ static int __btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
 	struct block_device *bdev;
 	struct list_head *head = &fs_devices->devices;
 	struct btrfs_device *device;
-	struct block_device *latest_bdev = NULL;
+	struct btrfs_device *latest_dev = NULL;
 	struct buffer_head *bh;
 	struct btrfs_super_block *disk_super;
-	u64 latest_devid = 0;
-	u64 latest_transid = 0;
 	u64 devid;
 	int seeding = 1;
 	int ret = 0;
@@ -832,11 +816,9 @@ static int __btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
 			goto error_brelse;
 
 		device->generation = btrfs_super_generation(disk_super);
-		if (!latest_transid || device->generation > latest_transid) {
-			latest_devid = devid;
-			latest_transid = device->generation;
-			latest_bdev = bdev;
-		}
+		if (!latest_dev ||
+		    device->generation > latest_dev->generation)
+			latest_dev = device;
 
 		if (btrfs_super_flags(disk_super) & BTRFS_SUPER_FLAG_SEEDING) {
 			device->writeable = 0;
@@ -879,9 +861,7 @@ static int __btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
 	}
 	fs_devices->seeding = seeding;
 	fs_devices->opened = 1;
-	fs_devices->latest_bdev = latest_bdev;
-	fs_devices->latest_devid = latest_devid;
-	fs_devices->latest_trans = latest_transid;
+	fs_devices->latest_bdev = latest_dev->bdev;
 	fs_devices->total_rw_bytes = 0;
 out:
 	return ret;

fs/btrfs/volumes.h

@@ -119,9 +119,6 @@ struct btrfs_device {
 struct btrfs_fs_devices {
 	u8 fsid[BTRFS_FSID_SIZE]; /* FS specific uuid */
 
-	/* the device with this id has the most recent copy of the super */
-	u64 latest_devid;
-	u64 latest_trans;
 	u64 num_devices;
 	u64 open_devices;
 	u64 rw_devices;