btrfs: Factor out metadata_uuid code from find_fsid.

find_fsid became rather hairy with the introduction of metadata uuid
changing feature. Alleviate this by factoring out the metadata uuid
specific code in a dedicated function which deals with finding
correct fsid for a device with changed uuid.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Su Yue <Damenly_Su@gmx.com>
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/volumes.c

@@ -441,7 +441,27 @@ static noinline struct btrfs_fs_devices *find_fsid(
 
 	ASSERT(fsid);
 
+	/* Handle non-split brain cases */
+	list_for_each_entry(fs_devices, &fs_uuids, fs_list) {
 		if (metadata_fsid) {
+			if (memcmp(fsid, fs_devices->fsid, BTRFS_FSID_SIZE) == 0
+			    && memcmp(metadata_fsid, fs_devices->metadata_uuid,
+				      BTRFS_FSID_SIZE) == 0)
+				return fs_devices;
+		} else {
+			if (memcmp(fsid, fs_devices->fsid, BTRFS_FSID_SIZE) == 0)
+				return fs_devices;
+		}
+	}
+	return NULL;
+}
+
+static struct btrfs_fs_devices *find_fsid_with_metadata_uuid(
+				struct btrfs_super_block *disk_super)
+{
+
+	struct btrfs_fs_devices *fs_devices;
+
 	/*
 	 * Handle scanned device having completed its fsid change but
 	 * belonging to a fs_devices that was created by first scanning
@@ -450,7 +470,7 @@ static noinline struct btrfs_fs_devices *find_fsid(
 	 */
 	list_for_each_entry(fs_devices, &fs_uuids, fs_list) {
 		if (fs_devices->fsid_change &&
-			    memcmp(metadata_fsid, fs_devices->fsid,
+		    memcmp(disk_super->metadata_uuid, fs_devices->fsid,
 			   BTRFS_FSID_SIZE) == 0 &&
 		    memcmp(fs_devices->fsid, fs_devices->metadata_uuid,
 			   BTRFS_FSID_SIZE) == 0) {
@@ -467,28 +487,16 @@ static noinline struct btrfs_fs_devices *find_fsid(
 		if (fs_devices->fsid_change &&
 		    memcmp(fs_devices->metadata_uuid,
 			   fs_devices->fsid, BTRFS_FSID_SIZE) != 0 &&
-			    memcmp(metadata_fsid, fs_devices->metadata_uuid,
+		    memcmp(disk_super->metadata_uuid, fs_devices->metadata_uuid,
 			   BTRFS_FSID_SIZE) == 0) {
 			return fs_devices;
 		}
 	}
-	}
 
-	/* Handle non-split brain cases */
-	list_for_each_entry(fs_devices, &fs_uuids, fs_list) {
-		if (metadata_fsid) {
-			if (memcmp(fsid, fs_devices->fsid, BTRFS_FSID_SIZE) == 0
-			    && memcmp(metadata_fsid, fs_devices->metadata_uuid,
-				      BTRFS_FSID_SIZE) == 0)
-				return fs_devices;
-		} else {
-			if (memcmp(fsid, fs_devices->fsid, BTRFS_FSID_SIZE) == 0)
-				return fs_devices;
-		}
-	}
-	return NULL;
+	return find_fsid(disk_super->fsid, disk_super->metadata_uuid);
 }
 
+
 static int
 btrfs_get_bdev_and_sb(const char *device_path, fmode_t flags, void *holder,
 		      int flush, struct block_device **bdev,
@@ -744,8 +752,7 @@ static noinline struct btrfs_device *device_list_add(const char *path,
 		else
 			fs_devices = find_fsid_changed(disk_super);
 	} else if (has_metadata_uuid) {
-		fs_devices = find_fsid(disk_super->fsid,
-				       disk_super->metadata_uuid);
+		fs_devices = find_fsid_with_metadata_uuid(disk_super);
 	} else {
 		fs_devices = find_fsid(disk_super->fsid, NULL);
 	}