btrfs: Add read_backup_root

	       sizeof(*root_backup) * BTRFS_NUM_BACKUP_ROOTS);

}

/*

 * read_backup_root - Reads a backup root based on the passed priority. Prio 0

 * is the newest, prio 1/2/3 are 2nd newest/3rd newest/4th (oldest) backup roots

 *

 * fs_info - filesystem whose backup roots need to be read

 * priority - priority of backup root required

 *

 * Returns backup root index on success and -EINVAL otherwise.

 */

static int read_backup_root(struct btrfs_fs_info *fs_info, u8 priority)

{

	int backup_index = find_newest_super_backup(fs_info);

	struct btrfs_super_block *super = fs_info->super_copy;

	struct btrfs_root_backup *root_backup;

	if (priority < BTRFS_NUM_BACKUP_ROOTS && backup_index >= 0) {

		if (priority == 0)

			return backup_index;

		backup_index = backup_index + BTRFS_NUM_BACKUP_ROOTS - priority;

		backup_index %= BTRFS_NUM_BACKUP_ROOTS;

	} else {

		return -EINVAL;

	}

	root_backup = super->super_roots + backup_index;

	btrfs_set_super_generation(super,

				   btrfs_backup_tree_root_gen(root_backup));

	btrfs_set_super_root(super, btrfs_backup_tree_root(root_backup));

	btrfs_set_super_root_level(super,

				   btrfs_backup_tree_root_level(root_backup));

	btrfs_set_super_bytes_used(super, btrfs_backup_bytes_used(root_backup));

	/*

	 * Fixme: the total bytes and num_devices need to match or we should

	 * need a fsck

	 */

	btrfs_set_super_total_bytes(super, btrfs_backup_total_bytes(root_backup));

	btrfs_set_super_num_devices(super, btrfs_backup_num_devices(root_backup));

	return backup_index;

}

/*

 * this copies info out of the root backup array and back into

 * the in-memory super block.  It is meant to help iterate through