Steps to reproduce:
# mkfs.btrfs -f /dev/sda9
# mount /dev/sda9 /mnt
# dd if=/dev/zero of=/mnt/data bs=1M count=1
# btrfs restore -r /dev/sda9 -r 2 -o /tmp
If users don't input a valid fs/file root objectid, btrfs restore still
continue and don't restore anything, this is unfriendly, we could
check it firstly.
Signed-off-by: Wang Shilong <wangsl.fnst@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.cz>