52db8f099a
When listing mounted devices, list the subvolid of the mountpoint, since a single btrfs disk can be mounted multiple times using subvolumes. Additionally tag snapshots with subvolid to keep track of this. This will break current usage, but users can manually tag old snapshots with subvolid's in order to migrate them. Add -s/--subvolid command line parameter to pass specified subvolid to program. Cf. #45.