Add parent volume as a parameter so we can waslk back up the tree.
Add __str__()
Add rootpath property.
Don't allow recursive (deep) subvolume creation.
btrfs subvolume list -o has a bug in Ubuntu Trusty Tahr.  With a suitable patch correct the parsing of the output.

https://bugs.launchpad.net/ubuntu/+source/btrfs-tools/+bug/1335796
Call the command on delete().  Add snapshot() and reset().