How can I delete a apt-btrfs-snapshot when the error is "Directory not empty?"

Question

There is one snapshot created by apt-btrfs-snapshot that won't delete

  Delete subvolume '/tmp/foo/@apt-snapshot-2013-04-XX_1X:3X:XX'
  ERROR: cannot delete '/tmp/foo/@apt-snapshot-2013-04-XX_1X:3X:XX' - Directory not empty

How can I delete it?

Answer 1

Answering my own question:

Problem was there was a subvolume within a subvolume. You need to delete all inner subvols before deleting containing vol.

btrfs subvol delete /tmp/foo/@apt-snapshot-2013-04-XX_1X:3X:XX/@ btrfs subvol delete /tmp/foo/@apt-snapshot-2013-04-XX_1X:3X:XX