Comment # 5 on bug 957198 from Kristoffer Gronlund

I'm having a similar problem:

# btrfs subvolume show '/var/lib/libvirt/images'
/var/lib/libvirt/images
    Name:             images
    UUID:             eee9ba57-5838-2b49-b21c-0799d1ddd4d4
    Parent UUID:         -
    Received UUID:         -
    Creation time:         2016-05-30 17:55:24 +0200
    Subvolume ID:         268
    Generation:         1990
    Gen at creation:     24
    Parent ID:         257
    Top level ID:         257
    Flags:             -
    Snapshot(s):
# btrfs subvolume delete '/var/lib/libvirt/images'
Delete subvolume (no-commit): '/var/lib/libvirt/images'
ERROR: cannot delete '/var/lib/libvirt/images': Invalid argument
# umount /var/lib/libvirt/images
# btrfs subvolume delete '/var/lib/libvirt/images'
ERROR: not a subvolume: /var/lib/libvirt/images

The help for btrfs subvolume is no help at all in figuring out if I'm using the
command correctly..