btrfs qgroup assign -> "ERROR: bad relation requested"

[Tomasz Chmielewski <mangoo@wpkg.org>]

I'm trying to use this feature of qgroup:

btrfs qgroup assign <srcid> <destid> <path>
    Assigns the lower level qgroup src to the higher level qgroup dest
    in the btrfs found in <path>. It is used to build qgroup
    hierarchies.


However, I fail to understand how this feature should work, and I'm
getting "ERROR: bad relation requested":

# btrfs sub create test1
Create subvolume './test1'

# btrfs sub create test2
Create subvolume './test2'

# btrfs sub list /mnt/lxc2 | grep test
ID 1177 gen 85131 top level 5 path test1
ID 1178 gen 85132 top level 5 path test2

# btrfs qgroup show /mnt/lxc2
0/1177 4096 4096
0/1178 4096 4096

# btrfs qgroup assign 1177 1178 /mnt/lx2
ERROR: bad relation requested '/mnt/lx2'


Could anyone give examples of proper usage of this feature?

This is Linux 3.10.


-- 
Tomasz Chmielewski
http://wpkg.org