Description of problem:

When nova fails to attach a volume to an instance, it will attempt to disconnect it. On a compute node with ceph 14.x (the version currently packaged on RHEL 8.2), this fails:

  Traceback (most recent call last):
    File "/usr/lib/python3.6/site-packages/nova/virt/block_device.py", line 582, in _volume_attach
      device_type=self['device_type'], encryption=encryption)
    File "/usr/lib/python3.6/site-packages/nova/virt/libvirt/driver.py", line 1806, in attach_volume
      encryption=encryption)
    File "/usr/lib/python3.6/site-packages/nova/virt/libvirt/driver.py", line 1594, in _connect_volume
      vol_driver.disconnect_volume(connection_info, instance)
    File "/usr/lib/python3.6/site-packages/nova/virt/libvirt/volume/net.py", line 96, in disconnect_volume
      self.connector.disconnect_volume(connection_info['data'], None)
    File "/usr/lib/python3.6/site-packages/os_brick/utils.py", line 150, in trace_logging_wrapper
      result = f(*args, **kwargs)
    File "/usr/lib/python3.6/site-packages/os_brick/initiator/connectors/rbd.py", line 248, in disconnect_volume
      root_device = self._find_root_device(connection_properties)
    File "/usr/lib/python3.6/site-packages/os_brick/initiator/connectors/rbd.py", line 229, in _find_root_device
      for index, mapping in jsonutils.loads(out).items():
  AttributeError: 'list' object has no attribute 'items'

The culprit appear to have been a change introduced in ceph v13.2.0 (Mimic). From [1].

  The rbd CLI’s showmapped JSON and XML output has changed.

This specific change appear to have been [2].

There appear to be additional issues here with regards to why the *attach* failed, but I can track those separately.

[1] https://docs.ceph.com/docs/master/releases/mimic/#upgrade-compatibility-notes
[2] https://github.com/ceph/ceph/commit/de97a3be483242eab14175a3cc3408df34d5c19a

Version-Release number of selected component (if applicable):

  python3-os-brick.noarch   2.10.3-0.20200605063441.55fc998.el8ost
  python3-nova.noarch       1:20.2.1-0.20200528080027.1e95025.el8ost

How reproducible:

  Always

Steps to Reproduce:
1. Attempt to attach an encrypted volume to an existing instance

Actual results:

It will fail (for reasons not covered here). When nova attempts to clean up after itself, the call to 'disconnect_volume' will also fail.

Expected results:

The volume should be disconnected.

Additional info:

This is being tracked upstream via https://bugs.launchpad.net/os-brick/+bug/1884052