New fix for rbd connector to work with ceph octopus

Found while testing cinder-backup with ceph on Ubuntu Focal, which
installs ceph Octopus.  Octopus apparently enforces the requirement
that the config file contain a '[global]' section for general
requirements.  The '[global]' section goes back at least to ceph
Hammer [0], so we will simply add it to the temporary ceph config
file that os-brick generates in the RBDConnector class.

[0] https://docs.ceph.com/docs/hammer/rados/configuration/mon-config-ref/

Co-authored-by: Alex Kavanagh <alex@ajkavanagh.co.uk>
Co-authored-by: Ivan Kolodyazhny <e0ne@e0ne.info>

Change-Id: I86eb31535d990291945de5d9846b1a03157ec2cf
Closes-bug: #1865754
(cherry picked from commit c6ad4d864c)
(cherry picked from commit 474583b4f8)
(cherry picked from commit 91c73a433a)

os_brick/initiator/connectors/rbd.py

@@ -97,7 +97,12 @@ class RBDConnector(base.BaseLinuxConnector):
         try:
             fd, ceph_conf_path = tempfile.mkstemp(prefix="brickrbd_")
             with os.fdopen(fd, 'w') as conf_file:
-                conf_file.writelines([mon_hosts, "\n", keyring, "\n"])
+                # Bug #1865754 - '[global]' has been the appropriate
+                # place for this stuff since at least Hammer, but in
+                # Octopus (15.2.0+), Ceph began enforcing this.
+                conf_file.writelines(["[global]", "\n",
+                                      mon_hosts, "\n",
+                                      keyring, "\n"])
             return ceph_conf_path
         except IOError:
             msg = (_("Failed to write data to %s.") % (ceph_conf_path))

os_brick/tests/initiator/connectors/test_rbd.py

@@ -171,6 +171,10 @@ class RBDConnectorTestCase(test_connector.ConnectorTestCase):
                 self.keyring)
         self.assertEqual(conf_path, tmpfile)
         mock_mkstemp.assert_called_once_with(prefix='brickrbd_')
+        # Bug #1865754 - make sure generated config file has a '[global]'
+        # section
+        _, args, _ = mockopen().writelines.mock_calls[0]
+        self.assertIn('[global]', args[0])
 
     @mock.patch.object(priv_rootwrap, 'execute', return_value=None)
     def test_connect_local_volume(self, mock_execute):

releasenotes/notes/bug-1865754-ceph-octopus-compatibility-0aa9b8bc1b028301.yaml

@@ -0,0 +1,12 @@
+---
+fixes:
+  - |
+    `Bug #1865754 <https://bugs.launchpad.net/cinder/+bug/1865754>`_:
+    the ``RBDConnector`` class generates a temporary configuration file
+    to connect to Ceph.  Previously, os-brick did not include a
+    ``[global]`` section to contain the options it sets, but with the
+    Octopus release (15.2.0+), Ceph has begun enforcing the presence
+    of this section marker, which dates back at least to the Hammer
+    release of Ceph.  With this release, os-brick includes the
+    ``[global]`` section in the generated configuration file, which
+    should be backward-compatible at least to Ceph Hammer.