Support shared_targets tristate value

Cinder microversion 3.69 adds an additional value to shared_targets
beyond true and false.  Now null/None is also a valid value that can be
used to force locking.

So we now have 3 possible values:

- True ==> Lock if iSCSI initiator doesn't support manual scans
- False ==> Never lock.
- None ==> Always lock.

This patch updates the guard_connection context manager to support the
3 possible values.

With this Cinder can now force locking for NVMe-oF drivers that share
subsystems.

Closes-Bug: #1961102
Depends-On: I8cda6d9830f39e27ac700b1d8796fe0489fd7c0a
Change-Id: Id872543ce08c934cefbbbdaff6ddc61e3828b1f1

os_brick/initiator/utils.py

@@ -36,8 +36,17 @@ ISCSI_SUPPORTS_MANUAL_SCAN = check_manual_scan()
 
 @contextlib.contextmanager
 def guard_connection(device):
-    """Context Manager handling locks for attach/detach operations."""
-    if ISCSI_SUPPORTS_MANUAL_SCAN or not device.get('shared_targets'):
+    """Context Manager handling locks for attach/detach operations.
+
+    In Cinder microversion 3.69 the shared_targets field for volumes are
+    tristate:
+
+    - True ==> Lock if iSCSI initiator doesn't support manual scans
+    - False ==> Never lock.
+    - None ==> Always lock.
+    """
+    shared = device.get('shared_targets', False)
+    if (shared is not None and ISCSI_SUPPORTS_MANUAL_SCAN) or shared is False:
         yield
     else:
         # Cinder passes an OVO, but Nova passes a dictionary, so we use dict

os_brick/tests/initiator/test_utils.py

@@ -47,6 +47,16 @@ class InitiatorUtilsTestCase(base.TestCase):
         with utils.guard_connection({'shared_targets': True}):
             mock_lock.assert_not_called()
 
+    @mock.patch('oslo_concurrency.lockutils.lock')
+    def test_guard_connection_manual_scan_support_forced(self, mock_lock):
+        """Guard locks when cinder forces locking."""
+        utils.ISCSI_SUPPORTS_MANUAL_SCAN = True
+        # We confirm that shared_targets is ignored
+        with utils.guard_connection({'service_uuid': mock.sentinel.uuid,
+                                     'shared_targets': None}):
+            mock_lock.assert_called_once_with(mock.sentinel.uuid, 'os-brick-',
+                                              external=True)
+
     @mock.patch('oslo_concurrency.lockutils.lock')
     def test_guard_connection_manual_scan_unsupported_not_shared(self,
                                                                  mock_lock):
@@ -55,7 +65,7 @@ class InitiatorUtilsTestCase(base.TestCase):
             mock_lock.assert_not_called()
 
     @mock.patch('oslo_concurrency.lockutils.lock')
-    def test_guard_connection_manual_scan_unsupported_hared(self, mock_lock):
+    def test_guard_connection_manual_scan_unsupported_shared(self, mock_lock):
         utils.ISCSI_SUPPORTS_MANUAL_SCAN = False
         with utils.guard_connection({'service_uuid': mock.sentinel.uuid,
                                      'shared_targets': True}):

releasenotes/notes/nvmeof-disconnect-83f9aaf17f8c8988.yaml

@@ -0,0 +1,8 @@
+---
+fixes:
+  - |
+    NVMe-oF connector `bug #1961102
+    <https://bugs.launchpad.net/os-brick/+bug/1961102>`_: Fixed leaving
+    controller devices (i.e., /dev/nvme0) behind on hosts.  Now NVMe-oF
+    subsytems are disconnected when disconnecting volumes if the subsytem
+    doesn't have additional volumes present in the host.