From ce2866a4f6c6ee06e835f19394c1dd02ef83cff5 Mon Sep 17 00:00:00 2001
From: Frode Nordahl <frode.nordahl@canonical.com>
Date: Fri, 5 Jun 2020 09:52:48 +0200
Subject: [PATCH] [OVN] Allow use of ovn-sync mechanism driver

The ``neutron-ovn-db-sync-util`` replaces the ``ovn`` mechanism
driver with the ``ovn-sync`` mechanism driver. Subsequently it
makes calls into the OVN L3 service plugin.

At present the OVN L3 service plugin assumes the ``ovn`` mechanism
driver to be present and produces a Traceback when it is not.

This patch fixes that by testing for both of the supported
mechanism drivers.

Change-Id: I1ac685a12f49119f5ef1428cbc504b639d783803
Closes-Bug: #1882202
Signed-off-by: Frode Nordahl <frode.nordahl@canonical.com>
(cherry picked from commit 206ce246768d6fb04b6bd92e189188f6702c74a7)
---
 neutron/services/ovn_l3/exceptions.py         | 21 +++++++++++++++++++
 neutron/services/ovn_l3/plugin.py             | 14 ++++++++++++-
 .../tests/unit/services/ovn_l3/test_plugin.py | 17 +++++++++++++++
 3 files changed, 51 insertions(+), 1 deletion(-)
 create mode 100644 neutron/services/ovn_l3/exceptions.py

diff --git a/neutron/services/ovn_l3/exceptions.py b/neutron/services/ovn_l3/exceptions.py
new file mode 100644
index 00000000000..72196785fb8
--- /dev/null
+++ b/neutron/services/ovn_l3/exceptions.py
@@ -0,0 +1,21 @@
+# Copyright 2020 Canonical Ltd.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+from neutron._i18n import _
+from neutron_lib import exceptions as n_exc
+
+
+class MechanismDriverNotFound(n_exc.NotFound):
+    message = _("None of the supported mechanism drivers found: "
+                "%(mechanism_drivers)s. Check your configuration.")
diff --git a/neutron/services/ovn_l3/plugin.py b/neutron/services/ovn_l3/plugin.py
index dfa39a0b62b..e11462eda56 100644
--- a/neutron/services/ovn_l3/plugin.py
+++ b/neutron/services/ovn_l3/plugin.py
@@ -40,6 +40,8 @@ from neutron.db import ovn_revision_numbers_db as db_rev
 from neutron.plugins.ml2.drivers.ovn.mech_driver.ovsdb import ovn_client
 from neutron.scheduler import l3_ovn_scheduler
 
+from neutron.services.ovn_l3 import exceptions as ovn_l3_exc
+
 
 LOG = log.getLogger(__name__)
 
@@ -105,7 +107,17 @@ class OVNL3RouterPlugin(service_base.ServicePluginBase,
     @property
     def _plugin_driver(self):
         if self._mech is None:
-            self._mech = self._plugin.mechanism_manager.mech_drivers['ovn'].obj
+            drivers = ('ovn', 'ovn-sync')
+            for driver in drivers:
+                try:
+                    self._mech = self._plugin.mechanism_manager.mech_drivers[
+                        driver].obj
+                    break
+                except KeyError:
+                    pass
+            else:
+                raise ovn_l3_exc.MechanismDriverNotFound(
+                        mechanism_drivers=drivers)
         return self._mech
 
     def get_plugin_type(self):
diff --git a/neutron/tests/unit/services/ovn_l3/test_plugin.py b/neutron/tests/unit/services/ovn_l3/test_plugin.py
index c9aa8f3c445..ebbcbe2b63a 100644
--- a/neutron/tests/unit/services/ovn_l3/test_plugin.py
+++ b/neutron/tests/unit/services/ovn_l3/test_plugin.py
@@ -284,6 +284,23 @@ class TestOVNL3RouterPlugin(test_mech_driver.Ml2PluginV2TestCase):
             return_value=False)
         self.mock_is_lb_member_fip.start()
 
+    def test__plugin_driver(self):
+        # No valid mech drivers should raise an exception.
+        self._mechanism_drivers = None
+        self.l3_inst._plugin.mechanism_manager.mech_drivers = {}
+        self.l3_inst._mech = None
+        self.assertRaises(n_exc.NotFound, lambda: self.l3_inst._plugin_driver)
+        # Populate the mechanism driver map with keys the code under test looks
+        # for and validate it finds them.
+        fake_mech_driver = mock.MagicMock()
+        for driver in ('ovn', 'ovn-sync'):
+            self.l3_inst._plugin.mechanism_manager.mech_drivers[
+                driver] = fake_mech_driver
+            result = self.l3_inst._plugin_driver
+            self.l3_inst._plugin.mechanism_manager.mech_drivers.pop(
+                driver, None)
+            self.assertEqual(fake_mech_driver.obj, result)
+
     @mock.patch('neutron.db.l3_db.L3_NAT_dbonly_mixin.add_router_interface')
     def test_add_router_interface(self, func):
         router_id = 'router-id'