openvswitch agent: add OVS_RESTARTED event

This new event is aimed at informing that OVS has restarted, and in particular
to let L2 extensions know that they may need to setup their flows again.

Change-Id: I9aebe7ccc3e2f565b4339d42842d89b911131b1f
Closes-Bug: 1646526
Partial-Bug: 1657689

neutron/callbacks/events.py

@@ -43,3 +43,5 @@ ABORT_DELETE = 'abort_delete'
 ABORT = 'abort_'
 BEFORE = 'before_'
 PRECOMMIT = 'precommit_'
+
+OVS_RESTARTED = 'ovs_restarted'

neutron/plugins/ml2/drivers/openvswitch/agent/ovs_neutron_agent.py

@@ -47,6 +47,7 @@ from neutron.api.rpc.handlers import dvr_rpc
 from neutron.api.rpc.handlers import securitygroups_rpc as sg_rpc
 from neutron.callbacks import events as callback_events
 from neutron.callbacks import registry
+from neutron.callbacks import resources as callback_resources
 from neutron.common import config
 from neutron.common import constants as c_const
 from neutron.common import topics
@@ -1966,6 +1967,11 @@ class OVSNeutronAgent(sg_rpc.SecurityGroupAgentRpcCallbackMixin,
                                                  self.patch_tun_ofport)
                     self.dvr_agent.reset_dvr_parameters()
                     self.dvr_agent.setup_dvr_flows()
+                # notify that OVS has restarted
+                registry.notify(
+                    callback_resources.AGENT,
+                    callback_events.OVS_RESTARTED,
+                    self)
                 # restart the polling manager so that it will signal as added
                 # all the current ports
                 # REVISIT (rossella_s) Define a method "reset" in

neutron/tests/functional/agent/test_l2_ovs_agent.py

@@ -14,8 +14,12 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import mock
 import time
 
+from neutron.callbacks import events
+from neutron.callbacks import registry
+from neutron.callbacks import resources
 from neutron.common import utils
 from neutron.plugins.ml2.drivers.openvswitch.agent.common import constants
 from neutron.tests.common import net_helpers
@@ -320,6 +324,24 @@ class TestOVSAgent(base.OVSAgentTestFramework):
             utils.WaitTimeout, self.wait_until_ports_state, [self.ports[1]],
             up=True, timeout=10)
 
+    def test_ovs_restarted_event(self):
+        callback = mock.Mock()
+
+        self.setup_agent_and_ports(
+            port_dicts=self.create_test_ports())
+
+        registry.subscribe(callback,
+                           resources.AGENT,
+                           events.OVS_RESTARTED)
+
+        self.agent.check_ovs_status.return_value = constants.OVS_RESTARTED
+
+        utils.wait_until_true(lambda: callback.call_count, timeout=10)
+
+        callback.assert_called_with(resources.AGENT,
+                                    events.OVS_RESTARTED,
+                                    mock.ANY)
+
 
 class TestOVSAgentExtensionConfig(base.OVSAgentTestFramework):
     def setUp(self):