Port update will trigger less notifications to the DHCP agents

After port update, DHCP agent will be notified about changes only if
one of the port's attributes related somehow to the DHCP will change.
Such fields are:
* fixed_ips,
* MAC address,
* dns_domain,
* dns_name,
* dns_assignment,
* extra_dhcp_opts.

In other cases there is no reason to send notifications to the agent.
This will results with less notifications to the DHCP agent and less
possibilities to race condition between DHCP and L2 agents while
switching ports from the DOWN to ACTIVE status and sending notifications
to nova.

Closes-Bug: #1982367
Change-Id: If7990bdec435af76ad2e88fd4ea2bc24a255fd5a

neutron/api/rpc/agentnotifiers/dhcp_rpc_agent_api.py

@@ -298,26 +298,23 @@ class DhcpAgentNotifyAPI(object):
         method_name = '.'.join((resource, action, 'end'))
         data = {resource: payload.latest_state}
         if resource == resources.PORT and event == events.AFTER_UPDATE:
-            if self._only_status_changed(payload.states[0],
-                                         payload.latest_state):
+            if not self._notification_is_needed(payload.states[0],
+                                                payload.latest_state):
                 # don't waste time updating the DHCP agent for status updates
                 return
         self.notify(payload.context, data, method_name)
 
-    def _only_status_changed(self, orig, new):
-        # a status change will manifest as a bumped revision number, a new
-        # updated_at timestamp, and a new status. If that's all that changed,
-        # return True, else False
+    def _notification_is_needed(self, orig, new):
+        # notification to the DHCP agent should be send only if DHCP related
+        # attributes of the port were changed, like: fixed_ips, mac_address,
+        # extra_dhcp_opts, dns_name, dns_assignment or dns_domain.
+        # Otherwise there is no need to waste DHCP agent's time for doing
+        # updates.
         if not orig or not new:
-            return False
-        if set(orig.keys()) != set(new.keys()):
-            return False
-        for k in orig.keys():
-            if k in ('status', 'updated_at', 'revision_number'):
-                continue
-            if orig[k] != new[k]:
-                return False
-        return True
+            return True
+        return any(orig.get(k) != new.get(k) for k in (
+            'fixed_ips', 'mac_address', 'extra_dhcp_opts',
+            'dns_name', 'dns_assignment', 'dns_domain'))
 
     def _send_dhcp_notification(self, resource, event, trigger, payload=None):
         action = payload.action.split('_')[0]

neutron/tests/unit/api/rpc/agentnotifiers/test_dhcp_rpc_agent_api.py

@@ -284,17 +284,41 @@ class TestDhcpAgentNotifyAPI(base.BaseTestCase):
                              payload=events.DBEventPayload(mock.Mock()))
             self.assertEqual([res], self.notifier._unsubscribed_resources)
 
-    def test__only_status_changed(self):
+    def test__notification_is_needed(self):
         p1 = {'id': 1, 'status': 'DOWN', 'updated_at': '10:00:00',
-              'revision_number': 1}
+              'revision_number': 1,
+              'fixed_ips': [{'ip_address': '10.0.0.10', 'subnet_id': 'aaa'}],
+              'mac_address': 'aa:bb:cc:dd:ee:ff'}
         p2 = dict(p1)
         p2['status'] = 'ACTIVE'
         p2['revision_number'] = 2
         p2['updated_at'] = '10:00:01'
-        self.assertTrue(self.notifier._only_status_changed(p1, p2))
+        self.assertFalse(self.notifier._notification_is_needed(p1, p2))
+
         p2['name'] = 'test'
-        self.assertFalse(self.notifier._only_status_changed(p1, p2))
-        p1['name'] = 'test'
-        self.assertTrue(self.notifier._only_status_changed(p1, p2))
-        p1['name'] = 'test1'
-        self.assertFalse(self.notifier._only_status_changed(p1, p2))
+        self.assertFalse(self.notifier._notification_is_needed(p1, p2))
+        p2.pop('name')
+
+        p2['mac_address'] = '11:22:33:44:55:66'
+        self.assertTrue(self.notifier._notification_is_needed(p1, p2))
+        p2['mac_address'] = p1['mac_address']
+
+        p2['fixed_ips'] = [{'ip_address': '10.0.0.11', 'subnet_id': 'aaa'}]
+        self.assertTrue(self.notifier._notification_is_needed(p1, p2))
+        p2['fixed_ips'] = p1['fixed_ips']
+
+        p2['extra_dhcp_opts'] = 'some-test-opt'
+        self.assertTrue(self.notifier._notification_is_needed(p1, p2))
+        p2.pop('extra_dhcp_opts')
+
+        p2['dns_name'] = 'test-dns-name'
+        self.assertTrue(self.notifier._notification_is_needed(p1, p2))
+        p2.pop('dns_name')
+
+        p2['dns_assignment'] = 'test-dns-assignment'
+        self.assertTrue(self.notifier._notification_is_needed(p1, p2))
+        p2.pop('dns_assignment')
+
+        p2['dns_domain'] = 'test-dns-domain'
+        self.assertTrue(self.notifier._notification_is_needed(p1, p2))
+        p2.pop('dns_domain')