Fix remove_router_from_l3_agent for 'dvr' mode agent

It's possible to run command remove_router_from_l3_agent to remove
a DVR router from an agent in 'dvr' mode. But the implicit *binding*
between DVR router and agent in 'dvr' mode should come and go as
dvr serviced port on host come and go, not manually managed.

Closes-Bug: #1540779
Change-Id: Ied6c88c85ced7b956fad3473ede4688020a357a4

neutron/db/l3_agentschedulers_db.py

@@ -243,6 +243,10 @@ class L3AgentSchedulerDbMixin(l3agentscheduler.L3AgentSchedulerPluginBase,
         which leads to re-schedule or be added to another agent manually.
         """
         agent = self._get_agent(context, agent_id)
+        agent_mode = self._get_agent_mode(agent)
+        if agent_mode == constants.L3_AGENT_MODE_DVR:
+            raise l3agentscheduler.DVRL3CannotRemoveFromDvrAgent()
+
         self._unbind_router(context, router_id, agent_id)
 
         router = self.get_router(context, router_id)

neutron/extensions/l3agentscheduler.py

@@ -178,6 +178,11 @@ class DVRL3CannotAssignToDvrAgent(exceptions.Conflict):
                 "agent in 'dvr' mode.")
 
 
+class DVRL3CannotRemoveFromDvrAgent(exceptions.Conflict):
+    message = _("Not allowed to manually remove a router from "
+                "an agent in 'dvr' mode.")
+
+
 class L3AgentSchedulerPluginBase(object):
     """REST API to operate the l3 agent scheduler.
 

neutron/tests/unit/scheduler/test_l3_agent_scheduler.py

@@ -507,6 +507,27 @@ class L3SchedulerTestBaseMixin(object):
                                           already_scheduled=True,
                                           external_gw=external_gw_info)
 
+    def test_remove_router_from_l3_agent_in_dvr_mode(self):
+        self._register_l3_dvr_agents()
+        self.assertRaises(l3agent.DVRL3CannotRemoveFromDvrAgent,
+                          self.remove_router_from_l3_agent,
+                          self.adminContext,
+                          self.l3_dvr_agent_id,
+                          mock.ANY)
+
+    def test_remove_router_from_l3_agent_in_dvr_snat_mode(self):
+        self._register_l3_dvr_agents()
+        router = self._create_router_for_l3_agent_dvr_test(
+            distributed=True)
+        agent_id = self.l3_dvr_snat_id
+        l3_notifier = mock.Mock()
+        self.agent_notifiers = {constants.AGENT_TYPE_L3: l3_notifier}
+        self.remove_router_from_l3_agent(self.adminContext, agent_id,
+                                         router['router']['id'])
+        l3_notifier.router_removed_from_agent.assert_called_once_with(
+            self.adminContext, router['router']['id'],
+            self.l3_dvr_snat_agent.host)
+
     def _prepare_schedule_dvr_tests(self):
         scheduler = l3_agent_scheduler.ChanceScheduler()
         agent = agents_db.Agent()