L2 agent extension manager: read extensions list from config file

This effectively disables qos extension in the OVS agent, but we don't
rely on it in any functional or fullstack tests so far.

To enable the extension, a user should add:

[agent]
extensions = qos

to their openvswitch_agent.ini file.

DocImpact
Partially-Implements: blueprint quantum-qos-api
Change-Id: Icfbf32c36f98cc6e203841b152c7f6fc4f48c20a

etc/neutron/plugins/ml2/openvswitch_agent.ini

@@ -133,6 +133,11 @@
 #
 # quitting_rpc_timeout = 10
 
+# (ListOpt) Extensions list to use
+# Example: extensions = qos
+#
+# extensions =
+
 [securitygroup]
 # Firewall driver for realizing neutron security group function.
 # firewall_driver = neutron.agent.firewall.NoopFirewallDriver

neutron/agent/l2/agent_extensions_manager.py

@@ -13,6 +13,7 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+from oslo_config import cfg
 from oslo_log import log
 import stevedore
 
@@ -21,23 +22,26 @@ from neutron.i18n import _LE, _LI
 LOG = log.getLogger(__name__)
 
 
+L2_AGENT_EXT_MANAGER_NAMESPACE = 'neutron.agent.l2.extensions'
+L2_AGENT_EXT_MANAGER_OPTS = [
+    cfg.ListOpt('extensions',
+                default=[],
+                help=_('Extensions list to use')),
+]
+
+
+def register_opts(conf):
+    conf.register_opts(L2_AGENT_EXT_MANAGER_OPTS, 'agent')
+
+
 class AgentExtensionsManager(stevedore.named.NamedExtensionManager):
     """Manage agent extensions."""
 
-    def __init__(self):
-        # Ordered list of agent extensions, defining
-        # the order in which the agent extensions are called.
-
-        #TODO(QoS): get extensions from config
-        agent_extensions = ('qos', )
-
-        LOG.info(_LI("Configured agent extensions names: %s"),
-                 agent_extensions)
-
+    def __init__(self, conf):
         super(AgentExtensionsManager, self).__init__(
-            'neutron.agent.l2.extensions', agent_extensions,
+            L2_AGENT_EXT_MANAGER_NAMESPACE, conf.agent.extensions,
             invoke_on_load=True, name_order=True)
-        LOG.info(_LI("Loaded agent extensions names: %s"), self.names())
+        LOG.info(_LI("Loaded agent extensions: %s"), self.names())
 
     def _call_on_agent_extensions(self, method_name, context, data):
         """Helper method for calling a method across all agent extensions."""

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

@@ -367,8 +367,9 @@ class OVSNeutronAgent(sg_rpc.SecurityGroupAgentRpcCallbackMixin,
                                                      start_listening=False)
 
     def init_agent_extensions_mgr(self):
+        agent_extensions_manager.register_opts(self.conf)
         self.agent_extensions_mgr = (
-            agent_extensions_manager.AgentExtensionsManager())
+            agent_extensions_manager.AgentExtensionsManager(self.conf))
         self.agent_extensions_mgr.initialize()
 
     def get_net_uuid(self, vif_id):

neutron/tests/unit/agent/l2/test_agent_extensions_manager.py

@@ -11,6 +11,7 @@
 #    under the License.
 
 import mock
+from oslo_config import cfg
 
 from neutron.agent.l2 import agent_extensions_manager
 from neutron.tests import base
@@ -22,7 +23,10 @@ class TestAgentExtensionsManager(base.BaseTestCase):
         super(TestAgentExtensionsManager, self).setUp()
         mock.patch('neutron.agent.l2.extensions.qos_agent.QosAgentExtension',
                    autospec=True).start()
-        self.manager = agent_extensions_manager.AgentExtensionsManager()
+        conf = cfg.CONF
+        agent_extensions_manager.register_opts(conf)
+        cfg.CONF.set_override('extensions', ['qos'], 'agent')
+        self.manager = agent_extensions_manager.AgentExtensionsManager(conf)
 
     def _get_extension(self):
         return self.manager.extensions[0].obj

neutron/tests/unit/plugins/ml2/drivers/openvswitch/agent/test_ovs_neutron_agent.py

@@ -374,12 +374,7 @@ class TestOvsNeutronAgent(object):
                                   return_value=None):
             self.assertFalse(get_dev_fn.called)
 
-    #TODO(QoS) that this mock should go away once we don't hardcode
-    #qos extension.
-    @mock.patch('neutron.api.rpc.handlers.resources_rpc.'
-                'ResourcesServerRpcApi.get_info', return_value=[])
-    def test_treat_devices_added_updated_updates_known_port(
-        self, *args):
+    def test_treat_devices_added_updated_updates_known_port(self):
         details = mock.MagicMock()
         details.__contains__.side_effect = lambda x: True
         self.assertTrue(self._mock_treat_devices_added_updated(