Only store segmenthostmapping when enable segment plugin

This patch adds a check to determine if the 'segments' service plugin is
enabled. The segment-host mapping db table should only be saved and
updated to the db table if the users configure the 'segments' service
plugin in the config file. The data should be available only in a routed
network resource situation.

Conflicts:
	neutron/tests/unit/extensions/test_segment.py

NOTE(s10): conflict is due to If6792d121e7b8e1ab4c7a548982a42e69023da2b
not being in Queens

Change-Id: I65a42aa2129bef696906a18d82575461dc02ba21
Closes-Bug: #1799328
(cherry picked from commit 06ba6a1ace)
(cherry picked from commit 7f8c446d5f)

neutron/services/segments/db.py

@@ -21,6 +21,7 @@ from neutron_lib import constants
 from neutron_lib import exceptions as n_exc
 from neutron_lib.plugins import directory
 from oslo_concurrency import lockutils
+from oslo_config import cfg
 from oslo_db import exception as db_exc
 from oslo_log import helpers as log_helpers
 from oslo_utils import uuidutils
@@ -36,6 +37,26 @@ from neutron.objects import network
 from neutron.services.segments import exceptions
 
 
+_USER_CONFIGURED_SEGMENT_PLUGIN = None
+
+
+def check_user_configured_segment_plugin():
+    global _USER_CONFIGURED_SEGMENT_PLUGIN
+    # _USER_CONFIGURED_SEGMENT_PLUGIN will contain 3 possible values:
+    # 1. None, this just happens during neutron-server startup.
+    # 2. True, this means that users configure the 'segments'
+    #    service plugin in neutron config file.
+    # 3. False, this means that can not find 'segments' service
+    #    plugin in neutron config file.
+    # This function just load once to store the result
+    # into _USER_CONFIGURED_SEGMENT_PLUGIN during neutron-server startup.
+    if _USER_CONFIGURED_SEGMENT_PLUGIN is None:
+        segment_class = 'neutron.services.segments.plugin.Plugin'
+        _USER_CONFIGURED_SEGMENT_PLUGIN = any(
+            p in cfg.CONF.service_plugins for p in ['segments', segment_class])
+    return _USER_CONFIGURED_SEGMENT_PLUGIN
+
+
 class SegmentDbMixin(common_db_mixin.CommonDbMixin):
     """Mixin class to add segment."""
 
@@ -251,7 +272,8 @@ def map_segment_to_hosts(context, segment_id, hosts):
 def _update_segment_host_mapping_for_agent(resource, event, trigger,
                                            context, host, plugin, agent):
     check_segment_for_agent = getattr(plugin, 'check_segment_for_agent', None)
-    if not check_segment_for_agent:
+    if (not check_user_configured_segment_plugin() or
+            not check_segment_for_agent):
         return
     phys_nets = _get_phys_nets(agent)
     if not phys_nets:
@@ -282,7 +304,8 @@ def _add_segment_host_mapping_for_segment(resource, event, trigger,
         return
     cp = directory.get_plugin()
     check_segment_for_agent = getattr(cp, 'check_segment_for_agent', None)
-    if not hasattr(cp, 'get_agents') or not check_segment_for_agent:
+    if not check_user_configured_segment_plugin() or not hasattr(
+            cp, 'get_agents') or not check_segment_for_agent:
         # not an agent-supporting plugin
         registry.unsubscribe(_add_segment_host_mapping_for_segment,
                              resources.SEGMENT, events.PRECOMMIT_CREATE)

neutron/tests/unit/extensions/test_segment.py

@@ -80,6 +80,7 @@ class SegmentTestCase(test_db_base_plugin_v2.NeutronDbPluginV2TestCase):
         if not plugin:
             plugin = TEST_PLUGIN_KLASS
         service_plugins = {'segments_plugin_name': SERVICE_PLUGIN_KLASS}
+        cfg.CONF.set_override('service_plugins', [SERVICE_PLUGIN_KLASS])
         ext_mgr = SegmentTestExtensionManager()
         super(SegmentTestCase, self).setUp(plugin=plugin, ext_mgr=ext_mgr,
                                            service_plugins=service_plugins)
@@ -2274,3 +2275,40 @@ class PlacementAPIClientTestCase(base.DietTestCase):
         self.mock_request.side_effect = ks_exc.EndpointNotFound
         self.assertRaises(neutron_exc.PlacementEndpointNotFound,
                           self.client.list_aggregates, rp_uuid)
+
+
+class TestSegmentHostMappingNoStore(
+        test_db_base_plugin_v2.NeutronDbPluginV2TestCase):
+
+    def setUp(self):
+        driver_type.register_ml2_drivers_vlan_opts()
+        cfg.CONF.set_override('network_vlan_ranges', ['phys_net1'],
+                              group='ml2_type_vlan')
+        cfg.CONF.set_override('service_plugins', [])
+        super(TestSegmentHostMappingNoStore, self).setUp(
+            plugin='neutron.plugins.ml2.plugin.Ml2Plugin')
+        # set to None for simulating server start
+        db._USER_CONFIGURED_SEGMENT_PLUGIN = None
+        db.subscribe()
+
+    @mock.patch('neutron.services.segments.db.update_segment_host_mapping')
+    @mock.patch('neutron.services.segments.db.map_segment_to_hosts')
+    def test_no_segmenthostmapping_when_disable_segment(
+            self, mock_map_segment_to_hosts, mock_update_segment_mapping):
+        with self.network(
+                arg_list=('provider:network_type',
+                          'provider:physical_network',
+                          'provider:segmentation_id'),
+                **{'provider:network_type': 'vlan',
+                   'provider:physical_network': 'phys_net1',
+                   'provider:segmentation_id': '400'}) as network:
+            network['network']
+        mock_map_segment_to_hosts.assert_not_called()
+
+        host1 = 'test_host'
+        physical_network = 'phys_net1'
+        helpers.register_ovs_agent(
+            host=host1,
+            bridge_mappings={physical_network: 'br-eth-1'},
+            plugin=self.plugin)
+        mock_update_segment_mapping.assert_not_called()