Allow the service plugin to import the extension

I hit this circular import which made it so that I couldn't import the
extension from db.py within the service plugin because the extension
imports the plugin.  This seems backwards to me.  The extension is the
interface and should pretty much stand alone shouldn't it?  The
service plugin is the implementation and should be free to import it
at will.

This patch fixes the circular import issue.

Change-Id: I3b84496bf65578b02b43bbffb227db9bb9879288
Partially-implements: bp/routed-networks

neutron/extensions/segment.py

@@ -22,7 +22,7 @@ from neutron.api import extensions
 from neutron.api.v2 import attributes
 from neutron.api.v2 import base
 from neutron.extensions import providernet
-from neutron.services.segments import plugin
+from neutron import manager
 
 SEGMENT = 'segment'
 SEGMENTS = '%ss' % SEGMENT
@@ -103,7 +103,7 @@ class Segment(extensions.ExtensionDescriptor):
         controller = base.create_resource(
             SEGMENTS,
             SEGMENT,
-            plugin.Plugin.get_instance(),
+            manager.NeutronManager.get_service_plugins()[SEGMENTS],
             resource_attributes)
         return [extensions.ResourceExtension(SEGMENTS,
                                              controller,
@@ -210,3 +210,9 @@ class SegmentPluginBase(object):
                         value.  Each result returned by this function will have
                         matched one of the values for each key in filters.
         """
+
+    def get_plugin_description(self):
+        return "Network Segments"
+
+    def get_plugin_type(self):
+        return SEGMENTS

neutron/services/segments/db.py

@@ -30,6 +30,7 @@ from neutron.api.v2 import attributes
 from neutron.db import common_db_mixin
 from neutron.db import model_base
 from neutron.db import segments_db as db
+from neutron.extensions import segment as extension
 from neutron.services.segments import exceptions
 
 
@@ -91,12 +92,11 @@ class SegmentDbMixin(common_db_mixin.CommonDbMixin):
         segment_id = segment.get('id') or uuidutils.generate_uuid()
         with context.session.begin(subtransactions=True):
             network_id = segment['network_id']
-            # FIXME couldn't use constants because of a circular import problem
-            physical_network = segment['physical_network']
+            physical_network = segment[extension.PHYSICAL_NETWORK]
             if physical_network == constants.ATTR_NOT_SPECIFIED:
                 physical_network = None
-            network_type = segment['network_type']
-            segmentation_id = segment['segmentation_id']
+            network_type = segment[extension.NETWORK_TYPE]
+            segmentation_id = segment[extension.SEGMENTATION_ID]
             if segmentation_id == constants.ATTR_NOT_SPECIFIED:
                 segmentation_id = None
             args = {'id': segment_id,

neutron/services/segments/plugin.py

@@ -15,10 +15,11 @@
 #    under the License.
 
 
+from neutron.extensions import segment
 from neutron.services.segments import db
 
 
-class Plugin(db.SegmentDbMixin):
+class Plugin(db.SegmentDbMixin, segment.SegmentPluginBase):
 
     _instance = None
 
@@ -29,9 +30,3 @@ class Plugin(db.SegmentDbMixin):
         if cls._instance is None:
             cls._instance = cls()
         return cls._instance
-
-    def get_plugin_description(self):
-        return "Network Segments"
-
-    def get_plugin_type(self):
-        return "segments"

neutron/tests/unit/extensions/test_segment.py

@@ -29,8 +29,9 @@ from neutron.services.segments import db
 from neutron.tests.common import helpers
 from neutron.tests.unit.db import test_db_base_plugin_v2
 
-DB_PLUGIN_KLASS = ('neutron.tests.unit.extensions.test_segment.'
-                   'SegmentTestPlugin')
+SERVICE_PLUGIN_KLASS = 'neutron.services.segments.plugin.Plugin'
+TEST_PLUGIN_KLASS = (
+    'neutron.tests.unit.extensions.test_segment.SegmentTestPlugin')
 
 
 class SegmentTestExtensionManager(object):
@@ -53,9 +54,10 @@ class SegmentTestExtensionManager(object):
 
 class SegmentTestCase(test_db_base_plugin_v2.NeutronDbPluginV2TestCase):
 
-    def setUp(self, plugin=None, service_plugins=None):
+    def setUp(self, plugin=None):
         if not plugin:
-            plugin = DB_PLUGIN_KLASS
+            plugin = TEST_PLUGIN_KLASS
+        service_plugins = {'segments_plugin_name': SERVICE_PLUGIN_KLASS}
         ext_mgr = SegmentTestExtensionManager()
         super(SegmentTestCase, self).setUp(plugin=plugin, ext_mgr=ext_mgr,
                                            service_plugins=service_plugins)
@@ -285,11 +287,7 @@ class HostSegmentMappingTestCase(SegmentTestCase):
                                      group='ml2')
         if not plugin:
             plugin = 'neutron.plugins.ml2.plugin.Ml2Plugin'
-        segments_plugin = ('neutron.tests.unit.extensions.test_segment.'
-                           'SegmentTestPlugin')
-        service_plugins = {'segments_plugin_name': segments_plugin}
-        super(HostSegmentMappingTestCase, self).setUp(
-              plugin=plugin, service_plugins=service_plugins)
+        super(HostSegmentMappingTestCase, self).setUp(plugin=plugin)
 
     def _get_segments_for_host(self, host):
         ctx = context.get_admin_context()