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diff --git a/openstack/common/plugin/plugin.py b/openstack/common/plugin/plugin.py
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+++ b/openstack/common/plugin/plugin.py
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+# Copyright 2012 OpenStack LLC.
+# All Rights Reserved.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+from openstack.common import log as logging
+from openstack.common.notifier import list_notifier
+
+
+LOG = logging.getLogger(__name__)
+
+
+class Plugin(object):
+    """Defines an interface for adding functionality to an OpenStack service.
+
+    A plugin interacts with a service via the following pathways:
+
+    - An optional set of notifiers, managed by calling add_notifier()
+      or by overriding _notifiers()
+
+    - A set of api extensions, managed via add_api_extension_descriptor()
+
+    - Direct calls to service functions.
+
+    - Whatever else the plugin wants to do on its own.
+
+    This is the reference implementation.
+    """
+
+    # The following functions are provided as convenience methods
+    # for subclasses.  Subclasses should call them but probably not
+    # override them.
+    def _add_api_extension_descriptor(self, descriptor):
+        """Subclass convenience method which adds an extension descriptor.
+
+           Subclass constructors should call this method when
+           extending a project's REST interface.
+
+           Note that once the api service has loaded, the
+           API extension set is more-or-less fixed, so
+           this should mainly be called by subclass constructors.
+        """
+        self._api_extension_descriptors.append(descriptor)
+
+    def _add_notifier(self, notifier):
+        """Subclass convenience method which adds a notifier.
+
+           Notifier objects should implement the function notify(message).
+           Each notifier receives a notify() call whenever an openstack
+           service broadcasts a notification.
+
+           Best to call this during construction.  Notifiers are enumerated
+           and registered by the pluginmanager at plugin load time.
+        """
+        self._notifiers.append(notifier)
+
+    # The following methods are called by OpenStack services to query
+    #  plugin features.  Subclasses should probably not override these.
+    def _notifiers(self):
+        """Returns list of notifiers for this plugin."""
+        return self._notifiers
+
+    notifiers = property(_notifiers)
+
+    def _api_extension_descriptors(self):
+        """Return a list of API extension descriptors.
+
+           Called by a project API during its load sequence.
+        """
+        return self._api_extension_descriptors
+
+    api_extension_descriptors = property(_api_extension_descriptors)
+
+    # Most plugins will override this:
+    def __init__(self, service_name):
+        self._notifiers = []
+        self._api_extension_descriptors = []