Add OPENSTACK_NOVA_EXTENSIONS_BLACKLIST option to settings

This lets us disable any Nova extension we like, not just the
simple tenant usage.

Closes-bug: #1474241
Change-Id: I21840054225cd59cc62fd4f070172a2847173b14

doc/source/topics/settings.rst

@@ -1076,6 +1076,18 @@ http://tinyurl.com/anticlickjack
   ``False`` to exclude the frame-busting code and allow iframe embedding.
 
 
+``OPENSTACK_NOVA_EXTENSIONS_BLACKLIST``
+---------------------------------------
+
+.. versionadded:: 8.0.0(Liberty)
+
+Default: ``[]``
+
+Ignore all listed Nova extensions, and behave as if they were unsupported.
+Can be used to selectively disable certain costly extensions for performance
+reasons.
+
+
 Django Settings (Partial)
 =========================
 

openstack_dashboard/api/nova.py

@@ -935,7 +935,15 @@ def interface_detach(request, server, port_id):
 
 @memoized
 def list_extensions(request):
-    return nova_list_extensions.ListExtManager(novaclient(request)).show_all()
+    """List all nova extensions, except the ones in the blacklist."""
+
+    blacklist = set(getattr(settings,
+                            'OPENSTACK_NOVA_EXTENSIONS_BLACKLIST', []))
+    return [
+        extension for extension in
+        nova_list_extensions.ListExtManager(novaclient(request)).show_all()
+        if extension.name not in blacklist
+    ]
 
 
 @memoized

openstack_dashboard/test/api_tests/nova_rest_tests.py

@@ -156,11 +156,14 @@ class NovaRestTestCase(test.TestCase):
     # Extensions
     #
     @mock.patch.object(nova.api, 'nova')
+    @mock.patch.object(settings,
+                       'OPENSTACK_NOVA_EXTENSIONS_BLACKLIST', ['baz'])
     def _test_extension_list(self, nc):
         request = self.mock_rest_request()
         nc.list_extensions.return_value = [
             mock.Mock(**{'to_dict.return_value': {'name': 'foo'}}),
             mock.Mock(**{'to_dict.return_value': {'name': 'bar'}}),
+            mock.Mock(**{'to_dict.return_value': {'name': 'baz'}}),
         ]
         response = nova.Extensions().get(request)
         self.assertStatusCode(response, 200)