Adds default fall-through to the multi scheduler.

Fixes bug 1009681

This offers a default scheduler driver that will be used by the
multischeduler for requests that are not destined for the
compute or volume topic. This is useful for openstack extensions
that want to use the nova-scheduler to schedule requests to
compute nodes but provide their own manager and topic.

Change-Id: I753e87fc8979fd0b62529974f00cf11fa55b3d63

3 files changed, 30 insertions, 4 deletions

diff --git a/Authors b/Authors
index 304eb2667..7742afc4c 100644
--- a/Authors
+++ b/Authors
@@ -48,6 +48,7 @@ Daniel P. Berrange <berrange@redhat.com>
 Dave Lapsley <dlapsley@nicira.com>
 Dave Walker <Dave.Walker@canonical.com>
 David Pravec <David.Pravec@danix.org>
+David Scannell <dscannell@gridcentric.com>
 David Shrewsbury <shrewsbury.dave@gmail.com>
 David Subiros <david.perez5@hp.com>
 Dean Troyer <dtroyer@gmail.com>
diff --git a/nova/scheduler/multi.py b/nova/scheduler/multi.py
index 8361e9e77..c6de3f825 100644
--- a/nova/scheduler/multi.py
+++ b/nova/scheduler/multi.py
@@ -35,6 +35,9 @@ multi_scheduler_opts = [
     cfg.StrOpt('volume_scheduler_driver',
                default='nova.scheduler.chance.ChanceScheduler',
                help='Driver to use for scheduling volume calls'),
+    cfg.StrOpt('default_scheduler_driver',
+               default='nova.scheduler.chance.ChanceScheduler',
+               help='Default driver to use for scheduling calls'),
     ]
 
 FLAGS = flags.FLAGS
@@ -60,9 +63,12 @@ class MultiScheduler(driver.Scheduler):
                 FLAGS.compute_scheduler_driver)
         volume_driver = importutils.import_object(
                 FLAGS.volume_scheduler_driver)
+        default_driver = importutils.import_object(
+                FLAGS.default_scheduler_driver)
 
         self.drivers = {'compute': compute_driver,
-                        'volume': volume_driver}
+                        'volume': volume_driver,
+                        'default': default_driver}
 
     def __getattr__(self, key):
         if not key.startswith('schedule_'):
@@ -73,7 +79,8 @@ class MultiScheduler(driver.Scheduler):
         return getattr(self.drivers[_METHOD_MAP[method]], key)
 
     def schedule(self, context, topic, method, *_args, **_kwargs):
-        return self.drivers[topic].schedule(context, topic,
+        driver = self.drivers.get(topic, self.drivers['default'])
+        return driver.schedule(context, topic,
                 method, *_args, **_kwargs)
 
     def schedule_run_instance(self, *args, **kwargs):
diff --git a/nova/tests/scheduler/test_multi_scheduler.py b/nova/tests/scheduler/test_multi_scheduler.py
index 4faf94443..d6a59450e 100644
--- a/nova/tests/scheduler/test_multi_scheduler.py
+++ b/nova/tests/scheduler/test_multi_scheduler.py
@@ -56,6 +56,17 @@ class FakeVolumeScheduler(driver.Scheduler):
         pass
 
 
+class FakeDefaultScheduler(driver.Scheduler):
+    is_fake_default = True
+
+    def __init__(self):
+        super(FakeDefaultScheduler, self).__init__()
+        self.is_update_caps_called = False
+
+    def schedule(self, *args, **kwargs):
+        pass
+
+
 class MultiDriverTestCase(test_scheduler.SchedulerTestCase):
     """Test case for multi driver"""
 
@@ -66,15 +77,18 @@ class MultiDriverTestCase(test_scheduler.SchedulerTestCase):
         base_name = 'nova.tests.scheduler.test_multi_scheduler.%s'
         compute_cls_name = base_name % 'FakeComputeScheduler'
         volume_cls_name = base_name % 'FakeVolumeScheduler'
+        default_cls_name = base_name % 'FakeDefaultScheduler'
         self.flags(compute_scheduler_driver=compute_cls_name,
-                volume_scheduler_driver=volume_cls_name)
+                volume_scheduler_driver=volume_cls_name,
+                default_scheduler_driver=default_cls_name)
         self._manager = multi.MultiScheduler()
 
     def test_drivers_inited(self):
         mgr = self._manager
-        self.assertEqual(len(mgr.drivers), 2)
+        self.assertEqual(len(mgr.drivers), 3)
         self.assertTrue(mgr.drivers['compute'].is_fake_compute)
         self.assertTrue(mgr.drivers['volume'].is_fake_volume)
+        self.assertTrue(mgr.drivers['default'].is_fake_default)
 
     def test_proxy_calls(self):
         mgr = self._manager
@@ -96,6 +110,7 @@ class MultiDriverTestCase(test_scheduler.SchedulerTestCase):
 
         self.mox.StubOutWithMock(mgr.drivers['compute'], 'schedule')
         self.mox.StubOutWithMock(mgr.drivers['volume'], 'schedule')
+        self.mox.StubOutWithMock(mgr.drivers['default'], 'schedule')
 
         ctxt = 'fake_context'
         method = 'fake_method'
@@ -107,10 +122,13 @@ class MultiDriverTestCase(test_scheduler.SchedulerTestCase):
                 *fake_args, **fake_kwargs)
         mgr.drivers['volume'].schedule(ctxt, 'volume', method,
                 *fake_args, **fake_kwargs)
+        mgr.drivers['default'].schedule(ctxt, 'random_topic', method,
+                *fake_args, **fake_kwargs)
 
         self.mox.ReplayAll()
         mgr.schedule(ctxt, 'compute', method, *fake_args, **fake_kwargs)
         mgr.schedule(ctxt, 'volume', method, *fake_args, **fake_kwargs)
+        mgr.schedule(ctxt, 'random_topic', method, *fake_args, **fake_kwargs)
 
     def test_update_service_capabilities(self):
         def fake_update_service_capabilities(self, service, host, caps):