placement: refactor driver select_destinations()

Refactors the scheduler *driver* class select_destinations() method to
return a sorted list of HostState objects instead of a list of dicts.

This allows us to eventually use these HostState objects in our claim
logic in future patches.

Change-Id: I8f173fc36af249150e656f4a611c5ea6f2141ae3
blueprint: placement-allocation-requests

nova/scheduler/chance.py

@@ -65,7 +65,7 @@ class ChanceScheduler(driver.Scheduler):
         dests = []
         for i in range(num_instances):
             host = self._schedule(context, CONF.compute_topic, spec_obj)
-            host_state = dict(host=host, nodename=None, limits=None)
+            host_state = self.host_manager.host_state_cls(host, None, None)
             dests.append(host_state)
 
         if len(dests) < num_instances:

nova/scheduler/driver.py

@@ -56,9 +56,8 @@ class Scheduler(object):
 
     @abc.abstractmethod
     def select_destinations(self, context, spec_obj, instance_uuids):
-        """Must override select_destinations method.
-
-        :return: A list of dicts with 'host', 'nodename' and 'limits' as keys
-            that satisfies the request_spec and filter_properties.
+        """Returns a list of HostState objects that have been chosen by the
+        scheduler driver, one for each requested instance
+        (spec_obj.num_instances)
         """
         return []

nova/scheduler/filter_scheduler.py

@@ -48,7 +48,9 @@ class FilterScheduler(driver.Scheduler):
         self.scheduler_client = scheduler_client.SchedulerClient()
 
     def select_destinations(self, context, spec_obj, instance_uuids):
-        """Selects a filtered set of hosts and nodes."""
+        """Returns a sorted list of HostState objects that satisfy the
+        supplied request_spec.
+        """
         self.notifier.info(
             context, 'scheduler.select_destinations.start',
             dict(request_spec=spec_obj.to_legacy_request_spec_dict()))
@@ -77,13 +79,10 @@ class FilterScheduler(driver.Scheduler):
             reason = _('There are not enough hosts available.')
             raise exception.NoValidHost(reason=reason)
 
-        dests = [dict(host=host.obj.host, nodename=host.obj.nodename,
-                      limits=host.obj.limits) for host in selected_hosts]
-
         self.notifier.info(
             context, 'scheduler.select_destinations.end',
             dict(request_spec=spec_obj.to_legacy_request_spec_dict()))
-        return dests
+        return [host.obj for host in selected_hosts]
 
     def _schedule(self, context, spec_obj, instance_uuids):
         """Returns a list of hosts that meet the required specs,

nova/scheduler/manager.py

@@ -41,6 +41,14 @@ CONF = nova.conf.CONF
 QUOTAS = quota.QUOTAS
 
 
+def _host_state_obj_to_dict(host_state):
+    return {
+        'host': host_state.host,
+        'nodename': host_state.nodename,
+        'limits': host_state.limits,
+    }
+
+
 class SchedulerManager(manager.Manager):
     """Chooses a host to run instances on."""
 
@@ -96,7 +104,8 @@ class SchedulerManager(manager.Manager):
                                                            request_spec,
                                                            filter_properties)
         dests = self.driver.select_destinations(ctxt, spec_obj, instance_uuids)
-        return jsonutils.to_primitive(dests)
+        dest_dicts = [_host_state_obj_to_dict(d) for d in dests]
+        return jsonutils.to_primitive(dest_dicts)
 
     def update_aggregates(self, ctxt, aggregates):
         """Updates HostManager internal aggregates information.

nova/tests/unit/scheduler/test_caching_scheduler.py

@@ -97,7 +97,7 @@ class CachingSchedulerTestCase(test_scheduler.SchedulerTestCase):
         result = self._test_select_destinations(spec_obj)
 
         self.assertEqual(1, len(result))
-        self.assertEqual(result[0]["host"], fake_host.host)
+        self.assertEqual(result[0].host, fake_host.host)
 
     def _test_select_destinations(self, spec_obj):
         return self.driver.select_destinations(
@@ -224,7 +224,7 @@ class CachingSchedulerTestCase(test_scheduler.SchedulerTestCase):
         }
         d = self.driver.select_destinations(self.context, spec_obj,
                 [spec_obj.instance_uuid])
-        self.assertIn(d[0]['host'], [hs.host for hs in host_states_cell2])
+        self.assertIn(d[0].host, [hs.host for hs in host_states_cell2])
 
 
 if __name__ == '__main__':

nova/tests/unit/scheduler/test_chance_scheduler.py

@@ -67,10 +67,10 @@ class ChanceSchedulerTestCase(test_scheduler.SchedulerTestCase):
                 [uuids.instance1, uuids.instance2])
 
         self.assertEqual(2, len(dests))
-        (host, node) = (dests[0]['host'], dests[0]['nodename'])
+        (host, node) = (dests[0].host, dests[0].nodename)
         self.assertEqual('host3', host)
         self.assertIsNone(node)
-        (host, node) = (dests[1]['host'], dests[1]['nodename'])
+        (host, node) = (dests[1].host, dests[1].nodename)
         self.assertEqual('host2', host)
         self.assertIsNone(node)
 

nova/tests/unit/scheduler/test_filter_scheduler.py

@@ -322,7 +322,7 @@ class FilterSchedulerTestCase(test_scheduler.SchedulerTestCase):
             dests = self.driver.select_destinations(self.context, spec_obj,
                     instance_uuids)
 
-        (host, node) = (dests[0]['host'], dests[0]['nodename'])
+        (host, node) = (dests[0].host, dests[0].nodename)
         self.assertEqual(host, selected_hosts[0])
         self.assertEqual(node, selected_nodes[0])