Change HostManager to allow scheduling to other cells

As part of the cross-cell resize work, we need to be able
to tell the scheduler that it's OK to select destinations
from cells in which the instance does not currently live.
This happens via the "allow_cross_cell_move" flag in the
RequestSpec.requested_destination field, which is not set
at this time (this is just plumbing which will be used later)
and defaults to False for backward compatibility.

Part of blueprint cross-cell-resize

Change-Id: Ib29a17f7fcc3280871d5c9ba31e1374eff98cf82

Author: mriedem

nova/scheduler/host_manager.py

@@ -755,9 +755,12 @@ def get_host_states_by_uuids(self, context, compute_uuids, spec_obj):
 
         if not self.cells:
             LOG.warning("No cells were found")
+        # Restrict to a single cell if and only if the request spec has a
+        # requested cell and allow_cross_cell_move=False.
         if (spec_obj and 'requested_destination' in spec_obj and
                 spec_obj.requested_destination and
-                'cell' in spec_obj.requested_destination):
+                'cell' in spec_obj.requested_destination and
+                not spec_obj.requested_destination.allow_cross_cell_move):
             only_cell = spec_obj.requested_destination.cell
         else:
             only_cell = None

nova/tests/unit/scheduler/test_host_manager.py

@@ -1319,6 +1319,29 @@ def test_get_host_states_by_uuids(self, mock_get_by_host, mock_get_all,
         num_hosts2 = len(list(host_states2))
         self.assertEqual(0, num_hosts2)
 
+    @mock.patch('nova.scheduler.host_manager.HostManager.'
+                '_get_computes_for_cells',
+                return_value=(mock.sentinel.compute_nodes,
+                              mock.sentinel.services))
+    @mock.patch('nova.scheduler.host_manager.HostManager._get_host_states')
+    def test_get_host_states_by_uuids_allow_cross_cell_move(
+            self, mock_get_host_states, mock_get_computes):
+        """Tests that get_host_states_by_uuids will not restrict to a given
+        cell if allow_cross_cell_move=True in the request spec.
+        """
+        ctxt = nova_context.get_admin_context()
+        compute_uuids = [uuids.compute_node_uuid]
+        spec_obj = objects.RequestSpec(
+            requested_destination=objects.Destination(
+                cell=objects.CellMapping(uuid=uuids.cell1),
+                allow_cross_cell_move=True))
+        self.host_manager.get_host_states_by_uuids(
+            ctxt, compute_uuids, spec_obj)
+        mock_get_computes.assert_called_once_with(
+            ctxt, self.host_manager.enabled_cells, compute_uuids=compute_uuids)
+        mock_get_host_states.assert_called_once_with(
+            ctxt, mock.sentinel.compute_nodes, mock.sentinel.services)
+
 
 class HostStateTestCase(test.NoDBTestCase):
     """Test case for HostState class."""