WIP: Cold-Migrate/Resize with multiple nodes

The driver and scheduler support conceptually multiple nodes
per compute host, but the resize api assumes a single node
per host as the only case of multiple nodes per host is ironic,
which does not support resizing or migration for obvious reasons.

This removes the assumption to fix resize/cold-migration on
hypervisors, which may support it (eventually vmware)

Change-Id: I9200dfea623458865f289c25fa5fb06a2140b1cb

nova/compute/api.py

@@ -4015,14 +4015,13 @@ def _validate_host_for_cold_migrate(
                 raise exception.ComputeHostNotFound(host=host_name)
 
             with nova_context.target_cell(context, hm.cell_mapping) as cctxt:
-                node = objects.ComputeNode.\
-                    get_first_node_by_host_for_old_compat(
-                        cctxt, host_name, use_slave=True)
+                nodes = objects.ComputeNodeList.get_all_by_host(
+                    cctxt, host_name, use_slave=True)
         else:
-            node = objects.ComputeNode.get_first_node_by_host_for_old_compat(
+            nodes = objects.ComputeNodeList.get_all_by_host(
                 context, host_name, use_slave=True)
 
-        return node
+        return nodes
 
     # TODO(stephenfin): This logic would be so much easier to grok if we
     # finally split resize and cold migration into separate code paths
@@ -4050,8 +4049,10 @@ def resize(self, context, instance, flavor_id=None, clean_shutdown=True,
             context, instance)
 
         if host_name is not None:
-            node = self._validate_host_for_cold_migrate(
+            nodes = self._validate_host_for_cold_migrate(
                 context, instance, host_name, allow_cross_cell_resize)
+        else:
+            nodes = None
 
         self._check_auto_disk_config(
             instance, auto_disk_config=auto_disk_config)
@@ -4076,9 +4077,8 @@ def resize(self, context, instance, flavor_id=None, clean_shutdown=True,
             if CONF.always_resize_on_same_host:
                 LOG.info('Setting resize to the same host')
                 host_name = instance.host
-                node = (
-                    objects.ComputeNode.get_first_node_by_host_for_old_compat(
-                        context, host_name, use_slave=True))
+                nodes = objects.ComputeNodeList.get_all_by_host(
+                            context, host_name, use_slave=True)
             new_flavor = flavors.get_flavor_by_flavor_id(
                 flavor_id, read_deleted="no")
             # NOTE(wenping): We use this instead of the 'block_accelerator'
@@ -4189,20 +4189,16 @@ def resize(self, context, instance, flavor_id=None, clean_shutdown=True,
         # which takes has filter_properties which in turn has
         # scheduler_hints (plural).
 
-        if host_name is None:
-            # If 'host_name' is not specified,
-            # clear the 'requested_destination' field of the RequestSpec
-            # except set the allow_cross_cell_move flag since conductor uses
-            # it prior to scheduling.
-            request_spec.requested_destination = objects.Destination(
-                allow_cross_cell_move=allow_cross_cell_resize)
+        if nodes and len(nodes) == 1:
+            node_name = nodes[0].hypervisor_hostname
         else:
-            # Set the host and the node so that the scheduler will
-            # validate them.
-            request_spec.requested_destination = objects.Destination(
-                host=node.host, node=node.hypervisor_hostname,
-                allow_cross_cell_move=allow_cross_cell_resize)
+            node_name = None
 
+        # Set the host and the node so that the scheduler will either
+        # validate them, or select one matching host and potentially node
+        request_spec.requested_destination = objects.Destination(
+            host=host_name, node=node_name,
+            allow_cross_cell_move=allow_cross_cell_resize)
         # Asynchronously RPC cast to conductor so the response is not blocked
         # during scheduling. If something fails the user can find out via
         # instance actions.