Add fill_metadata() to InstanceList

This adds a non-remotable method to InstanceList which will batch-
fill system_metadata for all the instances in the list that are
missing it in as efficient of a manner as possible. This does not
require an object bump because no remotable methods or fields are
changed.

Related to blueprint image-metadata-props-weigher

Change-Id: Icc47de2b677b3d212a7f6faa61a85ea9bff9f412

nova/db/main/api.py

@@ -1521,6 +1521,18 @@ def _instances_fill_metadata(context, instances, manual_joins=None):
     return filled_instances
 
 
+@require_context
+@pick_context_manager_reader
+def instances_fill_metadata(context, instances, manual_joins=None):
+    """Selectively fill instances with manually-joined metadata.
+
+    See _instances_fill_metadata(). This is only for use as a standalone
+    operation in its own transaction.
+    """
+    return _instances_fill_metadata(context, instances,
+                                    manual_joins=manual_joins)
+
+
 def _manual_join_columns(columns_to_join):
     """Separate manually joined columns from columns_to_join
 

nova/objects/instance.py

@@ -1588,6 +1588,26 @@ class InstanceList(base.ObjectListBase, base.NovaObject):
 
         return faults_by_uuid.keys()
 
+    def fill_metadata(self):
+        # NOTE(danms): This only fills system_metadata currently, but could
+        # be extended to support user metadata if needed in the future.
+        # Make a uuid-indexed dict of non-object instance dicts that the DB
+        # layer can use. They need only contain the uuid of the instances
+        # we are looking up. Any of them that already have system_metadata
+        # need not be included.
+        db_inst_shells = {inst.uuid: {'uuid': inst.uuid} for inst in self
+                          if 'system_metadata' not in inst}
+        if db_inst_shells:
+            updates = db.instances_fill_metadata(
+                self._context,
+                db_inst_shells.values(),
+                manual_joins=['system_metadata'])
+            updated = {i['uuid']: i for i in updates}
+            for inst in [i for i in self if i.uuid in updated]:
+                # Patch up our instances with system_metadata from the fill
+                # operation
+                inst.system_metadata = utils.instance_sys_meta(updated)
+
     @base.remotable_classmethod
     def get_uuids_by_host(cls, context, host):
         return db.instance_get_all_uuids_by_hosts(context, [host])[host]

nova/tests/unit/objects/test_instance.py

@@ -2060,6 +2060,49 @@ class TestInstanceListObject(test_objects._LocalTest,
                                                     {})
         self.assertEqual(2, len(insts))
 
+    def test_fill_metadata(self):
+        values = {'user_id': self.context.user_id,
+                  'project_id': self.context.project_id,
+                  'host': 'foo'}
+
+        for i in range(5):
+            db.instance_create(self.context,
+                               dict(values))
+
+        insts = objects.InstanceList.get_all(self.context)
+        self.assertEqual(5, len(insts))
+
+        # One instance has system_metadata populated *and* saved in the DB
+        insts[1].system_metadata = {'BTTF1': '1955'}
+        insts[1].save()
+
+        # One instance has system_metadata populated but dirty
+        insts[2].system_metadata = {'bttf3': '1885'}
+
+        # Three do not have system_metadata populated
+        self.assertEqual(3, len([i for i in insts
+                                 if 'system_metadata' not in i]))
+
+        insts.fill_metadata()
+
+        # Now all five have it populated
+        self.assertEqual(0, len([i for i in insts
+                                 if 'system_metadata' not in i]))
+
+        # Inst 2 should have not had its in-memory copy clobbered
+        self.assertEqual({'bttf3': '1885'}, insts[2].system_metadata)
+
+        # Inst 1 should have system_metadata loaded, but empty
+        self.assertIn('system_metadata', insts[0])
+        self.assertEqual({}, insts[0].system_metadata)
+
+    def test_fill_metadata_nop(self):
+        insts = objects.InstanceList([objects.Instance(uuid=uuids.inst,
+                                                       system_metadata={})])
+        # This would fail if it tries to actually load anything
+        # because context is None
+        insts.fill_metadata()
+
 
 class TestRemoteInstanceListObject(test_objects._RemoteTest,
                                    _TestInstanceListObject):