validate specified volumes to boot from at the API layer

This causes the create to fail fast instead of putting
the instance into error later in the process.

Related to bug: 1069904
Change-Id: I5f7c8d20d3ebf33ce1ce64bf0a8418bd2b5a6411

nova/compute/api.py

@@ -558,6 +558,11 @@ class API(base.Base):
                         security_group, block_device_mapping)
                 instances.append(instance)
                 instance_uuids.append(instance['uuid'])
+                self._validate_bdm(context, instance)
+                # send a state update notification for the initial create to
+                # show it going from non-existent to BUILDING
+                notifications.send_update_with_states(context, instance, None,
+                        vm_states.BUILDING, None, None, service="api")
 
         # In the case of any exceptions, attempt DB cleanup and rollback the
         # quota reservations.
@@ -704,6 +709,23 @@ class API(base.Base):
             self.db.block_device_mapping_update_or_create(elevated_context,
                                                           values)
 
+    def _validate_bdm(self, context, instance):
+        for bdm in self.db.block_device_mapping_get_all_by_instance(
+                context, instance['uuid']):
+            # NOTE(vish): For now, just make sure the volumes are accessible.
+            snapshot_id = bdm.get('snapshot_id')
+            volume_id = bdm.get('volume_id')
+            if volume_id is not None:
+                try:
+                    self.volume_api.get(context, volume_id)
+                except Exception:
+                    raise exception.InvalidBDMVolume(id=volume_id)
+            elif snapshot_id is not None:
+                try:
+                    self.volume_api.get_snapshot(context, snapshot_id)
+                except Exception:
+                    raise exception.InvalidBDMSnapshot(id=snapshot_id)
+
     def _populate_instance_for_bdm(self, context, instance, instance_type,
             image, block_device_mapping):
         """Populate instance block device mapping information."""
@@ -818,11 +840,6 @@ class API(base.Base):
         self._populate_instance_for_bdm(context, instance,
                 instance_type, image, block_device_mapping)
 
-        # send a state update notification for the initial create to
-        # show it going from non-existent to BUILDING
-        notifications.send_update_with_states(context, instance, None,
-                vm_states.BUILDING, None, None, service="api")
-
         return instance
 
     def _check_create_policies(self, context, availability_zone,

nova/exception.py

@@ -226,6 +226,20 @@ class Invalid(NovaException):
     code = 400
 
 
+class InvalidBDM(Invalid):
+    message = _("Block Device Mapping is Invalid.")
+
+
+class InvalidBDMSnapshot(InvalidBDM):
+    message = _("Block Device Mapping is Invalid: "
+                "failed to get snapshot %(id)s.")
+
+
+class InvalidBDMVolume(InvalidBDM):
+    message = _("Block Device Mapping is Invalid: "
+                "failed to get volume %(id)s.")
+
+
 class VolumeUnattached(Invalid):
     message = _("Volume %(volume_id)s is not attached to anything")