Add request filter functionality to scheduler

This adds a pre-placement step where we can call a number of modular
"request filters" to modify the request_spec before we move on to
construct the call to placement to get allocation candidates.

No filters are added at this time, this just adds the infrastructure.

Related to blueprint placement-req-filter

Change-Id: I1535158a0dbd4a8527bb987e085e9391e5b0fde4

nova/exception.py

@@ -1396,6 +1396,10 @@ class NoValidHost(NovaException):
     msg_fmt = _("No valid host was found. %(reason)s")
 
 
+class RequestFilterFailed(NovaException):
+    msg_fmt = _("Scheduling failed: %(reason)s")
+
+
 class MaxRetriesExceeded(NoValidHost):
     msg_fmt = _("Exceeded maximum number of retries. %(reason)s")
 

nova/scheduler/manager.py

@@ -35,6 +35,7 @@ from nova import objects
 from nova.objects import host_mapping as host_mapping_obj
 from nova import quota
 from nova.scheduler import client as scheduler_client
+from nova.scheduler import request_filter
 from nova.scheduler import utils
 
 
@@ -115,6 +116,12 @@ class SchedulerManager(manager.Manager):
             spec_obj = objects.RequestSpec.from_primitives(ctxt,
                                                            request_spec,
                                                            filter_properties)
+
+        try:
+            request_filter.process_reqspec(ctxt, spec_obj)
+        except exception.RequestFilterFailed as e:
+            raise exception.NoValidHost(reason=e.message)
+
         resources = utils.resources_from_request_spec(spec_obj)
         alloc_reqs_by_rp_uuid, provider_summaries, allocation_request_version \
             = None, None, None

nova/scheduler/request_filter.py

@@ -0,0 +1,33 @@
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+from oslo_log import log as logging
+
+import nova.conf
+
+
+CONF = nova.conf.CONF
+LOG = logging.getLogger(__name__)
+
+
+ALL_REQUEST_FILTERS = [
+]
+
+
+def process_reqspec(ctxt, request_spec):
+    """Process an objects.ReqestSpec before calling placement.
+
+    :param ctxt: A RequestContext
+    :param request_spec: An objects.RequestSpec to be inspected/modified
+    """
+    for filter in ALL_REQUEST_FILTERS:
+        filter(ctxt, request_spec)

nova/tests/unit/scheduler/test_request_filter.py

@@ -0,0 +1,35 @@
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+import mock
+
+from nova import context as nova_context
+from nova.scheduler import request_filter
+from nova import test
+from nova.tests import uuidsentinel as uuids
+
+
+class TestRequestFilter(test.NoDBTestCase):
+    def setUp(self):
+        super(TestRequestFilter, self).setUp()
+        self.context = nova_context.RequestContext(user_id=uuids.user,
+                                                   project_id=uuids.project)
+
+    def test_process_reqspec(self):
+        fake_filters = [mock.MagicMock(), mock.MagicMock()]
+        with mock.patch('nova.scheduler.request_filter.ALL_REQUEST_FILTERS',
+                        new=fake_filters):
+            request_filter.process_reqspec(mock.sentinel.context,
+                                           mock.sentinel.reqspec)
+        for filter in fake_filters:
+            filter.assert_called_once_with(mock.sentinel.context,
+                                           mock.sentinel.reqspec)