Added default value to the max_instances parameter of dpm.py

The default value is set to -1, which means that there is no artificial
upper bound for the number of instances on this CPC. The number of
instances is only limited by the number of (free) partitions on this
CPC.
closes-Bug: 1683318

Change-Id: I80f8b36fa21cef313e0b5a821a26877afd1af980

nova_dpm/conf/dpm.py

@@ -34,9 +34,14 @@ ALL_DPM_OPTS = [
     cfg.IntOpt('max_memory', help="""
     Maximum amount of memory (in MiB) on the target CPC that can be used for
     this OpenStack hypervisor host"""),
-    cfg.IntOpt('max_instances', help="""
+    cfg.IntOpt('max_instances', default=-1, min=-1, help="""
     Maximum number of instances (partitions) that can be created for this
-    OpenStack hypervisor host"""),
+    OpenStack hypervisor host. Valid values are:
+    -1: The number of instances is  only limited by the
+        number of free partitions on this CPC
+     0: A technically valid upper bound but useless.
+    >0: If this value is reached,
+        this host won't be able to spawn new instances."""),
     MultiStorageAdapterMappingOpt('physical_storage_adapter_mappings', help="""
     Physical storage adapter with port details for hba creation"""),
     cfg.ListOpt('target_wwpn_ignore_list', default='', help="""

nova_dpm/tests/unit/conf/test_dpm.py

@@ -0,0 +1,32 @@
+# Copyright 2017 IBM Corp. All Rights Reserved.
+#
+# 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 nova_dpm.conf
+
+from nova.test import TestCase
+
+
+class TestConfigParameters(TestCase):
+
+    def setUp(self):
+        super(TestConfigParameters, self).setUp()
+        self.CONF = nova_dpm.conf.CONF
+
+    def test_default_value(self):
+        max_instance = self.CONF.dpm.max_instances
+        self.assertEqual(-1, max_instance)
+
+    def test_min_value(self):
+        self.assertRaises(ValueError, self.CONF.set_override, "max_instances",
+                          -2, group="dpm")

releasenotes/notes/config-max_instances-default-value-7e530d2ae32c4c44.yaml

@@ -0,0 +1,7 @@
+---
+upgrade:
+  - |
+    Default value of -1 has been set for the configuration option
+    ``max_instances``.  This means that by default, there is no upper
+    limit set on the maximum number of instances that can be created for
+    this host.