Merge "Disallow CONF.compute.max_disk_devices_to_attach = 0" into stable/victoria

Author: Zuul

nova/compute/manager.py

@@ -1411,6 +1411,13 @@ def init_host(self):
                 eventlet.semaphore.BoundedSemaphore(
                     CONF.compute.max_concurrent_disk_ops)
 
+        if CONF.compute.max_disk_devices_to_attach == 0:
+            msg = _('[compute]max_disk_devices_to_attach has been set to 0, '
+                    'which will prevent instances from being able to boot. '
+                    'Set -1 for unlimited or set >= 1 to limit the maximum '
+                    'number of disk devices.')
+            raise exception.InvalidConfiguration(msg)
+
         self.driver.init_host(host=self.host)
         context = nova.context.get_admin_context()
         instances = objects.InstanceList.get_by_host(

nova/conf/compute.py

@@ -962,10 +962,16 @@
 The configured maximum is not enforced on shelved offloaded servers, as they
 have no compute host.
 
+.. warning:: If this option is set to 0, the ``nova-compute`` service will fail
+             to start, as 0 disk devices is an invalid configuration that would
+             prevent instances from being able to boot.
+
 Possible values:
 
 * -1 means unlimited
-* Any integer >= 0 represents the maximum allowed
+* Any integer >= 1 represents the maximum allowed. A value of 0 will cause the
+  ``nova-compute`` service to fail to start, as 0 disk devices is an invalid
+  configuration that would prevent instances from being able to boot.
 """),
     cfg.StrOpt('provider_config_location',
         default='/etc/nova/provider_config/',

nova/tests/unit/compute/test_compute_mgr.py

@@ -1111,6 +1111,11 @@ def test_get_nodes_node_not_found(
             "time this service is starting on this host, then you can ignore "
             "this warning.", 'fake-node1')
 
+    def test_init_host_disk_devices_configuration_failure(self):
+        self.flags(max_disk_devices_to_attach=0, group='compute')
+        self.assertRaises(exception.InvalidConfiguration,
+                          self.compute.init_host)
+
     @mock.patch.object(objects.InstanceList, 'get_by_host',
                        new=mock.Mock())
     @mock.patch('nova.compute.manager.ComputeManager.'