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

3 files changed, 19 insertions, 1 deletions

diff --git a/nova/compute/manager.py b/nova/compute/manager.py
index e34064ea4d..036c850f20 100644
--- a/nova/compute/manager.py
+++ b/nova/compute/manager.py
@@ -1394,6 +1394,13 @@ class ComputeManager(manager.Manager):
                 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(
diff --git a/nova/conf/compute.py b/nova/conf/compute.py
index 4656ac0df4..8faddc721c 100644
--- a/nova/conf/compute.py
+++ b/nova/conf/compute.py
@@ -949,10 +949,16 @@ on compute host B.
 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.
 """),
 ]
 
diff --git a/nova/tests/unit/compute/test_compute_mgr.py b/nova/tests/unit/compute/test_compute_mgr.py
index 86a30c9076..ee39a6491a 100644
--- a/nova/tests/unit/compute/test_compute_mgr.py
+++ b/nova/tests/unit/compute/test_compute_mgr.py
@@ -1078,6 +1078,11 @@ class ComputeManagerUnitTestCase(test.NoDBTestCase,
             "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.'