Boot from image fails without a clear error message

Booting an instance form image fails somewhere with
a magic error message.But as we do not support the boot
from image case. We should check that at first
when the spawn method is entered or even the
pre_for_spawn method is entered and abort with
an appropriate error message!

Closes-Bug: #1663550

Change-Id: I577b28d034322b109b81c978cb50a299be140510
Signed-off-by: Prabhat Ranjan <pranjank@in.ibm.com>

nova_dpm/tests/unit/virt/dpm/test_driver.py

@@ -142,13 +142,38 @@ class DPMdriverInitHostTestCase(TestCase):
     @mock.patch.object(vm.PartitionInstance, 'attach_hbas')
     @mock.patch.object(vm.PartitionInstance, 'get_partition')
     @mock.patch.object(vm.PartitionInstance, 'properties')
-    def test_prep_for_spawn(self, mock_properties,
-                            mock_partition, mock_attac_hbas,
-                            mock_create, mock_context, mock_flavor):
-        self.dpmdriver.prep_for_spawn(mock.Mock, mock.Mock())
+    def test_prep_for_spawn_volume(self, mock_properties,
+                                   mock_partition,
+                                   mock_attac_hbas,
+                                   mock_create,
+                                   mock_context,
+                                   mock_flavor):
+
+        instance = mock.Mock()
+        instance.image_ref = ''
+        self.dpmdriver.prep_for_spawn(mock.Mock, instance)
         mock_create.assert_called_once()
         mock_attac_hbas.assert_called_once()
 
+    @mock.patch.object(flavor_object.Flavor, 'get_by_id')
+    @mock.patch.object(context_object, 'get_admin_context')
+    @mock.patch.object(vm.PartitionInstance, 'create')
+    @mock.patch.object(vm.PartitionInstance, 'attach_hbas')
+    @mock.patch.object(vm.PartitionInstance, 'get_partition')
+    @mock.patch.object(vm.PartitionInstance, 'properties')
+    def test_prep_for_spawn_image(self, mock_properties,
+                                  mock_partition,
+                                  mock_attac_hbas,
+                                  mock_create,
+                                  mock_context,
+                                  mock_flavor):
+        instance = mock.Mock()
+        instance.image_ref = '6c77503d-4bff-4205-9e90-d75373c3c689'
+        self.assertRaises(
+            exceptions.BootFromImageNotSupported,
+            self.dpmdriver.prep_for_spawn,
+            mock.Mock(), instance)
+
     @mock.patch.object(vm.PartitionInstance, 'get_partition')
     def test_get_volume_connector(self, mock_get_partition):
         self.dpmdriver.get_volume_connector(mock.Mock())

nova_dpm/virt/dpm/driver.py

@@ -300,6 +300,10 @@ class DPMDriver(driver.ComputeDriver):
 
     def prep_for_spawn(self, context, instance,
                        flavor=None):
+
+        if instance.image_ref != '':
+            raise exceptions.BootFromImageNotSupported()
+
         if not flavor:
             context = context_object.get_admin_context(read_deleted='yes')
             flavor = (

nova_dpm/virt/dpm/exceptions.py

@@ -32,6 +32,10 @@ class BootOsSpecificParametersPropertyExceededError(NovaException):
                 "'boot-os-specific-parameters' property.")
 
 
+class BootFromImageNotSupported(NovaException):
+    msg_fmt = _("Boot from image is not supported in nova-dpm.")
+
+
 class UnsupportedVolumeTypeException(NovaException):
     msg_fmt = _("Driver volume type"
                 " %(vol_type)s is not supported by nova-dpm.")