Hyper-V: Fixes disk overhead claim issue

For each started VM, Hyper-V creates a VM memory file on the local
disk. The size of the file is the same as the size of the VM's
memory amount.

Implements the mentioned method in HyperVDriver.

Change-Id: Id40219dae96c0f7e60a86c0ed76fa08cea608aec
Closes-Bug: #1505681

nova/tests/unit/virt/hyperv/test_driver.py

@@ -127,6 +127,11 @@ class HyperVDriverTestCase(test_base.HyperVBaseTestCase):
         self.driver.list_instances()
         self.driver._vmops.list_instances.assert_called_once_with()
 
+    def test_estimate_instance_overhead(self):
+        self.driver.estimate_instance_overhead(mock.sentinel.instance)
+        self.driver._vmops.estimate_instance_overhead.assert_called_once_with(
+            mock.sentinel.instance)
+
     def test_spawn(self):
         self.driver.spawn(
             mock.sentinel.context, mock.sentinel.instance,

nova/tests/unit/virt/hyperv/test_vmops.py

@@ -100,6 +100,16 @@ class VMOpsTestCase(test_base.HyperVBaseTestCase):
         self._vmops._vmutils.list_instances.assert_called_once_with()
         self.assertEqual(response, [mock_instance])
 
+    def test_estimate_instance_overhead(self):
+        instance_info = {'memory_mb': 512}
+        overhead = self._vmops.estimate_instance_overhead(instance_info)
+        self.assertEqual(0, overhead['memory_mb'])
+        self.assertEqual(1, overhead['disk_gb'])
+
+        instance_info = {'memory_mb': 500}
+        overhead = self._vmops.estimate_instance_overhead(instance_info)
+        self.assertEqual(0, overhead['disk_gb'])
+
     def _test_get_info(self, vm_exists):
         mock_instance = fake_instance.fake_instance_obj(self.context)
         mock_info = mock.MagicMock(spec_set=dict)

nova/virt/hyperv/driver.py

@@ -137,6 +137,9 @@ class HyperVDriver(driver.ComputeDriver):
     def list_instances(self):
         return self._vmops.list_instances()
 
+    def estimate_instance_overhead(self, instance_info):
+        return self._vmops.estimate_instance_overhead(instance_info)
+
     def spawn(self, context, instance, image_meta, injected_files,
               admin_password, network_info=None, block_device_info=None):
         self._vmops.spawn(context, instance, image_meta, injected_files,

nova/virt/hyperv/vmops.py

@@ -131,6 +131,14 @@ class VMOps(object):
     def list_instances(self):
         return self._vmutils.list_instances()
 
+    def estimate_instance_overhead(self, instance_info):
+        # NOTE(claudiub): When an instance starts, Hyper-V creates a VM memory
+        # file on the local disk. The file size is the same as the VM's amount
+        # of memory. Since disk_gb must be an integer, and memory is MB, round
+        # up from X512 MB.
+        return {'memory_mb': 0,
+                'disk_gb': (instance_info['memory_mb'] + 512) // units.Ki}
+
     def get_info(self, instance):
         """Get information about the VM."""
         LOG.debug("get_info called for instance", instance=instance)