VMware: add method for getting hosts attached to datastore

Add in a method that returns hosts attached to a datastore. This will
enable us to validate if the cinder volume is accessible by a running
instance.

Change-Id: I840ffda4926cea879d5945886ba87da72fc90805
Partial-bug: #1490257

nova/tests/unit/virt/vmwareapi/test_ds_util.py

@@ -447,3 +447,30 @@ class DsUtilTestCase(test.NoDBTestCase):
                                                       "normal",
                                                       "VMFS",
                                                       datastore_regex))
+
+    def test_get_connected_hosts_none(self):
+        with mock.patch.object(self.session,
+                               '_call_method') as _call_method:
+            hosts = ds_util.get_connected_hosts(self.session,
+                                                'fake_datastore')
+            self.assertEqual([], hosts)
+            _call_method.assert_called_once_with(
+                    mock.ANY, 'get_object_property',
+                    'fake_datastore', 'host')
+
+    def test_get_connected_hosts(self):
+        host = mock.Mock(spec=object)
+        host.value = 'fake-host'
+        host_mount = mock.Mock(spec=object)
+        host_mount.key = host
+        host_mounts = mock.Mock(spec=object)
+        host_mounts.DatastoreHostMount = [host_mount]
+
+        with mock.patch.object(self.session, '_call_method',
+                               return_value=host_mounts) as _call_method:
+            hosts = ds_util.get_connected_hosts(self.session,
+                                                'fake_datastore')
+            self.assertEqual(['fake-host'], hosts)
+            _call_method.assert_called_once_with(
+                    mock.ANY, 'get_object_property',
+                    'fake_datastore', 'host')

nova/virt/vmwareapi/ds_util.py

@@ -484,3 +484,22 @@ def get_dc_info(session, ds_ref):
 def dc_cache_reset():
     global _DS_DC_MAPPING
     _DS_DC_MAPPING = {}
+
+
+def get_connected_hosts(session, datastore):
+    """Get all the hosts to which the datastore is connected.
+
+    :param datastore: Reference to the datastore entity
+    :return: List of managed object references of all connected
+             hosts
+    """
+    host_mounts = session._call_method(vutil, 'get_object_property',
+                                       datastore, 'host')
+    if not hasattr(host_mounts, 'DatastoreHostMount'):
+        return []
+
+    connected_hosts = []
+    for host_mount in host_mounts.DatastoreHostMount:
+        connected_hosts.append(host_mount.key.value)
+
+    return connected_hosts