Add host check while create snapshot

We may create a volume but the volume was not been scheduled for some
reasons(e.g. The disk space is unavailable, cinder-volume service is
down, etc...). Although this volume is in error status, we can force
create snapshot using `--force` flag, that's make no sense. What's worse,
it may carry some unexpected error: We can delete this error volume before
cleanup the snapshot, but we can't delete the snapshot any more via API for
its prarent volume not found. This patch just raises an InvalidVolume
exception when we create a snapshot on a volume without host. In
addtion, the volume state is mutable so I think it is not 100% reliable,
the user may reset state w/o checking host state. I think we need check
host state before go forward to create snapshot on it.

Change-Id: Ifb9388cc76c1ff8d2e7f5b24710acbe95b602825
Closes-Bug: #1641294

cinder/tests/unit/api/v1/test_snapshots.py

@@ -108,7 +108,7 @@ class SnapshotApiTest(test.TestCase):
         self.stubs.Set(volume.api.API,
                        "create_snapshot_force",
                        stub_snapshot_create)
-        self.stubs.Set(volume.api.API, 'get', stubs.stub_volume_get)
+        self.mock_object(volume.api.API, 'get', stubs.stub_volume_api_get)
         snapshot = {"volume_id": fake.VOLUME_ID,
                     "force": force_param,
                     "display_name": "Snapshot Test Name",
@@ -128,7 +128,7 @@ class SnapshotApiTest(test.TestCase):
         self.stubs.Set(volume.api.API,
                        "create_snapshot_force",
                        stub_snapshot_create)
-        self.stubs.Set(volume.api.API, 'get', stubs.stub_volume_get)
+        self.mock_object(volume.api.API, 'get', stubs.stub_volume_api_get)
         snapshot = {"volume_id": fake.VOLUME_ID,
                     "force": force_param,
                     "display_name": "Snapshot Test Name",
@@ -145,7 +145,7 @@ class SnapshotApiTest(test.TestCase):
         self.stubs.Set(volume.api.API,
                        "create_snapshot_force",
                        stub_snapshot_create)
-        self.stubs.Set(volume.api.API, 'get', stubs.stub_volume_get)
+        self.mock_object(volume.api.API, 'get', stubs.stub_volume_api_get)
         snapshot = {"volume_id": fake.SNAPSHOT_ID,
                     "force": "**&&^^%%$$##@@",
                     "display_name": "Snapshot Test Name",

cinder/tests/unit/test_volume.py

@@ -3097,6 +3097,19 @@ class VolumeTestCase(base.BaseVolumeTestCase):
                           'fake_description',
                           fake.CONSISTENCY_GROUP_ID)
 
+    def test_create_snapshot_failed_host_is_None(self):
+        """Test exception handling when create snapshot and host is None."""
+        test_volume = tests_utils.create_volume(
+            self.context,
+            host=None)
+        volume_api = cinder.volume.api.API()
+        self.assertRaises(exception.InvalidVolume,
+                          volume_api.create_snapshot,
+                          self.context,
+                          test_volume,
+                          'fake_name',
+                          'fake_description')
+
     def test_cannot_delete_volume_in_use(self):
         """Test volume can't be deleted in in-use status."""
         self._test_cannot_delete_volume('in-use')

cinder/volume/api.py

@@ -771,6 +771,11 @@ class API(base.Base):
                               group_snapshot_id=None):
         check_policy(context, 'create_snapshot', volume)
 
+        if not volume.host:
+            msg = _("The snapshot cannot be created because volume has "
+                    "not been scheduled to any host.")
+            raise exception.InvalidVolume(reason=msg)
+
         if volume['status'] == 'maintenance':
             LOG.info(_LI('Unable to create the snapshot for volume, '
                          'because it is in maintenance.'), resource=volume)