rbd: Remove unnecessary 'encode' calls

The ceph 'rbd' library (librados) now supports Python 3 and, by
extension, unicode strings [1]. There is no need to keep these encode
calls around: if a user is running nova under Python 3, then it is safe
to assume that they are using a Python 3-compatible version of librados.

[1] https://github.com/ceph/ceph/blob/v11.1.0/src/pybind/rados/rados.pyx#L30-L36

Change-Id: Ic1afb3e66bd0991047f97fa74f9d2fbbb837401a

nova/tests/unit/virt/libvirt/storage/test_rbd.py

@@ -13,7 +13,6 @@
 
 from eventlet import tpool
 import mock
-import six
 
 from nova.compute import task_states
 from nova import exception
@@ -223,7 +222,7 @@ class RbdTestCase(test.NoDBTestCase):
 
         self.driver.clone(location, self.volume_name)
 
-        args = [client_stack[0].ioctx, six.b(image), six.b(snap),
+        args = [client_stack[0].ioctx, image, snap,
                 client_stack[1].ioctx, str(self.volume_name)]
         kwargs = {'features': client.features}
         rbd.clone.assert_called_once_with(*args, **kwargs)

nova/virt/libvirt/storage/rbd_utils.py

@@ -66,10 +66,9 @@ class RBDVolumeProxy(object):
                  read_only=False):
         client, ioctx = driver._connect_to_rados(pool)
         try:
-            snap_name = snapshot.encode('utf8') if snapshot else None
-            self.volume = tpool.Proxy(rbd.Image(ioctx, name.encode('utf8'),
-                                      snapshot=snap_name,
-                                      read_only=read_only))
+            self.volume = tpool.Proxy(rbd.Image(ioctx, name,
+                                                snapshot=snapshot,
+                                                read_only=read_only))
         except rbd.ImageNotFound:
             with excutils.save_and_reraise_exception():
                 LOG.debug("rbd image %s does not exist", name)
@@ -236,8 +235,8 @@ class RBDDriver(object):
             with RADOSClient(self, dest_pool) as dest_client:
                 try:
                     RbdProxy().clone(src_client.ioctx,
-                                     image.encode('utf-8'),
-                                     snapshot.encode('utf-8'),
+                                     image,
+                                     snapshot,
                                      dest_client.ioctx,
                                      str(dest_name),
                                      features=src_client.features)

releasenotes/notes/ceph-minimum-version-bump-6ef4597c3e117201.yaml

@@ -0,0 +1,6 @@
+---
+upgrade:
+  - |
+    Nova now requires Ceph/librados >= 11.1.0 if running under Python 3 with
+    the RBD image backend for the libvirt driver. Requirements for Python 2
+    users or users using a different backend remain unchanged.