Deprecate defining c-vol backends in DEFAULT

We will, in future releases, remove support for this. For
now we will log a big warning when someone uses c-vol without
an enabled_backends config set.

DocImpact: Need to document upgrade path and new
recommended config.
Implements: blueprint shared-backend-config

Change-Id: Idf0a7346ae5d5ae45f9fc05a526ef5d66b162a3f

cinder/cmd/all.py

@@ -43,7 +43,7 @@ i18n.enable_lazy()
 from cinder.cmd import volume as volume_cmd
 from cinder.common import config   # noqa
 from cinder.db import api as session
-from cinder.i18n import _LE, _
+from cinder.i18n import _LE, _, _LW
 from cinder import objects
 from cinder import rpc
 from cinder import service
@@ -104,6 +104,10 @@ def main():
                 session.dispose_engine()
                 launcher.launch_service(server)
         else:
+            LOG.warning(_LW('Configuration for cinder-volume does not specify '
+                            '"enabled_backends", using DEFAULT as backend. '
+                            'Support for DEFAULT section to configure drivers '
+                            'will be removed in the next release.'))
             server = service.Service.create(binary='cinder-volume',
                                             coordination=True)
             launcher.launch_service(server)

cinder/cmd/volume.py

@@ -44,7 +44,7 @@ i18n.enable_lazy()
 # Need to register global_opts
 from cinder.common import config  # noqa
 from cinder.db import api as session
-from cinder.i18n import _
+from cinder.i18n import _, _LW
 from cinder import service
 from cinder import utils
 from cinder import version
@@ -91,6 +91,10 @@ def main():
                 launcher.launch_service(server)
                 service_started = True
     else:
+        LOG.warning(_LW('Configuration for cinder-volume does not specify '
+                        '"enabled_backends", using DEFAULT as backend. '
+                        'Support for DEFAULT section to configure drivers '
+                        'will be removed in the next release.'))
         server = service.Service.create(binary='cinder-volume',
                                         coordination=True)
         launcher.launch_service(server)

releasenotes/notes/deprecate-backends-in-default-b9784a2333fe22f2.yaml

@@ -0,0 +1,10 @@
+---
+upgrade:
+  - Any Volume Drivers configured in the DEFAULT config stanza should be moved
+    to their own stanza and enabled via the enabled_backends config option.
+    The older style of config with DEFAULT is deprecated and will be
+    removed in future releases.
+deprecations:
+  - Configuring Volume Drivers in the DEFAULT config stanza is not going to be
+    maintained and will be removed in the next release. All backends should use
+    the enabled_backends config option with separate stanza's for each.