Fix config option default value for sample config file

There are multiple places where nova set the new default
value for other (than nova) namespace config option for
example oslo lib config options. Examples:

- 20572809f2/nova/config.py (L62)
- 20572809f2/nova/policy.py (L48)

and these defaults are reflected in code also which is working
as expected. But when config sample file is generated via
oslo-config-generator tool (tox -egenconfig) then these defaults
which are set by Nova are not reflected as this tool take the
raw defaults. To solve this issue oslo config provide a option
to add hook to reflect the new default in config generator
- https://docs.openstack.org/oslo.config/latest/cli/generator.html#modifying-defaults-from-other-namespaces

We already doing it for middleware cors option
- 20572809f2/setup.cfg (L41)

Fixing existing default value and if we find more or any future
change for default value, we need to add those config generator hook.

Change-Id: Ib0e926aec069dfb4ffd1bbfe8506d62464511b51
Closes-Bug: #1904250

nova/config.py

@@ -18,11 +18,13 @@
 import logging
 
 from oslo_log import log
+from oslo_policy import opts as policy_opts
 from oslo_utils import importutils
 
 import nova.conf
 from nova.db.sqlalchemy import api as sqlalchemy_api
 from nova import middleware
+from nova import policy
 from nova import rpc
 from nova import version
 
@@ -32,20 +34,52 @@ profiler = importutils.try_import('osprofiler.opts')
 CONF = nova.conf.CONF
 
 
+def set_lib_defaults():
+    """Update default value for configuration options from other namespace.
+
+    Example, oslo lib config options. This is needed for
+    config generator tool to pick these default value changes.
+    https://docs.openstack.org/oslo.config/latest/cli/
+    generator.html#modifying-defaults-from-other-namespaces
+    """
+
+    # Update default value of oslo.middleware cors config option.
+    middleware.set_defaults()
+
+    # Update default value of RPC transport control_exchange config option.
+    rpc.set_defaults(control_exchange='nova')
+
+    # Update default value of oslo_log default_log_levels and
+    # logging_context_format_string config option.
+    set_log_defaults()
+
+    # Update default value of oslo.policy policy_file config option.
+    policy_opts.set_defaults(CONF, policy.DEFAULT_POLICY_FILE)
+
+
 def rabbit_heartbeat_filter(log_record):
     message = "Unexpected error during heartbeat thread processing"
     return message not in log_record.msg
 
 
-def parse_args(argv, default_config_files=None, configure_db=True,
-               init_rpc=True):
-    log.register_options(CONF)
+def set_log_defaults():
     # We use the oslo.log default log levels which includes suds=INFO
     # and add only the extra levels that Nova needs
     if CONF.glance.debug:
         extra_default_log_levels = ['glanceclient=DEBUG']
     else:
         extra_default_log_levels = ['glanceclient=WARN']
+    # NOTE(danms): DEBUG logging in privsep will result in some large
+    # and potentially sensitive things being logged.
+    extra_default_log_levels.append('oslo.privsep.daemon=INFO')
+
+    log.set_defaults(default_log_levels=log.get_default_log_levels() +
+                     extra_default_log_levels)
+
+
+def parse_args(argv, default_config_files=None, configure_db=True,
+               init_rpc=True):
+    log.register_options(CONF)
 
     # NOTE(sean-k-mooney): this filter addresses bug #1825584
     # https://bugs.launchpad.net/nova/+bug/1825584
@@ -53,16 +87,9 @@ def parse_args(argv, default_config_files=None, configure_db=True,
     rabbit_logger = logging.getLogger('oslo.messaging._drivers.impl_rabbit')
     rabbit_logger.addFilter(rabbit_heartbeat_filter)
 
-    # NOTE(danms): DEBUG logging in privsep will result in some large
-    # and potentially sensitive things being logged.
-    extra_default_log_levels.append('oslo.privsep.daemon=INFO')
-
-    log.set_defaults(default_log_levels=log.get_default_log_levels() +
-                     extra_default_log_levels)
-    rpc.set_defaults(control_exchange='nova')
+    set_lib_defaults()
     if profiler:
         profiler.set_defaults(CONF)
-    middleware.set_defaults()
 
     CONF(argv[1:],
          project='nova',

setup.cfg

@@ -38,7 +38,7 @@ packages =
 oslo.config.opts =
     nova.conf = nova.conf.opts:list_opts
 oslo.config.opts.defaults =
-    nova.conf = nova.middleware:set_defaults
+    nova.conf = nova.config:set_lib_defaults
 oslo.policy.enforcer =
     nova = nova.policy:get_enforcer
 oslo.policy.policies =