Only log deprecated config warnings once.

Updates Nova's deprecated warn function so that we only log
messages about deprecated config options once.

The motivation for this change is to cut down the log file noise
when deprecated config code gets called more than once.

Change-Id: If8919817330dc9461a0472fea982d43c78a86f66

nova/common/deprecated.py

@@ -14,6 +14,8 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import warnings
+
 from nova import exception
 from nova import flags
 from nova.openstack.common import cfg
@@ -30,6 +32,17 @@ FLAGS = flags.FLAGS
 FLAGS.register_opts(deprecate_opts)
 
 
+def _showwarning(message, category, filename, lineno, file=None, line=None):
+    """
+    Redirect warnings into logging.
+    """
+    LOG.warn(str(message))
+
+
+# Install our warnings handler
+warnings.showwarning = _showwarning
+
+
 def warn(msg=""):
     """
     Warn of a deprecated config option that an operator has specified.
@@ -37,6 +50,6 @@ def warn(msg=""):
     we use some operator changeable parameter to indicate that it will
     go away in a future version of OpenStack.
     """
-    LOG.warn(_("Deprecated Config: %s") % msg)
+    warnings.warn(_("Deprecated Config: %s") % msg)
     if FLAGS.fatal_deprecations:
         raise exception.DeprecatedConfig(msg=msg)

nova/tests/test_deprecated.py

@@ -38,3 +38,9 @@ class DeprecatedConfigTestCase(test.TestCase):
         self.assertRaises(exception.DeprecatedConfig,
                           deprecated.warn, "test2")
         self.assertEqual(self.logbuffer, 'Deprecated Config: test2')
+
+    def test_deprecated_logs_only_once(self):
+        deprecated.warn('only once!')
+        deprecated.warn('only once!')
+        deprecated.warn('only once!')
+        self.assertEqual(self.logbuffer, 'Deprecated Config: only once!')