Add common logging and notification.

This code is migrated from Nova, and will soon replace it.

Change-Id: I2dacac3ef251d419c7049154f6aaf0c18fdb9bb4

openstack/common/exception.py

@@ -19,6 +19,7 @@
 Exceptions common to OpenStack projects
 """
 
+import itertools
 import logging
 
 
@@ -145,3 +146,20 @@ class MalformedRequestBody(OpenstackException):
 
 class InvalidContentType(OpenstackException):
     message = "Invalid content type %(content_type)s"
+
+
+def get_context_from_function_and_args(function, args, kwargs):
+    """Find an arg of type RequestContext and return it.
+
+       This is useful in a couple of decorators where we don't
+       know much about the function we're wrapping.
+    """
+
+    # import here to avoid circularity:
+    from openstack.common import context
+
+    for arg in itertools.chain(kwargs.values(), args):
+        if isinstance(arg, context.RequestContext):
+            return arg
+
+    return None