Introduce ofpacts, an abstraction of OpenFlow actions.

OpenFlow actions have always been somewhat awkward to handle.
Moreover, over time we've started creating actions that require more
complicated parsing.  When we maintain those actions internally in
their wire format, we end up parsing them multiple times, whenever
we have to look at the set of actions.

When we add support for OpenFlow 1.1 or later protocols, the situation
will get worse, because these newer protocols support many of the same
actions but with different representations.  It becomes unrealistic to
handle each protocol in its wire format.

This commit adopts a new strategy, by converting OpenFlow actions into
an internal form from the wire format when they are read, and converting
them back to the wire format when flows are dumped.  I believe that this
will be more maintainable over time.

Thanks to Simon Horman and Pravin Shelar for reviews.

Signed-off-by: Ben Pfaff <blp@nicira.com>

lib/compiler.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008, 2009, 2010, 2011 Nicira, Inc.
+ * Copyright (c) 2008, 2009, 2010, 2011, 2012 Nicira, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -37,4 +37,22 @@
 #define SENTINEL(N)
 #endif
 
+/* ISO C says that a C implementation may choose any integer type for an enum
+ * that is sufficient to hold all of its values.  Common ABIs (such as the
+ * System V ABI used on i386 GNU/Linux) always use a full-sized "int", even
+ * when a smaller type would suffice.
+ *
+ * In GNU C, "enum __attribute__((packed)) name { ... }" defines 'name' as an
+ * enum compatible with a type that is no bigger than necessary.  This is the
+ * intended use of OVS_PACKED_ENUM.
+ *
+ * OVS_PACKED_ENUM is intended for use only as a space optimization, since it
+ * only works with GCC.  That means that it must not be used in wire protocols
+ * or otherwise exposed outside of a single process. */
+#if __GNUC__ && !__CHECKER__
+#define OVS_PACKED_ENUM __attribute__((__packed__))
+#else
+#define OVS_PACKED_ENUM
+#endif
+
 #endif /* compiler.h */