X-Git-Url: http://git.onelab.eu/?a=blobdiff_plain;f=lib%2Fcompiler.h;h=27612a74a8efb21618f9685e7439cf7fe1cbcb70;hb=f25d0cf3c366d92042269a4f787f19c741c2530c;hp=75e86103a7dabddcccfcc316f28ddf3326f1f0f7;hpb=690a61c50a4744603be2ee3de8e22c97f9140d94;p=sliver-openvswitch.git

diff --git a/lib/compiler.h b/lib/compiler.h
index 75e86103a..27612a74a 100644
--- a/lib/compiler.h
+++ b/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 */