#define read_barrier_depends() ((void)0)
#define set_rmb(var, value) do { xchg (&var, value); } while (0)
#define set_mb(var, value) set_rmb (var, value)
+#define set_wmb(var, value) do { var = value; wmb (); } while (0)
#define smp_mb() mb ()
#define smp_rmb() rmb ()