diff -r 598d92a5ae7a xen/include/public/io/ring.h
--- a/xen/include/public/io/ring.h	Wed Aug 20 14:45:21 2008 +0100
+++ b/xen/include/public/io/ring.h	Thu Aug 21 11:27:43 2008 +0200
@@ -30,9 +30,16 @@
 #include "../xen-compat.h"
 
 #if __XEN_INTERFACE_VERSION__ < 0x00030208
+#if defined(__Linux__)
 #define xen_mb()  mb()
 #define xen_rmb() rmb()
 #define xen_wmb() wmb()
+#endif
+#if defined(__NetBSD__)
+#define xen_mb()  x86_mfence()
+#define xen_rmb() x86_lfence()
+#define xen_wmb() x86_sfence()
+#endif
 #endif
 
 typedef unsigned int RING_IDX;