Index: head/sys/sys/systm.h
===================================================================
--- head/sys/sys/systm.h
+++ head/sys/sys/systm.h
@@ -107,15 +107,23 @@
 } while (0)
 #define	VNASSERT(exp, vp, msg) do {					\
 	if (__predict_false(!(exp))) {					\
-		vn_printf(vp, "VNASSERT failed\n");			\
+		vn_printf(vp, "VNASSERT failed: %s not true at %s:%d (%s)\n",\
+		   #exp, __FILE__, __LINE__, __func__);	 		\
 		kassert_panic msg;					\
 	}								\
 } while (0)
+#define	VNPASS(exp, vp)	do {						\
+	const char *_exp = #exp;					\
+	VNASSERT(exp, vp, ("condition %s not met at %s:%d (%s)",	\
+	    _exp, __FILE__, __LINE__, __func__));			\
+} while (0)
 #else
 #define	KASSERT(exp,msg) do { \
 } while (0)
 
 #define	VNASSERT(exp, vp, msg) do { \
+} while (0)
+#define	VNPASS(exp, vp) do { \
 } while (0)
 #endif