--- Net2/sys/trace.h	2018/04/24 18:03:58	1.1
+++ Net2/sys/trace.h	2018/04/24 18:16:40	1.1.1.2
@@ -30,9 +30,13 @@
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  *
- *	@(#)trace.h	7.6 (Berkeley) 5/5/91
+ *	from: @(#)trace.h	7.6 (Berkeley) 5/5/91
+ *	trace.h,v 1.3 1993/05/20 16:23:28 cgd Exp
  */
 
+#ifndef _SYS_TRACE_H_
+#define _SYS_TRACE_H_
+
 /*
  * File system buffer tracing points; all trace <pack(dev, size), bn>
  */
@@ -112,3 +116,5 @@ int	tracewhich;
 #define	trace(a,b,c)	;
 #endif
 #endif
+
+#endif /* !_SYS_TRACE_H_ */