From 76c0ce9a3599191b646311069f2c7e11a3be5098 Mon Sep 17 00:00:00 2001
From: millert <millert@openbsd.org>
Date: Mon, 13 Mar 2000 04:05:13 +0000
Subject: [PATCH] Get rid of leading NULs in /kern/msgbuf.  If the msgbuf
 modified in between reads at just the right time is is possible to get
 duplicate output but in practice this is extremely rare.  Joint effort with
 Theo.

---
 sys/kern/subr_prf.c              |  3 ++-
 sys/miscfs/kernfs/kernfs_vnops.c | 21 ++++++++++++++-------
 sys/sys/msgbuf.h                 |  3 ++-
 3 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/sys/kern/subr_prf.c b/sys/kern/subr_prf.c
index 5ab131ddc8d..5bd4b69546d 100644
--- a/sys/kern/subr_prf.c
+++ b/sys/kern/subr_prf.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: subr_prf.c,v 1.28 2000/03/02 10:50:29 art Exp $	*/
+/*	$OpenBSD: subr_prf.c,v 1.29 2000/03/13 04:05:15 millert Exp $	*/
 /*	$NetBSD: subr_prf.c,v 1.45 1997/10/24 18:14:25 chuck Exp $	*/
 
 /*-
@@ -335,6 +335,7 @@ putchar(c, flags, tp)
 			/* Nothing we can do */
 		}
 		mbp->msg_bufc[mbp->msg_bufx++] = c;
+		mbp->msg_bufl = min(mbp->msg_bufl+1, mbp->msg_bufs);
 		if (mbp->msg_bufx < 0 || mbp->msg_bufx >= mbp->msg_bufs)
 			mbp->msg_bufx = 0;
                 /* If the buffer is full, keep the most recent data. */
diff --git a/sys/miscfs/kernfs/kernfs_vnops.c b/sys/miscfs/kernfs/kernfs_vnops.c
index 23922ae3343..160e437ed0a 100644
--- a/sys/miscfs/kernfs/kernfs_vnops.c
+++ b/sys/miscfs/kernfs/kernfs_vnops.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: kernfs_vnops.c,v 1.18 2000/02/22 19:28:06 deraadt Exp $	*/
+/*	$OpenBSD: kernfs_vnops.c,v 1.19 2000/03/13 04:05:15 millert Exp $	*/
 /*	$NetBSD: kernfs_vnops.c,v 1.43 1996/03/16 23:52:47 christos Exp $	*/
 
 /*
@@ -269,12 +269,19 @@ kernfs_xread(kt, off, bufp, len)
 		 * message buffer header are corrupted, but that'll cause
 		 * the system to die anyway.
 		 */
-		if (off >= msgbufp->msg_bufs)
-			return (0);
-		n = msgbufp->msg_bufx + off;
-		if (n >= msgbufp->msg_bufs)
-			n -= msgbufp->msg_bufs;
-		len = min(msgbufp->msg_bufs - n, msgbufp->msg_bufs - off);
+		if (msgbufp->msg_bufl < msgbufp->msg_bufs) {
+			if (off >= msgbufp->msg_bufx)
+				return (0);
+			n = off;
+			len = msgbufp->msg_bufx - n;
+		} else {
+			if (off >= msgbufp->msg_bufs)
+				return (0);
+			n = msgbufp->msg_bufx + off;
+			if (n >= msgbufp->msg_bufs)
+				n -= msgbufp->msg_bufs;
+			len = min(msgbufp->msg_bufs - n, msgbufp->msg_bufs - off);
+		}
 		*bufp = msgbufp->msg_bufc + n;
 		return (len);
 	}
diff --git a/sys/sys/msgbuf.h b/sys/sys/msgbuf.h
index 1214c4cbc8d..a09cc13dc5c 100644
--- a/sys/sys/msgbuf.h
+++ b/sys/sys/msgbuf.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: msgbuf.h,v 1.3 2000/02/22 19:28:05 deraadt Exp $	*/
+/*	$OpenBSD: msgbuf.h,v 1.4 2000/03/13 04:05:13 millert Exp $	*/
 /*	$NetBSD: msgbuf.h,v 1.8 1995/03/26 20:24:27 jtc Exp $	*/
 
 /*
@@ -42,6 +42,7 @@ struct	msgbuf {
 	long	msg_bufx;		/* write pointer */
 	long	msg_bufr;		/* read pointer */
 	long	msg_bufs;		/* real msg_bufc size (bytes) */
+	long	msg_bufl;		/* # chars, <= msg_bufs */
 	char	msg_bufc[1];		/* buffer */
 };
 #ifdef _KERNEL
-- 
2.20.1