Talk a little about the system message buffer and cross-reference

MSGBUFSIZE in options(4).

sbin/dmesg/dmesg.8

@@ -1,4 +1,4 @@
-.\"	$NetBSD: dmesg.8,v 1.14 2003/08/07 10:04:13 agc Exp $
+.\"	$NetBSD: dmesg.8,v 1.15 2004/04/30 13:34:48 briggs Exp $
 .\"
 .\" Copyright (c) 1980, 1991, 1993
 .\"	The Regents of the University of California.  All rights reserved.
@@ -52,12 +52,27 @@ instead of the default ``/dev/mem''.
 Extract the name list from the specified system instead of the default
 ``/netbsd''.
 .El
+.Pp
+The system message buffer is a circular buffer of a fixed size.
+If the buffer has been filled, the first line of the
+.Nm
+output may not be complete.
+The size of the message buffer is configurable at compile-time on
+most systems with the
+.Em MSGBUFSIZE
+kernel option.
+Look for
+.Em MSGBUFSIZE
+in
+.Xr options 4
+for details.
 .Sh FILES
 .Bl -tag -width /var/run/dmesg.boot -compact
 .It Pa /var/run/dmesg.boot
 copy of dmesg at the time of last boot.
 .El
 .Sh SEE ALSO
+.Xr options 4
 .Xr syslogd 8
 .Sh HISTORY
 The