/*
 * Copyright (c) 1987 Regents of the University of California.
 * All rights reserved.
 * (c) UNIX System Laboratories, Inc.
 * All or some portions of this file are derived from material licensed
 * to the University of California by American Telephone and Telegraph
 * Co. or Unix System Laboratories, Inc. and are reproduced herein with
 * the permission of UNIX System Laboratories, Inc.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#ifndef lint
char copyright[] =
"@(#) Copyright (c) 1987 Regents of the University of California.\n\
 All rights reserved.\n";
#endif /* not lint */

#ifndef lint
/*static char sccsid[] = "from: @(#)mesg.c	4.7 (Berkeley) 3/1/91";*/
static char rcsid[] = "$Id: mesg.c,v 1.3 1994/05/17 04:15:59 cgd Exp $";
#endif /* not lint */

/*
 * mesg -- set current tty to accept or
 *	forbid write permission.
 *
 *	mesg [y] [n]
 *		y allow messages
 *		n forbid messages
 */

#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>

static char *tty;

main(argc, argv)
	int argc;
	char **argv;
{
	struct stat sbuf;
	char *ttyname();

	if (!(tty = ttyname(2))) {
		fputs("mesg: not a device in /dev.\n", stderr);
		exit(-1);
	}
	if (stat(tty, &sbuf) < 0) {
		perror("mesg");
		exit(-1);
	}
	if (argc < 2) {
		if (sbuf.st_mode & 020) {
			fputs("is y\n", stderr);
			exit(0);
		}
		fputs("is n\n", stderr);
		exit(1);
	}
#define	OTHER_WRITE	020
	switch(*argv[1]) {
	case 'y':
		newmode(sbuf.st_mode | OTHER_WRITE);
		exit(0);
	case 'n':
		newmode(sbuf.st_mode &~ OTHER_WRITE);
		exit(1);
	default:
		fputs("usage: mesg [y] [n]\n", stderr);
		exit(-1);
	}
	/*NOTREACHED*/
}

newmode(m)
	u_short m;
{
	if (chmod(tty, m) < 0) {
		perror("mesg");
		exit(-1);
	}
}