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rcsid[] and sccsid[] and copyright[] are essentially unmaintained (and
unmaintainable).  these days, people use source.  these id's do not provide
any benefit, and do hurt the small install media
(the 33,000 line diff is essentially mechanical)
ok with the idea millert, ok dms

/*	$OpenBSD: ttymsg.c,v 1.16 2009/10/27 23:59:49 deraadt Exp $	*/
/*	$NetBSD: ttymsg.c,v 1.3 1994/11/17 07:17:55 jtc Exp $	*/

/*
 * Copyright (c) 1989, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * 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. 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.
 */

#include <sys/types.h>
#include <sys/uio.h>
#include <signal.h>
#include <fcntl.h>
#include <dirent.h>
#include <errno.h>
#include <paths.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/stat.h>

char *ttymsg(struct iovec *, int, char *, int);

/*
 * Display the contents of a uio structure on a terminal.  Used by wall(1)
 * and talkd(8).  Forks and finishes in child if write would block,
 * waiting up to tmout seconds.  Returns pointer to error string on unexpected
 * error; string is not newline-terminated.  Various "normal" errors are
 * ignored (exclusive-use, lack of permission, etc.).
 */
char *
ttymsg(iov, iovcnt, line, tmout)
	struct iovec *iov;
	int iovcnt;
	char *line;
	int tmout;
{
	static char device[MAXNAMLEN] = _PATH_DEV;
	static char errbuf[1024];
	int cnt, fd, left, wret;
	struct iovec localiov[6];
	int forked = 0;
	struct stat st;
	sigset_t mask;

	if (iovcnt > sizeof(localiov) / sizeof(localiov[0]))
		return ("too many iov's (change code in wall/ttymsg.c)");

	/*
	 * Ignore lines that start with "ftp" or "uucp".
	 */
	if ((strncmp(line, "ftp", 3) == 0) ||
	    (strncmp(line, "uucp", 4) == 0))
		return (NULL);

	(void) strlcpy(device + sizeof(_PATH_DEV) - 1, line,
	    sizeof(device) - (sizeof(_PATH_DEV) - 1));
	if (strchr(device + sizeof(_PATH_DEV) - 1, '/')) {
		/* A slash is an attempt to break security... */
		(void) snprintf(errbuf, sizeof(errbuf), "'/' in \"%s\"",
		    device);
		return (errbuf);
	}

	if (getuid()) {
		if (stat(device, &st) < 0)
			return (NULL);
		if ((st.st_mode & S_IWGRP) == 0)
			return (NULL);
	}

	/*
	 * open will fail on slip lines or exclusive-use lines
	 * if not running as root; not an error.
	 */
	if ((fd = open(device, O_WRONLY|O_NONBLOCK, 0)) < 0) {
		if (errno == EBUSY || errno == EACCES)
			return (NULL);
		(void) snprintf(errbuf, sizeof(errbuf),
		    "%s: %s", device, strerror(errno));
		return (errbuf);
	}

	for (cnt = left = 0; cnt < iovcnt; ++cnt)
		left += iov[cnt].iov_len;

	for (;;) {
		wret = writev(fd, iov, iovcnt);
		if (wret >= left)
			break;
		if (wret >= 0) {
			left -= wret;
			if (iov != localiov) {
				bcopy(iov, localiov,
				    iovcnt * sizeof(struct iovec));
				iov = localiov;
			}
			for (cnt = 0; wret >= iov->iov_len; ++cnt) {
				wret -= iov->iov_len;
				++iov;
				--iovcnt;
			}
			if (wret) {
				char *base = iov->iov_base;

				iov->iov_base = base + wret;
				iov->iov_len -= wret;
			}
			continue;
		}
		if (errno == EWOULDBLOCK) {
			int off = 0;
			pid_t cpid;

			if (forked) {
				(void) close(fd);
				_exit(1);
			}
			cpid = fork();
			if (cpid < 0) {
				(void) snprintf(errbuf, sizeof(errbuf),
				    "fork: %s", strerror(errno));
				(void) close(fd);
				return (errbuf);
			}
			if (cpid) {	/* parent */
				(void) close(fd);
				return (NULL);
			}
			forked++;
			/* wait at most tmout seconds */
			(void) signal(SIGALRM, SIG_DFL);
			(void) signal(SIGTERM, SIG_DFL); /* XXX */
			(void) sigemptyset(&mask);
			(void) sigprocmask(SIG_SETMASK, &mask, NULL);
			(void) alarm((u_int)tmout);
			(void) fcntl(fd, O_NONBLOCK, &off);
			continue;
		}
		/*
		 * We get ENODEV on a slip line if we're running as root,
		 * and EIO if the line just went away.
		 */
		if (errno == ENODEV || errno == EIO)
			break;
		(void) close(fd);
		if (forked)
			_exit(1);
		(void) snprintf(errbuf, sizeof(errbuf),
		    "%s: %s", device, strerror(errno));
		return (errbuf);
	}

	(void) close(fd);
	if (forked)
		_exit(0);
	return (NULL);
}