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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: uucplock.c,v 1.12 2009/10/27 23:59:45 deraadt Exp $	*/
/*	$NetBSD: uucplock.c,v 1.7 1997/02/11 09:24:08 mrg Exp $	*/

/*
 * Copyright (c) 1988, 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/file.h>
#include <sys/dir.h>
#include <stdio.h>
#include <string.h>
#include <signal.h>
#include <unistd.h>
#include <stdlib.h>
#include <errno.h>
#include "pathnames.h"

/*
 * uucp style locking routines
 * return: 0 - success
 *	  -1 - failure
 */

int
uu_lock(char *ttyname)
{
	int fd, len;
	char tbuf[sizeof(_PATH_LOCKDIRNAME) + MAXNAMLEN];
	char text_pid[81];
	pid_t pid;

	(void)snprintf(tbuf, sizeof tbuf, _PATH_LOCKDIRNAME, ttyname);
	fd = open(tbuf, O_RDWR|O_CREAT|O_EXCL, 0660);
	if (fd < 0) {
		/*
		 * file is already locked
		 * check to see if the process holding the lock still exists
		 */
		fd = open(tbuf, O_RDWR, 0);
		if (fd < 0) {
			perror(tbuf);
			fprintf(stderr, "Can't open lock file.\n");
			return(-1);
		}
		len = read(fd, text_pid, sizeof(text_pid)-1);
		if (len<=0) {
			perror(tbuf);
			(void)close(fd);
			fprintf(stderr, "Can't read lock file.\n");
			return(-1);
		}
		text_pid[len] = 0;
		pid = atol(text_pid);

		if (kill(pid, 0) == 0 || errno != ESRCH) {
			(void)close(fd);	/* process is still running */
			return(-1);
		}
		/*
		 * The process that locked the file isn't running, so
		 * we'll lock it ourselves
		 */
		fprintf(stderr, "Stale lock on %s PID=%ld... overriding.\n",
			ttyname, (long)pid);
		if (lseek(fd, (off_t)0, SEEK_SET) < 0) {
			perror(tbuf);
			(void)close(fd);
			fprintf(stderr, "Can't seek lock file.\n");
			return(-1);
		}
		/* fall out and finish the locking process */
	}
	pid = getpid();
	(void)snprintf(text_pid, sizeof text_pid, "%10ld\n", (long)pid);
	len = strlen(text_pid);
	if (write(fd, text_pid, len) != len) {
		(void)close(fd);
		(void)unlink(tbuf);
		perror("lock write");
		return(-1);
	}
	(void)close(fd);
	return(0);
}

int
uu_unlock(char *ttyname)
{
	char tbuf[sizeof(_PATH_LOCKDIRNAME) + MAXNAMLEN];

	(void)snprintf(tbuf, sizeof tbuf, _PATH_LOCKDIRNAME, ttyname);
	return(unlink(tbuf));
}