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uucplock.c

/*
 * Copyright (c) 1988 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. 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
static char sccsid[] = "@(#)uucplock.c    5.5 (Berkeley) 6/1/90";
#endif /* not lint */

#include "config.h"

#include <sys/file.h>
#include <sys/dir.h>
#include <errno.h>

#include "pathnames.h"

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

uu_lock(ttyname)
      char *ttyname;
{
      extern int errno;
      int fd, pid;
      char tbuf[sizeof(_PATH_LOCKDIRNAME) + MAXNAMLEN];
      off_t lseek();

      (void)snprintf(tbuf, sizeof(tbuf), _PATH_LOCKDIRNAME, ttyname);
      fd = open(tbuf, O_RDWR|O_CREAT|O_EXCL, 0664);
      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("lock open");
                  return(-1);
            }
            if (read(fd, &pid, sizeof(pid)) != sizeof(pid)) {
                  (void)close(fd);
                  perror("lock read");
                  return(-1);
            }

            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
             */
            if (lseek(fd, 0L, L_SET) < 0) {
                  (void)close(fd);
                  perror("lock lseek");
                  return(-1);
            }
            /* fall out and finish the locking process */
      }
      pid = getpid();
      if (write(fd, (char *)&pid, sizeof(pid)) != sizeof(pid)) {
            (void)close(fd);
            (void)unlink(tbuf);
            perror("lock write");
            return(-1);
      }
      (void)close(fd);
      return(0);
}

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

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

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