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/* $OpenBSD: dotlock.c,v 1.1 1996/06/11 12:53:37 deraadt Exp $ */
/* $NetBSD: dotlock.c,v 1.1 1996/06/08 19:48:19 christos Exp $ */
/*
* Copyright (c) 1996 Christos Zoulas. 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 Christos Zoulas.
* 4. The name of the author may not be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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 rcsid[] = "$OpenBSD: dotlock.c,v 1.1 1996/06/11 12:53:37 deraadt Exp $";
#endif
#include <sys/types.h>
#include <sys/param.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <signal.h>
#include "extern.h"
#ifndef O_SYNC
#define O_SYNC 0
#endif
static int create_exclusive __P((const char *));
/*
* Create a unique file. O_EXCL does not really work over NFS so we follow
* the following trick: [Inspired by S.R. van den Berg]
*
* - make a mostly unique filename and try to create it.
* - link the unique filename to our target
* - get the link count of the target
* - unlink the mostly unique filename
* - if the link count was 2, then we are ok; else we've failed.
*/
static int
create_exclusive(fname)
const char *fname;
{
char path[MAXPATHLEN], hostname[MAXHOSTNAMELEN];
const char *ptr;
struct timeval tv;
pid_t pid;
size_t ntries, cookie;
int fd, serrno;
struct stat st;
(void) gettimeofday(&tv, NULL);
(void) gethostname(hostname, MAXHOSTNAMELEN);
pid = getpid();
cookie = pid ^ tv.tv_usec;
/*
* We generate a semi-unique filename, from hostname.(pid ^ usec)
*/
if ((ptr = strrchr(fname, '/')) == NULL)
ptr = fname;
else
ptr++;
(void) snprintf(path, sizeof(path), "%.*s.%s.%x",
ptr - fname, fname, hostname, cookie);
/*
* We try to create the unique filename.
*/
for (ntries = 0; ntries < 5; ntries++) {
fd = open(path, O_WRONLY|O_CREAT|O_TRUNC|O_EXCL|O_SYNC, 0);
if (fd != -1) {
(void) close(fd);
break;
}
else if (errno == EEXIST)
continue;
else
return -1;
}
/*
* We link the path to the name
*/
if (link(path, fname) == -1)
goto bad;
/*
* Note that we stat our own exclusively created name, not the
* destination, since the destination can be affected by others.
*/
if (stat(path, &st) == -1)
goto bad;
(void) unlink(path);
/*
* If the number of links was two (one for the unique file and one
* for the lock), we've won the race
*/
if (st.st_nlink != 2) {
errno = EEXIST;
return -1;
}
return 0;
bad:
serrno = errno;
(void) unlink(path);
errno = serrno;
return -1;
}
int
dot_lock(fname, pollinterval, fp, msg)
const char *fname; /* Pathname to lock */
int pollinterval; /* Interval to check for lock, -1 return */
FILE *fp; /* File to print message */
const char *msg; /* Message to print */
{
char path[MAXPATHLEN];
sigset_t nset, oset;
sigemptyset(&nset);
sigaddset(&nset, SIGHUP);
sigaddset(&nset, SIGINT);
sigaddset(&nset, SIGQUIT);
sigaddset(&nset, SIGTERM);
sigaddset(&nset, SIGTTIN);
sigaddset(&nset, SIGTTOU);
sigaddset(&nset, SIGTSTP);
sigaddset(&nset, SIGCHLD);
(void) snprintf(path, sizeof(path), "%s.lock", fname);
for (;;) {
(void) sigprocmask(SIG_BLOCK, &nset, &oset);
if (create_exclusive(path) != -1) {
(void) sigprocmask(SIG_SETMASK, &oset, NULL);
return 0;
}
else
(void) sigprocmask(SIG_SETMASK, &oset, NULL);
if (errno != EEXIST)
return -1;
if (fp && msg)
(void) fputs(msg, fp);
if (pollinterval) {
if (pollinterval == -1) {
errno = EEXIST;
return -1;
}
sleep(pollinterval);
}
}
}
void
dot_unlock(fname)
const char *fname;
{
char path[MAXPATHLEN];
(void) snprintf(path, sizeof(path), "%s.lock", fname);
(void) unlink(path);
}
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