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/* $NetBSD: dotlock.c,v 1.11 2009/10/21 01:07:46 snj 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.
*
* 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.
*/
#include "sh.h"
RCSID("$tcsh: dotlock.c,v 3.4 2015/11/03 21:04:13 christos Exp $")
#include <stdio.h>
#ifndef O_SYNC
#define O_SYNC 0
#endif
#include "dotlock.h"
static int create_exclusive(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(const char *fname)
{
char path[MAXPATHLEN], hostname[MAXHOSTNAMELEN + 1];
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, sizeof(hostname));
hostname[sizeof(hostname) - 1] = '\0';
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.%lx",
(int)(ptr - fname), fname, hostname, (u_long)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;
}
/*
* fname -- Pathname to lock
* pollinterval -- Interval (miliseconds) to check for lock, -1 return
*/
int
dot_lock(const char *fname, int pollinterval)
{
char path[MAXPATHLEN];
sigset_t nset, oset;
int retval;
(void)sigemptyset(&nset);
(void)sigaddset(&nset, SIGHUP);
(void)sigaddset(&nset, SIGINT);
(void)sigaddset(&nset, SIGQUIT);
(void)sigaddset(&nset, SIGTERM);
(void)sigaddset(&nset, SIGTTIN);
(void)sigaddset(&nset, SIGTTOU);
(void)sigaddset(&nset, SIGTSTP);
(void)sigaddset(&nset, SIGCHLD);
(void)snprintf(path, sizeof(path), "%s.lock", fname);
retval = -1;
for (;;) {
handle_pending_signals();
(void)sigprocmask(SIG_BLOCK, &nset, &oset);
if (create_exclusive(path) != -1) {
(void)sigprocmask(SIG_SETMASK, &oset, NULL);
retval = 0;
break;
}
else
(void)sigprocmask(SIG_SETMASK, &oset, NULL);
if (errno != EEXIST)
break;
if (pollinterval) {
if (pollinterval == -1) {
errno = EEXIST;
break;
}
(void)usleep((unsigned int)pollinterval * 1000);
}
}
handle_pending_signals();
return retval;
}
void
dot_unlock(const char *fname)
{
char path[MAXPATHLEN];
(void)snprintf(path, sizeof(path), "%s.lock", fname);
(void)unlink(path);
}
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