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lock_fcntl.c
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lock_fcntl.c
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/* lock_fcntl.c -- Lock files using fcntl()
$Id: lock_fcntl.c,v 1.16 2003/02/13 20:15:40 rjs3 Exp $
* Copyright (c) 1998-2003 Carnegie Mellon University. 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. The name "Carnegie Mellon University" must not be used to
* endorse or promote products derived from this software without
* prior written permission. For permission or any other legal
* details, please contact
* Office of Technology Transfer
* Carnegie Mellon University
* 5000 Forbes Avenue
* Pittsburgh, PA 15213-3890
* (412) 268-4387, fax: (412) 268-7395
* tech-transfer@andrew.cmu.edu
*
* 4. Redistributions of any form whatsoever must retain the following
* acknowledgment:
* "This product includes software developed by Computing Services
* at Carnegie Mellon University (http://www.cmu.edu/computing/)."
*
* CARNEGIE MELLON UNIVERSITY DISCLAIMS ALL WARRANTIES WITH REGARD TO
* THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
* AND FITNESS, IN NO EVENT SHALL CARNEGIE MELLON UNIVERSITY BE LIABLE
* FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN
* AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
* OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*
*
*/
#include <config.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include "lock.h"
const char *lock_method_desc = "fcntl";
/*
* Block until we obtain an exclusive lock on the file descriptor 'fd',
* opened for reading and writing on the file named 'filename'. If
* 'filename' is replaced, will re-open it as 'fd' and acquire a lock
* on the new file.
*
* On success, returns 0. If a pointer to a struct stat is given as
* 'sbuf', it is filled in.
*
* On failure, returns -1 with an error code in errno. If
* 'failaction' is provided, it is filled in with a pointer to a fixed
* string naming the action that failed.
*
*/
int lock_reopen(fd, filename, sbuf, failaction)
int fd;
const char *filename;
struct stat *sbuf;
const char **failaction;
{
int r;
struct flock fl;
struct stat sbuffile, sbufspare;
int newfd;
if (!sbuf) sbuf = &sbufspare;
for (;;) {
fl.l_type= F_WRLCK;
fl.l_whence = SEEK_SET;
fl.l_start = 0;
fl.l_len = 0;
r = fcntl(fd, F_SETLKW, &fl);
if (r == -1) {
if (errno == EINTR) continue;
if (failaction) *failaction = "locking";
return -1;
}
fstat(fd, sbuf);
r = stat(filename, &sbuffile);
if (r == -1) {
if (failaction) *failaction = "stating";
fl.l_type= F_UNLCK;
fl.l_whence = SEEK_SET;
fl.l_start = 0;
fl.l_len = 0;
r = fcntl(fd, F_SETLKW, &fl);
return -1;
}
if (sbuf->st_ino == sbuffile.st_ino) return 0;
newfd = open(filename, O_RDWR);
if (newfd == -1) {
if (failaction) *failaction = "opening";
fl.l_type= F_UNLCK;
fl.l_whence = SEEK_SET;
fl.l_start = 0;
fl.l_len = 0;
r = fcntl(fd, F_SETLKW, &fl);
return -1;
}
dup2(newfd, fd);
close(newfd);
}
}
/*
* Obtain an exclusive lock on 'fd'.
* Returns 0 for success, -1 for failure, with errno set to an
* appropriate error code.
*/
int lock_blocking(fd)
int fd;
{
int r;
struct flock fl;
for (;;) {
fl.l_type= F_WRLCK;
fl.l_whence = SEEK_SET;
fl.l_start = 0;
fl.l_len = 0;
r = fcntl(fd, F_SETLKW, &fl);
if (r != -1) return 0;
if (errno == EINTR) continue;
return -1;
}
}
/*
* Obtain a shared lock on 'fd'.
* Returns 0 for success, -1 for failure, with errno set to an
* appropriate error code.
*/
int lock_shared(fd)
int fd;
{
int r;
struct flock fl;
for (;;) {
fl.l_type= F_RDLCK;
fl.l_whence = SEEK_SET;
fl.l_start = 0;
fl.l_len = 0;
r = fcntl(fd, F_SETLKW, &fl);
if (r != -1) return 0;
if (errno == EINTR) continue;
return -1;
}
}
/*
* Attempt to get an exclusive lock on 'fd' without blocking.
* Returns 0 for success, -1 for failure, with errno set to an
* appropriate error code.
*/
int lock_nonblocking(fd)
int fd;
{
int r;
struct flock fl;
for (;;) {
fl.l_type= F_WRLCK;
fl.l_whence = SEEK_SET;
fl.l_start = 0;
fl.l_len = 0;
r = fcntl(fd, F_SETLK, &fl);
if (r != -1) return 0;
if (errno == EINTR) continue;
return -1;
}
}
/*
* Release any lock on 'fd'. Always returns success.
*/
int lock_unlock(int fd)
{
struct flock fl;
int r;
fl.l_type= F_UNLCK;
fl.l_whence = SEEK_SET;
fl.l_start = 0;
fl.l_len = 0;
for (;;) {
r = fcntl(fd, F_SETLKW, &fl);
if (r != -1) return 0;
if (errno == EINTR) continue;
/* xxx help! */
return -1;
}
}

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