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lock_flock.c
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lock_flock.c
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/* lock_flock.c -- Lock files using flock()
$Id: lock_flock.c,v 1.8 1998/05/15 21:51:56 neplokh Exp $
# Copyright 1998 by Carnegie Mellon University
#
# All Rights Reserved
#
# Permission to use, copy, modify, and distribute this software and its
# documentation for any purpose and without fee is hereby granted,
# provided that the above copyright notice appear in all copies and that
# both that copyright notice and this permission notice appear in
# supporting documentation, and that the name of CMU not be
# used in advertising or publicity pertaining to distribution of the
# software without specific, written prior permission.
#
# CMU DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING
# ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL
# CMU 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 <sys/file.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include "lock.h"
extern int errno;
/*
* 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 stat sbuffile, sbufspare;
int newfd;
if (!sbuf) sbuf = &sbufspare;
for (;;) {
r = flock(fd, LOCK_EX);
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";
flock(fd, LOCK_UN);
return -1;
}
if (sbuf->st_ino == sbuffile.st_ino) return 0;
newfd = open(filename, O_RDWR);
if (newfd == -1) {
if (failaction) *failaction = "opening";
flock(fd, LOCK_UN);
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;
for (;;) {
r = flock(fd, LOCK_EX);
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;
for (;;) {
r = flock(fd, LOCK_SH);
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;
for (;;) {
r = flock(fd, LOCK_EX|LOCK_NB);
if (r != -1) return 0;
if (errno == EINTR) continue;
return -1;
}
}
/*
* Release any lock on 'fd'. Always returns success.
*/
lock_unlock(fd)
int fd;
{
flock(fd, LOCK_UN);
return 0;
}

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