7f15c32d76
This is easy to confuse with the actual exit status of the program. Instead exit with EX_SOFTWARE if the command doesn't exit normally. MFC after: 1 month
238 lines
6.3 KiB
C
238 lines
6.3 KiB
C
/*
|
|
* Copyright (C) 1997 John D. Polstra. 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 JOHN D. POLSTRA 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 JOHN D. POLSTRA 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.
|
|
*/
|
|
|
|
#include <sys/cdefs.h>
|
|
__FBSDID("$FreeBSD$");
|
|
|
|
#include <sys/types.h>
|
|
#include <sys/wait.h>
|
|
|
|
#include <err.h>
|
|
#include <errno.h>
|
|
#include <fcntl.h>
|
|
#include <signal.h>
|
|
#include <stdio.h>
|
|
#include <stdlib.h>
|
|
#include <sysexits.h>
|
|
#include <unistd.h>
|
|
|
|
static int acquire_lock(const char *name, int flags);
|
|
static void cleanup(void);
|
|
static void killed(int sig);
|
|
static void timeout(int sig);
|
|
static void usage(void);
|
|
static void wait_for_lock(const char *name);
|
|
|
|
static const char *lockname;
|
|
static int lockfd = -1;
|
|
static int keep;
|
|
static volatile sig_atomic_t timed_out;
|
|
|
|
/*
|
|
* Execute an arbitrary command while holding a file lock.
|
|
*/
|
|
int
|
|
main(int argc, char **argv)
|
|
{
|
|
int ch, silent, status, waitsec;
|
|
pid_t child;
|
|
|
|
silent = keep = 0;
|
|
waitsec = -1; /* Infinite. */
|
|
while ((ch = getopt(argc, argv, "skt:")) != -1) {
|
|
switch (ch) {
|
|
case 'k':
|
|
keep = 1;
|
|
break;
|
|
case 's':
|
|
silent = 1;
|
|
break;
|
|
case 't':
|
|
{
|
|
char *endptr;
|
|
waitsec = strtol(optarg, &endptr, 0);
|
|
if (*optarg == '\0' || *endptr != '\0' || waitsec < 0)
|
|
errx(EX_USAGE,
|
|
"invalid timeout \"%s\"", optarg);
|
|
}
|
|
break;
|
|
default:
|
|
usage();
|
|
}
|
|
}
|
|
if (argc - optind < 2)
|
|
usage();
|
|
lockname = argv[optind++];
|
|
argc -= optind;
|
|
argv += optind;
|
|
if (waitsec > 0) { /* Set up a timeout. */
|
|
struct sigaction act;
|
|
|
|
act.sa_handler = timeout;
|
|
sigemptyset(&act.sa_mask);
|
|
act.sa_flags = 0; /* Note that we do not set SA_RESTART. */
|
|
sigaction(SIGALRM, &act, NULL);
|
|
alarm(waitsec);
|
|
}
|
|
/*
|
|
* If the "-k" option is not given, then we must not block when
|
|
* acquiring the lock. If we did, then the lock holder would
|
|
* unlink the file upon releasing the lock, and we would acquire
|
|
* a lock on a file with no directory entry. Then another
|
|
* process could come along and acquire the same lock. To avoid
|
|
* this problem, we separate out the actions of waiting for the
|
|
* lock to be available and of actually acquiring the lock.
|
|
*
|
|
* That approach produces behavior that is technically correct;
|
|
* however, it causes some performance & ordering problems for
|
|
* locks that have a lot of contention. First, it is unfair in
|
|
* the sense that a released lock isn't necessarily granted to
|
|
* the process that has been waiting the longest. A waiter may
|
|
* be starved out indefinitely. Second, it creates a thundering
|
|
* herd situation each time the lock is released.
|
|
*
|
|
* When the "-k" option is used, the unlink race no longer
|
|
* exists. In that case we can block while acquiring the lock,
|
|
* avoiding the separate step of waiting for the lock. This
|
|
* yields fairness and improved performance.
|
|
*/
|
|
lockfd = acquire_lock(lockname, O_NONBLOCK);
|
|
while (lockfd == -1 && !timed_out && waitsec != 0) {
|
|
if (keep)
|
|
lockfd = acquire_lock(lockname, 0);
|
|
else {
|
|
wait_for_lock(lockname);
|
|
lockfd = acquire_lock(lockname, O_NONBLOCK);
|
|
}
|
|
}
|
|
if (waitsec > 0)
|
|
alarm(0);
|
|
if (lockfd == -1) { /* We failed to acquire the lock. */
|
|
if (silent)
|
|
exit(EX_TEMPFAIL);
|
|
errx(EX_TEMPFAIL, "%s: already locked", lockname);
|
|
}
|
|
/* At this point, we own the lock. */
|
|
if (atexit(cleanup) == -1)
|
|
err(EX_OSERR, "atexit failed");
|
|
if ((child = fork()) == -1)
|
|
err(EX_OSERR, "cannot fork");
|
|
if (child == 0) { /* The child process. */
|
|
close(lockfd);
|
|
execvp(argv[0], argv);
|
|
warn("%s", argv[0]);
|
|
_exit(1);
|
|
}
|
|
/* This is the parent process. */
|
|
signal(SIGINT, SIG_IGN);
|
|
signal(SIGQUIT, SIG_IGN);
|
|
signal(SIGTERM, killed);
|
|
if (waitpid(child, &status, 0) == -1)
|
|
err(EX_OSERR, "waitpid failed");
|
|
return (WIFEXITED(status) ? WEXITSTATUS(status) : EX_SOFTWARE);
|
|
}
|
|
|
|
/*
|
|
* Try to acquire a lock on the given file, creating the file if
|
|
* necessary. The flags argument is O_NONBLOCK or 0, depending on
|
|
* whether we should wait for the lock. Returns an open file descriptor
|
|
* on success, or -1 on failure.
|
|
*/
|
|
static int
|
|
acquire_lock(const char *name, int flags)
|
|
{
|
|
int fd;
|
|
|
|
if ((fd = open(name, O_RDONLY|O_CREAT|O_EXLOCK|flags, 0666)) == -1) {
|
|
if (errno == EAGAIN || errno == EINTR)
|
|
return (-1);
|
|
err(EX_CANTCREAT, "cannot open %s", name);
|
|
}
|
|
return (fd);
|
|
}
|
|
|
|
/*
|
|
* Remove the lock file.
|
|
*/
|
|
static void
|
|
cleanup(void)
|
|
{
|
|
|
|
if (keep)
|
|
flock(lockfd, LOCK_UN);
|
|
else
|
|
unlink(lockname);
|
|
}
|
|
|
|
/*
|
|
* Signal handler for SIGTERM. Cleans up the lock file, then re-raises
|
|
* the signal.
|
|
*/
|
|
static void
|
|
killed(int sig)
|
|
{
|
|
|
|
cleanup();
|
|
signal(sig, SIG_DFL);
|
|
if (kill(getpid(), sig) == -1)
|
|
err(EX_OSERR, "kill failed");
|
|
}
|
|
|
|
/*
|
|
* Signal handler for SIGALRM.
|
|
*/
|
|
static void
|
|
timeout(int sig __unused)
|
|
{
|
|
|
|
timed_out = 1;
|
|
}
|
|
|
|
static void
|
|
usage(void)
|
|
{
|
|
|
|
fprintf(stderr,
|
|
"usage: lockf [-ks] [-t seconds] file command [arguments]\n");
|
|
exit(EX_USAGE);
|
|
}
|
|
|
|
/*
|
|
* Wait until it might be possible to acquire a lock on the given file.
|
|
* If the file does not exist, return immediately without creating it.
|
|
*/
|
|
static void
|
|
wait_for_lock(const char *name)
|
|
{
|
|
int fd;
|
|
|
|
if ((fd = open(name, O_RDONLY|O_EXLOCK, 0666)) == -1) {
|
|
if (errno == ENOENT || errno == EINTR)
|
|
return;
|
|
err(EX_CANTCREAT, "cannot open %s", name);
|
|
}
|
|
close(fd);
|
|
}
|