return EX_TEMPFAIL if the file was already locked. This makes it easier to distinguish between lock collisions and failures within the command being executed. Also, don't complain if the unlink() fails in the cleanup handler. It doesn't matter anyway, and it obscured the exit status returned from the command that was executed.
214 lines
4.9 KiB
C
214 lines
4.9 KiB
C
/*
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* Copyright (C) 1997 John D. Polstra. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY JOHN D. POLSTRA AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL JOHN D. POLSTRA OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* $Id: lockf.c,v 1.1.1.1 1997/01/08 20:12:59 jdp Exp $
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*/
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#include <sys/types.h>
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#include <sys/wait.h>
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#include <err.h>
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#include <errno.h>
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#include <fcntl.h>
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#include <signal.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <sysexits.h>
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#include <unistd.h>
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static int acquire_lock(const char *name);
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static void cleanup(void);
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static void killed(int sig);
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static void timeout(int sig);
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static void usage(void);
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static void wait_for_lock(const char *name);
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static const char *lockname;
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static volatile sig_atomic_t timed_out;
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/*
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* Execute an arbitrary command while holding a file lock.
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*/
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int
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main(int argc, char **argv)
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{
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int ch;
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int lockfd;
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int silent;
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int status;
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int waitsec;
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pid_t child;
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silent = 0;
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waitsec = -1; /* Infinite. */
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while ((ch = getopt(argc, argv, "st:")) != EOF) {
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switch (ch) {
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case 's':
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silent = 1;
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break;
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case 't':
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{
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char *endptr;
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waitsec = strtol(optarg, &endptr, 0);
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if (*optarg == '\0' || *endptr != '\0' || waitsec < 0)
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errx(EX_USAGE, "invalid timeout \"%s\"", optarg);
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}
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break;
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default:
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usage();
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}
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}
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if (argc - optind < 2)
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usage();
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lockname = argv[optind++];
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argc -= optind;
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argv += optind;
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if (waitsec > 0) { /* Set up a timeout. */
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struct sigaction act;
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act.sa_handler = timeout;
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sigemptyset(&act.sa_mask);
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act.sa_flags = 0; /* Note that we do not set SA_RESTART. */
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sigaction(SIGALRM, &act, NULL);
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alarm(waitsec);
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}
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lockfd = acquire_lock(lockname);
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while (lockfd == -1 && !timed_out && waitsec != 0) {
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wait_for_lock(lockname);
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lockfd = acquire_lock(lockname);
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}
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if (waitsec > 0)
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alarm(0);
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if (lockfd == -1) { /* We failed to acquire the lock. */
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if (silent)
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exit(EX_TEMPFAIL);
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errx(EX_TEMPFAIL, "%s: already locked", lockname);
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}
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/* At this point, we own the lock. */
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if (atexit(cleanup) == -1)
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err(EX_OSERR, "atexit failed");
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if ((child = fork()) == -1)
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err(EX_OSERR, "cannot fork");
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if (child == 0) { /* The child process. */
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close(lockfd);
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execvp(argv[0], argv);
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perror(argv[0]);
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_exit(1);
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}
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/* This is the parent process. */
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signal(SIGINT, SIG_IGN);
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signal(SIGQUIT, SIG_IGN);
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signal(SIGTERM, killed);
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if (waitpid(child, &status, 0) == -1)
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err(EX_OSERR, "waitpid failed");
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return WIFEXITED(status) ? WEXITSTATUS(status) : 1;
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}
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/*
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* Try to acquire a lock on the given file, but don't wait for it. Returns
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* an open file descriptor on success, or -1 on failure.
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*/
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static int
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acquire_lock(const char *name)
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{
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int fd;
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if ((fd = open(name, O_RDONLY|O_CREAT|O_EXLOCK|O_NONBLOCK, 0666)) == -1) {
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if (errno == EAGAIN || errno == EINTR)
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return -1;
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err(EX_CANTCREAT, "cannot open %s", name);
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}
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return fd;
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}
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/*
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* Remove the lock file.
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*/
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static void
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cleanup(void)
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{
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unlink(lockname);
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}
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/*
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* Signal handler for SIGTERM. Cleans up the lock file, then re-raises
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* the signal.
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*/
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static void
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killed(int sig)
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{
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cleanup();
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signal(sig, SIG_DFL);
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if (kill(getpid(), sig) == -1)
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err(EX_OSERR, "kill failed");
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}
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/*
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* Signal handler for SIGALRM.
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*/
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static void
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timeout(int sig)
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{
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timed_out = 1;
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}
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static void
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usage(void)
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{
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errx(EX_USAGE, "usage: lockf [-s] [-t seconds] file command [arguments]");
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}
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/*
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* Wait until it might be possible to acquire a lock on the given file.
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*/
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static void
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wait_for_lock(const char *name)
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{
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int fd;
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if ((fd = open(name, O_RDONLY|O_EXLOCK)) == -1) {
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if (errno == ENOENT || errno == EINTR)
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return;
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err(EX_CANTCREAT, "cannot open %s", name);
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}
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close(fd);
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return;
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}
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