d614ded66a
exist Apply EX_UNAVAILABLE patch part from PR 170775 to match the documentation. Checked with a command from PR 210770: lockf -n /tmp/doesnotexist echo; echo $? PR: 210770 MFC after: 1 week
246 lines
6.5 KiB
C
246 lines
6.5 KiB
C
/*-
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* SPDX-License-Identifier: BSD-2-Clause-FreeBSD
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*
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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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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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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, int flags);
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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 int lockfd = -1;
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static int keep;
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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, flags, silent, status, waitsec;
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pid_t child;
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silent = keep = 0;
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flags = O_CREAT;
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waitsec = -1; /* Infinite. */
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while ((ch = getopt(argc, argv, "sknt:")) != -1) {
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switch (ch) {
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case 'k':
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keep = 1;
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break;
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case 'n':
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flags &= ~O_CREAT;
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break;
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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,
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"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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/*
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* If the "-k" option is not given, then we must not block when
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* acquiring the lock. If we did, then the lock holder would
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* unlink the file upon releasing the lock, and we would acquire
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* a lock on a file with no directory entry. Then another
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* process could come along and acquire the same lock. To avoid
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* this problem, we separate out the actions of waiting for the
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* lock to be available and of actually acquiring the lock.
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*
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* That approach produces behavior that is technically correct;
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* however, it causes some performance & ordering problems for
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* locks that have a lot of contention. First, it is unfair in
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* the sense that a released lock isn't necessarily granted to
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* the process that has been waiting the longest. A waiter may
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* be starved out indefinitely. Second, it creates a thundering
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* herd situation each time the lock is released.
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*
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* When the "-k" option is used, the unlink race no longer
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* exists. In that case we can block while acquiring the lock,
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* avoiding the separate step of waiting for the lock. This
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* yields fairness and improved performance.
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*/
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lockfd = acquire_lock(lockname, flags | O_NONBLOCK);
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while (lockfd == -1 && !timed_out && waitsec != 0) {
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if (keep)
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lockfd = acquire_lock(lockname, flags);
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else {
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wait_for_lock(lockname);
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lockfd = acquire_lock(lockname, flags | O_NONBLOCK);
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}
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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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warn("%s", 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) : EX_SOFTWARE);
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}
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/*
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* Try to acquire a lock on the given file, creating the file if
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* necessary. The flags argument is O_NONBLOCK or 0, depending on
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* whether we should wait for the lock. Returns an open file descriptor
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* 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, int flags)
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{
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int fd;
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if ((fd = open(name, O_RDONLY|O_EXLOCK|flags, 0666)) == -1) {
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if (errno == EAGAIN || errno == EINTR)
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return (-1);
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else if (errno == ENOENT && (flags & O_CREAT) == 0)
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err(EX_UNAVAILABLE, "%s", name);
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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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if (keep)
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flock(lockfd, LOCK_UN);
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else
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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 __unused)
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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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fprintf(stderr,
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"usage: lockf [-kns] [-t seconds] file command [arguments]\n");
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exit(EX_USAGE);
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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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* If the file does not exist, return immediately without creating it.
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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, 0666)) == -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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}
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