1de7b4b805
Mainly focus on files that use BSD 2-Clause license, however the tool I was using misidentified many licenses so this was mostly a manual - error prone - task. The Software Package Data Exchange (SPDX) group provides a specification to make it easier for automated tools to detect and summarize well known opensource licenses. We are gradually adopting the specification, noting that the tags are considered only advisory and do not, in any way, superceed or replace the license texts. No functional change intended.
244 lines
6.4 KiB
C
244 lines
6.4 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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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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