Index: head/usr.bin/lockf/lockf.c =================================================================== --- head/usr.bin/lockf/lockf.c (revision 345317) +++ head/usr.bin/lockf/lockf.c (revision 345318) @@ -1,243 +1,245 @@ /*- * SPDX-License-Identifier: BSD-2-Clause-FreeBSD * * 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 __FBSDID("$FreeBSD$"); #include #include #include #include #include #include #include #include #include #include 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, flags, silent, status, waitsec; pid_t child; silent = keep = 0; flags = O_CREAT; waitsec = -1; /* Infinite. */ while ((ch = getopt(argc, argv, "sknt:")) != -1) { switch (ch) { case 'k': keep = 1; break; case 'n': flags &= ~O_CREAT; 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, flags | O_NONBLOCK); while (lockfd == -1 && !timed_out && waitsec != 0) { if (keep) lockfd = acquire_lock(lockname, flags); else { wait_for_lock(lockname); lockfd = acquire_lock(lockname, flags | 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_EXLOCK|flags, 0666)) == -1) { if (errno == EAGAIN || errno == EINTR) return (-1); + else if (errno == ENOENT && (flags & O_CREAT) == 0) + err(EX_UNAVAILABLE, "%s", name); 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 [-kns] [-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); }