1 /* 2 * Copyright (C) 1997 John D. Polstra. All rights reserved. 3 * 4 * Redistribution and use in source and binary forms, with or without 5 * modification, are permitted provided that the following conditions 6 * are met: 7 * 1. Redistributions of source code must retain the above copyright 8 * notice, this list of conditions and the following disclaimer. 9 * 2. Redistributions in binary form must reproduce the above copyright 10 * notice, this list of conditions and the following disclaimer in the 11 * documentation and/or other materials provided with the distribution. 12 * 13 * THIS SOFTWARE IS PROVIDED BY JOHN D. POLSTRA AND CONTRIBUTORS ``AS IS'' AND 14 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 15 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 16 * ARE DISCLAIMED. IN NO EVENT SHALL JOHN D. POLSTRA OR CONTRIBUTORS BE LIABLE 17 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 18 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 19 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 20 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 21 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 22 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 23 * SUCH DAMAGE. 24 * 25 * $Id: lockf.c,v 1.4 1997/02/22 19:55:54 peter Exp $ 26 */ 27 28 #include <sys/types.h> 29 #include <sys/wait.h> 30 31 #include <err.h> 32 #include <errno.h> 33 #include <fcntl.h> 34 #include <signal.h> 35 #include <stdio.h> 36 #include <stdlib.h> 37 #include <sysexits.h> 38 #include <unistd.h> 39 40 static int acquire_lock(const char *name); 41 static void cleanup(void); 42 static void killed(int sig); 43 static void timeout(int sig); 44 static void usage(void); 45 static void wait_for_lock(const char *name); 46 47 static const char *lockname; 48 static volatile sig_atomic_t timed_out; 49 50 /* 51 * Execute an arbitrary command while holding a file lock. 52 */ 53 int 54 main(int argc, char **argv) 55 { 56 int ch; 57 int lockfd; 58 int silent; 59 int status; 60 int waitsec; 61 pid_t child; 62 63 silent = 0; 64 waitsec = -1; /* Infinite. */ 65 while ((ch = getopt(argc, argv, "st:")) != -1) { 66 switch (ch) { 67 68 case 's': 69 silent = 1; 70 break; 71 72 case 't': 73 { 74 char *endptr; 75 waitsec = strtol(optarg, &endptr, 0); 76 if (*optarg == '\0' || *endptr != '\0' || waitsec < 0) 77 errx(EX_USAGE, "invalid timeout \"%s\"", optarg); 78 } 79 break; 80 81 default: 82 usage(); 83 } 84 } 85 if (argc - optind < 2) 86 usage(); 87 lockname = argv[optind++]; 88 argc -= optind; 89 argv += optind; 90 91 if (waitsec > 0) { /* Set up a timeout. */ 92 struct sigaction act; 93 94 act.sa_handler = timeout; 95 sigemptyset(&act.sa_mask); 96 act.sa_flags = 0; /* Note that we do not set SA_RESTART. */ 97 98 sigaction(SIGALRM, &act, NULL); 99 alarm(waitsec); 100 } 101 102 lockfd = acquire_lock(lockname); 103 while (lockfd == -1 && !timed_out && waitsec != 0) { 104 wait_for_lock(lockname); 105 lockfd = acquire_lock(lockname); 106 } 107 108 if (waitsec > 0) 109 alarm(0); 110 111 if (lockfd == -1) { /* We failed to acquire the lock. */ 112 if (silent) 113 exit(EX_TEMPFAIL); 114 errx(EX_TEMPFAIL, "%s: already locked", lockname); 115 } 116 117 /* At this point, we own the lock. */ 118 119 if (atexit(cleanup) == -1) 120 err(EX_OSERR, "atexit failed"); 121 122 if ((child = fork()) == -1) 123 err(EX_OSERR, "cannot fork"); 124 125 if (child == 0) { /* The child process. */ 126 close(lockfd); 127 execvp(argv[0], argv); 128 perror(argv[0]); 129 _exit(1); 130 } 131 132 /* This is the parent process. */ 133 134 signal(SIGINT, SIG_IGN); 135 signal(SIGQUIT, SIG_IGN); 136 signal(SIGTERM, killed); 137 138 if (waitpid(child, &status, 0) == -1) 139 err(EX_OSERR, "waitpid failed"); 140 141 return WIFEXITED(status) ? WEXITSTATUS(status) : 1; 142 } 143 144 /* 145 * Try to acquire a lock on the given file, but don't wait for it. Returns 146 * an open file descriptor on success, or -1 on failure. 147 */ 148 static int 149 acquire_lock(const char *name) 150 { 151 int fd; 152 153 if ((fd = open(name, O_RDONLY|O_CREAT|O_EXLOCK|O_NONBLOCK, 0666)) == -1) { 154 if (errno == EAGAIN || errno == EINTR) 155 return -1; 156 err(EX_CANTCREAT, "cannot open %s", name); 157 } 158 return fd; 159 } 160 161 /* 162 * Remove the lock file. 163 */ 164 static void 165 cleanup(void) 166 { 167 unlink(lockname); 168 } 169 170 /* 171 * Signal handler for SIGTERM. Cleans up the lock file, then re-raises 172 * the signal. 173 */ 174 static void 175 killed(int sig) 176 { 177 cleanup(); 178 signal(sig, SIG_DFL); 179 if (kill(getpid(), sig) == -1) 180 err(EX_OSERR, "kill failed"); 181 } 182 183 /* 184 * Signal handler for SIGALRM. 185 */ 186 static void 187 timeout(int sig) 188 { 189 timed_out = 1; 190 } 191 192 static void 193 usage(void) 194 { 195 errx(EX_USAGE, "usage: lockf [-s] [-t seconds] file command [arguments]"); 196 } 197 198 /* 199 * Wait until it might be possible to acquire a lock on the given file. 200 */ 201 static void 202 wait_for_lock(const char *name) 203 { 204 int fd; 205 206 if ((fd = open(name, O_RDONLY|O_EXLOCK)) == -1) { 207 if (errno == ENOENT || errno == EINTR) 208 return; 209 err(EX_CANTCREAT, "cannot open %s", name); 210 } 211 close(fd); 212 return; 213 } 214