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 * $FreeBSD: src/usr.bin/lockf/lockf.c,v 1.8 1999/08/28 01:03:07 peter Exp $
26 * $DragonFly: src/usr.bin/lockf/lockf.c,v 1.3 2005/01/05 00:46:52 cpressey Exp $
27 */
28
29 #include <sys/types.h>
30 #include <sys/wait.h>
31
32 #include <err.h>
33 #include <errno.h>
34 #include <fcntl.h>
35 #include <signal.h>
36 #include <stdio.h>
37 #include <stdlib.h>
38 #include <sysexits.h>
39 #include <unistd.h>
40
41 static int acquire_lock(const char *name);
42 static void cleanup(void);
43 static void killed(int sig);
44 static void timeout(int sig);
45 static void usage(void);
46 static void wait_for_lock(const char *name);
47
48 static const char *lockname;
49 static int lockfd;
50 static int keep;
51 static volatile sig_atomic_t timed_out;
52
53 /*
54 * Execute an arbitrary command while holding a file lock.
55 */
56 int
main(int argc,char ** argv)57 main(int argc, char **argv)
58 {
59 int ch;
60 int silent;
61 int status;
62 int waitsec;
63 pid_t child;
64
65 silent = 0;
66 keep = 0;
67 waitsec = -1; /* Infinite. */
68 while ((ch = getopt(argc, argv, "skt:")) != -1) {
69 switch (ch) {
70
71 case 'k':
72 keep = 1;
73 break;
74
75 case 's':
76 silent = 1;
77 break;
78
79 case 't':
80 {
81 char *endptr;
82 waitsec = strtol(optarg, &endptr, 0);
83 if (*optarg == '\0' || *endptr != '\0' || waitsec < 0)
84 errx(EX_USAGE, "invalid timeout \"%s\"", optarg);
85 }
86 break;
87
88 default:
89 usage();
90 }
91 }
92 if (argc - optind < 2)
93 usage();
94 lockname = argv[optind++];
95 argc -= optind;
96 argv += optind;
97
98 if (waitsec > 0) { /* Set up a timeout. */
99 struct sigaction act;
100
101 act.sa_handler = timeout;
102 sigemptyset(&act.sa_mask);
103 act.sa_flags = 0; /* Note that we do not set SA_RESTART. */
104
105 sigaction(SIGALRM, &act, NULL);
106 alarm(waitsec);
107 }
108
109 lockfd = acquire_lock(lockname);
110 while (lockfd == -1 && !timed_out && waitsec != 0) {
111 wait_for_lock(lockname);
112 lockfd = acquire_lock(lockname);
113 }
114
115 if (waitsec > 0)
116 alarm(0);
117
118 if (lockfd == -1) { /* We failed to acquire the lock. */
119 if (silent)
120 exit(EX_TEMPFAIL);
121 errx(EX_TEMPFAIL, "%s: already locked", lockname);
122 }
123
124 /* At this point, we own the lock. */
125
126 if (atexit(cleanup) == -1)
127 err(EX_OSERR, "atexit failed");
128
129 if ((child = fork()) == -1)
130 err(EX_OSERR, "cannot fork");
131
132 if (child == 0) { /* The child process. */
133 close(lockfd);
134 execvp(argv[0], argv);
135 perror(argv[0]);
136 _exit(1);
137 }
138
139 /* This is the parent process. */
140
141 signal(SIGINT, SIG_IGN);
142 signal(SIGQUIT, SIG_IGN);
143 signal(SIGTERM, killed);
144
145 if (waitpid(child, &status, 0) == -1)
146 err(EX_OSERR, "waitpid failed");
147
148 return WIFEXITED(status) ? WEXITSTATUS(status) : 1;
149 }
150
151 /*
152 * Try to acquire a lock on the given file, but don't wait for it. Returns
153 * an open file descriptor on success, or -1 on failure.
154 */
155 static int
acquire_lock(const char * name)156 acquire_lock(const char *name)
157 {
158 int fd;
159
160 if ((fd = open(name, O_RDONLY|O_CREAT|O_EXLOCK|O_NONBLOCK, 0666)) == -1) {
161 if (errno == EAGAIN || errno == EINTR)
162 return -1;
163 err(EX_CANTCREAT, "cannot open %s", name);
164 }
165 return fd;
166 }
167
168 /*
169 * Remove the lock file.
170 */
171 static void
cleanup(void)172 cleanup(void)
173 {
174 if (keep)
175 flock(lockfd, LOCK_UN);
176 else
177 unlink(lockname);
178 }
179
180 /*
181 * Signal handler for SIGTERM. Cleans up the lock file, then re-raises
182 * the signal.
183 */
184 static void
killed(int sig)185 killed(int sig)
186 {
187 cleanup();
188 signal(sig, SIG_DFL);
189 if (kill(getpid(), sig) == -1)
190 err(EX_OSERR, "kill failed");
191 }
192
193 /*
194 * Signal handler for SIGALRM.
195 */
196 static void
timeout(__unused int sig)197 timeout(__unused int sig)
198 {
199 timed_out = 1;
200 }
201
202 static void
usage(void)203 usage(void)
204 {
205 fprintf(stderr,
206 "usage: lockf [-ks] [-t seconds] file command [arguments]\n");
207 exit(EX_USAGE);
208 }
209
210 /*
211 * Wait until it might be possible to acquire a lock on the given file.
212 */
213 static void
wait_for_lock(const char * name)214 wait_for_lock(const char *name)
215 {
216 int fd;
217
218 if ((fd = open(name, O_RDONLY|O_EXLOCK)) == -1) {
219 if (errno == ENOENT || errno == EINTR)
220 return;
221 err(EX_CANTCREAT, "cannot open %s", name);
222 }
223 close(fd);
224 return;
225 }
226