locking.c: Refactor the main locking flow.
[misc] / locking.c
1 /* -*-c-*-
2 *
3 * Lock a file, run a program
4 *
5 * (c) 2003 Mark Wooding
6 */
7
8 /*----- Licensing notice --------------------------------------------------*
9 *
10 * This file is part of the Toys utilties collection.
11 *
12 * Toys is free software; you can redistribute it and/or modify
13 * it under the terms of the GNU General Public License as published by
14 * the Free Software Foundation; either version 2 of the License, or
15 * (at your option) any later version.
16 *
17 * Toys is distributed in the hope that it will be useful,
18 * but WITHOUT ANY WARRANTY; without even the implied warranty of
19 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
20 * GNU General Public License for more details.
21 *
22 * You should have received a copy of the GNU General Public License
23 * along with Toys; if not, write to the Free Software Foundation,
24 * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
25 */
26
27 /*----- Header files ------------------------------------------------------*/
28
29 #include <errno.h>
30 #include <setjmp.h>
31 #include <signal.h>
32 #include <stdio.h>
33 #include <stdlib.h>
34 #include <string.h>
35 #include <time.h>
36
37 #include <sys/types.h>
38 #include <sys/time.h>
39 #include <unistd.h>
40 #include <fcntl.h>
41 #include <sys/wait.h>
42
43 #include <mLib/mdwopt.h>
44 #include <mLib/quis.h>
45 #include <mLib/report.h>
46
47 /*----- Static variables --------------------------------------------------*/
48
49 static jmp_buf jmp;
50 static int err;
51
52 /*----- Main code ---------------------------------------------------------*/
53
54 static void alrm(int s) { longjmp(jmp, 1); }
55
56 static void usage(FILE *fp)
57 {
58 pquis(fp,
59 "Usage: $ [-cfwx] [-p REALPROG] [-t TIMEOUT] FILE PROG ARGS...\n");
60 }
61
62 static void version(FILE *fp)
63 { pquis(fp, "$ (version " VERSION ")\n"); }
64
65 static void help(FILE *fp)
66 {
67 version(fp);
68 putchar('\n');
69 usage(fp);
70 pquis(fp, "\n\
71 Lock FILE and run PROG, passing ARGS. Options are:\n\
72 \n\
73 -h, --help Show this help message.\n\
74 -v, --version Show version string.\n\
75 -u, --usage Show terse usage summary.\n\
76 \n\
77 -c, --[no-]create Create FILE if it doesn't exist [default: on].\n\
78 -f, --[no-]fail Fail if the file is already locked [default: off].\n\
79 -w, --[no-]wait Wait for the lock to be available [default: off].\n\
80 -x, --[no-]exclusive Get an exclusive (writer) lock [default: on].\n\
81 -p, --program=REALPROG Run REALPROG instead of PROG.\n\
82 -t, --timeout=TIME Wait for TIME for lock to become available.\n\
83 ");
84 }
85
86 int main(int argc, char *argv[])
87 {
88 const char *file = 0;
89 const char *prog = 0;
90 char *const *av;
91 void (*oalrm)(int) = 0;
92 int fd = -1;
93 struct flock l;
94 char *p;
95 int t = -1;
96 int oflag;
97 unsigned int ot = 0;
98 time_t nt;
99 pid_t kid;
100 int rc;
101
102 #define f_bogus 1u
103 #define f_wait 2u
104 #define f_fail 4u
105 #define f_create 8u
106 #define f_excl 16u
107
108 unsigned f = f_create | f_excl;
109
110 ego(argv[0]);
111
112 for (;;) {
113 static const struct option opts[] = {
114 { "help", 0, 0, 'h' },
115 { "version", 0, 0, 'v' },
116 { "usage", 0, 0, 'u' },
117 { "wait", OPTF_NEGATE, 0, 'w' },
118 { "fail", OPTF_NEGATE, 0, 'f' },
119 { "create", OPTF_NEGATE, 0, 'c' },
120 { "program", OPTF_ARGREQ, 0, 'p' },
121 { "timeout", OPTF_ARGREQ, 0, 't' },
122 { "exclusive", OPTF_NEGATE, 0, 'x' },
123 { 0, 0, 0, 0 }
124 };
125
126 int i = mdwopt(argc, argv, "-hvuw+f+c+x+p:t:", opts,
127 0, 0, OPTF_NEGATION);
128 if (i < 0) break;
129 switch (i) {
130 case 'h': help(stdout); exit(0);
131 case 'v': version(stdout); exit(0);
132 case 'u': usage(stdout); exit(0);
133 case 'w': f |= f_wait; break;
134 case 'w' | OPTF_NEGATED: f &= ~f_wait; break;
135 case 'f': f |= f_fail; break;
136 case 'f' | OPTF_NEGATED: f &= ~f_fail; break;
137 case 'c': f |= f_create; break;
138 case 'c' | OPTF_NEGATED: f &= ~f_create; break;
139 case 'x': f |= f_excl; break;
140 case 'x' | OPTF_NEGATED: f &= ~f_excl; break;
141 case 't':
142 errno = 0;
143 t = strtol(optarg, &p, 0);
144 switch (*p) {
145 case 'd': t *= 24;
146 case 'h': t *= 60;
147 case 'm': t *= 60;
148 case 's': p++;
149 case 0: break;
150 default: die(111, "unknown time unit `%c'", *p);
151 }
152 if (*p || t < 0 || errno) die(111, "bad time value `%s'", optarg);
153 f |= f_wait;
154 break;
155 case 'p': prog = optarg; break;
156 case 0:
157 if (file) { optind--; goto doneopts; }
158 file = optarg;
159 break;
160 default: f |= f_bogus; break;
161 }
162 }
163
164 doneopts:
165 if (f & f_bogus || argc - optind < 1) {
166 usage(stderr);
167 exit(EXIT_FAILURE);
168 }
169
170 av = &argv[optind];
171 if (!prog) prog = av[0];
172 oflag = f & f_excl ? O_RDWR : O_RDONLY;
173 if (f & f_create) oflag |= O_CREAT;
174 l.l_type = f & f_excl ? F_WRLCK : F_RDLCK;
175 l.l_whence = SEEK_SET;
176 l.l_start = 0;
177 l.l_len = 0;
178 nt = time(0);
179 if (setjmp(jmp)) {
180 err = EAGAIN;
181 nt = t;
182 goto done;
183 }
184 ot = alarm(0);
185 oalrm = signal(SIGALRM, alrm);
186 if (t >= 0) alarm(t);
187 if ((fd = open(file, oflag, 0666)) < 0)
188 die(111, "error opening `%s': %s", file, strerror(errno));
189 err = fcntl(fd, f & f_wait ? F_SETLKW : F_SETLK, &l) >= 0 ? 0 : errno;
190 done:
191 signal(SIGALRM, oalrm);
192 if (!ot)
193 alarm(0);
194 else {
195 nt = time(0) - nt;
196 if (nt > ot) raise(SIGALRM);
197 else alarm(ot - nt);
198 }
199 switch (err) {
200 case 0: break;
201 case EAGAIN:
202 #if defined(EWOULDBLOCK) && EWOULDBLOCK != EAGAIN
203 case EWOULDBLOCK:
204 #endif
205 case EACCES:
206 if (!(f & f_fail)) exit(0);
207 default:
208 die(111, "error locking `%s': %s", file, strerror(errno));
209 }
210 if ((kid = fork()) < 0) die(111, "error from fork: %s", strerror(errno));
211 if (!kid) {
212 close(fd);
213 execvp(prog, av);
214 die(111, "couldn't exec `%s': %s", prog, strerror(errno));
215 }
216 if (waitpid(kid, &rc, 0) < 0)
217 die(EXIT_FAILURE, "error from wait: %s", strerror(errno));
218 l.l_type = F_UNLCK;
219 l.l_whence = SEEK_SET;
220 l.l_start = 0;
221 l.l_len = 0;
222 fcntl(fd, F_SETLK, &l);
223 if (fd >= 0) close(fd);
224 if (WIFEXITED(rc)) exit(WEXITSTATUS(rc));
225 else exit(128 + WTERMSIG(rc));
226 }
227
228 /*----- That's all, folks -------------------------------------------------*/