mdw@git.distorted.org.uk Git - misc/blob - 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 #include <sys/stat.h>
  43
  44 #include <mLib/mdwopt.h>
  45 #include <mLib/quis.h>
  46 #include <mLib/report.h>
  47
  48 /*----- Static variables --------------------------------------------------*/
  49
  50 static jmp_buf jmp;
  51 static int err;
  52
  53 /*----- Main code ---------------------------------------------------------*/
  54
  55 static void alrm(int s) { longjmp(jmp, 1); }
  56
  57 static void usage(FILE *fp)
  58 {
  59   pquis(fp,
  60         "Usage: $ [-cfwx] [-p REALPROG] [-t TIMEOUT] FILE PROG ARGS...\n");
  61 }
  62
  63 static void version(FILE *fp)
  64   { pquis(fp, "$ (version " VERSION ")\n"); }
  65
  66 static void help(FILE *fp)
  67 {
  68   version(fp);
  69   putchar('\n');
  70   usage(fp);
  71   pquis(fp, "\n\
  72 Lock FILE and run PROG, passing ARGS.  Options are:\n\
  73 \n\
  74 -h, --help              Show this help message.\n\
  75 -v, --version           Show version string.\n\
  76 -u, --usage             Show terse usage summary.\n\
  77 \n\
  78 -c, --[no-]create       Create FILE if it doesn't exist [default: on].\n\
  79 -f, --[no-]fail         Fail if the file is already locked [default: off].\n\
  80 -w, --[no-]wait         Wait for the lock to be available [default: off].\n\
  81 -x, --[no-]exclusive    Get an exclusive (writer) lock [default: on].\n\
  82 -p, --program=REALPROG  Run REALPROG instead of PROG.\n\
  83 -t, --timeout=TIME      Wait for TIME for lock to become available.\n\
  84 ");
  85 }
  86
  87 int main(int argc, char *argv[])
  88 {
  89   const char *file = 0;
  90   const char *prog = 0;
  91   char *const *av;
  92   void (*oalrm)(int) = 0;
  93   int fd = -1;
  94   struct flock l;
  95   char *p;
  96   int t = -1;
  97   int oflag;
  98   unsigned int ot = 0;
  99   struct stat st, nst;
 100   time_t nt;
 101   pid_t kid;
 102   int rc;
 103
 104 #define f_bogus 1u
 105 #define f_wait 2u
 106 #define f_fail 4u
 107 #define f_create 8u
 108 #define f_excl 16u
 109
 110   unsigned f = f_create | f_excl;
 111
 112   ego(argv[0]);
 113
 114   for (;;) {
 115     static const struct option opts[] = {
 116       { "help",                 0,              0,      'h' },
 117       { "version",              0,              0,      'v' },
 118       { "usage",                0,              0,      'u' },
 119       { "wait",                 OPTF_NEGATE,    0,      'w' },
 120       { "fail",                 OPTF_NEGATE,    0,      'f' },
 121       { "create",               OPTF_NEGATE,    0,      'c' },
 122       { "program",              OPTF_ARGREQ,    0,      'p' },
 123       { "timeout",              OPTF_ARGREQ,    0,      't' },
 124       { "exclusive",            OPTF_NEGATE,    0,      'x' },
 125       { 0,                      0,              0,      0 }
 126     };
 127
 128     int i = mdwopt(argc, argv, "-hvuw+f+c+x+p:t:", opts,
 129                    0, 0, OPTF_NEGATION);
 130     if (i < 0) break;
 131     switch (i) {
 132       case 'h': help(stdout); exit(0);
 133       case 'v': version(stdout); exit(0);
 134       case 'u': usage(stdout); exit(0);
 135       case 'w': f |= f_wait; break;
 136       case 'w' | OPTF_NEGATED: f &= ~f_wait; break;
 137       case 'f': f |= f_fail; break;
 138       case 'f' | OPTF_NEGATED: f &= ~f_fail; break;
 139       case 'c': f |= f_create; break;
 140       case 'c' | OPTF_NEGATED: f &= ~f_create; break;
 141       case 'x': f |= f_excl; break;
 142       case 'x' | OPTF_NEGATED: f &= ~f_excl; break;
 143       case 't':
 144         errno = 0;
 145         t = strtol(optarg, &p, 0);
 146         switch (*p) {
 147           case 'd': t *= 24;
 148           case 'h': t *= 60;
 149           case 'm': t *= 60;
 150           case 's': p++;
 151           case 0: break;
 152           default: die(111, "unknown time unit `%c'", *p);
 153         }
 154         if (*p || t < 0 || errno) die(111, "bad time value `%s'", optarg);
 155         f |= f_wait;
 156         break;
 157       case 'p': prog = optarg; break;
 158       case 0:
 159         if (file) { optind--; goto doneopts; }
 160         file = optarg;
 161         break;
 162       default: f |= f_bogus; break;
 163     }
 164   }
 165
 166 doneopts:
 167   if (f & f_bogus || argc - optind < 1) {
 168     usage(stderr);
 169     exit(EXIT_FAILURE);
 170   }
 171
 172   av = &argv[optind];
 173   if (!prog) prog = av[0];
 174   oflag = f & f_excl ? O_RDWR : O_RDONLY;
 175   if (f & f_create) oflag |= O_CREAT;
 176   l.l_type = f & f_excl ? F_WRLCK : F_RDLCK;
 177   l.l_whence = SEEK_SET;
 178   l.l_start = 0;
 179   l.l_len = 0;
 180   nt = time(0);
 181   if (setjmp(jmp)) {
 182     err = EAGAIN;
 183     nt = t;
 184     goto done;
 185   }
 186   ot = alarm(0);
 187   oalrm = signal(SIGALRM, alrm);
 188   if (t >= 0) alarm(t);
 189 again:
 190   if ((fd = open(file, oflag, 0666)) < 0)
 191     die(111, "error opening `%s': %s", file, strerror(errno));
 192   if (fstat(fd, &st))
 193     die(111, "error from fstat on `%s': %s", file, strerror(errno));
 194   err = fcntl(fd, f & f_wait ? F_SETLKW : F_SETLK, &l) >= 0 ? 0 : errno;
 195   /* It's tempting to `optimize' this code by opening a new file descriptor
 196    * here so as to elide the additional call to fstat(2) above.  But this
 197    * doesn't work: if we successfully acquire the lock, we then have two file
 198    * descriptors open on the lock file, so we have to close one -- but, under
 199    * the daft fcntl(2) rules, even closing `nfd' will release the lock
 200    * immediately.
 201    */
 202   if (stat(file, &nst)) {
 203     if (errno == ENOENT) { close(fd); goto again; }
 204     else die(111, "error from stat on `%s': %s", file, strerror(errno));
 205   }
 206   if (st.st_dev != nst.st_dev || st.st_ino != nst.st_ino)
 207     { close(fd); goto again; }
 208 done:
 209   signal(SIGALRM, oalrm);
 210   if (!ot)
 211     alarm(0);
 212   else {
 213     nt = time(0) - nt;
 214     if (nt > ot) raise(SIGALRM);
 215     else alarm(ot - nt);
 216   }
 217   switch (err) {
 218     case 0: break;
 219     case EAGAIN:
 220 #if defined(EWOULDBLOCK) && EWOULDBLOCK != EAGAIN
 221     case EWOULDBLOCK:
 222 #endif
 223     case EACCES:
 224       if (!(f & f_fail)) exit(0);
 225     default:
 226       die(111, "error locking `%s': %s", file, strerror(errno));
 227   }
 228   if ((kid = fork()) < 0) die(111, "error from fork: %s", strerror(errno));
 229   if (!kid) {
 230     close(fd);
 231     execvp(prog, av);
 232     die(111, "couldn't exec `%s': %s", prog, strerror(errno));
 233   }
 234   if (waitpid(kid, &rc, 0) < 0)
 235     die(EXIT_FAILURE, "error from wait: %s", strerror(errno));
 236   l.l_type = F_UNLCK;
 237   l.l_whence = SEEK_SET;
 238   l.l_start = 0;
 239   l.l_len = 0;
 240   fcntl(fd, F_SETLK, &l);
 241   if (fd >= 0) close(fd);
 242   if (WIFEXITED(rc)) exit(WEXITSTATUS(rc));
 243   else exit(128 + WTERMSIG(rc));
 244 }
 245
 246 /*----- That's all, folks -------------------------------------------------*/