sys-utils/flock.c

   1 /*   Copyright 2003-2005 H. Peter Anvin - All Rights Reserved
   2  *
   3  *   Permission is hereby granted, free of charge, to any person
   4  *   obtaining a copy of this software and associated documentation
   5  *   files (the "Software"), to deal in the Software without
   6  *   restriction, including without limitation the rights to use,
   7  *   copy, modify, merge, publish, distribute, sublicense, and/or
   8  *   sell copies of the Software, and to permit persons to whom
   9  *   the Software is furnished to do so, subject to the following
  10  *   conditions:
  11  *
  12  *   The above copyright notice and this permission notice shall
  13  *   be included in all copies or substantial portions of the Software.
  14  *
  15  *   THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  16  *   EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
  17  *   OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  18  *   NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
  19  *   HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
  20  *   WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  21  *   FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
  22  *   OTHER DEALINGS IN THE SOFTWARE.
  23  */
  24
  25 #include <ctype.h>
  26 #include <errno.h>
  27 #include <fcntl.h>
  28 #include <getopt.h>
  29 #include <paths.h>
  30 #include <signal.h>
  31 #include <stdio.h>
  32 #include <stdlib.h>
  33 #include <string.h>
  34 #include <sysexits.h>
  35 #include <sys/file.h>
  36 #include <sys/stat.h>
  37 #include <sys/time.h>
  38 #include <sys/types.h>
  39 #include <sys/wait.h>
  40 #include <unistd.h>
  41
  42 #include "c.h"
  43 #include "nls.h"
  44 #include "strutils.h"
  45 #include "closestream.h"
  46 #include "monotonic.h"
  47 #include "timer.h"
  48
  49 static void __attribute__((__noreturn__)) usage(void)
  50 {
  51         fputs(USAGE_HEADER, stdout);
  52         printf(
  53                 _(" %1$s [options] <file>|<directory> <command> [<argument>...]\n"
  54                   " %1$s [options] <file>|<directory> -c <command>\n"
  55                   " %1$s [options] <file descriptor number>\n"),
  56                 program_invocation_short_name);
  57
  58         fputs(USAGE_SEPARATOR, stdout);
  59         fputs(_("Manage file locks from shell scripts.\n"), stdout);
  60
  61         fputs(USAGE_OPTIONS, stdout);
  62         fputs(_(  " -s, --shared             get a shared lock\n"), stdout);
  63         fputs(_(  " -x, --exclusive          get an exclusive lock (default)\n"), stdout);
  64         fputs(_(  " -u, --unlock             remove a lock\n"), stdout);
  65         fputs(_(  " -n, --nonblock           fail rather than wait\n"), stdout);
  66         fputs(_(  " -w, --timeout <secs>     wait for a limited amount of time\n"), stdout);
  67         fputs(_(  " -E, --conflict-exit-code <number>  exit code after conflict or timeout\n"), stdout);
  68         fputs(_(  " -o, --close              close file descriptor before running command\n"), stdout);
  69         fputs(_(  " -c, --command <command>  run a single command string through the shell\n"), stdout);
  70         fputs(_(  " -F, --no-fork            execute command without forking\n"), stdout);
  71         fputs(_(  "     --verbose            increase verbosity\n"), stdout);
  72         fputs(USAGE_SEPARATOR, stdout);
  73         printf(USAGE_HELP_OPTIONS(26));
  74         printf(USAGE_MAN_TAIL("flock(1)"));
  75         exit(EXIT_SUCCESS);
  76 }
  77
  78 static sig_atomic_t timeout_expired = 0;
  79
  80 static void timeout_handler(int sig __attribute__((__unused__)),
  81                             siginfo_t *info,
  82                             void *context __attribute__((__unused__)))
  83 {
  84 #ifdef HAVE_TIMER_CREATE
  85         if (info->si_code == SI_TIMER)
  86 #endif
  87                 timeout_expired = 1;
  88 }
  89
  90 static int open_file(const char *filename, int *flags)
  91 {
  92
  93         int fd;
  94         int fl = *flags == 0 ? O_RDONLY : *flags;
  95
  96         errno = 0;
  97         fl |= O_NOCTTY | O_CREAT;
  98         fd = open(filename, fl, 0666);
  99
 100         /* Linux doesn't like O_CREAT on a directory, even though it
 101          * should be a no-op; POSIX doesn't allow O_RDWR or O_WRONLY
 102          */
 103         if (fd < 0 && errno == EISDIR) {
 104                 fl = O_RDONLY | O_NOCTTY;
 105                 fd = open(filename, fl);
 106         }
 107         if (fd < 0) {
 108                 warn(_("cannot open lock file %s"), filename);
 109                 if (errno == ENOMEM || errno == EMFILE || errno == ENFILE)
 110                         exit(EX_OSERR);
 111                 if (errno == EROFS || errno == ENOSPC)
 112                         exit(EX_CANTCREAT);
 113                 exit(EX_NOINPUT);
 114         }
 115         *flags = fl;
 116         return fd;
 117 }
 118
 119 static void __attribute__((__noreturn__)) run_program(char **cmd_argv)
 120 {
 121         execvp(cmd_argv[0], cmd_argv);
 122
 123         warn(_("failed to execute %s"), cmd_argv[0]);
 124         _exit((errno == ENOMEM) ? EX_OSERR : EX_UNAVAILABLE);
 125 }
 126
 127 int main(int argc, char *argv[])
 128 {
 129         struct ul_timer timer;
 130         struct itimerval timeout;
 131         int have_timeout = 0;
 132         int type = LOCK_EX;
 133         int block = 0;
 134         int open_flags = 0;
 135         int fd = -1;
 136         int opt, ix;
 137         int do_close = 0;
 138         int no_fork = 0;
 139         int status;
 140         int verbose = 0;
 141         struct timeval time_start, time_done;
 142         /*
 143          * The default exit code for lock conflict or timeout
 144          * is specified in man flock.1
 145          */
 146         int conflict_exit_code = 1;
 147         char **cmd_argv = NULL, *sh_c_argv[4];
 148         const char *filename = NULL;
 149         enum {
 150                 OPT_VERBOSE = CHAR_MAX + 1
 151         };
 152         static const struct option long_options[] = {
 153                 {"shared", no_argument, NULL, 's'},
 154                 {"exclusive", no_argument, NULL, 'x'},
 155                 {"unlock", no_argument, NULL, 'u'},
 156                 {"nonblocking", no_argument, NULL, 'n'},
 157                 {"nb", no_argument, NULL, 'n'},
 158                 {"timeout", required_argument, NULL, 'w'},
 159                 {"wait", required_argument, NULL, 'w'},
 160                 {"conflict-exit-code", required_argument, NULL, 'E'},
 161                 {"close", no_argument, NULL, 'o'},
 162                 {"no-fork", no_argument, NULL, 'F'},
 163                 {"verbose", no_argument, NULL, OPT_VERBOSE},
 164                 {"help", no_argument, NULL, 'h'},
 165                 {"version", no_argument, NULL, 'V'},
 166                 {NULL, 0, NULL, 0}
 167         };
 168
 169         setlocale(LC_ALL, "");
 170         bindtextdomain(PACKAGE, LOCALEDIR);
 171         textdomain(PACKAGE);
 172         atexit(close_stdout);
 173
 174         strutils_set_exitcode(EX_USAGE);
 175
 176         if (argc < 2) {
 177                 warnx(_("not enough arguments"));
 178                 errtryhelp(EX_USAGE);
 179         }
 180
 181         memset(&timeout, 0, sizeof timeout);
 182
 183         optopt = 0;
 184         while ((opt =
 185                 getopt_long(argc, argv, "+sexnoFuw:E:hV?", long_options,
 186                             &ix)) != EOF) {
 187                 switch (opt) {
 188                 case 's':
 189                         type = LOCK_SH;
 190                         break;
 191                 case 'e':
 192                 case 'x':
 193                         type = LOCK_EX;
 194                         break;
 195                 case 'u':
 196                         type = LOCK_UN;
 197                         break;
 198                 case 'o':
 199                         do_close = 1;
 200                         break;
 201                 case 'F':
 202                         no_fork = 1;
 203                         break;
 204                 case 'n':
 205                         block = LOCK_NB;
 206                         break;
 207                 case 'w':
 208                         have_timeout = 1;
 209                         strtotimeval_or_err(optarg, &timeout.it_value,
 210                                 _("invalid timeout value"));
 211                         break;
 212                 case 'E':
 213                         conflict_exit_code = strtos32_or_err(optarg,
 214                                 _("invalid exit code"));
 215                         break;
 216                 case OPT_VERBOSE:
 217                         verbose = 1;
 218                         break;
 219                 case 'V':
 220                         printf(UTIL_LINUX_VERSION);
 221                         exit(EX_OK);
 222                 case 'h':
 223                         usage();
 224                 default:
 225                         errtryhelp(EX_USAGE);
 226                 }
 227         }
 228
 229         if (no_fork && do_close)
 230                 errx(EX_USAGE,
 231                         _("the --no-fork and --close options are incompatible"));
 232
 233         if (argc > optind + 1) {
 234                 /* Run command */
 235                 if (!strcmp(argv[optind + 1], "-c") ||
 236                     !strcmp(argv[optind + 1], "--command")) {
 237                         if (argc != optind + 3)
 238                                 errx(EX_USAGE,
 239                                      _("%s requires exactly one command argument"),
 240                                      argv[optind + 1]);
 241                         cmd_argv = sh_c_argv;
 242                         cmd_argv[0] = getenv("SHELL");
 243                         if (!cmd_argv[0] || !*cmd_argv[0])
 244                                 cmd_argv[0] = _PATH_BSHELL;
 245                         cmd_argv[1] = "-c";
 246                         cmd_argv[2] = argv[optind + 2];
 247                         cmd_argv[3] = NULL;
 248                 } else {
 249                         cmd_argv = &argv[optind + 1];
 250                 }
 251
 252                 filename = argv[optind];
 253                 fd = open_file(filename, &open_flags);
 254
 255         } else if (optind < argc) {
 256                 /* Use provided file descriptor */
 257                 fd = strtos32_or_err(argv[optind], _("bad file descriptor"));
 258         } else {
 259                 /* Bad options */
 260                 errx(EX_USAGE, _("requires file descriptor, file or directory"));
 261         }
 262
 263         if (have_timeout) {
 264                 if (timeout.it_value.tv_sec == 0 &&
 265                     timeout.it_value.tv_usec == 0) {
 266                         /* -w 0 is equivalent to -n; this has to be
 267                          * special-cased because setting an itimer to zero
 268                          * means disabled!
 269                          */
 270                         have_timeout = 0;
 271                         block = LOCK_NB;
 272                 } else
 273                         if (setup_timer(&timer, &timeout, &timeout_handler))
 274                                 err(EX_OSERR, _("cannot set up timer"));
 275         }
 276
 277         if (verbose)
 278                 gettime_monotonic(&time_start);
 279         while (flock(fd, type | block)) {
 280                 switch (errno) {
 281                 case EWOULDBLOCK:
 282                         /* -n option set and failed to lock. */
 283                         if (verbose)
 284                                 warnx(_("failed to get lock"));
 285                         exit(conflict_exit_code);
 286                 case EINTR:
 287                         /* Signal received */
 288                         if (timeout_expired) {
 289                                 /* -w option set and failed to lock. */
 290                                 if (verbose)
 291                                         warnx(_("timeout while waiting to get lock"));
 292                                 exit(conflict_exit_code);
 293                         }
 294                         /* otherwise try again */
 295                         continue;
 296                 case EIO:
 297                 case EBADF:             /* since Linux 3.4 (commit 55725513) */
 298                         /* Probably NFSv4 where flock() is emulated by fcntl().
 299                          * Let's try to reopen in read-write mode.
 300                          */
 301                         if (!(open_flags & O_RDWR) &&
 302                             type != LOCK_SH &&
 303                             filename &&
 304                             access(filename, R_OK | W_OK) == 0) {
 305
 306                                 close(fd);
 307                                 open_flags = O_RDWR;
 308                                 fd = open_file(filename, &open_flags);
 309
 310                                 if (open_flags & O_RDWR)
 311                                         break;
 312                         }
 313                         /* fallthrough */
 314                 default:
 315                         /* Other errors */
 316                         if (filename)
 317                                 warn("%s", filename);
 318                         else
 319                                 warn("%d", fd);
 320                         exit((errno == ENOLCK
 321                               || errno == ENOMEM) ? EX_OSERR : EX_DATAERR);
 322                 }
 323         }
 324
 325         if (have_timeout)
 326                 cancel_timer(&timer);
 327         if (verbose) {
 328                 struct timeval delta;
 329
 330                 gettime_monotonic(&time_done);
 331                 timersub(&time_done, &time_start, &delta);
 332                 printf(_("%s: getting lock took %ld.%06ld seconds\n"),
 333                        program_invocation_short_name, delta.tv_sec,
 334                        delta.tv_usec);
 335         }
 336         status = EX_OK;
 337
 338         if (cmd_argv) {
 339                 pid_t w, f;
 340                 /* Clear any inherited settings */
 341                 signal(SIGCHLD, SIG_DFL);
 342                 if (verbose)
 343                         printf(_("%s: executing %s\n"), program_invocation_short_name, cmd_argv[0]);
 344
 345                 if (!no_fork) {
 346                         f = fork();
 347                         if (f < 0)
 348                                 err(EX_OSERR, _("fork failed"));
 349
 350                         /* child */
 351                         else if (f == 0) {
 352                                 if (do_close)
 353                                         close(fd);
 354                                 run_program(cmd_argv);
 355
 356                         /* parent */
 357                         } else {
 358                                 do {
 359                                         w = waitpid(f, &status, 0);
 360                                         if (w == -1 && errno != EINTR)
 361                                                 break;
 362                                 } while (w != f);
 363
 364                                 if (w == -1) {
 365                                         status = EXIT_FAILURE;
 366                                         warn(_("waitpid failed"));
 367                                 } else if (WIFEXITED(status))
 368                                         status = WEXITSTATUS(status);
 369                                 else if (WIFSIGNALED(status))
 370                                         status = WTERMSIG(status) + 128;
 371                                 else
 372                                         /* WTF? */
 373                                         status = EX_OSERR;
 374                         }
 375
 376                 } else
 377                         /* no-fork execution */
 378                         run_program(cmd_argv);
 379         }
 380
 381         return status;
 382 }