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dotlock.c

/* $Id$ */

/*
 *
 * Copyright (C) 2004 David Mazieres (dm@uun.org)
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2, or (at
 * your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
 * USA
 *
 */

#include "local.h"
#include <signal.h>
#include <sys/socket.h>
#include <utime.h>
#include "getopt_long.h"

char *progname;
char *deleteme;

static void
clean (int sig)
{
  if (deleteme)
    unlink (deleteme);
  _exit (sig != 0);
}

static void
launch_locker (const char *path)
{
  int fds[2];
  pid_t pid;
  char c = 0;

  if (socketpair (AF_UNIX, SOCK_STREAM, 0, fds)) {
    perror ("socketpair");
    exit (1);
  }
  pid = fork ();
  if (pid == -1) {
    perror ("fork");
    exit (1);
  }

  if (!pid) {
    int dfd, lfd;
    fd_set fdsr;

    setsid ();
    close (fds[0]);
    signal (SIGINT, SIG_IGN);
    signal (SIGTERM, SIG_IGN);
    signal (SIGTSTP, SIG_IGN);
    if (dotlock (&dfd, &deleteme, path, &lfd))
      _exit (1);
    if (write (fds[1], &c, 1) != 0) {
      perror ("write");
      exit (1);
    }
    shutdown (fds[1], SHUT_WR);
    FD_ZERO (&fdsr);

    for (;;) {
      struct timeval tv;
      struct stat sb1, sb2;

      tv.tv_sec = 15;
      tv.tv_usec = 0;
      FD_SET (fds[1], &fdsr);
      if (select (fds[1]+1, &fdsr, NULL, NULL, &tv) == 1
        && read (fds[1], &c, 1) < 1)
      clean (0);
      if (fstat (lfd, &sb1) || lstat (deleteme, &sb2)
        || sb1.st_dev != sb2.st_dev || sb1.st_ino != sb2.st_ino) {
      fprintf (stderr, "%s: lost the lock on %s\n", progname, path);
      exit (1);
      }
      /* utime (path, NULL); */
      utime (deleteme, NULL);
    }
  }

  close (fds[1]);
  if (read (fds[0], &c, 1) < 1) {
    fprintf (stderr, "cannot lock %s\n", path);
    exit (1);
  }
}

static void usage (void) __attribute__ ((noreturn));
static void
usage (void)
{
  fprintf (stderr, "usage: %s [-LPW] mailbox command [arg ...]\n", progname);
  exit (1);
}

int
main (int argc, char **argv)
{
  struct option o[] = {
    { "version", no_argument, NULL, 'v' },
    { "fcntl", no_argument, NULL, 'P' },
    { "noflock", no_argument, NULL, 'L' },
    { "nowait", no_argument, NULL, 'W' },
    { NULL, 0, NULL, 0 }
  };
  int c;
  char **av;

  progname = strrchr (argv[0], '/');
  if (progname)
    progname++;
  else
    progname = argv[0];

  while ((c = getopt_long (argc, argv, "+LPW", o, NULL)) != -1)
    switch (c) {
    case 'L':
      opt_noflock = 1;
      break;
    case 'P':
      opt_fcntl = 1;
      break;
    case 'W':
      opt_nowait = 1;
      break;
    case 'v':
      version (progname, 1);
      exit (0);
      break;
    default:
      usage ();
      break;
    }

  argv += optind;
  argc -= optind;
  
  if (argc < 2)
    usage ();

  av = xmalloc (sizeof (av[0]) * argc);
  for (c = 1; c < argc; c++)
    av[c - 1] = argv[c];
  av[argc - 1] = NULL;

  launch_locker (argv[0]);
  execvp (av[0], av);
  perror (av[0]);
  exit (1);
}

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