locking.c: Refactor the main locking flow.

[misc] / locking.c

/* -*-c-*-
 *
 * Lock a file, run a program
 *
 * (c) 2003 Mark Wooding
 */

/*----- Licensing notice --------------------------------------------------*
 *
 * This file is part of the Toys utilties collection.
 *
 * Toys 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 of the License, or
 * (at your option) any later version.
 *
 * Toys 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 Toys; if not, write to the Free Software Foundation,
 * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 */

/*----- Header files ------------------------------------------------------*/

#include <errno.h>
#include <setjmp.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

#include <sys/types.h>
#include <sys/time.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/wait.h>

#include <mLib/mdwopt.h>
#include <mLib/quis.h>
#include <mLib/report.h>

/*----- Static variables --------------------------------------------------*/

static jmp_buf jmp;
static int err;

/*----- Main code ---------------------------------------------------------*/

static void alrm(int s) { longjmp(jmp, 1); }

static void usage(FILE *fp)
{
  pquis(fp,
	"Usage: $ [-cfwx] [-p REALPROG] [-t TIMEOUT] FILE PROG ARGS...\n");
}

static void version(FILE *fp)
  { pquis(fp, "$ (version " VERSION ")\n"); }

static void help(FILE *fp)
{
  version(fp);
  putchar('\n');
  usage(fp);
  pquis(fp, "\n\
Lock FILE and run PROG, passing ARGS.  Options are:\n\
\n\
-h, --help		Show this help message.\n\
-v, --version		Show version string.\n\
-u, --usage		Show terse usage summary.\n\
\n\
-c, --[no-]create	Create FILE if it doesn't exist [default: on].\n\
-f, --[no-]fail		Fail if the file is already locked [default: off].\n\
-w, --[no-]wait		Wait for the lock to be available [default: off].\n\
-x, --[no-]exclusive	Get an exclusive (writer) lock [default: on].\n\
-p, --program=REALPROG	Run REALPROG instead of PROG.\n\
-t, --timeout=TIME	Wait for TIME for lock to become available.\n\
");
}

int main(int argc, char *argv[])
{
  const char *file = 0;
  const char *prog = 0;
  char *const *av;
  void (*oalrm)(int) = 0;
  int fd = -1;
  struct flock l;
  char *p;
  int t = -1;
  int oflag;
  unsigned int ot = 0;
  time_t nt;
  pid_t kid;
  int rc;

#define f_bogus 1u
#define f_wait 2u
#define f_fail 4u
#define f_create 8u
#define f_excl 16u

  unsigned f = f_create | f_excl;

  ego(argv[0]);

  for (;;) {
    static const struct option opts[] = {
      { "help",			0,		0,	'h' },
      { "version",		0,		0,	'v' },
      { "usage",		0,		0,	'u' },
      { "wait",			OPTF_NEGATE,	0,	'w' },
      { "fail",			OPTF_NEGATE,	0,	'f' },
      { "create",		OPTF_NEGATE,	0,	'c' },
      { "program",		OPTF_ARGREQ,	0,	'p' },
      { "timeout",		OPTF_ARGREQ,	0,	't' },
      { "exclusive",		OPTF_NEGATE,	0,	'x' },
      {	0,			0,		0,	0 }
    };

    int i = mdwopt(argc, argv, "-hvuw+f+c+x+p:t:", opts,
		   0, 0, OPTF_NEGATION);
    if (i < 0) break;
    switch (i) {
      case 'h': help(stdout); exit(0);
      case 'v': version(stdout); exit(0);
      case 'u': usage(stdout); exit(0);
      case 'w': f |= f_wait; break;
      case 'w' | OPTF_NEGATED: f &= ~f_wait; break;
      case 'f': f |= f_fail; break;
      case 'f' | OPTF_NEGATED: f &= ~f_fail; break;
      case 'c': f |= f_create; break;
      case 'c' | OPTF_NEGATED: f &= ~f_create; break;
      case 'x': f |= f_excl; break;
      case 'x' | OPTF_NEGATED: f &= ~f_excl; break;
      case 't':
	errno = 0;
	t = strtol(optarg, &p, 0);
	switch (*p) {
	  case 'd': t *= 24;
	  case 'h': t *= 60;
	  case 'm': t *= 60;
	  case 's': p++;
	  case 0: break;
	  default: die(111, "unknown time unit `%c'", *p);
	}
	if (*p || t < 0 || errno) die(111, "bad time value `%s'", optarg);
	f |= f_wait;
	break;
      case 'p': prog = optarg; break;
      case 0:
	if (file) { optind--; goto doneopts; }
	file = optarg;
	break;
      default: f |= f_bogus; break;
    }
  }

doneopts:
  if (f & f_bogus || argc - optind < 1) {
    usage(stderr);
    exit(EXIT_FAILURE);
  }

  av = &argv[optind];
  if (!prog) prog = av[0];
  oflag = f & f_excl ? O_RDWR : O_RDONLY;
  if (f & f_create) oflag |= O_CREAT;
  l.l_type = f & f_excl ? F_WRLCK : F_RDLCK;
  l.l_whence = SEEK_SET;
  l.l_start = 0;
  l.l_len = 0;
  nt = time(0);
  if (setjmp(jmp)) {
    err = EAGAIN;
    nt = t;
    goto done;
  }
  ot = alarm(0);
  oalrm = signal(SIGALRM, alrm);
  if (t >= 0) alarm(t);
  if ((fd = open(file, oflag, 0666)) < 0)
    die(111, "error opening `%s': %s", file, strerror(errno));
  err = fcntl(fd, f & f_wait ? F_SETLKW : F_SETLK, &l) >= 0 ? 0 : errno;
done:
  signal(SIGALRM, oalrm);
  if (!ot)
    alarm(0);
  else {
    nt = time(0) - nt;
    if (nt > ot) raise(SIGALRM);
    else alarm(ot - nt);
  }
  switch (err) {
    case 0: break;
    case EAGAIN:
#if defined(EWOULDBLOCK) && EWOULDBLOCK != EAGAIN
    case EWOULDBLOCK:
#endif
    case EACCES:
      if (!(f & f_fail)) exit(0);
    default:
      die(111, "error locking `%s': %s", file, strerror(errno));
  }
  if ((kid = fork()) < 0) die(111, "error from fork: %s", strerror(errno));
  if (!kid) {
    close(fd);
    execvp(prog, av);
    die(111, "couldn't exec `%s': %s", prog, strerror(errno));
  }
  if (waitpid(kid, &rc, 0) < 0)
    die(EXIT_FAILURE, "error from wait: %s", strerror(errno));
  l.l_type = F_UNLCK;
  l.l_whence = SEEK_SET;
  l.l_start = 0;
  l.l_len = 0;
  fcntl(fd, F_SETLK, &l);
  if (fd >= 0) close(fd);
  if (WIFEXITED(rc)) exit(WEXITSTATUS(rc));
  else exit(128 + WTERMSIG(rc));
}

/*----- That's all, folks -------------------------------------------------*/