io/lockf.c

   1 /* Copyright (C) 1994 Free Software Foundation, Inc.
   2 This file is part of the GNU C Library.
   3
   4 The GNU C Library is free software; you can redistribute it and/or
   5 modify it under the terms of the GNU Library General Public License as
   6 published by the Free Software Foundation; either version 2 of the
   7 License, or (at your option) any later version.
   8
   9 The GNU C Library is distributed in the hope that it will be useful,
  10 but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12 Library General Public License for more details.
  13
  14 You should have received a copy of the GNU Library General Public
  15 License along with the GNU C Library; see the file COPYING.LIB.  If
  16 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  17 Cambridge, MA 02139, USA.  */
  18
  19 #include <sys/types.h>
  20 #include <unistd.h>
  21 #include <fcntl.h>
  22 #include <errno.h>
  23
  24 /* lockf is a simplified interface to fcntl's locking facilities.  */
  25
  26 int
  27 lockf (int fd, int cmd, off_t len)
  28 {
  29   struct flock fl;
  30
  31   switch (cmd)
  32     {
  33     case F_TEST:
  34       /* Test the lock: return 0 if FD is unlocked or locked by this process;
  35          return -1, set errno to EACCES, if another process holds the lock.  */
  36       if (fcntl (fd, F_GETLK, &fl) < 0)
  37         return -1;
  38       if (fl.l_type == F_UNLCK || fl.l_pid == getpid ())
  39         return 0;
  40       errno = EACCES;
  41       return -1;
  42
  43     case F_ULOCK:
  44       fl.l_type = F_UNLCK;
  45       cmd = F_SETLK;
  46       break;
  47     case F_LOCK:
  48       fl.l_type = F_WRLCK;
  49       cmd = F_SETLKW;
  50       break;
  51     case F_TLOCK:
  52       fl.l_type = F_WRLCK;
  53       cmd = F_SETLK;
  54       break;
  55
  56     default:
  57       errno = EINVAL;
  58       return -1;
  59     }
  60
  61   /* lockf is always relative to the current file position.  */
  62   fl.l_whence = SEEK_CUR;
  63   fl.l_start = 0;
  64
  65   fl.l_len = len;
  66
  67   return fcntl (fd, cmd, &fl);
  68 }