io/lockf.c

   1 /* Copyright (C) 1994, 1996, 1997 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 not,
  16    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  17    Boston, MA 02111-1307, USA.  */
  18
  19 #include <sys/types.h>
  20 #include <unistd.h>
  21 #include <fcntl.h>
  22 #include <errno.h>
  23 #include <string.h>
  24
  25 /* lockf is a simplified interface to fcntl's locking facilities.  */
  26
  27 int
  28 lockf (int fd, int cmd, off_t len)
  29 {
  30   struct flock fl;
  31
  32   memset ((char *) &fl, '\0', sizeof (fl));
  33
  34   switch (cmd)
  35     {
  36     case F_TEST:
  37       /* Test the lock: return 0 if FD is unlocked or locked by this process;
  38          return -1, set errno to EACCES, if another process holds the lock.  */
  39       if (fcntl (fd, F_GETLK, &fl) < 0)
  40         return -1;
  41       if (fl.l_type == F_UNLCK || fl.l_pid == getpid ())
  42         return 0;
  43       __set_errno (EACCES);
  44       return -1;
  45
  46     case F_ULOCK:
  47       fl.l_type = F_UNLCK;
  48       cmd = F_SETLK;
  49       break;
  50     case F_LOCK:
  51       fl.l_type = F_WRLCK;
  52       cmd = F_SETLKW;
  53       break;
  54     case F_TLOCK:
  55       fl.l_type = F_WRLCK;
  56       cmd = F_SETLK;
  57       break;
  58
  59     default:
  60       __set_errno (EINVAL);
  61       return -1;
  62     }
  63
  64   /* lockf is always relative to the current file position.  */
  65   fl.l_whence = SEEK_CUR;
  66   fl.l_start = 0;
  67
  68   fl.l_len = len;
  69
  70   return fcntl (fd, cmd, &fl);
  71 }