io/lockf.c

   1 /* Copyright (C) 1994,1996,1997,1998,2000,2003 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 Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the 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    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <http://www.gnu.org/licenses/>.  */
  17
  18 #include <sys/types.h>
  19 #include <unistd.h>
  20 #include <fcntl.h>
  21 #include <errno.h>
  22 #include <string.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   memset ((char *) &fl, '\0', sizeof (fl));
  32
  33   /* lockf is always relative to the current file position.  */
  34   fl.l_whence = SEEK_CUR;
  35   fl.l_start = 0;
  36   fl.l_len = len;
  37
  38   switch (cmd)
  39     {
  40     case F_TEST:
  41       /* Test the lock: return 0 if FD is unlocked or locked by this process;
  42          return -1, set errno to EACCES, if another process holds the lock.  */
  43       fl.l_type = F_RDLCK;
  44       if (__fcntl (fd, F_GETLK, &fl) < 0)
  45         return -1;
  46       if (fl.l_type == F_UNLCK || fl.l_pid == __getpid ())
  47         return 0;
  48       __set_errno (EACCES);
  49       return -1;
  50
  51     case F_ULOCK:
  52       fl.l_type = F_UNLCK;
  53       cmd = F_SETLK;
  54       break;
  55     case F_LOCK:
  56       fl.l_type = F_WRLCK;
  57       cmd = F_SETLKW;
  58       break;
  59     case F_TLOCK:
  60       fl.l_type = F_WRLCK;
  61       cmd = F_SETLK;
  62       break;
  63
  64     default:
  65       __set_errno (EINVAL);
  66       return -1;
  67     }
  68
  69   /* lockf() is a cancellation point but so is fcntl() if F_SETLKW is
  70      used.  Therefore we don't have to care about cancellation here,
  71      the fcntl() function will take care of it.  */
  72   return __fcntl (fd, cmd, &fl);
  73 }