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, write to the Free
  16    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  17    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   /* lockf is always relative to the current file position.  */
  35   fl.l_whence = SEEK_CUR;
  36   fl.l_start = 0;
  37   fl.l_len = len;
  38
  39   switch (cmd)
  40     {
  41     case F_TEST:
  42       /* Test the lock: return 0 if FD is unlocked or locked by this process;
  43          return -1, set errno to EACCES, if another process holds the lock.  */
  44       fl.l_type = F_RDLCK;
  45       if (__fcntl (fd, F_GETLK, &fl) < 0)
  46         return -1;
  47       if (fl.l_type == F_UNLCK || fl.l_pid == __getpid ())
  48         return 0;
  49       __set_errno (EACCES);
  50       return -1;
  51
  52     case F_ULOCK:
  53       fl.l_type = F_UNLCK;
  54       cmd = F_SETLK;
  55       break;
  56     case F_LOCK:
  57       fl.l_type = F_WRLCK;
  58       cmd = F_SETLKW;
  59       break;
  60     case F_TLOCK:
  61       fl.l_type = F_WRLCK;
  62       cmd = F_SETLK;
  63       break;
  64
  65     default:
  66       __set_errno (EINVAL);
  67       return -1;
  68     }
  69
  70   /* lockf() is a cancellation point but so is fcntl() if F_SETLKW is
  71      used.  Therefore we don't have to care about cancellation here,
  72      the fcntl() function will take care of it.  */
  73   return __fcntl (fd, cmd, &fl);
  74 }