io/lockf64.c

   1 /* Copyright (C) 1994-2017 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.c defines lockf64 as an alias if __OFF_T_MATCHES_OFF64_T.  */
  25 #ifndef __OFF_T_MATCHES_OFF64_T
  26
  27 /* lockf is a simplified interface to fcntl's locking facilities.  */
  28
  29 int
  30 lockf64 (int fd, int cmd, off64_t len64)
  31 {
  32   struct flock fl;
  33   off_t len = (off_t) len64;
  34
  35   if (len64 != (off64_t) len)
  36     {
  37       /* We can't represent the length.  */
  38       __set_errno (EOVERFLOW);
  39       return -1;
  40     }
  41
  42   memset ((char *) &fl, '\0', sizeof (fl));
  43
  44   /* lockf is always relative to the current file position.  */
  45   fl.l_whence = SEEK_CUR;
  46   fl.l_start = 0;
  47   fl.l_len = len;
  48
  49   switch (cmd)
  50     {
  51     case F_TEST:
  52       /* Test the lock: return 0 if FD is unlocked or locked by this process;
  53          return -1, set errno to EACCES, if another process holds the lock.  */
  54       fl.l_type = F_RDLCK;
  55       if (__fcntl (fd, F_GETLK, &fl) < 0)
  56         return -1;
  57       if (fl.l_type == F_UNLCK || fl.l_pid == __getpid ())
  58         return 0;
  59       __set_errno (EACCES);
  60       return -1;
  61
  62     case F_ULOCK:
  63       fl.l_type = F_UNLCK;
  64       cmd = F_SETLK;
  65       break;
  66     case F_LOCK:
  67       fl.l_type = F_WRLCK;
  68       cmd = F_SETLKW;
  69       break;
  70     case F_TLOCK:
  71       fl.l_type = F_WRLCK;
  72       cmd = F_SETLK;
  73       break;
  74
  75     default:
  76       __set_errno (EINVAL);
  77       return -1;
  78     }
  79
  80   return __fcntl (fd, cmd, &fl);
  81 }
  82
  83 #endif