io/lockf64.c

   1 /* Copyright (C) 1994-2024 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    <https://www.gnu.org/licenses/>.  */
  17
  18 #include <unistd.h>
  19 #include <fcntl.h>
  20 #include <errno.h>
  21
  22 /* lockf is a simplified interface to fcntl's locking facilities.  */
  23 int
  24 __lockf64 (int fd, int cmd, off64_t len64)
  25 {
  26   /* lockf is always relative to the current file position.  */
  27   struct flock64 fl64 = {
  28     .l_type = F_WRLCK,
  29     .l_whence = SEEK_CUR,
  30     .l_len = len64,
  31   };
  32
  33   /* lockf() is a cancellation point but so is fcntl() if F_SETLKW is
  34      used.  Therefore we don't have to care about cancellation here,
  35      the fcntl() function will take care of it.  */
  36   switch (cmd)
  37     {
  38     case F_TEST:
  39       /* Test the lock: return 0 if FD is unlocked or locked by this process;
  40          return -1, set errno to EACCES, if another process holds the lock.  */
  41       fl64.l_type = F_RDLCK;
  42       if (__fcntl (fd, F_GETLK64, &fl64) < 0)
  43         return -1;
  44       if (fl64.l_type == F_UNLCK || fl64.l_pid == __getpid ())
  45         return 0;
  46       __set_errno (EACCES);
  47       return -1;
  48     case F_ULOCK:
  49       fl64.l_type = F_UNLCK;
  50       return __fcntl64 (fd, F_SETLK64, &fl64);
  51     case F_LOCK:
  52       return __fcntl64 (fd, F_SETLKW64, &fl64);
  53     case F_TLOCK:
  54       return __fcntl64 (fd, F_SETLK64, &fl64);
  55     }
  56   __set_errno (EINVAL);
  57   return -1;
  58 }
  59 weak_alias (__lockf64, lockf64)
  60 #ifdef __OFF_T_MATCHES_OFF64_T
  61 weak_alias (lockf64, lockf)
  62 #endif