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