1  /* Copyright (C) 1994-2023 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