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 <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