1  /* Copyright (C) 1992-2023 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  /* This file implements the `flock' function in terms of the POSIX.1 `fcntl'
      19     locking mechanism.  In 4BSD, these are two incompatible locking mechanisms,
      20     perhaps with different semantics?  */
      21  
      22  #include <errno.h>
      23  #include <unistd.h>
      24  #include <fcntl.h>
      25  #include <sys/file.h>
      26  
      27  /* Apply or remove an advisory lock, according to OPERATION,
      28     on the file FD refers to.  */
      29  int
      30  __flock (int fd, int operation)
      31  {
      32    struct flock lbuf;
      33  
      34    switch (operation & ~LOCK_NB)
      35      {
      36      case LOCK_SH:
      37        lbuf.l_type = F_RDLCK;
      38        break;
      39      case LOCK_EX:
      40        lbuf.l_type = F_WRLCK;
      41        break;
      42      case LOCK_UN:
      43        lbuf.l_type = F_UNLCK;
      44        break;
      45      default:
      46        __set_errno (EINVAL);
      47        return -1;
      48      }
      49  
      50    lbuf.l_whence = SEEK_SET;
      51    lbuf.l_start = lbuf.l_len = 0L; /* Lock the whole file.  */
      52  
      53    return __fcntl (fd, (operation & LOCK_NB) ? F_SETLK : F_SETLKW, &lbuf);
      54  }
      55  
      56  weak_alias (__flock, flock)