1  /* Hook for making file descriptor functions close(), ioctl() extensible.
       2     Copyright (C) 2009-2023 Free Software Foundation, Inc.
       3     Written by Bruno Haible <bruno@clisp.org>, 2009.
       4  
       5     This file is free software: you can redistribute it and/or modify
       6     it under the terms of the GNU Lesser General Public License as
       7     published by the Free Software Foundation; either version 2.1 of the
       8     License, or (at your option) any later version.
       9  
      10     This file is distributed in the hope that it will be useful,
      11     but WITHOUT ANY WARRANTY; without even the implied warranty of
      12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
      13     GNU Lesser General Public License for more details.
      14  
      15     You should have received a copy of the GNU Lesser General Public License
      16     along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
      17  
      18  #include <config.h>
      19  
      20  /* Specification.  */
      21  #include "fd-hook.h"
      22  
      23  #include <stdlib.h>
      24  
      25  /* Currently, this entire code is only needed for the handling of sockets
      26     on native Windows platforms.  */
      27  #if WINDOWS_SOCKETS
      28  
      29  /* The first and last link in the doubly linked list.
      30     Initially the list is empty.  */
      31  static struct fd_hook anchor = { &anchor, &anchor, NULL, NULL };
      32  
      33  int
      34  execute_close_hooks (const struct fd_hook *remaining_list, gl_close_fn primary,
      35                       int fd)
      36  {
      37    if (remaining_list == &anchor)
      38      /* End of list reached.  */
      39      return primary (fd);
      40    else
      41      return remaining_list->private_close_fn (remaining_list->private_next,
      42                                               primary, fd);
      43  }
      44  
      45  int
      46  execute_all_close_hooks (gl_close_fn primary, int fd)
      47  {
      48    return execute_close_hooks (anchor.private_next, primary, fd);
      49  }
      50  
      51  int
      52  execute_ioctl_hooks (const struct fd_hook *remaining_list, gl_ioctl_fn primary,
      53                       int fd, int request, void *arg)
      54  {
      55    if (remaining_list == &anchor)
      56      /* End of list reached.  */
      57      return primary (fd, request, arg);
      58    else
      59      return remaining_list->private_ioctl_fn (remaining_list->private_next,
      60                                               primary, fd, request, arg);
      61  }
      62  
      63  int
      64  execute_all_ioctl_hooks (gl_ioctl_fn primary,
      65                           int fd, int request, void *arg)
      66  {
      67    return execute_ioctl_hooks (anchor.private_next, primary, fd, request, arg);
      68  }
      69  
      70  void
      71  register_fd_hook (close_hook_fn close_hook, ioctl_hook_fn ioctl_hook, struct fd_hook *link)
      72  {
      73    if (close_hook == NULL)
      74      close_hook = execute_close_hooks;
      75    if (ioctl_hook == NULL)
      76      ioctl_hook = execute_ioctl_hooks;
      77  
      78    if (link->private_next == NULL && link->private_prev == NULL)
      79      {
      80        /* Add the link to the doubly linked list.  */
      81        link->private_next = anchor.private_next;
      82        link->private_prev = &anchor;
      83        link->private_close_fn = close_hook;
      84        link->private_ioctl_fn = ioctl_hook;
      85        anchor.private_next->private_prev = link;
      86        anchor.private_next = link;
      87      }
      88    else
      89      {
      90        /* The link is already in use.  */
      91        if (link->private_close_fn != close_hook
      92            || link->private_ioctl_fn != ioctl_hook)
      93          abort ();
      94      }
      95  }
      96  
      97  void
      98  unregister_fd_hook (struct fd_hook *link)
      99  {
     100    struct fd_hook *next = link->private_next;
     101    struct fd_hook *prev = link->private_prev;
     102  
     103    if (next != NULL && prev != NULL)
     104      {
     105        /* The link is in use.  Remove it from the doubly linked list.  */
     106        prev->private_next = next;
     107        next->private_prev = prev;
     108        /* Clear the link, to mark it unused.  */
     109        link->private_next = NULL;
     110        link->private_prev = NULL;
     111        link->private_close_fn = NULL;
     112        link->private_ioctl_fn = NULL;
     113      }
     114  }
     115  
     116  #endif