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diff --git a/lib/fd-hook.c b/lib/fd-hook.c
new file mode 100644
index 0000000..8f4ffe2
--- /dev/null
+++ b/lib/fd-hook.c
@@ -0,0 +1,116 @@
+/* Hook for making making file descriptor functions close(), ioctl() extensible.
+   Copyright (C) 2009-2012 Free Software Foundation, Inc.
+   Written by Bruno Haible <bruno@clisp.org>, 2009.
+
+   This program is free software: you can redistribute it and/or modify it
+   under the terms of the GNU General Public License as published
+   by the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <config.h>
+
+/* Specification.  */
+#include "fd-hook.h"
+
+#include <stdlib.h>
+
+/* Currently, this entire code is only needed for the handling of sockets
+   on native Windows platforms.  */
+#if WINDOWS_SOCKETS
+
+/* The first and last link in the doubly linked list.
+   Initially the list is empty.  */
+static struct fd_hook anchor = { &anchor, &anchor, NULL, NULL };
+
+int
+execute_close_hooks (const struct fd_hook *remaining_list, gl_close_fn primary,
+                     int fd)
+{
+  if (remaining_list == &anchor)
+    /* End of list reached.  */
+    return primary (fd);
+  else
+    return remaining_list->private_close_fn (remaining_list->private_next,
+                                             primary, fd);
+}
+
+int
+execute_all_close_hooks (gl_close_fn primary, int fd)
+{
+  return execute_close_hooks (anchor.private_next, primary, fd);
+}
+
+int
+execute_ioctl_hooks (const struct fd_hook *remaining_list, gl_ioctl_fn primary,
+                     int fd, int request, void *arg)
+{
+  if (remaining_list == &anchor)
+    /* End of list reached.  */
+    return primary (fd, request, arg);
+  else
+    return remaining_list->private_ioctl_fn (remaining_list->private_next,
+                                             primary, fd, request, arg);
+}
+
+int
+execute_all_ioctl_hooks (gl_ioctl_fn primary,
+                         int fd, int request, void *arg)
+{
+  return execute_ioctl_hooks (anchor.private_next, primary, fd, request, arg);
+}
+
+void
+register_fd_hook (close_hook_fn close_hook, ioctl_hook_fn ioctl_hook, struct fd_hook *link)
+{
+  if (close_hook == NULL)
+    close_hook = execute_close_hooks;
+  if (ioctl_hook == NULL)
+    ioctl_hook = execute_ioctl_hooks;
+
+  if (link->private_next == NULL && link->private_prev == NULL)
+    {
+      /* Add the link to the doubly linked list.  */
+      link->private_next = anchor.private_next;
+      link->private_prev = &anchor;
+      link->private_close_fn = close_hook;
+      link->private_ioctl_fn = ioctl_hook;
+      anchor.private_next->private_prev = link;
+      anchor.private_next = link;
+    }
+  else
+    {
+      /* The link is already in use.  */
+      if (link->private_close_fn != close_hook
+          || link->private_ioctl_fn != ioctl_hook)
+        abort ();
+    }
+}
+
+void
+unregister_fd_hook (struct fd_hook *link)
+{
+  struct fd_hook *next = link->private_next;
+  struct fd_hook *prev = link->private_prev;
+
+  if (next != NULL && prev != NULL)
+    {
+      /* The link is in use.  Remove it from the doubly linked list.  */
+      prev->private_next = next;
+      next->private_prev = prev;
+      /* Clear the link, to mark it unused.  */
+      link->private_next = NULL;
+      link->private_prev = NULL;
+      link->private_close_fn = NULL;
+      link->private_ioctl_fn = NULL;
+    }
+}
+
+#endif