diff --git a/library/GNUmakefile.68k b/library/GNUmakefile.68k
index 90518a3..31487a1 100644
--- a/library/GNUmakefile.68k
+++ b/library/GNUmakefile.68k
@@ -1,5 +1,5 @@
 #
-# $Id: GNUmakefile.68k,v 1.98 2006-11-13 09:25:28 obarthel Exp $
+# $Id: GNUmakefile.68k,v 1.99 2006-11-15 09:17:04 obarthel Exp $
 #
 # :ts=8
 #
@@ -189,6 +189,8 @@ C_LIB = \
 	stat_stat.o \
 	stat_umask.o \
 	stdio_asprintf.o \
+	stdio_change_fd_action.o \
+	stdio_change_fd_user_data.o \
 	stdio_clearerr.o \
 	stdio_dropiobreadbuffer.o \
 	stdio_duplicate_fd.o \
@@ -228,6 +230,7 @@ C_LIB = \
 	stdio_getchar.o \
 	stdio_getchar_unlocked.o \
 	stdio_gets.o \
+	stdio_get_fd.o \
 	stdio_get_file_descriptor.o \
 	stdio_growfdtable.o \
 	stdio_growiobtable.o \
diff --git a/library/changes b/library/changes
index 46eec2d..b9e9bea 100644
--- a/library/changes
+++ b/library/changes
@@ -1,3 +1,7 @@
+- Added functions which modify the callback function and the userdata pointer
+  stored in a low level unbuffered file/socket data structure. These function
+  perform the proper locking and are thus safe to use in a thread-safe environment.
+
 - The low level unbuffered file/socket now has a public equivalent, which
   is defined (along with the typedefs and flags) in <sys/clib2_io.h>. Functions
   for tinkering with it are still to come.
diff --git a/library/include/sys/clib2_io.h b/library/include/sys/clib2_io.h
index 91149e8..53dcb63 100644
--- a/library/include/sys/clib2_io.h
+++ b/library/include/sys/clib2_io.h
@@ -1,5 +1,5 @@
 /*
- * $Id: clib2_io.h,v 1.1 2006-11-15 08:51:07 obarthel Exp $
+ * $Id: clib2_io.h,v 1.2 2006-11-15 09:17:04 obarthel Exp $
  *
  * :ts=4
  *
@@ -153,6 +153,27 @@ struct _fd
 
 /****************************************************************************/
 
+/* Obtain a pointer to the _fd data structure associated with a file
+   descriptor number. Note that this does not perform any locking, which
+   means that you have to be absolutely certain that the file will not be
+   closed while you are still looking at it. This function can return
+   NULL if the file descriptor you provided is not valid. */
+extern struct _fd * __get_fd(int file_descriptor);
+
+/* Replaces the action callback function and (optionally) returns the old
+   function pointer; returns 0 for success and -1 for failure if you
+   provided an invalid file descriptor. This function performs proper locking
+   and is thus safe to use in a thread-safe environment. */
+extern int __change_fd_action(int file_descriptor,_file_action_fd_t new_action,_file_action_fd_t * old_action_ptr);
+
+/* Replaces the user data pointer and (optionally) returns the old user
+   data pointer; returns 0 for success and -1 for failure if you
+   provided an invalid file descriptor. This function performs proper locking
+   and is thus safe to use in a thread-safe environment. */
+extern int __change_fd_user_data(int file_descriptor,void * new_user_data,void ** old_user_data_ptr);
+
+/****************************************************************************/
+
 #ifdef __cplusplus
 }
 #endif /* __cplusplus */
diff --git a/library/libc.gmk b/library/libc.gmk
index 527314e..290c009 100755
--- a/library/libc.gmk
+++ b/library/libc.gmk
@@ -1,5 +1,5 @@
 #
-# $Id: libc.gmk,v 1.2 2006-11-13 09:25:28 obarthel Exp $
+# $Id: libc.gmk,v 1.3 2006-11-15 09:17:04 obarthel Exp $
 #
 # :ts=8
 #
@@ -90,6 +90,8 @@ C_LIB := \
 	stat_stat.o \
 	stat_umask.o \
 	stdio_asprintf.o \
+	stdio_change_fd_action.o \
+	stdio_change_fd_user_data.o \
 	stdio_clearerr.o \
 	stdio_dropiobreadbuffer.o \
 	stdio_duplicate_fd.o \
@@ -129,6 +131,7 @@ C_LIB := \
 	stdio_getchar.o \
 	stdio_getchar_unlocked.o \
 	stdio_gets.o \
+	stdio_get_fd.o \
 	stdio_get_file_descriptor.o \
 	stdio_growfdtable.o \
 	stdio_growiobtable.o \
diff --git a/library/stdio_change_fd_action.c b/library/stdio_change_fd_action.c
new file mode 100644
index 0000000..c4247fe
--- /dev/null
+++ b/library/stdio_change_fd_action.c
@@ -0,0 +1,72 @@
+/*
+ * $Id: stdio_change_fd_action.c,v 1.1 2006-11-15 09:17:04 obarthel Exp $
+ *
+ * :ts=4
+ *
+ * Portable ISO 'C' (1994) runtime library for the Amiga computer
+ * Copyright (c) 2002-2006 by Olaf Barthel <olsen (at) sourcery.han.de>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ *   - Redistributions of source code must retain the above copyright
+ *     notice, this list of conditions and the following disclaimer.
+ *
+ *   - Neither the name of Olaf Barthel nor the names of contributors
+ *     may be used to endorse or promote products derived from this
+ *     software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef _STDIO_HEADERS_H
+#include "stdio_headers.h"
+#endif /* _STDIO_HEADERS_H */
+
+/****************************************************************************/
+
+int
+__change_fd_action(
+	int					file_descriptor,
+	_file_action_fd_t	new_action,
+	_file_action_fd_t *	old_action_ptr)
+{
+	int result = -1;
+	struct fd * fd;
+
+	if(old_action_ptr != NULL)
+		(*old_action_ptr) = NULL;
+
+	__stdio_lock();
+
+	fd = __get_file_descriptor(file_descriptor);
+	if(fd != NULL)
+	{
+		__fd_lock(fd);
+
+		if(old_action_ptr != NULL)
+			(*old_action_ptr) = (_file_action_fd_t)fd->fd_Action;
+
+		fd->fd_Action = (file_action_fd_t)new_action;
+
+		__fd_unlock(fd);
+
+		result = 0;
+	}
+
+	__stdio_unlock();
+
+	return(result);
+}
diff --git a/library/stdio_change_fd_user_data.c b/library/stdio_change_fd_user_data.c
new file mode 100644
index 0000000..9ef611c
--- /dev/null
+++ b/library/stdio_change_fd_user_data.c
@@ -0,0 +1,72 @@
+/*
+ * $Id: stdio_change_fd_user_data.c,v 1.1 2006-11-15 09:17:04 obarthel Exp $
+ *
+ * :ts=4
+ *
+ * Portable ISO 'C' (1994) runtime library for the Amiga computer
+ * Copyright (c) 2002-2006 by Olaf Barthel <olsen (at) sourcery.han.de>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ *   - Redistributions of source code must retain the above copyright
+ *     notice, this list of conditions and the following disclaimer.
+ *
+ *   - Neither the name of Olaf Barthel nor the names of contributors
+ *     may be used to endorse or promote products derived from this
+ *     software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef _STDIO_HEADERS_H
+#include "stdio_headers.h"
+#endif /* _STDIO_HEADERS_H */
+
+/****************************************************************************/
+
+int
+__change_fd_user_data(
+	int		file_descriptor,
+	void *	new_user_data,
+	void **	old_user_data_ptr)
+{
+	int result = -1;
+	struct fd * fd;
+
+	if(old_user_data_ptr != NULL)
+		(*old_user_data_ptr) = NULL;
+
+	__stdio_lock();
+
+	fd = __get_file_descriptor(file_descriptor);
+	if(fd != NULL)
+	{
+		__fd_lock(fd);
+
+		if(old_user_data_ptr != NULL)
+			(*old_user_data_ptr) = fd->fd_UserData;
+
+		fd->fd_UserData = new_user_data;
+
+		__fd_unlock(fd);
+
+		result = 0;
+	}
+
+	__stdio_unlock();
+
+	return(result);
+}
diff --git a/library/stdio_get_fd.c b/library/stdio_get_fd.c
new file mode 100644
index 0000000..6e0b540
--- /dev/null
+++ b/library/stdio_get_fd.c
@@ -0,0 +1,48 @@
+/*
+ * $Id: stdio_get_fd.c,v 1.1 2006-11-15 09:17:04 obarthel Exp $
+ *
+ * :ts=4
+ *
+ * Portable ISO 'C' (1994) runtime library for the Amiga computer
+ * Copyright (c) 2002-2006 by Olaf Barthel <olsen (at) sourcery.han.de>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ *   - Redistributions of source code must retain the above copyright
+ *     notice, this list of conditions and the following disclaimer.
+ *
+ *   - Neither the name of Olaf Barthel nor the names of contributors
+ *     may be used to endorse or promote products derived from this
+ *     software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef _STDIO_HEADERS_H
+#include "stdio_headers.h"
+#endif /* _STDIO_HEADERS_H */
+
+/****************************************************************************/
+
+struct _fd *
+__get_fd(int file_descriptor)
+{
+	struct _fd * result;
+
+	result = (struct _fd *)__get_file_descriptor(file_descriptor);
+
+	return(result);
+}