[PATCH 0/5 2.6.21-rc4] l2tp: introduce PPP over L2TP driver

This patch set adds a driver for PPP over L2TP. Patches to follow.

The implementation uses the existing PPPoX subsystem that is currently
used only by PPPoE. A userspace daemon handles all L2TP control
protocol messages, while a PPPoX socket carries user data. The system
architecture is similar to PPPoE, where a pppd plugin uses the PPPoX
socket to send/receive PPP frames over an L2TP tunnel. PPP control
frames are delivered to pppd while data frames are handled entirely by
the kernel.

There are 5 patches in the series:-

1 - pppol2tp driver core. New code.

2 - API changes for L2TP. Adds definitions for L2TP in existing headers.

3 - Change to PPPoX core to allow PPPoX protocol modules such as
    pppol2tp to be autoloaded via modprobe.conf.

4 - Kernel makefile and config file changes.

5 - Adds an entry to MAINTAINERS file.

The driver is being used on x86, ia64, ppc, arm, mips32 and possibly
other architectures. It is also known to work on multi-core SMP boxes.

Sparse emits some warnings to do with pointer namespaces in the
msg_iov code. The same warnings are output by net/socket.c from which
some of this code is derived.

Although this driver is being actively used in various L2TP setups,
I'm sure it would benefit from review here.

--
James Chapman
Katalix Systems Ltd
http://www.katalix.com
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