Date: Thu, 6 Dec 2007 06:30:16 +0100
To: Andi Kleen <andi@firstfloor.org>
Cc: linux-kernel@vger.kernel.org
Subject: Re: New Address Family: Inter Process Networking (IPN)
Message-ID: <20071206053016.GA1464@cs.unibo.it>
References: <20071205164055.GA2082@cs.unibo.it> <p73bq94k8yd.fsf@bingen.suse.de>
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From: renzo@cs.unibo.it (Renzo Davoli)
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On Thu, Dec 06, 2007 at 12:39:22AM +0100, Andi Kleen wrote:
> renzo@cs.unibo.it (Renzo Davoli) writes:
> 
> > Berkeley socket have been designed for client server or point to point
> > communication. All existing Address Families implement this idea.
> Netlink is multicast/broadcast by default for once. And BC/MC certainly
> works for IPv[46] and a couple of other protocols too.
> 
> > IPN is an Inter Process Communication paradigm where all the processes
> > appear as they were connected by a networking bus.
> 
> Sounds like netlink. See also RFC 3549

RFC 3549 says:
"This document describes Linux Netlink, which is used in Linux both as
   an intra-kernel messaging system as well as between kernel and user
   space."

We know AF_NETLINK, our user-space stack lwipv6 supports it.

AF_IPN is different. 
AF_IPN is the broadcast and peer-to-peer extension of AF_UNIX.
It supports communication among *user* processes. 

Example:

Qemu, User-Mode Linux, Kvm, our umview machines can use IPN as an
Ethernet Hub and communicate among themselves with the hosting computer 
and the world by a tap like interface.

You can also grab an interface (say eth1) and use eth0 for your hosting
computer and eth1 for the IPN network of virtual machines.

If you load the kvde_switch submodule IPN can be a virtual Ethernet switch.

This example is already working using the svn versions of ipn and
vdeplug.

Another Example:

You have a continuous stream of data packets generated by a process,
and you want to send this data to many processes.
Maybe the set of processes is not known in advance, you want to send the
data to any interested process. Some kind of publish&subscribe
communication service (among unix processes not on TCP-IP).
Without IPN you need a server. With IPN the sender creates the socket
connects to it and feed it with data packets. All the interested 
receivers connects to it and start reading. That's all.

I hope that this message can give a better undertanding of what IPN is.

	renzo
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