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Re: [PATCH, untested] Support for PPPOE on SMP

To: Jamal Hadi <hadi@xxxxxxxxxxxxxxxx>
Subject: Re: [PATCH, untested] Support for PPPOE on SMP
From: Stephen Hemminger <shemminger@xxxxxxxx>
Date: Wed, 25 Jun 2003 10:40:01 -0700
Cc: mostrows@xxxxxxxxxxxxxx, rusty@xxxxxxxxxxxxxxx, davem@xxxxxxxxxx, paulus@xxxxxxxxx, netdev@xxxxxxxxxxx, fcusack@xxxxxxxxx, dfs@xxxxxxxxxxxxxxxxxx, carlson@xxxxxxxxxxxxxxx
In-reply-to: <20030625125518.N84526@shell.cyberus.ca>
Organization: Open Source Development Lab
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On Wed, 25 Jun 2003 13:07:46 -0400 (EDT)
Jamal Hadi <hadi@xxxxxxxxxxxxxxxx> wrote:

> 
> 
> On Wed, 25 Jun 2003, Stephen Hemminger wrote:
> 
> > On Wed, 25 Jun 2003 12:22:35 -0400 (EDT)
> > Jamal Hadi <hadi@xxxxxxxxxxxxxxxx> wrote:
> >
> > > Placing control protocols in the kernel is plain wrong.
> >
> > What about arp, TCP, IP, routing protocols.
> 
> ARP should really be ripped off the kernel. I mentioned to you once
> the same in regards to STP and iirc you agreed.
> I  wouldnt call TCP or IP control protocols.
> 
> >The problem is that state management needs to be done in one place.
> 
> a protocol or implementation which wishes to do state maintanance
> properly oughta be able to do the synchronization on its own.
> Separation between policy and mechanism has been the strength of unix.
> A clean separation between control and a data path is very important.
> Control protocols tend to be very rich environments which are
> constantly changing. Take STP, there are so many features that could be
> added to STP that are much harder to add because it is in the kernel.

Rather than take an architectural approach about what is right and wrong,
I take the practical point of view.  If the protocol is small, and the 
policy can be done in the kernel fine; if the implementation gets messy
and the right information is not there, then it belongs in user space.

For PPPoE, the session management needs to be in kernel space, with the policy
in user space.  What if the kernel, initialized the session when it saw
the discovery and notified the pppd,  session would not be established
until ppd accepted the connection.  This would be more like a socket
protocol without auto-accept like TCP. Any data for the session would
then stay queued until it was accepted or rejected.

Having special non-SMP receive logic is bogus; and probably won't work
anyway with preempt and other races.

There is already work in moving STP out of the kernel, but even that
has shown that the problem is how to have the proper management hooks
to do the job. That is why it hasn't been a simple slam dunk.


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