netdev - Re: [RFC PATCH v0 1/2] net: bridge: propagate FDB table into hardware

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Date:	Tue, 13 Mar 2012 09:52:07 -0400
From:	Jamal Hadi Salim <jhs@...atatu.com>
To:	Lennert Buytenhek <buytenh@...tstofly.org>
Cc:	John Fastabend <john.r.fastabend@...el.com>,
	Stephen Hemminger <shemminger@...tta.com>,
	bhutchings@...arflare.com, roprabhu@...co.com,
	netdev@...r.kernel.org, mst@...hat.com, chrisw@...hat.com,
	davem@...emloft.net, gregory.v.rose@...el.com, kvm@...r.kernel.org,
	sri@...ibm.com, Chris Healy <chealy@...co-us.com>
Subject: Re: [RFC PATCH v0 1/2] net: bridge: propagate FDB table into
 hardware

On Mon, 2012-03-12 at 09:48 +0100, Lennert Buytenhek wrote:

> Since it can lead to problems (address database mismatches, doesn't
> correctly handle STP transitions or topology changes automatically),
> I think it should be avoided whenever possible.  I don't see any
> advantages of hardware based learning over software based learning
> anyway ('flexibility' doesn't seem like a very good argument).

Indeed address mismatches may happen if you have two databases. 
You have two choices then:
Do learning in user space or be able to tolerate some transient 
inconsistency (if you have some software that lazily looks at the
database). But there is a case where the database sits only in hardware.
In such a case, you cant have mismatches.
I think the STP problem can be handled by user space regardless of
whether address mismatch happens or not.

> It should be doable along the lines of the current DSA patch --
> add a VLAN ID argument to the interface add/remove callbacks, and
> when a VLAN virtual interface is added to the bridge, call the
> relevant callbacks with the parent interface + VLAN ID instead.
> (This doesn't work for stacked VLANs, but the current net/dsa
> supported chips don't handle those anyway.)

Sounds like a good start - we could have a different interface for
stacked variants. I think you should push in the patch.

cheers,
jamal

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