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

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Date:	Tue, 28 Feb 2012 20:40:06 -0800
From:	John Fastabend <john.r.fastabend@...el.com>
To:	jhs@...atatu.com
CC:	jamal <hadi@...erus.ca>, 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, kernel@...tstofly.org
Subject: Re: [RFC PATCH v0 1/2] net: bridge: propagate FDB table into hardware

On 2/18/2012 4:41 AM, jamal wrote:
> On Fri, 2012-02-17 at 09:10 -0800, John Fastabend wrote:
> 
>> Yes I agree that is the goal.
>>
>>> One last comment:
>>> With synchronization there are other challenges when the entry in the
>>> hardware conflicts with the entry in software when you intend the
>>> behavior to be the same. This is not such a big deal with bridging but
>>> becomes more apparent when you start offloading ACLs etc.
>>>
>>
>> OK and these sorts of conflicts certainly don't need to be resolved
>> by kernel code. So I think this is a reasonable reason to drive the
>> synchronization into a user space daemon.
> 
> 
> Yep. 
> Thanks for listening John. Waiting to see them patches.
> 
> cheers,
> jamal
> 
> 
> 

+Lennert

OK back to this. The last piece is where to put these messages...
we could take PF_ROUTE:RTM_*NEIGH

     PF_ROUTE:RTM_NEWNEIGH - Add a new FDB entry to an offloaded
                             switch.
     PF_ROUTE:RTM_DELNEIGH - Delete a FDB entry from an offlaoded
                             switch.
     PF_ROUTE:RTM_GETNEIGH - Dumps the embedded FDB table

The neighbor code is using the PF_UNSPEC protocol type so we won't
collide with these unless someone was using PF_ROUTE and relying on
falling back to PF_UNSPEC however I couldn't find any programs that
did this iproute2 certainly doesn't. And the bridge pieces are using
PF_BRIDGE so no collision there.

I briefly thought about trying to pull the PF_BRIDGE protocol out
and use this for both types but I think its better to leave the
bridge code alone and there is also the issue of disambiguating a msg
at a port which has both an embedded switch and has SW bridge for a
master.

Also if there are embedded switches with learning capabilities they
might want to trigger events to user space. In this case having
a protocol type makes user space a bit easier to manage. I've
added Lennert so maybe he can comment I think the Marvell chipsets
might support something along these lines. The SR-IOV chipsets I'm
aware of _today_ don't do learning. Learning makes the event model
more plausible.

The other mechanism would be to embed some more attributes into the
PF_UNSPEC:RTM_XXXLINK msg however I'm thinking that if we want to
support learning and triggering events then we likely also don't
want to send these events to every app with RTNLGRP_LINK set.

Plus there is already a proliferation of LINK attributes and dumping
the FDB out of this seems a bit much but could be done with some
bitmasks. Although the current ext_filter_mask u32 doesn't seem to
be sufficient for events to trigger this.

so much for a short note...

Thanks
.John

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