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

On 2/28/2012 8:40 PM, John Fastabend wrote:

On 2/18/2012 4:41 AM, jamal wrote:

quoted

On Fri, 2012-02-17 at 09:10 -0800, John Fastabend wrote:

quoted

Yes I agree that is the goal.

quoted

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.

Maybe I gave up too quickly here I could use a bit in the ndm_flags to
specify embedded or sw bridge. But would require having the bridge
module loaded.

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.

Just checked looks like the DSA infrastructure has commands to enable
STP so guess it is doing learning.

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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