netdev - Re: [PATCH] bonding: fix arp_validate on bonds inside a bridge

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Date:	Wed, 5 May 2010 15:33:01 +0200
From:	Jiri Bohac <jbohac@...e.cz>
To:	David Miller <davem@...emloft.net>
Cc:	fubar@...ibm.com, jbohac@...e.cz,
	bonding-devel@...ts.sourceforge.net, netdev@...r.kernel.org
Subject: Re: [PATCH] bonding: fix arp_validate on bonds inside a bridge

On Tue, May 04, 2010 at 04:18:15PM -0700, David Miller wrote:
> From: Jay Vosburgh <fubar@...ibm.com>
> > 	Tested and it looks to work as advertised.  I see only one minor
> > nit, there's a pr_debug that missed being renamed to the new function
> > name; here's the whole patch with that fixed.
> 
> I don't think you need the ugly arp hook.
> 
> Instead, it's much cleaner to provide a way for packet type taps to
> see the packet before bridge et al. decapsulation.  In fact this makes
> a lot of sense, wanting to see the device as __netif_receive_skb() saw
> it, with no changes whatsoever.
> 
> In fact ptype_all runs before bridging, ING, and MACVLAN decap the
> thing, so we could have a 'ptype_base_predecap[]' that we run over
> right after those.

I was considering exactly this, but I thought it would be
rejected because of the overhead for all packets received.

In fact, bonding could register the ARP handler in the ptype_all
list and check itself whether the packets were ARPs. This
would require no changes to __netif_receive_skb() at all, but
would cause an extra fuction call and a condition for _every_
packet once a bond with arp_validate would be up.

Having a ptype_base_predecap[] hashtable would still cause at
least a comparision for _every_ packet, even without bonding
being loaded (!).

The current patch causes an extra comparison only for packets
arriving on boding slaves.

If either of the ptype_all or ptype_base_predecap[] method is
preferred, I'll be happy to re-work the patch. I just thought
performance had bigger priority here.

-- 
Jiri Bohac <jbohac@...e.cz>
SUSE Labs, SUSE CZ

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