netdev - Re: [PATCH 0/2] Disable forwarding of LRO skbs

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Message-Id: <1209640688.4191.35.camel@moonstone.uk.level5networks.com>
Date:	Thu, 01 May 2008 12:18:08 +0100
From:	Kieran Mansley <kmansley@...arflare.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Ben Hutchings <bhutchings@...arflare.com>, davem@...emloft.net,
	shemminger@...tta.com, netdev@...r.kernel.org
Subject: Re: [PATCH 0/2] Disable forwarding of LRO skbs

On Thu, 2008-05-01 at 19:12 +0800, Herbert Xu wrote:
> On Thu, May 01, 2008 at 12:08:48PM +0100, Kieran Mansley wrote:
> >
> > Yes, everything works fine in that case.  It's only when LRO packets are
> > forwarded to another physical interface that things go wrong.  
> 
> Now this is definitely broken because it fiddles with TCP packets
> in the middle, but still it should *work* in as much as making the
> packet go out.  Well except that you need to fix up the checksum
> so that it only contains the pseudo-header on output.  That's
> probably what you need to address if we failed in avoiding LRO
> on forwarded traffic.

If I remember rightly it also gets upset when it comes to split the
packet because the frag_list is already in use; it expects this not to
be the case for GSO but it's valid for an LRO packet to do this I think.
I don't think there's anything fundamentally difficult here, it's just
that the code has never been written to cope.

Kieran

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