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

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Date:	Sun, 15 Jun 2008 02:46:58 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	davem@...emloft.net, kmansley@...arflare.com,
	shemminger@...tta.com, netdev@...r.kernel.org
Subject: Re: [PATCH 0/2] Disable forwarding of LRO skbs

Ben Hutchings wrote:
> Herbert Xu wrote:
> > On Thu, May 01, 2008 at 12:02:27PM +0100, Ben Hutchings wrote:
> > >
> > > My understanding is that at the points I'm adding the check, we're only
> > > considering received skbs and gso_size will only be set if LRO was used.
> > 
> > Unfortunately that's not the case.  The forwarding path can and
> > does occur for GSO packets sent from other guests.  The obvious
> > case would be a GSO packet from a guest forwarded by the host
> > (as opposed to bridged) to the outside world.
> 
> Can we distinguish them by testing skb->ip_summed == CHECKSUM_PARTIAL?
> That is a requirement for using hardware segmentation offload (see
> netif_needs_gso()) but an skb resulting from LRO should have ip_summed
> set to either CHECKSUM_UNNECESSARY or CHECKSUM_NONE.

Actually, it seems like there's a cleaner test: gso_size != 0 &&
gso_type == 0 (if we really want GSO then the latter must be set).
I'll have to try that out.

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
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