netdev - Re: [PATCH net] gre: Fix regression in gretap TSO support

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Date:	Thu, 30 Oct 2014 07:30:02 -0700
From:	Alexander Duyck <alexander.h.duyck@...hat.com>
To:	Neal Cardwell <ncardwell@...gle.com>,
	Pravin Shelar <pshelar@...ira.com>
CC:	alexander.duyck@...il.com, netdev <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	"H.K. Jerry Chu" <hkchu@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH net] gre: Fix regression in gretap TSO support


On 10/30/2014 06:51 AM, Neal Cardwell wrote:
> On Thu, Oct 30, 2014 at 1:14 AM, Pravin Shelar <pshelar@...ira.com> wrote:
>> On Wed, Oct 29, 2014 at 8:26 PM,  <alexander.duyck@...il.com> wrote:
>>> From: Alexander Duyck <alexander.h.duyck@...hat.com>
>>>
>>> On recent kernels I found that TSO on gretap interfaces didn't work.  After
>>> bisecting it I found that commit b884b1a4 had introduced a regression in
>>> which the Ethernet header was being included in the GRE header length.
>>>
>>> This change corrects that by basing the GRE header length on the inner mac
>>> header in the case of GRE tunnels using transparent Ethernet bridging, and
>>> uses the network header for all other GRE tunnel types.
>>>
>>> Fixes: b884b1a4 ("gre_offload: simplify GRE header length calculation in gre_gso_segment()")
> Hmm. There may be other protocols, either now or in the future, where
> we want to be able to have a mac header inside the GRE header, rather
> than a network header. AFAICT it would be safer to revert b884b1a4,
> and go back to the previous code (from c50cd357), where we parse the
> GRE header to figure out its length.
>
> neal

The change is consistent with how we handle this in other spots 
throughout the kernel.  If nothing else you can just search for 
ETH_P_TEB and you will find multiple spots in the kernel where IP 
tunnels differentiate between transparent Ethernet bridging and regular 
IP in IP tunnels by checking for the protocol ETH_P_TEB.

Thanks,

Alex
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