netdev - Re: [PATCH net-next 6/8] net: gre: Implement LCO for GRE over IPv4

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Message-ID: <8BD201BE-E272-4BA7-ABB4-8FDCE139495D@intel.com>
Date:	Wed, 20 Jan 2016 19:11:17 +0000
From:	"Rustad, Mark D" <mark.d.rustad@...el.com>
To:	Alexander Duyck <alexander.duyck@...il.com>
CC:	Edward Cree <ecree@...arflare.com>,
	David Laight <David.Laight@...lab.com>,
	David Miller <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-net-drivers@...arflare.com" <linux-net-drivers@...arflare.com>,
	"tom@...bertland.com" <tom@...bertland.com>
Subject: Re: [PATCH net-next 6/8] net: gre: Implement LCO for GRE over IPv4

Alexander Duyck <alexander.duyck@...il.com> wrote:

> Actually you may want to go the other way on that.  If they weren't
> flipping the checksum value for GRE before why should we start doing
> that now?  I'm pretty sure the checksum mangling is a very UDP centric
> thing.  There is no need to introduce it to other protocols.

If different checksum representations are needed, then there really should  
be an explicit indication of whether it is a UDP-style checksum or other in  
the skb I would think rather than guessing it based on the offset. Of  
course it would be convenient if all the protocols that use a one's  
complement checksum would tolerate the UDP representation. I have a long  
(and now old) history working with real one's complement machines, and so I  
would want to believe that any correct implementation would tolerate it,  
but I don't know for a fact that they do.

--
Mark Rustad, Networking Division, Intel Corporation

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