netdev - Re: [PATCH net-next] gro: relax ID check in inet_gro

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Message-ID: <1363882825.2736.4.camel@bwh-desktop.uk.solarflarecom.com>
Date:	Thu, 21 Mar 2013 16:20:25 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	David Miller <davem@...emloft.net>
CC:	<eric.dumazet@...il.com>, <netdev@...r.kernel.org>,
	<dmitry@...adcom.com>, <eilong@...adcom.com>, <pshelar@...ira.com>,
	<hkchu@...gle.com>, <maze@...gle.com>
Subject: Re: [PATCH net-next] gro: relax ID check in inet_gro_receive()

On Thu, 2013-03-21 at 11:46 -0400, David Miller wrote:
> From: Eric Dumazet <eric.dumazet@...il.com>
> Date: Wed, 20 Mar 2013 21:52:33 -0700
> 
> > GRE TSO support doesn't increment the ID in the inner IP header.
> 
> Is this a fundamental limitation of doing TSO over GRO or
> were the Broadcom folks just being lazy with their firmware
> implementation?
> 
> I really don't want to apply this patch, because ipv4 frames
> even with DF set should have an incrementing ID field, in
> order to accomodate various header compression schemes.
> 
> We go out of our way to do this for normal unencapsulated TCP stream
> packets, rather than set the ID field to zero (which we did for some
> time until the compression issue was pointed out to us).

Besides which, GRO has been reliably reversible until now.  (gso_size is
available through packet sockets, even if tcpdump doesn't appear to use
it yet.)  Ignoring IPv4 IDs will break that guarantee.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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