linux-kernel - Re: [PATCH] lro: IP fragment checking

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Message-ID: <49345CCA.1030209@myri.com>
Date:	Mon, 01 Dec 2008 16:53:14 -0500
From:	Andrew Gallatin <gallatin@...i.com>
To:	David Miller <davem@...emloft.net>
CC:	ossthema@...ibm.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, tklein@...ibm.com, raisch@...ibm.com,
	jb.billaud@...il.com, hering2@...ibm.com
Subject: Re: [PATCH] lro: IP fragment checking

David Miller wrote:
> From: Andrew Gallatin <gallatin@...i.com>
> Date: Mon, 01 Dec 2008 12:50:15 -0500
> 
>> As to whether or not to do it in the drivers/hardware or in the
>> LRO code, I favor doing it in the LRO code just so that it is not
>> missed in some driver.
> 
> Then there is no point in the hardware doing the check, if
> we're going to check it anyways.
> 
> That's part of my point about why this check doesn't belong
> here.

What hardware does an explicit check for fragmentation?
In most cases, aren't we just relying on the hardware checksum
to be wrong on fragmented packets? That works 99.999% of the time,
but the TCP checksum is pretty weak, and it is possible to
have a fragmented packet where the first fragment has the same
checksum as the entire packet.

I'd rather have a fragmentation check at the LRO layer to remove
any ambiguity. But if you still object, I'll at least have to
submit a patch  which adds an explicit check in myri10ge.

Drew
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