netdev - RE: Does CHECKSUM_COMPLETE work at all?

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Date:	Sat, 22 Feb 2014 02:36:44 +0000
From:	Dimitrios Michailidis <dm@...lsio.com>
To:	Tom Herbert <therbert@...gle.com>,
	Linux Netdev List <netdev@...r.kernel.org>
Subject: RE: Does CHECKSUM_COMPLETE work at all?

Tom Herbert wrote:
> If a driver sets CHECKSUM_COMPLETE in a packet, I don't see anywhere
> in either the Ethernet rcv path or ip_rcv where the skb->csum is being
> pulled (no *pull_rcsum calls). I believe CHECKSUM_COMPLETE means the
> checksum is over the whole packet (L2, L3, and L4), so it looks like
> TCP would never see a usable value.
> 
> Is this interpretation correct? There's only a handful of drivers
> providing CHECKSUM_COMPLETE can anyone who has access verify this?

AFAIK CHECKSUM_COMPLETE means the checksum is calculated over the L4 part of the frame but doesn't include the pseudoheader. It is completed by adding the pseudoheader.  I use it this way and it works.

By any chance are you asking this in the context of tunneling and how to get both the inner and outer checksums from the value the HW calculates?

> 
> Thanks,
> Tom