netdev - Questions about CHECKSUM

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Date:	Thu, 20 Oct 2011 23:05:25 -0400
From:	fengcheng lu <sparking.lu@...il.com>
To:	netdev@...r.kernel.org
Subject: Questions about CHECKSUM_COMPLETE

Hello everyone

I have one question about the CHECKSUM_COMPLETE. When
CHECK_SUM_COMPLETE is set, which data does the skb->csum computed by
hardware cover?

I thought skb->csum only covers the Transport header (e.g. TCP/UDP) +
Transport payload + pseudo header. However, after I read the vlan
codes (vlan_skb_recv in the vlan_dev.c of linux kernel 2.6.27.19), I
become confuse.

The vlan_skb_recv calls skb_pull_rcsum which updates the skb->csum if
CHECKSUM_COMPLETE is set. It implies the vlan  header is also covered
by the skb->csum. so I wonder if the skb->csum cover the whole data
besides the eth header (14 bytes).

Thanks
Steven Lu
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