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Re: problem in driver network code

To: Rask Ingemann Lambertsen <rask@xxxxxxxxxx>
Subject: Re: problem in driver network code
From: francois donzet <fdonzet@xxxxxxxx>
Date: Mon, 10 Nov 2003 09:14:17 +0100 (CET)
Cc: netdev@xxxxxxxxxxx
In-reply-to: <20031107181508.A1102@sygehus.dk>
Sender: netdev-bounce@xxxxxxxxxxx
 --- Rask Ingemann Lambertsen <rask@xxxxxxxxxx> a
écrit : > On Fri, Nov 07, 2003 at 09:38:44AM +0100,
francois
> donzet wrote:
> > 
> > It seems to me that there is a problem ;). If i
> store
> > in skb->csum a sum of all words of the packet
> data, it
> >  will be unusable by tcp (the skb->csum doesn't
> > contain the checksum of tcpheader plus data only,
> as
> > the ipheader is part of the packet when the sum is
> > computed)
> 
> That can be accounted for by the TCP code because
> the IP header is known to
> the TCP code. IIRC, the pseudoheader is similiar to
> a real IP header, so it
> may take just a few lines of code to make up for the
> difference, but I
> haven't checked that.

The theory seems fine, but there is no clue of this
way in the code.

> What do you do with an IEEE 802.1q (VLAN) or 802.2
> (LLC) packet? The VLAN
> code in vlan_skb_recv() does not adjust skb->csum or
> skb->ip_summed. Neither
> does the 802.2 code.

no matter the link layer header is 802.3,802.2 or
8021.q . Tcp checksum offloading is supported,
whatever the type of the link layer (as skb->csum is
computed without the link layer header).



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