netdev - Re: [PATCH 1/9] ipv6: implement dataplane support for rthdr type 4 (Segment Routing Header)

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Date:   Thu, 20 Oct 2016 15:04:59 +0200
From:   David Lebrun <david.lebrun@...ouvain.be>
To:     Tom Herbert <tom@...bertland.com>
CC:     Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH 1/9] ipv6: implement dataplane support for rthdr type
 4 (Segment Routing Header)

On 10/17/2016 07:01 PM, Tom Herbert wrote:
>> > +
>> > +       if (skb->ip_summed == CHECKSUM_COMPLETE)
>> > +               skb->ip_summed = CHECKSUM_NONE;
>> > +
> Because the packet is being changed? Would it make sense to update the
> checksum complete value based on the changes being made. Consider the
> case that the next hop is local to the host (someone may try to
> implement network virtualization this way).
> 

Rethinking about that: even if the next hop is local, I am not sure to
see the benefits of updating the checksum instead of setting
CHECKSUM_NONE. For example, if the next and final hop is local and the
packet carries a TCP payload, tcp_checksum_complete() would force the
recomputation of the checksum anyway (unless ip_summed ==
CHECKSUM_UNNECESSARY).

So I fail to see a path where updating the checksum would be beneficial.

Am I missing something ?

David

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