Is it correct to report checksum good when there is no checksum?

[Thomas Monjalon]

10/11/2022 11:08, Andrew Rybchenko:
> On 11/10/22 12:55, Morten Brørup wrote:
> >> From: Andrew Rybchenko [mailto:andrew.rybchenko at oktetlabs.ru]
> >> Sent: Thursday, 10 November 2022 10.26
> >>
> >> Hi all,
> >>
> >> some drivers report RTE_MBUF_F_RX_IP_CKSUM_GOOD for IPv6 packets.
> >> For me it looks strange, but I see some technical reasons behind.
> > 
> > Please note: IPv6 packets by definition have no IP checksum.
> > 
> >> Documentation in lib/mbuf/rte_mbuf_core.h is a bit vague.
> >> Should UNKNOWN or NONE be used instead?
> > 
> > Certainly not NONE. Its description says: "the IP checksum is *not* correct in the packet [...]". But there is no incorrect IP checksum in the packet.
> > 
> 
> Thanks, I should read the definition of none more careful.
> 
> > I will argue against UNKNOWN. Its description says: "no information about the RX IP checksum". But we do have information about it! We know that the IP checksum is not there (the value is "NULL"), and that it is not supposed to be there (the value is supposed to be "NULL").
> > 
> 
> I thought that "no checksum" => "no information" => UNKNOWN
> 
> > So I consider GOOD the correct response here.
> > 
> > GOOD also means that the application can proceed processing the packet normally without further IP header checksum checking, so it's good for performance.
> > 
> 
> It is very important point and would be nice to have in GOOD
> case definition (both IP and L4 cases). It is the right
> motivation why GOOD makes sense for IPv6.
> 
> > It should be added to the description of RTE_MBUF_F_RX_IP_CKSUM_GOOD that IPv6 packets always return this value, because IPv6 packets have no IP header checksum, and that is what is expected of them.
> 
> Could you make a patch?

That would be perfect. I agree to use GOOD for IPv6 checksum.

> Bonus question is UDP checksum 0 case. GOOD as well?
> (just want to clarify the documentation while we're on it).

Good question :)