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

["Morten Brørup" <mb@smartsharesystems.com>]

> From: Andrew Rybchenko [mailto:andrew.rybchenko@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.

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").

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 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.

-Morten