> From: Andrew Rybchenko [mailto:andrew.rybche...@oktetlabs.ru] > Sent: Thursday, 10 November 2022 11.09 > > On 11/10/22 12:55, Morten Brørup wrote: > >> From: Andrew Rybchenko [mailto:andrew.rybche...@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
That was my initial interpretation too, and it stuck with me for a while. But then I tried hard to read it differently, tweaking it to support the conclusion I was looking for. > > > 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? Too busy right now, but I'll put it on my todo list. :-) > > Bonus question is UDP checksum 0 case. GOOD as well? > (just want to clarify the documentation while we're on it). No. The UDP checksum is not optional in IPv6. RFC 2460 section 8.1 bullet 4 says: "Unlike IPv4, when UDP packets are originated by an IPv6 node, the UDP checksum is not optional. [...] IPv6 receivers must discard UDP packets containing a zero checksum, and should log the error." > > Thanks a lot, > Andrew. >
