On 11/10/22 14:02, Morten Brørup wrote:
From: Andrew Rybchenko [mailto:andrew.rybche...@oktetlabs.ru]
Sent: Thursday, 10 November 2022 11.34
On 11/10/22 13:29, Morten Brørup wrote:
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."
Yes I know, but I'm asking about IPv4 case with UDP checksum 0.
It cannot be UNKNOWN, because we do have information: The checksum was
intentionally omitted.
I think that UNKNOWN definition should be updated to say that
it means that checksum is present and could be verified, but
NIC has not done it and application should do it itself.
I would prefer GOOD, using the same logic as for the IPv6 header checksum.
Yes, since it correct checksum from UDP over IPv4 protocol
definition. Application simply has no information to verify
checksum, so it cannot be UNKNOWN.
Since application gets entry packet in DPDK case, in GOOD case
it could check if checksum is 0 or not itself and do extra
checks in 0 case if it is possible (higher layer checksums etc)
and required.
Trying very hard to tweak the meaning of NONE's description ("the L4 checksum is not correct in the
packet data, but the integrity of the L4 data is verified."), we could argue that "not
correct" != "intentionally omitted" (and an intentional omission is absolutely correct), and
conclude that it cannot be NONE. A seasoned politician would say this without blinking, but it is up to
individual interpretation.
We should settle on either GOOD or NONE, and write it in the documentation.
NONE requires "but the integrity of the L4 data is verified".
Who said that NIC has verified L4 data integrity?
In a perfect world, the PMD DPDK compliance tests should also check things like
this.
JFYI The initial IPv6 question comes from my attempt to
classify [1]. Now I understand that the test should be
fixed to expect GOOD in IPv6 case, not UNKNOWN.
[1]
https://ts-factory.io/bublik/v2/log/163204?focusId=164090&mode=treeAndinfoAndlog
