Re: [PATCH] app/test-pmd: fix L4 checksum with padding data

[Stephen Hemminger <stephen@networkplumber.org>]

On Fri, 17 Nov 2023 00:50:16 +0000
Ferruh Yigit <ferruh.yigit@amd.com> wrote:

> >> Hi Kaiwen,
> >>
> >> I am trying to understand the problem, what is the testcase that has
> >> checksum error?
> >>
> >> Are the received mbuf data_len & pkt_len wrong? Instead of trying to fix
> >> the mbuf during forwarding, can we fix where packet generated?  
> > 
> > The root cause is that get_udptcp_cksum_mbuf is using m->pkt_len
> > which maybe larger than the actual data. The real issue is there and
> > in rte_ip.h checksum code. The correct fix would be to use l3_len instead.
> >   
> 
> I see, you are right.
> 
> In 'rte_ipv4_udptcp_cksum_mbuf()',
> as payload length "mbuf->pkt_len - l4_off" is used, which includes
> padding and if padding is not zero it will end up producing wrong checksum.
> 
> 
> I agree using 'l3_len' instead is correct fix.
> 
> But this requires ABI/API change,
> plus do we have any reason to keep the padding, discarding it as this
> patch does is also simpler alternative.


Possibly an API version to change the args would work to fix.