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

[Ferruh Yigit <ferruh.yigit@amd.com>]

On 11/17/2023 3:28 AM, Stephen Hemminger wrote:
> 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.
>

rte_ipv4_udptcp_cksum_mbuf() and rte_ipv6_udptcp_cksum_mbuf() are inline
functions, unfortunately we can't version them.

But those functions already gets IP header as parameter, can't we use IP
header to get the payload size? If so this can be fixed without updating
API.