[PATCH 1/3] ethdev: fix telemetry xstats return null with some PMDs

[fengchengwen]

On 2022/4/25 18:16, Morten Brørup wrote:
>> From: fengchengwen [mailto:fengchengwen at huawei.com]
>> Sent: Sunday, 24 April 2022 05.45
>>
>> The root cause is: when the xstats is NULL and n less than required
>> number of
>> elements is zero, the return value of rte_eth_xstats_get is ambiguous
>> from
>> rte_ethdev.h's declaration.
>>
>> But the implementation of rte_eth_xstats_get return required number of
>> elements
>> when xstats is NULL and n less than required number of elements.
>>
>> There are two modification schemes:
>> a) the value of xstats cannot be NULL, and the value of n must be
>> greater than
>>    or equal to the required number, otherwise, an error code is
>> returned.
>> b) define the behavior as the same as rte_eth_xstats_get_names, which
>> means return
>>    required number of elelement when xstats is NULL and n less than
>> required number
>>    of elements.
>>
>> I prefer the scheme a because rte_eth_xstats_get and
>> rte_eth_xstats_get_name are
>> symbiotic, and it's not necessary to both implement the same logic.
>>
>> Also for scheme a, there is no need to modify the PMD implementation.
>>
>> What about your opinions ?
> 
> This is an excellent proposal.
> 
> And if the documentation for rte_eth_xstats_get() refers to rte_eth_xstats_get_names() for getting the number of elements, it is perfect.

Hi Morten,

   I did a deepin review and found that many application use rte_eth_xstats_get(port_id, NULL, 0),
and also many PMD already support return required number of entries when xstats is NULL. So in
the v2, I use the modified hns3/ipn3ke/mvpp2/axgbe PMD method and explicit return value when xstats
is NULL of rte_eth_xstats-get().

Thanks.

> 
>>
>> On 2022/4/21 14:49, Andrew Rybchenko wrote:
>>> On 4/16/22 04:38, Stephen Hemminger wrote:
>>>> On Sat, 16 Apr 2022 09:07:45 +0800
>>>> Chengwen Feng <fengchengwen at huawei.com> wrote:
>>>>
>>>>> Currently the telemetry xstats uses rte_eth_xstats_get() to
>> retrieve
>>>>> the number of elements. But the value to be returned when the
>> parameter
>>>>> 'xstats' is NULL is not specified, some PMDs (eg.
>> hns3/ipn3ke/mvpp2/
>>>>> axgbe) return zero while others return the required number of
>> elements.
>>>>
>>>> Lets fix the PMD's this impacts other code as well.
>>>
>>> +1
>>>
>>> .
>>
>