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

[Morten Brørup]

> 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.

> 
> 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
> >
> > .
>