netdev - Re: [RFC PATCH net-next 0/2] devlink: Add port stats

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Date:   Mon, 11 Apr 2022 11:01:57 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     Michael Guralnik <michaelgur@...dia.com>, netdev@...r.kernel.org,
        jiri@...dia.com, ariela@...dia.com, maorg@...dia.com,
        saeedm@...dia.com, moshe@...dia.com
Subject: Re: [RFC PATCH net-next 0/2] devlink: Add port stats

On Mon, 11 Apr 2022 12:31:53 +0200 Jiri Pirko wrote:
> Fri, Apr 08, 2022 at 05:16:38AM CEST, kuba@...nel.org wrote:
> >On Thu, 7 Apr 2022 11:40:48 +0300 Michael Guralnik wrote:  
> >> This patch set adds port statistics to the devlink port object.
> >> It allows device drivers to dynamically attach and detach counters from a
> >> devlink port object.  
> >
> >The challenge in defining APIs for stats is not in how to wrap a free
> >form string in a netlink message but how do define values that have
> >clear semantics and are of value to the user.  
> 
> Wait, does all stats have to be well-defined? I mean, look at the
> ethtool stats. They are free-form strings too. Do you mean that in
> devlink, we can only have well-defines enum-based stats?

That's my strong preference, yes.

First, and obvious argument is that it make lazy coding less likely
(see devlink params).

More importantly, tho, if your stats are not well defined - users don't
need to seem them. Really! If I can't draw a line between a statistic
and device behavior then keep that stat in the register dump, debugfs 
or /dev/null.

That's why it's important that we talk about _what_ you're trying to
expose.