netdev - Re: [PATCH net-next iproute2] iplink: display rx nohandler stats

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Message-ID: <1455079958.21021.5.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Tue, 09 Feb 2016 20:52:38 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Stephen Hemminger <stephen@...workplumber.org>
Cc:	Jarod Wilson <jarod@...hat.com>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	David Miller <davem@...emloft.net>,
	linux-kernel@...r.kernel.org, edumazet@...gle.com,
	jiri@...lanox.com, daniel@...earbox.net, tom@...bertland.com,
	j.vosburgh@...il.com, vfalico@...il.com, gospo@...ulusnetworks.com,
	netdev@...r.kernel.org
Subject: Re: [PATCH net-next iproute2] iplink: display rx nohandler stats

On Tue, 2016-02-09 at 17:41 -0800, Stephen Hemminger wrote:
> On Tue, 9 Feb 2016 18:51:35 -0500
> Jarod Wilson <jarod@...hat.com> wrote:
> 
> > On Tue, Feb 09, 2016 at 11:17:57AM -0800, Stephen Hemminger wrote:
> > > Support for the new rx_nohandler statistic.
> > > This code is designed to handle the case where the kernel reported statistic
> > > structure is smaller than the larger structure in later releases (and vice versa).
> > 
> > This seems to work here, for the most part. However, if you are running a
> > kernel with the new counter, and the counter happens to contain 0, aren't
> > we going to not print anything?
> 
> That is the desirable outcome, since if run on older system the
> output format will not change from current format.

The problem here is that a change in output might break some user
scripts using sed/whatever games.

So it might be better to output a zero field, so that such breakages are
detected early, even if no packet was dropped at the time the new kernel
was tested.

Having a binary that adds the new field only in some cases hides the
change. It looks fine for us humans, but not for programs processing the
output.