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

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Date:	Wed, 10 Feb 2016 10:06:32 -0500
From:	Andy Gospodarek <gospo@...ulusnetworks.com>
To:	Jarod Wilson <jarod@...hat.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Stephen Hemminger <stephen@...workplumber.org>,
	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, netdev@...r.kernel.org
Subject: Re: [PATCH net-next iproute2] iplink: display rx nohandler stats

On Wed, Feb 10, 2016 at 08:20:59AM -0500, Jarod Wilson wrote:
> On Tue, Feb 09, 2016 at 08:52:38PM -0800, Eric Dumazet wrote:
> > 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.
> 
> On my test setup, my bond's active interface currently has 0, while the
> backup interface has a few thousand, so I can alternate back and forth
> checking the interfaces, and one doesn't print the counter while the other
> does, which is what seemed odd to me and prompted the added ugliness. But
> most setups (anything outside of bond/team currently) should never have
> this counter incremented, we do have prior art with the compressed fields,
> and scripts really probably ought to be scraping stats out of sysfs rather
> than using ip, so I can sort of understand not wanting the added ugliness.
> I do tend to prefer consistency though.

FWIW, I tend to agree with Jarod and Eric on this.  Consistency seems
better, even if 0 all the time.