netdev - Re: Deleting child qdisc doesn't reset parent to default qdisc?

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Message-ID: <20160414151813.GE3715@orbyte.nwl.cc>
Date:	Thu, 14 Apr 2016 17:18:13 +0200
From:	Phil Sutter <phil@....cc>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Jiri Kosina <jikos@...nel.org>,
	Jamal Hadi Salim <jhs@...atatu.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: Deleting child qdisc doesn't reset parent to default qdisc?

On Thu, Apr 14, 2016 at 08:01:39AM -0700, Eric Dumazet wrote:
> On Thu, 2016-04-14 at 16:44 +0200, Jiri Kosina wrote:
> > Hi,
> > 
> > I've came across the behavior where adding a child qdisc and then deleting 
> > it again makes the networking dysfunctional (I guess that's because all of 
> > a sudden there is absolutely no working qdisc on the device, although 
> > there originally was a default one in the parent).
> > 
> > In a nutshell, is this expected behavior or bug?
> 
> This is the expected behavior.

OTOH some qdiscs (CBQ, DRR, DSMARK, HFSC, HTB, QFQ) assign the default
one upon deletion instead of noop_qdisc, hence I would describe
the situation using the words 'inconsistent' and 'accident' rather than
'expected'. :)

Anyhow, the problem with skilled admins is they accept quirks too easily
and just build their scripts around them - the same scripts we have to
keep compatible to then.

Cheers, Phil