netdev - Re: [PATCH] TBF: stop qdisc infanticide

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Message-ID: <20100513092728.766ee059@nehalam>
Date:	Thu, 13 May 2010 09:27:28 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Patrick McHardy <kaber@...sh.net>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH] TBF: stop qdisc infanticide

On Thu, 13 May 2010 18:22:56 +0200
Patrick McHardy <kaber@...sh.net> wrote:

> Stephen Hemminger wrote:
> > Several netem users have complained that when using TBF for rate control
> > that any change to TBF parameters destroys the child qdisc. A typical
> > use is to have a test that sets up netem + TBF then changes bandwidth
> > setting.  But every time the parameters of TBF are changed it destroys
> > the child qdisc, requiring reconfiguration. Other qdisc's like HTB
> > don't do this.
> > 
> > Signed-off-by: Stephen Hemminger <shemminger@...tta.com>
> > 
> > 
> > --- a/net/sched/sch_tbf.c	2010-05-12 20:41:06.257006386 -0700
> > +++ b/net/sched/sch_tbf.c	2010-05-12 20:52:35.671216316 -0700
> > @@ -273,7 +273,11 @@ static int tbf_change(struct Qdisc* sch,
> >  	if (max_size < 0)
> >  		goto done;
> >  
> > -	if (qopt->limit > 0) {
> > +	if (q->qdisc) {
> > +		err = fifo_set_limit(q->qdisc, qopt->limit);
> > +		if (err)
> > +			goto done;
> 
> q->qdisc is never NULL since a noop_qdisc is assigned by default. Also
> this should check that the child is in fact one of the *fifos.

But the child will be netem and fifo_set_limit ignores non-fifo.
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