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

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Message-ID: <4BEC2936.2060800@trash.net>
Date:	Thu, 13 May 2010 18:30:46 +0200
From:	Patrick McHardy <kaber@...sh.net>
To:	Stephen Hemminger <shemminger@...tta.com>
CC:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH] TBF: stop qdisc infanticide

Stephen Hemminger wrote:
> 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.

OK, but it does need to make sure the child is not a noop_qdisc,
otherwise it won't create the default bfifo.
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