netdev - Re: [PATCH v2 2/3] net_sched: Add accessor function for packet length for qdiscs

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Date:	Fri, 25 Jul 2008 12:08:49 +0000
From:	Jarek Poplawski <jarkao2@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	jussi.kivilinna@...et.fi, kaber@...sh.net, netdev@...r.kernel.org
Subject: Re: [PATCH v2 2/3] net_sched: Add accessor function for packet
	length for qdiscs

On Fri, Jul 25, 2008 at 04:52:15AM -0700, David Miller wrote:
> From: Jarek Poplawski <jarkao2@...il.com>
> Date: Fri, 25 Jul 2008 11:53:55 +0000
> 
> > On Fri, Jul 25, 2008 at 11:37:57AM +0000, Jarek Poplawski wrote:
> >
> > As a matter of fact it's a good example: in your patch we have this:
> > 
> > +		ret = cl->un.leaf.q->enqueue(skb, cl->un.leaf.q);
> > +		if (ret == NET_XMIT_DROP) {
> > +			sch->qstats.drops++;
> > +			cl->qstats.drops++;
> > +		} else {
> > +			cl->bstats.packets +=
> > +				skb_is_gso(skb)?skb_shinfo(skb)->gso_segs:1;
> > +			cl->bstats.bytes += skb->len;
> > 
> > So, if something works like noop_enqueue() and returns NET_XMIT_CN
> > here, we're just using skb after kfree...
> 
> noop_enqueue() can only be a root qdisc, never a leaf hanging off of a
> class

OK, sfq does the same.

> What TCP depends upon is that DROP means DROP, and that the
> packet never reached the device and has been freed.

IMHO, TCP should depend on it's skb "refcount". A qdisc, after
passing skb to other qdisc shouldn't depend on TCP's "refcount"
because not everything has to work like TCP.

Jarek P.
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