linux-kernel - Re: [PATCH 1/2] net: sched: make default fifo qdiscs appear in the dump

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Message-ID: <alpine.LSU.2.20.1703061158500.31814@cbobk.fhfr.pm>
Date:   Mon, 6 Mar 2017 12:03:38 +0100 (CET)
From:   Jiri Kosina <jikos@...nel.org>
To:     David Miller <davem@...emloft.net>
cc:     stephen@...workplumber.org, eric.dumazet@...il.com,
        jhs@...atatu.com, phil@....cc, xiyou.wangcong@...il.com,
        daniel@...earbox.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] net: sched: make default fifo qdiscs appear in the
 dump

On Wed, 1 Mar 2017, David Miller wrote:

> > @@ -1066,6 +1066,7 @@ hfsc_change_class(struct Qdisc *sch, u32 classid, u32 parentid,
> >  				      &pfifo_qdisc_ops, classid);
> >  	if (cl->qdisc == NULL)
> >  		cl->qdisc = &noop_qdisc;
> > +	qdisc_hash_add(cl->qdisc, true);
> >  	INIT_LIST_HEAD(&cl->children);
> >  	cl->vt_tree = RB_ROOT;
> >  	cl->cf_tree = RB_ROOT;
> > @@ -1425,6 +1426,7 @@ hfsc_init_qdisc(struct Qdisc *sch, struct nlattr *opt)
> >  					  sch->handle);
> >  	if (q->root.qdisc == NULL)
> >  		q->root.qdisc = &noop_qdisc;
> > +	qdisc_hash_add(q->root.qdisc, true);
> >  	INIT_LIST_HEAD(&q->root.children);
> >  	q->root.vt_tree = RB_ROOT;
> >  	q->root.cf_tree = RB_ROOT;
> 
> I'm not so sure it is legal is potentially pass &noop_qdisc into qdisc_hash_add().

Ah, right you are, thanks. The complete fix is not super trivial, as it 
needs some more surgery to tc_dump_qdisc_root(), tc_dump_tclass_root() and 
qdisc_match_from_root() (see 69012ae42 for some details).

There are two options:

- this gets fixed in two phases, in first everything *but* noop qdisc gets 
  dumped (in the "give me everything" dump) and later we finalize it by
  teaching the above functions about noop_qdisc as well

- I extend this patchset to handle noop qdisc from the very beginning; 
  I am unlikely to find time for this during coming weeks though. But OTOH
  this whole thing is very low priority anyway

What do you think?

Thanks,

-- 
Jiri Kosina
SUSE Labs