On Mon, 2016-06-06 at 23:20 +0200, Florian Westphal wrote:
> since initial revision of cbq in 2004 iproute2 never implemented
> support for TCA_CBQ_OVL_STRATEGY, which is what needs to be set to
> activate the class->drop() call (TC_CBQ_OVL_DROP strategy must be
> set by userspace).
>
> So lets remove this. We can even do this in a backwards compatible
> way by switching ovl_drop to perform a dequeue+drop on the leaf.
>
> A followup commit can then remove all .drop qdisc methods since this
> was the only caller.
>
> Signed-off-by: Florian Westphal <f...@strlen.de>
> ---
> On a related note, iproute2 doesn't support the TCA_CBQ_POLICE
> attribute either. If we'd remove that too we could then get rid
> of __parent and reshape_fail in struct Qdisc.
>
> However, in TCA_CBQ_POLICE case there is no way to replace
> the functionality, i.e. we'd have to -EOPNOTSUPP or ignore
> TCA_CBQ_POLICE if some other non-iproute2 tool presents it to us.
>
> AFAICS TCA_CBQ_POLICE doesn't work all that well even if userspace
> would set it, one needs to:
>
> add a class
> attach a qdisc to the class (default pfifo doesn't work as
> q->handle is 0 and cbq_set_police() is a no-op in this case)
> re-'add' the same class (tc class change ...) again
>
> user must also specifiy a defmap (e.g. 'split 1:0 defmap 3f'), since
> this 'police' feature relies on its presence
> the added qdisc (or the leaves) must be one of bfifo, pfifo, tbf or
> netem as only these implement qdisc_reshape_fail() call.
>
> If all of these conditions are met, then instead of drop the leaf
> qdiscs mentioned above would attempt to re-enqueue the skb in the
> cbq TC_PRIO_BESTEFFORT class if their limit is reached.
>
> I think it would be safe to just ignore TCA_CBQ_POLICE and change the
> qdiscs to drop right away.
>
> Does anyone have a reason to leave this in the tree? Thanks!
>
> diff --git a/net/sched/sch_cbq.c b/net/sched/sch_cbq.c
> index baafddf..df79791 100644
> --- a/net/sched/sch_cbq.c
> +++ b/net/sched/sch_cbq.c
> @@ -542,9 +542,14 @@ static void cbq_ovl_lowprio(struct cbq_class *cl)
>
> static void cbq_ovl_drop(struct cbq_class *cl)
> {
> - if (cl->q->ops->drop)
> - if (cl->q->ops->drop(cl->q))
> - cl->qdisc->q.qlen--;
> + struct sk_buff *skb = cl->q->ops->dequeue(cl->q);
> +
> + if (skb) {
> + cl->deficit -= qdisc_pkt_len(skb);
> + cl->qdisc->q.qlen--;
> + qdisc_drop(skb, cl->qdisc);
> + }
> +
> cl->xstats.overactions++;
> cbq_ovl_classic(cl);
> }
A drop() is not equivalent to a dequeue() followed by qdisc_drop() for
statistics.
dequeue() will update stats of _sent_ packets/bytes, while drop() should
not.
