pkt_sched: Add peek emulation for non-work-conserving qdiscs.

This patch adds qdisc_peek_dequeued() wrapper to emulate peek method
with qdisc->dequeue() and storing "peeked" skb in qdisc->gso_skb until
dequeuing. This is mainly for compatibility reasons not to break some
strange configs because peeking is expected for non-work-conserving
parent qdiscs to query work-conserving child qdiscs.

This implementation requires using qdisc_dequeue_peeked() wrapper
instead of directly calling qdisc->dequeue() for all qdiscs ever
querried with qdisc->ops->peek() or qdisc_peek_dequeued().

Signed-off-by: Jarek Poplawski <jarkao2@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_hfsc.c

@@ -1634,7 +1634,7 @@ hfsc_dequeue(struct Qdisc *sch)
 		}
 	}
 
-	skb = cl->qdisc->dequeue(cl->qdisc);
+	skb = qdisc_dequeue_peeked(cl->qdisc);
 	if (skb == NULL) {
 		if (net_ratelimit())
 			printk("HFSC: Non-work-conserving qdisc ?\n");
@@ -1727,6 +1727,7 @@ static struct Qdisc_ops hfsc_qdisc_ops __read_mostly = {
 	.dump		= hfsc_dump_qdisc,
 	.enqueue	= hfsc_enqueue,
 	.dequeue	= hfsc_dequeue,
+	.peek		= qdisc_peek_dequeued,
 	.requeue	= hfsc_requeue,
 	.drop		= hfsc_drop,
 	.cl_ops		= &hfsc_class_ops,