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>

1 files changed, 23 insertions, 0 deletions

diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index da6839a7ff50..9dcb5bfe094a 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -438,6 +438,29 @@ static inline struct sk_buff *qdisc_peek_head(struct Qdisc *sch)
         return skb_peek(&sch->q);
 }
 
+/* generic pseudo peek method for non-work-conserving qdisc */
+static inline struct sk_buff *qdisc_peek_dequeued(struct Qdisc *sch)
+{
+        /* we can reuse ->gso_skb because peek isn't called for root qdiscs */
+        if (!sch->gso_skb)
+                sch->gso_skb = sch->dequeue(sch);
+
+        return sch->gso_skb;
+}
+
+/* use instead of qdisc->dequeue() for all qdiscs queried with ->peek() */
+static inline struct sk_buff *qdisc_dequeue_peeked(struct Qdisc *sch)
+{
+        struct sk_buff *skb = sch->gso_skb;
+
+        if (skb)
+                sch->gso_skb = NULL;
+        else
+                skb = sch->dequeue(sch);
+
+        return skb;
+}
+
 static inline int __qdisc_requeue(struct sk_buff *skb, struct Qdisc *sch,
                                   struct sk_buff_head *list)
 {