pkt_sched: Add ->peek() methods for fifo, prio and SFQ qdiscs.

From: Patrick McHardy <kaber@trash.net>

Just as a demonstration how easy adding a peek operation to the
work-conserving qdiscs actually is. It doesn't need to keep or change
any internal state in many cases thanks to the guarantee that the
packet will either be dequeued or, if another packet arrives, the
upper qdisc will immediately ->peek again to reevaluate the state.

(This is only slightly modified Patrick's patch.)

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

1 files changed, 12 insertions, 0 deletions

diff --git a/net/sched/sch_sfq.c b/net/sched/sch_sfq.c
index fe1508ef0d3..198b83d42ba 100644
--- a/net/sched/sch_sfq.c
+++ b/net/sched/sch_sfq.c
@@ -391,8 +391,19 @@ sfq_requeue(struct sk_buff *skb, struct Qdisc *sch)
         return NET_XMIT_CN;
 }
 
+static struct sk_buff *
+sfq_peek(struct Qdisc *sch)
+{
+        struct sfq_sched_data *q = qdisc_priv(sch);
+        sfq_index a;
 
+        /* No active slots */
+        if (q->tail == SFQ_DEPTH)
+                return NULL;
 
+        a = q->next[q->tail];
+        return skb_peek(&q->qs[a]);
+}
 
 static struct sk_buff *
 sfq_dequeue(struct Qdisc *sch)
@@ -624,6 +635,7 @@ static struct Qdisc_ops sfq_qdisc_ops __read_mostly = {
         .priv_size      =       sizeof(struct sfq_sched_data),
         .enqueue        =       sfq_enqueue,
         .dequeue        =       sfq_dequeue,
+        .peek           =       sfq_peek,
         .requeue        =       sfq_requeue,
         .drop           =       sfq_drop,
         .init           =       sfq_init,