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>

7 files changed, 34 insertions, 6 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)
 {
diff --git a/net/sched/sch_atm.c b/net/sched/sch_atm.c
index 2ee0c1a8efa9..6eb9a650b63d 100644
--- a/net/sched/sch_atm.c
+++ b/net/sched/sch_atm.c
@@ -484,7 +484,7 @@ static void sch_atm_dequeue(unsigned long data)
                         if (!atm_may_send(flow->vcc, skb->truesize))
                                 break;
 
-                        skb = flow->q->dequeue(flow->q);
+                        skb = qdisc_dequeue_peeked(flow->q);
                         if (unlikely(!skb))
                                 break;
 
@@ -519,7 +519,7 @@ static struct sk_buff *atm_tc_dequeue(struct Qdisc *sch)
 
         pr_debug("atm_tc_dequeue(sch %p,[qdisc %p])\n", sch, p);
         tasklet_schedule(&p->task);
-        skb = p->link.q->dequeue(p->link.q);
+        skb = qdisc_dequeue_peeked(p->link.q);
         if (skb)
                 sch->q.qlen--;
         return skb;
diff --git a/net/sched/sch_cbq.c b/net/sched/sch_cbq.c
index 03e389e8d945..63efa70abbea 100644
--- a/net/sched/sch_cbq.c
+++ b/net/sched/sch_cbq.c
@@ -2066,6 +2066,7 @@ static struct Qdisc_ops cbq_qdisc_ops __read_mostly = {
         .priv_size      =       sizeof(struct cbq_sched_data),
         .enqueue        =       cbq_enqueue,
         .dequeue        =       cbq_dequeue,
+        .peek           =       qdisc_peek_dequeued,
         .requeue        =       cbq_requeue,
         .drop           =       cbq_drop,
         .init           =       cbq_init,
diff --git a/net/sched/sch_hfsc.c b/net/sched/sch_hfsc.c
index ddfc40887848..d90b1652f2af 100644
--- a/net/sched/sch_hfsc.c
+++ b/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,
diff --git a/net/sched/sch_htb.c b/net/sched/sch_htb.c
index d14f02056ae6..3fda8199713d 100644
--- a/net/sched/sch_htb.c
+++ b/net/sched/sch_htb.c
@@ -1565,6 +1565,7 @@ static struct Qdisc_ops htb_qdisc_ops __read_mostly = {
         .priv_size      =       sizeof(struct htb_sched),
         .enqueue        =       htb_enqueue,
         .dequeue        =       htb_dequeue,
+        .peek           =       qdisc_peek_dequeued,
         .requeue        =       htb_requeue,
         .drop           =       htb_drop,
         .init           =       htb_init,
diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
index 74fbdb52baed..3080bd6ee332 100644
--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c
@@ -290,8 +290,8 @@ static struct sk_buff *netem_dequeue(struct Qdisc *sch)
 
                 /* if more time remaining? */
                 if (cb->time_to_send <= now) {
-                        skb = q->qdisc->dequeue(q->qdisc);
-                        if (!skb)
+                        skb = qdisc_dequeue_peeked(q->qdisc);
+                        if (unlikely(!skb))
                                 return NULL;
 
                         pr_debug("netem_dequeue: return skb=%p\n", skb);
@@ -714,6 +714,7 @@ static struct Qdisc_ops netem_qdisc_ops __read_mostly = {
         .priv_size      =       sizeof(struct netem_sched_data),
         .enqueue        =       netem_enqueue,
         .dequeue        =       netem_dequeue,
+        .peek           =       qdisc_peek_dequeued,
         .requeue        =       netem_requeue,
         .drop           =       netem_drop,
         .init           =       netem_init,
diff --git a/net/sched/sch_tbf.c b/net/sched/sch_tbf.c
index 61fdc77a48d2..435076cf620e 100644
--- a/net/sched/sch_tbf.c
+++ b/net/sched/sch_tbf.c
@@ -192,7 +192,7 @@ static struct sk_buff *tbf_dequeue(struct Qdisc* sch)
                 toks -= L2T(q, len);
 
                 if ((toks|ptoks) >= 0) {
-                        skb = q->qdisc->dequeue(q->qdisc);
+                        skb = qdisc_dequeue_peeked(q->qdisc);
                         if (unlikely(!skb))
                                 return NULL;
 
@@ -467,6 +467,7 @@ static struct Qdisc_ops tbf_qdisc_ops __read_mostly = {
         .priv_size      =       sizeof(struct tbf_sched_data),
         .enqueue        =       tbf_enqueue,
         .dequeue        =       tbf_dequeue,
+        .peek           =       qdisc_peek_dequeued,
         .requeue        =       tbf_requeue,
         .drop           =       tbf_drop,
         .init           =       tbf_init,