[NETEM]: Support time based reordering

Change netem to support packets getting reordered because of variations in
delay. Introduce a special case version of FIFO that queues packets in order
based on the netem delay.

Since netem is classful, those users that don't want jitter based reordering
can just insert a pfifo instead of the default.

This required changes to generic skbuff code to allow finer grain manipulation
of sk_buff_head.  Insertion into the middle and reverse walk.

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>

2 files changed, 114 insertions, 9 deletions

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 4286d832166f..fdfb8fe8c38c 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -603,23 +603,23 @@ static inline void skb_queue_head_init(struct sk_buff_head *list)
  */
 
 /**
- *      __skb_queue_head - queue a buffer at the list head
+ *      __skb_queue_after - queue a buffer at the list head
  *      @list: list to use
+ *      @prev: place after this buffer
  *      @newsk: buffer to queue
  *
- *      Queue a buffer at the start of a list. This function takes no locks
+ *      Queue a buffer int the middle of a list. This function takes no locks
  *      and you must therefore hold required locks before calling it.
  *
  *      A buffer cannot be placed on two lists at the same time.
  */
-extern void skb_queue_head(struct sk_buff_head *list, struct sk_buff *newsk);
-static inline void __skb_queue_head(struct sk_buff_head *list,
-                                    struct sk_buff *newsk)
+static inline void __skb_queue_after(struct sk_buff_head *list,
+                                     struct sk_buff *prev,
+                                     struct sk_buff *newsk)
 {
-        struct sk_buff *prev, *next;
-
+        struct sk_buff *next;
         list->qlen++;
-        prev = (struct sk_buff *)list;
+
         next = prev->next;
         newsk->next = next;
         newsk->prev = prev;
@@ -627,6 +627,23 @@ static inline void __skb_queue_head(struct sk_buff_head *list,
 }
 
 /**
+ *      __skb_queue_head - queue a buffer at the list head
+ *      @list: list to use
+ *      @newsk: buffer to queue
+ *
+ *      Queue a buffer at the start of a list. This function takes no locks
+ *      and you must therefore hold required locks before calling it.
+ *
+ *      A buffer cannot be placed on two lists at the same time.
+ */
+extern void skb_queue_head(struct sk_buff_head *list, struct sk_buff *newsk);
+static inline void __skb_queue_head(struct sk_buff_head *list,
+                                    struct sk_buff *newsk)
+{
+        __skb_queue_after(list, (struct sk_buff *)list, newsk);
+}
+
+/**
  *      __skb_queue_tail - queue a buffer at the list tail
  *      @list: list to use
  *      @newsk: buffer to queue
@@ -1203,6 +1220,11 @@ static inline void kunmap_skb_frag(void *vaddr)
                      prefetch(skb->next), (skb != (struct sk_buff *)(queue));   \
                      skb = skb->next)
 
+#define skb_queue_reverse_walk(queue, skb) \
+                for (skb = (queue)->prev;                                       \
+                     prefetch(skb->prev), (skb != (struct sk_buff *)(queue));   \
+                     skb = skb->prev)
+
 
 extern struct sk_buff *skb_recv_datagram(struct sock *sk, unsigned flags,
                                          int noblock, int *err);
diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
index d871fe7f81a9..7c10ef3457d7 100644
--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c
@@ -300,11 +300,16 @@ static void netem_reset(struct Qdisc *sch)
         del_timer_sync(&q->timer);
 }
 
+/* Pass size change message down to embedded FIFO */
 static int set_fifo_limit(struct Qdisc *q, int limit)
 {
         struct rtattr *rta;
         int ret = -ENOMEM;
 
+        /* Hack to avoid sending change message to non-FIFO */
+        if (strncmp(q->ops->id + 1, "fifo", 4) != 0)
+                return 0;
+
         rta = kmalloc(RTA_LENGTH(sizeof(struct tc_fifo_qopt)), GFP_KERNEL);
         if (rta) {
                 rta->rta_type = RTM_NEWQDISC;
@@ -436,6 +441,84 @@ static int netem_change(struct Qdisc *sch, struct rtattr *opt)
         return 0;
 }
 
+/*
+ * Special case version of FIFO queue for use by netem.
+ * It queues in order based on timestamps in skb's
+ */
+struct fifo_sched_data {
+        u32 limit;
+};
+
+static int tfifo_enqueue(struct sk_buff *nskb, struct Qdisc *sch)
+{
+        struct fifo_sched_data *q = qdisc_priv(sch);
+        struct sk_buff_head *list = &sch->q;
+        const struct netem_skb_cb *ncb
+                = (const struct netem_skb_cb *)nskb->cb;
+        struct sk_buff *skb;
+
+        if (likely(skb_queue_len(list) < q->limit)) {
+                skb_queue_reverse_walk(list, skb) {
+                        const struct netem_skb_cb *cb
+                                = (const struct netem_skb_cb *)skb->cb;
+
+                        if (PSCHED_TLESS(cb->time_to_send, ncb->time_to_send))
+                                break;
+                }
+
+                __skb_queue_after(list, skb, nskb);
+
+                sch->qstats.backlog += nskb->len;
+                sch->bstats.bytes += nskb->len;
+                sch->bstats.packets++;
+
+                return NET_XMIT_SUCCESS;
+        }
+
+        return qdisc_drop(nskb, sch);
+}
+
+static int tfifo_init(struct Qdisc *sch, struct rtattr *opt)
+{
+        struct fifo_sched_data *q = qdisc_priv(sch);
+
+        if (opt) {
+                struct tc_fifo_qopt *ctl = RTA_DATA(opt);
+                if (RTA_PAYLOAD(opt) < sizeof(*ctl))
+                        return -EINVAL;
+
+                q->limit = ctl->limit;
+        } else
+                q->limit = max_t(u32, sch->dev->tx_queue_len, 1);
+
+        return 0;
+}
+
+static int tfifo_dump(struct Qdisc *sch, struct sk_buff *skb)
+{
+        struct fifo_sched_data *q = qdisc_priv(sch);
+        struct tc_fifo_qopt opt = { .limit = q->limit };
+
+        RTA_PUT(skb, TCA_OPTIONS, sizeof(opt), &opt);
+        return skb->len;
+
+rtattr_failure:
+        return -1;
+}
+
+static struct Qdisc_ops tfifo_qdisc_ops = {
+        .id             =       "tfifo",
+        .priv_size      =       sizeof(struct fifo_sched_data),
+        .enqueue        =       tfifo_enqueue,
+        .dequeue        =       qdisc_dequeue_head,
+        .requeue        =       qdisc_requeue,
+        .drop           =       qdisc_queue_drop,
+        .init           =       tfifo_init,
+        .reset          =       qdisc_reset_queue,
+        .change         =       tfifo_init,
+        .dump           =       tfifo_dump,
+};
+
 static int netem_init(struct Qdisc *sch, struct rtattr *opt)
 {
         struct netem_sched_data *q = qdisc_priv(sch);
@@ -448,7 +531,7 @@ static int netem_init(struct Qdisc *sch, struct rtattr *opt)
         q->timer.function = netem_watchdog;
         q->timer.data = (unsigned long) sch;
 
-        q->qdisc = qdisc_create_dflt(sch->dev, &pfifo_qdisc_ops);
+        q->qdisc = qdisc_create_dflt(sch->dev, &tfifo_qdisc_ops);
         if (!q->qdisc) {
                 pr_debug("netem: qdisc create failed\n");
                 return -ENOMEM;