[PKT_SCHED]: Add loss option to network delay scheduler.

This enhances the network simulation scheduler to do simple random loss.

The loss parameter is a simple 32 bit value such that 0 means no loss, and
0xffffffff is always drop.  I have a new version of the tc command which takes
care of conversion from percent to this value.

Same patch for 2.4 and 2.6
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: David S. Miller <davem@redhat.com>

include/linux/pkt_sched.h

@@ -437,5 +437,6 @@ struct tc_dly_qopt
 {
 	__u32	latency;
 	__u32   limit;
+	__u32	loss;
 };
 #endif

net/sched/sch_delay.c

@@ -40,6 +40,7 @@
 struct dly_sched_data {
 	u32	latency;
 	u32	limit;
+	u32	loss;
 	struct timer_list timer;
 	struct Qdisc *qdisc;
 };
@@ -58,6 +59,12 @@ static int dly_enqueue(struct sk_buff *skb, struct Qdisc *sch)
 	struct dly_skb_cb *cb = (struct dly_skb_cb *)skb->cb;
 	int ret;
 
+	/* Random packet drop 0 => none, ~0 => all */
+	if (q->loss >= net_random()) {
+		sch->stats.drops++;
+		return 0;	/* lie about loss so TCP doesn't know */
+	}
+
 	PSCHED_GET_TIME(cb->queuetime);
 
 	/* Queue to underlying scheduler */
@@ -197,6 +204,7 @@ static int dly_change(struct Qdisc *sch, struct rtattr *opt)
 	} else {
 		q->latency = qopt->latency;
 		q->limit = qopt->limit;
+		q->loss = qopt->loss;
 	}
 	return err;
 }
@@ -233,6 +241,7 @@ static int dly_dump(struct Qdisc *sch, struct sk_buff *skb)
 
 	qopt.latency = q->latency;
 	qopt.limit = q->limit;
+	qopt.loss = q->loss;
 
 	RTA_PUT(skb, TCA_OPTIONS, sizeof(qopt), &qopt);