netem: add ECN capability

Add ECN (Explicit Congestion Notification) marking capability to netem

tc qdisc add dev eth0 root netem drop 0.5 ecn

Instead of dropping packets, try to ECN mark them.

Signed-off-by: Eric Dumazet <[e-mail]>
Cc: Neal Cardwell <[e-mail]>
Cc: Tom Herbert <[e-mail]>
Cc: Hagen Paul Pfeifer <[e-mail]>
Cc: Stephen Hemminger <[e-mail]>
Acked-by: Hagen Paul Pfeifer <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/linux/pkt_sched.h

···
 	TCA_NETEM_CORRUPT,
 	TCA_NETEM_LOSS,
 	TCA_NETEM_RATE,
+	TCA_NETEM_ECN,
 	__TCA_NETEM_MAX,
 };
 

net/sched/sch_netem.c

···
 
 #include <net/netlink.h>
 #include <net/pkt_sched.h>
+#include <net/inet_ecn.h>
 
 #define VERSION "1.3"
 
···
 	psched_tdiff_t jitter;
 
 	u32 loss;
+	u32 ecn;
 	u32 limit;
 	u32 counter;
 	u32 gap;
···
 		++count;
 
 	/* Drop packet? */
-	if (loss_event(q))
-		--count;
-
+	if (loss_event(q)) {
+		if (q->ecn && INET_ECN_set_ce(skb))
+			sch->qstats.drops++; /* mark packet */
+		else
+			--count;
+	}
 	if (count == 0) {
 		sch->qstats.drops++;
 		kfree_skb(skb);
···
 	[TCA_NETEM_CORRUPT]	= { .len = sizeof(struct tc_netem_corrupt) },
 	[TCA_NETEM_RATE]	= { .len = sizeof(struct tc_netem_rate) },
 	[TCA_NETEM_LOSS]	= { .type = NLA_NESTED },
+	[TCA_NETEM_ECN]		= { .type = NLA_U32 },
 };
 
 static int parse_attr(struct nlattr *tb[], int maxtype, struct nlattr *nla,
···
 
 	if (tb[TCA_NETEM_RATE])
 		get_rate(sch, tb[TCA_NETEM_RATE]);
+
+	if (tb[TCA_NETEM_ECN])
+		q->ecn = nla_get_u32(tb[TCA_NETEM_ECN]);
 
 	q->loss_model = CLG_RANDOM;
 	if (tb[TCA_NETEM_LOSS])
···
 	rate.cell_size = q->cell_size;
 	rate.cell_overhead = q->cell_overhead;
 	if (nla_put(skb, TCA_NETEM_RATE, sizeof(rate), &rate))
+		goto nla_put_failure;
+
+	if (q->ecn && nla_put_u32(skb, TCA_NETEM_ECN, q->ecn))
 		goto nla_put_failure;
 
 	if (dump_loss_model(q, skb) != 0)