net_sched: sch_htb: add per class overlimits counter

HTB qdisc overlimits counter is properly increased, but we have no per
class counter, meaning it is difficult to diagnose HTB problems.

This patch adds this counter, visible in "tc -s class show dev eth0",
with current iproute2.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Denys Fedoryshchenko <nuclearcat@nuclearcat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_htb.c

@@ -142,6 +142,7 @@ struct htb_class {
 	struct rb_node		node[TC_HTB_NUMPRIO];	/* node for self or feed tree */
 
 	unsigned int drops ____cacheline_aligned_in_smp;
+	unsigned int		overlimits;
 };
 
 struct htb_level {
@@ -533,6 +534,9 @@ htb_change_class_mode(struct htb_sched *q, struct htb_class *cl, s64 *diff)
 	if (new_mode == cl->cmode)
 		return;
 
+	if (new_mode == HTB_CANT_SEND)
+		cl->overlimits++;
+
 	if (cl->prio_activity) {	/* not necessary: speed optimization */
 		if (cl->cmode != HTB_CANT_SEND)
 			htb_deactivate_prios(q, cl);
@@ -1143,6 +1147,7 @@ htb_dump_class_stats(struct Qdisc *sch, unsigned long arg, struct gnet_dump *d)
 	struct htb_class *cl = (struct htb_class *)arg;
 	struct gnet_stats_queue qs = {
 		.drops = cl->drops,
+		.overlimits = cl->overlimits,
 	};
 	__u32 qlen = 0;