tipc: add back link trace events

In the previous commit ("tipc: add Gap ACK blocks support for broadcast
link"), we have removed the following link trace events due to the code
changes:

- tipc_link_bc_ack
- tipc_link_retrans

This commit adds them back along with some minor changes to adapt to
the new code.

Acked-by: Ying Xue <ying.xue@windriver.com>
Acked-by: Jon Maloy <jmaloy@redhat.com>
Signed-off-by: Tuong Lien <tuong.t.lien@dektech.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/tipc/trace.h b/net/tipc/trace.h
index 4d8e004..e7535ab 100644
--- a/net/tipc/trace.h
+++ b/net/tipc/trace.h
@@ -299,8 +299,10 @@ DECLARE_EVENT_CLASS(tipc_link_transmq_class,
 		__entry->from = f;
 		__entry->to = t;
 		__entry->len = skb_queue_len(tq);
-		__entry->fseqno = msg_seqno(buf_msg(skb_peek(tq)));
-		__entry->lseqno = msg_seqno(buf_msg(skb_peek_tail(tq)));
+		__entry->fseqno = __entry->len ?
+				  msg_seqno(buf_msg(skb_peek(tq))) : 0;
+		__entry->lseqno = __entry->len ?
+				  msg_seqno(buf_msg(skb_peek_tail(tq))) : 0;
 	),
 
 	TP_printk("<%s> retrans req: [%u-%u] transmq: %u [%u-%u]\n",
@@ -308,15 +310,16 @@ DECLARE_EVENT_CLASS(tipc_link_transmq_class,
 		  __entry->len, __entry->fseqno, __entry->lseqno)
 );
 
-DEFINE_EVENT(tipc_link_transmq_class, tipc_link_retrans,
+DEFINE_EVENT_CONDITION(tipc_link_transmq_class, tipc_link_retrans,
 	TP_PROTO(struct tipc_link *r, u16 f, u16 t, struct sk_buff_head *tq),
-	TP_ARGS(r, f, t, tq)
+	TP_ARGS(r, f, t, tq),
+	TP_CONDITION(less_eq(f, t))
 );
 
 DEFINE_EVENT_PRINT(tipc_link_transmq_class, tipc_link_bc_ack,
 	TP_PROTO(struct tipc_link *r, u16 f, u16 t, struct sk_buff_head *tq),
 	TP_ARGS(r, f, t, tq),
-	TP_printk("<%s> acked: [%u-%u] transmq: %u [%u-%u]\n",
+	TP_printk("<%s> acked: %u gap: %u transmq: %u [%u-%u]\n",
 		  __entry->name, __entry->from, __entry->to,
 		  __entry->len, __entry->fseqno, __entry->lseqno)
 );