rxrpc: Add a tracepoint to follow the life of a packet in the Tx buffer

Add a tracepoint to follow the insertion of a packet into the transmit
buffer, its transmission and its rotation out of the buffer.

Signed-off-by: David Howells <dhowells@redhat.com>
diff --git a/net/rxrpc/sendmsg.c b/net/rxrpc/sendmsg.c
index 8bfddf4..28d8f73 100644
--- a/net/rxrpc/sendmsg.c
+++ b/net/rxrpc/sendmsg.c
@@ -56,6 +56,7 @@
 			break;
 		}
 
+		trace_rxrpc_transmit(call, rxrpc_transmit_wait);
 		release_sock(&rx->sk);
 		*timeo = schedule_timeout(*timeo);
 		lock_sock(&rx->sk);
@@ -104,8 +105,14 @@
 	smp_wmb();
 	call->rxtx_buffer[ix] = skb;
 	call->tx_top = seq;
-	if (last)
+	if (last) {
 		set_bit(RXRPC_CALL_TX_LAST, &call->flags);
+		trace_rxrpc_transmit(call, rxrpc_transmit_queue_last);
+	} else if (sp->hdr.flags & RXRPC_REQUEST_ACK) {
+		trace_rxrpc_transmit(call, rxrpc_transmit_queue_reqack);
+	} else {
+		trace_rxrpc_transmit(call, rxrpc_transmit_queue);
+	}
 
 	if (last || call->state == RXRPC_CALL_SERVER_ACK_REQUEST) {
 		_debug("________awaiting reply/ACK__________");