sctp: reuse sent_count to avoid retransmitted chunks for RTT measurements

Now sctp uses chunk->resent to record if a chunk is retransmitted, for
RTT measurements with retransmitted DATA chunks. chunk->sent_count was
introduced to record how many times one chunk has been sent for prsctp
RTX policy before. We actually can know if one chunk is retransmitted
by checking chunk->sent_count is greater than 1.

This patch is to remove resent from sctp_chunk and reuse sent_count
to avoid retransmitted chunks for RTT measurements.
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sctp/structs.h

@@ -641,7 +641,6 @@ struct sctp_chunk {
 #define SCTP_NEED_FRTX 0x1
 #define SCTP_DONT_FRTX 0x2
 	__u16	rtt_in_progress:1,	/* This chunk used for RTT calc? */
-		resent:1,		/* Has this chunk ever been resent. */
 		has_tsn:1,		/* Does this chunk have a TSN yet? */
 		has_ssn:1,		/* Does this chunk have a SSN yet? */
 		singleton:1,		/* Only chunk in the packet? */
@@ -656,6 +655,7 @@ struct sctp_chunk {
 		fast_retransmit:2;	/* Is this chunk fast retransmitted? */
 };
 
+#define sctp_chunk_retransmitted(chunk)	(chunk->sent_count > 1)
 void sctp_chunk_hold(struct sctp_chunk *);
 void sctp_chunk_put(struct sctp_chunk *);
 int sctp_user_addto_chunk(struct sctp_chunk *chunk, int len,

net/sctp/output.c

@@ -552,7 +552,8 @@ int sctp_packet_transmit(struct sctp_packet *packet, gfp_t gfp)
 				 * for a given destination transport address.
 				 */
 
-				if (!chunk->resent && !tp->rto_pending) {
+				if (!sctp_chunk_retransmitted(chunk) &&
+				    !tp->rto_pending) {
 					chunk->rtt_in_progress = 1;
 					tp->rto_pending = 1;
 				}

net/sctp/outqueue.c

@@ -507,8 +507,6 @@ void sctp_retransmit_mark(struct sctp_outq *q,
 				transport->rto_pending = 0;
 			}
 
-			chunk->resent = 1;
-
 			/* Move the chunk to the retransmit queue. The chunks
 			 * on the retransmit queue are always kept in order.
 			 */
@@ -1439,7 +1437,7 @@ static void sctp_check_transmitted(struct sctp_outq *q,
 				 * instance).
 				 */
 				if (!tchunk->tsn_gap_acked &&
-				    !tchunk->resent &&
+				    !sctp_chunk_retransmitted(tchunk) &&
 				    tchunk->rtt_in_progress) {
 					tchunk->rtt_in_progress = 0;
 					rtt = jiffies - tchunk->sent_at;