[SCTP] Window update SACK support.

include/net/sctp/structs.h

@@ -1360,6 +1360,9 @@ struct SCTP_association {
 	 */
 	__u32 rwnd;
 
+	/* This is the last advertised value of rwnd over a SACK chunk. */
+	__u32 a_rwnd;
+
 	/* Number of bytes by which the rwnd has slopped.  The rwnd is allowed
 	 * to slop over a maximum of the association's frag_point.
 	 */

net/sctp/associola.c

@@ -186,6 +186,8 @@ sctp_association_t *sctp_association_init(sctp_association_t *asoc,
 	else
 		asoc->rwnd = sk->rcvbuf;
 
+	asoc->a_rwnd = 0;
+
 	asoc->rwnd_over = 0;
 
 	/* Use my own max window until I learn something better.  */

net/sctp/sm_sideeffect.c

@@ -737,6 +737,9 @@ int sctp_gen_sack(sctp_association_t *asoc, int force, sctp_cmd_seq_t *commands)
 		if (!sack)
 			goto nomem;
 
+		/* Update the last advertised rwnd value. */
+		asoc->a_rwnd = asoc->rwnd;
+
 		asoc->peer.sack_needed = 0;
 		asoc->peer.next_dup_tsn = 0;
 

net/sctp/ulpevent.c

@@ -762,6 +762,8 @@ static void sctp_rcvmsg_rfree(struct sk_buff *skb)
 {
 	sctp_association_t *asoc;
 	sctp_ulpevent_t *event;
+	sctp_chunk_t *sack;
+	struct timer_list *timer;
 
 	/* Current stack structures assume that the rcv buffer is
 	 * per socket.   For UDP style sockets this is not true as
@@ -782,9 +784,39 @@ static void sctp_rcvmsg_rfree(struct sk_buff *skb)
 		asoc->rwnd += skb->len;
 	}
 
-	SCTP_DEBUG_PRINTK("rwnd increased by %d to (%u, %u)\n",
-			  skb->len, asoc->rwnd, asoc->rwnd_over);
+	SCTP_DEBUG_PRINTK("rwnd increased by %d to (%u, %u) - %u\n",
+			  skb->len, asoc->rwnd, asoc->rwnd_over, asoc->a_rwnd);
+
+	/* Send a window update SACK if the rwnd has increased by at least the
+	 * minimum of the association's PMTU and half of the receive buffer.
+	 * The algorithm used is similar to the one described in Section 4.2.3.3
+	 * of RFC 1122.
+	 */
+	if ((asoc->state == SCTP_STATE_ESTABLISHED) &&
+	    (asoc->rwnd > asoc->a_rwnd) &&
+	    ((asoc->rwnd - asoc->a_rwnd) >=
+		     min_t(__u32, (asoc->base.sk->rcvbuf >> 1), asoc->pmtu))) {
+		SCTP_DEBUG_PRINTK("Sending window update SACK- rwnd: %u "
+				  "a_rwnd: %u\n", asoc->rwnd, asoc->a_rwnd);
+		sack = sctp_make_sack(asoc); 
+		if (!sack)
+			goto out;
+
+		/* Update the last advertised rwnd value. */
+		asoc->a_rwnd = asoc->rwnd;
+
+		asoc->peer.sack_needed = 0;
+		asoc->peer.next_dup_tsn = 0;
+
+		sctp_push_outqueue(&asoc->outqueue, sack);
+
+		/* Stop the SACK timer.  */
+		timer = &asoc->timers[SCTP_EVENT_TIMEOUT_SACK];
+		if (timer_pending(timer) && del_timer(timer))
+			sctp_association_put(asoc);
+	} 
 
+out:
 	sctp_association_put(asoc);
 }