[PATCH 5/5]: Implement rfc3448bis changes to feedback reception

[Gerrit Renker <gerrit@erg.abdn.ac.uk>]

[CCID 3]: Implement rfc3448bis changes to feedback reception

This implements the algorithm to update the allowed sending rate X upon 
receiving feedback packets, as described in draft rfc3448bis, 4.2/4.3.

Some changes (use of Larger Initial Windows) were already present, this patch
adds the remaining ones. In particular:

 * use t_RTO to distinguish the case "initial feedback packet":
   as per earlier patch, it uses "state = NO_FBACK" to imply that 
     (a) either nofeedback timer expired (when t_RTO != 0) or
     (b) initial feedback packet         (when t_RTO = 0);
 * no reduction of sending rate afer nofeedback timer expiry when p = 0;
 * implements the clause ``if [...] not the first packet after a nofeedback 
   timer'' of draft rfc3448bis, 4.3.

Note: At some point of time this probably needs update wrt rfc3448bis, but see
      http://www.mail-archive.com/dccp%40ietf.org/msg00426.html

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
---
 net/dccp/ccids/ccid3.c |   64 ++++++++++++++++++++++++++-----------------------
 1 file changed, 34 insertions(+), 30 deletions(-)

--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -443,41 +443,45 @@ static void ccid3_hc_tx_packet_recv(stru
 	r_sample = dccp_sample_rtt(sk, ktime_delta(now, t_send));
 	hctx->ccid3hctx_rtt = tfrc_ewma(hctx->ccid3hctx_rtt, r_sample, 9);
 
+	/*
+	 *	Update allowed sending rate X as per draft rfc3448bis, 4.2/4.3
+	 */
 	if (hctx->ccid3hctx_state = TFRC_SSTATE_NO_FBACK) {
-		/*
-		 * Larger Initial Windows [RFC 4342, sec. 5]
-		 */
-		hctx->ccid3hctx_x    = rfc3390_initial_rate(sk);
-		hctx->ccid3hctx_t_ld = now;
-
-		ccid3_update_send_interval(hctx);
-
-		ccid3_pr_debug("%s(%p), s=%u, MSS=%u, "
-			       "R_sample=%uus, X=%u\n", dccp_role(sk),
-			       sk, hctx->ccid3hctx_s,
-			       dccp_sk(sk)->dccps_mss_cache, r_sample,
-			       (unsigned)(hctx->ccid3hctx_x >> 6));
 
 		ccid3_hc_tx_set_state(sk, TFRC_SSTATE_FBACK);
 
-	} else {
-		/* Update sending rate (step 4 of [RFC 3448, 4.3]) */
-		if (hctx->ccid3hctx_p > 0)
-			hctx->ccid3hctx_x_calc -				tfrc_calc_x(hctx->ccid3hctx_s,
-					    hctx->ccid3hctx_rtt,
-					    hctx->ccid3hctx_p);
-		ccid3_hc_tx_update_x(sk, &now);
-
-		ccid3_pr_debug("%s(%p), RTT=%uus (sample=%uus), s=%u, "
-			       "p=%u, X_calc=%u, X_recv=%u, X=%u\n",
-			       dccp_role(sk),
-			       sk, hctx->ccid3hctx_rtt, r_sample,
-			       hctx->ccid3hctx_s, hctx->ccid3hctx_p,
-			       hctx->ccid3hctx_x_calc,
-			       (unsigned)(hctx->ccid3hctx_x_recv >> 6),
-			       (unsigned)(hctx->ccid3hctx_x >> 6));
+		if (hctx->ccid3hctx_t_rto = 0) {
+			/*
+			 * Initial feedback packet: Larger Initial Windows (4.2)
+			 */
+			hctx->ccid3hctx_x    = rfc3390_initial_rate(sk);
+			hctx->ccid3hctx_t_ld = now;
+
+			ccid3_update_send_interval(hctx);
+
+			goto done_computing_x;
+
+		} else if (hctx->ccid3hctx_p = 0) {
+			/*
+			 * First feedback after nofeedback timer expiry (4.3)
+			 */
+			goto done_computing_x;
+		}
 	}
+	/* perform step (4) of draft rfc3448bis, section 4.3 */
+	if (hctx->ccid3hctx_p > 0)
+		hctx->ccid3hctx_x_calc = tfrc_calc_x(hctx->ccid3hctx_s,
+						     hctx->ccid3hctx_rtt,
+						     hctx->ccid3hctx_p);
+	ccid3_hc_tx_update_x(sk, &now);
+
+done_computing_x:
+	ccid3_pr_debug("%s(%p), RTT=%uus (sample=%uus), s=%u, p=%u, X_calc=%u, "
+		       "X_recv=%u, X=%u\n", dccp_role(sk), sk,
+		       hctx->ccid3hctx_rtt, r_sample, hctx->ccid3hctx_s,
+		       hctx->ccid3hctx_p, hctx->ccid3hctx_x_calc,
+		       (unsigned)(hctx->ccid3hctx_x_recv >> 6),
+		       (unsigned)(hctx->ccid3hctx_x >> 6));
 
 	/* unschedule no feedback timer */
 	sk_stop_timer(sk, &hctx->ccid3hctx_no_feedback_timer);