[CCID3]: Nofeedback timer according to rfc3448bis

This implements the changes to the nofeedback timer handling suggested
in draft rfc3448bis00, section 4.4. In particular, these changes mean:

 * better handling of the lossless case (p == 0)
 * the timestamp for computing t_ld becomes obsolete
 * much more recent document (RFC 3448 is almost 5 years old)
 * concepts in rfc3448bis arose from a real, working implementation
   (cf. sec. 12)

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: Ian McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 29 insertions, 34 deletions

diff --git a/net/dccp/ccids/ccid3.c b/net/dccp/ccids/ccid3.c
index 1156fef17471..d292f23c002e 100644
--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -131,12 +131,11 @@ static u32 ccid3_hc_tx_idle_rtt(struct ccid3_hc_tx_sock *hctx, ktime_t now)
  *
  */
 static void ccid3_hc_tx_update_x(struct sock *sk, ktime_t *stamp)
-
 {
         struct ccid3_hc_tx_sock *hctx = ccid3_hc_tx_sk(sk);
         __u64 min_rate = 2 * hctx->ccid3hctx_x_recv;
         const  __u64 old_x = hctx->ccid3hctx_x;
-        ktime_t now = stamp? *stamp : ktime_get_real();
+        ktime_t now = stamp ? *stamp : ktime_get_real();
 
         /*
          * Handle IDLE periods: do not reduce below RFC3390 initial sending rate
@@ -230,27 +229,27 @@ static void ccid3_hc_tx_no_feedback_timer(unsigned long data)
         ccid3_pr_debug("%s(%p, state=%s) - entry \n", dccp_role(sk), sk,
                        ccid3_tx_state_name(hctx->ccid3hctx_state));
 
-        switch (hctx->ccid3hctx_state) {
-        case TFRC_SSTATE_NO_FBACK:
-                /* RFC 3448, 4.4: Halve send rate directly */
+        if (hctx->ccid3hctx_state == TFRC_SSTATE_FBACK)
+                ccid3_hc_tx_set_state(sk, TFRC_SSTATE_NO_FBACK);
+        else if (hctx->ccid3hctx_state != TFRC_SSTATE_NO_FBACK)
+                goto out;
+
+        /*
+         * Determine new allowed sending rate X as per draft rfc3448bis-00, 4.4
+         */
+        if (hctx->ccid3hctx_t_rto == 0 ||       /* no feedback received yet */
+            hctx->ccid3hctx_p == 0) {
+
+                /* halve send rate directly */
                 hctx->ccid3hctx_x = max(hctx->ccid3hctx_x / 2,
                                         (((__u64)hctx->ccid3hctx_s) << 6) /
                                                                     TFRC_T_MBI);
-
-                ccid3_pr_debug("%s(%p, state=%s), updated tx rate to %u "
-                               "bytes/s\n", dccp_role(sk), sk,
-                               ccid3_tx_state_name(hctx->ccid3hctx_state),
-                               (unsigned)(hctx->ccid3hctx_x >> 6));
-                /* The value of R is still undefined and so we can not recompute
-                 * the timeout value. Keep initial value as per [RFC 4342, 5]. */
-                t_nfb = TFRC_INITIAL_TIMEOUT;
                 ccid3_update_send_interval(hctx);
-                break;
-        case TFRC_SSTATE_FBACK:
+        } else {
                 /*
-                 *  Modify the cached value of X_recv [RFC 3448, 4.4]
+                 *  Modify the cached value of X_recv
                  *
-                 *  If (p == 0 || X_calc > 2 * X_recv)
+                 *  If (X_calc > 2 * X_recv)
                  *    X_recv = max(X_recv / 2, s / (2 * t_mbi));
                  *  Else
                  *    X_recv = X_calc / 4;
@@ -259,32 +258,28 @@ static void ccid3_hc_tx_no_feedback_timer(unsigned long data)
                  */
                 BUG_ON(hctx->ccid3hctx_p && !hctx->ccid3hctx_x_calc);
 
-                if (hctx->ccid3hctx_p == 0 ||
-                    (hctx->ccid3hctx_x_calc > (hctx->ccid3hctx_x_recv >> 5))) {
-
+                if (hctx->ccid3hctx_x_calc > (hctx->ccid3hctx_x_recv >> 5))
                         hctx->ccid3hctx_x_recv =
                                 max(hctx->ccid3hctx_x_recv / 2,
                                     (((__u64)hctx->ccid3hctx_s) << 6) /
                                                               (2 * TFRC_T_MBI));
-                } else {
+                else {
                         hctx->ccid3hctx_x_recv = hctx->ccid3hctx_x_calc;
                         hctx->ccid3hctx_x_recv <<= 4;
                 }
-                /* Now recalculate X [RFC 3448, 4.3, step (4)] */
                 ccid3_hc_tx_update_x(sk, NULL);
-                /*
-                 * Schedule no feedback timer to expire in
-                 * max(t_RTO, 2 * s/X)  =  max(t_RTO, 2 * t_ipi)
-                 * See comments in packet_recv() regarding the value of t_RTO.
-                 */
-                t_nfb = max(hctx->ccid3hctx_t_rto, 2 * hctx->ccid3hctx_t_ipi);
-                break;
-        case TFRC_SSTATE_NO_SENT:
-                DCCP_BUG("%s(%p) - Illegal state NO_SENT", dccp_role(sk), sk);
-                /* fall through */
-        case TFRC_SSTATE_TERM:
-                goto out;
         }
+        ccid3_pr_debug("Reduced X to %llu/64 bytes/sec\n",
+                        (unsigned long long)hctx->ccid3hctx_x);
+
+        /*
+         * Set new timeout for the nofeedback timer.
+         * See comments in packet_recv() regarding the value of t_RTO.
+         */
+        if (unlikely(hctx->ccid3hctx_t_rto == 0))       /* no feedback yet */
+                t_nfb = TFRC_INITIAL_TIMEOUT;
+        else
+                t_nfb = max(hctx->ccid3hctx_t_rto, 2 * hctx->ccid3hctx_t_ipi);
 
 restart_timer:
         sk_reset_timer(sk, &hctx->ccid3hctx_no_feedback_timer,