Merge branch 'dccp' of git://eden-feed.erg.abdn.ac.uk/dccp_exp

Conflicts:

	net/dccp/input.c
	net/dccp/options.c

1 files changed, 301 insertions, 461 deletions

diff --git a/net/dccp/ccids/ccid3.c b/net/dccp/ccids/ccid3.c
index 3b8bd7ca6761..06cfdad84a6a 100644
--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -49,75 +49,41 @@ static int ccid3_debug;
 /*
  *      Transmitter Half-Connection Routines
  */
-#ifdef CONFIG_IP_DCCP_CCID3_DEBUG
-static const char *ccid3_tx_state_name(enum ccid3_hc_tx_states state)
-{
-        static char *ccid3_state_names[] = {
-        [TFRC_SSTATE_NO_SENT]  = "NO_SENT",
-        [TFRC_SSTATE_NO_FBACK] = "NO_FBACK",
-        [TFRC_SSTATE_FBACK]    = "FBACK",
-        [TFRC_SSTATE_TERM]     = "TERM",
-        };
-
-        return ccid3_state_names[state];
-}
-#endif
-
-static void ccid3_hc_tx_set_state(struct sock *sk,
-                                  enum ccid3_hc_tx_states state)
-{
-        struct ccid3_hc_tx_sock *hctx = ccid3_hc_tx_sk(sk);
-        enum ccid3_hc_tx_states oldstate = hctx->ccid3hctx_state;
-
-        ccid3_pr_debug("%s(%p) %-8.8s -> %s\n",
-                       dccp_role(sk), sk, ccid3_tx_state_name(oldstate),
-                       ccid3_tx_state_name(state));
-        WARN_ON(state == oldstate);
-        hctx->ccid3hctx_state = state;
-}
+/* Oscillation Prevention/Reduction: recommended by rfc3448bis, on by default */
+static int do_osc_prev = true;
 
 /*
  * Compute the initial sending rate X_init in the manner of RFC 3390:
  *
- *      X_init  =  min(4 * s, max(2 * s, 4380 bytes)) / RTT
+ *      X_init  =  min(4 * MPS, max(2 * MPS, 4380 bytes)) / RTT
  *
- * Note that RFC 3390 uses MSS, RFC 4342 refers to RFC 3390, and rfc3448bis
- * (rev-02) clarifies the use of RFC 3390 with regard to the above formula.
  * For consistency with other parts of the code, X_init is scaled by 2^6.
  */
 static inline u64 rfc3390_initial_rate(struct sock *sk)
 {
-        const struct ccid3_hc_tx_sock *hctx = ccid3_hc_tx_sk(sk);
-        const __u32 w_init = clamp_t(__u32, 4380U,
-                        2 * hctx->ccid3hctx_s, 4 * hctx->ccid3hctx_s);
+        const u32 mps = dccp_sk(sk)->dccps_mss_cache,
+               w_init = clamp(4380U, 2 * mps, 4 * mps);
 
-        return scaled_div(w_init << 6, hctx->ccid3hctx_rtt);
+        return scaled_div(w_init << 6, ccid3_hc_tx_sk(sk)->rtt);
 }
 
-/*
- * Recalculate t_ipi and delta (should be called whenever X changes)
+/**
+ * ccid3_update_send_interval  -  Calculate new t_ipi = s / X
+ * This respects the granularity of X (64 * bytes/second) and enforces the
+ * scaled minimum of s * 64 / t_mbi = `s' bytes/second as per RFC 3448/4342.
  */
 static void ccid3_update_send_interval(struct ccid3_hc_tx_sock *hctx)
 {
-        /* Calculate new t_ipi = s / X_inst (X_inst is in 64 * bytes/second) */
-        hctx->ccid3hctx_t_ipi = scaled_div32(((u64)hctx->ccid3hctx_s) << 6,
-                                             hctx->ccid3hctx_x);
-
-        /* Calculate new delta by delta = min(t_ipi / 2, t_gran / 2) */
-        hctx->ccid3hctx_delta = min_t(u32, hctx->ccid3hctx_t_ipi / 2,
-                                           TFRC_OPSYS_HALF_TIME_GRAN);
-
-        ccid3_pr_debug("t_ipi=%u, delta=%u, s=%u, X=%u\n",
-                       hctx->ccid3hctx_t_ipi, hctx->ccid3hctx_delta,
-                       hctx->ccid3hctx_s, (unsigned)(hctx->ccid3hctx_x >> 6));
-
+        if (unlikely(hctx->x <= hctx->s))
+                hctx->x = hctx->s;
+        hctx->t_ipi = scaled_div32(((u64)hctx->s) << 6, hctx->x);
 }
 
 static u32 ccid3_hc_tx_idle_rtt(struct ccid3_hc_tx_sock *hctx, ktime_t now)
 {
-        u32 delta = ktime_us_delta(now, hctx->ccid3hctx_t_last_win_count);
+        u32 delta = ktime_us_delta(now, hctx->t_last_win_count);
 
-        return delta / hctx->ccid3hctx_rtt;
+        return delta / hctx->rtt;
 }
 
 /**
@@ -133,8 +99,8 @@ 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;
+        u64 min_rate = 2 * hctx->x_recv;
+        const u64 old_x = hctx->x;
         ktime_t now = stamp ? *stamp : ktime_get_real();
 
         /*
@@ -145,50 +111,44 @@ static void ccid3_hc_tx_update_x(struct sock *sk, ktime_t *stamp)
          */
         if (ccid3_hc_tx_idle_rtt(hctx, now) >= 2) {
                 min_rate = rfc3390_initial_rate(sk);
-                min_rate = max(min_rate, 2 * hctx->ccid3hctx_x_recv);
+                min_rate = max(min_rate, 2 * hctx->x_recv);
         }
 
-        if (hctx->ccid3hctx_p > 0) {
+        if (hctx->p > 0) {
 
-                hctx->ccid3hctx_x = min(((__u64)hctx->ccid3hctx_x_calc) << 6,
-                                        min_rate);
-                hctx->ccid3hctx_x = max(hctx->ccid3hctx_x,
-                                        (((__u64)hctx->ccid3hctx_s) << 6) /
-                                                                TFRC_T_MBI);
+                hctx->x = min(((u64)hctx->x_calc) << 6, min_rate);
 
-        } else if (ktime_us_delta(now, hctx->ccid3hctx_t_ld)
-                                - (s64)hctx->ccid3hctx_rtt >= 0) {
+        } else if (ktime_us_delta(now, hctx->t_ld) - (s64)hctx->rtt >= 0) {
 
-                hctx->ccid3hctx_x = min(2 * hctx->ccid3hctx_x, min_rate);
-                hctx->ccid3hctx_x = max(hctx->ccid3hctx_x,
-                            scaled_div(((__u64)hctx->ccid3hctx_s) << 6,
-                                       hctx->ccid3hctx_rtt));
-                hctx->ccid3hctx_t_ld = now;
+                hctx->x = min(2 * hctx->x, min_rate);
+                hctx->x = max(hctx->x,
+                              scaled_div(((u64)hctx->s) << 6, hctx->rtt));
+                hctx->t_ld = now;
         }
 
-        if (hctx->ccid3hctx_x != old_x) {
+        if (hctx->x != old_x) {
                 ccid3_pr_debug("X_prev=%u, X_now=%u, X_calc=%u, "
                                "X_recv=%u\n", (unsigned)(old_x >> 6),
-                               (unsigned)(hctx->ccid3hctx_x >> 6),
-                               hctx->ccid3hctx_x_calc,
-                               (unsigned)(hctx->ccid3hctx_x_recv >> 6));
+                               (unsigned)(hctx->x >> 6), hctx->x_calc,
+                               (unsigned)(hctx->x_recv >> 6));
 
                 ccid3_update_send_interval(hctx);
         }
 }
 
 /*
- *      Track the mean packet size `s' (cf. RFC 4342, 5.3 and  RFC 3448, 4.1)
- *      @len: DCCP packet payload size in bytes
+ * ccid3_hc_tx_measure_packet_size  -  Measuring the packet size `s' (sec 4.1)
+ * @new_len: DCCP payload size in bytes (not used by all methods)
  */
-static inline void ccid3_hc_tx_update_s(struct ccid3_hc_tx_sock *hctx, int len)
+static u32 ccid3_hc_tx_measure_packet_size(struct sock *sk, const u16 new_len)
 {
-        const u16 old_s = hctx->ccid3hctx_s;
-
-        hctx->ccid3hctx_s = tfrc_ewma(hctx->ccid3hctx_s, len, 9);
-
-        if (hctx->ccid3hctx_s != old_s)
-                ccid3_update_send_interval(hctx);
+#if   defined(CONFIG_IP_DCCP_CCID3_MEASURE_S_AS_AVG)
+        return tfrc_ewma(ccid3_hc_tx_sk(sk)->s, new_len, 9);
+#elif defined(CONFIG_IP_DCCP_CCID3_MEASURE_S_AS_MAX)
+        return max(ccid3_hc_tx_sk(sk)->s, new_len);
+#else /* CONFIG_IP_DCCP_CCID3_MEASURE_S_AS_MPS  */
+        return dccp_sk(sk)->dccps_mss_cache;
+#endif
 }
 
 /*
@@ -198,13 +158,13 @@ static inline void ccid3_hc_tx_update_s(struct ccid3_hc_tx_sock *hctx, int len)
 static inline void ccid3_hc_tx_update_win_count(struct ccid3_hc_tx_sock *hctx,
                                                 ktime_t now)
 {
-        u32 delta = ktime_us_delta(now, hctx->ccid3hctx_t_last_win_count),
-            quarter_rtts = (4 * delta) / hctx->ccid3hctx_rtt;
+        u32 delta = ktime_us_delta(now, hctx->t_last_win_count),
+            quarter_rtts = (4 * delta) / hctx->rtt;
 
         if (quarter_rtts > 0) {
-                hctx->ccid3hctx_t_last_win_count = now;
-                hctx->ccid3hctx_last_win_count  += min(quarter_rtts, 5U);
-                hctx->ccid3hctx_last_win_count  &= 0xF;         /* mod 16 */
+                hctx->t_last_win_count = now;
+                hctx->last_win_count  += min(quarter_rtts, 5U);
+                hctx->last_win_count  &= 0xF;           /* mod 16 */
         }
 }
 
@@ -221,25 +181,26 @@ static void ccid3_hc_tx_no_feedback_timer(unsigned long data)
                 goto restart_timer;
         }
 
-        ccid3_pr_debug("%s(%p, state=%s) - entry \n", dccp_role(sk), sk,
-                       ccid3_tx_state_name(hctx->ccid3hctx_state));
+        ccid3_pr_debug("%s(%p) entry with%s feedback\n", dccp_role(sk), sk,
+                       hctx->feedback ? "" : "out");
 
-        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)
+        /* Ignore and do not restart after leaving the established state */
+        if ((1 << sk->sk_state) & ~(DCCPF_OPEN | DCCPF_PARTOPEN))
                 goto out;
 
+        /* Reset feedback state to "no feedback received" */
+        hctx->feedback = false;
+
         /*
          * Determine new allowed sending rate X as per draft rfc3448bis-00, 4.4
+         * RTO is 0 if and only if no feedback has been received yet.
          */
-        if (hctx->ccid3hctx_t_rto == 0 ||       /* no feedback received yet */
-            hctx->ccid3hctx_p == 0) {
+        if (hctx->t_rto == 0 || hctx->p == 0) {
 
                 /* halve send rate directly */
-                hctx->ccid3hctx_x = max(hctx->ccid3hctx_x / 2,
-                                        (((__u64)hctx->ccid3hctx_s) << 6) /
-                                                                    TFRC_T_MBI);
+                hctx->x /= 2;
                 ccid3_update_send_interval(hctx);
+
         } else {
                 /*
                  *  Modify the cached value of X_recv
@@ -251,44 +212,41 @@ static void ccid3_hc_tx_no_feedback_timer(unsigned long data)
                  *
                  *  Note that X_recv is scaled by 2^6 while X_calc is not
                  */
-                BUG_ON(hctx->ccid3hctx_p && !hctx->ccid3hctx_x_calc);
+                BUG_ON(hctx->p && !hctx->x_calc);
 
-                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));
+                if (hctx->x_calc > (hctx->x_recv >> 5))
+                        hctx->x_recv /= 2;
                 else {
-                        hctx->ccid3hctx_x_recv = hctx->ccid3hctx_x_calc;
-                        hctx->ccid3hctx_x_recv <<= 4;
+                        hctx->x_recv = hctx->x_calc;
+                        hctx->x_recv <<= 4;
                 }
                 ccid3_hc_tx_update_x(sk, NULL);
         }
         ccid3_pr_debug("Reduced X to %llu/64 bytes/sec\n",
-                        (unsigned long long)hctx->ccid3hctx_x);
+                        (unsigned long long)hctx->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 */
+        if (unlikely(hctx->t_rto == 0))         /* no feedback received yet */
                 t_nfb = TFRC_INITIAL_TIMEOUT;
         else
-                t_nfb = max(hctx->ccid3hctx_t_rto, 2 * hctx->ccid3hctx_t_ipi);
+                t_nfb = max(hctx->t_rto, 2 * hctx->t_ipi);
 
 restart_timer:
-        sk_reset_timer(sk, &hctx->ccid3hctx_no_feedback_timer,
+        sk_reset_timer(sk, &hctx->no_feedback_timer,
                            jiffies + usecs_to_jiffies(t_nfb));
 out:
         bh_unlock_sock(sk);
         sock_put(sk);
 }
 
-/*
- * returns
- *   > 0: delay (in msecs) that should pass before actually sending
- *   = 0: can send immediately
- *   < 0: error condition; do not send packet
+/**
+ * ccid3_hc_tx_send_packet  -  Delay-based dequeueing of TX packets
+ * @skb: next packet candidate to send on @sk
+ * This function uses the convention of ccid_packet_dequeue_eval() and
+ * returns a millisecond-delay value between 0 and t_mbi = 64000 msec.
  */
 static int ccid3_hc_tx_send_packet(struct sock *sk, struct sk_buff *skb)
 {
@@ -305,18 +263,14 @@ static int ccid3_hc_tx_send_packet(struct sock *sk, struct sk_buff *skb)
         if (unlikely(skb->len == 0))
                 return -EBADMSG;
 
-        switch (hctx->ccid3hctx_state) {
-        case TFRC_SSTATE_NO_SENT:
-                sk_reset_timer(sk, &hctx->ccid3hctx_no_feedback_timer,
-                               (jiffies +
+        if (hctx->s == 0) {
+                sk_reset_timer(sk, &hctx->no_feedback_timer, (jiffies +
                                 usecs_to_jiffies(TFRC_INITIAL_TIMEOUT)));
-                hctx->ccid3hctx_last_win_count   = 0;
-                hctx->ccid3hctx_t_last_win_count = now;
+                hctx->last_win_count   = 0;
+                hctx->t_last_win_count = now;
 
                 /* Set t_0 for initial packet */
-                hctx->ccid3hctx_t_nom = now;
-
-                hctx->ccid3hctx_s = skb->len;
+                hctx->t_nom = now;
 
                 /*
                  * Use initial RTT sample when available: recommended by erratum
@@ -325,9 +279,9 @@ static int ccid3_hc_tx_send_packet(struct sock *sk, struct sk_buff *skb)
                  */
                 if (dp->dccps_syn_rtt) {
                         ccid3_pr_debug("SYN RTT = %uus\n", dp->dccps_syn_rtt);
-                        hctx->ccid3hctx_rtt  = dp->dccps_syn_rtt;
-                        hctx->ccid3hctx_x    = rfc3390_initial_rate(sk);
-                        hctx->ccid3hctx_t_ld = now;
+                        hctx->rtt  = dp->dccps_syn_rtt;
+                        hctx->x    = rfc3390_initial_rate(sk);
+                        hctx->t_ld = now;
                 } else {
                         /*
                          * Sender does not have RTT sample:
@@ -335,17 +289,20 @@ static int ccid3_hc_tx_send_packet(struct sock *sk, struct sk_buff *skb)
                          *   is needed in several parts (e.g.  window counter);
                          * - set sending rate X_pps = 1pps as per RFC 3448, 4.2.
                          */
-                        hctx->ccid3hctx_rtt = DCCP_FALLBACK_RTT;
-                        hctx->ccid3hctx_x   = hctx->ccid3hctx_s;
-                        hctx->ccid3hctx_x <<= 6;
+                        hctx->rtt = DCCP_FALLBACK_RTT;
+                        hctx->x   = dp->dccps_mss_cache;
+                        hctx->x <<= 6;
                 }
+
+                /* Compute t_ipi = s / X */
+                hctx->s = ccid3_hc_tx_measure_packet_size(sk, skb->len);
                 ccid3_update_send_interval(hctx);
 
-                ccid3_hc_tx_set_state(sk, TFRC_SSTATE_NO_FBACK);
-                break;
-        case TFRC_SSTATE_NO_FBACK:
-        case TFRC_SSTATE_FBACK:
-                delay = ktime_us_delta(hctx->ccid3hctx_t_nom, now);
+                /* Seed value for Oscillation Prevention (sec. 4.5) */
+                hctx->r_sqmean = tfrc_scaled_sqrt(hctx->rtt);
+
+        } else {
+                delay = ktime_us_delta(hctx->t_nom, now);
                 ccid3_pr_debug("delay=%ld\n", (long)delay);
                 /*
                  *      Scheduling of packet transmissions [RFC 3448, 4.6]
@@ -355,99 +312,80 @@ static int ccid3_hc_tx_send_packet(struct sock *sk, struct sk_buff *skb)
                  * else
                  *       // send the packet in (t_nom - t_now) milliseconds.
                  */
-                if (delay - (s64)hctx->ccid3hctx_delta >= 1000)
-                        return (u32)delay / 1000L;
+                if (delay >= TFRC_T_DELTA)
+                        return (u32)delay / USEC_PER_MSEC;
 
                 ccid3_hc_tx_update_win_count(hctx, now);
-                break;
-        case TFRC_SSTATE_TERM:
-                DCCP_BUG("%s(%p) - Illegal state TERM", dccp_role(sk), sk);
-                return -EINVAL;
         }
 
         /* prepare to send now (add options etc.) */
         dp->dccps_hc_tx_insert_options = 1;
-        DCCP_SKB_CB(skb)->dccpd_ccval = hctx->ccid3hctx_last_win_count;
+        DCCP_SKB_CB(skb)->dccpd_ccval  = hctx->last_win_count;
 
         /* set the nominal send time for the next following packet */
-        hctx->ccid3hctx_t_nom = ktime_add_us(hctx->ccid3hctx_t_nom,
-                                             hctx->ccid3hctx_t_ipi);
-        return 0;
+        hctx->t_nom = ktime_add_us(hctx->t_nom, hctx->t_ipi);
+        return CCID_PACKET_SEND_AT_ONCE;
 }
 
-static void ccid3_hc_tx_packet_sent(struct sock *sk, int more,
-                                    unsigned int len)
+static void ccid3_hc_tx_packet_sent(struct sock *sk, unsigned int len)
 {
         struct ccid3_hc_tx_sock *hctx = ccid3_hc_tx_sk(sk);
 
-        ccid3_hc_tx_update_s(hctx, len);
+        /* Changes to s will become effective the next time X is computed */
+        hctx->s = ccid3_hc_tx_measure_packet_size(sk, len);
 
-        if (tfrc_tx_hist_add(&hctx->ccid3hctx_hist, dccp_sk(sk)->dccps_gss))
+        if (tfrc_tx_hist_add(&hctx->hist, dccp_sk(sk)->dccps_gss))
                 DCCP_CRIT("packet history - out of memory!");
 }
 
 static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
 {
         struct ccid3_hc_tx_sock *hctx = ccid3_hc_tx_sk(sk);
-        struct ccid3_options_received *opt_recv;
+        struct tfrc_tx_hist_entry *acked;
         ktime_t now;
         unsigned long t_nfb;
-        u32 pinv, r_sample;
+        u32 r_sample;
 
         /* we are only interested in ACKs */
         if (!(DCCP_SKB_CB(skb)->dccpd_type == DCCP_PKT_ACK ||
               DCCP_SKB_CB(skb)->dccpd_type == DCCP_PKT_DATAACK))
                 return;
-        /* ... and only in the established state */
-        if (hctx->ccid3hctx_state != TFRC_SSTATE_FBACK &&
-            hctx->ccid3hctx_state != TFRC_SSTATE_NO_FBACK)
-                return;
-
-        opt_recv = &hctx->ccid3hctx_options_received;
-        now = ktime_get_real();
-
-        /* Estimate RTT from history if ACK number is valid */
-        r_sample = tfrc_tx_hist_rtt(hctx->ccid3hctx_hist,
-                                    DCCP_SKB_CB(skb)->dccpd_ack_seq, now);
-        if (r_sample == 0) {
-                DCCP_WARN("%s(%p): %s with bogus ACK-%llu\n", dccp_role(sk), sk,
-                          dccp_packet_name(DCCP_SKB_CB(skb)->dccpd_type),
-                          (unsigned long long)DCCP_SKB_CB(skb)->dccpd_ack_seq);
+        /*
+         * Locate the acknowledged packet in the TX history.
+         *
+         * Returning "entry not found" here can for instance happen when
+         *  - the host has not sent out anything (e.g. a passive server),
+         *  - the Ack is outdated (packet with higher Ack number was received),
+         *  - it is a bogus Ack (for a packet not sent on this connection).
+         */
+        acked = tfrc_tx_hist_find_entry(hctx->hist, dccp_hdr_ack_seq(skb));
+        if (acked == NULL)
                 return;
-        }
+        /* For the sake of RTT sampling, ignore/remove all older entries */
+        tfrc_tx_hist_purge(&acked->next);
 
-        /* Update receive rate in units of 64 * bytes/second */
-        hctx->ccid3hctx_x_recv = opt_recv->ccid3or_receive_rate;
-        hctx->ccid3hctx_x_recv <<= 6;
+        /* Update the moving average for the RTT estimate (RFC 3448, 4.3) */
+        now       = ktime_get_real();
+        r_sample  = dccp_sample_rtt(sk, ktime_us_delta(now, acked->stamp));
+        hctx->rtt = tfrc_ewma(hctx->rtt, r_sample, 9);
 
-        /* Update loss event rate (which is scaled by 1e6) */
-        pinv = opt_recv->ccid3or_loss_event_rate;
-        if (pinv == ~0U || pinv == 0)          /* see RFC 4342, 8.5   */
-                hctx->ccid3hctx_p = 0;
-        else                                   /* can not exceed 100% */
-                hctx->ccid3hctx_p = scaled_div(1, pinv);
-        /*
-         * Validate new RTT sample and update moving average
-         */
-        r_sample = dccp_sample_rtt(sk, r_sample);
-        hctx->ccid3hctx_rtt = tfrc_ewma(hctx->ccid3hctx_rtt, r_sample, 9);
         /*
          * Update allowed sending rate X as per draft rfc3448bis-00, 4.2/3
          */
-        if (hctx->ccid3hctx_state == TFRC_SSTATE_NO_FBACK) {
-                ccid3_hc_tx_set_state(sk, TFRC_SSTATE_FBACK);
+        if (!hctx->feedback) {
+                hctx->feedback = true;
 
-                if (hctx->ccid3hctx_t_rto == 0) {
+                if (hctx->t_rto == 0) {
                         /*
                          * Initial feedback packet: Larger Initial Windows (4.2)
                          */
-                        hctx->ccid3hctx_x    = rfc3390_initial_rate(sk);
-                        hctx->ccid3hctx_t_ld = now;
+                        hctx->x    = rfc3390_initial_rate(sk);
+                        hctx->t_ld = now;
 
                         ccid3_update_send_interval(hctx);
 
                         goto done_computing_x;
-                } else if (hctx->ccid3hctx_p == 0) {
+                } else if (hctx->p == 0) {
                         /*
                          * First feedback after nofeedback timer expiry (4.3)
                          */
@@ -456,25 +394,52 @@ static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
         }
 
         /* 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);
+        if (hctx->p > 0)
+                hctx->x_calc = tfrc_calc_x(hctx->s, hctx->rtt, hctx->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));
+                               dccp_role(sk), sk, hctx->rtt, r_sample,
+                               hctx->s, hctx->p, hctx->x_calc,
+                               (unsigned)(hctx->x_recv >> 6),
+                               (unsigned)(hctx->x >> 6));
+        /*
+         * Oscillation Reduction (RFC 3448, 4.5) - modifying t_ipi according to
+         * RTT changes, multiplying by X/X_inst = sqrt(R_sample)/R_sqmean. This
+         * can be useful if few connections share a link, avoiding that buffer
+         * fill levels (RTT) oscillate as a result of frequent adjustments to X.
+         * A useful presentation with background information is in
+         *    Joerg Widmer, "Equation-Based Congestion Control",
+         *    MSc Thesis, University of Mannheim, Germany, 2000
+         * (sec. 3.6.4), who calls this ISM ("Inter-packet Space Modulation").
+         */
+        if (do_osc_prev) {
+                r_sample = tfrc_scaled_sqrt(r_sample);
+                /*
+                 * The modulation can work in both ways: increase/decrease t_ipi
+                 * according to long-term increases/decreases of the RTT. The
+                 * former is a useful measure, since it works against queue
+                 * build-up. The latter temporarily increases the sending rate,
+                 * so that buffers fill up more quickly. This in turn causes
+                 * the RTT to increase, so that either later reduction becomes
+                 * necessary or the RTT stays at a very high level. Decreasing
+                 * t_ipi is therefore not supported.
+                 * Furthermore, during the initial slow-start phase the RTT
+                 * naturally increases, where using the algorithm would cause
+                 * delays. Hence it is disabled during the initial slow-start.
+                 */
+                if (r_sample > hctx->r_sqmean && hctx->p > 0)
+                        hctx->t_ipi = div_u64((u64)hctx->t_ipi * (u64)r_sample,
+                                              hctx->r_sqmean);
+                hctx->t_ipi = min_t(u32, hctx->t_ipi, TFRC_T_MBI);
+                /* update R_sqmean _after_ computing the modulation factor */
+                hctx->r_sqmean = tfrc_ewma(hctx->r_sqmean, r_sample, 9);
+        }
 
         /* unschedule no feedback timer */
-        sk_stop_timer(sk, &hctx->ccid3hctx_no_feedback_timer);
+        sk_stop_timer(sk, &hctx->no_feedback_timer);
 
         /*
          * As we have calculated new ipi, delta, t_nom it is possible
@@ -488,95 +453,66 @@ done_computing_x:
          * This can help avoid triggering the nofeedback timer too
          * often ('spinning') on LANs with small RTTs.
          */
-        hctx->ccid3hctx_t_rto = max_t(u32, 4 * hctx->ccid3hctx_rtt,
-                                           (CONFIG_IP_DCCP_CCID3_RTO *
-                                            (USEC_PER_SEC / 1000)));
+        hctx->t_rto = max_t(u32, 4 * hctx->rtt, (CONFIG_IP_DCCP_CCID3_RTO *
+                                                 (USEC_PER_SEC / 1000)));
         /*
          * Schedule no feedback timer to expire in
          * max(t_RTO, 2 * s/X)  =  max(t_RTO, 2 * t_ipi)
          */
-        t_nfb = max(hctx->ccid3hctx_t_rto, 2 * hctx->ccid3hctx_t_ipi);
+        t_nfb = max(hctx->t_rto, 2 * hctx->t_ipi);
 
         ccid3_pr_debug("%s(%p), Scheduled no feedback timer to "
                        "expire in %lu jiffies (%luus)\n",
-                       dccp_role(sk),
-                       sk, usecs_to_jiffies(t_nfb), t_nfb);
+                       dccp_role(sk), sk, usecs_to_jiffies(t_nfb), t_nfb);
 
-        sk_reset_timer(sk, &hctx->ccid3hctx_no_feedback_timer,
+        sk_reset_timer(sk, &hctx->no_feedback_timer,
                            jiffies + usecs_to_jiffies(t_nfb));
 }
 
-static int ccid3_hc_tx_parse_options(struct sock *sk, unsigned char option,
-                                     unsigned char len, u16 idx,
-                                     unsigned char *value)
+static int ccid3_hc_tx_parse_options(struct sock *sk, u8 packet_type,
+                                     u8 option, u8 *optval, u8 optlen)
 {
-        int rc = 0;
-        const struct dccp_sock *dp = dccp_sk(sk);
         struct ccid3_hc_tx_sock *hctx = ccid3_hc_tx_sk(sk);
-        struct ccid3_options_received *opt_recv;
         __be32 opt_val;
 
-        opt_recv = &hctx->ccid3hctx_options_received;
-
-        if (opt_recv->ccid3or_seqno != dp->dccps_gsr) {
-                opt_recv->ccid3or_seqno              = dp->dccps_gsr;
-                opt_recv->ccid3or_loss_event_rate    = ~0;
-                opt_recv->ccid3or_loss_intervals_idx = 0;
-                opt_recv->ccid3or_loss_intervals_len = 0;
-                opt_recv->ccid3or_receive_rate       = 0;
-        }
-
         switch (option) {
+        case TFRC_OPT_RECEIVE_RATE:
         case TFRC_OPT_LOSS_EVENT_RATE:
-                if (unlikely(len != 4)) {
-                        DCCP_WARN("%s(%p), invalid len %d "
-                                  "for TFRC_OPT_LOSS_EVENT_RATE\n",
-                                  dccp_role(sk), sk, len);
-                        rc = -EINVAL;
-                } else {
-                        opt_val = get_unaligned((__be32 *)value);
-                        opt_recv->ccid3or_loss_event_rate = ntohl(opt_val);
-                        ccid3_pr_debug("%s(%p), LOSS_EVENT_RATE=%u\n",
-                                       dccp_role(sk), sk,
-                                       opt_recv->ccid3or_loss_event_rate);
+                /* Must be ignored on Data packets, cf. RFC 4342 8.3 and 8.5 */
+                if (packet_type == DCCP_PKT_DATA)
+                        break;
+                if (unlikely(optlen != 4)) {
+                        DCCP_WARN("%s(%p), invalid len %d for %u\n",
+                                  dccp_role(sk), sk, optlen, option);
+                        return -EINVAL;
                 }
-                break;
-        case TFRC_OPT_LOSS_INTERVALS:
-                opt_recv->ccid3or_loss_intervals_idx = idx;
-                opt_recv->ccid3or_loss_intervals_len = len;
-                ccid3_pr_debug("%s(%p), LOSS_INTERVALS=(%u, %u)\n",
-                               dccp_role(sk), sk,
-                               opt_recv->ccid3or_loss_intervals_idx,
-                               opt_recv->ccid3or_loss_intervals_len);
-                break;
-        case TFRC_OPT_RECEIVE_RATE:
-                if (unlikely(len != 4)) {
-                        DCCP_WARN("%s(%p), invalid len %d "
-                                  "for TFRC_OPT_RECEIVE_RATE\n",
-                                  dccp_role(sk), sk, len);
-                        rc = -EINVAL;
-                } else {
-                        opt_val = get_unaligned((__be32 *)value);
-                        opt_recv->ccid3or_receive_rate = ntohl(opt_val);
+                opt_val = ntohl(get_unaligned((__be32 *)optval));
+
+                if (option == TFRC_OPT_RECEIVE_RATE) {
+                        /* Receive Rate is kept in units of 64 bytes/second */
+                        hctx->x_recv = opt_val;
+                        hctx->x_recv <<= 6;
+
                         ccid3_pr_debug("%s(%p), RECEIVE_RATE=%u\n",
-                                       dccp_role(sk), sk,
-                                       opt_recv->ccid3or_receive_rate);
+                                       dccp_role(sk), sk, opt_val);
+                } else {
+                        /* Update the fixpoint Loss Event Rate fraction */
+                        hctx->p = tfrc_invert_loss_event_rate(opt_val);
+
+                        ccid3_pr_debug("%s(%p), LOSS_EVENT_RATE=%u\n",
+                                       dccp_role(sk), sk, opt_val);
                 }
-                break;
         }
-
-        return rc;
+        return 0;
 }
 
 static int ccid3_hc_tx_init(struct ccid *ccid, struct sock *sk)
 {
         struct ccid3_hc_tx_sock *hctx = ccid_priv(ccid);
 
-        hctx->ccid3hctx_state = TFRC_SSTATE_NO_SENT;
-        hctx->ccid3hctx_hist = NULL;
-        setup_timer(&hctx->ccid3hctx_no_feedback_timer,
-                        ccid3_hc_tx_no_feedback_timer, (unsigned long)sk);
-
+        hctx->hist  = NULL;
+        setup_timer(&hctx->no_feedback_timer,
+                    ccid3_hc_tx_no_feedback_timer, (unsigned long)sk);
         return 0;
 }
 
@@ -584,42 +520,36 @@ static void ccid3_hc_tx_exit(struct sock *sk)
 {
         struct ccid3_hc_tx_sock *hctx = ccid3_hc_tx_sk(sk);
 
-        ccid3_hc_tx_set_state(sk, TFRC_SSTATE_TERM);
-        sk_stop_timer(sk, &hctx->ccid3hctx_no_feedback_timer);
-
-        tfrc_tx_hist_purge(&hctx->ccid3hctx_hist);
+        sk_stop_timer(sk, &hctx->no_feedback_timer);
+        tfrc_tx_hist_purge(&hctx->hist);
 }
 
 static void ccid3_hc_tx_get_info(struct sock *sk, struct tcp_info *info)
 {
-        struct ccid3_hc_tx_sock *hctx;
-
-        /* Listen socks doesn't have a private CCID block */
-        if (sk->sk_state == DCCP_LISTEN)
-                return;
-
-        hctx = ccid3_hc_tx_sk(sk);
-        info->tcpi_rto = hctx->ccid3hctx_t_rto;
-        info->tcpi_rtt = hctx->ccid3hctx_rtt;
+        info->tcpi_rto = ccid3_hc_tx_sk(sk)->t_rto;
+        info->tcpi_rtt = ccid3_hc_tx_sk(sk)->rtt;
 }
 
 static int ccid3_hc_tx_getsockopt(struct sock *sk, const int optname, int len,
                                   u32 __user *optval, int __user *optlen)
 {
-        const struct ccid3_hc_tx_sock *hctx;
+        const struct ccid3_hc_tx_sock *hctx = ccid3_hc_tx_sk(sk);
+        struct tfrc_tx_info tfrc;
         const void *val;
 
-        /* Listen socks doesn't have a private CCID block */
-        if (sk->sk_state == DCCP_LISTEN)
-                return -EINVAL;
-
-        hctx = ccid3_hc_tx_sk(sk);
         switch (optname) {
         case DCCP_SOCKOPT_CCID_TX_INFO:
-                if (len < sizeof(hctx->ccid3hctx_tfrc))
+                if (len < sizeof(tfrc))
                         return -EINVAL;
-                len = sizeof(hctx->ccid3hctx_tfrc);
-                val = &hctx->ccid3hctx_tfrc;
+                tfrc.tfrctx_x      = hctx->x;
+                tfrc.tfrctx_x_recv = hctx->x_recv;
+                tfrc.tfrctx_x_calc = hctx->x_calc;
+                tfrc.tfrctx_rtt    = hctx->rtt;
+                tfrc.tfrctx_p      = hctx->p;
+                tfrc.tfrctx_rto    = hctx->t_rto;
+                tfrc.tfrctx_ipi    = hctx->t_ipi;
+                len = sizeof(tfrc);
+                val = &tfrc;
                 break;
         default:
                 return -ENOPROTOOPT;
@@ -634,112 +564,82 @@ static int ccid3_hc_tx_getsockopt(struct sock *sk, const int optname, int len,
 /*
  *      Receiver Half-Connection Routines
  */
-
-/* CCID3 feedback types */
-enum ccid3_fback_type {
-        CCID3_FBACK_NONE = 0,
-        CCID3_FBACK_INITIAL,
-        CCID3_FBACK_PERIODIC,
-        CCID3_FBACK_PARAM_CHANGE
-};
-
-#ifdef CONFIG_IP_DCCP_CCID3_DEBUG
-static const char *ccid3_rx_state_name(enum ccid3_hc_rx_states state)
-{
-        static char *ccid3_rx_state_names[] = {
-        [TFRC_RSTATE_NO_DATA] = "NO_DATA",
-        [TFRC_RSTATE_DATA]    = "DATA",
-        [TFRC_RSTATE_TERM]    = "TERM",
-        };
-
-        return ccid3_rx_state_names[state];
-}
-#endif
-
-static void ccid3_hc_rx_set_state(struct sock *sk,
-                                  enum ccid3_hc_rx_states state)
-{
-        struct ccid3_hc_rx_sock *hcrx = ccid3_hc_rx_sk(sk);
-        enum ccid3_hc_rx_states oldstate = hcrx->ccid3hcrx_state;
-
-        ccid3_pr_debug("%s(%p) %-8.8s -> %s\n",
-                       dccp_role(sk), sk, ccid3_rx_state_name(oldstate),
-                       ccid3_rx_state_name(state));
-        WARN_ON(state == oldstate);
-        hcrx->ccid3hcrx_state = state;
-}
-
 static void ccid3_hc_rx_send_feedback(struct sock *sk,
                                       const struct sk_buff *skb,
                                       enum ccid3_fback_type fbtype)
 {
         struct ccid3_hc_rx_sock *hcrx = ccid3_hc_rx_sk(sk);
-        struct dccp_sock *dp = dccp_sk(sk);
-        ktime_t now;
-        s64 delta = 0;
-
-        if (unlikely(hcrx->ccid3hcrx_state == TFRC_RSTATE_TERM))
-                return;
-
-        now = ktime_get_real();
 
         switch (fbtype) {
         case CCID3_FBACK_INITIAL:
-                hcrx->ccid3hcrx_x_recv = 0;
-                hcrx->ccid3hcrx_pinv   = ~0U;   /* see RFC 4342, 8.5 */
+                hcrx->x_recv = 0;
+                hcrx->p_inverse = ~0U;   /* see RFC 4342, 8.5 */
                 break;
         case CCID3_FBACK_PARAM_CHANGE:
+                if (unlikely(hcrx->feedback == CCID3_FBACK_NONE)) {
+                        /*
+                         * rfc3448bis-06, 6.3.1: First packet(s) lost or marked
+                         * FIXME: in rfc3448bis the receiver returns X_recv=0
+                         * here as it normally would in the first feedback packet.
+                         * However this is not possible yet, since the code still
+                         * uses RFC 3448, i.e.
+                         *    If (p > 0)
+                         *      Calculate X_calc using the TCP throughput equation.
+                         *      X = max(min(X_calc, 2*X_recv), s/t_mbi);
+                         * would bring X down to s/t_mbi. That is why we return
+                         * X_recv according to rfc3448bis-06 for the moment.
+                         */
+                        u32 s = tfrc_rx_hist_packet_size(&hcrx->hist),
+                            rtt = tfrc_rx_hist_rtt(&hcrx->hist);
+
+                        hcrx->x_recv = scaled_div32(s, 2 * rtt);
+                        break;
+                }
                 /*
                  * When parameters change (new loss or p > p_prev), we do not
                  * have a reliable estimate for R_m of [RFC 3448, 6.2] and so
-                 * need to  reuse the previous value of X_recv. However, when
-                 * X_recv was 0 (due to early loss), this would kill X down to
-                 * s/t_mbi (i.e. one packet in 64 seconds).
-                 * To avoid such drastic reduction, we approximate X_recv as
-                 * the number of bytes since last feedback.
-                 * This is a safe fallback, since X is bounded above by X_calc.
+                 * always check whether at least RTT time units were covered.
                  */
-                if (hcrx->ccid3hcrx_x_recv > 0)
-                        break;
-                /* fall through */
+                hcrx->x_recv = tfrc_rx_hist_x_recv(&hcrx->hist, hcrx->x_recv);
+                break;
         case CCID3_FBACK_PERIODIC:
-                delta = ktime_us_delta(now, hcrx->ccid3hcrx_tstamp_last_feedback);
-                if (delta <= 0)
-                        DCCP_BUG("delta (%ld) <= 0", (long)delta);
-                else
-                        hcrx->ccid3hcrx_x_recv =
-                                scaled_div32(hcrx->ccid3hcrx_bytes_recv, delta);
+                /*
+                 * Step (2) of rfc3448bis-06, 6.2:
+                 * - if no data packets have been received, just restart timer
+                 * - if data packets have been received, re-compute X_recv
+                 */
+                if (hcrx->hist.bytes_recvd == 0)
+                        goto prepare_for_next_time;
+                hcrx->x_recv = tfrc_rx_hist_x_recv(&hcrx->hist, hcrx->x_recv);
                 break;
         default:
                 return;
         }
 
-        ccid3_pr_debug("Interval %ldusec, X_recv=%u, 1/p=%u\n", (long)delta,
-                       hcrx->ccid3hcrx_x_recv, hcrx->ccid3hcrx_pinv);
-
-        hcrx->ccid3hcrx_tstamp_last_feedback = now;
-        hcrx->ccid3hcrx_last_counter         = dccp_hdr(skb)->dccph_ccval;
-        hcrx->ccid3hcrx_bytes_recv           = 0;
+        ccid3_pr_debug("X_recv=%u, 1/p=%u\n", hcrx->x_recv, hcrx->p_inverse);
 
-        dp->dccps_hc_rx_insert_options = 1;
+        dccp_sk(sk)->dccps_hc_rx_insert_options = 1;
         dccp_send_ack(sk);
+
+prepare_for_next_time:
+        tfrc_rx_hist_restart_byte_counter(&hcrx->hist);
+        hcrx->last_counter = dccp_hdr(skb)->dccph_ccval;
+        hcrx->feedback     = fbtype;
 }
 
 static int ccid3_hc_rx_insert_options(struct sock *sk, struct sk_buff *skb)
 {
-        const struct ccid3_hc_rx_sock *hcrx;
+        const struct ccid3_hc_rx_sock *hcrx = ccid3_hc_rx_sk(sk);
         __be32 x_recv, pinv;
 
         if (!(sk->sk_state == DCCP_OPEN || sk->sk_state == DCCP_PARTOPEN))
                 return 0;
 
-        hcrx = ccid3_hc_rx_sk(sk);
-
         if (dccp_packet_without_ack(skb))
                 return 0;
 
-        x_recv = htonl(hcrx->ccid3hcrx_x_recv);
-        pinv   = htonl(hcrx->ccid3hcrx_pinv);
+        x_recv = htonl(hcrx->x_recv);
+        pinv   = htonl(hcrx->p_inverse);
 
         if (dccp_insert_option(sk, skb, TFRC_OPT_LOSS_EVENT_RATE,
                                &pinv, sizeof(pinv)) ||
@@ -762,171 +662,95 @@ static int ccid3_hc_rx_insert_options(struct sock *sk, struct sk_buff *skb)
 static u32 ccid3_first_li(struct sock *sk)
 {
         struct ccid3_hc_rx_sock *hcrx = ccid3_hc_rx_sk(sk);
-        u32 x_recv, p, delta;
+        u32 s = tfrc_rx_hist_packet_size(&hcrx->hist),
+            rtt = tfrc_rx_hist_rtt(&hcrx->hist), x_recv, p;
         u64 fval;
 
-        if (hcrx->ccid3hcrx_rtt == 0) {
-                DCCP_WARN("No RTT estimate available, using fallback RTT\n");
-                hcrx->ccid3hcrx_rtt = DCCP_FALLBACK_RTT;
-        }
+        /*
+         * rfc3448bis-06, 6.3.1: First data packet(s) are marked or lost. Set p
+         * to give the equivalent of X_target = s/(2*R). Thus fval = 2 and so p
+         * is about 20.64%. This yields an interval length of 4.84 (rounded up).
+         */
+        if (unlikely(hcrx->feedback == CCID3_FBACK_NONE))
+                return 5;
 
-        delta = ktime_to_us(net_timedelta(hcrx->ccid3hcrx_tstamp_last_feedback));
-        x_recv = scaled_div32(hcrx->ccid3hcrx_bytes_recv, delta);
-        if (x_recv == 0) {              /* would also trigger divide-by-zero */
-                DCCP_WARN("X_recv==0\n");
-                if ((x_recv = hcrx->ccid3hcrx_x_recv) == 0) {
-                        DCCP_BUG("stored value of X_recv is zero");
-                        return ~0U;
-                }
-        }
+        x_recv = tfrc_rx_hist_x_recv(&hcrx->hist, hcrx->x_recv);
+        if (x_recv == 0)
+                goto failed;
 
-        fval = scaled_div(hcrx->ccid3hcrx_s, hcrx->ccid3hcrx_rtt);
-        fval = scaled_div32(fval, x_recv);
+        fval = scaled_div32(scaled_div(s, rtt), x_recv);
         p = tfrc_calc_x_reverse_lookup(fval);
 
         ccid3_pr_debug("%s(%p), receive rate=%u bytes/s, implied "
                        "loss rate=%u\n", dccp_role(sk), sk, x_recv, p);
 
-        return p == 0 ? ~0U : scaled_div(1, p);
+        if (p > 0)
+                return scaled_div(1, p);
+failed:
+        return UINT_MAX;
 }
 
 static void ccid3_hc_rx_packet_recv(struct sock *sk, struct sk_buff *skb)
 {
         struct ccid3_hc_rx_sock *hcrx = ccid3_hc_rx_sk(sk);
-        enum ccid3_fback_type do_feedback = CCID3_FBACK_NONE;
         const u64 ndp = dccp_sk(sk)->dccps_options_received.dccpor_ndp;
         const bool is_data_packet = dccp_data_packet(skb);
 
-        if (unlikely(hcrx->ccid3hcrx_state == TFRC_RSTATE_NO_DATA)) {
-                if (is_data_packet) {
-                        const u32 payload = skb->len - dccp_hdr(skb)->dccph_doff * 4;
-                        do_feedback = CCID3_FBACK_INITIAL;
-                        ccid3_hc_rx_set_state(sk, TFRC_RSTATE_DATA);
-                        hcrx->ccid3hcrx_s = payload;
-                        /*
-                         * Not necessary to update ccid3hcrx_bytes_recv here,
-                         * since X_recv = 0 for the first feedback packet (cf.
-                         * RFC 3448, 6.3) -- gerrit
-                         */
-                }
-                goto update_records;
-        }
-
-        if (tfrc_rx_hist_duplicate(&hcrx->ccid3hcrx_hist, skb))
-                return; /* done receiving */
-
-        if (is_data_packet) {
-                const u32 payload = skb->len - dccp_hdr(skb)->dccph_doff * 4;
-                /*
-                 * Update moving-average of s and the sum of received payload bytes
-                 */
-                hcrx->ccid3hcrx_s = tfrc_ewma(hcrx->ccid3hcrx_s, payload, 9);
-                hcrx->ccid3hcrx_bytes_recv += payload;
-        }
-
         /*
          * Perform loss detection and handle pending losses
          */
-        if (tfrc_rx_handle_loss(&hcrx->ccid3hcrx_hist, &hcrx->ccid3hcrx_li_hist,
-                                skb, ndp, ccid3_first_li, sk)) {
-                do_feedback = CCID3_FBACK_PARAM_CHANGE;
-                goto done_receiving;
-        }
-
-        if (tfrc_rx_hist_loss_pending(&hcrx->ccid3hcrx_hist))
-                return; /* done receiving */
-
+        if (tfrc_rx_congestion_event(&hcrx->hist, &hcrx->li_hist,
+                                     skb, ndp, ccid3_first_li, sk))
+                ccid3_hc_rx_send_feedback(sk, skb, CCID3_FBACK_PARAM_CHANGE);
         /*
-         * Handle data packets: RTT sampling and monitoring p
+         * Feedback for first non-empty data packet (RFC 3448, 6.3)
          */
-        if (unlikely(!is_data_packet))
-                goto update_records;
-
-        if (!tfrc_lh_is_initialised(&hcrx->ccid3hcrx_li_hist)) {
-                const u32 sample = tfrc_rx_hist_sample_rtt(&hcrx->ccid3hcrx_hist, skb);
-                /*
-                 * Empty loss history: no loss so far, hence p stays 0.
-                 * Sample RTT values, since an RTT estimate is required for the
-                 * computation of p when the first loss occurs; RFC 3448, 6.3.1.
-                 */
-                if (sample != 0)
-                        hcrx->ccid3hcrx_rtt = tfrc_ewma(hcrx->ccid3hcrx_rtt, sample, 9);
-
-        } else if (tfrc_lh_update_i_mean(&hcrx->ccid3hcrx_li_hist, skb)) {
-                /*
-                 * Step (3) of [RFC 3448, 6.1]: Recompute I_mean and, if I_mean
-                 * has decreased (resp. p has increased), send feedback now.
-                 */
-                do_feedback = CCID3_FBACK_PARAM_CHANGE;
-        }
-
+        else if (unlikely(hcrx->feedback == CCID3_FBACK_NONE && is_data_packet))
+                ccid3_hc_rx_send_feedback(sk, skb, CCID3_FBACK_INITIAL);
         /*
          * Check if the periodic once-per-RTT feedback is due; RFC 4342, 10.3
          */
-        if (SUB16(dccp_hdr(skb)->dccph_ccval, hcrx->ccid3hcrx_last_counter) > 3)
-                do_feedback = CCID3_FBACK_PERIODIC;
-
-update_records:
-        tfrc_rx_hist_add_packet(&hcrx->ccid3hcrx_hist, skb, ndp);
-
-done_receiving:
-        if (do_feedback)
-                ccid3_hc_rx_send_feedback(sk, skb, do_feedback);
+        else if (!tfrc_rx_hist_loss_pending(&hcrx->hist) && is_data_packet &&
+                 SUB16(dccp_hdr(skb)->dccph_ccval, hcrx->last_counter) > 3)
+                ccid3_hc_rx_send_feedback(sk, skb, CCID3_FBACK_PERIODIC);
 }
 
 static int ccid3_hc_rx_init(struct ccid *ccid, struct sock *sk)
 {
         struct ccid3_hc_rx_sock *hcrx = ccid_priv(ccid);
 
-        hcrx->ccid3hcrx_state = TFRC_RSTATE_NO_DATA;
-        tfrc_lh_init(&hcrx->ccid3hcrx_li_hist);
-        return tfrc_rx_hist_alloc(&hcrx->ccid3hcrx_hist);
+        tfrc_lh_init(&hcrx->li_hist);
+        return tfrc_rx_hist_init(&hcrx->hist, sk);
 }
 
 static void ccid3_hc_rx_exit(struct sock *sk)
 {
         struct ccid3_hc_rx_sock *hcrx = ccid3_hc_rx_sk(sk);
 
-        ccid3_hc_rx_set_state(sk, TFRC_RSTATE_TERM);
-
-        tfrc_rx_hist_purge(&hcrx->ccid3hcrx_hist);
-        tfrc_lh_cleanup(&hcrx->ccid3hcrx_li_hist);
+        tfrc_rx_hist_purge(&hcrx->hist);
+        tfrc_lh_cleanup(&hcrx->li_hist);
 }
 
 static void ccid3_hc_rx_get_info(struct sock *sk, struct tcp_info *info)
 {
-        const struct ccid3_hc_rx_sock *hcrx;
-
-        /* Listen socks doesn't have a private CCID block */
-        if (sk->sk_state == DCCP_LISTEN)
-                return;
-
-        hcrx = ccid3_hc_rx_sk(sk);
-        info->tcpi_ca_state = hcrx->ccid3hcrx_state;
         info->tcpi_options  |= TCPI_OPT_TIMESTAMPS;
-        info->tcpi_rcv_rtt  = hcrx->ccid3hcrx_rtt;
+        info->tcpi_rcv_rtt  = tfrc_rx_hist_rtt(&ccid3_hc_rx_sk(sk)->hist);
 }
 
 static int ccid3_hc_rx_getsockopt(struct sock *sk, const int optname, int len,
                                   u32 __user *optval, int __user *optlen)
 {
-        const struct ccid3_hc_rx_sock *hcrx;
+        const struct ccid3_hc_rx_sock *hcrx = ccid3_hc_rx_sk(sk);
         struct tfrc_rx_info rx_info;
         const void *val;
 
-        /* Listen socks doesn't have a private CCID block */
-        if (sk->sk_state == DCCP_LISTEN)
-                return -EINVAL;
-
-        hcrx = ccid3_hc_rx_sk(sk);
         switch (optname) {
         case DCCP_SOCKOPT_CCID_RX_INFO:
                 if (len < sizeof(rx_info))
                         return -EINVAL;
-                rx_info.tfrcrx_x_recv = hcrx->ccid3hcrx_x_recv;
-                rx_info.tfrcrx_rtt    = hcrx->ccid3hcrx_rtt;
-                rx_info.tfrcrx_p      = hcrx->ccid3hcrx_pinv == 0 ? ~0U :
-                                           scaled_div(1, hcrx->ccid3hcrx_pinv);
+                rx_info.tfrcrx_x_recv = hcrx->x_recv;
+                rx_info.tfrcrx_rtt    = tfrc_rx_hist_rtt(&hcrx->hist);
+                rx_info.tfrcrx_p      = tfrc_invert_loss_event_rate(hcrx->p_inverse);
                 len = sizeof(rx_info);
                 val = &rx_info;
                 break;
@@ -962,6 +786,9 @@ static struct ccid_operations ccid3 = {
         .ccid_hc_tx_getsockopt     = ccid3_hc_tx_getsockopt,
 };
 
+module_param(do_osc_prev, bool, 0644);
+MODULE_PARM_DESC(do_osc_prev, "Use Oscillation Prevention (RFC 3448, 4.5)");
+
 #ifdef CONFIG_IP_DCCP_CCID3_DEBUG
 module_param(ccid3_debug, bool, 0644);
 MODULE_PARM_DESC(ccid3_debug, "Enable debug messages");
@@ -969,6 +796,19 @@ MODULE_PARM_DESC(ccid3_debug, "Enable debug messages");
 
 static __init int ccid3_module_init(void)
 {
+        struct timespec tp;
+
+        /*
+         * Without a fine-grained clock resolution, RTTs/X_recv are not sampled
+         * correctly and feedback is sent either too early or too late.
+         */
+        hrtimer_get_res(CLOCK_MONOTONIC, &tp);
+        if (tp.tv_sec || tp.tv_nsec > DCCP_TIME_RESOLUTION * NSEC_PER_USEC) {
+                printk(KERN_ERR "%s: Timer too coarse (%ld usec), need %u-usec"
+                       " resolution - check your clocksource.\n", __func__,
+                       tp.tv_nsec/NSEC_PER_USEC, DCCP_TIME_RESOLUTION);
+                return -ESOCKTNOSUPPORT;
+        }
         return ccid_register(&ccid3);
 }
 module_init(ccid3_module_init);