dccp tfrc: Let dccp_tfrc_lib do the sampling work

This migrates more TFRC-related code into the dccp_tfrc_lib:
 * sampling of the packet size `s' (which is only needed until the first
   loss interval is computed (ccid3_first_li));
 * updating the byte-counter `bytes_recvd' in between sending feedbacks.
The result is a better separation of CCID-3 specific and TFRC specific
code, which aids future integration with ECN and e.g. CCID-4.

Further changes:
----------------
 * replaced magic number of 536 with equivalent constant TCP_MIN_RCVMSS;
   (this constant is also used when no estimate for `s' is available).

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>

5 files changed, 35 insertions, 35 deletions

diff --git a/net/dccp/ccids/ccid3.c b/net/dccp/ccids/ccid3.c
index 50dac01e48c5..8744590acb34 100644
--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -590,12 +590,9 @@ static void ccid3_hc_rx_send_feedback(struct sock *sk,
                          * would bring X down to s/t_mbi. That is why we return
                          * X_recv according to rfc3448bis-06 for the moment.
                          */
-                        u32 rtt = hcrx->rtt ? : DCCP_FALLBACK_RTT, s = hcrx->s;
+                        u32 rtt = hcrx->rtt ? : DCCP_FALLBACK_RTT,
+                            s   = tfrc_rx_hist_packet_size(&hcrx->hist);
 
-                        if (s == 0) {
-                                DCCP_WARN("No sample for s, using fallback\n");
-                                s = TCP_MIN_RCVMSS;
-                        }
                         hcrx->x_recv = scaled_div32(s, 2 * rtt);
                         break;
                 }
@@ -617,7 +614,7 @@ static void ccid3_hc_rx_send_feedback(struct sock *sk,
                 if (delta <= 0)
                         DCCP_BUG("delta (%ld) <= 0", (long)delta);
                 else
-                        hcrx->x_recv = scaled_div32(hcrx->bytes_recv, delta);
+                        hcrx->x_recv = scaled_div32(hcrx->hist.bytes_recvd, delta);
                 break;
         default:
                 return;
@@ -628,7 +625,7 @@ static void ccid3_hc_rx_send_feedback(struct sock *sk,
 
         hcrx->tstamp_last_feedback = now;
         hcrx->last_counter         = dccp_hdr(skb)->dccph_ccval;
-        hcrx->bytes_recv           = 0;
+        hcrx->hist.bytes_recvd     = 0;
 
         dp->dccps_hc_rx_insert_options = 1;
         dccp_send_ack(sk);
@@ -669,7 +666,8 @@ 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 x_recv, p, delta,
+            s = tfrc_rx_hist_packet_size(&hcrx->hist);
         u64 fval;
 
         /*
@@ -686,7 +684,7 @@ static u32 ccid3_first_li(struct sock *sk)
         }
 
         delta = ktime_to_us(net_timedelta(hcrx->tstamp_last_feedback));
-        x_recv = scaled_div32(hcrx->bytes_recv, delta);
+        x_recv = scaled_div32(hcrx->hist.bytes_recvd, delta);
         if (x_recv == 0) {              /* would also trigger divide-by-zero */
                 DCCP_WARN("X_recv==0\n");
                 if (hcrx->x_recv == 0) {
@@ -696,8 +694,7 @@ static u32 ccid3_first_li(struct sock *sk)
                 x_recv = hcrx->x_recv;
         }
 
-        fval = scaled_div(hcrx->s, hcrx->rtt);
-        fval = scaled_div32(fval, x_recv);
+        fval = scaled_div32(scaled_div(s, hcrx->rtt), x_recv);
         p = tfrc_calc_x_reverse_lookup(fval);
 
         ccid3_pr_debug("%s(%p), receive rate=%u bytes/s, implied "
@@ -724,31 +721,12 @@ static void ccid3_hc_rx_packet_recv(struct sock *sk, struct sk_buff *skb)
 
         if (unlikely(hcrx->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->s = payload;
-                        /*
-                         * Not necessary to update 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->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->s = tfrc_ewma(hcrx->s, payload, 9);
-                hcrx->bytes_recv += payload;
-        }
-
         if (tfrc_rx_hist_loss_pending(&hcrx->hist))
                 return; /* done receiving */
 
diff --git a/net/dccp/ccids/ccid3.h b/net/dccp/ccids/ccid3.h
index 1773a8dd36d8..0c4fadd85f94 100644
--- a/net/dccp/ccids/ccid3.h
+++ b/net/dccp/ccids/ccid3.h
@@ -124,25 +124,21 @@ enum ccid3_hc_rx_states {
  *
  *  @last_counter  -  Tracks window counter (RFC 4342, 8.1)
  *  @state  -  Receiver state, one of %ccid3_hc_rx_states
- *  @bytes_recv  -  Total sum of DCCP payload bytes
  *  @x_recv  -  Receiver estimate of send rate (RFC 3448, sec. 4.3)
  *  @rtt  -  Receiver estimate of RTT
  *  @tstamp_last_feedback  -  Time at which last feedback was sent
  *  @hist  -  Packet history (loss detection + RTT sampling)
  *  @li_hist  -  Loss Interval database
- *  @s  -  Received packet size in bytes
  *  @p_inverse  -  Inverse of Loss Event Rate (RFC 4342, sec. 8.5)
  */
 struct ccid3_hc_rx_sock {
         u8                              last_counter:4;
         enum ccid3_hc_rx_states         state:8;
-        u32                             bytes_recv;
         u32                             x_recv;
         u32                             rtt;
         ktime_t                         tstamp_last_feedback;
         struct tfrc_rx_hist             hist;
         struct tfrc_loss_hist           li_hist;
-        u16                             s;
 #define p_inverse                       li_hist.i_mean
 };
 
diff --git a/net/dccp/ccids/lib/packet_history.c b/net/dccp/ccids/lib/packet_history.c
index 8ea96903033d..ee34b4564242 100644
--- a/net/dccp/ccids/lib/packet_history.c
+++ b/net/dccp/ccids/lib/packet_history.c
@@ -352,6 +352,16 @@ int tfrc_rx_handle_loss(struct tfrc_rx_hist *h,
                 __three_after_loss(h);
         }
 
+        /*
+         * Update moving-average of `s' and the sum of received payload bytes.
+         */
+        if (dccp_data_packet(skb)) {
+                const u32 payload = skb->len - dccp_hdr(skb)->dccph_doff * 4;
+
+                h->packet_size = tfrc_ewma(h->packet_size, payload, 9);
+                h->bytes_recvd += payload;
+        }
+
         /* RFC 3448, 6.1: update I_0, whose growth implies p <= p_prev */
         if (!is_new_loss)
                 tfrc_lh_update_i_mean(lh, skb);
diff --git a/net/dccp/ccids/lib/packet_history.h b/net/dccp/ccids/lib/packet_history.h
index e9d8097947d5..b7c87a1a2720 100644
--- a/net/dccp/ccids/lib/packet_history.h
+++ b/net/dccp/ccids/lib/packet_history.h
@@ -91,12 +91,16 @@ struct tfrc_rx_hist_entry {
  * @loss_count:         Number of entries in circular history
  * @loss_start:         Movable index (for loss detection)
  * @rtt_sample_prev:    Used during RTT sampling, points to candidate entry
+ * @packet_size:        Packet size in bytes (as per RFC 3448, 3.1)
+ * @bytes_recvd:        Number of bytes received since last sending feedback
  */
 struct tfrc_rx_hist {
         struct tfrc_rx_hist_entry *ring[TFRC_NDUPACK + 1];
         u8                        loss_count:2,
                                   loss_start:2;
 #define rtt_sample_prev           loss_start
+        u32                       packet_size,
+                                  bytes_recvd;
 };
 
 /**
@@ -140,6 +144,18 @@ static inline bool tfrc_rx_hist_loss_pending(const struct tfrc_rx_hist *h)
         return h->loss_count > 0;
 }
 
+/*
+ * Accessor functions to retrieve parameters sampled by the RX history
+ */
+static inline u32 tfrc_rx_hist_packet_size(const struct tfrc_rx_hist *h)
+{
+        if (h->packet_size == 0) {
+                DCCP_WARN("No sample for s, using fallback\n");
+                return TCP_MIN_RCVMSS;
+        }
+        return h->packet_size;
+}
+
 extern void tfrc_rx_hist_add_packet(struct tfrc_rx_hist *h,
                                     const struct sk_buff *skb, const u64 ndp);
 
diff --git a/net/dccp/proto.c b/net/dccp/proto.c
index a3caa11aa836..ecf3be961e11 100644
--- a/net/dccp/proto.c
+++ b/net/dccp/proto.c
@@ -185,7 +185,7 @@ int dccp_init_sock(struct sock *sk, const __u8 ctl_sock_initialized)
         sk->sk_state            = DCCP_CLOSED;
         sk->sk_write_space      = dccp_write_space;
         icsk->icsk_sync_mss     = dccp_sync_mss;
-        dp->dccps_mss_cache     = 536;
+        dp->dccps_mss_cache     = TCP_MIN_RCVMSS;
         dp->dccps_rate_last     = jiffies;
         dp->dccps_role          = DCCP_ROLE_UNDEFINED;
         dp->dccps_service       = DCCP_SERVICE_CODE_IS_ABSENT;