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>

2 files changed, 26 insertions, 0 deletions

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);