tcp/dccp: Consolidate common code for RFC 3390 conversion

This patch consolidates initial-window code common to TCP and CCID-2:
 * TCP uses RFC 3390 in a packet-oriented manner (tcp_input.c) and
 * CCID-2 uses RFC 3390 in packet-oriented manner (RFC 4341).

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/net/tcp.h b/include/net/tcp.h
index df6a2eb20193f935bc72204ca22c7f2f21b5070f..a64022199b622fca576d7c10378254e28843b799 100644 (file)
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -779,6 +779,21 @@ static inline __u32 tcp_current_ssthresh(const struct sock *sk)
 /* Use define here intentionally to get WARN_ON location shown at the caller */
 #define tcp_verify_left_out(tp)        WARN_ON(tcp_left_out(tp) > tp->packets_out)
 
+/*
+ * Convert RFC 3390 larger initial window into an equivalent number of packets.
+ *
+ * John Heffner states:
+ *
+ *     The RFC specifies a window of no more than 4380 bytes
+ *     unless 2*MSS > 4380.  Reading the pseudocode in the RFC
+ *     is a bit misleading because they use a clamp at 4380 bytes
+ *     rather than a multiplier in the relevant range.
+ */
+static inline u32 rfc3390_bytes_to_packets(const u32 smss)
+{
+       return smss <= 1095 ? 4 : (smss > 1460 ? 2 : 3);
+}
+
 extern void tcp_enter_cwr(struct sock *sk, const int set_ssthresh);
 extern __u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst);
 

diff --git a/net/dccp/ccids/ccid2.c b/net/dccp/ccids/ccid2.c
index 8c95813bcc6795a89f23e4fcbba1a315421b51e4..b9c942a09c9825bf2a2a57e3fbb9f4a0a75382f2 100644 (file)
--- a/net/dccp/ccids/ccid2.c
+++ b/net/dccp/ccids/ccid2.c
@@ -641,12 +641,8 @@ static int ccid2_hc_tx_init(struct ccid *ccid, struct sock *sk)
        /* RFC 4341, 5: initialise ssthresh to arbitrarily high (max) value */
        hc->tx_ssthresh = ~0U;
 
-       /*
-        * RFC 4341, 5: "The cwnd parameter is initialized to at most four
-        * packets for new connections, following the rules from [RFC3390]".
-        * We need to convert the bytes of RFC3390 into the packets of RFC 4341.
-        */
-       hc->tx_cwnd = clamp(4380U / dp->dccps_mss_cache, 2U, 4U);
+       /* Use larger initial windows (RFC 4341, section 5). */
+       hc->tx_cwnd = rfc3390_bytes_to_packets(dp->dccps_mss_cache);
 
        /* Make sure that Ack Ratio is enabled and within bounds. */
        max_ratio = DIV_ROUND_UP(hc->tx_cwnd, 2);

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index e663b78a2ef6b6286b549aa65b418fe385f32184..1bc87a05c734e535e605fe388676816947bf3182 100644 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -805,25 +805,12 @@ void tcp_update_metrics(struct sock *sk)
        }
 }
 
-/* Numbers are taken from RFC3390.
- *
- * John Heffner states:
- *
- *     The RFC specifies a window of no more than 4380 bytes
- *     unless 2*MSS > 4380.  Reading the pseudocode in the RFC
- *     is a bit misleading because they use a clamp at 4380 bytes
- *     rather than use a multiplier in the relevant range.
- */
 __u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst)
 {
        __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
 
-       if (!cwnd) {
-               if (tp->mss_cache > 1460)
-                       cwnd = 2;
-               else
-                       cwnd = (tp->mss_cache > 1095) ? 3 : 4;
-       }
+       if (!cwnd)
+               cwnd = rfc3390_bytes_to_packets(tp->mss_cache);
        return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
 }