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>

2 files changed, 4 insertions, 21 deletions

diff --git a/net/dccp/ccids/ccid2.c b/net/dccp/ccids/ccid2.c
index 8c95813bcc67..b9c942a09c98 100644
--- 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 e663b78a2ef6..1bc87a05c734 100644
--- 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);
 }