1 files changed, 15 insertions, 0 deletions

diff --git a/include/net/tcp.h b/include/net/tcp.h
index df6a2eb20193..a64022199b62 100644
--- 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);