1 files changed, 29 insertions, 0 deletions

diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index 8353a538cd4c..8816a20c2597 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -132,6 +132,35 @@ static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
         }
 }
 
+/* This function calculates a "timeout" which is equivalent to the timeout of a
+ * TCP connection after "boundary" unsucessful, exponentially backed-off
+ * retransmissions with an initial RTO of TCP_RTO_MIN.
+ */
+static bool retransmits_timed_out(struct sock *sk,
+                                  unsigned int boundary)
+{
+        unsigned int timeout, linear_backoff_thresh;
+        unsigned int start_ts;
+
+        if (!inet_csk(sk)->icsk_retransmits)
+                return false;
+
+        if (unlikely(!tcp_sk(sk)->retrans_stamp))
+                start_ts = TCP_SKB_CB(tcp_write_queue_head(sk))->when;
+        else
+                start_ts = tcp_sk(sk)->retrans_stamp;
+
+        linear_backoff_thresh = ilog2(TCP_RTO_MAX/TCP_RTO_MIN);
+
+        if (boundary <= linear_backoff_thresh)
+                timeout = ((2 << boundary) - 1) * TCP_RTO_MIN;
+        else
+                timeout = ((2 << linear_backoff_thresh) - 1) * TCP_RTO_MIN +
+                          (boundary - linear_backoff_thresh) * TCP_RTO_MAX;
+
+        return (tcp_time_stamp - start_ts) >= timeout;
+}
+
 /* A write timeout has occurred. Process the after effects. */
 static int tcp_write_timeout(struct sock *sk)
 {