1 files changed, 32 insertions, 0 deletions
diff --git a/net/ipv4/tcp_recovery.c b/net/ipv4/tcp_recovery.c
new file mode 100644
index 000000000000..8f66a6584845
--- /dev/null
+++ b/net/ipv4/tcp_recovery.c
@@ -0,0 +1,32 @@
+#include <linux/tcp.h>
+#include <net/tcp.h>
+
+/* Record the most recently (re)sent time among the (s)acked packets */
+void tcp_rack_advance(struct tcp_sock *tp,
+		      const struct skb_mstamp *xmit_time, u8 sacked)
+{
+	if (tp->rack.mstamp.v64 &&
+	    !skb_mstamp_after(xmit_time, &tp->rack.mstamp))
+		return;
+
+	if (sacked & TCPCB_RETRANS) {
+		struct skb_mstamp now;
+
+		/* If the sacked packet was retransmitted, it's ambiguous
+		 * whether the retransmission or the original (or the prior
+		 * retransmission) was sacked.
+		 *
+		 * If the original is lost, there is no ambiguity. Otherwise
+		 * we assume the original can be delayed up to aRTT + min_rtt.
+		 * the aRTT term is bounded by the fast recovery or timeout,
+		 * so it's at least one RTT (i.e., retransmission is at least
+		 * an RTT later).
+		 */
+		skb_mstamp_get(&now);
+		if (skb_mstamp_us_delta(&now, xmit_time) < tcp_min_rtt(tp))
+			return;
+	}
+
+	tp->rack.mstamp = *xmit_time;
+	tp->rack.advanced = 1;
+}