- Add a new function tcp_twrecycleable, which tells us if the ISN which

we will generate for a given ip/port tuple has advanced far enough
for the time_wait socket in question to be safely recycled.

- Have in_pcblookup_local use tcp_twrecycleable to determine if
time_Wait sockets which are hogging local ports can be safely
freed.

This change preserves proper TIME_WAIT behavior under normal
circumstances while allowing for safe and fast recycling whenever
ephemeral port space is scarce.

1 files changed, 19 insertions, 0 deletions

diff --git a/sys/netinet/tcp_subr.c b/sys/netinet/tcp_subr.c
index d2a28c8..d77ab59 100644
--- a/sys/netinet/tcp_subr.c
+++ b/sys/netinet/tcp_subr.c
@@ -1637,6 +1637,7 @@ tcp_twstart(tp)
 
 	tw->snd_nxt = tp->snd_nxt;
 	tw->rcv_nxt = tp->rcv_nxt;
+	tw->iss     = tp->iss;
 	tw->cc_recv = tp->cc_recv;
 	tw->cc_send = tp->cc_send;
 	tw->t_starttime = tp->t_starttime;
@@ -1671,6 +1672,24 @@ tcp_twstart(tp)
 	INP_UNLOCK(inp);
 }
 
+/*
+ * Determine if the ISN we will generate has advanced beyond the last
+ * sequence number used by the previous connection.  If so, indicate
+ * that it is safe to recycle this tw socket by returning 1.
+ */
+int
+tcp_twrecycleable(struct tcptw *tw)
+{
+	tcp_seq new_isn = tw->iss;
+
+	new_isn += (ticks - tw->t_starttime) * (ISN_BYTES_PER_SECOND / hz);
+	
+	if (SEQ_GT(new_isn, tw->snd_nxt))
+		return 1;
+	else
+		return 0;
+}
+
 struct tcptw *
 tcp_twclose(struct tcptw *tw, int reuse)
 {