[PATCH 1/4] tcp: Remove non-working activity timeout mechanism

[David Gibson <david@gibson.dropbear.id.au>]

This mechanism was intended to remove connections which have had no
activity for two hours, even if they haven't closed or been reset
internally.  It operated by setting the two hour timeout if there are
no sooner TCP timeouts to schedule.

However, when the timer fires, the way we detect the case of the activity
timeout doesn't work: it resets the timer for another two hours, then
checks if the old timeout was two hours.  But the old timeout returned
by timerfd_settime() is not the original value of the timer, but the
remaining time.  Since the timer has just fired it will essentially always
be 0.

For now, just remove the mechanism, disarming the timer entirely if there
isn't another upcoming event.  We'll re-introduce some sort of activity
timeout by a different means later.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 tcp.c | 24 +++---------------------
 1 file changed, 3 insertions(+), 21 deletions(-)

diff --git a/tcp.c b/tcp.c
index 0a64892a..f8663369 100644
--- a/tcp.c
+++ b/tcp.c
@@ -190,9 +190,6 @@
  * - RTO_INIT_AFTER_SYN_RETRIES: if SYN retries happened during handshake and
  *   RTO is less than this, re-initialise RTO to this for data retransmissions
  *
- * - ACT_TIMEOUT, in the presence of any event: if no activity is detected on
- *   either side, the connection is reset
- *
  * - RTT / 2 elapsed after data segment received from tap without having
  *   sent an ACK segment, or zero-sized window advertised to tap/guest (flag
  *   ACK_TO_TAP_DUE): forcibly check if an ACK segment can be sent.
@@ -589,7 +586,9 @@ static void tcp_timer_ctl(const struct ctx *c, struct tcp_tap_conn *conn)
 		timeout <<= MAX(exp, 0);
 		it.it_value.tv_sec = MIN(timeout, c->tcp.rto_max);
 	} else {
-		it.it_value.tv_sec = ACT_TIMEOUT;
+		/* Disarm */
+		it.it_value.tv_sec = 0;
+		it.it_value.tv_nsec = 0;
 	}
 
 	if (conn->flags & ACK_TO_TAP_DUE) {
@@ -2598,23 +2597,6 @@ void tcp_timer_handler(const struct ctx *c, union epoll_ref ref)
 			tcp_data_from_sock(c, conn);
 			tcp_timer_ctl(c, conn);
 		}
-	} else {
-		struct itimerspec new = { { 0 }, { ACT_TIMEOUT, 0 } };
-		struct itimerspec old = { { 0 }, { 0 } };
-
-		/* Activity timeout: if it was already set, reset the
-		 * connection, otherwise, it was a left-over from ACK_TO_TAP_DUE
-		 * or ACK_FROM_TAP_DUE, so just set the long timeout in that
-		 * case. This avoids having to preemptively reset the timer on
-		 * ~ACK_TO_TAP_DUE or ~ACK_FROM_TAP_DUE.
-		 */
-		if (timerfd_settime(conn->timer, 0, &new, &old))
-			flow_perror(conn, "failed to set timer");
-
-		if (old.it_value.tv_sec == ACT_TIMEOUT) {
-			flow_dbg(conn, "activity timeout");
-			tcp_rst(c, conn);
-		}
 	}
 }
 
-- 
2.52.0