rxrpc: Add keepalive for a call

We need to transmit a packet every so often to act as a keepalive for the
peer (which has a timeout from the last time it received a packet) and also
to prevent any intervening firewalls from closing the route.

Do this by resetting a timer every time we transmit a packet.  If the timer
ever expires, we transmit a PING ACK packet and thereby also elicit a PING
RESPONSE ACK from the other side - which prevents our last-rx timeout from
expiring.

The timer is set to 1/6 of the last-rx timeout so that we can detect the
other side going away if it misses 6 replies in a row.

This is particularly necessary for servers where the processing of the
service function may take a significant amount of time.

Signed-off-by: David Howells <dhowells@redhat.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/net/rxrpc/call_event.c b/net/rxrpc/call_event.c
index c65666b2f39e..bda952ffe6a6 100644
--- a/net/rxrpc/call_event.c
+++ b/net/rxrpc/call_event.c
@@ -366,6 +366,15 @@ recheck_state:
 		set_bit(RXRPC_CALL_EV_ACK_LOST, &call->events);
 	}
 
+	t = READ_ONCE(call->keepalive_at);
+	if (time_after_eq(now, t)) {
+		trace_rxrpc_timer(call, rxrpc_timer_exp_keepalive, now);
+		cmpxchg(&call->keepalive_at, t, now + MAX_JIFFY_OFFSET);
+		rxrpc_propose_ACK(call, RXRPC_ACK_PING, 0, 0, true, true,
+				  rxrpc_propose_ack_ping_for_keepalive);
+		set_bit(RXRPC_CALL_EV_PING, &call->events);
+	}
+
 	t = READ_ONCE(call->ping_at);
 	if (time_after_eq(now, t)) {
 		trace_rxrpc_timer(call, rxrpc_timer_exp_ping, now);
@@ -423,6 +432,7 @@ recheck_state:
 	set(call->ack_at);
 	set(call->ack_lost_at);
 	set(call->resend_at);
+	set(call->keepalive_at);
 	set(call->ping_at);
 
 	now = jiffies;