rxrpc: Send pings to get RTT data

Send a PING ACK packet to the peer when we get a new incoming call from a
peer we don't have a record for.  The PING RESPONSE ACK packet will tell us
the following about the peer:

 (1) its receive window size

 (2) its MTU sizes

 (3) its support for jumbo DATA packets

 (4) if it supports slow start (similar to RFC 5681)

 (5) an estimate of the RTT

This is necessary because the peer won't normally send us an ACK until it
gets to the Rx phase and we send it a packet, but we would like to know
some of this information before we start sending packets.

A pair of tracepoints are added so that RTT determination can be observed.

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

1 files changed, 47 insertions, 1 deletions

diff --git a/net/rxrpc/input.c b/net/rxrpc/input.c
index aa261df9fc9e6..a0a5bd108c9e0 100644
--- a/net/rxrpc/input.c
+++ b/net/rxrpc/input.c
@@ -37,6 +37,19 @@ static void rxrpc_proto_abort(const char *why,
 }
 
 /*
+ * Ping the other end to fill our RTT cache and to retrieve the rwind
+ * and MTU parameters.
+ */
+static void rxrpc_send_ping(struct rxrpc_call *call, struct sk_buff *skb,
+			    int skew)
+{
+	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
+
+	rxrpc_propose_ACK(call, RXRPC_ACK_PING, skew, sp->hdr.serial,
+			  true, true);
+}
+
+/*
  * Apply a hard ACK by advancing the Tx window.
  */
 static void rxrpc_rotate_tx_window(struct rxrpc_call *call, rxrpc_seq_t to)
@@ -343,6 +356,32 @@ ack:
 }
 
 /*
+ * Process a ping response.
+ */
+static void rxrpc_input_ping_response(struct rxrpc_call *call,
+				      ktime_t resp_time,
+				      rxrpc_serial_t orig_serial,
+				      rxrpc_serial_t ack_serial)
+{
+	rxrpc_serial_t ping_serial;
+	ktime_t ping_time;
+
+	ping_time = call->ackr_ping_time;
+	smp_rmb();
+	ping_serial = call->ackr_ping;
+
+	if (!test_bit(RXRPC_CALL_PINGING, &call->flags) ||
+	    before(orig_serial, ping_serial))
+		return;
+	clear_bit(RXRPC_CALL_PINGING, &call->flags);
+	if (after(orig_serial, ping_serial))
+		return;
+
+	rxrpc_peer_add_rtt(call, rxrpc_rtt_rx_ping_response,
+			   orig_serial, ack_serial, ping_time, resp_time);
+}
+
+/*
  * Process the extra information that may be appended to an ACK packet
  */
 static void rxrpc_input_ackinfo(struct rxrpc_call *call, struct sk_buff *skb,
@@ -438,6 +477,7 @@ static void rxrpc_input_ack(struct rxrpc_call *call, struct sk_buff *skb,
 		struct rxrpc_ackinfo info;
 		u8 acks[RXRPC_MAXACKS];
 	} buf;
+	rxrpc_serial_t acked_serial;
 	rxrpc_seq_t first_soft_ack, hard_ack;
 	int nr_acks, offset;
 
@@ -449,6 +489,7 @@ static void rxrpc_input_ack(struct rxrpc_call *call, struct sk_buff *skb,
 	}
 	sp->offset += sizeof(buf.ack);
 
+	acked_serial = ntohl(buf.ack.serial);
 	first_soft_ack = ntohl(buf.ack.firstPacket);
 	hard_ack = first_soft_ack - 1;
 	nr_acks = buf.ack.nAcks;
@@ -460,10 +501,14 @@ static void rxrpc_input_ack(struct rxrpc_call *call, struct sk_buff *skb,
 	       ntohs(buf.ack.maxSkew),
 	       first_soft_ack,
 	       ntohl(buf.ack.previousPacket),
-	       ntohl(buf.ack.serial),
+	       acked_serial,
 	       rxrpc_acks(buf.ack.reason),
 	       buf.ack.nAcks);
 
+	if (buf.ack.reason == RXRPC_ACK_PING_RESPONSE)
+		rxrpc_input_ping_response(call, skb->tstamp, acked_serial,
+					  sp->hdr.serial);
+
 	if (buf.ack.reason == RXRPC_ACK_PING) {
 		_proto("Rx ACK %%%u PING Request", sp->hdr.serial);
 		rxrpc_propose_ACK(call, RXRPC_ACK_PING_RESPONSE,
@@ -830,6 +875,7 @@ void rxrpc_data_ready(struct sock *udp_sk)
 			rcu_read_unlock();
 			goto reject_packet;
 		}
+		rxrpc_send_ping(call, skb, skew);
 	}
 
 	rxrpc_input_call_packet(call, skb, skew);