rxrpc: Allow a delay to be injected into packet reception

If CONFIG_AF_RXRPC_DEBUG_RX_DELAY=y, then a delay is injected between
packets and errors being received and them being made available to the
processing code, thereby allowing the RTT to be artificially increased.

Signed-off-by: David Howells <[e-mail]>
cc: Marc Dionne <[e-mail]>
cc: [e-mail]

net/rxrpc/Kconfig

···
 	  Say Y here to inject packet loss by discarding some received and some
 	  transmitted packets.
 
+config AF_RXRPC_INJECT_RX_DELAY
+	bool "Inject delay into packet reception"
+	depends on SYSCTL
+	help
+	  Say Y here to inject a delay into packet reception, allowing an
+	  extended RTT time to be modelled.  The delay can be configured using
+	  /proc/sys/net/rxrpc/rxrpc_inject_rx_delay, setting a number of
+	  milliseconds up to 0.5s (note that the granularity is actually in
+	  jiffies).
 
 config AF_RXRPC_DEBUG
 	bool "RxRPC dynamic debugging"

net/rxrpc/ar-internal.h

···
 	struct completion	io_thread_ready; /* Indication that the I/O thread started */
 	struct rxrpc_sock	*service;	/* Service(s) listening on this endpoint */
 	struct rw_semaphore	defrag_sem;	/* control re-enablement of IP DF bit */
+#ifdef CONFIG_AF_RXRPC_INJECT_RX_DELAY
+	struct sk_buff_head	rx_delay_queue;	/* Delay injection queue */
+#endif
 	struct sk_buff_head	rx_queue;	/* Received packets */
 	struct list_head	conn_attend_q;	/* Conns requiring immediate attention */
 	struct list_head	call_attend_q;	/* Calls requiring immediate attention */
···
 extern unsigned int rxrpc_rx_window_size;
 extern unsigned int rxrpc_rx_mtu;
 extern unsigned int rxrpc_rx_jumbo_max;
+#ifdef CONFIG_AF_RXRPC_INJECT_RX_DELAY
+extern unsigned long rxrpc_inject_rx_delay;
+#endif
 
 /*
  * net_ns.c

net/rxrpc/io_thread.c

···
  */
 int rxrpc_encap_rcv(struct sock *udp_sk, struct sk_buff *skb)
 {
+	struct sk_buff_head *rx_queue;
 	struct rxrpc_local *local = rcu_dereference_sk_user_data(udp_sk);
 
 	if (unlikely(!local)) {
···
 
 	skb->mark = RXRPC_SKB_MARK_PACKET;
 	rxrpc_new_skb(skb, rxrpc_skb_new_encap_rcv);
-	skb_queue_tail(&local->rx_queue, skb);
+	rx_queue = &local->rx_queue;
+#ifdef CONFIG_AF_RXRPC_INJECT_RX_DELAY
+	if (rxrpc_inject_rx_delay ||
+	    !skb_queue_empty(&local->rx_delay_queue)) {
+		skb->tstamp = ktime_add_ms(skb->tstamp, rxrpc_inject_rx_delay);
+		rx_queue = &local->rx_delay_queue;
+	}
+#endif
+
+	skb_queue_tail(rx_queue, skb);
 	rxrpc_wake_up_io_thread(local);
 	return 0;
 }
···
 	struct rxrpc_local *local = data;
 	struct rxrpc_call *call;
 	struct sk_buff *skb;
+#ifdef CONFIG_AF_RXRPC_INJECT_RX_DELAY
+	ktime_t now;
+#endif
 	bool should_stop;
 
 	complete(&local->io_thread_ready);
···
 			continue;
 		}
 
+		/* Inject a delay into packets if requested. */
+#ifdef CONFIG_AF_RXRPC_INJECT_RX_DELAY
+		now = ktime_get_real();
+		while ((skb = skb_peek(&local->rx_delay_queue))) {
+			if (ktime_before(now, skb->tstamp))
+				break;
+			skb = skb_dequeue(&local->rx_delay_queue);
+			skb_queue_tail(&local->rx_queue, skb);
+		}
+#endif
+
 		if (!skb_queue_empty(&local->rx_queue)) {
 			spin_lock_irq(&local->rx_queue.lock);
 			skb_queue_splice_tail_init(&local->rx_queue, &rx_queue);
···
 
 		if (should_stop)
 			break;
+
+#ifdef CONFIG_AF_RXRPC_INJECT_RX_DELAY
+		skb = skb_peek(&local->rx_delay_queue);
+		if (skb) {
+			unsigned long timeout;
+			ktime_t tstamp = skb->tstamp;
+			ktime_t now = ktime_get_real();
+			s64 delay_ns = ktime_to_ns(ktime_sub(tstamp, now));
+
+			if (delay_ns <= 0) {
+				__set_current_state(TASK_RUNNING);
+				continue;
+			}
+
+			timeout = nsecs_to_jiffies(delay_ns);
+			timeout = max(timeout, 1UL);
+			schedule_timeout(timeout);
+			__set_current_state(TASK_RUNNING);
+			continue;
+		}
+#endif
+
 		schedule();
 	}
 

net/rxrpc/local_object.c

···
 		INIT_HLIST_NODE(&local->link);
 		init_rwsem(&local->defrag_sem);
 		init_completion(&local->io_thread_ready);
+#ifdef CONFIG_AF_RXRPC_INJECT_RX_DELAY
+		skb_queue_head_init(&local->rx_delay_queue);
+#endif
 		skb_queue_head_init(&local->rx_queue);
 		INIT_LIST_HEAD(&local->conn_attend_q);
 		INIT_LIST_HEAD(&local->call_attend_q);
···
 	/* At this point, there should be no more packets coming in to the
 	 * local endpoint.
 	 */
+#ifdef CONFIG_AF_RXRPC_INJECT_RX_DELAY
+	rxrpc_purge_queue(&local->rx_delay_queue);
+#endif
 	rxrpc_purge_queue(&local->rx_queue);
 	rxrpc_purge_client_connections(local);
 }

net/rxrpc/misc.c

···
  * sender that we're willing to handle.
  */
 unsigned int rxrpc_rx_jumbo_max = 4;
+
+#ifdef CONFIG_AF_RXRPC_INJECT_RX_DELAY
+/*
+ * The delay to inject into packet reception.
+ */
+unsigned long rxrpc_inject_rx_delay;
+#endif

net/rxrpc/sysctl.c

···
 static const unsigned int n_max_acks = 255;
 static const unsigned long one_jiffy = 1;
 static const unsigned long max_jiffies = MAX_JIFFY_OFFSET;
+#ifdef CONFIG_AF_RXRPC_INJECT_RX_DELAY
+static const unsigned long max_500 = 500;
+#endif
 
 /*
  * RxRPC operating parameters.
···
 		.extra1		= (void *)&one_jiffy,
 		.extra2		= (void *)&max_jiffies,
 	},
+
+	/* Values used in milliseconds */
+#ifdef CONFIG_AF_RXRPC_INJECT_RX_DELAY
+	{
+		.procname	= "inject_rx_delay",
+		.data		= &rxrpc_inject_rx_delay,
+		.maxlen		= sizeof(unsigned long),
+		.mode		= 0644,
+		.proc_handler	= proc_doulongvec_minmax,
+		.extra1		= (void *)SYSCTL_LONG_ZERO,
+		.extra2		= (void *)&max_500,
+	},
+#endif
 
 	/* Non-time values */
 	{
···
 		.extra1		= (void *)SYSCTL_ONE,
 		.extra2		= (void *)&four,
 	},
-
 	{ }
 };