drivers: net: loopback: Add interface to simulate packet drop

To allow for high level robustness tests on protocols, add an interface
to control the packet drop rate. A rate of 0 means no packet dropped, a
rate of 1 means all packets being dropped.

Signed-off-by: Sjors Hettinga <s.a.hettinga@gmail.com>

drivers/net/Kconfig

@@ -183,6 +183,12 @@ menuconfig NET_LOOPBACK
 
 if NET_LOOPBACK
 
+config NET_LOOPBACK_SIMULATE_PACKET_DROP
+	bool "Controlable packet drop"
+	help
+	  Enable interface to have a controlable packet drop rate, only for
+	  testing, should not be enabled for normal applications
+
 module = NET_LOOPBACK
 module-dep = LOG
 module-str = Log level for network loopback driver

drivers/net/loopback.c

@@ -21,6 +21,7 @@ LOG_MODULE_REGISTER(LOG_MODULE_NAME);
 #include <net/buf.h>
 #include <net/net_ip.h>
 #include <net/net_if.h>
+#include <net/loopback.h>
 
 #include <net/dummy.h>
 
@@ -60,6 +61,20 @@ static void loopback_init(struct net_if *iface)
 	}
 }
 
+#ifdef CONFIG_NET_LOOPBACK_SIMULATE_PACKET_DROP
+static float loopback_packet_drop_ratio = 0.0f;
+static float loopback_packet_drop_state = 0.0f;
+
+int loopback_set_packet_drop_ratio(float ratio)
+{
+	if (ratio < 0.0f || ratio > 1.0f) {
+		return -EINVAL;
+	}
+	loopback_packet_drop_ratio = ratio;
+	return 0;
+}
+#endif
+
 static int loopback_send(const struct device *dev, struct net_pkt *pkt)
 {
 	struct net_pkt *cloned;
@@ -103,6 +118,23 @@ static int loopback_send(const struct device *dev, struct net_pkt *pkt)
 		goto out;
 	}
 
+#ifdef CONFIG_NET_LOOPBACK_SIMULATE_PACKET_DROP
+	/* Drop packets based on the loopback_packet_drop_ratio
+	 * a ratio of 0.2 will drop one every 5 packets
+	 */
+	loopback_packet_drop_state += loopback_packet_drop_ratio;
+	if (loopback_packet_drop_state >= 1.0f) {
+		/* Administrate we dropped a packet */
+		loopback_packet_drop_state -= 1.0f;
+
+		/* Clean up the packet */
+		net_pkt_unref(cloned);
+		/* Pretent everything was fine */
+		res = 0;
+
+		goto out;
+	}
+#endif
 	res = net_recv_data(net_pkt_iface(cloned), cloned);
 	if (res < 0) {
 		LOG_ERR("Data receive failed.");

include/net/loopback.h

@@ -0,0 +1,33 @@
+/** @file
+ * @brief Loopback control interface
+ */
+
+/*
+ * Copyright (c) 2022 Radarxense B.V.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#ifndef ZEPHYR_INCLUDE_NET_LOOPBACK_H_
+#define ZEPHYR_INCLUDE_NET_LOOPBACK_H_
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifdef CONFIG_NET_LOOPBACK_SIMULATE_PACKET_DROP
+/**
+ * @brief Set the packet drop rate
+ *
+ * @param[in] ratio Value between 0 = no packet loss and 1 = all packets dropped
+ *
+ * @return 0 on success, otherwise a negative integer.
+ */
+int loopback_set_packet_drop_ratio(float ratio);
+#endif
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* ZEPHYR_INCLUDE_NET_LOOPBACK_H_ */