drivers: net: loopback: Network loopback interface driver

Loopback is a networking interface which doesn't actually transfer
any data via link layer externally, and instead just mirrors back
(i.e. any packet send to the loopback interface will be received from
it). This interface very useful for testing.

Signed-off-by: Paul Sokolovsky <[email protected]>

drivers/net/Kconfig

@@ -97,3 +97,30 @@ config	SLIP_MAC_ADDR
 	  random.
 
 endif
+
+#
+# Net loopback options
+#
+menuconfig NET_LOOPBACK
+	bool
+	prompt "Net loopback driver"
+	select NET_L2_DUMMY
+
+if NET_LOOPBACK
+
+config  SYS_LOG_NET_LOOPBACK_LEVEL
+        int
+        prompt "Net loopback driver log level"
+        depends on SYS_LOG && NET_LOOPBACK
+        default 0
+        range 0 4
+        help
+          Sets log level for the driver.
+          Levels are:
+          0 OFF, do not write
+          1 ERROR, only write SYS_LOG_ERR
+          2 WARNING, write SYS_LOG_WRN in addition to previous level
+          3 INFO, write SYS_LOG_INF in addition to previous levels
+          4 DEBUG, write SYS_LOG_DBG in addition to previous levels
+
+endif

drivers/net/Makefile

@@ -1 +1,2 @@
 obj-$(CONFIG_SLIP) = slip.o
+obj-$(CONFIG_NET_LOOPBACK) = loopback.o

drivers/net/loopback.c

@@ -0,0 +1,85 @@
+/*
+ * Copyright (c) 2015 Intel Corporation
+ * Copyright (c) 2017 Linaro Limited
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * @file
+ *
+ * Network loopback interface implementation.
+ */
+
+#define SYS_LOG_DOMAIN "netlo"
+#define SYS_LOG_LEVEL CONFIG_SYS_LOG_NETLO_LEVEL
+#include <logging/sys_log.h>
+
+#include <misc/printk.h>
+
+#include <net/net_pkt.h>
+#include <net/buf.h>
+#include <net/net_ip.h>
+#include <net/net_if.h>
+
+int loopback_dev_init(struct device *dev)
+{
+	return 0;
+}
+
+static void loopback_init(struct net_if *iface)
+{
+	/* RFC 7042, s.2.1.1. address to use in documentation */
+	net_if_set_link_addr(iface, "\x00\x00\x5e\x00\x53\xff", 6,
+			     NET_LINK_DUMMY);
+}
+
+static int loopback_send(struct net_if *iface, struct net_pkt *pkt)
+{
+	int res;
+
+	if (!pkt->frags) {
+		SYS_LOG_ERR("No data to send");
+		return -ENODATA;
+	}
+
+	/* We need to swap the IP addresses because otherwise
+	 * the packet will be dropped.
+	 */
+
+	if (net_pkt_family(pkt) == AF_INET6) {
+		struct in6_addr addr;
+
+		net_ipaddr_copy(&addr, &NET_IPV6_HDR(pkt)->src);
+		net_ipaddr_copy(&NET_IPV6_HDR(pkt)->src,
+				&NET_IPV6_HDR(pkt)->dst);
+		net_ipaddr_copy(&NET_IPV6_HDR(pkt)->dst, &addr);
+	} else {
+		struct in_addr addr;
+
+		net_ipaddr_copy(&addr, &NET_IPV4_HDR(pkt)->src);
+		net_ipaddr_copy(&NET_IPV4_HDR(pkt)->src,
+				&NET_IPV4_HDR(pkt)->dst);
+		net_ipaddr_copy(&NET_IPV4_HDR(pkt)->dst, &addr);
+	}
+
+	res = net_recv_data(iface, pkt);
+	if (res < 0) {
+		SYS_LOG_ERR("Data receive failed.");
+		net_pkt_unref(pkt);
+		return res;
+	}
+
+	return 0;
+}
+
+static struct net_if_api loopback_if_api = {
+	.init = loopback_init,
+	.send = loopback_send,
+};
+
+NET_DEVICE_INIT(loopback, "lo",
+		loopback_dev_init, NULL, NULL,
+		CONFIG_KERNEL_INIT_PRIORITY_DEFAULT,
+		&loopback_if_api, DUMMY_L2,
+		NET_L2_GET_CTX_TYPE(DUMMY_L2), 536);