netdevsim: add software driver for testing offloads

To be able to run selftests without any hardware required we
need a software model.  The model can also serve as an example
implementation for those implementing actual HW offloads.
The dummy driver have previously been extended to test SR-IOV,
but the general consensus seems to be against adding further
features to it.

Add a new driver for purposes of software modelling only.
eBPF and SR-IOV will be added here shortly, others are invited
to further extend the driver with their offload models.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

MAINTAINERS

@@ -9599,6 +9599,11 @@ NETWORKING [WIRELESS]
 L:	linux-wireless@vger.kernel.org
 Q:	http://patchwork.kernel.org/project/linux-wireless/list/
 
+NETDEVSIM
+M:	Jakub Kicinski <jakub.kicinski@netronome.com>
+S:	Maintained
+F:	drivers/net/netdevsim/*
+
 NETXEN (1/10) GbE SUPPORT
 M:	Manish Chopra <manish.chopra@cavium.com>
 M:	Rahul Verma <rahul.verma@cavium.com>

drivers/net/Kconfig

@@ -497,4 +497,15 @@ config THUNDERBOLT_NET
 
 source "drivers/net/hyperv/Kconfig"
 
+config NETDEVSIM
+	tristate "Simulated networking device"
+	depends on DEBUG_FS
+	help
+	  This driver is a developer testing tool and software model that can
+	  be used to test various control path networking APIs, especially
+	  HW-offload related.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called netdevsim.
+
 endif # NETDEVICES

drivers/net/Makefile

@@ -78,3 +78,4 @@ obj-$(CONFIG_FUJITSU_ES) += fjes/
 
 thunderbolt-net-y += thunderbolt.o
 obj-$(CONFIG_THUNDERBOLT_NET) += thunderbolt-net.o
+obj-$(CONFIG_NETDEVSIM) += netdevsim/

drivers/net/netdevsim/Makefile

+# SPDX-License-Identifier: GPL-2.0
+
+obj-$(CONFIG_NETDEVSIM) += netdevsim.o
+
+netdevsim-objs := \
+	netdev.o \

drivers/net/netdevsim/netdev.c

+/*
+ * Copyright (C) 2017 Netronome Systems, Inc.
+ *
+ * This software is licensed under the GNU General License Version 2,
+ * June 1991 as shown in the file COPYING in the top-level directory of this
+ * source tree.
+ *
+ * THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS"
+ * WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING,
+ * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE
+ * OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME
+ * THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
+ */
+
+#include <linux/etherdevice.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/netdevice.h>
+#include <linux/slab.h>
+#include <net/netlink.h>
+#include <net/rtnetlink.h>
+
+#include "netdevsim.h"
+
+static netdev_tx_t nsim_start_xmit(struct sk_buff *skb, struct net_device *dev)
+{
+	struct netdevsim *ns = netdev_priv(dev);
+
+	u64_stats_update_begin(&ns->syncp);
+	ns->tx_packets++;
+	ns->tx_bytes += skb->len;
+	u64_stats_update_end(&ns->syncp);
+
+	dev_kfree_skb(skb);
+
+	return NETDEV_TX_OK;
+}
+
+static void nsim_set_rx_mode(struct net_device *dev)
+{
+}
+
+static void
+nsim_get_stats64(struct net_device *dev, struct rtnl_link_stats64 *stats)
+{
+	struct netdevsim *ns = netdev_priv(dev);
+	unsigned int start;
+
+	do {
+		start = u64_stats_fetch_begin(&ns->syncp);
+		stats->tx_bytes = ns->tx_bytes;
+		stats->tx_packets = ns->tx_packets;
+	} while (u64_stats_fetch_retry(&ns->syncp, start));
+}
+
+static const struct net_device_ops nsim_netdev_ops = {
+	.ndo_start_xmit		= nsim_start_xmit,
+	.ndo_set_rx_mode	= nsim_set_rx_mode,
+	.ndo_set_mac_address	= eth_mac_addr,
+	.ndo_validate_addr	= eth_validate_addr,
+	.ndo_get_stats64	= nsim_get_stats64,
+};
+
+static void nsim_setup(struct net_device *dev)
+{
+	ether_setup(dev);
+	eth_hw_addr_random(dev);
+
+	dev->netdev_ops = &nsim_netdev_ops;
+	dev->needs_free_netdev = true;
+
+	dev->tx_queue_len = 0;
+	dev->flags |= IFF_NOARP;
+	dev->flags &= ~IFF_MULTICAST;
+	dev->priv_flags |= IFF_LIVE_ADDR_CHANGE |
+			   IFF_NO_QUEUE;
+	dev->features |= NETIF_F_HIGHDMA |
+			 NETIF_F_SG |
+			 NETIF_F_FRAGLIST |
+			 NETIF_F_HW_CSUM |
+			 NETIF_F_TSO;
+	dev->max_mtu = ETH_MAX_MTU;
+}
+
+static int nsim_validate(struct nlattr *tb[], struct nlattr *data[],
+			 struct netlink_ext_ack *extack)
+{
+	if (tb[IFLA_ADDRESS]) {
+		if (nla_len(tb[IFLA_ADDRESS]) != ETH_ALEN)
+			return -EINVAL;
+		if (!is_valid_ether_addr(nla_data(tb[IFLA_ADDRESS])))
+			return -EADDRNOTAVAIL;
+	}
+	return 0;
+}
+
+static struct rtnl_link_ops nsim_link_ops __read_mostly = {
+	.kind		= DRV_NAME,
+	.priv_size	= sizeof(struct netdevsim),
+	.setup		= nsim_setup,
+	.validate	= nsim_validate,
+};
+
+static int __init nsim_module_init(void)
+{
+	return rtnl_link_register(&nsim_link_ops);
+}
+
+static void __exit nsim_module_exit(void)
+{
+	rtnl_link_unregister(&nsim_link_ops);
+}
+
+module_init(nsim_module_init);
+module_exit(nsim_module_exit);
+MODULE_LICENSE("GPL");
+MODULE_ALIAS_RTNL_LINK(DRV_NAME);

drivers/net/netdevsim/netdevsim.h

+/*
+ * Copyright (C) 2017 Netronome Systems, Inc.
+ *
+ * This software is licensed under the GNU General License Version 2,
+ * June 1991 as shown in the file COPYING in the top-level directory of this
+ * source tree.
+ *
+ * THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS"
+ * WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING,
+ * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE
+ * OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME
+ * THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
+ */
+
+#include <linux/kernel.h>
+#include <linux/netdevice.h>
+#include <linux/u64_stats_sync.h>
+
+#define DRV_NAME	"netdevsim"
+
+struct netdevsim {
+	u64 tx_packets;
+	u64 tx_bytes;
+	struct u64_stats_sync syncp;
+};