// SPDX-License-Identifier: GPL-2.0-only

  #include <linux/module.h>
  #include <linux/kernel.h>
  #include <linux/netdevice.h>
  #include <linux/netlink.h>
  #include <net/net_namespace.h>
  #include <linux/if_arp.h>

  #include <net/rtnetlink.h>

  static netdev_tx_t nlmon_xmit(struct sk_buff *skb, struct net_device *dev)
  {

  	dev_lstats_add(dev, skb->len);

  
  	dev_kfree_skb(skb);
  
  	return NETDEV_TX_OK;
  }

  static int nlmon_dev_init(struct net_device *dev)
  {

  	dev->lstats = netdev_alloc_pcpu_stats(struct pcpu_lstats);

  	return dev->lstats == NULL ? -ENOMEM : 0;
  }
  
  static void nlmon_dev_uninit(struct net_device *dev)
  {
  	free_percpu(dev->lstats);
  }

  struct nlmon {
  	struct netlink_tap nt;
  };

  
  static int nlmon_open(struct net_device *dev)
  {

  	struct nlmon *nlmon = netdev_priv(dev);
  
  	nlmon->nt.dev = dev;
  	nlmon->nt.module = THIS_MODULE;
  	return netlink_add_tap(&nlmon->nt);

  }
  
  static int nlmon_close(struct net_device *dev)
  {

  	struct nlmon *nlmon = netdev_priv(dev);
  
  	return netlink_remove_tap(&nlmon->nt);

  }

  static void

  nlmon_get_stats64(struct net_device *dev, struct rtnl_link_stats64 *stats)
  {

  	u64 packets, bytes;

  	dev_lstats_read(dev, &packets, &bytes);

  
  	stats->rx_packets = packets;
  	stats->tx_packets = 0;
  
  	stats->rx_bytes = bytes;
  	stats->tx_bytes = 0;

  }
  
  static u32 always_on(struct net_device *dev)
  {
  	return 1;
  }
  
  static const struct ethtool_ops nlmon_ethtool_ops = {
  	.get_link = always_on,
  };
  
  static const struct net_device_ops nlmon_ops = {
  	.ndo_init = nlmon_dev_init,
  	.ndo_uninit = nlmon_dev_uninit,
  	.ndo_open = nlmon_open,
  	.ndo_stop = nlmon_close,
  	.ndo_start_xmit = nlmon_xmit,
  	.ndo_get_stats64 = nlmon_get_stats64,

  };

  static void nlmon_setup(struct net_device *dev)
  {
  	dev->type = ARPHRD_NETLINK;

  	dev->priv_flags |= IFF_NO_QUEUE;

  
  	dev->netdev_ops	= &nlmon_ops;
  	dev->ethtool_ops = &nlmon_ethtool_ops;

  	dev->needs_free_netdev = true;

  	dev->features = NETIF_F_SG | NETIF_F_FRAGLIST |
  			NETIF_F_HIGHDMA | NETIF_F_LLTX;

  	dev->flags = IFF_NOARP;
  
  	/* That's rather a softlimit here, which, of course,
  	 * can be altered. Not a real MTU, but what is to be
  	 * expected in most cases.
  	 */
  	dev->mtu = NLMSG_GOODSIZE;

  	dev->min_mtu = sizeof(struct nlmsghdr);

  }

  static int nlmon_validate(struct nlattr *tb[], struct nlattr *data[],
  			  struct netlink_ext_ack *extack)

  {

  	if (tb[IFLA_ADDRESS])
  		return -EINVAL;
  	return 0;
  }

  static struct rtnl_link_ops nlmon_link_ops __read_mostly = {
  	.kind			= "nlmon",
  	.priv_size		= sizeof(struct nlmon),
  	.setup			= nlmon_setup,
  	.validate		= nlmon_validate,
  };

  static __init int nlmon_register(void)
  {
  	return rtnl_link_register(&nlmon_link_ops);

  }
  
  static __exit void nlmon_unregister(void)
  {

  	rtnl_link_unregister(&nlmon_link_ops);

  }
  
  module_init(nlmon_register);
  module_exit(nlmon_unregister);
  
  MODULE_LICENSE("GPL v2");
  MODULE_AUTHOR("Daniel Borkmann <dborkman@redhat.com>");
  MODULE_AUTHOR("Mathieu Geli <geli@enseirb.fr>");
  MODULE_DESCRIPTION("Netlink monitoring device");

  MODULE_ALIAS_RTNL_LINK("nlmon");