text: /*
   *  TUN - Universal TUN/TAP device driver.
   *  Copyright (C) 1999-2002 Maxim Krasnyansky <maxk@qualcomm.com>
   *
   *  This program is free software; you can redistribute it and/or modify
   *  it under the terms of the GNU General Public License as published by
   *  the Free Software Foundation; either version 2 of the License, or
   *  (at your option) any later version.
   *
   *  This program is distributed in the hope that it will be useful,
   *  but WITHOUT ANY WARRANTY; without even the implied warranty of
   *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
   *  GNU General Public License for more details.
   *
   *  $Id: tun.c,v 1.15 2002/03/01 02:44:24 maxk Exp $
   */
  
  /*
   *  Changes:
   *
   *  Mike Kershaw <dragorn@kismetwireless.net> 2005/08/14
   *    Add TUNSETLINK ioctl to set the link encapsulation
   *
   *  Mark Smith <markzzzsmith@yahoo.com.au>
   *    Use eth_random_addr() for tap MAC address.
   *
   *  Harald Roelle <harald.roelle@ifi.lmu.de>  2004/04/20
   *    Fixes in packet dropping, queue length setting and queue wakeup.
   *    Increased default tx queue length.
   *    Added ethtool API.
   *    Minor cleanups
   *
   *  Daniel Podlejski <underley@underley.eu.org>
   *    Modifications for 2.3.99-pre5 kernel.
   */
  
  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  
  #define DRV_NAME	"tun"
  #define DRV_VERSION	"1.6"
  #define DRV_DESCRIPTION	"Universal TUN/TAP device driver"
  #define DRV_COPYRIGHT	"(C) 1999-2004 Max Krasnyansky <maxk@qualcomm.com>"
  
  #include <linux/module.h>
  #include <linux/errno.h>
  #include <linux/kernel.h>
  #include <linux/major.h>
  #include <linux/slab.h>
  #include <linux/poll.h>
  #include <linux/fcntl.h>
  #include <linux/init.h>
  #include <linux/skbuff.h>
  #include <linux/netdevice.h>
  #include <linux/etherdevice.h>
  #include <linux/miscdevice.h>
  #include <linux/ethtool.h>
  #include <linux/rtnetlink.h>
  #include <linux/compat.h>
  #include <linux/if.h>
  #include <linux/if_arp.h>
  #include <linux/if_ether.h>
  #include <linux/if_tun.h>
  #include <linux/if_vlan.h>
  #include <linux/crc32.h>
  #include <linux/nsproxy.h>
  #include <linux/virtio_net.h>
  #include <linux/rcupdate.h>
  #include <net/net_namespace.h>
  #include <net/netns/generic.h>
  #include <net/rtnetlink.h>
  #include <net/sock.h>
  #include <linux/seq_file.h>
  #include <linux/uio.h>
  
  #include <asm/uaccess.h>
  
  /* Uncomment to enable debugging */
  /* #define TUN_DEBUG 1 */
  
  #ifdef TUN_DEBUG
  static int debug;
  
  #define tun_debug(level, tun, fmt, args...)			\
  do {								\
  	if (tun->debug)						\
  		netdev_printk(level, tun->dev, fmt, ##args);	\
  } while (0)
  #define DBG1(level, fmt, args...)				\
  do {								\
  	if (debug == 2)						\
  		printk(level fmt, ##args);			\
  } while (0)
  #else
  #define tun_debug(level, tun, fmt, args...)			\
  do {								\
  	if (0)							\
  		netdev_printk(level, tun->dev, fmt, ##args);	\
  } while (0)
  #define DBG1(level, fmt, args...)				\
  do {								\
  	if (0)							\
  		printk(level fmt, ##args);			\
  } while (0)
  #endif
  
  /* TUN device flags */
  
  /* IFF_ATTACH_QUEUE is never stored in device flags,
   * overload it to mean fasync when stored there.
   */
  #define TUN_FASYNC	IFF_ATTACH_QUEUE
  /* High bits in flags field are unused. */
  #define TUN_VNET_LE     0x80000000
  
  #define TUN_FEATURES (IFF_NO_PI | IFF_ONE_QUEUE | IFF_VNET_HDR | \
  		      IFF_MULTI_QUEUE)
  #define GOODCOPY_LEN 128
  
  #define FLT_EXACT_COUNT 8
  struct tap_filter {
  	unsigned int    count;    /* Number of addrs. Zero means disabled */
  	u32             mask[2];  /* Mask of the hashed addrs */
  	unsigned char	addr[FLT_EXACT_COUNT][ETH_ALEN];
  };
  
  /* MAX_TAP_QUEUES 256 is chosen to allow rx/tx queues to be equal
   * to max number of VCPUs in guest. */
  #define MAX_TAP_QUEUES 256
  #define MAX_TAP_FLOWS  4096
  
  #define TUN_FLOW_EXPIRE (3 * HZ)
  
  /* A tun_file connects an open character device to a tuntap netdevice. It
   * also contains all socket related structures (except sock_fprog and tap_filter)
   * to serve as one transmit queue for tuntap device. The sock_fprog and
   * tap_filter were kept in tun_struct since they were used for filtering for the
   * netdevice not for a specific queue (at least I didn't see the requirement for
   * this).
   *
   * RCU usage:
   * The tun_file and tun_struct are loosely coupled, the pointer from one to the
   * other can only be read while rcu_read_lock or rtnl_lock is held.
   */
  struct tun_file {
  	struct sock sk;
  	struct socket socket;
  	struct socket_wq wq;
  	struct tun_struct __rcu *tun;
  	struct net *net;
  	struct fasync_struct *fasync;
  	/* only used for fasnyc */
  	unsigned int flags;
  	union {
  		u16 queue_index;
  		unsigned int ifindex;
  	};
  	struct list_head next;
  	struct tun_struct *detached;
  };
  
  struct tun_flow_entry {
  	struct hlist_node hash_link;
  	struct rcu_head rcu;
  	struct tun_struct *tun;
  
  	u32 rxhash;
  	u32 rps_rxhash;
  	int queue_index;
  	unsigned long updated;
  };
  
  #define TUN_NUM_FLOW_ENTRIES 1024
  
  /* Since the socket were moved to tun_file, to preserve the behavior of persist
   * device, socket filter, sndbuf and vnet header size were restore when the
   * file were attached to a persist device.
   */
  struct tun_struct {
  	struct tun_file __rcu	*tfiles[MAX_TAP_QUEUES];
  	unsigned int            numqueues;
  	unsigned int 		flags;
  	kuid_t			owner;
  	kgid_t			group;
  
  	struct net_device	*dev;
  	netdev_features_t	set_features;
  #define TUN_USER_FEATURES (NETIF_F_HW_CSUM|NETIF_F_TSO_ECN|NETIF_F_TSO| \
  			  NETIF_F_TSO6|NETIF_F_UFO)
  
  	int			vnet_hdr_sz;
  	int			sndbuf;
  	struct tap_filter	txflt;
  	struct sock_fprog	fprog;
  	/* protected by rtnl lock */
  	bool			filter_attached;
  #ifdef TUN_DEBUG
  	int debug;
  #endif
  	spinlock_t lock;
  	struct hlist_head flows[TUN_NUM_FLOW_ENTRIES];
  	struct timer_list flow_gc_timer;
  	unsigned long ageing_time;
  	unsigned int numdisabled;
  	struct list_head disabled;
  	void *security;
  	u32 flow_count;
  };
  
  static inline u16 tun16_to_cpu(struct tun_struct *tun, __virtio16 val)
  {
  	return __virtio16_to_cpu(tun->flags & TUN_VNET_LE, val);
  }
  
  static inline __virtio16 cpu_to_tun16(struct tun_struct *tun, u16 val)
  {
  	return __cpu_to_virtio16(tun->flags & TUN_VNET_LE, val);
  }
  
  static inline u32 tun_hashfn(u32 rxhash)
  {
  	return rxhash & 0x3ff;
  }
  
  static struct tun_flow_entry *tun_flow_find(struct hlist_head *head, u32 rxhash)
  {
  	struct tun_flow_entry *e;
  
  	hlist_for_each_entry_rcu(e, head, hash_link) {
  		if (e->rxhash == rxhash)
  			return e;
  	}
  	return NULL;
  }
  
  static struct tun_flow_entry *tun_flow_create(struct tun_struct *tun,
  					      struct hlist_head *head,
  					      u32 rxhash, u16 queue_index)
  {
  	struct tun_flow_entry *e = kmalloc(sizeof(*e), GFP_ATOMIC);
  
  	if (e) {
  		tun_debug(KERN_INFO, tun, "create flow: hash %u index %u\n",
  			  rxhash, queue_index);
  		e->updated = jiffies;
  		e->rxhash = rxhash;
  		e->rps_rxhash = 0;
  		e->queue_index = queue_index;
  		e->tun = tun;
  		hlist_add_head_rcu(&e->hash_link, head);
  		++tun->flow_count;
  	}
  	return e;
  }
  
  static void tun_flow_delete(struct tun_struct *tun, struct tun_flow_entry *e)
  {
  	tun_debug(KERN_INFO, tun, "delete flow: hash %u index %u\n",
  		  e->rxhash, e->queue_index);
  	hlist_del_rcu(&e->hash_link);
  	kfree_rcu(e, rcu);
  	--tun->flow_count;
  }
  
  static void tun_flow_flush(struct tun_struct *tun)
  {
  	int i;
  
  	spin_lock_bh(&tun->lock);
  	for (i = 0; i < TUN_NUM_FLOW_ENTRIES; i++) {
  		struct tun_flow_entry *e;
  		struct hlist_node *n;
  
  		hlist_for_each_entry_safe(e, n, &tun->flows[i], hash_link)
  			tun_flow_delete(tun, e);
  	}
  	spin_unlock_bh(&tun->lock);
  }
  
  static void tun_flow_delete_by_queue(struct tun_struct *tun, u16 queue_index)
  {
  	int i;
  
  	spin_lock_bh(&tun->lock);
  	for (i = 0; i < TUN_NUM_FLOW_ENTRIES; i++) {
  		struct tun_flow_entry *e;
  		struct hlist_node *n;
  
  		hlist_for_each_entry_safe(e, n, &tun->flows[i], hash_link) {
  			if (e->queue_index == queue_index)
  				tun_flow_delete(tun, e);
  		}
  	}
  	spin_unlock_bh(&tun->lock);
  }
  
  static void tun_flow_cleanup(unsigned long data)
  {
  	struct tun_struct *tun = (struct tun_struct *)data;
  	unsigned long delay = tun->ageing_time;
  	unsigned long next_timer = jiffies + delay;
  	unsigned long count = 0;
  	int i;
  
  	tun_debug(KERN_INFO, tun, "tun_flow_cleanup\n");
  
  	spin_lock_bh(&tun->lock);
  	for (i = 0; i < TUN_NUM_FLOW_ENTRIES; i++) {
  		struct tun_flow_entry *e;
  		struct hlist_node *n;
  
  		hlist_for_each_entry_safe(e, n, &tun->flows[i], hash_link) {
  			unsigned long this_timer;
  			count++;
  			this_timer = e->updated + delay;
  			if (time_before_eq(this_timer, jiffies))
  				tun_flow_delete(tun, e);
  			else if (time_before(this_timer, next_timer))
  				next_timer = this_timer;
  		}
  	}
  
  	if (count)
  		mod_timer(&tun->flow_gc_timer, round_jiffies_up(next_timer));
  	spin_unlock_bh(&tun->lock);
  }
  
  static void tun_flow_update(struct tun_struct *tun, u32 rxhash,
  			    struct tun_file *tfile)
  {
  	struct hlist_head *head;
  	struct tun_flow_entry *e;
  	unsigned long delay = tun->ageing_time;
  	u16 queue_index = tfile->queue_index;
  
  	if (!rxhash)
  		return;
  	else
  		head = &tun->flows[tun_hashfn(rxhash)];
  
  	rcu_read_lock();
  
  	/* We may get a very small possibility of OOO during switching, not
  	 * worth to optimize.*/
  	if (tun->numqueues == 1 || tfile->detached)
  		goto unlock;
  
  	e = tun_flow_find(head, rxhash);
  	if (likely(e)) {
  		/* TODO: keep queueing to old queue until it's empty? */
  		e->queue_index = queue_index;
  		e->updated = jiffies;
  		sock_rps_record_flow_hash(e->rps_rxhash);
  	} else {
  		spin_lock_bh(&tun->lock);
  		if (!tun_flow_find(head, rxhash) &&
  		    tun->flow_count < MAX_TAP_FLOWS)
  			tun_flow_create(tun, head, rxhash, queue_index);
  
  		if (!timer_pending(&tun->flow_gc_timer))
  			mod_timer(&tun->flow_gc_timer,
  				  round_jiffies_up(jiffies + delay));
  		spin_unlock_bh(&tun->lock);
  	}
  
  unlock:
  	rcu_read_unlock();
  }
  
  /**
   * Save the hash received in the stack receive path and update the
   * flow_hash table accordingly.
   */
  static inline void tun_flow_save_rps_rxhash(struct tun_flow_entry *e, u32 hash)
  {
  	if (unlikely(e->rps_rxhash != hash))
  		e->rps_rxhash = hash;
  }
  
  /* We try to identify a flow through its rxhash first. The reason that
   * we do not check rxq no. is because some cards(e.g 82599), chooses
   * the rxq based on the txq where the last packet of the flow comes. As
   * the userspace application move between processors, we may get a
   * different rxq no. here. If we could not get rxhash, then we would
   * hope the rxq no. may help here.
   */
  static u16 tun_select_queue(struct net_device *dev, struct sk_buff *skb,
  			    void *accel_priv, select_queue_fallback_t fallback)
  {
  	struct tun_struct *tun = netdev_priv(dev);
  	struct tun_flow_entry *e;
  	u32 txq = 0;
  	u32 numqueues = 0;
  
  	rcu_read_lock();
  	numqueues = ACCESS_ONCE(tun->numqueues);
  
  	txq = skb_get_hash(skb);
  	if (txq) {
  		e = tun_flow_find(&tun->flows[tun_hashfn(txq)], txq);
  		if (e) {
  			tun_flow_save_rps_rxhash(e, txq);
  			txq = e->queue_index;
  		} else
  			/* use multiply and shift instead of expensive divide */
  			txq = ((u64)txq * numqueues) >> 32;
  	} else if (likely(skb_rx_queue_recorded(skb))) {
  		txq = skb_get_rx_queue(skb);
  		while (unlikely(txq >= numqueues))
  			txq -= numqueues;
  	}
  
  	rcu_read_unlock();
  	return txq;
  }
  
  static inline bool tun_not_capable(struct tun_struct *tun)
  {
  	const struct cred *cred = current_cred();
  	struct net *net = dev_net(tun->dev);
  
  	return ((uid_valid(tun->owner) && !uid_eq(cred->euid, tun->owner)) ||
  		  (gid_valid(tun->group) && !in_egroup_p(tun->group))) &&
  		!ns_capable(net->user_ns, CAP_NET_ADMIN);
  }
  
  static void tun_set_real_num_queues(struct tun_struct *tun)
  {
  	netif_set_real_num_tx_queues(tun->dev, tun->numqueues);
  	netif_set_real_num_rx_queues(tun->dev, tun->numqueues);
  }
  
  static void tun_disable_queue(struct tun_struct *tun, struct tun_file *tfile)
  {
  	tfile->detached = tun;
  	list_add_tail(&tfile->next, &tun->disabled);
  	++tun->numdisabled;
  }
  
  static struct tun_struct *tun_enable_queue(struct tun_file *tfile)
  {
  	struct tun_struct *tun = tfile->detached;
  
  	tfile->detached = NULL;
  	list_del_init(&tfile->next);
  	--tun->numdisabled;
  	return tun;
  }
  
  static void tun_queue_purge(struct tun_file *tfile)
  {
  	skb_queue_purge(&tfile->sk.sk_receive_queue);
  	skb_queue_purge(&tfile->sk.sk_error_queue);
  }
  
  static void __tun_detach(struct tun_file *tfile, bool clean)
  {
  	struct tun_file *ntfile;
  	struct tun_struct *tun;
  
  	tun = rtnl_dereference(tfile->tun);
  
  	if (tun && !tfile->detached) {
  		u16 index = tfile->queue_index;
  		BUG_ON(index >= tun->numqueues);
  
  		rcu_assign_pointer(tun->tfiles[index],
  				   tun->tfiles[tun->numqueues - 1]);
  		ntfile = rtnl_dereference(tun->tfiles[index]);
  		ntfile->queue_index = index;
  
  		--tun->numqueues;
  		if (clean) {
  			RCU_INIT_POINTER(tfile->tun, NULL);
  			sock_put(&tfile->sk);
  		} else
  			tun_disable_queue(tun, tfile);
  
  		synchronize_net();
  		tun_flow_delete_by_queue(tun, tun->numqueues + 1);
  		/* Drop read queue */
  		tun_queue_purge(tfile);
  		tun_set_real_num_queues(tun);
  	} else if (tfile->detached && clean) {
  		tun = tun_enable_queue(tfile);
  		sock_put(&tfile->sk);
  	}
  
  	if (clean) {
  		if (tun && tun->numqueues == 0 && tun->numdisabled == 0) {
  			netif_carrier_off(tun->dev);
  
  			if (!(tun->flags & IFF_PERSIST) &&
  			    tun->dev->reg_state == NETREG_REGISTERED)
  				unregister_netdevice(tun->dev);
  		}
  
  		BUG_ON(!test_bit(SOCK_EXTERNALLY_ALLOCATED,
  				 &tfile->socket.flags));
  		sk_release_kernel(&tfile->sk);
  	}
  }
  
  static void tun_detach(struct tun_file *tfile, bool clean)
  {
  	rtnl_lock();
  	__tun_detach(tfile, clean);
  	rtnl_unlock();
  }
  
  static void tun_detach_all(struct net_device *dev)
  {
  	struct tun_struct *tun = netdev_priv(dev);
  	struct tun_file *tfile, *tmp;
  	int i, n = tun->numqueues;
  
  	for (i = 0; i < n; i++) {
  		tfile = rtnl_dereference(tun->tfiles[i]);
  		BUG_ON(!tfile);
  		tfile->socket.sk->sk_data_ready(tfile->socket.sk);
  		RCU_INIT_POINTER(tfile->tun, NULL);
  		--tun->numqueues;
  	}
  	list_for_each_entry(tfile, &tun->disabled, next) {
  		tfile->socket.sk->sk_data_ready(tfile->socket.sk);
  		RCU_INIT_POINTER(tfile->tun, NULL);
  	}
  	BUG_ON(tun->numqueues != 0);
  
  	synchronize_net();
  	for (i = 0; i < n; i++) {
  		tfile = rtnl_dereference(tun->tfiles[i]);
  		/* Drop read queue */
  		tun_queue_purge(tfile);
  		sock_put(&tfile->sk);
  	}
  	list_for_each_entry_safe(tfile, tmp, &tun->disabled, next) {
  		tun_enable_queue(tfile);
  		tun_queue_purge(tfile);
  		sock_put(&tfile->sk);
  	}
  	BUG_ON(tun->numdisabled != 0);
  
  	if (tun->flags & IFF_PERSIST)
  		module_put(THIS_MODULE);
  }
  
  static int tun_attach(struct tun_struct *tun, struct file *file, bool skip_filter)
  {
  	struct tun_file *tfile = file->private_data;
  	int err;
  
  	err = security_tun_dev_attach(tfile->socket.sk, tun->security);
  	if (err < 0)
  		goto out;
  
  	err = -EINVAL;
  	if (rtnl_dereference(tfile->tun) && !tfile->detached)
  		goto out;
  
  	err = -EBUSY;
  	if (!(tun->flags & IFF_MULTI_QUEUE) && tun->numqueues == 1)
  		goto out;
  
  	err = -E2BIG;
  	if (!tfile->detached &&
  	    tun->numqueues + tun->numdisabled == MAX_TAP_QUEUES)
  		goto out;
  
  	err = 0;
  
  	/* Re-attach the filter to persist device */
  	if (!skip_filter && (tun->filter_attached == true)) {
  		err = sk_attach_filter(&tun->fprog, tfile->socket.sk);
  		if (!err)
  			goto out;
  	}
  	tfile->queue_index = tun->numqueues;
  	rcu_assign_pointer(tfile->tun, tun);
  	rcu_assign_pointer(tun->tfiles[tun->numqueues], tfile);
  	tun->numqueues++;
  
  	if (tfile->detached)
  		tun_enable_queue(tfile);
  	else
  		sock_hold(&tfile->sk);
  
  	tun_set_real_num_queues(tun);
  
  	/* device is allowed to go away first, so no need to hold extra
  	 * refcnt.
  	 */
  
  out:
  	return err;
  }
  
  static struct tun_struct *__tun_get(struct tun_file *tfile)
  {
  	struct tun_struct *tun;
  
  	rcu_read_lock();
  	tun = rcu_dereference(tfile->tun);
  	if (tun)
  		dev_hold(tun->dev);
  	rcu_read_unlock();
  
  	return tun;
  }
  
  static struct tun_struct *tun_get(struct file *file)
  {
  	return __tun_get(file->private_data);
  }
  
  static void tun_put(struct tun_struct *tun)
  {
  	dev_put(tun->dev);
  }
  
  /* TAP filtering */
  static void addr_hash_set(u32 *mask, const u8 *addr)
  {
  	int n = ether_crc(ETH_ALEN, addr) >> 26;
  	mask[n >> 5] |= (1 << (n & 31));
  }
  
  static unsigned int addr_hash_test(const u32 *mask, const u8 *addr)
  {
  	int n = ether_crc(ETH_ALEN, addr) >> 26;
  	return mask[n >> 5] & (1 << (n & 31));
  }
  
  static int update_filter(struct tap_filter *filter, void __user *arg)
  {
  	struct { u8 u[ETH_ALEN]; } *addr;
  	struct tun_filter uf;
  	int err, alen, n, nexact;
  
  	if (copy_from_user(&uf, arg, sizeof(uf)))
  		return -EFAULT;
  
  	if (!uf.count) {
  		/* Disabled */
  		filter->count = 0;
  		return 0;
  	}
  
  	alen = ETH_ALEN * uf.count;
  	addr = kmalloc(alen, GFP_KERNEL);
  	if (!addr)
  		return -ENOMEM;
  
  	if (copy_from_user(addr, arg + sizeof(uf), alen)) {
  		err = -EFAULT;
  		goto done;
  	}
  
  	/* The filter is updated without holding any locks. Which is
  	 * perfectly safe. We disable it first and in the worst
  	 * case we'll accept a few undesired packets. */
  	filter->count = 0;
  	wmb();
  
  	/* Use first set of addresses as an exact filter */
  	for (n = 0; n < uf.count && n < FLT_EXACT_COUNT; n++)
  		memcpy(filter->addr[n], addr[n].u, ETH_ALEN);
  
  	nexact = n;
  
  	/* Remaining multicast addresses are hashed,
  	 * unicast will leave the filter disabled. */
  	memset(filter->mask, 0, sizeof(filter->mask));
  	for (; n < uf.count; n++) {
  		if (!is_multicast_ether_addr(addr[n].u)) {
  			err = 0; /* no filter */
  			goto done;
  		}
  		addr_hash_set(filter->mask, addr[n].u);
  	}
  
  	/* For ALLMULTI just set the mask to all ones.
  	 * This overrides the mask populated above. */
  	if ((uf.flags & TUN_FLT_ALLMULTI))
  		memset(filter->mask, ~0, sizeof(filter->mask));
  
  	/* Now enable the filter */
  	wmb();
  	filter->count = nexact;
  
  	/* Return the number of exact filters */
  	err = nexact;
  
  done:
  	kfree(addr);
  	return err;
  }
  
  /* Returns: 0 - drop, !=0 - accept */
  static int run_filter(struct tap_filter *filter, const struct sk_buff *skb)
  {
  	/* Cannot use eth_hdr(skb) here because skb_mac_hdr() is incorrect
  	 * at this point. */
  	struct ethhdr *eh = (struct ethhdr *) skb->data;
  	int i;
  
  	/* Exact match */
  	for (i = 0; i < filter->count; i++)
  		if (ether_addr_equal(eh->h_dest, filter->addr[i]))
  			return 1;
  
  	/* Inexact match (multicast only) */
  	if (is_multicast_ether_addr(eh->h_dest))
  		return addr_hash_test(filter->mask, eh->h_dest);
  
  	return 0;
  }
  
  /*
   * Checks whether the packet is accepted or not.
   * Returns: 0 - drop, !=0 - accept
   */
  static int check_filter(struct tap_filter *filter, const struct sk_buff *skb)
  {
  	if (!filter->count)
  		return 1;
  
  	return run_filter(filter, skb);
  }
  
  /* Network device part of the driver */
  
  static const struct ethtool_ops tun_ethtool_ops;
  
  /* Net device detach from fd. */
  static void tun_net_uninit(struct net_device *dev)
  {
  	tun_detach_all(dev);
  }
  
  /* Net device open. */
  static int tun_net_open(struct net_device *dev)
  {
  	netif_tx_start_all_queues(dev);
  	return 0;
  }
  
  /* Net device close. */
  static int tun_net_close(struct net_device *dev)
  {
  	netif_tx_stop_all_queues(dev);
  	return 0;
  }
  
  /* Net device start xmit */
  static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
  {
  	struct tun_struct *tun = netdev_priv(dev);
  	int txq = skb->queue_mapping;
  	struct tun_file *tfile;
  	u32 numqueues = 0;
  
  	rcu_read_lock();
  	tfile = rcu_dereference(tun->tfiles[txq]);
  	numqueues = ACCESS_ONCE(tun->numqueues);
  
  	/* Drop packet if interface is not attached */
  	if (txq >= numqueues)
  		goto drop;
  
  	if (numqueues == 1) {
  		/* Select queue was not called for the skbuff, so we extract the
  		 * RPS hash and save it into the flow_table here.
  		 */
  		__u32 rxhash;
  
  		rxhash = skb_get_hash(skb);
  		if (rxhash) {
  			struct tun_flow_entry *e;
  			e = tun_flow_find(&tun->flows[tun_hashfn(rxhash)],
  					rxhash);
  			if (e)
  				tun_flow_save_rps_rxhash(e, rxhash);
  		}
  	}
  
  	tun_debug(KERN_INFO, tun, "tun_net_xmit %d\n", skb->len);
  
  	BUG_ON(!tfile);
  
  	/* Drop if the filter does not like it.
  	 * This is a noop if the filter is disabled.
  	 * Filter can be enabled only for the TAP devices. */
  	if (!check_filter(&tun->txflt, skb))
  		goto drop;
  
  	if (tfile->socket.sk->sk_filter &&
  	    sk_filter(tfile->socket.sk, skb))
  		goto drop;
  
  	/* Limit the number of packets queued by dividing txq length with the
  	 * number of queues.
  	 */
  	if (skb_queue_len(&tfile->socket.sk->sk_receive_queue) * numqueues
  			  >= dev->tx_queue_len)
  		goto drop;
  
  	if (unlikely(skb_orphan_frags(skb, GFP_ATOMIC)))
  		goto drop;
  
  	skb_tx_timestamp(skb);
  
  	/* Orphan the skb - required as we might hang on to it
  	 * for indefinite time.
  	 */
  	skb_orphan(skb);
  
  	nf_reset(skb);
  
  	/* Enqueue packet */
  	skb_queue_tail(&tfile->socket.sk->sk_receive_queue, skb);
  
  	/* Notify and wake up reader process */
  	if (tfile->flags & TUN_FASYNC)
  		kill_fasync(&tfile->fasync, SIGIO, POLL_IN);
  	tfile->socket.sk->sk_data_ready(tfile->socket.sk);
  
  	rcu_read_unlock();
  	return NETDEV_TX_OK;
  
  drop:
  	dev->stats.tx_dropped++;
  	skb_tx_error(skb);
  	kfree_skb(skb);
  	rcu_read_unlock();
  	return NET_XMIT_DROP;
  }
  
  static void tun_net_mclist(struct net_device *dev)
  {
  	/*
  	 * This callback is supposed to deal with mc filter in
  	 * _rx_ path and has nothing to do with the _tx_ path.
  	 * In rx path we always accept everything userspace gives us.
  	 */
  }
  
  #define MIN_MTU 68
  #define MAX_MTU 65535
  
  static int
  tun_net_change_mtu(struct net_device *dev, int new_mtu)
  {
  	if (new_mtu < MIN_MTU || new_mtu + dev->hard_header_len > MAX_MTU)
  		return -EINVAL;
  	dev->mtu = new_mtu;
  	return 0;
  }
  
  static netdev_features_t tun_net_fix_features(struct net_device *dev,
  	netdev_features_t features)
  {
  	struct tun_struct *tun = netdev_priv(dev);
  
  	return (features & tun->set_features) | (features & ~TUN_USER_FEATURES);
  }
  #ifdef CONFIG_NET_POLL_CONTROLLER
  static void tun_poll_controller(struct net_device *dev)
  {
  	/*
  	 * Tun only receives frames when:
  	 * 1) the char device endpoint gets data from user space
  	 * 2) the tun socket gets a sendmsg call from user space
  	 * Since both of those are synchronous operations, we are guaranteed
  	 * never to have pending data when we poll for it
  	 * so there is nothing to do here but return.
  	 * We need this though so netpoll recognizes us as an interface that
  	 * supports polling, which enables bridge devices in virt setups to
  	 * still use netconsole
  	 */
  	return;
  }
  #endif
  static const struct net_device_ops tun_netdev_ops = {
  	.ndo_uninit		= tun_net_uninit,
  	.ndo_open		= tun_net_open,
  	.ndo_stop		= tun_net_close,
  	.ndo_start_xmit		= tun_net_xmit,
  	.ndo_change_mtu		= tun_net_change_mtu,
  	.ndo_fix_features	= tun_net_fix_features,
  	.ndo_select_queue	= tun_select_queue,
  #ifdef CONFIG_NET_POLL_CONTROLLER
  	.ndo_poll_controller	= tun_poll_controller,
  #endif
  };
  
  static const struct net_device_ops tap_netdev_ops = {
  	.ndo_uninit		= tun_net_uninit,
  	.ndo_open		= tun_net_open,
  	.ndo_stop		= tun_net_close,
  	.ndo_start_xmit		= tun_net_xmit,
  	.ndo_change_mtu		= tun_net_change_mtu,
  	.ndo_fix_features	= tun_net_fix_features,
  	.ndo_set_rx_mode	= tun_net_mclist,
  	.ndo_set_mac_address	= eth_mac_addr,
  	.ndo_validate_addr	= eth_validate_addr,
  	.ndo_select_queue	= tun_select_queue,
  #ifdef CONFIG_NET_POLL_CONTROLLER
  	.ndo_poll_controller	= tun_poll_controller,
  #endif
  };
  
  static void tun_flow_init(struct tun_struct *tun)
  {
  	int i;
  
  	for (i = 0; i < TUN_NUM_FLOW_ENTRIES; i++)
  		INIT_HLIST_HEAD(&tun->flows[i]);
  
  	tun->ageing_time = TUN_FLOW_EXPIRE;
  	setup_timer(&tun->flow_gc_timer, tun_flow_cleanup, (unsigned long)tun);
  	mod_timer(&tun->flow_gc_timer,
  		  round_jiffies_up(jiffies + tun->ageing_time));
  }
  
  static void tun_flow_uninit(struct tun_struct *tun)
  {
  	del_timer_sync(&tun->flow_gc_timer);
  	tun_flow_flush(tun);
  }
  
  /* Initialize net device. */
  static void tun_net_init(struct net_device *dev)
  {
  	struct tun_struct *tun = netdev_priv(dev);
  
  	switch (tun->flags & TUN_TYPE_MASK) {
  	case IFF_TUN:
  		dev->netdev_ops = &tun_netdev_ops;
  
  		/* Point-to-Point TUN Device */
  		dev->hard_header_len = 0;
  		dev->addr_len = 0;
  		dev->mtu = 1500;
  
  		/* Zero header length */
  		dev->type = ARPHRD_NONE;
  		dev->flags = IFF_POINTOPOINT | IFF_NOARP | IFF_MULTICAST;
  		dev->tx_queue_len = TUN_READQ_SIZE;  /* We prefer our own queue length */
  		break;
  
  	case IFF_TAP:
  		dev->netdev_ops = &tap_netdev_ops;
  		/* Ethernet TAP Device */
  		ether_setup(dev);
  		dev->priv_flags &= ~IFF_TX_SKB_SHARING;
  		dev->priv_flags |= IFF_LIVE_ADDR_CHANGE;
  
  		eth_hw_addr_random(dev);
  
  		dev->tx_queue_len = TUN_READQ_SIZE;  /* We prefer our own queue length */
  		break;
  	}
  }
  
  /* Character device part */
  
  /* Poll */
  static unsigned int tun_chr_poll(struct file *file, poll_table *wait)
  {
  	struct tun_file *tfile = file->private_data;
  	struct tun_struct *tun = __tun_get(tfile);
  	struct sock *sk;
  	unsigned int mask = 0;
  
  	if (!tun)
  		return POLLERR;
  
  	sk = tfile->socket.sk;
  
  	tun_debug(KERN_INFO, tun, "tun_chr_poll\n");
  
  	poll_wait(file, sk_sleep(sk), wait);
  
  	if (!skb_queue_empty(&sk->sk_receive_queue))
  		mask |= POLLIN | POLLRDNORM;
  
  	if (sock_writeable(sk) ||
  	    (!test_and_set_bit(SOCK_ASYNC_NOSPACE, &sk->sk_socket->flags) &&
  	     sock_writeable(sk)))
  		mask |= POLLOUT | POLLWRNORM;
  
  	if (tun->dev->reg_state != NETREG_REGISTERED)
  		mask = POLLERR;
  
  	tun_put(tun);
  	return mask;
  }
  
  /* prepad is the amount to reserve at front.  len is length after that.
   * linear is a hint as to how much to copy (usually headers). */
  static struct sk_buff *tun_alloc_skb(struct tun_file *tfile,
  				     size_t prepad, size_t len,
  				     size_t linear, int noblock)
  {
  	struct sock *sk = tfile->socket.sk;
  	struct sk_buff *skb;
  	int err;
  
  	/* Under a page?  Don't bother with paged skb. */
  	if (prepad + len < PAGE_SIZE || !linear)
  		linear = len;
  
  	skb = sock_alloc_send_pskb(sk, prepad + linear, len - linear, noblock,
  				   &err, 0);
  	if (!skb)
  		return ERR_PTR(err);
  
  	skb_reserve(skb, prepad);
  	skb_put(skb, linear);
  	skb->data_len = len - linear;
  	skb->len += len - linear;
  
  	return skb;
  }
  
  /* Get packet from user space buffer */
  static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
  			    void *msg_control, struct iov_iter *from,
  			    int noblock)
  {
  	struct tun_pi pi = { 0, cpu_to_be16(ETH_P_IP) };
  	struct sk_buff *skb;
  	size_t total_len = iov_iter_count(from);
  	size_t len = total_len, align = NET_SKB_PAD, linear;
  	struct virtio_net_hdr gso = { 0 };
  	int good_linear;
  	int copylen;
  	bool zerocopy = false;
  	int err;
  	u32 rxhash;
  	ssize_t n;
  
  	if (!(tun->flags & IFF_NO_PI)) {
  		if (len < sizeof(pi))
  			return -EINVAL;
  		len -= sizeof(pi);
  
  		n = copy_from_iter(&pi, sizeof(pi), from);
  		if (n != sizeof(pi))
  			return -EFAULT;
  	}
  
  	if (tun->flags & IFF_VNET_HDR) {
  		if (len < tun->vnet_hdr_sz)
  			return -EINVAL;
  		len -= tun->vnet_hdr_sz;
  
  		n = copy_from_iter(&gso, sizeof(gso), from);
  		if (n != sizeof(gso))
  			return -EFAULT;
  
  		if ((gso.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) &&
  		    tun16_to_cpu(tun, gso.csum_start) + tun16_to_cpu(tun, gso.csum_offset) + 2 > tun16_to_cpu(tun, gso.hdr_len))
  			gso.hdr_len = cpu_to_tun16(tun, tun16_to_cpu(tun, gso.csum_start) + tun16_to_cpu(tun, gso.csum_offset) + 2);
  
  		if (tun16_to_cpu(tun, gso.hdr_len) > len)
  			return -EINVAL;
  		iov_iter_advance(from, tun->vnet_hdr_sz - sizeof(gso));
  	}
  
  	if ((tun->flags & TUN_TYPE_MASK) == IFF_TAP) {
  		align += NET_IP_ALIGN;
  		if (unlikely(len < ETH_HLEN ||
  			     (gso.hdr_len && tun16_to_cpu(tun, gso.hdr_len) < ETH_HLEN)))
  			return -EINVAL;
  	}
  
  	good_linear = SKB_MAX_HEAD(align);
  
  	if (msg_control) {
  		struct iov_iter i = *from;
  
  		/* There are 256 bytes to be copied in skb, so there is
  		 * enough room for skb expand head in case it is used.
  		 * The rest of the buffer is mapped from userspace.
  		 */
  		copylen = gso.hdr_len ? tun16_to_cpu(tun, gso.hdr_len) : GOODCOPY_LEN;
  		if (copylen > good_linear)
  			copylen = good_linear;
  		linear = copylen;
  		iov_iter_advance(&i, copylen);
  		if (iov_iter_npages(&i, INT_MAX) <= MAX_SKB_FRAGS)
  			zerocopy = true;
  	}
  
  	if (!zerocopy) {
  		copylen = len;
  		if (tun16_to_cpu(tun, gso.hdr_len) > good_linear)
  			linear = good_linear;
  		else
  			linear = tun16_to_cpu(tun, gso.hdr_len);
  	}
  
  	skb = tun_alloc_skb(tfile, align, copylen, linear, noblock);
  	if (IS_ERR(skb)) {
  		if (PTR_ERR(skb) != -EAGAIN)
  			tun->dev->stats.rx_dropped++;
  		return PTR_ERR(skb);
  	}
  
  	if (zerocopy)
  		err = zerocopy_sg_from_iter(skb, from);
  	else {
  		err = skb_copy_datagram_from_iter(skb, 0, from, len);
  		if (!err && msg_control) {
  			struct ubuf_info *uarg = msg_control;
  			uarg->callback(uarg, false);
  		}
  	}
  
  	if (err) {
  		tun->dev->stats.rx_dropped++;
  		kfree_skb(skb);
  		return -EFAULT;
  	}
  
  	if (gso.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) {
  		if (!skb_partial_csum_set(skb, tun16_to_cpu(tun, gso.csum_start),
  					  tun16_to_cpu(tun, gso.csum_offset))) {
  			tun->dev->stats.rx_frame_errors++;
  			kfree_skb(skb);
  			return -EINVAL;
  		}
  	}
  
  	switch (tun->flags & TUN_TYPE_MASK) {
  	case IFF_TUN:
  		if (tun->flags & IFF_NO_PI) {
  			switch (skb->data[0] & 0xf0) {
  			case 0x40:
  				pi.proto = htons(ETH_P_IP);
  				break;
  			case 0x60:
  				pi.proto = htons(ETH_P_IPV6);
  				break;
  			default:
  				tun->dev->stats.rx_dropped++;
  				kfree_skb(skb);
  				return -EINVAL;
  			}
  		}
  
  		skb_reset_mac_header(skb);
  		skb->protocol = pi.proto;
  		skb->dev = tun->dev;
  		break;
  	case IFF_TAP:
  		skb->protocol = eth_type_trans(skb, tun->dev);
  		break;
  	}
  
  	if (gso.gso_type != VIRTIO_NET_HDR_GSO_NONE) {
  		pr_debug("GSO!\n");
  		switch (gso.gso_type & ~VIRTIO_NET_HDR_GSO_ECN) {
  		case VIRTIO_NET_HDR_GSO_TCPV4:
  			skb_shinfo(skb)->gso_type = SKB_GSO_TCPV4;
  			break;
  		case VIRTIO_NET_HDR_GSO_TCPV6:
  			skb_shinfo(skb)->gso_type = SKB_GSO_TCPV6;
  			break;
  		case VIRTIO_NET_HDR_GSO_UDP:
  			skb_shinfo(skb)->gso_type = SKB_GSO_UDP;
  			break;
  		default:
  			tun->dev->stats.rx_frame_errors++;
  			kfree_skb(skb);
  			return -EINVAL;
  		}
  
  		if (gso.gso_type & VIRTIO_NET_HDR_GSO_ECN)
  			skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN;
  
  		skb_shinfo(skb)->gso_size = tun16_to_cpu(tun, gso.gso_size);
  		if (skb_shinfo(skb)->gso_size == 0) {
  			tun->dev->stats.rx_frame_errors++;
  			kfree_skb(skb);
  			return -EINVAL;
  		}
  
  		/* Header must be checked, and gso_segs computed. */
  		skb_shinfo(skb)->gso_type |= SKB_GSO_DODGY;
  		skb_shinfo(skb)->gso_segs = 0;
  	}
  
  	/* copy skb_ubuf_info for callback when skb has no error */
  	if (zerocopy) {
  		skb_shinfo(skb)->destructor_arg = msg_control;
  		skb_shinfo(skb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
  		skb_shinfo(skb)->tx_flags |= SKBTX_SHARED_FRAG;
  	}
  
  	skb_reset_network_header(skb);
  	skb_probe_transport_header(skb, 0);
  
  	rxhash = skb_get_hash(skb);
  	netif_rx_ni(skb);
  
  	tun->dev->stats.rx_packets++;
  	tun->dev->stats.rx_bytes += len;
  
  	tun_flow_update(tun, rxhash, tfile);
  	return total_len;
  }
  
  static ssize_t tun_chr_write_iter(struct kiocb *iocb, struct iov_iter *from)
  {
  	struct file *file = iocb->ki_filp;
  	struct tun_struct *tun = tun_get(file);
  	struct tun_file *tfile = file->private_data;
  	ssize_t result;
  
  	if (!tun)
  		return -EBADFD;
  
  	result = tun_get_user(tun, tfile, NULL, from, file->f_flags & O_NONBLOCK);
  
  	tun_put(tun);
  	return result;
  }
  
  /* Put packet to the user space buffer */
  static ssize_t tun_put_user(struct tun_struct *tun,
  			    struct tun_file *tfile,
  			    struct sk_buff *skb,
  			    struct iov_iter *iter)
  {
  	struct tun_pi pi = { 0, skb->protocol };
  	ssize_t total;
  	int vlan_offset = 0;
  	int vlan_hlen = 0;
  	int vnet_hdr_sz = 0;
  
  	if (skb_vlan_tag_present(skb))
  		vlan_hlen = VLAN_HLEN;
  
  	if (tun->flags & IFF_VNET_HDR)
  		vnet_hdr_sz = tun->vnet_hdr_sz;
  
  	total = skb->len + vlan_hlen + vnet_hdr_sz;
  
  	if (!(tun->flags & IFF_NO_PI)) {
  		if (iov_iter_count(iter) < sizeof(pi))
  			return -EINVAL;
  
  		total += sizeof(pi);
  		if (iov_iter_count(iter) < total) {
  			/* Packet will be striped */
  			pi.flags |= TUN_PKT_STRIP;
  		}
  
  		if (copy_to_iter(&pi, sizeof(pi), iter) != sizeof(pi))
  			return -EFAULT;
  	}
  
  	if (vnet_hdr_sz) {
  		struct virtio_net_hdr gso = { 0 }; /* no info leak */
  		if (iov_iter_count(iter) < vnet_hdr_sz)
  			return -EINVAL;
  
  		if (skb_is_gso(skb)) {
  			struct skb_shared_info *sinfo = skb_shinfo(skb);
  
  			/* This is a hint as to how much should be linear. */
  			gso.hdr_len = cpu_to_tun16(tun, skb_headlen(skb));
  			gso.gso_size = cpu_to_tun16(tun, sinfo->gso_size);
  			if (sinfo->gso_type & SKB_GSO_TCPV4)
  				gso.gso_type = VIRTIO_NET_HDR_GSO_TCPV4;
  			else if (sinfo->gso_type & SKB_GSO_TCPV6)
  				gso.gso_type = VIRTIO_NET_HDR_GSO_TCPV6;
  			else if (sinfo->gso_type & SKB_GSO_UDP)
  				gso.gso_type = VIRTIO_NET_HDR_GSO_UDP;
  			else {
  				pr_err("unexpected GSO type: "
  				       "0x%x, gso_size %d, hdr_len %d\n",
  				       sinfo->gso_type, tun16_to_cpu(tun, gso.gso_size),
  				       tun16_to_cpu(tun, gso.hdr_len));
  				print_hex_dump(KERN_ERR, "tun: ",
  					       DUMP_PREFIX_NONE,
  					       16, 1, skb->head,
  					       min((int)tun16_to_cpu(tun, gso.hdr_len), 64), true);
  				WARN_ON_ONCE(1);
  				return -EINVAL;
  			}
  			if (sinfo->gso_type & SKB_GSO_TCP_ECN)
  				gso.gso_type |= VIRTIO_NET_HDR_GSO_ECN;
  		} else
  			gso.gso_type = VIRTIO_NET_HDR_GSO_NONE;
  
  		if (skb->ip_summed == CHECKSUM_PARTIAL) {
  			gso.flags = VIRTIO_NET_HDR_F_NEEDS_CSUM;
  			gso.csum_start = cpu_to_tun16(tun, skb_checksum_start_offset(skb) +
  						      vlan_hlen);
  			gso.csum_offset = cpu_to_tun16(tun, skb->csum_offset);
  		} else if (skb->ip_summed == CHECKSUM_UNNECESSARY) {
  			gso.flags = VIRTIO_NET_HDR_F_DATA_VALID;
  		} /* else everything is zero */
  
  		if (copy_to_iter(&gso, sizeof(gso), iter) != sizeof(gso))
  			return -EFAULT;
  
  		iov_iter_advance(iter, vnet_hdr_sz - sizeof(gso));
  	}
  
  	if (vlan_hlen) {
  		int ret;
  		struct {
  			__be16 h_vlan_proto;
  			__be16 h_vlan_TCI;
  		} veth;
  
  		veth.h_vlan_proto = skb->vlan_proto;
  		veth.h_vlan_TCI = htons(skb_vlan_tag_get(skb));
  
  		vlan_offset = offsetof(struct vlan_ethhdr, h_vlan_proto);
  
  		ret = skb_copy_datagram_iter(skb, 0, iter, vlan_offset);
  		if (ret || !iov_iter_count(iter))
  			goto done;
  
  		ret = copy_to_iter(&veth, sizeof(veth), iter);
  		if (ret != sizeof(veth) || !iov_iter_count(iter))
  			goto done;
  	}
  
  	skb_copy_datagram_iter(skb, vlan_offset, iter, skb->len - vlan_offset);
  
  done:
  	tun->dev->stats.tx_packets++;
  	tun->dev->stats.tx_bytes += skb->len + vlan_hlen;
  
  	return total;
  }
  
  static ssize_t tun_do_read(struct tun_struct *tun, struct tun_file *tfile,
  			   struct iov_iter *to,
  			   int noblock)
  {
  	struct sk_buff *skb;
  	ssize_t ret;
  	int peeked, err, off = 0;
  
  	tun_debug(KERN_INFO, tun, "tun_do_read\n");
  
  	if (!iov_iter_count(to))
  		return 0;
  
  	if (tun->dev->reg_state != NETREG_REGISTERED)
  		return -EIO;
  
  	/* Read frames from queue */
  	skb = __skb_recv_datagram(tfile->socket.sk, noblock ? MSG_DONTWAIT : 0,
  				  &peeked, &off, &err);
  	if (!skb)
  		return err;
  
  	ret = tun_put_user(tun, tfile, skb, to);
  	if (unlikely(ret < 0))
  		kfree_skb(skb);
  	else
  		consume_skb(skb);
  
  	return ret;
  }
  
  static ssize_t tun_chr_read_iter(struct kiocb *iocb, struct iov_iter *to)
  {
  	struct file *file = iocb->ki_filp;
  	struct tun_file *tfile = file->private_data;
  	struct tun_struct *tun = __tun_get(tfile);
  	ssize_t len = iov_iter_count(to), ret;
  
  	if (!tun)
  		return -EBADFD;
  	ret = tun_do_read(tun, tfile, to, file->f_flags & O_NONBLOCK);
  	ret = min_t(ssize_t, ret, len);
  	if (ret > 0)
  		iocb->ki_pos = ret;
  	tun_put(tun);
  	return ret;
  }
  
  static void tun_free_netdev(struct net_device *dev)
  {
  	struct tun_struct *tun = netdev_priv(dev);
  
  	BUG_ON(!(list_empty(&tun->disabled)));
  	tun_flow_uninit(tun);
  	security_tun_dev_free_security(tun->security);
  	free_netdev(dev);
  }
  
  static void tun_setup(struct net_device *dev)
  {
  	struct tun_struct *tun = netdev_priv(dev);
  
  	tun->owner = INVALID_UID;
  	tun->group = INVALID_GID;
  
  	dev->ethtool_ops = &tun_ethtool_ops;
  	dev->destructor = tun_free_netdev;
  }
  
  /* Trivial set of netlink ops to allow deleting tun or tap
   * device with netlink.
   */
  static int tun_validate(struct nlattr *tb[], struct nlattr *data[])
  {
  	return -EINVAL;
  }
  
  static struct rtnl_link_ops tun_link_ops __read_mostly = {
  	.kind		= DRV_NAME,
  	.priv_size	= sizeof(struct tun_struct),
  	.setup		= tun_setup,
  	.validate	= tun_validate,
  };
  
  static void tun_sock_write_space(struct sock *sk)
  {
  	struct tun_file *tfile;
  	wait_queue_head_t *wqueue;
  
  	if (!sock_writeable(sk))
  		return;
  
  	if (!test_and_clear_bit(SOCK_ASYNC_NOSPACE, &sk->sk_socket->flags))
  		return;
  
  	wqueue = sk_sleep(sk);
  	if (wqueue && waitqueue_active(wqueue))
  		wake_up_interruptible_sync_poll(wqueue, POLLOUT |
  						POLLWRNORM | POLLWRBAND);
  
  	tfile = container_of(sk, struct tun_file, sk);
  	kill_fasync(&tfile->fasync, SIGIO, POLL_OUT);
  }
  
  static int tun_sendmsg(struct socket *sock, struct msghdr *m, size_t total_len)
  {
  	int ret;
  	struct tun_file *tfile = container_of(sock, struct tun_file, socket);
  	struct tun_struct *tun = __tun_get(tfile);
  
  	if (!tun)
  		return -EBADFD;
  
  	ret = tun_get_user(tun, tfile, m->msg_control, &m->msg_iter,
  			   m->msg_flags & MSG_DONTWAIT);
  	tun_put(tun);
  	return ret;
  }
  
  static int tun_recvmsg(struct socket *sock, struct msghdr *m, size_t total_len,
  		       int flags)
  {
  	struct tun_file *tfile = container_of(sock, struct tun_file, socket);
  	struct tun_struct *tun = __tun_get(tfile);
  	int ret;
  
  	if (!tun)
  		return -EBADFD;
  
  	if (flags & ~(MSG_DONTWAIT|MSG_TRUNC|MSG_ERRQUEUE)) {
  		ret = -EINVAL;
  		goto out;
  	}
  	if (flags & MSG_ERRQUEUE) {
  		ret = sock_recv_errqueue(sock->sk, m, total_len,
  					 SOL_PACKET, TUN_TX_TIMESTAMP);
  		goto out;
  	}
  	ret = tun_do_read(tun, tfile, &m->msg_iter, flags & MSG_DONTWAIT);
  	if (ret > (ssize_t)total_len) {
  		m->msg_flags |= MSG_TRUNC;
  		ret = flags & MSG_TRUNC ? ret : total_len;
  	}
  out:
  	tun_put(tun);
  	return ret;
  }
  
  static int tun_release(struct socket *sock)
  {
  	if (sock->sk)
  		sock_put(sock->sk);
  	return 0;
  }
  
  /* Ops structure to mimic raw sockets with tun */
  static const struct proto_ops tun_socket_ops = {
  	.sendmsg = tun_sendmsg,
  	.recvmsg = tun_recvmsg,
  	.release = tun_release,
  };
  
  static struct proto tun_proto = {
  	.name		= "tun",
  	.owner		= THIS_MODULE,
  	.obj_size	= sizeof(struct tun_file),
  };
  
  static int tun_flags(struct tun_struct *tun)
  {
  	return tun->flags & (TUN_FEATURES | IFF_PERSIST | IFF_TUN | IFF_TAP);
  }
  
  static ssize_t tun_show_flags(struct device *dev, struct device_attribute *attr,
  			      char *buf)
  {
  	struct tun_struct *tun = netdev_priv(to_net_dev(dev));
  	return sprintf(buf, "0x%x\n", tun_flags(tun));
  }
  
  static ssize_t tun_show_owner(struct device *dev, struct device_attribute *attr,
  			      char *buf)
  {
  	struct tun_struct *tun = netdev_priv(to_net_dev(dev));
  	return uid_valid(tun->owner)?
  		sprintf(buf, "%u\n",
  			from_kuid_munged(current_user_ns(), tun->owner)):
  		sprintf(buf, "-1\n");
  }
  
  static ssize_t tun_show_group(struct device *dev, struct device_attribute *attr,
  			      char *buf)
  {
  	struct tun_struct *tun = netdev_priv(to_net_dev(dev));
  	return gid_valid(tun->group) ?
  		sprintf(buf, "%u\n",
  			from_kgid_munged(current_user_ns(), tun->group)):
  		sprintf(buf, "-1\n");
  }
  
  static DEVICE_ATTR(tun_flags, 0444, tun_show_flags, NULL);
  static DEVICE_ATTR(owner, 0444, tun_show_owner, NULL);
  static DEVICE_ATTR(group, 0444, tun_show_group, NULL);
  
  static struct attribute *tun_dev_attrs[] = {
  	&dev_attr_tun_flags.attr,
  	&dev_attr_owner.attr,
  	&dev_attr_group.attr,
  	NULL
  };
  
  static const struct attribute_group tun_attr_group = {
  	.attrs = tun_dev_attrs
  };
  
  static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
  {
  	struct tun_struct *tun;
  	struct tun_file *tfile = file->private_data;
  	struct net_device *dev;
  	int err;
  
  	if (tfile->detached)
  		return -EINVAL;
  
  	dev = __dev_get_by_name(net, ifr->ifr_name);
  	if (dev) {
  		if (ifr->ifr_flags & IFF_TUN_EXCL)
  			return -EBUSY;
  		if ((ifr->ifr_flags & IFF_TUN) && dev->netdev_ops == &tun_netdev_ops)
  			tun = netdev_priv(dev);
  		else if ((ifr->ifr_flags & IFF_TAP) && dev->netdev_ops == &tap_netdev_ops)
  			tun = netdev_priv(dev);
  		else
  			return -EINVAL;
  
  		if (!!(ifr->ifr_flags & IFF_MULTI_QUEUE) !=
  		    !!(tun->flags & IFF_MULTI_QUEUE))
  			return -EINVAL;
  
  		if (tun_not_capable(tun))
  			return -EPERM;
  		err = security_tun_dev_open(tun->security);
  		if (err < 0)
  			return err;
  
  		err = tun_attach(tun, file, ifr->ifr_flags & IFF_NOFILTER);
  		if (err < 0)
  			return err;
  
  		if (tun->flags & IFF_MULTI_QUEUE &&
  		    (tun->numqueues + tun->numdisabled > 1)) {
  			/* One or more queue has already been attached, no need
  			 * to initialize the device again.
  			 */
  			return 0;
  		}
  	}
  	else {
  		char *name;
  		unsigned long flags = 0;
  		int queues = ifr->ifr_flags & IFF_MULTI_QUEUE ?
  			     MAX_TAP_QUEUES : 1;
  
  		if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
  			return -EPERM;
  		err = security_tun_dev_create();
  		if (err < 0)
  			return err;
  
  		/* Set dev type */
  		if (ifr->ifr_flags & IFF_TUN) {
  			/* TUN device */
  			flags |= IFF_TUN;
  			name = "tun%d";
  		} else if (ifr->ifr_flags & IFF_TAP) {
  			/* TAP device */
  			flags |= IFF_TAP;
  			name = "tap%d";
  		} else
  			return -EINVAL;
  
  		if (*ifr->ifr_name)
  			name = ifr->ifr_name;
  
  		dev = alloc_netdev_mqs(sizeof(struct tun_struct), name,
  				       NET_NAME_UNKNOWN, tun_setup, queues,
  				       queues);
  
  		if (!dev)
  			return -ENOMEM;
  
  		dev_net_set(dev, net);
  		dev->rtnl_link_ops = &tun_link_ops;
  		dev->ifindex = tfile->ifindex;
  		dev->sysfs_groups[0] = &tun_attr_group;
  
  		tun = netdev_priv(dev);
  		tun->dev = dev;
  		tun->flags = flags;
  		tun->txflt.count = 0;
  		tun->vnet_hdr_sz = sizeof(struct virtio_net_hdr);
  
  		tun->filter_attached = false;
  		tun->sndbuf = tfile->socket.sk->sk_sndbuf;
  
  		spin_lock_init(&tun->lock);
  
  		err = security_tun_dev_alloc_security(&tun->security);
  		if (err < 0)
  			goto err_free_dev;
  
  		tun_net_init(dev);
  		tun_flow_init(tun);
  
  		dev->hw_features = NETIF_F_SG | NETIF_F_FRAGLIST |
  				   TUN_USER_FEATURES | NETIF_F_HW_VLAN_CTAG_TX |
  				   NETIF_F_HW_VLAN_STAG_TX;
  		dev->features = dev->hw_features;
  		dev->vlan_features = dev->features &
  				     ~(NETIF_F_HW_VLAN_CTAG_TX |
  				       NETIF_F_HW_VLAN_STAG_TX);
  
  		INIT_LIST_HEAD(&tun->disabled);
  		err = tun_attach(tun, file, false);
  		if (err < 0)
  			goto err_free_flow;
  
  		err = register_netdevice(tun->dev);
  		if (err < 0)
  			goto err_detach;
  	}
  
  	netif_carrier_on(tun->dev);
  
  	tun_debug(KERN_INFO, tun, "tun_set_iff\n");
  
  	tun->flags = (tun->flags & ~TUN_FEATURES) |
  		(ifr->ifr_flags & TUN_FEATURES);
  
  	/* Make sure persistent devices do not get stuck in
  	 * xoff state.
  	 */
  	if (netif_running(tun->dev))
  		netif_tx_wake_all_queues(tun->dev);
  
  	strcpy(ifr->ifr_name, tun->dev->name);
  	return 0;
  
  err_detach:
  	tun_detach_all(dev);
  err_free_flow:
  	tun_flow_uninit(tun);
  	security_tun_dev_free_security(tun->security);
  err_free_dev:
  	free_netdev(dev);
  	return err;
  }
  
  static void tun_get_iff(struct net *net, struct tun_struct *tun,
  		       struct ifreq *ifr)
  {
  	tun_debug(KERN_INFO, tun, "tun_get_iff\n");
  
  	strcpy(ifr->ifr_name, tun->dev->name);
  
  	ifr->ifr_flags = tun_flags(tun);
  
  }
  
  /* This is like a cut-down ethtool ops, except done via tun fd so no
   * privs required. */
  static int set_offload(struct tun_struct *tun, unsigned long arg)
  {
  	netdev_features_t features = 0;
  
  	if (arg & TUN_F_CSUM) {
  		features |= NETIF_F_HW_CSUM;
  		arg &= ~TUN_F_CSUM;
  
  		if (arg & (TUN_F_TSO4|TUN_F_TSO6)) {
  			if (arg & TUN_F_TSO_ECN) {
  				features |= NETIF_F_TSO_ECN;
  				arg &= ~TUN_F_TSO_ECN;
  			}
  			if (arg & TUN_F_TSO4)
  				features |= NETIF_F_TSO;
  			if (arg & TUN_F_TSO6)
  				features |= NETIF_F_TSO6;
  			arg &= ~(TUN_F_TSO4|TUN_F_TSO6);
  		}
  
  		if (arg & TUN_F_UFO) {
  			features |= NETIF_F_UFO;
  			arg &= ~TUN_F_UFO;
  		}
  	}
  
  	/* This gives the user a way to test for new features in future by
  	 * trying to set them. */
  	if (arg)
  		return -EINVAL;
  
  	tun->set_features = features;
  	netdev_update_features(tun->dev);
  
  	return 0;
  }
  
  static void tun_detach_filter(struct tun_struct *tun, int n)
  {
  	int i;
  	struct tun_file *tfile;
  
  	for (i = 0; i < n; i++) {
  		tfile = rtnl_dereference(tun->tfiles[i]);
  		sk_detach_filter(tfile->socket.sk);
  	}
  
  	tun->filter_attached = false;
  }
  
  static int tun_attach_filter(struct tun_struct *tun)
  {
  	int i, ret = 0;
  	struct tun_file *tfile;
  
  	for (i = 0; i < tun->numqueues; i++) {
  		tfile = rtnl_dereference(tun->tfiles[i]);
  		ret = sk_attach_filter(&tun->fprog, tfile->socket.sk);
  		if (ret) {
  			tun_detach_filter(tun, i);
  			return ret;
  		}
  	}
  
  	tun->filter_attached = true;
  	return ret;
  }
  
  static void tun_set_sndbuf(struct tun_struct *tun)
  {
  	struct tun_file *tfile;
  	int i;
  
  	for (i = 0; i < tun->numqueues; i++) {
  		tfile = rtnl_dereference(tun->tfiles[i]);
  		tfile->socket.sk->sk_sndbuf = tun->sndbuf;
  	}
  }
  
  static int tun_set_queue(struct file *file, struct ifreq *ifr)
  {
  	struct tun_file *tfile = file->private_data;
  	struct tun_struct *tun;
  	int ret = 0;
  
  	rtnl_lock();
  
  	if (ifr->ifr_flags & IFF_ATTACH_QUEUE) {
  		tun = tfile->detached;
  		if (!tun) {
  			ret = -EINVAL;
  			goto unlock;
  		}
  		ret = security_tun_dev_attach_queue(tun->security);
  		if (ret < 0)
  			goto unlock;
  		ret = tun_attach(tun, file, false);
  	} else if (ifr->ifr_flags & IFF_DETACH_QUEUE) {
  		tun = rtnl_dereference(tfile->tun);
  		if (!tun || !(tun->flags & IFF_MULTI_QUEUE) || tfile->detached)
  			ret = -EINVAL;
  		else
  			__tun_detach(tfile, false);
  	} else
  		ret = -EINVAL;
  
  unlock:
  	rtnl_unlock();
  	return ret;
  }
  
  static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
  			    unsigned long arg, int ifreq_len)
  {
  	struct tun_file *tfile = file->private_data;
  	struct tun_struct *tun;
  	void __user* argp = (void __user*)arg;
  	struct ifreq ifr;
  	kuid_t owner;
  	kgid_t group;
  	int sndbuf;
  	int vnet_hdr_sz;
  	unsigned int ifindex;
  	int le;
  	int ret;
  
  #ifdef CONFIG_ANDROID_PARANOID_NETWORK
  	if (cmd != TUNGETIFF && !capable(CAP_NET_ADMIN)) {
  		return -EPERM;
  	}
  #endif
  
  	if (cmd == TUNSETIFF || cmd == TUNSETQUEUE || _IOC_TYPE(cmd) == 0x89) {
  		if (copy_from_user(&ifr, argp, ifreq_len))
  			return -EFAULT;
  	} else {
  		memset(&ifr, 0, sizeof(ifr));
  	}
  	if (cmd == TUNGETFEATURES) {
  		/* Currently this just means: "what IFF flags are valid?".
  		 * This is needed because we never checked for invalid flags on
  		 * TUNSETIFF.
  		 */
  		return put_user(IFF_TUN | IFF_TAP | TUN_FEATURES,
  				(unsigned int __user*)argp);
  	} else if (cmd == TUNSETQUEUE)
  		return tun_set_queue(file, &ifr);
  
  	ret = 0;
  	rtnl_lock();
  
  	tun = __tun_get(tfile);
  	if (cmd == TUNSETIFF && !tun) {
  		ifr.ifr_name[IFNAMSIZ-1] = '\0';
  
  		ret = tun_set_iff(tfile->net, file, &ifr);
  
  		if (ret)
  			goto unlock;
  
  		if (copy_to_user(argp, &ifr, ifreq_len))
  			ret = -EFAULT;
  		goto unlock;
  	}
  	if (cmd == TUNSETIFINDEX) {
  		ret = -EPERM;
  		if (tun)
  			goto unlock;
  
  		ret = -EFAULT;
  		if (copy_from_user(&ifindex, argp, sizeof(ifindex)))
  			goto unlock;
  
  		ret = 0;
  		tfile->ifindex = ifindex;
  		goto unlock;
  	}
  
  	ret = -EBADFD;
  	if (!tun)
  		goto unlock;
  
  	tun_debug(KERN_INFO, tun, "tun_chr_ioctl cmd %u\n", cmd);
  
  	ret = 0;
  	switch (cmd) {
  	case TUNGETIFF:
  		tun_get_iff(current->nsproxy->net_ns, tun, &ifr);
  
  		if (tfile->detached)
  			ifr.ifr_flags |= IFF_DETACH_QUEUE;
  		if (!tfile->socket.sk->sk_filter)
  			ifr.ifr_flags |= IFF_NOFILTER;
  
  		if (copy_to_user(argp, &ifr, ifreq_len))
  			ret = -EFAULT;
  		break;
  
  	case TUNSETNOCSUM:
  		/* Disable/Enable checksum */
  
  		/* [unimplemented] */
  		tun_debug(KERN_INFO, tun, "ignored: set checksum %s\n",
  			  arg ? "disabled" : "enabled");
  		break;
  
  	case TUNSETPERSIST:
  		/* Disable/Enable persist mode. Keep an extra reference to the
  		 * module to prevent the module being unprobed.
  		 */
  		if (arg && !(tun->flags & IFF_PERSIST)) {
  			tun->flags |= IFF_PERSIST;
  			__module_get(THIS_MODULE);
  		}
  		if (!arg && (tun->flags & IFF_PERSIST)) {
  			tun->flags &= ~IFF_PERSIST;
  			module_put(THIS_MODULE);
  		}
  
  		tun_debug(KERN_INFO, tun, "persist %s\n",
  			  arg ? "enabled" : "disabled");
  		break;
  
  	case TUNSETOWNER:
  		/* Set owner of the device */
  		owner = make_kuid(current_user_ns(), arg);
  		if (!uid_valid(owner)) {
  			ret = -EINVAL;
  			break;
  		}
  		tun->owner = owner;
  		tun_debug(KERN_INFO, tun, "owner set to %u\n",
  			  from_kuid(&init_user_ns, tun->owner));
  		break;
  
  	case TUNSETGROUP:
  		/* Set group of the device */
  		group = make_kgid(current_user_ns(), arg);
  		if (!gid_valid(group)) {
  			ret = -EINVAL;
  			break;
  		}
  		tun->group = group;
  		tun_debug(KERN_INFO, tun, "group set to %u\n",
  			  from_kgid(&init_user_ns, tun->group));
  		break;
  
  	case TUNSETLINK:
  		/* Only allow setting the type when the interface is down */
  		if (tun->dev->flags & IFF_UP) {
  			tun_debug(KERN_INFO, tun,
  				  "Linktype set failed because interface is up\n");
  			ret = -EBUSY;
  		} else {
  			tun->dev->type = (int) arg;
  			tun_debug(KERN_INFO, tun, "linktype set to %d\n",
  				  tun->dev->type);
  			ret = 0;
  		}
  		break;
  
  #ifdef TUN_DEBUG
  	case TUNSETDEBUG:
  		tun->debug = arg;
  		break;
  #endif
  	case TUNSETOFFLOAD:
  		ret = set_offload(tun, arg);
  		break;
  
  	case TUNSETTXFILTER:
  		/* Can be set only for TAPs */
  		ret = -EINVAL;
  		if ((tun->flags & TUN_TYPE_MASK) != IFF_TAP)
  			break;
  		ret = update_filter(&tun->txflt, (void __user *)arg);
  		break;
  
  	case SIOCGIFHWADDR:
  		/* Get hw address */
  		memcpy(ifr.ifr_hwaddr.sa_data, tun->dev->dev_addr, ETH_ALEN);
  		ifr.ifr_hwaddr.sa_family = tun->dev->type;
  		if (copy_to_user(argp, &ifr, ifreq_len))
  			ret = -EFAULT;
  		break;
  
  	case SIOCSIFHWADDR:
  		/* Set hw address */
  		tun_debug(KERN_DEBUG, tun, "set hw address: %pM\n",
  			  ifr.ifr_hwaddr.sa_data);
  
  		ret = dev_set_mac_address(tun->dev, &ifr.ifr_hwaddr);
  		break;
  
  	case TUNGETSNDBUF:
  		sndbuf = tfile->socket.sk->sk_sndbuf;
  		if (copy_to_user(argp, &sndbuf, sizeof(sndbuf)))
  			ret = -EFAULT;
  		break;
  
  	case TUNSETSNDBUF:
  		if (copy_from_user(&sndbuf, argp, sizeof(sndbuf))) {
  			ret = -EFAULT;
  			break;
  		}
  
  		tun->sndbuf = sndbuf;
  		tun_set_sndbuf(tun);
  		break;
  
  	case TUNGETVNETHDRSZ:
  		vnet_hdr_sz = tun->vnet_hdr_sz;
  		if (copy_to_user(argp, &vnet_hdr_sz, sizeof(vnet_hdr_sz)))
  			ret = -EFAULT;
  		break;
  
  	case TUNSETVNETHDRSZ:
  		if (copy_from_user(&vnet_hdr_sz, argp, sizeof(vnet_hdr_sz))) {
  			ret = -EFAULT;
  			break;
  		}
  		if (vnet_hdr_sz < (int)sizeof(struct virtio_net_hdr)) {
  			ret = -EINVAL;
  			break;
  		}
  
  		tun->vnet_hdr_sz = vnet_hdr_sz;
  		break;
  
  	case TUNGETVNETLE:
  		le = !!(tun->flags & TUN_VNET_LE);
  		if (put_user(le, (int __user *)argp))
  			ret = -EFAULT;
  		break;
  
  	case TUNSETVNETLE:
  		if (get_user(le, (int __user *)argp)) {
  			ret = -EFAULT;
  			break;
  		}
  		if (le)
  			tun->flags |= TUN_VNET_LE;
  		else
  			tun->flags &= ~TUN_VNET_LE;
  		break;
  
  	case TUNATTACHFILTER:
  		/* Can be set only for TAPs */
  		ret = -EINVAL;
  		if ((tun->flags & TUN_TYPE_MASK) != IFF_TAP)
  			break;
  		ret = -EFAULT;
  		if (copy_from_user(&tun->fprog, argp, sizeof(tun->fprog)))
  			break;
  
  		ret = tun_attach_filter(tun);
  		break;
  
  	case TUNDETACHFILTER:
  		/* Can be set only for TAPs */
  		ret = -EINVAL;
  		if ((tun->flags & TUN_TYPE_MASK) != IFF_TAP)
  			break;
  		ret = 0;
  		tun_detach_filter(tun, tun->numqueues);
  		break;
  
  	case TUNGETFILTER:
  		ret = -EINVAL;
  		if ((tun->flags & TUN_TYPE_MASK) != IFF_TAP)
  			break;
  		ret = -EFAULT;
  		if (copy_to_user(argp, &tun->fprog, sizeof(tun->fprog)))
  			break;
  		ret = 0;
  		break;
  
  	default:
  		ret = -EINVAL;
  		break;
  	}
  
  unlock:
  	rtnl_unlock();
  	if (tun)
  		tun_put(tun);
  	return ret;
  }
  
  static long tun_chr_ioctl(struct file *file,
  			  unsigned int cmd, unsigned long arg)
  {
  	return __tun_chr_ioctl(file, cmd, arg, sizeof (struct ifreq));
  }
  
  #ifdef CONFIG_COMPAT
  static long tun_chr_compat_ioctl(struct file *file,
  			 unsigned int cmd, unsigned long arg)
  {
  	switch (cmd) {
  	case TUNSETIFF:
  	case TUNGETIFF:
  	case TUNSETTXFILTER:
  	case TUNGETSNDBUF:
  	case TUNSETSNDBUF:
  	case SIOCGIFHWADDR:
  	case SIOCSIFHWADDR:
  		arg = (unsigned long)compat_ptr(arg);
  		break;
  	default:
  		arg = (compat_ulong_t)arg;
  		break;
  	}
  
  	/*
  	 * compat_ifreq is shorter than ifreq, so we must not access beyond
  	 * the end of that structure. All fields that are used in this
  	 * driver are compatible though, we don't need to convert the
  	 * contents.
  	 */
  	return __tun_chr_ioctl(file, cmd, arg, sizeof(struct compat_ifreq));
  }
  #endif /* CONFIG_COMPAT */
  
  static int tun_chr_fasync(int fd, struct file *file, int on)
  {
  	struct tun_file *tfile = file->private_data;
  	int ret;
  
  	if ((ret = fasync_helper(fd, file, on, &tfile->fasync)) < 0)
  		goto out;
  
  	if (on) {
  		__f_setown(file, task_pid(current), PIDTYPE_PID, 0);
  		tfile->flags |= TUN_FASYNC;
  	} else
  		tfile->flags &= ~TUN_FASYNC;
  	ret = 0;
  out:
  	return ret;
  }
  
  static int tun_chr_open(struct inode *inode, struct file * file)
  {
  	struct tun_file *tfile;
  
  	DBG1(KERN_INFO, "tunX: tun_chr_open\n");
  
  	tfile = (struct tun_file *)sk_alloc(&init_net, AF_UNSPEC, GFP_KERNEL,
  					    &tun_proto);
  	if (!tfile)
  		return -ENOMEM;
  	RCU_INIT_POINTER(tfile->tun, NULL);
  	tfile->net = get_net(current->nsproxy->net_ns);
  	tfile->flags = 0;
  	tfile->ifindex = 0;
  
  	init_waitqueue_head(&tfile->wq.wait);
  	RCU_INIT_POINTER(tfile->socket.wq, &tfile->wq);
  
  	tfile->socket.file = file;
  	tfile->socket.ops = &tun_socket_ops;
  
  	sock_init_data(&tfile->socket, &tfile->sk);
  	sk_change_net(&tfile->sk, tfile->net);
  
  	tfile->sk.sk_write_space = tun_sock_write_space;
  	tfile->sk.sk_sndbuf = INT_MAX;
  
  	file->private_data = tfile;
  	set_bit(SOCK_EXTERNALLY_ALLOCATED, &tfile->socket.flags);
  	INIT_LIST_HEAD(&tfile->next);
  
  	sock_set_flag(&tfile->sk, SOCK_ZEROCOPY);
  
  	return 0;
  }
  
  static int tun_chr_close(struct inode *inode, struct file *file)
  {
  	struct tun_file *tfile = file->private_data;
  	struct net *net = tfile->net;
  
  	tun_detach(tfile, true);
  	put_net(net);
  
  	return 0;
  }
  
  #ifdef CONFIG_PROC_FS
  static void tun_chr_show_fdinfo(struct seq_file *m, struct file *f)
  {
  	struct tun_struct *tun;
  	struct ifreq ifr;
  
  	memset(&ifr, 0, sizeof(ifr));
  
  	rtnl_lock();
  	tun = tun_get(f);
  	if (tun)
  		tun_get_iff(current->nsproxy->net_ns, tun, &ifr);
  	rtnl_unlock();
  
  	if (tun)
  		tun_put(tun);
  
  	seq_printf(m, "iff:\t%s\n", ifr.ifr_name);
  }
  #endif
  
  static const struct file_operations tun_fops = {
  	.owner	= THIS_MODULE,
  	.llseek = no_llseek,
  	.read_iter  = tun_chr_read_iter,
  	.write_iter = tun_chr_write_iter,
  	.poll	= tun_chr_poll,
  	.unlocked_ioctl	= tun_chr_ioctl,
  #ifdef CONFIG_COMPAT
  	.compat_ioctl = tun_chr_compat_ioctl,
  #endif
  	.open	= tun_chr_open,
  	.release = tun_chr_close,
  	.fasync = tun_chr_fasync,
  #ifdef CONFIG_PROC_FS
  	.show_fdinfo = tun_chr_show_fdinfo,
  #endif
  };
  
  static struct miscdevice tun_miscdev = {
  	.minor = TUN_MINOR,
  	.name = "tun",
  	.nodename = "net/tun",
  	.fops = &tun_fops,
  };
  
  /* ethtool interface */
  
  static int tun_get_settings(struct net_device *dev, struct ethtool_cmd *cmd)
  {
  	cmd->supported		= 0;
  	cmd->advertising	= 0;
  	ethtool_cmd_speed_set(cmd, SPEED_10);
  	cmd->duplex		= DUPLEX_FULL;
  	cmd->port		= PORT_TP;
  	cmd->phy_address	= 0;
  	cmd->transceiver	= XCVR_INTERNAL;
  	cmd->autoneg		= AUTONEG_DISABLE;
  	cmd->maxtxpkt		= 0;
  	cmd->maxrxpkt		= 0;
  	return 0;
  }
  
  static void tun_get_drvinfo(struct net_device *dev, struct ethtool_drvinfo *info)
  {
  	struct tun_struct *tun = netdev_priv(dev);
  
  	strlcpy(info->driver, DRV_NAME, sizeof(info->driver));
  	strlcpy(info->version, DRV_VERSION, sizeof(info->version));
  
  	switch (tun->flags & TUN_TYPE_MASK) {
  	case IFF_TUN:
  		strlcpy(info->bus_info, "tun", sizeof(info->bus_info));
  		break;
  	case IFF_TAP:
  		strlcpy(info->bus_info, "tap", sizeof(info->bus_info));
  		break;
  	}
  }
  
  static u32 tun_get_msglevel(struct net_device *dev)
  {
  #ifdef TUN_DEBUG
  	struct tun_struct *tun = netdev_priv(dev);
  	return tun->debug;
  #else
  	return -EOPNOTSUPP;
  #endif
  }
  
  static void tun_set_msglevel(struct net_device *dev, u32 value)
  {
  #ifdef TUN_DEBUG
  	struct tun_struct *tun = netdev_priv(dev);
  	tun->debug = value;
  #endif
  }
  
  static const struct ethtool_ops tun_ethtool_ops = {
  	.get_settings	= tun_get_settings,
  	.get_drvinfo	= tun_get_drvinfo,
  	.get_msglevel	= tun_get_msglevel,
  	.set_msglevel	= tun_set_msglevel,
  	.get_link	= ethtool_op_get_link,
  	.get_ts_info	= ethtool_op_get_ts_info,
  };
  
  
  static int __init tun_init(void)
  {
  	int ret = 0;
  
  	pr_info("%s, %s\n", DRV_DESCRIPTION, DRV_VERSION);
  	pr_info("%s\n", DRV_COPYRIGHT);
  
  	ret = rtnl_link_register(&tun_link_ops);
  	if (ret) {
  		pr_err("Can't register link_ops\n");
  		goto err_linkops;
  	}
  
  	ret = misc_register(&tun_miscdev);
  	if (ret) {
  		pr_err("Can't register misc device %d\n", TUN_MINOR);
  		goto err_misc;
  	}
  	return  0;
  err_misc:
  	rtnl_link_unregister(&tun_link_ops);
  err_linkops:
  	return ret;
  }
  
  static void tun_cleanup(void)
  {
  	misc_deregister(&tun_miscdev);
  	rtnl_link_unregister(&tun_link_ops);
  }
  
  /* Get an underlying socket object from tun file.  Returns error unless file is
   * attached to a device.  The returned object works like a packet socket, it
   * can be used for sock_sendmsg/sock_recvmsg.  The caller is responsible for
   * holding a reference to the file for as long as the socket is in use. */
  struct socket *tun_get_socket(struct file *file)
  {
  	struct tun_file *tfile;
  	if (file->f_op != &tun_fops)
  		return ERR_PTR(-EINVAL);
  	tfile = file->private_data;
  	if (!tfile)
  		return ERR_PTR(-EBADFD);
  	return &tfile->socket;
  }
  EXPORT_SYMBOL_GPL(tun_get_socket);
  
  module_init(tun_init);
  module_exit(tun_cleanup);
  MODULE_DESCRIPTION(DRV_DESCRIPTION);
  MODULE_AUTHOR(DRV_COPYRIGHT);
  MODULE_LICENSE("GPL");
  MODULE_ALIAS_MISCDEV(TUN_MINOR);
  MODULE_ALIAS("devname:net/tun");
  