text: #include <linux/etherdevice.h>
  #include <linux/if_tap.h>
  #include <linux/if_vlan.h>
  #include <linux/interrupt.h>
  #include <linux/nsproxy.h>
  #include <linux/compat.h>
  #include <linux/if_tun.h>
  #include <linux/module.h>
  #include <linux/skbuff.h>
  #include <linux/cache.h>
  #include <linux/sched/signal.h>
  #include <linux/types.h>
  #include <linux/slab.h>
  #include <linux/wait.h>
  #include <linux/cdev.h>
  #include <linux/idr.h>
  #include <linux/fs.h>
  #include <linux/uio.h>
  
  #include <net/net_namespace.h>
  #include <net/rtnetlink.h>
  #include <net/sock.h>
  #include <linux/virtio_net.h>
  #include <linux/skb_array.h>
  
  #define TAP_IFFEATURES (IFF_VNET_HDR | IFF_MULTI_QUEUE)
  
  #define TAP_VNET_LE 0x80000000
  #define TAP_VNET_BE 0x40000000
  
  #ifdef CONFIG_TUN_VNET_CROSS_LE
  static inline bool tap_legacy_is_little_endian(struct tap_queue *q)
  {
  	return q->flags & TAP_VNET_BE ? false :
  		virtio_legacy_is_little_endian();
  }
  
  static long tap_get_vnet_be(struct tap_queue *q, int __user *sp)
  {
  	int s = !!(q->flags & TAP_VNET_BE);
  
  	if (put_user(s, sp))
  		return -EFAULT;
  
  	return 0;
  }
  
  static long tap_set_vnet_be(struct tap_queue *q, int __user *sp)
  {
  	int s;
  
  	if (get_user(s, sp))
  		return -EFAULT;
  
  	if (s)
  		q->flags |= TAP_VNET_BE;
  	else
  		q->flags &= ~TAP_VNET_BE;
  
  	return 0;
  }
  #else
  static inline bool tap_legacy_is_little_endian(struct tap_queue *q)
  {
  	return virtio_legacy_is_little_endian();
  }
  
  static long tap_get_vnet_be(struct tap_queue *q, int __user *argp)
  {
  	return -EINVAL;
  }
  
  static long tap_set_vnet_be(struct tap_queue *q, int __user *argp)
  {
  	return -EINVAL;
  }
  #endif /* CONFIG_TUN_VNET_CROSS_LE */
  
  static inline bool tap_is_little_endian(struct tap_queue *q)
  {
  	return q->flags & TAP_VNET_LE ||
  		tap_legacy_is_little_endian(q);
  }
  
  static inline u16 tap16_to_cpu(struct tap_queue *q, __virtio16 val)
  {
  	return __virtio16_to_cpu(tap_is_little_endian(q), val);
  }
  
  static inline __virtio16 cpu_to_tap16(struct tap_queue *q, u16 val)
  {
  	return __cpu_to_virtio16(tap_is_little_endian(q), val);
  }
  
  static struct proto tap_proto = {
  	.name = "tap",
  	.owner = THIS_MODULE,
  	.obj_size = sizeof(struct tap_queue),
  };
  
  #define TAP_NUM_DEVS (1U << MINORBITS)
  
  static LIST_HEAD(major_list);
  
  struct major_info {
  	struct rcu_head rcu;
  	dev_t major;
  	struct idr minor_idr;
  	spinlock_t minor_lock;
  	const char *device_name;
  	struct list_head next;
  };
  
  #define GOODCOPY_LEN 128
  
  static const struct proto_ops tap_socket_ops;
  
  #define RX_OFFLOADS (NETIF_F_GRO | NETIF_F_LRO)
  #define TAP_FEATURES (NETIF_F_GSO | NETIF_F_SG | NETIF_F_FRAGLIST)
  
  static struct tap_dev *tap_dev_get_rcu(const struct net_device *dev)
  {
  	return rcu_dereference(dev->rx_handler_data);
  }
  
  /*
   * RCU usage:
   * The tap_queue and the macvlan_dev are loosely coupled, the
   * pointers from one to the other can only be read while rcu_read_lock
   * or rtnl is held.
   *
   * Both the file and the macvlan_dev hold a reference on the tap_queue
   * through sock_hold(&q->sk). When the macvlan_dev goes away first,
   * q->vlan becomes inaccessible. When the files gets closed,
   * tap_get_queue() fails.
   *
   * There may still be references to the struct sock inside of the
   * queue from outbound SKBs, but these never reference back to the
   * file or the dev. The data structure is freed through __sk_free
   * when both our references and any pending SKBs are gone.
   */
  
  static int tap_enable_queue(struct tap_dev *tap, struct file *file,
  			    struct tap_queue *q)
  {
  	int err = -EINVAL;
  
  	ASSERT_RTNL();
  
  	if (q->enabled)
  		goto out;
  
  	err = 0;
  	rcu_assign_pointer(tap->taps[tap->numvtaps], q);
  	q->queue_index = tap->numvtaps;
  	q->enabled = true;
  
  	tap->numvtaps++;
  out:
  	return err;
  }
  
  /* Requires RTNL */
  static int tap_set_queue(struct tap_dev *tap, struct file *file,
  			 struct tap_queue *q)
  {
  	if (tap->numqueues == MAX_TAP_QUEUES)
  		return -EBUSY;
  
  	rcu_assign_pointer(q->tap, tap);
  	rcu_assign_pointer(tap->taps[tap->numvtaps], q);
  	sock_hold(&q->sk);
  
  	q->file = file;
  	q->queue_index = tap->numvtaps;
  	q->enabled = true;
  	file->private_data = q;
  	list_add_tail(&q->next, &tap->queue_list);
  
  	tap->numvtaps++;
  	tap->numqueues++;
  
  	return 0;
  }
  
  static int tap_disable_queue(struct tap_queue *q)
  {
  	struct tap_dev *tap;
  	struct tap_queue *nq;
  
  	ASSERT_RTNL();
  	if (!q->enabled)
  		return -EINVAL;
  
  	tap = rtnl_dereference(q->tap);
  
  	if (tap) {
  		int index = q->queue_index;
  		BUG_ON(index >= tap->numvtaps);
  		nq = rtnl_dereference(tap->taps[tap->numvtaps - 1]);
  		nq->queue_index = index;
  
  		rcu_assign_pointer(tap->taps[index], nq);
  		RCU_INIT_POINTER(tap->taps[tap->numvtaps - 1], NULL);
  		q->enabled = false;
  
  		tap->numvtaps--;
  	}
  
  	return 0;
  }
  
  /*
   * The file owning the queue got closed, give up both
   * the reference that the files holds as well as the
   * one from the macvlan_dev if that still exists.
   *
   * Using the spinlock makes sure that we don't get
   * to the queue again after destroying it.
   */
  static void tap_put_queue(struct tap_queue *q)
  {
  	struct tap_dev *tap;
  
  	rtnl_lock();
  	tap = rtnl_dereference(q->tap);
  
  	if (tap) {
  		if (q->enabled)
  			BUG_ON(tap_disable_queue(q));
  
  		tap->numqueues--;
  		RCU_INIT_POINTER(q->tap, NULL);
  		sock_put(&q->sk);
  		list_del_init(&q->next);
  	}
  
  	rtnl_unlock();
  
  	synchronize_rcu();
  	sock_put(&q->sk);
  }
  
  /*
   * Select a queue based on the rxq of the device on which this packet
   * arrived. If the incoming device is not mq, calculate a flow hash
   * to select a queue. If all fails, find the first available queue.
   * Cache vlan->numvtaps since it can become zero during the execution
   * of this function.
   */
  static struct tap_queue *tap_get_queue(struct tap_dev *tap,
  				       struct sk_buff *skb)
  {
  	struct tap_queue *queue = NULL;
  	/* Access to taps array is protected by rcu, but access to numvtaps
  	 * isn't. Below we use it to lookup a queue, but treat it as a hint
  	 * and validate that the result isn't NULL - in case we are
  	 * racing against queue removal.
  	 */
  	int numvtaps = ACCESS_ONCE(tap->numvtaps);
  	__u32 rxq;
  
  	if (!numvtaps)
  		goto out;
  
  	if (numvtaps == 1)
  		goto single;
  
  	/* Check if we can use flow to select a queue */
  	rxq = skb_get_hash(skb);
  	if (rxq) {
  		queue = rcu_dereference(tap->taps[rxq % numvtaps]);
  		goto out;
  	}
  
  	if (likely(skb_rx_queue_recorded(skb))) {
  		rxq = skb_get_rx_queue(skb);
  
  		while (unlikely(rxq >= numvtaps))
  			rxq -= numvtaps;
  
  		queue = rcu_dereference(tap->taps[rxq]);
  		goto out;
  	}
  
  single:
  	queue = rcu_dereference(tap->taps[0]);
  out:
  	return queue;
  }
  
  /*
   * The net_device is going away, give up the reference
   * that it holds on all queues and safely set the pointer
   * from the queues to NULL.
   */
  void tap_del_queues(struct tap_dev *tap)
  {
  	struct tap_queue *q, *tmp;
  
  	ASSERT_RTNL();
  	list_for_each_entry_safe(q, tmp, &tap->queue_list, next) {
  		list_del_init(&q->next);
  		RCU_INIT_POINTER(q->tap, NULL);
  		if (q->enabled)
  			tap->numvtaps--;
  		tap->numqueues--;
  		sock_put(&q->sk);
  	}
  	BUG_ON(tap->numvtaps);
  	BUG_ON(tap->numqueues);
  	/* guarantee that any future tap_set_queue will fail */
  	tap->numvtaps = MAX_TAP_QUEUES;
  }
  EXPORT_SYMBOL_GPL(tap_del_queues);
  
  rx_handler_result_t tap_handle_frame(struct sk_buff **pskb)
  {
  	struct sk_buff *skb = *pskb;
  	struct net_device *dev = skb->dev;
  	struct tap_dev *tap;
  	struct tap_queue *q;
  	netdev_features_t features = TAP_FEATURES;
  
  	tap = tap_dev_get_rcu(dev);
  	if (!tap)
  		return RX_HANDLER_PASS;
  
  	q = tap_get_queue(tap, skb);
  	if (!q)
  		return RX_HANDLER_PASS;
  
  	if (__skb_array_full(&q->skb_array))
  		goto drop;
  
  	skb_push(skb, ETH_HLEN);
  
  	/* Apply the forward feature mask so that we perform segmentation
  	 * according to users wishes.  This only works if VNET_HDR is
  	 * enabled.
  	 */
  	if (q->flags & IFF_VNET_HDR)
  		features |= tap->tap_features;
  	if (netif_needs_gso(skb, features)) {
  		struct sk_buff *segs = __skb_gso_segment(skb, features, false);
  
  		if (IS_ERR(segs))
  			goto drop;
  
  		if (!segs) {
  			if (skb_array_produce(&q->skb_array, skb))
  				goto drop;
  			goto wake_up;
  		}
  
  		consume_skb(skb);
  		while (segs) {
  			struct sk_buff *nskb = segs->next;
  
  			segs->next = NULL;
  			if (skb_array_produce(&q->skb_array, segs)) {
  				kfree_skb(segs);
  				kfree_skb_list(nskb);
  				break;
  			}
  			segs = nskb;
  		}
  	} else {
  		/* If we receive a partial checksum and the tap side
  		 * doesn't support checksum offload, compute the checksum.
  		 * Note: it doesn't matter which checksum feature to
  		 *	  check, we either support them all or none.
  		 */
  		if (skb->ip_summed == CHECKSUM_PARTIAL &&
  		    !(features & NETIF_F_CSUM_MASK) &&
  		    skb_checksum_help(skb))
  			goto drop;
  		if (skb_array_produce(&q->skb_array, skb))
  			goto drop;
  	}
  
  wake_up:
  	wake_up_interruptible_poll(sk_sleep(&q->sk), POLLIN | POLLRDNORM | POLLRDBAND);
  	return RX_HANDLER_CONSUMED;
  
  drop:
  	/* Count errors/drops only here, thus don't care about args. */
  	if (tap->count_rx_dropped)
  		tap->count_rx_dropped(tap);
  	kfree_skb(skb);
  	return RX_HANDLER_CONSUMED;
  }
  EXPORT_SYMBOL_GPL(tap_handle_frame);
  
  static struct major_info *tap_get_major(int major)
  {
  	struct major_info *tap_major;
  
  	list_for_each_entry_rcu(tap_major, &major_list, next) {
  		if (tap_major->major == major)
  			return tap_major;
  	}
  
  	return NULL;
  }
  
  int tap_get_minor(dev_t major, struct tap_dev *tap)
  {
  	int retval = -ENOMEM;
  	struct major_info *tap_major;
  
  	rcu_read_lock();
  	tap_major = tap_get_major(MAJOR(major));
  	if (!tap_major) {
  		retval = -EINVAL;
  		goto unlock;
  	}
  
  	spin_lock(&tap_major->minor_lock);
  	retval = idr_alloc(&tap_major->minor_idr, tap, 1, TAP_NUM_DEVS, GFP_ATOMIC);
  	if (retval >= 0) {
  		tap->minor = retval;
  	} else if (retval == -ENOSPC) {
  		netdev_err(tap->dev, "Too many tap devices\n");
  		retval = -EINVAL;
  	}
  	spin_unlock(&tap_major->minor_lock);
  
  unlock:
  	rcu_read_unlock();
  	return retval < 0 ? retval : 0;
  }
  EXPORT_SYMBOL_GPL(tap_get_minor);
  
  void tap_free_minor(dev_t major, struct tap_dev *tap)
  {
  	struct major_info *tap_major;
  
  	rcu_read_lock();
  	tap_major = tap_get_major(MAJOR(major));
  	if (!tap_major) {
  		goto unlock;
  	}
  
  	spin_lock(&tap_major->minor_lock);
  	if (tap->minor) {
  		idr_remove(&tap_major->minor_idr, tap->minor);
  		tap->minor = 0;
  	}
  	spin_unlock(&tap_major->minor_lock);
  
  unlock:
  	rcu_read_unlock();
  }
  EXPORT_SYMBOL_GPL(tap_free_minor);
  
  static struct tap_dev *dev_get_by_tap_file(int major, int minor)
  {
  	struct net_device *dev = NULL;
  	struct tap_dev *tap;
  	struct major_info *tap_major;
  
  	rcu_read_lock();
  	tap_major = tap_get_major(major);
  	if (!tap_major) {
  		tap = NULL;
  		goto unlock;
  	}
  
  	spin_lock(&tap_major->minor_lock);
  	tap = idr_find(&tap_major->minor_idr, minor);
  	if (tap) {
  		dev = tap->dev;
  		dev_hold(dev);
  	}
  	spin_unlock(&tap_major->minor_lock);
  
  unlock:
  	rcu_read_unlock();
  	return tap;
  }
  
  static void tap_sock_write_space(struct sock *sk)
  {
  	wait_queue_head_t *wqueue;
  
  	if (!sock_writeable(sk) ||
  	    !test_and_clear_bit(SOCKWQ_ASYNC_NOSPACE, &sk->sk_socket->flags))
  		return;
  
  	wqueue = sk_sleep(sk);
  	if (wqueue && waitqueue_active(wqueue))
  		wake_up_interruptible_poll(wqueue, POLLOUT | POLLWRNORM | POLLWRBAND);
  }
  
  static void tap_sock_destruct(struct sock *sk)
  {
  	struct tap_queue *q = container_of(sk, struct tap_queue, sk);
  
  	skb_array_cleanup(&q->skb_array);
  }
  
  static int tap_open(struct inode *inode, struct file *file)
  {
  	struct net *net = current->nsproxy->net_ns;
  	struct tap_dev *tap;
  	struct tap_queue *q;
  	int err = -ENODEV;
  
  	rtnl_lock();
  	tap = dev_get_by_tap_file(imajor(inode), iminor(inode));
  	if (!tap)
  		goto err;
  
  	err = -ENOMEM;
  	q = (struct tap_queue *)sk_alloc(net, AF_UNSPEC, GFP_KERNEL,
  					     &tap_proto, 0);
  	if (!q)
  		goto err;
  
  	RCU_INIT_POINTER(q->sock.wq, &q->wq);
  	init_waitqueue_head(&q->wq.wait);
  	q->sock.type = SOCK_RAW;
  	q->sock.state = SS_CONNECTED;
  	q->sock.file = file;
  	q->sock.ops = &tap_socket_ops;
  	sock_init_data(&q->sock, &q->sk);
  	q->sk.sk_write_space = tap_sock_write_space;
  	q->sk.sk_destruct = tap_sock_destruct;
  	q->flags = IFF_VNET_HDR | IFF_NO_PI | IFF_TAP;
  	q->vnet_hdr_sz = sizeof(struct virtio_net_hdr);
  
  	/*
  	 * so far only KVM virtio_net uses tap, enable zero copy between
  	 * guest kernel and host kernel when lower device supports zerocopy
  	 *
  	 * The macvlan supports zerocopy iff the lower device supports zero
  	 * copy so we don't have to look at the lower device directly.
  	 */
  	if ((tap->dev->features & NETIF_F_HIGHDMA) && (tap->dev->features & NETIF_F_SG))
  		sock_set_flag(&q->sk, SOCK_ZEROCOPY);
  
  	err = -ENOMEM;
  	if (skb_array_init(&q->skb_array, tap->dev->tx_queue_len, GFP_KERNEL))
  		goto err_array;
  
  	err = tap_set_queue(tap, file, q);
  	if (err)
  		goto err_queue;
  
  	dev_put(tap->dev);
  
  	rtnl_unlock();
  	return err;
  
  err_queue:
  	skb_array_cleanup(&q->skb_array);
  err_array:
  	sock_put(&q->sk);
  err:
  	if (tap)
  		dev_put(tap->dev);
  
  	rtnl_unlock();
  	return err;
  }
  
  static int tap_release(struct inode *inode, struct file *file)
  {
  	struct tap_queue *q = file->private_data;
  	tap_put_queue(q);
  	return 0;
  }
  
  static unsigned int tap_poll(struct file *file, poll_table *wait)
  {
  	struct tap_queue *q = file->private_data;
  	unsigned int mask = POLLERR;
  
  	if (!q)
  		goto out;
  
  	mask = 0;
  	poll_wait(file, &q->wq.wait, wait);
  
  	if (!skb_array_empty(&q->skb_array))
  		mask |= POLLIN | POLLRDNORM;
  
  	if (sock_writeable(&q->sk) ||
  	    (!test_and_set_bit(SOCKWQ_ASYNC_NOSPACE, &q->sock.flags) &&
  	     sock_writeable(&q->sk)))
  		mask |= POLLOUT | POLLWRNORM;
  
  out:
  	return mask;
  }
  
  static inline struct sk_buff *tap_alloc_skb(struct sock *sk, size_t prepad,
  					    size_t len, size_t linear,
  						int noblock, int *err)
  {
  	struct sk_buff *skb;
  
  	/* 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 NULL;
  
  	skb_reserve(skb, prepad);
  	skb_put(skb, linear);
  	skb->data_len = len - linear;
  	skb->len += len - linear;
  
  	return skb;
  }
  
  /* Neighbour code has some assumptions on HH_DATA_MOD alignment */
  #define TAP_RESERVE HH_DATA_OFF(ETH_HLEN)
  
  /* Get packet from user space buffer */
  static ssize_t tap_get_user(struct tap_queue *q, struct msghdr *m,
  			    struct iov_iter *from, int noblock)
  {
  	int good_linear = SKB_MAX_HEAD(TAP_RESERVE);
  	struct sk_buff *skb;
  	struct tap_dev *tap;
  	unsigned long total_len = iov_iter_count(from);
  	unsigned long len = total_len;
  	int err;
  	struct virtio_net_hdr vnet_hdr = { 0 };
  	int vnet_hdr_len = 0;
  	int copylen = 0;
  	int depth;
  	bool zerocopy = false;
  	size_t linear;
  
  	if (q->flags & IFF_VNET_HDR) {
  		vnet_hdr_len = READ_ONCE(q->vnet_hdr_sz);
  
  		err = -EINVAL;
  		if (len < vnet_hdr_len)
  			goto err;
  		len -= vnet_hdr_len;
  
  		err = -EFAULT;
  		if (!copy_from_iter_full(&vnet_hdr, sizeof(vnet_hdr), from))
  			goto err;
  		iov_iter_advance(from, vnet_hdr_len - sizeof(vnet_hdr));
  		if ((vnet_hdr.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) &&
  		     tap16_to_cpu(q, vnet_hdr.csum_start) +
  		     tap16_to_cpu(q, vnet_hdr.csum_offset) + 2 >
  			     tap16_to_cpu(q, vnet_hdr.hdr_len))
  			vnet_hdr.hdr_len = cpu_to_tap16(q,
  				 tap16_to_cpu(q, vnet_hdr.csum_start) +
  				 tap16_to_cpu(q, vnet_hdr.csum_offset) + 2);
  		err = -EINVAL;
  		if (tap16_to_cpu(q, vnet_hdr.hdr_len) > len)
  			goto err;
  	}
  
  	err = -EINVAL;
  	if (unlikely(len < ETH_HLEN))
  		goto err;
  
  	if (m && m->msg_control && sock_flag(&q->sk, SOCK_ZEROCOPY)) {
  		struct iov_iter i;
  
  		copylen = vnet_hdr.hdr_len ?
  			tap16_to_cpu(q, vnet_hdr.hdr_len) : GOODCOPY_LEN;
  		if (copylen > good_linear)
  			copylen = good_linear;
  		else if (copylen < ETH_HLEN)
  			copylen = ETH_HLEN;
  		linear = copylen;
  		i = *from;
  		iov_iter_advance(&i, copylen);
  		if (iov_iter_npages(&i, INT_MAX) <= MAX_SKB_FRAGS)
  			zerocopy = true;
  	}
  
  	if (!zerocopy) {
  		copylen = len;
  		linear = tap16_to_cpu(q, vnet_hdr.hdr_len);
  		if (linear > good_linear)
  			linear = good_linear;
  		else if (linear < ETH_HLEN)
  			linear = ETH_HLEN;
  	}
  
  	skb = tap_alloc_skb(&q->sk, TAP_RESERVE, copylen,
  			    linear, noblock, &err);
  	if (!skb)
  		goto err;
  
  	if (zerocopy)
  		err = zerocopy_sg_from_iter(skb, from);
  	else
  		err = skb_copy_datagram_from_iter(skb, 0, from, len);
  
  	if (err)
  		goto err_kfree;
  
  	skb_set_network_header(skb, ETH_HLEN);
  	skb_reset_mac_header(skb);
  	skb->protocol = eth_hdr(skb)->h_proto;
  
  	if (vnet_hdr_len) {
  		err = virtio_net_hdr_to_skb(skb, &vnet_hdr,
  					    tap_is_little_endian(q));
  		if (err)
  			goto err_kfree;
  	}
  
  	skb_probe_transport_header(skb, ETH_HLEN);
  
  	/* Move network header to the right position for VLAN tagged packets */
  	if ((skb->protocol == htons(ETH_P_8021Q) ||
  	     skb->protocol == htons(ETH_P_8021AD)) &&
  	    __vlan_get_protocol(skb, skb->protocol, &depth) != 0)
  		skb_set_network_header(skb, depth);
  
  	rcu_read_lock();
  	tap = rcu_dereference(q->tap);
  	/* copy skb_ubuf_info for callback when skb has no error */
  	if (zerocopy) {
  		skb_shinfo(skb)->destructor_arg = m->msg_control;
  		skb_shinfo(skb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
  		skb_shinfo(skb)->tx_flags |= SKBTX_SHARED_FRAG;
  	} else if (m && m->msg_control) {
  		struct ubuf_info *uarg = m->msg_control;
  		uarg->callback(uarg, false);
  	}
  
  	if (tap) {
  		skb->dev = tap->dev;
  		dev_queue_xmit(skb);
  	} else {
  		kfree_skb(skb);
  	}
  	rcu_read_unlock();
  
  	return total_len;
  
  err_kfree:
  	kfree_skb(skb);
  
  err:
  	rcu_read_lock();
  	tap = rcu_dereference(q->tap);
  	if (tap && tap->count_tx_dropped)
  		tap->count_tx_dropped(tap);
  	rcu_read_unlock();
  
  	return err;
  }
  
  static ssize_t tap_write_iter(struct kiocb *iocb, struct iov_iter *from)
  {
  	struct file *file = iocb->ki_filp;
  	struct tap_queue *q = file->private_data;
  
  	return tap_get_user(q, NULL, from, file->f_flags & O_NONBLOCK);
  }
  
  /* Put packet to the user space buffer */
  static ssize_t tap_put_user(struct tap_queue *q,
  			    const struct sk_buff *skb,
  			    struct iov_iter *iter)
  {
  	int ret;
  	int vnet_hdr_len = 0;
  	int vlan_offset = 0;
  	int total;
  
  	if (q->flags & IFF_VNET_HDR) {
  		struct virtio_net_hdr vnet_hdr;
  		vnet_hdr_len = READ_ONCE(q->vnet_hdr_sz);
  		if (iov_iter_count(iter) < vnet_hdr_len)
  			return -EINVAL;
  
  		if (virtio_net_hdr_from_skb(skb, &vnet_hdr,
  					    tap_is_little_endian(q), true))
  			BUG();
  
  		if (copy_to_iter(&vnet_hdr, sizeof(vnet_hdr), iter) !=
  		    sizeof(vnet_hdr))
  			return -EFAULT;
  
  		iov_iter_advance(iter, vnet_hdr_len - sizeof(vnet_hdr));
  	}
  	total = vnet_hdr_len;
  	total += skb->len;
  
  	if (skb_vlan_tag_present(skb)) {
  		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);
  		total += VLAN_HLEN;
  
  		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;
  	}
  
  	ret = skb_copy_datagram_iter(skb, vlan_offset, iter,
  				     skb->len - vlan_offset);
  
  done:
  	return ret ? ret : total;
  }
  
  static ssize_t tap_do_read(struct tap_queue *q,
  			   struct iov_iter *to,
  			   int noblock, struct sk_buff *skb)
  {
  	DEFINE_WAIT(wait);
  	ssize_t ret = 0;
  
  	if (!iov_iter_count(to))
  		return 0;
  
  	if (skb)
  		goto put;
  
  	while (1) {
  		if (!noblock)
  			prepare_to_wait(sk_sleep(&q->sk), &wait,
  					TASK_INTERRUPTIBLE);
  
  		/* Read frames from the queue */
  		skb = skb_array_consume(&q->skb_array);
  		if (skb)
  			break;
  		if (noblock) {
  			ret = -EAGAIN;
  			break;
  		}
  		if (signal_pending(current)) {
  			ret = -ERESTARTSYS;
  			break;
  		}
  		/* Nothing to read, let's sleep */
  		schedule();
  	}
  	if (!noblock)
  		finish_wait(sk_sleep(&q->sk), &wait);
  
  put:
  	if (skb) {
  		ret = tap_put_user(q, skb, to);
  		if (unlikely(ret < 0))
  			kfree_skb(skb);
  		else
  			consume_skb(skb);
  	}
  	return ret;
  }
  
  static ssize_t tap_read_iter(struct kiocb *iocb, struct iov_iter *to)
  {
  	struct file *file = iocb->ki_filp;
  	struct tap_queue *q = file->private_data;
  	ssize_t len = iov_iter_count(to), ret;
  
  	ret = tap_do_read(q, to, file->f_flags & O_NONBLOCK, NULL);
  	ret = min_t(ssize_t, ret, len);
  	if (ret > 0)
  		iocb->ki_pos = ret;
  	return ret;
  }
  
  static struct tap_dev *tap_get_tap_dev(struct tap_queue *q)
  {
  	struct tap_dev *tap;
  
  	ASSERT_RTNL();
  	tap = rtnl_dereference(q->tap);
  	if (tap)
  		dev_hold(tap->dev);
  
  	return tap;
  }
  
  static void tap_put_tap_dev(struct tap_dev *tap)
  {
  	dev_put(tap->dev);
  }
  
  static int tap_ioctl_set_queue(struct file *file, unsigned int flags)
  {
  	struct tap_queue *q = file->private_data;
  	struct tap_dev *tap;
  	int ret;
  
  	tap = tap_get_tap_dev(q);
  	if (!tap)
  		return -EINVAL;
  
  	if (flags & IFF_ATTACH_QUEUE)
  		ret = tap_enable_queue(tap, file, q);
  	else if (flags & IFF_DETACH_QUEUE)
  		ret = tap_disable_queue(q);
  	else
  		ret = -EINVAL;
  
  	tap_put_tap_dev(tap);
  	return ret;
  }
  
  static int set_offload(struct tap_queue *q, unsigned long arg)
  {
  	struct tap_dev *tap;
  	netdev_features_t features;
  	netdev_features_t feature_mask = 0;
  
  	tap = rtnl_dereference(q->tap);
  	if (!tap)
  		return -ENOLINK;
  
  	features = tap->dev->features;
  
  	if (arg & TUN_F_CSUM) {
  		feature_mask = NETIF_F_HW_CSUM;
  
  		if (arg & (TUN_F_TSO4 | TUN_F_TSO6)) {
  			if (arg & TUN_F_TSO_ECN)
  				feature_mask |= NETIF_F_TSO_ECN;
  			if (arg & TUN_F_TSO4)
  				feature_mask |= NETIF_F_TSO;
  			if (arg & TUN_F_TSO6)
  				feature_mask |= NETIF_F_TSO6;
  		}
  
  		if (arg & TUN_F_UFO)
  			feature_mask |= NETIF_F_UFO;
  	}
  
  	/* tun/tap driver inverts the usage for TSO offloads, where
  	 * setting the TSO bit means that the userspace wants to
  	 * accept TSO frames and turning it off means that user space
  	 * does not support TSO.
  	 * For tap, we have to invert it to mean the same thing.
  	 * When user space turns off TSO, we turn off GSO/LRO so that
  	 * user-space will not receive TSO frames.
  	 */
  	if (feature_mask & (NETIF_F_TSO | NETIF_F_TSO6 | NETIF_F_UFO))
  		features |= RX_OFFLOADS;
  	else
  		features &= ~RX_OFFLOADS;
  
  	/* tap_features are the same as features on tun/tap and
  	 * reflect user expectations.
  	 */
  	tap->tap_features = feature_mask;
  	if (tap->update_features)
  		tap->update_features(tap, features);
  
  	return 0;
  }
  
  /*
   * provide compatibility with generic tun/tap interface
   */
  static long tap_ioctl(struct file *file, unsigned int cmd,
  		      unsigned long arg)
  {
  	struct tap_queue *q = file->private_data;
  	struct tap_dev *tap;
  	void __user *argp = (void __user *)arg;
  	struct ifreq __user *ifr = argp;
  	unsigned int __user *up = argp;
  	unsigned short u;
  	int __user *sp = argp;
  	struct sockaddr sa;
  	int s;
  	int ret;
  
  	switch (cmd) {
  	case TUNSETIFF:
  		/* ignore the name, just look at flags */
  		if (get_user(u, &ifr->ifr_flags))
  			return -EFAULT;
  
  		ret = 0;
  		if ((u & ~TAP_IFFEATURES) != (IFF_NO_PI | IFF_TAP))
  			ret = -EINVAL;
  		else
  			q->flags = (q->flags & ~TAP_IFFEATURES) | u;
  
  		return ret;
  
  	case TUNGETIFF:
  		rtnl_lock();
  		tap = tap_get_tap_dev(q);
  		if (!tap) {
  			rtnl_unlock();
  			return -ENOLINK;
  		}
  
  		ret = 0;
  		u = q->flags;
  		if (copy_to_user(&ifr->ifr_name, tap->dev->name, IFNAMSIZ) ||
  		    put_user(u, &ifr->ifr_flags))
  			ret = -EFAULT;
  		tap_put_tap_dev(tap);
  		rtnl_unlock();
  		return ret;
  
  	case TUNSETQUEUE:
  		if (get_user(u, &ifr->ifr_flags))
  			return -EFAULT;
  		rtnl_lock();
  		ret = tap_ioctl_set_queue(file, u);
  		rtnl_unlock();
  		return ret;
  
  	case TUNGETFEATURES:
  		if (put_user(IFF_TAP | IFF_NO_PI | TAP_IFFEATURES, up))
  			return -EFAULT;
  		return 0;
  
  	case TUNSETSNDBUF:
  		if (get_user(s, sp))
  			return -EFAULT;
  
  		q->sk.sk_sndbuf = s;
  		return 0;
  
  	case TUNGETVNETHDRSZ:
  		s = q->vnet_hdr_sz;
  		if (put_user(s, sp))
  			return -EFAULT;
  		return 0;
  
  	case TUNSETVNETHDRSZ:
  		if (get_user(s, sp))
  			return -EFAULT;
  		if (s < (int)sizeof(struct virtio_net_hdr))
  			return -EINVAL;
  
  		q->vnet_hdr_sz = s;
  		return 0;
  
  	case TUNGETVNETLE:
  		s = !!(q->flags & TAP_VNET_LE);
  		if (put_user(s, sp))
  			return -EFAULT;
  		return 0;
  
  	case TUNSETVNETLE:
  		if (get_user(s, sp))
  			return -EFAULT;
  		if (s)
  			q->flags |= TAP_VNET_LE;
  		else
  			q->flags &= ~TAP_VNET_LE;
  		return 0;
  
  	case TUNGETVNETBE:
  		return tap_get_vnet_be(q, sp);
  
  	case TUNSETVNETBE:
  		return tap_set_vnet_be(q, sp);
  
  	case TUNSETOFFLOAD:
  		/* let the user check for future flags */
  		if (arg & ~(TUN_F_CSUM | TUN_F_TSO4 | TUN_F_TSO6 |
  			    TUN_F_TSO_ECN | TUN_F_UFO))
  			return -EINVAL;
  
  		rtnl_lock();
  		ret = set_offload(q, arg);
  		rtnl_unlock();
  		return ret;
  
  	case SIOCGIFHWADDR:
  		rtnl_lock();
  		tap = tap_get_tap_dev(q);
  		if (!tap) {
  			rtnl_unlock();
  			return -ENOLINK;
  		}
  		ret = 0;
  		u = tap->dev->type;
  		if (copy_to_user(&ifr->ifr_name, tap->dev->name, IFNAMSIZ) ||
  		    copy_to_user(&ifr->ifr_hwaddr.sa_data, tap->dev->dev_addr, ETH_ALEN) ||
  		    put_user(u, &ifr->ifr_hwaddr.sa_family))
  			ret = -EFAULT;
  		tap_put_tap_dev(tap);
  		rtnl_unlock();
  		return ret;
  
  	case SIOCSIFHWADDR:
  		if (copy_from_user(&sa, &ifr->ifr_hwaddr, sizeof(sa)))
  			return -EFAULT;
  		rtnl_lock();
  		tap = tap_get_tap_dev(q);
  		if (!tap) {
  			rtnl_unlock();
  			return -ENOLINK;
  		}
  		ret = dev_set_mac_address(tap->dev, &sa);
  		tap_put_tap_dev(tap);
  		rtnl_unlock();
  		return ret;
  
  	default:
  		return -EINVAL;
  	}
  }
  
  #ifdef CONFIG_COMPAT
  static long tap_compat_ioctl(struct file *file, unsigned int cmd,
  			     unsigned long arg)
  {
  	return tap_ioctl(file, cmd, (unsigned long)compat_ptr(arg));
  }
  #endif
  
  const struct file_operations tap_fops = {
  	.owner		= THIS_MODULE,
  	.open		= tap_open,
  	.release	= tap_release,
  	.read_iter	= tap_read_iter,
  	.write_iter	= tap_write_iter,
  	.poll		= tap_poll,
  	.llseek		= no_llseek,
  	.unlocked_ioctl	= tap_ioctl,
  #ifdef CONFIG_COMPAT
  	.compat_ioctl	= tap_compat_ioctl,
  #endif
  };
  
  static int tap_sendmsg(struct socket *sock, struct msghdr *m,
  		       size_t total_len)
  {
  	struct tap_queue *q = container_of(sock, struct tap_queue, sock);
  	return tap_get_user(q, m, &m->msg_iter, m->msg_flags & MSG_DONTWAIT);
  }
  
  static int tap_recvmsg(struct socket *sock, struct msghdr *m,
  		       size_t total_len, int flags)
  {
  	struct tap_queue *q = container_of(sock, struct tap_queue, sock);
  	int ret;
  	if (flags & ~(MSG_DONTWAIT|MSG_TRUNC))
  		return -EINVAL;
  	ret = tap_do_read(q, &m->msg_iter, flags & MSG_DONTWAIT,
  			  m->msg_control);
  	if (ret > total_len) {
  		m->msg_flags |= MSG_TRUNC;
  		ret = flags & MSG_TRUNC ? ret : total_len;
  	}
  	return ret;
  }
  
  static int tap_peek_len(struct socket *sock)
  {
  	struct tap_queue *q = container_of(sock, struct tap_queue,
  					       sock);
  	return skb_array_peek_len(&q->skb_array);
  }
  
  /* Ops structure to mimic raw sockets with tun */
  static const struct proto_ops tap_socket_ops = {
  	.sendmsg = tap_sendmsg,
  	.recvmsg = tap_recvmsg,
  	.peek_len = tap_peek_len,
  };
  
  /* 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 *tap_get_socket(struct file *file)
  {
  	struct tap_queue *q;
  	if (file->f_op != &tap_fops)
  		return ERR_PTR(-EINVAL);
  	q = file->private_data;
  	if (!q)
  		return ERR_PTR(-EBADFD);
  	return &q->sock;
  }
  EXPORT_SYMBOL_GPL(tap_get_socket);
  
  struct skb_array *tap_get_skb_array(struct file *file)
  {
  	struct tap_queue *q;
  
  	if (file->f_op != &tap_fops)
  		return ERR_PTR(-EINVAL);
  	q = file->private_data;
  	if (!q)
  		return ERR_PTR(-EBADFD);
  	return &q->skb_array;
  }
  EXPORT_SYMBOL_GPL(tap_get_skb_array);
  
  int tap_queue_resize(struct tap_dev *tap)
  {
  	struct net_device *dev = tap->dev;
  	struct tap_queue *q;
  	struct skb_array **arrays;
  	int n = tap->numqueues;
  	int ret, i = 0;
  
  	arrays = kmalloc(sizeof *arrays * n, GFP_KERNEL);
  	if (!arrays)
  		return -ENOMEM;
  
  	list_for_each_entry(q, &tap->queue_list, next)
  		arrays[i++] = &q->skb_array;
  
  	ret = skb_array_resize_multiple(arrays, n,
  					dev->tx_queue_len, GFP_KERNEL);
  
  	kfree(arrays);
  	return ret;
  }
  EXPORT_SYMBOL_GPL(tap_queue_resize);
  
  static int tap_list_add(dev_t major, const char *device_name)
  {
  	struct major_info *tap_major;
  
  	tap_major = kzalloc(sizeof(*tap_major), GFP_ATOMIC);
  	if (!tap_major)
  		return -ENOMEM;
  
  	tap_major->major = MAJOR(major);
  
  	idr_init(&tap_major->minor_idr);
  	spin_lock_init(&tap_major->minor_lock);
  
  	tap_major->device_name = device_name;
  
  	list_add_tail_rcu(&tap_major->next, &major_list);
  	return 0;
  }
  
  int tap_create_cdev(struct cdev *tap_cdev,
  		    dev_t *tap_major, const char *device_name)
  {
  	int err;
  
  	err = alloc_chrdev_region(tap_major, 0, TAP_NUM_DEVS, device_name);
  	if (err)
  		goto out1;
  
  	cdev_init(tap_cdev, &tap_fops);
  	err = cdev_add(tap_cdev, *tap_major, TAP_NUM_DEVS);
  	if (err)
  		goto out2;
  
  	err =  tap_list_add(*tap_major, device_name);
  	if (err)
  		goto out3;
  
  	return 0;
  
  out3:
  	cdev_del(tap_cdev);
  out2:
  	unregister_chrdev_region(*tap_major, TAP_NUM_DEVS);
  out1:
  	return err;
  }
  EXPORT_SYMBOL_GPL(tap_create_cdev);
  
  void tap_destroy_cdev(dev_t major, struct cdev *tap_cdev)
  {
  	struct major_info *tap_major, *tmp;
  
  	cdev_del(tap_cdev);
  	unregister_chrdev_region(major, TAP_NUM_DEVS);
  	list_for_each_entry_safe(tap_major, tmp, &major_list, next) {
  		if (tap_major->major == MAJOR(major)) {
  			idr_destroy(&tap_major->minor_idr);
  			list_del_rcu(&tap_major->next);
  			kfree_rcu(tap_major, rcu);
  		}
  	}
  }
  EXPORT_SYMBOL_GPL(tap_destroy_cdev);
  
  MODULE_AUTHOR("Arnd Bergmann <arnd@arndb.de>");
  MODULE_AUTHOR("Sainath Grandhi <sainath.grandhi@intel.com>");
  MODULE_LICENSE("GPL");
  