#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;
        if (skb_array_init(&q->skb_array, tap->dev->tx_queue_len, GFP_KERNEL)) {
                sk_free(&q->sk);
                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 = tap_set_queue(tap, file, q);
        if (err) {
                /* tap_sock_destruct() will take care of freeing skb_array */
                goto err_put;
        }

        dev_put(tap->dev);

        rtnl_unlock();
        return err;

err_put:
        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;
                }
        }

        /* 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))
                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;
                if (s <= 0)
                        return -EINVAL;

                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))
                        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

static 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_array(n, sizeof(*arrays), 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, struct module *module)
{
        int err;

        err = alloc_chrdev_region(tap_major, 0, TAP_NUM_DEVS, device_name);
        if (err)
                goto out1;

        cdev_init(tap_cdev, &tap_fops);
        tap_cdev->owner = module;
        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");