macvtap: eliminate linear search

[deliverable/linux.git] / drivers / net / macvtap.c

#include <linux/etherdevice.h>
#include <linux/if_macvlan.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.h>
#include <linux/types.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/wait.h>
#include <linux/cdev.h>
#include <linux/idr.h>
#include <linux/fs.h>

#include <net/net_namespace.h>
#include <net/rtnetlink.h>
#include <net/sock.h>
#include <linux/virtio_net.h>

/*
 * A macvtap queue is the central object of this driver, it connects
 * an open character device to a macvlan interface. There can be
 * multiple queues on one interface, which map back to queues
 * implemented in hardware on the underlying device.
 *
 * macvtap_proto is used to allocate queues through the sock allocation
 * mechanism.
 *
 * TODO: multiqueue support is currently not implemented, even though
 * macvtap is basically prepared for that. We will need to add this
 * here as well as in virtio-net and qemu to get line rate on 10gbit
 * adapters from a guest.
 */
struct macvtap_queue {
        struct sock sk;
        struct socket sock;
        struct socket_wq wq;
        int vnet_hdr_sz;
        struct macvlan_dev __rcu *vlan;
        struct file *file;
        unsigned int flags;
        u16 queue_index;
};

static struct proto macvtap_proto = {
        .name = "macvtap",
        .owner = THIS_MODULE,
        .obj_size = sizeof (struct macvtap_queue),
};

/*
 * Variables for dealing with macvtaps device numbers.
 */
static dev_t macvtap_major;
#define MACVTAP_NUM_DEVS (1U << MINORBITS)
static DEFINE_MUTEX(minor_lock);
static DEFINE_IDR(minor_idr);

#define GOODCOPY_LEN 128
static struct class *macvtap_class;
static struct cdev macvtap_cdev;

static const struct proto_ops macvtap_socket_ops;

/*
 * RCU usage:
 * The macvtap_queue and the macvlan_dev are loosely coupled, the
 * pointers from one to the other can only be read while rcu_read_lock
 * or macvtap_lock is held.
 *
 * Both the file and the macvlan_dev hold a reference on the macvtap_queue
 * through sock_hold(&q->sk). When the macvlan_dev goes away first,
 * q->vlan becomes inaccessible. When the files gets closed,
 * macvtap_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 DEFINE_SPINLOCK(macvtap_lock);

static int macvtap_set_queue(struct net_device *dev, struct file *file,
                                struct macvtap_queue *q)
{
        struct macvlan_dev *vlan = netdev_priv(dev);
        int err = -EBUSY;

        spin_lock(&macvtap_lock);
        if (vlan->numvtaps == MAX_MACVTAP_QUEUES)
                goto out;

        err = 0;
        rcu_assign_pointer(q->vlan, vlan);
        rcu_assign_pointer(vlan->taps[vlan->numvtaps], q);
        sock_hold(&q->sk);

        q->file = file;
        q->queue_index = vlan->numvtaps;
        file->private_data = q;

        vlan->numvtaps++;

out:
        spin_unlock(&macvtap_lock);
        return err;
}

/*
 * 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 macvtap_put_queue(struct macvtap_queue *q)
{
        struct macvtap_queue *nq;
        struct macvlan_dev *vlan;

        spin_lock(&macvtap_lock);
        vlan = rcu_dereference_protected(q->vlan,
                                         lockdep_is_held(&macvtap_lock));
        if (vlan) {
                int index = q->queue_index;
                BUG_ON(index >= vlan->numvtaps);

                nq = rcu_dereference_protected(vlan->taps[vlan->numvtaps - 1],
                                               lockdep_is_held(&macvtap_lock));
                rcu_assign_pointer(vlan->taps[index], nq);
                nq->queue_index = index;

                RCU_INIT_POINTER(vlan->taps[vlan->numvtaps - 1], NULL);
                RCU_INIT_POINTER(q->vlan, NULL);
                sock_put(&q->sk);
                --vlan->numvtaps;
        }

        spin_unlock(&macvtap_lock);

        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 macvtap_queue *macvtap_get_queue(struct net_device *dev,
                                               struct sk_buff *skb)
{
        struct macvlan_dev *vlan = netdev_priv(dev);
        struct macvtap_queue *tap = NULL;
        int numvtaps = ACCESS_ONCE(vlan->numvtaps);
        __u32 rxq;

        if (!numvtaps)
                goto out;

        /* Check if we can use flow to select a queue */
        rxq = skb_get_rxhash(skb);
        if (rxq) {
                tap = rcu_dereference(vlan->taps[rxq % numvtaps]);
                goto out;
        }

        if (likely(skb_rx_queue_recorded(skb))) {
                rxq = skb_get_rx_queue(skb);

                while (unlikely(rxq >= numvtaps))
                        rxq -= numvtaps;

                tap = rcu_dereference(vlan->taps[rxq]);
                goto out;
        }

        tap = rcu_dereference(vlan->taps[0]);
out:
        return tap;
}

/*
 * 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.
 */
static void macvtap_del_queues(struct net_device *dev)
{
        struct macvlan_dev *vlan = netdev_priv(dev);
        struct macvtap_queue *q, *qlist[MAX_MACVTAP_QUEUES];
        int i, j = 0;

        spin_lock(&macvtap_lock);
        for (i = 0; i < vlan->numvtaps; i++) {
                q = rcu_dereference_protected(vlan->taps[i],
                                              lockdep_is_held(&macvtap_lock));
                BUG_ON(q == NULL);
                qlist[j++] = q;
                RCU_INIT_POINTER(vlan->taps[i], NULL);
                RCU_INIT_POINTER(q->vlan, NULL);
        }
        /* guarantee that any future macvtap_set_queue will fail */
        vlan->numvtaps = MAX_MACVTAP_QUEUES;
        spin_unlock(&macvtap_lock);

        synchronize_rcu();

        for (--j; j >= 0; j--)
                sock_put(&qlist[j]->sk);
}

/*
 * Forward happens for data that gets sent from one macvlan
 * endpoint to another one in bridge mode. We just take
 * the skb and put it into the receive queue.
 */
static int macvtap_forward(struct net_device *dev, struct sk_buff *skb)
{
        struct macvtap_queue *q = macvtap_get_queue(dev, skb);
        if (!q)
                goto drop;

        if (skb_queue_len(&q->sk.sk_receive_queue) >= dev->tx_queue_len)
                goto drop;

        skb_queue_tail(&q->sk.sk_receive_queue, skb);
        wake_up_interruptible_poll(sk_sleep(&q->sk), POLLIN | POLLRDNORM | POLLRDBAND);
        return NET_RX_SUCCESS;

drop:
        kfree_skb(skb);
        return NET_RX_DROP;
}

/*
 * Receive is for data from the external interface (lowerdev),
 * in case of macvtap, we can treat that the same way as
 * forward, which macvlan cannot.
 */
static int macvtap_receive(struct sk_buff *skb)
{
        skb_push(skb, ETH_HLEN);
        return macvtap_forward(skb->dev, skb);
}

static int macvtap_get_minor(struct macvlan_dev *vlan)
{
        int retval = -ENOMEM;

        mutex_lock(&minor_lock);
        retval = idr_alloc(&minor_idr, vlan, 1, MACVTAP_NUM_DEVS, GFP_KERNEL);
        if (retval >= 0) {
                vlan->minor = retval;
        } else if (retval == -ENOSPC) {
                printk(KERN_ERR "too many macvtap devices\n");
                retval = -EINVAL;
        }
        mutex_unlock(&minor_lock);
        return retval < 0 ? retval : 0;
}

static void macvtap_free_minor(struct macvlan_dev *vlan)
{
        mutex_lock(&minor_lock);
        if (vlan->minor) {
                idr_remove(&minor_idr, vlan->minor);
                vlan->minor = 0;
        }
        mutex_unlock(&minor_lock);
}

static struct net_device *dev_get_by_macvtap_minor(int minor)
{
        struct net_device *dev = NULL;
        struct macvlan_dev *vlan;

        mutex_lock(&minor_lock);
        vlan = idr_find(&minor_idr, minor);
        if (vlan) {
                dev = vlan->dev;
                dev_hold(dev);
        }
        mutex_unlock(&minor_lock);
        return dev;
}

static int macvtap_newlink(struct net *src_net,
                           struct net_device *dev,
                           struct nlattr *tb[],
                           struct nlattr *data[])
{
        /* Don't put anything that may fail after macvlan_common_newlink
         * because we can't undo what it does.
         */
        return macvlan_common_newlink(src_net, dev, tb, data,
                                      macvtap_receive, macvtap_forward);
}

static void macvtap_dellink(struct net_device *dev,
                            struct list_head *head)
{
        macvtap_del_queues(dev);
        macvlan_dellink(dev, head);
}

static void macvtap_setup(struct net_device *dev)
{
        macvlan_common_setup(dev);
        dev->tx_queue_len = TUN_READQ_SIZE;
}

static struct rtnl_link_ops macvtap_link_ops __read_mostly = {
        .kind           = "macvtap",
        .setup          = macvtap_setup,
        .newlink        = macvtap_newlink,
        .dellink        = macvtap_dellink,
};


static void macvtap_sock_write_space(struct sock *sk)
{
        wait_queue_head_t *wqueue;

        if (!sock_writeable(sk) ||
            !test_and_clear_bit(SOCK_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 macvtap_sock_destruct(struct sock *sk)
{
        skb_queue_purge(&sk->sk_receive_queue);
}

static int macvtap_open(struct inode *inode, struct file *file)
{
        struct net *net = current->nsproxy->net_ns;
        struct net_device *dev = dev_get_by_macvtap_minor(iminor(inode));
        struct macvtap_queue *q;
        int err;

        err = -ENODEV;
        if (!dev)
                goto out;

        err = -ENOMEM;
        q = (struct macvtap_queue *)sk_alloc(net, AF_UNSPEC, GFP_KERNEL,
                                             &macvtap_proto);
        if (!q)
                goto out;

        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 = &macvtap_socket_ops;
        sock_init_data(&q->sock, &q->sk);
        q->sk.sk_write_space = macvtap_sock_write_space;
        q->sk.sk_destruct = macvtap_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 macvtap, 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 ((dev->features & NETIF_F_HIGHDMA) && (dev->features & NETIF_F_SG))
                sock_set_flag(&q->sk, SOCK_ZEROCOPY);

        err = macvtap_set_queue(dev, file, q);
        if (err)
                sock_put(&q->sk);

out:
        if (dev)
                dev_put(dev);

        return err;
}

static int macvtap_release(struct inode *inode, struct file *file)
{
        struct macvtap_queue *q = file->private_data;
        macvtap_put_queue(q);
        return 0;
}

static unsigned int macvtap_poll(struct file *file, poll_table * wait)
{
        struct macvtap_queue *q = file->private_data;
        unsigned int mask = POLLERR;

        if (!q)
                goto out;

        mask = 0;
        poll_wait(file, &q->wq.wait, wait);

        if (!skb_queue_empty(&q->sk.sk_receive_queue))
                mask |= POLLIN | POLLRDNORM;

        if (sock_writeable(&q->sk) ||
            (!test_and_set_bit(SOCK_ASYNC_NOSPACE, &q->sock.flags) &&
             sock_writeable(&q->sk)))
                mask |= POLLOUT | POLLWRNORM;

out:
        return mask;
}

static inline struct sk_buff *macvtap_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);
        if (!skb)
                return NULL;

        skb_reserve(skb, prepad);
        skb_put(skb, linear);
        skb->data_len = len - linear;
        skb->len += len - linear;

        return skb;
}

/* set skb frags from iovec, this can move to core network code for reuse */
static int zerocopy_sg_from_iovec(struct sk_buff *skb, const struct iovec *from,
                                  int offset, size_t count)
{
        int len = iov_length(from, count) - offset;
        int copy = skb_headlen(skb);
        int size, offset1 = 0;
        int i = 0;

        /* Skip over from offset */
        while (count && (offset >= from->iov_len)) {
                offset -= from->iov_len;
                ++from;
                --count;
        }

        /* copy up to skb headlen */
        while (count && (copy > 0)) {
                size = min_t(unsigned int, copy, from->iov_len - offset);
                if (copy_from_user(skb->data + offset1, from->iov_base + offset,
                                   size))
                        return -EFAULT;
                if (copy > size) {
                        ++from;
                        --count;
                        offset = 0;
                } else
                        offset += size;
                copy -= size;
                offset1 += size;
        }

        if (len == offset1)
                return 0;

        while (count--) {
                struct page *page[MAX_SKB_FRAGS];
                int num_pages;
                unsigned long base;
                unsigned long truesize;

                len = from->iov_len - offset;
                if (!len) {
                        offset = 0;
                        ++from;
                        continue;
                }
                base = (unsigned long)from->iov_base + offset;
                size = ((base & ~PAGE_MASK) + len + ~PAGE_MASK) >> PAGE_SHIFT;
                if (i + size > MAX_SKB_FRAGS)
                        return -EMSGSIZE;
                num_pages = get_user_pages_fast(base, size, 0, &page[i]);
                if (num_pages != size) {
                        for (i = 0; i < num_pages; i++)
                                put_page(page[i]);
                        return -EFAULT;
                }
                truesize = size * PAGE_SIZE;
                skb->data_len += len;
                skb->len += len;
                skb->truesize += truesize;
                atomic_add(truesize, &skb->sk->sk_wmem_alloc);
                while (len) {
                        int off = base & ~PAGE_MASK;
                        int size = min_t(int, len, PAGE_SIZE - off);
                        __skb_fill_page_desc(skb, i, page[i], off, size);
                        skb_shinfo(skb)->nr_frags++;
                        /* increase sk_wmem_alloc */
                        base += size;
                        len -= size;
                        i++;
                }
                offset = 0;
                ++from;
        }
        return 0;
}

/*
 * macvtap_skb_from_vnet_hdr and macvtap_skb_to_vnet_hdr should
 * be shared with the tun/tap driver.
 */
static int macvtap_skb_from_vnet_hdr(struct sk_buff *skb,
                                     struct virtio_net_hdr *vnet_hdr)
{
        unsigned short gso_type = 0;
        if (vnet_hdr->gso_type != VIRTIO_NET_HDR_GSO_NONE) {
                switch (vnet_hdr->gso_type & ~VIRTIO_NET_HDR_GSO_ECN) {
                case VIRTIO_NET_HDR_GSO_TCPV4:
                        gso_type = SKB_GSO_TCPV4;
                        break;
                case VIRTIO_NET_HDR_GSO_TCPV6:
                        gso_type = SKB_GSO_TCPV6;
                        break;
                case VIRTIO_NET_HDR_GSO_UDP:
                        gso_type = SKB_GSO_UDP;
                        break;
                default:
                        return -EINVAL;
                }

                if (vnet_hdr->gso_type & VIRTIO_NET_HDR_GSO_ECN)
                        gso_type |= SKB_GSO_TCP_ECN;

                if (vnet_hdr->gso_size == 0)
                        return -EINVAL;
        }

        if (vnet_hdr->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) {
                if (!skb_partial_csum_set(skb, vnet_hdr->csum_start,
                                          vnet_hdr->csum_offset))
                        return -EINVAL;
        }

        if (vnet_hdr->gso_type != VIRTIO_NET_HDR_GSO_NONE) {
                skb_shinfo(skb)->gso_size = vnet_hdr->gso_size;
                skb_shinfo(skb)->gso_type = gso_type;

                /* Header must be checked, and gso_segs computed. */
                skb_shinfo(skb)->gso_type |= SKB_GSO_DODGY;
                skb_shinfo(skb)->gso_segs = 0;
        }
        return 0;
}

static int macvtap_skb_to_vnet_hdr(const struct sk_buff *skb,
                                   struct virtio_net_hdr *vnet_hdr)
{
        memset(vnet_hdr, 0, sizeof(*vnet_hdr));

        if (skb_is_gso(skb)) {
                struct skb_shared_info *sinfo = skb_shinfo(skb);

                /* This is a hint as to how much should be linear. */
                vnet_hdr->hdr_len = skb_headlen(skb);
                vnet_hdr->gso_size = sinfo->gso_size;
                if (sinfo->gso_type & SKB_GSO_TCPV4)
                        vnet_hdr->gso_type = VIRTIO_NET_HDR_GSO_TCPV4;
                else if (sinfo->gso_type & SKB_GSO_TCPV6)
                        vnet_hdr->gso_type = VIRTIO_NET_HDR_GSO_TCPV6;
                else if (sinfo->gso_type & SKB_GSO_UDP)
                        vnet_hdr->gso_type = VIRTIO_NET_HDR_GSO_UDP;
                else
                        BUG();
                if (sinfo->gso_type & SKB_GSO_TCP_ECN)
                        vnet_hdr->gso_type |= VIRTIO_NET_HDR_GSO_ECN;
        } else
                vnet_hdr->gso_type = VIRTIO_NET_HDR_GSO_NONE;

        if (skb->ip_summed == CHECKSUM_PARTIAL) {
                vnet_hdr->flags = VIRTIO_NET_HDR_F_NEEDS_CSUM;
                vnet_hdr->csum_start = skb_checksum_start_offset(skb);
                vnet_hdr->csum_offset = skb->csum_offset;
        } else if (skb->ip_summed == CHECKSUM_UNNECESSARY) {
                vnet_hdr->flags = VIRTIO_NET_HDR_F_DATA_VALID;
        } /* else everything is zero */

        return 0;
}


/* Get packet from user space buffer */
static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *m,
                                const struct iovec *iv, unsigned long total_len,
                                size_t count, int noblock)
{
        struct sk_buff *skb;
        struct macvlan_dev *vlan;
        unsigned long len = total_len;
        int err;
        struct virtio_net_hdr vnet_hdr = { 0 };
        int vnet_hdr_len = 0;
        int copylen = 0;
        bool zerocopy = false;

        if (q->flags & IFF_VNET_HDR) {
                vnet_hdr_len = q->vnet_hdr_sz;

                err = -EINVAL;
                if (len < vnet_hdr_len)
                        goto err;
                len -= vnet_hdr_len;

                err = memcpy_fromiovecend((void *)&vnet_hdr, iv, 0,
                                           sizeof(vnet_hdr));
                if (err < 0)
                        goto err;
                if ((vnet_hdr.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) &&
                     vnet_hdr.csum_start + vnet_hdr.csum_offset + 2 >
                                                        vnet_hdr.hdr_len)
                        vnet_hdr.hdr_len = vnet_hdr.csum_start +
                                                vnet_hdr.csum_offset + 2;
                err = -EINVAL;
                if (vnet_hdr.hdr_len > len)
                        goto err;
        }

        err = -EINVAL;
        if (unlikely(len < ETH_HLEN))
                goto err;

        err = -EMSGSIZE;
        if (unlikely(count > UIO_MAXIOV))
                goto err;

        if (m && m->msg_control && sock_flag(&q->sk, SOCK_ZEROCOPY))
                zerocopy = true;

        if (zerocopy) {
                /* Userspace may produce vectors with count greater than
                 * MAX_SKB_FRAGS, so we need to linearize parts of the skb
                 * to let the rest of data to be fit in the frags.
                 */
                if (count > MAX_SKB_FRAGS) {
                        copylen = iov_length(iv, count - MAX_SKB_FRAGS);
                        if (copylen < vnet_hdr_len)
                                copylen = 0;
                        else
                                copylen -= vnet_hdr_len;
                }
                /* 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 buffer is mapped from userspace.
                 */
                if (copylen < vnet_hdr.hdr_len)
                        copylen = vnet_hdr.hdr_len;
                if (!copylen)
                        copylen = GOODCOPY_LEN;
        } else
                copylen = len;

        skb = macvtap_alloc_skb(&q->sk, NET_IP_ALIGN, copylen,
                                vnet_hdr.hdr_len, noblock, &err);
        if (!skb)
                goto err;

        if (zerocopy)
                err = zerocopy_sg_from_iovec(skb, iv, vnet_hdr_len, count);
        else
                err = skb_copy_datagram_from_iovec(skb, 0, iv, vnet_hdr_len,
                                                   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 = macvtap_skb_from_vnet_hdr(skb, &vnet_hdr);
                if (err)
                        goto err_kfree;
        }

        skb_probe_transport_header(skb, ETH_HLEN);

        rcu_read_lock_bh();
        vlan = rcu_dereference_bh(q->vlan);
        /* 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;
        }
        if (vlan)
                macvlan_start_xmit(skb, vlan->dev);
        else
                kfree_skb(skb);
        rcu_read_unlock_bh();

        return total_len;

err_kfree:
        kfree_skb(skb);

err:
        rcu_read_lock_bh();
        vlan = rcu_dereference_bh(q->vlan);
        if (vlan)
                vlan->dev->stats.tx_dropped++;
        rcu_read_unlock_bh();

        return err;
}

static ssize_t macvtap_aio_write(struct kiocb *iocb, const struct iovec *iv,
                                 unsigned long count, loff_t pos)
{
        struct file *file = iocb->ki_filp;
        ssize_t result = -ENOLINK;
        struct macvtap_queue *q = file->private_data;

        result = macvtap_get_user(q, NULL, iv, iov_length(iv, count), count,
                                  file->f_flags & O_NONBLOCK);
        return result;
}

/* Put packet to the user space buffer */
static ssize_t macvtap_put_user(struct macvtap_queue *q,
                                const struct sk_buff *skb,
                                const struct iovec *iv, int len)
{
        struct macvlan_dev *vlan;
        int ret;
        int vnet_hdr_len = 0;
        int vlan_offset = 0;
        int copied;

        if (q->flags & IFF_VNET_HDR) {
                struct virtio_net_hdr vnet_hdr;
                vnet_hdr_len = q->vnet_hdr_sz;
                if ((len -= vnet_hdr_len) < 0)
                        return -EINVAL;

                ret = macvtap_skb_to_vnet_hdr(skb, &vnet_hdr);
                if (ret)
                        return ret;

                if (memcpy_toiovecend(iv, (void *)&vnet_hdr, 0, sizeof(vnet_hdr)))
                        return -EFAULT;
        }
        copied = vnet_hdr_len;

        if (!vlan_tx_tag_present(skb))
                len = min_t(int, skb->len, len);
        else {
                int copy;
                struct {
                        __be16 h_vlan_proto;
                        __be16 h_vlan_TCI;
                } veth;
                veth.h_vlan_proto = htons(ETH_P_8021Q);
                veth.h_vlan_TCI = htons(vlan_tx_tag_get(skb));

                vlan_offset = offsetof(struct vlan_ethhdr, h_vlan_proto);
                len = min_t(int, skb->len + VLAN_HLEN, len);

                copy = min_t(int, vlan_offset, len);
                ret = skb_copy_datagram_const_iovec(skb, 0, iv, copied, copy);
                len -= copy;
                copied += copy;
                if (ret || !len)
                        goto done;

                copy = min_t(int, sizeof(veth), len);
                ret = memcpy_toiovecend(iv, (void *)&veth, copied, copy);
                len -= copy;
                copied += copy;
                if (ret || !len)
                        goto done;
        }

        ret = skb_copy_datagram_const_iovec(skb, vlan_offset, iv, copied, len);
        copied += len;

done:
        rcu_read_lock_bh();
        vlan = rcu_dereference_bh(q->vlan);
        if (vlan)
                macvlan_count_rx(vlan, copied - vnet_hdr_len, ret == 0, 0);
        rcu_read_unlock_bh();

        return ret ? ret : copied;
}

static ssize_t macvtap_do_read(struct macvtap_queue *q, struct kiocb *iocb,
                               const struct iovec *iv, unsigned long len,
                               int noblock)
{
        DEFINE_WAIT(wait);
        struct sk_buff *skb;
        ssize_t ret = 0;

        while (len) {
                if (!noblock)
                        prepare_to_wait(sk_sleep(&q->sk), &wait,
                                        TASK_INTERRUPTIBLE);

                /* Read frames from the queue */
                skb = skb_dequeue(&q->sk.sk_receive_queue);
                if (!skb) {
                        if (noblock) {
                                ret = -EAGAIN;
                                break;
                        }
                        if (signal_pending(current)) {
                                ret = -ERESTARTSYS;
                                break;
                        }
                        /* Nothing to read, let's sleep */
                        schedule();
                        continue;
                }
                ret = macvtap_put_user(q, skb, iv, len);
                kfree_skb(skb);
                break;
        }

        if (!noblock)
                finish_wait(sk_sleep(&q->sk), &wait);
        return ret;
}

static ssize_t macvtap_aio_read(struct kiocb *iocb, const struct iovec *iv,
                                unsigned long count, loff_t pos)
{
        struct file *file = iocb->ki_filp;
        struct macvtap_queue *q = file->private_data;
        ssize_t len, ret = 0;

        len = iov_length(iv, count);
        if (len < 0) {
                ret = -EINVAL;
                goto out;
        }

        ret = macvtap_do_read(q, iocb, iv, len, file->f_flags & O_NONBLOCK);
        ret = min_t(ssize_t, ret, len); /* XXX copied from tun.c. Why? */
out:
        return ret;
}

static struct macvlan_dev *macvtap_get_vlan(struct macvtap_queue *q)
{
        struct macvlan_dev *vlan;

        rcu_read_lock_bh();
        vlan = rcu_dereference_bh(q->vlan);
        if (vlan)
                dev_hold(vlan->dev);
        rcu_read_unlock_bh();

        return vlan;
}

static void macvtap_put_vlan(struct macvlan_dev *vlan)
{
        dev_put(vlan->dev);
}

/*
 * provide compatibility with generic tun/tap interface
 */
static long macvtap_ioctl(struct file *file, unsigned int cmd,
                          unsigned long arg)
{
        struct macvtap_queue *q = file->private_data;
        struct macvlan_dev *vlan;
        void __user *argp = (void __user *)arg;
        struct ifreq __user *ifr = argp;
        unsigned int __user *up = argp;
        unsigned int u;
        int __user *sp = argp;
        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 & ~IFF_VNET_HDR) != (IFF_NO_PI | IFF_TAP))
                        ret = -EINVAL;
                else
                        q->flags = u;

                return ret;

        case TUNGETIFF:
                vlan = macvtap_get_vlan(q);
                if (!vlan)
                        return -ENOLINK;

                ret = 0;
                if (copy_to_user(&ifr->ifr_name, vlan->dev->name, IFNAMSIZ) ||
                    put_user(q->flags, &ifr->ifr_flags))
                        ret = -EFAULT;
                macvtap_put_vlan(vlan);
                return ret;

        case TUNGETFEATURES:
                if (put_user(IFF_TAP | IFF_NO_PI | IFF_VNET_HDR, up))
                        return -EFAULT;
                return 0;

        case TUNSETSNDBUF:
                if (get_user(u, up))
                        return -EFAULT;

                q->sk.sk_sndbuf = u;
                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 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;

                /* TODO: only accept frames with the features that
                         got enabled for forwarded frames */
                if (!(q->flags & IFF_VNET_HDR))
                        return  -EINVAL;
                return 0;

        default:
                return -EINVAL;
        }
}

#ifdef CONFIG_COMPAT
static long macvtap_compat_ioctl(struct file *file, unsigned int cmd,
                                 unsigned long arg)
{
        return macvtap_ioctl(file, cmd, (unsigned long)compat_ptr(arg));
}
#endif

static const struct file_operations macvtap_fops = {
        .owner          = THIS_MODULE,
        .open           = macvtap_open,
        .release        = macvtap_release,
        .aio_read       = macvtap_aio_read,
        .aio_write      = macvtap_aio_write,
        .poll           = macvtap_poll,
        .llseek         = no_llseek,
        .unlocked_ioctl = macvtap_ioctl,
#ifdef CONFIG_COMPAT
        .compat_ioctl   = macvtap_compat_ioctl,
#endif
};

static int macvtap_sendmsg(struct kiocb *iocb, struct socket *sock,
                           struct msghdr *m, size_t total_len)
{
        struct macvtap_queue *q = container_of(sock, struct macvtap_queue, sock);
        return macvtap_get_user(q, m, m->msg_iov, total_len, m->msg_iovlen,
                            m->msg_flags & MSG_DONTWAIT);
}

static int macvtap_recvmsg(struct kiocb *iocb, struct socket *sock,
                           struct msghdr *m, size_t total_len,
                           int flags)
{
        struct macvtap_queue *q = container_of(sock, struct macvtap_queue, sock);
        int ret;
        if (flags & ~(MSG_DONTWAIT|MSG_TRUNC))
                return -EINVAL;
        ret = macvtap_do_read(q, iocb, m->msg_iov, total_len,
                          flags & MSG_DONTWAIT);
        if (ret > total_len) {
                m->msg_flags |= MSG_TRUNC;
                ret = flags & MSG_TRUNC ? ret : total_len;
        }
        return ret;
}

/* Ops structure to mimic raw sockets with tun */
static const struct proto_ops macvtap_socket_ops = {
        .sendmsg = macvtap_sendmsg,
        .recvmsg = macvtap_recvmsg,
};

/* 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 *macvtap_get_socket(struct file *file)
{
        struct macvtap_queue *q;
        if (file->f_op != &macvtap_fops)
                return ERR_PTR(-EINVAL);
        q = file->private_data;
        if (!q)
                return ERR_PTR(-EBADFD);
        return &q->sock;
}
EXPORT_SYMBOL_GPL(macvtap_get_socket);

static int macvtap_device_event(struct notifier_block *unused,
                                unsigned long event, void *ptr)
{
        struct net_device *dev = netdev_notifier_info_to_dev(ptr);
        struct macvlan_dev *vlan;
        struct device *classdev;
        dev_t devt;
        int err;

        if (dev->rtnl_link_ops != &macvtap_link_ops)
                return NOTIFY_DONE;

        vlan = netdev_priv(dev);

        switch (event) {
        case NETDEV_REGISTER:
                /* Create the device node here after the network device has
                 * been registered but before register_netdevice has
                 * finished running.
                 */
                err = macvtap_get_minor(vlan);
                if (err)
                        return notifier_from_errno(err);

                devt = MKDEV(MAJOR(macvtap_major), vlan->minor);
                classdev = device_create(macvtap_class, &dev->dev, devt,
                                         dev, "tap%d", dev->ifindex);
                if (IS_ERR(classdev)) {
                        macvtap_free_minor(vlan);
                        return notifier_from_errno(PTR_ERR(classdev));
                }
                break;
        case NETDEV_UNREGISTER:
                devt = MKDEV(MAJOR(macvtap_major), vlan->minor);
                device_destroy(macvtap_class, devt);
                macvtap_free_minor(vlan);
                break;
        }

        return NOTIFY_DONE;
}

static struct notifier_block macvtap_notifier_block __read_mostly = {
        .notifier_call  = macvtap_device_event,
};

static int macvtap_init(void)
{
        int err;

        err = alloc_chrdev_region(&macvtap_major, 0,
                                MACVTAP_NUM_DEVS, "macvtap");
        if (err)
                goto out1;

        cdev_init(&macvtap_cdev, &macvtap_fops);
        err = cdev_add(&macvtap_cdev, macvtap_major, MACVTAP_NUM_DEVS);
        if (err)
                goto out2;

        macvtap_class = class_create(THIS_MODULE, "macvtap");
        if (IS_ERR(macvtap_class)) {
                err = PTR_ERR(macvtap_class);
                goto out3;
        }

        err = register_netdevice_notifier(&macvtap_notifier_block);
        if (err)
                goto out4;

        err = macvlan_link_register(&macvtap_link_ops);
        if (err)
                goto out5;

        return 0;

out5:
        unregister_netdevice_notifier(&macvtap_notifier_block);
out4:
        class_unregister(macvtap_class);
out3:
        cdev_del(&macvtap_cdev);
out2:
        unregister_chrdev_region(macvtap_major, MACVTAP_NUM_DEVS);
out1:
        return err;
}
module_init(macvtap_init);

static void macvtap_exit(void)
{
        rtnl_link_unregister(&macvtap_link_ops);
        unregister_netdevice_notifier(&macvtap_notifier_block);
        class_unregister(macvtap_class);
        cdev_del(&macvtap_cdev);
        unregister_chrdev_region(macvtap_major, MACVTAP_NUM_DEVS);
}
module_exit(macvtap_exit);

MODULE_ALIAS_RTNL_LINK("macvtap");
MODULE_AUTHOR("Arnd Bergmann <arnd@arndb.de>");
MODULE_LICENSE("GPL");