macvtap.c

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#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;
};

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);

/*
 * get_slot: return a [unused/occupied] slot in vlan->taps[]:
 *  - if 'q' is NULL, return the first empty slot;
 *  - otherwise, return the slot this pointer occupies.
 */
static int get_slot(struct macvlan_dev *vlan, struct macvtap_queue *q)
{
    int i;

    for (i = 0; i < MAX_MACVTAP_QUEUES; i++) {
        if (rcu_dereference_protected(vlan->taps[i],
                          lockdep_is_held(&macvtap_lock)) == q)
            return i;
    }

    /* Should never happen */
    BUG_ON(1);
}

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

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

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

    q->file = file;
    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 macvlan_dev *vlan;

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

        RCU_INIT_POINTER(vlan->taps[index], 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 = 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]);
        if (tap)
            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]);
        if (tap)
            goto out;
    }

    /* Everything failed - find first available queue */
    for (rxq = 0; rxq < MAX_MACVTAP_QUEUES; rxq++) {
        tap = rcu_dereference(vlan->taps[rxq]);
        if (tap)
            break;
    }

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;

    /* macvtap_put_queue can free some slots, so go through all slots */
    spin_lock(&macvtap_lock);
    for (i = 0; i < MAX_MACVTAP_QUEUES && vlan->numvtaps; i++) {
        q = rcu_dereference_protected(vlan->taps[i],
                          lockdep_is_held(&macvtap_lock));
        if (q) {
            qlist[j++] = q;
            RCU_INIT_POINTER(vlan->taps[i], NULL);
            RCU_INIT_POINTER(q->vlan, NULL);
            vlan->numvtaps--;
        }
    }
    BUG_ON(vlan->numvtaps != 0);
    /* 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;
    int id;

    mutex_lock(&minor_lock);
    if (idr_pre_get(&minor_idr, GFP_KERNEL) == 0)
        goto exit;

    retval = idr_get_new_above(&minor_idr, vlan, 1, &id);
    if (retval < 0) {
        if (retval == -EAGAIN)
            retval = -ENOMEM;
        goto exit;
    }
    if (id < MACVTAP_NUM_DEVS) {
        vlan->minor = id;
    } else {
        printk(KERN_ERR "too many macvtap devices\n");
        retval = -EINVAL;
        idr_remove(&minor_idr, id);
    }
exit:
    mutex_unlock(&minor_lock);
    return retval;
}

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;
    }

    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;
    }
    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) {
        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;
    }

    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;
}

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

        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;
        dev_put(vlan->dev);
        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 = 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 <[email protected]>");
MODULE_LICENSE("GPL");