net.c

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/* Copyright (C) 2009 Red Hat, Inc.
 * Author: Michael S. Tsirkin <[email protected]>
 *
 * This work is licensed under the terms of the GNU GPL, version 2.
 *
 * virtio-net server in host kernel.
 */

#include <linux/compat.h>
#include <linux/eventfd.h>
#include <linux/vhost.h>
#include <linux/virtio_net.h>
#include <linux/miscdevice.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/mutex.h>
#include <linux/workqueue.h>
#include <linux/rcupdate.h>
#include <linux/file.h>
#include <linux/slab.h>

#include <linux/net.h>
#include <linux/if_packet.h>
#include <linux/if_arp.h>
#include <linux/if_tun.h>
#include <linux/if_macvlan.h>
#include <linux/if_vlan.h>

#include <net/sock.h>

#include "vhost.h"

static int experimental_zcopytx;
module_param(experimental_zcopytx, int, 0444);
MODULE_PARM_DESC(experimental_zcopytx, "Enable Experimental Zero Copy TX");

/* Max number of bytes transferred before requeueing the job.
 * Using this limit prevents one virtqueue from starving others. */
#define VHOST_NET_WEIGHT 0x80000

/* MAX number of TX used buffers for outstanding zerocopy */
#define VHOST_MAX_PEND 128
#define VHOST_GOODCOPY_LEN 256

enum {
    VHOST_NET_VQ_RX = 0,
    VHOST_NET_VQ_TX = 1,
    VHOST_NET_VQ_MAX = 2,
};

enum vhost_net_poll_state {
    VHOST_NET_POLL_DISABLED = 0,
    VHOST_NET_POLL_STARTED = 1,
    VHOST_NET_POLL_STOPPED = 2,
};

struct vhost_net {
    struct vhost_dev dev;
    struct vhost_virtqueue vqs[VHOST_NET_VQ_MAX];
    struct vhost_poll poll[VHOST_NET_VQ_MAX];
    /* Tells us whether we are polling a socket for TX.
     * We only do this when socket buffer fills up.
     * Protected by tx vq lock. */
    enum vhost_net_poll_state tx_poll_state;
};

static bool vhost_sock_zcopy(struct socket *sock)
{
    return unlikely(experimental_zcopytx) &&
        sock_flag(sock->sk, SOCK_ZEROCOPY);
}

/* Pop first len bytes from iovec. Return number of segments used. */
static int move_iovec_hdr(struct iovec *from, struct iovec *to,
              size_t len, int iov_count)
{
    int seg = 0;
    size_t size;

    while (len && seg < iov_count) {
        size = min(from->iov_len, len);
        to->iov_base = from->iov_base;
        to->iov_len = size;
        from->iov_len -= size;
        from->iov_base += size;
        len -= size;
        ++from;
        ++to;
        ++seg;
    }
    return seg;
}
/* Copy iovec entries for len bytes from iovec. */
static void copy_iovec_hdr(const struct iovec *from, struct iovec *to,
               size_t len, int iovcount)
{
    int seg = 0;
    size_t size;

    while (len && seg < iovcount) {
        size = min(from->iov_len, len);
        to->iov_base = from->iov_base;
        to->iov_len = size;
        len -= size;
        ++from;
        ++to;
        ++seg;
    }
}

/* Caller must have TX VQ lock */
static void tx_poll_stop(struct vhost_net *net)
{
    if (likely(net->tx_poll_state != VHOST_NET_POLL_STARTED))
        return;
    vhost_poll_stop(net->poll + VHOST_NET_VQ_TX);
    net->tx_poll_state = VHOST_NET_POLL_STOPPED;
}

/* Caller must have TX VQ lock */
static void tx_poll_start(struct vhost_net *net, struct socket *sock)
{
    if (unlikely(net->tx_poll_state != VHOST_NET_POLL_STOPPED))
        return;
    vhost_poll_start(net->poll + VHOST_NET_VQ_TX, sock->file);
    net->tx_poll_state = VHOST_NET_POLL_STARTED;
}

/* Expects to be always run from workqueue - which acts as
 * read-size critical section for our kind of RCU. */
static void handle_tx(struct vhost_net *net)
{
    struct vhost_virtqueue *vq = &net->dev.vqs[VHOST_NET_VQ_TX];
    unsigned out, in, s;
    int head;
    struct msghdr msg = {
        .msg_name = NULL,
        .msg_namelen = 0,
        .msg_control = NULL,
        .msg_controllen = 0,
        .msg_iov = vq->iov,
        .msg_flags = MSG_DONTWAIT,
    };
    size_t len, total_len = 0;
    int err, wmem;
    size_t hdr_size;
    struct socket *sock;
    struct vhost_ubuf_ref *uninitialized_var(ubufs);
    bool zcopy;

    /* TODO: check that we are running from vhost_worker? */
    sock = rcu_dereference_check(vq->private_data, 1);
    if (!sock)
        return;

    wmem = atomic_read(&sock->sk->sk_wmem_alloc);
    if (wmem >= sock->sk->sk_sndbuf) {
        mutex_lock(&vq->mutex);
        tx_poll_start(net, sock);
        mutex_unlock(&vq->mutex);
        return;
    }

    mutex_lock(&vq->mutex);
    vhost_disable_notify(&net->dev, vq);

    if (wmem < sock->sk->sk_sndbuf / 2)
        tx_poll_stop(net);
    hdr_size = vq->vhost_hlen;
    zcopy = vq->ubufs;

    for (;;) {
        /* Release DMAs done buffers first */
        if (zcopy)
            vhost_zerocopy_signal_used(vq);

        head = vhost_get_vq_desc(&net->dev, vq, vq->iov,
                     ARRAY_SIZE(vq->iov),
                     &out, &in,
                     NULL, NULL);
        /* On error, stop handling until the next kick. */
        if (unlikely(head < 0))
            break;
        /* Nothing new?  Wait for eventfd to tell us they refilled. */
        if (head == vq->num) {
            int num_pends;

            wmem = atomic_read(&sock->sk->sk_wmem_alloc);
            if (wmem >= sock->sk->sk_sndbuf * 3 / 4) {
                tx_poll_start(net, sock);
                set_bit(SOCK_ASYNC_NOSPACE, &sock->flags);
                break;
            }
            /* If more outstanding DMAs, queue the work.
             * Handle upend_idx wrap around
             */
            num_pends = likely(vq->upend_idx >= vq->done_idx) ?
                    (vq->upend_idx - vq->done_idx) :
                    (vq->upend_idx + UIO_MAXIOV - vq->done_idx);
            if (unlikely(num_pends > VHOST_MAX_PEND)) {
                tx_poll_start(net, sock);
                set_bit(SOCK_ASYNC_NOSPACE, &sock->flags);
                break;
            }
            if (unlikely(vhost_enable_notify(&net->dev, vq))) {
                vhost_disable_notify(&net->dev, vq);
                continue;
            }
            break;
        }
        if (in) {
            vq_err(vq, "Unexpected descriptor format for TX: "
                   "out %d, int %d\n", out, in);
            break;
        }
        /* Skip header. TODO: support TSO. */
        s = move_iovec_hdr(vq->iov, vq->hdr, hdr_size, out);
        msg.msg_iovlen = out;
        len = iov_length(vq->iov, out);
        /* Sanity check */
        if (!len) {
            vq_err(vq, "Unexpected header len for TX: "
                   "%zd expected %zd\n",
                   iov_length(vq->hdr, s), hdr_size);
            break;
        }
        /* use msg_control to pass vhost zerocopy ubuf info to skb */
        if (zcopy) {
            vq->heads[vq->upend_idx].id = head;
            if (len < VHOST_GOODCOPY_LEN) {
                /* copy don't need to wait for DMA done */
                vq->heads[vq->upend_idx].len =
                            VHOST_DMA_DONE_LEN;
                msg.msg_control = NULL;
                msg.msg_controllen = 0;
                ubufs = NULL;
            } else {
                struct ubuf_info *ubuf = &vq->ubuf_info[head];

                vq->heads[vq->upend_idx].len = len;
                ubuf->callback = vhost_zerocopy_callback;
                ubuf->ctx = vq->ubufs;
                ubuf->desc = vq->upend_idx;
                msg.msg_control = ubuf;
                msg.msg_controllen = sizeof(ubuf);
                ubufs = vq->ubufs;
                kref_get(&ubufs->kref);
            }
            vq->upend_idx = (vq->upend_idx + 1) % UIO_MAXIOV;
        }
        /* TODO: Check specific error and bomb out unless ENOBUFS? */
        err = sock->ops->sendmsg(NULL, sock, &msg, len);
        if (unlikely(err < 0)) {
            if (zcopy) {
                if (ubufs)
                    vhost_ubuf_put(ubufs);
                vq->upend_idx = ((unsigned)vq->upend_idx - 1) %
                    UIO_MAXIOV;
            }
            vhost_discard_vq_desc(vq, 1);
            if (err == -EAGAIN || err == -ENOBUFS)
                tx_poll_start(net, sock);
            break;
        }
        if (err != len)
            pr_debug("Truncated TX packet: "
                 " len %d != %zd\n", err, len);
        if (!zcopy)
            vhost_add_used_and_signal(&net->dev, vq, head, 0);
        else
            vhost_zerocopy_signal_used(vq);
        total_len += len;
        if (unlikely(total_len >= VHOST_NET_WEIGHT)) {
            vhost_poll_queue(&vq->poll);
            break;
        }
    }

    mutex_unlock(&vq->mutex);
}

static int peek_head_len(struct sock *sk)
{
    struct sk_buff *head;
    int len = 0;
    unsigned long flags;

    spin_lock_irqsave(&sk->sk_receive_queue.lock, flags);
    head = skb_peek(&sk->sk_receive_queue);
    if (likely(head)) {
        len = head->len;
        if (vlan_tx_tag_present(head))
            len += VLAN_HLEN;
    }

    spin_unlock_irqrestore(&sk->sk_receive_queue.lock, flags);
    return len;
}

/* This is a multi-buffer version of vhost_get_desc, that works if
 *  vq has read descriptors only.
 * @vq      - the relevant virtqueue
 * @datalen - data length we'll be reading
 * @iovcount    - returned count of io vectors we fill
 * @log     - vhost log
 * @log_num - log offset
 * @quota       - headcount quota, 1 for big buffer
 *  returns number of buffer heads allocated, negative on error
 */
static int get_rx_bufs(struct vhost_virtqueue *vq,
               struct vring_used_elem *heads,
               int datalen,
               unsigned *iovcount,
               struct vhost_log *log,
               unsigned *log_num,
               unsigned int quota)
{
    unsigned int out, in;
    int seg = 0;
    int headcount = 0;
    unsigned d;
    int r, nlogs = 0;

    while (datalen > 0 && headcount < quota) {
        if (unlikely(seg >= UIO_MAXIOV)) {
            r = -ENOBUFS;
            goto err;
        }
        d = vhost_get_vq_desc(vq->dev, vq, vq->iov + seg,
                      ARRAY_SIZE(vq->iov) - seg, &out,
                      &in, log, log_num);
        if (d == vq->num) {
            r = 0;
            goto err;
        }
        if (unlikely(out || in <= 0)) {
            vq_err(vq, "unexpected descriptor format for RX: "
                "out %d, in %d\n", out, in);
            r = -EINVAL;
            goto err;
        }
        if (unlikely(log)) {
            nlogs += *log_num;
            log += *log_num;
        }
        heads[headcount].id = d;
        heads[headcount].len = iov_length(vq->iov + seg, in);
        datalen -= heads[headcount].len;
        ++headcount;
        seg += in;
    }
    heads[headcount - 1].len += datalen;
    *iovcount = seg;
    if (unlikely(log))
        *log_num = nlogs;
    return headcount;
err:
    vhost_discard_vq_desc(vq, headcount);
    return r;
}

/* Expects to be always run from workqueue - which acts as
 * read-size critical section for our kind of RCU. */
static void handle_rx(struct vhost_net *net)
{
    struct vhost_virtqueue *vq = &net->dev.vqs[VHOST_NET_VQ_RX];
    unsigned uninitialized_var(in), log;
    struct vhost_log *vq_log;
    struct msghdr msg = {
        .msg_name = NULL,
        .msg_namelen = 0,
        .msg_control = NULL, /* FIXME: get and handle RX aux data. */
        .msg_controllen = 0,
        .msg_iov = vq->iov,
        .msg_flags = MSG_DONTWAIT,
    };
    struct virtio_net_hdr_mrg_rxbuf hdr = {
        .hdr.flags = 0,
        .hdr.gso_type = VIRTIO_NET_HDR_GSO_NONE
    };
    size_t total_len = 0;
    int err, mergeable;
    s16 headcount;
    size_t vhost_hlen, sock_hlen;
    size_t vhost_len, sock_len;
    /* TODO: check that we are running from vhost_worker? */
    struct socket *sock = rcu_dereference_check(vq->private_data, 1);

    if (!sock)
        return;

    mutex_lock(&vq->mutex);
    vhost_disable_notify(&net->dev, vq);
    vhost_hlen = vq->vhost_hlen;
    sock_hlen = vq->sock_hlen;

    vq_log = unlikely(vhost_has_feature(&net->dev, VHOST_F_LOG_ALL)) ?
        vq->log : NULL;
    mergeable = vhost_has_feature(&net->dev, VIRTIO_NET_F_MRG_RXBUF);

    while ((sock_len = peek_head_len(sock->sk))) {
        sock_len += sock_hlen;
        vhost_len = sock_len + vhost_hlen;
        headcount = get_rx_bufs(vq, vq->heads, vhost_len,
                    &in, vq_log, &log,
                    likely(mergeable) ? UIO_MAXIOV : 1);
        /* On error, stop handling until the next kick. */
        if (unlikely(headcount < 0))
            break;
        /* OK, now we need to know about added descriptors. */
        if (!headcount) {
            if (unlikely(vhost_enable_notify(&net->dev, vq))) {
                /* They have slipped one in as we were
                 * doing that: check again. */
                vhost_disable_notify(&net->dev, vq);
                continue;
            }
            /* Nothing new?  Wait for eventfd to tell us
             * they refilled. */
            break;
        }
        /* We don't need to be notified again. */
        if (unlikely((vhost_hlen)))
            /* Skip header. TODO: support TSO. */
            move_iovec_hdr(vq->iov, vq->hdr, vhost_hlen, in);
        else
            /* Copy the header for use in VIRTIO_NET_F_MRG_RXBUF:
             * needed because recvmsg can modify msg_iov. */
            copy_iovec_hdr(vq->iov, vq->hdr, sock_hlen, in);
        msg.msg_iovlen = in;
        err = sock->ops->recvmsg(NULL, sock, &msg,
                     sock_len, MSG_DONTWAIT | MSG_TRUNC);
        /* Userspace might have consumed the packet meanwhile:
         * it's not supposed to do this usually, but might be hard
         * to prevent. Discard data we got (if any) and keep going. */
        if (unlikely(err != sock_len)) {
            pr_debug("Discarded rx packet: "
                 " len %d, expected %zd\n", err, sock_len);
            vhost_discard_vq_desc(vq, headcount);
            continue;
        }
        if (unlikely(vhost_hlen) &&
            memcpy_toiovecend(vq->hdr, (unsigned char *)&hdr, 0,
                      vhost_hlen)) {
            vq_err(vq, "Unable to write vnet_hdr at addr %p\n",
                   vq->iov->iov_base);
            break;
        }
        /* TODO: Should check and handle checksum. */
        if (likely(mergeable) &&
            memcpy_toiovecend(vq->hdr, (unsigned char *)&headcount,
                      offsetof(typeof(hdr), num_buffers),
                      sizeof hdr.num_buffers)) {
            vq_err(vq, "Failed num_buffers write");
            vhost_discard_vq_desc(vq, headcount);
            break;
        }
        vhost_add_used_and_signal_n(&net->dev, vq, vq->heads,
                        headcount);
        if (unlikely(vq_log))
            vhost_log_write(vq, vq_log, log, vhost_len);
        total_len += vhost_len;
        if (unlikely(total_len >= VHOST_NET_WEIGHT)) {
            vhost_poll_queue(&vq->poll);
            break;
        }
    }

    mutex_unlock(&vq->mutex);
}

static void handle_tx_kick(struct vhost_work *work)
{
    struct vhost_virtqueue *vq = container_of(work, struct vhost_virtqueue,
                          poll.work);
    struct vhost_net *net = container_of(vq->dev, struct vhost_net, dev);

    handle_tx(net);
}

static void handle_rx_kick(struct vhost_work *work)
{
    struct vhost_virtqueue *vq = container_of(work, struct vhost_virtqueue,
                          poll.work);
    struct vhost_net *net = container_of(vq->dev, struct vhost_net, dev);

    handle_rx(net);
}

static void handle_tx_net(struct vhost_work *work)
{
    struct vhost_net *net = container_of(work, struct vhost_net,
                         poll[VHOST_NET_VQ_TX].work);
    handle_tx(net);
}

static void handle_rx_net(struct vhost_work *work)
{
    struct vhost_net *net = container_of(work, struct vhost_net,
                         poll[VHOST_NET_VQ_RX].work);
    handle_rx(net);
}

static int vhost_net_open(struct inode *inode, struct file *f)
{
    struct vhost_net *n = kmalloc(sizeof *n, GFP_KERNEL);
    struct vhost_dev *dev;
    int r;

    if (!n)
        return -ENOMEM;

    dev = &n->dev;
    n->vqs[VHOST_NET_VQ_TX].handle_kick = handle_tx_kick;
    n->vqs[VHOST_NET_VQ_RX].handle_kick = handle_rx_kick;
    r = vhost_dev_init(dev, n->vqs, VHOST_NET_VQ_MAX);
    if (r < 0) {
        kfree(n);
        return r;
    }

    vhost_poll_init(n->poll + VHOST_NET_VQ_TX, handle_tx_net, POLLOUT, dev);
    vhost_poll_init(n->poll + VHOST_NET_VQ_RX, handle_rx_net, POLLIN, dev);
    n->tx_poll_state = VHOST_NET_POLL_DISABLED;

    f->private_data = n;

    return 0;
}

static void vhost_net_disable_vq(struct vhost_net *n,
                 struct vhost_virtqueue *vq)
{
    if (!vq->private_data)
        return;
    if (vq == n->vqs + VHOST_NET_VQ_TX) {
        tx_poll_stop(n);
        n->tx_poll_state = VHOST_NET_POLL_DISABLED;
    } else
        vhost_poll_stop(n->poll + VHOST_NET_VQ_RX);
}

static void vhost_net_enable_vq(struct vhost_net *n,
                struct vhost_virtqueue *vq)
{
    struct socket *sock;

    sock = rcu_dereference_protected(vq->private_data,
                     lockdep_is_held(&vq->mutex));
    if (!sock)
        return;
    if (vq == n->vqs + VHOST_NET_VQ_TX) {
        n->tx_poll_state = VHOST_NET_POLL_STOPPED;
        tx_poll_start(n, sock);
    } else
        vhost_poll_start(n->poll + VHOST_NET_VQ_RX, sock->file);
}

static struct socket *vhost_net_stop_vq(struct vhost_net *n,
                    struct vhost_virtqueue *vq)
{
    struct socket *sock;

    mutex_lock(&vq->mutex);
    sock = rcu_dereference_protected(vq->private_data,
                     lockdep_is_held(&vq->mutex));
    vhost_net_disable_vq(n, vq);
    rcu_assign_pointer(vq->private_data, NULL);
    mutex_unlock(&vq->mutex);
    return sock;
}

static void vhost_net_stop(struct vhost_net *n, struct socket **tx_sock,
               struct socket **rx_sock)
{
    *tx_sock = vhost_net_stop_vq(n, n->vqs + VHOST_NET_VQ_TX);
    *rx_sock = vhost_net_stop_vq(n, n->vqs + VHOST_NET_VQ_RX);
}

static void vhost_net_flush_vq(struct vhost_net *n, int index)
{
    vhost_poll_flush(n->poll + index);
    vhost_poll_flush(&n->dev.vqs[index].poll);
}

static void vhost_net_flush(struct vhost_net *n)
{
    vhost_net_flush_vq(n, VHOST_NET_VQ_TX);
    vhost_net_flush_vq(n, VHOST_NET_VQ_RX);
}

static int vhost_net_release(struct inode *inode, struct file *f)
{
    struct vhost_net *n = f->private_data;
    struct socket *tx_sock;
    struct socket *rx_sock;

    vhost_net_stop(n, &tx_sock, &rx_sock);
    vhost_net_flush(n);
    vhost_dev_cleanup(&n->dev, false);
    if (tx_sock)
        fput(tx_sock->file);
    if (rx_sock)
        fput(rx_sock->file);
    /* We do an extra flush before freeing memory,
     * since jobs can re-queue themselves. */
    vhost_net_flush(n);
    kfree(n);
    return 0;
}

static struct socket *get_raw_socket(int fd)
{
    struct {
        struct sockaddr_ll sa;
        char  buf[MAX_ADDR_LEN];
    } uaddr;
    int uaddr_len = sizeof uaddr, r;
    struct socket *sock = sockfd_lookup(fd, &r);

    if (!sock)
        return ERR_PTR(-ENOTSOCK);

    /* Parameter checking */
    if (sock->sk->sk_type != SOCK_RAW) {
        r = -ESOCKTNOSUPPORT;
        goto err;
    }

    r = sock->ops->getname(sock, (struct sockaddr *)&uaddr.sa,
                   &uaddr_len, 0);
    if (r)
        goto err;

    if (uaddr.sa.sll_family != AF_PACKET) {
        r = -EPFNOSUPPORT;
        goto err;
    }
    return sock;
err:
    fput(sock->file);
    return ERR_PTR(r);
}

static struct socket *get_tap_socket(int fd)
{
    struct file *file = fget(fd);
    struct socket *sock;

    if (!file)
        return ERR_PTR(-EBADF);
    sock = tun_get_socket(file);
    if (!IS_ERR(sock))
        return sock;
    sock = macvtap_get_socket(file);
    if (IS_ERR(sock))
        fput(file);
    return sock;
}

static struct socket *get_socket(int fd)
{
    struct socket *sock;

    /* special case to disable backend */
    if (fd == -1)
        return NULL;
    sock = get_raw_socket(fd);
    if (!IS_ERR(sock))
        return sock;
    sock = get_tap_socket(fd);
    if (!IS_ERR(sock))
        return sock;
    return ERR_PTR(-ENOTSOCK);
}

static long vhost_net_set_backend(struct vhost_net *n, unsigned index, int fd)
{
    struct socket *sock, *oldsock;
    struct vhost_virtqueue *vq;
    struct vhost_ubuf_ref *ubufs, *oldubufs = NULL;
    int r;

    mutex_lock(&n->dev.mutex);
    r = vhost_dev_check_owner(&n->dev);
    if (r)
        goto err;

    if (index >= VHOST_NET_VQ_MAX) {
        r = -ENOBUFS;
        goto err;
    }
    vq = n->vqs + index;
    mutex_lock(&vq->mutex);

    /* Verify that ring has been setup correctly. */
    if (!vhost_vq_access_ok(vq)) {
        r = -EFAULT;
        goto err_vq;
    }
    sock = get_socket(fd);
    if (IS_ERR(sock)) {
        r = PTR_ERR(sock);
        goto err_vq;
    }

    /* start polling new socket */
    oldsock = rcu_dereference_protected(vq->private_data,
                        lockdep_is_held(&vq->mutex));
    if (sock != oldsock) {
        ubufs = vhost_ubuf_alloc(vq, sock && vhost_sock_zcopy(sock));
        if (IS_ERR(ubufs)) {
            r = PTR_ERR(ubufs);
            goto err_ubufs;
        }
        oldubufs = vq->ubufs;
        vq->ubufs = ubufs;
        vhost_net_disable_vq(n, vq);
        rcu_assign_pointer(vq->private_data, sock);
        vhost_net_enable_vq(n, vq);

        r = vhost_init_used(vq);
        if (r)
            goto err_vq;
    }

    mutex_unlock(&vq->mutex);

    if (oldubufs) {
        vhost_ubuf_put_and_wait(oldubufs);
        mutex_lock(&vq->mutex);
        vhost_zerocopy_signal_used(vq);
        mutex_unlock(&vq->mutex);
    }

    if (oldsock) {
        vhost_net_flush_vq(n, index);
        fput(oldsock->file);
    }

    mutex_unlock(&n->dev.mutex);
    return 0;

err_ubufs:
    fput(sock->file);
err_vq:
    mutex_unlock(&vq->mutex);
err:
    mutex_unlock(&n->dev.mutex);
    return r;
}

static long vhost_net_reset_owner(struct vhost_net *n)
{
    struct socket *tx_sock = NULL;
    struct socket *rx_sock = NULL;
    long err;

    mutex_lock(&n->dev.mutex);
    err = vhost_dev_check_owner(&n->dev);
    if (err)
        goto done;
    vhost_net_stop(n, &tx_sock, &rx_sock);
    vhost_net_flush(n);
    err = vhost_dev_reset_owner(&n->dev);
done:
    mutex_unlock(&n->dev.mutex);
    if (tx_sock)
        fput(tx_sock->file);
    if (rx_sock)
        fput(rx_sock->file);
    return err;
}

static int vhost_net_set_features(struct vhost_net *n, u64 features)
{
    size_t vhost_hlen, sock_hlen, hdr_len;
    int i;

    hdr_len = (features & (1 << VIRTIO_NET_F_MRG_RXBUF)) ?
            sizeof(struct virtio_net_hdr_mrg_rxbuf) :
            sizeof(struct virtio_net_hdr);
    if (features & (1 << VHOST_NET_F_VIRTIO_NET_HDR)) {
        /* vhost provides vnet_hdr */
        vhost_hlen = hdr_len;
        sock_hlen = 0;
    } else {
        /* socket provides vnet_hdr */
        vhost_hlen = 0;
        sock_hlen = hdr_len;
    }
    mutex_lock(&n->dev.mutex);
    if ((features & (1 << VHOST_F_LOG_ALL)) &&
        !vhost_log_access_ok(&n->dev)) {
        mutex_unlock(&n->dev.mutex);
        return -EFAULT;
    }
    n->dev.acked_features = features;
    smp_wmb();
    for (i = 0; i < VHOST_NET_VQ_MAX; ++i) {
        mutex_lock(&n->vqs[i].mutex);
        n->vqs[i].vhost_hlen = vhost_hlen;
        n->vqs[i].sock_hlen = sock_hlen;
        mutex_unlock(&n->vqs[i].mutex);
    }
    vhost_net_flush(n);
    mutex_unlock(&n->dev.mutex);
    return 0;
}

static long vhost_net_ioctl(struct file *f, unsigned int ioctl,
                unsigned long arg)
{
    struct vhost_net *n = f->private_data;
    void __user *argp = (void __user *)arg;
    u64 __user *featurep = argp;
    struct vhost_vring_file backend;
    u64 features;
    int r;

    switch (ioctl) {
    case VHOST_NET_SET_BACKEND:
        if (copy_from_user(&backend, argp, sizeof backend))
            return -EFAULT;
        return vhost_net_set_backend(n, backend.index, backend.fd);
    case VHOST_GET_FEATURES:
        features = VHOST_NET_FEATURES;
        if (copy_to_user(featurep, &features, sizeof features))
            return -EFAULT;
        return 0;
    case VHOST_SET_FEATURES:
        if (copy_from_user(&features, featurep, sizeof features))
            return -EFAULT;
        if (features & ~VHOST_NET_FEATURES)
            return -EOPNOTSUPP;
        return vhost_net_set_features(n, features);
    case VHOST_RESET_OWNER:
        return vhost_net_reset_owner(n);
    default:
        mutex_lock(&n->dev.mutex);
        r = vhost_dev_ioctl(&n->dev, ioctl, arg);
        vhost_net_flush(n);
        mutex_unlock(&n->dev.mutex);
        return r;
    }
}

#ifdef CONFIG_COMPAT
static long vhost_net_compat_ioctl(struct file *f, unsigned int ioctl,
                   unsigned long arg)
{
    return vhost_net_ioctl(f, ioctl, (unsigned long)compat_ptr(arg));
}
#endif

static const struct file_operations vhost_net_fops = {
    .owner          = THIS_MODULE,
    .release        = vhost_net_release,
    .unlocked_ioctl = vhost_net_ioctl,
#ifdef CONFIG_COMPAT
    .compat_ioctl   = vhost_net_compat_ioctl,
#endif
    .open           = vhost_net_open,
    .llseek     = noop_llseek,
};

static struct miscdevice vhost_net_misc = {
    .minor = VHOST_NET_MINOR,
    .name = "vhost-net",
    .fops = &vhost_net_fops,
};

static int vhost_net_init(void)
{
    if (experimental_zcopytx)
        vhost_enable_zcopy(VHOST_NET_VQ_TX);
    return misc_register(&vhost_net_misc);
}
module_init(vhost_net_init);

static void vhost_net_exit(void)
{
    misc_deregister(&vhost_net_misc);
}
module_exit(vhost_net_exit);

MODULE_VERSION("0.0.1");
MODULE_LICENSE("GPL v2");
MODULE_AUTHOR("Michael S. Tsirkin");
MODULE_DESCRIPTION("Host kernel accelerator for virtio net");
MODULE_ALIAS_MISCDEV(VHOST_NET_MINOR);
MODULE_ALIAS("devname:vhost-net");