vhost-net: reduce vq polling on tx zerocopy

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

/* Copyright (C) 2009 Red Hat, Inc.
 * Author: Michael S. Tsirkin <mst@redhat.com>
 *
 * 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

/*
 * For transmit, used buffer len is unused; we override it to track buffer
 * status internally; used for zerocopy tx only.
 */
/* Lower device DMA failed */
#define VHOST_DMA_FAILED_LEN    3
/* Lower device DMA done */
#define VHOST_DMA_DONE_LEN      2
/* Lower device DMA in progress */
#define VHOST_DMA_IN_PROGRESS   1
/* Buffer unused */
#define VHOST_DMA_CLEAR_LEN     0

#define VHOST_DMA_IS_DONE(len) ((len) >= VHOST_DMA_DONE_LEN)

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;
        /* Number of TX recently submitted.
         * Protected by tx vq lock. */
        unsigned tx_packets;
        /* Number of times zerocopy TX recently failed.
         * Protected by tx vq lock. */
        unsigned tx_zcopy_err;
};

static void vhost_net_tx_packet(struct vhost_net *net)
{
        ++net->tx_packets;
        if (net->tx_packets < 1024)
                return;
        net->tx_packets = 0;
        net->tx_zcopy_err = 0;
}

static void vhost_net_tx_err(struct vhost_net *net)
{
        ++net->tx_zcopy_err;
}

static bool vhost_net_tx_select_zcopy(struct vhost_net *net)
{
        return net->tx_packets / 64 >= net->tx_zcopy_err;
}

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;
}

/* In case of DMA done not in order in lower device driver for some reason.
 * upend_idx is used to track end of used idx, done_idx is used to track head
 * of used idx. Once lower device DMA done contiguously, we will signal KVM
 * guest used idx.
 */
static int vhost_zerocopy_signal_used(struct vhost_net *net,
                                      struct vhost_virtqueue *vq)
{
        int i;
        int j = 0;

        for (i = vq->done_idx; i != vq->upend_idx; i = (i + 1) % UIO_MAXIOV) {
                if (vq->heads[i].len == VHOST_DMA_FAILED_LEN)
                        vhost_net_tx_err(net);
                if (VHOST_DMA_IS_DONE(vq->heads[i].len)) {
                        vq->heads[i].len = VHOST_DMA_CLEAR_LEN;
                        vhost_add_used_and_signal(vq->dev, vq,
                                                  vq->heads[i].id, 0);
                        ++j;
                } else
                        break;
        }
        if (j)
                vq->done_idx = i;
        return j;
}

static void vhost_zerocopy_callback(struct ubuf_info *ubuf, bool success)
{
        struct vhost_ubuf_ref *ubufs = ubuf->ctx;
        struct vhost_virtqueue *vq = ubufs->vq;
        int cnt = atomic_read(&ubufs->kref.refcount);

        /*
         * Trigger polling thread if guest stopped submitting new buffers:
         * in this case, the refcount after decrement will eventually reach 1
         * so here it is 2.
         * We also trigger polling periodically after each 16 packets
         * (the value 16 here is more or less arbitrary, it's tuned to trigger
         * less than 10% of times).
         */
        if (cnt <= 2 || !(cnt % 16))
                vhost_poll_queue(&vq->poll);
        /* set len to mark this desc buffers done DMA */
        vq->heads[ubuf->desc].len = success ?
                VHOST_DMA_DONE_LEN : VHOST_DMA_FAILED_LEN;
        vhost_ubuf_put(ubufs);
}

/* 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(net, 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 (!vhost_net_tx_select_zcopy(net) ||
                            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 =
                                        VHOST_DMA_IN_PROGRESS;
                                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(net, vq);
                total_len += len;
                vhost_net_tx_packet(net);
                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, headcount, mergeable;
        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;
        int i;

        vhost_net_stop(n, &tx_sock, &rx_sock);
        vhost_net_flush(n);
        vhost_dev_stop(&n->dev);
        for (i = 0; i < n->dev.nvqs; ++i) {
                /* Wait for all lower device DMAs done. */
                if (n->dev.vqs[i].ubufs)
                        vhost_ubuf_put_and_wait(n->dev.vqs[i].ubufs);

                vhost_zerocopy_signal_used(n, &n->dev.vqs[i]);
        }
        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(n, 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");