// SPDX-License-Identifier: GPL-2.0-only
/* Copyright (C) 2009 Red Hat, Inc.
 * Author: Michael S. Tsirkin <mst@redhat.com>
 *
 * 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/file.h>
#include <linux/slab.h>
#include <linux/sched/clock.h>
#include <linux/sched/signal.h>
#include <linux/vmalloc.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_tap.h>
#include <linux/if_vlan.h>
#include <linux/skb_array.h>
#include <linux/skbuff.h>

#include <net/sock.h>
#include <net/xdp.h>

#include "vhost.h"

static int experimental_zcopytx = 0;
module_param(experimental_zcopytx, int, 0444);
MODULE_PARM_DESC(experimental_zcopytx, "Enable Zero Copy TX;"
                                       " 1 -Enable; 0 - Disable");

/* 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 packets transferred before requeueing the job.
 * Using this limit prevents one virtqueue from starving others with small
 * pkts.
 */
#define VHOST_NET_PKT_WEIGHT 256

/* 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    ((__force __virtio32)3)
/* Lower device DMA done */
#define VHOST_DMA_DONE_LEN      ((__force __virtio32)2)
/* Lower device DMA in progress */
#define VHOST_DMA_IN_PROGRESS   ((__force __virtio32)1)
/* Buffer unused */
#define VHOST_DMA_CLEAR_LEN     ((__force __virtio32)0)

#define VHOST_DMA_IS_DONE(len) ((__force u32)(len) >= (__force u32)VHOST_DMA_DONE_LEN)

enum {
        VHOST_NET_FEATURES = VHOST_FEATURES |
                         (1ULL << VHOST_NET_F_VIRTIO_NET_HDR) |
                         (1ULL << VIRTIO_NET_F_MRG_RXBUF) |
                         (1ULL << VIRTIO_F_IOMMU_PLATFORM)
};

enum {
        VHOST_NET_BACKEND_FEATURES = (1ULL << VHOST_BACKEND_F_IOTLB_MSG_V2)
};

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

struct vhost_net_ubuf_ref {
        /* refcount follows semantics similar to kref:
         *  0: object is released
         *  1: no outstanding ubufs
         * >1: outstanding ubufs
         */
        atomic_t refcount;
        wait_queue_head_t wait;
        struct vhost_virtqueue *vq;
};

#define VHOST_NET_BATCH 64
struct vhost_net_buf {
        void **queue;
        int tail;
        int head;
};

struct vhost_net_virtqueue {
        struct vhost_virtqueue vq;
        size_t vhost_hlen;
        size_t sock_hlen;
        /* vhost zerocopy support fields below: */
        /* last used idx for outstanding DMA zerocopy buffers */
        int upend_idx;
        /* For TX, first used idx for DMA done zerocopy buffers
         * For RX, number of batched heads
         */
        int done_idx;
        /* Number of XDP frames batched */
        int batched_xdp;
        /* an array of userspace buffers info */
        struct ubuf_info *ubuf_info;
        /* Reference counting for outstanding ubufs.
         * Protected by vq mutex. Writers must also take device mutex. */
        struct vhost_net_ubuf_ref *ubufs;
        struct ptr_ring *rx_ring;
        struct vhost_net_buf rxq;
        /* Batched XDP buffs */
        struct xdp_buff *xdp;
};

struct vhost_net {
        struct vhost_dev dev;
        struct vhost_net_virtqueue vqs[VHOST_NET_VQ_MAX];
        struct vhost_poll poll[VHOST_NET_VQ_MAX];
        /* 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;
        /* Flush in progress. Protected by tx vq lock. */
        bool tx_flush;
        /* Private page frag */
        struct page_frag page_frag;
        /* Refcount bias of page frag */
        int refcnt_bias;
};

static unsigned vhost_net_zcopy_mask __read_mostly;

static void *vhost_net_buf_get_ptr(struct vhost_net_buf *rxq)
{
        if (rxq->tail != rxq->head)
                return rxq->queue[rxq->head];
        else
                return NULL;
}

static int vhost_net_buf_get_size(struct vhost_net_buf *rxq)
{
        return rxq->tail - rxq->head;
}

static int vhost_net_buf_is_empty(struct vhost_net_buf *rxq)
{
        return rxq->tail == rxq->head;
}

static void *vhost_net_buf_consume(struct vhost_net_buf *rxq)
{
        void *ret = vhost_net_buf_get_ptr(rxq);
        ++rxq->head;
        return ret;
}

static int vhost_net_buf_produce(struct vhost_net_virtqueue *nvq)
{
        struct vhost_net_buf *rxq = &nvq->rxq;

        rxq->head = 0;
        rxq->tail = ptr_ring_consume_batched(nvq->rx_ring, rxq->queue,
                                              VHOST_NET_BATCH);
        return rxq->tail;
}

static void vhost_net_buf_unproduce(struct vhost_net_virtqueue *nvq)
{
        struct vhost_net_buf *rxq = &nvq->rxq;

        if (nvq->rx_ring && !vhost_net_buf_is_empty(rxq)) {
                ptr_ring_unconsume(nvq->rx_ring, rxq->queue + rxq->head,
                                   vhost_net_buf_get_size(rxq),
                                   tun_ptr_free);
                rxq->head = rxq->tail = 0;
        }
}

static int vhost_net_buf_peek_len(void *ptr)
{
        if (tun_is_xdp_frame(ptr)) {
                struct xdp_frame *xdpf = tun_ptr_to_xdp(ptr);

                return xdpf->len;
        }

        return __skb_array_len_with_tag(ptr);
}

static int vhost_net_buf_peek(struct vhost_net_virtqueue *nvq)
{
        struct vhost_net_buf *rxq = &nvq->rxq;

        if (!vhost_net_buf_is_empty(rxq))
                goto out;

        if (!vhost_net_buf_produce(nvq))
                return 0;

out:
        return vhost_net_buf_peek_len(vhost_net_buf_get_ptr(rxq));
}

static void vhost_net_buf_init(struct vhost_net_buf *rxq)
{
        rxq->head = rxq->tail = 0;
}

static void vhost_net_enable_zcopy(int vq)
{
        vhost_net_zcopy_mask |= 0x1 << vq;
}

static struct vhost_net_ubuf_ref *
vhost_net_ubuf_alloc(struct vhost_virtqueue *vq, bool zcopy)
{
        struct vhost_net_ubuf_ref *ubufs;
        /* No zero copy backend? Nothing to count. */
        if (!zcopy)
                return NULL;
        ubufs = kmalloc(sizeof(*ubufs), GFP_KERNEL);
        if (!ubufs)
                return ERR_PTR(-ENOMEM);
        atomic_set(&ubufs->refcount, 1);
        init_waitqueue_head(&ubufs->wait);
        ubufs->vq = vq;
        return ubufs;
}

static int vhost_net_ubuf_put(struct vhost_net_ubuf_ref *ubufs)
{
        int r = atomic_sub_return(1, &ubufs->refcount);
        if (unlikely(!r))
                wake_up(&ubufs->wait);
        return r;
}

static void vhost_net_ubuf_put_and_wait(struct vhost_net_ubuf_ref *ubufs)
{
        vhost_net_ubuf_put(ubufs);
        wait_event(ubufs->wait, !atomic_read(&ubufs->refcount));
}

static void vhost_net_ubuf_put_wait_and_free(struct vhost_net_ubuf_ref *ubufs)
{
        vhost_net_ubuf_put_and_wait(ubufs);
        kfree(ubufs);
}

static void vhost_net_clear_ubuf_info(struct vhost_net *n)
{
        int i;

        for (i = 0; i < VHOST_NET_VQ_MAX; ++i) {
                kfree(n->vqs[i].ubuf_info);
                n->vqs[i].ubuf_info = NULL;
        }
}

static int vhost_net_set_ubuf_info(struct vhost_net *n)
{
        bool zcopy;
        int i;

        for (i = 0; i < VHOST_NET_VQ_MAX; ++i) {
                zcopy = vhost_net_zcopy_mask & (0x1 << i);
                if (!zcopy)
                        continue;
                n->vqs[i].ubuf_info =
                        kmalloc_array(UIO_MAXIOV,
                                      sizeof(*n->vqs[i].ubuf_info),
                                      GFP_KERNEL);
                if  (!n->vqs[i].ubuf_info)
                        goto err;
        }
        return 0;

err:
        vhost_net_clear_ubuf_info(n);
        return -ENOMEM;
}

static void vhost_net_vq_reset(struct vhost_net *n)
{
        int i;

        vhost_net_clear_ubuf_info(n);

        for (i = 0; i < VHOST_NET_VQ_MAX; i++) {
                n->vqs[i].done_idx = 0;
                n->vqs[i].upend_idx = 0;
                n->vqs[i].ubufs = NULL;
                n->vqs[i].vhost_hlen = 0;
                n->vqs[i].sock_hlen = 0;
                vhost_net_buf_init(&n->vqs[i].rxq);
        }

}

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)
{
        /* TX flush waits for outstanding DMAs to be done.
         * Don't start new DMAs.
         */
        return !net->tx_flush &&
                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);
}

static bool vhost_sock_xdp(struct socket *sock)
{
        return sock_flag(sock->sk, SOCK_XDP);
}

/* 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 void vhost_zerocopy_signal_used(struct vhost_net *net,
                                       struct vhost_virtqueue *vq)
{
        struct vhost_net_virtqueue *nvq =
                container_of(vq, struct vhost_net_virtqueue, vq);
        int i, add;
        int j = 0;

        for (i = nvq->done_idx; i != nvq->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;
                        ++j;
                } else
                        break;
        }
        while (j) {
                add = min(UIO_MAXIOV - nvq->done_idx, j);
                vhost_add_used_and_signal_n(vq->dev, vq,
                                            &vq->heads[nvq->done_idx], add);
                nvq->done_idx = (nvq->done_idx + add) % UIO_MAXIOV;
                j -= add;
        }
}

static void vhost_zerocopy_callback(struct ubuf_info *ubuf, bool success)
{
        struct vhost_net_ubuf_ref *ubufs = ubuf->ctx;
        struct vhost_virtqueue *vq = ubufs->vq;
        int cnt;

        rcu_read_lock_bh();

        /* set len to mark this desc buffers done DMA */
        vq->heads[ubuf->desc].len = success ?
                VHOST_DMA_DONE_LEN : VHOST_DMA_FAILED_LEN;
        cnt = vhost_net_ubuf_put(ubufs);

        /*
         * Trigger polling thread if guest stopped submitting new buffers:
         * in this case, the refcount after decrement will eventually reach 1.
         * 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 <= 1 || !(cnt % 16))
                vhost_poll_queue(&vq->poll);

        rcu_read_unlock_bh();
}

static inline unsigned long busy_clock(void)
{
        return local_clock() >> 10;
}

static bool vhost_can_busy_poll(unsigned long endtime)
{
        return likely(!need_resched() && !time_after(busy_clock(), endtime) &&
                      !signal_pending(current));
}

static void vhost_net_disable_vq(struct vhost_net *n,
                                 struct vhost_virtqueue *vq)
{
        struct vhost_net_virtqueue *nvq =
                container_of(vq, struct vhost_net_virtqueue, vq);
        struct vhost_poll *poll = n->poll + (nvq - n->vqs);
        if (!vq->private_data)
                return;
        vhost_poll_stop(poll);
}

static int vhost_net_enable_vq(struct vhost_net *n,
                                struct vhost_virtqueue *vq)
{
        struct vhost_net_virtqueue *nvq =
                container_of(vq, struct vhost_net_virtqueue, vq);
        struct vhost_poll *poll = n->poll + (nvq - n->vqs);
        struct socket *sock;

        sock = vq->private_data;
        if (!sock)
                return 0;

        return vhost_poll_start(poll, sock->file);
}

static void vhost_net_signal_used(struct vhost_net_virtqueue *nvq)
{
        struct vhost_virtqueue *vq = &nvq->vq;
        struct vhost_dev *dev = vq->dev;

        if (!nvq->done_idx)
                return;

        vhost_add_used_and_signal_n(dev, vq, vq->heads, nvq->done_idx);
        nvq->done_idx = 0;
}

static void vhost_tx_batch(struct vhost_net *net,
                           struct vhost_net_virtqueue *nvq,
                           struct socket *sock,
                           struct msghdr *msghdr)
{
        struct tun_msg_ctl ctl = {
                .type = TUN_MSG_PTR,
                .num = nvq->batched_xdp,
                .ptr = nvq->xdp,
        };
        int err;

        if (nvq->batched_xdp == 0)
                goto signal_used;

        msghdr->msg_control = &ctl;
        err = sock->ops->sendmsg(sock, msghdr, 0);
        if (unlikely(err < 0)) {
                vq_err(&nvq->vq, "Fail to batch sending packets\n");
                return;
        }

signal_used:
        vhost_net_signal_used(nvq);
        nvq->batched_xdp = 0;
}

static int sock_has_rx_data(struct socket *sock)
{
        if (unlikely(!sock))
                return 0;

        if (sock->ops->peek_len)
                return sock->ops->peek_len(sock);

        return skb_queue_empty(&sock->sk->sk_receive_queue);
}

static void vhost_net_busy_poll_try_queue(struct vhost_net *net,
                                          struct vhost_virtqueue *vq)
{
        if (!vhost_vq_avail_empty(&net->dev, vq)) {
                vhost_poll_queue(&vq->poll);
        } else if (unlikely(vhost_enable_notify(&net->dev, vq))) {
                vhost_disable_notify(&net->dev, vq);
                vhost_poll_queue(&vq->poll);
        }
}

static void vhost_net_busy_poll(struct vhost_net *net,
                                struct vhost_virtqueue *rvq,
                                struct vhost_virtqueue *tvq,
                                bool *busyloop_intr,
                                bool poll_rx)
{
        unsigned long busyloop_timeout;
        unsigned long endtime;
        struct socket *sock;
        struct vhost_virtqueue *vq = poll_rx ? tvq : rvq;

        /* Try to hold the vq mutex of the paired virtqueue. We can't
         * use mutex_lock() here since we could not guarantee a
         * consistenet lock ordering.
         */
        if (!mutex_trylock(&vq->mutex))
                return;

        vhost_disable_notify(&net->dev, vq);
        sock = rvq->private_data;

        busyloop_timeout = poll_rx ? rvq->busyloop_timeout:
                                     tvq->busyloop_timeout;

        preempt_disable();
        endtime = busy_clock() + busyloop_timeout;

        while (vhost_can_busy_poll(endtime)) {
                if (vhost_has_work(&net->dev)) {
                        *busyloop_intr = true;
                        break;
                }

                if ((sock_has_rx_data(sock) &&
                     !vhost_vq_avail_empty(&net->dev, rvq)) ||
                    !vhost_vq_avail_empty(&net->dev, tvq))
                        break;

                cpu_relax();
        }

        preempt_enable();

        if (poll_rx || sock_has_rx_data(sock))
                vhost_net_busy_poll_try_queue(net, vq);
        else if (!poll_rx) /* On tx here, sock has no rx data. */
                vhost_enable_notify(&net->dev, rvq);

        mutex_unlock(&vq->mutex);
}

static int vhost_net_tx_get_vq_desc(struct vhost_net *net,
                                    struct vhost_net_virtqueue *tnvq,
                                    unsigned int *out_num, unsigned int *in_num,
                                    struct msghdr *msghdr, bool *busyloop_intr)
{
        struct vhost_net_virtqueue *rnvq = &net->vqs[VHOST_NET_VQ_RX];
        struct vhost_virtqueue *rvq = &rnvq->vq;
        struct vhost_virtqueue *tvq = &tnvq->vq;

        int r = vhost_get_vq_desc(tvq, tvq->iov, ARRAY_SIZE(tvq->iov),
                                  out_num, in_num, NULL, NULL);

        if (r == tvq->num && tvq->busyloop_timeout) {
                /* Flush batched packets first */
                if (!vhost_sock_zcopy(tvq->private_data))
                        vhost_tx_batch(net, tnvq, tvq->private_data, msghdr);

                vhost_net_busy_poll(net, rvq, tvq, busyloop_intr, false);

                r = vhost_get_vq_desc(tvq, tvq->iov, ARRAY_SIZE(tvq->iov),
                                      out_num, in_num, NULL, NULL);
        }

        return r;
}

static bool vhost_exceeds_maxpend(struct vhost_net *net)
{
        struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX];
        struct vhost_virtqueue *vq = &nvq->vq;

        return (nvq->upend_idx + UIO_MAXIOV - nvq->done_idx) % UIO_MAXIOV >
               min_t(unsigned int, VHOST_MAX_PEND, vq->num >> 2);
}

static size_t init_iov_iter(struct vhost_virtqueue *vq, struct iov_iter *iter,
                            size_t hdr_size, int out)
{
        /* Skip header. TODO: support TSO. */
        size_t len = iov_length(vq->iov, out);

        iov_iter_init(iter, WRITE, vq->iov, out, len);
        iov_iter_advance(iter, hdr_size);

        return iov_iter_count(iter);
}

static int get_tx_bufs(struct vhost_net *net,
                       struct vhost_net_virtqueue *nvq,
                       struct msghdr *msg,
                       unsigned int *out, unsigned int *in,
                       size_t *len, bool *busyloop_intr)
{
        struct vhost_virtqueue *vq = &nvq->vq;
        int ret;

        ret = vhost_net_tx_get_vq_desc(net, nvq, out, in, msg, busyloop_intr);

        if (ret < 0 || ret == vq->num)
                return ret;

        if (*in) {
                vq_err(vq, "Unexpected descriptor format for TX: out %d, int %d\n",
                        *out, *in);
                return -EFAULT;
        }

        /* Sanity check */
        *len = init_iov_iter(vq, &msg->msg_iter, nvq->vhost_hlen, *out);
        if (*len == 0) {
                vq_err(vq, "Unexpected header len for TX: %zd expected %zd\n",
                        *len, nvq->vhost_hlen);
                return -EFAULT;
        }

        return ret;
}

static bool tx_can_batch(struct vhost_virtqueue *vq, size_t total_len)
{
        return total_len < VHOST_NET_WEIGHT &&
               !vhost_vq_avail_empty(vq->dev, vq);
}

#define SKB_FRAG_PAGE_ORDER     get_order(32768)

static bool vhost_net_page_frag_refill(struct vhost_net *net, unsigned int sz,
                                       struct page_frag *pfrag, gfp_t gfp)
{
        if (pfrag->page) {
                if (pfrag->offset + sz <= pfrag->size)
                        return true;
                __page_frag_cache_drain(pfrag->page, net->refcnt_bias);
        }

        pfrag->offset = 0;
        net->refcnt_bias = 0;
        if (SKB_FRAG_PAGE_ORDER) {
                /* Avoid direct reclaim but allow kswapd to wake */
                pfrag->page = alloc_pages((gfp & ~__GFP_DIRECT_RECLAIM) |
                                          __GFP_COMP | __GFP_NOWARN |
                                          __GFP_NORETRY,
                                          SKB_FRAG_PAGE_ORDER);
                if (likely(pfrag->page)) {
                        pfrag->size = PAGE_SIZE << SKB_FRAG_PAGE_ORDER;
                        goto done;
                }
        }
        pfrag->page = alloc_page(gfp);
        if (likely(pfrag->page)) {
                pfrag->size = PAGE_SIZE;
                goto done;
        }
        return false;

done:
        net->refcnt_bias = USHRT_MAX;
        page_ref_add(pfrag->page, USHRT_MAX - 1);
        return true;
}

#define VHOST_NET_RX_PAD (NET_IP_ALIGN + NET_SKB_PAD)

static int vhost_net_build_xdp(struct vhost_net_virtqueue *nvq,
                               struct iov_iter *from)
{
        struct vhost_virtqueue *vq = &nvq->vq;
        struct vhost_net *net = container_of(vq->dev, struct vhost_net,
                                             dev);
        struct socket *sock = vq->private_data;
        struct page_frag *alloc_frag = &net->page_frag;
        struct virtio_net_hdr *gso;
        struct xdp_buff *xdp = &nvq->xdp[nvq->batched_xdp];
        struct tun_xdp_hdr *hdr;
        size_t len = iov_iter_count(from);
        int headroom = vhost_sock_xdp(sock) ? XDP_PACKET_HEADROOM : 0;
        int buflen = SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
        int pad = SKB_DATA_ALIGN(VHOST_NET_RX_PAD + headroom + nvq->sock_hlen);
        int sock_hlen = nvq->sock_hlen;
        void *buf;
        int copied;

        if (unlikely(len < nvq->sock_hlen))
                return -EFAULT;

        if (SKB_DATA_ALIGN(len + pad) +
            SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) > PAGE_SIZE)
                return -ENOSPC;

        buflen += SKB_DATA_ALIGN(len + pad);
        alloc_frag->offset = ALIGN((u64)alloc_frag->offset, SMP_CACHE_BYTES);
        if (unlikely(!vhost_net_page_frag_refill(net, buflen,
                                                 alloc_frag, GFP_KERNEL)))
                return -ENOMEM;

        buf = (char *)page_address(alloc_frag->page) + alloc_frag->offset;
        copied = copy_page_from_iter(alloc_frag->page,
                                     alloc_frag->offset +
                                     offsetof(struct tun_xdp_hdr, gso),
                                     sock_hlen, from);
        if (copied != sock_hlen)
                return -EFAULT;

        hdr = buf;
        gso = &hdr->gso;

        if ((gso->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) &&
            vhost16_to_cpu(vq, gso->csum_start) +
            vhost16_to_cpu(vq, gso->csum_offset) + 2 >
            vhost16_to_cpu(vq, gso->hdr_len)) {
                gso->hdr_len = cpu_to_vhost16(vq,
                               vhost16_to_cpu(vq, gso->csum_start) +
                               vhost16_to_cpu(vq, gso->csum_offset) + 2);

                if (vhost16_to_cpu(vq, gso->hdr_len) > len)
                        return -EINVAL;
        }

        len -= sock_hlen;
        copied = copy_page_from_iter(alloc_frag->page,
                                     alloc_frag->offset + pad,
                                     len, from);
        if (copied != len)
                return -EFAULT;

        xdp->data_hard_start = buf;
        xdp->data = buf + pad;
        xdp->data_end = xdp->data + len;
        hdr->buflen = buflen;

        --net->refcnt_bias;
        alloc_frag->offset += buflen;

        ++nvq->batched_xdp;

        return 0;
}

static void handle_tx_copy(struct vhost_net *net, struct socket *sock)
{
        struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX];
        struct vhost_virtqueue *vq = &nvq->vq;
        unsigned out, in;
        int head;
        struct msghdr msg = {
                .msg_name = NULL,
                .msg_namelen = 0,
                .msg_control = NULL,
                .msg_controllen = 0,
                .msg_flags = MSG_DONTWAIT,
        };
        size_t len, total_len = 0;
        int err;
        int sent_pkts = 0;
        bool sock_can_batch = (sock->sk->sk_sndbuf == INT_MAX);

        do {
                bool busyloop_intr = false;

                if (nvq->done_idx == VHOST_NET_BATCH)
                        vhost_tx_batch(net, nvq, sock, &msg);

                head = get_tx_bufs(net, nvq, &msg, &out, &in, &len,
                                   &busyloop_intr);
                /* 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) {
                        if (unlikely(busyloop_intr)) {
                                vhost_poll_queue(&vq->poll);
                        } else if (unlikely(vhost_enable_notify(&net->dev,
                                                                vq))) {
                                vhost_disable_notify(&net->dev, vq);
                                continue;
                        }
                        break;
                }

                total_len += len;

                /* For simplicity, TX batching is only enabled if
                 * sndbuf is unlimited.
                 */
                if (sock_can_batch) {
                        err = vhost_net_build_xdp(nvq, &msg.msg_iter);
                        if (!err) {
                                goto done;
                        } else if (unlikely(err != -ENOSPC)) {
                                vhost_tx_batch(net, nvq, sock, &msg);
                                vhost_discard_vq_desc(vq, 1);
                                vhost_net_enable_vq(net, vq);
                                break;
                        }

                        /* We can't build XDP buff, go for single
                         * packet path but let's flush batched
                         * packets.
                         */
                        vhost_tx_batch(net, nvq, sock, &msg);
                        msg.msg_control = NULL;
                } else {
                        if (tx_can_batch(vq, total_len))
                                msg.msg_flags |= MSG_MORE;
                        else
                                msg.msg_flags &= ~MSG_MORE;
                }

                /* TODO: Check specific error and bomb out unless ENOBUFS? */
                err = sock->ops->sendmsg(sock, &msg, len);
                if (unlikely(err < 0)) {
                        vhost_discard_vq_desc(vq, 1);
                        vhost_net_enable_vq(net, vq);
                        break;
                }
                if (err != len)
                        pr_debug("Truncated TX packet: len %d != %zd\n",
                                 err, len);
done:
                vq->heads[nvq->done_idx].id = cpu_to_vhost32(vq, head);
                vq->heads[nvq->done_idx].len = 0;
                ++nvq->done_idx;
        } while (likely(!vhost_exceeds_weight(vq, ++sent_pkts, total_len)));

        vhost_tx_batch(net, nvq, sock, &msg);
}

static void handle_tx_zerocopy(struct vhost_net *net, struct socket *sock)
{
        struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX];
        struct vhost_virtqueue *vq = &nvq->vq;
        unsigned out, in;
        int head;
        struct msghdr msg = {
                .msg_name = NULL,
                .msg_namelen = 0,
                .msg_control = NULL,
                .msg_controllen = 0,
                .msg_flags = MSG_DONTWAIT,
        };
        struct tun_msg_ctl ctl;
        size_t len, total_len = 0;
        int err;
        struct vhost_net_ubuf_ref *uninitialized_var(ubufs);
        bool zcopy_used;
        int sent_pkts = 0;

        do {
                bool busyloop_intr;

                /* Release DMAs done buffers first */
                vhost_zerocopy_signal_used(net, vq);

                busyloop_intr = false;
                head = get_tx_bufs(net, nvq, &msg, &out, &in, &len,
                                   &busyloop_intr);
                /* 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) {
                        if (unlikely(busyloop_intr)) {
                                vhost_poll_queue(&vq->poll);
                        } else if (unlikely(vhost_enable_notify(&net->dev, vq))) {
                                vhost_disable_notify(&net->dev, vq);
                                continue;
                        }
                        break;
                }

                zcopy_used = len >= VHOST_GOODCOPY_LEN
                             && !vhost_exceeds_maxpend(net)
                             && vhost_net_tx_select_zcopy(net);

                /* use msg_control to pass vhost zerocopy ubuf info to skb */
                if (zcopy_used) {
                        struct ubuf_info *ubuf;
                        ubuf = nvq->ubuf_info + nvq->upend_idx;

                        vq->heads[nvq->upend_idx].id = cpu_to_vhost32(vq, head);
                        vq->heads[nvq->upend_idx].len = VHOST_DMA_IN_PROGRESS;
                        ubuf->callback = vhost_zerocopy_callback;
                        ubuf->ctx = nvq->ubufs;
                        ubuf->desc = nvq->upend_idx;
                        refcount_set(&ubuf->refcnt, 1);
                        msg.msg_control = &ctl;
                        ctl.type = TUN_MSG_UBUF;
                        ctl.ptr = ubuf;
                        msg.msg_controllen = sizeof(ctl);
                        ubufs = nvq->ubufs;
                        atomic_inc(&ubufs->refcount);
                        nvq->upend_idx = (nvq->upend_idx + 1) % UIO_MAXIOV;
                } else {
                        msg.msg_control = NULL;
                        ubufs = NULL;
                }
                total_len += len;
                if (tx_can_batch(vq, total_len) &&
                    likely(!vhost_exceeds_maxpend(net))) {
                        msg.msg_flags |= MSG_MORE;
                } else {
                        msg.msg_flags &= ~MSG_MORE;
                }

                /* TODO: Check specific error and bomb out unless ENOBUFS? */
                err = sock->ops->sendmsg(sock, &msg, len);
                if (unlikely(err < 0)) {
                        if (zcopy_used) {
                                vhost_net_ubuf_put(ubufs);
                                nvq->upend_idx = ((unsigned)nvq->upend_idx - 1)
                                        % UIO_MAXIOV;
                        }
                        vhost_discard_vq_desc(vq, 1);
                        vhost_net_enable_vq(net, vq);
                        break;
                }
                if (err != len)
                        pr_debug("Truncated TX packet: "
                                 " len %d != %zd\n", err, len);
                if (!zcopy_used)
                        vhost_add_used_and_signal(&net->dev, vq, head, 0);
                else
                        vhost_zerocopy_signal_used(net, vq);
                vhost_net_tx_packet(net);
        } while (likely(!vhost_exceeds_weight(vq, ++sent_pkts, total_len)));
}

/* 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_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX];
        struct vhost_virtqueue *vq = &nvq->vq;
        struct socket *sock;

        mutex_lock_nested(&vq->mutex, VHOST_NET_VQ_TX);
        sock = vq->private_data;
        if (!sock)
                goto out;

        if (!vq_meta_prefetch(vq))
                goto out;

        vhost_disable_notify(&net->dev, vq);
        vhost_net_disable_vq(net, vq);

        if (vhost_sock_zcopy(sock))
                handle_tx_zerocopy(net, sock);
        else
                handle_tx_copy(net, sock);

out:
        mutex_unlock(&vq->mutex);
}

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

        if (rvq->rx_ring)
                return vhost_net_buf_peek(rvq);

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

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

static int vhost_net_rx_peek_head_len(struct vhost_net *net, struct sock *sk,
                                      bool *busyloop_intr)
{
        struct vhost_net_virtqueue *rnvq = &net->vqs[VHOST_NET_VQ_RX];
        struct vhost_net_virtqueue *tnvq = &net->vqs[VHOST_NET_VQ_TX];
        struct vhost_virtqueue *rvq = &rnvq->vq;

        struct vhost_virtqueue *tvq = &tnvq->vq;
        int len = peek_head_len(rnvq, sk);

        if (!len && rvq->busyloop_timeout) {
                /* Flush batched heads first */
                vhost_net_signal_used(rnvq);
                /* Both tx vq and rx socket were polled here */
                vhost_net_busy_poll(net, rvq, tvq, busyloop_intr, true);

                len = peek_head_len(rnvq, sk);
        }

        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;
        /* len is always initialized before use since we are always called with
         * datalen > 0.
         */
        u32 uninitialized_var(len);

        while (datalen > 0 && headcount < quota) {
                if (unlikely(seg >= UIO_MAXIOV)) {
                        r = -ENOBUFS;
                        goto err;
                }
                r = vhost_get_vq_desc(vq, vq->iov + seg,
                                      ARRAY_SIZE(vq->iov) - seg, &out,
                                      &in, log, log_num);
                if (unlikely(r < 0))
                        goto err;

                d = r;
                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 = cpu_to_vhost32(vq, d);
                len = iov_length(vq->iov + seg, in);
                heads[headcount].len = cpu_to_vhost32(vq, len);
                datalen -= len;
                ++headcount;
                seg += in;
        }
        heads[headcount - 1].len = cpu_to_vhost32(vq, len + datalen);
        *iovcount = seg;
        if (unlikely(log))
                *log_num = nlogs;

        /* Detect overrun */
        if (unlikely(datalen > 0)) {
                r = UIO_MAXIOV + 1;
                goto err;
        }
        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_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_RX];
        struct vhost_virtqueue *vq = &nvq->vq;
        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_flags = MSG_DONTWAIT,
        };
        struct virtio_net_hdr hdr = {
                .flags = 0,
                .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;
        bool busyloop_intr = false;
        struct socket *sock;
        struct iov_iter fixup;
        __virtio16 num_buffers;
        int recv_pkts = 0;

        mutex_lock_nested(&vq->mutex, VHOST_NET_VQ_RX);
        sock = vq->private_data;
        if (!sock)
                goto out;

        if (!vq_meta_prefetch(vq))
                goto out;

        vhost_disable_notify(&net->dev, vq);
        vhost_net_disable_vq(net, vq);

        vhost_hlen = nvq->vhost_hlen;
        sock_hlen = nvq->sock_hlen;

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

        do {
                sock_len = vhost_net_rx_peek_head_len(net, sock->sk,
                                                      &busyloop_intr);
                if (!sock_len)
                        break;
                sock_len += sock_hlen;
                vhost_len = sock_len + vhost_hlen;
                headcount = get_rx_bufs(vq, vq->heads + nvq->done_idx,
                                        vhost_len, &in, vq_log, &log,
                                        likely(mergeable) ? UIO_MAXIOV : 1);
                /* On error, stop handling until the next kick. */
                if (unlikely(headcount < 0))
                        goto out;
                /* OK, now we need to know about added descriptors. */
                if (!headcount) {
                        if (unlikely(busyloop_intr)) {
                                vhost_poll_queue(&vq->poll);
                        } else 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. */
                        goto out;
                }
                busyloop_intr = false;
                if (nvq->rx_ring)
                        msg.msg_control = vhost_net_buf_consume(&nvq->rxq);
                /* On overrun, truncate and discard */
                if (unlikely(headcount > UIO_MAXIOV)) {
                        iov_iter_init(&msg.msg_iter, READ, vq->iov, 1, 1);
                        err = sock->ops->recvmsg(sock, &msg,
                                                 1, MSG_DONTWAIT | MSG_TRUNC);
                        pr_debug("Discarded rx packet: len %zd\n", sock_len);
                        continue;
                }
                /* We don't need to be notified again. */
                iov_iter_init(&msg.msg_iter, READ, vq->iov, in, vhost_len);
                fixup = msg.msg_iter;
                if (unlikely((vhost_hlen))) {
                        /* We will supply the header ourselves
                         * TODO: support TSO.
                         */
                        iov_iter_advance(&msg.msg_iter, vhost_hlen);
                }
                err = sock->ops->recvmsg(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;
                }
                /* Supply virtio_net_hdr if VHOST_NET_F_VIRTIO_NET_HDR */
                if (unlikely(vhost_hlen)) {
                        if (copy_to_iter(&hdr, sizeof(hdr),
                                         &fixup) != sizeof(hdr)) {
                                vq_err(vq, "Unable to write vnet_hdr "
                                       "at addr %p\n", vq->iov->iov_base);
                                goto out;
                        }
                } else {
                        /* Header came from socket; we'll need to patch
                         * ->num_buffers over if VIRTIO_NET_F_MRG_RXBUF
                         */
                        iov_iter_advance(&fixup, sizeof(hdr));
                }
                /* TODO: Should check and handle checksum. */

                num_buffers = cpu_to_vhost16(vq, headcount);
                if (likely(mergeable) &&
                    copy_to_iter(&num_buffers, sizeof num_buffers,
                                 &fixup) != sizeof num_buffers) {
                        vq_err(vq, "Failed num_buffers write");
                        vhost_discard_vq_desc(vq, headcount);
                        goto out;
                }
                nvq->done_idx += headcount;
                if (nvq->done_idx > VHOST_NET_BATCH)
                        vhost_net_signal_used(nvq);
                if (unlikely(vq_log))
                        vhost_log_write(vq, vq_log, log, vhost_len,
                                        vq->iov, in);
                total_len += vhost_len;
        } while (likely(!vhost_exceeds_weight(vq, ++recv_pkts, total_len)));

        if (unlikely(busyloop_intr))
                vhost_poll_queue(&vq->poll);
        else if (!sock_len)
                vhost_net_enable_vq(net, vq);
out:
        vhost_net_signal_used(nvq);
        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;
        struct vhost_dev *dev;
        struct vhost_virtqueue **vqs;
        void **queue;
        struct xdp_buff *xdp;
        int i;

        n = kvmalloc(sizeof *n, GFP_KERNEL | __GFP_RETRY_MAYFAIL);
        if (!n)
                return -ENOMEM;
        vqs = kmalloc_array(VHOST_NET_VQ_MAX, sizeof(*vqs), GFP_KERNEL);
        if (!vqs) {
                kvfree(n);
                return -ENOMEM;
        }

        queue = kmalloc_array(VHOST_NET_BATCH, sizeof(void *),
                              GFP_KERNEL);
        if (!queue) {
                kfree(vqs);
                kvfree(n);
                return -ENOMEM;
        }
        n->vqs[VHOST_NET_VQ_RX].rxq.queue = queue;

        xdp = kmalloc_array(VHOST_NET_BATCH, sizeof(*xdp), GFP_KERNEL);
        if (!xdp) {
                kfree(vqs);
                kvfree(n);
                kfree(queue);
                return -ENOMEM;
        }
        n->vqs[VHOST_NET_VQ_TX].xdp = xdp;

        dev = &n->dev;
        vqs[VHOST_NET_VQ_TX] = &n->vqs[VHOST_NET_VQ_TX].vq;
        vqs[VHOST_NET_VQ_RX] = &n->vqs[VHOST_NET_VQ_RX].vq;
        n->vqs[VHOST_NET_VQ_TX].vq.handle_kick = handle_tx_kick;
        n->vqs[VHOST_NET_VQ_RX].vq.handle_kick = handle_rx_kick;
        for (i = 0; i < VHOST_NET_VQ_MAX; i++) {
                n->vqs[i].ubufs = NULL;
                n->vqs[i].ubuf_info = NULL;
                n->vqs[i].upend_idx = 0;
                n->vqs[i].done_idx = 0;
                n->vqs[i].batched_xdp = 0;
                n->vqs[i].vhost_hlen = 0;
                n->vqs[i].sock_hlen = 0;
                n->vqs[i].rx_ring = NULL;
                vhost_net_buf_init(&n->vqs[i].rxq);
        }
        vhost_dev_init(dev, vqs, VHOST_NET_VQ_MAX,
                       UIO_MAXIOV + VHOST_NET_BATCH,
                       VHOST_NET_PKT_WEIGHT, VHOST_NET_WEIGHT);

        vhost_poll_init(n->poll + VHOST_NET_VQ_TX, handle_tx_net, EPOLLOUT, dev);
        vhost_poll_init(n->poll + VHOST_NET_VQ_RX, handle_rx_net, EPOLLIN, dev);

        f->private_data = n;
        n->page_frag.page = NULL;
        n->refcnt_bias = 0;

        return 0;
}

static struct socket *vhost_net_stop_vq(struct vhost_net *n,
                                        struct vhost_virtqueue *vq)
{
        struct socket *sock;
        struct vhost_net_virtqueue *nvq =
                container_of(vq, struct vhost_net_virtqueue, vq);

        mutex_lock(&vq->mutex);
        sock = vq->private_data;
        vhost_net_disable_vq(n, vq);
        vq->private_data = NULL;
        vhost_net_buf_unproduce(nvq);
        nvq->rx_ring = 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].vq);
        *rx_sock = vhost_net_stop_vq(n, &n->vqs[VHOST_NET_VQ_RX].vq);
}

static void vhost_net_flush_vq(struct vhost_net *n, int index)
{
        vhost_poll_flush(n->poll + index);
        vhost_poll_flush(&n->vqs[index].vq.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);
        if (n->vqs[VHOST_NET_VQ_TX].ubufs) {
                mutex_lock(&n->vqs[VHOST_NET_VQ_TX].vq.mutex);
                n->tx_flush = true;
                mutex_unlock(&n->vqs[VHOST_NET_VQ_TX].vq.mutex);
                /* Wait for all lower device DMAs done. */
                vhost_net_ubuf_put_and_wait(n->vqs[VHOST_NET_VQ_TX].ubufs);
                mutex_lock(&n->vqs[VHOST_NET_VQ_TX].vq.mutex);
                n->tx_flush = false;
                atomic_set(&n->vqs[VHOST_NET_VQ_TX].ubufs->refcount, 1);
                mutex_unlock(&n->vqs[VHOST_NET_VQ_TX].vq.mutex);
        }
}

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_stop(&n->dev);
        vhost_dev_cleanup(&n->dev);
        vhost_net_vq_reset(n);
        if (tx_sock)
                sockfd_put(tx_sock);
        if (rx_sock)
                sockfd_put(rx_sock);
        /* Make sure no callbacks are outstanding */
        synchronize_rcu();
        /* We do an extra flush before freeing memory,
         * since jobs can re-queue themselves. */
        vhost_net_flush(n);
        kfree(n->vqs[VHOST_NET_VQ_RX].rxq.queue);
        kfree(n->vqs[VHOST_NET_VQ_TX].xdp);
        kfree(n->dev.vqs);
        if (n->page_frag.page)
                __page_frag_cache_drain(n->page_frag.page, n->refcnt_bias);
        kvfree(n);
        return 0;
}

static struct socket *get_raw_socket(int fd)
{
        struct {
                struct sockaddr_ll sa;
                char  buf[MAX_ADDR_LEN];
        } uaddr;
        int 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, 0);
        if (r < 0)
                goto err;

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

static struct ptr_ring *get_tap_ptr_ring(int fd)
{
        struct ptr_ring *ring;
        struct file *file = fget(fd);

        if (!file)
                return NULL;
        ring = tun_get_tx_ring(file);
        if (!IS_ERR(ring))
                goto out;
        ring = tap_get_ptr_ring(file);
        if (!IS_ERR(ring))
                goto out;
        ring = NULL;
out:
        fput(file);
        return ring;
}

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 = tap_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_net_virtqueue *nvq;
        struct vhost_net_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].vq;
        nvq = &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 = vq->private_data;
        if (sock != oldsock) {
                ubufs = vhost_net_ubuf_alloc(vq,
                                             sock && vhost_sock_zcopy(sock));
                if (IS_ERR(ubufs)) {
                        r = PTR_ERR(ubufs);
                        goto err_ubufs;
                }

                vhost_net_disable_vq(n, vq);
                vq->private_data = sock;
                vhost_net_buf_unproduce(nvq);
                r = vhost_vq_init_access(vq);
                if (r)
                        goto err_used;
                r = vhost_net_enable_vq(n, vq);
                if (r)
                        goto err_used;
                if (index == VHOST_NET_VQ_RX)
                        nvq->rx_ring = get_tap_ptr_ring(fd);

                oldubufs = nvq->ubufs;
                nvq->ubufs = ubufs;

                n->tx_packets = 0;
                n->tx_zcopy_err = 0;
                n->tx_flush = false;
        }

        mutex_unlock(&vq->mutex);

        if (oldubufs) {
                vhost_net_ubuf_put_wait_and_free(oldubufs);
                mutex_lock(&vq->mutex);
                vhost_zerocopy_signal_used(n, vq);
                mutex_unlock(&vq->mutex);
        }

        if (oldsock) {
                vhost_net_flush_vq(n, index);
                sockfd_put(oldsock);
        }

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

err_used:
        vq->private_data = oldsock;
        vhost_net_enable_vq(n, vq);
        if (ubufs)
                vhost_net_ubuf_put_wait_and_free(ubufs);
err_ubufs:
        if (sock)
                sockfd_put(sock);
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;
        struct vhost_umem *umem;

        mutex_lock(&n->dev.mutex);
        err = vhost_dev_check_owner(&n->dev);
        if (err)
                goto done;
        umem = vhost_dev_reset_owner_prepare();
        if (!umem) {
                err = -ENOMEM;
                goto done;
        }
        vhost_net_stop(n, &tx_sock, &rx_sock);
        vhost_net_flush(n);
        vhost_dev_stop(&n->dev);
        vhost_dev_reset_owner(&n->dev, umem);
        vhost_net_vq_reset(n);
done:
        mutex_unlock(&n->dev.mutex);
        if (tx_sock)
                sockfd_put(tx_sock);
        if (rx_sock)
                sockfd_put(rx_sock);
        return err;
}

static int vhost_net_set_backend_features(struct vhost_net *n, u64 features)
{
        int i;

        mutex_lock(&n->dev.mutex);
        for (i = 0; i < VHOST_NET_VQ_MAX; ++i) {
                mutex_lock(&n->vqs[i].vq.mutex);
                n->vqs[i].vq.acked_backend_features = features;
                mutex_unlock(&n->vqs[i].vq.mutex);
        }
        mutex_unlock(&n->dev.mutex);

        return 0;
}

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 & ((1ULL << VIRTIO_NET_F_MRG_RXBUF) |
                               (1ULL << VIRTIO_F_VERSION_1))) ?
                        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))
                goto out_unlock;

        if ((features & (1ULL << VIRTIO_F_IOMMU_PLATFORM))) {
                if (vhost_init_device_iotlb(&n->dev, true))
                        goto out_unlock;
        }

        for (i = 0; i < VHOST_NET_VQ_MAX; ++i) {
                mutex_lock(&n->vqs[i].vq.mutex);
                n->vqs[i].vq.acked_features = features;
                n->vqs[i].vhost_hlen = vhost_hlen;
                n->vqs[i].sock_hlen = sock_hlen;
                mutex_unlock(&n->vqs[i].vq.mutex);
        }
        mutex_unlock(&n->dev.mutex);
        return 0;

out_unlock:
        mutex_unlock(&n->dev.mutex);
        return -EFAULT;
}

static long vhost_net_set_owner(struct vhost_net *n)
{
        int r;

        mutex_lock(&n->dev.mutex);
        if (vhost_dev_has_owner(&n->dev)) {
                r = -EBUSY;
                goto out;
        }
        r = vhost_net_set_ubuf_info(n);
        if (r)
                goto out;
        r = vhost_dev_set_owner(&n->dev);
        if (r)
                vhost_net_clear_ubuf_info(n);
        vhost_net_flush(n);
out:
        mutex_unlock(&n->dev.mutex);
        return r;
}

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_GET_BACKEND_FEATURES:
                features = VHOST_NET_BACKEND_FEATURES;
                if (copy_to_user(featurep, &features, sizeof(features)))
                        return -EFAULT;
                return 0;
        case VHOST_SET_BACKEND_FEATURES:
                if (copy_from_user(&features, featurep, sizeof(features)))
                        return -EFAULT;
                if (features & ~VHOST_NET_BACKEND_FEATURES)
                        return -EOPNOTSUPP;
                return vhost_net_set_backend_features(n, features);
        case VHOST_RESET_OWNER:
                return vhost_net_reset_owner(n);
        case VHOST_SET_OWNER:
                return vhost_net_set_owner(n);
        default:
                mutex_lock(&n->dev.mutex);
                r = vhost_dev_ioctl(&n->dev, ioctl, argp);
                if (r == -ENOIOCTLCMD)
                        r = vhost_vring_ioctl(&n->dev, ioctl, argp);
                else
                        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 ssize_t vhost_net_chr_read_iter(struct kiocb *iocb, struct iov_iter *to)
{
        struct file *file = iocb->ki_filp;
        struct vhost_net *n = file->private_data;
        struct vhost_dev *dev = &n->dev;
        int noblock = file->f_flags & O_NONBLOCK;

        return vhost_chr_read_iter(dev, to, noblock);
}

static ssize_t vhost_net_chr_write_iter(struct kiocb *iocb,
                                        struct iov_iter *from)
{
        struct file *file = iocb->ki_filp;
        struct vhost_net *n = file->private_data;
        struct vhost_dev *dev = &n->dev;

        return vhost_chr_write_iter(dev, from);
}

static __poll_t vhost_net_chr_poll(struct file *file, poll_table *wait)
{
        struct vhost_net *n = file->private_data;
        struct vhost_dev *dev = &n->dev;

        return vhost_chr_poll(file, dev, wait);
}

static const struct file_operations vhost_net_fops = {
        .owner          = THIS_MODULE,
        .release        = vhost_net_release,
        .read_iter      = vhost_net_chr_read_iter,
        .write_iter     = vhost_net_chr_write_iter,
        .poll           = vhost_net_chr_poll,
        .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_net_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");