Archipelago » qemu

/*

 * Virtio Network Device

 *

 * Copyright IBM, Corp. 2007

 *

 * Authors:

 *  Anthony Liguori   <aliguori@us.ibm.com>

 *

 * This work is licensed under the terms of the GNU GPL, version 2.  See

 * the COPYING file in the top-level directory.

 *

 */

#include "iov.h"

#include "virtio.h"

#include "net.h"

#include "net/checksum.h"

#include "net/tap.h"

#include "qemu-error.h"

#include "qemu-timer.h"

#include "virtio-net.h"

#include "vhost_net.h"

#define VIRTIO_NET_VM_VERSION    11

#define MAC_TABLE_ENTRIES    64

#define MAX_VLAN    (1 << 12)   /* Per 802.1Q definition */

typedef struct VirtIONet

{

    VirtIODevice vdev;

    uint8_t mac[ETH_ALEN];

    uint16_t status;

    VirtQueue *rx_vq;

    VirtQueue *tx_vq;

    VirtQueue *ctrl_vq;

    NICState *nic;

    QEMUTimer *tx_timer;

    QEMUBH *tx_bh;

    uint32_t tx_timeout;

    int32_t tx_burst;

    int tx_waiting;

    uint32_t has_vnet_hdr;

    uint8_t has_ufo;

    struct {

        VirtQueueElement elem;

        ssize_t len;

    } async_tx;

    int mergeable_rx_bufs;

    uint8_t promisc;

    uint8_t allmulti;

    uint8_t alluni;

    uint8_t nomulti;

    uint8_t nouni;

    uint8_t nobcast;

    uint8_t vhost_started;

    bool vm_running;

    VMChangeStateEntry *vmstate;

    struct {

        int in_use;

        int first_multi;

        uint8_t multi_overflow;

        uint8_t uni_overflow;

        uint8_t *macs;

    } mac_table;

    uint32_t *vlans;

    DeviceState *qdev;

} VirtIONet;

/* TODO

 * - we could suppress RX interrupt if we were so inclined.

 */

static VirtIONet *to_virtio_net(VirtIODevice *vdev)

{

    return (VirtIONet *)vdev;

}

static void virtio_net_get_config(VirtIODevice *vdev, uint8_t *config)

{

    VirtIONet *n = to_virtio_net(vdev);

    struct virtio_net_config netcfg;

    netcfg.status = n->status;

    memcpy(netcfg.mac, n->mac, ETH_ALEN);

    memcpy(config, &netcfg, sizeof(netcfg));

}

static void virtio_net_set_config(VirtIODevice *vdev, const uint8_t *config)

{

    VirtIONet *n = to_virtio_net(vdev);

    struct virtio_net_config netcfg;

    memcpy(&netcfg, config, sizeof(netcfg));

    if (memcmp(netcfg.mac, n->mac, ETH_ALEN)) {

        memcpy(n->mac, netcfg.mac, ETH_ALEN);

        qemu_format_nic_info_str(&n->nic->nc, n->mac);

    }

}

static void virtio_net_set_status(struct VirtIODevice *vdev, uint8_t status)

{

    VirtIONet *n = to_virtio_net(vdev);

    if (!n->nic->nc.peer) {

        return;

    }

    if (n->nic->nc.peer->info->type != NET_CLIENT_TYPE_TAP) {

        return;

    }

    if (!tap_get_vhost_net(n->nic->nc.peer)) {

        return;

    }

    if (!!n->vhost_started == ((status & VIRTIO_CONFIG_S_DRIVER_OK) &&

                               (n->status & VIRTIO_NET_S_LINK_UP) &&

                               n->vm_running)) {

        return;

    }

    if (!n->vhost_started) {

        int r = vhost_net_start(tap_get_vhost_net(n->nic->nc.peer), &n->vdev);

        if (r < 0) {

            fprintf(stderr, "unable to start vhost net: %d: "

                    "falling back on userspace virtio\n", -r);

        } else {

            n->vhost_started = 1;

        }

    } else {

        vhost_net_stop(tap_get_vhost_net(n->nic->nc.peer), &n->vdev);

        n->vhost_started = 0;

    }

}

static void virtio_net_set_link_status(VLANClientState *nc)

{

    VirtIONet *n = DO_UPCAST(NICState, nc, nc)->opaque;

    uint16_t old_status = n->status;

    if (nc->link_down)

        n->status &= ~VIRTIO_NET_S_LINK_UP;

    else

        n->status |= VIRTIO_NET_S_LINK_UP;

    if (n->status != old_status)

        virtio_notify_config(&n->vdev);

    virtio_net_set_status(&n->vdev, n->vdev.status);

}

static void virtio_net_reset(VirtIODevice *vdev)

{

    VirtIONet *n = to_virtio_net(vdev);

    /* Reset back to compatibility mode */

    n->promisc = 1;

    n->allmulti = 0;

    n->alluni = 0;

    n->nomulti = 0;

    n->nouni = 0;

    n->nobcast = 0;

    /* Flush any MAC and VLAN filter table state */

    n->mac_table.in_use = 0;

    n->mac_table.first_multi = 0;

    n->mac_table.multi_overflow = 0;

    n->mac_table.uni_overflow = 0;

    memset(n->mac_table.macs, 0, MAC_TABLE_ENTRIES * ETH_ALEN);

    memset(n->vlans, 0, MAX_VLAN >> 3);

}

static int peer_has_vnet_hdr(VirtIONet *n)

{

    if (!n->nic->nc.peer)

        return 0;

    if (n->nic->nc.peer->info->type != NET_CLIENT_TYPE_TAP)

        return 0;

    n->has_vnet_hdr = tap_has_vnet_hdr(n->nic->nc.peer);

    return n->has_vnet_hdr;

}

static int peer_has_ufo(VirtIONet *n)

{

    if (!peer_has_vnet_hdr(n))

        return 0;

    n->has_ufo = tap_has_ufo(n->nic->nc.peer);

    return n->has_ufo;

}

static uint32_t virtio_net_get_features(VirtIODevice *vdev, uint32_t features)

{

    VirtIONet *n = to_virtio_net(vdev);

    features |= (1 << VIRTIO_NET_F_MAC);

    if (peer_has_vnet_hdr(n)) {

        tap_using_vnet_hdr(n->nic->nc.peer, 1);

    } else {

        features &= ~(0x1 << VIRTIO_NET_F_CSUM);

        features &= ~(0x1 << VIRTIO_NET_F_HOST_TSO4);

        features &= ~(0x1 << VIRTIO_NET_F_HOST_TSO6);

        features &= ~(0x1 << VIRTIO_NET_F_HOST_ECN);

        features &= ~(0x1 << VIRTIO_NET_F_GUEST_CSUM);

        features &= ~(0x1 << VIRTIO_NET_F_GUEST_TSO4);

        features &= ~(0x1 << VIRTIO_NET_F_GUEST_TSO6);

        features &= ~(0x1 << VIRTIO_NET_F_GUEST_ECN);

    }

    if (!peer_has_vnet_hdr(n) || !peer_has_ufo(n)) {

        features &= ~(0x1 << VIRTIO_NET_F_GUEST_UFO);

        features &= ~(0x1 << VIRTIO_NET_F_HOST_UFO);

    }

    if (!n->nic->nc.peer ||

        n->nic->nc.peer->info->type != NET_CLIENT_TYPE_TAP) {

        return features;

    }

    if (!tap_get_vhost_net(n->nic->nc.peer)) {

        return features;

    }

    return vhost_net_get_features(tap_get_vhost_net(n->nic->nc.peer), features);

}

static uint32_t virtio_net_bad_features(VirtIODevice *vdev)

{

    uint32_t features = 0;

    /* Linux kernel 2.6.25.  It understood MAC (as everyone must),

     * but also these: */

    features |= (1 << VIRTIO_NET_F_MAC);

    features |= (1 << VIRTIO_NET_F_CSUM);

    features |= (1 << VIRTIO_NET_F_HOST_TSO4);

    features |= (1 << VIRTIO_NET_F_HOST_TSO6);

    features |= (1 << VIRTIO_NET_F_HOST_ECN);

    return features;

}

static void virtio_net_set_features(VirtIODevice *vdev, uint32_t features)

{

    VirtIONet *n = to_virtio_net(vdev);

    n->mergeable_rx_bufs = !!(features & (1 << VIRTIO_NET_F_MRG_RXBUF));

    if (n->has_vnet_hdr) {

        tap_set_offload(n->nic->nc.peer,

                        (features >> VIRTIO_NET_F_GUEST_CSUM) & 1,

                        (features >> VIRTIO_NET_F_GUEST_TSO4) & 1,

                        (features >> VIRTIO_NET_F_GUEST_TSO6) & 1,

                        (features >> VIRTIO_NET_F_GUEST_ECN)  & 1,

                        (features >> VIRTIO_NET_F_GUEST_UFO)  & 1);

    }

    if (!n->nic->nc.peer ||

        n->nic->nc.peer->info->type != NET_CLIENT_TYPE_TAP) {

        return;

    }

    if (!tap_get_vhost_net(n->nic->nc.peer)) {

        return;

    }

    vhost_net_ack_features(tap_get_vhost_net(n->nic->nc.peer), features);

}

static int virtio_net_handle_rx_mode(VirtIONet *n, uint8_t cmd,

                                     VirtQueueElement *elem)

{

    uint8_t on;

    if (elem->out_num != 2 || elem->out_sg[1].iov_len != sizeof(on)) {

        fprintf(stderr, "virtio-net ctrl invalid rx mode command\n");

        exit(1);

    }

    on = ldub_p(elem->out_sg[1].iov_base);

    if (cmd == VIRTIO_NET_CTRL_RX_MODE_PROMISC)

        n->promisc = on;

    else if (cmd == VIRTIO_NET_CTRL_RX_MODE_ALLMULTI)

        n->allmulti = on;

    else if (cmd == VIRTIO_NET_CTRL_RX_MODE_ALLUNI)

        n->alluni = on;

    else if (cmd == VIRTIO_NET_CTRL_RX_MODE_NOMULTI)

        n->nomulti = on;

    else if (cmd == VIRTIO_NET_CTRL_RX_MODE_NOUNI)

        n->nouni = on;

    else if (cmd == VIRTIO_NET_CTRL_RX_MODE_NOBCAST)

        n->nobcast = on;

    else

        return VIRTIO_NET_ERR;

    return VIRTIO_NET_OK;

}

static int virtio_net_handle_mac(VirtIONet *n, uint8_t cmd,

                                 VirtQueueElement *elem)

{

    struct virtio_net_ctrl_mac mac_data;

    if (cmd != VIRTIO_NET_CTRL_MAC_TABLE_SET || elem->out_num != 3 ||

        elem->out_sg[1].iov_len < sizeof(mac_data) ||

        elem->out_sg[2].iov_len < sizeof(mac_data))

        return VIRTIO_NET_ERR;

    n->mac_table.in_use = 0;

    n->mac_table.first_multi = 0;

    n->mac_table.uni_overflow = 0;

    n->mac_table.multi_overflow = 0;

    memset(n->mac_table.macs, 0, MAC_TABLE_ENTRIES * ETH_ALEN);

    mac_data.entries = ldl_le_p(elem->out_sg[1].iov_base);

    if (sizeof(mac_data.entries) +

        (mac_data.entries * ETH_ALEN) > elem->out_sg[1].iov_len)

        return VIRTIO_NET_ERR;

    if (mac_data.entries <= MAC_TABLE_ENTRIES) {

        memcpy(n->mac_table.macs, elem->out_sg[1].iov_base + sizeof(mac_data),

               mac_data.entries * ETH_ALEN);

        n->mac_table.in_use += mac_data.entries;

    } else {

        n->mac_table.uni_overflow = 1;

    }

    n->mac_table.first_multi = n->mac_table.in_use;

    mac_data.entries = ldl_le_p(elem->out_sg[2].iov_base);

    if (sizeof(mac_data.entries) +

        (mac_data.entries * ETH_ALEN) > elem->out_sg[2].iov_len)

        return VIRTIO_NET_ERR;

    if (mac_data.entries) {

        if (n->mac_table.in_use + mac_data.entries <= MAC_TABLE_ENTRIES) {

            memcpy(n->mac_table.macs + (n->mac_table.in_use * ETH_ALEN),

                   elem->out_sg[2].iov_base + sizeof(mac_data),

                   mac_data.entries * ETH_ALEN);

            n->mac_table.in_use += mac_data.entries;

        } else {

            n->mac_table.multi_overflow = 1;

        }

    }

    return VIRTIO_NET_OK;

}

static int virtio_net_handle_vlan_table(VirtIONet *n, uint8_t cmd,

                                        VirtQueueElement *elem)

{

    uint16_t vid;

    if (elem->out_num != 2 || elem->out_sg[1].iov_len != sizeof(vid)) {

        fprintf(stderr, "virtio-net ctrl invalid vlan command\n");

        return VIRTIO_NET_ERR;

    }

    vid = lduw_le_p(elem->out_sg[1].iov_base);

    if (vid >= MAX_VLAN)

        return VIRTIO_NET_ERR;

    if (cmd == VIRTIO_NET_CTRL_VLAN_ADD)

        n->vlans[vid >> 5] |= (1U << (vid & 0x1f));

    else if (cmd == VIRTIO_NET_CTRL_VLAN_DEL)

        n->vlans[vid >> 5] &= ~(1U << (vid & 0x1f));

    else

        return VIRTIO_NET_ERR;

    return VIRTIO_NET_OK;

}

static void virtio_net_handle_ctrl(VirtIODevice *vdev, VirtQueue *vq)

{

    VirtIONet *n = to_virtio_net(vdev);

    struct virtio_net_ctrl_hdr ctrl;

    virtio_net_ctrl_ack status = VIRTIO_NET_ERR;

    VirtQueueElement elem;

    while (virtqueue_pop(vq, &elem)) {

        if ((elem.in_num < 1) || (elem.out_num < 1)) {

            fprintf(stderr, "virtio-net ctrl missing headers\n");

            exit(1);

        }

        if (elem.out_sg[0].iov_len < sizeof(ctrl) ||

            elem.in_sg[elem.in_num - 1].iov_len < sizeof(status)) {

            fprintf(stderr, "virtio-net ctrl header not in correct element\n");

            exit(1);

        }

        ctrl.class = ldub_p(elem.out_sg[0].iov_base);

        ctrl.cmd = ldub_p(elem.out_sg[0].iov_base + sizeof(ctrl.class));

        if (ctrl.class == VIRTIO_NET_CTRL_RX_MODE)

            status = virtio_net_handle_rx_mode(n, ctrl.cmd, &elem);

        else if (ctrl.class == VIRTIO_NET_CTRL_MAC)

            status = virtio_net_handle_mac(n, ctrl.cmd, &elem);

        else if (ctrl.class == VIRTIO_NET_CTRL_VLAN)

            status = virtio_net_handle_vlan_table(n, ctrl.cmd, &elem);

        stb_p(elem.in_sg[elem.in_num - 1].iov_base, status);

        virtqueue_push(vq, &elem, sizeof(status));

        virtio_notify(vdev, vq);

    }

}

/* RX */

static void virtio_net_handle_rx(VirtIODevice *vdev, VirtQueue *vq)

{

    VirtIONet *n = to_virtio_net(vdev);

    qemu_flush_queued_packets(&n->nic->nc);

    /* We now have RX buffers, signal to the IO thread to break out of the

     * select to re-poll the tap file descriptor */

    qemu_notify_event();

}

static int virtio_net_can_receive(VLANClientState *nc)

{

    VirtIONet *n = DO_UPCAST(NICState, nc, nc)->opaque;

    if (!virtio_queue_ready(n->rx_vq) ||

        !(n->vdev.status & VIRTIO_CONFIG_S_DRIVER_OK))

        return 0;

    return 1;

}

static int virtio_net_has_buffers(VirtIONet *n, int bufsize)

{

    if (virtio_queue_empty(n->rx_vq) ||

        (n->mergeable_rx_bufs &&

         !virtqueue_avail_bytes(n->rx_vq, bufsize, 0))) {

        virtio_queue_set_notification(n->rx_vq, 1);

        /* To avoid a race condition where the guest has made some buffers

         * available after the above check but before notification was

         * enabled, check for available buffers again.

         */

        if (virtio_queue_empty(n->rx_vq) ||

            (n->mergeable_rx_bufs &&

             !virtqueue_avail_bytes(n->rx_vq, bufsize, 0)))

            return 0;

    }

    virtio_queue_set_notification(n->rx_vq, 0);

    return 1;

}

/* dhclient uses AF_PACKET but doesn't pass auxdata to the kernel so

 * it never finds out that the packets don't have valid checksums.  This

 * causes dhclient to get upset.  Fedora's carried a patch for ages to

 * fix this with Xen but it hasn't appeared in an upstream release of

 * dhclient yet.

 *

 * To avoid breaking existing guests, we catch udp packets and add

 * checksums.  This is terrible but it's better than hacking the guest

 * kernels.

 *

 * N.B. if we introduce a zero-copy API, this operation is no longer free so

 * we should provide a mechanism to disable it to avoid polluting the host

 * cache.

 */

static void work_around_broken_dhclient(struct virtio_net_hdr *hdr,

                                        const uint8_t *buf, size_t size)

{

    if ((hdr->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) && /* missing csum */

        (size > 27 && size < 1500) && /* normal sized MTU */

        (buf[12] == 0x08 && buf[13] == 0x00) && /* ethertype == IPv4 */

        (buf[23] == 17) && /* ip.protocol == UDP */

        (buf[34] == 0 && buf[35] == 67)) { /* udp.srcport == bootps */

        /* FIXME this cast is evil */

        net_checksum_calculate((uint8_t *)buf, size);

        hdr->flags &= ~VIRTIO_NET_HDR_F_NEEDS_CSUM;

    }

}

static int receive_header(VirtIONet *n, struct iovec *iov, int iovcnt,

                          const void *buf, size_t size, size_t hdr_len)

{

    struct virtio_net_hdr *hdr = (struct virtio_net_hdr *)iov[0].iov_base;

    int offset = 0;

    hdr->flags = 0;

    hdr->gso_type = VIRTIO_NET_HDR_GSO_NONE;

    if (n->has_vnet_hdr) {

        memcpy(hdr, buf, sizeof(*hdr));

        offset = sizeof(*hdr);

        work_around_broken_dhclient(hdr, buf + offset, size - offset);

    }

    /* We only ever receive a struct virtio_net_hdr from the tapfd,

     * but we may be passing along a larger header to the guest.

     */

    iov[0].iov_base += hdr_len;

    iov[0].iov_len  -= hdr_len;

    return offset;

}

static int receive_filter(VirtIONet *n, const uint8_t *buf, int size)

{

    static const uint8_t bcast[] = {0xff, 0xff, 0xff, 0xff, 0xff, 0xff};

    static const uint8_t vlan[] = {0x81, 0x00};

    uint8_t *ptr = (uint8_t *)buf;

    int i;

    if (n->promisc)

        return 1;

    if (n->has_vnet_hdr) {

        ptr += sizeof(struct virtio_net_hdr);

    }

    if (!memcmp(&ptr[12], vlan, sizeof(vlan))) {

        int vid = be16_to_cpup((uint16_t *)(ptr + 14)) & 0xfff;

        if (!(n->vlans[vid >> 5] & (1U << (vid & 0x1f))))

            return 0;

    }

    if (ptr[0] & 1) { // multicast

        if (!memcmp(ptr, bcast, sizeof(bcast))) {

            return !n->nobcast;

        } else if (n->nomulti) {

            return 0;

        } else if (n->allmulti || n->mac_table.multi_overflow) {

            return 1;

        }

        for (i = n->mac_table.first_multi; i < n->mac_table.in_use; i++) {

            if (!memcmp(ptr, &n->mac_table.macs[i * ETH_ALEN], ETH_ALEN)) {

                return 1;

            }

        }

    } else { // unicast

        if (n->nouni) {

            return 0;

        } else if (n->alluni || n->mac_table.uni_overflow) {

            return 1;

        } else if (!memcmp(ptr, n->mac, ETH_ALEN)) {

            return 1;

        }

        for (i = 0; i < n->mac_table.first_multi; i++) {

            if (!memcmp(ptr, &n->mac_table.macs[i * ETH_ALEN], ETH_ALEN)) {

                return 1;

            }

        }

    }

    return 0;

}

static ssize_t virtio_net_receive(VLANClientState *nc, const uint8_t *buf, size_t size)

{

    VirtIONet *n = DO_UPCAST(NICState, nc, nc)->opaque;

    struct virtio_net_hdr_mrg_rxbuf *mhdr = NULL;

    size_t guest_hdr_len, offset, i, host_hdr_len;

    if (!virtio_net_can_receive(&n->nic->nc))

        return -1;

    /* hdr_len refers to the header we supply to the guest */

    guest_hdr_len = n->mergeable_rx_bufs ?

        sizeof(struct virtio_net_hdr_mrg_rxbuf) : sizeof(struct virtio_net_hdr);

    host_hdr_len = n->has_vnet_hdr ? sizeof(struct virtio_net_hdr) : 0;

    if (!virtio_net_has_buffers(n, size + guest_hdr_len - host_hdr_len))

        return 0;

    if (!receive_filter(n, buf, size))

        return size;

    offset = i = 0;

    while (offset < size) {

        VirtQueueElement elem;

        int len, total;

        struct iovec sg[VIRTQUEUE_MAX_SIZE];

        total = 0;

        if (virtqueue_pop(n->rx_vq, &elem) == 0) {

            if (i == 0)

                return -1;

            fprintf(stderr, "virtio-net unexpected empty queue: "

                    "i %zd mergeable %d offset %zd, size %zd, "

                    "guest hdr len %zd, host hdr len %zd guest features 0x%x\n",

                    i, n->mergeable_rx_bufs, offset, size,

                    guest_hdr_len, host_hdr_len, n->vdev.guest_features);

            exit(1);

        }

        if (elem.in_num < 1) {

            fprintf(stderr, "virtio-net receive queue contains no in buffers\n");

            exit(1);

        }

        if (!n->mergeable_rx_bufs && elem.in_sg[0].iov_len != guest_hdr_len) {

            fprintf(stderr, "virtio-net header not in first element\n");

            exit(1);

        }

        memcpy(&sg, &elem.in_sg[0], sizeof(sg[0]) * elem.in_num);

        if (i == 0) {

            if (n->mergeable_rx_bufs)

                mhdr = (struct virtio_net_hdr_mrg_rxbuf *)sg[0].iov_base;

            offset += receive_header(n, sg, elem.in_num,

                                     buf + offset, size - offset, guest_hdr_len);

            total += guest_hdr_len;

        }

        /* copy in packet.  ugh */

        len = iov_from_buf(sg, elem.in_num,

                           buf + offset, size - offset);

        total += len;

        offset += len;

        /* If buffers can't be merged, at this point we

         * must have consumed the complete packet.

         * Otherwise, drop it. */

        if (!n->mergeable_rx_bufs && offset < size) {

#if 0

            fprintf(stderr, "virtio-net truncated non-mergeable packet: "

                    "i %zd mergeable %d offset %zd, size %zd, "

                    "guest hdr len %zd, host hdr len %zd\n",

                    i, n->mergeable_rx_bufs,

                    offset, size, guest_hdr_len, host_hdr_len);

#endif

            return size;

        }

        /* signal other side */

        virtqueue_fill(n->rx_vq, &elem, total, i++);

    }

    if (mhdr)

        mhdr->num_buffers = i;

    virtqueue_flush(n->rx_vq, i);

    virtio_notify(&n->vdev, n->rx_vq);

    return size;

}

static int32_t virtio_net_flush_tx(VirtIONet *n, VirtQueue *vq);

static void virtio_net_tx_complete(VLANClientState *nc, ssize_t len)

{

    VirtIONet *n = DO_UPCAST(NICState, nc, nc)->opaque;

    virtqueue_push(n->tx_vq, &n->async_tx.elem, n->async_tx.len);

    virtio_notify(&n->vdev, n->tx_vq);

    n->async_tx.elem.out_num = n->async_tx.len = 0;

    virtio_queue_set_notification(n->tx_vq, 1);

    virtio_net_flush_tx(n, n->tx_vq);

}

/* TX */

static int32_t virtio_net_flush_tx(VirtIONet *n, VirtQueue *vq)

{

    VirtQueueElement elem;

    int32_t num_packets = 0;

    if (!(n->vdev.status & VIRTIO_CONFIG_S_DRIVER_OK)) {

        return num_packets;

    }

    if (n->async_tx.elem.out_num) {

        virtio_queue_set_notification(n->tx_vq, 0);

        return num_packets;

    }

    while (virtqueue_pop(vq, &elem)) {

        ssize_t ret, len = 0;

        unsigned int out_num = elem.out_num;

        struct iovec *out_sg = &elem.out_sg[0];

        unsigned hdr_len;

        /* hdr_len refers to the header received from the guest */

        hdr_len = n->mergeable_rx_bufs ?

            sizeof(struct virtio_net_hdr_mrg_rxbuf) :

            sizeof(struct virtio_net_hdr);

        if (out_num < 1 || out_sg->iov_len != hdr_len) {

            fprintf(stderr, "virtio-net header not in first element\n");

            exit(1);

        }

        /* ignore the header if GSO is not supported */

        if (!n->has_vnet_hdr) {

            out_num--;

            out_sg++;

            len += hdr_len;

        } else if (n->mergeable_rx_bufs) {

            /* tapfd expects a struct virtio_net_hdr */

            hdr_len -= sizeof(struct virtio_net_hdr);

            out_sg->iov_len -= hdr_len;

            len += hdr_len;

        }

        ret = qemu_sendv_packet_async(&n->nic->nc, out_sg, out_num,

                                      virtio_net_tx_complete);

        if (ret == 0) {

            virtio_queue_set_notification(n->tx_vq, 0);

            n->async_tx.elem = elem;

            n->async_tx.len  = len;

            return -EBUSY;

        }

        len += ret;

        virtqueue_push(vq, &elem, len);

        virtio_notify(&n->vdev, vq);

        if (++num_packets >= n->tx_burst) {

            break;

        }

    }

    return num_packets;

}

static void virtio_net_handle_tx_timer(VirtIODevice *vdev, VirtQueue *vq)

{

    VirtIONet *n = to_virtio_net(vdev);

    if (n->tx_waiting) {

        virtio_queue_set_notification(vq, 1);

        qemu_del_timer(n->tx_timer);

        n->tx_waiting = 0;

        virtio_net_flush_tx(n, vq);

    } else {

        qemu_mod_timer(n->tx_timer,

                       qemu_get_clock(vm_clock) + n->tx_timeout);

        n->tx_waiting = 1;

        virtio_queue_set_notification(vq, 0);

    }

}

static void virtio_net_handle_tx_bh(VirtIODevice *vdev, VirtQueue *vq)

{

    VirtIONet *n = to_virtio_net(vdev);

    if (unlikely(n->tx_waiting)) {

        return;

    }

    virtio_queue_set_notification(vq, 0);

    qemu_bh_schedule(n->tx_bh);

    n->tx_waiting = 1;

}

static void virtio_net_tx_timer(void *opaque)

{

    VirtIONet *n = opaque;

    n->tx_waiting = 0;

    /* Just in case the driver is not ready on more */

    if (!(n->vdev.status & VIRTIO_CONFIG_S_DRIVER_OK))

        return;

    virtio_queue_set_notification(n->tx_vq, 1);

    virtio_net_flush_tx(n, n->tx_vq);

}

static void virtio_net_tx_bh(void *opaque)

{

    VirtIONet *n = opaque;

    int32_t ret;

    n->tx_waiting = 0;

    /* Just in case the driver is not ready on more */

    if (unlikely(!(n->vdev.status & VIRTIO_CONFIG_S_DRIVER_OK)))

        return;

    ret = virtio_net_flush_tx(n, n->tx_vq);

    if (ret == -EBUSY) {

        return; /* Notification re-enable handled by tx_complete */

    }

    /* If we flush a full burst of packets, assume there are

     * more coming and immediately reschedule */

    if (ret >= n->tx_burst) {

        qemu_bh_schedule(n->tx_bh);

        n->tx_waiting = 1;

        return;

    }

    /* If less than a full burst, re-enable notification and flush

     * anything that may have come in while we weren't looking.  If

     * we find something, assume the guest is still active and reschedule */

    virtio_queue_set_notification(n->tx_vq, 1);

    if (virtio_net_flush_tx(n, n->tx_vq) > 0) {

        virtio_queue_set_notification(n->tx_vq, 0);

        qemu_bh_schedule(n->tx_bh);

        n->tx_waiting = 1;

    }

}

static void virtio_net_save(QEMUFile *f, void *opaque)

{

    VirtIONet *n = opaque;

    /* At this point, backend must be stopped, otherwise

     * it might keep writing to memory. */

    assert(!n->vhost_started);

    virtio_save(&n->vdev, f);

    qemu_put_buffer(f, n->mac, ETH_ALEN);

    qemu_put_be32(f, n->tx_waiting);

    qemu_put_be32(f, n->mergeable_rx_bufs);

    qemu_put_be16(f, n->status);

    qemu_put_byte(f, n->promisc);

    qemu_put_byte(f, n->allmulti);

    qemu_put_be32(f, n->mac_table.in_use);

    qemu_put_buffer(f, n->mac_table.macs, n->mac_table.in_use * ETH_ALEN);

    qemu_put_buffer(f, (uint8_t *)n->vlans, MAX_VLAN >> 3);

    qemu_put_be32(f, n->has_vnet_hdr);

    qemu_put_byte(f, n->mac_table.multi_overflow);

    qemu_put_byte(f, n->mac_table.uni_overflow);

    qemu_put_byte(f, n->alluni);

    qemu_put_byte(f, n->nomulti);

    qemu_put_byte(f, n->nouni);

    qemu_put_byte(f, n->nobcast);

    qemu_put_byte(f, n->has_ufo);

}

static int virtio_net_load(QEMUFile *f, void *opaque, int version_id)

{

    VirtIONet *n = opaque;

    int i;

    if (version_id < 2 || version_id > VIRTIO_NET_VM_VERSION)

        return -EINVAL;

    virtio_load(&n->vdev, f);

    qemu_get_buffer(f, n->mac, ETH_ALEN);

    n->tx_waiting = qemu_get_be32(f);

    n->mergeable_rx_bufs = qemu_get_be32(f);

    if (version_id >= 3)

        n->status = qemu_get_be16(f);

    if (version_id >= 4) {

        if (version_id < 8) {

            n->promisc = qemu_get_be32(f);

            n->allmulti = qemu_get_be32(f);

        } else {

            n->promisc = qemu_get_byte(f);

            n->allmulti = qemu_get_byte(f);

        }

    }

    if (version_id >= 5) {

        n->mac_table.in_use = qemu_get_be32(f);

        /* MAC_TABLE_ENTRIES may be different from the saved image */

        if (n->mac_table.in_use <= MAC_TABLE_ENTRIES) {

            qemu_get_buffer(f, n->mac_table.macs,

                            n->mac_table.in_use * ETH_ALEN);

        } else if (n->mac_table.in_use) {

            qemu_fseek(f, n->mac_table.in_use * ETH_ALEN, SEEK_CUR);

            n->mac_table.multi_overflow = n->mac_table.uni_overflow = 1;

            n->mac_table.in_use = 0;

        }

    }

    if (version_id >= 6)

        qemu_get_buffer(f, (uint8_t *)n->vlans, MAX_VLAN >> 3);

    if (version_id >= 7) {

        if (qemu_get_be32(f) && !peer_has_vnet_hdr(n)) {

            error_report("virtio-net: saved image requires vnet_hdr=on");

            return -1;

        }

        if (n->has_vnet_hdr) {

            tap_using_vnet_hdr(n->nic->nc.peer, 1);

            tap_set_offload(n->nic->nc.peer,

                    (n->vdev.guest_features >> VIRTIO_NET_F_GUEST_CSUM) & 1,

                    (n->vdev.guest_features >> VIRTIO_NET_F_GUEST_TSO4) & 1,

                    (n->vdev.guest_features >> VIRTIO_NET_F_GUEST_TSO6) & 1,

                    (n->vdev.guest_features >> VIRTIO_NET_F_GUEST_ECN)  & 1,

                    (n->vdev.guest_features >> VIRTIO_NET_F_GUEST_UFO)  & 1);

        }

    }

    if (version_id >= 9) {

        n->mac_table.multi_overflow = qemu_get_byte(f);

        n->mac_table.uni_overflow = qemu_get_byte(f);

    }