/* A network driver using virtio.
 *
 * Copyright 2007 Rusty Russell <rusty@rustcorp.com.au> IBM Corporation
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */
//#define DEBUG
#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/ethtool.h>
#include <linux/module.h>
#include <linux/virtio.h>
#include <linux/virtio_net.h>
#include <linux/scatterlist.h>
#include <linux/if_vlan.h>
#include <linux/slab.h>

static int napi_weight = 128;
module_param(napi_weight, int, 0444);

static bool csum = true, gso = true;
module_param(csum, bool, 0444);
module_param(gso, bool, 0444);

/* FIXME: MTU in config. */
#define MAX_PACKET_LEN (ETH_HLEN + VLAN_HLEN + ETH_DATA_LEN)
#define GOOD_COPY_LEN   128

#define VIRTNET_SEND_COMMAND_SG_MAX    2
#define VIRTNET_DRIVER_VERSION "1.0.0"

struct virtnet_stats {
        struct u64_stats_sync syncp;
        u64 tx_bytes;
        u64 tx_packets;

        u64 rx_bytes;
        u64 rx_packets;
};

struct virtnet_info {
        struct virtio_device *vdev;
        struct virtqueue *rvq, *svq, *cvq;
        struct net_device *dev;
        struct napi_struct napi;
        unsigned int status;

        /* Number of input buffers, and max we've ever had. */
        unsigned int num, max;

        /* I like... big packets and I cannot lie! */
        bool big_packets;

        /* Host will merge rx buffers for big packets (shake it! shake it!) */
        bool mergeable_rx_bufs;

        /* Active statistics */
        struct virtnet_stats __percpu *stats;

        /* Work struct for refilling if we run low on memory. */
        struct delayed_work refill;

        /* Chain pages by the private ptr. */
        struct page *pages;

        /* fragments + linear part + virtio header */
        struct scatterlist rx_sg[MAX_SKB_FRAGS + 2];
        struct scatterlist tx_sg[MAX_SKB_FRAGS + 2];
};

struct skb_vnet_hdr {
        union {
                struct virtio_net_hdr hdr;
                struct virtio_net_hdr_mrg_rxbuf mhdr;
        };
        unsigned int num_sg;
};

struct padded_vnet_hdr {
        struct virtio_net_hdr hdr;
        /*
         * virtio_net_hdr should be in a separated sg buffer because of a
         * QEMU bug, and data sg buffer shares same page with this header sg.
         * This padding makes next sg 16 byte aligned after virtio_net_hdr.
         */
        char padding[6];
};

static inline struct skb_vnet_hdr *skb_vnet_hdr(struct sk_buff *skb)
{
        return (struct skb_vnet_hdr *)skb->cb;
}

/*
 * private is used to chain pages for big packets, put the whole
 * most recent used list in the beginning for reuse
 */
static void give_pages(struct virtnet_info *vi, struct page *page)
{
        struct page *end;

        /* Find end of list, sew whole thing into vi->pages. */
        for (end = page; end->private; end = (struct page *)end->private);
        end->private = (unsigned long)vi->pages;
        vi->pages = page;
}

static struct page *get_a_page(struct virtnet_info *vi, gfp_t gfp_mask)
{
        struct page *p = vi->pages;

        if (p) {
                vi->pages = (struct page *)p->private;
                /* clear private here, it is used to chain pages */
                p->private = 0;
        } else
                p = alloc_page(gfp_mask);
        return p;
}

static void skb_xmit_done(struct virtqueue *svq)
{
        struct virtnet_info *vi = svq->vdev->priv;

        /* Suppress further interrupts. */
        virtqueue_disable_cb(svq);

        /* We were probably waiting for more output buffers. */
        netif_wake_queue(vi->dev);
}

static void set_skb_frag(struct sk_buff *skb, struct page *page,
                         unsigned int offset, unsigned int *len)
{
        int size = min((unsigned)PAGE_SIZE - offset, *len);
        int i = skb_shinfo(skb)->nr_frags;

        __skb_fill_page_desc(skb, i, page, offset, size);

        skb->data_len += size;
        skb->len += size;
        skb->truesize += PAGE_SIZE;
        skb_shinfo(skb)->nr_frags++;
        *len -= size;
}

/* Called from bottom half context */
static struct sk_buff *page_to_skb(struct virtnet_info *vi,
                                   struct page *page, unsigned int len)
{
        struct sk_buff *skb;
        struct skb_vnet_hdr *hdr;
        unsigned int copy, hdr_len, offset;
        char *p;

        p = page_address(page);

        /* copy small packet so we can reuse these pages for small data */
        skb = netdev_alloc_skb_ip_align(vi->dev, GOOD_COPY_LEN);
        if (unlikely(!skb))
                return NULL;

        hdr = skb_vnet_hdr(skb);

        if (vi->mergeable_rx_bufs) {
                hdr_len = sizeof hdr->mhdr;
                offset = hdr_len;
        } else {
                hdr_len = sizeof hdr->hdr;
                offset = sizeof(struct padded_vnet_hdr);
        }

        memcpy(hdr, p, hdr_len);

        len -= hdr_len;
        p += offset;

        copy = len;
        if (copy > skb_tailroom(skb))
                copy = skb_tailroom(skb);
        memcpy(skb_put(skb, copy), p, copy);

        len -= copy;
        offset += copy;

        /*
         * Verify that we can indeed put this data into a skb.
         * This is here to handle cases when the device erroneously
         * tries to receive more than is possible. This is usually
         * the case of a broken device.
         */
        if (unlikely(len > MAX_SKB_FRAGS * PAGE_SIZE)) {
                if (net_ratelimit())
                        pr_debug("%s: too much data\n", skb->dev->name);
                dev_kfree_skb(skb);
                return NULL;
        }

        while (len) {
                set_skb_frag(skb, page, offset, &len);
                page = (struct page *)page->private;
                offset = 0;
        }

        if (page)
                give_pages(vi, page);

        return skb;
}

static int receive_mergeable(struct virtnet_info *vi, struct sk_buff *skb)
{
        struct skb_vnet_hdr *hdr = skb_vnet_hdr(skb);
        struct page *page;
        int num_buf, i, len;

        num_buf = hdr->mhdr.num_buffers;
        while (--num_buf) {
                i = skb_shinfo(skb)->nr_frags;
                if (i >= MAX_SKB_FRAGS) {
                        pr_debug("%s: packet too long\n", skb->dev->name);
                        skb->dev->stats.rx_length_errors++;
                        return -EINVAL;
                }
                page = virtqueue_get_buf(vi->rvq, &len);
                if (!page) {
                        pr_debug("%s: rx error: %d buffers missing\n",
                                 skb->dev->name, hdr->mhdr.num_buffers);
                        skb->dev->stats.rx_length_errors++;
                        return -EINVAL;
                }

                if (len > PAGE_SIZE)
                        len = PAGE_SIZE;

                set_skb_frag(skb, page, 0, &len);

                --vi->num;
        }
        return 0;
}

static void receive_buf(struct net_device *dev, void *buf, unsigned int len)
{
        struct virtnet_info *vi = netdev_priv(dev);
        struct virtnet_stats __percpu *stats = this_cpu_ptr(vi->stats);
        struct sk_buff *skb;
        struct page *page;
        struct skb_vnet_hdr *hdr;

        if (unlikely(len < sizeof(struct virtio_net_hdr) + ETH_HLEN)) {
                pr_debug("%s: short packet %i\n", dev->name, len);
                dev->stats.rx_length_errors++;
                if (vi->mergeable_rx_bufs || vi->big_packets)
                        give_pages(vi, buf);
                else
                        dev_kfree_skb(buf);
                return;
        }

        if (!vi->mergeable_rx_bufs && !vi->big_packets) {
                skb = buf;
                len -= sizeof(struct virtio_net_hdr);
                skb_trim(skb, len);
        } else {
                page = buf;
                skb = page_to_skb(vi, page, len);
                if (unlikely(!skb)) {
                        dev->stats.rx_dropped++;
                        give_pages(vi, page);
                        return;
                }
                if (vi->mergeable_rx_bufs)
                        if (receive_mergeable(vi, skb)) {
                                dev_kfree_skb(skb);
                                return;
                        }
        }

        hdr = skb_vnet_hdr(skb);

        u64_stats_update_begin(&stats->syncp);
        stats->rx_bytes += skb->len;
        stats->rx_packets++;
        u64_stats_update_end(&stats->syncp);

        if (hdr->hdr.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) {
                pr_debug("Needs csum!\n");
                if (!skb_partial_csum_set(skb,
                                          hdr->hdr.csum_start,
                                          hdr->hdr.csum_offset))
                        goto frame_err;
        } else if (hdr->hdr.flags & VIRTIO_NET_HDR_F_DATA_VALID) {
                skb->ip_summed = CHECKSUM_UNNECESSARY;
        }

        skb->protocol = eth_type_trans(skb, dev);
        pr_debug("Receiving skb proto 0x%04x len %i type %i\n",
                 ntohs(skb->protocol), skb->len, skb->pkt_type);

        if (hdr->hdr.gso_type != VIRTIO_NET_HDR_GSO_NONE) {
                pr_debug("GSO!\n");
                switch (hdr->hdr.gso_type & ~VIRTIO_NET_HDR_GSO_ECN) {
                case VIRTIO_NET_HDR_GSO_TCPV4:
                        skb_shinfo(skb)->gso_type = SKB_GSO_TCPV4;
                        break;
                case VIRTIO_NET_HDR_GSO_UDP:
                        skb_shinfo(skb)->gso_type = SKB_GSO_UDP;
                        break;
                case VIRTIO_NET_HDR_GSO_TCPV6:
                        skb_shinfo(skb)->gso_type = SKB_GSO_TCPV6;
                        break;
                default:
                        if (net_ratelimit())
                                printk(KERN_WARNING "%s: bad gso type %u.\n",
                                       dev->name, hdr->hdr.gso_type);
                        goto frame_err;
                }

                if (hdr->hdr.gso_type & VIRTIO_NET_HDR_GSO_ECN)
                        skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN;

                skb_shinfo(skb)->gso_size = hdr->hdr.gso_size;
                if (skb_shinfo(skb)->gso_size == 0) {
                        if (net_ratelimit())
                                printk(KERN_WARNING "%s: zero gso size.\n",
                                       dev->name);
                        goto frame_err;
                }

                /* Header must be checked, and gso_segs computed. */
                skb_shinfo(skb)->gso_type |= SKB_GSO_DODGY;
                skb_shinfo(skb)->gso_segs = 0;
        }

        netif_receive_skb(skb);
        return;

frame_err:
        dev->stats.rx_frame_errors++;
        dev_kfree_skb(skb);
}

static int add_recvbuf_small(struct virtnet_info *vi, gfp_t gfp)
{
        struct sk_buff *skb;
        struct skb_vnet_hdr *hdr;
        int err;

        skb = __netdev_alloc_skb_ip_align(vi->dev, MAX_PACKET_LEN, gfp);
        if (unlikely(!skb))
                return -ENOMEM;

        skb_put(skb, MAX_PACKET_LEN);

        hdr = skb_vnet_hdr(skb);
        sg_set_buf(vi->rx_sg, &hdr->hdr, sizeof hdr->hdr);

        skb_to_sgvec(skb, vi->rx_sg + 1, 0, skb->len);

        err = virtqueue_add_buf(vi->rvq, vi->rx_sg, 0, 2, skb, gfp);
        if (err < 0)
                dev_kfree_skb(skb);

        return err;
}

static int add_recvbuf_big(struct virtnet_info *vi, gfp_t gfp)
{
        struct page *first, *list = NULL;
        char *p;
        int i, err, offset;

        /* page in vi->rx_sg[MAX_SKB_FRAGS + 1] is list tail */
        for (i = MAX_SKB_FRAGS + 1; i > 1; --i) {
                first = get_a_page(vi, gfp);
                if (!first) {
                        if (list)
                                give_pages(vi, list);
                        return -ENOMEM;
                }
                sg_set_buf(&vi->rx_sg[i], page_address(first), PAGE_SIZE);

                /* chain new page in list head to match sg */
                first->private = (unsigned long)list;
                list = first;
        }

        first = get_a_page(vi, gfp);
        if (!first) {
                give_pages(vi, list);
                return -ENOMEM;
        }
        p = page_address(first);

        /* vi->rx_sg[0], vi->rx_sg[1] share the same page */
        /* a separated vi->rx_sg[0] for virtio_net_hdr only due to QEMU bug */
        sg_set_buf(&vi->rx_sg[0], p, sizeof(struct virtio_net_hdr));

        /* vi->rx_sg[1] for data packet, from offset */
        offset = sizeof(struct padded_vnet_hdr);
        sg_set_buf(&vi->rx_sg[1], p + offset, PAGE_SIZE - offset);

        /* chain first in list head */
        first->private = (unsigned long)list;
        err = virtqueue_add_buf(vi->rvq, vi->rx_sg, 0, MAX_SKB_FRAGS + 2,
                                first, gfp);
        if (err < 0)
                give_pages(vi, first);

        return err;
}

static int add_recvbuf_mergeable(struct virtnet_info *vi, gfp_t gfp)
{
        struct page *page;
        int err;

        page = get_a_page(vi, gfp);
        if (!page)
                return -ENOMEM;

        sg_init_one(vi->rx_sg, page_address(page), PAGE_SIZE);

        err = virtqueue_add_buf(vi->rvq, vi->rx_sg, 0, 1, page, gfp);
        if (err < 0)
                give_pages(vi, page);

        return err;
}

/*
 * Returns false if we couldn't fill entirely (OOM).
 *
 * Normally run in the receive path, but can also be run from ndo_open
 * before we're receiving packets, or from refill_work which is
 * careful to disable receiving (using napi_disable).
 */
static bool try_fill_recv(struct virtnet_info *vi, gfp_t gfp)
{
        int err;
        bool oom;

        do {
                if (vi->mergeable_rx_bufs)
                        err = add_recvbuf_mergeable(vi, gfp);
                else if (vi->big_packets)
                        err = add_recvbuf_big(vi, gfp);
                else
                        err = add_recvbuf_small(vi, gfp);

                oom = err == -ENOMEM;
                if (err < 0)
                        break;
                ++vi->num;
        } while (err > 0);
        if (unlikely(vi->num > vi->max))
                vi->max = vi->num;
        virtqueue_kick(vi->rvq);
        return !oom;
}

static void skb_recv_done(struct virtqueue *rvq)
{
        struct virtnet_info *vi = rvq->vdev->priv;
        /* Schedule NAPI, Suppress further interrupts if successful. */
        if (napi_schedule_prep(&vi->napi)) {
                virtqueue_disable_cb(rvq);
                __napi_schedule(&vi->napi);
        }
}

static void virtnet_napi_enable(struct virtnet_info *vi)
{
        napi_enable(&vi->napi);

        /* If all buffers were filled by other side before we napi_enabled, we
         * won't get another interrupt, so process any outstanding packets
         * now.  virtnet_poll wants re-enable the queue, so we disable here.
         * We synchronize against interrupts via NAPI_STATE_SCHED */
        if (napi_schedule_prep(&vi->napi)) {
                virtqueue_disable_cb(vi->rvq);
                __napi_schedule(&vi->napi);
        }
}

static void refill_work(struct work_struct *work)
{
        struct virtnet_info *vi;
        bool still_empty;

        vi = container_of(work, struct virtnet_info, refill.work);
        napi_disable(&vi->napi);
        still_empty = !try_fill_recv(vi, GFP_KERNEL);
        virtnet_napi_enable(vi);

        /* In theory, this can happen: if we don't get any buffers in
         * we will *never* try to fill again. */
        if (still_empty)
                queue_delayed_work(system_nrt_wq, &vi->refill, HZ/2);
}

static int virtnet_poll(struct napi_struct *napi, int budget)
{
        struct virtnet_info *vi = container_of(napi, struct virtnet_info, napi);
        void *buf;
        unsigned int len, received = 0;

again:
        while (received < budget &&
               (buf = virtqueue_get_buf(vi->rvq, &len)) != NULL) {
                receive_buf(vi->dev, buf, len);
                --vi->num;
                received++;
        }

        if (vi->num < vi->max / 2) {
                if (!try_fill_recv(vi, GFP_ATOMIC))
                        queue_delayed_work(system_nrt_wq, &vi->refill, 0);
        }

        /* Out of packets? */
        if (received < budget) {
                napi_complete(napi);
                if (unlikely(!virtqueue_enable_cb(vi->rvq)) &&
                    napi_schedule_prep(napi)) {
                        virtqueue_disable_cb(vi->rvq);
                        __napi_schedule(napi);
                        goto again;
                }
        }

        return received;
}

static unsigned int free_old_xmit_skbs(struct virtnet_info *vi)
{
        struct sk_buff *skb;
        unsigned int len, tot_sgs = 0;
        struct virtnet_stats __percpu *stats = this_cpu_ptr(vi->stats);

        while ((skb = virtqueue_get_buf(vi->svq, &len)) != NULL) {
                pr_debug("Sent skb %p\n", skb);

                u64_stats_update_begin(&stats->syncp);
                stats->tx_bytes += skb->len;
                stats->tx_packets++;
                u64_stats_update_end(&stats->syncp);

                tot_sgs += skb_vnet_hdr(skb)->num_sg;
                dev_kfree_skb_any(skb);
        }
        return tot_sgs;
}

static int xmit_skb(struct virtnet_info *vi, struct sk_buff *skb)
{
        struct skb_vnet_hdr *hdr = skb_vnet_hdr(skb);
        const unsigned char *dest = ((struct ethhdr *)skb->data)->h_dest;

        pr_debug("%s: xmit %p %pM\n", vi->dev->name, skb, dest);

        if (skb->ip_summed == CHECKSUM_PARTIAL) {
                hdr->hdr.flags = VIRTIO_NET_HDR_F_NEEDS_CSUM;
                hdr->hdr.csum_start = skb_checksum_start_offset(skb);
                hdr->hdr.csum_offset = skb->csum_offset;
        } else {
                hdr->hdr.flags = 0;
                hdr->hdr.csum_offset = hdr->hdr.csum_start = 0;
        }

        if (skb_is_gso(skb)) {
                hdr->hdr.hdr_len = skb_headlen(skb);
                hdr->hdr.gso_size = skb_shinfo(skb)->gso_size;
                if (skb_shinfo(skb)->gso_type & SKB_GSO_TCPV4)
                        hdr->hdr.gso_type = VIRTIO_NET_HDR_GSO_TCPV4;
                else if (skb_shinfo(skb)->gso_type & SKB_GSO_TCPV6)
                        hdr->hdr.gso_type = VIRTIO_NET_HDR_GSO_TCPV6;
                else if (skb_shinfo(skb)->gso_type & SKB_GSO_UDP)
                        hdr->hdr.gso_type = VIRTIO_NET_HDR_GSO_UDP;
                else
                        BUG();
                if (skb_shinfo(skb)->gso_type & SKB_GSO_TCP_ECN)
                        hdr->hdr.gso_type |= VIRTIO_NET_HDR_GSO_ECN;
        } else {
                hdr->hdr.gso_type = VIRTIO_NET_HDR_GSO_NONE;
                hdr->hdr.gso_size = hdr->hdr.hdr_len = 0;
        }

        hdr->mhdr.num_buffers = 0;

        /* Encode metadata header at front. */
        if (vi->mergeable_rx_bufs)
                sg_set_buf(vi->tx_sg, &hdr->mhdr, sizeof hdr->mhdr);
        else
                sg_set_buf(vi->tx_sg, &hdr->hdr, sizeof hdr->hdr);

        hdr->num_sg = skb_to_sgvec(skb, vi->tx_sg + 1, 0, skb->len) + 1;
        return virtqueue_add_buf(vi->svq, vi->tx_sg, hdr->num_sg,
                                 0, skb, GFP_ATOMIC);
}

static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
{
        struct virtnet_info *vi = netdev_priv(dev);
        int capacity;

        /* Free up any pending old buffers before queueing new ones. */
        free_old_xmit_skbs(vi);

        /* Try to transmit */
        capacity = xmit_skb(vi, skb);

        /* This can happen with OOM and indirect buffers. */
        if (unlikely(capacity < 0)) {
                if (net_ratelimit()) {
                        if (likely(capacity == -ENOMEM)) {
                                dev_warn(&dev->dev,
                                         "TX queue failure: out of memory\n");
                        } else {
                                dev->stats.tx_fifo_errors++;
                                dev_warn(&dev->dev,
                                         "Unexpected TX queue failure: %d\n",
                                         capacity);
                        }
                }
                dev->stats.tx_dropped++;
                kfree_skb(skb);
                return NETDEV_TX_OK;
        }
        virtqueue_kick(vi->svq);

        /* Don't wait up for transmitted skbs to be freed. */
        skb_orphan(skb);
        nf_reset(skb);

        /* Apparently nice girls don't return TX_BUSY; stop the queue
         * before it gets out of hand.  Naturally, this wastes entries. */
        if (capacity < 2+MAX_SKB_FRAGS) {
                netif_stop_queue(dev);
                if (unlikely(!virtqueue_enable_cb_delayed(vi->svq))) {
                        /* More just got used, free them then recheck. */
                        capacity += free_old_xmit_skbs(vi);
                        if (capacity >= 2+MAX_SKB_FRAGS) {
                                netif_start_queue(dev);
                                virtqueue_disable_cb(vi->svq);
                        }
                }
        }

        return NETDEV_TX_OK;
}

static int virtnet_set_mac_address(struct net_device *dev, void *p)
{
        struct virtnet_info *vi = netdev_priv(dev);
        struct virtio_device *vdev = vi->vdev;
        int ret;

        ret = eth_mac_addr(dev, p);
        if (ret)
                return ret;

        if (virtio_has_feature(vdev, VIRTIO_NET_F_MAC))
                vdev->config->set(vdev, offsetof(struct virtio_net_config, mac),
                                  dev->dev_addr, dev->addr_len);

        return 0;
}

static struct rtnl_link_stats64 *virtnet_stats(struct net_device *dev,
                                               struct rtnl_link_stats64 *tot)
{
        struct virtnet_info *vi = netdev_priv(dev);
        int cpu;
        unsigned int start;

        for_each_possible_cpu(cpu) {
                struct virtnet_stats __percpu *stats
                        = per_cpu_ptr(vi->stats, cpu);
                u64 tpackets, tbytes, rpackets, rbytes;

                do {
                        start = u64_stats_fetch_begin(&stats->syncp);
                        tpackets = stats->tx_packets;
                        tbytes   = stats->tx_bytes;
                        rpackets = stats->rx_packets;
                        rbytes   = stats->rx_bytes;
                } while (u64_stats_fetch_retry(&stats->syncp, start));

                tot->rx_packets += rpackets;
                tot->tx_packets += tpackets;
                tot->rx_bytes   += rbytes;
                tot->tx_bytes   += tbytes;
        }

        tot->tx_dropped = dev->stats.tx_dropped;
        tot->tx_fifo_errors = dev->stats.tx_fifo_errors;
        tot->rx_dropped = dev->stats.rx_dropped;
        tot->rx_length_errors = dev->stats.rx_length_errors;
        tot->rx_frame_errors = dev->stats.rx_frame_errors;

        return tot;
}

#ifdef CONFIG_NET_POLL_CONTROLLER
static void virtnet_netpoll(struct net_device *dev)
{
        struct virtnet_info *vi = netdev_priv(dev);

        napi_schedule(&vi->napi);
}
#endif

static int virtnet_open(struct net_device *dev)
{
        struct virtnet_info *vi = netdev_priv(dev);

        /* Make sure we have some buffers: if oom use wq. */
        if (!try_fill_recv(vi, GFP_KERNEL))
                queue_delayed_work(system_nrt_wq, &vi->refill, 0);

        virtnet_napi_enable(vi);
        return 0;
}

/*
 * Send command via the control virtqueue and check status.  Commands
 * supported by the hypervisor, as indicated by feature bits, should
 * never fail unless improperly formated.
 */
static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8 cmd,
                                 struct scatterlist *data, int out, int in)
{
        struct scatterlist *s, sg[VIRTNET_SEND_COMMAND_SG_MAX + 2];
        struct virtio_net_ctrl_hdr ctrl;
        virtio_net_ctrl_ack status = ~0;
        unsigned int tmp;
        int i;

        /* Caller should know better */
        BUG_ON(!virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_VQ) ||
                (out + in > VIRTNET_SEND_COMMAND_SG_MAX));

        out++; /* Add header */
        in++; /* Add return status */

        ctrl.class = class;
        ctrl.cmd = cmd;

        sg_init_table(sg, out + in);

        sg_set_buf(&sg[0], &ctrl, sizeof(ctrl));
        for_each_sg(data, s, out + in - 2, i)
                sg_set_buf(&sg[i + 1], sg_virt(s), s->length);
        sg_set_buf(&sg[out + in - 1], &status, sizeof(status));

        BUG_ON(virtqueue_add_buf(vi->cvq, sg, out, in, vi, GFP_ATOMIC) < 0);

        virtqueue_kick(vi->cvq);

        /*
         * Spin for a response, the kick causes an ioport write, trapping
         * into the hypervisor, so the request should be handled immediately.
         */
        while (!virtqueue_get_buf(vi->cvq, &tmp))
                cpu_relax();

        return status == VIRTIO_NET_OK;
}

static int virtnet_close(struct net_device *dev)
{
        struct virtnet_info *vi = netdev_priv(dev);

        /* Make sure refill_work doesn't re-enable napi! */
        cancel_delayed_work_sync(&vi->refill);
        napi_disable(&vi->napi);

        return 0;
}

static void virtnet_set_rx_mode(struct net_device *dev)
{
        struct virtnet_info *vi = netdev_priv(dev);
        struct scatterlist sg[2];
        u8 promisc, allmulti;
        struct virtio_net_ctrl_mac *mac_data;
        struct netdev_hw_addr *ha;
        int uc_count;
        int mc_count;
        void *buf;
        int i;

        /* We can't dynamicaly set ndo_set_rx_mode, so return gracefully */
        if (!virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_RX))
                return;

        promisc = ((dev->flags & IFF_PROMISC) != 0);
        allmulti = ((dev->flags & IFF_ALLMULTI) != 0);

        sg_init_one(sg, &promisc, sizeof(promisc));

        if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_RX,
                                  VIRTIO_NET_CTRL_RX_PROMISC,
                                  sg, 1, 0))
                dev_warn(&dev->dev, "Failed to %sable promisc mode.\n",
                         promisc ? "en" : "dis");

        sg_init_one(sg, &allmulti, sizeof(allmulti));

        if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_RX,
                                  VIRTIO_NET_CTRL_RX_ALLMULTI,
                                  sg, 1, 0))
                dev_warn(&dev->dev, "Failed to %sable allmulti mode.\n",
                         allmulti ? "en" : "dis");

        uc_count = netdev_uc_count(dev);
        mc_count = netdev_mc_count(dev);
        /* MAC filter - use one buffer for both lists */
        buf = kzalloc(((uc_count + mc_count) * ETH_ALEN) +
                      (2 * sizeof(mac_data->entries)), GFP_ATOMIC);
        mac_data = buf;
        if (!buf) {
                dev_warn(&dev->dev, "No memory for MAC address buffer\n");
                return;
        }

        sg_init_table(sg, 2);

        /* Store the unicast list and count in the front of the buffer */
        mac_data->entries = uc_count;
        i = 0;
        netdev_for_each_uc_addr(ha, dev)
                memcpy(&mac_data->macs[i++][0], ha->addr, ETH_ALEN);

        sg_set_buf(&sg[0], mac_data,
                   sizeof(mac_data->entries) + (uc_count * ETH_ALEN));

        /* multicast list and count fill the end */
        mac_data = (void *)&mac_data->macs[uc_count][0];

        mac_data->entries = mc_count;
        i = 0;
        netdev_for_each_mc_addr(ha, dev)
                memcpy(&mac_data->macs[i++][0], ha->addr, ETH_ALEN);

        sg_set_buf(&sg[1], mac_data,
                   sizeof(mac_data->entries) + (mc_count * ETH_ALEN));

        if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_MAC,
                                  VIRTIO_NET_CTRL_MAC_TABLE_SET,
                                  sg, 2, 0))
                dev_warn(&dev->dev, "Failed to set MAC fitler table.\n");

        kfree(buf);
}

static int virtnet_vlan_rx_add_vid(struct net_device *dev, u16 vid)
{
        struct virtnet_info *vi = netdev_priv(dev);
        struct scatterlist sg;

        sg_init_one(&sg, &vid, sizeof(vid));

        if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_VLAN,
                                  VIRTIO_NET_CTRL_VLAN_ADD, &sg, 1, 0))
                dev_warn(&dev->dev, "Failed to add VLAN ID %d.\n", vid);
        return 0;
}

static int virtnet_vlan_rx_kill_vid(struct net_device *dev, u16 vid)
{
        struct virtnet_info *vi = netdev_priv(dev);
        struct scatterlist sg;

        sg_init_one(&sg, &vid, sizeof(vid));

        if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_VLAN,
                                  VIRTIO_NET_CTRL_VLAN_DEL, &sg, 1, 0))
                dev_warn(&dev->dev, "Failed to kill VLAN ID %d.\n", vid);
        return 0;
}

static void virtnet_get_ringparam(struct net_device *dev,
                                struct ethtool_ringparam *ring)
{
        struct virtnet_info *vi = netdev_priv(dev);

        ring->rx_max_pending = virtqueue_get_vring_size(vi->rvq);
        ring->tx_max_pending = virtqueue_get_vring_size(vi->svq);
        ring->rx_pending = ring->rx_max_pending;
        ring->tx_pending = ring->tx_max_pending;

}


static void virtnet_get_drvinfo(struct net_device *dev,
                                struct ethtool_drvinfo *info)
{
        struct virtnet_info *vi = netdev_priv(dev);
        struct virtio_device *vdev = vi->vdev;

        strlcpy(info->driver, KBUILD_MODNAME, sizeof(info->driver));
        strlcpy(info->version, VIRTNET_DRIVER_VERSION, sizeof(info->version));
        strlcpy(info->bus_info, virtio_bus_name(vdev), sizeof(info->bus_info));

}

static const struct ethtool_ops virtnet_ethtool_ops = {
        .get_drvinfo = virtnet_get_drvinfo,
        .get_link = ethtool_op_get_link,
        .get_ringparam = virtnet_get_ringparam,
};

#define MIN_MTU 68
#define MAX_MTU 65535

static int virtnet_change_mtu(struct net_device *dev, int new_mtu)
{
        if (new_mtu < MIN_MTU || new_mtu > MAX_MTU)
                return -EINVAL;
        dev->mtu = new_mtu;
        return 0;
}

static const struct net_device_ops virtnet_netdev = {
        .ndo_open            = virtnet_open,
        .ndo_stop            = virtnet_close,
        .ndo_start_xmit      = start_xmit,
        .ndo_validate_addr   = eth_validate_addr,
        .ndo_set_mac_address = virtnet_set_mac_address,
        .ndo_set_rx_mode     = virtnet_set_rx_mode,
        .ndo_change_mtu      = virtnet_change_mtu,
        .ndo_get_stats64     = virtnet_stats,
        .ndo_vlan_rx_add_vid = virtnet_vlan_rx_add_vid,
        .ndo_vlan_rx_kill_vid = virtnet_vlan_rx_kill_vid,
#ifdef CONFIG_NET_POLL_CONTROLLER
        .ndo_poll_controller = virtnet_netpoll,
#endif
};

static void virtnet_update_status(struct virtnet_info *vi)
{
        u16 v;

        if (virtio_config_val(vi->vdev, VIRTIO_NET_F_STATUS,
                              offsetof(struct virtio_net_config, status),
                              &v) < 0)
                return;

        /* Ignore unknown (future) status bits */
        v &= VIRTIO_NET_S_LINK_UP;

        if (vi->status == v)
                return;

        vi->status = v;

        if (vi->status & VIRTIO_NET_S_LINK_UP) {
                netif_carrier_on(vi->dev);
                netif_wake_queue(vi->dev);
        } else {
                netif_carrier_off(vi->dev);
                netif_stop_queue(vi->dev);
        }
}

static void virtnet_config_changed(struct virtio_device *vdev)
{
        struct virtnet_info *vi = vdev->priv;

        virtnet_update_status(vi);
}

static int init_vqs(struct virtnet_info *vi)
{
        struct virtqueue *vqs[3];
        vq_callback_t *callbacks[] = { skb_recv_done, skb_xmit_done, NULL};
        const char *names[] = { "input", "output", "control" };
        int nvqs, err;

        /* We expect two virtqueues, receive then send,
         * and optionally control. */
        nvqs = virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_VQ) ? 3 : 2;

        err = vi->vdev->config->find_vqs(vi->vdev, nvqs, vqs, callbacks, names);
        if (err)

                return err;

        vi->rvq = vqs[0];
        vi->svq = vqs[1];

        if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_VQ)) {
                vi->cvq = vqs[2];

                if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_VLAN))
                        vi->dev->features |= NETIF_F_HW_VLAN_FILTER;
        }
        return 0;
}

static int virtnet_probe(struct virtio_device *vdev)
{
        int err;
        struct net_device *dev;
        struct virtnet_info *vi;

        /* Allocate ourselves a network device with room for our info */
        dev = alloc_etherdev(sizeof(struct virtnet_info));
        if (!dev)
                return -ENOMEM;

        /* Set up network device as normal. */
        dev->priv_flags |= IFF_UNICAST_FLT;
        dev->netdev_ops = &virtnet_netdev;
        dev->features = NETIF_F_HIGHDMA;

        SET_ETHTOOL_OPS(dev, &virtnet_ethtool_ops);
        SET_NETDEV_DEV(dev, &vdev->dev);

        /* Do we support "hardware" checksums? */
        if (virtio_has_feature(vdev, VIRTIO_NET_F_CSUM)) {
                /* This opens up the world of extra features. */
                dev->hw_features |= NETIF_F_HW_CSUM|NETIF_F_SG|NETIF_F_FRAGLIST;
                if (csum)
                        dev->features |= NETIF_F_HW_CSUM|NETIF_F_SG|NETIF_F_FRAGLIST;

                if (virtio_has_feature(vdev, VIRTIO_NET_F_GSO)) {
                        dev->hw_features |= NETIF_F_TSO | NETIF_F_UFO
                                | NETIF_F_TSO_ECN | NETIF_F_TSO6;
                }
                /* Individual feature bits: what can host handle? */
                if (virtio_has_feature(vdev, VIRTIO_NET_F_HOST_TSO4))
                        dev->hw_features |= NETIF_F_TSO;
                if (virtio_has_feature(vdev, VIRTIO_NET_F_HOST_TSO6))
                        dev->hw_features |= NETIF_F_TSO6;
                if (virtio_has_feature(vdev, VIRTIO_NET_F_HOST_ECN))
                        dev->hw_features |= NETIF_F_TSO_ECN;
                if (virtio_has_feature(vdev, VIRTIO_NET_F_HOST_UFO))
                        dev->hw_features |= NETIF_F_UFO;

                if (gso)
                        dev->features |= dev->hw_features & (NETIF_F_ALL_TSO|NETIF_F_UFO);
                /* (!csum && gso) case will be fixed by register_netdev() */
        }

        /* Configuration may specify what MAC to use.  Otherwise random. */
        if (virtio_config_val_len(vdev, VIRTIO_NET_F_MAC,
                                  offsetof(struct virtio_net_config, mac),
                                  dev->dev_addr, dev->addr_len) < 0)
                random_ether_addr(dev->dev_addr);

        /* Set up our device-specific information */
        vi = netdev_priv(dev);
        netif_napi_add(dev, &vi->napi, virtnet_poll, napi_weight);
        vi->dev = dev;
        vi->vdev = vdev;
        vdev->priv = vi;
        vi->pages = NULL;
        vi->stats = alloc_percpu(struct virtnet_stats);
        err = -ENOMEM;
        if (vi->stats == NULL)
                goto free;

        INIT_DELAYED_WORK(&vi->refill, refill_work);
        sg_init_table(vi->rx_sg, ARRAY_SIZE(vi->rx_sg));
        sg_init_table(vi->tx_sg, ARRAY_SIZE(vi->tx_sg));

        /* If we can receive ANY GSO packets, we must allocate large ones. */
        if (virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO4) ||
            virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO6) ||
            virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_ECN))
                vi->big_packets = true;

        if (virtio_has_feature(vdev, VIRTIO_NET_F_MRG_RXBUF))
                vi->mergeable_rx_bufs = true;

        err = init_vqs(vi);
        if (err)
                goto free_stats;

        err = register_netdev(dev);
        if (err) {
                pr_debug("virtio_net: registering device failed\n");
                goto free_vqs;
        }

        /* Last of all, set up some receive buffers. */
        try_fill_recv(vi, GFP_KERNEL);

        /* If we didn't even get one input buffer, we're useless. */
        if (vi->num == 0) {
                err = -ENOMEM;
                goto unregister;
        }

        /* Assume link up if device can't report link status,
           otherwise get link status from config. */
        if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_STATUS)) {
                netif_carrier_off(dev);
                virtnet_update_status(vi);
        } else {
                vi->status = VIRTIO_NET_S_LINK_UP;
                netif_carrier_on(dev);
        }

        pr_debug("virtnet: registered device %s\n", dev->name);
        return 0;

unregister:
        unregister_netdev(dev);
free_vqs:
        vdev->config->del_vqs(vdev);
free_stats:
        free_percpu(vi->stats);
free:
        free_netdev(dev);
        return err;
}

static void free_unused_bufs(struct virtnet_info *vi)
{
        void *buf;
        while (1) {
                buf = virtqueue_detach_unused_buf(vi->svq);
                if (!buf)
                        break;
                dev_kfree_skb(buf);
        }
        while (1) {
                buf = virtqueue_detach_unused_buf(vi->rvq);
                if (!buf)
                        break;
                if (vi->mergeable_rx_bufs || vi->big_packets)
                        give_pages(vi, buf);
                else
                        dev_kfree_skb(buf);
                --vi->num;
        }
        BUG_ON(vi->num != 0);
}

static void remove_vq_common(struct virtnet_info *vi)
{
        vi->vdev->config->reset(vi->vdev);

        /* Free unused buffers in both send and recv, if any. */
        free_unused_bufs(vi);

        vi->vdev->config->del_vqs(vi->vdev);

        while (vi->pages)
                __free_pages(get_a_page(vi, GFP_KERNEL), 0);
}

static void __devexit virtnet_remove(struct virtio_device *vdev)
{
        struct virtnet_info *vi = vdev->priv;

        unregister_netdev(vi->dev);

        remove_vq_common(vi);

        free_percpu(vi->stats);
        free_netdev(vi->dev);
}

#ifdef CONFIG_PM
static int virtnet_freeze(struct virtio_device *vdev)
{
        struct virtnet_info *vi = vdev->priv;

        virtqueue_disable_cb(vi->rvq);
        virtqueue_disable_cb(vi->svq);
        if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_VQ))
                virtqueue_disable_cb(vi->cvq);

        netif_device_detach(vi->dev);
        cancel_delayed_work_sync(&vi->refill);

        if (netif_running(vi->dev))
                napi_disable(&vi->napi);

        remove_vq_common(vi);

        return 0;
}

static int virtnet_restore(struct virtio_device *vdev)
{
        struct virtnet_info *vi = vdev->priv;
        int err;

        err = init_vqs(vi);
        if (err)
                return err;

        if (netif_running(vi->dev))
                virtnet_napi_enable(vi);

        netif_device_attach(vi->dev);

        if (!try_fill_recv(vi, GFP_KERNEL))
                queue_delayed_work(system_nrt_wq, &vi->refill, 0);

        return 0;
}
#endif

static struct virtio_device_id id_table[] = {
        { VIRTIO_ID_NET, VIRTIO_DEV_ANY_ID },
        { 0 },
};

static unsigned int features[] = {
        VIRTIO_NET_F_CSUM, VIRTIO_NET_F_GUEST_CSUM,
        VIRTIO_NET_F_GSO, VIRTIO_NET_F_MAC,
        VIRTIO_NET_F_HOST_TSO4, VIRTIO_NET_F_HOST_UFO, VIRTIO_NET_F_HOST_TSO6,
        VIRTIO_NET_F_HOST_ECN, VIRTIO_NET_F_GUEST_TSO4, VIRTIO_NET_F_GUEST_TSO6,
        VIRTIO_NET_F_GUEST_ECN, VIRTIO_NET_F_GUEST_UFO,
        VIRTIO_NET_F_MRG_RXBUF, VIRTIO_NET_F_STATUS, VIRTIO_NET_F_CTRL_VQ,
        VIRTIO_NET_F_CTRL_RX, VIRTIO_NET_F_CTRL_VLAN,
};

static struct virtio_driver virtio_net_driver = {
        .feature_table = features,
        .feature_table_size = ARRAY_SIZE(features),
        .driver.name =  KBUILD_MODNAME,
        .driver.owner = THIS_MODULE,
        .id_table =     id_table,
        .probe =        virtnet_probe,
        .remove =       __devexit_p(virtnet_remove),
        .config_changed = virtnet_config_changed,
#ifdef CONFIG_PM
        .freeze =       virtnet_freeze,
        .restore =      virtnet_restore,
#endif
};

static int __init init(void)
{
        return register_virtio_driver(&virtio_net_driver);
}

static void __exit fini(void)
{
        unregister_virtio_driver(&virtio_net_driver);
}
module_init(init);
module_exit(fini);

MODULE_DEVICE_TABLE(virtio, id_table);
MODULE_DESCRIPTION("Virtio network driver");
MODULE_LICENSE("GPL");