Merge tag 'v3.10.107' into update

[GitHub/mt8127/android_kernel_alcatel_ttab.git] / drivers / net / xen-netfront.c

/*
 * Virtual network driver for conversing with remote driver backends.
 *
 * Copyright (c) 2002-2005, K A Fraser
 * Copyright (c) 2005, XenSource Ltd
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License version 2
 * as published by the Free Software Foundation; or, when distributed
 * separately from the Linux kernel or incorporated into other
 * software packages, subject to the following license:
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this source file (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use, copy, modify,
 * merge, publish, distribute, sublicense, and/or sell copies of the Software,
 * and to permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/skbuff.h>
#include <linux/ethtool.h>
#include <linux/if_ether.h>
#include <net/tcp.h>
#include <linux/udp.h>
#include <linux/moduleparam.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <net/ip.h>

#include <asm/xen/page.h>
#include <xen/xen.h>
#include <xen/xenbus.h>
#include <xen/events.h>
#include <xen/page.h>
#include <xen/platform_pci.h>
#include <xen/grant_table.h>

#include <xen/interface/io/netif.h>
#include <xen/interface/memory.h>
#include <xen/interface/grant_table.h>

static const struct ethtool_ops xennet_ethtool_ops;

struct netfront_cb {
        int pull_to;
};

#define NETFRONT_SKB_CB(skb)    ((struct netfront_cb *)((skb)->cb))

#define RX_COPY_THRESHOLD 256

#define GRANT_INVALID_REF       0

#define NET_TX_RING_SIZE __CONST_RING_SIZE(xen_netif_tx, PAGE_SIZE)
#define NET_RX_RING_SIZE __CONST_RING_SIZE(xen_netif_rx, PAGE_SIZE)
#define TX_MAX_TARGET min_t(int, NET_TX_RING_SIZE, 256)

struct netfront_stats {
        u64                     rx_packets;
        u64                     tx_packets;
        u64                     rx_bytes;
        u64                     tx_bytes;
        struct u64_stats_sync   syncp;
};

struct netfront_info {
        struct list_head list;
        struct net_device *netdev;

        struct napi_struct napi;

        unsigned int evtchn;
        struct xenbus_device *xbdev;

        spinlock_t   tx_lock;
        struct xen_netif_tx_front_ring tx;
        int tx_ring_ref;

        /*
         * {tx,rx}_skbs store outstanding skbuffs. Free tx_skb entries
         * are linked from tx_skb_freelist through skb_entry.link.
         *
         *  NB. Freelist index entries are always going to be less than
         *  PAGE_OFFSET, whereas pointers to skbs will always be equal or
         *  greater than PAGE_OFFSET: we use this property to distinguish
         *  them.
         */
        union skb_entry {
                struct sk_buff *skb;
                unsigned long link;
        } tx_skbs[NET_TX_RING_SIZE];
        grant_ref_t gref_tx_head;
        grant_ref_t grant_tx_ref[NET_TX_RING_SIZE];
        struct page *grant_tx_page[NET_TX_RING_SIZE];
        unsigned tx_skb_freelist;

        spinlock_t   rx_lock ____cacheline_aligned_in_smp;
        struct xen_netif_rx_front_ring rx;
        int rx_ring_ref;

        /* Receive-ring batched refills. */
#define RX_MIN_TARGET 8
#define RX_DFL_MIN_TARGET 64
#define RX_MAX_TARGET min_t(int, NET_RX_RING_SIZE, 256)
        unsigned rx_min_target, rx_max_target, rx_target;
        struct sk_buff_head rx_batch;

        struct timer_list rx_refill_timer;

        struct sk_buff *rx_skbs[NET_RX_RING_SIZE];
        grant_ref_t gref_rx_head;
        grant_ref_t grant_rx_ref[NET_RX_RING_SIZE];

        unsigned long rx_pfn_array[NET_RX_RING_SIZE];
        struct multicall_entry rx_mcl[NET_RX_RING_SIZE+1];
        struct mmu_update rx_mmu[NET_RX_RING_SIZE];

        /* Statistics */
        struct netfront_stats __percpu *stats;

        unsigned long rx_gso_checksum_fixup;
};

struct netfront_rx_info {
        struct xen_netif_rx_response rx;
        struct xen_netif_extra_info extras[XEN_NETIF_EXTRA_TYPE_MAX - 1];
};

static void skb_entry_set_link(union skb_entry *list, unsigned short id)
{
        list->link = id;
}

static int skb_entry_is_link(const union skb_entry *list)
{
        BUILD_BUG_ON(sizeof(list->skb) != sizeof(list->link));
        return (unsigned long)list->skb < PAGE_OFFSET;
}

/*
 * Access macros for acquiring freeing slots in tx_skbs[].
 */

static void add_id_to_freelist(unsigned *head, union skb_entry *list,
                               unsigned short id)
{
        skb_entry_set_link(&list[id], *head);
        *head = id;
}

static unsigned short get_id_from_freelist(unsigned *head,
                                           union skb_entry *list)
{
        unsigned int id = *head;
        *head = list[id].link;
        return id;
}

static int xennet_rxidx(RING_IDX idx)
{
        return idx & (NET_RX_RING_SIZE - 1);
}

static struct sk_buff *xennet_get_rx_skb(struct netfront_info *np,
                                         RING_IDX ri)
{
        int i = xennet_rxidx(ri);
        struct sk_buff *skb = np->rx_skbs[i];
        np->rx_skbs[i] = NULL;
        return skb;
}

static grant_ref_t xennet_get_rx_ref(struct netfront_info *np,
                                            RING_IDX ri)
{
        int i = xennet_rxidx(ri);
        grant_ref_t ref = np->grant_rx_ref[i];
        np->grant_rx_ref[i] = GRANT_INVALID_REF;
        return ref;
}

#ifdef CONFIG_SYSFS
static int xennet_sysfs_addif(struct net_device *netdev);
static void xennet_sysfs_delif(struct net_device *netdev);
#else /* !CONFIG_SYSFS */
#define xennet_sysfs_addif(dev) (0)
#define xennet_sysfs_delif(dev) do { } while (0)
#endif

static bool xennet_can_sg(struct net_device *dev)
{
        return dev->features & NETIF_F_SG;
}


static void rx_refill_timeout(unsigned long data)
{
        struct net_device *dev = (struct net_device *)data;
        struct netfront_info *np = netdev_priv(dev);
        napi_schedule(&np->napi);
}

static int netfront_tx_slot_available(struct netfront_info *np)
{
        return (np->tx.req_prod_pvt - np->tx.rsp_cons) <
                (TX_MAX_TARGET - MAX_SKB_FRAGS - 2);
}

static void xennet_maybe_wake_tx(struct net_device *dev)
{
        struct netfront_info *np = netdev_priv(dev);

        if (unlikely(netif_queue_stopped(dev)) &&
            netfront_tx_slot_available(np) &&
            likely(netif_running(dev)))
                netif_wake_queue(dev);
}

static void xennet_alloc_rx_buffers(struct net_device *dev)
{
        unsigned short id;
        struct netfront_info *np = netdev_priv(dev);
        struct sk_buff *skb;
        struct page *page;
        int i, batch_target, notify;
        RING_IDX req_prod = np->rx.req_prod_pvt;
        grant_ref_t ref;
        unsigned long pfn;
        void *vaddr;
        struct xen_netif_rx_request *req;

        if (unlikely(!netif_carrier_ok(dev)))
                return;

        /*
         * Allocate skbuffs greedily, even though we batch updates to the
         * receive ring. This creates a less bursty demand on the memory
         * allocator, so should reduce the chance of failed allocation requests
         * both for ourself and for other kernel subsystems.
         */
        batch_target = np->rx_target - (req_prod - np->rx.rsp_cons);
        for (i = skb_queue_len(&np->rx_batch); i < batch_target; i++) {
                skb = __netdev_alloc_skb(dev, RX_COPY_THRESHOLD + NET_IP_ALIGN,
                                         GFP_ATOMIC | __GFP_NOWARN);
                if (unlikely(!skb))
                        goto no_skb;

                /* Align ip header to a 16 bytes boundary */
                skb_reserve(skb, NET_IP_ALIGN);

                page = alloc_page(GFP_ATOMIC | __GFP_NOWARN);
                if (!page) {
                        kfree_skb(skb);
no_skb:
                        /* Any skbuffs queued for refill? Force them out. */
                        if (i != 0)
                                goto refill;
                        /* Could not allocate any skbuffs. Try again later. */
                        mod_timer(&np->rx_refill_timer,
                                  jiffies + (HZ/10));
                        break;
                }

                skb_add_rx_frag(skb, 0, page, 0, 0, PAGE_SIZE);
                __skb_queue_tail(&np->rx_batch, skb);
        }

        /* Is the batch large enough to be worthwhile? */
        if (i < (np->rx_target/2)) {
                if (req_prod > np->rx.sring->req_prod)
                        goto push;
                return;
        }

        /* Adjust our fill target if we risked running out of buffers. */
        if (((req_prod - np->rx.sring->rsp_prod) < (np->rx_target / 4)) &&
            ((np->rx_target *= 2) > np->rx_max_target))
                np->rx_target = np->rx_max_target;

 refill:
        for (i = 0; ; i++) {
                skb = __skb_dequeue(&np->rx_batch);
                if (skb == NULL)
                        break;

                skb->dev = dev;

                id = xennet_rxidx(req_prod + i);

                BUG_ON(np->rx_skbs[id]);
                np->rx_skbs[id] = skb;

                ref = gnttab_claim_grant_reference(&np->gref_rx_head);
                BUG_ON((signed short)ref < 0);
                np->grant_rx_ref[id] = ref;

                pfn = page_to_pfn(skb_frag_page(&skb_shinfo(skb)->frags[0]));
                vaddr = page_address(skb_frag_page(&skb_shinfo(skb)->frags[0]));

                req = RING_GET_REQUEST(&np->rx, req_prod + i);
                gnttab_grant_foreign_access_ref(ref,
                                                np->xbdev->otherend_id,
                                                pfn_to_mfn(pfn),
                                                0);

                req->id = id;
                req->gref = ref;
        }

        wmb();          /* barrier so backend seens requests */

        /* Above is a suitable barrier to ensure backend will see requests. */
        np->rx.req_prod_pvt = req_prod + i;
 push:
        RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(&np->rx, notify);
        if (notify)
                notify_remote_via_irq(np->netdev->irq);
}

static int xennet_open(struct net_device *dev)
{
        struct netfront_info *np = netdev_priv(dev);

        napi_enable(&np->napi);

        spin_lock_bh(&np->rx_lock);
        if (netif_carrier_ok(dev)) {
                xennet_alloc_rx_buffers(dev);
                np->rx.sring->rsp_event = np->rx.rsp_cons + 1;
                if (RING_HAS_UNCONSUMED_RESPONSES(&np->rx))
                        napi_schedule(&np->napi);
        }
        spin_unlock_bh(&np->rx_lock);

        netif_start_queue(dev);

        return 0;
}

static void xennet_tx_buf_gc(struct net_device *dev)
{
        RING_IDX cons, prod;
        unsigned short id;
        struct netfront_info *np = netdev_priv(dev);
        struct sk_buff *skb;

        BUG_ON(!netif_carrier_ok(dev));

        do {
                prod = np->tx.sring->rsp_prod;
                rmb(); /* Ensure we see responses up to 'rp'. */

                for (cons = np->tx.rsp_cons; cons != prod; cons++) {
                        struct xen_netif_tx_response *txrsp;

                        txrsp = RING_GET_RESPONSE(&np->tx, cons);
                        if (txrsp->status == XEN_NETIF_RSP_NULL)
                                continue;

                        id  = txrsp->id;
                        skb = np->tx_skbs[id].skb;
                        if (unlikely(gnttab_query_foreign_access(
                                np->grant_tx_ref[id]) != 0)) {
                                printk(KERN_ALERT "xennet_tx_buf_gc: warning "
                                       "-- grant still in use by backend "
                                       "domain.\n");
                                BUG();
                        }
                        gnttab_end_foreign_access_ref(
                                np->grant_tx_ref[id], GNTMAP_readonly);
                        gnttab_release_grant_reference(
                                &np->gref_tx_head, np->grant_tx_ref[id]);
                        np->grant_tx_ref[id] = GRANT_INVALID_REF;
                        np->grant_tx_page[id] = NULL;
                        add_id_to_freelist(&np->tx_skb_freelist, np->tx_skbs, id);
                        dev_kfree_skb_irq(skb);
                }

                np->tx.rsp_cons = prod;

                /*
                 * Set a new event, then check for race with update of tx_cons.
                 * Note that it is essential to schedule a callback, no matter
                 * how few buffers are pending. Even if there is space in the
                 * transmit ring, higher layers may be blocked because too much
                 * data is outstanding: in such cases notification from Xen is
                 * likely to be the only kick that we'll get.
                 */
                np->tx.sring->rsp_event =
                        prod + ((np->tx.sring->req_prod - prod) >> 1) + 1;
                mb();           /* update shared area */
        } while ((cons == prod) && (prod != np->tx.sring->rsp_prod));

        xennet_maybe_wake_tx(dev);
}

static void xennet_make_frags(struct sk_buff *skb, struct net_device *dev,
                              struct xen_netif_tx_request *tx)
{
        struct netfront_info *np = netdev_priv(dev);
        char *data = skb->data;
        unsigned long mfn;
        RING_IDX prod = np->tx.req_prod_pvt;
        int frags = skb_shinfo(skb)->nr_frags;
        unsigned int offset = offset_in_page(data);
        unsigned int len = skb_headlen(skb);
        unsigned int id;
        grant_ref_t ref;
        int i;

        /* While the header overlaps a page boundary (including being
           larger than a page), split it it into page-sized chunks. */
        while (len > PAGE_SIZE - offset) {
                tx->size = PAGE_SIZE - offset;
                tx->flags |= XEN_NETTXF_more_data;
                len -= tx->size;
                data += tx->size;
                offset = 0;

                id = get_id_from_freelist(&np->tx_skb_freelist, np->tx_skbs);
                np->tx_skbs[id].skb = skb_get(skb);
                tx = RING_GET_REQUEST(&np->tx, prod++);
                tx->id = id;
                ref = gnttab_claim_grant_reference(&np->gref_tx_head);
                BUG_ON((signed short)ref < 0);

                mfn = virt_to_mfn(data);
                gnttab_grant_foreign_access_ref(ref, np->xbdev->otherend_id,
                                                mfn, GNTMAP_readonly);

                np->grant_tx_page[id] = virt_to_page(data);
                tx->gref = np->grant_tx_ref[id] = ref;
                tx->offset = offset;
                tx->size = len;
                tx->flags = 0;
        }

        /* Grant backend access to each skb fragment page. */
        for (i = 0; i < frags; i++) {
                skb_frag_t *frag = skb_shinfo(skb)->frags + i;
                struct page *page = skb_frag_page(frag);

                len = skb_frag_size(frag);
                offset = frag->page_offset;

                /* Skip unused frames from start of page */
                page += offset >> PAGE_SHIFT;
                offset &= ~PAGE_MASK;

                while (len > 0) {
                        unsigned long bytes;

                        bytes = PAGE_SIZE - offset;
                        if (bytes > len)
                                bytes = len;

                        tx->flags |= XEN_NETTXF_more_data;

                        id = get_id_from_freelist(&np->tx_skb_freelist,
                                                  np->tx_skbs);
                        np->tx_skbs[id].skb = skb_get(skb);
                        tx = RING_GET_REQUEST(&np->tx, prod++);
                        tx->id = id;
                        ref = gnttab_claim_grant_reference(&np->gref_tx_head);
                        BUG_ON((signed short)ref < 0);

                        mfn = pfn_to_mfn(page_to_pfn(page));
                        gnttab_grant_foreign_access_ref(ref,
                                                        np->xbdev->otherend_id,
                                                        mfn, GNTMAP_readonly);

                        np->grant_tx_page[id] = page;
                        tx->gref = np->grant_tx_ref[id] = ref;
                        tx->offset = offset;
                        tx->size = bytes;
                        tx->flags = 0;

                        offset += bytes;
                        len -= bytes;

                        /* Next frame */
                        if (offset == PAGE_SIZE && len) {
                                BUG_ON(!PageCompound(page));
                                page++;
                                offset = 0;
                        }
                }
        }

        np->tx.req_prod_pvt = prod;
}

/*
 * Count how many ring slots are required to send the frags of this
 * skb. Each frag might be a compound page.
 */
static int xennet_count_skb_frag_slots(struct sk_buff *skb)
{
        int i, frags = skb_shinfo(skb)->nr_frags;
        int pages = 0;

        for (i = 0; i < frags; i++) {
                skb_frag_t *frag = skb_shinfo(skb)->frags + i;
                unsigned long size = skb_frag_size(frag);
                unsigned long offset = frag->page_offset;

                /* Skip unused frames from start of page */
                offset &= ~PAGE_MASK;

                pages += PFN_UP(offset + size);
        }

        return pages;
}

static int xennet_start_xmit(struct sk_buff *skb, struct net_device *dev)
{
        unsigned short id;
        struct netfront_info *np = netdev_priv(dev);
        struct netfront_stats *stats = this_cpu_ptr(np->stats);
        struct xen_netif_tx_request *tx;
        char *data = skb->data;
        RING_IDX i;
        grant_ref_t ref;
        unsigned long mfn;
        int notify;
        int slots;
        unsigned int offset = offset_in_page(data);
        unsigned int len = skb_headlen(skb);
        unsigned long flags;

        /* If skb->len is too big for wire format, drop skb and alert
         * user about misconfiguration.
         */
        if (unlikely(skb->len > XEN_NETIF_MAX_TX_SIZE)) {
                net_alert_ratelimited(
                        "xennet: skb->len = %u, too big for wire format\n",
                        skb->len);
                goto drop;
        }

        slots = DIV_ROUND_UP(offset + len, PAGE_SIZE) +
                xennet_count_skb_frag_slots(skb);
        if (unlikely(slots > MAX_SKB_FRAGS + 1)) {
                net_alert_ratelimited(
                        "xennet: skb rides the rocket: %d slots\n", slots);
                goto drop;
        }

        spin_lock_irqsave(&np->tx_lock, flags);

        if (unlikely(!netif_carrier_ok(dev) ||
                     (slots > 1 && !xennet_can_sg(dev)) ||
                     netif_needs_gso(skb, netif_skb_features(skb)))) {
                spin_unlock_irqrestore(&np->tx_lock, flags);
                goto drop;
        }

        i = np->tx.req_prod_pvt;

        id = get_id_from_freelist(&np->tx_skb_freelist, np->tx_skbs);
        np->tx_skbs[id].skb = skb;

        tx = RING_GET_REQUEST(&np->tx, i);

        tx->id   = id;
        ref = gnttab_claim_grant_reference(&np->gref_tx_head);
        BUG_ON((signed short)ref < 0);
        mfn = virt_to_mfn(data);
        gnttab_grant_foreign_access_ref(
                ref, np->xbdev->otherend_id, mfn, GNTMAP_readonly);
        np->grant_tx_page[id] = virt_to_page(data);
        tx->gref = np->grant_tx_ref[id] = ref;
        tx->offset = offset;
        tx->size = len;

        tx->flags = 0;
        if (skb->ip_summed == CHECKSUM_PARTIAL)
                /* local packet? */
                tx->flags |= XEN_NETTXF_csum_blank | XEN_NETTXF_data_validated;
        else if (skb->ip_summed == CHECKSUM_UNNECESSARY)
                /* remote but checksummed. */
                tx->flags |= XEN_NETTXF_data_validated;

        if (skb_shinfo(skb)->gso_size) {
                struct xen_netif_extra_info *gso;

                gso = (struct xen_netif_extra_info *)
                        RING_GET_REQUEST(&np->tx, ++i);

                tx->flags |= XEN_NETTXF_extra_info;

                gso->u.gso.size = skb_shinfo(skb)->gso_size;
                gso->u.gso.type = XEN_NETIF_GSO_TYPE_TCPV4;
                gso->u.gso.pad = 0;
                gso->u.gso.features = 0;

                gso->type = XEN_NETIF_EXTRA_TYPE_GSO;
                gso->flags = 0;
        }

        np->tx.req_prod_pvt = i + 1;

        xennet_make_frags(skb, dev, tx);
        tx->size = skb->len;

        RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(&np->tx, notify);
        if (notify)
                notify_remote_via_irq(np->netdev->irq);

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

        /* Note: It is not safe to access skb after xennet_tx_buf_gc()! */
        xennet_tx_buf_gc(dev);

        if (!netfront_tx_slot_available(np))
                netif_stop_queue(dev);

        spin_unlock_irqrestore(&np->tx_lock, flags);

        return NETDEV_TX_OK;

 drop:
        dev->stats.tx_dropped++;
        dev_kfree_skb(skb);
        return NETDEV_TX_OK;
}

static int xennet_close(struct net_device *dev)
{
        struct netfront_info *np = netdev_priv(dev);
        netif_stop_queue(np->netdev);
        napi_disable(&np->napi);
        return 0;
}

static void xennet_move_rx_slot(struct netfront_info *np, struct sk_buff *skb,
                                grant_ref_t ref)
{
        int new = xennet_rxidx(np->rx.req_prod_pvt);

        BUG_ON(np->rx_skbs[new]);
        np->rx_skbs[new] = skb;
        np->grant_rx_ref[new] = ref;
        RING_GET_REQUEST(&np->rx, np->rx.req_prod_pvt)->id = new;
        RING_GET_REQUEST(&np->rx, np->rx.req_prod_pvt)->gref = ref;
        np->rx.req_prod_pvt++;
}

static int xennet_get_extras(struct netfront_info *np,
                             struct xen_netif_extra_info *extras,
                             RING_IDX rp)

{
        struct xen_netif_extra_info *extra;
        struct device *dev = &np->netdev->dev;
        RING_IDX cons = np->rx.rsp_cons;
        int err = 0;

        do {
                struct sk_buff *skb;
                grant_ref_t ref;

                if (unlikely(cons + 1 == rp)) {
                        if (net_ratelimit())
                                dev_warn(dev, "Missing extra info\n");
                        err = -EBADR;
                        break;
                }

                extra = (struct xen_netif_extra_info *)
                        RING_GET_RESPONSE(&np->rx, ++cons);

                if (unlikely(!extra->type ||
                             extra->type >= XEN_NETIF_EXTRA_TYPE_MAX)) {
                        if (net_ratelimit())
                                dev_warn(dev, "Invalid extra type: %d\n",
                                        extra->type);
                        err = -EINVAL;
                } else {
                        memcpy(&extras[extra->type - 1], extra,
                               sizeof(*extra));
                }

                skb = xennet_get_rx_skb(np, cons);
                ref = xennet_get_rx_ref(np, cons);
                xennet_move_rx_slot(np, skb, ref);
        } while (extra->flags & XEN_NETIF_EXTRA_FLAG_MORE);

        np->rx.rsp_cons = cons;
        return err;
}

static int xennet_get_responses(struct netfront_info *np,
                                struct netfront_rx_info *rinfo, RING_IDX rp,
                                struct sk_buff_head *list)
{
        struct xen_netif_rx_response *rx = &rinfo->rx;
        struct xen_netif_extra_info *extras = rinfo->extras;
        struct device *dev = &np->netdev->dev;
        RING_IDX cons = np->rx.rsp_cons;
        struct sk_buff *skb = xennet_get_rx_skb(np, cons);
        grant_ref_t ref = xennet_get_rx_ref(np, cons);
        int max = MAX_SKB_FRAGS + (rx->status <= RX_COPY_THRESHOLD);
        int slots = 1;
        int err = 0;
        unsigned long ret;

        if (rx->flags & XEN_NETRXF_extra_info) {
                err = xennet_get_extras(np, extras, rp);
                cons = np->rx.rsp_cons;
        }

        for (;;) {
                if (unlikely(rx->status < 0 ||
                             rx->offset + rx->status > PAGE_SIZE)) {
                        if (net_ratelimit())
                                dev_warn(dev, "rx->offset: %x, size: %u\n",
                                         rx->offset, rx->status);
                        xennet_move_rx_slot(np, skb, ref);
                        err = -EINVAL;
                        goto next;
                }

                /*
                 * This definitely indicates a bug, either in this driver or in
                 * the backend driver. In future this should flag the bad
                 * situation to the system controller to reboot the backend.
                 */
                if (ref == GRANT_INVALID_REF) {
                        if (net_ratelimit())
                                dev_warn(dev, "Bad rx response id %d.\n",
                                         rx->id);
                        err = -EINVAL;
                        goto next;
                }

                ret = gnttab_end_foreign_access_ref(ref, 0);
                BUG_ON(!ret);

                gnttab_release_grant_reference(&np->gref_rx_head, ref);

                __skb_queue_tail(list, skb);

next:
                if (!(rx->flags & XEN_NETRXF_more_data))
                        break;

                if (cons + slots == rp) {
                        if (net_ratelimit())
                                dev_warn(dev, "Need more slots\n");
                        err = -ENOENT;
                        break;
                }

                rx = RING_GET_RESPONSE(&np->rx, cons + slots);
                skb = xennet_get_rx_skb(np, cons + slots);
                ref = xennet_get_rx_ref(np, cons + slots);
                slots++;
        }

        if (unlikely(slots > max)) {
                if (net_ratelimit())
                        dev_warn(dev, "Too many slots\n");
                err = -E2BIG;
        }

        if (unlikely(err))
                np->rx.rsp_cons = cons + slots;

        return err;
}

static int xennet_set_skb_gso(struct sk_buff *skb,
                              struct xen_netif_extra_info *gso)
{
        if (!gso->u.gso.size) {
                if (net_ratelimit())
                        printk(KERN_WARNING "GSO size must not be zero.\n");
                return -EINVAL;
        }

        /* Currently only TCPv4 S.O. is supported. */
        if (gso->u.gso.type != XEN_NETIF_GSO_TYPE_TCPV4) {
                if (net_ratelimit())
                        printk(KERN_WARNING "Bad GSO type %d.\n", gso->u.gso.type);
                return -EINVAL;
        }

        skb_shinfo(skb)->gso_size = gso->u.gso.size;
        skb_shinfo(skb)->gso_type = SKB_GSO_TCPV4;

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

        return 0;
}

static RING_IDX xennet_fill_frags(struct netfront_info *np,
                                  struct sk_buff *skb,
                                  struct sk_buff_head *list)
{
        struct skb_shared_info *shinfo = skb_shinfo(skb);
        RING_IDX cons = np->rx.rsp_cons;
        struct sk_buff *nskb;

        while ((nskb = __skb_dequeue(list))) {
                struct xen_netif_rx_response *rx =
                        RING_GET_RESPONSE(&np->rx, ++cons);
                skb_frag_t *nfrag = &skb_shinfo(nskb)->frags[0];

                if (shinfo->nr_frags == MAX_SKB_FRAGS) {
                        unsigned int pull_to = NETFRONT_SKB_CB(skb)->pull_to;

                        BUG_ON(pull_to <= skb_headlen(skb));
                        __pskb_pull_tail(skb, pull_to - skb_headlen(skb));
                }
                BUG_ON(shinfo->nr_frags >= MAX_SKB_FRAGS);

                skb_add_rx_frag(skb, shinfo->nr_frags, skb_frag_page(nfrag),
                                rx->offset, rx->status, PAGE_SIZE);

                skb_shinfo(nskb)->nr_frags = 0;
                kfree_skb(nskb);
        }

        return cons;
}

static int checksum_setup(struct net_device *dev, struct sk_buff *skb)
{
        struct iphdr *iph;
        unsigned char *th;
        int err = -EPROTO;
        int recalculate_partial_csum = 0;

        /*
         * A GSO SKB must be CHECKSUM_PARTIAL. However some buggy
         * peers can fail to set NETRXF_csum_blank when sending a GSO
         * frame. In this case force the SKB to CHECKSUM_PARTIAL and
         * recalculate the partial checksum.
         */
        if (skb->ip_summed != CHECKSUM_PARTIAL && skb_is_gso(skb)) {
                struct netfront_info *np = netdev_priv(dev);
                np->rx_gso_checksum_fixup++;
                skb->ip_summed = CHECKSUM_PARTIAL;
                recalculate_partial_csum = 1;
        }

        /* A non-CHECKSUM_PARTIAL SKB does not require setup. */
        if (skb->ip_summed != CHECKSUM_PARTIAL)
                return 0;

        if (skb->protocol != htons(ETH_P_IP))
                goto out;

        iph = (void *)skb->data;
        th = skb->data + 4 * iph->ihl;
        if (th >= skb_tail_pointer(skb))
                goto out;

        skb->csum_start = th - skb->head;
        switch (iph->protocol) {
        case IPPROTO_TCP:
                skb->csum_offset = offsetof(struct tcphdr, check);

                if (recalculate_partial_csum) {
                        struct tcphdr *tcph = (struct tcphdr *)th;
                        tcph->check = ~csum_tcpudp_magic(iph->saddr, iph->daddr,
                                                         skb->len - iph->ihl*4,
                                                         IPPROTO_TCP, 0);
                }
                break;
        case IPPROTO_UDP:
                skb->csum_offset = offsetof(struct udphdr, check);

                if (recalculate_partial_csum) {
                        struct udphdr *udph = (struct udphdr *)th;
                        udph->check = ~csum_tcpudp_magic(iph->saddr, iph->daddr,
                                                         skb->len - iph->ihl*4,
                                                         IPPROTO_UDP, 0);
                }
                break;
        default:
                if (net_ratelimit())
                        printk(KERN_ERR "Attempting to checksum a non-"
                               "TCP/UDP packet, dropping a protocol"
                               " %d packet", iph->protocol);
                goto out;
        }

        if ((th + skb->csum_offset + 2) > skb_tail_pointer(skb))
                goto out;

        err = 0;

out:
        return err;
}

static int handle_incoming_queue(struct net_device *dev,
                                 struct sk_buff_head *rxq)
{
        struct netfront_info *np = netdev_priv(dev);
        struct netfront_stats *stats = this_cpu_ptr(np->stats);
        int packets_dropped = 0;
        struct sk_buff *skb;

        while ((skb = __skb_dequeue(rxq)) != NULL) {
                int pull_to = NETFRONT_SKB_CB(skb)->pull_to;

                if (pull_to > skb_headlen(skb))
                        __pskb_pull_tail(skb, pull_to - skb_headlen(skb));

                /* Ethernet work: Delayed to here as it peeks the header. */
                skb->protocol = eth_type_trans(skb, dev);

                if (checksum_setup(dev, skb)) {
                        kfree_skb(skb);
                        packets_dropped++;
                        dev->stats.rx_errors++;
                        continue;
                }

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

                /* Pass it up. */
                netif_receive_skb(skb);
        }

        return packets_dropped;
}

static int xennet_poll(struct napi_struct *napi, int budget)
{
        struct netfront_info *np = container_of(napi, struct netfront_info, napi);
        struct net_device *dev = np->netdev;
        struct sk_buff *skb;
        struct netfront_rx_info rinfo;
        struct xen_netif_rx_response *rx = &rinfo.rx;
        struct xen_netif_extra_info *extras = rinfo.extras;
        RING_IDX i, rp;
        int work_done;
        struct sk_buff_head rxq;
        struct sk_buff_head errq;
        struct sk_buff_head tmpq;
        unsigned long flags;
        int err;

        spin_lock(&np->rx_lock);

        skb_queue_head_init(&rxq);
        skb_queue_head_init(&errq);
        skb_queue_head_init(&tmpq);

        rp = np->rx.sring->rsp_prod;
        rmb(); /* Ensure we see queued responses up to 'rp'. */

        i = np->rx.rsp_cons;
        work_done = 0;
        while ((i != rp) && (work_done < budget)) {
                memcpy(rx, RING_GET_RESPONSE(&np->rx, i), sizeof(*rx));
                memset(extras, 0, sizeof(rinfo.extras));

                err = xennet_get_responses(np, &rinfo, rp, &tmpq);

                if (unlikely(err)) {
err:
                        while ((skb = __skb_dequeue(&tmpq)))
                                __skb_queue_tail(&errq, skb);
                        dev->stats.rx_errors++;
                        i = np->rx.rsp_cons;
                        continue;
                }

                skb = __skb_dequeue(&tmpq);

                if (extras[XEN_NETIF_EXTRA_TYPE_GSO - 1].type) {
                        struct xen_netif_extra_info *gso;
                        gso = &extras[XEN_NETIF_EXTRA_TYPE_GSO - 1];

                        if (unlikely(xennet_set_skb_gso(skb, gso))) {
                                __skb_queue_head(&tmpq, skb);
                                np->rx.rsp_cons += skb_queue_len(&tmpq);
                                goto err;
                        }
                }

                NETFRONT_SKB_CB(skb)->pull_to = rx->status;
                if (NETFRONT_SKB_CB(skb)->pull_to > RX_COPY_THRESHOLD)
                        NETFRONT_SKB_CB(skb)->pull_to = RX_COPY_THRESHOLD;

                skb_shinfo(skb)->frags[0].page_offset = rx->offset;
                skb_frag_size_set(&skb_shinfo(skb)->frags[0], rx->status);
                skb->data_len = rx->status;
                skb->len += rx->status;

                i = xennet_fill_frags(np, skb, &tmpq);

                if (rx->flags & XEN_NETRXF_csum_blank)
                        skb->ip_summed = CHECKSUM_PARTIAL;
                else if (rx->flags & XEN_NETRXF_data_validated)
                        skb->ip_summed = CHECKSUM_UNNECESSARY;

                __skb_queue_tail(&rxq, skb);

                np->rx.rsp_cons = ++i;
                work_done++;
        }

        __skb_queue_purge(&errq);

        work_done -= handle_incoming_queue(dev, &rxq);

        /* If we get a callback with very few responses, reduce fill target. */
        /* NB. Note exponential increase, linear decrease. */
        if (((np->rx.req_prod_pvt - np->rx.sring->rsp_prod) >
             ((3*np->rx_target) / 4)) &&
            (--np->rx_target < np->rx_min_target))
                np->rx_target = np->rx_min_target;

        xennet_alloc_rx_buffers(dev);

        if (work_done < budget) {
                int more_to_do = 0;

                local_irq_save(flags);

                RING_FINAL_CHECK_FOR_RESPONSES(&np->rx, more_to_do);
                if (!more_to_do)
                        __napi_complete(napi);

                local_irq_restore(flags);
        }

        spin_unlock(&np->rx_lock);

        return work_done;
}

static int xennet_change_mtu(struct net_device *dev, int mtu)
{
        int max = xennet_can_sg(dev) ?
                XEN_NETIF_MAX_TX_SIZE - MAX_TCP_HEADER : ETH_DATA_LEN;

        if (mtu > max)
                return -EINVAL;
        dev->mtu = mtu;
        return 0;
}

static struct rtnl_link_stats64 *xennet_get_stats64(struct net_device *dev,
                                                    struct rtnl_link_stats64 *tot)
{
        struct netfront_info *np = netdev_priv(dev);
        int cpu;

        for_each_possible_cpu(cpu) {
                struct netfront_stats *stats = per_cpu_ptr(np->stats, cpu);
                u64 rx_packets, rx_bytes, tx_packets, tx_bytes;
                unsigned int start;

                do {
                        start = u64_stats_fetch_begin_bh(&stats->syncp);

                        rx_packets = stats->rx_packets;
                        tx_packets = stats->tx_packets;
                        rx_bytes = stats->rx_bytes;
                        tx_bytes = stats->tx_bytes;
                } while (u64_stats_fetch_retry_bh(&stats->syncp, start));

                tot->rx_packets += rx_packets;
                tot->tx_packets += tx_packets;
                tot->rx_bytes   += rx_bytes;
                tot->tx_bytes   += tx_bytes;
        }

        tot->rx_errors  = dev->stats.rx_errors;
        tot->tx_dropped = dev->stats.tx_dropped;

        return tot;
}

static void xennet_release_tx_bufs(struct netfront_info *np)
{
        struct sk_buff *skb;
        int i;

        for (i = 0; i < NET_TX_RING_SIZE; i++) {
                /* Skip over entries which are actually freelist references */
                if (skb_entry_is_link(&np->tx_skbs[i]))
                        continue;

                skb = np->tx_skbs[i].skb;
                get_page(np->grant_tx_page[i]);
                gnttab_end_foreign_access(np->grant_tx_ref[i],
                                          GNTMAP_readonly,
                                          (unsigned long)page_address(np->grant_tx_page[i]));
                np->grant_tx_page[i] = NULL;
                np->grant_tx_ref[i] = GRANT_INVALID_REF;
                add_id_to_freelist(&np->tx_skb_freelist, np->tx_skbs, i);
                dev_kfree_skb_irq(skb);
        }
}

static void xennet_release_rx_bufs(struct netfront_info *np)
{
        int id, ref;

        spin_lock_bh(&np->rx_lock);

        for (id = 0; id < NET_RX_RING_SIZE; id++) {
                struct sk_buff *skb;
                struct page *page;

                skb = np->rx_skbs[id];
                if (!skb)
                        continue;

                ref = np->grant_rx_ref[id];
                if (ref == GRANT_INVALID_REF)
                        continue;

                page = skb_frag_page(&skb_shinfo(skb)->frags[0]);

                /* gnttab_end_foreign_access() needs a page ref until
                 * foreign access is ended (which may be deferred).
                 */
                get_page(page);
                gnttab_end_foreign_access(ref, 0,
                                          (unsigned long)page_address(page));
                np->grant_rx_ref[id] = GRANT_INVALID_REF;

                kfree_skb(skb);
        }

        spin_unlock_bh(&np->rx_lock);
}

static void xennet_uninit(struct net_device *dev)
{
        struct netfront_info *np = netdev_priv(dev);
        xennet_release_tx_bufs(np);
        xennet_release_rx_bufs(np);
        gnttab_free_grant_references(np->gref_tx_head);
        gnttab_free_grant_references(np->gref_rx_head);
}

static netdev_features_t xennet_fix_features(struct net_device *dev,
        netdev_features_t features)
{
        struct netfront_info *np = netdev_priv(dev);
        int val;

        if (features & NETIF_F_SG) {
                if (xenbus_scanf(XBT_NIL, np->xbdev->otherend, "feature-sg",
                                 "%d", &val) < 0)
                        val = 0;

                if (!val)
                        features &= ~NETIF_F_SG;
        }

        if (features & NETIF_F_TSO) {
                if (xenbus_scanf(XBT_NIL, np->xbdev->otherend,
                                 "feature-gso-tcpv4", "%d", &val) < 0)
                        val = 0;

                if (!val)
                        features &= ~NETIF_F_TSO;
        }

        return features;
}

static int xennet_set_features(struct net_device *dev,
        netdev_features_t features)
{
        if (!(features & NETIF_F_SG) && dev->mtu > ETH_DATA_LEN) {
                netdev_info(dev, "Reducing MTU because no SG offload");
                dev->mtu = ETH_DATA_LEN;
        }

        return 0;
}

static irqreturn_t xennet_interrupt(int irq, void *dev_id)
{
        struct net_device *dev = dev_id;
        struct netfront_info *np = netdev_priv(dev);
        unsigned long flags;

        spin_lock_irqsave(&np->tx_lock, flags);

        if (likely(netif_carrier_ok(dev))) {
                xennet_tx_buf_gc(dev);
                /* Under tx_lock: protects access to rx shared-ring indexes. */
                if (RING_HAS_UNCONSUMED_RESPONSES(&np->rx))
                        napi_schedule(&np->napi);
        }

        spin_unlock_irqrestore(&np->tx_lock, flags);

        return IRQ_HANDLED;
}

#ifdef CONFIG_NET_POLL_CONTROLLER
static void xennet_poll_controller(struct net_device *dev)
{
        xennet_interrupt(0, dev);
}
#endif

static const struct net_device_ops xennet_netdev_ops = {
        .ndo_open            = xennet_open,
        .ndo_uninit          = xennet_uninit,
        .ndo_stop            = xennet_close,
        .ndo_start_xmit      = xennet_start_xmit,
        .ndo_change_mtu      = xennet_change_mtu,
        .ndo_get_stats64     = xennet_get_stats64,
        .ndo_set_mac_address = eth_mac_addr,
        .ndo_validate_addr   = eth_validate_addr,
        .ndo_fix_features    = xennet_fix_features,
        .ndo_set_features    = xennet_set_features,
#ifdef CONFIG_NET_POLL_CONTROLLER
        .ndo_poll_controller = xennet_poll_controller,
#endif
};

static struct net_device *xennet_create_dev(struct xenbus_device *dev)
{
        int i, err;
        struct net_device *netdev;
        struct netfront_info *np;

        netdev = alloc_etherdev(sizeof(struct netfront_info));
        if (!netdev)
                return ERR_PTR(-ENOMEM);

        np                   = netdev_priv(netdev);
        np->xbdev            = dev;

        spin_lock_init(&np->tx_lock);
        spin_lock_init(&np->rx_lock);

        skb_queue_head_init(&np->rx_batch);
        np->rx_target     = RX_DFL_MIN_TARGET;
        np->rx_min_target = RX_DFL_MIN_TARGET;
        np->rx_max_target = RX_MAX_TARGET;

        init_timer(&np->rx_refill_timer);
        np->rx_refill_timer.data = (unsigned long)netdev;
        np->rx_refill_timer.function = rx_refill_timeout;

        err = -ENOMEM;
        np->stats = alloc_percpu(struct netfront_stats);
        if (np->stats == NULL)
                goto exit;

        /* Initialise tx_skbs as a free chain containing every entry. */
        np->tx_skb_freelist = 0;
        for (i = 0; i < NET_TX_RING_SIZE; i++) {
                skb_entry_set_link(&np->tx_skbs[i], i+1);
                np->grant_tx_ref[i] = GRANT_INVALID_REF;
        }

        /* Clear out rx_skbs */
        for (i = 0; i < NET_RX_RING_SIZE; i++) {
                np->rx_skbs[i] = NULL;
                np->grant_rx_ref[i] = GRANT_INVALID_REF;
                np->grant_tx_page[i] = NULL;
        }

        /* A grant for every tx ring slot */
        if (gnttab_alloc_grant_references(TX_MAX_TARGET,
                                          &np->gref_tx_head) < 0) {
                printk(KERN_ALERT "#### netfront can't alloc tx grant refs\n");
                err = -ENOMEM;
                goto exit_free_stats;
        }
        /* A grant for every rx ring slot */
        if (gnttab_alloc_grant_references(RX_MAX_TARGET,
                                          &np->gref_rx_head) < 0) {
                printk(KERN_ALERT "#### netfront can't alloc rx grant refs\n");
                err = -ENOMEM;
                goto exit_free_tx;
        }

        netdev->netdev_ops      = &xennet_netdev_ops;

        netif_napi_add(netdev, &np->napi, xennet_poll, 64);
        netdev->features        = NETIF_F_IP_CSUM | NETIF_F_RXCSUM |
                                  NETIF_F_GSO_ROBUST;
        netdev->hw_features     = NETIF_F_IP_CSUM | NETIF_F_SG | NETIF_F_TSO;

        /*
         * Assume that all hw features are available for now. This set
         * will be adjusted by the call to netdev_update_features() in
         * xennet_connect() which is the earliest point where we can
         * negotiate with the backend regarding supported features.
         */
        netdev->features |= netdev->hw_features;

        SET_ETHTOOL_OPS(netdev, &xennet_ethtool_ops);
        SET_NETDEV_DEV(netdev, &dev->dev);

        netif_set_gso_max_size(netdev, XEN_NETIF_MAX_TX_SIZE - MAX_TCP_HEADER);

        np->netdev = netdev;

        netif_carrier_off(netdev);

        return netdev;

 exit_free_tx:
        gnttab_free_grant_references(np->gref_tx_head);
 exit_free_stats:
        free_percpu(np->stats);
 exit:
        free_netdev(netdev);
        return ERR_PTR(err);
}

/**
 * Entry point to this code when a new device is created.  Allocate the basic
 * structures and the ring buffers for communication with the backend, and
 * inform the backend of the appropriate details for those.
 */
static int netfront_probe(struct xenbus_device *dev,
                          const struct xenbus_device_id *id)
{
        int err;
        struct net_device *netdev;
        struct netfront_info *info;

        netdev = xennet_create_dev(dev);
        if (IS_ERR(netdev)) {
                err = PTR_ERR(netdev);
                xenbus_dev_fatal(dev, err, "creating netdev");
                return err;
        }

        info = netdev_priv(netdev);
        dev_set_drvdata(&dev->dev, info);

        err = register_netdev(info->netdev);
        if (err) {
                printk(KERN_WARNING "%s: register_netdev err=%d\n",
                       __func__, err);
                goto fail;
        }

        err = xennet_sysfs_addif(info->netdev);
        if (err) {
                unregister_netdev(info->netdev);
                printk(KERN_WARNING "%s: add sysfs failed err=%d\n",
                       __func__, err);
                goto fail;
        }

        return 0;

 fail:
        free_netdev(netdev);
        dev_set_drvdata(&dev->dev, NULL);
        return err;
}

static void xennet_end_access(int ref, void *page)
{
        /* This frees the page as a side-effect */
        if (ref != GRANT_INVALID_REF)
                gnttab_end_foreign_access(ref, 0, (unsigned long)page);
}

static void xennet_disconnect_backend(struct netfront_info *info)
{
        /* Stop old i/f to prevent errors whilst we rebuild the state. */
        spin_lock_bh(&info->rx_lock);
        spin_lock_irq(&info->tx_lock);
        netif_carrier_off(info->netdev);
        spin_unlock_irq(&info->tx_lock);
        spin_unlock_bh(&info->rx_lock);

        if (info->netdev->irq)
                unbind_from_irqhandler(info->netdev->irq, info->netdev);
        info->evtchn = info->netdev->irq = 0;

        /* End access and free the pages */
        xennet_end_access(info->tx_ring_ref, info->tx.sring);
        xennet_end_access(info->rx_ring_ref, info->rx.sring);

        info->tx_ring_ref = GRANT_INVALID_REF;
        info->rx_ring_ref = GRANT_INVALID_REF;
        info->tx.sring = NULL;
        info->rx.sring = NULL;
}

/**
 * We are reconnecting to the backend, due to a suspend/resume, or a backend
 * driver restart.  We tear down our netif structure and recreate it, but
 * leave the device-layer structures intact so that this is transparent to the
 * rest of the kernel.
 */
static int netfront_resume(struct xenbus_device *dev)
{
        struct netfront_info *info = dev_get_drvdata(&dev->dev);

        dev_dbg(&dev->dev, "%s\n", dev->nodename);

        xennet_disconnect_backend(info);
        return 0;
}

static int xen_net_read_mac(struct xenbus_device *dev, u8 mac[])
{
        char *s, *e, *macstr;
        int i;

        macstr = s = xenbus_read(XBT_NIL, dev->nodename, "mac", NULL);
        if (IS_ERR(macstr))
                return PTR_ERR(macstr);

        for (i = 0; i < ETH_ALEN; i++) {
                mac[i] = simple_strtoul(s, &e, 16);
                if ((s == e) || (*e != ((i == ETH_ALEN-1) ? '\0' : ':'))) {
                        kfree(macstr);
                        return -ENOENT;
                }
                s = e+1;
        }

        kfree(macstr);
        return 0;
}

static int setup_netfront(struct xenbus_device *dev, struct netfront_info *info)
{
        struct xen_netif_tx_sring *txs;
        struct xen_netif_rx_sring *rxs;
        int err;
        struct net_device *netdev = info->netdev;

        info->tx_ring_ref = GRANT_INVALID_REF;
        info->rx_ring_ref = GRANT_INVALID_REF;
        info->rx.sring = NULL;
        info->tx.sring = NULL;
        netdev->irq = 0;

        err = xen_net_read_mac(dev, netdev->dev_addr);
        if (err) {
                xenbus_dev_fatal(dev, err, "parsing %s/mac", dev->nodename);
                goto fail;
        }

        txs = (struct xen_netif_tx_sring *)get_zeroed_page(GFP_NOIO | __GFP_HIGH);
        if (!txs) {
                err = -ENOMEM;
                xenbus_dev_fatal(dev, err, "allocating tx ring page");
                goto fail;
        }
        SHARED_RING_INIT(txs);
        FRONT_RING_INIT(&info->tx, txs, PAGE_SIZE);

        err = xenbus_grant_ring(dev, virt_to_mfn(txs));
        if (err < 0) {
                free_page((unsigned long)txs);
                goto fail;
        }

        info->tx_ring_ref = err;
        rxs = (struct xen_netif_rx_sring *)get_zeroed_page(GFP_NOIO | __GFP_HIGH);
        if (!rxs) {
                err = -ENOMEM;
                xenbus_dev_fatal(dev, err, "allocating rx ring page");
                goto fail;
        }
        SHARED_RING_INIT(rxs);
        FRONT_RING_INIT(&info->rx, rxs, PAGE_SIZE);

        err = xenbus_grant_ring(dev, virt_to_mfn(rxs));
        if (err < 0) {
                free_page((unsigned long)rxs);
                goto fail;
        }
        info->rx_ring_ref = err;

        err = xenbus_alloc_evtchn(dev, &info->evtchn);
        if (err)
                goto fail;

        err = bind_evtchn_to_irqhandler(info->evtchn, xennet_interrupt,
                                        0, netdev->name, netdev);
        if (err < 0)
                goto fail;
        netdev->irq = err;
        return 0;

 fail:
        return err;
}

/* Common code used when first setting up, and when resuming. */
static int talk_to_netback(struct xenbus_device *dev,
                           struct netfront_info *info)
{
        const char *message;
        struct xenbus_transaction xbt;
        int err;

        /* Create shared ring, alloc event channel. */
        err = setup_netfront(dev, info);
        if (err)
                goto out;

again:
        err = xenbus_transaction_start(&xbt);
        if (err) {
                xenbus_dev_fatal(dev, err, "starting transaction");
                goto destroy_ring;
        }

        err = xenbus_printf(xbt, dev->nodename, "tx-ring-ref", "%u",
                            info->tx_ring_ref);
        if (err) {
                message = "writing tx ring-ref";
                goto abort_transaction;
        }
        err = xenbus_printf(xbt, dev->nodename, "rx-ring-ref", "%u",
                            info->rx_ring_ref);
        if (err) {
                message = "writing rx ring-ref";
                goto abort_transaction;
        }
        err = xenbus_printf(xbt, dev->nodename,
                            "event-channel", "%u", info->evtchn);
        if (err) {
                message = "writing event-channel";
                goto abort_transaction;
        }

        err = xenbus_printf(xbt, dev->nodename, "request-rx-copy", "%u",
                            1);
        if (err) {
                message = "writing request-rx-copy";
                goto abort_transaction;
        }

        err = xenbus_printf(xbt, dev->nodename, "feature-rx-notify", "%d", 1);
        if (err) {
                message = "writing feature-rx-notify";
                goto abort_transaction;
        }

        err = xenbus_printf(xbt, dev->nodename, "feature-sg", "%d", 1);
        if (err) {
                message = "writing feature-sg";
                goto abort_transaction;
        }

        err = xenbus_printf(xbt, dev->nodename, "feature-gso-tcpv4", "%d", 1);
        if (err) {
                message = "writing feature-gso-tcpv4";
                goto abort_transaction;
        }

        err = xenbus_transaction_end(xbt, 0);
        if (err) {
                if (err == -EAGAIN)
                        goto again;
                xenbus_dev_fatal(dev, err, "completing transaction");
                goto destroy_ring;
        }

        return 0;

 abort_transaction:
        xenbus_transaction_end(xbt, 1);
        xenbus_dev_fatal(dev, err, "%s", message);
 destroy_ring:
        xennet_disconnect_backend(info);
 out:
        return err;
}

static int xennet_connect(struct net_device *dev)
{
        struct netfront_info *np = netdev_priv(dev);
        int i, requeue_idx, err;
        struct sk_buff *skb;
        grant_ref_t ref;
        struct xen_netif_rx_request *req;
        unsigned int feature_rx_copy;

        err = xenbus_scanf(XBT_NIL, np->xbdev->otherend,
                           "feature-rx-copy", "%u", &feature_rx_copy);
        if (err != 1)
                feature_rx_copy = 0;

        if (!feature_rx_copy) {
                dev_info(&dev->dev,
                         "backend does not support copying receive path\n");
                return -ENODEV;
        }

        err = talk_to_netback(np->xbdev, np);
        if (err)
                return err;

        rtnl_lock();
        netdev_update_features(dev);
        rtnl_unlock();

        spin_lock_bh(&np->rx_lock);
        spin_lock_irq(&np->tx_lock);

        /* Step 1: Discard all pending TX packet fragments. */
        xennet_release_tx_bufs(np);

        /* Step 2: Rebuild the RX buffer freelist and the RX ring itself. */
        for (requeue_idx = 0, i = 0; i < NET_RX_RING_SIZE; i++) {
                skb_frag_t *frag;
                const struct page *page;
                if (!np->rx_skbs[i])
                        continue;

                skb = np->rx_skbs[requeue_idx] = xennet_get_rx_skb(np, i);
                ref = np->grant_rx_ref[requeue_idx] = xennet_get_rx_ref(np, i);
                req = RING_GET_REQUEST(&np->rx, requeue_idx);

                frag = &skb_shinfo(skb)->frags[0];
                page = skb_frag_page(frag);
                gnttab_grant_foreign_access_ref(
                        ref, np->xbdev->otherend_id,
                        pfn_to_mfn(page_to_pfn(page)),
                        0);
                req->gref = ref;
                req->id   = requeue_idx;

                requeue_idx++;
        }

        np->rx.req_prod_pvt = requeue_idx;

        /*
         * Step 3: All public and private state should now be sane.  Get
         * ready to start sending and receiving packets and give the driver
         * domain a kick because we've probably just requeued some
         * packets.
         */
        netif_carrier_on(np->netdev);
        notify_remote_via_irq(np->netdev->irq);
        xennet_tx_buf_gc(dev);
        xennet_alloc_rx_buffers(dev);

        spin_unlock_irq(&np->tx_lock);
        spin_unlock_bh(&np->rx_lock);

        return 0;
}

/**
 * Callback received when the backend's state changes.
 */
static void netback_changed(struct xenbus_device *dev,
                            enum xenbus_state backend_state)
{
        struct netfront_info *np = dev_get_drvdata(&dev->dev);
        struct net_device *netdev = np->netdev;

        dev_dbg(&dev->dev, "%s\n", xenbus_strstate(backend_state));

        switch (backend_state) {
        case XenbusStateInitialising:
        case XenbusStateInitialised:
        case XenbusStateReconfiguring:
        case XenbusStateReconfigured:
        case XenbusStateUnknown:
        case XenbusStateClosed:
                break;

        case XenbusStateInitWait:
                if (dev->state != XenbusStateInitialising)
                        break;
                if (xennet_connect(netdev) != 0)
                        break;
                xenbus_switch_state(dev, XenbusStateConnected);
                break;

        case XenbusStateConnected:
                netdev_notify_peers(netdev);
                break;

        case XenbusStateClosing:
                xenbus_frontend_closed(dev);
                break;
        }
}

static const struct xennet_stat {
        char name[ETH_GSTRING_LEN];
        u16 offset;
} xennet_stats[] = {
        {
                "rx_gso_checksum_fixup",
                offsetof(struct netfront_info, rx_gso_checksum_fixup)
        },
};

static int xennet_get_sset_count(struct net_device *dev, int string_set)
{
        switch (string_set) {
        case ETH_SS_STATS:
                return ARRAY_SIZE(xennet_stats);
        default:
                return -EINVAL;
        }
}

static void xennet_get_ethtool_stats(struct net_device *dev,
                                     struct ethtool_stats *stats, u64 * data)
{
        void *np = netdev_priv(dev);
        int i;

        for (i = 0; i < ARRAY_SIZE(xennet_stats); i++)
                data[i] = *(unsigned long *)(np + xennet_stats[i].offset);
}

static void xennet_get_strings(struct net_device *dev, u32 stringset, u8 * data)
{
        int i;

        switch (stringset) {
        case ETH_SS_STATS:
                for (i = 0; i < ARRAY_SIZE(xennet_stats); i++)
                        memcpy(data + i * ETH_GSTRING_LEN,
                               xennet_stats[i].name, ETH_GSTRING_LEN);
                break;
        }
}

static const struct ethtool_ops xennet_ethtool_ops =
{
        .get_link = ethtool_op_get_link,

        .get_sset_count = xennet_get_sset_count,
        .get_ethtool_stats = xennet_get_ethtool_stats,
        .get_strings = xennet_get_strings,
};

#ifdef CONFIG_SYSFS
static ssize_t show_rxbuf_min(struct device *dev,
                              struct device_attribute *attr, char *buf)
{
        struct net_device *netdev = to_net_dev(dev);
        struct netfront_info *info = netdev_priv(netdev);

        return sprintf(buf, "%u\n", info->rx_min_target);
}

static ssize_t store_rxbuf_min(struct device *dev,
                               struct device_attribute *attr,
                               const char *buf, size_t len)
{
        struct net_device *netdev = to_net_dev(dev);
        struct netfront_info *np = netdev_priv(netdev);
        char *endp;
        unsigned long target;

        if (!capable(CAP_NET_ADMIN))
                return -EPERM;

        target = simple_strtoul(buf, &endp, 0);
        if (endp == buf)
                return -EBADMSG;

        if (target < RX_MIN_TARGET)
                target = RX_MIN_TARGET;
        if (target > RX_MAX_TARGET)
                target = RX_MAX_TARGET;

        spin_lock_bh(&np->rx_lock);
        if (target > np->rx_max_target)
                np->rx_max_target = target;
        np->rx_min_target = target;
        if (target > np->rx_target)
                np->rx_target = target;

        xennet_alloc_rx_buffers(netdev);

        spin_unlock_bh(&np->rx_lock);
        return len;
}

static ssize_t show_rxbuf_max(struct device *dev,
                              struct device_attribute *attr, char *buf)
{
        struct net_device *netdev = to_net_dev(dev);
        struct netfront_info *info = netdev_priv(netdev);

        return sprintf(buf, "%u\n", info->rx_max_target);
}

static ssize_t store_rxbuf_max(struct device *dev,
                               struct device_attribute *attr,
                               const char *buf, size_t len)
{
        struct net_device *netdev = to_net_dev(dev);
        struct netfront_info *np = netdev_priv(netdev);
        char *endp;
        unsigned long target;

        if (!capable(CAP_NET_ADMIN))
                return -EPERM;

        target = simple_strtoul(buf, &endp, 0);
        if (endp == buf)
                return -EBADMSG;

        if (target < RX_MIN_TARGET)
                target = RX_MIN_TARGET;
        if (target > RX_MAX_TARGET)
                target = RX_MAX_TARGET;

        spin_lock_bh(&np->rx_lock);
        if (target < np->rx_min_target)
                np->rx_min_target = target;
        np->rx_max_target = target;
        if (target < np->rx_target)
                np->rx_target = target;

        xennet_alloc_rx_buffers(netdev);

        spin_unlock_bh(&np->rx_lock);
        return len;
}

static ssize_t show_rxbuf_cur(struct device *dev,
                              struct device_attribute *attr, char *buf)
{
        struct net_device *netdev = to_net_dev(dev);
        struct netfront_info *info = netdev_priv(netdev);

        return sprintf(buf, "%u\n", info->rx_target);
}

static struct device_attribute xennet_attrs[] = {
        __ATTR(rxbuf_min, S_IRUGO|S_IWUSR, show_rxbuf_min, store_rxbuf_min),
        __ATTR(rxbuf_max, S_IRUGO|S_IWUSR, show_rxbuf_max, store_rxbuf_max),
        __ATTR(rxbuf_cur, S_IRUGO, show_rxbuf_cur, NULL),
};

static int xennet_sysfs_addif(struct net_device *netdev)
{
        int i;
        int err;

        for (i = 0; i < ARRAY_SIZE(xennet_attrs); i++) {
                err = device_create_file(&netdev->dev,
                                           &xennet_attrs[i]);
                if (err)
                        goto fail;
        }
        return 0;

 fail:
        while (--i >= 0)
                device_remove_file(&netdev->dev, &xennet_attrs[i]);
        return err;
}

static void xennet_sysfs_delif(struct net_device *netdev)
{
        int i;

        for (i = 0; i < ARRAY_SIZE(xennet_attrs); i++)
                device_remove_file(&netdev->dev, &xennet_attrs[i]);
}

#endif /* CONFIG_SYSFS */

static const struct xenbus_device_id netfront_ids[] = {
        { "vif" },
        { "" }
};


static int xennet_remove(struct xenbus_device *dev)
{
        struct netfront_info *info = dev_get_drvdata(&dev->dev);

        dev_dbg(&dev->dev, "%s\n", dev->nodename);

        xennet_disconnect_backend(info);

        xennet_sysfs_delif(info->netdev);

        unregister_netdev(info->netdev);

        del_timer_sync(&info->rx_refill_timer);

        free_percpu(info->stats);

        free_netdev(info->netdev);

        return 0;
}

static DEFINE_XENBUS_DRIVER(netfront, ,
        .probe = netfront_probe,
        .remove = xennet_remove,
        .resume = netfront_resume,
        .otherend_changed = netback_changed,
);

static int __init netif_init(void)
{
        if (!xen_domain())
                return -ENODEV;

        if (xen_hvm_domain() && !xen_platform_pci_unplug)
                return -ENODEV;

        printk(KERN_INFO "Initialising Xen virtual ethernet driver.\n");

        return xenbus_register_frontend(&netfront_driver);
}
module_init(netif_init);


static void __exit netif_exit(void)
{
        xenbus_unregister_driver(&netfront_driver);
}
module_exit(netif_exit);

MODULE_DESCRIPTION("Xen virtual network device frontend");
MODULE_LICENSE("GPL");
MODULE_ALIAS("xen:vif");
MODULE_ALIAS("xennet");