/*
   * 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.
   */

  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

  #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 <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>

  /* Module parameters */

  #define MAX_QUEUES_DEFAULT 8

  static unsigned int xennet_max_queues;
  module_param_named(max_queues, xennet_max_queues, uint, 0644);
  MODULE_PARM_DESC(max_queues,
  		 "Maximum number of queues per virtual interface");

  #define XENNET_TIMEOUT  (5 * HZ)

  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, XEN_PAGE_SIZE)
  #define NET_RX_RING_SIZE __CONST_RING_SIZE(xen_netif_rx, XEN_PAGE_SIZE)

  
  /* Minimum number of Rx slots (includes slot for GSO metadata). */
  #define NET_RX_SLOTS_MIN (XEN_NETIF_NR_SLOTS_MIN + 1)

  /* Queue name is interface name with "-qNNN" appended */
  #define QUEUE_NAME_SIZE (IFNAMSIZ + 6)
  
  /* IRQ name is queue name with "-tx" or "-rx" appended */
  #define IRQ_NAME_SIZE (QUEUE_NAME_SIZE + 3)

  static DECLARE_WAIT_QUEUE_HEAD(module_wq);

  struct netfront_stats {

  	u64			packets;
  	u64			bytes;

  	struct u64_stats_sync	syncp;
  };

  struct netfront_info;
  
  struct netfront_queue {
  	unsigned int id; /* Queue ID, 0-based */
  	char name[QUEUE_NAME_SIZE]; /* DEVNAME-qN */
  	struct netfront_info *info;

  	struct napi_struct napi;

  	/* Split event channels support, tx_* == rx_* when using
  	 * single event channel.
  	 */
  	unsigned int tx_evtchn, rx_evtchn;
  	unsigned int tx_irq, rx_irq;
  	/* Only used when split event channels support is enabled */

  	char tx_irq_name[IRQ_NAME_SIZE]; /* DEVNAME-qN-tx */
  	char rx_irq_name[IRQ_NAME_SIZE]; /* DEVNAME-qN-rx */

  	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;

  	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];

  };
  
  struct netfront_info {
  	struct list_head list;
  	struct net_device *netdev;
  
  	struct xenbus_device *xbdev;
  
  	/* Multi-queue support */
  	struct netfront_queue *queues;

  
  	/* Statistics */

  	struct netfront_stats __percpu *rx_stats;
  	struct netfront_stats __percpu *tx_stats;

  	atomic_t 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_queue *queue,

  					 RING_IDX ri)
  {
  	int i = xennet_rxidx(ri);

  	struct sk_buff *skb = queue->rx_skbs[i];
  	queue->rx_skbs[i] = NULL;

  	return skb;
  }

  static grant_ref_t xennet_get_rx_ref(struct netfront_queue *queue,

  					    RING_IDX ri)
  {
  	int i = xennet_rxidx(ri);

  	grant_ref_t ref = queue->grant_rx_ref[i];
  	queue->grant_rx_ref[i] = GRANT_INVALID_REF;

  	return ref;
  }
  
  #ifdef CONFIG_SYSFS

  static const struct attribute_group xennet_dev_group;

  #endif

  static bool xennet_can_sg(struct net_device *dev)

  {

  	return dev->features & NETIF_F_SG;

  }

  static void rx_refill_timeout(struct timer_list *t)

  {

  	struct netfront_queue *queue = from_timer(queue, t, rx_refill_timer);

  	napi_schedule(&queue->napi);

  }

  static int netfront_tx_slot_available(struct netfront_queue *queue)

  {

  	return (queue->tx.req_prod_pvt - queue->tx.rsp_cons) <

  		(NET_TX_RING_SIZE - XEN_NETIF_NR_SLOTS_MIN - 1);

  }

  static void xennet_maybe_wake_tx(struct netfront_queue *queue)

  {

  	struct net_device *dev = queue->info->netdev;
  	struct netdev_queue *dev_queue = netdev_get_tx_queue(dev, queue->id);

  	if (unlikely(netif_tx_queue_stopped(dev_queue)) &&
  	    netfront_tx_slot_available(queue) &&

  	    likely(netif_running(dev)))

  		netif_tx_wake_queue(netdev_get_tx_queue(dev, queue->id));

  }

  
  static struct sk_buff *xennet_alloc_one_rx_buffer(struct netfront_queue *queue)

  {

  	struct sk_buff *skb;
  	struct page *page;

  	skb = __netdev_alloc_skb(queue->info->netdev,
  				 RX_COPY_THRESHOLD + NET_IP_ALIGN,
  				 GFP_ATOMIC | __GFP_NOWARN);
  	if (unlikely(!skb))
  		return NULL;

  	page = alloc_page(GFP_ATOMIC | __GFP_NOWARN);
  	if (!page) {
  		kfree_skb(skb);
  		return NULL;

  	}

  	skb_add_rx_frag(skb, 0, page, 0, 0, PAGE_SIZE);
  
  	/* Align ip header to a 16 bytes boundary */
  	skb_reserve(skb, NET_IP_ALIGN);
  	skb->dev = queue->info->netdev;
  
  	return skb;
  }

  
  static void xennet_alloc_rx_buffers(struct netfront_queue *queue)
  {
  	RING_IDX req_prod = queue->rx.req_prod_pvt;
  	int notify;

  	int err = 0;

  
  	if (unlikely(!netif_carrier_ok(queue->info->netdev)))

  		return;

  	for (req_prod = queue->rx.req_prod_pvt;
  	     req_prod - queue->rx.rsp_cons < NET_RX_RING_SIZE;
  	     req_prod++) {
  		struct sk_buff *skb;
  		unsigned short id;
  		grant_ref_t ref;

  		struct page *page;

  		struct xen_netif_rx_request *req;

  		skb = xennet_alloc_one_rx_buffer(queue);

  		if (!skb) {
  			err = -ENOMEM;

  			break;

  		}

  		id = xennet_rxidx(req_prod);

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

  		ref = gnttab_claim_grant_reference(&queue->gref_rx_head);

  		WARN_ON_ONCE(IS_ERR_VALUE((unsigned long)(int)ref));

  		queue->grant_rx_ref[id] = ref;

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

  		req = RING_GET_REQUEST(&queue->rx, req_prod);

  		gnttab_page_grant_foreign_access_ref_one(ref,
  							 queue->info->xbdev->otherend_id,
  							 page,
  							 0);

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

  	queue->rx.req_prod_pvt = req_prod;

  	/* Try again later if there are not enough requests or skb allocation
  	 * failed.
  	 * Enough requests is quantified as the sum of newly created slots and
  	 * the unconsumed slots at the backend.
  	 */
  	if (req_prod - queue->rx.rsp_cons < NET_RX_SLOTS_MIN ||
  	    unlikely(err)) {

  		mod_timer(&queue->rx_refill_timer, jiffies + (HZ/10));
  		return;
  	}

  	RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(&queue->rx, notify);

  	if (notify)

  		notify_remote_via_irq(queue->rx_irq);

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

  	unsigned int num_queues = dev->real_num_tx_queues;
  	unsigned int i = 0;
  	struct netfront_queue *queue = NULL;

  	if (!np->queues)
  		return -ENODEV;

  	for (i = 0; i < num_queues; ++i) {
  		queue = &np->queues[i];
  		napi_enable(&queue->napi);
  
  		spin_lock_bh(&queue->rx_lock);
  		if (netif_carrier_ok(dev)) {
  			xennet_alloc_rx_buffers(queue);
  			queue->rx.sring->rsp_event = queue->rx.rsp_cons + 1;
  			if (RING_HAS_UNCONSUMED_RESPONSES(&queue->rx))
  				napi_schedule(&queue->napi);
  		}
  		spin_unlock_bh(&queue->rx_lock);

  	}

  	netif_tx_start_all_queues(dev);

  
  	return 0;
  }

  static void xennet_tx_buf_gc(struct netfront_queue *queue)

  {
  	RING_IDX cons, prod;
  	unsigned short id;

  	struct sk_buff *skb;

  	bool more_to_do;

  	BUG_ON(!netif_carrier_ok(queue->info->netdev));

  
  	do {

  		prod = queue->tx.sring->rsp_prod;

  		rmb(); /* Ensure we see responses up to 'rp'. */

  		for (cons = queue->tx.rsp_cons; cons != prod; cons++) {

  			struct xen_netif_tx_response *txrsp;

  			txrsp = RING_GET_RESPONSE(&queue->tx, cons);

  			if (txrsp->status == XEN_NETIF_RSP_NULL)

  				continue;
  
  			id  = txrsp->id;

  			skb = queue->tx_skbs[id].skb;

  			if (unlikely(gnttab_query_foreign_access(

  				queue->grant_tx_ref[id]) != 0)) {

  				pr_alert("%s: warning -- grant still in use by backend domain
  ",
  					 __func__);

  				BUG();
  			}
  			gnttab_end_foreign_access_ref(

  				queue->grant_tx_ref[id], GNTMAP_readonly);

  			gnttab_release_grant_reference(

  				&queue->gref_tx_head, queue->grant_tx_ref[id]);
  			queue->grant_tx_ref[id] = GRANT_INVALID_REF;
  			queue->grant_tx_page[id] = NULL;
  			add_id_to_freelist(&queue->tx_skb_freelist, queue->tx_skbs, id);

  			dev_kfree_skb_irq(skb);
  		}

  		queue->tx.rsp_cons = prod;

  		RING_FINAL_CHECK_FOR_RESPONSES(&queue->tx, more_to_do);
  	} while (more_to_do);

  	xennet_maybe_wake_tx(queue);

  }

  struct xennet_gnttab_make_txreq {
  	struct netfront_queue *queue;
  	struct sk_buff *skb;
  	struct page *page;
  	struct xen_netif_tx_request *tx; /* Last request */
  	unsigned int size;
  };
  
  static void xennet_tx_setup_grant(unsigned long gfn, unsigned int offset,
  				  unsigned int len, void *data)

  {

  	struct xennet_gnttab_make_txreq *info = data;

  	unsigned int id;

  	struct xen_netif_tx_request *tx;

  	grant_ref_t ref;

  	/* convenient aliases */
  	struct page *page = info->page;
  	struct netfront_queue *queue = info->queue;
  	struct sk_buff *skb = info->skb;

  	id = get_id_from_freelist(&queue->tx_skb_freelist, queue->tx_skbs);
  	tx = RING_GET_REQUEST(&queue->tx, queue->tx.req_prod_pvt++);
  	ref = gnttab_claim_grant_reference(&queue->gref_tx_head);

  	WARN_ON_ONCE(IS_ERR_VALUE((unsigned long)(int)ref));

  	gnttab_grant_foreign_access_ref(ref, queue->info->xbdev->otherend_id,
  					gfn, GNTMAP_readonly);

  	queue->tx_skbs[id].skb = skb;
  	queue->grant_tx_page[id] = page;
  	queue->grant_tx_ref[id] = ref;

  	tx->id = id;
  	tx->gref = ref;
  	tx->offset = offset;
  	tx->size = len;
  	tx->flags = 0;

  	info->tx = tx;
  	info->size += tx->size;
  }
  
  static struct xen_netif_tx_request *xennet_make_first_txreq(
  	struct netfront_queue *queue, struct sk_buff *skb,
  	struct page *page, unsigned int offset, unsigned int len)
  {
  	struct xennet_gnttab_make_txreq info = {
  		.queue = queue,
  		.skb = skb,
  		.page = page,
  		.size = 0,
  	};
  
  	gnttab_for_one_grant(page, offset, len, xennet_tx_setup_grant, &info);
  
  	return info.tx;
  }
  
  static void xennet_make_one_txreq(unsigned long gfn, unsigned int offset,
  				  unsigned int len, void *data)
  {
  	struct xennet_gnttab_make_txreq *info = data;
  
  	info->tx->flags |= XEN_NETTXF_more_data;
  	skb_get(info->skb);
  	xennet_tx_setup_grant(gfn, offset, len, data);

  }

  static struct xen_netif_tx_request *xennet_make_txreqs(
  	struct netfront_queue *queue, struct xen_netif_tx_request *tx,
  	struct sk_buff *skb, struct page *page,
  	unsigned int offset, unsigned int len)
  {

  	struct xennet_gnttab_make_txreq info = {
  		.queue = queue,
  		.skb = skb,
  		.tx = tx,
  	};

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

  	while (len) {

  		info.page = page;
  		info.size = 0;
  
  		gnttab_foreach_grant_in_range(page, offset, len,
  					      xennet_make_one_txreq,
  					      &info);

  		page++;
  		offset = 0;

  		len -= info.size;

  	}

  	return info.tx;

  }

  /*

   * Count how many ring slots are required to send this skb. Each frag
   * might be a compound page.

   */

  static int xennet_count_skb_slots(struct sk_buff *skb)

  {
  	int i, frags = skb_shinfo(skb)->nr_frags;

  	int slots;

  	slots = gnttab_count_grant(offset_in_page(skb->data),
  				   skb_headlen(skb));

  
  	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 = skb_frag_off(frag);

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

  		slots += gnttab_count_grant(offset, size);

  	}

  	return slots;

  }

  static u16 xennet_select_queue(struct net_device *dev, struct sk_buff *skb,

  			       struct net_device *sb_dev)

  {

  	unsigned int num_queues = dev->real_num_tx_queues;
  	u32 hash;
  	u16 queue_idx;
  
  	/* First, check if there is only one queue */
  	if (num_queues == 1) {
  		queue_idx = 0;
  	} else {
  		hash = skb_get_hash(skb);
  		queue_idx = hash % num_queues;
  	}
  
  	return queue_idx;

  }

  #define MAX_XEN_SKB_FRAGS (65536 / XEN_PAGE_SIZE + 1)

  static netdev_tx_t xennet_start_xmit(struct sk_buff *skb, struct net_device *dev)

  {

  	struct netfront_info *np = netdev_priv(dev);

  	struct netfront_stats *tx_stats = this_cpu_ptr(np->tx_stats);

  	struct xen_netif_tx_request *tx, *first_tx;
  	unsigned int i;

  	int notify;

  	int slots;

  	struct page *page;
  	unsigned int offset;
  	unsigned int len;

  	unsigned long flags;

  	struct netfront_queue *queue = NULL;
  	unsigned int num_queues = dev->real_num_tx_queues;
  	u16 queue_index;

  	struct sk_buff *nskb;

  
  	/* Drop the packet if no queues are set up */
  	if (num_queues < 1)
  		goto drop;
  	/* Determine which queue to transmit this SKB on */
  	queue_index = skb_get_queue_mapping(skb);
  	queue = &np->queues[queue_index];

  	/* 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
  ",
  			skb->len);
  		goto drop;
  	}

  	slots = xennet_count_skb_slots(skb);

  	if (unlikely(slots > MAX_XEN_SKB_FRAGS + 1)) {

  		net_dbg_ratelimited("xennet: skb rides the rocket: %d slots, %d bytes
  ",
  				    slots, skb->len);
  		if (skb_linearize(skb))
  			goto drop;

  	}

  	page = virt_to_page(skb->data);
  	offset = offset_in_page(skb->data);

  
  	/* The first req should be at least ETH_HLEN size or the packet will be
  	 * dropped by netback.
  	 */
  	if (unlikely(PAGE_SIZE - offset < ETH_HLEN)) {
  		nskb = skb_copy(skb, GFP_ATOMIC);
  		if (!nskb)
  			goto drop;

  		dev_consume_skb_any(skb);

  		skb = nskb;
  		page = virt_to_page(skb->data);
  		offset = offset_in_page(skb->data);
  	}

  	len = skb_headlen(skb);

  	spin_lock_irqsave(&queue->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(&queue->tx_lock, flags);

  		goto drop;
  	}

  	/* First request for the linear area. */

  	first_tx = tx = xennet_make_first_txreq(queue, skb,
  						page, offset, len);
  	offset += tx->size;
  	if (offset == PAGE_SIZE) {
  		page++;
  		offset = 0;
  	}

  	len -= tx->size;

  	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;

  	/* Optional extra info after the first request. */

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

  			RING_GET_REQUEST(&queue->tx, queue->tx.req_prod_pvt++);

  		tx->flags |= XEN_NETTXF_extra_info;

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

  		gso->u.gso.type = (skb_shinfo(skb)->gso_type & SKB_GSO_TCPV6) ?
  			XEN_NETIF_GSO_TYPE_TCPV6 :
  			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;

  	}

  	/* Requests for the rest of the linear area. */
  	tx = xennet_make_txreqs(queue, tx, skb, page, offset, len);
  
  	/* Requests for all the frags. */
  	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
  		skb_frag_t *frag = &skb_shinfo(skb)->frags[i];

  		tx = xennet_make_txreqs(queue, tx, skb, skb_frag_page(frag),
  					skb_frag_off(frag),

  					skb_frag_size(frag));
  	}

  	/* First request has the packet length. */
  	first_tx->size = skb->len;

  	RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(&queue->tx, notify);

  	if (notify)

  		notify_remote_via_irq(queue->tx_irq);

  	u64_stats_update_begin(&tx_stats->syncp);
  	tx_stats->bytes += skb->len;
  	tx_stats->packets++;
  	u64_stats_update_end(&tx_stats->syncp);

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

  	xennet_tx_buf_gc(queue);

  	if (!netfront_tx_slot_available(queue))
  		netif_tx_stop_queue(netdev_get_tx_queue(dev, queue->id));

  	spin_unlock_irqrestore(&queue->tx_lock, flags);

  	return NETDEV_TX_OK;

  
   drop:

  	dev->stats.tx_dropped++;

  	dev_kfree_skb_any(skb);

  	return NETDEV_TX_OK;

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

  	unsigned int num_queues = dev->real_num_tx_queues;
  	unsigned int i;
  	struct netfront_queue *queue;
  	netif_tx_stop_all_queues(np->netdev);
  	for (i = 0; i < num_queues; ++i) {
  		queue = &np->queues[i];
  		napi_disable(&queue->napi);
  	}

  	return 0;
  }

  static void xennet_move_rx_slot(struct netfront_queue *queue, struct sk_buff *skb,

  				grant_ref_t ref)
  {

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

  }

  static int xennet_get_extras(struct netfront_queue *queue,

  			     struct xen_netif_extra_info *extras,
  			     RING_IDX rp)
  
  {
  	struct xen_netif_extra_info *extra;

  	struct device *dev = &queue->info->netdev->dev;
  	RING_IDX cons = queue->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
  ");
  			err = -EBADR;
  			break;
  		}
  
  		extra = (struct xen_netif_extra_info *)

  			RING_GET_RESPONSE(&queue->rx, ++cons);

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

  		skb = xennet_get_rx_skb(queue, cons);
  		ref = xennet_get_rx_ref(queue, cons);
  		xennet_move_rx_slot(queue, skb, ref);

  	} while (extra->flags & XEN_NETIF_EXTRA_FLAG_MORE);

  	queue->rx.rsp_cons = cons;

  	return err;
  }

  static int xennet_get_responses(struct netfront_queue *queue,

  				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 = &queue->info->netdev->dev;
  	RING_IDX cons = queue->rx.rsp_cons;
  	struct sk_buff *skb = xennet_get_rx_skb(queue, cons);
  	grant_ref_t ref = xennet_get_rx_ref(queue, cons);

  	int max = XEN_NETIF_NR_SLOTS_MIN + (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(queue, extras, rp);
  		cons = queue->rx.rsp_cons;

  	}
  
  	for (;;) {
  		if (unlikely(rx->status < 0 ||

  			     rx->offset + rx->status > XEN_PAGE_SIZE)) {

  			if (net_ratelimit())

  				dev_warn(dev, "rx->offset: %u, size: %d
  ",

  					 rx->offset, rx->status);

  			xennet_move_rx_slot(queue, 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.
  ",
  					 rx->id);
  			err = -EINVAL;
  			goto next;
  		}
  
  		ret = gnttab_end_foreign_access_ref(ref, 0);
  		BUG_ON(!ret);

  		gnttab_release_grant_reference(&queue->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
  ");

  			err = -ENOENT;
  			break;
  		}

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

  		slots++;

  	}

  	if (unlikely(slots > max)) {

  		if (net_ratelimit())

  			dev_warn(dev, "Too many slots
  ");

  		err = -E2BIG;
  	}
  
  	if (unlikely(err))

  		queue->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())

  			pr_warn("GSO size must not be zero
  ");

  		return -EINVAL;
  	}

  	if (gso->u.gso.type != XEN_NETIF_GSO_TYPE_TCPV4 &&
  	    gso->u.gso.type != XEN_NETIF_GSO_TYPE_TCPV6) {

  		if (net_ratelimit())

  			pr_warn("Bad GSO type %d
  ", gso->u.gso.type);

  		return -EINVAL;
  	}
  
  	skb_shinfo(skb)->gso_size = gso->u.gso.size;

  	skb_shinfo(skb)->gso_type =
  		(gso->u.gso.type == XEN_NETIF_GSO_TYPE_TCPV4) ?
  		SKB_GSO_TCPV4 :
  		SKB_GSO_TCPV6;

  
  	/* 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 int xennet_fill_frags(struct netfront_queue *queue,
  			     struct sk_buff *skb,
  			     struct sk_buff_head *list)

  {

  	RING_IDX cons = queue->rx.rsp_cons;

  	struct sk_buff *nskb;
  
  	while ((nskb = __skb_dequeue(list))) {
  		struct xen_netif_rx_response *rx =

  			RING_GET_RESPONSE(&queue->rx, ++cons);

  		skb_frag_t *nfrag = &skb_shinfo(nskb)->frags[0];

  		if (skb_shinfo(skb)->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));
  		}

  		if (unlikely(skb_shinfo(skb)->nr_frags >= MAX_SKB_FRAGS)) {

  			queue->rx.rsp_cons = ++cons + skb_queue_len(list);

  			kfree_skb(nskb);

  			return -ENOENT;

  		}

  		skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags,
  				skb_frag_page(nfrag),

  				rx->offset, rx->status, PAGE_SIZE);

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

  	}

  	queue->rx.rsp_cons = cons;
  
  	return 0;

  }

  static int checksum_setup(struct net_device *dev, struct sk_buff *skb)

  {

  	bool recalculate_partial_csum = false;

  
  	/*
  	 * 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);

  		atomic_inc(&np->rx_gso_checksum_fixup);

  		skb->ip_summed = CHECKSUM_PARTIAL;

  		recalculate_partial_csum = true;

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

  	return skb_checksum_setup(skb, recalculate_partial_csum);

  }

  static int handle_incoming_queue(struct netfront_queue *queue,

  				 struct sk_buff_head *rxq)

  {

  	struct netfront_stats *rx_stats = this_cpu_ptr(queue->info->rx_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, queue->info->netdev);

  		skb_reset_network_header(skb);

  		if (checksum_setup(queue->info->netdev, skb)) {

  			kfree_skb(skb);
  			packets_dropped++;

  			queue->info->netdev->stats.rx_errors++;

  			continue;

  		}

  		u64_stats_update_begin(&rx_stats->syncp);
  		rx_stats->packets++;
  		rx_stats->bytes += skb->len;
  		u64_stats_update_end(&rx_stats->syncp);

  
  		/* Pass it up. */

  		napi_gro_receive(&queue->napi, skb);

  	}
  
  	return packets_dropped;
  }

  static int xennet_poll(struct napi_struct *napi, int budget)

  {

  	struct netfront_queue *queue = container_of(napi, struct netfront_queue, napi);
  	struct net_device *dev = queue->info->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;

  	int err;

  	spin_lock(&queue->rx_lock);

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

  	rp = queue->rx.sring->rsp_prod;

  	rmb(); /* Ensure we see queued responses up to 'rp'. */

  	i = queue->rx.rsp_cons;

  	work_done = 0;
  	while ((i != rp) && (work_done < budget)) {

  		memcpy(rx, RING_GET_RESPONSE(&queue->rx, i), sizeof(*rx));

  		memset(extras, 0, sizeof(rinfo.extras));

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

  
  		if (unlikely(err)) {
  err:
  			while ((skb = __skb_dequeue(&tmpq)))
  				__skb_queue_tail(&errq, skb);

  			dev->stats.rx_errors++;

  			i = queue->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);

  				queue->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_frag_off_set(&skb_shinfo(skb)->frags[0], rx->offset);

  		skb_frag_size_set(&skb_shinfo(skb)->frags[0], rx->status);
  		skb->data_len = rx->status;

  		skb->len += rx->status;

  		if (unlikely(xennet_fill_frags(queue, skb, &tmpq)))

  			goto err;

  		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);

  		i = ++queue->rx.rsp_cons;

  		work_done++;
  	}

  	__skb_queue_purge(&errq);

  	work_done -= handle_incoming_queue(queue, &rxq);

  	xennet_alloc_rx_buffers(queue);

  	if (work_done < budget) {

  		int more_to_do = 0;

  		napi_complete_done(napi, work_done);

  		RING_FINAL_CHECK_FOR_RESPONSES(&queue->rx, more_to_do);

  		if (more_to_do)
  			napi_schedule(napi);

  	}

  	spin_unlock(&queue->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 : ETH_DATA_LEN;

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

  static void 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 *rx_stats = per_cpu_ptr(np->rx_stats, cpu);
  		struct netfront_stats *tx_stats = per_cpu_ptr(np->tx_stats, cpu);

  		u64 rx_packets, rx_bytes, tx_packets, tx_bytes;
  		unsigned int start;
  
  		do {

  			start = u64_stats_fetch_begin_irq(&tx_stats->syncp);
  			tx_packets = tx_stats->packets;
  			tx_bytes = tx_stats->bytes;
  		} while (u64_stats_fetch_retry_irq(&tx_stats->syncp, start));

  		do {
  			start = u64_stats_fetch_begin_irq(&rx_stats->syncp);
  			rx_packets = rx_stats->packets;
  			rx_bytes = rx_stats->bytes;
  		} while (u64_stats_fetch_retry_irq(&rx_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;

  }

  static void xennet_release_tx_bufs(struct netfront_queue *queue)

  {
  	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(&queue->tx_skbs[i]))

  			continue;

  		skb = queue->tx_skbs[i].skb;
  		get_page(queue->grant_tx_page[i]);
  		gnttab_end_foreign_access(queue->grant_tx_ref[i],

  					  GNTMAP_readonly,

  					  (unsigned long)page_address(queue->grant_tx_page[i]));
  		queue->grant_tx_page[i] = NULL;
  		queue->grant_tx_ref[i] = GRANT_INVALID_REF;
  		add_id_to_freelist(&queue->tx_skb_freelist, queue->tx_skbs, i);

  		dev_kfree_skb_irq(skb);
  	}
  }

  static void xennet_release_rx_bufs(struct netfront_queue *queue)

  {

  	int id, ref;

  	spin_lock_bh(&queue->rx_lock);

  
  	for (id = 0; id < NET_RX_RING_SIZE; id++) {

  		struct sk_buff *skb;
  		struct page *page;

  		skb = queue->rx_skbs[id];

  		if (!skb)

  			continue;

  		ref = queue->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));

  		queue->grant_rx_ref[id] = GRANT_INVALID_REF;

  		kfree_skb(skb);

  	}

  	spin_unlock_bh(&queue->rx_lock);

  }

  static netdev_features_t xennet_fix_features(struct net_device *dev,
  	netdev_features_t features)

  {
  	struct netfront_info *np = netdev_priv(dev);

  	if (features & NETIF_F_SG &&
  	    !xenbus_read_unsigned(np->xbdev->otherend, "feature-sg", 0))
  		features &= ~NETIF_F_SG;

  	if (features & NETIF_F_IPV6_CSUM &&
  	    !xenbus_read_unsigned(np->xbdev->otherend,
  				  "feature-ipv6-csum-offload", 0))
  		features &= ~NETIF_F_IPV6_CSUM;

  	if (features & NETIF_F_TSO &&
  	    !xenbus_read_unsigned(np->xbdev->otherend, "feature-gso-tcpv4", 0))
  		features &= ~NETIF_F_TSO;

  	if (features & NETIF_F_TSO6 &&
  	    !xenbus_read_unsigned(np->xbdev->otherend, "feature-gso-tcpv6", 0))
  		features &= ~NETIF_F_TSO6;

  	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_tx_interrupt(int irq, void *dev_id)

  {

  	struct netfront_queue *queue = dev_id;

  	unsigned long flags;

  	spin_lock_irqsave(&queue->tx_lock, flags);
  	xennet_tx_buf_gc(queue);
  	spin_unlock_irqrestore(&queue->tx_lock, flags);

  	return IRQ_HANDLED;
  }
  
  static irqreturn_t xennet_rx_interrupt(int irq, void *dev_id)
  {

  	struct netfront_queue *queue = dev_id;
  	struct net_device *dev = queue->info->netdev;

  
  	if (likely(netif_carrier_ok(dev) &&

  		   RING_HAS_UNCONSUMED_RESPONSES(&queue->rx)))

  		napi_schedule(&queue->napi);

  	return IRQ_HANDLED;
  }

  static irqreturn_t xennet_interrupt(int irq, void *dev_id)
  {
  	xennet_tx_interrupt(irq, dev_id);
  	xennet_rx_interrupt(irq, dev_id);

  	return IRQ_HANDLED;
  }
  
  #ifdef CONFIG_NET_POLL_CONTROLLER
  static void xennet_poll_controller(struct net_device *dev)
  {

  	/* Poll each queue */
  	struct netfront_info *info = netdev_priv(dev);
  	unsigned int num_queues = dev->real_num_tx_queues;
  	unsigned int i;
  	for (i = 0; i < num_queues; ++i)
  		xennet_interrupt(0, &info->queues[i]);

  }
  #endif

  static const struct net_device_ops xennet_netdev_ops = {
  	.ndo_open            = xennet_open,

  	.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,

  	.ndo_select_queue    = xennet_select_queue,

  #ifdef CONFIG_NET_POLL_CONTROLLER
  	.ndo_poll_controller = xennet_poll_controller,
  #endif

  };

  static void xennet_free_netdev(struct net_device *netdev)
  {
  	struct netfront_info *np = netdev_priv(netdev);
  
  	free_percpu(np->rx_stats);
  	free_percpu(np->tx_stats);
  	free_netdev(netdev);
  }

  static struct net_device *xennet_create_dev(struct xenbus_device *dev)

  {

  	int err;

  	struct net_device *netdev;
  	struct netfront_info *np;

  	netdev = alloc_etherdev_mq(sizeof(struct netfront_info), xennet_max_queues);

  	if (!netdev)

  		return ERR_PTR(-ENOMEM);

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

  	np->queues = NULL;

  	err = -ENOMEM;

  	np->rx_stats = netdev_alloc_pcpu_stats(struct netfront_stats);
  	if (np->rx_stats == NULL)
  		goto exit;
  	np->tx_stats = netdev_alloc_pcpu_stats(struct netfront_stats);
  	if (np->tx_stats == NULL)

  		goto exit;

  	netdev->netdev_ops	= &xennet_netdev_ops;

  	netdev->features        = NETIF_F_IP_CSUM | NETIF_F_RXCSUM |
  				  NETIF_F_GSO_ROBUST;

  	netdev->hw_features	= NETIF_F_SG |
  				  NETIF_F_IPV6_CSUM |
  				  NETIF_F_TSO | NETIF_F_TSO6;

  	/*
           * 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;

  	netdev->ethtool_ops = &xennet_ethtool_ops;

  	netdev->min_mtu = ETH_MIN_MTU;

  	netdev->max_mtu = XEN_NETIF_MAX_TX_SIZE;

  	SET_NETDEV_DEV(netdev, &dev->dev);
  
  	np->netdev = netdev;
  
  	netif_carrier_off(netdev);

  	do {
  		xenbus_switch_state(dev, XenbusStateInitialising);
  		err = wait_event_timeout(module_wq,
  				 xenbus_read_driver_state(dev->otherend) !=
  				 XenbusStateClosed &&
  				 xenbus_read_driver_state(dev->otherend) !=
  				 XenbusStateUnknown, XENNET_TIMEOUT);
  	} while (!err);

  	return netdev;

   exit:

  	xennet_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);

  #ifdef CONFIG_SYSFS
  	info->netdev->sysfs_groups[0] = &xennet_dev_group;
  #endif

  	return 0;

  }
  
  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)
  {

  	unsigned int i = 0;

  	unsigned int num_queues = info->netdev->real_num_tx_queues;

  	netif_carrier_off(info->netdev);

  	for (i = 0; i < num_queues && info->queues; ++i) {

  		struct netfront_queue *queue = &info->queues[i];

  		del_timer_sync(&queue->rx_refill_timer);

  		if (queue->tx_irq && (queue->tx_irq == queue->rx_irq))
  			unbind_from_irqhandler(queue->tx_irq, queue);
  		if (queue->tx_irq && (queue->tx_irq != queue->rx_irq)) {
  			unbind_from_irqhandler(queue->tx_irq, queue);
  			unbind_from_irqhandler(queue->rx_irq, queue);
  		}
  		queue->tx_evtchn = queue->rx_evtchn = 0;
  		queue->tx_irq = queue->rx_irq = 0;

  		if (netif_running(info->netdev))
  			napi_synchronize(&queue->napi);

  		xennet_release_tx_bufs(queue);
  		xennet_release_rx_bufs(queue);
  		gnttab_free_grant_references(queue->gref_tx_head);
  		gnttab_free_grant_references(queue->gref_rx_head);

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

  		queue->tx_ring_ref = GRANT_INVALID_REF;
  		queue->rx_ring_ref = GRANT_INVALID_REF;
  		queue->tx.sring = NULL;
  		queue->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
  ", 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_single(struct netfront_queue *queue)

  {
  	int err;

  	err = xenbus_alloc_evtchn(queue->info->xbdev, &queue->tx_evtchn);

  	if (err < 0)
  		goto fail;

  	err = bind_evtchn_to_irqhandler(queue->tx_evtchn,

  					xennet_interrupt,

  					0, queue->info->netdev->name, queue);

  	if (err < 0)
  		goto bind_fail;

  	queue->rx_evtchn = queue->tx_evtchn;
  	queue->rx_irq = queue->tx_irq = err;

  
  	return 0;
  
  bind_fail:

  	xenbus_free_evtchn(queue->info->xbdev, queue->tx_evtchn);
  	queue->tx_evtchn = 0;

  fail:
  	return err;
  }

  static int setup_netfront_split(struct netfront_queue *queue)

  {
  	int err;

  	err = xenbus_alloc_evtchn(queue->info->xbdev, &queue->tx_evtchn);

  	if (err < 0)
  		goto fail;

  	err = xenbus_alloc_evtchn(queue->info->xbdev, &queue->rx_evtchn);

  	if (err < 0)
  		goto alloc_rx_evtchn_fail;

  	snprintf(queue->tx_irq_name, sizeof(queue->tx_irq_name),
  		 "%s-tx", queue->name);
  	err = bind_evtchn_to_irqhandler(queue->tx_evtchn,

  					xennet_tx_interrupt,

  					0, queue->tx_irq_name, queue);

  	if (err < 0)
  		goto bind_tx_fail;

  	queue->tx_irq = err;

  	snprintf(queue->rx_irq_name, sizeof(queue->rx_irq_name),
  		 "%s-rx", queue->name);
  	err = bind_evtchn_to_irqhandler(queue->rx_evtchn,

  					xennet_rx_interrupt,

  					0, queue->rx_irq_name, queue);

  	if (err < 0)
  		goto bind_rx_fail;

  	queue->rx_irq = err;

  
  	return 0;
  
  bind_rx_fail:

  	unbind_from_irqhandler(queue->tx_irq, queue);
  	queue->tx_irq = 0;

  bind_tx_fail:

  	xenbus_free_evtchn(queue->info->xbdev, queue->rx_evtchn);
  	queue->rx_evtchn = 0;

  alloc_rx_evtchn_fail:

  	xenbus_free_evtchn(queue->info->xbdev, queue->tx_evtchn);
  	queue->tx_evtchn = 0;

  fail:
  	return err;
  }

  static int setup_netfront(struct xenbus_device *dev,
  			struct netfront_queue *queue, unsigned int feature_split_evtchn)

  {
  	struct xen_netif_tx_sring *txs;
  	struct xen_netif_rx_sring *rxs;

  	grant_ref_t gref;

  	int err;

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

  	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(&queue->tx, txs, XEN_PAGE_SIZE);

  	err = xenbus_grant_ring(dev, txs, 1, &gref);

  	if (err < 0)
  		goto grant_tx_ring_fail;

  	queue->tx_ring_ref = gref;

  	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 alloc_rx_ring_fail;

  	}
  	SHARED_RING_INIT(rxs);

  	FRONT_RING_INIT(&queue->rx, rxs, XEN_PAGE_SIZE);

  	err = xenbus_grant_ring(dev, rxs, 1, &gref);

  	if (err < 0)
  		goto grant_rx_ring_fail;

  	queue->rx_ring_ref = gref;

  	if (feature_split_evtchn)

  		err = setup_netfront_split(queue);

  	/* setup single event channel if
  	 *  a) feature-split-event-channels == 0
  	 *  b) feature-split-event-channels == 1 but failed to setup
  	 */
  	if (!feature_split_evtchn || (feature_split_evtchn && err))

  		err = setup_netfront_single(queue);

  	if (err)

  		goto alloc_evtchn_fail;