/*
   * Back-end of the driver for virtual network devices. This portion of the
   * driver exports a 'unified' network-device interface that can be accessed
   * by any operating system that implements a compatible front end. A
   * reference front-end implementation can be found in:
   *  drivers/net/xen-netfront.c
   *
   * Copyright (c) 2002-2005, K A Fraser
   *
   * 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 "common.h"
  
  #include <linux/kthread.h>
  #include <linux/if_vlan.h>
  #include <linux/udp.h>
  
  #include <net/tcp.h>
  
  #include <xen/xen.h>
  #include <xen/events.h>
  #include <xen/interface/memory.h>
  
  #include <asm/xen/hypercall.h>
  #include <asm/xen/page.h>
  
  /* Provide an option to disable split event channels at load time as
   * event channels are limited resource. Split event channels are
   * enabled by default.
   */
  bool separate_tx_rx_irq = 1;
  module_param(separate_tx_rx_irq, bool, 0644);
  
  /*
   * This is the maximum slots a skb can have. If a guest sends a skb
   * which exceeds this limit it is considered malicious.
   */
  #define FATAL_SKB_SLOTS_DEFAULT 20
  static unsigned int fatal_skb_slots = FATAL_SKB_SLOTS_DEFAULT;
  module_param(fatal_skb_slots, uint, 0444);
  
  /*
   * To avoid confusion, we define XEN_NETBK_LEGACY_SLOTS_MAX indicating
   * the maximum slots a valid packet can use. Now this value is defined
   * to be XEN_NETIF_NR_SLOTS_MIN, which is supposed to be supported by
   * all backend.
   */
  #define XEN_NETBK_LEGACY_SLOTS_MAX XEN_NETIF_NR_SLOTS_MIN
  
  /*
   * If head != INVALID_PENDING_RING_IDX, it means this tx request is head of
   * one or more merged tx requests, otherwise it is the continuation of
   * previous tx request.
   */
  static inline int pending_tx_is_head(struct xenvif *vif, RING_IDX idx)
  {
  	return vif->pending_tx_info[idx].head != INVALID_PENDING_RING_IDX;
  }
  
  static void xenvif_idx_release(struct xenvif *vif, u16 pending_idx,
  			       u8 status);
  
  static void make_tx_response(struct xenvif *vif,
  			     struct xen_netif_tx_request *txp,
  			     s8       st);
  
  static inline int tx_work_todo(struct xenvif *vif);
  static inline int rx_work_todo(struct xenvif *vif);
  
  static struct xen_netif_rx_response *make_rx_response(struct xenvif *vif,
  					     u16      id,
  					     s8       st,
  					     u16      offset,
  					     u16      size,
  					     u16      flags);
  
  static inline unsigned long idx_to_pfn(struct xenvif *vif,
  				       u16 idx)
  {
  	return page_to_pfn(vif->mmap_pages[idx]);
  }
  
  static inline unsigned long idx_to_kaddr(struct xenvif *vif,
  					 u16 idx)
  {
  	return (unsigned long)pfn_to_kaddr(idx_to_pfn(vif, idx));
  }
  
  /* This is a miniumum size for the linear area to avoid lots of
   * calls to __pskb_pull_tail() as we set up checksum offsets. The
   * value 128 was chosen as it covers all IPv4 and most likely
   * IPv6 headers.
   */
  #define PKT_PROT_LEN 128
  
  static u16 frag_get_pending_idx(skb_frag_t *frag)
  {
  	return (u16)frag->page_offset;
  }
  
  static void frag_set_pending_idx(skb_frag_t *frag, u16 pending_idx)
  {
  	frag->page_offset = pending_idx;
  }
  
  static inline pending_ring_idx_t pending_index(unsigned i)
  {
  	return i & (MAX_PENDING_REQS-1);
  }
  
  static inline pending_ring_idx_t nr_pending_reqs(struct xenvif *vif)
  {
  	return MAX_PENDING_REQS -
  		vif->pending_prod + vif->pending_cons;
  }
  
  bool xenvif_rx_ring_slots_available(struct xenvif *vif, int needed)
  {
  	RING_IDX prod, cons;
  
  	do {
  		prod = vif->rx.sring->req_prod;
  		cons = vif->rx.req_cons;
  
  		if (prod - cons >= needed)
  			return true;
  
  		vif->rx.sring->req_event = prod + 1;
  
  		/* Make sure event is visible before we check prod
  		 * again.
  		 */
  		mb();
  	} while (vif->rx.sring->req_prod != prod);
  
  	return false;
  }
  
  /*
   * Returns true if we should start a new receive buffer instead of
   * adding 'size' bytes to a buffer which currently contains 'offset'
   * bytes.
   */
  static bool start_new_rx_buffer(int offset, unsigned long size, int head)
  {
  	/* simple case: we have completely filled the current buffer. */
  	if (offset == MAX_BUFFER_OFFSET)
  		return true;
  
  	/*
  	 * complex case: start a fresh buffer if the current frag
  	 * would overflow the current buffer but only if:
  	 *     (i)   this frag would fit completely in the next buffer
  	 * and (ii)  there is already some data in the current buffer
  	 * and (iii) this is not the head buffer.
  	 *
  	 * Where:
  	 * - (i) stops us splitting a frag into two copies
  	 *   unless the frag is too large for a single buffer.
  	 * - (ii) stops us from leaving a buffer pointlessly empty.
  	 * - (iii) stops us leaving the first buffer
  	 *   empty. Strictly speaking this is already covered
  	 *   by (ii) but is explicitly checked because
  	 *   netfront relies on the first buffer being
  	 *   non-empty and can crash otherwise.
  	 *
  	 * This means we will effectively linearise small
  	 * frags but do not needlessly split large buffers
  	 * into multiple copies tend to give large frags their
  	 * own buffers as before.
  	 */
  	BUG_ON(size > MAX_BUFFER_OFFSET);
  	if ((offset + size > MAX_BUFFER_OFFSET) && offset && !head)
  		return true;
  
  	return false;
  }
  
  struct netrx_pending_operations {
  	unsigned copy_prod, copy_cons;
  	unsigned meta_prod, meta_cons;
  	struct gnttab_copy *copy;
  	struct xenvif_rx_meta *meta;
  	int copy_off;
  	grant_ref_t copy_gref;
  };
  
  static struct xenvif_rx_meta *get_next_rx_buffer(struct xenvif *vif,
  						 struct netrx_pending_operations *npo)
  {
  	struct xenvif_rx_meta *meta;
  	struct xen_netif_rx_request *req;
  
  	req = RING_GET_REQUEST(&vif->rx, vif->rx.req_cons++);
  
  	meta = npo->meta + npo->meta_prod++;
  	meta->gso_type = XEN_NETIF_GSO_TYPE_NONE;
  	meta->gso_size = 0;
  	meta->size = 0;
  	meta->id = req->id;
  
  	npo->copy_off = 0;
  	npo->copy_gref = req->gref;
  
  	return meta;
  }
  
  /*
   * Set up the grant operations for this fragment. If it's a flipping
   * interface, we also set up the unmap request from here.
   */
  static void xenvif_gop_frag_copy(struct xenvif *vif, struct sk_buff *skb,
  				 struct netrx_pending_operations *npo,
  				 struct page *page, unsigned long size,
  				 unsigned long offset, int *head)
  {
  	struct gnttab_copy *copy_gop;
  	struct xenvif_rx_meta *meta;
  	unsigned long bytes;
  	int gso_type = XEN_NETIF_GSO_TYPE_NONE;
  
  	/* Data must not cross a page boundary. */
  	BUG_ON(size + offset > PAGE_SIZE<<compound_order(page));
  
  	meta = npo->meta + npo->meta_prod - 1;
  
  	/* Skip unused frames from start of page */
  	page += offset >> PAGE_SHIFT;
  	offset &= ~PAGE_MASK;
  
  	while (size > 0) {
  		BUG_ON(offset >= PAGE_SIZE);
  		BUG_ON(npo->copy_off > MAX_BUFFER_OFFSET);
  
  		bytes = PAGE_SIZE - offset;
  
  		if (bytes > size)
  			bytes = size;
  
  		if (start_new_rx_buffer(npo->copy_off, bytes, *head)) {
  			/*
  			 * Netfront requires there to be some data in the head
  			 * buffer.
  			 */
  			BUG_ON(*head);
  
  			meta = get_next_rx_buffer(vif, npo);
  		}
  
  		if (npo->copy_off + bytes > MAX_BUFFER_OFFSET)
  			bytes = MAX_BUFFER_OFFSET - npo->copy_off;
  
  		copy_gop = npo->copy + npo->copy_prod++;
  		copy_gop->flags = GNTCOPY_dest_gref;
  		copy_gop->len = bytes;
  
  		copy_gop->source.domid = DOMID_SELF;
  		copy_gop->source.u.gmfn = virt_to_mfn(page_address(page));
  		copy_gop->source.offset = offset;
  
  		copy_gop->dest.domid = vif->domid;
  		copy_gop->dest.offset = npo->copy_off;
  		copy_gop->dest.u.ref = npo->copy_gref;
  
  		npo->copy_off += bytes;
  		meta->size += bytes;
  
  		offset += bytes;
  		size -= bytes;
  
  		/* Next frame */
  		if (offset == PAGE_SIZE && size) {
  			BUG_ON(!PageCompound(page));
  			page++;
  			offset = 0;
  		}
  
  		/* Leave a gap for the GSO descriptor. */
  		if (skb_is_gso(skb)) {
  			if (skb_shinfo(skb)->gso_type & SKB_GSO_TCPV4)
  				gso_type = XEN_NETIF_GSO_TYPE_TCPV4;
  			else if (skb_shinfo(skb)->gso_type & SKB_GSO_TCPV6)
  				gso_type = XEN_NETIF_GSO_TYPE_TCPV6;
  		}
  
  		if (*head && ((1 << gso_type) & vif->gso_mask))
  			vif->rx.req_cons++;
  
  		*head = 0; /* There must be something in this buffer now. */
  
  	}
  }
  
  /*
   * Prepare an SKB to be transmitted to the frontend.
   *
   * This function is responsible for allocating grant operations, meta
   * structures, etc.
   *
   * It returns the number of meta structures consumed. The number of
   * ring slots used is always equal to the number of meta slots used
   * plus the number of GSO descriptors used. Currently, we use either
   * zero GSO descriptors (for non-GSO packets) or one descriptor (for
   * frontend-side LRO).
   */
  static int xenvif_gop_skb(struct sk_buff *skb,
  			  struct netrx_pending_operations *npo)
  {
  	struct xenvif *vif = netdev_priv(skb->dev);
  	int nr_frags = skb_shinfo(skb)->nr_frags;
  	int i;
  	struct xen_netif_rx_request *req;
  	struct xenvif_rx_meta *meta;
  	unsigned char *data;
  	int head = 1;
  	int old_meta_prod;
  	int gso_type;
  
  	old_meta_prod = npo->meta_prod;
  
  	gso_type = XEN_NETIF_GSO_TYPE_NONE;
  	if (skb_is_gso(skb)) {
  		if (skb_shinfo(skb)->gso_type & SKB_GSO_TCPV4)
  			gso_type = XEN_NETIF_GSO_TYPE_TCPV4;
  		else if (skb_shinfo(skb)->gso_type & SKB_GSO_TCPV6)
  			gso_type = XEN_NETIF_GSO_TYPE_TCPV6;
  	}
  
  	/* Set up a GSO prefix descriptor, if necessary */
  	if ((1 << gso_type) & vif->gso_prefix_mask) {
  		req = RING_GET_REQUEST(&vif->rx, vif->rx.req_cons++);
  		meta = npo->meta + npo->meta_prod++;
  		meta->gso_type = gso_type;
  		meta->gso_size = skb_shinfo(skb)->gso_size;
  		meta->size = 0;
  		meta->id = req->id;
  	}
  
  	req = RING_GET_REQUEST(&vif->rx, vif->rx.req_cons++);
  	meta = npo->meta + npo->meta_prod++;
  
  	if ((1 << gso_type) & vif->gso_mask) {
  		meta->gso_type = gso_type;
  		meta->gso_size = skb_shinfo(skb)->gso_size;
  	} else {
  		meta->gso_type = XEN_NETIF_GSO_TYPE_NONE;
  		meta->gso_size = 0;
  	}
  
  	meta->size = 0;
  	meta->id = req->id;
  	npo->copy_off = 0;
  	npo->copy_gref = req->gref;
  
  	data = skb->data;
  	while (data < skb_tail_pointer(skb)) {
  		unsigned int offset = offset_in_page(data);
  		unsigned int len = PAGE_SIZE - offset;
  
  		if (data + len > skb_tail_pointer(skb))
  			len = skb_tail_pointer(skb) - data;
  
  		xenvif_gop_frag_copy(vif, skb, npo,
  				     virt_to_page(data), len, offset, &head);
  		data += len;
  	}
  
  	for (i = 0; i < nr_frags; i++) {
  		xenvif_gop_frag_copy(vif, skb, npo,
  				     skb_frag_page(&skb_shinfo(skb)->frags[i]),
  				     skb_frag_size(&skb_shinfo(skb)->frags[i]),
  				     skb_shinfo(skb)->frags[i].page_offset,
  				     &head);
  	}
  
  	return npo->meta_prod - old_meta_prod;
  }
  
  /*
   * This is a twin to xenvif_gop_skb.  Assume that xenvif_gop_skb was
   * used to set up the operations on the top of
   * netrx_pending_operations, which have since been done.  Check that
   * they didn't give any errors and advance over them.
   */
  static int xenvif_check_gop(struct xenvif *vif, int nr_meta_slots,
  			    struct netrx_pending_operations *npo)
  {
  	struct gnttab_copy     *copy_op;
  	int status = XEN_NETIF_RSP_OKAY;
  	int i;
  
  	for (i = 0; i < nr_meta_slots; i++) {
  		copy_op = npo->copy + npo->copy_cons++;
  		if (copy_op->status != GNTST_okay) {
  			netdev_dbg(vif->dev,
  				   "Bad status %d from copy to DOM%d.
  ",
  				   copy_op->status, vif->domid);
  			status = XEN_NETIF_RSP_ERROR;
  		}
  	}
  
  	return status;
  }
  
  static void xenvif_add_frag_responses(struct xenvif *vif, int status,
  				      struct xenvif_rx_meta *meta,
  				      int nr_meta_slots)
  {
  	int i;
  	unsigned long offset;
  
  	/* No fragments used */
  	if (nr_meta_slots <= 1)
  		return;
  
  	nr_meta_slots--;
  
  	for (i = 0; i < nr_meta_slots; i++) {
  		int flags;
  		if (i == nr_meta_slots - 1)
  			flags = 0;
  		else
  			flags = XEN_NETRXF_more_data;
  
  		offset = 0;
  		make_rx_response(vif, meta[i].id, status, offset,
  				 meta[i].size, flags);
  	}
  }
  
  struct skb_cb_overlay {
  	int meta_slots_used;
  };
  
  void xenvif_kick_thread(struct xenvif *vif)
  {
  	wake_up(&vif->wq);
  }
  
  static void xenvif_rx_action(struct xenvif *vif)
  {
  	s8 status;
  	u16 flags;
  	struct xen_netif_rx_response *resp;
  	struct sk_buff_head rxq;
  	struct sk_buff *skb;
  	LIST_HEAD(notify);
  	int ret;
  	unsigned long offset;
  	struct skb_cb_overlay *sco;
  	bool need_to_notify = false;
  
  	struct netrx_pending_operations npo = {
  		.copy  = vif->grant_copy_op,
  		.meta  = vif->meta,
  	};
  
  	skb_queue_head_init(&rxq);
  
  	while ((skb = skb_dequeue(&vif->rx_queue)) != NULL) {
  		RING_IDX max_slots_needed;
  		RING_IDX old_req_cons;
  		RING_IDX ring_slots_used;
  		int i;
  
  		/* We need a cheap worse case estimate for the number of
  		 * slots we'll use.
  		 */
  
  		max_slots_needed = DIV_ROUND_UP(offset_in_page(skb->data) +
  						skb_headlen(skb),
  						PAGE_SIZE);
  		for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
  			unsigned int size;
  			unsigned int offset;
  
  			size = skb_frag_size(&skb_shinfo(skb)->frags[i]);
  			offset = skb_shinfo(skb)->frags[i].page_offset;
  
  			/* For a worse-case estimate we need to factor in
  			 * the fragment page offset as this will affect the
  			 * number of times xenvif_gop_frag_copy() will
  			 * call start_new_rx_buffer().
  			 */
  			max_slots_needed += DIV_ROUND_UP(offset + size,
  							 PAGE_SIZE);
  		}
  
  		/* To avoid the estimate becoming too pessimal for some
  		 * frontends that limit posted rx requests, cap the estimate
  		 * at MAX_SKB_FRAGS.
  		 */
  		if (max_slots_needed > MAX_SKB_FRAGS)
  			max_slots_needed = MAX_SKB_FRAGS;
  
  		/* We may need one more slot for GSO metadata */
  		if (skb_is_gso(skb) &&
  		   (skb_shinfo(skb)->gso_type & SKB_GSO_TCPV4 ||
  		    skb_shinfo(skb)->gso_type & SKB_GSO_TCPV6))
  			max_slots_needed++;
  
  		/* If the skb may not fit then bail out now */
  		if (!xenvif_rx_ring_slots_available(vif, max_slots_needed)) {
  			skb_queue_head(&vif->rx_queue, skb);
  			need_to_notify = true;
  			vif->rx_last_skb_slots = max_slots_needed;
  			break;
  		} else
  			vif->rx_last_skb_slots = 0;
  
  		sco = (struct skb_cb_overlay *)skb->cb;
  
  		old_req_cons = vif->rx.req_cons;
  		sco->meta_slots_used = xenvif_gop_skb(skb, &npo);
  		ring_slots_used = vif->rx.req_cons - old_req_cons;
  
  		BUG_ON(ring_slots_used > max_slots_needed);
  
  		__skb_queue_tail(&rxq, skb);
  	}
  
  	BUG_ON(npo.meta_prod > ARRAY_SIZE(vif->meta));
  
  	if (!npo.copy_prod)
  		goto done;
  
  	BUG_ON(npo.copy_prod > MAX_GRANT_COPY_OPS);
  	gnttab_batch_copy(vif->grant_copy_op, npo.copy_prod);
  
  	while ((skb = __skb_dequeue(&rxq)) != NULL) {
  		sco = (struct skb_cb_overlay *)skb->cb;
  
  		if ((1 << vif->meta[npo.meta_cons].gso_type) &
  		    vif->gso_prefix_mask) {
  			resp = RING_GET_RESPONSE(&vif->rx,
  						 vif->rx.rsp_prod_pvt++);
  
  			resp->flags = XEN_NETRXF_gso_prefix | XEN_NETRXF_more_data;
  
  			resp->offset = vif->meta[npo.meta_cons].gso_size;
  			resp->id = vif->meta[npo.meta_cons].id;
  			resp->status = sco->meta_slots_used;
  
  			npo.meta_cons++;
  			sco->meta_slots_used--;
  		}
  
  
  		vif->dev->stats.tx_bytes += skb->len;
  		vif->dev->stats.tx_packets++;
  
  		status = xenvif_check_gop(vif, sco->meta_slots_used, &npo);
  
  		if (sco->meta_slots_used == 1)
  			flags = 0;
  		else
  			flags = XEN_NETRXF_more_data;
  
  		if (skb->ip_summed == CHECKSUM_PARTIAL) /* local packet? */
  			flags |= XEN_NETRXF_csum_blank | XEN_NETRXF_data_validated;
  		else if (skb->ip_summed == CHECKSUM_UNNECESSARY)
  			/* remote but checksummed. */
  			flags |= XEN_NETRXF_data_validated;
  
  		offset = 0;
  		resp = make_rx_response(vif, vif->meta[npo.meta_cons].id,
  					status, offset,
  					vif->meta[npo.meta_cons].size,
  					flags);
  
  		if ((1 << vif->meta[npo.meta_cons].gso_type) &
  		    vif->gso_mask) {
  			struct xen_netif_extra_info *gso =
  				(struct xen_netif_extra_info *)
  				RING_GET_RESPONSE(&vif->rx,
  						  vif->rx.rsp_prod_pvt++);
  
  			resp->flags |= XEN_NETRXF_extra_info;
  
  			gso->u.gso.type = vif->meta[npo.meta_cons].gso_type;
  			gso->u.gso.size = vif->meta[npo.meta_cons].gso_size;
  			gso->u.gso.pad = 0;
  			gso->u.gso.features = 0;
  
  			gso->type = XEN_NETIF_EXTRA_TYPE_GSO;
  			gso->flags = 0;
  		}
  
  		xenvif_add_frag_responses(vif, status,
  					  vif->meta + npo.meta_cons + 1,
  					  sco->meta_slots_used);
  
  		RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&vif->rx, ret);
  
  		need_to_notify |= !!ret;
  
  		npo.meta_cons += sco->meta_slots_used;
  		dev_kfree_skb(skb);
  	}
  
  done:
  	if (need_to_notify)
  		notify_remote_via_irq(vif->rx_irq);
  }
  
  void xenvif_check_rx_xenvif(struct xenvif *vif)
  {
  	int more_to_do;
  
  	RING_FINAL_CHECK_FOR_REQUESTS(&vif->tx, more_to_do);
  
  	if (more_to_do)
  		napi_schedule(&vif->napi);
  }
  
  static void tx_add_credit(struct xenvif *vif)
  {
  	unsigned long max_burst, max_credit;
  
  	/*
  	 * Allow a burst big enough to transmit a jumbo packet of up to 128kB.
  	 * Otherwise the interface can seize up due to insufficient credit.
  	 */
  	max_burst = RING_GET_REQUEST(&vif->tx, vif->tx.req_cons)->size;
  	max_burst = min(max_burst, 131072UL);
  	max_burst = max(max_burst, vif->credit_bytes);
  
  	/* Take care that adding a new chunk of credit doesn't wrap to zero. */
  	max_credit = vif->remaining_credit + vif->credit_bytes;
  	if (max_credit < vif->remaining_credit)
  		max_credit = ULONG_MAX; /* wrapped: clamp to ULONG_MAX */
  
  	vif->remaining_credit = min(max_credit, max_burst);
  }
  
  static void tx_credit_callback(unsigned long data)
  {
  	struct xenvif *vif = (struct xenvif *)data;
  	tx_add_credit(vif);
  	xenvif_check_rx_xenvif(vif);
  }
  
  static void xenvif_tx_err(struct xenvif *vif,
  			  struct xen_netif_tx_request *txp, RING_IDX end)
  {
  	RING_IDX cons = vif->tx.req_cons;
  
  	do {
  		make_tx_response(vif, txp, XEN_NETIF_RSP_ERROR);
  		if (cons == end)
  			break;
  		txp = RING_GET_REQUEST(&vif->tx, cons++);
  	} while (1);
  	vif->tx.req_cons = cons;
  }
  
  static void xenvif_fatal_tx_err(struct xenvif *vif)
  {
  	netdev_err(vif->dev, "fatal error; disabling device
  ");
  	vif->disabled = true;
  	xenvif_kick_thread(vif);
  }
  
  static int xenvif_count_requests(struct xenvif *vif,
  				 struct xen_netif_tx_request *first,
  				 struct xen_netif_tx_request *txp,
  				 int work_to_do)
  {
  	RING_IDX cons = vif->tx.req_cons;
  	int slots = 0;
  	int drop_err = 0;
  	int more_data;
  
  	if (!(first->flags & XEN_NETTXF_more_data))
  		return 0;
  
  	do {
  		struct xen_netif_tx_request dropped_tx = { 0 };
  
  		if (slots >= work_to_do) {
  			netdev_err(vif->dev,
  				   "Asked for %d slots but exceeds this limit
  ",
  				   work_to_do);
  			xenvif_fatal_tx_err(vif);
  			return -ENODATA;
  		}
  
  		/* This guest is really using too many slots and
  		 * considered malicious.
  		 */
  		if (unlikely(slots >= fatal_skb_slots)) {
  			netdev_err(vif->dev,
  				   "Malicious frontend using %d slots, threshold %u
  ",
  				   slots, fatal_skb_slots);
  			xenvif_fatal_tx_err(vif);
  			return -E2BIG;
  		}
  
  		/* Xen network protocol had implicit dependency on
  		 * MAX_SKB_FRAGS. XEN_NETBK_LEGACY_SLOTS_MAX is set to
  		 * the historical MAX_SKB_FRAGS value 18 to honor the
  		 * same behavior as before. Any packet using more than
  		 * 18 slots but less than fatal_skb_slots slots is
  		 * dropped
  		 */
  		if (!drop_err && slots >= XEN_NETBK_LEGACY_SLOTS_MAX) {
  			if (net_ratelimit())
  				netdev_dbg(vif->dev,
  					   "Too many slots (%d) exceeding limit (%d), dropping packet
  ",
  					   slots, XEN_NETBK_LEGACY_SLOTS_MAX);
  			drop_err = -E2BIG;
  		}
  
  		if (drop_err)
  			txp = &dropped_tx;
  
  		memcpy(txp, RING_GET_REQUEST(&vif->tx, cons + slots),
  		       sizeof(*txp));
  
  		/* If the guest submitted a frame >= 64 KiB then
  		 * first->size overflowed and following slots will
  		 * appear to be larger than the frame.
  		 *
  		 * This cannot be fatal error as there are buggy
  		 * frontends that do this.
  		 *
  		 * Consume all slots and drop the packet.
  		 */
  		if (!drop_err && txp->size > first->size) {
  			if (net_ratelimit())
  				netdev_dbg(vif->dev,
  					   "Invalid tx request, slot size %u > remaining size %u
  ",
  					   txp->size, first->size);
  			drop_err = -EIO;
  		}
  
  		first->size -= txp->size;
  		slots++;
  
  		if (unlikely((txp->offset + txp->size) > PAGE_SIZE)) {
  			netdev_err(vif->dev, "Cross page boundary, txp->offset: %x, size: %u
  ",
  				 txp->offset, txp->size);
  			xenvif_fatal_tx_err(vif);
  			return -EINVAL;
  		}
  
  		more_data = txp->flags & XEN_NETTXF_more_data;
  
  		if (!drop_err)
  			txp++;
  
  	} while (more_data);
  
  	if (drop_err) {
  		xenvif_tx_err(vif, first, cons + slots);
  		return drop_err;
  	}
  
  	return slots;
  }
  
  static struct page *xenvif_alloc_page(struct xenvif *vif,
  				      u16 pending_idx)
  {
  	struct page *page;
  
  	page = alloc_page(GFP_ATOMIC|__GFP_COLD);
  	if (!page)
  		return NULL;
  	vif->mmap_pages[pending_idx] = page;
  
  	return page;
  }
  
  static struct gnttab_copy *xenvif_get_requests(struct xenvif *vif,
  					       struct sk_buff *skb,
  					       struct xen_netif_tx_request *txp,
  					       struct gnttab_copy *gop)
  {
  	struct skb_shared_info *shinfo = skb_shinfo(skb);
  	skb_frag_t *frags = shinfo->frags;
  	u16 pending_idx = *((u16 *)skb->data);
  	u16 head_idx = 0;
  	int slot, start;
  	struct page *page;
  	pending_ring_idx_t index, start_idx = 0;
  	uint16_t dst_offset;
  	unsigned int nr_slots;
  	struct pending_tx_info *first = NULL;
  
  	/* At this point shinfo->nr_frags is in fact the number of
  	 * slots, which can be as large as XEN_NETBK_LEGACY_SLOTS_MAX.
  	 */
  	nr_slots = shinfo->nr_frags;
  
  	/* Skip first skb fragment if it is on same page as header fragment. */
  	start = (frag_get_pending_idx(&shinfo->frags[0]) == pending_idx);
  
  	/* Coalesce tx requests, at this point the packet passed in
  	 * should be <= 64K. Any packets larger than 64K have been
  	 * handled in xenvif_count_requests().
  	 */
  	for (shinfo->nr_frags = slot = start; slot < nr_slots;
  	     shinfo->nr_frags++) {
  		struct pending_tx_info *pending_tx_info =
  			vif->pending_tx_info;
  
  		page = alloc_page(GFP_ATOMIC|__GFP_COLD);
  		if (!page)
  			goto err;
  
  		dst_offset = 0;
  		first = NULL;
  		while (dst_offset < PAGE_SIZE && slot < nr_slots) {
  			gop->flags = GNTCOPY_source_gref;
  
  			gop->source.u.ref = txp->gref;
  			gop->source.domid = vif->domid;
  			gop->source.offset = txp->offset;
  
  			gop->dest.domid = DOMID_SELF;
  
  			gop->dest.offset = dst_offset;
  			gop->dest.u.gmfn = virt_to_mfn(page_address(page));
  
  			if (dst_offset + txp->size > PAGE_SIZE) {
  				/* This page can only merge a portion
  				 * of tx request. Do not increment any
  				 * pointer / counter here. The txp
  				 * will be dealt with in future
  				 * rounds, eventually hitting the
  				 * `else` branch.
  				 */
  				gop->len = PAGE_SIZE - dst_offset;
  				txp->offset += gop->len;
  				txp->size -= gop->len;
  				dst_offset += gop->len; /* quit loop */
  			} else {
  				/* This tx request can be merged in the page */
  				gop->len = txp->size;
  				dst_offset += gop->len;
  
  				index = pending_index(vif->pending_cons++);
  
  				pending_idx = vif->pending_ring[index];
  
  				memcpy(&pending_tx_info[pending_idx].req, txp,
  				       sizeof(*txp));
  
  				/* Poison these fields, corresponding
  				 * fields for head tx req will be set
  				 * to correct values after the loop.
  				 */
  				vif->mmap_pages[pending_idx] = (void *)(~0UL);
  				pending_tx_info[pending_idx].head =
  					INVALID_PENDING_RING_IDX;
  
  				if (!first) {
  					first = &pending_tx_info[pending_idx];
  					start_idx = index;
  					head_idx = pending_idx;
  				}
  
  				txp++;
  				slot++;
  			}
  
  			gop++;
  		}
  
  		first->req.offset = 0;
  		first->req.size = dst_offset;
  		first->head = start_idx;
  		vif->mmap_pages[head_idx] = page;
  		frag_set_pending_idx(&frags[shinfo->nr_frags], head_idx);
  	}
  
  	BUG_ON(shinfo->nr_frags > MAX_SKB_FRAGS);
  
  	return gop;
  err:
  	/* Unwind, freeing all pages and sending error responses. */
  	while (shinfo->nr_frags-- > start) {
  		xenvif_idx_release(vif,
  				frag_get_pending_idx(&frags[shinfo->nr_frags]),
  				XEN_NETIF_RSP_ERROR);
  	}
  	/* The head too, if necessary. */
  	if (start)
  		xenvif_idx_release(vif, pending_idx, XEN_NETIF_RSP_ERROR);
  
  	return NULL;
  }
  
  static int xenvif_tx_check_gop(struct xenvif *vif,
  			       struct sk_buff *skb,
  			       struct gnttab_copy **gopp)
  {
  	struct gnttab_copy *gop = *gopp;
  	u16 pending_idx = *((u16 *)skb->data);
  	struct skb_shared_info *shinfo = skb_shinfo(skb);
  	struct pending_tx_info *tx_info;
  	int nr_frags = shinfo->nr_frags;
  	int i, err, start;
  	u16 peek; /* peek into next tx request */
  
  	/* Check status of header. */
  	err = gop->status;
  	if (unlikely(err))
  		xenvif_idx_release(vif, pending_idx, XEN_NETIF_RSP_ERROR);
  
  	/* Skip first skb fragment if it is on same page as header fragment. */
  	start = (frag_get_pending_idx(&shinfo->frags[0]) == pending_idx);
  
  	for (i = start; i < nr_frags; i++) {
  		int j, newerr;
  		pending_ring_idx_t head;
  
  		pending_idx = frag_get_pending_idx(&shinfo->frags[i]);
  		tx_info = &vif->pending_tx_info[pending_idx];
  		head = tx_info->head;
  
  		/* Check error status: if okay then remember grant handle. */
  		do {
  			newerr = (++gop)->status;
  			if (newerr)
  				break;
  			peek = vif->pending_ring[pending_index(++head)];
  		} while (!pending_tx_is_head(vif, peek));
  
  		if (likely(!newerr)) {
  			/* Had a previous error? Invalidate this fragment. */
  			if (unlikely(err))
  				xenvif_idx_release(vif, pending_idx,
  						   XEN_NETIF_RSP_OKAY);
  			continue;
  		}
  
  		/* Error on this fragment: respond to client with an error. */
  		xenvif_idx_release(vif, pending_idx, XEN_NETIF_RSP_ERROR);
  
  		/* Not the first error? Preceding frags already invalidated. */
  		if (err)
  			continue;
  
  		/* First error: invalidate header and preceding fragments. */
  		pending_idx = *((u16 *)skb->data);
  		xenvif_idx_release(vif, pending_idx, XEN_NETIF_RSP_OKAY);
  		for (j = start; j < i; j++) {
  			pending_idx = frag_get_pending_idx(&shinfo->frags[j]);
  			xenvif_idx_release(vif, pending_idx,
  					   XEN_NETIF_RSP_OKAY);
  		}
  
  		/* Remember the error: invalidate all subsequent fragments. */
  		err = newerr;
  	}
  
  	*gopp = gop + 1;
  	return err;
  }
  
  static void xenvif_fill_frags(struct xenvif *vif, struct sk_buff *skb)
  {
  	struct skb_shared_info *shinfo = skb_shinfo(skb);
  	int nr_frags = shinfo->nr_frags;
  	int i;
  
  	for (i = 0; i < nr_frags; i++) {
  		skb_frag_t *frag = shinfo->frags + i;
  		struct xen_netif_tx_request *txp;
  		struct page *page;
  		u16 pending_idx;
  
  		pending_idx = frag_get_pending_idx(frag);
  
  		txp = &vif->pending_tx_info[pending_idx].req;
  		page = virt_to_page(idx_to_kaddr(vif, pending_idx));
  		__skb_fill_page_desc(skb, i, page, txp->offset, txp->size);
  		skb->len += txp->size;
  		skb->data_len += txp->size;
  		skb->truesize += txp->size;
  
  		/* Take an extra reference to offset xenvif_idx_release */
  		get_page(vif->mmap_pages[pending_idx]);
  		xenvif_idx_release(vif, pending_idx, XEN_NETIF_RSP_OKAY);
  	}
  }
  
  static int xenvif_get_extras(struct xenvif *vif,
  				struct xen_netif_extra_info *extras,
  				int work_to_do)
  {
  	struct xen_netif_extra_info extra;
  	RING_IDX cons = vif->tx.req_cons;
  
  	do {
  		if (unlikely(work_to_do-- <= 0)) {
  			netdev_err(vif->dev, "Missing extra info
  ");
  			xenvif_fatal_tx_err(vif);
  			return -EBADR;
  		}
  
  		memcpy(&extra, RING_GET_REQUEST(&vif->tx, cons),
  		       sizeof(extra));
  		if (unlikely(!extra.type ||
  			     extra.type >= XEN_NETIF_EXTRA_TYPE_MAX)) {
  			vif->tx.req_cons = ++cons;
  			netdev_err(vif->dev,
  				   "Invalid extra type: %d
  ", extra.type);
  			xenvif_fatal_tx_err(vif);
  			return -EINVAL;
  		}
  
  		memcpy(&extras[extra.type - 1], &extra, sizeof(extra));
  		vif->tx.req_cons = ++cons;
  	} while (extra.flags & XEN_NETIF_EXTRA_FLAG_MORE);
  
  	return work_to_do;
  }
  
  static int xenvif_set_skb_gso(struct xenvif *vif,
  			      struct sk_buff *skb,
  			      struct xen_netif_extra_info *gso)
  {
  	if (!gso->u.gso.size) {
  		netdev_err(vif->dev, "GSO size must not be zero.
  ");
  		xenvif_fatal_tx_err(vif);
  		return -EINVAL;
  	}
  
  	switch (gso->u.gso.type) {
  	case XEN_NETIF_GSO_TYPE_TCPV4:
  		skb_shinfo(skb)->gso_type = SKB_GSO_TCPV4;
  		break;
  	case XEN_NETIF_GSO_TYPE_TCPV6:
  		skb_shinfo(skb)->gso_type = SKB_GSO_TCPV6;
  		break;
  	default:
  		netdev_err(vif->dev, "Bad GSO type %d.
  ", gso->u.gso.type);
  		xenvif_fatal_tx_err(vif);
  		return -EINVAL;
  	}
  
  	skb_shinfo(skb)->gso_size = gso->u.gso.size;
  	/* gso_segs will be calculated later */
  
  	return 0;
  }
  
  static int checksum_setup(struct xenvif *vif, 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)) {
  		vif->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 bool tx_credit_exceeded(struct xenvif *vif, unsigned size)
  {
  	u64 now = get_jiffies_64();
  	u64 next_credit = vif->credit_window_start +
  		msecs_to_jiffies(vif->credit_usec / 1000);
  
  	/* Timer could already be pending in rare cases. */
  	if (timer_pending(&vif->credit_timeout))
  		return true;
  
  	/* Passed the point where we can replenish credit? */
  	if (time_after_eq64(now, next_credit)) {
  		vif->credit_window_start = now;
  		tx_add_credit(vif);
  	}
  
  	/* Still too big to send right now? Set a callback. */
  	if (size > vif->remaining_credit) {
  		vif->credit_timeout.data     =
  			(unsigned long)vif;
  		vif->credit_timeout.function =
  			tx_credit_callback;
  		mod_timer(&vif->credit_timeout,
  			  next_credit);
  		vif->credit_window_start = next_credit;
  
  		return true;
  	}
  
  	return false;
  }
  
  static unsigned xenvif_tx_build_gops(struct xenvif *vif, int budget)
  {
  	struct gnttab_copy *gop = vif->tx_copy_ops, *request_gop;
  	struct sk_buff *skb;
  	int ret;
  
  	while ((nr_pending_reqs(vif) + XEN_NETBK_LEGACY_SLOTS_MAX
  		< MAX_PENDING_REQS) &&
  	       (skb_queue_len(&vif->tx_queue) < budget)) {
  		struct xen_netif_tx_request txreq;
  		struct xen_netif_tx_request txfrags[XEN_NETBK_LEGACY_SLOTS_MAX];
  		struct page *page;
  		struct xen_netif_extra_info extras[XEN_NETIF_EXTRA_TYPE_MAX-1];
  		u16 pending_idx;
  		RING_IDX idx;
  		int work_to_do;
  		unsigned int data_len;
  		pending_ring_idx_t index;
  
  		if (vif->tx.sring->req_prod - vif->tx.req_cons >
  		    XEN_NETIF_TX_RING_SIZE) {
  			netdev_err(vif->dev,
  				   "Impossible number of requests. "
  				   "req_prod %d, req_cons %d, size %ld
  ",
  				   vif->tx.sring->req_prod, vif->tx.req_cons,
  				   XEN_NETIF_TX_RING_SIZE);
  			xenvif_fatal_tx_err(vif);
  			break;
  		}
  
  		work_to_do = RING_HAS_UNCONSUMED_REQUESTS(&vif->tx);
  		if (!work_to_do)
  			break;
  
  		idx = vif->tx.req_cons;
  		rmb(); /* Ensure that we see the request before we copy it. */
  		memcpy(&txreq, RING_GET_REQUEST(&vif->tx, idx), sizeof(txreq));
  
  		/* Credit-based scheduling. */
  		if (txreq.size > vif->remaining_credit &&
  		    tx_credit_exceeded(vif, txreq.size))
  			break;
  
  		vif->remaining_credit -= txreq.size;
  
  		work_to_do--;
  		vif->tx.req_cons = ++idx;
  
  		memset(extras, 0, sizeof(extras));
  		if (txreq.flags & XEN_NETTXF_extra_info) {
  			work_to_do = xenvif_get_extras(vif, extras,
  						       work_to_do);
  			idx = vif->tx.req_cons;
  			if (unlikely(work_to_do < 0))
  				break;
  		}
  
  		ret = xenvif_count_requests(vif, &txreq, txfrags, work_to_do);
  		if (unlikely(ret < 0))
  			break;
  
  		idx += ret;
  
  		if (unlikely(txreq.size < ETH_HLEN)) {
  			netdev_dbg(vif->dev,
  				   "Bad packet size: %d
  ", txreq.size);
  			xenvif_tx_err(vif, &txreq, idx);
  			break;
  		}
  
  		/* No crossing a page as the payload mustn't fragment. */
  		if (unlikely((txreq.offset + txreq.size) > PAGE_SIZE)) {
  			netdev_err(vif->dev,
  				   "txreq.offset: %x, size: %u, end: %lu
  ",
  				   txreq.offset, txreq.size,
  				   (txreq.offset&~PAGE_MASK) + txreq.size);
  			xenvif_fatal_tx_err(vif);
  			break;
  		}
  
  		index = pending_index(vif->pending_cons);
  		pending_idx = vif->pending_ring[index];
  
  		data_len = (txreq.size > PKT_PROT_LEN &&
  			    ret < XEN_NETBK_LEGACY_SLOTS_MAX) ?
  			PKT_PROT_LEN : txreq.size;
  
  		skb = alloc_skb(data_len + NET_SKB_PAD + NET_IP_ALIGN,
  				GFP_ATOMIC | __GFP_NOWARN);
  		if (unlikely(skb == NULL)) {
  			netdev_dbg(vif->dev,
  				   "Can't allocate a skb in start_xmit.
  ");
  			xenvif_tx_err(vif, &txreq, idx);
  			break;
  		}
  
  		/* Packets passed to netif_rx() must have some headroom. */
  		skb_reserve(skb, NET_SKB_PAD + NET_IP_ALIGN);
  
  		if (extras[XEN_NETIF_EXTRA_TYPE_GSO - 1].type) {
  			struct xen_netif_extra_info *gso;
  			gso = &extras[XEN_NETIF_EXTRA_TYPE_GSO - 1];
  
  			if (xenvif_set_skb_gso(vif, skb, gso)) {
  				/* Failure in xenvif_set_skb_gso is fatal. */
  				kfree_skb(skb);
  				break;
  			}
  		}
  
  		/* XXX could copy straight to head */
  		page = xenvif_alloc_page(vif, pending_idx);
  		if (!page) {
  			kfree_skb(skb);
  			xenvif_tx_err(vif, &txreq, idx);
  			break;
  		}
  
  		gop->source.u.ref = txreq.gref;
  		gop->source.domid = vif->domid;
  		gop->source.offset = txreq.offset;
  
  		gop->dest.u.gmfn = virt_to_mfn(page_address(page));
  		gop->dest.domid = DOMID_SELF;
  		gop->dest.offset = txreq.offset;
  
  		gop->len = txreq.size;
  		gop->flags = GNTCOPY_source_gref;
  
  		gop++;
  
  		memcpy(&vif->pending_tx_info[pending_idx].req,
  		       &txreq, sizeof(txreq));
  		vif->pending_tx_info[pending_idx].head = index;
  		*((u16 *)skb->data) = pending_idx;
  
  		__skb_put(skb, data_len);
  
  		skb_shinfo(skb)->nr_frags = ret;
  		if (data_len < txreq.size) {
  			skb_shinfo(skb)->nr_frags++;
  			frag_set_pending_idx(&skb_shinfo(skb)->frags[0],
  					     pending_idx);
  		} else {
  			frag_set_pending_idx(&skb_shinfo(skb)->frags[0],
  					     INVALID_PENDING_IDX);
  		}
  
  		vif->pending_cons++;
  
  		request_gop = xenvif_get_requests(vif, skb, txfrags, gop);
  		if (request_gop == NULL) {
  			kfree_skb(skb);
  			xenvif_tx_err(vif, &txreq, idx);
  			break;
  		}
  		gop = request_gop;
  
  		__skb_queue_tail(&vif->tx_queue, skb);
  
  		vif->tx.req_cons = idx;
  
  		if ((gop-vif->tx_copy_ops) >= ARRAY_SIZE(vif->tx_copy_ops))
  			break;
  	}
  
  	return gop - vif->tx_copy_ops;
  }
  
  
  static int xenvif_tx_submit(struct xenvif *vif)
  {
  	struct gnttab_copy *gop = vif->tx_copy_ops;
  	struct sk_buff *skb;
  	int work_done = 0;
  
  	while ((skb = __skb_dequeue(&vif->tx_queue)) != NULL) {
  		struct xen_netif_tx_request *txp;
  		u16 pending_idx;
  		unsigned data_len;
  
  		pending_idx = *((u16 *)skb->data);
  		txp = &vif->pending_tx_info[pending_idx].req;
  
  		/* Check the remap error code. */
  		if (unlikely(xenvif_tx_check_gop(vif, skb, &gop))) {
  			netdev_dbg(vif->dev, "netback grant failed.
  ");
  			skb_shinfo(skb)->nr_frags = 0;
  			kfree_skb(skb);
  			continue;
  		}
  
  		data_len = skb->len;
  		memcpy(skb->data,
  		       (void *)(idx_to_kaddr(vif, pending_idx)|txp->offset),
  		       data_len);
  		if (data_len < txp->size) {
  			/* Append the packet payload as a fragment. */
  			txp->offset += data_len;
  			txp->size -= data_len;
  		} else {
  			/* Schedule a response immediately. */
  			xenvif_idx_release(vif, pending_idx,
  					   XEN_NETIF_RSP_OKAY);
  		}
  
  		if (txp->flags & XEN_NETTXF_csum_blank)
  			skb->ip_summed = CHECKSUM_PARTIAL;
  		else if (txp->flags & XEN_NETTXF_data_validated)
  			skb->ip_summed = CHECKSUM_UNNECESSARY;
  
  		xenvif_fill_frags(vif, skb);
  
  		if (skb_is_nonlinear(skb) && skb_headlen(skb) < PKT_PROT_LEN) {
  			int target = min_t(int, skb->len, PKT_PROT_LEN);
  			__pskb_pull_tail(skb, target - skb_headlen(skb));
  		}
  
  		skb->dev      = vif->dev;
  		skb->protocol = eth_type_trans(skb, skb->dev);
  		skb_reset_network_header(skb);
  
  		if (checksum_setup(vif, skb)) {
  			netdev_dbg(vif->dev,
  				   "Can't setup checksum in net_tx_action
  ");
  			kfree_skb(skb);
  			continue;
  		}
  
  		skb_probe_transport_header(skb, 0);
  
  		/* If the packet is GSO then we will have just set up the
  		 * transport header offset in checksum_setup so it's now
  		 * straightforward to calculate gso_segs.
  		 */
  		if (skb_is_gso(skb)) {
  			int mss = skb_shinfo(skb)->gso_size;
  			int hdrlen = skb_transport_header(skb) -
  				skb_mac_header(skb) +
  				tcp_hdrlen(skb);
  
  			skb_shinfo(skb)->gso_segs =
  				DIV_ROUND_UP(skb->len - hdrlen, mss);
  		}
  
  		vif->dev->stats.rx_bytes += skb->len;
  		vif->dev->stats.rx_packets++;
  
  		work_done++;
  
  		netif_receive_skb(skb);
  	}
  
  	return work_done;
  }
  
  /* Called after netfront has transmitted */
  int xenvif_tx_action(struct xenvif *vif, int budget)
  {
  	unsigned nr_gops;
  	int work_done;
  
  	if (unlikely(!tx_work_todo(vif)))
  		return 0;
  
  	nr_gops = xenvif_tx_build_gops(vif, budget);
  
  	if (nr_gops == 0)
  		return 0;
  
  	gnttab_batch_copy(vif->tx_copy_ops, nr_gops);
  
  	work_done = xenvif_tx_submit(vif);
  
  	return work_done;
  }
  
  static void xenvif_idx_release(struct xenvif *vif, u16 pending_idx,
  			       u8 status)
  {
  	struct pending_tx_info *pending_tx_info;
  	pending_ring_idx_t head;
  	u16 peek; /* peek into next tx request */
  
  	BUG_ON(vif->mmap_pages[pending_idx] == (void *)(~0UL));
  
  	/* Already complete? */
  	if (vif->mmap_pages[pending_idx] == NULL)
  		return;
  
  	pending_tx_info = &vif->pending_tx_info[pending_idx];
  
  	head = pending_tx_info->head;
  
  	BUG_ON(!pending_tx_is_head(vif, head));
  	BUG_ON(vif->pending_ring[pending_index(head)] != pending_idx);
  
  	do {
  		pending_ring_idx_t index;
  		pending_ring_idx_t idx = pending_index(head);
  		u16 info_idx = vif->pending_ring[idx];
  
  		pending_tx_info = &vif->pending_tx_info[info_idx];
  		make_tx_response(vif, &pending_tx_info->req, status);
  
  		/* Setting any number other than
  		 * INVALID_PENDING_RING_IDX indicates this slot is
  		 * starting a new packet / ending a previous packet.
  		 */
  		pending_tx_info->head = 0;
  
  		index = pending_index(vif->pending_prod++);
  		vif->pending_ring[index] = vif->pending_ring[info_idx];
  
  		peek = vif->pending_ring[pending_index(++head)];
  
  	} while (!pending_tx_is_head(vif, peek));
  
  	put_page(vif->mmap_pages[pending_idx]);
  	vif->mmap_pages[pending_idx] = NULL;
  }
  
  
  static void make_tx_response(struct xenvif *vif,
  			     struct xen_netif_tx_request *txp,
  			     s8       st)
  {
  	RING_IDX i = vif->tx.rsp_prod_pvt;
  	struct xen_netif_tx_response *resp;
  	int notify;
  
  	resp = RING_GET_RESPONSE(&vif->tx, i);
  	resp->id     = txp->id;
  	resp->status = st;
  
  	if (txp->flags & XEN_NETTXF_extra_info)
  		RING_GET_RESPONSE(&vif->tx, ++i)->status = XEN_NETIF_RSP_NULL;
  
  	vif->tx.rsp_prod_pvt = ++i;
  	RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&vif->tx, notify);
  	if (notify)
  		notify_remote_via_irq(vif->tx_irq);
  }
  
  static struct xen_netif_rx_response *make_rx_response(struct xenvif *vif,
  					     u16      id,
  					     s8       st,
  					     u16      offset,
  					     u16      size,
  					     u16      flags)
  {
  	RING_IDX i = vif->rx.rsp_prod_pvt;
  	struct xen_netif_rx_response *resp;
  
  	resp = RING_GET_RESPONSE(&vif->rx, i);
  	resp->offset     = offset;
  	resp->flags      = flags;
  	resp->id         = id;
  	resp->status     = (s16)size;
  	if (st < 0)
  		resp->status = (s16)st;
  
  	vif->rx.rsp_prod_pvt = ++i;
  
  	return resp;
  }
  
  static inline int rx_work_todo(struct xenvif *vif)
  {
  	return !skb_queue_empty(&vif->rx_queue) &&
  	       xenvif_rx_ring_slots_available(vif, vif->rx_last_skb_slots);
  }
  
  static inline int tx_work_todo(struct xenvif *vif)
  {
  
  	if (likely(RING_HAS_UNCONSUMED_REQUESTS(&vif->tx)) &&
  	    (nr_pending_reqs(vif) + XEN_NETBK_LEGACY_SLOTS_MAX
  	     < MAX_PENDING_REQS))
  		return 1;
  
  	return 0;
  }
  
  void xenvif_unmap_frontend_rings(struct xenvif *vif)
  {
  	if (vif->tx.sring)
  		xenbus_unmap_ring_vfree(xenvif_to_xenbus_device(vif),
  					vif->tx.sring);
  	if (vif->rx.sring)
  		xenbus_unmap_ring_vfree(xenvif_to_xenbus_device(vif),
  					vif->rx.sring);
  }
  
  int xenvif_map_frontend_rings(struct xenvif *vif,
  			      grant_ref_t tx_ring_ref,
  			      grant_ref_t rx_ring_ref)
  {
  	void *addr;
  	struct xen_netif_tx_sring *txs;
  	struct xen_netif_rx_sring *rxs;
  
  	int err = -ENOMEM;
  
  	err = xenbus_map_ring_valloc(xenvif_to_xenbus_device(vif),
  				     tx_ring_ref, &addr);
  	if (err)
  		goto err;
  
  	txs = (struct xen_netif_tx_sring *)addr;
  	BACK_RING_INIT(&vif->tx, txs, PAGE_SIZE);
  
  	err = xenbus_map_ring_valloc(xenvif_to_xenbus_device(vif),
  				     rx_ring_ref, &addr);
  	if (err)
  		goto err;
  
  	rxs = (struct xen_netif_rx_sring *)addr;
  	BACK_RING_INIT(&vif->rx, rxs, PAGE_SIZE);
  
  	return 0;
  
  err:
  	xenvif_unmap_frontend_rings(vif);
  	return err;
  }
  
  void xenvif_stop_queue(struct xenvif *vif)
  {
  	if (!vif->can_queue)
  		return;
  
  	netif_stop_queue(vif->dev);
  }
  
  static void xenvif_start_queue(struct xenvif *vif)
  {
  	if (xenvif_schedulable(vif))
  		netif_wake_queue(vif->dev);
  }
  
  int xenvif_kthread(void *data)
  {
  	struct xenvif *vif = data;
  	struct sk_buff *skb;
  
  	while (!kthread_should_stop()) {
  		wait_event_interruptible(vif->wq,
  					 rx_work_todo(vif) ||
  					 vif->disabled ||
  					 kthread_should_stop());
  
  		/* This frontend is found to be rogue, disable it in
  		 * kthread context. Currently this is only set when
  		 * netback finds out frontend sends malformed packet,
  		 * but we cannot disable the interface in softirq
  		 * context so we defer it here.
  		 */
  		if (unlikely(vif->disabled && netif_carrier_ok(vif->dev)))
  			xenvif_carrier_off(vif);
  
  		if (kthread_should_stop())
  			break;
  
  		if (!skb_queue_empty(&vif->rx_queue))
  			xenvif_rx_action(vif);
  
  		if (skb_queue_empty(&vif->rx_queue) &&
  		    netif_queue_stopped(vif->dev))
  			xenvif_start_queue(vif);
  
  		cond_resched();
  	}
  
  	/* Bin any remaining skbs */
  	while ((skb = skb_dequeue(&vif->rx_queue)) != NULL)
  		dev_kfree_skb(skb);
  
  	return 0;
  }
  
  static int __init netback_init(void)
  {
  	int rc = 0;
  
  	if (!xen_domain())
  		return -ENODEV;
  
  	if (fatal_skb_slots < XEN_NETBK_LEGACY_SLOTS_MAX) {
  		pr_info("fatal_skb_slots too small (%d), bump it to XEN_NETBK_LEGACY_SLOTS_MAX (%d)
  ",
  			fatal_skb_slots, XEN_NETBK_LEGACY_SLOTS_MAX);
  		fatal_skb_slots = XEN_NETBK_LEGACY_SLOTS_MAX;
  	}
  
  	rc = xenvif_xenbus_init();
  	if (rc)
  		goto failed_init;
  
  	return 0;
  
  failed_init:
  	return rc;
  }
  
  module_init(netback_init);
  
  static void __exit netback_fini(void)
  {
  	xenvif_xenbus_fini();
  }
  module_exit(netback_fini);
  
  MODULE_LICENSE("Dual BSD/GPL");
  MODULE_ALIAS("xen-backend:vif");