static int xenvif_tx_submit(struct xenvif *vif)
{
	struct gnttab_map_grant_ref *gop = vif->tx_map_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 = XENVIF_TX_CB(skb)->pending_idx;
		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.\n");
			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);
		callback_param(vif, pending_idx).ctx = NULL;
		if (data_len < txp->size) {
			/* Append the packet payload as a fragment. */
			txp->offset += data_len;
			txp->size -= data_len;
			skb_shinfo(skb)->destructor_arg =
				&callback_param(vif, pending_idx);
		} else {
			/* Schedule a response immediately. */
			xenvif_idx_unmap(vif, pending_idx);
		}

		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 (unlikely(skb_has_frag_list(skb))) {
			if (xenvif_handle_frag_list(vif, skb)) {
				if (net_ratelimit())
					netdev_err(vif->dev,
						   "Not enough memory to consolidate frag_list!\n");
				skb_shinfo(skb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
				kfree_skb(skb);
				continue;
			}
		}

		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\n");
			/* We have to set this flag to trigger the callback */
			if (skb_shinfo(skb)->destructor_arg)
				skb_shinfo(skb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
			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++;

		/* Set this flag right before netif_receive_skb, otherwise
		 * someone might think this packet already left netback, and
		 * do a skb_copy_ubufs while we are still in control of the
		 * skb. E.g. the __pskb_pull_tail earlier can do such thing.
		 */
		if (skb_shinfo(skb)->destructor_arg) {
			skb_shinfo(skb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
			vif->tx_zerocopy_sent++;
		}

		netif_receive_skb(skb);
	}

	return work_done;
}
static int xenvif_tx_submit(struct xenvif *vif)
{
	struct gnttab_map_grant_ref *gop = vif->tx_map_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 = XENVIF_TX_CB(skb)->pending_idx;
		txp = &vif->pending_tx_info[pending_idx].req;

		 
		if (unlikely(xenvif_tx_check_gop(vif, skb, &gop))) {
			netdev_dbg(vif->dev, "netback grant failed.\n");
			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);
		callback_param(vif, pending_idx).ctx = NULL;
		if (data_len < txp->size) {
			 
			txp->offset += data_len;
			txp->size -= data_len;
			skb_shinfo(skb)->destructor_arg =
				&callback_param(vif, pending_idx);
		} else {
			 
			xenvif_idx_unmap(vif, pending_idx);
		}

		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 (unlikely(skb_has_frag_list(skb))) {
			if (xenvif_handle_frag_list(vif, skb)) {
				if (net_ratelimit())
					netdev_err(vif->dev,
						   "Not enough memory to consolidate frag_list!\n");
				skb_shinfo(skb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
				kfree_skb(skb);
				continue;
			}
		}

		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\n");
			 
			if (skb_shinfo(skb)->destructor_arg)
				skb_shinfo(skb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
			kfree_skb(skb);
			continue;
		}

		skb_probe_transport_header(skb, 0);

		 
		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++;

		 
		if (skb_shinfo(skb)->destructor_arg) {
			skb_shinfo(skb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
			vif->tx_zerocopy_sent++;
		}

		netif_receive_skb(skb);
	}

	return work_done;
}