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

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

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

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

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

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

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

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

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

	err = 0;

out:
	return err;
}
static int checksum_setup(struct xenvif *vif, struct sk_buff *skb)
{
	struct iphdr *iph;
	unsigned char *th;
	int err = -EPROTO;
	int recalculate_partial_csum = 0;

	 
	if (skb->ip_summed != CHECKSUM_PARTIAL && skb_is_gso(skb)) {
		vif->rx_gso_checksum_fixup++;
		skb->ip_summed = CHECKSUM_PARTIAL;
		recalculate_partial_csum = 1;
	}

	 
	if (skb->ip_summed != CHECKSUM_PARTIAL)
		return 0;

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

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

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

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

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

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

	err = 0;

out:
	return err;
}