+static __sum16 nf_ip_checksum_partial(struct sk_buff *skb, unsigned int hook,
+ unsigned int dataoff, unsigned int len,
+ u_int8_t protocol)
+{
+ const struct iphdr *iph = ip_hdr(skb);
+ __sum16 csum = 0;
+
+ switch (skb->ip_summed) {
+ case CHECKSUM_COMPLETE:
+ if (len == skb->len - dataoff)
+ return nf_ip_checksum(skb, hook, dataoff, protocol);
+ /* fall through */
+ case CHECKSUM_NONE:
+ skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr, protocol,
+ skb->len - dataoff, 0);
+ skb->ip_summed = CHECKSUM_NONE;
+ csum = __skb_checksum_complete_head(skb, dataoff + len);
+ if (!csum)
+ skb->ip_summed = CHECKSUM_UNNECESSARY;
+ }
+ return csum;
+}
+