+ /* Calculate UDP checksum if configured to do so */
+ if (sk_tun->sk_no_check == UDP_CSUM_NOXMIT)
+ skb->ip_summed = CHECKSUM_NONE;
+ else if (!(skb->dst->dev->features & NETIF_F_V4_CSUM)) {
+ skb->ip_summed = CHECKSUM_COMPLETE;
+ csum = skb_checksum(skb, 0, udp_len, 0);
+ uh->check = csum_tcpudp_magic(inet->saddr, inet->daddr,
+ udp_len, IPPROTO_UDP, csum);
+ if (uh->check == 0)
+ uh->check = CSUM_MANGLED_0;
+ } else {
+ skb->ip_summed = CHECKSUM_PARTIAL;
+ skb->csum_start = skb_transport_header(skb) - skb->head;
+ skb->csum_offset = offsetof(struct udphdr, check);
+ uh->check = ~csum_tcpudp_magic(inet->saddr, inet->daddr,
+ udp_len, IPPROTO_UDP, 0);
+ }
+