+/**
+ * udp4_hwcsum_outgoing - handle outgoing HW checksumming
+ * @sk: socket we are sending on
+ * @skb: sk_buff containing the filled-in UDP header
+ * (checksum field must be zeroed out)
+ */
+static void udp4_hwcsum_outgoing(struct sock *sk, struct sk_buff *skb,
+ __be32 src, __be32 dst, int len )
+{
+ unsigned int offset;
+ struct udphdr *uh = skb->h.uh;
+ __wsum csum = 0;
+
+ if (skb_queue_len(&sk->sk_write_queue) == 1) {
+ /*
+ * Only one fragment on the socket.
+ */
+ skb->csum_offset = offsetof(struct udphdr, check);
+ uh->check = ~csum_tcpudp_magic(src, dst, len, IPPROTO_UDP, 0);
+ } else {
+ /*
+ * HW-checksum won't work as there are two or more
+ * fragments on the socket so that all csums of sk_buffs
+ * should be together
+ */
+ offset = skb->h.raw - skb->data;
+ skb->csum = skb_checksum(skb, offset, skb->len - offset, 0);
+
+ skb->ip_summed = CHECKSUM_NONE;
+
+ skb_queue_walk(&sk->sk_write_queue, skb) {
+ csum = csum_add(csum, skb->csum);
+ }
+
+ uh->check = csum_tcpudp_magic(src, dst, len, IPPROTO_UDP, csum);
+ if (uh->check == 0)
+ uh->check = CSUM_MANGLED_0;
+ }
+}
+