BPF_CALL_2(bpf_csum_update, struct sk_buff *, skb, __wsum, csum)
{
	/* The interface is to be used in combination with bpf_csum_diff()
	 * for direct packet writes. csum rotation for alignment as well
	 * as emulating csum_sub() can be done from the eBPF program.
	 */
	if (skb->ip_summed == CHECKSUM_COMPLETE)
		return (skb->csum = csum_add(skb->csum, csum));

	return -ENOTSUPP;
}
Unknown