BPF_CALL_5(bpf_csum_diff, __be32 *, from, u32, from_size,
	   __be32 *, to, u32, to_size, __wsum, seed)
{
	struct bpf_scratchpad *sp = this_cpu_ptr(&bpf_sp);
	u32 diff_size = from_size + to_size;
	int i, j = 0;

	/* This is quite flexible, some examples:
	 *
	 * from_size == 0, to_size > 0,  seed := csum --> pushing data
	 * from_size > 0,  to_size == 0, seed := csum --> pulling data
	 * from_size > 0,  to_size > 0,  seed := 0    --> diffing data
	 *
	 * Even for diffing, from_size and to_size don't need to be equal.
	 */
	if (unlikely(((from_size | to_size) & (sizeof(__be32) - 1)) ||
		     diff_size > sizeof(sp->diff)))
		return -EINVAL;

	for (i = 0; i < from_size / sizeof(__be32); i++, j++)
		sp->diff[j] = ~from[i];
	for (i = 0; i <   to_size / sizeof(__be32); i++, j++)
		sp->diff[j] = to[i];

	return csum_partial(sp->diff, diff_size, seed);
}
BPF_CALL_5(bpf_csum_diff, __be32 *, from, u32, from_size,
	   __be32 *, to, u32, to_size, __wsum, seed)
{
	struct bpf_scratchpad *sp = this_cpu_ptr(&bpf_sp);
	u32 diff_size = from_size + to_size;
	int i, j = 0;

	 
	if (unlikely(((from_size | to_size) & (sizeof(__be32) - 1)) ||
		     diff_size > sizeof(sp->diff)))
		return -EINVAL;

	for (i = 0; i < from_size / sizeof(__be32); i++, j++)
		sp->diff[j] = ~from[i];
	for (i = 0; i <   to_size / sizeof(__be32); i++, j++)
		sp->diff[j] = to[i];

	return csum_partial(sp->diff, diff_size, seed);
}