csum_and_copy_to_user
extern __wsum csum_and_copy_to_user(const void *src, void __user *dst,
__wsum csum_and_copy_to_user(const void *src, void __user *dst, int len);
extern __wsum csum_and_copy_to_user(const void *src, void __user *dst, int len);
next = csum_and_copy_to_user(from + progress, iter_to, len);