I define structt iov_iter___old and struct iov_iter___new, and then use bpf_core_field_exists(((struct iov_iter___new )0)->__iov) to judge whether to use struct iov_iter___new iter = (void )&msg->msg_iter or struct iov_iter___old iter = (void *)&msg->msg_iter
Sure, but I developed a project by myself after learning the basic grammar, and reviewed it repeatedly during the development. I think this method is very effective.