sk_attach_filter
ret = sk_attach_filter(&tun->fprog, tfile->socket.sk);
err = sk_attach_filter(&tun->fprog, tfile->socket.sk);
int sk_attach_filter(struct sock_fprog *fprog, struct sock *sk);
EXPORT_SYMBOL_GPL(sk_attach_filter);
ret = sk_attach_filter(&fprog, sk);