fd_prepare_fd
handlereq.fd = fd_prepare_fd(fdf);
atomic_inc_return(&mdev->request_id), fd_prepare_fd(fdf));
error = put_user(fd_prepare_fd(fdf), ufd);
mc.out_fd = fd_prepare_fd(fdf);
err = req->hr_proto->hp_accept(req, info, fd_prepare_fd(fdf));
trace_handshake_cmd_accept(net, req, req->hr_sk, fd_prepare_fd(fdf));
info.fd = fd_prepare_fd(fdf);