add: put_fd(descriptor);
context: user_ioctl(int fd, ulong op, void *buffer, size_t length){	struct file_descriptor *descriptor;	int status;	CHECK_USER_ADDR(buffer)	PRINT(("user_ioctl: fd %d\n", fd));	descriptor = get_fd(get_current_io_context(false), fd);	if (!descriptor)		return EBADF;	if (descriptor->ops->fd_ioctl)		status = descriptor->ops->fd_ioctl(descriptor, op, buffer, length);	else		status = EOPNOTSUPP;	return status;}