Using devfs to address device driver

Hi All I am writing a device driver that should use the existing serial port + custom hardware. Problem is that I want to use loadable modules and need to talk with the serial port driver via the devfs (is this the best way ?). I can get a file handle , no problem, but when I want to call the tty_open() procedure it requires parameters (inode, file *). How do I get hold of them ?

Thanks in advance reyems