struct tty_port;
================

----------------
void tty_port_init(struct tty_port *port);

/**
 * tty_port_destroy -- destroy inited port
 * @port: tty port to be doestroyed
 *
 * When a port was initialized using tty_port_init, one has to destroy the
 * port by this function. Either indirectly by using tty_port refcounting
 * (tty_port_put) or directly if refcounting is not used.
 */
void tty_port_destroy(struct tty_port *port);

----------------
struct tty_port_operations {
    ...
	/* Called when the last close completes or a hangup finishes
	   IFF the port was initialized. Do not use to free resources. Called
	   under the port mutex to serialize against activate/shutdowns */
	void (*shutdown)(struct tty_port *port);
    ...
	/* Called under the port mutex from tty_port_open, serialized using
	   the port mutex */
        /* FIXME: long term getting the tty argument *out* of this would be
           good for consoles */
	int (*activate)(struct tty_port *port, struct tty_struct *tty);
    ...
};

int tty_port_open(struct tty_port *port,
				struct tty_struct *tty, struct file *filp);

void tty_port_close(struct tty_port *port,
				struct tty_struct *tty, struct file *filp);

struct tty_operations {
    ...
	int  (*open)(struct tty_struct * tty, struct file * filp);
	void (*close)(struct tty_struct * tty, struct file * filp);
    ...
}

tty_operations -> open
    tty_port_open
        //call activate if and only if first process open tty
        tty_port_operations -> activate

tty_operations -> close
    tty_port_close
        //call shutdown if and only if last process close tty
        tty_port_operations -> shutdown

----------------
/**
 * tty_port_register_device - register tty device
 * @port: tty_port of the device
 * @driver: tty_driver for this device
 * @index: index of the tty
 * @device: parent if exists, otherwise NULL
 *
 * It is the same as tty_register_device except the provided @port is linked to
 * a concrete tty specified by @index. Use this or tty_port_install (or both).
 * Call tty_port_link_device as a last resort.
 */
struct device *tty_port_register_device(struct tty_port *port,
		struct tty_driver *driver, unsigned index,
		struct device *device);