tty: tty_port: Add a kref object to the tty port

Users of tty port need a way to refcount ports when hotplugging is
involved.

Signed-off-by: Alan Cox <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/char/tty_port.c

···
 	spin_lock_init(&port->lock);
 	port->close_delay = (50 * HZ) / 100;
 	port->closing_wait = (3000 * HZ) / 100;
+	kref_init(&port->kref);
 }
 EXPORT_SYMBOL(tty_port_init);
 
···
 }
 EXPORT_SYMBOL(tty_port_free_xmit_buf);
 
+static void tty_port_destructor(struct kref *kref)
+{
+	struct tty_port *port = container_of(kref, struct tty_port, kref);
+	if (port->xmit_buf)
+		free_page((unsigned long)port->xmit_buf);
+	if (port->ops->destruct)
+		port->ops->destruct(port);
+	else
+		kfree(port);
+}
+
+void tty_port_put(struct tty_port *port)
+{
+	if (port)
+		kref_put(&port->kref, tty_port_destructor);
+}
+EXPORT_SYMBOL(tty_port_put);
 
 /**
  *	tty_port_tty_get	-	get a tty reference

include/linux/tty.h

···
         /* 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);
+	/* Called on the final put of a port */
+	void (*destruct)(struct tty_port *port);
 };
 	
 struct tty_port {
···
 	int			drain_delay;	/* Set to zero if no pure time
 						   based drain is needed else
 						   set to size of fifo */
+	struct kref		kref;		/* Ref counter */
 };
 
 /*
···
 extern void tty_port_init(struct tty_port *port);
 extern int tty_port_alloc_xmit_buf(struct tty_port *port);
 extern void tty_port_free_xmit_buf(struct tty_port *port);
+extern void tty_port_put(struct tty_port *port);
+
+extern inline struct tty_port *tty_port_get(struct tty_port *port)
+{
+	if (port)
+		kref_get(&port->kref);
+	return port;
+}
+
 extern struct tty_struct *tty_port_tty_get(struct tty_port *port);
 extern void tty_port_tty_set(struct tty_port *port, struct tty_struct *tty);
 extern int tty_port_carrier_raised(struct tty_port *port);