tty: Introduce a tty_port generic block_til_ready

Start sucking more commonality out of the drivers into a single piece of
core code.

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/tty.h b/include/linux/tty.h
index a1a9314..61a0ab3 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -439,6 +439,8 @@
 extern int tty_port_carrier_raised(struct tty_port *port);
 extern void tty_port_raise_dtr_rts(struct tty_port *port);
 extern void tty_port_hangup(struct tty_port *port);
+extern int tty_port_block_til_ready(struct tty_port *port,
+				struct tty_struct *tty, struct file *filp);
 
 extern int tty_register_ldisc(int disc, struct tty_ldisc_ops *new_ldisc);
 extern int tty_unregister_ldisc(int disc);