TTY: introduce deinit helpers for proper ldisc shutdown

Introduce deinitialize_tty_struct which should be called after
initialize_tty_struct and before successfull tty_ldisc_setup.

It calls tty_ldisc_deinit which is opposite of tty_ldisc_init. It only
puts a reference to ldisc and assigns NULL to tty->ldisc.

It will be used to shut down ldisc when tty_release cannot be called
yet.
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/tty/tty_io.c

@@ -2886,6 +2886,20 @@ void initialize_tty_struct(struct tty_struct *tty,
 	tty->dev = tty_get_device(tty);
 }
 
+/**
+ *	deinitialize_tty_struct
+ *	@tty: tty to deinitialize
+ *
+ *	This subroutine deinitializes a tty structure that has been newly
+ *	allocated but tty_release cannot be called on that yet.
+ *
+ *	Locking: none - tty in question must not be exposed at this point
+ */
+void deinitialize_tty_struct(struct tty_struct *tty)
+{
+	tty_ldisc_deinit(tty);
+}
+
 /**
  *	tty_put_char	-	write one character to a tty
  *	@tty: tty

drivers/tty/tty_ldisc.c

@@ -956,6 +956,19 @@ void tty_ldisc_init(struct tty_struct *tty)
 	tty_ldisc_assign(tty, ld);
 }
 
+/**
+ *	tty_ldisc_init		-	ldisc cleanup for new tty
+ *	@tty: tty that was allocated recently
+ *
+ *	The tty structure must not becompletely set up (tty_ldisc_setup) when
+ *      this call is made.
+ */
+void tty_ldisc_deinit(struct tty_struct *tty)
+{
+	put_ldisc(tty->ldisc);
+	tty_ldisc_assign(tty, NULL);
+}
+
 void tty_ldisc_begin(void)
 {
 	/* Setup the default TTY line discipline. */

include/linux/tty.h

@@ -472,6 +472,7 @@ extern int tty_add_file(struct tty_struct *tty, struct file *file);
 extern void free_tty_struct(struct tty_struct *tty);
 extern void initialize_tty_struct(struct tty_struct *tty,
 		struct tty_driver *driver, int idx);
+extern void deinitialize_tty_struct(struct tty_struct *tty);
 extern struct tty_struct *tty_init_dev(struct tty_driver *driver, int idx,
 								int first_ok);
 extern int tty_release(struct inode *inode, struct file *filp);
@@ -525,6 +526,7 @@ extern int tty_set_ldisc(struct tty_struct *tty, int ldisc);
 extern int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty);
 extern void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty);
 extern void tty_ldisc_init(struct tty_struct *tty);
+extern void tty_ldisc_deinit(struct tty_struct *tty);
 extern void tty_ldisc_begin(void);
 /* This last one is just for the tty layer internals and shouldn't be used elsewhere */
 extern void tty_ldisc_enable(struct tty_struct *tty);