tty: Split ldisc code into its own file

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 724 insertions, 628 deletions

diff --git a/drivers/char/Makefile b/drivers/char/Makefile
index 0e0d12a06462..dc5a327d72d5 100644
--- a/drivers/char/Makefile
+++ b/drivers/char/Makefile
@@ -7,7 +7,7 @@
 #
 FONTMAPFILE = cp437.uni
 
-obj-y	 += mem.o random.o tty_io.o n_tty.o tty_ioctl.o
+obj-y	 += mem.o random.o tty_io.o n_tty.o tty_ioctl.o tty_ldisc.o 
 
 obj-$(CONFIG_LEGACY_PTYS)	+= pty.o
 obj-$(CONFIG_UNIX98_PTYS)	+= pty.o
diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index 82f6a8c86332..d27a08b374d0 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -656,558 +656,6 @@ EXPORT_SYMBOL_GPL(tty_prepare_flip_string_flags);
 
 
 /**
- *	tty_set_termios_ldisc		-	set ldisc field
- *	@tty: tty structure
- *	@num: line discipline number
- *
- *	This is probably overkill for real world processors but
- *	they are not on hot paths so a little discipline won't do
- *	any harm.
- *
- *	Locking: takes termios_mutex
- */
-
-static void tty_set_termios_ldisc(struct tty_struct *tty, int num)
-{
-	mutex_lock(&tty->termios_mutex);
-	tty->termios->c_line = num;
-	mutex_unlock(&tty->termios_mutex);
-}
-
-/*
- *	This guards the refcounted line discipline lists. The lock
- *	must be taken with irqs off because there are hangup path
- *	callers who will do ldisc lookups and cannot sleep.
- */
-
-static DEFINE_SPINLOCK(tty_ldisc_lock);
-static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_wait);
-/* Line disc dispatch table */
-static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
-
-/**
- *	tty_register_ldisc	-	install a line discipline
- *	@disc: ldisc number
- *	@new_ldisc: pointer to the ldisc object
- *
- *	Installs a new line discipline into the kernel. The discipline
- *	is set up as unreferenced and then made available to the kernel
- *	from this point onwards.
- *
- *	Locking:
- *		takes tty_ldisc_lock to guard against ldisc races
- */
-
-int tty_register_ldisc(int disc, struct tty_ldisc_ops *new_ldisc)
-{
-	unsigned long flags;
-	int ret = 0;
-
-	if (disc < N_TTY || disc >= NR_LDISCS)
-		return -EINVAL;
-
-	spin_lock_irqsave(&tty_ldisc_lock, flags);
-	tty_ldiscs[disc] = new_ldisc;
-	new_ldisc->num = disc;
-	new_ldisc->refcount = 0;
-	spin_unlock_irqrestore(&tty_ldisc_lock, flags);
-
-	return ret;
-}
-EXPORT_SYMBOL(tty_register_ldisc);
-
-/**
- *	tty_unregister_ldisc	-	unload a line discipline
- *	@disc: ldisc number
- *	@new_ldisc: pointer to the ldisc object
- *
- *	Remove a line discipline from the kernel providing it is not
- *	currently in use.
- *
- *	Locking:
- *		takes tty_ldisc_lock to guard against ldisc races
- */
-
-int tty_unregister_ldisc(int disc)
-{
-	unsigned long flags;
-	int ret = 0;
-
-	if (disc < N_TTY || disc >= NR_LDISCS)
-		return -EINVAL;
-
-	spin_lock_irqsave(&tty_ldisc_lock, flags);
-	if (tty_ldiscs[disc]->refcount)
-		ret = -EBUSY;
-	else
-		tty_ldiscs[disc] = NULL;
-	spin_unlock_irqrestore(&tty_ldisc_lock, flags);
-
-	return ret;
-}
-EXPORT_SYMBOL(tty_unregister_ldisc);
-
-
-/**
- *	tty_ldisc_try_get	-	try and reference an ldisc
- *	@disc: ldisc number
- *	@ld: tty ldisc structure to complete
- *
- *	Attempt to open and lock a line discipline into place. Return
- *	the line discipline refcounted and assigned in ld. On an error
- *	report the error code back
- */
-
-static int tty_ldisc_try_get(int disc, struct tty_ldisc *ld)
-{
-	unsigned long flags;
-	struct tty_ldisc_ops *ldops;
-	int err = -EINVAL;
-	
-	spin_lock_irqsave(&tty_ldisc_lock, flags);
-	ld->ops = NULL;
-	ldops = tty_ldiscs[disc];
-	/* Check the entry is defined */
-	if (ldops) {
-		/* If the module is being unloaded we can't use it */
-		if (!try_module_get(ldops->owner))
-			err = -EAGAIN;
-		else {
-			/* lock it */
-			ldops->refcount++;
-			ld->ops = ldops;
-			err = 0;
-		}
-	}
-	spin_unlock_irqrestore(&tty_ldisc_lock, flags);
-	return err;
-}
-
-/**
- *	tty_ldisc_get		-	take a reference to an ldisc
- *	@disc: ldisc number
- *	@ld: tty line discipline structure to use
- *
- *	Takes a reference to a line discipline. Deals with refcounts and
- *	module locking counts. Returns NULL if the discipline is not available.
- *	Returns a pointer to the discipline and bumps the ref count if it is
- *	available
- *
- *	Locking:
- *		takes tty_ldisc_lock to guard against ldisc races
- */
-
-static int tty_ldisc_get(int disc, struct tty_ldisc *ld)
-{
-	int err;
-
-	if (disc < N_TTY || disc >= NR_LDISCS)
-		return -EINVAL;
-	err = tty_ldisc_try_get(disc, ld);
-	if (err == -EAGAIN) {
-		request_module("tty-ldisc-%d", disc);
-		err = tty_ldisc_try_get(disc, ld);
-	}
-	return err;
-}
-
-/**
- *	tty_ldisc_put		-	drop ldisc reference
- *	@disc: ldisc number
- *
- *	Drop a reference to a line discipline. Manage refcounts and
- *	module usage counts
- *
- *	Locking:
- *		takes tty_ldisc_lock to guard against ldisc races
- */
-
-static void tty_ldisc_put(struct tty_ldisc_ops *ld)
-{
-	unsigned long flags;
-	int disc = ld->num;
-
-	BUG_ON(disc < N_TTY || disc >= NR_LDISCS);
-
-	spin_lock_irqsave(&tty_ldisc_lock, flags);
-	ld = tty_ldiscs[disc];
-	BUG_ON(ld->refcount == 0);
-	ld->refcount--;
-	module_put(ld->owner);
-	spin_unlock_irqrestore(&tty_ldisc_lock, flags);
-}
-
-static void * tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos)
-{
-	return (*pos < NR_LDISCS) ? pos : NULL;
-}
-
-static void * tty_ldiscs_seq_next(struct seq_file *m, void *v, loff_t *pos)
-{
-	(*pos)++;
-	return (*pos < NR_LDISCS) ? pos : NULL;
-}
-
-static void tty_ldiscs_seq_stop(struct seq_file *m, void *v)
-{
-}
-
-static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
-{
-	int i = *(loff_t *)v;
-	struct tty_ldisc ld;
-	
-	if (tty_ldisc_get(i, &ld) < 0)
-		return 0;
-	seq_printf(m, "%-10s %2d\n", ld.ops->name ? ld.ops->name : "???", i);
-	tty_ldisc_put(ld.ops);
-	return 0;
-}
-
-static const struct seq_operations tty_ldiscs_seq_ops = {
-	.start	= tty_ldiscs_seq_start,
-	.next	= tty_ldiscs_seq_next,
-	.stop	= tty_ldiscs_seq_stop,
-	.show	= tty_ldiscs_seq_show,
-};
-
-static int proc_tty_ldiscs_open(struct inode *inode, struct file *file)
-{
-	return seq_open(file, &tty_ldiscs_seq_ops);
-}
-
-const struct file_operations tty_ldiscs_proc_fops = {
-	.owner		= THIS_MODULE,
-	.open		= proc_tty_ldiscs_open,
-	.read		= seq_read,
-	.llseek		= seq_lseek,
-	.release	= seq_release,
-};
-
-/**
- *	tty_ldisc_assign	-	set ldisc on a tty
- *	@tty: tty to assign
- *	@ld: line discipline
- *
- *	Install an instance of a line discipline into a tty structure. The
- *	ldisc must have a reference count above zero to ensure it remains/
- *	The tty instance refcount starts at zero.
- *
- *	Locking:
- *		Caller must hold references
- */
-
-static void tty_ldisc_assign(struct tty_struct *tty, struct tty_ldisc *ld)
-{
-	ld->refcount = 0;
-	tty->ldisc = *ld;
-}
-
-/**
- *	tty_ldisc_try		-	internal helper
- *	@tty: the tty
- *
- *	Make a single attempt to grab and bump the refcount on
- *	the tty ldisc. Return 0 on failure or 1 on success. This is
- *	used to implement both the waiting and non waiting versions
- *	of tty_ldisc_ref
- *
- *	Locking: takes tty_ldisc_lock
- */
-
-static int tty_ldisc_try(struct tty_struct *tty)
-{
-	unsigned long flags;
-	struct tty_ldisc *ld;
-	int ret = 0;
-
-	spin_lock_irqsave(&tty_ldisc_lock, flags);
-	ld = &tty->ldisc;
-	if (test_bit(TTY_LDISC, &tty->flags)) {
-		ld->refcount++;
-		ret = 1;
-	}
-	spin_unlock_irqrestore(&tty_ldisc_lock, flags);
-	return ret;
-}
-
-/**
- *	tty_ldisc_ref_wait	-	wait for the tty ldisc
- *	@tty: tty device
- *
- *	Dereference the line discipline for the terminal and take a
- *	reference to it. If the line discipline is in flux then
- *	wait patiently until it changes.
- *
- *	Note: Must not be called from an IRQ/timer context. The caller
- *	must also be careful not to hold other locks that will deadlock
- *	against a discipline change, such as an existing ldisc reference
- *	(which we check for)
- *
- *	Locking: call functions take tty_ldisc_lock
- */
-
-struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
-{
-	/* wait_event is a macro */
-	wait_event(tty_ldisc_wait, tty_ldisc_try(tty));
-	if (tty->ldisc.refcount == 0)
-		printk(KERN_ERR "tty_ldisc_ref_wait\n");
-	return &tty->ldisc;
-}
-
-EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
-
-/**
- *	tty_ldisc_ref		-	get the tty ldisc
- *	@tty: tty device
- *
- *	Dereference the line discipline for the terminal and take a
- *	reference to it. If the line discipline is in flux then
- *	return NULL. Can be called from IRQ and timer functions.
- *
- *	Locking: called functions take tty_ldisc_lock
- */
-
-struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
-{
-	if (tty_ldisc_try(tty))
-		return &tty->ldisc;
-	return NULL;
-}
-
-EXPORT_SYMBOL_GPL(tty_ldisc_ref);
-
-/**
- *	tty_ldisc_deref		-	free a tty ldisc reference
- *	@ld: reference to free up
- *
- *	Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May
- *	be called in IRQ context.
- *
- *	Locking: takes tty_ldisc_lock
- */
-
-void tty_ldisc_deref(struct tty_ldisc *ld)
-{
-	unsigned long flags;
-
-	BUG_ON(ld == NULL);
-
-	spin_lock_irqsave(&tty_ldisc_lock, flags);
-	if (ld->refcount == 0)
-		printk(KERN_ERR "tty_ldisc_deref: no references.\n");
-	else
-		ld->refcount--;
-	if (ld->refcount == 0)
-		wake_up(&tty_ldisc_wait);
-	spin_unlock_irqrestore(&tty_ldisc_lock, flags);
-}
-
-EXPORT_SYMBOL_GPL(tty_ldisc_deref);
-
-/**
- *	tty_ldisc_enable	-	allow ldisc use
- *	@tty: terminal to activate ldisc on
- *
- *	Set the TTY_LDISC flag when the line discipline can be called
- *	again. Do necessary wakeups for existing sleepers.
- *
- *	Note: nobody should set this bit except via this function. Clearing
- *	directly is allowed.
- */
-
-static void tty_ldisc_enable(struct tty_struct *tty)
-{
-	set_bit(TTY_LDISC, &tty->flags);
-	wake_up(&tty_ldisc_wait);
-}
-
-/**
- *	tty_ldisc_restore	-	helper for tty ldisc change
- *	@tty: tty to recover
- *	@old: previous ldisc
- *
- *	Restore the previous line discipline or N_TTY when a line discipline
- *	change fails due to an open error
- */
-
-static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
-{
-	char buf[64];
-	struct tty_ldisc new_ldisc;
-
-	/* There is an outstanding reference here so this is safe */
-	tty_ldisc_get(old->ops->num, old);
-	tty_ldisc_assign(tty, old);
-	tty_set_termios_ldisc(tty, old->ops->num);
-	if (old->ops->open && (old->ops->open(tty) < 0)) {
-		tty_ldisc_put(old->ops);
-		/* This driver is always present */
-		if (tty_ldisc_get(N_TTY, &new_ldisc) < 0)
-			panic("n_tty: get");
-		tty_ldisc_assign(tty, &new_ldisc);
-		tty_set_termios_ldisc(tty, N_TTY);
-		if (new_ldisc.ops->open) {
-			int r = new_ldisc.ops->open(tty);
-				if (r < 0)
-				panic("Couldn't open N_TTY ldisc for "
-				      "%s --- error %d.",
-				      tty_name(tty, buf), r);
-		}
-	}
-}
-
-/**
- *	tty_set_ldisc		-	set line discipline
- *	@tty: the terminal to set
- *	@ldisc: the line discipline
- *
- *	Set the discipline of a tty line. Must be called from a process
- *	context.
- *
- *	Locking: takes tty_ldisc_lock.
- *		 called functions take termios_mutex
- */
-
-static int tty_set_ldisc(struct tty_struct *tty, int ldisc)
-{
-	int retval;
-	struct tty_ldisc o_ldisc, new_ldisc;
-	int work;
-	unsigned long flags;
-	struct tty_struct *o_tty;
-
-restart:
-	/* This is a bit ugly for now but means we can break the 'ldisc
-	   is part of the tty struct' assumption later */
-	retval = tty_ldisc_get(ldisc, &new_ldisc);
-	if (retval)
-		return retval;
-
-	/*
-	 *	Problem: What do we do if this blocks ?
-	 */
-
-	tty_wait_until_sent(tty, 0);
-
-	if (tty->ldisc.ops->num == ldisc) {
-		tty_ldisc_put(new_ldisc.ops);
-		return 0;
-	}
-
-	/*
-	 *	No more input please, we are switching. The new ldisc
-	 *	will update this value in the ldisc open function
-	 */
-
-	tty->receive_room = 0;
-
-	o_ldisc = tty->ldisc;
-	o_tty = tty->link;
-
-	/*
-	 *	Make sure we don't change while someone holds a
-	 *	reference to the line discipline. The TTY_LDISC bit
-	 *	prevents anyone taking a reference once it is clear.
-	 *	We need the lock to avoid racing reference takers.
-	 */
-
-	spin_lock_irqsave(&tty_ldisc_lock, flags);
-	if (tty->ldisc.refcount || (o_tty && o_tty->ldisc.refcount)) {
-		if (tty->ldisc.refcount) {
-			/* Free the new ldisc we grabbed. Must drop the lock
-			   first. */
-			spin_unlock_irqrestore(&tty_ldisc_lock, flags);
-			tty_ldisc_put(o_ldisc.ops);
-			/*
-			 * There are several reasons we may be busy, including
-			 * random momentary I/O traffic. We must therefore
-			 * retry. We could distinguish between blocking ops
-			 * and retries if we made tty_ldisc_wait() smarter.
-			 * That is up for discussion.
-			 */
-			if (wait_event_interruptible(tty_ldisc_wait, tty->ldisc.refcount == 0) < 0)
-				return -ERESTARTSYS;
-			goto restart;
-		}
-		if (o_tty && o_tty->ldisc.refcount) {
-			spin_unlock_irqrestore(&tty_ldisc_lock, flags);
-			tty_ldisc_put(o_tty->ldisc.ops);
-			if (wait_event_interruptible(tty_ldisc_wait, o_tty->ldisc.refcount == 0) < 0)
-				return -ERESTARTSYS;
-			goto restart;
-		}
-	}
-	/*
-	 *	If the TTY_LDISC bit is set, then we are racing against
-	 *	another ldisc change
-	 */
-	if (!test_bit(TTY_LDISC, &tty->flags)) {
-		struct tty_ldisc *ld;
-		spin_unlock_irqrestore(&tty_ldisc_lock, flags);
-		tty_ldisc_put(new_ldisc.ops);
-		ld = tty_ldisc_ref_wait(tty);
-		tty_ldisc_deref(ld);
-		goto restart;
-	}
-
-	clear_bit(TTY_LDISC, &tty->flags);
-	if (o_tty)
-		clear_bit(TTY_LDISC, &o_tty->flags);
-	spin_unlock_irqrestore(&tty_ldisc_lock, flags);
-	
-	/*
-	 *	From this point on we know nobody has an ldisc
-	 *	usage reference, nor can they obtain one until
-	 *	we say so later on.
-	 */
-
-	work = cancel_delayed_work(&tty->buf.work);
-	/*
-	 * Wait for ->hangup_work and ->buf.work handlers to terminate
-	 * MUST NOT hold locks here.
-	 */
-	flush_scheduled_work();
-	/* Shutdown the current discipline. */
-	if (o_ldisc.ops->close)
-		(o_ldisc.ops->close)(tty);
-
-	/* Now set up the new line discipline. */
-	tty_ldisc_assign(tty, &new_ldisc);
-	tty_set_termios_ldisc(tty, ldisc);
-	if (new_ldisc.ops->open)
-		retval = (new_ldisc.ops->open)(tty);
-	if (retval < 0) {
-		tty_ldisc_put(new_ldisc.ops);
-		tty_ldisc_restore(tty, &o_ldisc);
-	}
-	/* At this point we hold a reference to the new ldisc and a
-	   a reference to the old ldisc. If we ended up flipping back
-	   to the existing ldisc we have two references to it */
-
-	if (tty->ldisc.ops->num != o_ldisc.ops->num && tty->ops->set_ldisc)
-		tty->ops->set_ldisc(tty);
-
-	tty_ldisc_put(o_ldisc.ops);
-
-	/*
-	 *	Allow ldisc referencing to occur as soon as the driver
-	 *	ldisc callback completes.
-	 */
-
-	tty_ldisc_enable(tty);
-	if (o_tty)
-		tty_ldisc_enable(o_tty);
-
-	/* Restart it in case no characters kick it off. Safe if
-	   already running */
-	if (work)
-		schedule_delayed_work(&tty->buf.work, 1);
-	return retval;
-}
-
-/**
  *	get_tty_driver		-	find device of a tty
  *	@dev_t: device identifier
  *	@index: returns the index of the tty
@@ -2193,7 +1641,6 @@ static int init_dev(struct tty_driver *driver, int idx,
 	struct ktermios *tp, **tp_loc, *o_tp, **o_tp_loc;
 	struct ktermios *ltp, **ltp_loc, *o_ltp, **o_ltp_loc;
 	int retval = 0;
-	struct tty_ldisc *ld;
 
 	/* check whether we're reopening an existing tty */
 	if (driver->flags & TTY_DRIVER_DEVPTS_MEM) {
@@ -2342,25 +1789,12 @@ static int init_dev(struct tty_driver *driver, int idx,
 	 * If we fail here just call release_tty to clean up.  No need
 	 * to decrement the use counts, as release_tty doesn't care.
 	 */
-	 
-	ld = &tty->ldisc;
 
-	if (ld->ops->open) {
-		retval = (ld->ops->open)(tty);
-		if (retval)
-			goto release_mem_out;
-	}
-	if (o_tty && o_tty->ldisc.ops->open) {
-		retval = (o_tty->ldisc.ops->open)(o_tty);
-		if (retval) {
-			if (ld->ops->close)
-				(ld->ops->close)(tty);
-			goto release_mem_out;
-		}
-		tty_ldisc_enable(o_tty);
-	}
-	tty_ldisc_enable(tty);
-	goto success;
+	retval = tty_ldisc_setup(tty, o_tty);
+
+	if (retval)
+		goto release_mem_out;
+	 goto success;
 
 	/*
 	 * This fast open can be used if the tty is already open.
@@ -2498,12 +1932,10 @@ static void release_tty(struct tty_struct *tty, int idx)
 static void release_dev(struct file *filp)
 {
 	struct tty_struct *tty, *o_tty;
-	struct tty_ldisc ld;
 	int	pty_master, tty_closing, o_tty_closing, do_sleep;
 	int	devpts;
 	int	idx;
 	char	buf[64];
-	unsigned long flags;
 
 	tty = (struct tty_struct *)filp->private_data;
 	if (tty_paranoia_check(tty, filp->f_path.dentry->d_inode,
@@ -2705,56 +2137,9 @@ static void release_dev(struct file *filp)
 	printk(KERN_DEBUG "freeing tty structure...");
 #endif
 	/*
-	 * Prevent flush_to_ldisc() from rescheduling the work for later.  Then
-	 * kill any delayed work. As this is the final close it does not
-	 * race with the set_ldisc code path.
-	 */
-	clear_bit(TTY_LDISC, &tty->flags);
-	cancel_delayed_work(&tty->buf.work);
-
-	/*
-	 * Wait for ->hangup_work and ->buf.work handlers to terminate
-	 */
-
-	flush_scheduled_work();
-
-	/*
-	 * Wait for any short term users (we know they are just driver
-	 * side waiters as the file is closing so user count on the file
-	 * side is zero.
+	 * Ask the line discipline code to release its structures
 	 */
-	spin_lock_irqsave(&tty_ldisc_lock, flags);
-	while (tty->ldisc.refcount) {
-		spin_unlock_irqrestore(&tty_ldisc_lock, flags);
-		wait_event(tty_ldisc_wait, tty->ldisc.refcount == 0);
-		spin_lock_irqsave(&tty_ldisc_lock, flags);
-	}
-	spin_unlock_irqrestore(&tty_ldisc_lock, flags);
-	/*
-	 * Shutdown the current line discipline, and reset it to N_TTY.
-	 *
-	 * FIXME: this MUST get fixed for the new reflocking
-	 */
-	if (tty->ldisc.ops->close)
-		(tty->ldisc.ops->close)(tty);
-	tty_ldisc_put(tty->ldisc.ops);
-
-	/*
-	 *	Switch the line discipline back
-	 */
-	WARN_ON(tty_ldisc_get(N_TTY, &ld));
-	tty_ldisc_assign(tty, &ld);
-	tty_set_termios_ldisc(tty, N_TTY);
-	if (o_tty) {
-		/* FIXME: could o_tty be in setldisc here ? */
-		clear_bit(TTY_LDISC, &o_tty->flags);
-		if (o_tty->ldisc.ops->close)
-			(o_tty->ldisc.ops->close)(o_tty);
-		tty_ldisc_put(o_tty->ldisc.ops);
-		WARN_ON(tty_ldisc_get(N_TTY, &ld));
-		tty_ldisc_assign(o_tty, &ld);
-		tty_set_termios_ldisc(o_tty, N_TTY);
-	}
+	tty_ldisc_release(tty, o_tty);
 	/*
 	 * The release_tty function takes care of the details of clearing
 	 * the slots and preserving the termios structure.
@@ -3962,12 +3347,9 @@ EXPORT_SYMBOL(tty_flip_buffer_push);
 
 static void initialize_tty_struct(struct tty_struct *tty)
 {
-	struct tty_ldisc ld;
 	memset(tty, 0, sizeof(struct tty_struct));
 	tty->magic = TTY_MAGIC;
-	if (tty_ldisc_get(N_TTY, &ld) < 0)
-		panic("n_tty: init_tty");
-	tty_ldisc_assign(tty, &ld);
+	tty_ldisc_init(tty);
 	tty->session = NULL;
 	tty->pgrp = NULL;
 	tty->overrun_time = jiffies;
@@ -4280,7 +3662,7 @@ void __init console_init(void)
 	initcall_t *call;
 
 	/* Setup the default TTY line discipline. */
-	(void) tty_register_ldisc(N_TTY, &tty_ldisc_N_TTY);
+	tty_ldisc_begin();
 
 	/*
 	 * set up the console device so that later boot sequences can
diff --git a/drivers/char/tty_ldisc.c b/drivers/char/tty_ldisc.c
new file mode 100644
index 000000000000..241cbdea65ab
--- /dev/null
+++ b/drivers/char/tty_ldisc.c
@@ -0,0 +1,714 @@
+#include <linux/types.h>
+#include <linux/major.h>
+#include <linux/errno.h>
+#include <linux/signal.h>
+#include <linux/fcntl.h>
+#include <linux/sched.h>
+#include <linux/interrupt.h>
+#include <linux/tty.h>
+#include <linux/tty_driver.h>
+#include <linux/tty_flip.h>
+#include <linux/devpts_fs.h>
+#include <linux/file.h>
+#include <linux/fdtable.h>
+#include <linux/console.h>
+#include <linux/timer.h>
+#include <linux/ctype.h>
+#include <linux/kd.h>
+#include <linux/mm.h>
+#include <linux/string.h>
+#include <linux/slab.h>
+#include <linux/poll.h>
+#include <linux/proc_fs.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/smp_lock.h>
+#include <linux/device.h>
+#include <linux/wait.h>
+#include <linux/bitops.h>
+#include <linux/delay.h>
+#include <linux/seq_file.h>
+
+#include <linux/uaccess.h>
+#include <asm/system.h>
+
+#include <linux/kbd_kern.h>
+#include <linux/vt_kern.h>
+#include <linux/selection.h>
+
+#include <linux/kmod.h>
+#include <linux/nsproxy.h>
+
+/*
+ *	This guards the refcounted line discipline lists. The lock
+ *	must be taken with irqs off because there are hangup path
+ *	callers who will do ldisc lookups and cannot sleep.
+ */
+
+static DEFINE_SPINLOCK(tty_ldisc_lock);
+static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_wait);
+/* Line disc dispatch table */
+static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
+
+/**
+ *	tty_register_ldisc	-	install a line discipline
+ *	@disc: ldisc number
+ *	@new_ldisc: pointer to the ldisc object
+ *
+ *	Installs a new line discipline into the kernel. The discipline
+ *	is set up as unreferenced and then made available to the kernel
+ *	from this point onwards.
+ *
+ *	Locking:
+ *		takes tty_ldisc_lock to guard against ldisc races
+ */
+
+int tty_register_ldisc(int disc, struct tty_ldisc_ops *new_ldisc)
+{
+	unsigned long flags;
+	int ret = 0;
+
+	if (disc < N_TTY || disc >= NR_LDISCS)
+		return -EINVAL;
+
+	spin_lock_irqsave(&tty_ldisc_lock, flags);
+	tty_ldiscs[disc] = new_ldisc;
+	new_ldisc->num = disc;
+	new_ldisc->refcount = 0;
+	spin_unlock_irqrestore(&tty_ldisc_lock, flags);
+
+	return ret;
+}
+EXPORT_SYMBOL(tty_register_ldisc);
+
+/**
+ *	tty_unregister_ldisc	-	unload a line discipline
+ *	@disc: ldisc number
+ *	@new_ldisc: pointer to the ldisc object
+ *
+ *	Remove a line discipline from the kernel providing it is not
+ *	currently in use.
+ *
+ *	Locking:
+ *		takes tty_ldisc_lock to guard against ldisc races
+ */
+
+int tty_unregister_ldisc(int disc)
+{
+	unsigned long flags;
+	int ret = 0;
+
+	if (disc < N_TTY || disc >= NR_LDISCS)
+		return -EINVAL;
+
+	spin_lock_irqsave(&tty_ldisc_lock, flags);
+	if (tty_ldiscs[disc]->refcount)
+		ret = -EBUSY;
+	else
+		tty_ldiscs[disc] = NULL;
+	spin_unlock_irqrestore(&tty_ldisc_lock, flags);
+
+	return ret;
+}
+EXPORT_SYMBOL(tty_unregister_ldisc);
+
+
+/**
+ *	tty_ldisc_try_get	-	try and reference an ldisc
+ *	@disc: ldisc number
+ *	@ld: tty ldisc structure to complete
+ *
+ *	Attempt to open and lock a line discipline into place. Return
+ *	the line discipline refcounted and assigned in ld. On an error
+ *	report the error code back
+ */
+
+static int tty_ldisc_try_get(int disc, struct tty_ldisc *ld)
+{
+	unsigned long flags;
+	struct tty_ldisc_ops *ldops;
+	int err = -EINVAL;
+	
+	spin_lock_irqsave(&tty_ldisc_lock, flags);
+	ld->ops = NULL;
+	ldops = tty_ldiscs[disc];
+	/* Check the entry is defined */
+	if (ldops) {
+		/* If the module is being unloaded we can't use it */
+		if (!try_module_get(ldops->owner))
+			err = -EAGAIN;
+		else {
+			/* lock it */
+			ldops->refcount++;
+			ld->ops = ldops;
+			err = 0;
+		}
+	}
+	spin_unlock_irqrestore(&tty_ldisc_lock, flags);
+	return err;
+}
+
+/**
+ *	tty_ldisc_get		-	take a reference to an ldisc
+ *	@disc: ldisc number
+ *	@ld: tty line discipline structure to use
+ *
+ *	Takes a reference to a line discipline. Deals with refcounts and
+ *	module locking counts. Returns NULL if the discipline is not available.
+ *	Returns a pointer to the discipline and bumps the ref count if it is
+ *	available
+ *
+ *	Locking:
+ *		takes tty_ldisc_lock to guard against ldisc races
+ */
+
+static int tty_ldisc_get(int disc, struct tty_ldisc *ld)
+{
+	int err;
+
+	if (disc < N_TTY || disc >= NR_LDISCS)
+		return -EINVAL;
+	err = tty_ldisc_try_get(disc, ld);
+	if (err == -EAGAIN) {
+		request_module("tty-ldisc-%d", disc);
+		err = tty_ldisc_try_get(disc, ld);
+	}
+	return err;
+}
+
+/**
+ *	tty_ldisc_put		-	drop ldisc reference
+ *	@disc: ldisc number
+ *
+ *	Drop a reference to a line discipline. Manage refcounts and
+ *	module usage counts
+ *
+ *	Locking:
+ *		takes tty_ldisc_lock to guard against ldisc races
+ */
+
+static void tty_ldisc_put(struct tty_ldisc_ops *ld)
+{
+	unsigned long flags;
+	int disc = ld->num;
+
+	BUG_ON(disc < N_TTY || disc >= NR_LDISCS);
+
+	spin_lock_irqsave(&tty_ldisc_lock, flags);
+	ld = tty_ldiscs[disc];
+	BUG_ON(ld->refcount == 0);
+	ld->refcount--;
+	module_put(ld->owner);
+	spin_unlock_irqrestore(&tty_ldisc_lock, flags);
+}
+
+static void * tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos)
+{
+	return (*pos < NR_LDISCS) ? pos : NULL;
+}
+
+static void * tty_ldiscs_seq_next(struct seq_file *m, void *v, loff_t *pos)
+{
+	(*pos)++;
+	return (*pos < NR_LDISCS) ? pos : NULL;
+}
+
+static void tty_ldiscs_seq_stop(struct seq_file *m, void *v)
+{
+}
+
+static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
+{
+	int i = *(loff_t *)v;
+	struct tty_ldisc ld;
+	
+	if (tty_ldisc_get(i, &ld) < 0)
+		return 0;
+	seq_printf(m, "%-10s %2d\n", ld.ops->name ? ld.ops->name : "???", i);
+	tty_ldisc_put(ld.ops);
+	return 0;
+}
+
+static const struct seq_operations tty_ldiscs_seq_ops = {
+	.start	= tty_ldiscs_seq_start,
+	.next	= tty_ldiscs_seq_next,
+	.stop	= tty_ldiscs_seq_stop,
+	.show	= tty_ldiscs_seq_show,
+};
+
+static int proc_tty_ldiscs_open(struct inode *inode, struct file *file)
+{
+	return seq_open(file, &tty_ldiscs_seq_ops);
+}
+
+const struct file_operations tty_ldiscs_proc_fops = {
+	.owner		= THIS_MODULE,
+	.open		= proc_tty_ldiscs_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= seq_release,
+};
+
+/**
+ *	tty_ldisc_assign	-	set ldisc on a tty
+ *	@tty: tty to assign
+ *	@ld: line discipline
+ *
+ *	Install an instance of a line discipline into a tty structure. The
+ *	ldisc must have a reference count above zero to ensure it remains/
+ *	The tty instance refcount starts at zero.
+ *
+ *	Locking:
+ *		Caller must hold references
+ */
+
+static void tty_ldisc_assign(struct tty_struct *tty, struct tty_ldisc *ld)
+{
+	ld->refcount = 0;
+	tty->ldisc = *ld;
+}
+
+/**
+ *	tty_ldisc_try		-	internal helper
+ *	@tty: the tty
+ *
+ *	Make a single attempt to grab and bump the refcount on
+ *	the tty ldisc. Return 0 on failure or 1 on success. This is
+ *	used to implement both the waiting and non waiting versions
+ *	of tty_ldisc_ref
+ *
+ *	Locking: takes tty_ldisc_lock
+ */
+
+static int tty_ldisc_try(struct tty_struct *tty)
+{
+	unsigned long flags;
+	struct tty_ldisc *ld;
+	int ret = 0;
+
+	spin_lock_irqsave(&tty_ldisc_lock, flags);
+	ld = &tty->ldisc;
+	if (test_bit(TTY_LDISC, &tty->flags)) {
+		ld->refcount++;
+		ret = 1;
+	}
+	spin_unlock_irqrestore(&tty_ldisc_lock, flags);
+	return ret;
+}
+
+/**
+ *	tty_ldisc_ref_wait	-	wait for the tty ldisc
+ *	@tty: tty device
+ *
+ *	Dereference the line discipline for the terminal and take a
+ *	reference to it. If the line discipline is in flux then
+ *	wait patiently until it changes.
+ *
+ *	Note: Must not be called from an IRQ/timer context. The caller
+ *	must also be careful not to hold other locks that will deadlock
+ *	against a discipline change, such as an existing ldisc reference
+ *	(which we check for)
+ *
+ *	Locking: call functions take tty_ldisc_lock
+ */
+
+struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
+{
+	/* wait_event is a macro */
+	wait_event(tty_ldisc_wait, tty_ldisc_try(tty));
+	if (tty->ldisc.refcount == 0)
+		printk(KERN_ERR "tty_ldisc_ref_wait\n");
+	return &tty->ldisc;
+}
+
+EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
+
+/**
+ *	tty_ldisc_ref		-	get the tty ldisc
+ *	@tty: tty device
+ *
+ *	Dereference the line discipline for the terminal and take a
+ *	reference to it. If the line discipline is in flux then
+ *	return NULL. Can be called from IRQ and timer functions.
+ *
+ *	Locking: called functions take tty_ldisc_lock
+ */
+
+struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
+{
+	if (tty_ldisc_try(tty))
+		return &tty->ldisc;
+	return NULL;
+}
+
+EXPORT_SYMBOL_GPL(tty_ldisc_ref);
+
+/**
+ *	tty_ldisc_deref		-	free a tty ldisc reference
+ *	@ld: reference to free up
+ *
+ *	Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May
+ *	be called in IRQ context.
+ *
+ *	Locking: takes tty_ldisc_lock
+ */
+
+void tty_ldisc_deref(struct tty_ldisc *ld)
+{
+	unsigned long flags;
+
+	BUG_ON(ld == NULL);
+
+	spin_lock_irqsave(&tty_ldisc_lock, flags);
+	if (ld->refcount == 0)
+		printk(KERN_ERR "tty_ldisc_deref: no references.\n");
+	else
+		ld->refcount--;
+	if (ld->refcount == 0)
+		wake_up(&tty_ldisc_wait);
+	spin_unlock_irqrestore(&tty_ldisc_lock, flags);
+}
+
+EXPORT_SYMBOL_GPL(tty_ldisc_deref);
+
+/**
+ *	tty_ldisc_enable	-	allow ldisc use
+ *	@tty: terminal to activate ldisc on
+ *
+ *	Set the TTY_LDISC flag when the line discipline can be called
+ *	again. Do necessary wakeups for existing sleepers.
+ *
+ *	Note: nobody should set this bit except via this function. Clearing
+ *	directly is allowed.
+ */
+
+void tty_ldisc_enable(struct tty_struct *tty)
+{
+	set_bit(TTY_LDISC, &tty->flags);
+	wake_up(&tty_ldisc_wait);
+}
+
+/**
+ *	tty_set_termios_ldisc		-	set ldisc field
+ *	@tty: tty structure
+ *	@num: line discipline number
+ *
+ *	This is probably overkill for real world processors but
+ *	they are not on hot paths so a little discipline won't do
+ *	any harm.
+ *
+ *	Locking: takes termios_mutex
+ */
+
+static void tty_set_termios_ldisc(struct tty_struct *tty, int num)
+{
+	mutex_lock(&tty->termios_mutex);
+	tty->termios->c_line = num;
+	mutex_unlock(&tty->termios_mutex);
+}
+
+
+/**
+ *	tty_ldisc_restore	-	helper for tty ldisc change
+ *	@tty: tty to recover
+ *	@old: previous ldisc
+ *
+ *	Restore the previous line discipline or N_TTY when a line discipline
+ *	change fails due to an open error
+ */
+
+static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
+{
+	char buf[64];
+	struct tty_ldisc new_ldisc;
+
+	/* There is an outstanding reference here so this is safe */
+	tty_ldisc_get(old->ops->num, old);
+	tty_ldisc_assign(tty, old);
+	tty_set_termios_ldisc(tty, old->ops->num);
+	if (old->ops->open && (old->ops->open(tty) < 0)) {
+		tty_ldisc_put(old->ops);
+		/* This driver is always present */
+		if (tty_ldisc_get(N_TTY, &new_ldisc) < 0)
+			panic("n_tty: get");
+		tty_ldisc_assign(tty, &new_ldisc);
+		tty_set_termios_ldisc(tty, N_TTY);
+		if (new_ldisc.ops->open) {
+			int r = new_ldisc.ops->open(tty);
+				if (r < 0)
+				panic("Couldn't open N_TTY ldisc for "
+				      "%s --- error %d.",
+				      tty_name(tty, buf), r);
+		}
+	}
+}
+
+/**
+ *	tty_set_ldisc		-	set line discipline
+ *	@tty: the terminal to set
+ *	@ldisc: the line discipline
+ *
+ *	Set the discipline of a tty line. Must be called from a process
+ *	context.
+ *
+ *	Locking: takes tty_ldisc_lock.
+ *		 called functions take termios_mutex
+ */
+
+int tty_set_ldisc(struct tty_struct *tty, int ldisc)
+{
+	int retval;
+	struct tty_ldisc o_ldisc, new_ldisc;
+	int work;
+	unsigned long flags;
+	struct tty_struct *o_tty;
+
+restart:
+	/* This is a bit ugly for now but means we can break the 'ldisc
+	   is part of the tty struct' assumption later */
+	retval = tty_ldisc_get(ldisc, &new_ldisc);
+	if (retval)
+		return retval;
+
+	/*
+	 *	Problem: What do we do if this blocks ?
+	 */
+
+	tty_wait_until_sent(tty, 0);
+
+	if (tty->ldisc.ops->num == ldisc) {
+		tty_ldisc_put(new_ldisc.ops);
+		return 0;
+	}
+
+	/*
+	 *	No more input please, we are switching. The new ldisc
+	 *	will update this value in the ldisc open function
+	 */
+
+	tty->receive_room = 0;
+
+	o_ldisc = tty->ldisc;
+	o_tty = tty->link;
+
+	/*
+	 *	Make sure we don't change while someone holds a
+	 *	reference to the line discipline. The TTY_LDISC bit
+	 *	prevents anyone taking a reference once it is clear.
+	 *	We need the lock to avoid racing reference takers.
+	 */
+
+	spin_lock_irqsave(&tty_ldisc_lock, flags);
+	if (tty->ldisc.refcount || (o_tty && o_tty->ldisc.refcount)) {
+		if (tty->ldisc.refcount) {
+			/* Free the new ldisc we grabbed. Must drop the lock
+			   first. */
+			spin_unlock_irqrestore(&tty_ldisc_lock, flags);
+			tty_ldisc_put(o_ldisc.ops);
+			/*
+			 * There are several reasons we may be busy, including
+			 * random momentary I/O traffic. We must therefore
+			 * retry. We could distinguish between blocking ops
+			 * and retries if we made tty_ldisc_wait() smarter.
+			 * That is up for discussion.
+			 */
+			if (wait_event_interruptible(tty_ldisc_wait, tty->ldisc.refcount == 0) < 0)
+				return -ERESTARTSYS;
+			goto restart;
+		}
+		if (o_tty && o_tty->ldisc.refcount) {
+			spin_unlock_irqrestore(&tty_ldisc_lock, flags);
+			tty_ldisc_put(o_tty->ldisc.ops);
+			if (wait_event_interruptible(tty_ldisc_wait, o_tty->ldisc.refcount == 0) < 0)
+				return -ERESTARTSYS;
+			goto restart;
+		}
+	}
+	/*
+	 *	If the TTY_LDISC bit is set, then we are racing against
+	 *	another ldisc change
+	 */
+	if (!test_bit(TTY_LDISC, &tty->flags)) {
+		struct tty_ldisc *ld;
+		spin_unlock_irqrestore(&tty_ldisc_lock, flags);
+		tty_ldisc_put(new_ldisc.ops);
+		ld = tty_ldisc_ref_wait(tty);
+		tty_ldisc_deref(ld);
+		goto restart;
+	}
+
+	clear_bit(TTY_LDISC, &tty->flags);
+	if (o_tty)
+		clear_bit(TTY_LDISC, &o_tty->flags);
+	spin_unlock_irqrestore(&tty_ldisc_lock, flags);
+	
+	/*
+	 *	From this point on we know nobody has an ldisc
+	 *	usage reference, nor can they obtain one until
+	 *	we say so later on.
+	 */
+
+	work = cancel_delayed_work(&tty->buf.work);
+	/*
+	 * Wait for ->hangup_work and ->buf.work handlers to terminate
+	 * MUST NOT hold locks here.
+	 */
+	flush_scheduled_work();
+	/* Shutdown the current discipline. */
+	if (o_ldisc.ops->close)
+		(o_ldisc.ops->close)(tty);
+
+	/* Now set up the new line discipline. */
+	tty_ldisc_assign(tty, &new_ldisc);
+	tty_set_termios_ldisc(tty, ldisc);
+	if (new_ldisc.ops->open)
+		retval = (new_ldisc.ops->open)(tty);
+	if (retval < 0) {
+		tty_ldisc_put(new_ldisc.ops);
+		tty_ldisc_restore(tty, &o_ldisc);
+	}
+	/* At this point we hold a reference to the new ldisc and a
+	   a reference to the old ldisc. If we ended up flipping back
+	   to the existing ldisc we have two references to it */
+
+	if (tty->ldisc.ops->num != o_ldisc.ops->num && tty->ops->set_ldisc)
+		tty->ops->set_ldisc(tty);
+
+	tty_ldisc_put(o_ldisc.ops);
+
+	/*
+	 *	Allow ldisc referencing to occur as soon as the driver
+	 *	ldisc callback completes.
+	 */
+
+	tty_ldisc_enable(tty);
+	if (o_tty)
+		tty_ldisc_enable(o_tty);
+
+	/* Restart it in case no characters kick it off. Safe if
+	   already running */
+	if (work)
+		schedule_delayed_work(&tty->buf.work, 1);
+	return retval;
+}
+
+
+/**
+ *	tty_ldisc_setup			-	open line discipline
+ *	@tty: tty being shut down
+ *	@o_tty: pair tty for pty/tty pairs
+ *
+ *	Called during the initial open of a tty/pty pair in order to set up the
+ *	line discplines and bind them to the tty.
+ */
+
+int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
+{
+	struct tty_ldisc *ld = &tty->ldisc;
+	int retval;
+
+	if (ld->ops->open) {
+		retval = (ld->ops->open)(tty);
+		if (retval)
+			return retval;
+	}
+	if (o_tty && o_tty->ldisc.ops->open) {
+		retval = (o_tty->ldisc.ops->open)(o_tty);
+		if (retval) {
+			if (ld->ops->close)
+				(ld->ops->close)(tty);
+			return retval;
+		}
+		tty_ldisc_enable(o_tty);
+	}
+	tty_ldisc_enable(tty);
+	return 0;
+}
+
+/**
+ *	tty_ldisc_release		-	release line discipline
+ *	@tty: tty being shut down
+ *	@o_tty: pair tty for pty/tty pairs
+ *
+ *	Called during the final close of a tty/pty pair in order to shut down the
+ *	line discpline layer.
+ */
+
+void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty)
+{
+	unsigned long flags;
+	struct tty_ldisc ld;
+	/*
+	 * Prevent flush_to_ldisc() from rescheduling the work for later.  Then
+	 * kill any delayed work. As this is the final close it does not
+	 * race with the set_ldisc code path.
+	 */
+	clear_bit(TTY_LDISC, &tty->flags);
+	cancel_delayed_work(&tty->buf.work);
+
+	/*
+	 * Wait for ->hangup_work and ->buf.work handlers to terminate
+	 */
+
+	flush_scheduled_work();
+
+	/*
+	 * Wait for any short term users (we know they are just driver
+	 * side waiters as the file is closing so user count on the file
+	 * side is zero.
+	 */
+	spin_lock_irqsave(&tty_ldisc_lock, flags);
+	while (tty->ldisc.refcount) {
+		spin_unlock_irqrestore(&tty_ldisc_lock, flags);
+		wait_event(tty_ldisc_wait, tty->ldisc.refcount == 0);
+		spin_lock_irqsave(&tty_ldisc_lock, flags);
+	}
+	spin_unlock_irqrestore(&tty_ldisc_lock, flags);
+	/*
+	 * Shutdown the current line discipline, and reset it to N_TTY.
+	 *
+	 * FIXME: this MUST get fixed for the new reflocking
+	 */
+	if (tty->ldisc.ops->close)
+		(tty->ldisc.ops->close)(tty);
+	tty_ldisc_put(tty->ldisc.ops);
+
+	/*
+	 *	Switch the line discipline back
+	 */
+	WARN_ON(tty_ldisc_get(N_TTY, &ld));
+	tty_ldisc_assign(tty, &ld);
+	tty_set_termios_ldisc(tty, N_TTY);
+	if (o_tty) {
+		/* FIXME: could o_tty be in setldisc here ? */
+		clear_bit(TTY_LDISC, &o_tty->flags);
+		if (o_tty->ldisc.ops->close)
+			(o_tty->ldisc.ops->close)(o_tty);
+		tty_ldisc_put(o_tty->ldisc.ops);
+		WARN_ON(tty_ldisc_get(N_TTY, &ld));
+		tty_ldisc_assign(o_tty, &ld);
+		tty_set_termios_ldisc(o_tty, N_TTY);
+	}
+}
+
+/**
+ *	tty_ldisc_init		-	ldisc setup for new tty
+ *	@tty: tty being allocated
+ *
+ *	Set up the line discipline objects for a newly allocated tty. Note that
+ *	the tty structure is not completely set up when this call is made.
+ */
+
+void tty_ldisc_init(struct tty_struct *tty)
+{
+	struct tty_ldisc ld;
+	if (tty_ldisc_get(N_TTY, &ld) < 0)
+		panic("n_tty: init_tty");
+	tty_ldisc_assign(tty, &ld);
+}
+
+void tty_ldisc_begin(void)
+{
+	/* Setup the default TTY line discipline. */
+	(void) tty_register_ldisc(N_TTY, &tty_ldisc_N_TTY);
+}