Adding upstream version 5.10.209.upstream/5.10.209

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 887 insertions, 0 deletions

diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
new file mode 100644
index 000000000..c23938b86
--- /dev/null
+++ b/drivers/tty/tty_ldisc.c
@@ -0,0 +1,887 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/types.h>
+#include <linux/errno.h>
+#include <linux/kmod.h>
+#include <linux/sched.h>
+#include <linux/interrupt.h>
+#include <linux/tty.h>
+#include <linux/tty_driver.h>
+#include <linux/file.h>
+#include <linux/mm.h>
+#include <linux/string.h>
+#include <linux/slab.h>
+#include <linux/poll.h>
+#include <linux/proc_fs.h>
+#include <linux/module.h>
+#include <linux/device.h>
+#include <linux/wait.h>
+#include <linux/bitops.h>
+#include <linux/seq_file.h>
+#include <linux/uaccess.h>
+#include <linux/ratelimit.h>
+#include "tty.h"
+
+#undef LDISC_DEBUG_HANGUP
+
+#ifdef LDISC_DEBUG_HANGUP
+#define tty_ldisc_debug(tty, f, args...)	tty_debug(tty, f, ##args)
+#else
+#define tty_ldisc_debug(tty, f, args...)
+#endif
+
+/* lockdep nested classes for tty->ldisc_sem */
+enum {
+	LDISC_SEM_NORMAL,
+	LDISC_SEM_OTHER,
+};
+
+
+/*
+ *	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_RAW_SPINLOCK(tty_ldiscs_lock);
+/* 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_ldiscs_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;
+
+	raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
+	tty_ldiscs[disc] = new_ldisc;
+	new_ldisc->num = disc;
+	new_ldisc->refcount = 0;
+	raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
+
+	return ret;
+}
+EXPORT_SYMBOL(tty_register_ldisc);
+
+/**
+ *	tty_unregister_ldisc	-	unload a line discipline
+ *	@disc: ldisc number
+ *
+ *	Remove a line discipline from the kernel providing it is not
+ *	currently in use.
+ *
+ *	Locking:
+ *		takes tty_ldiscs_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;
+
+	raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
+	if (tty_ldiscs[disc]->refcount)
+		ret = -EBUSY;
+	else
+		tty_ldiscs[disc] = NULL;
+	raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
+
+	return ret;
+}
+EXPORT_SYMBOL(tty_unregister_ldisc);
+
+static struct tty_ldisc_ops *get_ldops(int disc)
+{
+	unsigned long flags;
+	struct tty_ldisc_ops *ldops, *ret;
+
+	raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
+	ret = ERR_PTR(-EINVAL);
+	ldops = tty_ldiscs[disc];
+	if (ldops) {
+		ret = ERR_PTR(-EAGAIN);
+		if (try_module_get(ldops->owner)) {
+			ldops->refcount++;
+			ret = ldops;
+		}
+	}
+	raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
+	return ret;
+}
+
+static void put_ldops(struct tty_ldisc_ops *ldops)
+{
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
+	ldops->refcount--;
+	module_put(ldops->owner);
+	raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
+}
+
+/**
+ *	tty_ldisc_get		-	take a reference to an ldisc
+ *	@disc: ldisc number
+ *
+ *	Takes a reference to a line discipline. Deals with refcounts and
+ *	module locking counts.
+ *
+ *	Returns: -EINVAL if the discipline index is not [N_TTY..NR_LDISCS] or
+ *			 if the discipline is not registered
+ *		 -EAGAIN if request_module() failed to load or register the
+ *			 the discipline
+ *		 -ENOMEM if allocation failure
+ *
+ *		 Otherwise, returns a pointer to the discipline and bumps the
+ *		 ref count
+ *
+ *	Locking:
+ *		takes tty_ldiscs_lock to guard against ldisc races
+ */
+
+static int tty_ldisc_autoload = IS_BUILTIN(CONFIG_LDISC_AUTOLOAD);
+
+static struct tty_ldisc *tty_ldisc_get(struct tty_struct *tty, int disc)
+{
+	struct tty_ldisc *ld;
+	struct tty_ldisc_ops *ldops;
+
+	if (disc < N_TTY || disc >= NR_LDISCS)
+		return ERR_PTR(-EINVAL);
+
+	/*
+	 * Get the ldisc ops - we may need to request them to be loaded
+	 * dynamically and try again.
+	 */
+	ldops = get_ldops(disc);
+	if (IS_ERR(ldops)) {
+		if (!capable(CAP_SYS_MODULE) && !tty_ldisc_autoload)
+			return ERR_PTR(-EPERM);
+		request_module("tty-ldisc-%d", disc);
+		ldops = get_ldops(disc);
+		if (IS_ERR(ldops))
+			return ERR_CAST(ldops);
+	}
+
+	/*
+	 * There is no way to handle allocation failure of only 16 bytes.
+	 * Let's simplify error handling and save more memory.
+	 */
+	ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL | __GFP_NOFAIL);
+	ld->ops = ldops;
+	ld->tty = tty;
+
+	return ld;
+}
+
+/**
+ *	tty_ldisc_put		-	release the ldisc
+ *
+ *	Complement of tty_ldisc_get().
+ */
+static void tty_ldisc_put(struct tty_ldisc *ld)
+{
+	if (WARN_ON_ONCE(!ld))
+		return;
+
+	put_ldops(ld->ops);
+	kfree(ld);
+}
+
+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_ops *ldops;
+
+	ldops = get_ldops(i);
+	if (IS_ERR(ldops))
+		return 0;
+	seq_printf(m, "%-10s %2d\n", ldops->name ? ldops->name : "???", i);
+	put_ldops(ldops);
+	return 0;
+}
+
+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,
+};
+
+/**
+ *	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.
+ *
+ *	Returns: NULL if the tty has been hungup and not re-opened with
+ *		 a new file descriptor, otherwise valid ldisc reference
+ *
+ *	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)
+ *
+ *	Note: a file_operations routine (read/poll/write) should use this
+ *	function to wait for any ldisc lifetime events to finish.
+ */
+
+struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
+{
+	struct tty_ldisc *ld;
+
+	ldsem_down_read(&tty->ldisc_sem, MAX_SCHEDULE_TIMEOUT);
+	ld = tty->ldisc;
+	if (!ld)
+		ldsem_up_read(&tty->ldisc_sem);
+	return ld;
+}
+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.
+ */
+
+struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
+{
+	struct tty_ldisc *ld = NULL;
+
+	if (ldsem_down_read_trylock(&tty->ldisc_sem)) {
+		ld = tty->ldisc;
+		if (!ld)
+			ldsem_up_read(&tty->ldisc_sem);
+	}
+	return ld;
+}
+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.
+ */
+
+void tty_ldisc_deref(struct tty_ldisc *ld)
+{
+	ldsem_up_read(&ld->tty->ldisc_sem);
+}
+EXPORT_SYMBOL_GPL(tty_ldisc_deref);
+
+
+static inline int
+__tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
+{
+	return ldsem_down_write(&tty->ldisc_sem, timeout);
+}
+
+static inline int
+__tty_ldisc_lock_nested(struct tty_struct *tty, unsigned long timeout)
+{
+	return ldsem_down_write_nested(&tty->ldisc_sem,
+				       LDISC_SEM_OTHER, timeout);
+}
+
+static inline void __tty_ldisc_unlock(struct tty_struct *tty)
+{
+	ldsem_up_write(&tty->ldisc_sem);
+}
+
+int tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
+{
+	int ret;
+
+	/* Kindly asking blocked readers to release the read side */
+	set_bit(TTY_LDISC_CHANGING, &tty->flags);
+	wake_up_interruptible_all(&tty->read_wait);
+	wake_up_interruptible_all(&tty->write_wait);
+
+	ret = __tty_ldisc_lock(tty, timeout);
+	if (!ret)
+		return -EBUSY;
+	set_bit(TTY_LDISC_HALTED, &tty->flags);
+	return 0;
+}
+
+void tty_ldisc_unlock(struct tty_struct *tty)
+{
+	clear_bit(TTY_LDISC_HALTED, &tty->flags);
+	/* Can be cleared here - ldisc_unlock will wake up writers firstly */
+	clear_bit(TTY_LDISC_CHANGING, &tty->flags);
+	__tty_ldisc_unlock(tty);
+}
+
+static int
+tty_ldisc_lock_pair_timeout(struct tty_struct *tty, struct tty_struct *tty2,
+			    unsigned long timeout)
+{
+	int ret;
+
+	if (tty < tty2) {
+		ret = __tty_ldisc_lock(tty, timeout);
+		if (ret) {
+			ret = __tty_ldisc_lock_nested(tty2, timeout);
+			if (!ret)
+				__tty_ldisc_unlock(tty);
+		}
+	} else {
+		/* if this is possible, it has lots of implications */
+		WARN_ON_ONCE(tty == tty2);
+		if (tty2 && tty != tty2) {
+			ret = __tty_ldisc_lock(tty2, timeout);
+			if (ret) {
+				ret = __tty_ldisc_lock_nested(tty, timeout);
+				if (!ret)
+					__tty_ldisc_unlock(tty2);
+			}
+		} else
+			ret = __tty_ldisc_lock(tty, timeout);
+	}
+
+	if (!ret)
+		return -EBUSY;
+
+	set_bit(TTY_LDISC_HALTED, &tty->flags);
+	if (tty2)
+		set_bit(TTY_LDISC_HALTED, &tty2->flags);
+	return 0;
+}
+
+static void tty_ldisc_lock_pair(struct tty_struct *tty, struct tty_struct *tty2)
+{
+	tty_ldisc_lock_pair_timeout(tty, tty2, MAX_SCHEDULE_TIMEOUT);
+}
+
+static void tty_ldisc_unlock_pair(struct tty_struct *tty,
+				  struct tty_struct *tty2)
+{
+	__tty_ldisc_unlock(tty);
+	if (tty2)
+		__tty_ldisc_unlock(tty2);
+}
+
+/**
+ *	tty_ldisc_flush	-	flush line discipline queue
+ *	@tty: tty
+ *
+ *	Flush the line discipline queue (if any) and the tty flip buffers
+ *	for this tty.
+ */
+
+void tty_ldisc_flush(struct tty_struct *tty)
+{
+	struct tty_ldisc *ld = tty_ldisc_ref(tty);
+
+	tty_buffer_flush(tty, ld);
+	if (ld)
+		tty_ldisc_deref(ld);
+}
+EXPORT_SYMBOL_GPL(tty_ldisc_flush);
+
+/**
+ *	tty_set_termios_ldisc		-	set ldisc field
+ *	@tty: tty structure
+ *	@disc: 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.
+ *
+ *	The line discipline-related tty_struct fields are reset to
+ *	prevent the ldisc driver from re-using stale information for
+ *	the new ldisc instance.
+ *
+ *	Locking: takes termios_rwsem
+ */
+
+static void tty_set_termios_ldisc(struct tty_struct *tty, int disc)
+{
+	down_write(&tty->termios_rwsem);
+	tty->termios.c_line = disc;
+	up_write(&tty->termios_rwsem);
+
+	tty->disc_data = NULL;
+	tty->receive_room = 0;
+}
+
+/**
+ *	tty_ldisc_open		-	open a line discipline
+ *	@tty: tty we are opening the ldisc on
+ *	@ld: discipline to open
+ *
+ *	A helper opening method. Also a convenient debugging and check
+ *	point.
+ *
+ *	Locking: always called with BTM already held.
+ */
+
+static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
+{
+	WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
+	if (ld->ops->open) {
+		int ret;
+                /* BTM here locks versus a hangup event */
+		ret = ld->ops->open(tty);
+		if (ret)
+			clear_bit(TTY_LDISC_OPEN, &tty->flags);
+
+		tty_ldisc_debug(tty, "%p: opened\n", ld);
+		return ret;
+	}
+	return 0;
+}
+
+/**
+ *	tty_ldisc_close		-	close a line discipline
+ *	@tty: tty we are opening the ldisc on
+ *	@ld: discipline to close
+ *
+ *	A helper close method. Also a convenient debugging and check
+ *	point.
+ */
+
+static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
+{
+	lockdep_assert_held_write(&tty->ldisc_sem);
+	WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags));
+	clear_bit(TTY_LDISC_OPEN, &tty->flags);
+	if (ld->ops->close)
+		ld->ops->close(tty);
+	tty_ldisc_debug(tty, "%p: closed\n", ld);
+}
+
+/**
+ *	tty_ldisc_failto	-	helper for ldisc failback
+ *	@tty: tty to open the ldisc on
+ *	@ld: ldisc we are trying to fail back to
+ *
+ *	Helper to try and recover a tty when switching back to the old
+ *	ldisc fails and we need something attached.
+ */
+
+static int tty_ldisc_failto(struct tty_struct *tty, int ld)
+{
+	struct tty_ldisc *disc = tty_ldisc_get(tty, ld);
+	int r;
+
+	lockdep_assert_held_write(&tty->ldisc_sem);
+	if (IS_ERR(disc))
+		return PTR_ERR(disc);
+	tty->ldisc = disc;
+	tty_set_termios_ldisc(tty, ld);
+	if ((r = tty_ldisc_open(tty, disc)) < 0)
+		tty_ldisc_put(disc);
+	return r;
+}
+
+/**
+ *	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)
+{
+	/* There is an outstanding reference here so this is safe */
+	if (tty_ldisc_failto(tty, old->ops->num) < 0) {
+		const char *name = tty_name(tty);
+
+		pr_warn("Falling back ldisc for %s.\n", name);
+		/* The traditional behaviour is to fall back to N_TTY, we
+		   want to avoid falling back to N_NULL unless we have no
+		   choice to avoid the risk of breaking anything */
+		if (tty_ldisc_failto(tty, N_TTY) < 0 &&
+		    tty_ldisc_failto(tty, N_NULL) < 0)
+			panic("Couldn't open N_NULL ldisc for %s.", name);
+	}
+}
+
+/**
+ *	tty_set_ldisc		-	set line discipline
+ *	@tty: the terminal to set
+ *	@disc: the line discipline number
+ *
+ *	Set the discipline of a tty line. Must be called from a process
+ *	context. The ldisc change logic has to protect itself against any
+ *	overlapping ldisc change (including on the other end of pty pairs),
+ *	the close of one side of a tty/pty pair, and eventually hangup.
+ */
+
+int tty_set_ldisc(struct tty_struct *tty, int disc)
+{
+	int retval;
+	struct tty_ldisc *old_ldisc, *new_ldisc;
+
+	new_ldisc = tty_ldisc_get(tty, disc);
+	if (IS_ERR(new_ldisc))
+		return PTR_ERR(new_ldisc);
+
+	tty_lock(tty);
+	retval = tty_ldisc_lock(tty, 5 * HZ);
+	if (retval)
+		goto err;
+
+	if (!tty->ldisc) {
+		retval = -EIO;
+		goto out;
+	}
+
+	/* Check the no-op case */
+	if (tty->ldisc->ops->num == disc)
+		goto out;
+
+	if (test_bit(TTY_HUPPED, &tty->flags)) {
+		/* We were raced by hangup */
+		retval = -EIO;
+		goto out;
+	}
+
+	old_ldisc = tty->ldisc;
+
+	/* Shutdown the old discipline. */
+	tty_ldisc_close(tty, old_ldisc);
+
+	/* Now set up the new line discipline. */
+	tty->ldisc = new_ldisc;
+	tty_set_termios_ldisc(tty, disc);
+
+	retval = tty_ldisc_open(tty, new_ldisc);
+	if (retval < 0) {
+		/* Back to the old one or N_TTY if we can't */
+		tty_ldisc_put(new_ldisc);
+		tty_ldisc_restore(tty, old_ldisc);
+	}
+
+	if (tty->ldisc->ops->num != old_ldisc->ops->num && tty->ops->set_ldisc) {
+		down_read(&tty->termios_rwsem);
+		tty->ops->set_ldisc(tty);
+		up_read(&tty->termios_rwsem);
+	}
+
+	/* At this point we hold a reference to the new ldisc and a
+	   reference to the old ldisc, or we hold two references to
+	   the old ldisc (if it was restored as part of error cleanup
+	   above). In either case, releasing a single reference from
+	   the old ldisc is correct. */
+	new_ldisc = old_ldisc;
+out:
+	tty_ldisc_unlock(tty);
+
+	/* Restart the work queue in case no characters kick it off. Safe if
+	   already running */
+	tty_buffer_restart_work(tty->port);
+err:
+	tty_ldisc_put(new_ldisc);	/* drop the extra reference */
+	tty_unlock(tty);
+	return retval;
+}
+EXPORT_SYMBOL_GPL(tty_set_ldisc);
+
+/**
+ *	tty_ldisc_kill	-	teardown ldisc
+ *	@tty: tty being released
+ *
+ *	Perform final close of the ldisc and reset tty->ldisc
+ */
+static void tty_ldisc_kill(struct tty_struct *tty)
+{
+	lockdep_assert_held_write(&tty->ldisc_sem);
+	if (!tty->ldisc)
+		return;
+	/*
+	 * Now kill off the ldisc
+	 */
+	tty_ldisc_close(tty, tty->ldisc);
+	tty_ldisc_put(tty->ldisc);
+	/* Force an oops if we mess this up */
+	tty->ldisc = NULL;
+}
+
+/**
+ *	tty_reset_termios	-	reset terminal state
+ *	@tty: tty to reset
+ *
+ *	Restore a terminal to the driver default state.
+ */
+
+static void tty_reset_termios(struct tty_struct *tty)
+{
+	down_write(&tty->termios_rwsem);
+	tty->termios = tty->driver->init_termios;
+	tty->termios.c_ispeed = tty_termios_input_baud_rate(&tty->termios);
+	tty->termios.c_ospeed = tty_termios_baud_rate(&tty->termios);
+	up_write(&tty->termios_rwsem);
+}
+
+
+/**
+ *	tty_ldisc_reinit	-	reinitialise the tty ldisc
+ *	@tty: tty to reinit
+ *	@disc: line discipline to reinitialize
+ *
+ *	Completely reinitialize the line discipline state, by closing the
+ *	current instance, if there is one, and opening a new instance. If
+ *	an error occurs opening the new non-N_TTY instance, the instance
+ *	is dropped and tty->ldisc reset to NULL. The caller can then retry
+ *	with N_TTY instead.
+ *
+ *	Returns 0 if successful, otherwise error code < 0
+ */
+
+int tty_ldisc_reinit(struct tty_struct *tty, int disc)
+{
+	struct tty_ldisc *ld;
+	int retval;
+
+	lockdep_assert_held_write(&tty->ldisc_sem);
+	ld = tty_ldisc_get(tty, disc);
+	if (IS_ERR(ld)) {
+		BUG_ON(disc == N_TTY);
+		return PTR_ERR(ld);
+	}
+
+	if (tty->ldisc) {
+		tty_ldisc_close(tty, tty->ldisc);
+		tty_ldisc_put(tty->ldisc);
+	}
+
+	/* switch the line discipline */
+	tty->ldisc = ld;
+	tty_set_termios_ldisc(tty, disc);
+	retval = tty_ldisc_open(tty, tty->ldisc);
+	if (retval) {
+		tty_ldisc_put(tty->ldisc);
+		tty->ldisc = NULL;
+	}
+	return retval;
+}
+
+/**
+ *	tty_ldisc_hangup		-	hangup ldisc reset
+ *	@tty: tty being hung up
+ *
+ *	Some tty devices reset their termios when they receive a hangup
+ *	event. In that situation we must also switch back to N_TTY properly
+ *	before we reset the termios data.
+ *
+ *	Locking: We can take the ldisc mutex as the rest of the code is
+ *	careful to allow for this.
+ *
+ *	In the pty pair case this occurs in the close() path of the
+ *	tty itself so we must be careful about locking rules.
+ */
+
+void tty_ldisc_hangup(struct tty_struct *tty, bool reinit)
+{
+	struct tty_ldisc *ld;
+
+	tty_ldisc_debug(tty, "%p: hangup\n", tty->ldisc);
+
+	ld = tty_ldisc_ref(tty);
+	if (ld != NULL) {
+		if (ld->ops->flush_buffer)
+			ld->ops->flush_buffer(tty);
+		tty_driver_flush_buffer(tty);
+		if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
+		    ld->ops->write_wakeup)
+			ld->ops->write_wakeup(tty);
+		if (ld->ops->hangup)
+			ld->ops->hangup(tty);
+		tty_ldisc_deref(ld);
+	}
+
+	wake_up_interruptible_poll(&tty->write_wait, EPOLLOUT);
+	wake_up_interruptible_poll(&tty->read_wait, EPOLLIN);
+
+	/*
+	 * Shutdown the current line discipline, and reset it to
+	 * N_TTY if need be.
+	 *
+	 * Avoid racing set_ldisc or tty_ldisc_release
+	 */
+	tty_ldisc_lock(tty, MAX_SCHEDULE_TIMEOUT);
+
+	if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS)
+		tty_reset_termios(tty);
+
+	if (tty->ldisc) {
+		if (reinit) {
+			if (tty_ldisc_reinit(tty, tty->termios.c_line) < 0 &&
+			    tty_ldisc_reinit(tty, N_TTY) < 0)
+				WARN_ON(tty_ldisc_reinit(tty, N_NULL) < 0);
+		} else
+			tty_ldisc_kill(tty);
+	}
+	tty_ldisc_unlock(tty);
+}
+
+/**
+ *	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 disciplines and bind them to the tty. This has no locking issues
+ *	as the device isn't yet active.
+ */
+
+int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
+{
+	int retval = tty_ldisc_open(tty, tty->ldisc);
+	if (retval)
+		return retval;
+
+	if (o_tty) {
+		/*
+		 * Called without o_tty->ldisc_sem held, as o_tty has been
+		 * just allocated and no one has a reference to it.
+		 */
+		retval = tty_ldisc_open(o_tty, o_tty->ldisc);
+		if (retval) {
+			tty_ldisc_close(tty, tty->ldisc);
+			return retval;
+		}
+	}
+	return 0;
+}
+
+/**
+ *	tty_ldisc_release		-	release line discipline
+ *	@tty: tty being shut down (or one end of pty pair)
+ *
+ *	Called during the final close of a tty or a pty pair in order to shut
+ *	down the line discpline layer. On exit, each tty's ldisc is NULL.
+ */
+
+void tty_ldisc_release(struct tty_struct *tty)
+{
+	struct tty_struct *o_tty = tty->link;
+
+	/*
+	 * Shutdown this line discipline. As this is the final close,
+	 * it does not race with the set_ldisc code path.
+	 */
+
+	tty_ldisc_lock_pair(tty, o_tty);
+	tty_ldisc_kill(tty);
+	if (o_tty)
+		tty_ldisc_kill(o_tty);
+	tty_ldisc_unlock_pair(tty, o_tty);
+
+	/* And the memory resources remaining (buffers, termios) will be
+	   disposed of when the kref hits zero */
+
+	tty_ldisc_debug(tty, "released\n");
+}
+EXPORT_SYMBOL_GPL(tty_ldisc_release);
+
+/**
+ *	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.
+ */
+
+int tty_ldisc_init(struct tty_struct *tty)
+{
+	struct tty_ldisc *ld = tty_ldisc_get(tty, N_TTY);
+	if (IS_ERR(ld))
+		return PTR_ERR(ld);
+	tty->ldisc = ld;
+	return 0;
+}
+
+/**
+ *	tty_ldisc_deinit	-	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)
+{
+	/* no ldisc_sem, tty is being destroyed */
+	if (tty->ldisc)
+		tty_ldisc_put(tty->ldisc);
+	tty->ldisc = NULL;
+}
+
+static struct ctl_table tty_table[] = {
+	{
+		.procname	= "ldisc_autoload",
+		.data		= &tty_ldisc_autoload,
+		.maxlen		= sizeof(tty_ldisc_autoload),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec,
+		.extra1		= SYSCTL_ZERO,
+		.extra2		= SYSCTL_ONE,
+	},
+	{ }
+};
+
+static struct ctl_table tty_dir_table[] = {
+	{
+		.procname	= "tty",
+		.mode		= 0555,
+		.child		= tty_table,
+	},
+	{ }
+};
+
+static struct ctl_table tty_root_table[] = {
+	{
+		.procname	= "dev",
+		.mode		= 0555,
+		.child		= tty_dir_table,
+	},
+	{ }
+};
+
+void tty_sysctl_init(void)
+{
+	register_sysctl_table(tty_root_table);
+}