xref: /openbmc/linux/drivers/tty/tty_io.c (revision 88a6f899)

// SPDX-License-Identifier: GPL-2.0
/*
 *  Copyright (C) 1991, 1992  Linus Torvalds
 */

/*
 * 'tty_io.c' gives an orthogonal feeling to tty's, be they consoles
 * or rs-channels. It also implements echoing, cooked mode etc.
 *
 * Kill-line thanks to John T Kohl, who also corrected VMIN = VTIME = 0.
 *
 * Modified by Theodore Ts'o, 9/14/92, to dynamically allocate the
 * tty_struct and tty_queue structures.  Previously there was an array
 * of 256 tty_struct's which was statically allocated, and the
 * tty_queue structures were allocated at boot time.  Both are now
 * dynamically allocated only when the tty is open.
 *
 * Also restructured routines so that there is more of a separation
 * between the high-level tty routines (tty_io.c and tty_ioctl.c) and
 * the low-level tty routines (serial.c, pty.c, console.c).  This
 * makes for cleaner and more compact code.  -TYT, 9/17/92
 *
 * Modified by Fred N. van Kempen, 01/29/93, to add line disciplines
 * which can be dynamically activated and de-activated by the line
 * discipline handling modules (like SLIP).
 *
 * NOTE: pay no attention to the line discipline code (yet); its
 * interface is still subject to change in this version...
 * -- TYT, 1/31/92
 *
 * Added functionality to the OPOST tty handling.  No delays, but all
 * other bits should be there.
 *	-- Nick Holloway <alfie@dcs.warwick.ac.uk>, 27th May 1993.
 *
 * Rewrote canonical mode and added more termios flags.
 *	-- julian@uhunix.uhcc.hawaii.edu (J. Cowley), 13Jan94
 *
 * Reorganized FASYNC support so mouse code can share it.
 *	-- ctm@ardi.com, 9Sep95
 *
 * New TIOCLINUX variants added.
 *	-- mj@k332.feld.cvut.cz, 19-Nov-95
 *
 * Restrict vt switching via ioctl()
 *      -- grif@cs.ucr.edu, 5-Dec-95
 *
 * Move console and virtual terminal code to more appropriate files,
 * implement CONFIG_VT and generalize console device interface.
 *	-- Marko Kohtala <Marko.Kohtala@hut.fi>, March 97
 *
 * Rewrote tty_init_dev and tty_release_dev to eliminate races.
 *	-- Bill Hawes <whawes@star.net>, June 97
 *
 * Added devfs support.
 *      -- C. Scott Ananian <cananian@alumni.princeton.edu>, 13-Jan-1998
 *
 * Added support for a Unix98-style ptmx device.
 *      -- C. Scott Ananian <cananian@alumni.princeton.edu>, 14-Jan-1998
 *
 * Reduced memory usage for older ARM systems
 *      -- Russell King <rmk@arm.linux.org.uk>
 *
 * Move do_SAK() into process context.  Less stack use in devfs functions.
 * alloc_tty_struct() always uses kmalloc()
 *			 -- Andrew Morton <andrewm@uow.edu.eu> 17Mar01
 */

#include <linux/types.h>
#include <linux/major.h>
#include <linux/errno.h>
#include <linux/signal.h>
#include <linux/fcntl.h>
#include <linux/sched/signal.h>
#include <linux/sched/task.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/ppp-ioctl.h>
#include <linux/proc_fs.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/device.h>
#include <linux/wait.h>
#include <linux/bitops.h>
#include <linux/delay.h>
#include <linux/seq_file.h>
#include <linux/serial.h>
#include <linux/ratelimit.h>
#include <linux/compat.h>
#include <linux/uaccess.h>
#include <linux/termios_internal.h>
#include <linux/fs.h>

#include <linux/kbd_kern.h>
#include <linux/vt_kern.h>
#include <linux/selection.h>

#include <linux/kmod.h>
#include <linux/nsproxy.h>
#include "tty.h"

#undef TTY_DEBUG_HANGUP
#ifdef TTY_DEBUG_HANGUP
# define tty_debug_hangup(tty, f, args...)	tty_debug(tty, f, ##args)
#else
# define tty_debug_hangup(tty, f, args...)	do { } while (0)
#endif

#define TTY_PARANOIA_CHECK 1
#define CHECK_TTY_COUNT 1

struct ktermios tty_std_termios = {	/* for the benefit of tty drivers  */
	.c_iflag = ICRNL | IXON,
	.c_oflag = OPOST | ONLCR,
	.c_cflag = B38400 | CS8 | CREAD | HUPCL,
	.c_lflag = ISIG | ICANON | ECHO | ECHOE | ECHOK |
		   ECHOCTL | ECHOKE | IEXTEN,
	.c_cc = INIT_C_CC,
	.c_ispeed = 38400,
	.c_ospeed = 38400,
	/* .c_line = N_TTY, */
};
EXPORT_SYMBOL(tty_std_termios);

/* This list gets poked at by procfs and various bits of boot up code. This
 * could do with some rationalisation such as pulling the tty proc function
 * into this file.
 */

LIST_HEAD(tty_drivers);			/* linked list of tty drivers */

/* Mutex to protect creating and releasing a tty */
DEFINE_MUTEX(tty_mutex);

static ssize_t tty_read(struct kiocb *, struct iov_iter *);
static ssize_t tty_write(struct kiocb *, struct iov_iter *);
static __poll_t tty_poll(struct file *, poll_table *);
static int tty_open(struct inode *, struct file *);
#ifdef CONFIG_COMPAT
static long tty_compat_ioctl(struct file *file, unsigned int cmd,
				unsigned long arg);
#else
#define tty_compat_ioctl NULL
#endif
static int __tty_fasync(int fd, struct file *filp, int on);
static int tty_fasync(int fd, struct file *filp, int on);
static void release_tty(struct tty_struct *tty, int idx);

/**
 * free_tty_struct	-	free a disused tty
 * @tty: tty struct to free
 *
 * Free the write buffers, tty queue and tty memory itself.
 *
 * Locking: none. Must be called after tty is definitely unused
 */
static void free_tty_struct(struct tty_struct *tty)
{
	tty_ldisc_deinit(tty);
	put_device(tty->dev);
	kvfree(tty->write_buf);
	kfree(tty);
}

static inline struct tty_struct *file_tty(struct file *file)
{
	return ((struct tty_file_private *)file->private_data)->tty;
}

int tty_alloc_file(struct file *file)
{
	struct tty_file_private *priv;

	priv = kmalloc(sizeof(*priv), GFP_KERNEL);
	if (!priv)
		return -ENOMEM;

	file->private_data = priv;

	return 0;
}

/* Associate a new file with the tty structure */
void tty_add_file(struct tty_struct *tty, struct file *file)
{
	struct tty_file_private *priv = file->private_data;

	priv->tty = tty;
	priv->file = file;

	spin_lock(&tty->files_lock);
	list_add(&priv->list, &tty->tty_files);
	spin_unlock(&tty->files_lock);
}

/**
 * tty_free_file - free file->private_data
 * @file: to free private_data of
 *
 * This shall be used only for fail path handling when tty_add_file was not
 * called yet.
 */
void tty_free_file(struct file *file)
{
	struct tty_file_private *priv = file->private_data;

	file->private_data = NULL;
	kfree(priv);
}

/* Delete file from its tty */
static void tty_del_file(struct file *file)
{
	struct tty_file_private *priv = file->private_data;
	struct tty_struct *tty = priv->tty;

	spin_lock(&tty->files_lock);
	list_del(&priv->list);
	spin_unlock(&tty->files_lock);
	tty_free_file(file);
}

/**
 * tty_name	-	return tty naming
 * @tty: tty structure
 *
 * Convert a tty structure into a name. The name reflects the kernel naming
 * policy and if udev is in use may not reflect user space
 *
 * Locking: none
 */
const char *tty_name(const struct tty_struct *tty)
{
	if (!tty) /* Hmm.  NULL pointer.  That's fun. */
		return "NULL tty";
	return tty->name;
}
EXPORT_SYMBOL(tty_name);

const char *tty_driver_name(const struct tty_struct *tty)
{
	if (!tty || !tty->driver)
		return "";
	return tty->driver->name;
}

static int tty_paranoia_check(struct tty_struct *tty, struct inode *inode,
			      const char *routine)
{
#ifdef TTY_PARANOIA_CHECK
	if (!tty) {
		pr_warn("(%d:%d): %s: NULL tty\n",
			imajor(inode), iminor(inode), routine);
		return 1;
	}
#endif
	return 0;
}

/* Caller must hold tty_lock */
static int check_tty_count(struct tty_struct *tty, const char *routine)
{
#ifdef CHECK_TTY_COUNT
	struct list_head *p;
	int count = 0, kopen_count = 0;

	spin_lock(&tty->files_lock);
	list_for_each(p, &tty->tty_files) {
		count++;
	}
	spin_unlock(&tty->files_lock);
	if (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
	    tty->driver->subtype == PTY_TYPE_SLAVE &&
	    tty->link && tty->link->count)
		count++;
	if (tty_port_kopened(tty->port))
		kopen_count++;
	if (tty->count != (count + kopen_count)) {
		tty_warn(tty, "%s: tty->count(%d) != (#fd's(%d) + #kopen's(%d))\n",
			 routine, tty->count, count, kopen_count);
		return (count + kopen_count);
	}
#endif
	return 0;
}

/**
 * get_tty_driver		-	find device of a tty
 * @device: device identifier
 * @index: returns the index of the tty
 *
 * This routine returns a tty driver structure, given a device number and also
 * passes back the index number.
 *
 * Locking: caller must hold tty_mutex
 */
static struct tty_driver *get_tty_driver(dev_t device, int *index)
{
	struct tty_driver *p;

	list_for_each_entry(p, &tty_drivers, tty_drivers) {
		dev_t base = MKDEV(p->major, p->minor_start);

		if (device < base || device >= base + p->num)
			continue;
		*index = device - base;
		return tty_driver_kref_get(p);
	}
	return NULL;
}

/**
 * tty_dev_name_to_number	-	return dev_t for device name
 * @name: user space name of device under /dev
 * @number: pointer to dev_t that this function will populate
 *
 * This function converts device names like ttyS0 or ttyUSB1 into dev_t like
 * (4, 64) or (188, 1). If no corresponding driver is registered then the
 * function returns -%ENODEV.
 *
 * Locking: this acquires tty_mutex to protect the tty_drivers list from
 *	being modified while we are traversing it, and makes sure to
 *	release it before exiting.
 */
int tty_dev_name_to_number(const char *name, dev_t *number)
{
	struct tty_driver *p;
	int ret;
	int index, prefix_length = 0;
	const char *str;

	for (str = name; *str && !isdigit(*str); str++)
		;

	if (!*str)
		return -EINVAL;

	ret = kstrtoint(str, 10, &index);
	if (ret)
		return ret;

	prefix_length = str - name;
	mutex_lock(&tty_mutex);

	list_for_each_entry(p, &tty_drivers, tty_drivers)
		if (prefix_length == strlen(p->name) && strncmp(name,
					p->name, prefix_length) == 0) {
			if (index < p->num) {
				*number = MKDEV(p->major, p->minor_start + index);
				goto out;
			}
		}

	/* if here then driver wasn't found */
	ret = -ENODEV;
out:
	mutex_unlock(&tty_mutex);
	return ret;
}
EXPORT_SYMBOL_GPL(tty_dev_name_to_number);

#ifdef CONFIG_CONSOLE_POLL

/**
 * tty_find_polling_driver	-	find device of a polled tty
 * @name: name string to match
 * @line: pointer to resulting tty line nr
 *
 * This routine returns a tty driver structure, given a name and the condition
 * that the tty driver is capable of polled operation.
 */
struct tty_driver *tty_find_polling_driver(char *name, int *line)
{
	struct tty_driver *p, *res = NULL;
	int tty_line = 0;
	int len;
	char *str, *stp;

	for (str = name; *str; str++)
		if ((*str >= '0' && *str <= '9') || *str == ',')
			break;
	if (!*str)
		return NULL;

	len = str - name;
	tty_line = simple_strtoul(str, &str, 10);

	mutex_lock(&tty_mutex);
	/* Search through the tty devices to look for a match */
	list_for_each_entry(p, &tty_drivers, tty_drivers) {
		if (!len || strncmp(name, p->name, len) != 0)
			continue;
		stp = str;
		if (*stp == ',')
			stp++;
		if (*stp == '\0')
			stp = NULL;

		if (tty_line >= 0 && tty_line < p->num && p->ops &&
		    p->ops->poll_init && !p->ops->poll_init(p, tty_line, stp)) {
			res = tty_driver_kref_get(p);
			*line = tty_line;
			break;
		}
	}
	mutex_unlock(&tty_mutex);

	return res;
}
EXPORT_SYMBOL_GPL(tty_find_polling_driver);
#endif

static ssize_t hung_up_tty_read(struct kiocb *iocb, struct iov_iter *to)
{
	return 0;
}

static ssize_t hung_up_tty_write(struct kiocb *iocb, struct iov_iter *from)
{
	return -EIO;
}

/* No kernel lock held - none needed ;) */
static __poll_t hung_up_tty_poll(struct file *filp, poll_table *wait)
{
	return EPOLLIN | EPOLLOUT | EPOLLERR | EPOLLHUP | EPOLLRDNORM | EPOLLWRNORM;
}

static long hung_up_tty_ioctl(struct file *file, unsigned int cmd,
		unsigned long arg)
{
	return cmd == TIOCSPGRP ? -ENOTTY : -EIO;
}

static long hung_up_tty_compat_ioctl(struct file *file,
				     unsigned int cmd, unsigned long arg)
{
	return cmd == TIOCSPGRP ? -ENOTTY : -EIO;
}

static int hung_up_tty_fasync(int fd, struct file *file, int on)
{
	return -ENOTTY;
}

static void tty_show_fdinfo(struct seq_file *m, struct file *file)
{
	struct tty_struct *tty = file_tty(file);

	if (tty && tty->ops && tty->ops->show_fdinfo)
		tty->ops->show_fdinfo(tty, m);
}

static const struct file_operations tty_fops = {
	.llseek		= no_llseek,
	.read_iter	= tty_read,
	.write_iter	= tty_write,
	.splice_read	= copy_splice_read,
	.splice_write	= iter_file_splice_write,
	.poll		= tty_poll,
	.unlocked_ioctl	= tty_ioctl,
	.compat_ioctl	= tty_compat_ioctl,
	.open		= tty_open,
	.release	= tty_release,
	.fasync		= tty_fasync,
	.show_fdinfo	= tty_show_fdinfo,
};

static const struct file_operations console_fops = {
	.llseek		= no_llseek,
	.read_iter	= tty_read,
	.write_iter	= redirected_tty_write,
	.splice_read	= copy_splice_read,
	.splice_write	= iter_file_splice_write,
	.poll		= tty_poll,
	.unlocked_ioctl	= tty_ioctl,
	.compat_ioctl	= tty_compat_ioctl,
	.open		= tty_open,
	.release	= tty_release,
	.fasync		= tty_fasync,
};

static const struct file_operations hung_up_tty_fops = {
	.llseek		= no_llseek,
	.read_iter	= hung_up_tty_read,
	.write_iter	= hung_up_tty_write,
	.poll		= hung_up_tty_poll,
	.unlocked_ioctl	= hung_up_tty_ioctl,
	.compat_ioctl	= hung_up_tty_compat_ioctl,
	.release	= tty_release,
	.fasync		= hung_up_tty_fasync,
};

static DEFINE_SPINLOCK(redirect_lock);
static struct file *redirect;

/**
 * tty_wakeup	-	request more data
 * @tty: terminal
 *
 * Internal and external helper for wakeups of tty. This function informs the
 * line discipline if present that the driver is ready to receive more output
 * data.
 */
void tty_wakeup(struct tty_struct *tty)
{
	struct tty_ldisc *ld;

	if (test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) {
		ld = tty_ldisc_ref(tty);
		if (ld) {
			if (ld->ops->write_wakeup)
				ld->ops->write_wakeup(tty);
			tty_ldisc_deref(ld);
		}
	}
	wake_up_interruptible_poll(&tty->write_wait, EPOLLOUT);
}
EXPORT_SYMBOL_GPL(tty_wakeup);

/**
 * tty_release_redirect	-	Release a redirect on a pty if present
 * @tty: tty device
 *
 * This is available to the pty code so if the master closes, if the slave is a
 * redirect it can release the redirect.
 */
static struct file *tty_release_redirect(struct tty_struct *tty)
{
	struct file *f = NULL;

	spin_lock(&redirect_lock);
	if (redirect && file_tty(redirect) == tty) {
		f = redirect;
		redirect = NULL;
	}
	spin_unlock(&redirect_lock);

	return f;
}

/**
 * __tty_hangup		-	actual handler for hangup events
 * @tty: tty device
 * @exit_session: if non-zero, signal all foreground group processes
 *
 * This can be called by a "kworker" kernel thread. That is process synchronous
 * but doesn't hold any locks, so we need to make sure we have the appropriate
 * locks for what we're doing.
 *
 * The hangup event clears any pending redirections onto the hung up device. It
 * ensures future writes will error and it does the needed line discipline
 * hangup and signal delivery. The tty object itself remains intact.
 *
 * Locking:
 *  * BTM
 *
 *   * redirect lock for undoing redirection
 *   * file list lock for manipulating list of ttys
 *   * tty_ldiscs_lock from called functions
 *   * termios_rwsem resetting termios data
 *   * tasklist_lock to walk task list for hangup event
 *
 *    * ->siglock to protect ->signal/->sighand
 *
 */
static void __tty_hangup(struct tty_struct *tty, int exit_session)
{
	struct file *cons_filp = NULL;
	struct file *filp, *f;
	struct tty_file_private *priv;
	int    closecount = 0, n;
	int refs;

	if (!tty)
		return;

	f = tty_release_redirect(tty);

	tty_lock(tty);

	if (test_bit(TTY_HUPPED, &tty->flags)) {
		tty_unlock(tty);
		return;
	}

	/*
	 * Some console devices aren't actually hung up for technical and
	 * historical reasons, which can lead to indefinite interruptible
	 * sleep in n_tty_read().  The following explicitly tells
	 * n_tty_read() to abort readers.
	 */
	set_bit(TTY_HUPPING, &tty->flags);

	/* inuse_filps is protected by the single tty lock,
	 * this really needs to change if we want to flush the
	 * workqueue with the lock held.
	 */
	check_tty_count(tty, "tty_hangup");

	spin_lock(&tty->files_lock);
	/* This breaks for file handles being sent over AF_UNIX sockets ? */
	list_for_each_entry(priv, &tty->tty_files, list) {
		filp = priv->file;
		if (filp->f_op->write_iter == redirected_tty_write)
			cons_filp = filp;
		if (filp->f_op->write_iter != tty_write)
			continue;
		closecount++;
		__tty_fasync(-1, filp, 0);	/* can't block */
		filp->f_op = &hung_up_tty_fops;
	}
	spin_unlock(&tty->files_lock);

	refs = tty_signal_session_leader(tty, exit_session);
	/* Account for the p->signal references we killed */
	while (refs--)
		tty_kref_put(tty);

	tty_ldisc_hangup(tty, cons_filp != NULL);

	spin_lock_irq(&tty->ctrl.lock);
	clear_bit(TTY_THROTTLED, &tty->flags);
	clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
	put_pid(tty->ctrl.session);
	put_pid(tty->ctrl.pgrp);
	tty->ctrl.session = NULL;
	tty->ctrl.pgrp = NULL;
	tty->ctrl.pktstatus = 0;
	spin_unlock_irq(&tty->ctrl.lock);

	/*
	 * If one of the devices matches a console pointer, we
	 * cannot just call hangup() because that will cause
	 * tty->count and state->count to go out of sync.
	 * So we just call close() the right number of times.
	 */
	if (cons_filp) {
		if (tty->ops->close)
			for (n = 0; n < closecount; n++)
				tty->ops->close(tty, cons_filp);
	} else if (tty->ops->hangup)
		tty->ops->hangup(tty);
	/*
	 * We don't want to have driver/ldisc interactions beyond the ones
	 * we did here. The driver layer expects no calls after ->hangup()
	 * from the ldisc side, which is now guaranteed.
	 */
	set_bit(TTY_HUPPED, &tty->flags);
	clear_bit(TTY_HUPPING, &tty->flags);
	tty_unlock(tty);

	if (f)
		fput(f);
}

static void do_tty_hangup(struct work_struct *work)
{
	struct tty_struct *tty =
		container_of(work, struct tty_struct, hangup_work);

	__tty_hangup(tty, 0);
}

/**
 * tty_hangup		-	trigger a hangup event
 * @tty: tty to hangup
 *
 * A carrier loss (virtual or otherwise) has occurred on @tty. Schedule a
 * hangup sequence to run after this event.
 */
void tty_hangup(struct tty_struct *tty)
{
	tty_debug_hangup(tty, "hangup\n");
	schedule_work(&tty->hangup_work);
}
EXPORT_SYMBOL(tty_hangup);

/**
 * tty_vhangup		-	process vhangup
 * @tty: tty to hangup
 *
 * The user has asked via system call for the terminal to be hung up. We do
 * this synchronously so that when the syscall returns the process is complete.
 * That guarantee is necessary for security reasons.
 */
void tty_vhangup(struct tty_struct *tty)
{
	tty_debug_hangup(tty, "vhangup\n");
	__tty_hangup(tty, 0);
}
EXPORT_SYMBOL(tty_vhangup);


/**
 * tty_vhangup_self	-	process vhangup for own ctty
 *
 * Perform a vhangup on the current controlling tty
 */
void tty_vhangup_self(void)
{
	struct tty_struct *tty;

	tty = get_current_tty();
	if (tty) {
		tty_vhangup(tty);
		tty_kref_put(tty);
	}
}

/**
 * tty_vhangup_session	-	hangup session leader exit
 * @tty: tty to hangup
 *
 * The session leader is exiting and hanging up its controlling terminal.
 * Every process in the foreground process group is signalled %SIGHUP.
 *
 * We do this synchronously so that when the syscall returns the process is
 * complete. That guarantee is necessary for security reasons.
 */
void tty_vhangup_session(struct tty_struct *tty)
{
	tty_debug_hangup(tty, "session hangup\n");
	__tty_hangup(tty, 1);
}

/**
 * tty_hung_up_p	-	was tty hung up
 * @filp: file pointer of tty
 *
 * Return: true if the tty has been subject to a vhangup or a carrier loss
 */
int tty_hung_up_p(struct file *filp)
{
	return (filp && filp->f_op == &hung_up_tty_fops);
}
EXPORT_SYMBOL(tty_hung_up_p);

void __stop_tty(struct tty_struct *tty)
{
	if (tty->flow.stopped)
		return;
	tty->flow.stopped = true;
	if (tty->ops->stop)
		tty->ops->stop(tty);
}

/**
 * stop_tty	-	propagate flow control
 * @tty: tty to stop
 *
 * Perform flow control to the driver. May be called on an already stopped
 * device and will not re-call the &tty_driver->stop() method.
 *
 * This functionality is used by both the line disciplines for halting incoming
 * flow and by the driver. It may therefore be called from any context, may be
 * under the tty %atomic_write_lock but not always.
 *
 * Locking:
 *	flow.lock
 */
void stop_tty(struct tty_struct *tty)
{
	unsigned long flags;

	spin_lock_irqsave(&tty->flow.lock, flags);
	__stop_tty(tty);
	spin_unlock_irqrestore(&tty->flow.lock, flags);
}
EXPORT_SYMBOL(stop_tty);

void __start_tty(struct tty_struct *tty)
{
	if (!tty->flow.stopped || tty->flow.tco_stopped)
		return;
	tty->flow.stopped = false;
	if (tty->ops->start)
		tty->ops->start(tty);
	tty_wakeup(tty);
}

/**
 * start_tty	-	propagate flow control
 * @tty: tty to start
 *
 * Start a tty that has been stopped if at all possible. If @tty was previously
 * stopped and is now being started, the &tty_driver->start() method is invoked
 * and the line discipline woken.
 *
 * Locking:
 *	flow.lock
 */
void start_tty(struct tty_struct *tty)
{
	unsigned long flags;

	spin_lock_irqsave(&tty->flow.lock, flags);
	__start_tty(tty);
	spin_unlock_irqrestore(&tty->flow.lock, flags);
}
EXPORT_SYMBOL(start_tty);

static void tty_update_time(struct tty_struct *tty, bool mtime)
{
	time64_t sec = ktime_get_real_seconds();
	struct tty_file_private *priv;

	spin_lock(&tty->files_lock);
	list_for_each_entry(priv, &tty->tty_files, list) {
		struct inode *inode = file_inode(priv->file);
		struct timespec64 *time = mtime ? &inode->i_mtime : &inode->i_atime;

		/*
		 * We only care if the two values differ in anything other than the
		 * lower three bits (i.e every 8 seconds).  If so, then we can update
		 * the time of the tty device, otherwise it could be construded as a
		 * security leak to let userspace know the exact timing of the tty.
		 */
		if ((sec ^ time->tv_sec) & ~7)
			time->tv_sec = sec;
	}
	spin_unlock(&tty->files_lock);
}

/*
 * Iterate on the ldisc ->read() function until we've gotten all
 * the data the ldisc has for us.
 *
 * The "cookie" is something that the ldisc read function can fill
 * in to let us know that there is more data to be had.
 *
 * We promise to continue to call the ldisc until it stops returning
 * data or clears the cookie. The cookie may be something that the
 * ldisc maintains state for and needs to free.
 */
static int iterate_tty_read(struct tty_ldisc *ld, struct tty_struct *tty,
		struct file *file, struct iov_iter *to)
{
	int retval = 0;
	void *cookie = NULL;
	unsigned long offset = 0;
	char kernel_buf[64];
	size_t count = iov_iter_count(to);

	do {
		int size, copied;

		size = count > sizeof(kernel_buf) ? sizeof(kernel_buf) : count;
		size = ld->ops->read(tty, file, kernel_buf, size, &cookie, offset);
		if (!size)
			break;

		if (size < 0) {
			/* Did we have an earlier error (ie -EFAULT)? */
			if (retval)
				break;
			retval = size;

			/*
			 * -EOVERFLOW means we didn't have enough space
			 * for a whole packet, and we shouldn't return
			 * a partial result.
			 */
			if (retval == -EOVERFLOW)
				offset = 0;
			break;
		}

		copied = copy_to_iter(kernel_buf, size, to);
		offset += copied;
		count -= copied;

		/*
		 * If the user copy failed, we still need to do another ->read()
		 * call if we had a cookie to let the ldisc clear up.
		 *
		 * But make sure size is zeroed.
		 */
		if (unlikely(copied != size)) {
			count = 0;
			retval = -EFAULT;
		}
	} while (cookie);

	/* We always clear tty buffer in case they contained passwords */
	memzero_explicit(kernel_buf, sizeof(kernel_buf));
	return offset ? offset : retval;
}


/**
 * tty_read	-	read method for tty device files
 * @iocb: kernel I/O control block
 * @to: destination for the data read
 *
 * Perform the read system call function on this terminal device. Checks
 * for hung up devices before calling the line discipline method.
 *
 * Locking:
 *	Locks the line discipline internally while needed. Multiple read calls
 *	may be outstanding in parallel.
 */
static ssize_t tty_read(struct kiocb *iocb, struct iov_iter *to)
{
	int i;
	struct file *file = iocb->ki_filp;
	struct inode *inode = file_inode(file);
	struct tty_struct *tty = file_tty(file);
	struct tty_ldisc *ld;

	if (tty_paranoia_check(tty, inode, "tty_read"))
		return -EIO;
	if (!tty || tty_io_error(tty))
		return -EIO;

	/* We want to wait for the line discipline to sort out in this
	 * situation.
	 */
	ld = tty_ldisc_ref_wait(tty);
	if (!ld)
		return hung_up_tty_read(iocb, to);
	i = -EIO;
	if (ld->ops->read)
		i = iterate_tty_read(ld, tty, file, to);
	tty_ldisc_deref(ld);

	if (i > 0)
		tty_update_time(tty, false);

	return i;
}

void tty_write_unlock(struct tty_struct *tty)
{
	mutex_unlock(&tty->atomic_write_lock);
	wake_up_interruptible_poll(&tty->write_wait, EPOLLOUT);
}

int tty_write_lock(struct tty_struct *tty, int ndelay)
{
	if (!mutex_trylock(&tty->atomic_write_lock)) {
		if (ndelay)
			return -EAGAIN;
		if (mutex_lock_interruptible(&tty->atomic_write_lock))
			return -ERESTARTSYS;
	}
	return 0;
}

/*
 * Split writes up in sane blocksizes to avoid
 * denial-of-service type attacks
 */
static inline ssize_t do_tty_write(
	ssize_t (*write)(struct tty_struct *, struct file *, const unsigned char *, size_t),
	struct tty_struct *tty,
	struct file *file,
	struct iov_iter *from)
{
	size_t count = iov_iter_count(from);
	ssize_t ret, written = 0;
	unsigned int chunk;

	ret = tty_write_lock(tty, file->f_flags & O_NDELAY);
	if (ret < 0)
		return ret;

	/*
	 * We chunk up writes into a temporary buffer. This
	 * simplifies low-level drivers immensely, since they
	 * don't have locking issues and user mode accesses.
	 *
	 * But if TTY_NO_WRITE_SPLIT is set, we should use a
	 * big chunk-size..
	 *
	 * The default chunk-size is 2kB, because the NTTY
	 * layer has problems with bigger chunks. It will
	 * claim to be able to handle more characters than
	 * it actually does.
	 */
	chunk = 2048;
	if (test_bit(TTY_NO_WRITE_SPLIT, &tty->flags))
		chunk = 65536;
	if (count < chunk)
		chunk = count;

	/* write_buf/write_cnt is protected by the atomic_write_lock mutex */
	if (tty->write_cnt < chunk) {
		unsigned char *buf_chunk;

		if (chunk < 1024)
			chunk = 1024;

		buf_chunk = kvmalloc(chunk, GFP_KERNEL | __GFP_RETRY_MAYFAIL);
		if (!buf_chunk) {
			ret = -ENOMEM;
			goto out;
		}
		kvfree(tty->write_buf);
		tty->write_cnt = chunk;
		tty->write_buf = buf_chunk;
	}

	/* Do the write .. */
	for (;;) {
		size_t size = count;

		if (size > chunk)
			size = chunk;

		ret = -EFAULT;
		if (copy_from_iter(tty->write_buf, size, from) != size)
			break;

		ret = write(tty, file, tty->write_buf, size);
		if (ret <= 0)
			break;

		written += ret;
		if (ret > size)
			break;

		/* FIXME! Have Al check this! */
		if (ret != size)
			iov_iter_revert(from, size-ret);

		count -= ret;
		if (!count)
			break;
		ret = -ERESTARTSYS;
		if (signal_pending(current))
			break;
		cond_resched();
	}
	if (written) {
		tty_update_time(tty, true);
		ret = written;
	}
out:
	tty_write_unlock(tty);
	return ret;
}

/**
 * tty_write_message - write a message to a certain tty, not just the console.
 * @tty: the destination tty_struct
 * @msg: the message to write
 *
 * This is used for messages that need to be redirected to a specific tty. We
 * don't put it into the syslog queue right now maybe in the future if really
 * needed.
 *
 * We must still hold the BTM and test the CLOSING flag for the moment.
 */
void tty_write_message(struct tty_struct *tty, char *msg)
{
	if (tty) {
		mutex_lock(&tty->atomic_write_lock);
		tty_lock(tty);
		if (tty->ops->write && tty->count > 0)
			tty->ops->write(tty, msg, strlen(msg));
		tty_unlock(tty);
		tty_write_unlock(tty);
	}
}

static ssize_t file_tty_write(struct file *file, struct kiocb *iocb, struct iov_iter *from)
{
	struct tty_struct *tty = file_tty(file);
	struct tty_ldisc *ld;
	ssize_t ret;

	if (tty_paranoia_check(tty, file_inode(file), "tty_write"))
		return -EIO;
	if (!tty || !tty->ops->write ||	tty_io_error(tty))
		return -EIO;
	/* Short term debug to catch buggy drivers */
	if (tty->ops->write_room == NULL)
		tty_err(tty, "missing write_room method\n");
	ld = tty_ldisc_ref_wait(tty);
	if (!ld)
		return hung_up_tty_write(iocb, from);
	if (!ld->ops->write)
		ret = -EIO;
	else
		ret = do_tty_write(ld->ops->write, tty, file, from);
	tty_ldisc_deref(ld);
	return ret;
}

/**
 * tty_write		-	write method for tty device file
 * @iocb: kernel I/O control block
 * @from: iov_iter with data to write
 *
 * Write data to a tty device via the line discipline.
 *
 * Locking:
 *	Locks the line discipline as required
 *	Writes to the tty driver are serialized by the atomic_write_lock
 *	and are then processed in chunks to the device. The line
 *	discipline write method will not be invoked in parallel for
 *	each device.
 */
static ssize_t tty_write(struct kiocb *iocb, struct iov_iter *from)
{
	return file_tty_write(iocb->ki_filp, iocb, from);
}

ssize_t redirected_tty_write(struct kiocb *iocb, struct iov_iter *iter)
{
	struct file *p = NULL;

	spin_lock(&redirect_lock);
	if (redirect)
		p = get_file(redirect);
	spin_unlock(&redirect_lock);

	/*
	 * We know the redirected tty is just another tty, we can
	 * call file_tty_write() directly with that file pointer.
	 */
	if (p) {
		ssize_t res;

		res = file_tty_write(p, iocb, iter);
		fput(p);
		return res;
	}
	return tty_write(iocb, iter);
}

/**
 * tty_send_xchar	-	send priority character
 * @tty: the tty to send to
 * @ch: xchar to send
 *
 * Send a high priority character to the tty even if stopped.
 *
 * Locking: none for xchar method, write ordering for write method.
 */
int tty_send_xchar(struct tty_struct *tty, char ch)
{
	bool was_stopped = tty->flow.stopped;

	if (tty->ops->send_xchar) {
		down_read(&tty->termios_rwsem);
		tty->ops->send_xchar(tty, ch);
		up_read(&tty->termios_rwsem);
		return 0;
	}

	if (tty_write_lock(tty, 0) < 0)
		return -ERESTARTSYS;

	down_read(&tty->termios_rwsem);
	if (was_stopped)
		start_tty(tty);
	tty->ops->write(tty, &ch, 1);
	if (was_stopped)
		stop_tty(tty);
	up_read(&tty->termios_rwsem);
	tty_write_unlock(tty);
	return 0;
}

/**
 * pty_line_name	-	generate name for a pty
 * @driver: the tty driver in use
 * @index: the minor number
 * @p: output buffer of at least 6 bytes
 *
 * Generate a name from a @driver reference and write it to the output buffer
 * @p.
 *
 * Locking: None
 */
static void pty_line_name(struct tty_driver *driver, int index, char *p)
{
	static const char ptychar[] = "pqrstuvwxyzabcde";
	int i = index + driver->name_base;
	/* ->name is initialized to "ttyp", but "tty" is expected */
	sprintf(p, "%s%c%x",
		driver->subtype == PTY_TYPE_SLAVE ? "tty" : driver->name,
		ptychar[i >> 4 & 0xf], i & 0xf);
}

/**
 * tty_line_name	-	generate name for a tty
 * @driver: the tty driver in use
 * @index: the minor number
 * @p: output buffer of at least 7 bytes
 *
 * Generate a name from a @driver reference and write it to the output buffer
 * @p.
 *
 * Locking: None
 */
static ssize_t tty_line_name(struct tty_driver *driver, int index, char *p)
{
	if (driver->flags & TTY_DRIVER_UNNUMBERED_NODE)
		return sprintf(p, "%s", driver->name);
	else
		return sprintf(p, "%s%d", driver->name,
			       index + driver->name_base);
}

/**
 * tty_driver_lookup_tty() - find an existing tty, if any
 * @driver: the driver for the tty
 * @file: file object
 * @idx: the minor number
 *
 * Return: the tty, if found. If not found, return %NULL or ERR_PTR() if the
 * driver lookup() method returns an error.
 *
 * Locking: tty_mutex must be held. If the tty is found, bump the tty kref.
 */
static struct tty_struct *tty_driver_lookup_tty(struct tty_driver *driver,
		struct file *file, int idx)
{
	struct tty_struct *tty;

	if (driver->ops->lookup) {
		if (!file)
			tty = ERR_PTR(-EIO);
		else
			tty = driver->ops->lookup(driver, file, idx);
	} else {
		if (idx >= driver->num)
			return ERR_PTR(-EINVAL);
		tty = driver->ttys[idx];
	}
	if (!IS_ERR(tty))
		tty_kref_get(tty);
	return tty;
}

/**
 * tty_init_termios	-  helper for termios setup
 * @tty: the tty to set up
 *
 * Initialise the termios structure for this tty. This runs under the
 * %tty_mutex currently so we can be relaxed about ordering.
 */
void tty_init_termios(struct tty_struct *tty)
{
	struct ktermios *tp;
	int idx = tty->index;

	if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS)
		tty->termios = tty->driver->init_termios;
	else {
		/* Check for lazy saved data */
		tp = tty->driver->termios[idx];
		if (tp != NULL) {
			tty->termios = *tp;
			tty->termios.c_line  = tty->driver->init_termios.c_line;
		} else
			tty->termios = tty->driver->init_termios;
	}
	/* Compatibility until drivers always set this */
	tty->termios.c_ispeed = tty_termios_input_baud_rate(&tty->termios);
	tty->termios.c_ospeed = tty_termios_baud_rate(&tty->termios);
}
EXPORT_SYMBOL_GPL(tty_init_termios);

/**
 * tty_standard_install - usual tty->ops->install
 * @driver: the driver for the tty
 * @tty: the tty
 *
 * If the @driver overrides @tty->ops->install, it still can call this function
 * to perform the standard install operations.
 */
int tty_standard_install(struct tty_driver *driver, struct tty_struct *tty)
{
	tty_init_termios(tty);
	tty_driver_kref_get(driver);
	tty->count++;
	driver->ttys[tty->index] = tty;
	return 0;
}
EXPORT_SYMBOL_GPL(tty_standard_install);

/**
 * tty_driver_install_tty() - install a tty entry in the driver
 * @driver: the driver for the tty
 * @tty: the tty
 *
 * Install a tty object into the driver tables. The @tty->index field will be
 * set by the time this is called. This method is responsible for ensuring any
 * need additional structures are allocated and configured.
 *
 * Locking: tty_mutex for now
 */
static int tty_driver_install_tty(struct tty_driver *driver,
						struct tty_struct *tty)
{
	return driver->ops->install ? driver->ops->install(driver, tty) :
		tty_standard_install(driver, tty);
}

/**
 * tty_driver_remove_tty() - remove a tty from the driver tables
 * @driver: the driver for the tty
 * @tty: tty to remove
 *
 * Remove a tty object from the driver tables. The tty->index field will be set
 * by the time this is called.
 *
 * Locking: tty_mutex for now
 */
static void tty_driver_remove_tty(struct tty_driver *driver, struct tty_struct *tty)
{
	if (driver->ops->remove)
		driver->ops->remove(driver, tty);
	else
		driver->ttys[tty->index] = NULL;
}

/**
 * tty_reopen()	- fast re-open of an open tty
 * @tty: the tty to open
 *
 * Re-opens on master ptys are not allowed and return -%EIO.
 *
 * Locking: Caller must hold tty_lock
 * Return: 0 on success, -errno on error.
 */
static int tty_reopen(struct tty_struct *tty)
{
	struct tty_driver *driver = tty->driver;
	struct tty_ldisc *ld;
	int retval = 0;

	if (driver->type == TTY_DRIVER_TYPE_PTY &&
	    driver->subtype == PTY_TYPE_MASTER)
		return -EIO;

	if (!tty->count)
		return -EAGAIN;

	if (test_bit(TTY_EXCLUSIVE, &tty->flags) && !capable(CAP_SYS_ADMIN))
		return -EBUSY;

	ld = tty_ldisc_ref_wait(tty);
	if (ld) {
		tty_ldisc_deref(ld);
	} else {
		retval = tty_ldisc_lock(tty, 5 * HZ);
		if (retval)
			return retval;

		if (!tty->ldisc)
			retval = tty_ldisc_reinit(tty, tty->termios.c_line);
		tty_ldisc_unlock(tty);
	}

	if (retval == 0)
		tty->count++;

	return retval;
}

/**
 * tty_init_dev		-	initialise a tty device
 * @driver: tty driver we are opening a device on
 * @idx: device index
 *
 * Prepare a tty device. This may not be a "new" clean device but could also be
 * an active device. The pty drivers require special handling because of this.
 *
 * Locking:
 *	The function is called under the tty_mutex, which protects us from the
 *	tty struct or driver itself going away.
 *
 * On exit the tty device has the line discipline attached and a reference
 * count of 1. If a pair was created for pty/tty use and the other was a pty
 * master then it too has a reference count of 1.
 *
 * WSH 06/09/97: Rewritten to remove races and properly clean up after a failed
 * open. The new code protects the open with a mutex, so it's really quite
 * straightforward. The mutex locking can probably be relaxed for the (most
 * common) case of reopening a tty.
 *
 * Return: new tty structure
 */
struct tty_struct *tty_init_dev(struct tty_driver *driver, int idx)
{
	struct tty_struct *tty;
	int retval;

	/*
	 * First time open is complex, especially for PTY devices.
	 * This code guarantees that either everything succeeds and the
	 * TTY is ready for operation, or else the table slots are vacated
	 * and the allocated memory released.  (Except that the termios
	 * may be retained.)
	 */

	if (!try_module_get(driver->owner))
		return ERR_PTR(-ENODEV);

	tty = alloc_tty_struct(driver, idx);
	if (!tty) {
		retval = -ENOMEM;
		goto err_module_put;
	}

	tty_lock(tty);
	retval = tty_driver_install_tty(driver, tty);
	if (retval < 0)
		goto err_free_tty;

	if (!tty->port)
		tty->port = driver->ports[idx];

	if (WARN_RATELIMIT(!tty->port,
			"%s: %s driver does not set tty->port. This would crash the kernel. Fix the driver!\n",
			__func__, tty->driver->name)) {
		retval = -EINVAL;
		goto err_release_lock;
	}

	retval = tty_ldisc_lock(tty, 5 * HZ);
	if (retval)
		goto err_release_lock;
	tty->port->itty = tty;

	/*
	 * Structures all installed ... call the ldisc open routines.
	 * If we fail here just call release_tty to clean up.  No need
	 * to decrement the use counts, as release_tty doesn't care.
	 */
	retval = tty_ldisc_setup(tty, tty->link);
	if (retval)
		goto err_release_tty;
	tty_ldisc_unlock(tty);
	/* Return the tty locked so that it cannot vanish under the caller */
	return tty;

err_free_tty:
	tty_unlock(tty);
	free_tty_struct(tty);
err_module_put:
	module_put(driver->owner);
	return ERR_PTR(retval);

	/* call the tty release_tty routine to clean out this slot */
err_release_tty:
	tty_ldisc_unlock(tty);
	tty_info_ratelimited(tty, "ldisc open failed (%d), clearing slot %d\n",
			     retval, idx);
err_release_lock:
	tty_unlock(tty);
	release_tty(tty, idx);
	return ERR_PTR(retval);
}

/**
 * tty_save_termios() - save tty termios data in driver table
 * @tty: tty whose termios data to save
 *
 * Locking: Caller guarantees serialisation with tty_init_termios().
 */
void tty_save_termios(struct tty_struct *tty)
{
	struct ktermios *tp;
	int idx = tty->index;

	/* If the port is going to reset then it has no termios to save */
	if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS)
		return;

	/* Stash the termios data */
	tp = tty->driver->termios[idx];
	if (tp == NULL) {
		tp = kmalloc(sizeof(*tp), GFP_KERNEL);
		if (tp == NULL)
			return;
		tty->driver->termios[idx] = tp;
	}
	*tp = tty->termios;
}
EXPORT_SYMBOL_GPL(tty_save_termios);

/**
 * tty_flush_works	-	flush all works of a tty/pty pair
 * @tty: tty device to flush works for (or either end of a pty pair)
 *
 * Sync flush all works belonging to @tty (and the 'other' tty).
 */
static void tty_flush_works(struct tty_struct *tty)
{
	flush_work(&tty->SAK_work);
	flush_work(&tty->hangup_work);
	if (tty->link) {
		flush_work(&tty->link->SAK_work);
		flush_work(&tty->link->hangup_work);
	}
}

/**
 * release_one_tty	-	release tty structure memory
 * @work: work of tty we are obliterating
 *
 * Releases memory associated with a tty structure, and clears out the
 * driver table slots. This function is called when a device is no longer
 * in use. It also gets called when setup of a device fails.
 *
 * Locking:
 *	takes the file list lock internally when working on the list of ttys
 *	that the driver keeps.
 *
 * This method gets called from a work queue so that the driver private
 * cleanup ops can sleep (needed for USB at least)
 */
static void release_one_tty(struct work_struct *work)
{
	struct tty_struct *tty =
		container_of(work, struct tty_struct, hangup_work);
	struct tty_driver *driver = tty->driver;
	struct module *owner = driver->owner;

	if (tty->ops->cleanup)
		tty->ops->cleanup(tty);

	tty_driver_kref_put(driver);
	module_put(owner);

	spin_lock(&tty->files_lock);
	list_del_init(&tty->tty_files);
	spin_unlock(&tty->files_lock);

	put_pid(tty->ctrl.pgrp);
	put_pid(tty->ctrl.session);
	free_tty_struct(tty);
}

static void queue_release_one_tty(struct kref *kref)
{
	struct tty_struct *tty = container_of(kref, struct tty_struct, kref);

	/* The hangup queue is now free so we can reuse it rather than
	 *  waste a chunk of memory for each port.
	 */
	INIT_WORK(&tty->hangup_work, release_one_tty);
	schedule_work(&tty->hangup_work);
}

/**
 * tty_kref_put		-	release a tty kref
 * @tty: tty device
 *
 * Release a reference to the @tty device and if need be let the kref layer
 * destruct the object for us.
 */
void tty_kref_put(struct tty_struct *tty)
{
	if (tty)
		kref_put(&tty->kref, queue_release_one_tty);
}
EXPORT_SYMBOL(tty_kref_put);

/**
 * release_tty		-	release tty structure memory
 * @tty: tty device release
 * @idx: index of the tty device release
 *
 * Release both @tty and a possible linked partner (think pty pair),
 * and decrement the refcount of the backing module.
 *
 * Locking:
 *	tty_mutex
 *	takes the file list lock internally when working on the list of ttys
 *	that the driver keeps.
 */
static void release_tty(struct tty_struct *tty, int idx)
{
	/* This should always be true but check for the moment */
	WARN_ON(tty->index != idx);
	WARN_ON(!mutex_is_locked(&tty_mutex));
	if (tty->ops->shutdown)
		tty->ops->shutdown(tty);
	tty_save_termios(tty);
	tty_driver_remove_tty(tty->driver, tty);
	if (tty->port)
		tty->port->itty = NULL;
	if (tty->link)
		tty->link->port->itty = NULL;
	if (tty->port)
		tty_buffer_cancel_work(tty->port);
	if (tty->link)
		tty_buffer_cancel_work(tty->link->port);

	tty_kref_put(tty->link);
	tty_kref_put(tty);
}

/**
 * tty_release_checks - check a tty before real release
 * @tty: tty to check
 * @idx: index of the tty
 *
 * Performs some paranoid checking before true release of the @tty. This is a
 * no-op unless %TTY_PARANOIA_CHECK is defined.
 */
static int tty_release_checks(struct tty_struct *tty, int idx)
{
#ifdef TTY_PARANOIA_CHECK
	if (idx < 0 || idx >= tty->driver->num) {
		tty_debug(tty, "bad idx %d\n", idx);
		return -1;
	}

	/* not much to check for devpts */
	if (tty->driver->flags & TTY_DRIVER_DEVPTS_MEM)
		return 0;

	if (tty != tty->driver->ttys[idx]) {
		tty_debug(tty, "bad driver table[%d] = %p\n",
			  idx, tty->driver->ttys[idx]);
		return -1;
	}
	if (tty->driver->other) {
		struct tty_struct *o_tty = tty->link;

		if (o_tty != tty->driver->other->ttys[idx]) {
			tty_debug(tty, "bad other table[%d] = %p\n",
				  idx, tty->driver->other->ttys[idx]);
			return -1;
		}
		if (o_tty->link != tty) {
			tty_debug(tty, "bad link = %p\n", o_tty->link);
			return -1;
		}
	}
#endif
	return 0;
}

/**
 * tty_kclose      -       closes tty opened by tty_kopen
 * @tty: tty device
 *
 * Performs the final steps to release and free a tty device. It is the same as
 * tty_release_struct() except that it also resets %TTY_PORT_KOPENED flag on
 * @tty->port.
 */
void tty_kclose(struct tty_struct *tty)
{
	/*
	 * Ask the line discipline code to release its structures
	 */
	tty_ldisc_release(tty);

	/* Wait for pending work before tty destruction commences */
	tty_flush_works(tty);

	tty_debug_hangup(tty, "freeing structure\n");
	/*
	 * The release_tty function takes care of the details of clearing
	 * the slots and preserving the termios structure.
	 */
	mutex_lock(&tty_mutex);
	tty_port_set_kopened(tty->port, 0);
	release_tty(tty, tty->index);
	mutex_unlock(&tty_mutex);
}
EXPORT_SYMBOL_GPL(tty_kclose);

/**
 * tty_release_struct	-	release a tty struct
 * @tty: tty device
 * @idx: index of the tty
 *
 * Performs the final steps to release and free a tty device. It is roughly the
 * reverse of tty_init_dev().
 */
void tty_release_struct(struct tty_struct *tty, int idx)
{
	/*
	 * Ask the line discipline code to release its structures
	 */
	tty_ldisc_release(tty);

	/* Wait for pending work before tty destruction commmences */
	tty_flush_works(tty);

	tty_debug_hangup(tty, "freeing structure\n");
	/*
	 * The release_tty function takes care of the details of clearing
	 * the slots and preserving the termios structure.
	 */
	mutex_lock(&tty_mutex);
	release_tty(tty, idx);
	mutex_unlock(&tty_mutex);
}
EXPORT_SYMBOL_GPL(tty_release_struct);

/**
 * tty_release		-	vfs callback for close
 * @inode: inode of tty
 * @filp: file pointer for handle to tty
 *
 * Called the last time each file handle is closed that references this tty.
 * There may however be several such references.
 *
 * Locking:
 *	Takes BKL. See tty_release_dev().
 *
 * Even releasing the tty structures is a tricky business. We have to be very
 * careful that the structures are all released at the same time, as interrupts
 * might otherwise get the wrong pointers.
 *
 * WSH 09/09/97: rewritten to avoid some nasty race conditions that could
 * lead to double frees or releasing memory still in use.
 */
int tty_release(struct inode *inode, struct file *filp)
{
	struct tty_struct *tty = file_tty(filp);
	struct tty_struct *o_tty = NULL;
	int	do_sleep, final;
	int	idx;
	long	timeout = 0;
	int	once = 1;

	if (tty_paranoia_check(tty, inode, __func__))
		return 0;

	tty_lock(tty);
	check_tty_count(tty, __func__);

	__tty_fasync(-1, filp, 0);

	idx = tty->index;
	if (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
	    tty->driver->subtype == PTY_TYPE_MASTER)
		o_tty = tty->link;

	if (tty_release_checks(tty, idx)) {
		tty_unlock(tty);
		return 0;
	}

	tty_debug_hangup(tty, "releasing (count=%d)\n", tty->count);

	if (tty->ops->close)
		tty->ops->close(tty, filp);

	/* If tty is pty master, lock the slave pty (stable lock order) */
	tty_lock_slave(o_tty);

	/*
	 * Sanity check: if tty->count is going to zero, there shouldn't be
	 * any waiters on tty->read_wait or tty->write_wait.  We test the
	 * wait queues and kick everyone out _before_ actually starting to
	 * close.  This ensures that we won't block while releasing the tty
	 * structure.
	 *
	 * The test for the o_tty closing is necessary, since the master and
	 * slave sides may close in any order.  If the slave side closes out
	 * first, its count will be one, since the master side holds an open.
	 * Thus this test wouldn't be triggered at the time the slave closed,
	 * so we do it now.
	 */
	while (1) {
		do_sleep = 0;

		if (tty->count <= 1) {
			if (waitqueue_active(&tty->read_wait)) {
				wake_up_poll(&tty->read_wait, EPOLLIN);
				do_sleep++;
			}
			if (waitqueue_active(&tty->write_wait)) {
				wake_up_poll(&tty->write_wait, EPOLLOUT);
				do_sleep++;
			}
		}
		if (o_tty && o_tty->count <= 1) {
			if (waitqueue_active(&o_tty->read_wait)) {
				wake_up_poll(&o_tty->read_wait, EPOLLIN);
				do_sleep++;
			}
			if (waitqueue_active(&o_tty->write_wait)) {
				wake_up_poll(&o_tty->write_wait, EPOLLOUT);
				do_sleep++;
			}
		}
		if (!do_sleep)
			break;

		if (once) {
			once = 0;
			tty_warn(tty, "read/write wait queue active!\n");
		}
		schedule_timeout_killable(timeout);
		if (timeout < 120 * HZ)
			timeout = 2 * timeout + 1;
		else
			timeout = MAX_SCHEDULE_TIMEOUT;
	}

	if (o_tty) {
		if (--o_tty->count < 0) {
			tty_warn(tty, "bad slave count (%d)\n", o_tty->count);
			o_tty->count = 0;
		}
	}
	if (--tty->count < 0) {
		tty_warn(tty, "bad tty->count (%d)\n", tty->count);
		tty->count = 0;
	}

	/*
	 * We've decremented tty->count, so we need to remove this file
	 * descriptor off the tty->tty_files list; this serves two
	 * purposes:
	 *  - check_tty_count sees the correct number of file descriptors
	 *    associated with this tty.
	 *  - do_tty_hangup no longer sees this file descriptor as
	 *    something that needs to be handled for hangups.
	 */
	tty_del_file(filp);

	/*
	 * Perform some housekeeping before deciding whether to return.
	 *
	 * If _either_ side is closing, make sure there aren't any
	 * processes that still think tty or o_tty is their controlling
	 * tty.
	 */
	if (!tty->count) {
		read_lock(&tasklist_lock);
		session_clear_tty(tty->ctrl.session);
		if (o_tty)
			session_clear_tty(o_tty->ctrl.session);
		read_unlock(&tasklist_lock);
	}

	/* check whether both sides are closing ... */
	final = !tty->count && !(o_tty && o_tty->count);

	tty_unlock_slave(o_tty);
	tty_unlock(tty);

	/* At this point, the tty->count == 0 should ensure a dead tty
	 * cannot be re-opened by a racing opener.
	 */

	if (!final)
		return 0;

	tty_debug_hangup(tty, "final close\n");

	tty_release_struct(tty, idx);
	return 0;
}

/**
 * tty_open_current_tty - get locked tty of current task
 * @device: device number
 * @filp: file pointer to tty
 * @return: locked tty of the current task iff @device is /dev/tty
 *
 * Performs a re-open of the current task's controlling tty.
 *
 * We cannot return driver and index like for the other nodes because devpts
 * will not work then. It expects inodes to be from devpts FS.
 */
static struct tty_struct *tty_open_current_tty(dev_t device, struct file *filp)
{
	struct tty_struct *tty;
	int retval;

	if (device != MKDEV(TTYAUX_MAJOR, 0))
		return NULL;

	tty = get_current_tty();
	if (!tty)
		return ERR_PTR(-ENXIO);

	filp->f_flags |= O_NONBLOCK; /* Don't let /dev/tty block */
	/* noctty = 1; */
	tty_lock(tty);
	tty_kref_put(tty);	/* safe to drop the kref now */

	retval = tty_reopen(tty);
	if (retval < 0) {
		tty_unlock(tty);
		tty = ERR_PTR(retval);
	}
	return tty;
}

/**
 * tty_lookup_driver - lookup a tty driver for a given device file
 * @device: device number
 * @filp: file pointer to tty
 * @index: index for the device in the @return driver
 *
 * If returned value is not erroneous, the caller is responsible to decrement
 * the refcount by tty_driver_kref_put().
 *
 * Locking: %tty_mutex protects get_tty_driver()
 *
 * Return: driver for this inode (with increased refcount)
 */
static struct tty_driver *tty_lookup_driver(dev_t device, struct file *filp,
		int *index)
{
	struct tty_driver *driver = NULL;

	switch (device) {
#ifdef CONFIG_VT
	case MKDEV(TTY_MAJOR, 0): {
		extern struct tty_driver *console_driver;

		driver = tty_driver_kref_get(console_driver);
		*index = fg_console;
		break;
	}
#endif
	case MKDEV(TTYAUX_MAJOR, 1): {
		struct tty_driver *console_driver = console_device(index);

		if (console_driver) {
			driver = tty_driver_kref_get(console_driver);
			if (driver && filp) {
				/* Don't let /dev/console block */
				filp->f_flags |= O_NONBLOCK;
				break;
			}
		}
		if (driver)
			tty_driver_kref_put(driver);
		return ERR_PTR(-ENODEV);
	}
	default:
		driver = get_tty_driver(device, index);
		if (!driver)
			return ERR_PTR(-ENODEV);
		break;
	}
	return driver;
}

static struct tty_struct *tty_kopen(dev_t device, int shared)
{
	struct tty_struct *tty;
	struct tty_driver *driver;
	int index = -1;

	mutex_lock(&tty_mutex);
	driver = tty_lookup_driver(device, NULL, &index);
	if (IS_ERR(driver)) {
		mutex_unlock(&tty_mutex);
		return ERR_CAST(driver);
	}

	/* check whether we're reopening an existing tty */
	tty = tty_driver_lookup_tty(driver, NULL, index);
	if (IS_ERR(tty) || shared)
		goto out;

	if (tty) {
		/* drop kref from tty_driver_lookup_tty() */
		tty_kref_put(tty);
		tty = ERR_PTR(-EBUSY);
	} else { /* tty_init_dev returns tty with the tty_lock held */
		tty = tty_init_dev(driver, index);
		if (IS_ERR(tty))
			goto out;
		tty_port_set_kopened(tty->port, 1);
	}
out:
	mutex_unlock(&tty_mutex);
	tty_driver_kref_put(driver);
	return tty;
}

/**
 * tty_kopen_exclusive	-	open a tty device for kernel
 * @device: dev_t of device to open
 *
 * Opens tty exclusively for kernel. Performs the driver lookup, makes sure
 * it's not already opened and performs the first-time tty initialization.
 *
 * Claims the global %tty_mutex to serialize:
 *  * concurrent first-time tty initialization
 *  * concurrent tty driver removal w/ lookup
 *  * concurrent tty removal from driver table
 *
 * Return: the locked initialized &tty_struct
 */
struct tty_struct *tty_kopen_exclusive(dev_t device)
{
	return tty_kopen(device, 0);
}
EXPORT_SYMBOL_GPL(tty_kopen_exclusive);

/**
 * tty_kopen_shared	-	open a tty device for shared in-kernel use
 * @device: dev_t of device to open
 *
 * Opens an already existing tty for in-kernel use. Compared to
 * tty_kopen_exclusive() above it doesn't ensure to be the only user.
 *
 * Locking: identical to tty_kopen() above.
 */
struct tty_struct *tty_kopen_shared(dev_t device)
{
	return tty_kopen(device, 1);
}
EXPORT_SYMBOL_GPL(tty_kopen_shared);

/**
 * tty_open_by_driver	-	open a tty device
 * @device: dev_t of device to open
 * @filp: file pointer to tty
 *
 * Performs the driver lookup, checks for a reopen, or otherwise performs the
 * first-time tty initialization.
 *
 *
 * Claims the global tty_mutex to serialize:
 *  * concurrent first-time tty initialization
 *  * concurrent tty driver removal w/ lookup
 *  * concurrent tty removal from driver table
 *
 * Return: the locked initialized or re-opened &tty_struct
 */
static struct tty_struct *tty_open_by_driver(dev_t device,
					     struct file *filp)
{
	struct tty_struct *tty;
	struct tty_driver *driver = NULL;
	int index = -1;
	int retval;

	mutex_lock(&tty_mutex);
	driver = tty_lookup_driver(device, filp, &index);
	if (IS_ERR(driver)) {
		mutex_unlock(&tty_mutex);
		return ERR_CAST(driver);
	}

	/* check whether we're reopening an existing tty */
	tty = tty_driver_lookup_tty(driver, filp, index);
	if (IS_ERR(tty)) {
		mutex_unlock(&tty_mutex);
		goto out;
	}

	if (tty) {
		if (tty_port_kopened(tty->port)) {
			tty_kref_put(tty);
			mutex_unlock(&tty_mutex);
			tty = ERR_PTR(-EBUSY);
			goto out;
		}
		mutex_unlock(&tty_mutex);
		retval = tty_lock_interruptible(tty);
		tty_kref_put(tty);  /* drop kref from tty_driver_lookup_tty() */
		if (retval) {
			if (retval == -EINTR)
				retval = -ERESTARTSYS;
			tty = ERR_PTR(retval);
			goto out;
		}
		retval = tty_reopen(tty);
		if (retval < 0) {
			tty_unlock(tty);
			tty = ERR_PTR(retval);
		}
	} else { /* Returns with the tty_lock held for now */
		tty = tty_init_dev(driver, index);
		mutex_unlock(&tty_mutex);
	}
out:
	tty_driver_kref_put(driver);
	return tty;
}

/**
 * tty_open	-	open a tty device
 * @inode: inode of device file
 * @filp: file pointer to tty
 *
 * tty_open() and tty_release() keep up the tty count that contains the number
 * of opens done on a tty. We cannot use the inode-count, as different inodes
 * might point to the same tty.
 *
 * Open-counting is needed for pty masters, as well as for keeping track of
 * serial lines: DTR is dropped when the last close happens.
 * (This is not done solely through tty->count, now.  - Ted 1/27/92)
 *
 * The termios state of a pty is reset on the first open so that settings don't
 * persist across reuse.
 *
 * Locking:
 *  * %tty_mutex protects tty, tty_lookup_driver() and tty_init_dev().
 *  * @tty->count should protect the rest.
 *  * ->siglock protects ->signal/->sighand
 *
 * Note: the tty_unlock/lock cases without a ref are only safe due to %tty_mutex
 */
static int tty_open(struct inode *inode, struct file *filp)
{
	struct tty_struct *tty;
	int noctty, retval;
	dev_t device = inode->i_rdev;
	unsigned saved_flags = filp->f_flags;

	nonseekable_open(inode, filp);

retry_open:
	retval = tty_alloc_file(filp);
	if (retval)
		return -ENOMEM;

	tty = tty_open_current_tty(device, filp);
	if (!tty)
		tty = tty_open_by_driver(device, filp);

	if (IS_ERR(tty)) {
		tty_free_file(filp);
		retval = PTR_ERR(tty);
		if (retval != -EAGAIN || signal_pending(current))
			return retval;
		schedule();
		goto retry_open;
	}

	tty_add_file(tty, filp);

	check_tty_count(tty, __func__);
	tty_debug_hangup(tty, "opening (count=%d)\n", tty->count);

	if (tty->ops->open)
		retval = tty->ops->open(tty, filp);
	else
		retval = -ENODEV;
	filp->f_flags = saved_flags;

	if (retval) {
		tty_debug_hangup(tty, "open error %d, releasing\n", retval);

		tty_unlock(tty); /* need to call tty_release without BTM */
		tty_release(inode, filp);
		if (retval != -ERESTARTSYS)
			return retval;

		if (signal_pending(current))
			return retval;

		schedule();
		/*
		 * Need to reset f_op in case a hangup happened.
		 */
		if (tty_hung_up_p(filp))
			filp->f_op = &tty_fops;
		goto retry_open;
	}
	clear_bit(TTY_HUPPED, &tty->flags);

	noctty = (filp->f_flags & O_NOCTTY) ||
		 (IS_ENABLED(CONFIG_VT) && device == MKDEV(TTY_MAJOR, 0)) ||
		 device == MKDEV(TTYAUX_MAJOR, 1) ||
		 (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
		  tty->driver->subtype == PTY_TYPE_MASTER);
	if (!noctty)
		tty_open_proc_set_tty(filp, tty);
	tty_unlock(tty);
	return 0;
}


/**
 * tty_poll	-	check tty status
 * @filp: file being polled
 * @wait: poll wait structures to update
 *
 * Call the line discipline polling method to obtain the poll status of the
 * device.
 *
 * Locking: locks called line discipline but ldisc poll method may be
 * re-entered freely by other callers.
 */
static __poll_t tty_poll(struct file *filp, poll_table *wait)
{
	struct tty_struct *tty = file_tty(filp);
	struct tty_ldisc *ld;
	__poll_t ret = 0;

	if (tty_paranoia_check(tty, file_inode(filp), "tty_poll"))
		return 0;

	ld = tty_ldisc_ref_wait(tty);
	if (!ld)
		return hung_up_tty_poll(filp, wait);
	if (ld->ops->poll)
		ret = ld->ops->poll(tty, filp, wait);
	tty_ldisc_deref(ld);
	return ret;
}

static int __tty_fasync(int fd, struct file *filp, int on)
{
	struct tty_struct *tty = file_tty(filp);
	unsigned long flags;
	int retval = 0;

	if (tty_paranoia_check(tty, file_inode(filp), "tty_fasync"))
		goto out;

	retval = fasync_helper(fd, filp, on, &tty->fasync);
	if (retval <= 0)
		goto out;

	if (on) {
		enum pid_type type;
		struct pid *pid;

		spin_lock_irqsave(&tty->ctrl.lock, flags);
		if (tty->ctrl.pgrp) {
			pid = tty->ctrl.pgrp;
			type = PIDTYPE_PGID;
		} else {
			pid = task_pid(current);
			type = PIDTYPE_TGID;
		}
		get_pid(pid);
		spin_unlock_irqrestore(&tty->ctrl.lock, flags);
		__f_setown(filp, pid, type, 0);
		put_pid(pid);
		retval = 0;
	}
out:
	return retval;
}

static int tty_fasync(int fd, struct file *filp, int on)
{
	struct tty_struct *tty = file_tty(filp);
	int retval = -ENOTTY;

	tty_lock(tty);
	if (!tty_hung_up_p(filp))
		retval = __tty_fasync(fd, filp, on);
	tty_unlock(tty);

	return retval;
}

static bool tty_legacy_tiocsti __read_mostly = IS_ENABLED(CONFIG_LEGACY_TIOCSTI);
/**
 * tiocsti		-	fake input character
 * @tty: tty to fake input into
 * @p: pointer to character
 *
 * Fake input to a tty device. Does the necessary locking and input management.
 *
 * FIXME: does not honour flow control ??
 *
 * Locking:
 *  * Called functions take tty_ldiscs_lock
 *  * current->signal->tty check is safe without locks
 */
static int tiocsti(struct tty_struct *tty, char __user *p)
{
	char ch, mbz = 0;
	struct tty_ldisc *ld;

	if (!tty_legacy_tiocsti && !capable(CAP_SYS_ADMIN))
		return -EIO;

	if ((current->signal->tty != tty) && !capable(CAP_SYS_ADMIN))
		return -EPERM;
	if (get_user(ch, p))
		return -EFAULT;
	tty_audit_tiocsti(tty, ch);
	ld = tty_ldisc_ref_wait(tty);
	if (!ld)
		return -EIO;
	tty_buffer_lock_exclusive(tty->port);
	if (ld->ops->receive_buf)
		ld->ops->receive_buf(tty, &ch, &mbz, 1);
	tty_buffer_unlock_exclusive(tty->port);
	tty_ldisc_deref(ld);
	return 0;
}

/**
 * tiocgwinsz		-	implement window query ioctl
 * @tty: tty
 * @arg: user buffer for result
 *
 * Copies the kernel idea of the window size into the user buffer.
 *
 * Locking: @tty->winsize_mutex is taken to ensure the winsize data is
 * consistent.
 */
static int tiocgwinsz(struct tty_struct *tty, struct winsize __user *arg)
{
	int err;

	mutex_lock(&tty->winsize_mutex);
	err = copy_to_user(arg, &tty->winsize, sizeof(*arg));
	mutex_unlock(&tty->winsize_mutex);

	return err ? -EFAULT : 0;
}

/**
 * tty_do_resize	-	resize event
 * @tty: tty being resized
 * @ws: new dimensions
 *
 * Update the termios variables and send the necessary signals to peform a
 * terminal resize correctly.
 */
int tty_do_resize(struct tty_struct *tty, struct winsize *ws)
{
	struct pid *pgrp;

	/* Lock the tty */
	mutex_lock(&tty->winsize_mutex);
	if (!memcmp(ws, &tty->winsize, sizeof(*ws)))
		goto done;

	/* Signal the foreground process group */
	pgrp = tty_get_pgrp(tty);
	if (pgrp)
		kill_pgrp(pgrp, SIGWINCH, 1);
	put_pid(pgrp);

	tty->winsize = *ws;
done:
	mutex_unlock(&tty->winsize_mutex);
	return 0;
}
EXPORT_SYMBOL(tty_do_resize);

/**
 * tiocswinsz		-	implement window size set ioctl
 * @tty: tty side of tty
 * @arg: user buffer for result
 *
 * Copies the user idea of the window size to the kernel. Traditionally this is
 * just advisory information but for the Linux console it actually has driver
 * level meaning and triggers a VC resize.
 *
 * Locking:
 *	Driver dependent. The default do_resize method takes the tty termios
 *	mutex and ctrl.lock. The console takes its own lock then calls into the
 *	default method.
 */
static int tiocswinsz(struct tty_struct *tty, struct winsize __user *arg)
{
	struct winsize tmp_ws;

	if (copy_from_user(&tmp_ws, arg, sizeof(*arg)))
		return -EFAULT;

	if (tty->ops->resize)
		return tty->ops->resize(tty, &tmp_ws);
	else
		return tty_do_resize(tty, &tmp_ws);
}

/**
 * tioccons	-	allow admin to move logical console
 * @file: the file to become console
 *
 * Allow the administrator to move the redirected console device.
 *
 * Locking: uses redirect_lock to guard the redirect information
 */
static int tioccons(struct file *file)
{
	if (!capable(CAP_SYS_ADMIN))
		return -EPERM;
	if (file->f_op->write_iter == redirected_tty_write) {
		struct file *f;

		spin_lock(&redirect_lock);
		f = redirect;
		redirect = NULL;
		spin_unlock(&redirect_lock);
		if (f)
			fput(f);
		return 0;
	}
	if (file->f_op->write_iter != tty_write)
		return -ENOTTY;
	if (!(file->f_mode & FMODE_WRITE))
		return -EBADF;
	if (!(file->f_mode & FMODE_CAN_WRITE))
		return -EINVAL;
	spin_lock(&redirect_lock);
	if (redirect) {
		spin_unlock(&redirect_lock);
		return -EBUSY;
	}
	redirect = get_file(file);
	spin_unlock(&redirect_lock);
	return 0;
}

/**
 * tiocsetd	-	set line discipline
 * @tty: tty device
 * @p: pointer to user data
 *
 * Set the line discipline according to user request.
 *
 * Locking: see tty_set_ldisc(), this function is just a helper
 */
static int tiocsetd(struct tty_struct *tty, int __user *p)
{
	int disc;
	int ret;

	if (get_user(disc, p))
		return -EFAULT;

	ret = tty_set_ldisc(tty, disc);

	return ret;
}

/**
 * tiocgetd	-	get line discipline
 * @tty: tty device
 * @p: pointer to user data
 *
 * Retrieves the line discipline id directly from the ldisc.
 *
 * Locking: waits for ldisc reference (in case the line discipline is changing
 * or the @tty is being hungup)
 */
static int tiocgetd(struct tty_struct *tty, int __user *p)
{
	struct tty_ldisc *ld;
	int ret;

	ld = tty_ldisc_ref_wait(tty);
	if (!ld)
		return -EIO;
	ret = put_user(ld->ops->num, p);
	tty_ldisc_deref(ld);
	return ret;
}

/**
 * send_break	-	performed time break
 * @tty: device to break on
 * @duration: timeout in mS
 *
 * Perform a timed break on hardware that lacks its own driver level timed
 * break functionality.
 *
 * Locking:
 *	@tty->atomic_write_lock serializes
 */
static int send_break(struct tty_struct *tty, unsigned int duration)
{
	int retval;

	if (tty->ops->break_ctl == NULL)
		return 0;

	if (tty->driver->flags & TTY_DRIVER_HARDWARE_BREAK)
		retval = tty->ops->break_ctl(tty, duration);
	else {
		/* Do the work ourselves */
		if (tty_write_lock(tty, 0) < 0)
			return -EINTR;
		retval = tty->ops->break_ctl(tty, -1);
		if (retval)
			goto out;
		if (!signal_pending(current))
			msleep_interruptible(duration);
		retval = tty->ops->break_ctl(tty, 0);
out:
		tty_write_unlock(tty);
		if (signal_pending(current))
			retval = -EINTR;
	}
	return retval;
}

/**
 * tty_tiocmget		-	get modem status
 * @tty: tty device
 * @p: pointer to result
 *
 * Obtain the modem status bits from the tty driver if the feature is
 * supported. Return -%ENOTTY if it is not available.
 *
 * Locking: none (up to the driver)
 */
static int tty_tiocmget(struct tty_struct *tty, int __user *p)
{
	int retval = -ENOTTY;

	if (tty->ops->tiocmget) {
		retval = tty->ops->tiocmget(tty);

		if (retval >= 0)
			retval = put_user(retval, p);
	}
	return retval;
}

/**
 * tty_tiocmset		-	set modem status
 * @tty: tty device
 * @cmd: command - clear bits, set bits or set all
 * @p: pointer to desired bits
 *
 * Set the modem status bits from the tty driver if the feature
 * is supported. Return -%ENOTTY if it is not available.
 *
 * Locking: none (up to the driver)
 */
static int tty_tiocmset(struct tty_struct *tty, unsigned int cmd,
	     unsigned __user *p)
{
	int retval;
	unsigned int set, clear, val;

	if (tty->ops->tiocmset == NULL)
		return -ENOTTY;

	retval = get_user(val, p);
	if (retval)
		return retval;
	set = clear = 0;
	switch (cmd) {
	case TIOCMBIS:
		set = val;
		break;
	case TIOCMBIC:
		clear = val;
		break;
	case TIOCMSET:
		set = val;
		clear = ~val;
		break;
	}
	set &= TIOCM_DTR|TIOCM_RTS|TIOCM_OUT1|TIOCM_OUT2|TIOCM_LOOP;
	clear &= TIOCM_DTR|TIOCM_RTS|TIOCM_OUT1|TIOCM_OUT2|TIOCM_LOOP;
	return tty->ops->tiocmset(tty, set, clear);
}

/**
 * tty_get_icount	-	get tty statistics
 * @tty: tty device
 * @icount: output parameter
 *
 * Gets a copy of the @tty's icount statistics.
 *
 * Locking: none (up to the driver)
 */
int tty_get_icount(struct tty_struct *tty,
		   struct serial_icounter_struct *icount)
{
	memset(icount, 0, sizeof(*icount));

	if (tty->ops->get_icount)
		return tty->ops->get_icount(tty, icount);
	else
		return -ENOTTY;
}
EXPORT_SYMBOL_GPL(tty_get_icount);

static int tty_tiocgicount(struct tty_struct *tty, void __user *arg)
{
	struct serial_icounter_struct icount;
	int retval;

	retval = tty_get_icount(tty, &icount);
	if (retval != 0)
		return retval;

	if (copy_to_user(arg, &icount, sizeof(icount)))
		return -EFAULT;
	return 0;
}

static int tty_set_serial(struct tty_struct *tty, struct serial_struct *ss)
{
	char comm[TASK_COMM_LEN];
	int flags;

	flags = ss->flags & ASYNC_DEPRECATED;

	if (flags)
		pr_warn_ratelimited("%s: '%s' is using deprecated serial flags (with no effect): %.8x\n",
				__func__, get_task_comm(comm, current), flags);

	if (!tty->ops->set_serial)
		return -ENOTTY;

	return tty->ops->set_serial(tty, ss);
}

static int tty_tiocsserial(struct tty_struct *tty, struct serial_struct __user *ss)
{
	struct serial_struct v;

	if (copy_from_user(&v, ss, sizeof(*ss)))
		return -EFAULT;

	return tty_set_serial(tty, &v);
}

static int tty_tiocgserial(struct tty_struct *tty, struct serial_struct __user *ss)
{
	struct serial_struct v;
	int err;

	memset(&v, 0, sizeof(v));
	if (!tty->ops->get_serial)
		return -ENOTTY;
	err = tty->ops->get_serial(tty, &v);
	if (!err && copy_to_user(ss, &v, sizeof(v)))
		err = -EFAULT;
	return err;
}

/*
 * if pty, return the slave side (real_tty)
 * otherwise, return self
 */
static struct tty_struct *tty_pair_get_tty(struct tty_struct *tty)
{
	if (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
	    tty->driver->subtype == PTY_TYPE_MASTER)
		tty = tty->link;
	return tty;
}

/*
 * Split this up, as gcc can choke on it otherwise..
 */
long tty_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
	struct tty_struct *tty = file_tty(file);
	struct tty_struct *real_tty;
	void __user *p = (void __user *)arg;
	int retval;
	struct tty_ldisc *ld;

	if (tty_paranoia_check(tty, file_inode(file), "tty_ioctl"))
		return -EINVAL;

	real_tty = tty_pair_get_tty(tty);

	/*
	 * Factor out some common prep work
	 */
	switch (cmd) {
	case TIOCSETD:
	case TIOCSBRK:
	case TIOCCBRK:
	case TCSBRK:
	case TCSBRKP:
		retval = tty_check_change(tty);
		if (retval)
			return retval;
		if (cmd != TIOCCBRK) {
			tty_wait_until_sent(tty, 0);
			if (signal_pending(current))
				return -EINTR;
		}
		break;
	}

	/*
	 *	Now do the stuff.
	 */
	switch (cmd) {
	case TIOCSTI:
		return tiocsti(tty, p);
	case TIOCGWINSZ:
		return tiocgwinsz(real_tty, p);
	case TIOCSWINSZ:
		return tiocswinsz(real_tty, p);
	case TIOCCONS:
		return real_tty != tty ? -EINVAL : tioccons(file);
	case TIOCEXCL:
		set_bit(TTY_EXCLUSIVE, &tty->flags);
		return 0;
	case TIOCNXCL:
		clear_bit(TTY_EXCLUSIVE, &tty->flags);
		return 0;
	case TIOCGEXCL:
	{
		int excl = test_bit(TTY_EXCLUSIVE, &tty->flags);

		return put_user(excl, (int __user *)p);
	}
	case TIOCGETD:
		return tiocgetd(tty, p);
	case TIOCSETD:
		return tiocsetd(tty, p);
	case TIOCVHANGUP:
		if (!capable(CAP_SYS_ADMIN))
			return -EPERM;
		tty_vhangup(tty);
		return 0;
	case TIOCGDEV:
	{
		unsigned int ret = new_encode_dev(tty_devnum(real_tty));

		return put_user(ret, (unsigned int __user *)p);
	}
	/*
	 * Break handling
	 */
	case TIOCSBRK:	/* Turn break on, unconditionally */
		if (tty->ops->break_ctl)
			return tty->ops->break_ctl(tty, -1);
		return 0;
	case TIOCCBRK:	/* Turn break off, unconditionally */
		if (tty->ops->break_ctl)
			return tty->ops->break_ctl(tty, 0);
		return 0;
	case TCSBRK:   /* SVID version: non-zero arg --> no break */
		/* non-zero arg means wait for all output data
		 * to be sent (performed above) but don't send break.
		 * This is used by the tcdrain() termios function.
		 */
		if (!arg)
			return send_break(tty, 250);
		return 0;
	case TCSBRKP:	/* support for POSIX tcsendbreak() */
		return send_break(tty, arg ? arg*100 : 250);

	case TIOCMGET:
		return tty_tiocmget(tty, p);
	case TIOCMSET:
	case TIOCMBIC:
	case TIOCMBIS:
		return tty_tiocmset(tty, cmd, p);
	case TIOCGICOUNT:
		return tty_tiocgicount(tty, p);
	case TCFLSH:
		switch (arg) {
		case TCIFLUSH:
		case TCIOFLUSH:
		/* flush tty buffer and allow ldisc to process ioctl */
			tty_buffer_flush(tty, NULL);
			break;
		}
		break;
	case TIOCSSERIAL:
		return tty_tiocsserial(tty, p);
	case TIOCGSERIAL:
		return tty_tiocgserial(tty, p);
	case TIOCGPTPEER:
		/* Special because the struct file is needed */
		return ptm_open_peer(file, tty, (int)arg);
	default:
		retval = tty_jobctrl_ioctl(tty, real_tty, file, cmd, arg);
		if (retval != -ENOIOCTLCMD)
			return retval;
	}
	if (tty->ops->ioctl) {
		retval = tty->ops->ioctl(tty, cmd, arg);
		if (retval != -ENOIOCTLCMD)
			return retval;
	}
	ld = tty_ldisc_ref_wait(tty);
	if (!ld)
		return hung_up_tty_ioctl(file, cmd, arg);
	retval = -EINVAL;
	if (ld->ops->ioctl) {
		retval = ld->ops->ioctl(tty, cmd, arg);
		if (retval == -ENOIOCTLCMD)
			retval = -ENOTTY;
	}
	tty_ldisc_deref(ld);
	return retval;
}

#ifdef CONFIG_COMPAT

struct serial_struct32 {
	compat_int_t    type;
	compat_int_t    line;
	compat_uint_t   port;
	compat_int_t    irq;
	compat_int_t    flags;
	compat_int_t    xmit_fifo_size;
	compat_int_t    custom_divisor;
	compat_int_t    baud_base;
	unsigned short  close_delay;
	char    io_type;
	char    reserved_char;
	compat_int_t    hub6;
	unsigned short  closing_wait; /* time to wait before closing */
	unsigned short  closing_wait2; /* no longer used... */
	compat_uint_t   iomem_base;
	unsigned short  iomem_reg_shift;
	unsigned int    port_high;
	/* compat_ulong_t  iomap_base FIXME */
	compat_int_t    reserved;
};

static int compat_tty_tiocsserial(struct tty_struct *tty,
		struct serial_struct32 __user *ss)
{
	struct serial_struct32 v32;
	struct serial_struct v;

	if (copy_from_user(&v32, ss, sizeof(*ss)))
		return -EFAULT;

	memcpy(&v, &v32, offsetof(struct serial_struct32, iomem_base));
	v.iomem_base = compat_ptr(v32.iomem_base);
	v.iomem_reg_shift = v32.iomem_reg_shift;
	v.port_high = v32.port_high;
	v.iomap_base = 0;

	return tty_set_serial(tty, &v);
}

static int compat_tty_tiocgserial(struct tty_struct *tty,
			struct serial_struct32 __user *ss)
{
	struct serial_struct32 v32;
	struct serial_struct v;
	int err;

	memset(&v, 0, sizeof(v));
	memset(&v32, 0, sizeof(v32));

	if (!tty->ops->get_serial)
		return -ENOTTY;
	err = tty->ops->get_serial(tty, &v);
	if (!err) {
		memcpy(&v32, &v, offsetof(struct serial_struct32, iomem_base));
		v32.iomem_base = (unsigned long)v.iomem_base >> 32 ?
			0xfffffff : ptr_to_compat(v.iomem_base);
		v32.iomem_reg_shift = v.iomem_reg_shift;
		v32.port_high = v.port_high;
		if (copy_to_user(ss, &v32, sizeof(v32)))
			err = -EFAULT;
	}
	return err;
}
static long tty_compat_ioctl(struct file *file, unsigned int cmd,
				unsigned long arg)
{
	struct tty_struct *tty = file_tty(file);
	struct tty_ldisc *ld;
	int retval = -ENOIOCTLCMD;

	switch (cmd) {
	case TIOCOUTQ:
	case TIOCSTI:
	case TIOCGWINSZ:
	case TIOCSWINSZ:
	case TIOCGEXCL:
	case TIOCGETD:
	case TIOCSETD:
	case TIOCGDEV:
	case TIOCMGET:
	case TIOCMSET:
	case TIOCMBIC:
	case TIOCMBIS:
	case TIOCGICOUNT:
	case TIOCGPGRP:
	case TIOCSPGRP:
	case TIOCGSID:
	case TIOCSERGETLSR:
	case TIOCGRS485:
	case TIOCSRS485:
#ifdef TIOCGETP
	case TIOCGETP:
	case TIOCSETP:
	case TIOCSETN:
#endif
#ifdef TIOCGETC
	case TIOCGETC:
	case TIOCSETC:
#endif
#ifdef TIOCGLTC
	case TIOCGLTC:
	case TIOCSLTC:
#endif
	case TCSETSF:
	case TCSETSW:
	case TCSETS:
	case TCGETS:
#ifdef TCGETS2
	case TCGETS2:
	case TCSETSF2:
	case TCSETSW2:
	case TCSETS2:
#endif
	case TCGETA:
	case TCSETAF:
	case TCSETAW:
	case TCSETA:
	case TIOCGLCKTRMIOS:
	case TIOCSLCKTRMIOS:
#ifdef TCGETX
	case TCGETX:
	case TCSETX:
	case TCSETXW:
	case TCSETXF:
#endif
	case TIOCGSOFTCAR:
	case TIOCSSOFTCAR:

	case PPPIOCGCHAN:
	case PPPIOCGUNIT:
		return tty_ioctl(file, cmd, (unsigned long)compat_ptr(arg));
	case TIOCCONS:
	case TIOCEXCL:
	case TIOCNXCL:
	case TIOCVHANGUP:
	case TIOCSBRK:
	case TIOCCBRK:
	case TCSBRK:
	case TCSBRKP:
	case TCFLSH:
	case TIOCGPTPEER:
	case TIOCNOTTY:
	case TIOCSCTTY:
	case TCXONC:
	case TIOCMIWAIT:
	case TIOCSERCONFIG:
		return tty_ioctl(file, cmd, arg);
	}

	if (tty_paranoia_check(tty, file_inode(file), "tty_ioctl"))
		return -EINVAL;

	switch (cmd) {
	case TIOCSSERIAL:
		return compat_tty_tiocsserial(tty, compat_ptr(arg));
	case TIOCGSERIAL:
		return compat_tty_tiocgserial(tty, compat_ptr(arg));
	}
	if (tty->ops->compat_ioctl) {
		retval = tty->ops->compat_ioctl(tty, cmd, arg);
		if (retval != -ENOIOCTLCMD)
			return retval;
	}

	ld = tty_ldisc_ref_wait(tty);
	if (!ld)
		return hung_up_tty_compat_ioctl(file, cmd, arg);
	if (ld->ops->compat_ioctl)
		retval = ld->ops->compat_ioctl(tty, cmd, arg);
	if (retval == -ENOIOCTLCMD && ld->ops->ioctl)
		retval = ld->ops->ioctl(tty, (unsigned long)compat_ptr(cmd),
				arg);
	tty_ldisc_deref(ld);

	return retval;
}
#endif

static int this_tty(const void *t, struct file *file, unsigned fd)
{
	if (likely(file->f_op->read_iter != tty_read))
		return 0;
	return file_tty(file) != t ? 0 : fd + 1;
}

/*
 * This implements the "Secure Attention Key" ---  the idea is to
 * prevent trojan horses by killing all processes associated with this
 * tty when the user hits the "Secure Attention Key".  Required for
 * super-paranoid applications --- see the Orange Book for more details.
 *
 * This code could be nicer; ideally it should send a HUP, wait a few
 * seconds, then send a INT, and then a KILL signal.  But you then
 * have to coordinate with the init process, since all processes associated
 * with the current tty must be dead before the new getty is allowed
 * to spawn.
 *
 * Now, if it would be correct ;-/ The current code has a nasty hole -
 * it doesn't catch files in flight. We may send the descriptor to ourselves
 * via AF_UNIX socket, close it and later fetch from socket. FIXME.
 *
 * Nasty bug: do_SAK is being called in interrupt context.  This can
 * deadlock.  We punt it up to process context.  AKPM - 16Mar2001
 */
void __do_SAK(struct tty_struct *tty)
{
	struct task_struct *g, *p;
	struct pid *session;
	int i;
	unsigned long flags;

	spin_lock_irqsave(&tty->ctrl.lock, flags);
	session = get_pid(tty->ctrl.session);
	spin_unlock_irqrestore(&tty->ctrl.lock, flags);

	tty_ldisc_flush(tty);

	tty_driver_flush_buffer(tty);

	read_lock(&tasklist_lock);
	/* Kill the entire session */
	do_each_pid_task(session, PIDTYPE_SID, p) {
		tty_notice(tty, "SAK: killed process %d (%s): by session\n",
			   task_pid_nr(p), p->comm);
		group_send_sig_info(SIGKILL, SEND_SIG_PRIV, p, PIDTYPE_SID);
	} while_each_pid_task(session, PIDTYPE_SID, p);

	/* Now kill any processes that happen to have the tty open */
	for_each_process_thread(g, p) {
		if (p->signal->tty == tty) {
			tty_notice(tty, "SAK: killed process %d (%s): by controlling tty\n",
				   task_pid_nr(p), p->comm);
			group_send_sig_info(SIGKILL, SEND_SIG_PRIV, p,
					PIDTYPE_SID);
			continue;
		}
		task_lock(p);
		i = iterate_fd(p->files, 0, this_tty, tty);
		if (i != 0) {
			tty_notice(tty, "SAK: killed process %d (%s): by fd#%d\n",
				   task_pid_nr(p), p->comm, i - 1);
			group_send_sig_info(SIGKILL, SEND_SIG_PRIV, p,
					PIDTYPE_SID);
		}
		task_unlock(p);
	}
	read_unlock(&tasklist_lock);
	put_pid(session);
}

static void do_SAK_work(struct work_struct *work)
{
	struct tty_struct *tty =
		container_of(work, struct tty_struct, SAK_work);
	__do_SAK(tty);
}

/*
 * The tq handling here is a little racy - tty->SAK_work may already be queued.
 * Fortunately we don't need to worry, because if ->SAK_work is already queued,
 * the values which we write to it will be identical to the values which it
 * already has. --akpm
 */
void do_SAK(struct tty_struct *tty)
{
	if (!tty)
		return;
	schedule_work(&tty->SAK_work);
}
EXPORT_SYMBOL(do_SAK);

/* Must put_device() after it's unused! */
static struct device *tty_get_device(struct tty_struct *tty)
{
	dev_t devt = tty_devnum(tty);

	return class_find_device_by_devt(&tty_class, devt);
}


/**
 * alloc_tty_struct - allocate a new tty
 * @driver: driver which will handle the returned tty
 * @idx: minor of the tty
 *
 * This subroutine allocates and initializes a tty structure.
 *
 * Locking: none - @tty in question is not exposed at this point
 */
struct tty_struct *alloc_tty_struct(struct tty_driver *driver, int idx)
{
	struct tty_struct *tty;

	tty = kzalloc(sizeof(*tty), GFP_KERNEL_ACCOUNT);
	if (!tty)
		return NULL;

	kref_init(&tty->kref);
	if (tty_ldisc_init(tty)) {
		kfree(tty);
		return NULL;
	}
	tty->ctrl.session = NULL;
	tty->ctrl.pgrp = NULL;
	mutex_init(&tty->legacy_mutex);
	mutex_init(&tty->throttle_mutex);
	init_rwsem(&tty->termios_rwsem);
	mutex_init(&tty->winsize_mutex);
	init_ldsem(&tty->ldisc_sem);
	init_waitqueue_head(&tty->write_wait);
	init_waitqueue_head(&tty->read_wait);
	INIT_WORK(&tty->hangup_work, do_tty_hangup);
	mutex_init(&tty->atomic_write_lock);
	spin_lock_init(&tty->ctrl.lock);
	spin_lock_init(&tty->flow.lock);
	spin_lock_init(&tty->files_lock);
	INIT_LIST_HEAD(&tty->tty_files);
	INIT_WORK(&tty->SAK_work, do_SAK_work);

	tty->driver = driver;
	tty->ops = driver->ops;
	tty->index = idx;
	tty_line_name(driver, idx, tty->name);
	tty->dev = tty_get_device(tty);

	return tty;
}

/**
 * tty_put_char	- write one character to a tty
 * @tty: tty
 * @ch: character to write
 *
 * Write one byte to the @tty using the provided @tty->ops->put_char() method
 * if present.
 *
 * Note: the specific put_char operation in the driver layer may go
 * away soon. Don't call it directly, use this method
 *
 * Return: the number of characters successfully output.
 */
int tty_put_char(struct tty_struct *tty, unsigned char ch)
{
	if (tty->ops->put_char)
		return tty->ops->put_char(tty, ch);
	return tty->ops->write(tty, &ch, 1);
}
EXPORT_SYMBOL_GPL(tty_put_char);

static int tty_cdev_add(struct tty_driver *driver, dev_t dev,
		unsigned int index, unsigned int count)
{
	int err;

	/* init here, since reused cdevs cause crashes */
	driver->cdevs[index] = cdev_alloc();
	if (!driver->cdevs[index])
		return -ENOMEM;
	driver->cdevs[index]->ops = &tty_fops;
	driver->cdevs[index]->owner = driver->owner;
	err = cdev_add(driver->cdevs[index], dev, count);
	if (err)
		kobject_put(&driver->cdevs[index]->kobj);
	return err;
}

/**
 * tty_register_device - register a tty device
 * @driver: the tty driver that describes the tty device
 * @index: the index in the tty driver for this tty device
 * @device: a struct device that is associated with this tty device.
 *	This field is optional, if there is no known struct device
 *	for this tty device it can be set to NULL safely.
 *
 * This call is required to be made to register an individual tty device
 * if the tty driver's flags have the %TTY_DRIVER_DYNAMIC_DEV bit set.  If
 * that bit is not set, this function should not be called by a tty
 * driver.
 *
 * Locking: ??
 *
 * Return: A pointer to the struct device for this tty device (or
 * ERR_PTR(-EFOO) on error).
 */
struct device *tty_register_device(struct tty_driver *driver, unsigned index,
				   struct device *device)
{
	return tty_register_device_attr(driver, index, device, NULL, NULL);
}
EXPORT_SYMBOL(tty_register_device);

static void tty_device_create_release(struct device *dev)
{
	dev_dbg(dev, "releasing...\n");
	kfree(dev);
}

/**
 * tty_register_device_attr - register a tty device
 * @driver: the tty driver that describes the tty device
 * @index: the index in the tty driver for this tty device
 * @device: a struct device that is associated with this tty device.
 *	This field is optional, if there is no known struct device
 *	for this tty device it can be set to %NULL safely.
 * @drvdata: Driver data to be set to device.
 * @attr_grp: Attribute group to be set on device.
 *
 * This call is required to be made to register an individual tty device if the
 * tty driver's flags have the %TTY_DRIVER_DYNAMIC_DEV bit set. If that bit is
 * not set, this function should not be called by a tty driver.
 *
 * Locking: ??
 *
 * Return: A pointer to the struct device for this tty device (or
 * ERR_PTR(-EFOO) on error).
 */
struct device *tty_register_device_attr(struct tty_driver *driver,
				   unsigned index, struct device *device,
				   void *drvdata,
				   const struct attribute_group **attr_grp)
{
	char name[64];
	dev_t devt = MKDEV(driver->major, driver->minor_start) + index;
	struct ktermios *tp;
	struct device *dev;
	int retval;

	if (index >= driver->num) {
		pr_err("%s: Attempt to register invalid tty line number (%d)\n",
		       driver->name, index);
		return ERR_PTR(-EINVAL);
	}

	if (driver->type == TTY_DRIVER_TYPE_PTY)
		pty_line_name(driver, index, name);
	else
		tty_line_name(driver, index, name);

	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
	if (!dev)
		return ERR_PTR(-ENOMEM);

	dev->devt = devt;
	dev->class = &tty_class;
	dev->parent = device;
	dev->release = tty_device_create_release;
	dev_set_name(dev, "%s", name);
	dev->groups = attr_grp;
	dev_set_drvdata(dev, drvdata);

	dev_set_uevent_suppress(dev, 1);

	retval = device_register(dev);
	if (retval)
		goto err_put;

	if (!(driver->flags & TTY_DRIVER_DYNAMIC_ALLOC)) {
		/*
		 * Free any saved termios data so that the termios state is
		 * reset when reusing a minor number.
		 */
		tp = driver->termios[index];
		if (tp) {
			driver->termios[index] = NULL;
			kfree(tp);
		}

		retval = tty_cdev_add(driver, devt, index, 1);
		if (retval)
			goto err_del;
	}

	dev_set_uevent_suppress(dev, 0);
	kobject_uevent(&dev->kobj, KOBJ_ADD);

	return dev;

err_del:
	device_del(dev);
err_put:
	put_device(dev);

	return ERR_PTR(retval);
}
EXPORT_SYMBOL_GPL(tty_register_device_attr);

/**
 * tty_unregister_device - unregister a tty device
 * @driver: the tty driver that describes the tty device
 * @index: the index in the tty driver for this tty device
 *
 * If a tty device is registered with a call to tty_register_device() then
 * this function must be called when the tty device is gone.
 *
 * Locking: ??
 */
void tty_unregister_device(struct tty_driver *driver, unsigned index)
{
	device_destroy(&tty_class, MKDEV(driver->major, driver->minor_start) + index);
	if (!(driver->flags & TTY_DRIVER_DYNAMIC_ALLOC)) {
		cdev_del(driver->cdevs[index]);
		driver->cdevs[index] = NULL;
	}
}
EXPORT_SYMBOL(tty_unregister_device);

/**
 * __tty_alloc_driver -- allocate tty driver
 * @lines: count of lines this driver can handle at most
 * @owner: module which is responsible for this driver
 * @flags: some of %TTY_DRIVER_ flags, will be set in driver->flags
 *
 * This should not be called directly, some of the provided macros should be
 * used instead. Use IS_ERR() and friends on @retval.
 */
struct tty_driver *__tty_alloc_driver(unsigned int lines, struct module *owner,
		unsigned long flags)
{
	struct tty_driver *driver;
	unsigned int cdevs = 1;
	int err;

	if (!lines || (flags & TTY_DRIVER_UNNUMBERED_NODE && lines > 1))
		return ERR_PTR(-EINVAL);

	driver = kzalloc(sizeof(*driver), GFP_KERNEL);
	if (!driver)
		return ERR_PTR(-ENOMEM);

	kref_init(&driver->kref);
	driver->num = lines;
	driver->owner = owner;
	driver->flags = flags;

	if (!(flags & TTY_DRIVER_DEVPTS_MEM)) {
		driver->ttys = kcalloc(lines, sizeof(*driver->ttys),
				GFP_KERNEL);
		driver->termios = kcalloc(lines, sizeof(*driver->termios),
				GFP_KERNEL);
		if (!driver->ttys || !driver->termios) {
			err = -ENOMEM;
			goto err_free_all;
		}
	}

	if (!(flags & TTY_DRIVER_DYNAMIC_ALLOC)) {
		driver->ports = kcalloc(lines, sizeof(*driver->ports),
				GFP_KERNEL);
		if (!driver->ports) {
			err = -ENOMEM;
			goto err_free_all;
		}
		cdevs = lines;
	}

	driver->cdevs = kcalloc(cdevs, sizeof(*driver->cdevs), GFP_KERNEL);
	if (!driver->cdevs) {
		err = -ENOMEM;
		goto err_free_all;
	}

	return driver;
err_free_all:
	kfree(driver->ports);
	kfree(driver->ttys);
	kfree(driver->termios);
	kfree(driver->cdevs);
	kfree(driver);
	return ERR_PTR(err);
}
EXPORT_SYMBOL(__tty_alloc_driver);

static void destruct_tty_driver(struct kref *kref)
{
	struct tty_driver *driver = container_of(kref, struct tty_driver, kref);
	int i;
	struct ktermios *tp;

	if (driver->flags & TTY_DRIVER_INSTALLED) {
		for (i = 0; i < driver->num; i++) {
			tp = driver->termios[i];
			if (tp) {
				driver->termios[i] = NULL;
				kfree(tp);
			}
			if (!(driver->flags & TTY_DRIVER_DYNAMIC_DEV))
				tty_unregister_device(driver, i);
		}
		proc_tty_unregister_driver(driver);
		if (driver->flags & TTY_DRIVER_DYNAMIC_ALLOC)
			cdev_del(driver->cdevs[0]);
	}
	kfree(driver->cdevs);
	kfree(driver->ports);
	kfree(driver->termios);
	kfree(driver->ttys);
	kfree(driver);
}

/**
 * tty_driver_kref_put -- drop a reference to a tty driver
 * @driver: driver of which to drop the reference
 *
 * The final put will destroy and free up the driver.
 */
void tty_driver_kref_put(struct tty_driver *driver)
{
	kref_put(&driver->kref, destruct_tty_driver);
}
EXPORT_SYMBOL(tty_driver_kref_put);

/**
 * tty_register_driver -- register a tty driver
 * @driver: driver to register
 *
 * Called by a tty driver to register itself.
 */
int tty_register_driver(struct tty_driver *driver)
{
	int error;
	int i;
	dev_t dev;
	struct device *d;

	if (!driver->major) {
		error = alloc_chrdev_region(&dev, driver->minor_start,
						driver->num, driver->name);
		if (!error) {
			driver->major = MAJOR(dev);
			driver->minor_start = MINOR(dev);
		}
	} else {
		dev = MKDEV(driver->major, driver->minor_start);
		error = register_chrdev_region(dev, driver->num, driver->name);
	}
	if (error < 0)
		goto err;

	if (driver->flags & TTY_DRIVER_DYNAMIC_ALLOC) {
		error = tty_cdev_add(driver, dev, 0, driver->num);
		if (error)
			goto err_unreg_char;
	}

	mutex_lock(&tty_mutex);
	list_add(&driver->tty_drivers, &tty_drivers);
	mutex_unlock(&tty_mutex);

	if (!(driver->flags & TTY_DRIVER_DYNAMIC_DEV)) {
		for (i = 0; i < driver->num; i++) {
			d = tty_register_device(driver, i, NULL);
			if (IS_ERR(d)) {
				error = PTR_ERR(d);
				goto err_unreg_devs;
			}
		}
	}
	proc_tty_register_driver(driver);
	driver->flags |= TTY_DRIVER_INSTALLED;
	return 0;

err_unreg_devs:
	for (i--; i >= 0; i--)
		tty_unregister_device(driver, i);

	mutex_lock(&tty_mutex);
	list_del(&driver->tty_drivers);
	mutex_unlock(&tty_mutex);

err_unreg_char:
	unregister_chrdev_region(dev, driver->num);
err:
	return error;
}
EXPORT_SYMBOL(tty_register_driver);

/**
 * tty_unregister_driver -- unregister a tty driver
 * @driver: driver to unregister
 *
 * Called by a tty driver to unregister itself.
 */
void tty_unregister_driver(struct tty_driver *driver)
{
	unregister_chrdev_region(MKDEV(driver->major, driver->minor_start),
				driver->num);
	mutex_lock(&tty_mutex);
	list_del(&driver->tty_drivers);
	mutex_unlock(&tty_mutex);
}
EXPORT_SYMBOL(tty_unregister_driver);

dev_t tty_devnum(struct tty_struct *tty)
{
	return MKDEV(tty->driver->major, tty->driver->minor_start) + tty->index;
}
EXPORT_SYMBOL(tty_devnum);

void tty_default_fops(struct file_operations *fops)
{
	*fops = tty_fops;
}

static char *tty_devnode(const struct device *dev, umode_t *mode)
{
	if (!mode)
		return NULL;
	if (dev->devt == MKDEV(TTYAUX_MAJOR, 0) ||
	    dev->devt == MKDEV(TTYAUX_MAJOR, 2))
		*mode = 0666;
	return NULL;
}

const struct class tty_class = {
	.name		= "tty",
	.devnode	= tty_devnode,
};

static int __init tty_class_init(void)
{
	return class_register(&tty_class);
}

postcore_initcall(tty_class_init);

/* 3/2004 jmc: why do these devices exist? */
static struct cdev tty_cdev, console_cdev;

static ssize_t show_cons_active(struct device *dev,
				struct device_attribute *attr, char *buf)
{
	struct console *cs[16];
	int i = 0;
	struct console *c;
	ssize_t count = 0;

	/*
	 * Hold the console_list_lock to guarantee that no consoles are
	 * unregistered until all console processing is complete.
	 * This also allows safe traversal of the console list and
	 * race-free reading of @flags.
	 */
	console_list_lock();

	for_each_console(c) {
		if (!c->device)
			continue;
		if (!c->write)
			continue;
		if ((c->flags & CON_ENABLED) == 0)
			continue;
		cs[i++] = c;
		if (i >= ARRAY_SIZE(cs))
			break;
	}

	/*
	 * Take console_lock to serialize device() callback with
	 * other console operations. For example, fg_console is
	 * modified under console_lock when switching vt.
	 */
	console_lock();
	while (i--) {
		int index = cs[i]->index;
		struct tty_driver *drv = cs[i]->device(cs[i], &index);

		/* don't resolve tty0 as some programs depend on it */
		if (drv && (cs[i]->index > 0 || drv->major != TTY_MAJOR))
			count += tty_line_name(drv, index, buf + count);
		else
			count += sprintf(buf + count, "%s%d",
					 cs[i]->name, cs[i]->index);

		count += sprintf(buf + count, "%c", i ? ' ':'\n');
	}
	console_unlock();

	console_list_unlock();

	return count;
}
static DEVICE_ATTR(active, S_IRUGO, show_cons_active, NULL);

static struct attribute *cons_dev_attrs[] = {
	&dev_attr_active.attr,
	NULL
};

ATTRIBUTE_GROUPS(cons_dev);

static struct device *consdev;

void console_sysfs_notify(void)
{
	if (consdev)
		sysfs_notify(&consdev->kobj, NULL, "active");
}

static struct ctl_table tty_table[] = {
	{
		.procname	= "legacy_tiocsti",
		.data		= &tty_legacy_tiocsti,
		.maxlen		= sizeof(tty_legacy_tiocsti),
		.mode		= 0644,
		.proc_handler	= proc_dobool,
	},
	{
		.procname	= "ldisc_autoload",
		.data		= &tty_ldisc_autoload,
		.maxlen		= sizeof(tty_ldisc_autoload),
		.mode		= 0644,
		.proc_handler	= proc_dointvec,
		.extra1		= SYSCTL_ZERO,
		.extra2		= SYSCTL_ONE,
	},
	{ }
};

/*
 * Ok, now we can initialize the rest of the tty devices and can count
 * on memory allocations, interrupts etc..
 */
int __init tty_init(void)
{
	register_sysctl_init("dev/tty", tty_table);
	cdev_init(&tty_cdev, &tty_fops);
	if (cdev_add(&tty_cdev, MKDEV(TTYAUX_MAJOR, 0), 1) ||
	    register_chrdev_region(MKDEV(TTYAUX_MAJOR, 0), 1, "/dev/tty") < 0)
		panic("Couldn't register /dev/tty driver\n");
	device_create(&tty_class, NULL, MKDEV(TTYAUX_MAJOR, 0), NULL, "tty");

	cdev_init(&console_cdev, &console_fops);
	if (cdev_add(&console_cdev, MKDEV(TTYAUX_MAJOR, 1), 1) ||
	    register_chrdev_region(MKDEV(TTYAUX_MAJOR, 1), 1, "/dev/console") < 0)
		panic("Couldn't register /dev/console driver\n");
	consdev = device_create_with_groups(&tty_class, NULL,
					    MKDEV(TTYAUX_MAJOR, 1), NULL,
					    cons_dev_groups, "console");
	if (IS_ERR(consdev))
		consdev = NULL;

#ifdef CONFIG_VT
	vty_init(&console_fops);
#endif
	return 0;
}