// SPDX-License-Identifier: GPL-2.0

  /*

   *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
   *
   * 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).
   */
  
  #include <linux/types.h>
  #include <linux/termios.h>
  #include <linux/errno.h>

  #include <linux/sched/signal.h>

  #include <linux/kernel.h>
  #include <linux/major.h>
  #include <linux/tty.h>
  #include <linux/fcntl.h>
  #include <linux/string.h>
  #include <linux/mm.h>
  #include <linux/module.h>
  #include <linux/bitops.h>

  #include <linux/mutex.h>

  #include <linux/compat.h>

  
  #include <asm/io.h>

  #include <linux/uaccess.h>

  
  #undef TTY_DEBUG_WAIT_UNTIL_SENT

  #ifdef TTY_DEBUG_WAIT_UNTIL_SENT
  # define tty_debug_wait_until_sent(tty, f, args...)    tty_debug(tty, f, ##args)
  #else
  # define tty_debug_wait_until_sent(tty, f, args...)    do {} while (0)
  #endif

  #undef	DEBUG
  
  /*
   * Internal flag options for termios setting behavior
   */
  #define TERMIOS_FLUSH	1
  #define TERMIOS_WAIT	2
  #define TERMIOS_TERMIO	4

  #define TERMIOS_OLD	8

  /**
   *	tty_chars_in_buffer	-	characters pending
   *	@tty: terminal
   *
   *	Return the number of bytes of data in the device private
   *	output queue. If no private method is supplied there is assumed
   *	to be no queue on the device.
   */

  int tty_chars_in_buffer(struct tty_struct *tty)
  {
  	if (tty->ops->chars_in_buffer)
  		return tty->ops->chars_in_buffer(tty);
  	else
  		return 0;
  }

  EXPORT_SYMBOL(tty_chars_in_buffer);

  /**
   *	tty_write_room		-	write queue space
   *	@tty: terminal
   *
   *	Return the number of bytes that can be queued to this device
   *	at the present time. The result should be treated as a guarantee
   *	and the driver cannot offer a value it later shrinks by more than
   *	the number of bytes written. If no method is provided 2K is always
   *	returned and data may be lost as there will be no flow control.
   */
   

  int tty_write_room(struct tty_struct *tty)
  {
  	if (tty->ops->write_room)
  		return tty->ops->write_room(tty);
  	return 2048;
  }

  EXPORT_SYMBOL(tty_write_room);

  /**
   *	tty_driver_flush_buffer	-	discard internal buffer
   *	@tty: terminal
   *
   *	Discard the internal output buffer for this device. If no method
   *	is provided then either the buffer cannot be hardware flushed or
   *	there is no buffer driver side.
   */

  void tty_driver_flush_buffer(struct tty_struct *tty)
  {
  	if (tty->ops->flush_buffer)
  		tty->ops->flush_buffer(tty);
  }

  EXPORT_SYMBOL(tty_driver_flush_buffer);

  /**
   *	tty_throttle		-	flow control
   *	@tty: terminal
   *
   *	Indicate that a tty should stop transmitting data down the stack.

   *	Takes the termios rwsem to protect against parallel throttle/unthrottle

   *	and also to ensure the driver can consistently reference its own
   *	termios data at this point when implementing software flow control.

   */

  void tty_throttle(struct tty_struct *tty)
  {

  	down_write(&tty->termios_rwsem);

  	/* check TTY_THROTTLED first so it indicates our state */
  	if (!test_and_set_bit(TTY_THROTTLED, &tty->flags) &&
  	    tty->ops->throttle)
  		tty->ops->throttle(tty);

  	tty->flow_change = 0;

  	up_write(&tty->termios_rwsem);

  }
  EXPORT_SYMBOL(tty_throttle);

  /**
   *	tty_unthrottle		-	flow control
   *	@tty: terminal
   *
   *	Indicate that a tty may continue transmitting data down the stack.

   *	Takes the termios rwsem to protect against parallel throttle/unthrottle

   *	and also to ensure the driver can consistently reference its own
   *	termios data at this point when implementing software flow control.
   *
   *	Drivers should however remember that the stack can issue a throttle,
   *	then change flow control method, then unthrottle.

   */

  void tty_unthrottle(struct tty_struct *tty)
  {

  	down_write(&tty->termios_rwsem);

  	if (test_and_clear_bit(TTY_THROTTLED, &tty->flags) &&
  	    tty->ops->unthrottle)
  		tty->ops->unthrottle(tty);

  	tty->flow_change = 0;

  	up_write(&tty->termios_rwsem);

  }
  EXPORT_SYMBOL(tty_unthrottle);

  /**

   *	tty_throttle_safe	-	flow control
   *	@tty: terminal
   *
   *	Similar to tty_throttle() but will only attempt throttle
   *	if tty->flow_change is TTY_THROTTLE_SAFE. Prevents an accidental
   *	throttle due to race conditions when throttling is conditional
   *	on factors evaluated prior to throttling.
   *
   *	Returns 0 if tty is throttled (or was already throttled)
   */
  
  int tty_throttle_safe(struct tty_struct *tty)
  {
  	int ret = 0;

  	mutex_lock(&tty->throttle_mutex);

  	if (!tty_throttled(tty)) {

  		if (tty->flow_change != TTY_THROTTLE_SAFE)
  			ret = 1;
  		else {

  			set_bit(TTY_THROTTLED, &tty->flags);

  			if (tty->ops->throttle)
  				tty->ops->throttle(tty);
  		}
  	}

  	mutex_unlock(&tty->throttle_mutex);

  
  	return ret;
  }
  
  /**
   *	tty_unthrottle_safe	-	flow control
   *	@tty: terminal
   *
   *	Similar to tty_unthrottle() but will only attempt unthrottle
   *	if tty->flow_change is TTY_UNTHROTTLE_SAFE. Prevents an accidental
   *	unthrottle due to race conditions when unthrottling is conditional
   *	on factors evaluated prior to unthrottling.
   *
   *	Returns 0 if tty is unthrottled (or was already unthrottled)
   */
  
  int tty_unthrottle_safe(struct tty_struct *tty)
  {
  	int ret = 0;

  	mutex_lock(&tty->throttle_mutex);

  	if (tty_throttled(tty)) {

  		if (tty->flow_change != TTY_UNTHROTTLE_SAFE)
  			ret = 1;
  		else {

  			clear_bit(TTY_THROTTLED, &tty->flags);

  			if (tty->ops->unthrottle)
  				tty->ops->unthrottle(tty);
  		}
  	}

  	mutex_unlock(&tty->throttle_mutex);

  
  	return ret;
  }
  
  /**

   *	tty_wait_until_sent	-	wait for I/O to finish
   *	@tty: tty we are waiting for
   *	@timeout: how long we will wait
   *
   *	Wait for characters pending in a tty driver to hit the wire, or
   *	for a timeout to occur (eg due to flow control)
   *
   *	Locking: none
   */

  void tty_wait_until_sent(struct tty_struct *tty, long timeout)

  {

  	tty_debug_wait_until_sent(tty, "wait until sent, timeout=%ld
  ", timeout);

  	if (!timeout)
  		timeout = MAX_SCHEDULE_TIMEOUT;

  	timeout = wait_event_interruptible_timeout(tty->write_wait,
  			!tty_chars_in_buffer(tty), timeout);
  	if (timeout <= 0)

  		return;

  
  	if (timeout == MAX_SCHEDULE_TIMEOUT)
  		timeout = 0;
  
  	if (tty->ops->wait_until_sent)
  		tty->ops->wait_until_sent(tty, timeout);

  }

  EXPORT_SYMBOL(tty_wait_until_sent);

  
  /*
   *		Termios Helper Methods
   */

  static void unset_locked_termios(struct tty_struct *tty, struct ktermios *old)

  {

  	struct ktermios *termios = &tty->termios;
  	struct ktermios *locked  = &tty->termios_locked;

  	int	i;

  
  #define NOSET_MASK(x, y, z) (x = ((x) & ~(z)) | ((y) & (z)))

  	NOSET_MASK(termios->c_iflag, old->c_iflag, locked->c_iflag);
  	NOSET_MASK(termios->c_oflag, old->c_oflag, locked->c_oflag);
  	NOSET_MASK(termios->c_cflag, old->c_cflag, locked->c_cflag);
  	NOSET_MASK(termios->c_lflag, old->c_lflag, locked->c_lflag);
  	termios->c_line = locked->c_line ? old->c_line : termios->c_line;

  	for (i = 0; i < NCCS; i++)

  		termios->c_cc[i] = locked->c_cc[i] ?
  			old->c_cc[i] : termios->c_cc[i];

  	/* FIXME: What should we do for i/ospeed */

  }

  /**

   *	tty_termios_copy_hw	-	copy hardware settings
   *	@new: New termios
   *	@old: Old termios
   *

   *	Propagate the hardware specific terminal setting bits from

   *	the old termios structure to the new one. This is used in cases
   *	where the hardware does not support reconfiguration or as a helper
   *	in some cases where only minimal reconfiguration is supported
   */
  
  void tty_termios_copy_hw(struct ktermios *new, struct ktermios *old)
  {
  	/* The bits a dumb device handles in software. Smart devices need
  	   to always provide a set_termios method */
  	new->c_cflag &= HUPCL | CREAD | CLOCAL;
  	new->c_cflag |= old->c_cflag & ~(HUPCL | CREAD | CLOCAL);
  	new->c_ispeed = old->c_ispeed;
  	new->c_ospeed = old->c_ospeed;
  }

  EXPORT_SYMBOL(tty_termios_copy_hw);
  
  /**

   *	tty_termios_hw_change	-	check for setting change
   *	@a: termios
   *	@b: termios to compare
   *
   *	Check if any of the bits that affect a dumb device have changed
   *	between the two termios structures, or a speed change is needed.
   */

  int tty_termios_hw_change(const struct ktermios *a, const struct ktermios *b)

  {
  	if (a->c_ispeed != b->c_ispeed || a->c_ospeed != b->c_ospeed)
  		return 1;
  	if ((a->c_cflag ^ b->c_cflag) & ~(HUPCL | CREAD | CLOCAL))
  		return 1;
  	return 0;
  }
  EXPORT_SYMBOL(tty_termios_hw_change);
  
  /**

   *	tty_set_termios		-	update termios values

   *	@tty: tty to update
   *	@new_termios: desired new value
   *

   *	Perform updates to the termios values set on this terminal.

   *	A master pty's termios should never be set.
   *

   *	Locking: termios_rwsem

   */

  int tty_set_termios(struct tty_struct *tty, struct ktermios *new_termios)

  {

  	struct ktermios old_termios;

  	struct tty_ldisc *ld;

  	WARN_ON(tty->driver->type == TTY_DRIVER_TYPE_PTY &&
  		tty->driver->subtype == PTY_TYPE_MASTER);

  	/*
  	 *	Perform the actual termios internal changes under lock.
  	 */

  
  	/* FIXME: we need to decide on some locking/ordering semantics
  	   for the set_termios notification eventually */

  	down_write(&tty->termios_rwsem);

  	old_termios = tty->termios;
  	tty->termios = *new_termios;

  	unset_locked_termios(tty, &old_termios);

  	if (tty->ops->set_termios)

  		tty->ops->set_termios(tty, &old_termios);

  	else

  		tty_termios_copy_hw(&tty->termios, &old_termios);

  
  	ld = tty_ldisc_ref(tty);
  	if (ld != NULL) {

  		if (ld->ops->set_termios)

  			ld->ops->set_termios(tty, &old_termios);

  		tty_ldisc_deref(ld);
  	}

  	up_write(&tty->termios_rwsem);

  	return 0;

  }

  EXPORT_SYMBOL_GPL(tty_set_termios);

  /**
   *	set_termios		-	set termios values for a tty
   *	@tty: terminal device
   *	@arg: user data
   *	@opt: option information
   *

   *	Helper function to prepare termios data and run necessary other

   *	functions before using tty_set_termios to do the actual changes.

   *
   *	Locking:

   *		Called functions take ldisc and termios_rwsem locks

   */

  static int set_termios(struct tty_struct *tty, void __user *arg, int opt)

  {

  	struct ktermios tmp_termios;

  	struct tty_ldisc *ld;
  	int retval = tty_check_change(tty);
  
  	if (retval)
  		return retval;

  	down_read(&tty->termios_rwsem);

  	tmp_termios = tty->termios;

  	up_read(&tty->termios_rwsem);

  	if (opt & TERMIOS_TERMIO) {

  		if (user_termio_to_kernel_termios(&tmp_termios,
  						(struct termio __user *)arg))
  			return -EFAULT;

  #ifdef TCGETS2
  	} else if (opt & TERMIOS_OLD) {

  		if (user_termios_to_kernel_termios_1(&tmp_termios,

  						(struct termios __user *)arg))

  			return -EFAULT;

  	} else {
  		if (user_termios_to_kernel_termios(&tmp_termios,

  						(struct termios2 __user *)arg))

  			return -EFAULT;
  	}

  #else
  	} else if (user_termios_to_kernel_termios(&tmp_termios,
  					(struct termios __user *)arg))
  		return -EFAULT;
  #endif

  	/* If old style Bfoo values are used then load c_ispeed/c_ospeed
  	 * with the real speed so its unconditionally usable */

  	tmp_termios.c_ispeed = tty_termios_input_baud_rate(&tmp_termios);
  	tmp_termios.c_ospeed = tty_termios_baud_rate(&tmp_termios);

  	ld = tty_ldisc_ref(tty);

  	if (ld != NULL) {

  		if ((opt & TERMIOS_FLUSH) && ld->ops->flush_buffer)
  			ld->ops->flush_buffer(tty);

  		tty_ldisc_deref(ld);
  	}

  	if (opt & TERMIOS_WAIT) {
  		tty_wait_until_sent(tty, 0);
  		if (signal_pending(current))

  			return -ERESTARTSYS;

  	}

  	tty_set_termios(tty, &tmp_termios);

  
  	/* FIXME: Arguably if tmp_termios == tty->termios AND the
  	   actual requested termios was not tmp_termios then we may
  	   want to return an error as no user requested change has
  	   succeeded */

  	return 0;
  }

  static void copy_termios(struct tty_struct *tty, struct ktermios *kterm)
  {

  	down_read(&tty->termios_rwsem);

  	*kterm = tty->termios;

  	up_read(&tty->termios_rwsem);

  }
  
  static void copy_termios_locked(struct tty_struct *tty, struct ktermios *kterm)
  {

  	down_read(&tty->termios_rwsem);

  	*kterm = tty->termios_locked;

  	up_read(&tty->termios_rwsem);

  }

  static int get_termio(struct tty_struct *tty, struct termio __user *termio)

  {

  	struct ktermios kterm;
  	copy_termios(tty, &kterm);
  	if (kernel_termios_to_user_termio(termio, &kterm))

  		return -EFAULT;
  	return 0;
  }

  
  #ifdef TCGETX
  
  /**
   *	set_termiox	-	set termiox fields if possible
   *	@tty: terminal
   *	@arg: termiox structure from user
   *	@opt: option flags for ioctl type
   *
   *	Implement the device calling points for the SYS5 termiox ioctl
   *	interface in Linux
   */
  
  static int set_termiox(struct tty_struct *tty, void __user *arg, int opt)
  {
  	struct termiox tnew;
  	struct tty_ldisc *ld;
  
  	if (tty->termiox == NULL)
  		return -EINVAL;
  	if (copy_from_user(&tnew, arg, sizeof(struct termiox)))
  		return -EFAULT;
  
  	ld = tty_ldisc_ref(tty);
  	if (ld != NULL) {
  		if ((opt & TERMIOS_FLUSH) && ld->ops->flush_buffer)
  			ld->ops->flush_buffer(tty);
  		tty_ldisc_deref(ld);
  	}
  	if (opt & TERMIOS_WAIT) {
  		tty_wait_until_sent(tty, 0);
  		if (signal_pending(current))

  			return -ERESTARTSYS;

  	}

  	down_write(&tty->termios_rwsem);

  	if (tty->ops->set_termiox)
  		tty->ops->set_termiox(tty, &tnew);

  	up_write(&tty->termios_rwsem);

  	return 0;
  }
  
  #endif

  
  #ifdef TIOCGETP
  /*
   * These are deprecated, but there is limited support..
   *
   * The "sg_flags" translation is a joke..
   */

  static int get_sgflags(struct tty_struct *tty)

  {
  	int flags = 0;

  	if (!L_ICANON(tty)) {
  		if (L_ISIG(tty))

  			flags |= 0x02;		/* cbreak */
  		else
  			flags |= 0x20;		/* raw */
  	}

  	if (L_ECHO(tty))

  		flags |= 0x08;			/* echo */

  	if (O_OPOST(tty))
  		if (O_ONLCR(tty))

  			flags |= 0x10;		/* crmod */
  	return flags;
  }

  static int get_sgttyb(struct tty_struct *tty, struct sgttyb __user *sgttyb)

  {
  	struct sgttyb tmp;

  	down_read(&tty->termios_rwsem);

  	tmp.sg_ispeed = tty->termios.c_ispeed;
  	tmp.sg_ospeed = tty->termios.c_ospeed;
  	tmp.sg_erase = tty->termios.c_cc[VERASE];
  	tmp.sg_kill = tty->termios.c_cc[VKILL];

  	tmp.sg_flags = get_sgflags(tty);

  	up_read(&tty->termios_rwsem);

  	return copy_to_user(sgttyb, &tmp, sizeof(tmp)) ? -EFAULT : 0;
  }

  static void set_sgflags(struct ktermios *termios, int flags)

  {

  	termios->c_iflag = ICRNL | IXON;
  	termios->c_oflag = 0;
  	termios->c_lflag = ISIG | ICANON;

  	if (flags & 0x02) {	/* cbreak */

  		termios->c_iflag = 0;
  		termios->c_lflag &= ~ICANON;

  	}
  	if (flags & 0x08) {		/* echo */

  		termios->c_lflag |= ECHO | ECHOE | ECHOK |

  				    ECHOCTL | ECHOKE | IEXTEN;
  	}
  	if (flags & 0x10) {		/* crmod */

  		termios->c_oflag |= OPOST | ONLCR;

  	}
  	if (flags & 0x20) {	/* raw */

  		termios->c_iflag = 0;
  		termios->c_lflag &= ~(ISIG | ICANON);

  	}

  	if (!(termios->c_lflag & ICANON)) {
  		termios->c_cc[VMIN] = 1;
  		termios->c_cc[VTIME] = 0;

  	}
  }

  /**
   *	set_sgttyb		-	set legacy terminal values
   *	@tty: tty structure
   *	@sgttyb: pointer to old style terminal structure
   *
   *	Updates a terminal from the legacy BSD style terminal information
   *	structure.
   *

   *	Locking: termios_rwsem

   */

  static int set_sgttyb(struct tty_struct *tty, struct sgttyb __user *sgttyb)

  {
  	int retval;
  	struct sgttyb tmp;

  	struct ktermios termios;

  
  	retval = tty_check_change(tty);
  	if (retval)
  		return retval;

  	if (copy_from_user(&tmp, sgttyb, sizeof(tmp)))
  		return -EFAULT;

  	down_write(&tty->termios_rwsem);

  	termios = tty->termios;

  	termios.c_cc[VERASE] = tmp.sg_erase;
  	termios.c_cc[VKILL] = tmp.sg_kill;
  	set_sgflags(&termios, tmp.sg_flags);

  	/* Try and encode into Bfoo format */
  #ifdef BOTHER

  	tty_termios_encode_baud_rate(&termios, termios.c_ispeed,
  						termios.c_ospeed);

  #endif

  	up_write(&tty->termios_rwsem);

  	tty_set_termios(tty, &termios);

  	return 0;
  }
  #endif
  
  #ifdef TIOCGETC

  static int get_tchars(struct tty_struct *tty, struct tchars __user *tchars)

  {
  	struct tchars tmp;

  	down_read(&tty->termios_rwsem);

  	tmp.t_intrc = tty->termios.c_cc[VINTR];
  	tmp.t_quitc = tty->termios.c_cc[VQUIT];
  	tmp.t_startc = tty->termios.c_cc[VSTART];
  	tmp.t_stopc = tty->termios.c_cc[VSTOP];
  	tmp.t_eofc = tty->termios.c_cc[VEOF];
  	tmp.t_brkc = tty->termios.c_cc[VEOL2];	/* what is brkc anyway? */

  	up_read(&tty->termios_rwsem);

  	return copy_to_user(tchars, &tmp, sizeof(tmp)) ? -EFAULT : 0;
  }

  static int set_tchars(struct tty_struct *tty, struct tchars __user *tchars)

  {
  	struct tchars tmp;
  
  	if (copy_from_user(&tmp, tchars, sizeof(tmp)))
  		return -EFAULT;

  	down_write(&tty->termios_rwsem);

  	tty->termios.c_cc[VINTR] = tmp.t_intrc;
  	tty->termios.c_cc[VQUIT] = tmp.t_quitc;
  	tty->termios.c_cc[VSTART] = tmp.t_startc;
  	tty->termios.c_cc[VSTOP] = tmp.t_stopc;
  	tty->termios.c_cc[VEOF] = tmp.t_eofc;
  	tty->termios.c_cc[VEOL2] = tmp.t_brkc;	/* what is brkc anyway? */

  	up_write(&tty->termios_rwsem);

  	return 0;
  }
  #endif
  
  #ifdef TIOCGLTC

  static int get_ltchars(struct tty_struct *tty, struct ltchars __user *ltchars)

  {
  	struct ltchars tmp;

  	down_read(&tty->termios_rwsem);

  	tmp.t_suspc = tty->termios.c_cc[VSUSP];

  	/* what is dsuspc anyway? */

  	tmp.t_dsuspc = tty->termios.c_cc[VSUSP];
  	tmp.t_rprntc = tty->termios.c_cc[VREPRINT];

  	/* what is flushc anyway? */

  	tmp.t_flushc = tty->termios.c_cc[VEOL2];
  	tmp.t_werasc = tty->termios.c_cc[VWERASE];
  	tmp.t_lnextc = tty->termios.c_cc[VLNEXT];

  	up_read(&tty->termios_rwsem);

  	return copy_to_user(ltchars, &tmp, sizeof(tmp)) ? -EFAULT : 0;
  }

  static int set_ltchars(struct tty_struct *tty, struct ltchars __user *ltchars)

  {
  	struct ltchars tmp;
  
  	if (copy_from_user(&tmp, ltchars, sizeof(tmp)))
  		return -EFAULT;

  	down_write(&tty->termios_rwsem);

  	tty->termios.c_cc[VSUSP] = tmp.t_suspc;

  	/* what is dsuspc anyway? */

  	tty->termios.c_cc[VEOL2] = tmp.t_dsuspc;
  	tty->termios.c_cc[VREPRINT] = tmp.t_rprntc;

  	/* what is flushc anyway? */

  	tty->termios.c_cc[VEOL2] = tmp.t_flushc;
  	tty->termios.c_cc[VWERASE] = tmp.t_werasc;
  	tty->termios.c_cc[VLNEXT] = tmp.t_lnextc;

  	up_write(&tty->termios_rwsem);

  	return 0;
  }
  #endif

  /**

   *	tty_change_softcar	-	carrier change ioctl helper
   *	@tty: tty to update
   *	@arg: enable/disable CLOCAL
   *
   *	Perform a change to the CLOCAL state and call into the driver

   *	layer to make it visible. All done with the termios rwsem

   */
  
  static int tty_change_softcar(struct tty_struct *tty, int arg)
  {
  	int ret = 0;
  	int bit = arg ? CLOCAL : 0;

  	struct ktermios old;

  	down_write(&tty->termios_rwsem);

  	old = tty->termios;
  	tty->termios.c_cflag &= ~CLOCAL;
  	tty->termios.c_cflag |= bit;

  	if (tty->ops->set_termios)
  		tty->ops->set_termios(tty, &old);

  	if (C_CLOCAL(tty) != bit)

  		ret = -EINVAL;

  	up_write(&tty->termios_rwsem);

  	return ret;
  }
  
  /**

   *	tty_mode_ioctl		-	mode related ioctls
   *	@tty: tty for the ioctl
   *	@file: file pointer for the tty
   *	@cmd: command
   *	@arg: ioctl argument
   *
   *	Perform non line discipline specific mode control ioctls. This
   *	is designed to be called by line disciplines to ensure they provide
   *	consistent mode setting.
   */

  int tty_mode_ioctl(struct tty_struct *tty, struct file *file,

  			unsigned int cmd, unsigned long arg)

  {

  	struct tty_struct *real_tty;

  	void __user *p = (void __user *)arg;

  	int ret = 0;

  	struct ktermios kterm;

  	BUG_ON(file == NULL);

  	if (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
  	    tty->driver->subtype == PTY_TYPE_MASTER)
  		real_tty = tty->link;
  	else
  		real_tty = tty;
  
  	switch (cmd) {
  #ifdef TIOCGETP

  	case TIOCGETP:
  		return get_sgttyb(real_tty, (struct sgttyb __user *) arg);
  	case TIOCSETP:
  	case TIOCSETN:
  		return set_sgttyb(real_tty, (struct sgttyb __user *) arg);

  #endif
  #ifdef TIOCGETC

  	case TIOCGETC:
  		return get_tchars(real_tty, p);
  	case TIOCSETC:
  		return set_tchars(real_tty, p);

  #endif
  #ifdef TIOCGLTC

  	case TIOCGLTC:
  		return get_ltchars(real_tty, p);
  	case TIOCSLTC:
  		return set_ltchars(real_tty, p);

  #endif

  	case TCSETSF:
  		return set_termios(real_tty, p,  TERMIOS_FLUSH | TERMIOS_WAIT | TERMIOS_OLD);
  	case TCSETSW:
  		return set_termios(real_tty, p, TERMIOS_WAIT | TERMIOS_OLD);
  	case TCSETS:
  		return set_termios(real_tty, p, TERMIOS_OLD);

  #ifndef TCGETS2

  	case TCGETS:

  		copy_termios(real_tty, &kterm);
  		if (kernel_termios_to_user_termios((struct termios __user *)arg, &kterm))

  			ret = -EFAULT;

  		return ret;

  #else

  	case TCGETS:

  		copy_termios(real_tty, &kterm);
  		if (kernel_termios_to_user_termios_1((struct termios __user *)arg, &kterm))

  			ret = -EFAULT;

  		return ret;

  	case TCGETS2:

  		copy_termios(real_tty, &kterm);
  		if (kernel_termios_to_user_termios((struct termios2 __user *)arg, &kterm))

  			ret = -EFAULT;

  		return ret;

  	case TCSETSF2:
  		return set_termios(real_tty, p,  TERMIOS_FLUSH | TERMIOS_WAIT);
  	case TCSETSW2:
  		return set_termios(real_tty, p, TERMIOS_WAIT);
  	case TCSETS2:
  		return set_termios(real_tty, p, 0);

  #endif

  	case TCGETA:
  		return get_termio(real_tty, p);
  	case TCSETAF:
  		return set_termios(real_tty, p, TERMIOS_FLUSH | TERMIOS_WAIT | TERMIOS_TERMIO);
  	case TCSETAW:
  		return set_termios(real_tty, p, TERMIOS_WAIT | TERMIOS_TERMIO);
  	case TCSETA:
  		return set_termios(real_tty, p, TERMIOS_TERMIO);

  #ifndef TCGETS2

  	case TIOCGLCKTRMIOS:

  		copy_termios_locked(real_tty, &kterm);
  		if (kernel_termios_to_user_termios((struct termios __user *)arg, &kterm))

  			ret = -EFAULT;

  		return ret;

  	case TIOCSLCKTRMIOS:
  		if (!capable(CAP_SYS_ADMIN))
  			return -EPERM;

  		copy_termios_locked(real_tty, &kterm);
  		if (user_termios_to_kernel_termios(&kterm,

  					       (struct termios __user *) arg))

  			return -EFAULT;

  		down_write(&real_tty->termios_rwsem);

  		real_tty->termios_locked = kterm;

  		up_write(&real_tty->termios_rwsem);

  		return 0;

  #else

  	case TIOCGLCKTRMIOS:

  		copy_termios_locked(real_tty, &kterm);
  		if (kernel_termios_to_user_termios_1((struct termios __user *)arg, &kterm))

  			ret = -EFAULT;

  		return ret;

  	case TIOCSLCKTRMIOS:
  		if (!capable(CAP_SYS_ADMIN))

  			return -EPERM;
  		copy_termios_locked(real_tty, &kterm);
  		if (user_termios_to_kernel_termios_1(&kterm,

  					       (struct termios __user *) arg))

  			return -EFAULT;

  		down_write(&real_tty->termios_rwsem);

  		real_tty->termios_locked = kterm;

  		up_write(&real_tty->termios_rwsem);

  		return ret;

  #endif

  #ifdef TCGETX

  	case TCGETX: {
  		struct termiox ktermx;

  		if (real_tty->termiox == NULL)
  			return -EINVAL;

  		down_read(&real_tty->termios_rwsem);

  		memcpy(&ktermx, real_tty->termiox, sizeof(struct termiox));

  		up_read(&real_tty->termios_rwsem);

  		if (copy_to_user(p, &ktermx, sizeof(struct termiox)))
  			ret = -EFAULT;

  		return ret;

  	}

  	case TCSETX:
  		return set_termiox(real_tty, p, 0);
  	case TCSETXW:
  		return set_termiox(real_tty, p, TERMIOS_WAIT);
  	case TCSETXF:
  		return set_termiox(real_tty, p, TERMIOS_FLUSH);
  #endif		

  	case TIOCGSOFTCAR:

  		copy_termios(real_tty, &kterm);
  		ret = put_user((kterm.c_cflag & CLOCAL) ? 1 : 0,

  						(int __user *)arg);

  		return ret;

  	case TIOCSSOFTCAR:
  		if (get_user(arg, (unsigned int __user *) arg))
  			return -EFAULT;

  		return tty_change_softcar(real_tty, arg);

  	default:
  		return -ENOIOCTLCMD;

  	}
  }

  EXPORT_SYMBOL_GPL(tty_mode_ioctl);

  
  /* Caller guarantees ldisc reference is held */
  static int __tty_perform_flush(struct tty_struct *tty, unsigned long arg)

  {

  	struct tty_ldisc *ld = tty->ldisc;

  	switch (arg) {
  	case TCIFLUSH:

  		if (ld && ld->ops->flush_buffer) {

  			ld->ops->flush_buffer(tty);

  			tty_unthrottle(tty);
  		}

  		break;
  	case TCIOFLUSH:

  		if (ld && ld->ops->flush_buffer) {

  			ld->ops->flush_buffer(tty);

  			tty_unthrottle(tty);
  		}

  		fallthrough;

  	case TCOFLUSH:

  		tty_driver_flush_buffer(tty);

  		break;
  	default:

  		return -EINVAL;
  	}

  	return 0;
  }

  
  int tty_perform_flush(struct tty_struct *tty, unsigned long arg)
  {
  	struct tty_ldisc *ld;
  	int retval = tty_check_change(tty);
  	if (retval)
  		return retval;
  
  	ld = tty_ldisc_ref_wait(tty);
  	retval = __tty_perform_flush(tty, arg);
  	if (ld)
  		tty_ldisc_deref(ld);
  	return retval;
  }

  EXPORT_SYMBOL_GPL(tty_perform_flush);

  int n_tty_ioctl_helper(struct tty_struct *tty, struct file *file,

  		       unsigned int cmd, unsigned long arg)
  {

  	int retval;

  	switch (cmd) {

  	case TCXONC:
  		retval = tty_check_change(tty);
  		if (retval)
  			return retval;
  		switch (arg) {
  		case TCOOFF:

  			spin_lock_irq(&tty->flow_lock);

  			if (!tty->flow_stopped) {
  				tty->flow_stopped = 1;

  				__stop_tty(tty);

  			}

  			spin_unlock_irq(&tty->flow_lock);

  			break;
  		case TCOON:

  			spin_lock_irq(&tty->flow_lock);

  			if (tty->flow_stopped) {
  				tty->flow_stopped = 0;

  				__start_tty(tty);

  			}

  			spin_unlock_irq(&tty->flow_lock);

  			break;
  		case TCIOFF:
  			if (STOP_CHAR(tty) != __DISABLED_CHAR)

  				retval = tty_send_xchar(tty, STOP_CHAR(tty));

  			break;
  		case TCION:
  			if (START_CHAR(tty) != __DISABLED_CHAR)

  				retval = tty_send_xchar(tty, START_CHAR(tty));

  			break;

  		default:

  			return -EINVAL;

  		}

  		return retval;

  	case TCFLSH:

  		retval = tty_check_change(tty);
  		if (retval)
  			return retval;

  		return __tty_perform_flush(tty, arg);

  	default:
  		/* Try the mode commands */
  		return tty_mode_ioctl(tty, file, cmd, arg);
  	}

  }

  EXPORT_SYMBOL(n_tty_ioctl_helper);