text: /*
   *  Copyright (C) 1991, 1992  Linus Torvalds
   *
   *  Added support for a Unix98-style ptmx device.
   *    -- C. Scott Ananian <cananian@alumni.princeton.edu>, 14-Jan-1998
   *
   */
  
  #include <linux/module.h>
  #include <linux/errno.h>
  #include <linux/interrupt.h>
  #include <linux/tty.h>
  #include <linux/tty_flip.h>
  #include <linux/fcntl.h>
  #include <linux/sched/signal.h>
  #include <linux/string.h>
  #include <linux/major.h>
  #include <linux/mm.h>
  #include <linux/init.h>
  #include <linux/device.h>
  #include <linux/uaccess.h>
  #include <linux/bitops.h>
  #include <linux/devpts_fs.h>
  #include <linux/slab.h>
  #include <linux/mutex.h>
  #include <linux/poll.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
  
  #ifdef CONFIG_UNIX98_PTYS
  static struct tty_driver *ptm_driver;
  static struct tty_driver *pts_driver;
  static DEFINE_MUTEX(devpts_mutex);
  #endif
  
  static void pty_close(struct tty_struct *tty, struct file *filp)
  {
  	BUG_ON(!tty);
  	if (tty->driver->subtype == PTY_TYPE_MASTER)
  		WARN_ON(tty->count > 1);
  	else {
  		if (tty_io_error(tty))
  			return;
  		if (tty->count > 2)
  			return;
  	}
  	set_bit(TTY_IO_ERROR, &tty->flags);
  	wake_up_interruptible(&tty->read_wait);
  	wake_up_interruptible(&tty->write_wait);
  	spin_lock_irq(&tty->ctrl_lock);
  	tty->packet = 0;
  	spin_unlock_irq(&tty->ctrl_lock);
  	/* Review - krefs on tty_link ?? */
  	if (!tty->link)
  		return;
  	set_bit(TTY_OTHER_CLOSED, &tty->link->flags);
  	wake_up_interruptible(&tty->link->read_wait);
  	wake_up_interruptible(&tty->link->write_wait);
  	if (tty->driver->subtype == PTY_TYPE_MASTER) {
  		set_bit(TTY_OTHER_CLOSED, &tty->flags);
  #ifdef CONFIG_UNIX98_PTYS
  		if (tty->driver == ptm_driver) {
  			mutex_lock(&devpts_mutex);
  			if (tty->link->driver_data)
  				devpts_pty_kill(tty->link->driver_data);
  			mutex_unlock(&devpts_mutex);
  		}
  #endif
  		tty_vhangup(tty->link);
  	}
  }
  
  /*
   * The unthrottle routine is called by the line discipline to signal
   * that it can receive more characters.  For PTY's, the TTY_THROTTLED
   * flag is always set, to force the line discipline to always call the
   * unthrottle routine when there are fewer than TTY_THRESHOLD_UNTHROTTLE
   * characters in the queue.  This is necessary since each time this
   * happens, we need to wake up any sleeping processes that could be
   * (1) trying to send data to the pty, or (2) waiting in wait_until_sent()
   * for the pty buffer to be drained.
   */
  static void pty_unthrottle(struct tty_struct *tty)
  {
  	tty_wakeup(tty->link);
  	set_bit(TTY_THROTTLED, &tty->flags);
  }
  
  /**
   *	pty_write		-	write to a pty
   *	@tty: the tty we write from
   *	@buf: kernel buffer of data
   *	@count: bytes to write
   *
   *	Our "hardware" write method. Data is coming from the ldisc which
   *	may be in a non sleeping state. We simply throw this at the other
   *	end of the link as if we were an IRQ handler receiving stuff for
   *	the other side of the pty/tty pair.
   */
  
  static int pty_write(struct tty_struct *tty, const unsigned char *buf, int c)
  {
  	struct tty_struct *to = tty->link;
  
  	if (tty->stopped)
  		return 0;
  
  	if (c > 0) {
  		/* Stuff the data into the input queue of the other end */
  		c = tty_insert_flip_string(to->port, buf, c);
  		/* And shovel */
  		if (c)
  			tty_flip_buffer_push(to->port);
  	}
  	return c;
  }
  
  /**
   *	pty_write_room	-	write space
   *	@tty: tty we are writing from
   *
   *	Report how many bytes the ldisc can send into the queue for
   *	the other device.
   */
  
  static int pty_write_room(struct tty_struct *tty)
  {
  	if (tty->stopped)
  		return 0;
  	return tty_buffer_space_avail(tty->link->port);
  }
  
  /**
   *	pty_chars_in_buffer	-	characters currently in our tx queue
   *	@tty: our tty
   *
   *	Report how much we have in the transmit queue. As everything is
   *	instantly at the other end this is easy to implement.
   */
  
  static int pty_chars_in_buffer(struct tty_struct *tty)
  {
  	return 0;
  }
  
  /* Set the lock flag on a pty */
  static int pty_set_lock(struct tty_struct *tty, int __user *arg)
  {
  	int val;
  	if (get_user(val, arg))
  		return -EFAULT;
  	if (val)
  		set_bit(TTY_PTY_LOCK, &tty->flags);
  	else
  		clear_bit(TTY_PTY_LOCK, &tty->flags);
  	return 0;
  }
  
  static int pty_get_lock(struct tty_struct *tty, int __user *arg)
  {
  	int locked = test_bit(TTY_PTY_LOCK, &tty->flags);
  	return put_user(locked, arg);
  }
  
  /* Set the packet mode on a pty */
  static int pty_set_pktmode(struct tty_struct *tty, int __user *arg)
  {
  	int pktmode;
  
  	if (get_user(pktmode, arg))
  		return -EFAULT;
  
  	spin_lock_irq(&tty->ctrl_lock);
  	if (pktmode) {
  		if (!tty->packet) {
  			tty->link->ctrl_status = 0;
  			smp_mb();
  			tty->packet = 1;
  		}
  	} else
  		tty->packet = 0;
  	spin_unlock_irq(&tty->ctrl_lock);
  
  	return 0;
  }
  
  /* Get the packet mode of a pty */
  static int pty_get_pktmode(struct tty_struct *tty, int __user *arg)
  {
  	int pktmode = tty->packet;
  	return put_user(pktmode, arg);
  }
  
  /* Send a signal to the slave */
  static int pty_signal(struct tty_struct *tty, int sig)
  {
  	struct pid *pgrp;
  
  	if (sig != SIGINT && sig != SIGQUIT && sig != SIGTSTP)
  		return -EINVAL;
  
  	if (tty->link) {
  		pgrp = tty_get_pgrp(tty->link);
  		if (pgrp)
  			kill_pgrp(pgrp, sig, 1);
  		put_pid(pgrp);
  	}
  	return 0;
  }
  
  static void pty_flush_buffer(struct tty_struct *tty)
  {
  	struct tty_struct *to = tty->link;
  	struct tty_ldisc *ld;
  
  	if (!to)
  		return;
  
  	ld = tty_ldisc_ref(to);
  	tty_buffer_flush(to, ld);
  	if (ld)
  		tty_ldisc_deref(ld);
  
  	if (to->packet) {
  		spin_lock_irq(&tty->ctrl_lock);
  		tty->ctrl_status |= TIOCPKT_FLUSHWRITE;
  		wake_up_interruptible(&to->read_wait);
  		spin_unlock_irq(&tty->ctrl_lock);
  	}
  }
  
  static int pty_open(struct tty_struct *tty, struct file *filp)
  {
  	if (!tty || !tty->link)
  		return -ENODEV;
  
  	if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
  		goto out;
  	if (test_bit(TTY_PTY_LOCK, &tty->link->flags))
  		goto out;
  	if (tty->driver->subtype == PTY_TYPE_SLAVE && tty->link->count != 1)
  		goto out;
  
  	clear_bit(TTY_IO_ERROR, &tty->flags);
  	clear_bit(TTY_OTHER_CLOSED, &tty->link->flags);
  	set_bit(TTY_THROTTLED, &tty->flags);
  	return 0;
  
  out:
  	set_bit(TTY_IO_ERROR, &tty->flags);
  	return -EIO;
  }
  
  static void pty_set_termios(struct tty_struct *tty,
  					struct ktermios *old_termios)
  {
  	/* See if packet mode change of state. */
  	if (tty->link && tty->link->packet) {
  		int extproc = (old_termios->c_lflag & EXTPROC) | L_EXTPROC(tty);
  		int old_flow = ((old_termios->c_iflag & IXON) &&
  				(old_termios->c_cc[VSTOP] == '\023') &&
  				(old_termios->c_cc[VSTART] == '\021'));
  		int new_flow = (I_IXON(tty) &&
  				STOP_CHAR(tty) == '\023' &&
  				START_CHAR(tty) == '\021');
  		if ((old_flow != new_flow) || extproc) {
  			spin_lock_irq(&tty->ctrl_lock);
  			if (old_flow != new_flow) {
  				tty->ctrl_status &= ~(TIOCPKT_DOSTOP | TIOCPKT_NOSTOP);
  				if (new_flow)
  					tty->ctrl_status |= TIOCPKT_DOSTOP;
  				else
  					tty->ctrl_status |= TIOCPKT_NOSTOP;
  			}
  			if (extproc)
  				tty->ctrl_status |= TIOCPKT_IOCTL;
  			spin_unlock_irq(&tty->ctrl_lock);
  			wake_up_interruptible(&tty->link->read_wait);
  		}
  	}
  
  	tty->termios.c_cflag &= ~(CSIZE | PARENB);
  	tty->termios.c_cflag |= (CS8 | CREAD);
  }
  
  /**
   *	pty_do_resize		-	resize event
   *	@tty: tty being resized
   *	@ws: window size being set.
   *
   *	Update the termios variables and send the necessary signals to
   *	peform a terminal resize correctly
   */
  
  static int pty_resize(struct tty_struct *tty,  struct winsize *ws)
  {
  	struct pid *pgrp, *rpgrp;
  	struct tty_struct *pty = tty->link;
  
  	/* For a PTY we need to lock the tty side */
  	mutex_lock(&tty->winsize_mutex);
  	if (!memcmp(ws, &tty->winsize, sizeof(*ws)))
  		goto done;
  
  	/* Signal the foreground process group of both ptys */
  	pgrp = tty_get_pgrp(tty);
  	rpgrp = tty_get_pgrp(pty);
  
  	if (pgrp)
  		kill_pgrp(pgrp, SIGWINCH, 1);
  	if (rpgrp != pgrp && rpgrp)
  		kill_pgrp(rpgrp, SIGWINCH, 1);
  
  	put_pid(pgrp);
  	put_pid(rpgrp);
  
  	tty->winsize = *ws;
  	pty->winsize = *ws;	/* Never used so will go away soon */
  done:
  	mutex_unlock(&tty->winsize_mutex);
  	return 0;
  }
  
  /**
   *	pty_start - start() handler
   *	pty_stop  - stop() handler
   *	@tty: tty being flow-controlled
   *
   *	Propagates the TIOCPKT status to the master pty.
   *
   *	NB: only the master pty can be in packet mode so only the slave
   *	    needs start()/stop() handlers
   */
  static void pty_start(struct tty_struct *tty)
  {
  	unsigned long flags;
  
  	if (tty->link && tty->link->packet) {
  		spin_lock_irqsave(&tty->ctrl_lock, flags);
  		tty->ctrl_status &= ~TIOCPKT_STOP;
  		tty->ctrl_status |= TIOCPKT_START;
  		spin_unlock_irqrestore(&tty->ctrl_lock, flags);
  		wake_up_interruptible_poll(&tty->link->read_wait, POLLIN);
  	}
  }
  
  static void pty_stop(struct tty_struct *tty)
  {
  	unsigned long flags;
  
  	if (tty->link && tty->link->packet) {
  		spin_lock_irqsave(&tty->ctrl_lock, flags);
  		tty->ctrl_status &= ~TIOCPKT_START;
  		tty->ctrl_status |= TIOCPKT_STOP;
  		spin_unlock_irqrestore(&tty->ctrl_lock, flags);
  		wake_up_interruptible_poll(&tty->link->read_wait, POLLIN);
  	}
  }
  
  /**
   *	pty_common_install		-	set up the pty pair
   *	@driver: the pty driver
   *	@tty: the tty being instantiated
   *	@legacy: true if this is BSD style
   *
   *	Perform the initial set up for the tty/pty pair. Called from the
   *	tty layer when the port is first opened.
   *
   *	Locking: the caller must hold the tty_mutex
   */
  static int pty_common_install(struct tty_driver *driver, struct tty_struct *tty,
  		bool legacy)
  {
  	struct tty_struct *o_tty;
  	struct tty_port *ports[2];
  	int idx = tty->index;
  	int retval = -ENOMEM;
  
  	/* Opening the slave first has always returned -EIO */
  	if (driver->subtype != PTY_TYPE_MASTER)
  		return -EIO;
  
  	ports[0] = kmalloc(sizeof **ports, GFP_KERNEL);
  	ports[1] = kmalloc(sizeof **ports, GFP_KERNEL);
  	if (!ports[0] || !ports[1])
  		goto err;
  	if (!try_module_get(driver->other->owner)) {
  		/* This cannot in fact currently happen */
  		goto err;
  	}
  	o_tty = alloc_tty_struct(driver->other, idx);
  	if (!o_tty)
  		goto err_put_module;
  
  	tty_set_lock_subclass(o_tty);
  	lockdep_set_subclass(&o_tty->termios_rwsem, TTY_LOCK_SLAVE);
  
  	if (legacy) {
  		/* We always use new tty termios data so we can do this
  		   the easy way .. */
  		tty_init_termios(tty);
  		tty_init_termios(o_tty);
  
  		driver->other->ttys[idx] = o_tty;
  		driver->ttys[idx] = tty;
  	} else {
  		memset(&tty->termios_locked, 0, sizeof(tty->termios_locked));
  		tty->termios = driver->init_termios;
  		memset(&o_tty->termios_locked, 0, sizeof(tty->termios_locked));
  		o_tty->termios = driver->other->init_termios;
  	}
  
  	/*
  	 * Everything allocated ... set up the o_tty structure.
  	 */
  	tty_driver_kref_get(driver->other);
  	/* Establish the links in both directions */
  	tty->link   = o_tty;
  	o_tty->link = tty;
  	tty_port_init(ports[0]);
  	tty_port_init(ports[1]);
  	tty_buffer_set_limit(ports[0], 8192);
  	tty_buffer_set_limit(ports[1], 8192);
  	o_tty->port = ports[0];
  	tty->port = ports[1];
  	o_tty->port->itty = o_tty;
  
  	tty_buffer_set_lock_subclass(o_tty->port);
  
  	tty_driver_kref_get(driver);
  	tty->count++;
  	o_tty->count++;
  	return 0;
  
  err_put_module:
  	module_put(driver->other->owner);
  err:
  	kfree(ports[0]);
  	kfree(ports[1]);
  	return retval;
  }
  
  static void pty_cleanup(struct tty_struct *tty)
  {
  	tty_port_put(tty->port);
  }
  
  /* Traditional BSD devices */
  #ifdef CONFIG_LEGACY_PTYS
  
  static int pty_install(struct tty_driver *driver, struct tty_struct *tty)
  {
  	return pty_common_install(driver, tty, true);
  }
  
  static void pty_remove(struct tty_driver *driver, struct tty_struct *tty)
  {
  	struct tty_struct *pair = tty->link;
  	driver->ttys[tty->index] = NULL;
  	if (pair)
  		pair->driver->ttys[pair->index] = NULL;
  }
  
  static int pty_bsd_ioctl(struct tty_struct *tty,
  			 unsigned int cmd, unsigned long arg)
  {
  	switch (cmd) {
  	case TIOCSPTLCK: /* Set PT Lock (disallow slave open) */
  		return pty_set_lock(tty, (int __user *) arg);
  	case TIOCGPTLCK: /* Get PT Lock status */
  		return pty_get_lock(tty, (int __user *)arg);
  	case TIOCPKT: /* Set PT packet mode */
  		return pty_set_pktmode(tty, (int __user *)arg);
  	case TIOCGPKT: /* Get PT packet mode */
  		return pty_get_pktmode(tty, (int __user *)arg);
  	case TIOCSIG:    /* Send signal to other side of pty */
  		return pty_signal(tty, (int) arg);
  	case TIOCGPTN: /* TTY returns ENOTTY, but glibc expects EINVAL here */
  		return -EINVAL;
  	}
  	return -ENOIOCTLCMD;
  }
  
  static int legacy_count = CONFIG_LEGACY_PTY_COUNT;
  /*
   * not really modular, but the easiest way to keep compat with existing
   * bootargs behaviour is to continue using module_param here.
   */
  module_param(legacy_count, int, 0);
  
  /*
   * The master side of a pty can do TIOCSPTLCK and thus
   * has pty_bsd_ioctl.
   */
  static const struct tty_operations master_pty_ops_bsd = {
  	.install = pty_install,
  	.open = pty_open,
  	.close = pty_close,
  	.write = pty_write,
  	.write_room = pty_write_room,
  	.flush_buffer = pty_flush_buffer,
  	.chars_in_buffer = pty_chars_in_buffer,
  	.unthrottle = pty_unthrottle,
  	.ioctl = pty_bsd_ioctl,
  	.cleanup = pty_cleanup,
  	.resize = pty_resize,
  	.remove = pty_remove
  };
  
  static const struct tty_operations slave_pty_ops_bsd = {
  	.install = pty_install,
  	.open = pty_open,
  	.close = pty_close,
  	.write = pty_write,
  	.write_room = pty_write_room,
  	.flush_buffer = pty_flush_buffer,
  	.chars_in_buffer = pty_chars_in_buffer,
  	.unthrottle = pty_unthrottle,
  	.set_termios = pty_set_termios,
  	.cleanup = pty_cleanup,
  	.resize = pty_resize,
  	.start = pty_start,
  	.stop = pty_stop,
  	.remove = pty_remove
  };
  
  static void __init legacy_pty_init(void)
  {
  	struct tty_driver *pty_driver, *pty_slave_driver;
  
  	if (legacy_count <= 0)
  		return;
  
  	pty_driver = tty_alloc_driver(legacy_count,
  			TTY_DRIVER_RESET_TERMIOS |
  			TTY_DRIVER_REAL_RAW |
  			TTY_DRIVER_DYNAMIC_ALLOC);
  	if (IS_ERR(pty_driver))
  		panic("Couldn't allocate pty driver");
  
  	pty_slave_driver = tty_alloc_driver(legacy_count,
  			TTY_DRIVER_RESET_TERMIOS |
  			TTY_DRIVER_REAL_RAW |
  			TTY_DRIVER_DYNAMIC_ALLOC);
  	if (IS_ERR(pty_slave_driver))
  		panic("Couldn't allocate pty slave driver");
  
  	pty_driver->driver_name = "pty_master";
  	pty_driver->name = "pty";
  	pty_driver->major = PTY_MASTER_MAJOR;
  	pty_driver->minor_start = 0;
  	pty_driver->type = TTY_DRIVER_TYPE_PTY;
  	pty_driver->subtype = PTY_TYPE_MASTER;
  	pty_driver->init_termios = tty_std_termios;
  	pty_driver->init_termios.c_iflag = 0;
  	pty_driver->init_termios.c_oflag = 0;
  	pty_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
  	pty_driver->init_termios.c_lflag = 0;
  	pty_driver->init_termios.c_ispeed = 38400;
  	pty_driver->init_termios.c_ospeed = 38400;
  	pty_driver->other = pty_slave_driver;
  	tty_set_operations(pty_driver, &master_pty_ops_bsd);
  
  	pty_slave_driver->driver_name = "pty_slave";
  	pty_slave_driver->name = "ttyp";
  	pty_slave_driver->major = PTY_SLAVE_MAJOR;
  	pty_slave_driver->minor_start = 0;
  	pty_slave_driver->type = TTY_DRIVER_TYPE_PTY;
  	pty_slave_driver->subtype = PTY_TYPE_SLAVE;
  	pty_slave_driver->init_termios = tty_std_termios;
  	pty_slave_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
  	pty_slave_driver->init_termios.c_ispeed = 38400;
  	pty_slave_driver->init_termios.c_ospeed = 38400;
  	pty_slave_driver->other = pty_driver;
  	tty_set_operations(pty_slave_driver, &slave_pty_ops_bsd);
  
  	if (tty_register_driver(pty_driver))
  		panic("Couldn't register pty driver");
  	if (tty_register_driver(pty_slave_driver))
  		panic("Couldn't register pty slave driver");
  }
  #else
  static inline void legacy_pty_init(void) { }
  #endif
  
  /* Unix98 devices */
  #ifdef CONFIG_UNIX98_PTYS
  
  static struct cdev ptmx_cdev;
  
  static int pty_unix98_ioctl(struct tty_struct *tty,
  			    unsigned int cmd, unsigned long arg)
  {
  	switch (cmd) {
  	case TIOCSPTLCK: /* Set PT Lock (disallow slave open) */
  		return pty_set_lock(tty, (int __user *)arg);
  	case TIOCGPTLCK: /* Get PT Lock status */
  		return pty_get_lock(tty, (int __user *)arg);
  	case TIOCPKT: /* Set PT packet mode */
  		return pty_set_pktmode(tty, (int __user *)arg);
  	case TIOCGPKT: /* Get PT packet mode */
  		return pty_get_pktmode(tty, (int __user *)arg);
  	case TIOCGPTN: /* Get PT Number */
  		return put_user(tty->index, (unsigned int __user *)arg);
  	case TIOCSIG:    /* Send signal to other side of pty */
  		return pty_signal(tty, (int) arg);
  	}
  
  	return -ENOIOCTLCMD;
  }
  
  /**
   *	ptm_unix98_lookup	-	find a pty master
   *	@driver: ptm driver
   *	@idx: tty index
   *
   *	Look up a pty master device. Called under the tty_mutex for now.
   *	This provides our locking.
   */
  
  static struct tty_struct *ptm_unix98_lookup(struct tty_driver *driver,
  		struct file *file, int idx)
  {
  	/* Master must be open via /dev/ptmx */
  	return ERR_PTR(-EIO);
  }
  
  /**
   *	pts_unix98_lookup	-	find a pty slave
   *	@driver: pts driver
   *	@idx: tty index
   *
   *	Look up a pty master device. Called under the tty_mutex for now.
   *	This provides our locking for the tty pointer.
   */
  
  static struct tty_struct *pts_unix98_lookup(struct tty_driver *driver,
  		struct file *file, int idx)
  {
  	struct tty_struct *tty;
  
  	mutex_lock(&devpts_mutex);
  	tty = devpts_get_priv(file->f_path.dentry);
  	mutex_unlock(&devpts_mutex);
  	/* Master must be open before slave */
  	if (!tty)
  		return ERR_PTR(-EIO);
  	return tty;
  }
  
  static int pty_unix98_install(struct tty_driver *driver, struct tty_struct *tty)
  {
  	return pty_common_install(driver, tty, false);
  }
  
  /* this is called once with whichever end is closed last */
  static void pty_unix98_remove(struct tty_driver *driver, struct tty_struct *tty)
  {
  	struct pts_fs_info *fsi;
  
  	if (tty->driver->subtype == PTY_TYPE_MASTER)
  		fsi = tty->driver_data;
  	else
  		fsi = tty->link->driver_data;
  
  	if (fsi) {
  		devpts_kill_index(fsi, tty->index);
  		devpts_release(fsi);
  	}
  }
  
  static const struct tty_operations ptm_unix98_ops = {
  	.lookup = ptm_unix98_lookup,
  	.install = pty_unix98_install,
  	.remove = pty_unix98_remove,
  	.open = pty_open,
  	.close = pty_close,
  	.write = pty_write,
  	.write_room = pty_write_room,
  	.flush_buffer = pty_flush_buffer,
  	.chars_in_buffer = pty_chars_in_buffer,
  	.unthrottle = pty_unthrottle,
  	.ioctl = pty_unix98_ioctl,
  	.resize = pty_resize,
  	.cleanup = pty_cleanup
  };
  
  static const struct tty_operations pty_unix98_ops = {
  	.lookup = pts_unix98_lookup,
  	.install = pty_unix98_install,
  	.remove = pty_unix98_remove,
  	.open = pty_open,
  	.close = pty_close,
  	.write = pty_write,
  	.write_room = pty_write_room,
  	.flush_buffer = pty_flush_buffer,
  	.chars_in_buffer = pty_chars_in_buffer,
  	.unthrottle = pty_unthrottle,
  	.set_termios = pty_set_termios,
  	.start = pty_start,
  	.stop = pty_stop,
  	.cleanup = pty_cleanup,
  };
  
  /**
   *	ptmx_open		-	open a unix 98 pty master
   *	@inode: inode of device file
   *	@filp: file pointer to tty
   *
   *	Allocate a unix98 pty master device from the ptmx driver.
   *
   *	Locking: tty_mutex protects the init_dev work. tty->count should
   *		protect the rest.
   *		allocated_ptys_lock handles the list of free pty numbers
   */
  
  static int ptmx_open(struct inode *inode, struct file *filp)
  {
  	struct pts_fs_info *fsi;
  	struct tty_struct *tty;
  	struct dentry *dentry;
  	int retval;
  	int index;
  
  	nonseekable_open(inode, filp);
  
  	/* We refuse fsnotify events on ptmx, since it's a shared resource */
  	filp->f_mode |= FMODE_NONOTIFY;
  
  	retval = tty_alloc_file(filp);
  	if (retval)
  		return retval;
  
  	fsi = devpts_acquire(filp);
  	if (IS_ERR(fsi)) {
  		retval = PTR_ERR(fsi);
  		goto out_free_file;
  	}
  
  	/* find a device that is not in use. */
  	mutex_lock(&devpts_mutex);
  	index = devpts_new_index(fsi);
  	mutex_unlock(&devpts_mutex);
  
  	retval = index;
  	if (index < 0)
  		goto out_put_fsi;
  
  
  	mutex_lock(&tty_mutex);
  	tty = tty_init_dev(ptm_driver, index);
  	/* The tty returned here is locked so we can safely
  	   drop the mutex */
  	mutex_unlock(&tty_mutex);
  
  	retval = PTR_ERR(tty);
  	if (IS_ERR(tty))
  		goto out;
  
  	/*
  	 * From here on out, the tty is "live", and the index and
  	 * fsi will be killed/put by the tty_release()
  	 */
  	set_bit(TTY_PTY_LOCK, &tty->flags); /* LOCK THE SLAVE */
  	tty->driver_data = fsi;
  
  	tty_add_file(tty, filp);
  
  	dentry = devpts_pty_new(fsi, index, tty->link);
  	if (IS_ERR(dentry)) {
  		retval = PTR_ERR(dentry);
  		goto err_release;
  	}
  	tty->link->driver_data = dentry;
  
  	retval = ptm_driver->ops->open(tty, filp);
  	if (retval)
  		goto err_release;
  
  	tty_debug_hangup(tty, "opening (count=%d)\n", tty->count);
  
  	tty_unlock(tty);
  	return 0;
  err_release:
  	tty_unlock(tty);
  	// This will also put-ref the fsi
  	tty_release(inode, filp);
  	return retval;
  out:
  	devpts_kill_index(fsi, index);
  out_put_fsi:
  	devpts_release(fsi);
  out_free_file:
  	tty_free_file(filp);
  	return retval;
  }
  
  static struct file_operations ptmx_fops __ro_after_init;
  
  static void __init unix98_pty_init(void)
  {
  	ptm_driver = tty_alloc_driver(NR_UNIX98_PTY_MAX,
  			TTY_DRIVER_RESET_TERMIOS |
  			TTY_DRIVER_REAL_RAW |
  			TTY_DRIVER_DYNAMIC_DEV |
  			TTY_DRIVER_DEVPTS_MEM |
  			TTY_DRIVER_DYNAMIC_ALLOC);
  	if (IS_ERR(ptm_driver))
  		panic("Couldn't allocate Unix98 ptm driver");
  	pts_driver = tty_alloc_driver(NR_UNIX98_PTY_MAX,
  			TTY_DRIVER_RESET_TERMIOS |
  			TTY_DRIVER_REAL_RAW |
  			TTY_DRIVER_DYNAMIC_DEV |
  			TTY_DRIVER_DEVPTS_MEM |
  			TTY_DRIVER_DYNAMIC_ALLOC);
  	if (IS_ERR(pts_driver))
  		panic("Couldn't allocate Unix98 pts driver");
  
  	ptm_driver->driver_name = "pty_master";
  	ptm_driver->name = "ptm";
  	ptm_driver->major = UNIX98_PTY_MASTER_MAJOR;
  	ptm_driver->minor_start = 0;
  	ptm_driver->type = TTY_DRIVER_TYPE_PTY;
  	ptm_driver->subtype = PTY_TYPE_MASTER;
  	ptm_driver->init_termios = tty_std_termios;
  	ptm_driver->init_termios.c_iflag = 0;
  	ptm_driver->init_termios.c_oflag = 0;
  	ptm_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
  	ptm_driver->init_termios.c_lflag = 0;
  	ptm_driver->init_termios.c_ispeed = 38400;
  	ptm_driver->init_termios.c_ospeed = 38400;
  	ptm_driver->other = pts_driver;
  	tty_set_operations(ptm_driver, &ptm_unix98_ops);
  
  	pts_driver->driver_name = "pty_slave";
  	pts_driver->name = "pts";
  	pts_driver->major = UNIX98_PTY_SLAVE_MAJOR;
  	pts_driver->minor_start = 0;
  	pts_driver->type = TTY_DRIVER_TYPE_PTY;
  	pts_driver->subtype = PTY_TYPE_SLAVE;
  	pts_driver->init_termios = tty_std_termios;
  	pts_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
  	pts_driver->init_termios.c_ispeed = 38400;
  	pts_driver->init_termios.c_ospeed = 38400;
  	pts_driver->other = ptm_driver;
  	tty_set_operations(pts_driver, &pty_unix98_ops);
  
  	if (tty_register_driver(ptm_driver))
  		panic("Couldn't register Unix98 ptm driver");
  	if (tty_register_driver(pts_driver))
  		panic("Couldn't register Unix98 pts driver");
  
  	/* Now create the /dev/ptmx special device */
  	tty_default_fops(&ptmx_fops);
  	ptmx_fops.open = ptmx_open;
  
  	cdev_init(&ptmx_cdev, &ptmx_fops);
  	if (cdev_add(&ptmx_cdev, MKDEV(TTYAUX_MAJOR, 2), 1) ||
  	    register_chrdev_region(MKDEV(TTYAUX_MAJOR, 2), 1, "/dev/ptmx") < 0)
  		panic("Couldn't register /dev/ptmx driver");
  	device_create(tty_class, NULL, MKDEV(TTYAUX_MAJOR, 2), NULL, "ptmx");
  }
  
  #else
  static inline void unix98_pty_init(void) { }
  #endif
  
  static int __init pty_init(void)
  {
  	legacy_pty_init();
  	unix98_pty_init();
  	return 0;
  }
  device_initcall(pty_init);
  