/*

   *  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.h>
  #include <linux/interrupt.h>
  #include <linux/tty.h>
  #include <linux/tty_driver.h>
  #include <linux/tty_flip.h>
  #include <linux/devpts_fs.h>
  #include <linux/file.h>

  #include <linux/fdtable.h>

  #include <linux/console.h>
  #include <linux/timer.h>
  #include <linux/ctype.h>
  #include <linux/kd.h>
  #include <linux/mm.h>
  #include <linux/string.h>
  #include <linux/slab.h>
  #include <linux/poll.h>
  #include <linux/proc_fs.h>
  #include <linux/init.h>
  #include <linux/module.h>

  #include <linux/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/uaccess.h>

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

  
  #include <linux/kmod.h>

  #include <linux/nsproxy.h>

  
  #undef TTY_DEBUG_HANGUP
  
  #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

  };
  
  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. This is shared with

     vt.c for deeply disgusting hack reasons */

  DEFINE_MUTEX(tty_mutex);

  EXPORT_SYMBOL(tty_mutex);

  /* Spinlock to protect the tty->tty_files list */
  DEFINE_SPINLOCK(tty_files_lock);

  static ssize_t tty_read(struct file *, char __user *, size_t, loff_t *);
  static ssize_t tty_write(struct file *, const char __user *, size_t, loff_t *);

  ssize_t redirected_tty_write(struct file *, const char __user *,
  							size_t, loff_t *);

  static unsigned int tty_poll(struct file *, poll_table *);
  static int tty_open(struct inode *, struct file *);

  long tty_ioctl(struct file *file, unsigned int cmd, unsigned long arg);

  #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);

  static void __proc_set_tty(struct task_struct *tsk, struct tty_struct *tty);

  static void proc_set_tty(struct task_struct *tsk, struct tty_struct *tty);

  /**
   *	alloc_tty_struct	-	allocate a tty object
   *
   *	Return a new empty tty structure. The data fields have not
   *	been initialized in any way but has been zeroed
   *
   *	Locking: none

   */

  struct tty_struct *alloc_tty_struct(void)

  {

  	return kzalloc(sizeof(struct tty_struct), GFP_KERNEL);

  }

  /**
   *	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
   */

  void free_tty_struct(struct tty_struct *tty)

  {

  	if (tty->dev)
  		put_device(tty->dev);

  	kfree(tty->write_buf);

  	tty_buffer_free_all(tty);

  	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
   *
   * 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 */
  void tty_del_file(struct file *file)
  {
  	struct tty_file_private *priv = file->private_data;
  
  	spin_lock(&tty_files_lock);
  	list_del(&priv->list);
  	spin_unlock(&tty_files_lock);

  	tty_free_file(file);

  }

  #define TTY_NUMBER(tty) ((tty)->index + (tty)->driver->name_base)

  /**
   *	tty_name	-	return tty naming
   *	@tty: tty structure
   *	@buf: buffer for output
   *
   *	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
   */

  char *tty_name(struct tty_struct *tty, char *buf)
  {
  	if (!tty) /* Hmm.  NULL pointer.  That's fun. */
  		strcpy(buf, "NULL tty");
  	else
  		strcpy(buf, tty->name);
  	return buf;
  }
  
  EXPORT_SYMBOL(tty_name);

  int tty_paranoia_check(struct tty_struct *tty, struct inode *inode,

  			      const char *routine)
  {
  #ifdef TTY_PARANOIA_CHECK
  	if (!tty) {
  		printk(KERN_WARNING
  			"null TTY for (%d:%d) in %s
  ",
  			imajor(inode), iminor(inode), routine);
  		return 1;
  	}
  	if (tty->magic != TTY_MAGIC) {
  		printk(KERN_WARNING
  			"bad magic number for tty struct (%d:%d) in %s
  ",
  			imajor(inode), iminor(inode), routine);
  		return 1;
  	}
  #endif
  	return 0;
  }
  
  static int check_tty_count(struct tty_struct *tty, const char *routine)
  {
  #ifdef CHECK_TTY_COUNT
  	struct list_head *p;
  	int 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->count != count) {
  		printk(KERN_WARNING "Warning: dev (%s) tty->count(%d) "
  				    "!= #fd's(%d) in %s
  ",
  		       tty->name, tty->count, count, routine);
  		return count;

  	}

  #endif
  	return 0;
  }

  /**

   *	get_tty_driver		-	find device of a tty
   *	@dev_t: 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;
  }

  #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 (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

  /**
   *	tty_check_change	-	check for POSIX terminal changes
   *	@tty: tty to check
   *
   *	If we try to write to, or set the state of, a terminal and we're
   *	not in the foreground, send a SIGTTOU.  If the signal is blocked or
   *	ignored, go ahead and perform the operation.  (POSIX 7.2)
   *

   *	Locking: ctrl_lock

   */

  int tty_check_change(struct tty_struct *tty)

  {

  	unsigned long flags;
  	int ret = 0;

  	if (current->signal->tty != tty)
  		return 0;

  
  	spin_lock_irqsave(&tty->ctrl_lock, flags);

  	if (!tty->pgrp) {
  		printk(KERN_WARNING "tty_check_change: tty->pgrp == NULL!
  ");

  		goto out_unlock;

  	}

  	if (task_pgrp(current) == tty->pgrp)

  		goto out_unlock;
  	spin_unlock_irqrestore(&tty->ctrl_lock, flags);

  	if (is_ignored(SIGTTOU))

  		goto out;
  	if (is_current_pgrp_orphaned()) {
  		ret = -EIO;
  		goto out;
  	}

  	kill_pgrp(task_pgrp(current), SIGTTOU, 1);
  	set_thread_flag(TIF_SIGPENDING);

  	ret = -ERESTARTSYS;
  out:

  	return ret;
  out_unlock:

  	spin_unlock_irqrestore(&tty->ctrl_lock, flags);
  	return ret;

  }
  
  EXPORT_SYMBOL(tty_check_change);

  static ssize_t hung_up_tty_read(struct file *file, char __user *buf,

  				size_t count, loff_t *ppos)
  {
  	return 0;
  }

  static ssize_t hung_up_tty_write(struct file *file, const char __user *buf,

  				 size_t count, loff_t *ppos)
  {
  	return -EIO;
  }
  
  /* No kernel lock held - none needed ;) */

  static unsigned int hung_up_tty_poll(struct file *filp, poll_table *wait)

  {
  	return POLLIN | POLLOUT | POLLERR | POLLHUP | POLLRDNORM | POLLWRNORM;
  }

  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 const struct file_operations tty_fops = {

  	.llseek		= no_llseek,
  	.read		= tty_read,
  	.write		= tty_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 console_fops = {

  	.llseek		= no_llseek,
  	.read		= tty_read,
  	.write		= redirected_tty_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		= hung_up_tty_read,
  	.write		= 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,
  };
  
  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, POLLOUT);

  }
  
  EXPORT_SYMBOL_GPL(tty_wakeup);
  
  /**

   *	__tty_hangup		-	actual handler for hangup events

   *	@work: tty device

   *

   *	This can be called by the "eventd" 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_ldisc_lock from called functions
   *		  termios_mutex resetting termios data
   *		  tasklist_lock to walk task list for hangup event
   *		    ->siglock to protect ->signal/->sighand

   */

  void __tty_hangup(struct tty_struct *tty)

  {

  	struct file *cons_filp = NULL;

  	struct file *filp, *f = NULL;
  	struct task_struct *p;

  	struct tty_file_private *priv;

  	int    closecount = 0, n;

  	unsigned long flags;

  	int refs = 0;

  
  	if (!tty)
  		return;

  
  	spin_lock(&redirect_lock);

  	if (redirect && file_tty(redirect) == tty) {

  		f = redirect;
  		redirect = NULL;
  	}
  	spin_unlock(&redirect_lock);

  	tty_lock();

  	/* some functions below drop BTM, so we need this bit */
  	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 == redirected_tty_write)
  			cons_filp = filp;
  		if (filp->f_op->write != tty_write)
  			continue;
  		closecount++;

  		__tty_fasync(-1, filp, 0);	/* can't block */

  		filp->f_op = &hung_up_tty_fops;
  	}

  	spin_unlock(&tty_files_lock);

  	/*
  	 * it drops BTM and thus races with reopen
  	 * we protect the race by TTY_HUPPING
  	 */

  	tty_ldisc_hangup(tty);

  	read_lock(&tasklist_lock);

  	if (tty->session) {
  		do_each_pid_task(tty->session, PIDTYPE_SID, p) {

  			spin_lock_irq(&p->sighand->siglock);

  			if (p->signal->tty == tty) {

  				p->signal->tty = NULL;

  				/* We defer the dereferences outside fo
  				   the tasklist lock */
  				refs++;
  			}

  			if (!p->signal->leader) {
  				spin_unlock_irq(&p->sighand->siglock);

  				continue;

  			}
  			__group_send_sig_info(SIGHUP, SEND_SIG_PRIV, p);
  			__group_send_sig_info(SIGCONT, SEND_SIG_PRIV, p);

  			put_pid(p->signal->tty_old_pgrp);  /* A noop */

  			spin_lock_irqsave(&tty->ctrl_lock, flags);

  			if (tty->pgrp)
  				p->signal->tty_old_pgrp = get_pid(tty->pgrp);

  			spin_unlock_irqrestore(&tty->ctrl_lock, flags);

  			spin_unlock_irq(&p->sighand->siglock);

  		} while_each_pid_task(tty->session, PIDTYPE_SID, p);

  	}
  	read_unlock(&tasklist_lock);

  	spin_lock_irqsave(&tty->ctrl_lock, flags);

  	clear_bit(TTY_THROTTLED, &tty->flags);
  	clear_bit(TTY_PUSH, &tty->flags);
  	clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);

  	put_pid(tty->session);
  	put_pid(tty->pgrp);

  	tty->session = NULL;
  	tty->pgrp = NULL;

  	tty->ctrl_status = 0;

  	spin_unlock_irqrestore(&tty->ctrl_lock, flags);

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

  	/*

  	 * 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. However we
  	 * can't yet guarantee all that.
  	 */

  	set_bit(TTY_HUPPED, &tty->flags);

  	clear_bit(TTY_HUPPING, &tty->flags);

  	tty_ldisc_enable(tty);

  
  	tty_unlock();

  	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);

  }

  /**
   *	tty_hangup		-	trigger a hangup event
   *	@tty: tty to hangup
   *
   *	A carrier loss (virtual or otherwise) has occurred on this like
   *	schedule a hangup sequence to run after this event.
   */

  void tty_hangup(struct tty_struct *tty)

  {
  #ifdef TTY_DEBUG_HANGUP
  	char	buf[64];

  	printk(KERN_DEBUG "%s hangup...
  ", tty_name(tty, buf));
  #endif
  	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)

  {
  #ifdef TTY_DEBUG_HANGUP
  	char	buf[64];
  
  	printk(KERN_DEBUG "%s vhangup...
  ", tty_name(tty, buf));
  #endif

  	__tty_hangup(tty);

  }

  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_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->f_op == &hung_up_tty_fops);
  }
  
  EXPORT_SYMBOL(tty_hung_up_p);

  static void session_clear_tty(struct pid *session)

  {
  	struct task_struct *p;

  	do_each_pid_task(session, PIDTYPE_SID, p) {

  		proc_clear_tty(p);

  	} while_each_pid_task(session, PIDTYPE_SID, p);

  }

  /**
   *	disassociate_ctty	-	disconnect controlling tty
   *	@on_exit: true if exiting so need to "hang up" the session

   *

   *	This function is typically called only by the session leader, when
   *	it wants to disassociate itself from its controlling tty.
   *
   *	It performs the following functions:

   * 	(1)  Sends a SIGHUP and SIGCONT to the foreground process group
   * 	(2)  Clears the tty from being controlling the session
   * 	(3)  Clears the controlling tty for all processes in the
   * 		session group.
   *

   *	The argument on_exit is set to 1 if called when a process is
   *	exiting; it is 0 if called by the ioctl TIOCNOTTY.
   *

   *	Locking:

   *		BTM is taken for hysterical raisins, and held when
   *		  called from no_tty().

   *		  tty_mutex is taken to protect tty
   *		  ->siglock is taken to protect ->signal/->sighand
   *		  tasklist_lock is taken to walk process list for sessions
   *		    ->siglock is taken to protect ->signal/->sighand

   */

  void disassociate_ctty(int on_exit)
  {
  	struct tty_struct *tty;

  	if (!current->signal->leader)
  		return;

  	tty = get_current_tty();

  	if (tty) {

  		struct pid *tty_pgrp = get_pid(tty->pgrp);

  		if (on_exit) {

  			if (tty->driver->type != TTY_DRIVER_TYPE_PTY)

  				tty_vhangup(tty);

  		}

  		tty_kref_put(tty);

  		if (tty_pgrp) {
  			kill_pgrp(tty_pgrp, SIGHUP, on_exit);
  			if (!on_exit)
  				kill_pgrp(tty_pgrp, SIGCONT, on_exit);
  			put_pid(tty_pgrp);
  		}

  	} else if (on_exit) {

  		struct pid *old_pgrp;

  		spin_lock_irq(&current->sighand->siglock);
  		old_pgrp = current->signal->tty_old_pgrp;

  		current->signal->tty_old_pgrp = NULL;

  		spin_unlock_irq(&current->sighand->siglock);

  		if (old_pgrp) {

  			kill_pgrp(old_pgrp, SIGHUP, on_exit);
  			kill_pgrp(old_pgrp, SIGCONT, on_exit);
  			put_pid(old_pgrp);

  		}

  		return;
  	}

  	spin_lock_irq(&current->sighand->siglock);

  	put_pid(current->signal->tty_old_pgrp);

  	current->signal->tty_old_pgrp = NULL;

  	spin_unlock_irq(&current->sighand->siglock);

  	tty = get_current_tty();
  	if (tty) {

  		unsigned long flags;
  		spin_lock_irqsave(&tty->ctrl_lock, flags);

  		put_pid(tty->session);
  		put_pid(tty->pgrp);
  		tty->session = NULL;
  		tty->pgrp = NULL;

  		spin_unlock_irqrestore(&tty->ctrl_lock, flags);

  		tty_kref_put(tty);

  	} else {
  #ifdef TTY_DEBUG_HANGUP
  		printk(KERN_DEBUG "error attempted to write to tty [0x%p]"
  		       " = NULL", tty);
  #endif
  	}

  
  	/* Now clear signal->tty under the lock */
  	read_lock(&tasklist_lock);

  	session_clear_tty(task_session(current));

  	read_unlock(&tasklist_lock);

  }

  /**
   *
   *	no_tty	- Ensure the current process does not have a controlling tty
   */
  void no_tty(void)
  {
  	struct task_struct *tsk = current;

  	tty_lock();

  	disassociate_ctty(0);

  	tty_unlock();

  	proc_clear_tty(tsk);
  }

  
  /**

   *	stop_tty	-	propagate flow control

   *	@tty: tty to stop
   *
   *	Perform flow control to the driver. For PTY/TTY pairs we

   *	must also propagate the TIOCKPKT status. May be called

   *	on an already stopped device and will not re-call the driver
   *	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:

   *		Uses the tty control lock internally

   */

  void stop_tty(struct tty_struct *tty)
  {

  	unsigned long flags;
  	spin_lock_irqsave(&tty->ctrl_lock, flags);
  	if (tty->stopped) {
  		spin_unlock_irqrestore(&tty->ctrl_lock, flags);

  		return;

  	}

  	tty->stopped = 1;
  	if (tty->link && tty->link->packet) {
  		tty->ctrl_status &= ~TIOCPKT_START;
  		tty->ctrl_status |= TIOCPKT_STOP;

  		wake_up_interruptible_poll(&tty->link->read_wait, POLLIN);

  	}

  	spin_unlock_irqrestore(&tty->ctrl_lock, flags);

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

  }
  
  EXPORT_SYMBOL(stop_tty);

  /**

   *	start_tty	-	propagate flow control

   *	@tty: tty to start
   *
   *	Start a tty that has been stopped if at all possible. Perform

   *	any necessary wakeups and propagate the TIOCPKT status. If this

   *	is the tty was previous stopped and is being started then the
   *	driver start method is invoked and the line discipline woken.
   *
   *	Locking:

   *		ctrl_lock

   */

  void start_tty(struct tty_struct *tty)
  {

  	unsigned long flags;
  	spin_lock_irqsave(&tty->ctrl_lock, flags);
  	if (!tty->stopped || tty->flow_stopped) {
  		spin_unlock_irqrestore(&tty->ctrl_lock, flags);

  		return;

  	}

  	tty->stopped = 0;
  	if (tty->link && tty->link->packet) {
  		tty->ctrl_status &= ~TIOCPKT_STOP;
  		tty->ctrl_status |= TIOCPKT_START;

  		wake_up_interruptible_poll(&tty->link->read_wait, POLLIN);

  	}

  	spin_unlock_irqrestore(&tty->ctrl_lock, flags);

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

  	/* If we have a running line discipline it may need kicking */
  	tty_wakeup(tty);

  }
  
  EXPORT_SYMBOL(start_tty);

  /**
   *	tty_read	-	read method for tty device files
   *	@file: pointer to tty file
   *	@buf: user buffer
   *	@count: size of user buffer
   *	@ppos: unused
   *
   *	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 file *file, char __user *buf, size_t count,

  			loff_t *ppos)
  {
  	int i;

  	struct inode *inode = file->f_path.dentry->d_inode;
  	struct tty_struct *tty = file_tty(file);

  	struct tty_ldisc *ld;

  	if (tty_paranoia_check(tty, inode, "tty_read"))
  		return -EIO;
  	if (!tty || (test_bit(TTY_IO_ERROR, &tty->flags)))
  		return -EIO;
  
  	/* We want to wait for the line discipline to sort out in this
  	   situation */
  	ld = tty_ldisc_ref_wait(tty);

  	if (ld->ops->read)
  		i = (ld->ops->read)(tty, file, buf, count);

  	else
  		i = -EIO;
  	tty_ldisc_deref(ld);

  	if (i > 0)
  		inode->i_atime = current_fs_time(inode->i_sb);
  	return i;
  }

  void tty_write_unlock(struct tty_struct *tty)

  	__releases(&tty->atomic_write_lock)

  {
  	mutex_unlock(&tty->atomic_write_lock);

  	wake_up_interruptible_poll(&tty->write_wait, POLLOUT);

  }
  
  int tty_write_lock(struct tty_struct *tty, int ndelay)

  	__acquires(&tty->atomic_write_lock)

  {
  	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,
  	const char __user *buf,
  	size_t count)
  {

  	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.

  	 *
  	 * FIXME: This can probably go away now except that 64K chunks
  	 * are too likely to fail unless switched to vmalloc...

  	 */
  	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 = kmalloc(chunk, GFP_KERNEL);
  		if (!buf_chunk) {

  			ret = -ENOMEM;
  			goto out;

  		}
  		kfree(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_user(tty->write_buf, buf, size))
  			break;

  		ret = write(tty, file, tty->write_buf, size);

  		if (ret <= 0)
  			break;
  		written += ret;
  		buf += ret;
  		count -= ret;
  		if (!count)
  			break;
  		ret = -ERESTARTSYS;
  		if (signal_pending(current))
  			break;
  		cond_resched();
  	}
  	if (written) {

  		struct inode *inode = file->f_path.dentry->d_inode;

  		inode->i_mtime = current_fs_time(inode->i_sb);
  		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();

  		if (tty->ops->write && !test_bit(TTY_CLOSING, &tty->flags)) {

  			tty_unlock();

  			tty->ops->write(tty, msg, strlen(msg));

  		} else

  			tty_unlock();

  		tty_write_unlock(tty);
  	}

  	return;
  }

  /**
   *	tty_write		-	write method for tty device file
   *	@file: tty file pointer
   *	@buf: user data to write
   *	@count: bytes to write
   *	@ppos: unused
   *
   *	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 file *file, const char __user *buf,
  						size_t count, loff_t *ppos)

  {

  	struct inode *inode = file->f_path.dentry->d_inode;

  	struct tty_struct *tty = file_tty(file);
   	struct tty_ldisc *ld;

  	ssize_t ret;

  	if (tty_paranoia_check(tty, inode, "tty_write"))
  		return -EIO;

  	if (!tty || !tty->ops->write ||

  		(test_bit(TTY_IO_ERROR, &tty->flags)))
  			return -EIO;

  	/* Short term debug to catch buggy drivers */
  	if (tty->ops->write_room == NULL)
  		printk(KERN_ERR "tty driver %s lacks a write_room method.
  ",
  			tty->driver->name);

  	ld = tty_ldisc_ref_wait(tty);

  	if (!ld->ops->write)

  		ret = -EIO;
  	else

  		ret = do_tty_write(ld->ops->write, tty, file, buf, count);

  	tty_ldisc_deref(ld);
  	return ret;
  }

  ssize_t redirected_tty_write(struct file *file, const char __user *buf,
  						size_t count, loff_t *ppos)

  {
  	struct file *p = NULL;
  
  	spin_lock(&redirect_lock);
  	if (redirect) {
  		get_file(redirect);
  		p = redirect;
  	}
  	spin_unlock(&redirect_lock);
  
  	if (p) {
  		ssize_t res;
  		res = vfs_write(p, buf, count, &p->f_pos);
  		fput(p);
  		return res;
  	}

  	return tty_write(file, buf, count, ppos);
  }
  
  static char ptychar[] = "pqrstuvwxyzabcde";

  /**
   *	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.
   *
   *	Locking: None
   */
  static void pty_line_name(struct tty_driver *driver, int index, char *p)

  {
  	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.
   *
   *	Locking: None
   */
  static void tty_line_name(struct tty_driver *driver, int index, char *p)

  {
  	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
   *	@idx:	 the minor number

   *

   *	Return the tty, if found or ERR_PTR() otherwise.

   *

   *	Locking: tty_mutex must be held. If tty is found, the mutex must
   *	be held until the 'fast-open' is also done. Will change once we
   *	have refcounting in the driver and per driver locking

   */

  static struct tty_struct *tty_driver_lookup_tty(struct tty_driver *driver,

  		struct inode *inode, int idx)

  {
  	struct tty_struct *tty;

  	if (driver->ops->lookup)

  		return driver->ops->lookup(driver, inode, idx);

  	tty = driver->ttys[idx];

  	return tty;
  }

  /**

   *	tty_init_termios	-  helper for termios setup
   *	@tty: the tty to set up
   *
   *	Initialise the termios structures for this tty. Thus runs under
   *	the tty_mutex currently so we can be relaxed about ordering.
   */
  
  int tty_init_termios(struct tty_struct *tty)
  {

  	struct ktermios *tp;

  	int idx = tty->index;
  
  	tp = tty->driver->termios[idx];

  	if (tp == NULL) {

  		tp = kzalloc(sizeof(struct ktermios[2]), GFP_KERNEL);
  		if (tp == NULL)

  			return -ENOMEM;

  		memcpy(tp, &tty->driver->init_termios,
  						sizeof(struct ktermios));
  		tty->driver->termios[idx] = tp;

  	}
  	tty->termios = tp;

  	tty->termios_locked = tp + 1;

  
  	/* 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);
  	return 0;
  }

  EXPORT_SYMBOL_GPL(tty_init_termios);

  
  /**

   *	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)
  {

  	int idx = tty->index;

  	int ret;

  	if (driver->ops->install) {

  		ret = driver->ops->install(driver, tty);

  		return ret;
  	}

  
  	if (tty_init_termios(tty) == 0) {
  		tty_driver_kref_get(driver);
  		tty->count++;
  		driver->ttys[idx] = tty;
  		return 0;
  	}
  	return -ENOMEM;

  }
  
  /**
   *	tty_driver_remove_tty() - remove a tty from the driver tables
   *	@driver: the driver for the tty
   *	@idx:	 the minor number
   *
   *	Remvoe 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
   */

  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

   *

   *	Return 0 on success, -errno on error.

   *

   *	Locking: tty_mutex must be held from the time the tty was found
   *		 till this open completes.

   */

  static int tty_reopen(struct tty_struct *tty)

  {
  	struct tty_driver *driver = tty->driver;

  	if (test_bit(TTY_CLOSING, &tty->flags) ||

  			test_bit(TTY_HUPPING, &tty->flags) ||

  			test_bit(TTY_LDISC_CHANGING, &tty->flags))

  		return -EIO;
  
  	if (driver->type == TTY_DRIVER_TYPE_PTY &&
  	    driver->subtype == PTY_TYPE_MASTER) {
  		/*
  		 * special case for PTY masters: only one open permitted,
  		 * and the slave side open count is incremented as well.
  		 */
  		if (tty->count)
  			return -EIO;
  
  		tty->link->count++;
  	}
  	tty->count++;
  	tty->driver = driver; /* N.B. why do this every time?? */

  	mutex_lock(&tty->ldisc_mutex);

  	WARN_ON(!test_bit(TTY_LDISC, &tty->flags));

  	mutex_unlock(&tty->ldisc_mutex);

  
  	return 0;
  }

  /**

   *	tty_init_dev		-	initialise a tty device

   *	@driver: tty driver we are opening a device on
   *	@idx: device index

   *	@ret_tty: returned tty structure
   *	@first_ok: ok to open a new device (used by ptmx)

   *
   *	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.
   */

  struct tty_struct *tty_init_dev(struct tty_driver *driver, int idx,
  								int first_ok)

  {

  	struct tty_struct *tty;

  	int retval;

  	/* Check if pty master is being opened multiple times */

  	if (driver->subtype == PTY_TYPE_MASTER &&

  		(driver->flags & TTY_DRIVER_DEVPTS_MEM) && !first_ok) {

  		return ERR_PTR(-EIO);

  	}

  	/*
  	 * 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

  	 * and locked termios may be retained.)
  	 */

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

  	tty = alloc_tty_struct();

  	if (!tty) {
  		retval = -ENOMEM;
  		goto err_module_put;
  	}

  	initialize_tty_struct(tty, driver, idx);

  	retval = tty_driver_install_tty(driver, tty);

  	if (retval < 0)

  		goto err_deinit_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;

  	return tty;

  err_deinit_tty:
  	deinitialize_tty_struct(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:

  	printk_ratelimited(KERN_INFO "tty_init_dev: ldisc open failed, "

  				 "clearing slot %d
  ", idx);

  	release_tty(tty, idx);

  	return ERR_PTR(retval);

  }

  void tty_free_termios(struct tty_struct *tty)
  {
  	struct ktermios *tp;
  	int idx = tty->index;
  	/* Kill this flag and push into drivers for locking etc */
  	if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS) {
  		/* FIXME: Locking on ->termios array */
  		tp = tty->termios;
  		tty->driver->termios[idx] = NULL;
  		kfree(tp);

  	}
  }
  EXPORT_SYMBOL(tty_free_termios);
  
  void tty_shutdown(struct tty_struct *tty)
  {

  	tty_driver_remove_tty(tty->driver, tty);

  	tty_free_termios(tty);
  }
  EXPORT_SYMBOL(tty_shutdown);

  /**

   *	release_one_tty		-	release tty structure memory

   *	@kref: kref 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:
   *		tty_mutex - sometimes only
   *		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;

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

  	tty->magic = 0;

  	tty_driver_kref_put(driver);

  	module_put(driver->owner);

  	spin_lock(&tty_files_lock);

  	list_del_init(&tty->tty_files);

  	spin_unlock(&tty_files_lock);

  	put_pid(tty->pgrp);
  	put_pid(tty->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);

  
  	if (tty->ops->shutdown)
  		tty->ops->shutdown(tty);
  	else
  		tty_shutdown(tty);

  	/* 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 a 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
   *
   *	Release both @tty and a possible linked partner (think pty pair),
   *	and decrement the refcount of the backing module.
   *
   *	Locking:
   *		tty_mutex - sometimes only
   *		takes the file list lock internally when working on the list
   *	of ttys that the driver keeps.
   *		FIXME: should we require tty_mutex is held here ??

   *

   */
  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);

  	if (tty->link)

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

  }

  /**

   *	tty_release_checks - check a tty before real release
   *	@tty: tty to check
   *	@o_tty: link of @tty (if any)
   *	@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, struct tty_struct *o_tty,
  		int idx)
  {
  #ifdef TTY_PARANOIA_CHECK
  	if (idx < 0 || idx >= tty->driver->num) {

  		printk(KERN_DEBUG "%s: bad idx when trying to free (%s)
  ",
  				__func__, tty->name);

  		return -1;
  	}
  
  	/* not much to check for devpts */
  	if (tty->driver->flags & TTY_DRIVER_DEVPTS_MEM)
  		return 0;
  
  	if (tty != tty->driver->ttys[idx]) {

  		printk(KERN_DEBUG "%s: driver.table[%d] not tty for (%s)
  ",
  				__func__, idx, tty->name);

  		return -1;
  	}
  	if (tty->termios != tty->driver->termios[idx]) {

  		printk(KERN_DEBUG "%s: driver.termios[%d] not termios for (%s)
  ",
  				__func__, idx, tty->name);

  		return -1;
  	}
  	if (tty->driver->other) {
  		if (o_tty != tty->driver->other->ttys[idx]) {

  			printk(KERN_DEBUG "%s: other->table[%d] not o_tty for (%s)
  ",
  					__func__, idx, tty->name);

  			return -1;
  		}
  		if (o_tty->termios != tty->driver->other->termios[idx]) {

  			printk(KERN_DEBUG "%s: other->termios[%d] not o_termios for (%s)
  ",
  					__func__, idx, tty->name);

  			return -1;
  		}
  		if (o_tty->link != tty) {

  			printk(KERN_DEBUG "%s: bad pty pointers
  ", __func__);

  			return -1;
  		}
  	}
  #endif
  	return 0;
  }
  
  /**

   *	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;

  	int	pty_master, tty_closing, o_tty_closing, do_sleep;

  	int	devpts;

  	int	idx;
  	char	buf[64];

  	if (tty_paranoia_check(tty, inode, __func__))

  		return 0;

  	tty_lock();

  	check_tty_count(tty, __func__);

  	__tty_fasync(-1, filp, 0);

  
  	idx = tty->index;
  	pty_master = (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
  		      tty->driver->subtype == PTY_TYPE_MASTER);
  	devpts = (tty->driver->flags & TTY_DRIVER_DEVPTS_MEM) != 0;

  	o_tty = tty->link;

  	if (tty_release_checks(tty, o_tty, idx)) {

  		tty_unlock();

  		return 0;

  	}

  
  #ifdef TTY_DEBUG_HANGUP

  	printk(KERN_DEBUG "%s: %s (tty count=%d)...
  ", __func__,
  			tty_name(tty, buf), tty->count);

  #endif

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

  	tty_unlock();

  	/*
  	 * 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 closes,
  	 * so we do it now.
  	 *
  	 * Note that it's possible for the tty to be opened again while we're
  	 * flushing out waiters.  By recalculating the closing flags before
  	 * each iteration we avoid any problems.
  	 */
  	while (1) {
  		/* Guard against races with tty->count changes elsewhere and
  		   opens on /dev/tty */

  		mutex_lock(&tty_mutex);

  		tty_lock();

  		tty_closing = tty->count <= 1;
  		o_tty_closing = o_tty &&
  			(o_tty->count <= (pty_master ? 1 : 0));

  		do_sleep = 0;
  
  		if (tty_closing) {
  			if (waitqueue_active(&tty->read_wait)) {

  				wake_up_poll(&tty->read_wait, POLLIN);

  				do_sleep++;
  			}
  			if (waitqueue_active(&tty->write_wait)) {

  				wake_up_poll(&tty->write_wait, POLLOUT);

  				do_sleep++;
  			}
  		}
  		if (o_tty_closing) {
  			if (waitqueue_active(&o_tty->read_wait)) {

  				wake_up_poll(&o_tty->read_wait, POLLIN);

  				do_sleep++;
  			}
  			if (waitqueue_active(&o_tty->write_wait)) {

  				wake_up_poll(&o_tty->write_wait, POLLOUT);

  				do_sleep++;
  			}
  		}
  		if (!do_sleep)
  			break;

  		printk(KERN_WARNING "%s: %s: read/write wait queue active!
  ",
  				__func__, tty_name(tty, buf));

  		tty_unlock();

  		mutex_unlock(&tty_mutex);

  		schedule();

  	}

  
  	/*

  	 * The closing flags are now consistent with the open counts on
  	 * both sides, and we've completed the last operation that could

  	 * block, so it's safe to proceed with closing.
  	 */

  	if (pty_master) {
  		if (--o_tty->count < 0) {

  			printk(KERN_WARNING "%s: bad pty slave count (%d) for %s
  ",
  				__func__, o_tty->count, tty_name(o_tty, buf));

  			o_tty->count = 0;
  		}
  	}
  	if (--tty->count < 0) {

  		printk(KERN_WARNING "%s: bad tty->count (%d) for %s
  ",
  				__func__, tty->count, tty_name(tty, buf));

  		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.
  	 *
  	 * Set the TTY_CLOSING flag if this was the last open.  In the
  	 * case of a pty we may have to wait around for the other side
  	 * to close, and TTY_CLOSING makes sure we can't be reopened.
  	 */

  	if (tty_closing)

  		set_bit(TTY_CLOSING, &tty->flags);