text: /*
   *  linux/drivers/char/tty_io.c
   *
   *  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/smp_lock.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/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);
  
  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 *);
  static int tty_release(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 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)
  {
  	kfree(tty->write_buf);
  	tty_buffer_free_all(tty);
  	kfree(tty);
  }
  
  #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\n",
  			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\n",
  			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;
  
  	file_list_lock();
  	list_for_each(p, &tty->tty_files) {
  		count++;
  	}
  	file_list_unlock();
  	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\n",
  		       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!\n");
  		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);
  
  /**
   *	do_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:
   *		BKL
   *		  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
   */
  static void do_tty_hangup(struct work_struct *work)
  {
  	struct tty_struct *tty =
  		container_of(work, struct tty_struct, hangup_work);
  	struct file *cons_filp = NULL;
  	struct file *filp, *f = NULL;
  	struct task_struct *p;
  	int    closecount = 0, n;
  	unsigned long flags;
  	int refs = 0;
  
  	if (!tty)
  		return;
  
  	/* inuse_filps is protected by the single kernel lock */
  	lock_kernel();
  
  	spin_lock(&redirect_lock);
  	if (redirect && redirect->private_data == tty) {
  		f = redirect;
  		redirect = NULL;
  	}
  	spin_unlock(&redirect_lock);
  
  	check_tty_count(tty, "do_tty_hangup");
  	file_list_lock();
  	/* This breaks for file handles being sent over AF_UNIX sockets ? */
  	list_for_each_entry(filp, &tty->tty_files, f_u.fu_list) {
  		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;
  	}
  	file_list_unlock();
  
  	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;
  	set_bit(TTY_HUPPED, &tty->flags);
  	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);
  	tty_ldisc_enable(tty);
  	unlock_kernel();
  	if (f)
  		fput(f);
  }
  
  /**
   *	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...\n", 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...\n", tty_name(tty, buf));
  #endif
  	do_tty_hangup(&tty->hangup_work);
  }
  
  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:
   *		BKL is taken for hysterical raisins
   *		  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;
  	struct pid *tty_pgrp = NULL;
  
  
  	tty = get_current_tty();
  	if (tty) {
  		tty_pgrp = get_pid(tty->pgrp);
  		lock_kernel();
  		if (on_exit && tty->driver->type != TTY_DRIVER_TYPE_PTY)
  			tty_vhangup(tty);
  		unlock_kernel();
  		tty_kref_put(tty);
  	} 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;
  	}
  	if (tty_pgrp) {
  		kill_pgrp(tty_pgrp, SIGHUP, on_exit);
  		if (!on_exit)
  			kill_pgrp(tty_pgrp, SIGCONT, on_exit);
  		put_pid(tty_pgrp);
  	}
  
  	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;
  	lock_kernel();
  	if (tsk->signal->leader)
  		disassociate_ctty(0);
  	unlock_kernel();
  	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 tty_struct *tty;
  	struct inode *inode;
  	struct tty_ldisc *ld;
  
  	tty = (struct tty_struct *)file->private_data;
  	inode = file->f_path.dentry->d_inode;
  	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)
  {
  	mutex_unlock(&tty->atomic_write_lock);
  	wake_up_interruptible_poll(&tty->write_wait, POLLOUT);
  }
  
  int tty_write_lock(struct tty_struct *tty, int ndelay)
  {
  	if (!mutex_trylock(&tty->atomic_write_lock)) {
  		if (ndelay)
  			return -EAGAIN;
  		if (mutex_lock_interruptible(&tty->atomic_write_lock))
  			return -ERESTARTSYS;
  	}
  	return 0;
  }
  
  /*
   * Split writes up in sane blocksizes to avoid
   * denial-of-service type attacks
   */
  static inline ssize_t do_tty_write(
  	ssize_t (*write)(struct tty_struct *, struct file *, const unsigned char *, size_t),
  	struct tty_struct *tty,
  	struct file *file,
  	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 BKL and test the CLOSING flag for the moment.
   */
  
  void tty_write_message(struct tty_struct *tty, char *msg)
  {
  	lock_kernel();
  	if (tty) {
  		mutex_lock(&tty->atomic_write_lock);
  		if (tty->ops->write && !test_bit(TTY_CLOSING, &tty->flags))
  			tty->ops->write(tty, msg, strlen(msg));
  		tty_write_unlock(tty);
  	}
  	unlock_kernel();
  	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 tty_struct *tty;
  	struct inode *inode = file->f_path.dentry->d_inode;
  	ssize_t ret;
  	struct tty_ldisc *ld;
  
  	tty = (struct tty_struct *)file->private_data;
  	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.\n",
  			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;
  
  	if (driver->ops->install)
  		return driver->ops->install(driver, tty);
  
  	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
   */
  static void tty_driver_remove_tty(struct tty_driver *driver,
  						struct tty_struct *tty)
  {
  	if (driver->ops->remove)
  		driver->ops->remove(driver, tty);
  	else
  		driver->ttys[tty->index] = NULL;
  }
  
  /*
   * 	tty_reopen()	- fast re-open of an open tty
   * 	@tty	- the tty to open
   *
   *	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))
  		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)
  		goto fail_no_mem;
  	initialize_tty_struct(tty, driver, idx);
  
  	retval = tty_driver_install_tty(driver, tty);
  	if (retval < 0) {
  		free_tty_struct(tty);
  		module_put(driver->owner);
  		return ERR_PTR(retval);
  	}
  
  	/*
  	 * 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 release_mem_out;
  	return tty;
  
  fail_no_mem:
  	module_put(driver->owner);
  	return ERR_PTR(-ENOMEM);
  
  	/* call the tty release_tty routine to clean out this slot */
  release_mem_out:
  	if (printk_ratelimit())
  		printk(KERN_INFO "tty_init_dev: ldisc open failed, "
  				 "clearing slot %d\n", 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);
  
  	file_list_lock();
  	list_del_init(&tty->tty_files);
  	file_list_unlock();
  
  	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);
  }
  
  /*
   * 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.
   */
  void tty_release_dev(struct file *filp)
  {
  	struct tty_struct *tty, *o_tty;
  	int	pty_master, tty_closing, o_tty_closing, do_sleep;
  	int	devpts;
  	int	idx;
  	char	buf[64];
  	long	timeout = 0;
  	struct 	inode *inode;
  
  	inode = filp->f_path.dentry->d_inode;
  	tty = (struct tty_struct *)filp->private_data;
  	if (tty_paranoia_check(tty, inode, "tty_release_dev"))
  		return;
  
  	check_tty_count(tty, "tty_release_dev");
  
  	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;
  
  #ifdef TTY_PARANOIA_CHECK
  	if (idx < 0 || idx >= tty->driver->num) {
  		printk(KERN_DEBUG "tty_release_dev: bad idx when trying to "
  				  "free (%s)\n", tty->name);
  		return;
  	}
  	if (!devpts) {
  		if (tty != tty->driver->ttys[idx]) {
  			printk(KERN_DEBUG "tty_release_dev: driver.table[%d] not tty "
  			       "for (%s)\n", idx, tty->name);
  			return;
  		}
  		if (tty->termios != tty->driver->termios[idx]) {
  			printk(KERN_DEBUG "tty_release_dev: driver.termios[%d] not termios "
  			       "for (%s)\n",
  			       idx, tty->name);
  			return;
  		}
  	}
  #endif
  
  #ifdef TTY_DEBUG_HANGUP
  	printk(KERN_DEBUG "tty_release_dev of %s (tty count=%d)...",
  	       tty_name(tty, buf), tty->count);
  #endif
  
  #ifdef TTY_PARANOIA_CHECK
  	if (tty->driver->other &&
  	     !(tty->driver->flags & TTY_DRIVER_DEVPTS_MEM)) {
  		if (o_tty != tty->driver->other->ttys[idx]) {
  			printk(KERN_DEBUG "tty_release_dev: other->table[%d] "
  					  "not o_tty for (%s)\n",
  			       idx, tty->name);
  			return;
  		}
  		if (o_tty->termios != tty->driver->other->termios[idx]) {
  			printk(KERN_DEBUG "tty_release_dev: other->termios[%d] "
  					  "not o_termios for (%s)\n",
  			       idx, tty->name);
  			return;
  		}
  		if (o_tty->link != tty) {
  			printk(KERN_DEBUG "tty_release_dev: bad pty pointers\n");
  			return;
  		}
  	}
  #endif
  	if (tty->ops->close)
  		tty->ops->close(tty, filp);
  
  	/*
  	 * 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_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 "tty_release_dev: %s: read/write wait queue "
  				    "active!\n", tty_name(tty, buf));
  		mutex_unlock(&tty_mutex);
  		schedule_timeout_killable(timeout);
  		if (timeout < 120 * HZ)
  			timeout = 2 * timeout + 1;
  		else
  			timeout = MAX_SCHEDULE_TIMEOUT;
  	}
  
  	/*
  	 * 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 "tty_release_dev: bad pty slave count "
  					    "(%d) for %s\n",
  			       o_tty->count, tty_name(o_tty, buf));
  			o_tty->count = 0;
  		}
  	}
  	if (--tty->count < 0) {
  		printk(KERN_WARNING "tty_release_dev: bad tty->count (%d) for %s\n",
  		       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.
  	 */
  	file_kill(filp);
  	filp->private_data = NULL;
  
  	/*
  	 * 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);
  	if (o_tty_closing)
  		set_bit(TTY_CLOSING, &o_tty->flags);
  
  	/*
  	 * If _either_ side is closing, make sure there aren't any
  	 * processes that still think tty or o_tty is their controlling
  	 * tty.
  	 */
  	if (tty_closing || o_tty_closing) {
  		read_lock(&tasklist_lock);
  		session_clear_tty(tty->session);
  		if (o_tty)
  			session_clear_tty(o_tty->session);
  		read_unlock(&tasklist_lock);
  	}
  
  	mutex_unlock(&tty_mutex);
  
  	/* check whether both sides are closing ... */
  	if (!tty_closing || (o_tty && !o_tty_closing))
  		return;
  
  #ifdef TTY_DEBUG_HANGUP
  	printk(KERN_DEBUG "freeing tty structure...");
  #endif
  	/*
  	 * Ask the line discipline code to release its structures
  	 */
  	tty_ldisc_release(tty, o_tty);
  	/*
  	 * The release_tty function takes care of the details of clearing
  	 * the slots and preserving the termios structure.
  	 */
  	release_tty(tty, idx);
  
  	/* Make this pty number available for reallocation */
  	if (devpts)
  		devpts_kill_index(inode, idx);
  }
  
  /**
   *	__tty_open		-	open a tty device
   *	@inode: inode of device file
   *	@filp: file pointer to tty
   *
   *	tty_open and tty_release keep up the tty count that contains the
   *	number of opens done on a tty. We cannot use the inode-count, as
   *	different inodes might point to the same tty.
   *
   *	Open-counting is needed for pty masters, as well as for keeping
   *	track of serial lines: DTR is dropped when the last close happens.
   *	(This is not done solely through tty->count, now.  - Ted 1/27/92)
   *
   *	The termios state of a pty is reset on first open so that
   *	settings don't persist across reuse.
   *
   *	Locking: tty_mutex protects tty, get_tty_driver and tty_init_dev work.
   *		 tty->count should protect the rest.
   *		 ->siglock protects ->signal/->sighand
   */
  
  static int __tty_open(struct inode *inode, struct file *filp)
  {
  	struct tty_struct *tty = NULL;
  	int noctty, retval;
  	struct tty_driver *driver;
  	int index;
  	dev_t device = inode->i_rdev;
  	unsigned saved_flags = filp->f_flags;
  
  	nonseekable_open(inode, filp);
  
  retry_open:
  	noctty = filp->f_flags & O_NOCTTY;
  	index  = -1;
  	retval = 0;
  
  	mutex_lock(&tty_mutex);
  
  	if (device == MKDEV(TTYAUX_MAJOR, 0)) {
  		tty = get_current_tty();
  		if (!tty) {
  			mutex_unlock(&tty_mutex);
  			return -ENXIO;
  		}
  		driver = tty_driver_kref_get(tty->driver);
  		index = tty->index;
  		filp->f_flags |= O_NONBLOCK; /* Don't let /dev/tty block */
  		/* noctty = 1; */
  		/* FIXME: Should we take a driver reference ? */
  		tty_kref_put(tty);
  		goto got_driver;
  	}
  #ifdef CONFIG_VT
  	if (device == MKDEV(TTY_MAJOR, 0)) {
  		extern struct tty_driver *console_driver;
  		driver = tty_driver_kref_get(console_driver);
  		index = fg_console;
  		noctty = 1;
  		goto got_driver;
  	}
  #endif
  	if (device == MKDEV(TTYAUX_MAJOR, 1)) {
  		struct tty_driver *console_driver = console_device(&index);
  		if (console_driver) {
  			driver = tty_driver_kref_get(console_driver);
  			if (driver) {
  				/* Don't let /dev/console block */
  				filp->f_flags |= O_NONBLOCK;
  				noctty = 1;
  				goto got_driver;
  			}
  		}
  		mutex_unlock(&tty_mutex);
  		return -ENODEV;
  	}
  
  	driver = get_tty_driver(device, &index);
  	if (!driver) {
  		mutex_unlock(&tty_mutex);
  		return -ENODEV;
  	}
  got_driver:
  	if (!tty) {
  		/* check whether we're reopening an existing tty */
  		tty = tty_driver_lookup_tty(driver, inode, index);
  
  		if (IS_ERR(tty)) {
  			mutex_unlock(&tty_mutex);
  			tty_driver_kref_put(driver);
  			return PTR_ERR(tty);
  		}
  	}
  
  	if (tty) {
  		retval = tty_reopen(tty);
  		if (retval)
  			tty = ERR_PTR(retval);
  	} else
  		tty = tty_init_dev(driver, index, 0);
  
  	mutex_unlock(&tty_mutex);
  	tty_driver_kref_put(driver);
  	if (IS_ERR(tty))
  		return PTR_ERR(tty);
  
  	filp->private_data = tty;
  	file_move(filp, &tty->tty_files);
  	check_tty_count(tty, "tty_open");
  	if (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
  	    tty->driver->subtype == PTY_TYPE_MASTER)
  		noctty = 1;
  #ifdef TTY_DEBUG_HANGUP
  	printk(KERN_DEBUG "opening %s...", tty->name);
  #endif
  	if (!retval) {
  		if (tty->ops->open)
  			retval = tty->ops->open(tty, filp);
  		else
  			retval = -ENODEV;
  	}
  	filp->f_flags = saved_flags;
  
  	if (!retval && test_bit(TTY_EXCLUSIVE, &tty->flags) &&
  						!capable(CAP_SYS_ADMIN))
  		retval = -EBUSY;
  
  	if (retval) {
  #ifdef TTY_DEBUG_HANGUP
  		printk(KERN_DEBUG "error %d in opening %s...", retval,
  		       tty->name);
  #endif
  		tty_release_dev(filp);
  		if (retval != -ERESTARTSYS)
  			return retval;
  		if (signal_pending(current))
  			return retval;
  		schedule();
  		/*
  		 * Need to reset f_op in case a hangup happened.
  		 */
  		if (filp->f_op == &hung_up_tty_fops)
  			filp->f_op = &tty_fops;
  		goto retry_open;
  	}
  
  	mutex_lock(&tty_mutex);
  	spin_lock_irq(&current->sighand->siglock);
  	if (!noctty &&
  	    current->signal->leader &&
  	    !current->signal->tty &&
  	    tty->session == NULL)
  		__proc_set_tty(current, tty);
  	spin_unlock_irq(&current->sighand->siglock);
  	mutex_unlock(&tty_mutex);
  	return 0;
  }
  
  /* BKL pushdown: scary code avoidance wrapper */
  static int tty_open(struct inode *inode, struct file *filp)
  {
  	int ret;
  
  	lock_kernel();
  	ret = __tty_open(inode, filp);
  	unlock_kernel();
  	return ret;
  }
  
  
  
  
  /**
   *	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
   */
  
  static int tty_release(struct inode *inode, struct file *filp)
  {
  	lock_kernel();
  	tty_release_dev(filp);
  	unlock_kernel();
  	return 0;
  }
  
  /**
   *	tty_poll	-	check tty status
   *	@filp: file being polled
   *	@wait: poll wait structures to update
   *
   *	Call the line discipline polling method to obtain the poll
   *	status of the device.
   *
   *	Locking: locks called line discipline but ldisc poll method
   *	may be re-entered freely by other callers.
   */
  
  static unsigned int tty_poll(struct file *filp, poll_table *wait)
  {
  	struct tty_struct *tty;
  	struct tty_ldisc *ld;
  	int ret = 0;
  
  	tty = (struct tty_struct *)filp->private_data;
  	if (tty_paranoia_check(tty, filp->f_path.dentry->d_inode, "tty_poll"))
  		return 0;
  
  	ld = tty_ldisc_ref_wait(tty);
  	if (ld->ops->poll)
  		ret = (ld->ops->poll)(tty, filp, wait);
  	tty_ldisc_deref(ld);
  	return ret;
  }
  
  static int tty_fasync(int fd, struct file *filp, int on)
  {
  	struct tty_struct *tty;
  	unsigned long flags;
  	int retval = 0;
  
  	lock_kernel();
  	tty = (struct tty_struct *)filp->private_data;
  	if (tty_paranoia_check(tty, filp->f_path.dentry->d_inode, "tty_fasync"))
  		goto out;
  
  	retval = fasync_helper(fd, filp, on, &tty->fasync);
  	if (retval <= 0)
  		goto out;
  
  	if (on) {
  		enum pid_type type;
  		struct pid *pid;
  		if (!waitqueue_active(&tty->read_wait))
  			tty->minimum_to_wake = 1;
  		spin_lock_irqsave(&tty->ctrl_lock, flags);
  		if (tty->pgrp) {
  			pid = tty->pgrp;
  			type = PIDTYPE_PGID;
  		} else {
  			pid = task_pid(current);
  			type = PIDTYPE_PID;
  		}
  		get_pid(pid);
  		spin_unlock_irqrestore(&tty->ctrl_lock, flags);
  		retval = __f_setown(filp, pid, type, 0);
  		put_pid(pid);
  		if (retval)
  			goto out;
  	} else {
  		if (!tty->fasync && !waitqueue_active(&tty->read_wait))
  			tty->minimum_to_wake = N_TTY_BUF_SIZE;
  	}
  	retval = 0;
  out:
  	unlock_kernel();
  	return retval;
  }
  
  /**
   *	tiocsti			-	fake input character
   *	@tty: tty to fake input into
   *	@p: pointer to character
   *
   *	Fake input to a tty device. Does the necessary locking and
   *	input management.
   *
   *	FIXME: does not honour flow control ??
   *
   *	Locking:
   *		Called functions take tty_ldisc_lock
   *		current->signal->tty check is safe without locks
   *
   *	FIXME: may race normal receive processing
   */
  
  static int tiocsti(struct tty_struct *tty, char __user *p)
  {
  	char ch, mbz = 0;
  	struct tty_ldisc *ld;
  
  	if ((current->signal->tty != tty) && !capable(CAP_SYS_ADMIN))
  		return -EPERM;
  	if (get_user(ch, p))
  		return -EFAULT;
  	tty_audit_tiocsti(tty, ch);
  	ld = tty_ldisc_ref_wait(tty);
  	ld->ops->receive_buf(tty, &ch, &mbz, 1);
  	tty_ldisc_deref(ld);
  	return 0;
  }
  
  /**
   *	tiocgwinsz		-	implement window query ioctl
   *	@tty; tty
   *	@arg: user buffer for result
   *
   *	Copies the kernel idea of the window size into the user buffer.
   *
   *	Locking: tty->termios_mutex is taken to ensure the winsize data
   *		is consistent.
   */
  
  static int tiocgwinsz(struct tty_struct *tty, struct winsize __user *arg)
  {
  	int err;
  
  	mutex_lock(&tty->termios_mutex);
  	err = copy_to_user(arg, &tty->winsize, sizeof(*arg));
  	mutex_unlock(&tty->termios_mutex);
  
  	return err ? -EFAULT: 0;
  }
  
  /**
   *	tty_do_resize		-	resize event
   *	@tty: tty being resized
   *	@rows: rows (character)
   *	@cols: cols (character)
   *
   *	Update the termios variables and send the neccessary signals to
   *	peform a terminal resize correctly
   */
  
  int tty_do_resize(struct tty_struct *tty, struct winsize *ws)
  {
  	struct pid *pgrp;
  	unsigned long flags;
  
  	/* Lock the tty */
  	mutex_lock(&tty->termios_mutex);
  	if (!memcmp(ws, &tty->winsize, sizeof(*ws)))
  		goto done;
  	/* Get the PID values and reference them so we can
  	   avoid holding the tty ctrl lock while sending signals */
  	spin_lock_irqsave(&tty->ctrl_lock, flags);
  	pgrp = get_pid(tty->pgrp);
  	spin_unlock_irqrestore(&tty->ctrl_lock, flags);
  
  	if (pgrp)
  		kill_pgrp(pgrp, SIGWINCH, 1);
  	put_pid(pgrp);
  
  	tty->winsize = *ws;
  done:
  	mutex_unlock(&tty->termios_mutex);
  	return 0;
  }
  
  /**
   *	tiocswinsz		-	implement window size set ioctl
   *	@tty; tty side of tty
   *	@arg: user buffer for result
   *
   *	Copies the user idea of the window size to the kernel. Traditionally
   *	this is just advisory information but for the Linux console it
   *	actually has driver level meaning and triggers a VC resize.
   *
   *	Locking:
   *		Driver dependant. The default do_resize method takes the
   *	tty termios mutex and ctrl_lock. The console takes its own lock
   *	then calls into the default method.
   */
  
  static int tiocswinsz(struct tty_struct *tty, struct winsize __user *arg)
  {
  	struct winsize tmp_ws;
  	if (copy_from_user(&tmp_ws, arg, sizeof(*arg)))
  		return -EFAULT;
  
  	if (tty->ops->resize)
  		return tty->ops->resize(tty, &tmp_ws);
  	else
  		return tty_do_resize(tty, &tmp_ws);
  }
  
  /**
   *	tioccons	-	allow admin to move logical console
   *	@file: the file to become console
   *
   *	Allow the adminstrator to move the redirected console device
   *
   *	Locking: uses redirect_lock to guard the redirect information
   */
  
  static int tioccons(struct file *file)
  {
  	if (!capable(CAP_SYS_ADMIN))
  		return -EPERM;
  	if (file->f_op->write == redirected_tty_write) {
  		struct file *f;
  		spin_lock(&redirect_lock);
  		f = redirect;
  		redirect = NULL;
  		spin_unlock(&redirect_lock);
  		if (f)
  			fput(f);
  		return 0;
  	}
  	spin_lock(&redirect_lock);
  	if (redirect) {
  		spin_unlock(&redirect_lock);
  		return -EBUSY;
  	}
  	get_file(file);
  	redirect = file;
  	spin_unlock(&redirect_lock);
  	return 0;
  }
  
  /**
   *	fionbio		-	non blocking ioctl
   *	@file: file to set blocking value
   *	@p: user parameter
   *
   *	Historical tty interfaces had a blocking control ioctl before
   *	the generic functionality existed. This piece of history is preserved
   *	in the expected tty API of posix OS's.
   *
   *	Locking: none, the open file handle ensures it won't go away.
   */
  
  static int fionbio(struct file *file, int __user *p)
  {
  	int nonblock;
  
  	if (get_user(nonblock, p))
  		return -EFAULT;
  
  	spin_lock(&file->f_lock);
  	if (nonblock)
  		file->f_flags |= O_NONBLOCK;
  	else
  		file->f_flags &= ~O_NONBLOCK;
  	spin_unlock(&file->f_lock);
  	return 0;
  }
  
  /**
   *	tiocsctty	-	set controlling tty
   *	@tty: tty structure
   *	@arg: user argument
   *
   *	This ioctl is used to manage job control. It permits a session
   *	leader to set this tty as the controlling tty for the session.
   *
   *	Locking:
   *		Takes tty_mutex() to protect tty instance
   *		Takes tasklist_lock internally to walk sessions
   *		Takes ->siglock() when updating signal->tty
   */
  
  static int tiocsctty(struct tty_struct *tty, int arg)
  {
  	int ret = 0;
  	if (current->signal->leader && (task_session(current) == tty->session))
  		return ret;
  
  	mutex_lock(&tty_mutex);
  	/*
  	 * The process must be a session leader and
  	 * not have a controlling tty already.
  	 */
  	if (!current->signal->leader || current->signal->tty) {
  		ret = -EPERM;
  		goto unlock;
  	}
  
  	if (tty->session) {
  		/*
  		 * This tty is already the controlling
  		 * tty for another session group!
  		 */
  		if (arg == 1 && capable(CAP_SYS_ADMIN)) {
  			/*
  			 * Steal it away
  			 */
  			read_lock(&tasklist_lock);
  			session_clear_tty(tty->session);
  			read_unlock(&tasklist_lock);
  		} else {
  			ret = -EPERM;
  			goto unlock;
  		}
  	}
  	proc_set_tty(current, tty);
  unlock:
  	mutex_unlock(&tty_mutex);
  	return ret;
  }
  
  /**
   *	tty_get_pgrp	-	return a ref counted pgrp pid
   *	@tty: tty to read
   *
   *	Returns a refcounted instance of the pid struct for the process
   *	group controlling the tty.
   */
  
  struct pid *tty_get_pgrp(struct tty_struct *tty)
  {
  	unsigned long flags;
  	struct pid *pgrp;
  
  	spin_lock_irqsave(&tty->ctrl_lock, flags);
  	pgrp = get_pid(tty->pgrp);
  	spin_unlock_irqrestore(&tty->ctrl_lock, flags);
  
  	return pgrp;
  }
  EXPORT_SYMBOL_GPL(tty_get_pgrp);
  
  /**
   *	tiocgpgrp		-	get process group
   *	@tty: tty passed by user
   *	@real_tty: tty side of the tty pased by the user if a pty else the tty
   *	@p: returned pid
   *
   *	Obtain the process group of the tty. If there is no process group
   *	return an error.
   *
   *	Locking: none. Reference to current->signal->tty is safe.
   */
  
  static int tiocgpgrp(struct tty_struct *tty, struct tty_struct *real_tty, pid_t __user *p)
  {
  	struct pid *pid;
  	int ret;
  	/*
  	 * (tty == real_tty) is a cheap way of
  	 * testing if the tty is NOT a master pty.
  	 */
  	if (tty == real_tty && current->signal->tty != real_tty)
  		return -ENOTTY;
  	pid = tty_get_pgrp(real_tty);
  	ret =  put_user(pid_vnr(pid), p);
  	put_pid(pid);
  	return ret;
  }
  
  /**
   *	tiocspgrp		-	attempt to set process group
   *	@tty: tty passed by user
   *	@real_tty: tty side device matching tty passed by user
   *	@p: pid pointer
   *
   *	Set the process group of the tty to the session passed. Only
   *	permitted where the tty session is our session.
   *
   *	Locking: RCU, ctrl lock
   */
  
  static int tiocspgrp(struct tty_struct *tty, struct tty_struct *real_tty, pid_t __user *p)
  {
  	struct pid *pgrp;
  	pid_t pgrp_nr;
  	int retval = tty_check_change(real_tty);
  	unsigned long flags;
  
  	if (retval == -EIO)
  		return -ENOTTY;
  	if (retval)
  		return retval;
  	if (!current->signal->tty ||
  	    (current->signal->tty != real_tty) ||
  	    (real_tty->session != task_session(current)))
  		return -ENOTTY;
  	if (get_user(pgrp_nr, p))
  		return -EFAULT;
  	if (pgrp_nr < 0)
  		return -EINVAL;
  	rcu_read_lock();
  	pgrp = find_vpid(pgrp_nr);
  	retval = -ESRCH;
  	if (!pgrp)
  		goto out_unlock;
  	retval = -EPERM;
  	if (session_of_pgrp(pgrp) != task_session(current))
  		goto out_unlock;
  	retval = 0;
  	spin_lock_irqsave(&tty->ctrl_lock, flags);
  	put_pid(real_tty->pgrp);
  	real_tty->pgrp = get_pid(pgrp);
  	spin_unlock_irqrestore(&tty->ctrl_lock, flags);
  out_unlock:
  	rcu_read_unlock();
  	return retval;
  }
  
  /**
   *	tiocgsid		-	get session id
   *	@tty: tty passed by user
   *	@real_tty: tty side of the tty pased by the user if a pty else the tty
   *	@p: pointer to returned session id
   *
   *	Obtain the session id of the tty. If there is no session
   *	return an error.
   *
   *	Locking: none. Reference to current->signal->tty is safe.
   */
  
  static int tiocgsid(struct tty_struct *tty, struct tty_struct *real_tty, pid_t __user *p)
  {
  	/*
  	 * (tty == real_tty) is a cheap way of
  	 * testing if the tty is NOT a master pty.
  	*/
  	if (tty == real_tty && current->signal->tty != real_tty)
  		return -ENOTTY;
  	if (!real_tty->session)
  		return -ENOTTY;
  	return put_user(pid_vnr(real_tty->session), p);
  }
  
  /**
   *	tiocsetd	-	set line discipline
   *	@tty: tty device
   *	@p: pointer to user data
   *
   *	Set the line discipline according to user request.
   *
   *	Locking: see tty_set_ldisc, this function is just a helper
   */
  
  static int tiocsetd(struct tty_struct *tty, int __user *p)
  {
  	int ldisc;
  	int ret;
  
  	if (get_user(ldisc, p))
  		return -EFAULT;
  
  	lock_kernel();
  	ret = tty_set_ldisc(tty, ldisc);
  	unlock_kernel();
  
  	return ret;
  }
  
  /**
   *	tiocgetd	-	get line discipline
   *	@tty: tty device
   *	@p: pointer to user data
   *
   *	Retrieves the line discipline id directly from the ldisc.
   *
   *	Locking: waits for ldisc reference (in case the line discipline
   *		is changing or the tty is being hungup)
   */
  
  static int tiocgetd(struct tty_struct *tty, int __user *p)
  {
  	struct tty_ldisc *ld;
  	int ret;
  
  	ld = tty_ldisc_ref_wait(tty);
  	ret = put_user(ld->ops->num, p);
  	tty_ldisc_deref(ld);
  	return ret;
  }
  
  /**
   *	send_break	-	performed time break
   *	@tty: device to break on
   *	@duration: timeout in mS
   *
   *	Perform a timed break on hardware that lacks its own driver level
   *	timed break functionality.
   *
   *	Locking:
   *		atomic_write_lock serializes
   *
   */
  
  static int send_break(struct tty_struct *tty, unsigned int duration)
  {
  	int retval;
  
  	if (tty->ops->break_ctl == NULL)
  		return 0;
  
  	if (tty->driver->flags & TTY_DRIVER_HARDWARE_BREAK)
  		retval = tty->ops->break_ctl(tty, duration);
  	else {
  		/* Do the work ourselves */
  		if (tty_write_lock(tty, 0) < 0)
  			return -EINTR;
  		retval = tty->ops->break_ctl(tty, -1);
  		if (retval)
  			goto out;
  		if (!signal_pending(current))
  			msleep_interruptible(duration);
  		retval = tty->ops->break_ctl(tty, 0);
  out:
  		tty_write_unlock(tty);
  		if (signal_pending(current))
  			retval = -EINTR;
  	}
  	return retval;
  }
  
  /**
   *	tty_tiocmget		-	get modem status
   *	@tty: tty device
   *	@file: user file pointer
   *	@p: pointer to result
   *
   *	Obtain the modem status bits from the tty driver if the feature
   *	is supported. Return -EINVAL if it is not available.
   *
   *	Locking: none (up to the driver)
   */
  
  static int tty_tiocmget(struct tty_struct *tty, struct file *file, int __user *p)
  {
  	int retval = -EINVAL;
  
  	if (tty->ops->tiocmget) {
  		retval = tty->ops->tiocmget(tty, file);
  
  		if (retval >= 0)
  			retval = put_user(retval, p);
  	}
  	return retval;
  }
  
  /**
   *	tty_tiocmset		-	set modem status
   *	@tty: tty device
   *	@file: user file pointer
   *	@cmd: command - clear bits, set bits or set all
   *	@p: pointer to desired bits
   *
   *	Set the modem status bits from the tty driver if the feature
   *	is supported. Return -EINVAL if it is not available.
   *
   *	Locking: none (up to the driver)
   */
  
  static int tty_tiocmset(struct tty_struct *tty, struct file *file, unsigned int cmd,
  	     unsigned __user *p)
  {
  	int retval;
  	unsigned int set, clear, val;
  
  	if (tty->ops->tiocmset == NULL)
  		return -EINVAL;
  
  	retval = get_user(val, p);
  	if (retval)
  		return retval;
  	set = clear = 0;
  	switch (cmd) {
  	case TIOCMBIS:
  		set = val;
  		break;
  	case TIOCMBIC:
  		clear = val;
  		break;
  	case TIOCMSET:
  		set = val;
  		clear = ~val;
  		break;
  	}
  	set &= TIOCM_DTR|TIOCM_RTS|TIOCM_OUT1|TIOCM_OUT2|TIOCM_LOOP;
  	clear &= TIOCM_DTR|TIOCM_RTS|TIOCM_OUT1|TIOCM_OUT2|TIOCM_LOOP;
  	return tty->ops->tiocmset(tty, file, set, clear);
  }
  
  static int tty_tiocgicount(struct tty_struct *tty, void __user *arg)
  {
  	int retval = -EINVAL;
  	struct serial_icounter_struct icount;
  	memset(&icount, 0, sizeof(icount));
  	if (tty->ops->get_icount)
  		retval = tty->ops->get_icount(tty, &icount);
  	if (retval != 0)
  		return retval;
  	if (copy_to_user(arg, &icount, sizeof(icount)))
  		return -EFAULT;
  	return 0;
  }
  
  struct tty_struct *tty_pair_get_tty(struct tty_struct *tty)
  {
  	if (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
  	    tty->driver->subtype == PTY_TYPE_MASTER)
  		tty = tty->link;
  	return tty;
  }
  EXPORT_SYMBOL(tty_pair_get_tty);
  
  struct tty_struct *tty_pair_get_pty(struct tty_struct *tty)
  {
  	if (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
  	    tty->driver->subtype == PTY_TYPE_MASTER)
  	    return tty;
  	return tty->link;
  }
  EXPORT_SYMBOL(tty_pair_get_pty);
  
  /*
   * Split this up, as gcc can choke on it otherwise..
   */
  long tty_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
  {
  	struct tty_struct *tty, *real_tty;
  	void __user *p = (void __user *)arg;
  	int retval;
  	struct tty_ldisc *ld;
  	struct inode *inode = file->f_dentry->d_inode;
  
  	tty = (struct tty_struct *)file->private_data;
  	if (tty_paranoia_check(tty, inode, "tty_ioctl"))
  		return -EINVAL;
  
  	real_tty = tty_pair_get_tty(tty);
  
  	/*
  	 * Factor out some common prep work
  	 */
  	switch (cmd) {
  	case TIOCSETD:
  	case TIOCSBRK:
  	case TIOCCBRK:
  	case TCSBRK:
  	case TCSBRKP:
  		retval = tty_check_change(tty);
  		if (retval)
  			return retval;
  		if (cmd != TIOCCBRK) {
  			tty_wait_until_sent(tty, 0);
  			if (signal_pending(current))
  				return -EINTR;
  		}
  		break;
  	}
  
  	/*
  	 *	Now do the stuff.
  	 */
  	switch (cmd) {
  	case TIOCSTI:
  		return tiocsti(tty, p);
  	case TIOCGWINSZ:
  		return tiocgwinsz(real_tty, p);
  	case TIOCSWINSZ:
  		return tiocswinsz(real_tty, p);
  	case TIOCCONS:
  		return real_tty != tty ? -EINVAL : tioccons(file);
  	case FIONBIO:
  		return fionbio(file, p);
  	case TIOCEXCL:
  		set_bit(TTY_EXCLUSIVE, &tty->flags);
  		return 0;
  	case TIOCNXCL:
  		clear_bit(TTY_EXCLUSIVE, &tty->flags);
  		return 0;
  	case TIOCNOTTY:
  		if (current->signal->tty != tty)
  			return -ENOTTY;
  		no_tty();
  		return 0;
  	case TIOCSCTTY:
  		return tiocsctty(tty, arg);
  	case TIOCGPGRP:
  		return tiocgpgrp(tty, real_tty, p);
  	case TIOCSPGRP:
  		return tiocspgrp(tty, real_tty, p);
  	case TIOCGSID:
  		return tiocgsid(tty, real_tty, p);
  	case TIOCGETD:
  		return tiocgetd(tty, p);
  	case TIOCSETD:
  		return tiocsetd(tty, p);
  	/*
  	 * Break handling
  	 */
  	case TIOCSBRK:	/* Turn break on, unconditionally */
  		if (tty->ops->break_ctl)
  			return tty->ops->break_ctl(tty, -1);
  		return 0;
  	case TIOCCBRK:	/* Turn break off, unconditionally */
  		if (tty->ops->break_ctl)
  			return tty->ops->break_ctl(tty, 0);
  		return 0;
  	case TCSBRK:   /* SVID version: non-zero arg --> no break */
  		/* non-zero arg means wait for all output data
  		 * to be sent (performed above) but don't send break.
  		 * This is used by the tcdrain() termios function.
  		 */
  		if (!arg)
  			return send_break(tty, 250);
  		return 0;
  	case TCSBRKP:	/* support for POSIX tcsendbreak() */
  		return send_break(tty, arg ? arg*100 : 250);
  
  	case TIOCMGET:
  		return tty_tiocmget(tty, file, p);
  	case TIOCMSET:
  	case TIOCMBIC:
  	case TIOCMBIS:
  		return tty_tiocmset(tty, file, cmd, p);
  	case TIOCGICOUNT:
  		retval = tty_tiocgicount(tty, p);
  		/* For the moment allow fall through to the old method */
          	if (retval != -EINVAL)
  			return retval;
  		break;
  	case TCFLSH:
  		switch (arg) {
  		case TCIFLUSH:
  		case TCIOFLUSH:
  		/* flush tty buffer and allow ldisc to process ioctl */
  			tty_buffer_flush(tty);
  			break;
  		}
  		break;
  	}
  	if (tty->ops->ioctl) {
  		retval = (tty->ops->ioctl)(tty, file, cmd, arg);
  		if (retval != -ENOIOCTLCMD)
  			return retval;
  	}
  	ld = tty_ldisc_ref_wait(tty);
  	retval = -EINVAL;
  	if (ld->ops->ioctl) {
  		retval = ld->ops->ioctl(tty, file, cmd, arg);
  		if (retval == -ENOIOCTLCMD)
  			retval = -EINVAL;
  	}
  	tty_ldisc_deref(ld);
  	return retval;
  }
  
  #ifdef CONFIG_COMPAT
  static long tty_compat_ioctl(struct file *file, unsigned int cmd,
  				unsigned long arg)
  {
  	struct inode *inode = file->f_dentry->d_inode;
  	struct tty_struct *tty = file->private_data;
  	struct tty_ldisc *ld;
  	int retval = -ENOIOCTLCMD;
  
  	if (tty_paranoia_check(tty, inode, "tty_ioctl"))
  		return -EINVAL;
  
  	if (tty->ops->compat_ioctl) {
  		retval = (tty->ops->compat_ioctl)(tty, file, cmd, arg);
  		if (retval != -ENOIOCTLCMD)
  			return retval;
  	}
  
  	ld = tty_ldisc_ref_wait(tty);
  	if (ld->ops->compat_ioctl)
  		retval = ld->ops->compat_ioctl(tty, file, cmd, arg);
  	tty_ldisc_deref(ld);
  
  	return retval;
  }
  #endif
  
  /*
   * This implements the "Secure Attention Key" ---  the idea is to
   * prevent trojan horses by killing all processes associated with this
   * tty when the user hits the "Secure Attention Key".  Required for
   * super-paranoid applications --- see the Orange Book for more details.
   *
   * This code could be nicer; ideally it should send a HUP, wait a few
   * seconds, then send a INT, and then a KILL signal.  But you then
   * have to coordinate with the init process, since all processes associated
   * with the current tty must be dead before the new getty is allowed
   * to spawn.
   *
   * Now, if it would be correct ;-/ The current code has a nasty hole -
   * it doesn't catch files in flight. We may send the descriptor to ourselves
   * via AF_UNIX socket, close it and later fetch from socket. FIXME.
   *
   * Nasty bug: do_SAK is being called in interrupt context.  This can
   * deadlock.  We punt it up to process context.  AKPM - 16Mar2001
   */
  void __do_SAK(struct tty_struct *tty)
  {
  #ifdef TTY_SOFT_SAK
  	tty_hangup(tty);
  #else
  	struct task_struct *g, *p;
  	struct pid *session;
  	int		i;
  	struct file	*filp;
  	struct fdtable *fdt;
  
  	if (!tty)
  		return;
  	session = tty->session;
  
  	tty_ldisc_flush(tty);
  
  	tty_driver_flush_buffer(tty);
  
  	read_lock(&tasklist_lock);
  	/* Kill the entire session */
  	do_each_pid_task(session, PIDTYPE_SID, p) {
  		printk(KERN_NOTICE "SAK: killed process %d"
  			" (%s): task_session(p)==tty->session\n",
  			task_pid_nr(p), p->comm);
  		send_sig(SIGKILL, p, 1);
  	} while_each_pid_task(session, PIDTYPE_SID, p);
  	/* Now kill any processes that happen to have the
  	 * tty open.
  	 */
  	do_each_thread(g, p) {
  		if (p->signal->tty == tty) {
  			printk(KERN_NOTICE "SAK: killed process %d"
  			    " (%s): task_session(p)==tty->session\n",
  			    task_pid_nr(p), p->comm);
  			send_sig(SIGKILL, p, 1);
  			continue;
  		}
  		task_lock(p);
  		if (p->files) {
  			/*
  			 * We don't take a ref to the file, so we must
  			 * hold ->file_lock instead.
  			 */
  			spin_lock(&p->files->file_lock);
  			fdt = files_fdtable(p->files);
  			for (i = 0; i < fdt->max_fds; i++) {
  				filp = fcheck_files(p->files, i);
  				if (!filp)
  					continue;
  				if (filp->f_op->read == tty_read &&
  				    filp->private_data == tty) {
  					printk(KERN_NOTICE "SAK: killed process %d"
  					    " (%s): fd#%d opened to the tty\n",
  					    task_pid_nr(p), p->comm, i);
  					force_sig(SIGKILL, p);
  					break;
  				}
  			}
  			spin_unlock(&p->files->file_lock);
  		}
  		task_unlock(p);
  	} while_each_thread(g, p);
  	read_unlock(&tasklist_lock);
  #endif
  }
  
  static void do_SAK_work(struct work_struct *work)
  {
  	struct tty_struct *tty =
  		container_of(work, struct tty_struct, SAK_work);
  	__do_SAK(tty);
  }
  
  /*
   * The tq handling here is a little racy - tty->SAK_work may already be queued.
   * Fortunately we don't need to worry, because if ->SAK_work is already queued,
   * the values which we write to it will be identical to the values which it
   * already has. --akpm
   */
  void do_SAK(struct tty_struct *tty)
  {
  	if (!tty)
  		return;
  	schedule_work(&tty->SAK_work);
  }
  
  EXPORT_SYMBOL(do_SAK);
  
  /**
   *	initialize_tty_struct
   *	@tty: tty to initialize
   *
   *	This subroutine initializes a tty structure that has been newly
   *	allocated.
   *
   *	Locking: none - tty in question must not be exposed at this point
   */
  
  void initialize_tty_struct(struct tty_struct *tty,
  		struct tty_driver *driver, int idx)
  {
  	memset(tty, 0, sizeof(struct tty_struct));
  	kref_init(&tty->kref);
  	tty->magic = TTY_MAGIC;
  	tty_ldisc_init(tty);
  	tty->session = NULL;
  	tty->pgrp = NULL;
  	tty->overrun_time = jiffies;
  	tty->buf.head = tty->buf.tail = NULL;
  	tty_buffer_init(tty);
  	mutex_init(&tty->termios_mutex);
  	mutex_init(&tty->ldisc_mutex);
  	init_waitqueue_head(&tty->write_wait);
  	init_waitqueue_head(&tty->read_wait);
  	INIT_WORK(&tty->hangup_work, do_tty_hangup);
  	mutex_init(&tty->atomic_read_lock);
  	mutex_init(&tty->atomic_write_lock);
  	mutex_init(&tty->output_lock);
  	mutex_init(&tty->echo_lock);
  	spin_lock_init(&tty->read_lock);
  	spin_lock_init(&tty->ctrl_lock);
  	INIT_LIST_HEAD(&tty->tty_files);
  	INIT_WORK(&tty->SAK_work, do_SAK_work);
  
  	tty->driver = driver;
  	tty->ops = driver->ops;
  	tty->index = idx;
  	tty_line_name(driver, idx, tty->name);
  }
  
  /**
   *	tty_put_char	-	write one character to a tty
   *	@tty: tty
   *	@ch: character
   *
   *	Write one byte to the tty using the provided put_char method
   *	if present. Returns the number of characters successfully output.
   *
   *	Note: the specific put_char operation in the driver layer may go
   *	away soon. Don't call it directly, use this method
   */
  
  int tty_put_char(struct tty_struct *tty, unsigned char ch)
  {
  	if (tty->ops->put_char)
  		return tty->ops->put_char(tty, ch);
  	return tty->ops->write(tty, &ch, 1);
  }
  EXPORT_SYMBOL_GPL(tty_put_char);
  
  struct class *tty_class;
  
  /**
   *	tty_register_device - register a tty device
   *	@driver: the tty driver that describes the tty device
   *	@index: the index in the tty driver for this tty device
   *	@device: a struct device that is associated with this tty device.
   *		This field is optional, if there is no known struct device
   *		for this tty device it can be set to NULL safely.
   *
   *	Returns a pointer to the struct device for this tty device
   *	(or ERR_PTR(-EFOO) on error).
   *
   *	This call is required to be made to register an individual tty device
   *	if the tty driver's flags have the TTY_DRIVER_DYNAMIC_DEV bit set.  If
   *	that bit is not set, this function should not be called by a tty
   *	driver.
   *
   *	Locking: ??
   */
  
  struct device *tty_register_device(struct tty_driver *driver, unsigned index,
  				   struct device *device)
  {
  	char name[64];
  	dev_t dev = MKDEV(driver->major, driver->minor_start) + index;
  
  	if (index >= driver->num) {
  		printk(KERN_ERR "Attempt to register invalid tty line number "
  		       " (%d).\n", index);
  		return ERR_PTR(-EINVAL);
  	}
  
  	if (driver->type == TTY_DRIVER_TYPE_PTY)
  		pty_line_name(driver, index, name);
  	else
  		tty_line_name(driver, index, name);
  
  	return device_create(tty_class, device, dev, NULL, name);
  }
  EXPORT_SYMBOL(tty_register_device);
  
  /**
   * 	tty_unregister_device - unregister a tty device
   * 	@driver: the tty driver that describes the tty device
   * 	@index: the index in the tty driver for this tty device
   *
   * 	If a tty device is registered with a call to tty_register_device() then
   *	this function must be called when the tty device is gone.
   *
   *	Locking: ??
   */
  
  void tty_unregister_device(struct tty_driver *driver, unsigned index)
  {
  	device_destroy(tty_class,
  		MKDEV(driver->major, driver->minor_start) + index);
  }
  EXPORT_SYMBOL(tty_unregister_device);
  
  struct tty_driver *alloc_tty_driver(int lines)
  {
  	struct tty_driver *driver;
  
  	driver = kzalloc(sizeof(struct tty_driver), GFP_KERNEL);
  	if (driver) {
  		kref_init(&driver->kref);
  		driver->magic = TTY_DRIVER_MAGIC;
  		driver->num = lines;
  		/* later we'll move allocation of tables here */
  	}
  	return driver;
  }
  EXPORT_SYMBOL(alloc_tty_driver);
  
  static void destruct_tty_driver(struct kref *kref)
  {
  	struct tty_driver *driver = container_of(kref, struct tty_driver, kref);
  	int i;
  	struct ktermios *tp;
  	void *p;
  
  	if (driver->flags & TTY_DRIVER_INSTALLED) {
  		/*
  		 * Free the termios and termios_locked structures because
  		 * we don't want to get memory leaks when modular tty
  		 * drivers are removed from the kernel.
  		 */
  		for (i = 0; i < driver->num; i++) {
  			tp = driver->termios[i];
  			if (tp) {
  				driver->termios[i] = NULL;
  				kfree(tp);
  			}
  			if (!(driver->flags & TTY_DRIVER_DYNAMIC_DEV))
  				tty_unregister_device(driver, i);
  		}
  		p = driver->ttys;
  		proc_tty_unregister_driver(driver);
  		driver->ttys = NULL;
  		driver->termios = NULL;
  		kfree(p);
  		cdev_del(&driver->cdev);
  	}
  	kfree(driver);
  }
  
  void tty_driver_kref_put(struct tty_driver *driver)
  {
  	kref_put(&driver->kref, destruct_tty_driver);
  }
  EXPORT_SYMBOL(tty_driver_kref_put);
  
  void tty_set_operations(struct tty_driver *driver,
  			const struct tty_operations *op)
  {
  	driver->ops = op;
  };
  EXPORT_SYMBOL(tty_set_operations);
  
  void put_tty_driver(struct tty_driver *d)
  {
  	tty_driver_kref_put(d);
  }
  EXPORT_SYMBOL(put_tty_driver);
  
  /*
   * Called by a tty driver to register itself.
   */
  int tty_register_driver(struct tty_driver *driver)
  {
  	int error;
  	int i;
  	dev_t dev;
  	void **p = NULL;
  
  	if (!(driver->flags & TTY_DRIVER_DEVPTS_MEM) && driver->num) {
  		p = kzalloc(driver->num * 2 * sizeof(void *), GFP_KERNEL);
  		if (!p)
  			return -ENOMEM;
  	}
  
  	if (!driver->major) {
  		error = alloc_chrdev_region(&dev, driver->minor_start,
  						driver->num, driver->name);
  		if (!error) {
  			driver->major = MAJOR(dev);
  			driver->minor_start = MINOR(dev);
  		}
  	} else {
  		dev = MKDEV(driver->major, driver->minor_start);
  		error = register_chrdev_region(dev, driver->num, driver->name);
  	}
  	if (error < 0) {
  		kfree(p);
  		return error;
  	}
  
  	if (p) {
  		driver->ttys = (struct tty_struct **)p;
  		driver->termios = (struct ktermios **)(p + driver->num);
  	} else {
  		driver->ttys = NULL;
  		driver->termios = NULL;
  	}
  
  	cdev_init(&driver->cdev, &tty_fops);
  	driver->cdev.owner = driver->owner;
  	error = cdev_add(&driver->cdev, dev, driver->num);
  	if (error) {
  		unregister_chrdev_region(dev, driver->num);
  		driver->ttys = NULL;
  		driver->termios = NULL;
  		kfree(p);
  		return error;
  	}
  
  	mutex_lock(&tty_mutex);
  	list_add(&driver->tty_drivers, &tty_drivers);
  	mutex_unlock(&tty_mutex);
  
  	if (!(driver->flags & TTY_DRIVER_DYNAMIC_DEV)) {
  		for (i = 0; i < driver->num; i++)
  		    tty_register_device(driver, i, NULL);
  	}
  	proc_tty_register_driver(driver);
  	driver->flags |= TTY_DRIVER_INSTALLED;
  	return 0;
  }
  
  EXPORT_SYMBOL(tty_register_driver);
  
  /*
   * Called by a tty driver to unregister itself.
   */
  int tty_unregister_driver(struct tty_driver *driver)
  {
  #if 0
  	/* FIXME */
  	if (driver->refcount)
  		return -EBUSY;
  #endif
  	unregister_chrdev_region(MKDEV(driver->major, driver->minor_start),
  				driver->num);
  	mutex_lock(&tty_mutex);
  	list_del(&driver->tty_drivers);
  	mutex_unlock(&tty_mutex);
  	return 0;
  }
  
  EXPORT_SYMBOL(tty_unregister_driver);
  
  dev_t tty_devnum(struct tty_struct *tty)
  {
  	return MKDEV(tty->driver->major, tty->driver->minor_start) + tty->index;
  }
  EXPORT_SYMBOL(tty_devnum);
  
  void proc_clear_tty(struct task_struct *p)
  {
  	unsigned long flags;
  	struct tty_struct *tty;
  	spin_lock_irqsave(&p->sighand->siglock, flags);
  	tty = p->signal->tty;
  	p->signal->tty = NULL;
  	spin_unlock_irqrestore(&p->sighand->siglock, flags);
  	tty_kref_put(tty);
  }
  
  /* Called under the sighand lock */
  
  static void __proc_set_tty(struct task_struct *tsk, struct tty_struct *tty)
  {
  	if (tty) {
  		unsigned long flags;
  		/* We should not have a session or pgrp to put here but.... */
  		spin_lock_irqsave(&tty->ctrl_lock, flags);
  		put_pid(tty->session);
  		put_pid(tty->pgrp);
  		tty->pgrp = get_pid(task_pgrp(tsk));
  		spin_unlock_irqrestore(&tty->ctrl_lock, flags);
  		tty->session = get_pid(task_session(tsk));
  		if (tsk->signal->tty) {
  			printk(KERN_DEBUG "tty not NULL!!\n");
  			tty_kref_put(tsk->signal->tty);
  		}
  	}
  	put_pid(tsk->signal->tty_old_pgrp);
  	tsk->signal->tty = tty_kref_get(tty);
  	tsk->signal->tty_old_pgrp = NULL;
  }
  
  static void proc_set_tty(struct task_struct *tsk, struct tty_struct *tty)
  {
  	spin_lock_irq(&tsk->sighand->siglock);
  	__proc_set_tty(tsk, tty);
  	spin_unlock_irq(&tsk->sighand->siglock);
  }
  
  struct tty_struct *get_current_tty(void)
  {
  	struct tty_struct *tty;
  	unsigned long flags;
  
  	spin_lock_irqsave(&current->sighand->siglock, flags);
  	tty = tty_kref_get(current->signal->tty);
  	spin_unlock_irqrestore(&current->sighand->siglock, flags);
  	return tty;
  }
  EXPORT_SYMBOL_GPL(get_current_tty);
  
  void tty_default_fops(struct file_operations *fops)
  {
  	*fops = tty_fops;
  }
  
  /*
   * Initialize the console device. This is called *early*, so
   * we can't necessarily depend on lots of kernel help here.
   * Just do some early initializations, and do the complex setup
   * later.
   */
  void __init console_init(void)
  {
  	initcall_t *call;
  
  	/* Setup the default TTY line discipline. */
  	tty_ldisc_begin();
  
  	/*
  	 * set up the console device so that later boot sequences can
  	 * inform about problems etc..
  	 */
  	call = __con_initcall_start;
  	while (call < __con_initcall_end) {
  		(*call)();
  		call++;
  	}
  }
  
  static char *tty_devnode(struct device *dev, mode_t *mode)
  {
  	if (!mode)
  		return NULL;
  	if (dev->devt == MKDEV(TTYAUX_MAJOR, 0) ||
  	    dev->devt == MKDEV(TTYAUX_MAJOR, 2))
  		*mode = 0666;
  	return NULL;
  }
  
  static int __init tty_class_init(void)
  {
  	tty_class = class_create(THIS_MODULE, "tty");
  	if (IS_ERR(tty_class))
  		return PTR_ERR(tty_class);
  	tty_class->devnode = tty_devnode;
  	return 0;
  }
  
  postcore_initcall(tty_class_init);
  
  /* 3/2004 jmc: why do these devices exist? */
  
  static struct cdev tty_cdev, console_cdev;
  
  /*
   * Ok, now we can initialize the rest of the tty devices and can count
   * on memory allocations, interrupts etc..
   */
  static int __init tty_init(void)
  {
  	cdev_init(&tty_cdev, &tty_fops);
  	if (cdev_add(&tty_cdev, MKDEV(TTYAUX_MAJOR, 0), 1) ||
  	    register_chrdev_region(MKDEV(TTYAUX_MAJOR, 0), 1, "/dev/tty") < 0)
  		panic("Couldn't register /dev/tty driver\n");
  	device_create(tty_class, NULL, MKDEV(TTYAUX_MAJOR, 0), NULL,
  			      "tty");
  
  	cdev_init(&console_cdev, &console_fops);
  	if (cdev_add(&console_cdev, MKDEV(TTYAUX_MAJOR, 1), 1) ||
  	    register_chrdev_region(MKDEV(TTYAUX_MAJOR, 1), 1, "/dev/console") < 0)
  		panic("Couldn't register /dev/console driver\n");
  	device_create(tty_class, NULL, MKDEV(TTYAUX_MAJOR, 1), NULL,
  			      "console");
  
  #ifdef CONFIG_VT
  	vty_init(&console_fops);
  #endif
  	return 0;
  }
  module_init(tty_init);
  