/*
   * n_tty.c --- implements the N_TTY line discipline.

   *

   * This code used to be in tty_io.c, but things are getting hairy
   * enough that it made sense to split things off.  (The N_TTY
   * processing has changed so much that it's hardly recognizable,
   * anyway...)
   *
   * Note that the open routine for N_TTY is guaranteed never to return
   * an error.  This is because Linux will fall back to setting a line

   * to N_TTY if it can not switch to any other line discipline.

   *
   * Written by Theodore Ts'o, Copyright 1994.

   *

   * This file also contains code originally written by Linus Torvalds,
   * Copyright 1991, 1992, 1993, and by Julian Cowley, Copyright 1994.

   *

   * This file may be redistributed under the terms of the GNU General Public
   * License.
   *
   * Reduced memory usage for older ARM systems  - Russell King.
   *

   * 2000/01/20   Fixed SMP locking on put_tty_queue using bits of

   *		the patch by Andrew J. Kroll <ag784@freenet.buffalo.edu>
   *		who actually finally proved there really was a race.
   *
   * 2002/03/18   Implemented n_tty_wakeup to send SIGIO POLL_OUTs to
   *		waiting writing processes-Sapan Bhatia <sapan@corewars.org>.

   *		Also fixed a bug in BLOCKING mode where n_tty_write returns

   *		EAGAIN
   */
  
  #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/timer.h>
  #include <linux/ctype.h>
  #include <linux/mm.h>
  #include <linux/string.h>
  #include <linux/slab.h>
  #include <linux/poll.h>
  #include <linux/bitops.h>

  #include <linux/audit.h>
  #include <linux/file.h>

  
  #include <asm/uaccess.h>
  #include <asm/system.h>
  
  /* number of characters left in xmit buffer before select has we have room */
  #define WAKEUP_CHARS 256
  
  /*
   * This defines the low- and high-watermarks for throttling and
   * unthrottling the TTY driver.  These watermarks are used for
   * controlling the space in the read buffer.
   */
  #define TTY_THRESHOLD_THROTTLE		128 /* now based on remaining room */
  #define TTY_THRESHOLD_UNTHROTTLE 	128
  
  static inline unsigned char *alloc_buf(void)
  {

  	gfp_t prio = in_interrupt() ? GFP_ATOMIC : GFP_KERNEL;

  
  	if (PAGE_SIZE != N_TTY_BUF_SIZE)
  		return kmalloc(N_TTY_BUF_SIZE, prio);
  	else
  		return (unsigned char *)__get_free_page(prio);
  }
  
  static inline void free_buf(unsigned char *buf)
  {
  	if (PAGE_SIZE != N_TTY_BUF_SIZE)
  		kfree(buf);
  	else
  		free_page((unsigned long) buf);
  }

  static inline int tty_put_user(struct tty_struct *tty, unsigned char x,
  			       unsigned char __user *ptr)
  {
  	tty_audit_add_data(tty, &x, 1);
  	return put_user(x, ptr);
  }

  /**
   *	n_tty_set__room	-	receive space
   *	@tty: terminal
   *
   *	Called by the driver to find out how much data it is
   *	permitted to feed to the line discipline without any being lost
   *	and thus to manage flow control. Not serialized. Answers for the
   *	"instant".
   */
  
  static void n_tty_set_room(struct tty_struct *tty)
  {

  	/* tty->read_cnt is not read locked ? */

  	int	left = N_TTY_BUF_SIZE - tty->read_cnt - 1;
  
  	/*
  	 * If we are doing input canonicalization, and there are no
  	 * pending newlines, let characters through without limit, so
  	 * that erase characters will be handled.  Other excess
  	 * characters will be beeped.
  	 */
  	if (left <= 0)
  		left = tty->icanon && !tty->canon_data;
  	tty->receive_room = left;
  }
  
  static void put_tty_queue_nolock(unsigned char c, struct tty_struct *tty)

  {
  	if (tty->read_cnt < N_TTY_BUF_SIZE) {
  		tty->read_buf[tty->read_head] = c;
  		tty->read_head = (tty->read_head + 1) & (N_TTY_BUF_SIZE-1);
  		tty->read_cnt++;
  	}
  }

  /**
   *	put_tty_queue		-	add character to tty
   *	@c: character
   *	@tty: tty device
   *
   *	Add a character to the tty read_buf queue. This is done under the
   *	read_lock to serialize character addition and also to protect us
   *	against parallel reads or flushes
   */

  static void put_tty_queue(unsigned char c, struct tty_struct *tty)

  {
  	unsigned long flags;
  	/*
  	 *	The problem of stomping on the buffers ends here.
  	 *	Why didn't anyone see this one coming? --AJK
  	*/
  	spin_lock_irqsave(&tty->read_lock, flags);
  	put_tty_queue_nolock(c, tty);
  	spin_unlock_irqrestore(&tty->read_lock, flags);
  }
  
  /**
   *	check_unthrottle	-	allow new receive data
   *	@tty; tty device
   *

   *	Check whether to call the driver unthrottle functions
   *

   *	Can sleep, may be called under the atomic_read_lock mutex but

   *	this is not guaranteed.
   */

  static void check_unthrottle(struct tty_struct *tty)

  {

  	if (tty->count)
  		tty_unthrottle(tty);

  }
  
  /**
   *	reset_buffer_flags	-	reset buffer state
   *	@tty: terminal to reset
   *

   *	Reset the read buffer counters, clear the flags,

   *	and make sure the driver is unthrottled. Called
   *	from n_tty_open() and n_tty_flush_buffer().

   *
   *	Locking: tty_read_lock for read fields.

   */
  static void reset_buffer_flags(struct tty_struct *tty)
  {
  	unsigned long flags;
  
  	spin_lock_irqsave(&tty->read_lock, flags);
  	tty->read_head = tty->read_tail = tty->read_cnt = 0;
  	spin_unlock_irqrestore(&tty->read_lock, flags);
  	tty->canon_head = tty->canon_data = tty->erasing = 0;
  	memset(&tty->read_flags, 0, sizeof tty->read_flags);

  	n_tty_set_room(tty);

  	check_unthrottle(tty);
  }
  
  /**
   *	n_tty_flush_buffer	-	clean input queue
   *	@tty:	terminal device
   *
   *	Flush the input buffer. Called when the line discipline is
   *	being closed, when the tty layer wants the buffer flushed (eg
   *	at hangup) or when the N_TTY line discipline internally has to
   *	clean the pending queue (for example some signals).
   *

   *	Locking: ctrl_lock, read_lock.

   */

  
  static void n_tty_flush_buffer(struct tty_struct *tty)

  {

  	unsigned long flags;

  	/* clear everything and unthrottle the driver */
  	reset_buffer_flags(tty);

  	if (!tty->link)
  		return;

  	spin_lock_irqsave(&tty->ctrl_lock, flags);

  	if (tty->link->packet) {
  		tty->ctrl_status |= TIOCPKT_FLUSHREAD;
  		wake_up_interruptible(&tty->link->read_wait);
  	}

  	spin_unlock_irqrestore(&tty->ctrl_lock, flags);

  }
  
  /**
   *	n_tty_chars_in_buffer	-	report available bytes
   *	@tty: tty device
   *
   *	Report the number of characters buffered to be delivered to user

   *	at this instant in time.

   *
   *	Locking: read_lock

   */

  static ssize_t n_tty_chars_in_buffer(struct tty_struct *tty)
  {
  	unsigned long flags;
  	ssize_t n = 0;
  
  	spin_lock_irqsave(&tty->read_lock, flags);
  	if (!tty->icanon) {
  		n = tty->read_cnt;
  	} else if (tty->canon_data) {
  		n = (tty->canon_head > tty->read_tail) ?
  			tty->canon_head - tty->read_tail :
  			tty->canon_head + (N_TTY_BUF_SIZE - tty->read_tail);
  	}
  	spin_unlock_irqrestore(&tty->read_lock, flags);
  	return n;
  }
  
  /**
   *	is_utf8_continuation	-	utf8 multibyte check
   *	@c: byte to check
   *
   *	Returns true if the utf8 character 'c' is a multibyte continuation
   *	character. We use this to correctly compute the on screen size
   *	of the character when printing
   */

  static inline int is_utf8_continuation(unsigned char c)
  {
  	return (c & 0xc0) == 0x80;
  }
  
  /**
   *	is_continuation		-	multibyte check
   *	@c: byte to check
   *
   *	Returns true if the utf8 character 'c' is a multibyte continuation
   *	character and the terminal is in unicode mode.
   */

  static inline int is_continuation(unsigned char c, struct tty_struct *tty)
  {
  	return I_IUTF8(tty) && is_utf8_continuation(c);
  }
  
  /**
   *	opost			-	output post processor
   *	@c: character (or partial unicode symbol)
   *	@tty: terminal device
   *
   *	Perform OPOST processing.  Returns -1 when the output device is
   *	full and the character must be retried. Note that Linux currently
   *	ignores TABDLY, CRDLY, VTDLY, FFDLY and NLDLY. They simply aren't
   *	relevant in the world today. If you ever need them, add them here.
   *
   *	Called from both the receive and transmit sides and can be called

   *	re-entrantly. Relies on lock_kernel() for tty->column state.

   */

  static int opost(unsigned char c, struct tty_struct *tty)
  {
  	int	space, spaces;

  	space = tty_write_room(tty);

  	if (!space)
  		return -1;

  	lock_kernel();

  	if (O_OPOST(tty)) {
  		switch (c) {
  		case '
  ':
  			if (O_ONLRET(tty))
  				tty->column = 0;
  			if (O_ONLCR(tty)) {

  				if (space < 2) {
  					unlock_kernel();

  					return -1;

  				}

  				tty_put_char(tty, '\r');

  				tty->column = 0;
  			}
  			tty->canon_column = tty->column;
  			break;
  		case '\r':

  			if (O_ONOCR(tty) && tty->column == 0) {
  				unlock_kernel();

  				return 0;

  			}

  			if (O_OCRNL(tty)) {
  				c = '
  ';
  				if (O_ONLRET(tty))
  					tty->canon_column = tty->column = 0;
  				break;
  			}
  			tty->canon_column = tty->column = 0;
  			break;
  		case '\t':
  			spaces = 8 - (tty->column & 7);
  			if (O_TABDLY(tty) == XTABS) {

  				if (space < spaces) {
  					unlock_kernel();

  					return -1;

  				}

  				tty->column += spaces;

  				tty->ops->write(tty, "        ", spaces);

  				unlock_kernel();

  				return 0;
  			}
  			tty->column += spaces;
  			break;
  		case '\b':
  			if (tty->column > 0)
  				tty->column--;
  			break;
  		default:
  			if (O_OLCUC(tty))
  				c = toupper(c);
  			if (!iscntrl(c) && !is_continuation(c, tty))
  				tty->column++;
  			break;
  		}
  	}

  	tty_put_char(tty, c);

  	unlock_kernel();

  	return 0;
  }
  
  /**
   *	opost_block		-	block postprocess
   *	@tty: terminal device
   *	@inbuf: user buffer
   *	@nr: number of bytes
   *
   *	This path is used to speed up block console writes, among other
   *	things when processing blocks of output data. It handles only
   *	the simple cases normally found and helps to generate blocks of
   *	symbols for the console driver and thus improve performance.
   *

   *	Called from n_tty_write under the tty layer write lock. Relies

   *	on lock_kernel for the tty->column state.

   */

  
  static ssize_t opost_block(struct tty_struct *tty,
  		       const unsigned char *buf, unsigned int nr)

  {
  	int	space;
  	int 	i;
  	const unsigned char *cp;

  	space = tty_write_room(tty);

  	if (!space)
  		return 0;
  	if (nr > space)
  		nr = space;

  	lock_kernel();

  	for (i = 0, cp = buf; i < nr; i++, cp++) {
  		switch (*cp) {
  		case '
  ':
  			if (O_ONLRET(tty))
  				tty->column = 0;
  			if (O_ONLCR(tty))
  				goto break_out;
  			tty->canon_column = tty->column;
  			break;
  		case '\r':
  			if (O_ONOCR(tty) && tty->column == 0)
  				goto break_out;
  			if (O_OCRNL(tty))
  				goto break_out;
  			tty->canon_column = tty->column = 0;
  			break;
  		case '\t':
  			goto break_out;
  		case '\b':
  			if (tty->column > 0)
  				tty->column--;
  			break;
  		default:
  			if (O_OLCUC(tty))
  				goto break_out;
  			if (!iscntrl(*cp))
  				tty->column++;
  			break;
  		}
  	}
  break_out:

  	if (tty->ops->flush_chars)
  		tty->ops->flush_chars(tty);
  	i = tty->ops->write(tty, buf, i);

  	unlock_kernel();

  	return i;
  }
  
  
  /**

   *	echo_char	-	echo characters
   *	@c: unicode byte to echo
   *	@tty: terminal device
   *

   *	Echo user input back onto the screen. This must be called only when

   *	L_ECHO(tty) is true. Called from the driver receive_buf path.

   *
   *	Relies on BKL for tty column locking

   */
  
  static void echo_char(unsigned char c, struct tty_struct *tty)
  {
  	if (L_ECHOCTL(tty) && iscntrl(c) && c != '\t') {

  		tty_put_char(tty, '^');
  		tty_put_char(tty, c ^ 0100);

  		tty->column += 2;
  	} else
  		opost(c, tty);
  }

  /**
   *	finsh_erasing		-	complete erase
   *	@tty: tty doing the erase
   *
   *	Relies on BKL for tty column locking
   */

  static inline void finish_erasing(struct tty_struct *tty)
  {
  	if (tty->erasing) {

  		tty_put_char(tty, '/');

  		tty->column++;
  		tty->erasing = 0;
  	}
  }
  
  /**
   *	eraser		-	handle erase function
   *	@c: character input
   *	@tty: terminal device
   *

   *	Perform erase and necessary output when an erase character is

   *	present in the stream from the driver layer. Handles the complexities
   *	of UTF-8 multibyte symbols.

   *
   *	Locking: read_lock for tty buffers, BKL for column/erasing state

   */

  static void eraser(unsigned char c, struct tty_struct *tty)
  {
  	enum { ERASE, WERASE, KILL } kill_type;
  	int head, seen_alnums, cnt;
  	unsigned long flags;

  	/* FIXME: locking needed ? */

  	if (tty->read_head == tty->canon_head) {
  		/* opost('\a', tty); */		/* what do you think? */
  		return;
  	}
  	if (c == ERASE_CHAR(tty))
  		kill_type = ERASE;
  	else if (c == WERASE_CHAR(tty))
  		kill_type = WERASE;
  	else {
  		if (!L_ECHO(tty)) {
  			spin_lock_irqsave(&tty->read_lock, flags);
  			tty->read_cnt -= ((tty->read_head - tty->canon_head) &
  					  (N_TTY_BUF_SIZE - 1));
  			tty->read_head = tty->canon_head;
  			spin_unlock_irqrestore(&tty->read_lock, flags);
  			return;
  		}
  		if (!L_ECHOK(tty) || !L_ECHOKE(tty) || !L_ECHOE(tty)) {
  			spin_lock_irqsave(&tty->read_lock, flags);
  			tty->read_cnt -= ((tty->read_head - tty->canon_head) &
  					  (N_TTY_BUF_SIZE - 1));
  			tty->read_head = tty->canon_head;
  			spin_unlock_irqrestore(&tty->read_lock, flags);
  			finish_erasing(tty);
  			echo_char(KILL_CHAR(tty), tty);
  			/* Add a newline if ECHOK is on and ECHOKE is off. */
  			if (L_ECHOK(tty))
  				opost('
  ', tty);
  			return;
  		}
  		kill_type = KILL;
  	}
  
  	seen_alnums = 0;

  	/* FIXME: Locking ?? */

  	while (tty->read_head != tty->canon_head) {
  		head = tty->read_head;
  
  		/* erase a single possibly multibyte character */
  		do {
  			head = (head - 1) & (N_TTY_BUF_SIZE-1);
  			c = tty->read_buf[head];
  		} while (is_continuation(c, tty) && head != tty->canon_head);
  
  		/* do not partially erase */
  		if (is_continuation(c, tty))
  			break;
  
  		if (kill_type == WERASE) {
  			/* Equivalent to BSD's ALTWERASE. */
  			if (isalnum(c) || c == '_')
  				seen_alnums++;
  			else if (seen_alnums)
  				break;
  		}
  		cnt = (tty->read_head - head) & (N_TTY_BUF_SIZE-1);
  		spin_lock_irqsave(&tty->read_lock, flags);
  		tty->read_head = head;
  		tty->read_cnt -= cnt;
  		spin_unlock_irqrestore(&tty->read_lock, flags);
  		if (L_ECHO(tty)) {
  			if (L_ECHOPRT(tty)) {
  				if (!tty->erasing) {

  					tty_put_char(tty, '\\');

  					tty->column++;
  					tty->erasing = 1;
  				}
  				/* if cnt > 1, output a multi-byte character */
  				echo_char(c, tty);
  				while (--cnt > 0) {
  					head = (head+1) & (N_TTY_BUF_SIZE-1);

  					tty_put_char(tty, tty->read_buf[head]);

  				}
  			} else if (kill_type == ERASE && !L_ECHOE(tty)) {
  				echo_char(ERASE_CHAR(tty), tty);
  			} else if (c == '\t') {
  				unsigned int col = tty->canon_column;
  				unsigned long tail = tty->canon_head;
  
  				/* Find the column of the last char. */
  				while (tail != tty->read_head) {
  					c = tty->read_buf[tail];
  					if (c == '\t')
  						col = (col | 7) + 1;
  					else if (iscntrl(c)) {
  						if (L_ECHOCTL(tty))
  							col += 2;
  					} else if (!is_continuation(c, tty))
  						col++;
  					tail = (tail+1) & (N_TTY_BUF_SIZE-1);
  				}
  
  				/* should never happen */
  				if (tty->column > 0x80000000)

  					tty->column = 0;

  
  				/* Now backup to that column. */
  				while (tty->column > col) {
  					/* Can't use opost here. */

  					tty_put_char(tty, '\b');

  					if (tty->column > 0)
  						tty->column--;
  				}
  			} else {
  				if (iscntrl(c) && L_ECHOCTL(tty)) {

  					tty_put_char(tty, '\b');
  					tty_put_char(tty, ' ');
  					tty_put_char(tty, '\b');

  					if (tty->column > 0)
  						tty->column--;
  				}
  				if (!iscntrl(c) || L_ECHOCTL(tty)) {

  					tty_put_char(tty, '\b');
  					tty_put_char(tty, ' ');
  					tty_put_char(tty, '\b');

  					if (tty->column > 0)
  						tty->column--;
  				}
  			}
  		}
  		if (kill_type == ERASE)
  			break;
  	}
  	if (tty->read_head == tty->canon_head)
  		finish_erasing(tty);
  }
  
  /**
   *	isig		-	handle the ISIG optio
   *	@sig: signal
   *	@tty: terminal
   *	@flush: force flush
   *
   *	Called when a signal is being sent due to terminal input. This
   *	may caus terminal flushing to take place according to the termios
   *	settings and character used. Called from the driver receive_buf
   *	path so serialized.

   *
   *	Locking: ctrl_lock, read_lock (both via flush buffer)

   */

  static inline void isig(int sig, struct tty_struct *tty, int flush)
  {

  	if (tty->pgrp)
  		kill_pgrp(tty->pgrp, sig, 1);

  	if (flush || !L_NOFLSH(tty)) {
  		n_tty_flush_buffer(tty);

  		tty_driver_flush_buffer(tty);

  	}
  }
  
  /**
   *	n_tty_receive_break	-	handle break
   *	@tty: terminal
   *
   *	An RS232 break event has been hit in the incoming bitstream. This
   *	can cause a variety of events depending upon the termios settings.
   *
   *	Called from the receive_buf path so single threaded.
   */

  static inline void n_tty_receive_break(struct tty_struct *tty)
  {
  	if (I_IGNBRK(tty))
  		return;
  	if (I_BRKINT(tty)) {
  		isig(SIGINT, tty, 1);
  		return;
  	}
  	if (I_PARMRK(tty)) {
  		put_tty_queue('\377', tty);
  		put_tty_queue('\0', tty);
  	}
  	put_tty_queue('\0', tty);
  	wake_up_interruptible(&tty->read_wait);
  }
  
  /**
   *	n_tty_receive_overrun	-	handle overrun reporting
   *	@tty: terminal
   *
   *	Data arrived faster than we could process it. While the tty
   *	driver has flagged this the bits that were missed are gone
   *	forever.
   *
   *	Called from the receive_buf path so single threaded. Does not
   *	need locking as num_overrun and overrun_time are function
   *	private.
   */

  static inline void n_tty_receive_overrun(struct tty_struct *tty)
  {
  	char buf[64];
  
  	tty->num_overrun++;
  	if (time_before(tty->overrun_time, jiffies - HZ) ||
  			time_after(tty->overrun_time, jiffies)) {
  		printk(KERN_WARNING "%s: %d input overrun(s)
  ",
  			tty_name(tty, buf),
  			tty->num_overrun);
  		tty->overrun_time = jiffies;
  		tty->num_overrun = 0;
  	}
  }
  
  /**
   *	n_tty_receive_parity_error	-	error notifier
   *	@tty: terminal device
   *	@c: character
   *
   *	Process a parity error and queue the right data to indicate

   *	the error case if necessary. Locking as per n_tty_receive_buf.

   */
  static inline void n_tty_receive_parity_error(struct tty_struct *tty,
  					      unsigned char c)
  {

  	if (I_IGNPAR(tty))

  		return;

  	if (I_PARMRK(tty)) {
  		put_tty_queue('\377', tty);
  		put_tty_queue('\0', tty);
  		put_tty_queue(c, tty);
  	} else	if (I_INPCK(tty))
  		put_tty_queue('\0', tty);
  	else
  		put_tty_queue(c, tty);
  	wake_up_interruptible(&tty->read_wait);
  }
  
  /**
   *	n_tty_receive_char	-	perform processing
   *	@tty: terminal device
   *	@c: character
   *
   *	Process an individual character of input received from the driver.

   *	This is serialized with respect to itself by the rules for the

   *	driver above.
   */
  
  static inline void n_tty_receive_char(struct tty_struct *tty, unsigned char c)
  {
  	unsigned long flags;
  
  	if (tty->raw) {
  		put_tty_queue(c, tty);
  		return;
  	}

  	if (I_ISTRIP(tty))
  		c &= 0x7f;
  	if (I_IUCLC(tty) && L_IEXTEN(tty))
  		c=tolower(c);

  	if (tty->stopped && !tty->flow_stopped && I_IXON(tty) &&
  	    ((I_IXANY(tty) && c != START_CHAR(tty) && c != STOP_CHAR(tty)) ||

  	     c == INTR_CHAR(tty) || c == QUIT_CHAR(tty) || c == SUSP_CHAR(tty)))

  		start_tty(tty);

  	if (tty->closing) {
  		if (I_IXON(tty)) {
  			if (c == START_CHAR(tty))
  				start_tty(tty);
  			else if (c == STOP_CHAR(tty))
  				stop_tty(tty);
  		}
  		return;
  	}
  
  	/*
  	 * If the previous character was LNEXT, or we know that this
  	 * character is not one of the characters that we'll have to
  	 * handle specially, do shortcut processing to speed things
  	 * up.
  	 */
  	if (!test_bit(c, tty->process_char_map) || tty->lnext) {
  		finish_erasing(tty);
  		tty->lnext = 0;
  		if (L_ECHO(tty)) {
  			if (tty->read_cnt >= N_TTY_BUF_SIZE-1) {

  				tty_put_char(tty, '\a'); /* beep if no space */

  				return;
  			}
  			/* Record the column of first canon char. */
  			if (tty->canon_head == tty->read_head)
  				tty->canon_column = tty->column;
  			echo_char(c, tty);
  		}
  		if (I_PARMRK(tty) && c == (unsigned char) '\377')
  			put_tty_queue(c, tty);
  		put_tty_queue(c, tty);
  		return;
  	}

  	if (I_IXON(tty)) {
  		if (c == START_CHAR(tty)) {
  			start_tty(tty);
  			return;
  		}
  		if (c == STOP_CHAR(tty)) {
  			stop_tty(tty);
  			return;
  		}
  	}

  	if (L_ISIG(tty)) {
  		int signal;
  		signal = SIGINT;
  		if (c == INTR_CHAR(tty))
  			goto send_signal;
  		signal = SIGQUIT;
  		if (c == QUIT_CHAR(tty))
  			goto send_signal;
  		signal = SIGTSTP;
  		if (c == SUSP_CHAR(tty)) {
  send_signal:

  			/*
  			 * Echo character, and then send the signal.
  			 * Note that we do not use isig() here because we want
  			 * the order to be:
  			 * 1) flush, 2) echo, 3) signal
  			 */
  			if (!L_NOFLSH(tty)) {
  				n_tty_flush_buffer(tty);

  				tty_driver_flush_buffer(tty);

  			}
  			if (L_ECHO(tty))
  				echo_char(c, tty);
  			if (tty->pgrp)
  				kill_pgrp(tty->pgrp, signal, 1);

  			return;
  		}
  	}

  
  	if (c == '\r') {
  		if (I_IGNCR(tty))
  			return;
  		if (I_ICRNL(tty))
  			c = '
  ';
  	} else if (c == '
  ' && I_INLCR(tty))
  		c = '\r';

  	if (tty->icanon) {
  		if (c == ERASE_CHAR(tty) || c == KILL_CHAR(tty) ||
  		    (c == WERASE_CHAR(tty) && L_IEXTEN(tty))) {
  			eraser(c, tty);
  			return;
  		}
  		if (c == LNEXT_CHAR(tty) && L_IEXTEN(tty)) {
  			tty->lnext = 1;
  			if (L_ECHO(tty)) {
  				finish_erasing(tty);
  				if (L_ECHOCTL(tty)) {

  					tty_put_char(tty, '^');
  					tty_put_char(tty, '\b');

  				}
  			}
  			return;
  		}
  		if (c == REPRINT_CHAR(tty) && L_ECHO(tty) &&
  		    L_IEXTEN(tty)) {
  			unsigned long tail = tty->canon_head;
  
  			finish_erasing(tty);
  			echo_char(c, tty);
  			opost('
  ', tty);
  			while (tail != tty->read_head) {
  				echo_char(tty->read_buf[tail], tty);
  				tail = (tail+1) & (N_TTY_BUF_SIZE-1);
  			}
  			return;
  		}
  		if (c == '
  ') {
  			if (L_ECHO(tty) || L_ECHONL(tty)) {

  				if (tty->read_cnt >= N_TTY_BUF_SIZE-1)

  					tty_put_char(tty, '\a');

  				opost('
  ', tty);
  			}
  			goto handle_newline;
  		}
  		if (c == EOF_CHAR(tty)) {

  			if (tty->canon_head != tty->read_head)
  				set_bit(TTY_PUSH, &tty->flags);

  			c = __DISABLED_CHAR;
  			goto handle_newline;
  		}
  		if ((c == EOL_CHAR(tty)) ||
  		    (c == EOL2_CHAR(tty) && L_IEXTEN(tty))) {
  			/*
  			 * XXX are EOL_CHAR and EOL2_CHAR echoed?!?
  			 */
  			if (L_ECHO(tty)) {

  				if (tty->read_cnt >= N_TTY_BUF_SIZE-1)

  					tty_put_char(tty, '\a');

  				/* Record the column of first canon char. */
  				if (tty->canon_head == tty->read_head)
  					tty->canon_column = tty->column;
  				echo_char(c, tty);
  			}
  			/*
  			 * XXX does PARMRK doubling happen for
  			 * EOL_CHAR and EOL2_CHAR?
  			 */
  			if (I_PARMRK(tty) && c == (unsigned char) '\377')
  				put_tty_queue(c, tty);

  handle_newline:

  			spin_lock_irqsave(&tty->read_lock, flags);
  			set_bit(tty->read_head, tty->read_flags);
  			put_tty_queue_nolock(c, tty);
  			tty->canon_head = tty->read_head;
  			tty->canon_data++;
  			spin_unlock_irqrestore(&tty->read_lock, flags);
  			kill_fasync(&tty->fasync, SIGIO, POLL_IN);
  			if (waitqueue_active(&tty->read_wait))
  				wake_up_interruptible(&tty->read_wait);
  			return;
  		}
  	}

  	finish_erasing(tty);
  	if (L_ECHO(tty)) {
  		if (tty->read_cnt >= N_TTY_BUF_SIZE-1) {

  			tty_put_char(tty, '\a'); /* beep if no space */

  			return;
  		}
  		if (c == '
  ')
  			opost('
  ', tty);
  		else {
  			/* Record the column of first canon char. */
  			if (tty->canon_head == tty->read_head)
  				tty->canon_column = tty->column;
  			echo_char(c, tty);
  		}
  	}
  
  	if (I_PARMRK(tty) && c == (unsigned char) '\377')
  		put_tty_queue(c, tty);
  
  	put_tty_queue(c, tty);

  }

  
  /**
   *	n_tty_write_wakeup	-	asynchronous I/O notifier
   *	@tty: tty device
   *
   *	Required for the ptys, serial driver etc. since processes
   *	that attach themselves to the master and rely on ASYNC
   *	IO must be woken up
   */
  
  static void n_tty_write_wakeup(struct tty_struct *tty)
  {

  	if (tty->fasync) {
  		set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);

  		kill_fasync(&tty->fasync, SIGIO, POLL_OUT);
  	}

  }
  
  /**
   *	n_tty_receive_buf	-	data receive
   *	@tty: terminal device
   *	@cp: buffer
   *	@fp: flag buffer
   *	@count: characters
   *
   *	Called by the terminal driver when a block of characters has
   *	been received. This function must be called from soft contexts
   *	not from interrupt context. The driver is responsible for making
   *	calls one at a time and in order (or using flush_to_ldisc)
   */

  static void n_tty_receive_buf(struct tty_struct *tty, const unsigned char *cp,
  			      char *fp, int count)
  {
  	const unsigned char *p;
  	char *f, flags = TTY_NORMAL;
  	int	i;
  	char	buf[64];
  	unsigned long cpuflags;
  
  	if (!tty->read_buf)
  		return;
  
  	if (tty->real_raw) {
  		spin_lock_irqsave(&tty->read_lock, cpuflags);
  		i = min(N_TTY_BUF_SIZE - tty->read_cnt,
  			N_TTY_BUF_SIZE - tty->read_head);
  		i = min(count, i);
  		memcpy(tty->read_buf + tty->read_head, cp, i);
  		tty->read_head = (tty->read_head + i) & (N_TTY_BUF_SIZE-1);
  		tty->read_cnt += i;
  		cp += i;
  		count -= i;
  
  		i = min(N_TTY_BUF_SIZE - tty->read_cnt,
  			N_TTY_BUF_SIZE - tty->read_head);
  		i = min(count, i);
  		memcpy(tty->read_buf + tty->read_head, cp, i);
  		tty->read_head = (tty->read_head + i) & (N_TTY_BUF_SIZE-1);
  		tty->read_cnt += i;
  		spin_unlock_irqrestore(&tty->read_lock, cpuflags);
  	} else {

  		for (i = count, p = cp, f = fp; i; i--, p++) {

  			if (f)
  				flags = *f++;
  			switch (flags) {
  			case TTY_NORMAL:
  				n_tty_receive_char(tty, *p);
  				break;
  			case TTY_BREAK:
  				n_tty_receive_break(tty);
  				break;
  			case TTY_PARITY:
  			case TTY_FRAME:
  				n_tty_receive_parity_error(tty, *p);
  				break;
  			case TTY_OVERRUN:
  				n_tty_receive_overrun(tty);
  				break;
  			default:

  				printk(KERN_ERR "%s: unknown flag %d
  ",

  				       tty_name(tty, buf), flags);
  				break;
  			}
  		}

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

  	}

  	n_tty_set_room(tty);

  	if (!tty->icanon && (tty->read_cnt >= tty->minimum_to_wake)) {
  		kill_fasync(&tty->fasync, SIGIO, POLL_IN);
  		if (waitqueue_active(&tty->read_wait))
  			wake_up_interruptible(&tty->read_wait);
  	}
  
  	/*
  	 * Check the remaining room for the input canonicalization
  	 * mode.  We don't want to throttle the driver if we're in
  	 * canonical mode and don't have a newline yet!
  	 */

  	if (tty->receive_room < TTY_THRESHOLD_THROTTLE)
  		tty_throttle(tty);

  }
  
  int is_ignored(int sig)
  {
  	return (sigismember(&current->blocked, sig) ||

  		current->sighand->action[sig-1].sa.sa_handler == SIG_IGN);

  }
  
  /**
   *	n_tty_set_termios	-	termios data changed
   *	@tty: terminal
   *	@old: previous data
   *
   *	Called by the tty layer when the user changes termios flags so
   *	that the line discipline can plan ahead. This function cannot sleep

   *	and is protected from re-entry by the tty layer. The user is

   *	guaranteed that this function will not be re-entered or in progress
   *	when the ldisc is closed.

   *
   *	Locking: Caller holds tty->termios_mutex

   */

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

  {

  	int canon_change = 1;
  	BUG_ON(!tty);
  
  	if (old)
  		canon_change = (old->c_lflag ^ tty->termios->c_lflag) & ICANON;
  	if (canon_change) {
  		memset(&tty->read_flags, 0, sizeof tty->read_flags);
  		tty->canon_head = tty->read_tail;
  		tty->canon_data = 0;
  		tty->erasing = 0;
  	}
  
  	if (canon_change && !L_ICANON(tty) && tty->read_cnt)
  		wake_up_interruptible(&tty->read_wait);

  	tty->icanon = (L_ICANON(tty) != 0);
  	if (test_bit(TTY_HW_COOK_IN, &tty->flags)) {
  		tty->raw = 1;
  		tty->real_raw = 1;

  		n_tty_set_room(tty);

  		return;
  	}
  	if (I_ISTRIP(tty) || I_IUCLC(tty) || I_IGNCR(tty) ||
  	    I_ICRNL(tty) || I_INLCR(tty) || L_ICANON(tty) ||
  	    I_IXON(tty) || L_ISIG(tty) || L_ECHO(tty) ||
  	    I_PARMRK(tty)) {
  		memset(tty->process_char_map, 0, 256/8);
  
  		if (I_IGNCR(tty) || I_ICRNL(tty))
  			set_bit('\r', tty->process_char_map);
  		if (I_INLCR(tty))
  			set_bit('
  ', tty->process_char_map);
  
  		if (L_ICANON(tty)) {
  			set_bit(ERASE_CHAR(tty), tty->process_char_map);
  			set_bit(KILL_CHAR(tty), tty->process_char_map);
  			set_bit(EOF_CHAR(tty), tty->process_char_map);
  			set_bit('
  ', tty->process_char_map);
  			set_bit(EOL_CHAR(tty), tty->process_char_map);
  			if (L_IEXTEN(tty)) {
  				set_bit(WERASE_CHAR(tty),
  					tty->process_char_map);
  				set_bit(LNEXT_CHAR(tty),
  					tty->process_char_map);
  				set_bit(EOL2_CHAR(tty),
  					tty->process_char_map);
  				if (L_ECHO(tty))
  					set_bit(REPRINT_CHAR(tty),
  						tty->process_char_map);
  			}
  		}
  		if (I_IXON(tty)) {
  			set_bit(START_CHAR(tty), tty->process_char_map);
  			set_bit(STOP_CHAR(tty), tty->process_char_map);
  		}
  		if (L_ISIG(tty)) {
  			set_bit(INTR_CHAR(tty), tty->process_char_map);
  			set_bit(QUIT_CHAR(tty), tty->process_char_map);
  			set_bit(SUSP_CHAR(tty), tty->process_char_map);
  		}
  		clear_bit(__DISABLED_CHAR, tty->process_char_map);
  		tty->raw = 0;
  		tty->real_raw = 0;
  	} else {
  		tty->raw = 1;
  		if ((I_IGNBRK(tty) || (!I_BRKINT(tty) && !I_PARMRK(tty))) &&
  		    (I_IGNPAR(tty) || !I_INPCK(tty)) &&
  		    (tty->driver->flags & TTY_DRIVER_REAL_RAW))
  			tty->real_raw = 1;
  		else
  			tty->real_raw = 0;
  	}

  	n_tty_set_room(tty);

  	/* The termios change make the tty ready for I/O */
  	wake_up_interruptible(&tty->write_wait);
  	wake_up_interruptible(&tty->read_wait);

  }
  
  /**
   *	n_tty_close		-	close the ldisc for this tty
   *	@tty: device
   *

   *	Called from the terminal layer when this line discipline is
   *	being shut down, either because of a close or becsuse of a

   *	discipline change. The function will not be called while other
   *	ldisc methods are in progress.
   */

  static void n_tty_close(struct tty_struct *tty)
  {
  	n_tty_flush_buffer(tty);
  	if (tty->read_buf) {
  		free_buf(tty->read_buf);
  		tty->read_buf = NULL;
  	}
  }
  
  /**
   *	n_tty_open		-	open an ldisc
   *	@tty: terminal to open
   *

   *	Called when this line discipline is being attached to the

   *	terminal device. Can sleep. Called serialized so that no
   *	other events will occur in parallel. No further open will occur
   *	until a close.
   */
  
  static int n_tty_open(struct tty_struct *tty)
  {
  	if (!tty)
  		return -EINVAL;
  
  	/* This one is ugly. Currently a malloc failure here can panic */
  	if (!tty->read_buf) {
  		tty->read_buf = alloc_buf();
  		if (!tty->read_buf)
  			return -ENOMEM;
  	}
  	memset(tty->read_buf, 0, N_TTY_BUF_SIZE);
  	reset_buffer_flags(tty);
  	tty->column = 0;
  	n_tty_set_termios(tty, NULL);
  	tty->minimum_to_wake = 1;
  	tty->closing = 0;
  	return 0;
  }
  
  static inline int input_available_p(struct tty_struct *tty, int amt)
  {
  	if (tty->icanon) {
  		if (tty->canon_data)
  			return 1;
  	} else if (tty->read_cnt >= (amt ? amt : 1))
  		return 1;
  
  	return 0;
  }
  
  /**
   * 	copy_from_read_buf	-	copy read data directly
   *	@tty: terminal device
   *	@b: user data
   *	@nr: size of data
   *

   *	Helper function to speed up n_tty_read.  It is only called when

   *	ICANON is off; it copies characters straight from the tty queue to
   *	user space directly.  It can be profitably called twice; once to
   *	drain the space from the tail pointer to the (physical) end of the
   *	buffer, and once to drain the space from the (physical) beginning of
   *	the buffer to head pointer.
   *

   *	Called under the tty->atomic_read_lock sem

   *
   */

  static int copy_from_read_buf(struct tty_struct *tty,

  				      unsigned char __user **b,
  				      size_t *nr)
  
  {
  	int retval;
  	size_t n;
  	unsigned long flags;
  
  	retval = 0;
  	spin_lock_irqsave(&tty->read_lock, flags);
  	n = min(tty->read_cnt, N_TTY_BUF_SIZE - tty->read_tail);
  	n = min(*nr, n);
  	spin_unlock_irqrestore(&tty->read_lock, flags);
  	if (n) {

  		retval = copy_to_user(*b, &tty->read_buf[tty->read_tail], n);
  		n -= retval;

  		tty_audit_add_data(tty, &tty->read_buf[tty->read_tail], n);

  		spin_lock_irqsave(&tty->read_lock, flags);
  		tty->read_tail = (tty->read_tail + n) & (N_TTY_BUF_SIZE-1);
  		tty->read_cnt -= n;
  		spin_unlock_irqrestore(&tty->read_lock, flags);
  		*b += n;
  		*nr -= n;
  	}
  	return retval;
  }

  extern ssize_t redirected_tty_write(struct file *, const char __user *,

  							size_t, loff_t *);

  
  /**
   *	job_control		-	check job control
   *	@tty: tty
   *	@file: file handle
   *
   *	Perform job control management checks on this file/tty descriptor

   *	and if appropriate send any needed signals and return a negative

   *	error code if action should be taken.

   *
   *	FIXME:
   *	Locking: None - redirected write test is safe, testing
   *	current->signal should possibly lock current->sighand
   *	pgrp locking ?

   */

  static int job_control(struct tty_struct *tty, struct file *file)
  {
  	/* Job control check -- must be done at start and after
  	   every sleep (POSIX.1 7.1.1.4). */
  	/* NOTE: not yet done after every sleep pending a thorough
  	   check of the logic of this change. -- jlc */
  	/* don't stop on /dev/console */
  	if (file->f_op->write != redirected_tty_write &&
  	    current->signal->tty == tty) {

  		if (!tty->pgrp)

  			printk(KERN_ERR "n_tty_read: no tty->pgrp!
  ");

  		else if (task_pgrp(current) != tty->pgrp) {

  			if (is_ignored(SIGTTIN) ||

  			    is_current_pgrp_orphaned())

  				return -EIO;

  			kill_pgrp(task_pgrp(current), SIGTTIN, 1);

  			set_thread_flag(TIF_SIGPENDING);

  			return -ERESTARTSYS;
  		}
  	}
  	return 0;
  }

  
  /**

   *	n_tty_read		-	read function for tty

   *	@tty: tty device
   *	@file: file object
   *	@buf: userspace buffer pointer
   *	@nr: size of I/O
   *
   *	Perform reads for the line discipline. We are guaranteed that the
   *	line discipline will not be closed under us but we may get multiple
   *	parallel readers and must handle this ourselves. We may also get
   *	a hangup. Always called in user context, may sleep.
   *
   *	This code must be sure never to sleep through a hangup.
   */

  static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,

  			 unsigned char __user *buf, size_t nr)
  {
  	unsigned char __user *b = buf;
  	DECLARE_WAITQUEUE(wait, current);
  	int c;
  	int minimum, time;
  	ssize_t retval = 0;
  	ssize_t size;
  	long timeout;
  	unsigned long flags;

  	int packet;

  
  do_it_again:

  	BUG_ON(!tty->read_buf);

  
  	c = job_control(tty, file);

  	if (c < 0)

  		return c;

  	minimum = time = 0;
  	timeout = MAX_SCHEDULE_TIMEOUT;
  	if (!tty->icanon) {
  		time = (HZ / 10) * TIME_CHAR(tty);
  		minimum = MIN_CHAR(tty);
  		if (minimum) {
  			if (time)
  				tty->minimum_to_wake = 1;
  			else if (!waitqueue_active(&tty->read_wait) ||
  				 (tty->minimum_to_wake > minimum))
  				tty->minimum_to_wake = minimum;
  		} else {
  			timeout = 0;
  			if (time) {
  				timeout = time;
  				time = 0;
  			}
  			tty->minimum_to_wake = minimum = 1;
  		}
  	}
  
  	/*
  	 *	Internal serialization of reads.
  	 */
  	if (file->f_flags & O_NONBLOCK) {

  		if (!mutex_trylock(&tty->atomic_read_lock))

  			return -EAGAIN;

  	} else {

  		if (mutex_lock_interruptible(&tty->atomic_read_lock))

  			return -ERESTARTSYS;
  	}

  	packet = tty->packet;

  
  	add_wait_queue(&tty->read_wait, &wait);

  	while (nr) {
  		/* First test for status change. */

  		if (packet && tty->link->ctrl_status) {

  			unsigned char cs;
  			if (b != buf)
  				break;

  			spin_lock_irqsave(&tty->link->ctrl_lock, flags);

  			cs = tty->link->ctrl_status;
  			tty->link->ctrl_status = 0;

  			spin_unlock_irqrestore(&tty->link->ctrl_lock, flags);

  			if (tty_put_user(tty, cs, b++)) {

  				retval = -EFAULT;
  				b--;
  				break;
  			}
  			nr--;
  			break;
  		}
  		/* This statement must be first before checking for input
  		   so that any interrupt will set the state back to
  		   TASK_RUNNING. */
  		set_current_state(TASK_INTERRUPTIBLE);

  		if (((minimum - (b - buf)) < tty->minimum_to_wake) &&
  		    ((minimum - (b - buf)) >= 1))
  			tty->minimum_to_wake = (minimum - (b - buf));

  		if (!input_available_p(tty, 0)) {
  			if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
  				retval = -EIO;
  				break;
  			}
  			if (tty_hung_up_p(file))
  				break;
  			if (!timeout)
  				break;
  			if (file->f_flags & O_NONBLOCK) {
  				retval = -EAGAIN;
  				break;
  			}
  			if (signal_pending(current)) {
  				retval = -ERESTARTSYS;
  				break;
  			}

  			/* FIXME: does n_tty_set_room need locking ? */

  			n_tty_set_room(tty);

  			timeout = schedule_timeout(timeout);

  			continue;
  		}
  		__set_current_state(TASK_RUNNING);
  
  		/* Deal with packet mode. */

  		if (packet && b == buf) {

  			if (tty_put_user(tty, TIOCPKT_DATA, b++)) {

  				retval = -EFAULT;
  				b--;
  				break;
  			}
  			nr--;
  		}
  
  		if (tty->icanon) {
  			/* N.B. avoid overrun if nr == 0 */
  			while (nr && tty->read_cnt) {

  				int eol;

  
  				eol = test_and_clear_bit(tty->read_tail,
  						tty->read_flags);
  				c = tty->read_buf[tty->read_tail];
  				spin_lock_irqsave(&tty->read_lock, flags);
  				tty->read_tail = ((tty->read_tail+1) &
  						  (N_TTY_BUF_SIZE-1));
  				tty->read_cnt--;
  				if (eol) {
  					/* this test should be redundant:
  					 * we shouldn't be reading data if
  					 * canon_data is 0
  					 */
  					if (--tty->canon_data < 0)
  						tty->canon_data = 0;
  				}
  				spin_unlock_irqrestore(&tty->read_lock, flags);
  
  				if (!eol || (c != __DISABLED_CHAR)) {

  					if (tty_put_user(tty, c, b++)) {

  						retval = -EFAULT;
  						b--;
  						break;
  					}
  					nr--;
  				}

  				if (eol) {
  					tty_audit_push(tty);

  					break;

  				}

  			}
  			if (retval)
  				break;
  		} else {
  			int uncopied;

  			/* The copy function takes the read lock and handles
  			   locking internally for this case */

  			uncopied = copy_from_read_buf(tty, &b, &nr);
  			uncopied += copy_from_read_buf(tty, &b, &nr);
  			if (uncopied) {
  				retval = -EFAULT;
  				break;
  			}
  		}
  
  		/* If there is enough space in the read buffer now, let the
  		 * low-level driver know. We use n_tty_chars_in_buffer() to
  		 * check the buffer, as it now knows about canonical mode.
  		 * Otherwise, if the driver is throttled and the line is
  		 * longer than TTY_THRESHOLD_UNTHROTTLE in canonical mode,
  		 * we won't get any more characters.
  		 */

  		if (n_tty_chars_in_buffer(tty) <= TTY_THRESHOLD_UNTHROTTLE) {
  			n_tty_set_room(tty);

  			check_unthrottle(tty);

  		}

  
  		if (b - buf >= minimum)
  			break;
  		if (time)
  			timeout = time;
  	}

  	mutex_unlock(&tty->atomic_read_lock);

  	remove_wait_queue(&tty->read_wait, &wait);
  
  	if (!waitqueue_active(&tty->read_wait))
  		tty->minimum_to_wake = minimum;
  
  	__set_current_state(TASK_RUNNING);
  	size = b - buf;
  	if (size) {
  		retval = size;
  		if (nr)

  			clear_bit(TTY_PUSH, &tty->flags);

  	} else if (test_and_clear_bit(TTY_PUSH, &tty->flags))
  		 goto do_it_again;

  	n_tty_set_room(tty);

  	return retval;
  }
  
  /**

   *	n_tty_write		-	write function for tty

   *	@tty: tty device
   *	@file: file object
   *	@buf: userspace buffer pointer
   *	@nr: size of I/O
   *
   *	Write function of the terminal device. This is serialized with
   *	respect to other write callers but not to termios changes, reads
   *	and other such events. We must be careful with N_TTY as the receive
   *	code will echo characters, thus calling driver write methods.
   *
   *	This code must be sure never to sleep through a hangup.
   */

  static ssize_t n_tty_write(struct tty_struct *tty, struct file *file,

  			  const unsigned char *buf, size_t nr)

  {
  	const unsigned char *b = buf;
  	DECLARE_WAITQUEUE(wait, current);
  	int c;
  	ssize_t retval = 0;
  
  	/* Job control check -- must be done at start (POSIX.1 7.1.1.4). */
  	if (L_TOSTOP(tty) && file->f_op->write != redirected_tty_write) {
  		retval = tty_check_change(tty);
  		if (retval)
  			return retval;
  	}
  
  	add_wait_queue(&tty->write_wait, &wait);
  	while (1) {
  		set_current_state(TASK_INTERRUPTIBLE);
  		if (signal_pending(current)) {
  			retval = -ERESTARTSYS;
  			break;
  		}
  		if (tty_hung_up_p(file) || (tty->link && !tty->link->count)) {
  			retval = -EIO;
  			break;
  		}
  		if (O_OPOST(tty) && !(test_bit(TTY_HW_COOK_OUT, &tty->flags))) {
  			while (nr > 0) {
  				ssize_t num = opost_block(tty, b, nr);
  				if (num < 0) {
  					if (num == -EAGAIN)
  						break;
  					retval = num;
  					goto break_out;
  				}
  				b += num;
  				nr -= num;
  				if (nr == 0)
  					break;
  				c = *b;
  				if (opost(c, tty) < 0)
  					break;
  				b++; nr--;
  			}

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

  		} else {

  			while (nr > 0) {

  				c = tty->ops->write(tty, b, nr);

  				if (c < 0) {
  					retval = c;
  					goto break_out;
  				}
  				if (!c)
  					break;
  				b += c;
  				nr -= c;

  			}

  		}
  		if (!nr)
  			break;
  		if (file->f_flags & O_NONBLOCK) {
  			retval = -EAGAIN;
  			break;
  		}
  		schedule();
  	}
  break_out:
  	__set_current_state(TASK_RUNNING);
  	remove_wait_queue(&tty->write_wait, &wait);
  	return (b - buf) ? b - buf : retval;
  }
  
  /**

   *	n_tty_poll		-	poll method for N_TTY

   *	@tty: terminal device
   *	@file: file accessing it
   *	@wait: poll table
   *
   *	Called when the line discipline is asked to poll() for data or
   *	for special events. This code is not serialized with respect to
   *	other events save open/close.
   *
   *	This code must be sure never to sleep through a hangup.
   *	Called without the kernel lock held - fine

   */

  static unsigned int n_tty_poll(struct tty_struct *tty, struct file *file,

  							poll_table *wait)

  {
  	unsigned int mask = 0;
  
  	poll_wait(file, &tty->read_wait, wait);
  	poll_wait(file, &tty->write_wait, wait);
  	if (input_available_p(tty, TIME_CHAR(tty) ? 0 : MIN_CHAR(tty)))
  		mask |= POLLIN | POLLRDNORM;
  	if (tty->packet && tty->link->ctrl_status)
  		mask |= POLLPRI | POLLIN | POLLRDNORM;
  	if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
  		mask |= POLLHUP;
  	if (tty_hung_up_p(file))
  		mask |= POLLHUP;
  	if (!(mask & (POLLHUP | POLLIN | POLLRDNORM))) {
  		if (MIN_CHAR(tty) && !TIME_CHAR(tty))
  			tty->minimum_to_wake = MIN_CHAR(tty);
  		else
  			tty->minimum_to_wake = 1;
  	}

  	if (tty->ops->write && !tty_is_writelocked(tty) &&
  			tty_chars_in_buffer(tty) < WAKEUP_CHARS &&
  			tty_write_room(tty) > 0)

  		mask |= POLLOUT | POLLWRNORM;
  	return mask;
  }

  static unsigned long inq_canon(struct tty_struct *tty)
  {
  	int nr, head, tail;

  	if (!tty->canon_data)

  		return 0;
  	head = tty->canon_head;
  	tail = tty->read_tail;
  	nr = (head - tail) & (N_TTY_BUF_SIZE-1);
  	/* Skip EOF-chars.. */
  	while (head != tail) {
  		if (test_bit(tail, tty->read_flags) &&
  		    tty->read_buf[tail] == __DISABLED_CHAR)
  			nr--;
  		tail = (tail+1) & (N_TTY_BUF_SIZE-1);
  	}
  	return nr;
  }
  
  static int n_tty_ioctl(struct tty_struct *tty, struct file *file,
  		       unsigned int cmd, unsigned long arg)
  {
  	int retval;
  
  	switch (cmd) {
  	case TIOCOUTQ:
  		return put_user(tty_chars_in_buffer(tty), (int __user *) arg);
  	case TIOCINQ:

  		/* FIXME: Locking */

  		retval = tty->read_cnt;
  		if (L_ICANON(tty))
  			retval = inq_canon(tty);
  		return put_user(retval, (unsigned int __user *) arg);
  	default:
  		return n_tty_ioctl_helper(tty, file, cmd, arg);
  	}
  }

  struct tty_ldisc_ops tty_ldisc_N_TTY = {

  	.magic           = TTY_LDISC_MAGIC,
  	.name            = "n_tty",
  	.open            = n_tty_open,
  	.close           = n_tty_close,
  	.flush_buffer    = n_tty_flush_buffer,
  	.chars_in_buffer = n_tty_chars_in_buffer,

  	.read            = n_tty_read,
  	.write           = n_tty_write,

  	.ioctl           = n_tty_ioctl,
  	.set_termios     = n_tty_set_termios,

  	.poll            = n_tty_poll,

  	.receive_buf     = n_tty_receive_buf,
  	.write_wakeup    = n_tty_write_wakeup

  };