Linux-2.6.12-rc2v2.6.12-rc2

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!

1 files changed, 1562 insertions, 0 deletions

diff --git a/drivers/char/n_tty.c b/drivers/char/n_tty.c
new file mode 100644
index 000000000000..edba5a35bf21
--- /dev/null
+++ b/drivers/char/n_tty.c
@@ -0,0 +1,1562 @@
+/*
+ * 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 write_chan 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 <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)
+{
+	int 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 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++;
+	}
+}
+
+static inline 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 function.
+ *	We test the TTY_THROTTLED bit first so that it always
+ *	indicates the current state. The decision about whether
+ *	it is worth allowing more input has been taken by the caller.
+ *	Can sleep, may be called under the atomic_read semaphore but
+ *	this is not guaranteed.
+ */
+ 
+static void check_unthrottle(struct tty_struct * tty)
+{
+	if (tty->count &&
+	    test_and_clear_bit(TTY_THROTTLED, &tty->flags) && 
+	    tty->driver->unthrottle)
+		tty->driver->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().
+ */
+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);
+	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).
+ *
+ *	FIXME: tty->ctrl_status is not spinlocked and relies on
+ *	lock_kernel() still.
+ */
+ 
+static void n_tty_flush_buffer(struct tty_struct * tty)
+{
+	/* clear everything and unthrottle the driver */
+	reset_buffer_flags(tty);
+	
+	if (!tty->link)
+		return;
+
+	if (tty->link->packet) {
+		tty->ctrl_status |= TIOCPKT_FLUSHREAD;
+		wake_up_interruptible(&tty->link->read_wait);
+	}
+}
+
+/**
+ *	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. 
+ */
+ 
+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() still.
+ */
+ 
+static int opost(unsigned char c, struct tty_struct *tty)
+{
+	int	space, spaces;
+
+	space = tty->driver->write_room(tty);
+	if (!space)
+		return -1;
+
+	if (O_OPOST(tty)) {
+		switch (c) {
+		case '\n':
+			if (O_ONLRET(tty))
+				tty->column = 0;
+			if (O_ONLCR(tty)) {
+				if (space < 2)
+					return -1;
+				tty->driver->put_char(tty, '\r');
+				tty->column = 0;
+			}
+			tty->canon_column = tty->column;
+			break;
+		case '\r':
+			if (O_ONOCR(tty) && tty->column == 0)
+				return 0;
+			if (O_OCRNL(tty)) {
+				c = '\n';
+				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)
+					return -1;
+				tty->column += spaces;
+				tty->driver->write(tty, "        ", spaces);
+				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->driver->put_char(tty, c);
+	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 write_chan under the tty layer write lock.
+ */
+ 
+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->driver->write_room(tty);
+	if (!space)
+		return 0;
+	if (nr > space)
+		nr = space;
+
+	for (i = 0, cp = buf; i < nr; i++, cp++) {
+		switch (*cp) {
+		case '\n':
+			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->driver->flush_chars)
+		tty->driver->flush_chars(tty);
+	i = tty->driver->write(tty, buf, i);	
+	return i;
+}
+
+
+/**
+ *	put_char	-	write character to driver
+ *	@c: character (or part of unicode symbol)
+ *	@tty: terminal device
+ *
+ *	Queue a byte to the driver layer for output
+ */
+ 
+static inline void put_char(unsigned char c, struct tty_struct *tty)
+{
+	tty->driver->put_char(tty, c);
+}
+
+/**
+ *	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.
+ */
+
+static void echo_char(unsigned char c, struct tty_struct *tty)
+{
+	if (L_ECHOCTL(tty) && iscntrl(c) && c != '\t') {
+		put_char('^', tty);
+		put_char(c ^ 0100, tty);
+		tty->column += 2;
+	} else
+		opost(c, tty);
+}
+
+static inline void finish_erasing(struct tty_struct *tty)
+{
+	if (tty->erasing) {
+		put_char('/', tty);
+		tty->column++;
+		tty->erasing = 0;
+	}
+}
+
+/**
+ *	eraser		-	handle erase function
+ *	@c: character input
+ *	@tty: terminal device
+ *
+ *	Perform erase and neccessary output when an erase character is
+ *	present in the stream from the driver layer. Handles the complexities
+ *	of UTF-8 multibyte symbols.
+ */
+ 
+static void eraser(unsigned char c, struct tty_struct *tty)
+{
+	enum { ERASE, WERASE, KILL } kill_type;
+	int head, seen_alnums, cnt;
+	unsigned long flags;
+
+	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('\n', tty);
+			return;
+		}
+		kill_type = KILL;
+	}
+
+	seen_alnums = 0;
+	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) {
+					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);
+					put_char(tty->read_buf[head], tty);
+				}
+			} 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. */
+					put_char('\b', tty);
+					if (tty->column > 0)
+						tty->column--;
+				}
+			} else {
+				if (iscntrl(c) && L_ECHOCTL(tty)) {
+					put_char('\b', tty);
+					put_char(' ', tty);
+					put_char('\b', tty);
+					if (tty->column > 0)
+						tty->column--;
+				}
+				if (!iscntrl(c) || L_ECHOCTL(tty)) {
+					put_char('\b', tty);
+					put_char(' ', tty);
+					put_char('\b', tty);
+					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.
+ */
+ 
+static inline void isig(int sig, struct tty_struct *tty, int flush)
+{
+	if (tty->pgrp > 0)
+		kill_pg(tty->pgrp, sig, 1);
+	if (flush || !L_NOFLSH(tty)) {
+		n_tty_flush_buffer(tty);
+		if (tty->driver->flush_buffer)
+			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)\n",
+			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 neccessary. 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 (tty->stopped && !tty->flow_stopped &&
+	    I_IXON(tty) && I_IXANY(tty)) {
+		start_tty(tty);
+		return;
+	}
+	
+	if (I_ISTRIP(tty))
+		c &= 0x7f;
+	if (I_IUCLC(tty) && L_IEXTEN(tty))
+		c=tolower(c);
+
+	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) {
+				put_char('\a', tty); /* 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 (c == '\r') {
+		if (I_IGNCR(tty))
+			return;
+		if (I_ICRNL(tty))
+			c = '\n';
+	} else if (c == '\n' && I_INLCR(tty))
+		c = '\r';
+	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:
+			isig(signal, tty, 0);
+			return;
+		}
+	}
+	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)) {
+					put_char('^', tty);
+					put_char('\b', tty);
+				}
+			}
+			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('\n', tty);
+			while (tail != tty->read_head) {
+				echo_char(tty->read_buf[tail], tty);
+				tail = (tail+1) & (N_TTY_BUF_SIZE-1);
+			}
+			return;
+		}
+		if (c == '\n') {
+			if (L_ECHO(tty) || L_ECHONL(tty)) {
+				if (tty->read_cnt >= N_TTY_BUF_SIZE-1) {
+					put_char('\a', tty);
+					return;
+				}
+				opost('\n', 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) {
+					put_char('\a', tty);
+					return;
+				}
+				/* 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) {
+			put_char('\a', tty); /* beep if no space */
+			return;
+		}
+		if (c == '\n')
+			opost('\n', 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_receive_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 int n_tty_receive_room(struct tty_struct *tty)
+{
+	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 (tty->icanon && !tty->canon_data)
+		return N_TTY_BUF_SIZE;
+
+	if (left > 0)
+		return left;
+	return 0;
+}
+
+/**
+ *	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);
+	}
+	return;
+}
+
+/**
+ *	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("%s: unknown flag %d\n",
+				       tty_name(tty, buf), flags);
+				break;
+			}
+		}
+		if (tty->driver->flush_chars)
+			tty->driver->flush_chars(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 (n_tty_receive_room(tty) < TTY_THRESHOLD_THROTTLE) {
+		/* check TTY_THROTTLED first so it indicates our state */
+		if (!test_and_set_bit(TTY_THROTTLED, &tty->flags) &&
+		    tty->driver->throttle)
+			tty->driver->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.
+ */
+ 
+static void n_tty_set_termios(struct tty_struct *tty, struct termios * old)
+{
+	if (!tty)
+		return;
+	
+	tty->icanon = (L_ICANON(tty) != 0);
+	if (test_bit(TTY_HW_COOK_IN, &tty->flags)) {
+		tty->raw = 1;
+		tty->real_raw = 1;
+		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('\n', 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('\n', 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_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 read_chan.  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 sem and with TTY_DONT_FLIP set
+ *
+ */
+ 
+static inline 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) {
+		mb();
+		retval = copy_to_user(*b, &tty->read_buf[tty->read_tail], n);
+		n -= retval;
+		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 *,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.
+ */
+ 
+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 <= 0)
+			printk("read_chan: tty->pgrp <= 0!\n");
+		else if (process_group(current) != tty->pgrp) {
+			if (is_ignored(SIGTTIN) ||
+			    is_orphaned_pgrp(process_group(current)))
+				return -EIO;
+			kill_pg(process_group(current), SIGTTIN, 1);
+			return -ERESTARTSYS;
+		}
+	}
+	return 0;
+}
+ 
+
+/**
+ *	read_chan		-	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 read_chan(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;
+
+do_it_again:
+
+	if (!tty->read_buf) {
+		printk("n_tty_read_chan: called with read_buf == NULL?!?\n");
+		return -EIO;
+	}
+
+	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 (down_trylock(&tty->atomic_read))
+			return -EAGAIN;
+	}
+	else {
+		if (down_interruptible(&tty->atomic_read))
+			return -ERESTARTSYS;
+	}
+
+	add_wait_queue(&tty->read_wait, &wait);
+	set_bit(TTY_DONT_FLIP, &tty->flags);
+	while (nr) {
+		/* First test for status change. */
+		if (tty->packet && tty->link->ctrl_status) {
+			unsigned char cs;
+			if (b != buf)
+				break;
+			cs = tty->link->ctrl_status;
+			tty->link->ctrl_status = 0;
+			if (put_user(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;
+			}
+			clear_bit(TTY_DONT_FLIP, &tty->flags);
+			timeout = schedule_timeout(timeout);
+			set_bit(TTY_DONT_FLIP, &tty->flags);
+			continue;
+		}
+		__set_current_state(TASK_RUNNING);
+
+		/* Deal with packet mode. */
+		if (tty->packet && b == buf) {
+			if (put_user(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 (put_user(c, b++)) {
+						retval = -EFAULT;
+						b--;
+						break;
+					}
+					nr--;
+				}
+				if (eol)
+					break;
+			}
+			if (retval)
+				break;
+		} else {
+			int uncopied;
+			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)
+			check_unthrottle(tty);
+
+		if (b - buf >= minimum)
+			break;
+		if (time)
+			timeout = time;
+	}
+	clear_bit(TTY_DONT_FLIP, &tty->flags);
+	up(&tty->atomic_read);
+	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;
+
+	return retval;
+}
+
+/**
+ *	write_chan		-	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 write_chan(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->driver->flush_chars)
+				tty->driver->flush_chars(tty);
+		} else {
+			c = tty->driver->write(tty, b, nr);
+			if (c < 0) {
+				retval = c;
+				goto break_out;
+			}
+			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;
+}
+
+/**
+ *	normal_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
+ *
+ *	FIXME: if someone changes the VMIN or discipline settings for the
+ *	terminal while another process is in poll() the poll does not
+ *	recompute the new limits. Possibly set_termios should issue
+ *	a read wakeup to fix this bug.
+ */
+ 
+static unsigned int normal_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->driver->chars_in_buffer(tty) < WAKEUP_CHARS &&
+			tty->driver->write_room(tty) > 0)
+		mask |= POLLOUT | POLLWRNORM;
+	return mask;
+}
+
+struct tty_ldisc tty_ldisc_N_TTY = {
+	TTY_LDISC_MAGIC,	/* magic */
+	"n_tty",		/* name */
+	0,			/* num */
+	0,			/* flags */
+	n_tty_open,		/* open */
+	n_tty_close,		/* close */
+	n_tty_flush_buffer,	/* flush_buffer */
+	n_tty_chars_in_buffer,	/* chars_in_buffer */
+	read_chan,		/* read */
+	write_chan,		/* write */
+	n_tty_ioctl,		/* ioctl */
+	n_tty_set_termios,	/* set_termios */
+	normal_poll,		/* poll */
+	NULL,			/* hangup */
+	n_tty_receive_buf,	/* receive_buf */
+	n_tty_receive_room,	/* receive_room */
+	n_tty_write_wakeup	/* write_wakeup */
+};
+