Import of Linus's Linux 1.1.68

1 files changed, 1007 insertions, 0 deletions

diff --git a/drivers/char/n_tty.c b/drivers/char/n_tty.c
new file mode 100644
index 000000000..f8111121f
--- /dev/null
+++ b/drivers/char/n_tty.c
@@ -0,0 +1,1007 @@
+/*
+ * 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 Public
+ * License.
+ */
+
+#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/kd.h>
+#include <linux/mm.h>
+#include <linux/string.h>
+#include <linux/malloc.h>
+
+#include <asm/segment.h>
+#include <asm/system.h>
+#include <asm/bitops.h>
+
+#define CONSOLE_DEV MKDEV(TTY_MAJOR,0)
+
+#ifndef MIN
+#define MIN(a,b)	((a) < (b) ? (a) : (b))
+#endif
+
+/* 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		(N_TTY_BUF_SIZE - 128)
+#define TTY_THRESHOLD_UNTHROTTLE 	128
+
+static inline void put_tty_queue(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++;
+	}
+}
+
+/*
+ * Flush the input buffer
+ */
+void n_tty_flush_buffer(struct tty_struct * tty)
+{
+	tty->read_head = tty->read_tail = tty->read_cnt = 0;
+	tty->canon_head = tty->canon_data = tty->erasing = 0;
+	memset(&tty->read_flags, 0, sizeof tty->read_flags);
+	
+	if (!tty->link)
+		return;
+
+	if (tty->driver.unthrottle)
+		(tty->driver.unthrottle)(tty);
+	if (tty->link->packet) {
+		tty->ctrl_status |= TIOCPKT_FLUSHREAD;
+		wake_up_interruptible(&tty->link->read_wait);
+	}
+}
+
+/*
+ * Return number of characters buffered to be delivered to user
+ */
+int n_tty_chars_in_buffer(struct tty_struct *tty)
+{
+	return tty->read_cnt;
+}
+
+/*
+ * Perform OPOST processing.  Returns -1 when the output device is
+ * full and the character must be retried.
+ */
+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, 0, "        ", 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))
+				tty->column++;
+			break;
+		}
+	}
+	tty->driver.put_char(tty, c);
+	return 0;
+}
+
+static inline void put_char(unsigned char c, struct tty_struct *tty)
+{
+	tty->driver.put_char(tty, c);
+}
+
+/* Must be called only when L_ECHO(tty) is true. */
+
+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 += 2;
+		tty->erasing = 0;
+	}
+}
+
+static void eraser(unsigned char c, struct tty_struct *tty)
+{
+	enum { ERASE, WERASE, KILL } kill_type;
+	int head, seen_alnums;
+
+	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)) {
+			tty->read_cnt -= ((tty->read_head - tty->canon_head) &
+					  (N_TTY_BUF_SIZE - 1));
+			tty->read_head = tty->canon_head;
+			return;
+		}
+		if (!L_ECHOK(tty) || !L_ECHOKE(tty)) {
+			tty->read_cnt -= ((tty->read_head - tty->canon_head) &
+					  (N_TTY_BUF_SIZE - 1));
+			tty->read_head = tty->canon_head;
+			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 - 1) & (N_TTY_BUF_SIZE-1);
+		c = tty->read_buf[head];
+		if (kill_type == WERASE) {
+			/* Equivalent to BSD's ALTWERASE. */
+			if (isalnum(c) || c == '_')
+				seen_alnums++;
+			else if (seen_alnums)
+				break;
+		}
+		tty->read_head = head;
+		tty->read_cnt--;
+		if (L_ECHO(tty)) {
+			if (L_ECHOPRT(tty)) {
+				if (!tty->erasing) {
+					put_char('\\', tty);
+					tty->column++;
+					tty->erasing = 1;
+				}
+				echo_char(c, tty);
+			} else if (!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
+						col++;
+					tail = (tail+1) & (N_TTY_BUF_SIZE-1);
+				}
+
+				/* Now backup to that column. */
+				while (tty->column > col) {
+					/* Can't use opost here. */
+					put_char('\b', tty);
+					tty->column--;
+				}
+			} else {
+				if (iscntrl(c) && L_ECHOCTL(tty)) {
+					put_char('\b', tty);
+					put_char(' ', tty);
+					put_char('\b', tty);
+					tty->column--;
+				}
+				if (!iscntrl(c) || L_ECHOCTL(tty)) {
+					put_char('\b', tty);
+					put_char(' ', tty);
+					put_char('\b', tty);
+					tty->column--;
+				}
+			}
+		}
+		if (kill_type == ERASE)
+			break;
+	}
+	if (tty->read_head == tty->canon_head)
+		finish_erasing(tty);
+}
+
+static void isig(int sig, struct tty_struct *tty)
+{
+	if (tty->pgrp > 0)
+		kill_pg(tty->pgrp, sig, 1);
+	if (!L_NOFLSH(tty)) {
+		n_tty_flush_buffer(tty);
+		if (tty->driver.flush_buffer)
+			tty->driver.flush_buffer(tty);
+	}
+}
+
+static inline void n_tty_receive_break(struct tty_struct *tty)
+{
+	if (I_IGNBRK(tty))
+		return;
+	if (I_BRKINT(tty)) {
+		isig(SIGINT, tty);
+		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);
+}
+
+static inline void n_tty_receive_overrun(struct tty_struct *tty)
+{
+	char buf[64];
+
+	tty->num_overrun++;
+	if (tty->overrun_time < (jiffies - HZ)) {
+		printk("%s: %d input overrun(s)\n", _tty_name(tty, buf),
+		       tty->num_overrun);
+		tty->overrun_time = jiffies;
+		tty->num_overrun = 0;
+	}
+}
+
+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
+		put_tty_queue('\0', tty);
+	wake_up_interruptible(&tty->read_wait);
+}
+
+static inline void n_tty_receive_char(struct tty_struct *tty, unsigned char c)
+{
+	if (tty->raw) {
+		put_tty_queue(c, tty);
+		return;
+	}
+	
+	if (tty->stopped && I_IXON(tty) && I_IXANY(tty) && L_IEXTEN(tty)) {
+		start_tty(tty);
+		return;
+	}
+	
+	if (I_ISTRIP(tty))
+		c &= 0x7f;
+	if (I_IUCLC(tty) && L_IEXTEN(tty))
+		c=tolower(c);
+
+	/*
+	 * 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)) {
+		if (c == INTR_CHAR(tty)) {
+			isig(SIGINT, tty);
+			return;
+		}
+		if (c == QUIT_CHAR(tty)) {
+			isig(SIGQUIT, tty);
+			return;
+		}
+		if (c == SUSP_CHAR(tty)) {
+			if (!is_orphaned_pgrp(tty->pgrp))
+				isig(SIGTSTP, tty);
+			return;
+		}
+	}
+	if (L_ICANON(tty)) {
+		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:
+			set_bit(tty->read_head, &tty->read_flags);
+			put_tty_queue(c, tty);
+			tty->canon_head = tty->read_head;
+			tty->canon_data++;
+			if (tty->fasync)
+				kill_fasync(tty->fasync, SIGIO);
+			if (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);
+}	
+
+static void n_tty_receive_buf(struct tty_struct *tty, unsigned char *cp,
+			      char *fp, int count)
+{
+	unsigned char *p;
+	char *f, flags = 0;
+	int	i;
+
+	if (!tty->read_buf)
+		return;
+
+	if (tty->real_raw) {
+		i = MIN(count, MIN(N_TTY_BUF_SIZE - tty->read_cnt,
+				   N_TTY_BUF_SIZE - tty->read_head));
+		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(count, MIN(N_TTY_BUF_SIZE - tty->read_cnt,
+			       N_TTY_BUF_SIZE - tty->read_head));
+		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;
+	} 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),
+				       flags);
+				break;
+			}
+		}
+		if (tty->driver.flush_chars)
+			tty->driver.flush_chars(tty);
+	}
+
+	if (!tty->icanon && (tty->read_cnt >= tty->minimum_to_wake)) {
+		if (tty->fasync)
+			kill_fasync(tty->fasync, SIGIO);
+		if (tty->read_wait)
+			wake_up_interruptible(&tty->read_wait);
+	}
+
+	if ((tty->read_cnt >= TTY_THRESHOLD_THROTTLE) &&
+	    tty->driver.throttle &&
+	    !set_bit(TTY_THROTTLED, &tty->flags))
+		tty->driver.throttle(tty);
+}
+
+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;
+}
+
+int is_ignored(int sig)
+{
+	return ((current->blocked & (1<<(sig-1))) ||
+	        (current->sigaction[sig-1].sa_handler == SIG_IGN));
+}
+
+static void n_tty_set_termios(struct tty_struct *tty, struct termios * old)
+{
+	if (!tty)
+		return;
+	
+	tty->icanon = (L_ICANON(tty) != 0);
+	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)) {
+		cli();
+		memset(tty->process_char_map, 0, 256/32);
+
+		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);
+		sti();
+		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;
+	}
+}
+
+static void n_tty_close(struct tty_struct *tty)
+{
+	wait_until_sent(tty, 0);
+	n_tty_flush_buffer(tty);
+	if (tty->read_buf) {
+		free_page((unsigned long) tty->read_buf);
+		tty->read_buf = 0;
+	}
+}
+
+static int n_tty_open(struct tty_struct *tty)
+{
+	if (!tty)
+		return -EINVAL;
+
+	if (!tty->read_buf) {
+		tty->read_buf = (unsigned char *)
+			get_free_page(intr_count ? GFP_ATOMIC : GFP_KERNEL);
+		if (!tty->read_buf)
+			return -ENOMEM;
+	}
+	memset(tty->read_buf, 0, N_TTY_BUF_SIZE);
+	tty->read_head = tty->read_tail = tty->read_cnt = 0;
+	memset(tty->read_flags, 0, sizeof(tty->read_flags));
+	n_tty_set_termios(tty, 0);
+	tty->minimum_to_wake = 1;
+	return 0;
+}
+
+static inline int input_available_p(struct tty_struct *tty, int amt)
+{
+	if (L_ICANON(tty)) {
+		if (tty->canon_data)
+			return 1;
+	} else if (tty->read_cnt >= (amt ? amt : 1))
+		return 1;
+
+	return 0;
+}
+
+/*
+ * 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.
+ */
+static inline void copy_from_read_buf(struct tty_struct *tty,
+				      unsigned char **b,
+				      unsigned int *nr)
+
+{
+	int	n;
+
+	n = MIN(*nr, MIN(tty->read_cnt, N_TTY_BUF_SIZE - tty->read_tail));
+	if (!n)
+		return;
+	memcpy_tofs(*b, &tty->read_buf[tty->read_tail], n);
+	tty->read_tail = (tty->read_tail + n) & (N_TTY_BUF_SIZE-1);
+	tty->read_cnt -= n;
+	*b += n;
+	*nr -= n;
+}
+
+static int read_chan(struct tty_struct *tty, struct file *file,
+		     unsigned char *buf, unsigned int nr)
+{
+	struct wait_queue wait = { current, NULL };
+	int c;
+	unsigned char *b = buf;
+	int minimum, time;
+	int retval = 0;
+	int size;
+
+do_it_again:
+
+	if (!tty->read_buf) {
+		printk("n_tty_read_chan: called with read_buf == NULL?!?\n");
+		return -EIO;
+	}
+
+	/* 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_inode->i_rdev != CONSOLE_DEV &&
+	    current->tty == tty) {
+		if (tty->pgrp <= 0)
+			printk("read_chan: tty->pgrp <= 0!\n");
+		else if (current->pgrp != tty->pgrp) {
+			if (is_ignored(SIGTTIN) ||
+			    is_orphaned_pgrp(current->pgrp))
+				return -EIO;
+			kill_pg(current->pgrp, SIGTTIN, 1);
+			return -ERESTARTSYS;
+		}
+	}
+
+	if (L_ICANON(tty)) {
+		minimum = time = 0;
+		current->timeout = (unsigned long) -1;
+	} else {
+		time = (HZ / 10) * TIME_CHAR(tty);
+		minimum = MIN_CHAR(tty);
+		if (minimum) {
+		  	current->timeout = (unsigned long) -1;
+			if (time)
+				tty->minimum_to_wake = 1;
+			else if (!tty->read_wait ||
+				 (tty->minimum_to_wake > minimum))
+				tty->minimum_to_wake = minimum;
+		} else {
+			if (time) {
+				current->timeout = time + jiffies;
+				time = 0;
+			} else
+				current->timeout = 0;
+			tty->minimum_to_wake = minimum = 1;
+		}
+	}
+
+	add_wait_queue(&tty->read_wait, &wait);
+	while (1) {
+		/* First test for status change. */
+		if (tty->packet && tty->link->ctrl_status) {
+			if (b != buf)
+				break;
+			put_fs_byte(tty->link->ctrl_status, b++);
+			tty->link->ctrl_status = 0;
+			break;
+		}
+		/* This statement must be first before checking for input
+		   so that any interrupt will set the state back to
+		   TASK_RUNNING. */
+		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 (tty->flags & (1 << TTY_SLAVE_CLOSED)) {
+				retval = -EIO;
+				break;
+			}
+			if (tty_hung_up_p(file))
+				break;
+			if (!current->timeout)
+				break;
+			if (file->f_flags & O_NONBLOCK) {
+				retval = -EAGAIN;
+				break;
+			}
+			if (current->signal & ~current->blocked) {
+				retval = -ERESTARTSYS;
+				break;
+			}
+			schedule();
+			continue;
+		}
+		current->state = TASK_RUNNING;
+
+		/* Deal with packet mode. */
+		if (tty->packet && b == buf) {
+			put_fs_byte(TIOCPKT_DATA, b++);
+			nr--;
+		}
+
+		if (L_ICANON(tty)) {
+			while (1) {
+				int eol;
+
+				disable_bh(TQUEUE_BH);
+				if (!tty->read_cnt) {
+					enable_bh(TQUEUE_BH);
+					break;
+				}
+				eol = clear_bit(tty->read_tail,
+						&tty->read_flags);
+				c = tty->read_buf[tty->read_tail];
+				tty->read_tail = ((tty->read_tail+1) &
+						  (N_TTY_BUF_SIZE-1));
+				tty->read_cnt--;
+				enable_bh(TQUEUE_BH);
+				if (!eol) {
+					put_fs_byte(c, b++);
+					if (--nr)
+						continue;
+					break;
+				}
+				if (--tty->canon_data < 0) {
+					tty->canon_data = 0;
+				}
+				if (c != __DISABLED_CHAR) {
+					put_fs_byte(c, b++);
+					nr--;
+				}
+				break;
+			}
+		} else {
+			disable_bh(TQUEUE_BH);
+			copy_from_read_buf(tty, &b, &nr);
+			copy_from_read_buf(tty, &b, &nr);
+			enable_bh(TQUEUE_BH);
+		}
+
+		/* If there is enough space in the read buffer now, let the
+		   low-level driver know. */
+		if (tty->driver.unthrottle &&
+		    (tty->read_cnt <= TTY_THRESHOLD_UNTHROTTLE)
+		    && clear_bit(TTY_THROTTLED, &tty->flags))
+			tty->driver.unthrottle(tty);
+
+		if (b - buf >= minimum || !nr)
+			break;
+		if (time)
+			current->timeout = time + jiffies;
+	}
+	remove_wait_queue(&tty->read_wait, &wait);
+
+	if (!tty->read_wait)
+		tty->minimum_to_wake = minimum;
+
+	current->state = TASK_RUNNING;
+	current->timeout = 0;
+	size = b - buf;
+	if (size && nr)
+	        clear_bit(TTY_PUSH, &tty->flags);
+        if (!size && clear_bit(TTY_PUSH, &tty->flags))
+                goto do_it_again;
+	if (!size && !retval)
+	        clear_bit(TTY_PUSH, &tty->flags);
+        return (size ? size : retval);
+}
+
+static int write_chan(struct tty_struct * tty, struct file * file,
+		      unsigned char * buf, unsigned int nr)
+{
+	struct wait_queue wait = { current, NULL };
+	int c;
+	unsigned char *b = buf;
+	int retval = 0;
+
+	/* Job control check -- must be done at start (POSIX.1 7.1.1.4). */
+	if (L_TOSTOP(tty) && file->f_inode->i_rdev != CONSOLE_DEV) {
+		retval = tty_check_change(tty);
+		if (retval)
+			return retval;
+	}
+
+	add_wait_queue(&tty->write_wait, &wait);
+	while (1) {
+		current->state = TASK_INTERRUPTIBLE;
+		if (current->signal & ~current->blocked) {
+			retval = -ERESTARTSYS;
+			break;
+		}
+		if (tty_hung_up_p(file) || (tty->link && !tty->link->count)) {
+			retval = -EIO;
+			break;
+		}
+		if (O_OPOST(tty)) {
+			while (nr > 0) {
+				c = get_fs_byte(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, 1, b, nr);
+			b += c;
+			nr -= c;
+		}
+		if (!nr)
+			break;
+		if (file->f_flags & O_NONBLOCK) {
+			retval = -EAGAIN;
+			break;
+		}
+		schedule();
+	}
+	current->state = TASK_RUNNING;
+	remove_wait_queue(&tty->write_wait, &wait);
+	return (b - buf) ? b - buf : retval;
+}
+
+static int normal_select(struct tty_struct * tty, struct inode * inode,
+			 struct file * file, int sel_type, select_table *wait)
+{
+	switch (sel_type) {
+		case SEL_IN:
+			if (input_available_p(tty, TIME_CHAR(tty) ? 0 :
+					      MIN_CHAR(tty)))
+				return 1;
+			/* fall through */
+		case SEL_EX:
+			if (tty->packet && tty->link->ctrl_status)
+				return 1;
+			if (tty->flags & (1 << TTY_SLAVE_CLOSED))
+				return 1;
+			if (tty_hung_up_p(file))
+				return 1;
+			if (!tty->read_wait) {
+				if (MIN_CHAR(tty) && !TIME_CHAR(tty))
+					tty->minimum_to_wake = MIN_CHAR(tty);
+				else
+					tty->minimum_to_wake = 1;
+			}
+			select_wait(&tty->read_wait, wait);
+			return 0;
+		case SEL_OUT:
+			if (tty->driver.chars_in_buffer(tty) < WAKEUP_CHARS)
+				return 1;
+			select_wait(&tty->write_wait, wait);
+			return 0;
+	}
+	return 0;
+}
+
+struct tty_ldisc tty_ldisc_N_TTY = {
+	TTY_LDISC_MAGIC,	/* magic */
+	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_select,		/* select */
+	n_tty_receive_buf,	/* receive_buf */
+	n_tty_receive_room,	/* receive_room */
+	0			/* write_wakeup */
+};
+