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[linux-2.6/linux-mips.git] / drivers / char / n_tty.c

/*
 * 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.
 *
 * 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.
 */

#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 <linux/poll.h>

#include <asm/uaccess.h>
#include <asm/system.h>
#include <asm/bitops.h>

#define CONSOLE_DEV MKDEV(TTY_MAJOR,0)
#define SYSCONS_DEV  MKDEV(TTYAUX_MAJOR,1)

#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          128 /* now based on remaining room */
#define TTY_THRESHOLD_UNTHROTTLE        128

static inline unsigned char *alloc_buf(void)
{
        unsigned char *p;
        int prio = in_interrupt() ? GFP_ATOMIC : GFP_KERNEL;

        if (PAGE_SIZE != N_TTY_BUF_SIZE) {
                p = kmalloc(N_TTY_BUF_SIZE, prio);
                if (p)
                        memset(p, 0, N_TTY_BUF_SIZE);
        } else
                p = (unsigned char *)get_zeroed_page(prio);

        return p;
}

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(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 comming? --AJK
        */
        spin_lock_irqsave(&tty->read_lock, flags);
        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++;
        }
        spin_unlock_irqrestore(&tty->read_lock, flags);
}

/* 
 * Check whether to call the driver.unthrottle function.
 * We test the TTY_THROTTLED bit first so that it always
 * indicates the current state.
 */
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 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);
}

/*
 * Flush the input buffer
 */
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);
        }
}

/*
 * Return number of characters buffered to be delivered to user
 */
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;
}

/*
 * 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;
}

/*
 * opost_block --- to speed up block console writes, among other
 * things.
 */
static ssize_t opost_block(struct tty_struct * tty,
                       const unsigned char * inbuf, unsigned int nr)
{
        char    buf[80];
        int     space;
        int     i;
        char    *cp;

        space = tty->driver.write_room(tty);
        if (!space)
                return 0;
        if (nr > space)
                nr = space;
        if (nr > sizeof(buf))
            nr = sizeof(buf);

        if (copy_from_user(buf, inbuf, nr))
                return -EFAULT;

        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)) {
                                *cp = '\n';
                                if (O_ONLRET(tty))
                                        tty->canon_column = tty->column = 0;
                                break;
                        }
                        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))
                                *cp = toupper(*cp);
                        if (!iscntrl(*cp))
                                tty->column++;
                        break;
                }
        }
break_out:
        if (tty->driver.flush_chars)
                tty->driver.flush_chars(tty);
        i = tty->driver.write(tty, 0, buf, i);  
        return i;
}



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;
        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 - 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;
                }
                spin_lock_irqsave(&tty->read_lock, flags);
                tty->read_head = head;
                tty->read_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;
                                }
                                echo_char(c, 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
                                                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);
}

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);
        }
}

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);
}

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)) {
                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  if (I_INPCK(tty))
                put_tty_queue('\0', tty);
        else
                put_tty_queue(c, 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 && !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:
                        set_bit(tty->read_head, &tty->read_flags);
                        put_tty_queue(c, tty);
                        tty->canon_head = tty->read_head;
                        tty->canon_data++;
                        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);
}       

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;
}

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(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;
                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->sig->action[sig-1].sa.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 (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)) {
                cli();
                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);
                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)
{
        n_tty_flush_buffer(tty);
        if (tty->read_buf) {
                free_buf(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 = 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, 0);
        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;
}

/*
 * 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 int copy_from_read_buf(struct tty_struct *tty,
                                      unsigned char **b,
                                      size_t *nr)

{
        int retval;
        ssize_t n;
        unsigned long flags;

        retval = 0;
        spin_lock_irqsave(&tty->read_lock, flags);
        n = MIN(*nr, MIN(tty->read_cnt, N_TTY_BUF_SIZE - tty->read_tail));
        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;
}

static ssize_t read_chan(struct tty_struct *tty, struct file *file,
                         unsigned char *buf, size_t nr)
{
        unsigned char *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;
        }

        /* 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_dentry->d_inode->i_rdev != CONSOLE_DEV &&
            file->f_dentry->d_inode->i_rdev != SYSCONS_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;
                }
        }

        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;
                }
        }

        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;
                        put_user(cs, b++);
                        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;
                }
                current->state = TASK_RUNNING;

                /* Deal with packet mode. */
                if (tty->packet && b == buf) {
                        put_user(TIOCPKT_DATA, b++);
                        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--;
                                spin_unlock_irqrestore(&tty->read_lock, flags);

                                if (!eol || (c != __DISABLED_CHAR)) {
                                        put_user(c, b++);
                                        nr--;
                                }
                                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;
                                        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;

        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;
}

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_dentry->d_inode->i_rdev != CONSOLE_DEV &&
            file->f_dentry->d_inode->i_rdev != SYSCONS_DEV) {
                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) {
                                        retval = num;
                                        goto break_out;
                                }
                                b += num;
                                nr -= num;
                                if (nr == 0)
                                        break;
                                get_user(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, 1, 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:
        current->state = TASK_RUNNING;
        remove_wait_queue(&tty->write_wait, &wait);
        return (b - buf) ? b - buf : retval;
}

/* Called without the kernel lock held - fine */
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)
                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 */
        n_tty_receive_buf,      /* receive_buf */
        n_tty_receive_room,     /* receive_room */
        0                       /* write_wakeup */
};