tty_ttydisc.c

Go to the documentation of this file.

/*-
 * Copyright (c) 2008 Ed Schouten <ed@FreeBSD.org>
 * All rights reserved.
 *
 * Portions of this software were developed under sponsorship from Snow
 * B.V., the Netherlands.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/cdefs.h>
__FBSDID("$BSDSUniX$");

#include <sys/param.h>
#include <sys/fcntl.h>
#include <sys/filio.h>
#include <sys/kernel.h>
#include <sys/signal.h>
#include <sys/sysctl.h>
#include <sys/systm.h>
#include <sys/tty.h>
#include <sys/ttycom.h>
#include <sys/ttydefaults.h>
#include <sys/uio.h>
#include <sys/vnode.h>

/*
 * Standard TTYDISC `termios' line discipline.
 */

/* Statistics. */
static unsigned long tty_nin = 0;
SYSCTL_ULONG(_kern, OID_AUTO, tty_nin, CTLFLAG_RD,
        &tty_nin, 0, "Total amount of bytes received");
static unsigned long tty_nout = 0;
SYSCTL_ULONG(_kern, OID_AUTO, tty_nout, CTLFLAG_RD,
        &tty_nout, 0, "Total amount of bytes transmitted");

/* termios comparison macro's. */
#define CMP_CC(v,c) (tp->t_termios.c_cc[v] != _POSIX_VDISABLE && \
                        tp->t_termios.c_cc[v] == (c))
#define CMP_FLAG(field,opt) (tp->t_termios.c_ ## field ## flag & (opt))

/* Characters that cannot be modified through c_cc. */
#define CTAB    '\t'
#define CNL     '\n'
#define CCR     '\r'

/* Character is a control character. */
#define CTL_VALID(c)    ((c) == 0x7f || (unsigned char)(c) < 0x20)
/* Control character should be processed on echo. */
#define CTL_ECHO(c,q)   (!(q) && ((c) == CERASE2 || (c) == CTAB || \
    (c) == CNL || (c) == CCR))
/* Control character should be printed using ^X notation. */
#define CTL_PRINT(c,q)  ((c) == 0x7f || ((unsigned char)(c) < 0x20 && \
    ((q) || ((c) != CTAB && (c) != CNL))))
/* Character is whitespace. */
#define CTL_WHITE(c)    ((c) == ' ' || (c) == CTAB)
/* Character is alphanumeric. */
#define CTL_ALNUM(c)    (((c) >= '0' && (c) <= '9') || \
    ((c) >= 'a' && (c) <= 'z') || ((c) >= 'A' && (c) <= 'Z'))

#define TTY_STACKBUF    256

void
ttydisc_open(struct tty *tp)
{
        ttydisc_optimize(tp);
}

void
ttydisc_close(struct tty *tp)
{

        /* Clean up our flags when leaving the discipline. */
        tp->t_flags &= ~(TF_STOPPED|TF_HIWAT|TF_ZOMBIE);

        /* POSIX states we should flush when close() is called. */
        ttyinq_flush(&tp->t_inq);
        ttyoutq_flush(&tp->t_outq);

        if (!tty_gone(tp)) {
                ttydevsw_inwakeup(tp);
                ttydevsw_outwakeup(tp);
        }

        if (ttyhook_hashook(tp, close))
                ttyhook_close(tp);
}

static int
ttydisc_read_canonical(struct tty *tp, struct uio *uio, int ioflag)
{
        char breakc[4] = { CNL }; /* enough to hold \n, VEOF and VEOL. */
        int error;
        size_t clen, flen = 0, n = 1;
        unsigned char lastc = _POSIX_VDISABLE;

#define BREAK_ADD(c) do { \
        if (tp->t_termios.c_cc[c] != _POSIX_VDISABLE)   \
                breakc[n++] = tp->t_termios.c_cc[c];    \
} while (0)
        /* Determine which characters we should trigger on. */
        BREAK_ADD(VEOF);
        BREAK_ADD(VEOL);
#undef BREAK_ADD
        breakc[n] = '\0';

        do {
                error = tty_wait_background(tp, curthread, SIGTTIN);
                if (error)
                        return (error);

                /*
                 * Quite a tricky case: unlike the old TTY
                 * implementation, this implementation copies data back
                 * to userspace in large chunks. Unfortunately, we can't
                 * calculate the line length on beforehand if it crosses
                 * ttyinq_block boundaries, because multiple reads could
                 * then make this code read beyond the newline.
                 *
                 * This is why we limit the read to:
                 * - The size the user has requested
                 * - The blocksize (done in tty_inq.c)
                 * - The amount of bytes until the newline
                 *
                 * This causes the line length to be recalculated after
                 * each block has been copied to userspace. This will
                 * cause the TTY layer to return data in chunks using
                 * the blocksize (except the first and last blocks).
                 */
                clen = ttyinq_findchar(&tp->t_inq, breakc, uio->uio_resid,
                    &lastc);

                /* No more data. */
                if (clen == 0) {
                        if (tp->t_flags & TF_ZOMBIE)
                                return (0);
                        else if (ioflag & IO_NDELAY)
                                return (EWOULDBLOCK);

                        error = tty_wait(tp, &tp->t_inwait);
                        if (error)
                                return (error);
                        continue;
                }

                /* Don't send the EOF char back to userspace. */
                if (CMP_CC(VEOF, lastc))
                        flen = 1;

                MPASS(flen <= clen);

                /* Read and throw away the EOF character. */
                error = ttyinq_read_uio(&tp->t_inq, tp, uio, clen, flen);
                if (error)
                        return (error);

        } while (uio->uio_resid > 0 && lastc == _POSIX_VDISABLE);

        return (0);
}

static int
ttydisc_read_raw_no_timer(struct tty *tp, struct uio *uio, int ioflag)
{
        size_t vmin = tp->t_termios.c_cc[VMIN];
        ssize_t oresid = uio->uio_resid;
        int error;

        MPASS(tp->t_termios.c_cc[VTIME] == 0);

        /*
         * This routine implements the easy cases of read()s while in
         * non-canonical mode, namely case B and D, where we don't have
         * any timers at all.
         */

        for (;;) {
                error = tty_wait_background(tp, curthread, SIGTTIN);
                if (error)
                        return (error);

                error = ttyinq_read_uio(&tp->t_inq, tp, uio,
                    uio->uio_resid, 0);
                if (error)
                        return (error);
                if (uio->uio_resid == 0 || (oresid - uio->uio_resid) >= vmin)
                        return (0);

                /* We have to wait for more. */
                if (tp->t_flags & TF_ZOMBIE)
                        return (0);
                else if (ioflag & IO_NDELAY)
                        return (EWOULDBLOCK);

                error = tty_wait(tp, &tp->t_inwait);
                if (error)
                        return (error);
        }
}

static int
ttydisc_read_raw_read_timer(struct tty *tp, struct uio *uio, int ioflag,
    int oresid)
{
        size_t vmin = MAX(tp->t_termios.c_cc[VMIN], 1);
        unsigned int vtime = tp->t_termios.c_cc[VTIME];
        struct timeval end, now, left;
        int error, hz;

        MPASS(tp->t_termios.c_cc[VTIME] != 0);

        /* Determine when the read should be expired. */
        end.tv_sec = vtime / 10;
        end.tv_usec = (vtime % 10) * 100000;
        getmicrotime(&now);
        timevaladd(&end, &now);

        for (;;) {
                error = tty_wait_background(tp, curthread, SIGTTIN);
                if (error)
                        return (error);

                error = ttyinq_read_uio(&tp->t_inq, tp, uio,
                    uio->uio_resid, 0);
                if (error)
                        return (error);
                if (uio->uio_resid == 0 || (oresid - uio->uio_resid) >= vmin)
                        return (0);

                /* Calculate how long we should wait. */
                getmicrotime(&now);
                if (timevalcmp(&now, &end, >))
                        return (0);
                left = end;
                timevalsub(&left, &now);
                hz = tvtohz(&left);

                /*
                 * We have to wait for more. If the timer expires, we
                 * should return a 0-byte read.
                 */
                if (tp->t_flags & TF_ZOMBIE)
                        return (0);
                else if (ioflag & IO_NDELAY)
                        return (EWOULDBLOCK);

                error = tty_timedwait(tp, &tp->t_inwait, hz);
                if (error)
                        return (error == EWOULDBLOCK ? 0 : error);
        }

        return (0);
}

static int
ttydisc_read_raw_interbyte_timer(struct tty *tp, struct uio *uio, int ioflag)
{
        size_t vmin = tp->t_termios.c_cc[VMIN];
        ssize_t oresid = uio->uio_resid;
        int error;

        MPASS(tp->t_termios.c_cc[VMIN] != 0);
        MPASS(tp->t_termios.c_cc[VTIME] != 0);

        /*
         * When using the interbyte timer, the timer should be started
         * after the first byte has been received. We just call into the
         * generic read timer code after we've received the first byte.
         */

        for (;;) {
                error = tty_wait_background(tp, curthread, SIGTTIN);
                if (error)
                        return (error);

                error = ttyinq_read_uio(&tp->t_inq, tp, uio,
                    uio->uio_resid, 0);
                if (error)
                        return (error);
                if (uio->uio_resid == 0 || (oresid - uio->uio_resid) >= vmin)
                        return (0);

                /*
                 * Not enough data, but we did receive some, which means
                 * we'll now start using the interbyte timer.
                 */
                if (oresid != uio->uio_resid)
                        break;

                /* We have to wait for more. */
                if (tp->t_flags & TF_ZOMBIE)
                        return (0);
                else if (ioflag & IO_NDELAY)
                        return (EWOULDBLOCK);

                error = tty_wait(tp, &tp->t_inwait);
                if (error)
                        return (error);
        }

        return ttydisc_read_raw_read_timer(tp, uio, ioflag, oresid);
}

int
ttydisc_read(struct tty *tp, struct uio *uio, int ioflag)
{
        int error;

        tty_lock_assert(tp, MA_OWNED);

        if (uio->uio_resid == 0)
                return (0);

        if (CMP_FLAG(l, ICANON))
                error = ttydisc_read_canonical(tp, uio, ioflag);
        else if (tp->t_termios.c_cc[VTIME] == 0)
                error = ttydisc_read_raw_no_timer(tp, uio, ioflag);
        else if (tp->t_termios.c_cc[VMIN] == 0)
                error = ttydisc_read_raw_read_timer(tp, uio, ioflag,
                    uio->uio_resid);
        else
                error = ttydisc_read_raw_interbyte_timer(tp, uio, ioflag);

        if (ttyinq_bytesleft(&tp->t_inq) >= tp->t_inlow ||
            ttyinq_bytescanonicalized(&tp->t_inq) == 0) {
                /* Unset the input watermark when we've got enough space. */
                tty_hiwat_in_unblock(tp);
        }

        return (error);
}

static __inline unsigned int
ttydisc_findchar(const char *obstart, unsigned int oblen)
{
        const char *c = obstart;

        while (oblen--) {
                if (CTL_VALID(*c))
                        break;
                c++;
        }

        return (c - obstart);
}

static int
ttydisc_write_oproc(struct tty *tp, char c)
{
        unsigned int scnt, error;

        MPASS(CMP_FLAG(o, OPOST));
        MPASS(CTL_VALID(c));

#define PRINT_NORMAL() ttyoutq_write_nofrag(&tp->t_outq, &c, 1)
        switch (c) {
        case CEOF:
                /* End-of-text dropping. */
                if (CMP_FLAG(o, ONOEOT))
                        return (0);
                return PRINT_NORMAL();

        case CERASE2:
                /* Handle backspace to fix tab expansion. */
                if (PRINT_NORMAL() != 0)
                        return (-1);
                if (tp->t_column > 0)
                        tp->t_column--;
                return (0);

        case CTAB:
                /* Tab expansion. */
                scnt = 8 - (tp->t_column & 7);
                if (CMP_FLAG(o, TAB3)) {
                        error = ttyoutq_write_nofrag(&tp->t_outq,
                            "        ", scnt);
                } else {
                        error = PRINT_NORMAL();
                }
                if (error)
                        return (-1);

                tp->t_column += scnt;
                MPASS((tp->t_column % 8) == 0);
                return (0);

        case CNL:
                /* Newline conversion. */
                if (CMP_FLAG(o, ONLCR)) {
                        /* Convert \n to \r\n. */
                        error = ttyoutq_write_nofrag(&tp->t_outq, "\r\n", 2);
                } else {
                        error = PRINT_NORMAL();
                }
                if (error)
                        return (-1);

                if (CMP_FLAG(o, ONLCR|ONLRET)) {
                        tp->t_column = tp->t_writepos = 0;
                        ttyinq_reprintpos_set(&tp->t_inq);
                }
                return (0);

        case CCR:
                /* Carriage return to newline conversion. */
                if (CMP_FLAG(o, OCRNL))
                        c = CNL;
                /* Omit carriage returns on column 0. */
                if (CMP_FLAG(o, ONOCR) && tp->t_column == 0)
                        return (0);
                if (PRINT_NORMAL() != 0)
                        return (-1);

                tp->t_column = tp->t_writepos = 0;
                ttyinq_reprintpos_set(&tp->t_inq);
                return (0);
        }

        /*
         * Invisible control character. Print it, but don't
         * increase the column count.
         */
        return PRINT_NORMAL();
#undef PRINT_NORMAL
}

/*
 * Just like the old TTY implementation, we need to copy data in chunks
 * into a temporary buffer. One of the reasons why we need to do this,
 * is because output processing (only TAB3 though) may allow the buffer
 * to grow eight times.
 */
int
ttydisc_write(struct tty *tp, struct uio *uio, int ioflag)
{
        char ob[TTY_STACKBUF];
        char *obstart;
        int error = 0;
        unsigned int oblen = 0;

        tty_lock_assert(tp, MA_OWNED);

        if (tp->t_flags & TF_ZOMBIE)
                return (EIO);

        /*
         * We don't need to check whether the process is the foreground
         * process group or if we have a carrier. This is already done
         * in ttydev_write().
         */

        while (uio->uio_resid > 0) {
                unsigned int nlen;

                MPASS(oblen == 0);

                /* Step 1: read data. */
                obstart = ob;
                nlen = MIN(uio->uio_resid, sizeof ob);
                tty_unlock(tp);
                error = uiomove(ob, nlen, uio);
                tty_lock(tp);
                if (error != 0)
                        break;
                oblen = nlen;

                if (tty_gone(tp)) {
                        error = ENXIO;
                        break;
                }

                MPASS(oblen > 0);

                /* Step 2: process data. */
                do {
                        unsigned int plen, wlen;

                        /* Search for special characters for post processing. */
                        if (CMP_FLAG(o, OPOST)) {
                                plen = ttydisc_findchar(obstart, oblen);
                        } else {
                                plen = oblen;
                        }

                        if (plen == 0) {
                                /*
                                 * We're going to process a character
                                 * that needs processing
                                 */
                                if (ttydisc_write_oproc(tp, *obstart) == 0) {
                                        obstart++;
                                        oblen--;

                                        tp->t_writepos = tp->t_column;
                                        ttyinq_reprintpos_set(&tp->t_inq);
                                        continue;
                                }
                        } else {
                                /* We're going to write regular data. */
                                wlen = ttyoutq_write(&tp->t_outq, obstart, plen);
                                obstart += wlen;
                                oblen -= wlen;
                                tp->t_column += wlen;

                                tp->t_writepos = tp->t_column;
                                ttyinq_reprintpos_set(&tp->t_inq);

                                if (wlen == plen)
                                        continue;
                        }

                        /* Watermark reached. Try to sleep. */
                        tp->t_flags |= TF_HIWAT_OUT;

                        if (ioflag & IO_NDELAY) {
                                error = EWOULDBLOCK;
                                goto done;
                        }

                        /*
                         * The driver may write back the data
                         * synchronously. Be sure to check the high
                         * water mark before going to sleep.
                         */
                        ttydevsw_outwakeup(tp);
                        if ((tp->t_flags & TF_HIWAT_OUT) == 0)
                                continue;

                        error = tty_wait(tp, &tp->t_outwait);
                        if (error)
                                goto done;

                        if (tp->t_flags & TF_ZOMBIE) {
                                error = EIO;
                                goto done;
                        }
                } while (oblen > 0);
        }

done:
        if (!tty_gone(tp))
                ttydevsw_outwakeup(tp);

        /*
         * Add the amount of bytes that we didn't process back to the
         * uio counters. We need to do this to make sure write() doesn't
         * count the bytes we didn't store in the queue.
         */
        uio->uio_resid += oblen;
        return (error);
}

void
ttydisc_optimize(struct tty *tp)
{
        tty_lock_assert(tp, MA_OWNED);

        if (ttyhook_hashook(tp, rint_bypass)) {
                tp->t_flags |= TF_BYPASS;
        } else if (ttyhook_hashook(tp, rint)) {
                tp->t_flags &= ~TF_BYPASS;
        } else if (!CMP_FLAG(i, ICRNL|IGNCR|IMAXBEL|INLCR|ISTRIP|IXON) &&
            (!CMP_FLAG(i, BRKINT) || CMP_FLAG(i, IGNBRK)) &&
            (!CMP_FLAG(i, PARMRK) ||
                CMP_FLAG(i, IGNPAR|IGNBRK) == (IGNPAR|IGNBRK)) &&
            !CMP_FLAG(l, ECHO|ICANON|IEXTEN|ISIG|PENDIN)) {
                tp->t_flags |= TF_BYPASS;
        } else {
                tp->t_flags &= ~TF_BYPASS;
        }
}

void
ttydisc_modem(struct tty *tp, int open)
{

        tty_lock_assert(tp, MA_OWNED);

        if (open)
                cv_broadcast(&tp->t_dcdwait);

        /*
         * Ignore modem status lines when CLOCAL is turned on, but don't
         * enter the zombie state when the TTY isn't opened, because
         * that would cause the TTY to be in zombie state after being
         * opened.
         */
        if (!tty_opened(tp) || CMP_FLAG(c, CLOCAL))
                return;

        if (open == 0) {
                /*
                 * Lost carrier.
                 */
                tp->t_flags |= TF_ZOMBIE;

                tty_signal_sessleader(tp, SIGHUP);
                tty_flush(tp, FREAD|FWRITE);
        } else {
                /*
                 * Carrier is back again.
                 */

                /* XXX: what should we do here? */
        }
}

static int
ttydisc_echo_force(struct tty *tp, char c, int quote)
{

        if (CMP_FLAG(o, OPOST) && CTL_ECHO(c, quote)) {
                /*
                 * Only perform postprocessing when OPOST is turned on
                 * and the character is an unquoted BS/TB/NL/CR.
                 */
                return ttydisc_write_oproc(tp, c);
        } else if (CMP_FLAG(l, ECHOCTL) && CTL_PRINT(c, quote)) {
                /*
                 * Only use ^X notation when ECHOCTL is turned on and
                 * we've got an quoted control character.
                 *
                 * Print backspaces when echoing an end-of-file.
                 */
                char ob[4] = "^?\b\b";

                /* Print ^X notation. */
                if (c != 0x7f)
                        ob[1] = c + 'A' - 1;

                if (!quote && CMP_CC(VEOF, c)) {
                        return ttyoutq_write_nofrag(&tp->t_outq, ob, 4);
                } else {
                        tp->t_column += 2;
                        return ttyoutq_write_nofrag(&tp->t_outq, ob, 2);
                }
        } else {
                /* Can just be printed. */
                tp->t_column++;
                return ttyoutq_write_nofrag(&tp->t_outq, &c, 1);
        }
}

static int
ttydisc_echo(struct tty *tp, char c, int quote)
{

        /*
         * Only echo characters when ECHO is turned on, or ECHONL when
         * the character is an unquoted newline.
         */
        if (!CMP_FLAG(l, ECHO) &&
            (!CMP_FLAG(l, ECHONL) || c != CNL || quote))
                return (0);

        return ttydisc_echo_force(tp, c, quote);
}


static void
ttydisc_reprint_char(void *d, char c, int quote)
{
        struct tty *tp = d;

        ttydisc_echo(tp, c, quote);
}

static void
ttydisc_reprint(struct tty *tp)
{
        cc_t c;

        /* Print  ^R\n, followed by the line. */
        c = tp->t_termios.c_cc[VREPRINT];
        if (c != _POSIX_VDISABLE)
                ttydisc_echo(tp, c, 0);
        ttydisc_echo(tp, CNL, 0);
        ttyinq_reprintpos_reset(&tp->t_inq);

        ttyinq_line_iterate_from_linestart(&tp->t_inq, ttydisc_reprint_char, tp);
}

struct ttydisc_recalc_length {
        struct tty *tp;
        unsigned int curlen;
};

static void
ttydisc_recalc_charlength(void *d, char c, int quote)
{
        struct ttydisc_recalc_length *data = d;
        struct tty *tp = data->tp;

        if (CTL_PRINT(c, quote)) {
                if (CMP_FLAG(l, ECHOCTL))
                        data->curlen += 2;
        } else if (c == CTAB) {
                data->curlen += 8 - (data->curlen & 7);
        } else {
                data->curlen++;
        }
}

static unsigned int
ttydisc_recalc_linelength(struct tty *tp)
{
        struct ttydisc_recalc_length data = { tp, tp->t_writepos };

        ttyinq_line_iterate_from_reprintpos(&tp->t_inq,
            ttydisc_recalc_charlength, &data);
        return (data.curlen);
}

static int
ttydisc_rubchar(struct tty *tp)
{
        char c;
        int quote;
        unsigned int prevpos, tablen;

        if (ttyinq_peekchar(&tp->t_inq, &c, &quote) != 0)
                return (-1);
        ttyinq_unputchar(&tp->t_inq);

        if (CMP_FLAG(l, ECHO)) {
                /*
                 * Remove the character from the screen. This is even
                 * safe for characters that span multiple characters
                 * (tabs, quoted, etc).
                 */
                if (tp->t_writepos >= tp->t_column) {
                        /* Retype the sentence. */
                        ttydisc_reprint(tp);
                } else if (CMP_FLAG(l, ECHOE)) {
                        if (CTL_PRINT(c, quote)) {
                                /* Remove ^X formatted chars. */
                                if (CMP_FLAG(l, ECHOCTL)) {
                                        tp->t_column -= 2;
                                        ttyoutq_write_nofrag(&tp->t_outq,
                                            "\b\b  \b\b", 6);
                                }
                        } else if (c == ' ') {
                                /* Space character needs no rubbing. */
                                tp->t_column -= 1;
                                ttyoutq_write_nofrag(&tp->t_outq, "\b", 1);
                        } else if (c == CTAB) {
                                /*
                                 * Making backspace work with tabs is
                                 * quite hard. Recalculate the length of
                                 * this character and remove it.
                                 *
                                 * Because terminal settings could be
                                 * changed while the line is being
                                 * inserted, the calculations don't have
                                 * to be correct. Make sure we keep the
                                 * tab length within proper bounds.
                                 */
                                prevpos = ttydisc_recalc_linelength(tp);
                                if (prevpos >= tp->t_column)
                                        tablen = 1;
                                else
                                        tablen = tp->t_column - prevpos;
                                if (tablen > 8)
                                        tablen = 8;

                                tp->t_column = prevpos;
                                ttyoutq_write_nofrag(&tp->t_outq,
                                    "\b\b\b\b\b\b\b\b", tablen);
                                return (0);
                        } else {
                                /*
                                 * Remove a regular character by
                                 * punching a space over it.
                                 */
                                tp->t_column -= 1;
                                ttyoutq_write_nofrag(&tp->t_outq, "\b \b", 3);
                        }
                } else {
                        /* Don't print spaces. */
                        ttydisc_echo(tp, tp->t_termios.c_cc[VERASE], 0);
                }
        }

        return (0);
}

static void
ttydisc_rubword(struct tty *tp)
{
        char c;
        int quote, alnum;

        /* Strip whitespace first. */
        for (;;) {
                if (ttyinq_peekchar(&tp->t_inq, &c, &quote) != 0)
                        return;
                if (!CTL_WHITE(c))
                        break;
                ttydisc_rubchar(tp);
        }

        /*
         * Record whether the last character from the previous iteration
         * was alphanumeric or not. We need this to implement ALTWERASE.
         */
        alnum = CTL_ALNUM(c);
        for (;;) {
                ttydisc_rubchar(tp);

                if (ttyinq_peekchar(&tp->t_inq, &c, &quote) != 0)
                        return;
                if (CTL_WHITE(c))
                        return;
                if (CMP_FLAG(l, ALTWERASE) && CTL_ALNUM(c) != alnum)
                        return;
        }
}

int
ttydisc_rint(struct tty *tp, char c, int flags)
{
        int signal, quote = 0;
        char ob[3] = { 0xff, 0x00 };
        size_t ol;

        tty_lock_assert(tp, MA_OWNED);

        atomic_add_long(&tty_nin, 1);

        if (ttyhook_hashook(tp, rint))
                return ttyhook_rint(tp, c, flags);

        if (tp->t_flags & TF_BYPASS)
                goto processed;

        if (flags) {
                if (flags & TRE_BREAK) {
                        if (CMP_FLAG(i, IGNBRK)) {
                                /* Ignore break characters. */
                                return (0);
                        } else if (CMP_FLAG(i, BRKINT)) {
                                /* Generate SIGINT on break. */
                                tty_flush(tp, FREAD|FWRITE);
                                tty_signal_pgrp(tp, SIGINT);
                                return (0);
                        } else {
                                /* Just print it. */
                                goto parmrk;
                        }
                } else if (flags & TRE_FRAMING ||
                    (flags & TRE_PARITY && CMP_FLAG(i, INPCK))) {
                        if (CMP_FLAG(i, IGNPAR)) {
                                /* Ignore bad characters. */
                                return (0);
                        } else {
                                /* Just print it. */
                                goto parmrk;
                        }
                }
        }

        /* Allow any character to perform a wakeup. */
        if (CMP_FLAG(i, IXANY))
                tp->t_flags &= ~TF_STOPPED;

        /* Remove the top bit. */
        if (CMP_FLAG(i, ISTRIP))
                c &= ~0x80;

        /* Skip input processing when we want to print it literally. */
        if (tp->t_flags & TF_LITERAL) {
                tp->t_flags &= ~TF_LITERAL;
                quote = 1;
                goto processed;
        }

        /* Special control characters that are implementation dependent. */
        if (CMP_FLAG(l, IEXTEN)) {
                /* Accept the next character as literal. */
                if (CMP_CC(VLNEXT, c)) {
                        if (CMP_FLAG(l, ECHO)) {
                                if (CMP_FLAG(l, ECHOE))
                                        ttyoutq_write_nofrag(&tp->t_outq, "^\b", 2);
                                else
                                        ttydisc_echo(tp, c, 0);
                        }
                        tp->t_flags |= TF_LITERAL;
                        return (0);
                }
        }

        /*
         * Handle signal processing.
         */
        if (CMP_FLAG(l, ISIG)) {
                if (CMP_FLAG(l, ICANON|IEXTEN) == (ICANON|IEXTEN)) {
                        if (CMP_CC(VSTATUS, c)) {
                                tty_signal_pgrp(tp, SIGINFO);
                                return (0);
                        }
                }

                /*
                 * When compared to the old implementation, this
                 * implementation also flushes the output queue. POSIX
                 * is really brief about this, but does makes us assume
                 * we have to do so.
                 */
                signal = 0;
                if (CMP_CC(VINTR, c)) {
                        signal = SIGINT;
                } else if (CMP_CC(VQUIT, c)) {
                        signal = SIGQUIT;
                } else if (CMP_CC(VSUSP, c)) {
                        signal = SIGTSTP;
                }

                if (signal != 0) {
                        /*
                         * Echo the character before signalling the
                         * processes.
                         */
                        if (!CMP_FLAG(l, NOFLSH))
                                tty_flush(tp, FREAD|FWRITE);
                        ttydisc_echo(tp, c, 0);
                        tty_signal_pgrp(tp, signal);
                        return (0);
                }
        }

        /*
         * Handle start/stop characters.
         */
        if (CMP_FLAG(i, IXON)) {
                if (CMP_CC(VSTOP, c)) {
                        /* Stop it if we aren't stopped yet. */
                        if ((tp->t_flags & TF_STOPPED) == 0) {
                                tp->t_flags |= TF_STOPPED;
                                return (0);
                        }
                        /*
                         * Fallthrough:
                         * When VSTART == VSTOP, we should make this key
                         * toggle it.
                         */
                        if (!CMP_CC(VSTART, c))
                                return (0);
                }
                if (CMP_CC(VSTART, c)) {
                        tp->t_flags &= ~TF_STOPPED;
                        return (0);
                }
        }

        /* Conversion of CR and NL. */
        switch (c) {
        case CCR:
                if (CMP_FLAG(i, IGNCR))
                        return (0);
                if (CMP_FLAG(i, ICRNL))
                        c = CNL;
                break;
        case CNL:
                if (CMP_FLAG(i, INLCR))
                        c = CCR;
                break;
        }

        /* Canonical line editing. */
        if (CMP_FLAG(l, ICANON)) {
                if (CMP_CC(VERASE, c) || CMP_CC(VERASE2, c)) {
                        ttydisc_rubchar(tp);
                        return (0);
                } else if (CMP_CC(VKILL, c)) {
                        while (ttydisc_rubchar(tp) == 0);
                        return (0);
                } else if (CMP_FLAG(l, IEXTEN)) {
                        if (CMP_CC(VWERASE, c)) {
                                ttydisc_rubword(tp);
                                return (0);
                        } else if (CMP_CC(VREPRINT, c)) {
                                ttydisc_reprint(tp);
                                return (0);
                        }
                }
        }

processed:
        if (CMP_FLAG(i, PARMRK) && (unsigned char)c == 0xff) {
                /* Print 0xff 0xff. */
                ob[1] = 0xff;
                ol = 2;
                quote = 1;
        } else {
                ob[0] = c;
                ol = 1;
        }

        goto print;

parmrk:
        if (CMP_FLAG(i, PARMRK)) {
                /* Prepend 0xff 0x00 0x.. */
                ob[2] = c;
                ol = 3;
                quote = 1;
        } else {
                ob[0] = c;
                ol = 1;
        }

print:
        /* See if we can store this on the input queue. */
        if (ttyinq_write_nofrag(&tp->t_inq, ob, ol, quote) != 0) {
                if (CMP_FLAG(i, IMAXBEL))
                        ttyoutq_write_nofrag(&tp->t_outq, "\a", 1);

                /*
                 * Prevent a deadlock here. It may be possible that a
                 * user has entered so much data, there is no data
                 * available to read(), but the buffers are full anyway.
                 *
                 * Only enter the high watermark if the device driver
                 * can actually transmit something.
                 */
                if (ttyinq_bytescanonicalized(&tp->t_inq) == 0)
                        return (0);

                tty_hiwat_in_block(tp);
                return (-1);
        }

        /*
         * In raw mode, we canonicalize after receiving a single
         * character. Otherwise, we canonicalize when we receive a
         * newline, VEOL or VEOF, but only when it isn't quoted.
         */
        if (!CMP_FLAG(l, ICANON) ||
            (!quote && (c == CNL || CMP_CC(VEOL, c) || CMP_CC(VEOF, c)))) {
                ttyinq_canonicalize(&tp->t_inq);
        }

        ttydisc_echo(tp, c, quote);

        return (0);
}

size_t
ttydisc_rint_simple(struct tty *tp, const void *buf, size_t len)
{
        const char *cbuf;

        if (ttydisc_can_bypass(tp))
                return (ttydisc_rint_bypass(tp, buf, len));

        for (cbuf = buf; len-- > 0; cbuf++) {
                if (ttydisc_rint(tp, *cbuf, 0) != 0)
                        break;
        }

        return (cbuf - (const char *)buf);
}

size_t
ttydisc_rint_bypass(struct tty *tp, const void *buf, size_t len)
{
        size_t ret;

        tty_lock_assert(tp, MA_OWNED);

        MPASS(tp->t_flags & TF_BYPASS);

        atomic_add_long(&tty_nin, len);

        if (ttyhook_hashook(tp, rint_bypass))
                return ttyhook_rint_bypass(tp, buf, len);

        ret = ttyinq_write(&tp->t_inq, buf, len, 0);
        ttyinq_canonicalize(&tp->t_inq);
        if (ret < len)
                tty_hiwat_in_block(tp);

        return (ret);
}

void
ttydisc_rint_done(struct tty *tp)
{

        tty_lock_assert(tp, MA_OWNED);

        if (ttyhook_hashook(tp, rint_done))
                ttyhook_rint_done(tp);

        /* Wake up readers. */
        tty_wakeup(tp, FREAD);
        /* Wake up driver for echo. */
        ttydevsw_outwakeup(tp);
}

size_t
ttydisc_rint_poll(struct tty *tp)
{
        size_t l;

        tty_lock_assert(tp, MA_OWNED);

        if (ttyhook_hashook(tp, rint_poll))
                return ttyhook_rint_poll(tp);

        /*
         * XXX: Still allow character input when there's no space in the
         * buffers, but we haven't entered the high watermark. This is
         * to allow backspace characters to be inserted when in
         * canonical mode.
         */
        l = ttyinq_bytesleft(&tp->t_inq);
        if (l == 0 && (tp->t_flags & TF_HIWAT_IN) == 0)
                return (1);

        return (l);
}

static void
ttydisc_wakeup_watermark(struct tty *tp)
{
        size_t c;

        c = ttyoutq_bytesleft(&tp->t_outq);
        if (tp->t_flags & TF_HIWAT_OUT) {
                /* Only allow us to run when we're below the watermark. */
                if (c < tp->t_outlow)
                        return;

                /* Reset the watermark. */
                tp->t_flags &= ~TF_HIWAT_OUT;
        } else {
                /* Only run when we have data at all. */
                if (c == 0)
                        return;
        }
        tty_wakeup(tp, FWRITE);
}

size_t
ttydisc_getc(struct tty *tp, void *buf, size_t len)
{

        tty_lock_assert(tp, MA_OWNED);

        if (tp->t_flags & TF_STOPPED)
                return (0);

        if (ttyhook_hashook(tp, getc_inject))
                return ttyhook_getc_inject(tp, buf, len);

        len = ttyoutq_read(&tp->t_outq, buf, len);

        if (ttyhook_hashook(tp, getc_capture))
                ttyhook_getc_capture(tp, buf, len);

        ttydisc_wakeup_watermark(tp);
        atomic_add_long(&tty_nout, len);

        return (len);
}

int
ttydisc_getc_uio(struct tty *tp, struct uio *uio)
{
        int error = 0;
        ssize_t obytes = uio->uio_resid;
        size_t len;
        char buf[TTY_STACKBUF];

        tty_lock_assert(tp, MA_OWNED);

        if (tp->t_flags & TF_STOPPED)
                return (0);

        /*
         * When a TTY hook is attached, we cannot perform unbuffered
         * copying to userspace. Just call ttydisc_getc() and
         * temporarily store data in a shadow buffer.
         */
        if (ttyhook_hashook(tp, getc_capture) ||
            ttyhook_hashook(tp, getc_inject)) {
                while (uio->uio_resid > 0) {
                        /* Read to shadow buffer. */
                        len = ttydisc_getc(tp, buf,
                            MIN(uio->uio_resid, sizeof buf));
                        if (len == 0)
                                break;

                        /* Copy to userspace. */
                        tty_unlock(tp);
                        error = uiomove(buf, len, uio);
                        tty_lock(tp);

                        if (error != 0)
                                break;
                }
        } else {
                error = ttyoutq_read_uio(&tp->t_outq, tp, uio);

                ttydisc_wakeup_watermark(tp);
                atomic_add_long(&tty_nout, obytes - uio->uio_resid);
        }

        return (error);
}

size_t
ttydisc_getc_poll(struct tty *tp)
{

        tty_lock_assert(tp, MA_OWNED);

        if (tp->t_flags & TF_STOPPED)
                return (0);

        if (ttyhook_hashook(tp, getc_poll))
                return ttyhook_getc_poll(tp);

        return ttyoutq_bytesused(&tp->t_outq);
}

/*
 * XXX: not really related to the TTYDISC, but we'd better put
 * tty_putchar() here, because we need to perform proper output
 * processing.
 */

int
tty_putchar(struct tty *tp, char c)
{
        tty_lock_assert(tp, MA_OWNED);

        if (tty_gone(tp))
                return (-1);

        ttydisc_echo_force(tp, c, 0);
        tp->t_writepos = tp->t_column;
        ttyinq_reprintpos_set(&tp->t_inq);

        ttydevsw_outwakeup(tp);
        return (0);
}