tty.c

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/*-
 * 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 "opt_capsicum.h"
#include "opt_compat.h"

#include <sys/param.h>
#include <sys/capability.h>
#include <sys/conf.h>
#include <sys/cons.h>
#include <sys/fcntl.h>
#include <sys/file.h>
#include <sys/filedesc.h>
#include <sys/filio.h>
#ifdef COMPAT_43TTY
#include <sys/ioctl_compat.h>
#endif /* COMPAT_43TTY */
#include <sys/kernel.h>
#include <sys/limits.h>
#include <sys/malloc.h>
#include <sys/mount.h>
#include <sys/poll.h>
#include <sys/priv.h>
#include <sys/proc.h>
#include <sys/serial.h>
#include <sys/signal.h>
#include <sys/stat.h>
#include <sys/sx.h>
#include <sys/sysctl.h>
#include <sys/systm.h>
#include <sys/tty.h>
#include <sys/ttycom.h>
#define TTYDEFCHARS
#include <sys/ttydefaults.h>
#undef TTYDEFCHARS
#include <sys/ucred.h>
#include <sys/vnode.h>

#include <machine/stdarg.h>

static MALLOC_DEFINE(M_TTY, "tty", "tty device");

static void tty_rel_free(struct tty *tp);

static TAILQ_HEAD(, tty) tty_list = TAILQ_HEAD_INITIALIZER(tty_list);
static struct sx tty_list_sx;
SX_SYSINIT(tty_list, &tty_list_sx, "tty list");
static unsigned int tty_list_count = 0;

/* Character device of /dev/console. */
static struct cdev      *dev_console;
static const char       *dev_console_filename;

/*
 * Flags that are supported and stored by this implementation.
 */
#define TTYSUP_IFLAG    (IGNBRK|BRKINT|IGNPAR|PARMRK|INPCK|ISTRIP|\
                        INLCR|IGNCR|ICRNL|IXON|IXOFF|IXANY|IMAXBEL)
#define TTYSUP_OFLAG    (OPOST|ONLCR|TAB3|ONOEOT|OCRNL|ONOCR|ONLRET)
#define TTYSUP_LFLAG    (ECHOKE|ECHOE|ECHOK|ECHO|ECHONL|ECHOPRT|\
                        ECHOCTL|ISIG|ICANON|ALTWERASE|IEXTEN|TOSTOP|\
                        FLUSHO|NOKERNINFO|NOFLSH)
#define TTYSUP_CFLAG    (CIGNORE|CSIZE|CSTOPB|CREAD|PARENB|PARODD|\
                        HUPCL|CLOCAL|CCTS_OFLOW|CRTS_IFLOW|CDTR_IFLOW|\
                        CDSR_OFLOW|CCAR_OFLOW)

#define TTY_CALLOUT(tp,d) (dev2unit(d) & TTYUNIT_CALLOUT)

/*
 * Set TTY buffer sizes.
 */

#define TTYBUF_MAX      65536

static void
tty_watermarks(struct tty *tp)
{
        size_t bs = 0;

        /* Provide an input buffer for 0.2 seconds of data. */
        if (tp->t_termios.c_cflag & CREAD)
                bs = MIN(tp->t_termios.c_ispeed / 5, TTYBUF_MAX);
        ttyinq_setsize(&tp->t_inq, tp, bs);

        /* Set low watermark at 10% (when 90% is available). */
        tp->t_inlow = (ttyinq_getallocatedsize(&tp->t_inq) * 9) / 10;

        /* Provide an ouput buffer for 0.2 seconds of data. */
        bs = MIN(tp->t_termios.c_ospeed / 5, TTYBUF_MAX);
        ttyoutq_setsize(&tp->t_outq, tp, bs);

        /* Set low watermark at 10% (when 90% is available). */
        tp->t_outlow = (ttyoutq_getallocatedsize(&tp->t_outq) * 9) / 10;
}

static int
tty_drain(struct tty *tp)
{
        int error;

        if (ttyhook_hashook(tp, getc_inject))
                /* buffer is inaccessible */
                return (0);

        while (ttyoutq_bytesused(&tp->t_outq) > 0) {
                ttydevsw_outwakeup(tp);
                /* Could be handled synchronously. */
                if (ttyoutq_bytesused(&tp->t_outq) == 0)
                        return (0);

                /* Wait for data to be drained. */
                error = tty_wait(tp, &tp->t_outwait);
                if (error)
                        return (error);
        }

        return (0);
}

/*
 * Though ttydev_enter() and ttydev_leave() seem to be related, they
 * don't have to be used together. ttydev_enter() is used by the cdev
 * operations to prevent an actual operation from being processed when
 * the TTY has been abandoned. ttydev_leave() is used by ttydev_open()
 * and ttydev_close() to determine whether per-TTY data should be
 * deallocated.
 */

static __inline int
ttydev_enter(struct tty *tp)
{
        tty_lock(tp);

        if (tty_gone(tp) || !tty_opened(tp)) {
                /* Device is already gone. */
                tty_unlock(tp);
                return (ENXIO);
        }

        return (0);
}

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

        if (tty_opened(tp) || tp->t_flags & TF_OPENCLOSE) {
                /* Device is still opened somewhere. */
                tty_unlock(tp);
                return;
        }

        tp->t_flags |= TF_OPENCLOSE;

        /* Stop asynchronous I/O. */
        funsetown(&tp->t_sigio);

        /* Remove console TTY. */
        if (constty == tp)
                constty_clear();

        /* Drain any output. */
        MPASS((tp->t_flags & TF_STOPPED) == 0);
        if (!tty_gone(tp))
                tty_drain(tp);

        ttydisc_close(tp);

        /* Destroy associated buffers already. */
        ttyinq_free(&tp->t_inq);
        tp->t_inlow = 0;
        ttyoutq_free(&tp->t_outq);
        tp->t_outlow = 0;

        knlist_clear(&tp->t_inpoll.si_note, 1);
        knlist_clear(&tp->t_outpoll.si_note, 1);

        if (!tty_gone(tp))
                ttydevsw_close(tp);

        tp->t_flags &= ~TF_OPENCLOSE;
        cv_broadcast(&tp->t_dcdwait);
        tty_rel_free(tp);
}

/*
 * Operations that are exposed through the character device in /dev.
 */
static int
ttydev_open(struct cdev *dev, int oflags, int devtype, struct thread *td)
{
        struct tty *tp;
        int error = 0;

        while ((tp = dev->si_drv1) == NULL) {
                error = tsleep(&dev->si_drv1, PCATCH, "ttdrv1", 1);
                if (error != EWOULDBLOCK)
                        return (error);
        }

        tty_lock(tp);
        if (tty_gone(tp)) {
                /* Device is already gone. */
                tty_unlock(tp);
                return (ENXIO);
        }

        /*
         * Block when other processes are currently opening or closing
         * the TTY.
         */
        while (tp->t_flags & TF_OPENCLOSE) {
                error = tty_wait(tp, &tp->t_dcdwait);
                if (error != 0) {
                        tty_unlock(tp);
                        return (error);
                }
        }
        tp->t_flags |= TF_OPENCLOSE;

        /*
         * Make sure the "tty" and "cua" device cannot be opened at the
         * same time.
         */
        if (TTY_CALLOUT(tp, dev)) {
                if (tp->t_flags & TF_OPENED_IN) {
                        error = EBUSY;
                        goto done;
                }
        } else {
                if (tp->t_flags & TF_OPENED_OUT) {
                        error = EBUSY;
                        goto done;
                }
        }

        if (tp->t_flags & TF_EXCLUDE && priv_check(td, PRIV_TTY_EXCLUSIVE)) {
                error = EBUSY;
                goto done;
        }

        if (!tty_opened(tp)) {
                /* Set proper termios flags. */
                if (TTY_CALLOUT(tp, dev))
                        tp->t_termios = tp->t_termios_init_out;
                else
                        tp->t_termios = tp->t_termios_init_in;
                ttydevsw_param(tp, &tp->t_termios);
                /* Prevent modem control on callout devices and /dev/console. */
                if (TTY_CALLOUT(tp, dev) || dev == dev_console)
                        tp->t_termios.c_cflag |= CLOCAL;

                ttydevsw_modem(tp, SER_DTR|SER_RTS, 0);

                error = ttydevsw_open(tp);
                if (error != 0)
                        goto done;

                ttydisc_open(tp);
                tty_watermarks(tp);
        }

        /* Wait for Carrier Detect. */
        if ((oflags & O_NONBLOCK) == 0 &&
            (tp->t_termios.c_cflag & CLOCAL) == 0) {
                while ((ttydevsw_modem(tp, 0, 0) & SER_DCD) == 0) {
                        error = tty_wait(tp, &tp->t_dcdwait);
                        if (error != 0)
                                goto done;
                }
        }

        if (dev == dev_console)
                tp->t_flags |= TF_OPENED_CONS;
        else if (TTY_CALLOUT(tp, dev))
                tp->t_flags |= TF_OPENED_OUT;
        else
                tp->t_flags |= TF_OPENED_IN;

done:   tp->t_flags &= ~TF_OPENCLOSE;
        cv_broadcast(&tp->t_dcdwait);
        ttydev_leave(tp);

        return (error);
}

static int
ttydev_close(struct cdev *dev, int fflag, int devtype, struct thread *td)
{
        struct tty *tp = dev->si_drv1;

        tty_lock(tp);

        /*
         * Don't actually close the device if it is being used as the
         * console.
         */
        MPASS((tp->t_flags & TF_OPENED) != TF_OPENED);
        if (dev == dev_console)
                tp->t_flags &= ~TF_OPENED_CONS;
        else
                tp->t_flags &= ~(TF_OPENED_IN|TF_OPENED_OUT);

        if (tp->t_flags & TF_OPENED) {
                tty_unlock(tp);
                return (0);
        }

        /*
         * This can only be called once. The callin and the callout
         * devices cannot be opened at the same time.
         */
        tp->t_flags &= ~(TF_EXCLUDE|TF_STOPPED);

        /* Properly wake up threads that are stuck - revoke(). */
        tp->t_revokecnt++;
        tty_wakeup(tp, FREAD|FWRITE);
        cv_broadcast(&tp->t_bgwait);
        cv_broadcast(&tp->t_dcdwait);

        ttydev_leave(tp);

        return (0);
}

static __inline int
tty_is_ctty(struct tty *tp, struct proc *p)
{
        tty_lock_assert(tp, MA_OWNED);

        return (p->p_session == tp->t_session && p->p_flag & P_CONTROLT);
}

int
tty_wait_background(struct tty *tp, struct thread *td, int sig)
{
        struct proc *p = td->td_proc;
        struct pgrp *pg;
        ksiginfo_t ksi;
        int error;

        MPASS(sig == SIGTTIN || sig == SIGTTOU);
        tty_lock_assert(tp, MA_OWNED);

        for (;;) {
                PROC_LOCK(p);
                /*
                 * The process should only sleep, when:
                 * - This terminal is the controling terminal
                 * - Its process group is not the foreground process
                 *   group
                 * - The parent process isn't waiting for the child to
                 *   exit
                 * - the signal to send to the process isn't masked
                 */
                if (!tty_is_ctty(tp, p) || p->p_pgrp == tp->t_pgrp) {
                        /* Allow the action to happen. */
                        PROC_UNLOCK(p);
                        return (0);
                }

                if (SIGISMEMBER(p->p_sigacts->ps_sigignore, sig) ||
                    SIGISMEMBER(td->td_sigmask, sig)) {
                        /* Only allow them in write()/ioctl(). */
                        PROC_UNLOCK(p);
                        return (sig == SIGTTOU ? 0 : EIO);
                }

                pg = p->p_pgrp;
                if (p->p_flag & P_PPWAIT || pg->pg_jobc == 0) {
                        /* Don't allow the action to happen. */
                        PROC_UNLOCK(p);
                        return (EIO);
                }
                PROC_UNLOCK(p);

                /*
                 * Send the signal and sleep until we're the new
                 * foreground process group.
                 */
                if (sig != 0) {
                        ksiginfo_init(&ksi);
                        ksi.ksi_code = SI_KERNEL;
                        ksi.ksi_signo = sig;
                        sig = 0;
                }
                PGRP_LOCK(pg);
                pgsignal(pg, ksi.ksi_signo, 1, &ksi);
                PGRP_UNLOCK(pg);

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

static int
ttydev_read(struct cdev *dev, struct uio *uio, int ioflag)
{
        struct tty *tp = dev->si_drv1;
        int error;

        error = ttydev_enter(tp);
        if (error)
                goto done;
        error = ttydisc_read(tp, uio, ioflag);
        tty_unlock(tp);

        /*
         * The read() call should not throw an error when the device is
         * being destroyed. Silently convert it to an EOF.
         */
done:   if (error == ENXIO)
                error = 0;
        return (error);
}

static int
ttydev_write(struct cdev *dev, struct uio *uio, int ioflag)
{
        struct tty *tp = dev->si_drv1;
        int error;

        error = ttydev_enter(tp);
        if (error)
                return (error);

        if (tp->t_termios.c_lflag & TOSTOP) {
                error = tty_wait_background(tp, curthread, SIGTTOU);
                if (error)
                        goto done;
        }

        if (ioflag & IO_NDELAY && tp->t_flags & TF_BUSY_OUT) {
                /* Allow non-blocking writes to bypass serialization. */
                error = ttydisc_write(tp, uio, ioflag);
        } else {
                /* Serialize write() calls. */
                while (tp->t_flags & TF_BUSY_OUT) {
                        error = tty_wait(tp, &tp->t_outserwait);
                        if (error)
                                goto done;
                }

                tp->t_flags |= TF_BUSY_OUT;
                error = ttydisc_write(tp, uio, ioflag);
                tp->t_flags &= ~TF_BUSY_OUT;
                cv_signal(&tp->t_outserwait);
        }

done:   tty_unlock(tp);
        return (error);
}

static int
ttydev_ioctl(struct cdev *dev, u_long cmd, caddr_t data, int fflag,
    struct thread *td)
{
        struct tty *tp = dev->si_drv1;
        int error;

        error = ttydev_enter(tp);
        if (error)
                return (error);

        switch (cmd) {
        case TIOCCBRK:
        case TIOCCONS:
        case TIOCDRAIN:
        case TIOCEXCL:
        case TIOCFLUSH:
        case TIOCNXCL:
        case TIOCSBRK:
        case TIOCSCTTY:
        case TIOCSETA:
        case TIOCSETAF:
        case TIOCSETAW:
        case TIOCSPGRP:
        case TIOCSTART:
        case TIOCSTAT:
        case TIOCSTI:
        case TIOCSTOP:
        case TIOCSWINSZ:
#if 0
        case TIOCSDRAINWAIT:
        case TIOCSETD:
#endif
#ifdef COMPAT_43TTY
        case  TIOCLBIC:
        case  TIOCLBIS:
        case  TIOCLSET:
        case  TIOCSETC:
        case OTIOCSETD:
        case  TIOCSETN:
        case  TIOCSETP:
        case  TIOCSLTC:
#endif /* COMPAT_43TTY */
                /*
                 * If the ioctl() causes the TTY to be modified, let it
                 * wait in the background.
                 */
                error = tty_wait_background(tp, curthread, SIGTTOU);
                if (error)
                        goto done;
        }

        if (cmd == TIOCSETA || cmd == TIOCSETAW || cmd == TIOCSETAF) {
                struct termios *old = &tp->t_termios;
                struct termios *new = (struct termios *)data;
                struct termios *lock = TTY_CALLOUT(tp, dev) ?
                    &tp->t_termios_lock_out : &tp->t_termios_lock_in;
                int cc;

                /*
                 * Lock state devices.  Just overwrite the values of the
                 * commands that are currently in use.
                 */
                new->c_iflag = (old->c_iflag & lock->c_iflag) |
                    (new->c_iflag & ~lock->c_iflag);
                new->c_oflag = (old->c_oflag & lock->c_oflag) |
                    (new->c_oflag & ~lock->c_oflag);
                new->c_cflag = (old->c_cflag & lock->c_cflag) |
                    (new->c_cflag & ~lock->c_cflag);
                new->c_lflag = (old->c_lflag & lock->c_lflag) |
                    (new->c_lflag & ~lock->c_lflag);
                for (cc = 0; cc < NCCS; ++cc)
                        if (lock->c_cc[cc])
                                new->c_cc[cc] = old->c_cc[cc];
                if (lock->c_ispeed)
                        new->c_ispeed = old->c_ispeed;
                if (lock->c_ospeed)
                        new->c_ospeed = old->c_ospeed;
        }

        error = tty_ioctl(tp, cmd, data, fflag, td);
done:   tty_unlock(tp);

        return (error);
}

static int
ttydev_poll(struct cdev *dev, int events, struct thread *td)
{
        struct tty *tp = dev->si_drv1;
        int error, revents = 0;

        error = ttydev_enter(tp);
        if (error)
                return ((events & (POLLIN|POLLRDNORM)) | POLLHUP);

        if (events & (POLLIN|POLLRDNORM)) {
                /* See if we can read something. */
                if (ttydisc_read_poll(tp) > 0)
                        revents |= events & (POLLIN|POLLRDNORM);
        }

        if (tp->t_flags & TF_ZOMBIE) {
                /* Hangup flag on zombie state. */
                revents |= POLLHUP;
        } else if (events & (POLLOUT|POLLWRNORM)) {
                /* See if we can write something. */
                if (ttydisc_write_poll(tp) > 0)
                        revents |= events & (POLLOUT|POLLWRNORM);
        }

        if (revents == 0) {
                if (events & (POLLIN|POLLRDNORM))
                        selrecord(td, &tp->t_inpoll);
                if (events & (POLLOUT|POLLWRNORM))
                        selrecord(td, &tp->t_outpoll);
        }

        tty_unlock(tp);

        return (revents);
}

static int
ttydev_mmap(struct cdev *dev, vm_ooffset_t offset, vm_paddr_t *paddr,
    int nprot, vm_memattr_t *memattr)
{
        struct tty *tp = dev->si_drv1;
        int error;

        /* Handle mmap() through the driver. */

        error = ttydev_enter(tp);
        if (error)
                return (-1);
        error = ttydevsw_mmap(tp, offset, paddr, nprot, memattr);
        tty_unlock(tp);

        return (error);
}

/*
 * kqueue support.
 */

static void
tty_kqops_read_detach(struct knote *kn)
{
        struct tty *tp = kn->kn_hook;

        knlist_remove(&tp->t_inpoll.si_note, kn, 0);
}

static int
tty_kqops_read_event(struct knote *kn, long hint)
{
        struct tty *tp = kn->kn_hook;

        tty_lock_assert(tp, MA_OWNED);

        if (tty_gone(tp) || tp->t_flags & TF_ZOMBIE) {
                kn->kn_flags |= EV_EOF;
                return (1);
        } else {
                kn->kn_data = ttydisc_read_poll(tp);
                return (kn->kn_data > 0);
        }
}

static void
tty_kqops_write_detach(struct knote *kn)
{
        struct tty *tp = kn->kn_hook;

        knlist_remove(&tp->t_outpoll.si_note, kn, 0);
}

static int
tty_kqops_write_event(struct knote *kn, long hint)
{
        struct tty *tp = kn->kn_hook;

        tty_lock_assert(tp, MA_OWNED);

        if (tty_gone(tp)) {
                kn->kn_flags |= EV_EOF;
                return (1);
        } else {
                kn->kn_data = ttydisc_write_poll(tp);
                return (kn->kn_data > 0);
        }
}

static struct filterops tty_kqops_read = {
        .f_isfd = 1,
        .f_detach = tty_kqops_read_detach,
        .f_event = tty_kqops_read_event,
};
static struct filterops tty_kqops_write = {
        .f_isfd = 1,
        .f_detach = tty_kqops_write_detach,
        .f_event = tty_kqops_write_event,
};

static int
ttydev_kqfilter(struct cdev *dev, struct knote *kn)
{
        struct tty *tp = dev->si_drv1;
        int error;

        error = ttydev_enter(tp);
        if (error)
                return (error);

        switch (kn->kn_filter) {
        case EVFILT_READ:
                kn->kn_hook = tp;
                kn->kn_fop = &tty_kqops_read;
                knlist_add(&tp->t_inpoll.si_note, kn, 1);
                break;
        case EVFILT_WRITE:
                kn->kn_hook = tp;
                kn->kn_fop = &tty_kqops_write;
                knlist_add(&tp->t_outpoll.si_note, kn, 1);
                break;
        default:
                error = EINVAL;
                break;
        }

        tty_unlock(tp);
        return (error);
}

static struct cdevsw ttydev_cdevsw = {
        .d_version      = D_VERSION,
        .d_open         = ttydev_open,
        .d_close        = ttydev_close,
        .d_read         = ttydev_read,
        .d_write        = ttydev_write,
        .d_ioctl        = ttydev_ioctl,
        .d_kqfilter     = ttydev_kqfilter,
        .d_poll         = ttydev_poll,
        .d_mmap         = ttydev_mmap,
        .d_name         = "ttydev",
        .d_flags        = D_TTY,
};

/*
 * Init/lock-state devices
 */

static int
ttyil_open(struct cdev *dev, int oflags, int devtype, struct thread *td)
{
        struct tty *tp;
        int error = 0;

        while ((tp = dev->si_drv1) == NULL) {
                error = tsleep(&dev->si_drv1, PCATCH, "ttdrv1", 1);
                if (error != EWOULDBLOCK)
                        return (error);
        }
        tty_lock(tp);
        if (tty_gone(tp))
                error = ENODEV;
        tty_unlock(tp);

        return (error);
}

static int
ttyil_close(struct cdev *dev, int flag, int mode, struct thread *td)
{
        return (0);
}

static int
ttyil_rdwr(struct cdev *dev, struct uio *uio, int ioflag)
{
        return (ENODEV);
}

static int
ttyil_ioctl(struct cdev *dev, u_long cmd, caddr_t data, int fflag,
    struct thread *td)
{
        struct tty *tp = dev->si_drv1;
        int error;

        tty_lock(tp);
        if (tty_gone(tp)) {
                error = ENODEV;
                goto done;
        }

        error = ttydevsw_cioctl(tp, dev2unit(dev), cmd, data, td);
        if (error != ENOIOCTL)
                goto done;
        error = 0;

        switch (cmd) {
        case TIOCGETA:
                /* Obtain terminal flags through tcgetattr(). */
                *(struct termios*)data = *(struct termios*)dev->si_drv2;
                break;
        case TIOCSETA:
                /* Set terminal flags through tcsetattr(). */
                error = priv_check(td, PRIV_TTY_SETA);
                if (error)
                        break;
                *(struct termios*)dev->si_drv2 = *(struct termios*)data;
                break;
        case TIOCGETD:
                *(int *)data = TTYDISC;
                break;
        case TIOCGWINSZ:
                bzero(data, sizeof(struct winsize));
                break;
        default:
                error = ENOTTY;
        }

done:   tty_unlock(tp);
        return (error);
}

static struct cdevsw ttyil_cdevsw = {
        .d_version      = D_VERSION,
        .d_open         = ttyil_open,
        .d_close        = ttyil_close,
        .d_read         = ttyil_rdwr,
        .d_write        = ttyil_rdwr,
        .d_ioctl        = ttyil_ioctl,
        .d_name         = "ttyil",
        .d_flags        = D_TTY,
};

static void
tty_init_termios(struct tty *tp)
{
        struct termios *t = &tp->t_termios_init_in;

        t->c_cflag = TTYDEF_CFLAG;
        t->c_iflag = TTYDEF_IFLAG;
        t->c_lflag = TTYDEF_LFLAG;
        t->c_oflag = TTYDEF_OFLAG;
        t->c_ispeed = TTYDEF_SPEED;
        t->c_ospeed = TTYDEF_SPEED;
        memcpy(&t->c_cc, ttydefchars, sizeof ttydefchars);

        tp->t_termios_init_out = *t;
}

void
tty_init_console(struct tty *tp, speed_t s)
{
        struct termios *ti = &tp->t_termios_init_in;
        struct termios *to = &tp->t_termios_init_out;

        if (s != 0) {
                ti->c_ispeed = ti->c_ospeed = s;
                to->c_ispeed = to->c_ospeed = s;
        }

        ti->c_cflag |= CLOCAL;
        to->c_cflag |= CLOCAL;
}

/*
 * Standard device routine implementations, mostly meant for
 * pseudo-terminal device drivers. When a driver creates a new terminal
 * device class, missing routines are patched.
 */

static int
ttydevsw_defopen(struct tty *tp)
{

        return (0);
}

static void
ttydevsw_defclose(struct tty *tp)
{
}

static void
ttydevsw_defoutwakeup(struct tty *tp)
{

        panic("Terminal device has output, while not implemented");
}

static void
ttydevsw_definwakeup(struct tty *tp)
{
}

static int
ttydevsw_defioctl(struct tty *tp, u_long cmd, caddr_t data, struct thread *td)
{

        return (ENOIOCTL);
}

static int
ttydevsw_defcioctl(struct tty *tp, int unit, u_long cmd, caddr_t data, struct thread *td)
{

        return (ENOIOCTL);
}

static int
ttydevsw_defparam(struct tty *tp, struct termios *t)
{

        /*
         * Allow the baud rate to be adjusted for pseudo-devices, but at
         * least restrict it to 115200 to prevent excessive buffer
         * usage.  Also disallow 0, to prevent foot shooting.
         */
        if (t->c_ispeed < B50)
                t->c_ispeed = B50;
        else if (t->c_ispeed > B115200)
                t->c_ispeed = B115200;
        if (t->c_ospeed < B50)
                t->c_ospeed = B50;
        else if (t->c_ospeed > B115200)
                t->c_ospeed = B115200;
        t->c_cflag |= CREAD;

        return (0);
}

static int
ttydevsw_defmodem(struct tty *tp, int sigon, int sigoff)
{

        /* Simulate a carrier to make the TTY layer happy. */
        return (SER_DCD);
}

static int
ttydevsw_defmmap(struct tty *tp, vm_ooffset_t offset, vm_paddr_t *paddr,
    int nprot, vm_memattr_t *memattr)
{

        return (-1);
}

static void
ttydevsw_defpktnotify(struct tty *tp, char event)
{
}

static void
ttydevsw_deffree(void *softc)
{

        panic("Terminal device freed without a free-handler");
}

/*
 * TTY allocation and deallocation. TTY devices can be deallocated when
 * the driver doesn't use it anymore, when the TTY isn't a session's
 * controlling TTY and when the device node isn't opened through devfs.
 */

struct tty *
tty_alloc(struct ttydevsw *tsw, void *sc)
{

        return (tty_alloc_mutex(tsw, sc, NULL));
}

struct tty *
tty_alloc_mutex(struct ttydevsw *tsw, void *sc, struct mtx *mutex)
{
        struct tty *tp;

        /* Make sure the driver defines all routines. */
#define PATCH_FUNC(x) do {                              \
        if (tsw->tsw_ ## x == NULL)                     \
                tsw->tsw_ ## x = ttydevsw_def ## x;     \
} while (0)
        PATCH_FUNC(open);
        PATCH_FUNC(close);
        PATCH_FUNC(outwakeup);
        PATCH_FUNC(inwakeup);
        PATCH_FUNC(ioctl);
        PATCH_FUNC(cioctl);
        PATCH_FUNC(param);
        PATCH_FUNC(modem);
        PATCH_FUNC(mmap);
        PATCH_FUNC(pktnotify);
        PATCH_FUNC(free);
#undef PATCH_FUNC

        tp = malloc(sizeof(struct tty), M_TTY, M_WAITOK|M_ZERO);
        tp->t_devsw = tsw;
        tp->t_devswsoftc = sc;
        tp->t_flags = tsw->tsw_flags;

        tty_init_termios(tp);

        cv_init(&tp->t_inwait, "ttyin");
        cv_init(&tp->t_outwait, "ttyout");
        cv_init(&tp->t_outserwait, "ttyosr");
        cv_init(&tp->t_bgwait, "ttybg");
        cv_init(&tp->t_dcdwait, "ttydcd");

        /* Allow drivers to use a custom mutex to lock the TTY. */
        if (mutex != NULL) {
                tp->t_mtx = mutex;
        } else {
                tp->t_mtx = &tp->t_mtxobj;
                mtx_init(&tp->t_mtxobj, "ttymtx", NULL, MTX_DEF);
        }

        knlist_init_mtx(&tp->t_inpoll.si_note, tp->t_mtx);
        knlist_init_mtx(&tp->t_outpoll.si_note, tp->t_mtx);

        sx_xlock(&tty_list_sx);
        TAILQ_INSERT_TAIL(&tty_list, tp, t_list);
        tty_list_count++;
        sx_xunlock(&tty_list_sx);

        return (tp);
}

static void
tty_dealloc(void *arg)
{
        struct tty *tp = arg;

        sx_xlock(&tty_list_sx);
        TAILQ_REMOVE(&tty_list, tp, t_list);
        tty_list_count--;
        sx_xunlock(&tty_list_sx);

        /* Make sure we haven't leaked buffers. */
        MPASS(ttyinq_getsize(&tp->t_inq) == 0);
        MPASS(ttyoutq_getsize(&tp->t_outq) == 0);

        seldrain(&tp->t_inpoll);
        seldrain(&tp->t_outpoll);
        knlist_destroy(&tp->t_inpoll.si_note);
        knlist_destroy(&tp->t_outpoll.si_note);

        cv_destroy(&tp->t_inwait);
        cv_destroy(&tp->t_outwait);
        cv_destroy(&tp->t_bgwait);
        cv_destroy(&tp->t_dcdwait);
        cv_destroy(&tp->t_outserwait);

        if (tp->t_mtx == &tp->t_mtxobj)
                mtx_destroy(&tp->t_mtxobj);
        ttydevsw_free(tp);
        free(tp, M_TTY);
}

static void
tty_rel_free(struct tty *tp)
{
        struct cdev *dev;

        tty_lock_assert(tp, MA_OWNED);

#define TF_ACTIVITY     (TF_GONE|TF_OPENED|TF_HOOK|TF_OPENCLOSE)
        if (tp->t_sessioncnt != 0 || (tp->t_flags & TF_ACTIVITY) != TF_GONE) {
                /* TTY is still in use. */
                tty_unlock(tp);
                return;
        }

        /* TTY can be deallocated. */
        dev = tp->t_dev;
        tp->t_dev = NULL;
        tty_unlock(tp);

        if (dev != NULL)
                destroy_dev_sched_cb(dev, tty_dealloc, tp);
}

void
tty_rel_pgrp(struct tty *tp, struct pgrp *pg)
{
        MPASS(tp->t_sessioncnt > 0);
        tty_lock_assert(tp, MA_OWNED);

        if (tp->t_pgrp == pg)
                tp->t_pgrp = NULL;

        tty_unlock(tp);
}

void
tty_rel_sess(struct tty *tp, struct session *sess)
{
        MPASS(tp->t_sessioncnt > 0);

        /* Current session has left. */
        if (tp->t_session == sess) {
                tp->t_session = NULL;
                MPASS(tp->t_pgrp == NULL);
        }
        tp->t_sessioncnt--;
        tty_rel_free(tp);
}

void
tty_rel_gone(struct tty *tp)
{
        MPASS(!tty_gone(tp));

        /* Simulate carrier removal. */
        ttydisc_modem(tp, 0);

        /* Wake up all blocked threads. */
        tty_wakeup(tp, FREAD|FWRITE);
        cv_broadcast(&tp->t_bgwait);
        cv_broadcast(&tp->t_dcdwait);

        tp->t_flags |= TF_GONE;
        tty_rel_free(tp);
}

/*
 * Exposing information about current TTY's through sysctl
 */

static void
tty_to_xtty(struct tty *tp, struct xtty *xt)
{
        tty_lock_assert(tp, MA_OWNED);

        xt->xt_size = sizeof(struct xtty);
        xt->xt_insize = ttyinq_getsize(&tp->t_inq);
        xt->xt_incc = ttyinq_bytescanonicalized(&tp->t_inq);
        xt->xt_inlc = ttyinq_bytesline(&tp->t_inq);
        xt->xt_inlow = tp->t_inlow;
        xt->xt_outsize = ttyoutq_getsize(&tp->t_outq);
        xt->xt_outcc = ttyoutq_bytesused(&tp->t_outq);
        xt->xt_outlow = tp->t_outlow;
        xt->xt_column = tp->t_column;
        xt->xt_pgid = tp->t_pgrp ? tp->t_pgrp->pg_id : 0;
        xt->xt_sid = tp->t_session ? tp->t_session->s_sid : 0;
        xt->xt_flags = tp->t_flags;
        xt->xt_dev = tp->t_dev ? dev2udev(tp->t_dev) : NODEV;
}

static int
sysctl_kern_ttys(SYSCTL_HANDLER_ARGS)
{
        unsigned long lsize;
        struct xtty *xtlist, *xt;
        struct tty *tp;
        int error;

        sx_slock(&tty_list_sx);
        lsize = tty_list_count * sizeof(struct xtty);
        if (lsize == 0) {
                sx_sunlock(&tty_list_sx);
                return (0);
        }

        xtlist = xt = malloc(lsize, M_TTY, M_WAITOK);

        TAILQ_FOREACH(tp, &tty_list, t_list) {
                tty_lock(tp);
                tty_to_xtty(tp, xt);
                tty_unlock(tp);
                xt++;
        }
        sx_sunlock(&tty_list_sx);

        error = SYSCTL_OUT(req, xtlist, lsize);
        free(xtlist, M_TTY);
        return (error);
}

SYSCTL_PROC(_kern, OID_AUTO, ttys, CTLTYPE_OPAQUE|CTLFLAG_RD|CTLFLAG_MPSAFE,
        0, 0, sysctl_kern_ttys, "S,xtty", "List of TTYs");

/*
 * Device node creation. Device has been set up, now we can expose it to
 * the user.
 */

void
tty_makedev(struct tty *tp, struct ucred *cred, const char *fmt, ...)
{
        va_list ap;
        struct cdev *dev;
        const char *prefix = "tty";
        char name[SPECNAMELEN - 3]; /* for "tty" and "cua". */
        uid_t uid;
        gid_t gid;
        mode_t mode;

        /* Remove "tty" prefix from devices like PTY's. */
        if (tp->t_flags & TF_NOPREFIX)
                prefix = "";

        va_start(ap, fmt);
        vsnrprintf(name, sizeof name, 32, fmt, ap);
        va_end(ap);

        if (cred == NULL) {
                /* System device. */
                uid = UID_ROOT;
                gid = GID_WHEEL;
                mode = S_IRUSR|S_IWUSR;
        } else {
                /* User device. */
                uid = cred->cr_ruid;
                gid = GID_TTY;
                mode = S_IRUSR|S_IWUSR|S_IWGRP;
        }

        /* Master call-in device. */
        dev = make_dev_cred(&ttydev_cdevsw, 0, cred,
            uid, gid, mode, "%s%s", prefix, name);
        dev->si_drv1 = tp;
        wakeup(&dev->si_drv1);
        tp->t_dev = dev;

        /* Slave call-in devices. */
        if (tp->t_flags & TF_INITLOCK) {
                dev = make_dev_cred(&ttyil_cdevsw, TTYUNIT_INIT, cred,
                    uid, gid, mode, "%s%s.init", prefix, name);
                dev_depends(tp->t_dev, dev);
                dev->si_drv1 = tp;
                wakeup(&dev->si_drv1);
                dev->si_drv2 = &tp->t_termios_init_in;

                dev = make_dev_cred(&ttyil_cdevsw, TTYUNIT_LOCK, cred,
                    uid, gid, mode, "%s%s.lock", prefix, name);
                dev_depends(tp->t_dev, dev);
                dev->si_drv1 = tp;
                wakeup(&dev->si_drv1);
                dev->si_drv2 = &tp->t_termios_lock_in;
        }

        /* Call-out devices. */
        if (tp->t_flags & TF_CALLOUT) {
                dev = make_dev_cred(&ttydev_cdevsw, TTYUNIT_CALLOUT, cred,
                    UID_UUCP, GID_DIALER, 0660, "cua%s", name);
                dev_depends(tp->t_dev, dev);
                dev->si_drv1 = tp;
                wakeup(&dev->si_drv1);

                /* Slave call-out devices. */
                if (tp->t_flags & TF_INITLOCK) {
                        dev = make_dev_cred(&ttyil_cdevsw, 
                            TTYUNIT_CALLOUT | TTYUNIT_INIT, cred,
                            UID_UUCP, GID_DIALER, 0660, "cua%s.init", name);
                        dev_depends(tp->t_dev, dev);
                        dev->si_drv1 = tp;
                        wakeup(&dev->si_drv1);
                        dev->si_drv2 = &tp->t_termios_init_out;

                        dev = make_dev_cred(&ttyil_cdevsw,
                            TTYUNIT_CALLOUT | TTYUNIT_LOCK, cred,
                            UID_UUCP, GID_DIALER, 0660, "cua%s.lock", name);
                        dev_depends(tp->t_dev, dev);
                        dev->si_drv1 = tp;
                        wakeup(&dev->si_drv1);
                        dev->si_drv2 = &tp->t_termios_lock_out;
                }
        }
}

/*
 * Signalling processes.
 */

void
tty_signal_sessleader(struct tty *tp, int sig)
{
        struct proc *p;

        tty_lock_assert(tp, MA_OWNED);
        MPASS(sig >= 1 && sig < NSIG);

        /* Make signals start output again. */
        tp->t_flags &= ~TF_STOPPED;

        if (tp->t_session != NULL && tp->t_session->s_leader != NULL) {
                p = tp->t_session->s_leader;
                PROC_LOCK(p);
                kern_psignal(p, sig);
                PROC_UNLOCK(p);
        }
}

void
tty_signal_pgrp(struct tty *tp, int sig)
{
        ksiginfo_t ksi;

        tty_lock_assert(tp, MA_OWNED);
        MPASS(sig >= 1 && sig < NSIG);

        /* Make signals start output again. */
        tp->t_flags &= ~TF_STOPPED;

        if (sig == SIGINFO && !(tp->t_termios.c_lflag & NOKERNINFO))
                tty_info(tp);
        if (tp->t_pgrp != NULL) {
                ksiginfo_init(&ksi);
                ksi.ksi_signo = sig;
                ksi.ksi_code = SI_KERNEL;
                PGRP_LOCK(tp->t_pgrp);
                pgsignal(tp->t_pgrp, sig, 1, &ksi);
                PGRP_UNLOCK(tp->t_pgrp);
        }
}

void
tty_wakeup(struct tty *tp, int flags)
{
        if (tp->t_flags & TF_ASYNC && tp->t_sigio != NULL)
                pgsigio(&tp->t_sigio, SIGIO, (tp->t_session != NULL));

        if (flags & FWRITE) {
                cv_broadcast(&tp->t_outwait);
                selwakeup(&tp->t_outpoll);
                KNOTE_LOCKED(&tp->t_outpoll.si_note, 0);
        }
        if (flags & FREAD) {
                cv_broadcast(&tp->t_inwait);
                selwakeup(&tp->t_inpoll);
                KNOTE_LOCKED(&tp->t_inpoll.si_note, 0);
        }
}

int
tty_wait(struct tty *tp, struct cv *cv)
{
        int error;
        int revokecnt = tp->t_revokecnt;

        tty_lock_assert(tp, MA_OWNED|MA_NOTRECURSED);
        MPASS(!tty_gone(tp));

        error = cv_wait_sig(cv, tp->t_mtx);

        /* Restart the system call when we may have been revoked. */
        if (tp->t_revokecnt != revokecnt)
                return (ERESTART);

        /* Bail out when the device slipped away. */
        if (tty_gone(tp))
                return (ENXIO);

        return (error);
}

int
tty_timedwait(struct tty *tp, struct cv *cv, int hz)
{
        int error;
        int revokecnt = tp->t_revokecnt;

        tty_lock_assert(tp, MA_OWNED|MA_NOTRECURSED);
        MPASS(!tty_gone(tp));

        error = cv_timedwait_sig(cv, tp->t_mtx, hz);

        /* Restart the system call when we may have been revoked. */
        if (tp->t_revokecnt != revokecnt)
                return (ERESTART);

        /* Bail out when the device slipped away. */
        if (tty_gone(tp))
                return (ENXIO);

        return (error);
}

void
tty_flush(struct tty *tp, int flags)
{
        if (flags & FWRITE) {
                tp->t_flags &= ~TF_HIWAT_OUT;
                ttyoutq_flush(&tp->t_outq);
                tty_wakeup(tp, FWRITE);
                ttydevsw_pktnotify(tp, TIOCPKT_FLUSHWRITE);
        }
        if (flags & FREAD) {
                tty_hiwat_in_unblock(tp);
                ttyinq_flush(&tp->t_inq);
                ttydevsw_inwakeup(tp);
                ttydevsw_pktnotify(tp, TIOCPKT_FLUSHREAD);
        }
}

void
tty_set_winsize(struct tty *tp, const struct winsize *wsz)
{

        if (memcmp(&tp->t_winsize, wsz, sizeof(*wsz)) == 0)
                return;
        tp->t_winsize = *wsz;
        tty_signal_pgrp(tp, SIGWINCH);
}

static int
tty_generic_ioctl(struct tty *tp, u_long cmd, void *data, int fflag,
    struct thread *td)
{
        int error;

        switch (cmd) {
        /*
         * Modem commands.
         * The SER_* and TIOCM_* flags are the same, but one bit
         * shifted. I don't know why.
         */
        case TIOCSDTR:
                ttydevsw_modem(tp, SER_DTR, 0);
                return (0);
        case TIOCCDTR:
                ttydevsw_modem(tp, 0, SER_DTR);
                return (0);
        case TIOCMSET: {
                int bits = *(int *)data;
                ttydevsw_modem(tp,
                    (bits & (TIOCM_DTR | TIOCM_RTS)) >> 1,
                    ((~bits) & (TIOCM_DTR | TIOCM_RTS)) >> 1);
                return (0);
        }
        case TIOCMBIS: {
                int bits = *(int *)data;
                ttydevsw_modem(tp, (bits & (TIOCM_DTR | TIOCM_RTS)) >> 1, 0);
                return (0);
        }
        case TIOCMBIC: {
                int bits = *(int *)data;
                ttydevsw_modem(tp, 0, (bits & (TIOCM_DTR | TIOCM_RTS)) >> 1);
                return (0);
        }
        case TIOCMGET:
                *(int *)data = TIOCM_LE + (ttydevsw_modem(tp, 0, 0) << 1);
                return (0);

        case FIOASYNC:
                if (*(int *)data)
                        tp->t_flags |= TF_ASYNC;
                else
                        tp->t_flags &= ~TF_ASYNC;
                return (0);
        case FIONBIO:
                /* This device supports non-blocking operation. */
                return (0);
        case FIONREAD:
                *(int *)data = ttyinq_bytescanonicalized(&tp->t_inq);
                return (0);
        case FIONWRITE:
        case TIOCOUTQ:
                *(int *)data = ttyoutq_bytesused(&tp->t_outq);
                return (0);
        case FIOSETOWN:
                if (tp->t_session != NULL && !tty_is_ctty(tp, td->td_proc))
                        /* Not allowed to set ownership. */
                        return (ENOTTY);

                /* Temporarily unlock the TTY to set ownership. */
                tty_unlock(tp);
                error = fsetown(*(int *)data, &tp->t_sigio);
                tty_lock(tp);
                return (error);
        case FIOGETOWN:
                if (tp->t_session != NULL && !tty_is_ctty(tp, td->td_proc))
                        /* Not allowed to set ownership. */
                        return (ENOTTY);

                /* Get ownership. */
                *(int *)data = fgetown(&tp->t_sigio);
                return (0);
        case TIOCGETA:
                /* Obtain terminal flags through tcgetattr(). */
                *(struct termios*)data = tp->t_termios;
                return (0);
        case TIOCSETA:
        case TIOCSETAW:
        case TIOCSETAF: {
                struct termios *t = data;

                /*
                 * Who makes up these funny rules? According to POSIX,
                 * input baud rate is set equal to the output baud rate
                 * when zero.
                 */
                if (t->c_ispeed == 0)
                        t->c_ispeed = t->c_ospeed;

                /* Discard any unsupported bits. */
                t->c_iflag &= TTYSUP_IFLAG;
                t->c_oflag &= TTYSUP_OFLAG;
                t->c_lflag &= TTYSUP_LFLAG;
                t->c_cflag &= TTYSUP_CFLAG;

                /* Set terminal flags through tcsetattr(). */
                if (cmd == TIOCSETAW || cmd == TIOCSETAF) {
                        error = tty_drain(tp);
                        if (error)
                                return (error);
                        if (cmd == TIOCSETAF)
                                tty_flush(tp, FREAD);
                }

                /*
                 * Only call param() when the flags really change.
                 */
                if ((t->c_cflag & CIGNORE) == 0 &&
                    (tp->t_termios.c_cflag != t->c_cflag ||
                    ((tp->t_termios.c_iflag ^ t->c_iflag) &
                    (IXON|IXOFF|IXANY)) ||
                    tp->t_termios.c_ispeed != t->c_ispeed ||
                    tp->t_termios.c_ospeed != t->c_ospeed)) {
                        error = ttydevsw_param(tp, t);
                        if (error)
                                return (error);

                        /* XXX: CLOCAL? */

                        tp->t_termios.c_cflag = t->c_cflag & ~CIGNORE;
                        tp->t_termios.c_ispeed = t->c_ispeed;
                        tp->t_termios.c_ospeed = t->c_ospeed;

                        /* Baud rate has changed - update watermarks. */
                        tty_watermarks(tp);
                }

                /* Copy new non-device driver parameters. */
                tp->t_termios.c_iflag = t->c_iflag;
                tp->t_termios.c_oflag = t->c_oflag;
                tp->t_termios.c_lflag = t->c_lflag;
                memcpy(&tp->t_termios.c_cc, t->c_cc, sizeof t->c_cc);

                ttydisc_optimize(tp);

                if ((t->c_lflag & ICANON) == 0) {
                        /*
                         * When in non-canonical mode, wake up all
                         * readers. Canonicalize any partial input. VMIN
                         * and VTIME could also be adjusted.
                         */
                        ttyinq_canonicalize(&tp->t_inq);
                        tty_wakeup(tp, FREAD);
                }

                /*
                 * For packet mode: notify the PTY consumer that VSTOP
                 * and VSTART may have been changed.
                 */
                if (tp->t_termios.c_iflag & IXON &&
                    tp->t_termios.c_cc[VSTOP] == CTRL('S') &&
                    tp->t_termios.c_cc[VSTART] == CTRL('Q'))
                        ttydevsw_pktnotify(tp, TIOCPKT_DOSTOP);
                else
                        ttydevsw_pktnotify(tp, TIOCPKT_NOSTOP);
                return (0);
        }
        case TIOCGETD:
                /* For compatibility - we only support TTYDISC. */
                *(int *)data = TTYDISC;
                return (0);
        case TIOCGPGRP:
                if (!tty_is_ctty(tp, td->td_proc))
                        return (ENOTTY);

                if (tp->t_pgrp != NULL)
                        *(int *)data = tp->t_pgrp->pg_id;
                else
                        *(int *)data = NO_PID;
                return (0);
        case TIOCGSID:
                if (!tty_is_ctty(tp, td->td_proc))
                        return (ENOTTY);

                MPASS(tp->t_session);
                *(int *)data = tp->t_session->s_sid;
                return (0);
        case TIOCSCTTY: {
                struct proc *p = td->td_proc;

                /* XXX: This looks awful. */
                tty_unlock(tp);
                sx_xlock(&proctree_lock);
                tty_lock(tp);

                if (!SESS_LEADER(p)) {
                        /* Only the session leader may do this. */
                        sx_xunlock(&proctree_lock);
                        return (EPERM);
                }

                if (tp->t_session != NULL && tp->t_session == p->p_session) {
                        /* This is already our controlling TTY. */
                        sx_xunlock(&proctree_lock);
                        return (0);
                }

                if (p->p_session->s_ttyp != NULL ||
                    (tp->t_session != NULL && tp->t_session->s_ttyvp != NULL &&
                    tp->t_session->s_ttyvp->v_type != VBAD)) {
                        /*
                         * There is already a relation between a TTY and
                         * a session, or the caller is not the session
                         * leader.
                         *
                         * Allow the TTY to be stolen when the vnode is
                         * invalid, but the reference to the TTY is
                         * still active.  This allows immediate reuse of
                         * TTYs of which the session leader has been
                         * killed or the TTY revoked.
                         */
                        sx_xunlock(&proctree_lock);
                        return (EPERM);
                }

                /* Connect the session to the TTY. */
                tp->t_session = p->p_session;
                tp->t_session->s_ttyp = tp;
                tp->t_sessioncnt++;
                sx_xunlock(&proctree_lock);

                /* Assign foreground process group. */
                tp->t_pgrp = p->p_pgrp;
                PROC_LOCK(p);
                p->p_flag |= P_CONTROLT;
                PROC_UNLOCK(p);

                return (0);
        }
        case TIOCSPGRP: {
                struct pgrp *pg;

                /*
                 * XXX: Temporarily unlock the TTY to locate the process
                 * group. This code would be lot nicer if we would ever
                 * decompose proctree_lock.
                 */
                tty_unlock(tp);
                sx_slock(&proctree_lock);
                pg = pgfind(*(int *)data);
                if (pg != NULL)
                        PGRP_UNLOCK(pg);
                if (pg == NULL || pg->pg_session != td->td_proc->p_session) {
                        sx_sunlock(&proctree_lock);
                        tty_lock(tp);
                        return (EPERM);
                }
                tty_lock(tp);

                /*
                 * Determine if this TTY is the controlling TTY after
                 * relocking the TTY.
                 */
                if (!tty_is_ctty(tp, td->td_proc)) {
                        sx_sunlock(&proctree_lock);
                        return (ENOTTY);
                }
                tp->t_pgrp = pg;
                sx_sunlock(&proctree_lock);

                /* Wake up the background process groups. */
                cv_broadcast(&tp->t_bgwait);
                return (0);
        }
        case TIOCFLUSH: {
                int flags = *(int *)data;

                if (flags == 0)
                        flags = (FREAD|FWRITE);
                else
                        flags &= (FREAD|FWRITE);
                tty_flush(tp, flags);
                return (0);
        }
        case TIOCDRAIN:
                /* Drain TTY output. */
                return tty_drain(tp);
        case TIOCCONS:
                /* Set terminal as console TTY. */
                if (*(int *)data) {
                        error = priv_check(td, PRIV_TTY_CONSOLE);
                        if (error)
                                return (error);

                        /*
                         * XXX: constty should really need to be locked!
                         * XXX: allow disconnected constty's to be stolen!
                         */

                        if (constty == tp)
                                return (0);
                        if (constty != NULL)
                                return (EBUSY);

                        tty_unlock(tp);
                        constty_set(tp);
                        tty_lock(tp);
                } else if (constty == tp) {
                        constty_clear();
                }
                return (0);
        case TIOCGWINSZ:
                /* Obtain window size. */
                *(struct winsize*)data = tp->t_winsize;
                return (0);
        case TIOCSWINSZ:
                /* Set window size. */
                tty_set_winsize(tp, data);
                return (0);
        case TIOCEXCL:
                tp->t_flags |= TF_EXCLUDE;
                return (0);
        case TIOCNXCL:
                tp->t_flags &= ~TF_EXCLUDE;
                return (0);
        case TIOCSTOP:
                tp->t_flags |= TF_STOPPED;
                ttydevsw_pktnotify(tp, TIOCPKT_STOP);
                return (0);
        case TIOCSTART:
                tp->t_flags &= ~TF_STOPPED;
                ttydevsw_outwakeup(tp);
                ttydevsw_pktnotify(tp, TIOCPKT_START);
                return (0);
        case TIOCSTAT:
                tty_info(tp);
                return (0);
        case TIOCSTI:
                if ((fflag & FREAD) == 0 && priv_check(td, PRIV_TTY_STI))
                        return (EPERM);
                if (!tty_is_ctty(tp, td->td_proc) &&
                    priv_check(td, PRIV_TTY_STI))
                        return (EACCES);
                ttydisc_rint(tp, *(char *)data, 0);
                ttydisc_rint_done(tp);
                return (0);
        }

#ifdef COMPAT_43TTY
        return tty_ioctl_compat(tp, cmd, data, fflag, td);
#else /* !COMPAT_43TTY */
        return (ENOIOCTL);
#endif /* COMPAT_43TTY */
}

int
tty_ioctl(struct tty *tp, u_long cmd, void *data, int fflag, struct thread *td)
{
        int error;

        tty_lock_assert(tp, MA_OWNED);

        if (tty_gone(tp))
                return (ENXIO);

        error = ttydevsw_ioctl(tp, cmd, data, td);
        if (error == ENOIOCTL)
                error = tty_generic_ioctl(tp, cmd, data, fflag, td);

        return (error);
}

dev_t
tty_udev(struct tty *tp)
{
        if (tp->t_dev)
                return dev2udev(tp->t_dev);
        else
                return NODEV;
}

int
tty_checkoutq(struct tty *tp)
{

        /* 256 bytes should be enough to print a log message. */
        return (ttyoutq_bytesleft(&tp->t_outq) >= 256);
}

void
tty_hiwat_in_block(struct tty *tp)
{

        if ((tp->t_flags & TF_HIWAT_IN) == 0 &&
            tp->t_termios.c_iflag & IXOFF &&
            tp->t_termios.c_cc[VSTOP] != _POSIX_VDISABLE) {
                /*
                 * Input flow control. Only enter the high watermark when we
                 * can successfully store the VSTOP character.
                 */
                if (ttyoutq_write_nofrag(&tp->t_outq,
                    &tp->t_termios.c_cc[VSTOP], 1) == 0)
                        tp->t_flags |= TF_HIWAT_IN;
        } else {
                /* No input flow control. */
                tp->t_flags |= TF_HIWAT_IN;
        }
}

void
tty_hiwat_in_unblock(struct tty *tp)
{

        if (tp->t_flags & TF_HIWAT_IN &&
            tp->t_termios.c_iflag & IXOFF &&
            tp->t_termios.c_cc[VSTART] != _POSIX_VDISABLE) {
                /*
                 * Input flow control. Only leave the high watermark when we
                 * can successfully store the VSTART character.
                 */
                if (ttyoutq_write_nofrag(&tp->t_outq,
                    &tp->t_termios.c_cc[VSTART], 1) == 0)
                        tp->t_flags &= ~TF_HIWAT_IN;
        } else {
                /* No input flow control. */
                tp->t_flags &= ~TF_HIWAT_IN;
        }

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

/*
 * TTY hooks interface.
 */

static int
ttyhook_defrint(struct tty *tp, char c, int flags)
{

        if (ttyhook_rint_bypass(tp, &c, 1) != 1)
                return (-1);

        return (0);
}

int
ttyhook_register(struct tty **rtp, struct proc *p, int fd,
    struct ttyhook *th, void *softc)
{
        struct tty *tp;
        struct file *fp;
#ifdef CAPABILITIES
        struct file *fp_cap;
#endif
        struct cdev *dev;
        struct cdevsw *cdp;
        struct filedesc *fdp;
        int error, ref;

        /* Validate the file descriptor. */
        if ((fdp = p->p_fd) == NULL)
                return (EBADF);

        fp = fget_unlocked(fdp, fd);
        if (fp == NULL)
                return (EBADF);
        if (fp->f_ops == &badfileops) {
                error = EBADF;
                goto done1;
        }

#ifdef CAPABILITIES
        fp_cap = fp;
        error = cap_funwrap(fp_cap, CAP_TTYHOOK, &fp);
        if (error)
                return (error);
#endif

        /*
         * Make sure the vnode is bound to a character device.
         * Unlocked check for the vnode type is ok there, because we
         * only shall prevent calling devvn_refthread on the file that
         * never has been opened over a character device.
         */
        if (fp->f_type != DTYPE_VNODE || fp->f_vnode->v_type != VCHR) {
                error = EINVAL;
                goto done1;
        }

        /* Make sure it is a TTY. */
        cdp = devvn_refthread(fp->f_vnode, &dev, &ref);
        if (cdp == NULL) {
                error = ENXIO;
                goto done1;
        }
        if (dev != fp->f_data) {
                error = ENXIO;
                goto done2;
        }
        if (cdp != &ttydev_cdevsw) {
                error = ENOTTY;
                goto done2;
        }
        tp = dev->si_drv1;

        /* Try to attach the hook to the TTY. */
        error = EBUSY;
        tty_lock(tp);
        MPASS((tp->t_hook == NULL) == ((tp->t_flags & TF_HOOK) == 0));
        if (tp->t_flags & TF_HOOK)
                goto done3;

        tp->t_flags |= TF_HOOK;
        tp->t_hook = th;
        tp->t_hooksoftc = softc;
        *rtp = tp;
        error = 0;

        /* Maybe we can switch into bypass mode now. */
        ttydisc_optimize(tp);

        /* Silently convert rint() calls to rint_bypass() when possible. */
        if (!ttyhook_hashook(tp, rint) && ttyhook_hashook(tp, rint_bypass))
                th->th_rint = ttyhook_defrint;

done3:  tty_unlock(tp);
done2:  dev_relthread(dev, ref);
done1:  fdrop(fp, curthread);
        return (error);
}

void
ttyhook_unregister(struct tty *tp)
{

        tty_lock_assert(tp, MA_OWNED);
        MPASS(tp->t_flags & TF_HOOK);

        /* Disconnect the hook. */
        tp->t_flags &= ~TF_HOOK;
        tp->t_hook = NULL;

        /* Maybe we need to leave bypass mode. */
        ttydisc_optimize(tp);

        /* Maybe deallocate the TTY as well. */
        tty_rel_free(tp);
}

/*
 * /dev/console handling.
 */

static int
ttyconsdev_open(struct cdev *dev, int oflags, int devtype, struct thread *td)
{
        struct tty *tp;

        /* System has no console device. */
        if (dev_console_filename == NULL)
                return (ENXIO);

        /* Look up corresponding TTY by device name. */
        sx_slock(&tty_list_sx);
        TAILQ_FOREACH(tp, &tty_list, t_list) {
                if (strcmp(dev_console_filename, tty_devname(tp)) == 0) {
                        dev_console->si_drv1 = tp;
                        break;
                }
        }
        sx_sunlock(&tty_list_sx);

        /* System console has no TTY associated. */
        if (dev_console->si_drv1 == NULL)
                return (ENXIO);

        return (ttydev_open(dev, oflags, devtype, td));
}

static int
ttyconsdev_write(struct cdev *dev, struct uio *uio, int ioflag)
{

        log_console(uio);

        return (ttydev_write(dev, uio, ioflag));
}

/*
 * /dev/console is a little different than normal TTY's.  When opened,
 * it determines which TTY to use.  When data gets written to it, it
 * will be logged in the kernel message buffer.
 */
static struct cdevsw ttyconsdev_cdevsw = {
        .d_version      = D_VERSION,
        .d_open         = ttyconsdev_open,
        .d_close        = ttydev_close,
        .d_read         = ttydev_read,
        .d_write        = ttyconsdev_write,
        .d_ioctl        = ttydev_ioctl,
        .d_kqfilter     = ttydev_kqfilter,
        .d_poll         = ttydev_poll,
        .d_mmap         = ttydev_mmap,
        .d_name         = "ttyconsdev",
        .d_flags        = D_TTY,
};

static void
ttyconsdev_init(void *unused)
{

        dev_console = make_dev_credf(MAKEDEV_ETERNAL, &ttyconsdev_cdevsw, 0,
            NULL, UID_ROOT, GID_WHEEL, 0600, "console");
}

SYSINIT(tty, SI_SUB_DRIVERS, SI_ORDER_FIRST, ttyconsdev_init, NULL);

void
ttyconsdev_select(const char *name)
{

        dev_console_filename = name;
}

/*
 * Debugging routines.
 */

#include "opt_ddb.h"
#ifdef DDB
#include <ddb/ddb.h>
#include <ddb/db_sym.h>

static struct {
        int flag;
        char val;
} ttystates[] = {
#if 0
        { TF_NOPREFIX,          'N' },
#endif
        { TF_INITLOCK,          'I' },
        { TF_CALLOUT,           'C' },

        /* Keep these together -> 'Oi' and 'Oo'. */
        { TF_OPENED,            'O' },
        { TF_OPENED_IN,         'i' },
        { TF_OPENED_OUT,        'o' },
        { TF_OPENED_CONS,       'c' },

        { TF_GONE,              'G' },
        { TF_OPENCLOSE,         'B' },
        { TF_ASYNC,             'Y' },
        { TF_LITERAL,           'L' },

        /* Keep these together -> 'Hi' and 'Ho'. */
        { TF_HIWAT,             'H' },
        { TF_HIWAT_IN,          'i' },
        { TF_HIWAT_OUT,         'o' },

        { TF_STOPPED,           'S' },
        { TF_EXCLUDE,           'X' },
        { TF_BYPASS,            'l' },
        { TF_ZOMBIE,            'Z' },
        { TF_HOOK,              's' },

        /* Keep these together -> 'bi' and 'bo'. */
        { TF_BUSY,              'b' },
        { TF_BUSY_IN,           'i' },
        { TF_BUSY_OUT,          'o' },

        { 0,                    '\0'},
};

#define TTY_FLAG_BITS \
        "\20\1NOPREFIX\2INITLOCK\3CALLOUT\4OPENED_IN\5OPENED_OUT\6GONE" \
        "\7OPENCLOSE\10ASYNC\11LITERAL\12HIWAT_IN\13HIWAT_OUT\14STOPPED" \
        "\15EXCLUDE\16BYPASS\17ZOMBIE\20HOOK"

#define DB_PRINTSYM(name, addr) \
        db_printf("%s  " #name ": ", sep); \
        db_printsym((db_addr_t) addr, DB_STGY_ANY); \
        db_printf("\n");

static void
_db_show_devsw(const char *sep, const struct ttydevsw *tsw)
{
        db_printf("%sdevsw: ", sep);
        db_printsym((db_addr_t)tsw, DB_STGY_ANY);
        db_printf(" (%p)\n", tsw);
        DB_PRINTSYM(open, tsw->tsw_open);
        DB_PRINTSYM(close, tsw->tsw_close);
        DB_PRINTSYM(outwakeup, tsw->tsw_outwakeup);
        DB_PRINTSYM(inwakeup, tsw->tsw_inwakeup);
        DB_PRINTSYM(ioctl, tsw->tsw_ioctl);
        DB_PRINTSYM(param, tsw->tsw_param);
        DB_PRINTSYM(modem, tsw->tsw_modem);
        DB_PRINTSYM(mmap, tsw->tsw_mmap);
        DB_PRINTSYM(pktnotify, tsw->tsw_pktnotify);
        DB_PRINTSYM(free, tsw->tsw_free);
}
static void
_db_show_hooks(const char *sep, const struct ttyhook *th)
{
        db_printf("%shook: ", sep);
        db_printsym((db_addr_t)th, DB_STGY_ANY);
        db_printf(" (%p)\n", th);
        if (th == NULL)
                return;
        DB_PRINTSYM(rint, th->th_rint);
        DB_PRINTSYM(rint_bypass, th->th_rint_bypass);
        DB_PRINTSYM(rint_done, th->th_rint_done);
        DB_PRINTSYM(rint_poll, th->th_rint_poll);
        DB_PRINTSYM(getc_inject, th->th_getc_inject);
        DB_PRINTSYM(getc_capture, th->th_getc_capture);
        DB_PRINTSYM(getc_poll, th->th_getc_poll);
        DB_PRINTSYM(close, th->th_close);
}

static void
_db_show_termios(const char *name, const struct termios *t)
{

        db_printf("%s: iflag 0x%x oflag 0x%x cflag 0x%x "
            "lflag 0x%x ispeed %u ospeed %u\n", name,
            t->c_iflag, t->c_oflag, t->c_cflag, t->c_lflag,
            t->c_ispeed, t->c_ospeed);
}

/* DDB command to show TTY statistics. */
DB_SHOW_COMMAND(tty, db_show_tty)
{
        struct tty *tp;

        if (!have_addr) {
                db_printf("usage: show tty <addr>\n");
                return;
        }
        tp = (struct tty *)addr;

        db_printf("0x%p: %s\n", tp, tty_devname(tp));
        db_printf("\tmtx: %p\n", tp->t_mtx);
        db_printf("\tflags: %b\n", tp->t_flags, TTY_FLAG_BITS);
        db_printf("\trevokecnt: %u\n", tp->t_revokecnt);

        /* Buffering mechanisms. */
        db_printf("\tinq: %p begin %u linestart %u reprint %u end %u "
            "nblocks %u quota %u\n", &tp->t_inq, tp->t_inq.ti_begin,
            tp->t_inq.ti_linestart, tp->t_inq.ti_reprint, tp->t_inq.ti_end,
            tp->t_inq.ti_nblocks, tp->t_inq.ti_quota);
        db_printf("\toutq: %p begin %u end %u nblocks %u quota %u\n",
            &tp->t_outq, tp->t_outq.to_begin, tp->t_outq.to_end,
            tp->t_outq.to_nblocks, tp->t_outq.to_quota);
        db_printf("\tinlow: %zu\n", tp->t_inlow);
        db_printf("\toutlow: %zu\n", tp->t_outlow);
        _db_show_termios("\ttermios", &tp->t_termios);
        db_printf("\twinsize: row %u col %u xpixel %u ypixel %u\n",
            tp->t_winsize.ws_row, tp->t_winsize.ws_col,
            tp->t_winsize.ws_xpixel, tp->t_winsize.ws_ypixel);
        db_printf("\tcolumn: %u\n", tp->t_column);
        db_printf("\twritepos: %u\n", tp->t_writepos);
        db_printf("\tcompatflags: 0x%x\n", tp->t_compatflags);

        /* Init/lock-state devices. */
        _db_show_termios("\ttermios_init_in", &tp->t_termios_init_in);
        _db_show_termios("\ttermios_init_out", &tp->t_termios_init_out);
        _db_show_termios("\ttermios_lock_in", &tp->t_termios_lock_in);
        _db_show_termios("\ttermios_lock_out", &tp->t_termios_lock_out);

        /* Hooks */
        _db_show_devsw("\t", tp->t_devsw);
        _db_show_hooks("\t", tp->t_hook);

        /* Process info. */
        db_printf("\tpgrp: %p gid %d jobc %d\n", tp->t_pgrp,
            tp->t_pgrp ? tp->t_pgrp->pg_id : 0,
            tp->t_pgrp ? tp->t_pgrp->pg_jobc : 0);
        db_printf("\tsession: %p", tp->t_session);
        if (tp->t_session != NULL)
            db_printf(" count %u leader %p tty %p sid %d login %s",
                tp->t_session->s_count, tp->t_session->s_leader,
                tp->t_session->s_ttyp, tp->t_session->s_sid,
                tp->t_session->s_login);
        db_printf("\n");
        db_printf("\tsessioncnt: %u\n", tp->t_sessioncnt);
        db_printf("\tdevswsoftc: %p\n", tp->t_devswsoftc);
        db_printf("\thooksoftc: %p\n", tp->t_hooksoftc);
        db_printf("\tdev: %p\n", tp->t_dev);
}

/* DDB command to list TTYs. */
DB_SHOW_ALL_COMMAND(ttys, db_show_all_ttys)
{
        struct tty *tp;
        size_t isiz, osiz;
        int i, j;

        /* Make the output look like `pstat -t'. */
        db_printf("PTR        ");
#if defined(__LP64__)
        db_printf("        ");
#endif
        db_printf("      LINE   INQ  CAN  LIN  LOW  OUTQ  USE  LOW   "
            "COL  SESS  PGID STATE\n");

        TAILQ_FOREACH(tp, &tty_list, t_list) {
                isiz = tp->t_inq.ti_nblocks * TTYINQ_DATASIZE;
                osiz = tp->t_outq.to_nblocks * TTYOUTQ_DATASIZE;

                db_printf("%p %10s %5zu %4u %4u %4zu %5zu %4u %4zu %5u %5d %5d ",
                    tp,
                    tty_devname(tp),
                    isiz,
                    tp->t_inq.ti_linestart - tp->t_inq.ti_begin,
                    tp->t_inq.ti_end - tp->t_inq.ti_linestart,
                    isiz - tp->t_inlow,
                    osiz,
                    tp->t_outq.to_end - tp->t_outq.to_begin,
                    osiz - tp->t_outlow,
                    MIN(tp->t_column, 99999),
                    tp->t_session ? tp->t_session->s_sid : 0,
                    tp->t_pgrp ? tp->t_pgrp->pg_id : 0);

                /* Flag bits. */
                for (i = j = 0; ttystates[i].flag; i++)
                        if (tp->t_flags & ttystates[i].flag) {
                                db_printf("%c", ttystates[i].val);
                                j++;
                        }
                if (j == 0)
                        db_printf("-");
                db_printf("\n");
        }
}
#endif /* DDB */