FreeBSD/Linux Kernel Cross Reference
sys/kern/tty.c

     /*-
      * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
      *
      * 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("$FreeBSD: releng/12.0/sys/kern/tty.c 335997 2018-07-05 16:28:43Z kevans $");
    
    #include "opt_capsicum.h"
    
    #include <sys/param.h>
    #include <sys/capsicum.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)
    
    static int  tty_drainwait = 5 * 60;
   SYSCTL_INT(_kern, OID_AUTO, tty_drainwait, CTLFLAG_RWTUN,
       &tty_drainwait, 0, "Default output drain timeout in seconds");
   
   /*
    * Set TTY buffer sizes.
    */
   
   #define TTYBUF_MAX      65536
   
   /*
    * Allocate buffer space if necessary, and set low watermarks, based on speed.
    * Note that the ttyxxxq_setsize() functions may drop and then reacquire the tty
    * lock during memory allocation.  They will return ENXIO if the tty disappears
    * while unlocked.
    */
   static int
   tty_watermarks(struct tty *tp)
   {
           size_t bs = 0;
           int error;
   
           /* Provide an input buffer for 2 seconds of data. */
           if (tp->t_termios.c_cflag & CREAD)
                   bs = MIN(tp->t_termios.c_ispeed / 5, TTYBUF_MAX);
           error = ttyinq_setsize(&tp->t_inq, tp, bs);
           if (error != 0)
                   return (error);
   
           /* Set low watermark at 10% (when 90% is available). */
           tp->t_inlow = (ttyinq_getallocatedsize(&tp->t_inq) * 9) / 10;
   
           /* Provide an output buffer for 2 seconds of data. */
           bs = MIN(tp->t_termios.c_ospeed / 5, TTYBUF_MAX);
           error = ttyoutq_setsize(&tp->t_outq, tp, bs);
           if (error != 0)
                   return (error);
   
           /* Set low watermark at 10% (when 90% is available). */
           tp->t_outlow = (ttyoutq_getallocatedsize(&tp->t_outq) * 9) / 10;
   
           return (0);
   }
   
   static int
   tty_drain(struct tty *tp, int leaving)
   {
           sbintime_t timeout_at;
           size_t bytes;
           int error;
   
           if (ttyhook_hashook(tp, getc_inject))
                   /* buffer is inaccessible */
                   return (0);
   
           /*
            * For close(), use the recent historic timeout of "1 second without
            * making progress".  For tcdrain(), use t_drainwait as the timeout,
            * with zero meaning "no timeout" which gives POSIX behavior.
            */
           if (leaving)
                   timeout_at = getsbinuptime() + SBT_1S;
           else if (tp->t_drainwait != 0)
                   timeout_at = getsbinuptime() + SBT_1S * tp->t_drainwait;
           else
                   timeout_at = 0;
   
           /*
            * Poll the output buffer and the hardware for completion, at 10 Hz.
            * Polling is required for devices which are not able to signal an
            * interrupt when the transmitter becomes idle (most USB serial devs).
            * The unusual structure of this loop ensures we check for busy one more
            * time after tty_timedwait() returns EWOULDBLOCK, so that success has
            * higher priority than timeout if the IO completed in the last 100mS.
            */
           error = 0;
           bytes = ttyoutq_bytesused(&tp->t_outq);
           for (;;) {
                   if (ttyoutq_bytesused(&tp->t_outq) == 0 && !ttydevsw_busy(tp))
                           return (0);
                   if (error != 0)
                           return (error);
                   ttydevsw_outwakeup(tp);
                   error = tty_timedwait(tp, &tp->t_outwait, hz / 10);
                   if (error != 0 && error != EWOULDBLOCK)
                           return (error);
                   else if (timeout_at == 0 || getsbinuptime() < timeout_at)
                           error = 0;
                   else if (leaving && ttyoutq_bytesused(&tp->t_outq) < bytes) {
                           /* In close, making progress, grant an extra second. */
                           error = 0;
                           timeout_at += SBT_1S;
                           bytes = ttyoutq_bytesused(&tp->t_outq);
                   }
           }
   }
   
   /*
    * 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. */
           if (!tty_gone(tp))
                   tty_drain(tp, 1);
   
           ttydisc_close(tp);
   
           /* Free i/o queues now since they might be large. */
           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 __unused,
       struct thread *td)
   {
           struct tty *tp;
           int error;
   
           tp = dev->si_drv1;
           error = 0;
           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.  The console is a "tty" device.
            */
           if (TTY_CALLOUT(tp, dev)) {
                   if (tp->t_flags & (TF_OPENED_CONS | 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);
                   error = tty_watermarks(tp);
                   if (error != 0)
                           goto done;
           }
   
           /* 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;
           MPASS((tp->t_flags & (TF_OPENED_CONS | TF_OPENED_IN)) == 0 ||
               (tp->t_flags & TF_OPENED_OUT) == 0);
   
   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 __unused,
       struct thread *td __unused)
   {
           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_CONS | TF_OPENED_IN)) == 0 ||
               (tp->t_flags & TF_OPENED_OUT) == 0);
           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);
           }
   
           /* If revoking, flush output now to avoid draining it later. */
           if (fflag & FREVOKE)
                   tty_flush(tp, FWRITE);
   
           tp->t_flags &= ~TF_EXCLUDE;
   
           /* 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 controlling 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 __unused)
   {
           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 __unused)
   {
           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 __unused, int devtype __unused,
       struct thread *td)
   {
           struct tty *tp;
           int error;
   
           tp = dev->si_drv1;
           error = 0;
           tty_lock(tp);
           if (tty_gone(tp))
                   error = ENODEV;
           tty_unlock(tp);
   
           return (error);
   }
   
   static int
   ttyil_close(struct cdev *dev __unused, int flag __unused, int mode __unused,
       struct thread *td __unused)
   {
   
           return (0);
   }
   
   static int
   ttyil_rdwr(struct cdev *dev __unused, struct uio *uio __unused,
       int ioflag __unused)
   {
   
           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 __unused)
   {
   
           return (0);
   }
   
   static void
   ttydevsw_defclose(struct tty *tp __unused)
   {
   
   }
   
   static void
   ttydevsw_defoutwakeup(struct tty *tp __unused)
   {
   
           panic("Terminal device has output, while not implemented");
   }
   
   static void
   ttydevsw_definwakeup(struct tty *tp __unused)
   {
   
   }
   
   static int
   ttydevsw_defioctl(struct tty *tp __unused, u_long cmd __unused,
       caddr_t data __unused, struct thread *td __unused)
   {
   
           return (ENOIOCTL);
   }
   
   static int
   ttydevsw_defcioctl(struct tty *tp __unused, int unit __unused,
       u_long cmd __unused, caddr_t data __unused, struct thread *td __unused)
   {
   
           return (ENOIOCTL);
   }
   
   static int
   ttydevsw_defparam(struct tty *tp __unused, 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 __unused, int sigon __unused,
       int sigoff __unused)
   {
   
           /* Simulate a carrier to make the TTY layer happy. */
           return (SER_DCD);
   }
   
   static int
   ttydevsw_defmmap(struct tty *tp __unused, vm_ooffset_t offset __unused,
       vm_paddr_t *paddr __unused, int nprot __unused,
       vm_memattr_t *memattr __unused)
   {
   
           return (-1);
   }
   
   static void
   ttydevsw_defpktnotify(struct tty *tp __unused, char event __unused)
   {
  
  }
  
  static void
  ttydevsw_deffree(void *softc __unused)
  {
  
          panic("Terminal device freed without a free-handler");
  }
  
  static bool
  ttydevsw_defbusy(struct tty *tp __unused)
  {
  
          return (FALSE);
  }
  
  /*
   * 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);
          PATCH_FUNC(busy);
  #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;
          tp->t_drainwait = tty_drainwait;
  
          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);
  
          return (tp);
  }
  
  static void
  tty_dealloc(void *arg)
  {
          struct tty *tp = arg;
  
          /*
           * ttyydev_leave() usually frees the i/o queues earlier, but it is
           * not always called between queue allocation and here.  The queues
           * may be allocated by ioctls on a pty control device without the
           * corresponding pty slave device ever being open, or after it is
           * closed.
           */
          ttyinq_free(&tp->t_inq);
          ttyoutq_free(&tp->t_outq);
          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) {
                  sx_xlock(&tty_list_sx);
                  TAILQ_REMOVE(&tty_list, tp, t_list);
                  tty_list_count--;
                  sx_xunlock(&tty_list_sx);
                  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) : (uint32_t)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.
   */
  
  int
  tty_makedevf(struct tty *tp, struct ucred *cred, int flags,
      const char *fmt, ...)
  {
          va_list ap;
          struct make_dev_args args;
          struct cdev *dev, *init, *lock, *cua, *cinit, *clock;
          const char *prefix = "tty";
          char name[SPECNAMELEN - 3]; /* for "tty" and "cua". */
          uid_t uid;
          gid_t gid;
          mode_t mode;
          int error;
  
          /* 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;
          }
  
          flags = flags & TTYMK_CLONING ? MAKEDEV_REF : 0;
          flags |= MAKEDEV_CHECKNAME;
  
          /* Master call-in device. */
          make_dev_args_init(&args);
          args.mda_flags = flags;
          args.mda_devsw = &ttydev_cdevsw;
          args.mda_cr = cred;
          args.mda_uid = uid;
          args.mda_gid = gid;
          args.mda_mode = mode;
          args.mda_si_drv1 = tp;
          error = make_dev_s(&args, &dev, "%s%s", prefix, name);
          if (error != 0)
                  return (error);
          tp->t_dev = dev;
  
          init = lock = cua = cinit = clock = NULL;
  
          /* Slave call-in devices. */
          if (tp->t_flags & TF_INITLOCK) {
                  args.mda_devsw = &ttyil_cdevsw;
                  args.mda_unit = TTYUNIT_INIT;
                  args.mda_si_drv1 = tp;
                  args.mda_si_drv2 = &tp->t_termios_init_in;
                  error = make_dev_s(&args, &init, "%s%s.init", prefix, name);
                  if (error != 0)
                          goto fail;
                  dev_depends(dev, init);
  
                  args.mda_unit = TTYUNIT_LOCK;
                  args.mda_si_drv2 = &tp->t_termios_lock_in;
                  error = make_dev_s(&args, &lock, "%s%s.lock", prefix, name);
                  if (error != 0)
                          goto fail;
                  dev_depends(dev, lock);
          }
  
          /* Call-out devices. */
          if (tp->t_flags & TF_CALLOUT) {
                  make_dev_args_init(&args);
                  args.mda_flags = flags;
                  args.mda_devsw = &ttydev_cdevsw;
                  args.mda_cr = cred;
                  args.mda_uid = UID_UUCP;
                  args.mda_gid = GID_DIALER;
                  args.mda_mode = 0660;
                  args.mda_unit = TTYUNIT_CALLOUT;
                  args.mda_si_drv1 = tp;
                  error = make_dev_s(&args, &cua, "cua%s", name);
                  if (error != 0)
                          goto fail;
                  dev_depends(dev, cua);
  
                  /* Slave call-out devices. */
                  if (tp->t_flags & TF_INITLOCK) {
                          args.mda_devsw = &ttyil_cdevsw;
                          args.mda_unit = TTYUNIT_CALLOUT | TTYUNIT_INIT;
                          args.mda_si_drv2 = &tp->t_termios_init_out;
                          error = make_dev_s(&args, &cinit, "cua%s.init", name);
                          if (error != 0)
                                  goto fail;
                          dev_depends(dev, cinit);
  
                          args.mda_unit = TTYUNIT_CALLOUT | TTYUNIT_LOCK;
                          args.mda_si_drv2 = &tp->t_termios_lock_out;
                          error = make_dev_s(&args, &clock, "cua%s.lock", name);
                          if (error != 0)
                                  goto fail;
                          dev_depends(dev, clock);
                  }
          }
  
          sx_xlock(&tty_list_sx);
          TAILQ_INSERT_TAIL(&tty_list, tp, t_list);
          tty_list_count++;
          sx_xunlock(&tty_list_sx);
  
          return (0);
  
  fail:
          destroy_dev(dev);
          if (init)
                  destroy_dev(init);
          if (lock)
                  destroy_dev(lock);
          if (cinit)
                  destroy_dev(cinit);
          if (clock)
                  destroy_dev(clock);
  
          return (error);
  }
  
  /*
   * 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);
  
          /* Bail out when the device slipped away. */
          if (tty_gone(tp))
                  return (ENXIO);
  
          /* Restart the system call when we may have been revoked. */
          if (tp->t_revokecnt != revokecnt)
                  return (ERESTART);
  
          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);
  
          /* Bail out when the device slipped away. */
          if (tty_gone(tp))
                  return (ENXIO);
  
          /* Restart the system call when we may have been revoked. */
          if (tp->t_revokecnt != revokecnt)
                  return (ERESTART);
  
          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);
                  if (!tty_gone(tp)) {
                          ttydevsw_outwakeup(tp);
                          ttydevsw_pktnotify(tp, TIOCPKT_FLUSHWRITE);
                  }
          }
          if (flags & FREAD) {
                  tty_hiwat_in_unblock(tp);
                  ttyinq_flush(&tp->t_inq);
                  tty_wakeup(tp, FREAD);
                  if (!tty_gone(tp)) {
                          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, 0);
                          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. */
                          error = tty_watermarks(tp);
                          if (error)
                                  return (error);
                  }
  
                  /* 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, 0);
          case TIOCGDRAINWAIT:
                  *(int *)data = tp->t_drainwait;
                  return (0);
          case TIOCSDRAINWAIT:
                  error = priv_check(td, PRIV_TTY_DRAINWAIT);
                  if (error == 0)
                          tp->t_drainwait = *(int *)data;
                  return (error);
          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;
          struct cdev *dev;
          struct cdevsw *cdp;
          struct filedesc *fdp;
          cap_rights_t rights;
          int error, ref;
  
          /* Validate the file descriptor. */
          fdp = p->p_fd;
          error = fget_unlocked(fdp, fd, cap_rights_init(&rights, CAP_TTYHOOK),
              &fp, NULL);
          if (error != 0)
                  return (error);
          if (fp->f_ops == &badfileops) {
                  error = EBADF;
                  goto done1;
          }
  
          /*
           * 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 __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 const 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 \
          "\2\1NOPREFIX\2INITLOCK\3CALLOUT\4OPENED_IN" \
          "\5OPENED_OUT\6OPENED_CONS\7GONE\10OPENCLOSE" \
          "\11ASYNC\12LITERAL\13HIWAT_IN\14HIWAT_OUT" \
          "\15STOPPED\16EXCLUDE\17BYPASS\20ZOMBIE" \
          "\21HOOK\22BUSY_IN\23BUSY_OUT"
  
  #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("%p: %s\n", tp, tty_devname(tp));
          db_printf("\tmtx: %p\n", tp->t_mtx);
          db_printf("\tflags: 0x%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 */

Cache object: 136bd813e21eac738820a4d7bfc497dc