/*      $NetBSD: tty_conf.c,v 1.57 2021/08/09 20:49:10 andvar Exp $     */

/*-
* Copyright (c) 2005, 2007 The NetBSD Foundation, Inc.
* All rights reserved.
*
* This code is derived from software contributed to The NetBSD Foundation
* by Jason R. Thorpe.
*
* 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 NETBSD FOUNDATION, INC. 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 FOUNDATION 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.
*/

/*-
* Copyright (c) 1982, 1986, 1991, 1993
*      The Regents of the University of California.  All rights reserved.
* (c) UNIX System Laboratories, Inc.
* All or some portions of this file are derived from material licensed
* to the University of California by American Telephone and Telegraph
* Co. or Unix System Laboratories, Inc. and are reproduced herein with
* the permission of UNIX System Laboratories, Inc.
*
* 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.
* 3. Neither the name of the University nor the names of its contributors
*    may be used to endorse or promote products derived from this software
*    without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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.
*
*      @(#)tty_conf.c  8.5 (Berkeley) 1/9/95
*/

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: tty_conf.c,v 1.57 2021/08/09 20:49:10 andvar Exp $");

#define TTY_ALLOW_PRIVATE

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/poll.h>
#include <sys/proc.h>
#include <sys/tty.h>
#include <sys/ttycom.h>
#include <sys/conf.h>
#include <sys/mutex.h>
#include <sys/queue.h>

static struct linesw termios_disc = {
       .l_name = "termios",
       .l_open = ttylopen,
       .l_close = ttylclose,
       .l_read = ttread,
       .l_write = ttwrite,
       .l_ioctl = ttynullioctl,
       .l_rint = ttyinput,
       .l_start = ttstart,
       .l_modem = ttymodem,
       .l_poll = ttpoll
};

/*
* This is for the benefit of old BSD TTY compatibility, but since it is
* identical to termios (except for the name), don't bother conditionalizing
* it.
*/
static struct linesw ntty_disc = {      /* old NTTYDISC */
       .l_name = "ntty",
       .l_open = ttylopen,
       .l_close = ttylclose,
       .l_read = ttread,
       .l_write = ttwrite,
       .l_ioctl = ttynullioctl,
       .l_rint = ttyinput,
       .l_start = ttstart,
       .l_modem = ttymodem,
       .l_poll = ttpoll
};

static LIST_HEAD(, linesw) ttyldisc_list = LIST_HEAD_INITIALIZER(ttyldisc_head);

/*
* Note: We don't bother refcounting termios_disc and ntty_disc; they can't
* be removed from the list, and termios_disc is likely to have very many
* references (could we overflow the count?).
*/
#define TTYLDISC_ISSTATIC(disc)                                 \
       ((disc) == &termios_disc || (disc) == &ntty_disc)

#define TTYLDISC_HOLD(disc)                                     \
do {                                                            \
       if (! TTYLDISC_ISSTATIC(disc)) {                        \
               KASSERT((disc)->l_refcnt != UINT_MAX);          \
               (disc)->l_refcnt++;                             \
       }                                                       \
} while (/*CONSTCOND*/0)

#define TTYLDISC_RELE(disc)                                     \
do {                                                            \
       if (! TTYLDISC_ISSTATIC(disc)) {                        \
               KASSERT((disc)->l_refcnt != 0);                 \
               (disc)->l_refcnt--;                             \
       }                                                       \
} while (/*CONSTCOND*/0)

#define TTYLDISC_ISINUSE(disc)                                  \
       (TTYLDISC_ISSTATIC(disc) || (disc)->l_refcnt != 0)

/*
* Do nothing specific version of line
* discipline specific ioctl command.
*/
/*ARGSUSED*/
int
ttynullioctl(struct tty *tp, u_long cmd, void *data, int flags, struct lwp *l)
{

       return (EPASSTHROUGH);
}

/*
* Return error to line discipline
* specific poll call.
*/
/*ARGSUSED*/
int
ttyerrpoll(struct tty *tp, int events, struct lwp *l)
{

       return (POLLERR);
}

void
ttyldisc_init(void)
{

       if (ttyldisc_attach(&termios_disc) != 0)
               panic("ttyldisc_init: termios_disc");
       if (ttyldisc_attach(&ntty_disc) != 0)
               panic("ttyldisc_init: ntty_disc");
}

static struct linesw *
ttyldisc_lookup_locked(const char *name)
{
       struct linesw *disc;

       LIST_FOREACH(disc, &ttyldisc_list, l_list) {
               if (strcmp(name, disc->l_name) == 0)
                       return (disc);
       }

       return (NULL);
}

/*
* Look up a line discipline by its name.  Caller holds a reference on
* the returned line discipline.
*/
struct linesw *
ttyldisc_lookup(const char *name)
{
       struct linesw *disc;

       mutex_spin_enter(&tty_lock);
       disc = ttyldisc_lookup_locked(name);
       if (disc != NULL)
               TTYLDISC_HOLD(disc);
       mutex_spin_exit(&tty_lock);

       return (disc);
}

/*
* Look up a line discipline by its legacy number.  Caller holds a
* reference on the returned line discipline.
*/
struct linesw *
ttyldisc_lookup_bynum(int num)
{
       struct linesw *disc;

       mutex_spin_enter(&tty_lock);

       LIST_FOREACH(disc, &ttyldisc_list, l_list) {
               if (disc->l_no == num) {
                       TTYLDISC_HOLD(disc);
                       mutex_spin_exit(&tty_lock);
                       return (disc);
               }
       }

       mutex_spin_exit(&tty_lock);
       return (NULL);
}

/*
* Release a reference on a line discipline previously added by
* ttyldisc_lookup() or ttyldisc_lookup_bynum().
*/
void
ttyldisc_release(struct linesw *disc)
{

       if (disc == NULL)
               return;

       mutex_spin_enter(&tty_lock);
       TTYLDISC_RELE(disc);
       mutex_spin_exit(&tty_lock);
}

#define TTYLDISC_LEGACY_NUMBER_MIN      10
#define TTYLDISC_LEGACY_NUMBER_MAX      INT_MAX

static void
ttyldisc_assign_legacy_number(struct linesw *disc)
{
       static const struct {
               const char *name;
               int num;
       } table[] = {
               { "termios",            TTYDISC },
               { "ntty",               2 /* XXX old NTTYDISC */ },
               { "tablet",             TABLDISC },
               { "slip",               SLIPDISC },
               { "ppp",                PPPDISC },
               { "strip",              STRIPDISC },
               { "hdlc",               HDLCDISC },
               { NULL,                 0 }
       };
       struct linesw *ldisc;
       int i;

       for (i = 0; table[i].name != NULL; i++) {
               if (strcmp(disc->l_name, table[i].name) == 0) {
                       disc->l_no = table[i].num;
                       return;
               }
       }

       disc->l_no = TTYLDISC_LEGACY_NUMBER_MIN;

       LIST_FOREACH(ldisc, &ttyldisc_list, l_list) {
               if (disc->l_no == ldisc->l_no) {
                       KASSERT(disc->l_no < TTYLDISC_LEGACY_NUMBER_MAX);
                       disc->l_no++;
               }
       }
}

/*
* Register a line discipline.
*/
int
ttyldisc_attach(struct linesw *disc)
{

       KASSERT(disc->l_name != NULL);
       KASSERT(disc->l_open != NULL);
       KASSERT(disc->l_close != NULL);
       KASSERT(disc->l_read != NULL);
       KASSERT(disc->l_write != NULL);
       KASSERT(disc->l_ioctl != NULL);
       KASSERT(disc->l_rint != NULL);
       KASSERT(disc->l_start != NULL);
       KASSERT(disc->l_modem != NULL);
       KASSERT(disc->l_poll != NULL);

       /* You are not allowed to exceed TTLINEDNAMELEN */
       if (strlen(disc->l_name) >= TTLINEDNAMELEN)
               return (ENAMETOOLONG);

       mutex_spin_enter(&tty_lock);

       if (ttyldisc_lookup_locked(disc->l_name) != NULL) {
               mutex_spin_exit(&tty_lock);
               return (EEXIST);
       }

       ttyldisc_assign_legacy_number(disc);
       LIST_INSERT_HEAD(&ttyldisc_list, disc, l_list);

       mutex_spin_exit(&tty_lock);

       return (0);
}

/*
* Remove a line discipline.
*/
int
ttyldisc_detach(struct linesw *disc)
{
#ifdef DIAGNOSTIC
       struct linesw *ldisc = ttyldisc_lookup(disc->l_name);

       KASSERT(ldisc != NULL);
       KASSERT(ldisc == disc);
       ttyldisc_release(ldisc);
#endif

       mutex_spin_enter(&tty_lock);

       if (TTYLDISC_ISINUSE(disc)) {
               mutex_spin_exit(&tty_lock);
               return (EBUSY);
       }

       LIST_REMOVE(disc, l_list);

       mutex_spin_exit(&tty_lock);

       return (0);
}

/*
* Return the default line discipline.
*/
struct linesw *
ttyldisc_default(void)
{

       return (&termios_disc);
}

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