// SPDX-License-Identifier: GPL-2.0
/*
 *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
 *
 * Modified by Fred N. van Kempen, 01/29/93, to add line disciplines
 * which can be dynamically activated and de-activated by the line
 * discipline handling modules (like SLIP).
 */

#include <linux/bits.h>
#include <linux/types.h>
#include <linux/termios.h>
#include <linux/errno.h>
#include <linux/sched/signal.h>
#include <linux/kernel.h>
#include <linux/major.h>
#include <linux/tty.h>
#include <linux/fcntl.h>
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/bitops.h>
#include <linux/mutex.h>
#include <linux/compat.h>
#include <linux/termios_internal.h>
#include "tty.h"

#include <asm/io.h>
#include <linux/uaccess.h>

#undef  DEBUG

/*
 * Internal flag options for termios setting behavior
 */
#define TERMIOS_FLUSH   BIT(0)
#define TERMIOS_WAIT    BIT(1)
#define TERMIOS_TERMIO  BIT(2)
#define TERMIOS_OLD     BIT(3)

/**
 * tty_chars_in_buffer - characters pending
 * @tty: terminal
 *
 * Returns: the number of bytes of data in the device private output queue. If
 * no private method is supplied there is assumed to be no queue on the device.
 */
unsigned int tty_chars_in_buffer(struct tty_struct *tty)
{
        if (tty->ops->chars_in_buffer)
                return tty->ops->chars_in_buffer(tty);
        return 0;
}
EXPORT_SYMBOL(tty_chars_in_buffer);

/**
 * tty_write_room - write queue space
 * @tty: terminal
 *
 * Returns: the number of bytes that can be queued to this device at the present
 * time. The result should be treated as a guarantee and the driver cannot
 * offer a value it later shrinks by more than the number of bytes written. If
 * no method is provided, 2K is always returned and data may be lost as there
 * will be no flow control.
 */
unsigned int tty_write_room(struct tty_struct *tty)
{
        if (tty->ops->write_room)
                return tty->ops->write_room(tty);
        return 2048;
}
EXPORT_SYMBOL(tty_write_room);

/**
 * tty_driver_flush_buffer - discard internal buffer
 * @tty: terminal
 *
 * Discard the internal output buffer for this device. If no method is provided,
 * then either the buffer cannot be hardware flushed or there is no buffer
 * driver side.
 */
void tty_driver_flush_buffer(struct tty_struct *tty)
{
        if (tty->ops->flush_buffer)
                tty->ops->flush_buffer(tty);
}
EXPORT_SYMBOL(tty_driver_flush_buffer);

/**
 * tty_unthrottle - flow control
 * @tty: terminal
 *
 * Indicate that a @tty may continue transmitting data down the stack. Takes
 * the &tty_struct->termios_rwsem to protect against parallel
 * throttle/unthrottle and also to ensure the driver can consistently reference
 * its own termios data at this point when implementing software flow control.
 *
 * Drivers should however remember that the stack can issue a throttle, then
 * change flow control method, then unthrottle.
 */
void tty_unthrottle(struct tty_struct *tty)
{
        down_write(&tty->termios_rwsem);
        if (test_and_clear_bit(TTY_THROTTLED, &tty->flags) &&
            tty->ops->unthrottle)
                tty->ops->unthrottle(tty);
        tty->flow_change = TTY_FLOW_NO_CHANGE;
        up_write(&tty->termios_rwsem);
}
EXPORT_SYMBOL(tty_unthrottle);

/**
 * tty_throttle_safe - flow control
 * @tty: terminal
 *
 * Indicate that a @tty should stop transmitting data down the stack.
 * tty_throttle_safe() will only attempt throttle if @tty->flow_change is
 * %TTY_THROTTLE_SAFE. Prevents an accidental throttle due to race conditions
 * when throttling is conditional on factors evaluated prior to throttling.
 *
 * Returns: %true if @tty is throttled (or was already throttled)
 */
bool tty_throttle_safe(struct tty_struct *tty)
{
        guard(mutex)(&tty->throttle_mutex);

        if (tty_throttled(tty))
                return true;

        if (tty->flow_change != TTY_THROTTLE_SAFE)
                return false;

        set_bit(TTY_THROTTLED, &tty->flags);
        if (tty->ops->throttle)
                tty->ops->throttle(tty);

        return true;
}

/**
 * tty_unthrottle_safe - flow control
 * @tty: terminal
 *
 * Similar to tty_unthrottle() but will only attempt unthrottle if
 * @tty->flow_change is %TTY_UNTHROTTLE_SAFE. Prevents an accidental unthrottle
 * due to race conditions when unthrottling is conditional on factors evaluated
 * prior to unthrottling.
 *
 * Returns: %true if @tty is unthrottled (or was already unthrottled)
 */
bool tty_unthrottle_safe(struct tty_struct *tty)
{
        guard(mutex)(&tty->throttle_mutex);

        if (!tty_throttled(tty))
                return true;

        if (tty->flow_change != TTY_UNTHROTTLE_SAFE)
                return false;

        clear_bit(TTY_THROTTLED, &tty->flags);
        if (tty->ops->unthrottle)
                tty->ops->unthrottle(tty);

        return true;
}

/**
 * tty_wait_until_sent - wait for I/O to finish
 * @tty: tty we are waiting for
 * @timeout: how long we will wait
 *
 * Wait for characters pending in a tty driver to hit the wire, or for a
 * timeout to occur (eg due to flow control).
 *
 * Locking: none
 */

void tty_wait_until_sent(struct tty_struct *tty, long timeout)
{
        if (!timeout)
                timeout = MAX_SCHEDULE_TIMEOUT;

        timeout = wait_event_interruptible_timeout(tty->write_wait,
                        !tty_chars_in_buffer(tty), timeout);
        if (timeout <= 0)
                return;

        if (timeout == MAX_SCHEDULE_TIMEOUT)
                timeout = 0;

        if (tty->ops->wait_until_sent)
                tty->ops->wait_until_sent(tty, timeout);
}
EXPORT_SYMBOL(tty_wait_until_sent);


/*
 *              Termios Helper Methods
 */

static void unset_locked_termios(struct tty_struct *tty, const struct ktermios *old)
{
        struct ktermios *termios = &tty->termios;
        struct ktermios *locked  = &tty->termios_locked;
        int     i;

#define NOSET_MASK(x, y, z) (x = ((x) & ~(z)) | ((y) & (z)))

        NOSET_MASK(termios->c_iflag, old->c_iflag, locked->c_iflag);
        NOSET_MASK(termios->c_oflag, old->c_oflag, locked->c_oflag);
        NOSET_MASK(termios->c_cflag, old->c_cflag, locked->c_cflag);
        NOSET_MASK(termios->c_lflag, old->c_lflag, locked->c_lflag);
        termios->c_line = locked->c_line ? old->c_line : termios->c_line;
        for (i = 0; i < NCCS; i++)
                termios->c_cc[i] = locked->c_cc[i] ?
                        old->c_cc[i] : termios->c_cc[i];
        /* FIXME: What should we do for i/ospeed */
}

/**
 * tty_termios_copy_hw - copy hardware settings
 * @new: new termios
 * @old: old termios
 *
 * Propagate the hardware specific terminal setting bits from the @old termios
 * structure to the @new one. This is used in cases where the hardware does not
 * support reconfiguration or as a helper in some cases where only minimal
 * reconfiguration is supported.
 */
void tty_termios_copy_hw(struct ktermios *new, const struct ktermios *old)
{
        /* The bits a dumb device handles in software. Smart devices need
           to always provide a set_termios method */
        new->c_cflag &= HUPCL | CREAD | CLOCAL;
        new->c_cflag |= old->c_cflag & ~(HUPCL | CREAD | CLOCAL);
        new->c_ispeed = old->c_ispeed;
        new->c_ospeed = old->c_ospeed;
}
EXPORT_SYMBOL(tty_termios_copy_hw);

/**
 * tty_termios_hw_change - check for setting change
 * @a: termios
 * @b: termios to compare
 *
 * Check if any of the bits that affect a dumb device have changed between the
 * two termios structures, or a speed change is needed.
 *
 * Returns: %true if change is needed
 */
bool tty_termios_hw_change(const struct ktermios *a, const struct ktermios *b)
{
        if (a->c_ispeed != b->c_ispeed || a->c_ospeed != b->c_ospeed)
                return true;
        if ((a->c_cflag ^ b->c_cflag) & ~(HUPCL | CREAD | CLOCAL))
                return true;
        return false;
}
EXPORT_SYMBOL(tty_termios_hw_change);

/**
 * tty_get_char_size - get size of a character
 * @cflag: termios cflag value
 *
 * Returns: size (in bits) of a character depending on @cflag's %CSIZE setting
 */
unsigned char tty_get_char_size(unsigned int cflag)
{
        switch (cflag & CSIZE) {
        case CS5:
                return 5;
        case CS6:
                return 6;
        case CS7:
                return 7;
        case CS8:
        default:
                return 8;
        }
}
EXPORT_SYMBOL_GPL(tty_get_char_size);

/**
 * tty_get_frame_size - get size of a frame
 * @cflag: termios cflag value
 *
 * Get the size (in bits) of a frame depending on @cflag's %CSIZE, %CSTOPB, and
 * %PARENB setting. The result is a sum of character size, start and stop bits
 * -- one bit each -- second stop bit (if set), and parity bit (if set).
 *
 * Returns: size (in bits) of a frame depending on @cflag's setting.
 */
unsigned char tty_get_frame_size(unsigned int cflag)
{
        unsigned char bits = 2 + tty_get_char_size(cflag);

        if (cflag & CSTOPB)
                bits++;
        if (cflag & PARENB)
                bits++;
        if (cflag & ADDRB)
                bits++;

        return bits;
}
EXPORT_SYMBOL_GPL(tty_get_frame_size);

/**
 * tty_set_termios - update termios values
 * @tty: tty to update
 * @new_termios: desired new value
 *
 * Perform updates to the termios values set on this @tty. A master pty's
 * termios should never be set.
 *
 * Locking: &tty_struct->termios_rwsem
 */
int tty_set_termios(struct tty_struct *tty, struct ktermios *new_termios)
{
        struct ktermios old_termios;
        struct tty_ldisc *ld;

        WARN_ON(tty->driver->type == TTY_DRIVER_TYPE_PTY &&
                tty->driver->subtype == PTY_TYPE_MASTER);
        /*
         *      Perform the actual termios internal changes under lock.
         */


        /* FIXME: we need to decide on some locking/ordering semantics
           for the set_termios notification eventually */
        down_write(&tty->termios_rwsem);
        old_termios = tty->termios;
        tty->termios = *new_termios;
        unset_locked_termios(tty, &old_termios);
        /* Reset any ADDRB changes, ADDRB is changed through ->rs485_config() */
        tty->termios.c_cflag ^= (tty->termios.c_cflag ^ old_termios.c_cflag) & ADDRB;

        if (tty->ops->set_termios)
                tty->ops->set_termios(tty, &old_termios);
        else
                tty_termios_copy_hw(&tty->termios, &old_termios);

        ld = tty_ldisc_ref(tty);
        if (ld != NULL) {
                if (ld->ops->set_termios)
                        ld->ops->set_termios(tty, &old_termios);
                tty_ldisc_deref(ld);
        }
        up_write(&tty->termios_rwsem);
        return 0;
}
EXPORT_SYMBOL_GPL(tty_set_termios);


/*
 * Translate a "termio" structure into a "termios". Ugh.
 */
__weak int user_termio_to_kernel_termios(struct ktermios *termios,
                                                struct termio __user *termio)
{
        struct termio v;

        if (copy_from_user(&v, termio, sizeof(struct termio)))
                return -EFAULT;

        termios->c_iflag = (0xffff0000 & termios->c_iflag) | v.c_iflag;
        termios->c_oflag = (0xffff0000 & termios->c_oflag) | v.c_oflag;
        termios->c_cflag = (0xffff0000 & termios->c_cflag) | v.c_cflag;
        termios->c_lflag = (0xffff0000 & termios->c_lflag) | v.c_lflag;
        termios->c_line = (0xffff0000 & termios->c_lflag) | v.c_line;
        memcpy(termios->c_cc, v.c_cc, NCC);
        return 0;
}

/*
 * Translate a "termios" structure into a "termio". Ugh.
 */
__weak int kernel_termios_to_user_termio(struct termio __user *termio,
                                                struct ktermios *termios)
{
        struct termio v;
        memset(&v, 0, sizeof(struct termio));
        v.c_iflag = termios->c_iflag;
        v.c_oflag = termios->c_oflag;
        v.c_cflag = termios->c_cflag;
        v.c_lflag = termios->c_lflag;
        v.c_line = termios->c_line;
        memcpy(v.c_cc, termios->c_cc, NCC);
        return copy_to_user(termio, &v, sizeof(struct termio));
}

#ifdef TCGETS2
__weak int user_termios_to_kernel_termios(struct ktermios *k,
                                                 struct termios2 __user *u)
{
        return copy_from_user(k, u, sizeof(struct termios2));
}
__weak int kernel_termios_to_user_termios(struct termios2 __user *u,
                                                 struct ktermios *k)
{
        return copy_to_user(u, k, sizeof(struct termios2));
}
__weak int user_termios_to_kernel_termios_1(struct ktermios *k,
                                                   struct termios __user *u)
{
        return copy_from_user(k, u, sizeof(struct termios));
}
__weak int kernel_termios_to_user_termios_1(struct termios __user *u,
                                                   struct ktermios *k)
{
        return copy_to_user(u, k, sizeof(struct termios));
}

#else

__weak int user_termios_to_kernel_termios(struct ktermios *k,
                                                 struct termios __user *u)
{
        return copy_from_user(k, u, sizeof(struct termios));
}
__weak int kernel_termios_to_user_termios(struct termios __user *u,
                                                 struct ktermios *k)
{
        return copy_to_user(u, k, sizeof(struct termios));
}
#endif /* TCGETS2 */

/**
 * set_termios - set termios values for a tty
 * @tty: terminal device
 * @arg: user data
 * @opt: option information
 *
 * Helper function to prepare termios data and run necessary other functions
 * before using tty_set_termios() to do the actual changes.
 *
 * Locking: called functions take &tty_struct->ldisc_sem and
 * &tty_struct->termios_rwsem locks
 *
 * Returns: 0 on success, an error otherwise
 */
static int set_termios(struct tty_struct *tty, void __user *arg, int opt)
{
        struct ktermios tmp_termios;
        struct tty_ldisc *ld;
        int retval = tty_check_change(tty);

        if (retval)
                return retval;

        down_read(&tty->termios_rwsem);
        tmp_termios = tty->termios;
        up_read(&tty->termios_rwsem);

        if (opt & TERMIOS_TERMIO) {
                if (user_termio_to_kernel_termios(&tmp_termios,
                                                (struct termio __user *)arg))
                        return -EFAULT;
#ifdef TCGETS2
        } else if (opt & TERMIOS_OLD) {
                if (user_termios_to_kernel_termios_1(&tmp_termios,
                                                (struct termios __user *)arg))
                        return -EFAULT;
        } else {
                if (user_termios_to_kernel_termios(&tmp_termios,
                                                (struct termios2 __user *)arg))
                        return -EFAULT;
        }
#else
        } else if (user_termios_to_kernel_termios(&tmp_termios,
                                        (struct termios __user *)arg))
                return -EFAULT;
#endif

        /* If old style Bfoo values are used then load c_ispeed/c_ospeed
         * with the real speed so its unconditionally usable */
        tmp_termios.c_ispeed = tty_termios_input_baud_rate(&tmp_termios);
        tmp_termios.c_ospeed = tty_termios_baud_rate(&tmp_termios);

        if (opt & (TERMIOS_FLUSH|TERMIOS_WAIT)) {
retry_write_wait:
                retval = wait_event_interruptible(tty->write_wait, !tty_chars_in_buffer(tty));
                if (retval < 0)
                        return retval;

                if (tty_write_lock(tty, false) < 0)
                        goto retry_write_wait;

                /* Racing writer? */
                if (tty_chars_in_buffer(tty)) {
                        tty_write_unlock(tty);
                        goto retry_write_wait;
                }

                ld = tty_ldisc_ref(tty);
                if (ld != NULL) {
                        if ((opt & TERMIOS_FLUSH) && ld->ops->flush_buffer)
                                ld->ops->flush_buffer(tty);
                        tty_ldisc_deref(ld);
                }

                if ((opt & TERMIOS_WAIT) && tty->ops->wait_until_sent) {
                        tty->ops->wait_until_sent(tty, 0);
                        if (signal_pending(current)) {
                                tty_write_unlock(tty);
                                return -ERESTARTSYS;
                        }
                }

                tty_set_termios(tty, &tmp_termios);

                tty_write_unlock(tty);
        } else {
                tty_set_termios(tty, &tmp_termios);
        }

        /* FIXME: Arguably if tmp_termios == tty->termios AND the
           actual requested termios was not tmp_termios then we may
           want to return an error as no user requested change has
           succeeded */
        return 0;
}

static void copy_termios(struct tty_struct *tty, struct ktermios *kterm)
{
        down_read(&tty->termios_rwsem);
        *kterm = tty->termios;
        up_read(&tty->termios_rwsem);
}

static void copy_termios_locked(struct tty_struct *tty, struct ktermios *kterm)
{
        down_read(&tty->termios_rwsem);
        *kterm = tty->termios_locked;
        up_read(&tty->termios_rwsem);
}

static int get_termio(struct tty_struct *tty, struct termio __user *termio)
{
        struct ktermios kterm;
        copy_termios(tty, &kterm);
        if (kernel_termios_to_user_termio(termio, &kterm))
                return -EFAULT;
        return 0;
}

#ifdef TIOCGETP
/*
 * These are deprecated, but there is limited support..
 *
 * The "sg_flags" translation is a joke..
 */
static int get_sgflags(struct tty_struct *tty)
{
        int flags = 0;

        if (!L_ICANON(tty)) {
                if (L_ISIG(tty))
                        flags |= 0x02;          /* cbreak */
                else
                        flags |= 0x20;          /* raw */
        }
        if (L_ECHO(tty))
                flags |= 0x08;                  /* echo */
        if (O_OPOST(tty))
                if (O_ONLCR(tty))
                        flags |= 0x10;          /* crmod */
        return flags;
}

static int get_sgttyb(struct tty_struct *tty, struct sgttyb __user *sgttyb)
{
        struct sgttyb tmp;

        down_read(&tty->termios_rwsem);
        tmp.sg_ispeed = tty->termios.c_ispeed;
        tmp.sg_ospeed = tty->termios.c_ospeed;
        tmp.sg_erase = tty->termios.c_cc[VERASE];
        tmp.sg_kill = tty->termios.c_cc[VKILL];
        tmp.sg_flags = get_sgflags(tty);
        up_read(&tty->termios_rwsem);

        return copy_to_user(sgttyb, &tmp, sizeof(tmp)) ? -EFAULT : 0;
}

static void set_sgflags(struct ktermios *termios, int flags)
{
        termios->c_iflag = ICRNL | IXON;
        termios->c_oflag = 0;
        termios->c_lflag = ISIG | ICANON;
        if (flags & 0x02) {     /* cbreak */
                termios->c_iflag = 0;
                termios->c_lflag &= ~ICANON;
        }
        if (flags & 0x08) {             /* echo */
                termios->c_lflag |= ECHO | ECHOE | ECHOK |
                                    ECHOCTL | ECHOKE | IEXTEN;
        }
        if (flags & 0x10) {             /* crmod */
                termios->c_oflag |= OPOST | ONLCR;
        }
        if (flags & 0x20) {     /* raw */
                termios->c_iflag = 0;
                termios->c_lflag &= ~(ISIG | ICANON);
        }
        if (!(termios->c_lflag & ICANON)) {
                termios->c_cc[VMIN] = 1;
                termios->c_cc[VTIME] = 0;
        }
}

/**
 * set_sgttyb - set legacy terminal values
 * @tty: tty structure
 * @sgttyb: pointer to old style terminal structure
 *
 * Updates a terminal from the legacy BSD style terminal information structure.
 *
 * Locking: &tty_struct->termios_rwsem
 *
 * Returns: 0 on success, an error otherwise
 */
static int set_sgttyb(struct tty_struct *tty, struct sgttyb __user *sgttyb)
{
        int retval;
        struct sgttyb tmp;
        struct ktermios termios;

        retval = tty_check_change(tty);
        if (retval)
                return retval;

        if (copy_from_user(&tmp, sgttyb, sizeof(tmp)))
                return -EFAULT;

        down_write(&tty->termios_rwsem);
        termios = tty->termios;
        termios.c_cc[VERASE] = tmp.sg_erase;
        termios.c_cc[VKILL] = tmp.sg_kill;
        set_sgflags(&termios, tmp.sg_flags);
        /* Try and encode into Bfoo format */
        tty_termios_encode_baud_rate(&termios, termios.c_ispeed,
                                                termios.c_ospeed);
        up_write(&tty->termios_rwsem);
        tty_set_termios(tty, &termios);
        return 0;
}
#endif

#ifdef TIOCGETC
static int get_tchars(struct tty_struct *tty, struct tchars __user *tchars)
{
        struct tchars tmp;

        down_read(&tty->termios_rwsem);
        tmp.t_intrc = tty->termios.c_cc[VINTR];
        tmp.t_quitc = tty->termios.c_cc[VQUIT];
        tmp.t_startc = tty->termios.c_cc[VSTART];
        tmp.t_stopc = tty->termios.c_cc[VSTOP];
        tmp.t_eofc = tty->termios.c_cc[VEOF];
        tmp.t_brkc = tty->termios.c_cc[VEOL2];  /* what is brkc anyway? */
        up_read(&tty->termios_rwsem);
        return copy_to_user(tchars, &tmp, sizeof(tmp)) ? -EFAULT : 0;
}

static int set_tchars(struct tty_struct *tty, struct tchars __user *tchars)
{
        struct tchars tmp;

        if (copy_from_user(&tmp, tchars, sizeof(tmp)))
                return -EFAULT;
        down_write(&tty->termios_rwsem);
        tty->termios.c_cc[VINTR] = tmp.t_intrc;
        tty->termios.c_cc[VQUIT] = tmp.t_quitc;
        tty->termios.c_cc[VSTART] = tmp.t_startc;
        tty->termios.c_cc[VSTOP] = tmp.t_stopc;
        tty->termios.c_cc[VEOF] = tmp.t_eofc;
        tty->termios.c_cc[VEOL2] = tmp.t_brkc;  /* what is brkc anyway? */
        up_write(&tty->termios_rwsem);
        return 0;
}
#endif

#ifdef TIOCGLTC
static int get_ltchars(struct tty_struct *tty, struct ltchars __user *ltchars)
{
        struct ltchars tmp;

        down_read(&tty->termios_rwsem);
        tmp.t_suspc = tty->termios.c_cc[VSUSP];
        /* what is dsuspc anyway? */
        tmp.t_dsuspc = tty->termios.c_cc[VSUSP];
        tmp.t_rprntc = tty->termios.c_cc[VREPRINT];
        /* what is flushc anyway? */
        tmp.t_flushc = tty->termios.c_cc[VEOL2];
        tmp.t_werasc = tty->termios.c_cc[VWERASE];
        tmp.t_lnextc = tty->termios.c_cc[VLNEXT];
        up_read(&tty->termios_rwsem);
        return copy_to_user(ltchars, &tmp, sizeof(tmp)) ? -EFAULT : 0;
}

static int set_ltchars(struct tty_struct *tty, struct ltchars __user *ltchars)
{
        struct ltchars tmp;

        if (copy_from_user(&tmp, ltchars, sizeof(tmp)))
                return -EFAULT;

        down_write(&tty->termios_rwsem);
        tty->termios.c_cc[VSUSP] = tmp.t_suspc;
        /* what is dsuspc anyway? */
        tty->termios.c_cc[VEOL2] = tmp.t_dsuspc;
        tty->termios.c_cc[VREPRINT] = tmp.t_rprntc;
        /* what is flushc anyway? */
        tty->termios.c_cc[VEOL2] = tmp.t_flushc;
        tty->termios.c_cc[VWERASE] = tmp.t_werasc;
        tty->termios.c_cc[VLNEXT] = tmp.t_lnextc;
        up_write(&tty->termios_rwsem);
        return 0;
}
#endif

/**
 * tty_change_softcar - carrier change ioctl helper
 * @tty: tty to update
 * @enable: enable/disable %CLOCAL
 *
 * Perform a change to the %CLOCAL state and call into the driver layer to make
 * it visible.
 *
 * Locking: &tty_struct->termios_rwsem.
 *
 * Returns: 0 on success, an error otherwise
 */
static int tty_change_softcar(struct tty_struct *tty, bool enable)
{
        int ret = 0;
        struct ktermios old;
        tcflag_t bit = enable ? CLOCAL : 0;

        down_write(&tty->termios_rwsem);
        old = tty->termios;
        tty->termios.c_cflag &= ~CLOCAL;
        tty->termios.c_cflag |= bit;
        if (tty->ops->set_termios)
                tty->ops->set_termios(tty, &old);
        if (C_CLOCAL(tty) != bit)
                ret = -EINVAL;
        up_write(&tty->termios_rwsem);
        return ret;
}

/**
 * tty_mode_ioctl - mode related ioctls
 * @tty: tty for the ioctl
 * @cmd: command
 * @arg: ioctl argument
 *
 * Perform non-line discipline specific mode control ioctls. This is designed
 * to be called by line disciplines to ensure they provide consistent mode
 * setting.
 */
int tty_mode_ioctl(struct tty_struct *tty, unsigned int cmd, unsigned long arg)
{
        struct tty_struct *real_tty;
        void __user *p = (void __user *)arg;
        int ret = 0;
        struct ktermios kterm;

        if (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
            tty->driver->subtype == PTY_TYPE_MASTER)
                real_tty = tty->link;
        else
                real_tty = tty;

        switch (cmd) {
#ifdef TIOCGETP
        case TIOCGETP:
                return get_sgttyb(real_tty, (struct sgttyb __user *) arg);
        case TIOCSETP:
        case TIOCSETN:
                return set_sgttyb(real_tty, (struct sgttyb __user *) arg);
#endif
#ifdef TIOCGETC
        case TIOCGETC:
                return get_tchars(real_tty, p);
        case TIOCSETC:
                return set_tchars(real_tty, p);
#endif
#ifdef TIOCGLTC
        case TIOCGLTC:
                return get_ltchars(real_tty, p);
        case TIOCSLTC:
                return set_ltchars(real_tty, p);
#endif
        case TCSETSF:
                return set_termios(real_tty, p,  TERMIOS_FLUSH | TERMIOS_WAIT | TERMIOS_OLD);
        case TCSETSW:
                return set_termios(real_tty, p, TERMIOS_WAIT | TERMIOS_OLD);
        case TCSETS:
                return set_termios(real_tty, p, TERMIOS_OLD);
#ifndef TCGETS2
        case TCGETS:
                copy_termios(real_tty, &kterm);
                if (kernel_termios_to_user_termios((struct termios __user *)arg, &kterm))
                        ret = -EFAULT;
                return ret;
#else
        case TCGETS:
                copy_termios(real_tty, &kterm);
                if (kernel_termios_to_user_termios_1((struct termios __user *)arg, &kterm))
                        ret = -EFAULT;
                return ret;
        case TCGETS2:
                copy_termios(real_tty, &kterm);
                if (kernel_termios_to_user_termios((struct termios2 __user *)arg, &kterm))
                        ret = -EFAULT;
                return ret;
        case TCSETSF2:
                return set_termios(real_tty, p,  TERMIOS_FLUSH | TERMIOS_WAIT);
        case TCSETSW2:
                return set_termios(real_tty, p, TERMIOS_WAIT);
        case TCSETS2:
                return set_termios(real_tty, p, 0);
#endif
        case TCGETA:
                return get_termio(real_tty, p);
        case TCSETAF:
                return set_termios(real_tty, p, TERMIOS_FLUSH | TERMIOS_WAIT | TERMIOS_TERMIO);
        case TCSETAW:
                return set_termios(real_tty, p, TERMIOS_WAIT | TERMIOS_TERMIO);
        case TCSETA:
                return set_termios(real_tty, p, TERMIOS_TERMIO);
#ifndef TCGETS2
        case TIOCGLCKTRMIOS:
                copy_termios_locked(real_tty, &kterm);
                if (kernel_termios_to_user_termios((struct termios __user *)arg, &kterm))
                        ret = -EFAULT;
                return ret;
        case TIOCSLCKTRMIOS:
                if (!checkpoint_restore_ns_capable(&init_user_ns))
                        return -EPERM;
                copy_termios_locked(real_tty, &kterm);
                if (user_termios_to_kernel_termios(&kterm,
                                               (struct termios __user *) arg))
                        return -EFAULT;
                down_write(&real_tty->termios_rwsem);
                real_tty->termios_locked = kterm;
                up_write(&real_tty->termios_rwsem);
                return 0;
#else
        case TIOCGLCKTRMIOS:
                copy_termios_locked(real_tty, &kterm);
                if (kernel_termios_to_user_termios_1((struct termios __user *)arg, &kterm))
                        ret = -EFAULT;
                return ret;
        case TIOCSLCKTRMIOS:
                if (!checkpoint_restore_ns_capable(&init_user_ns))
                        return -EPERM;
                copy_termios_locked(real_tty, &kterm);
                if (user_termios_to_kernel_termios_1(&kterm,
                                               (struct termios __user *) arg))
                        return -EFAULT;
                down_write(&real_tty->termios_rwsem);
                real_tty->termios_locked = kterm;
                up_write(&real_tty->termios_rwsem);
                return ret;
#endif
#ifdef TCGETX
        case TCGETX:
        case TCSETX:
        case TCSETXW:
        case TCSETXF:
                return -ENOTTY;
#endif
        case TIOCGSOFTCAR:
                copy_termios(real_tty, &kterm);
                ret = put_user((kterm.c_cflag & CLOCAL) ? 1 : 0,
                                                (int __user *)arg);
                return ret;
        case TIOCSSOFTCAR:
                if (get_user(arg, (unsigned int __user *) arg))
                        return -EFAULT;
                return tty_change_softcar(real_tty, arg);
        default:
                return -ENOIOCTLCMD;
        }
}
EXPORT_SYMBOL_GPL(tty_mode_ioctl);


/* Caller guarantees ldisc reference is held */
static int __tty_perform_flush(struct tty_struct *tty, unsigned long arg)
{
        struct tty_ldisc *ld = tty->ldisc;

        switch (arg) {
        case TCIFLUSH:
                if (ld && ld->ops->flush_buffer) {
                        ld->ops->flush_buffer(tty);
                        tty_unthrottle(tty);
                }
                break;
        case TCIOFLUSH:
                if (ld && ld->ops->flush_buffer) {
                        ld->ops->flush_buffer(tty);
                        tty_unthrottle(tty);
                }
                fallthrough;
        case TCOFLUSH:
                tty_driver_flush_buffer(tty);
                break;
        default:
                return -EINVAL;
        }
        return 0;
}

int tty_perform_flush(struct tty_struct *tty, unsigned long arg)
{
        struct tty_ldisc *ld;
        int retval = tty_check_change(tty);
        if (retval)
                return retval;

        ld = tty_ldisc_ref_wait(tty);
        retval = __tty_perform_flush(tty, arg);
        if (ld)
                tty_ldisc_deref(ld);
        return retval;
}
EXPORT_SYMBOL_GPL(tty_perform_flush);

int n_tty_ioctl_helper(struct tty_struct *tty, unsigned int cmd,
                unsigned long arg)
{
        int retval;

        switch (cmd) {
        case TCXONC:
                retval = tty_check_change(tty);
                if (retval)
                        return retval;
                switch (arg) {
                case TCOOFF:
                        spin_lock_irq(&tty->flow.lock);
                        if (!tty->flow.tco_stopped) {
                                tty->flow.tco_stopped = true;
                                __stop_tty(tty);
                        }
                        spin_unlock_irq(&tty->flow.lock);
                        break;
                case TCOON:
                        spin_lock_irq(&tty->flow.lock);
                        if (tty->flow.tco_stopped) {
                                tty->flow.tco_stopped = false;
                                __start_tty(tty);
                        }
                        spin_unlock_irq(&tty->flow.lock);
                        break;
                case TCIOFF:
                        if (STOP_CHAR(tty) != __DISABLED_CHAR)
                                retval = tty_send_xchar(tty, STOP_CHAR(tty));
                        break;
                case TCION:
                        if (START_CHAR(tty) != __DISABLED_CHAR)
                                retval = tty_send_xchar(tty, START_CHAR(tty));
                        break;
                default:
                        return -EINVAL;
                }
                return retval;
        case TCFLSH:
                retval = tty_check_change(tty);
                if (retval)
                        return retval;
                return __tty_perform_flush(tty, arg);
        default:
                /* Try the mode commands */
                return tty_mode_ioctl(tty, cmd, arg);
        }
}
EXPORT_SYMBOL(n_tty_ioctl_helper);