Merge tag 'block-5.11-2021-01-10' of git://git.kernel.dk/linux-block

[linux/fpc-iii.git] / drivers / tty / tty_ioctl.c

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

#undef TTY_DEBUG_WAIT_UNTIL_SENT

#ifdef TTY_DEBUG_WAIT_UNTIL_SENT
# define tty_debug_wait_until_sent(tty, f, args...)    tty_debug(tty, f, ##args)
#else
# define tty_debug_wait_until_sent(tty, f, args...)    do {} while (0)
#endif

#undef  DEBUG

/*
 * Internal flag options for termios setting behavior
 */
#define TERMIOS_FLUSH   1
#define TERMIOS_WAIT    2
#define TERMIOS_TERMIO  4
#define TERMIOS_OLD     8


/**
 *      tty_chars_in_buffer     -       characters pending
 *      @tty: terminal
 *
 *      Return 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.
 */

int tty_chars_in_buffer(struct tty_struct *tty)
{
        if (tty->ops->chars_in_buffer)
                return tty->ops->chars_in_buffer(tty);
        else
                return 0;
}
EXPORT_SYMBOL(tty_chars_in_buffer);

/**
 *      tty_write_room          -       write queue space
 *      @tty: terminal
 *
 *      Return 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.
 */
 
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_throttle            -       flow control
 *      @tty: terminal
 *
 *      Indicate that a tty should stop transmitting data down the stack.
 *      Takes the 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.
 */

void tty_throttle(struct tty_struct *tty)
{
        down_write(&tty->termios_rwsem);
        /* check TTY_THROTTLED first so it indicates our state */
        if (!test_and_set_bit(TTY_THROTTLED, &tty->flags) &&
            tty->ops->throttle)
                tty->ops->throttle(tty);
        tty->flow_change = 0;
        up_write(&tty->termios_rwsem);
}
EXPORT_SYMBOL(tty_throttle);

/**
 *      tty_unthrottle          -       flow control
 *      @tty: terminal
 *
 *      Indicate that a tty may continue transmitting data down the stack.
 *      Takes the 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 = 0;
        up_write(&tty->termios_rwsem);
}
EXPORT_SYMBOL(tty_unthrottle);

/**
 *      tty_throttle_safe       -       flow control
 *      @tty: terminal
 *
 *      Similar to tty_throttle() but 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 0 if tty is throttled (or was already throttled)
 */

int tty_throttle_safe(struct tty_struct *tty)
{
        int ret = 0;

        mutex_lock(&tty->throttle_mutex);
        if (!tty_throttled(tty)) {
                if (tty->flow_change != TTY_THROTTLE_SAFE)
                        ret = 1;
                else {
                        set_bit(TTY_THROTTLED, &tty->flags);
                        if (tty->ops->throttle)
                                tty->ops->throttle(tty);
                }
        }
        mutex_unlock(&tty->throttle_mutex);

        return ret;
}

/**
 *      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 0 if tty is unthrottled (or was already unthrottled)
 */

int tty_unthrottle_safe(struct tty_struct *tty)
{
        int ret = 0;

        mutex_lock(&tty->throttle_mutex);
        if (tty_throttled(tty)) {
                if (tty->flow_change != TTY_UNTHROTTLE_SAFE)
                        ret = 1;
                else {
                        clear_bit(TTY_THROTTLED, &tty->flags);
                        if (tty->ops->unthrottle)
                                tty->ops->unthrottle(tty);
                }
        }
        mutex_unlock(&tty->throttle_mutex);

        return ret;
}

/**
 *      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)
{
        tty_debug_wait_until_sent(tty, "wait until sent, timeout=%ld\n", 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, 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, 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.
 */

int 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 1;
        if ((a->c_cflag ^ b->c_cflag) & ~(HUPCL | CREAD | CLOCAL))
                return 1;
        return 0;
}
EXPORT_SYMBOL(tty_termios_hw_change);

/**
 *      tty_set_termios         -       update termios values
 *      @tty: tty to update
 *      @new_termios: desired new value
 *
 *      Perform updates to the termios values set on this terminal.
 *      A master pty's termios should never be set.
 *
 *      Locking: 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);

        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);

/**
 *      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 ldisc and termios_rwsem locks
 */

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);

        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_wait_until_sent(tty, 0);
                if (signal_pending(current))
                        return -ERESTARTSYS;
        }

        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: termios_rwsem
 */

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 */
#ifdef BOTHER
        tty_termios_encode_baud_rate(&termios, termios.c_ispeed,
                                                termios.c_ospeed);
#endif
        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
 *      @arg: enable/disable CLOCAL
 *
 *      Perform a change to the CLOCAL state and call into the driver
 *      layer to make it visible. All done with the termios rwsem
 */

static int tty_change_softcar(struct tty_struct *tty, int arg)
{
        int ret = 0;
        int bit = arg ? CLOCAL : 0;
        struct ktermios old;

        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
 *      @file: file pointer for the tty
 *      @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, struct file *file,
                        unsigned int cmd, unsigned long arg)
{
        struct tty_struct *real_tty;
        void __user *p = (void __user *)arg;
        int ret = 0;
        struct ktermios kterm;

        BUG_ON(file == NULL);

        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 (!capable(CAP_SYS_ADMIN))
                        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 (!capable(CAP_SYS_ADMIN))
                        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 -EINVAL;
#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, struct file *file,
                       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_stopped) {
                                tty->flow_stopped = 1;
                                __stop_tty(tty);
                        }
                        spin_unlock_irq(&tty->flow_lock);
                        break;
                case TCOON:
                        spin_lock_irq(&tty->flow_lock);
                        if (tty->flow_stopped) {
                                tty->flow_stopped = 0;
                                __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, file, cmd, arg);
        }
}
EXPORT_SYMBOL(n_tty_ioctl_helper);