Merge branches 'sh/pm-runtime' and 'common/clkfwk' into sh-fixes-for-linus

[mirror_ubuntu-zesty-kernel.git] / drivers / tty / pty.c

/*
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  Added support for a Unix98-style ptmx device.
 *    -- C. Scott Ananian <cananian@alumni.princeton.edu>, 14-Jan-1998
 *
 *  When reading this code see also fs/devpts. In particular note that the
 *  driver_data field is used by the devpts side as a binding to the devpts
 *  inode.
 */

#include <linux/module.h>

#include <linux/errno.h>
#include <linux/interrupt.h>
#include <linux/tty.h>
#include <linux/tty_flip.h>
#include <linux/fcntl.h>
#include <linux/sched.h>
#include <linux/string.h>
#include <linux/major.h>
#include <linux/mm.h>
#include <linux/init.h>
#include <linux/sysctl.h>
#include <linux/device.h>
#include <linux/uaccess.h>
#include <linux/bitops.h>
#include <linux/devpts_fs.h>
#include <linux/slab.h>

#include <asm/system.h>

#ifdef CONFIG_UNIX98_PTYS
static struct tty_driver *ptm_driver;
static struct tty_driver *pts_driver;
#endif

static void pty_close(struct tty_struct *tty, struct file *filp)
{
        BUG_ON(!tty);
        if (tty->driver->subtype == PTY_TYPE_MASTER)
                WARN_ON(tty->count > 1);
        else {
                if (tty->count > 2)
                        return;
        }
        wake_up_interruptible(&tty->read_wait);
        wake_up_interruptible(&tty->write_wait);
        tty->packet = 0;
        if (!tty->link)
                return;
        tty->link->packet = 0;
        set_bit(TTY_OTHER_CLOSED, &tty->link->flags);
        wake_up_interruptible(&tty->link->read_wait);
        wake_up_interruptible(&tty->link->write_wait);
        if (tty->driver->subtype == PTY_TYPE_MASTER) {
                set_bit(TTY_OTHER_CLOSED, &tty->flags);
#ifdef CONFIG_UNIX98_PTYS
                if (tty->driver == ptm_driver)
                        devpts_pty_kill(tty->link);
#endif
                tty_unlock();
                tty_vhangup(tty->link);
                tty_lock();
        }
}

/*
 * The unthrottle routine is called by the line discipline to signal
 * that it can receive more characters.  For PTY's, the TTY_THROTTLED
 * flag is always set, to force the line discipline to always call the
 * unthrottle routine when there are fewer than TTY_THRESHOLD_UNTHROTTLE
 * characters in the queue.  This is necessary since each time this
 * happens, we need to wake up any sleeping processes that could be
 * (1) trying to send data to the pty, or (2) waiting in wait_until_sent()
 * for the pty buffer to be drained.
 */
static void pty_unthrottle(struct tty_struct *tty)
{
        tty_wakeup(tty->link);
        set_bit(TTY_THROTTLED, &tty->flags);
}

/**
 *      pty_space       -       report space left for writing
 *      @to: tty we are writing into
 *
 *      The tty buffers allow 64K but we sneak a peak and clip at 8K this
 *      allows a lot of overspill room for echo and other fun messes to
 *      be handled properly
 */

static int pty_space(struct tty_struct *to)
{
        int n = 8192 - to->buf.memory_used;
        if (n < 0)
                return 0;
        return n;
}

/**
 *      pty_write               -       write to a pty
 *      @tty: the tty we write from
 *      @buf: kernel buffer of data
 *      @count: bytes to write
 *
 *      Our "hardware" write method. Data is coming from the ldisc which
 *      may be in a non sleeping state. We simply throw this at the other
 *      end of the link as if we were an IRQ handler receiving stuff for
 *      the other side of the pty/tty pair.
 */

static int pty_write(struct tty_struct *tty, const unsigned char *buf, int c)
{
        struct tty_struct *to = tty->link;

        if (tty->stopped)
                return 0;

        if (c > 0) {
                /* Stuff the data into the input queue of the other end */
                c = tty_insert_flip_string(to, buf, c);
                /* And shovel */
                if (c) {
                        tty_flip_buffer_push(to);
                        tty_wakeup(tty);
                }
        }
        return c;
}

/**
 *      pty_write_room  -       write space
 *      @tty: tty we are writing from
 *
 *      Report how many bytes the ldisc can send into the queue for
 *      the other device.
 */

static int pty_write_room(struct tty_struct *tty)
{
        if (tty->stopped)
                return 0;
        return pty_space(tty->link);
}

/**
 *      pty_chars_in_buffer     -       characters currently in our tx queue
 *      @tty: our tty
 *
 *      Report how much we have in the transmit queue. As everything is
 *      instantly at the other end this is easy to implement.
 */

static int pty_chars_in_buffer(struct tty_struct *tty)
{
        return 0;
}

/* Set the lock flag on a pty */
static int pty_set_lock(struct tty_struct *tty, int __user *arg)
{
        int val;
        if (get_user(val, arg))
                return -EFAULT;
        if (val)
                set_bit(TTY_PTY_LOCK, &tty->flags);
        else
                clear_bit(TTY_PTY_LOCK, &tty->flags);
        return 0;
}

/* Send a signal to the slave */
static int pty_signal(struct tty_struct *tty, int sig)
{
        unsigned long flags;
        struct pid *pgrp;

        if (tty->link) {
                spin_lock_irqsave(&tty->link->ctrl_lock, flags);
                pgrp = get_pid(tty->link->pgrp);
                spin_unlock_irqrestore(&tty->link->ctrl_lock, flags);

                kill_pgrp(pgrp, sig, 1);
                put_pid(pgrp);
        }
        return 0;
}

static void pty_flush_buffer(struct tty_struct *tty)
{
        struct tty_struct *to = tty->link;
        unsigned long flags;

        if (!to)
                return;
        /* tty_buffer_flush(to); FIXME */
        if (to->packet) {
                spin_lock_irqsave(&tty->ctrl_lock, flags);
                tty->ctrl_status |= TIOCPKT_FLUSHWRITE;
                wake_up_interruptible(&to->read_wait);
                spin_unlock_irqrestore(&tty->ctrl_lock, flags);
        }
}

static int pty_open(struct tty_struct *tty, struct file *filp)
{
        int     retval = -ENODEV;

        if (!tty || !tty->link)
                goto out;

        retval = -EIO;
        if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
                goto out;
        if (test_bit(TTY_PTY_LOCK, &tty->link->flags))
                goto out;
        if (tty->link->count != 1)
                goto out;

        clear_bit(TTY_OTHER_CLOSED, &tty->link->flags);
        set_bit(TTY_THROTTLED, &tty->flags);
        retval = 0;
out:
        return retval;
}

static void pty_set_termios(struct tty_struct *tty,
                                        struct ktermios *old_termios)
{
        tty->termios->c_cflag &= ~(CSIZE | PARENB);
        tty->termios->c_cflag |= (CS8 | CREAD);
}

/**
 *      pty_do_resize           -       resize event
 *      @tty: tty being resized
 *      @ws: window size being set.
 *
 *      Update the termios variables and send the necessary signals to
 *      peform a terminal resize correctly
 */

int pty_resize(struct tty_struct *tty,  struct winsize *ws)
{
        struct pid *pgrp, *rpgrp;
        unsigned long flags;
        struct tty_struct *pty = tty->link;

        /* For a PTY we need to lock the tty side */
        mutex_lock(&tty->termios_mutex);
        if (!memcmp(ws, &tty->winsize, sizeof(*ws)))
                goto done;

        /* Get the PID values and reference them so we can
           avoid holding the tty ctrl lock while sending signals.
           We need to lock these individually however. */

        spin_lock_irqsave(&tty->ctrl_lock, flags);
        pgrp = get_pid(tty->pgrp);
        spin_unlock_irqrestore(&tty->ctrl_lock, flags);

        spin_lock_irqsave(&pty->ctrl_lock, flags);
        rpgrp = get_pid(pty->pgrp);
        spin_unlock_irqrestore(&pty->ctrl_lock, flags);

        if (pgrp)
                kill_pgrp(pgrp, SIGWINCH, 1);
        if (rpgrp != pgrp && rpgrp)
                kill_pgrp(rpgrp, SIGWINCH, 1);

        put_pid(pgrp);
        put_pid(rpgrp);

        tty->winsize = *ws;
        pty->winsize = *ws;     /* Never used so will go away soon */
done:
        mutex_unlock(&tty->termios_mutex);
        return 0;
}

/* Traditional BSD devices */
#ifdef CONFIG_LEGACY_PTYS

static int pty_install(struct tty_driver *driver, struct tty_struct *tty)
{
        struct tty_struct *o_tty;
        int idx = tty->index;
        int retval;

        o_tty = alloc_tty_struct();
        if (!o_tty)
                return -ENOMEM;
        if (!try_module_get(driver->other->owner)) {
                /* This cannot in fact currently happen */
                retval = -ENOMEM;
                goto err_free_tty;
        }
        initialize_tty_struct(o_tty, driver->other, idx);

        /* We always use new tty termios data so we can do this
           the easy way .. */
        retval = tty_init_termios(tty);
        if (retval)
                goto err_deinit_tty;

        retval = tty_init_termios(o_tty);
        if (retval)
                goto err_free_termios;

        /*
         * Everything allocated ... set up the o_tty structure.
         */
        driver->other->ttys[idx] = o_tty;
        tty_driver_kref_get(driver->other);
        if (driver->subtype == PTY_TYPE_MASTER)
                o_tty->count++;
        /* Establish the links in both directions */
        tty->link   = o_tty;
        o_tty->link = tty;

        tty_driver_kref_get(driver);
        tty->count++;
        driver->ttys[idx] = tty;
        return 0;
err_free_termios:
        tty_free_termios(tty);
err_deinit_tty:
        deinitialize_tty_struct(o_tty);
        module_put(o_tty->driver->owner);
err_free_tty:
        free_tty_struct(o_tty);
        return retval;
}

static int pty_bsd_ioctl(struct tty_struct *tty,
                         unsigned int cmd, unsigned long arg)
{
        switch (cmd) {
        case TIOCSPTLCK: /* Set PT Lock (disallow slave open) */
                return pty_set_lock(tty, (int __user *) arg);
        case TIOCSIG:    /* Send signal to other side of pty */
                return pty_signal(tty, (int) arg);
        }
        return -ENOIOCTLCMD;
}

static int legacy_count = CONFIG_LEGACY_PTY_COUNT;
module_param(legacy_count, int, 0);

/*
 * The master side of a pty can do TIOCSPTLCK and thus
 * has pty_bsd_ioctl.
 */
static const struct tty_operations master_pty_ops_bsd = {
        .install = pty_install,
        .open = pty_open,
        .close = pty_close,
        .write = pty_write,
        .write_room = pty_write_room,
        .flush_buffer = pty_flush_buffer,
        .chars_in_buffer = pty_chars_in_buffer,
        .unthrottle = pty_unthrottle,
        .set_termios = pty_set_termios,
        .ioctl = pty_bsd_ioctl,
        .resize = pty_resize
};

static const struct tty_operations slave_pty_ops_bsd = {
        .install = pty_install,
        .open = pty_open,
        .close = pty_close,
        .write = pty_write,
        .write_room = pty_write_room,
        .flush_buffer = pty_flush_buffer,
        .chars_in_buffer = pty_chars_in_buffer,
        .unthrottle = pty_unthrottle,
        .set_termios = pty_set_termios,
        .resize = pty_resize
};

static void __init legacy_pty_init(void)
{
        struct tty_driver *pty_driver, *pty_slave_driver;

        if (legacy_count <= 0)
                return;

        pty_driver = alloc_tty_driver(legacy_count);
        if (!pty_driver)
                panic("Couldn't allocate pty driver");

        pty_slave_driver = alloc_tty_driver(legacy_count);
        if (!pty_slave_driver)
                panic("Couldn't allocate pty slave driver");

        pty_driver->owner = THIS_MODULE;
        pty_driver->driver_name = "pty_master";
        pty_driver->name = "pty";
        pty_driver->major = PTY_MASTER_MAJOR;
        pty_driver->minor_start = 0;
        pty_driver->type = TTY_DRIVER_TYPE_PTY;
        pty_driver->subtype = PTY_TYPE_MASTER;
        pty_driver->init_termios = tty_std_termios;
        pty_driver->init_termios.c_iflag = 0;
        pty_driver->init_termios.c_oflag = 0;
        pty_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
        pty_driver->init_termios.c_lflag = 0;
        pty_driver->init_termios.c_ispeed = 38400;
        pty_driver->init_termios.c_ospeed = 38400;
        pty_driver->flags = TTY_DRIVER_RESET_TERMIOS | TTY_DRIVER_REAL_RAW;
        pty_driver->other = pty_slave_driver;
        tty_set_operations(pty_driver, &master_pty_ops_bsd);

        pty_slave_driver->owner = THIS_MODULE;
        pty_slave_driver->driver_name = "pty_slave";
        pty_slave_driver->name = "ttyp";
        pty_slave_driver->major = PTY_SLAVE_MAJOR;
        pty_slave_driver->minor_start = 0;
        pty_slave_driver->type = TTY_DRIVER_TYPE_PTY;
        pty_slave_driver->subtype = PTY_TYPE_SLAVE;
        pty_slave_driver->init_termios = tty_std_termios;
        pty_slave_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
        pty_slave_driver->init_termios.c_ispeed = 38400;
        pty_slave_driver->init_termios.c_ospeed = 38400;
        pty_slave_driver->flags = TTY_DRIVER_RESET_TERMIOS |
                                        TTY_DRIVER_REAL_RAW;
        pty_slave_driver->other = pty_driver;
        tty_set_operations(pty_slave_driver, &slave_pty_ops_bsd);

        if (tty_register_driver(pty_driver))
                panic("Couldn't register pty driver");
        if (tty_register_driver(pty_slave_driver))
                panic("Couldn't register pty slave driver");
}
#else
static inline void legacy_pty_init(void) { }
#endif

/* Unix98 devices */
#ifdef CONFIG_UNIX98_PTYS
/*
 * sysctl support for setting limits on the number of Unix98 ptys allocated.
 * Otherwise one can eat up all kernel memory by opening /dev/ptmx repeatedly.
 */
int pty_limit = NR_UNIX98_PTY_DEFAULT;
static int pty_limit_min;
static int pty_limit_max = NR_UNIX98_PTY_MAX;
static int tty_count;
static int pty_count;

static inline void pty_inc_count(void)
{
        pty_count = (++tty_count) / 2;
}

static inline void pty_dec_count(void)
{
        pty_count = (--tty_count) / 2;
}

static struct cdev ptmx_cdev;

static struct ctl_table pty_table[] = {
        {
                .procname       = "max",
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .data           = &pty_limit,
                .proc_handler   = proc_dointvec_minmax,
                .extra1         = &pty_limit_min,
                .extra2         = &pty_limit_max,
        }, {
                .procname       = "nr",
                .maxlen         = sizeof(int),
                .mode           = 0444,
                .data           = &pty_count,
                .proc_handler   = proc_dointvec,
        }, 
        {}
};

static struct ctl_table pty_kern_table[] = {
        {
                .procname       = "pty",
                .mode           = 0555,
                .child          = pty_table,
        },
        {}
};

static struct ctl_table pty_root_table[] = {
        {
                .procname       = "kernel",
                .mode           = 0555,
                .child          = pty_kern_table,
        },
        {}
};


static int pty_unix98_ioctl(struct tty_struct *tty,
                            unsigned int cmd, unsigned long arg)
{
        switch (cmd) {
        case TIOCSPTLCK: /* Set PT Lock (disallow slave open) */
                return pty_set_lock(tty, (int __user *)arg);
        case TIOCGPTN: /* Get PT Number */
                return put_user(tty->index, (unsigned int __user *)arg);
        case TIOCSIG:    /* Send signal to other side of pty */
                return pty_signal(tty, (int) arg);
        }

        return -ENOIOCTLCMD;
}

/**
 *      ptm_unix98_lookup       -       find a pty master
 *      @driver: ptm driver
 *      @idx: tty index
 *
 *      Look up a pty master device. Called under the tty_mutex for now.
 *      This provides our locking.
 */

static struct tty_struct *ptm_unix98_lookup(struct tty_driver *driver,
                struct inode *ptm_inode, int idx)
{
        struct tty_struct *tty = devpts_get_tty(ptm_inode, idx);
        if (tty)
                tty = tty->link;
        return tty;
}

/**
 *      pts_unix98_lookup       -       find a pty slave
 *      @driver: pts driver
 *      @idx: tty index
 *
 *      Look up a pty master device. Called under the tty_mutex for now.
 *      This provides our locking.
 */

static struct tty_struct *pts_unix98_lookup(struct tty_driver *driver,
                struct inode *pts_inode, int idx)
{
        struct tty_struct *tty = devpts_get_tty(pts_inode, idx);
        /* Master must be open before slave */
        if (!tty)
                return ERR_PTR(-EIO);
        return tty;
}

static void pty_unix98_shutdown(struct tty_struct *tty)
{
        tty_driver_remove_tty(tty->driver, tty);
        /* We have our own method as we don't use the tty index */
        kfree(tty->termios);
}

/* We have no need to install and remove our tty objects as devpts does all
   the work for us */

static int pty_unix98_install(struct tty_driver *driver, struct tty_struct *tty)
{
        struct tty_struct *o_tty;
        int idx = tty->index;

        o_tty = alloc_tty_struct();
        if (!o_tty)
                return -ENOMEM;
        if (!try_module_get(driver->other->owner)) {
                /* This cannot in fact currently happen */
                goto err_free_tty;
        }
        initialize_tty_struct(o_tty, driver->other, idx);

        tty->termios = kzalloc(sizeof(struct ktermios[2]), GFP_KERNEL);
        if (tty->termios == NULL)
                goto err_free_mem;
        *tty->termios = driver->init_termios;
        tty->termios_locked = tty->termios + 1;

        o_tty->termios = kzalloc(sizeof(struct ktermios[2]), GFP_KERNEL);
        if (o_tty->termios == NULL)
                goto err_free_mem;
        *o_tty->termios = driver->other->init_termios;
        o_tty->termios_locked = o_tty->termios + 1;

        tty_driver_kref_get(driver->other);
        if (driver->subtype == PTY_TYPE_MASTER)
                o_tty->count++;
        /* Establish the links in both directions */
        tty->link   = o_tty;
        o_tty->link = tty;
        /*
         * All structures have been allocated, so now we install them.
         * Failures after this point use release_tty to clean up, so
         * there's no need to null out the local pointers.
         */
        tty_driver_kref_get(driver);
        tty->count++;
        pty_inc_count(); /* tty */
        pty_inc_count(); /* tty->link */
        return 0;
err_free_mem:
        deinitialize_tty_struct(o_tty);
        kfree(o_tty->termios);
        kfree(tty->termios);
        module_put(o_tty->driver->owner);
err_free_tty:
        free_tty_struct(o_tty);
        return -ENOMEM;
}

static void pty_unix98_remove(struct tty_driver *driver, struct tty_struct *tty)
{
        pty_dec_count();
}

static const struct tty_operations ptm_unix98_ops = {
        .lookup = ptm_unix98_lookup,
        .install = pty_unix98_install,
        .remove = pty_unix98_remove,
        .open = pty_open,
        .close = pty_close,
        .write = pty_write,
        .write_room = pty_write_room,
        .flush_buffer = pty_flush_buffer,
        .chars_in_buffer = pty_chars_in_buffer,
        .unthrottle = pty_unthrottle,
        .set_termios = pty_set_termios,
        .ioctl = pty_unix98_ioctl,
        .shutdown = pty_unix98_shutdown,
        .resize = pty_resize
};

static const struct tty_operations pty_unix98_ops = {
        .lookup = pts_unix98_lookup,
        .install = pty_unix98_install,
        .remove = pty_unix98_remove,
        .open = pty_open,
        .close = pty_close,
        .write = pty_write,
        .write_room = pty_write_room,
        .flush_buffer = pty_flush_buffer,
        .chars_in_buffer = pty_chars_in_buffer,
        .unthrottle = pty_unthrottle,
        .set_termios = pty_set_termios,
        .shutdown = pty_unix98_shutdown
};

/**
 *      ptmx_open               -       open a unix 98 pty master
 *      @inode: inode of device file
 *      @filp: file pointer to tty
 *
 *      Allocate a unix98 pty master device from the ptmx driver.
 *
 *      Locking: tty_mutex protects the init_dev work. tty->count should
 *              protect the rest.
 *              allocated_ptys_lock handles the list of free pty numbers
 */

static int ptmx_open(struct inode *inode, struct file *filp)
{
        struct tty_struct *tty;
        int retval;
        int index;

        nonseekable_open(inode, filp);

        retval = tty_alloc_file(filp);
        if (retval)
                return retval;

        /* find a device that is not in use. */
        tty_lock();
        index = devpts_new_index(inode);
        tty_unlock();
        if (index < 0) {
                retval = index;
                goto err_file;
        }

        mutex_lock(&tty_mutex);
        tty_lock();
        tty = tty_init_dev(ptm_driver, index, 1);
        mutex_unlock(&tty_mutex);

        if (IS_ERR(tty)) {
                retval = PTR_ERR(tty);
                goto out;
        }

        set_bit(TTY_PTY_LOCK, &tty->flags); /* LOCK THE SLAVE */

        tty_add_file(tty, filp);

        retval = devpts_pty_new(inode, tty->link);
        if (retval)
                goto err_release;

        retval = ptm_driver->ops->open(tty, filp);
        if (retval)
                goto err_release;

        tty_unlock();
        return 0;
err_release:
        tty_unlock();
        tty_release(inode, filp);
        return retval;
out:
        devpts_kill_index(inode, index);
        tty_unlock();
err_file:
        tty_free_file(filp);
        return retval;
}

static struct file_operations ptmx_fops;

static void __init unix98_pty_init(void)
{
        ptm_driver = alloc_tty_driver(NR_UNIX98_PTY_MAX);
        if (!ptm_driver)
                panic("Couldn't allocate Unix98 ptm driver");
        pts_driver = alloc_tty_driver(NR_UNIX98_PTY_MAX);
        if (!pts_driver)
                panic("Couldn't allocate Unix98 pts driver");

        ptm_driver->owner = THIS_MODULE;
        ptm_driver->driver_name = "pty_master";
        ptm_driver->name = "ptm";
        ptm_driver->major = UNIX98_PTY_MASTER_MAJOR;
        ptm_driver->minor_start = 0;
        ptm_driver->type = TTY_DRIVER_TYPE_PTY;
        ptm_driver->subtype = PTY_TYPE_MASTER;
        ptm_driver->init_termios = tty_std_termios;
        ptm_driver->init_termios.c_iflag = 0;
        ptm_driver->init_termios.c_oflag = 0;
        ptm_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
        ptm_driver->init_termios.c_lflag = 0;
        ptm_driver->init_termios.c_ispeed = 38400;
        ptm_driver->init_termios.c_ospeed = 38400;
        ptm_driver->flags = TTY_DRIVER_RESET_TERMIOS | TTY_DRIVER_REAL_RAW |
                TTY_DRIVER_DYNAMIC_DEV | TTY_DRIVER_DEVPTS_MEM;
        ptm_driver->other = pts_driver;
        tty_set_operations(ptm_driver, &ptm_unix98_ops);

        pts_driver->owner = THIS_MODULE;
        pts_driver->driver_name = "pty_slave";
        pts_driver->name = "pts";
        pts_driver->major = UNIX98_PTY_SLAVE_MAJOR;
        pts_driver->minor_start = 0;
        pts_driver->type = TTY_DRIVER_TYPE_PTY;
        pts_driver->subtype = PTY_TYPE_SLAVE;
        pts_driver->init_termios = tty_std_termios;
        pts_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
        pts_driver->init_termios.c_ispeed = 38400;
        pts_driver->init_termios.c_ospeed = 38400;
        pts_driver->flags = TTY_DRIVER_RESET_TERMIOS | TTY_DRIVER_REAL_RAW |
                TTY_DRIVER_DYNAMIC_DEV | TTY_DRIVER_DEVPTS_MEM;
        pts_driver->other = ptm_driver;
        tty_set_operations(pts_driver, &pty_unix98_ops);

        if (tty_register_driver(ptm_driver))
                panic("Couldn't register Unix98 ptm driver");
        if (tty_register_driver(pts_driver))
                panic("Couldn't register Unix98 pts driver");

        register_sysctl_table(pty_root_table);

        /* Now create the /dev/ptmx special device */
        tty_default_fops(&ptmx_fops);
        ptmx_fops.open = ptmx_open;

        cdev_init(&ptmx_cdev, &ptmx_fops);
        if (cdev_add(&ptmx_cdev, MKDEV(TTYAUX_MAJOR, 2), 1) ||
            register_chrdev_region(MKDEV(TTYAUX_MAJOR, 2), 1, "/dev/ptmx") < 0)
                panic("Couldn't register /dev/ptmx driver\n");
        device_create(tty_class, NULL, MKDEV(TTYAUX_MAJOR, 2), NULL, "ptmx");
}

#else
static inline void unix98_pty_init(void) { }
#endif

static int __init pty_init(void)
{
        legacy_pty_init();
        unix98_pty_init();
        return 0;
}
module_init(pty_init);