Linux 4.5-rc4

[deliverable/linux.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
 *
 */

#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/device.h>
#include <linux/uaccess.h>
#include <linux/bitops.h>
#include <linux/devpts_fs.h>
#include <linux/slab.h>
#include <linux/mutex.h>
#include <linux/poll.h>

#undef TTY_DEBUG_HANGUP
#ifdef TTY_DEBUG_HANGUP
# define tty_debug_hangup(tty, f, args...)      tty_debug(tty, f, ##args)
#else
# define tty_debug_hangup(tty, f, args...)      do {} while (0)
#endif

#ifdef CONFIG_UNIX98_PTYS
static struct tty_driver *ptm_driver;
static struct tty_driver *pts_driver;
static DEFINE_MUTEX(devpts_mutex);
#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 (test_bit(TTY_IO_ERROR, &tty->flags))
                        return;
                if (tty->count > 2)
                        return;
        }
        set_bit(TTY_IO_ERROR, &tty->flags);
        wake_up_interruptible(&tty->read_wait);
        wake_up_interruptible(&tty->write_wait);
        spin_lock_irq(&tty->ctrl_lock);
        tty->packet = 0;
        spin_unlock_irq(&tty->ctrl_lock);
        /* Review - krefs on tty_link ?? */
        if (!tty->link)
                return;
        set_bit(TTY_OTHER_CLOSED, &tty->link->flags);
        tty_flip_buffer_push(tty->link->port);
        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) {
                        mutex_lock(&devpts_mutex);
                        if (tty->link->driver_data)
                                devpts_pty_kill(tty->link->driver_data);
                        mutex_unlock(&devpts_mutex);
                }
#endif
                tty_vhangup(tty->link);
        }
}

/*
 * 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_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->port, buf, c);
                /* And shovel */
                if (c)
                        tty_flip_buffer_push(to->port);
        }
        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 tty_buffer_space_avail(tty->link->port);
}

/**
 *      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;
}

static int pty_get_lock(struct tty_struct *tty, int __user *arg)
{
        int locked = test_bit(TTY_PTY_LOCK, &tty->flags);
        return put_user(locked, arg);
}

/* Set the packet mode on a pty */
static int pty_set_pktmode(struct tty_struct *tty, int __user *arg)
{
        int pktmode;

        if (get_user(pktmode, arg))
                return -EFAULT;

        spin_lock_irq(&tty->ctrl_lock);
        if (pktmode) {
                if (!tty->packet) {
                        tty->link->ctrl_status = 0;
                        smp_mb();
                        tty->packet = 1;
                }
        } else
                tty->packet = 0;
        spin_unlock_irq(&tty->ctrl_lock);

        return 0;
}

/* Get the packet mode of a pty */
static int pty_get_pktmode(struct tty_struct *tty, int __user *arg)
{
        int pktmode = tty->packet;
        return put_user(pktmode, arg);
}

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

        if (sig != SIGINT && sig != SIGQUIT && sig != SIGTSTP)
                return -EINVAL;

        if (tty->link) {
                pgrp = tty_get_pgrp(tty->link);
                if (pgrp)
                        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;
        struct tty_ldisc *ld;

        if (!to)
                return;

        ld = tty_ldisc_ref(to);
        tty_buffer_flush(to, ld);
        if (ld)
                tty_ldisc_deref(ld);

        if (to->packet) {
                spin_lock_irq(&tty->ctrl_lock);
                tty->ctrl_status |= TIOCPKT_FLUSHWRITE;
                wake_up_interruptible(&to->read_wait);
                spin_unlock_irq(&tty->ctrl_lock);
        }
}

static int pty_open(struct tty_struct *tty, struct file *filp)
{
        if (!tty || !tty->link)
                return -ENODEV;

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

        clear_bit(TTY_IO_ERROR, &tty->flags);
        /* TTY_OTHER_CLOSED must be cleared before TTY_OTHER_DONE */
        clear_bit(TTY_OTHER_CLOSED, &tty->link->flags);
        clear_bit(TTY_OTHER_DONE, &tty->link->flags);
        set_bit(TTY_THROTTLED, &tty->flags);
        return 0;

out:
        set_bit(TTY_IO_ERROR, &tty->flags);
        return -EIO;
}

static void pty_set_termios(struct tty_struct *tty,
                                        struct ktermios *old_termios)
{
        /* See if packet mode change of state. */
        if (tty->link && tty->link->packet) {
                int extproc = (old_termios->c_lflag & EXTPROC) |
                                (tty->termios.c_lflag & EXTPROC);
                int old_flow = ((old_termios->c_iflag & IXON) &&
                                (old_termios->c_cc[VSTOP] == '\023') &&
                                (old_termios->c_cc[VSTART] == '\021'));
                int new_flow = (I_IXON(tty) &&
                                STOP_CHAR(tty) == '\023' &&
                                START_CHAR(tty) == '\021');
                if ((old_flow != new_flow) || extproc) {
                        spin_lock_irq(&tty->ctrl_lock);
                        if (old_flow != new_flow) {
                                tty->ctrl_status &= ~(TIOCPKT_DOSTOP | TIOCPKT_NOSTOP);
                                if (new_flow)
                                        tty->ctrl_status |= TIOCPKT_DOSTOP;
                                else
                                        tty->ctrl_status |= TIOCPKT_NOSTOP;
                        }
                        if (extproc)
                                tty->ctrl_status |= TIOCPKT_IOCTL;
                        spin_unlock_irq(&tty->ctrl_lock);
                        wake_up_interruptible(&tty->link->read_wait);
                }
        }

        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
 */

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

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

        /* Signal the foreground process group of both ptys */
        pgrp = tty_get_pgrp(tty);
        rpgrp = tty_get_pgrp(pty);

        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->winsize_mutex);
        return 0;
}

/**
 *      pty_start - start() handler
 *      pty_stop  - stop() handler
 *      @tty: tty being flow-controlled
 *
 *      Propagates the TIOCPKT status to the master pty.
 *
 *      NB: only the master pty can be in packet mode so only the slave
 *          needs start()/stop() handlers
 */
static void pty_start(struct tty_struct *tty)
{
        unsigned long flags;

        if (tty->link && tty->link->packet) {
                spin_lock_irqsave(&tty->ctrl_lock, flags);
                tty->ctrl_status &= ~TIOCPKT_STOP;
                tty->ctrl_status |= TIOCPKT_START;
                spin_unlock_irqrestore(&tty->ctrl_lock, flags);
                wake_up_interruptible_poll(&tty->link->read_wait, POLLIN);
        }
}

static void pty_stop(struct tty_struct *tty)
{
        unsigned long flags;

        if (tty->link && tty->link->packet) {
                spin_lock_irqsave(&tty->ctrl_lock, flags);
                tty->ctrl_status &= ~TIOCPKT_START;
                tty->ctrl_status |= TIOCPKT_STOP;
                spin_unlock_irqrestore(&tty->ctrl_lock, flags);
                wake_up_interruptible_poll(&tty->link->read_wait, POLLIN);
        }
}

/**
 *      pty_common_install              -       set up the pty pair
 *      @driver: the pty driver
 *      @tty: the tty being instantiated
 *      @legacy: true if this is BSD style
 *
 *      Perform the initial set up for the tty/pty pair. Called from the
 *      tty layer when the port is first opened.
 *
 *      Locking: the caller must hold the tty_mutex
 */
static int pty_common_install(struct tty_driver *driver, struct tty_struct *tty,
                bool legacy)
{
        struct tty_struct *o_tty;
        struct tty_port *ports[2];
        int idx = tty->index;
        int retval = -ENOMEM;

        /* Opening the slave first has always returned -EIO */
        if (driver->subtype != PTY_TYPE_MASTER)
                return -EIO;

        ports[0] = kmalloc(sizeof **ports, GFP_KERNEL);
        ports[1] = kmalloc(sizeof **ports, GFP_KERNEL);
        if (!ports[0] || !ports[1])
                goto err;
        if (!try_module_get(driver->other->owner)) {
                /* This cannot in fact currently happen */
                goto err;
        }
        o_tty = alloc_tty_struct(driver->other, idx);
        if (!o_tty)
                goto err_put_module;

        tty_set_lock_subclass(o_tty);
        lockdep_set_subclass(&o_tty->termios_rwsem, TTY_LOCK_SLAVE);

        if (legacy) {
                /* 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;

                driver->other->ttys[idx] = o_tty;
                driver->ttys[idx] = tty;
        } else {
                memset(&tty->termios_locked, 0, sizeof(tty->termios_locked));
                tty->termios = driver->init_termios;
                memset(&o_tty->termios_locked, 0, sizeof(tty->termios_locked));
                o_tty->termios = driver->other->init_termios;
        }

        /*
         * Everything allocated ... set up the o_tty structure.
         */
        tty_driver_kref_get(driver->other);
        /* Establish the links in both directions */
        tty->link   = o_tty;
        o_tty->link = tty;
        tty_port_init(ports[0]);
        tty_port_init(ports[1]);
        tty_buffer_set_limit(ports[0], 8192);
        tty_buffer_set_limit(ports[1], 8192);
        o_tty->port = ports[0];
        tty->port = ports[1];
        o_tty->port->itty = o_tty;

        tty_buffer_set_lock_subclass(o_tty->port);

        tty_driver_kref_get(driver);
        tty->count++;
        o_tty->count++;
        return 0;
err_free_termios:
        if (legacy)
                tty_free_termios(tty);
err_deinit_tty:
        deinitialize_tty_struct(o_tty);
        free_tty_struct(o_tty);
err_put_module:
        module_put(driver->other->owner);
err:
        kfree(ports[0]);
        kfree(ports[1]);
        return retval;
}

static void pty_cleanup(struct tty_struct *tty)
{
        tty_port_put(tty->port);
}

/* Traditional BSD devices */
#ifdef CONFIG_LEGACY_PTYS

static int pty_install(struct tty_driver *driver, struct tty_struct *tty)
{
        return pty_common_install(driver, tty, true);
}

static void pty_remove(struct tty_driver *driver, struct tty_struct *tty)
{
        struct tty_struct *pair = tty->link;
        driver->ttys[tty->index] = NULL;
        if (pair)
                pair->driver->ttys[pair->index] = NULL;
}

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 TIOCGPTLCK: /* Get PT Lock status */
                return pty_get_lock(tty, (int __user *)arg);
        case TIOCPKT: /* Set PT packet mode */
                return pty_set_pktmode(tty, (int __user *)arg);
        case TIOCGPKT: /* Get PT packet mode */
                return pty_get_pktmode(tty, (int __user *)arg);
        case TIOCSIG:    /* Send signal to other side of pty */
                return pty_signal(tty, (int) arg);
        case TIOCGPTN: /* TTY returns ENOTTY, but glibc expects EINVAL here */
                return -EINVAL;
        }
        return -ENOIOCTLCMD;
}

static int legacy_count = CONFIG_LEGACY_PTY_COUNT;
/*
 * not really modular, but the easiest way to keep compat with existing
 * bootargs behaviour is to continue using module_param here.
 */
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,
        .ioctl = pty_bsd_ioctl,
        .cleanup = pty_cleanup,
        .resize = pty_resize,
        .remove = pty_remove
};

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,
        .cleanup = pty_cleanup,
        .resize = pty_resize,
        .start = pty_start,
        .stop = pty_stop,
        .remove = pty_remove
};

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

        if (legacy_count <= 0)
                return;

        pty_driver = tty_alloc_driver(legacy_count,
                        TTY_DRIVER_RESET_TERMIOS |
                        TTY_DRIVER_REAL_RAW |
                        TTY_DRIVER_DYNAMIC_ALLOC);
        if (IS_ERR(pty_driver))
                panic("Couldn't allocate pty driver");

        pty_slave_driver = tty_alloc_driver(legacy_count,
                        TTY_DRIVER_RESET_TERMIOS |
                        TTY_DRIVER_REAL_RAW |
                        TTY_DRIVER_DYNAMIC_ALLOC);
        if (IS_ERR(pty_slave_driver))
                panic("Couldn't allocate pty slave driver");

        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->other = pty_slave_driver;
        tty_set_operations(pty_driver, &master_pty_ops_bsd);

        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->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

static struct cdev ptmx_cdev;

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 TIOCGPTLCK: /* Get PT Lock status */
                return pty_get_lock(tty, (int __user *)arg);
        case TIOCPKT: /* Set PT packet mode */
                return pty_set_pktmode(tty, (int __user *)arg);
        case TIOCGPKT: /* Get PT packet mode */
                return pty_get_pktmode(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)
{
        /* Master must be open via /dev/ptmx */
        return ERR_PTR(-EIO);
}

/**
 *      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 for the tty pointer.
 */

static struct tty_struct *pts_unix98_lookup(struct tty_driver *driver,
                struct inode *pts_inode, int idx)
{
        struct tty_struct *tty;

        mutex_lock(&devpts_mutex);
        tty = devpts_get_priv(pts_inode);
        mutex_unlock(&devpts_mutex);
        /* Master must be open before slave */
        if (!tty)
                return ERR_PTR(-EIO);
        return tty;
}

/* 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)
{
        return pty_common_install(driver, tty, false);
}

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

/* this is called once with whichever end is closed last */
static void pty_unix98_shutdown(struct tty_struct *tty)
{
        struct inode *ptmx_inode;

        if (tty->driver->subtype == PTY_TYPE_MASTER)
                ptmx_inode = tty->driver_data;
        else
                ptmx_inode = tty->link->driver_data;
        devpts_kill_index(ptmx_inode, tty->index);
        devpts_del_ref(ptmx_inode);
}

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,
        .ioctl = pty_unix98_ioctl,
        .resize = pty_resize,
        .shutdown = pty_unix98_shutdown,
        .cleanup = pty_cleanup
};

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,
        .start = pty_start,
        .stop = pty_stop,
        .shutdown = pty_unix98_shutdown,
        .cleanup = pty_cleanup,
};

/**
 *      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;
        struct inode *slave_inode;
        int retval;
        int index;

        nonseekable_open(inode, filp);

        /* We refuse fsnotify events on ptmx, since it's a shared resource */
        filp->f_mode |= FMODE_NONOTIFY;

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

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

        mutex_unlock(&devpts_mutex);

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

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

        /* The tty returned here is locked so we can safely
           drop the mutex */
        mutex_unlock(&tty_mutex);

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

        /*
         * In the case where all references to ptmx inode are dropped and we
         * still have /dev/tty opened pointing to the master/slave pair (ptmx
         * is closed/released before /dev/tty), we must make sure that the inode
         * is still valid when we call the final pty_unix98_shutdown, thus we
         * hold an additional reference to the ptmx inode. For the same /dev/tty
         * last close case, we also need to make sure the super_block isn't
         * destroyed (devpts instance unmounted), before /dev/tty is closed and
         * on its release devpts_kill_index is called.
         */
        devpts_add_ref(inode);

        tty_add_file(tty, filp);

        slave_inode = devpts_pty_new(inode,
                        MKDEV(UNIX98_PTY_SLAVE_MAJOR, index), index,
                        tty->link);
        if (IS_ERR(slave_inode)) {
                retval = PTR_ERR(slave_inode);
                goto err_release;
        }
        tty->link->driver_data = slave_inode;

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

        tty_debug_hangup(tty, "opening (count=%d)\n", tty->count);

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

static struct file_operations ptmx_fops;

static void __init unix98_pty_init(void)
{
        ptm_driver = tty_alloc_driver(NR_UNIX98_PTY_MAX,
                        TTY_DRIVER_RESET_TERMIOS |
                        TTY_DRIVER_REAL_RAW |
                        TTY_DRIVER_DYNAMIC_DEV |
                        TTY_DRIVER_DEVPTS_MEM |
                        TTY_DRIVER_DYNAMIC_ALLOC);
        if (IS_ERR(ptm_driver))
                panic("Couldn't allocate Unix98 ptm driver");
        pts_driver = tty_alloc_driver(NR_UNIX98_PTY_MAX,
                        TTY_DRIVER_RESET_TERMIOS |
                        TTY_DRIVER_REAL_RAW |
                        TTY_DRIVER_DYNAMIC_DEV |
                        TTY_DRIVER_DEVPTS_MEM |
                        TTY_DRIVER_DYNAMIC_ALLOC);
        if (IS_ERR(pts_driver))
                panic("Couldn't allocate Unix98 pts driver");

        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->other = pts_driver;
        tty_set_operations(ptm_driver, &ptm_unix98_ops);

        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->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");

        /* 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");
        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;
}
device_initcall(pty_init);