pty.c

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/*
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  Added support for a Unix98-style ptmx device.
 *    -- C. Scott Ananian <[email protected]>, 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/device.h>
#include <linux/uaccess.h>
#include <linux/bitops.h>
#include <linux/devpts_fs.h>
#include <linux/slab.h>
#include <linux/mutex.h>


#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 (tty->count > 2)
            return;
    }
    wake_up_interruptible(&tty->read_wait);
    wake_up_interruptible(&tty->write_wait);
    tty->packet = 0;
    /* Review - krefs on tty_link ?? */
    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) {
                mutex_lock(&devpts_mutex);
            devpts_pty_kill(tty->link);
                mutex_unlock(&devpts_mutex);
        }
#endif
        tty_unlock(tty);
        tty_vhangup(tty->link);
        tty_lock(tty);
    }
}

/*
 * 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);
}

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

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;
}

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

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);
}

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;
}

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;

    o_tty = alloc_tty_struct();
    if (!o_tty)
        goto err;
    ports[0] = kmalloc(sizeof **ports, GFP_KERNEL);
    ports[1] = kmalloc(sizeof **ports, GFP_KERNEL);
    if (!ports[0] || !ports[1])
        goto err_free_tty;
    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);

    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);
    if (driver->subtype == PTY_TYPE_MASTER)
        o_tty->count++;
    /* Establish the links in both directions */
    tty->link   = o_tty;
    o_tty->link = tty;
    tty_port_init(ports[0]);
    tty_port_init(ports[1]);
    o_tty->port = ports[0];
    tty->port = ports[1];

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

static void pty_cleanup(struct tty_struct *tty)
{
    kfree(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 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,
    .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,
    .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 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;
}

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);
}

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_tty(pts_inode, idx);
    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)
{
}

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,
    .resize = pty_resize,
    .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,
    .cleanup = pty_cleanup,
};

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. */
    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_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(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\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);