tty_io.c

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/*
 *  Copyright (C) 1991, 1992  Linus Torvalds
 */

/*
 * 'tty_io.c' gives an orthogonal feeling to tty's, be they consoles
 * or rs-channels. It also implements echoing, cooked mode etc.
 *
 * Kill-line thanks to John T Kohl, who also corrected VMIN = VTIME = 0.
 *
 * Modified by Theodore Ts'o, 9/14/92, to dynamically allocate the
 * tty_struct and tty_queue structures.  Previously there was an array
 * of 256 tty_struct's which was statically allocated, and the
 * tty_queue structures were allocated at boot time.  Both are now
 * dynamically allocated only when the tty is open.
 *
 * Also restructured routines so that there is more of a separation
 * between the high-level tty routines (tty_io.c and tty_ioctl.c) and
 * the low-level tty routines (serial.c, pty.c, console.c).  This
 * makes for cleaner and more compact code.  -TYT, 9/17/92
 *
 * 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).
 *
 * NOTE: pay no attention to the line discipline code (yet); its
 * interface is still subject to change in this version...
 * -- TYT, 1/31/92
 *
 * Added functionality to the OPOST tty handling.  No delays, but all
 * other bits should be there.
 *  -- Nick Holloway <[email protected]>, 27th May 1993.
 *
 * Rewrote canonical mode and added more termios flags.
 *  -- [email protected] (J. Cowley), 13Jan94
 *
 * Reorganized FASYNC support so mouse code can share it.
 *  -- [email protected], 9Sep95
 *
 * New TIOCLINUX variants added.
 *  -- [email protected], 19-Nov-95
 *
 * Restrict vt switching via ioctl()
 *      -- [email protected], 5-Dec-95
 *
 * Move console and virtual terminal code to more appropriate files,
 * implement CONFIG_VT and generalize console device interface.
 *  -- Marko Kohtala <[email protected]>, March 97
 *
 * Rewrote tty_init_dev and tty_release_dev to eliminate races.
 *  -- Bill Hawes <[email protected]>, June 97
 *
 * Added devfs support.
 *      -- C. Scott Ananian <[email protected]>, 13-Jan-1998
 *
 * Added support for a Unix98-style ptmx device.
 *      -- C. Scott Ananian <[email protected]>, 14-Jan-1998
 *
 * Reduced memory usage for older ARM systems
 *      -- Russell King <[email protected]>
 *
 * Move do_SAK() into process context.  Less stack use in devfs functions.
 * alloc_tty_struct() always uses kmalloc()
 *           -- Andrew Morton <[email protected]> 17Mar01
 */

#include <linux/types.h>
#include <linux/major.h>
#include <linux/errno.h>
#include <linux/signal.h>
#include <linux/fcntl.h>
#include <linux/sched.h>
#include <linux/interrupt.h>
#include <linux/tty.h>
#include <linux/tty_driver.h>
#include <linux/tty_flip.h>
#include <linux/devpts_fs.h>
#include <linux/file.h>
#include <linux/fdtable.h>
#include <linux/console.h>
#include <linux/timer.h>
#include <linux/ctype.h>
#include <linux/kd.h>
#include <linux/mm.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/poll.h>
#include <linux/proc_fs.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/device.h>
#include <linux/wait.h>
#include <linux/bitops.h>
#include <linux/delay.h>
#include <linux/seq_file.h>
#include <linux/serial.h>
#include <linux/ratelimit.h>

#include <linux/uaccess.h>

#include <linux/kbd_kern.h>
#include <linux/vt_kern.h>
#include <linux/selection.h>

#include <linux/kmod.h>
#include <linux/nsproxy.h>

#undef TTY_DEBUG_HANGUP

#define TTY_PARANOIA_CHECK 1
#define CHECK_TTY_COUNT 1

struct ktermios tty_std_termios = { /* for the benefit of tty drivers  */
    .c_iflag = ICRNL | IXON,
    .c_oflag = OPOST | ONLCR,
    .c_cflag = B38400 | CS8 | CREAD | HUPCL,
    .c_lflag = ISIG | ICANON | ECHO | ECHOE | ECHOK |
           ECHOCTL | ECHOKE | IEXTEN,
    .c_cc = INIT_C_CC,
    .c_ispeed = 38400,
    .c_ospeed = 38400
};

EXPORT_SYMBOL(tty_std_termios);

/* This list gets poked at by procfs and various bits of boot up code. This
   could do with some rationalisation such as pulling the tty proc function
   into this file */

LIST_HEAD(tty_drivers);         /* linked list of tty drivers */

/* Mutex to protect creating and releasing a tty. This is shared with
   vt.c for deeply disgusting hack reasons */
DEFINE_MUTEX(tty_mutex);
EXPORT_SYMBOL(tty_mutex);

/* Spinlock to protect the tty->tty_files list */
DEFINE_SPINLOCK(tty_files_lock);

static ssize_t tty_read(struct file *, char __user *, size_t, loff_t *);
static ssize_t tty_write(struct file *, const char __user *, size_t, loff_t *);
ssize_t redirected_tty_write(struct file *, const char __user *,
                            size_t, loff_t *);
static unsigned int tty_poll(struct file *, poll_table *);
static int tty_open(struct inode *, struct file *);
long tty_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
#ifdef CONFIG_COMPAT
static long tty_compat_ioctl(struct file *file, unsigned int cmd,
                unsigned long arg);
#else
#define tty_compat_ioctl NULL
#endif
static int __tty_fasync(int fd, struct file *filp, int on);
static int tty_fasync(int fd, struct file *filp, int on);
static void release_tty(struct tty_struct *tty, int idx);
static void __proc_set_tty(struct task_struct *tsk, struct tty_struct *tty);
static void proc_set_tty(struct task_struct *tsk, struct tty_struct *tty);

struct tty_struct *alloc_tty_struct(void)
{
    return kzalloc(sizeof(struct tty_struct), GFP_KERNEL);
}

void free_tty_struct(struct tty_struct *tty)
{
    if (!tty)
        return;
    if (tty->dev)
        put_device(tty->dev);
    kfree(tty->write_buf);
    tty_buffer_free_all(tty);
    tty->magic = 0xDEADDEAD;
    kfree(tty);
}

static inline struct tty_struct *file_tty(struct file *file)
{
    return ((struct tty_file_private *)file->private_data)->tty;
}

int tty_alloc_file(struct file *file)
{
    struct tty_file_private *priv;

    priv = kmalloc(sizeof(*priv), GFP_KERNEL);
    if (!priv)
        return -ENOMEM;

    file->private_data = priv;

    return 0;
}

/* Associate a new file with the tty structure */
void tty_add_file(struct tty_struct *tty, struct file *file)
{
    struct tty_file_private *priv = file->private_data;

    priv->tty = tty;
    priv->file = file;

    spin_lock(&tty_files_lock);
    list_add(&priv->list, &tty->tty_files);
    spin_unlock(&tty_files_lock);
}

void tty_free_file(struct file *file)
{
    struct tty_file_private *priv = file->private_data;

    file->private_data = NULL;
    kfree(priv);
}

/* Delete file from its tty */
void tty_del_file(struct file *file)
{
    struct tty_file_private *priv = file->private_data;

    spin_lock(&tty_files_lock);
    list_del(&priv->list);
    spin_unlock(&tty_files_lock);
    tty_free_file(file);
}


#define TTY_NUMBER(tty) ((tty)->index + (tty)->driver->name_base)

char *tty_name(struct tty_struct *tty, char *buf)
{
    if (!tty) /* Hmm.  NULL pointer.  That's fun. */
        strcpy(buf, "NULL tty");
    else
        strcpy(buf, tty->name);
    return buf;
}

EXPORT_SYMBOL(tty_name);

int tty_paranoia_check(struct tty_struct *tty, struct inode *inode,
                  const char *routine)
{
#ifdef TTY_PARANOIA_CHECK
    if (!tty) {
        printk(KERN_WARNING
            "null TTY for (%d:%d) in %s\n",
            imajor(inode), iminor(inode), routine);
        return 1;
    }
    if (tty->magic != TTY_MAGIC) {
        printk(KERN_WARNING
            "bad magic number for tty struct (%d:%d) in %s\n",
            imajor(inode), iminor(inode), routine);
        return 1;
    }
#endif
    return 0;
}

static int check_tty_count(struct tty_struct *tty, const char *routine)
{
#ifdef CHECK_TTY_COUNT
    struct list_head *p;
    int count = 0;

    spin_lock(&tty_files_lock);
    list_for_each(p, &tty->tty_files) {
        count++;
    }
    spin_unlock(&tty_files_lock);
    if (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
        tty->driver->subtype == PTY_TYPE_SLAVE &&
        tty->link && tty->link->count)
        count++;
    if (tty->count != count) {
        printk(KERN_WARNING "Warning: dev (%s) tty->count(%d) "
                    "!= #fd's(%d) in %s\n",
               tty->name, tty->count, count, routine);
        return count;
    }
#endif
    return 0;
}

static struct tty_driver *get_tty_driver(dev_t device, int *index)
{
    struct tty_driver *p;

    list_for_each_entry(p, &tty_drivers, tty_drivers) {
        dev_t base = MKDEV(p->major, p->minor_start);
        if (device < base || device >= base + p->num)
            continue;
        *index = device - base;
        return tty_driver_kref_get(p);
    }
    return NULL;
}

#ifdef CONFIG_CONSOLE_POLL

struct tty_driver *tty_find_polling_driver(char *name, int *line)
{
    struct tty_driver *p, *res = NULL;
    int tty_line = 0;
    int len;
    char *str, *stp;

    for (str = name; *str; str++)
        if ((*str >= '0' && *str <= '9') || *str == ',')
            break;
    if (!*str)
        return NULL;

    len = str - name;
    tty_line = simple_strtoul(str, &str, 10);

    mutex_lock(&tty_mutex);
    /* Search through the tty devices to look for a match */
    list_for_each_entry(p, &tty_drivers, tty_drivers) {
        if (strncmp(name, p->name, len) != 0)
            continue;
        stp = str;
        if (*stp == ',')
            stp++;
        if (*stp == '\0')
            stp = NULL;

        if (tty_line >= 0 && tty_line < p->num && p->ops &&
            p->ops->poll_init && !p->ops->poll_init(p, tty_line, stp)) {
            res = tty_driver_kref_get(p);
            *line = tty_line;
            break;
        }
    }
    mutex_unlock(&tty_mutex);

    return res;
}
EXPORT_SYMBOL_GPL(tty_find_polling_driver);
#endif

int tty_check_change(struct tty_struct *tty)
{
    unsigned long flags;
    int ret = 0;

    if (current->signal->tty != tty)
        return 0;

    spin_lock_irqsave(&tty->ctrl_lock, flags);

    if (!tty->pgrp) {
        printk(KERN_WARNING "tty_check_change: tty->pgrp == NULL!\n");
        goto out_unlock;
    }
    if (task_pgrp(current) == tty->pgrp)
        goto out_unlock;
    spin_unlock_irqrestore(&tty->ctrl_lock, flags);
    if (is_ignored(SIGTTOU))
        goto out;
    if (is_current_pgrp_orphaned()) {
        ret = -EIO;
        goto out;
    }
    kill_pgrp(task_pgrp(current), SIGTTOU, 1);
    set_thread_flag(TIF_SIGPENDING);
    ret = -ERESTARTSYS;
out:
    return ret;
out_unlock:
    spin_unlock_irqrestore(&tty->ctrl_lock, flags);
    return ret;
}

EXPORT_SYMBOL(tty_check_change);

static ssize_t hung_up_tty_read(struct file *file, char __user *buf,
                size_t count, loff_t *ppos)
{
    return 0;
}

static ssize_t hung_up_tty_write(struct file *file, const char __user *buf,
                 size_t count, loff_t *ppos)
{
    return -EIO;
}

/* No kernel lock held - none needed ;) */
static unsigned int hung_up_tty_poll(struct file *filp, poll_table *wait)
{
    return POLLIN | POLLOUT | POLLERR | POLLHUP | POLLRDNORM | POLLWRNORM;
}

static long hung_up_tty_ioctl(struct file *file, unsigned int cmd,
        unsigned long arg)
{
    return cmd == TIOCSPGRP ? -ENOTTY : -EIO;
}

static long hung_up_tty_compat_ioctl(struct file *file,
                     unsigned int cmd, unsigned long arg)
{
    return cmd == TIOCSPGRP ? -ENOTTY : -EIO;
}

static const struct file_operations tty_fops = {
    .llseek     = no_llseek,
    .read       = tty_read,
    .write      = tty_write,
    .poll       = tty_poll,
    .unlocked_ioctl = tty_ioctl,
    .compat_ioctl   = tty_compat_ioctl,
    .open       = tty_open,
    .release    = tty_release,
    .fasync     = tty_fasync,
};

static const struct file_operations console_fops = {
    .llseek     = no_llseek,
    .read       = tty_read,
    .write      = redirected_tty_write,
    .poll       = tty_poll,
    .unlocked_ioctl = tty_ioctl,
    .compat_ioctl   = tty_compat_ioctl,
    .open       = tty_open,
    .release    = tty_release,
    .fasync     = tty_fasync,
};

static const struct file_operations hung_up_tty_fops = {
    .llseek     = no_llseek,
    .read       = hung_up_tty_read,
    .write      = hung_up_tty_write,
    .poll       = hung_up_tty_poll,
    .unlocked_ioctl = hung_up_tty_ioctl,
    .compat_ioctl   = hung_up_tty_compat_ioctl,
    .release    = tty_release,
};

static DEFINE_SPINLOCK(redirect_lock);
static struct file *redirect;

void tty_wakeup(struct tty_struct *tty)
{
    struct tty_ldisc *ld;

    if (test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) {
        ld = tty_ldisc_ref(tty);
        if (ld) {
            if (ld->ops->write_wakeup)
                ld->ops->write_wakeup(tty);
            tty_ldisc_deref(ld);
        }
    }
    wake_up_interruptible_poll(&tty->write_wait, POLLOUT);
}

EXPORT_SYMBOL_GPL(tty_wakeup);

void __tty_hangup(struct tty_struct *tty)
{
    struct file *cons_filp = NULL;
    struct file *filp, *f = NULL;
    struct task_struct *p;
    struct tty_file_private *priv;
    int    closecount = 0, n;
    unsigned long flags;
    int refs = 0;

    if (!tty)
        return;


    spin_lock(&redirect_lock);
    if (redirect && file_tty(redirect) == tty) {
        f = redirect;
        redirect = NULL;
    }
    spin_unlock(&redirect_lock);

    tty_lock(tty);

    /* some functions below drop BTM, so we need this bit */
    set_bit(TTY_HUPPING, &tty->flags);

    /* inuse_filps is protected by the single tty lock,
       this really needs to change if we want to flush the
       workqueue with the lock held */
    check_tty_count(tty, "tty_hangup");

    spin_lock(&tty_files_lock);
    /* This breaks for file handles being sent over AF_UNIX sockets ? */
    list_for_each_entry(priv, &tty->tty_files, list) {
        filp = priv->file;
        if (filp->f_op->write == redirected_tty_write)
            cons_filp = filp;
        if (filp->f_op->write != tty_write)
            continue;
        closecount++;
        __tty_fasync(-1, filp, 0);  /* can't block */
        filp->f_op = &hung_up_tty_fops;
    }
    spin_unlock(&tty_files_lock);

    /*
     * it drops BTM and thus races with reopen
     * we protect the race by TTY_HUPPING
     */
    tty_ldisc_hangup(tty);

    read_lock(&tasklist_lock);
    if (tty->session) {
        do_each_pid_task(tty->session, PIDTYPE_SID, p) {
            spin_lock_irq(&p->sighand->siglock);
            if (p->signal->tty == tty) {
                p->signal->tty = NULL;
                /* We defer the dereferences outside fo
                   the tasklist lock */
                refs++;
            }
            if (!p->signal->leader) {
                spin_unlock_irq(&p->sighand->siglock);
                continue;
            }
            __group_send_sig_info(SIGHUP, SEND_SIG_PRIV, p);
            __group_send_sig_info(SIGCONT, SEND_SIG_PRIV, p);
            put_pid(p->signal->tty_old_pgrp);  /* A noop */
            spin_lock_irqsave(&tty->ctrl_lock, flags);
            if (tty->pgrp)
                p->signal->tty_old_pgrp = get_pid(tty->pgrp);
            spin_unlock_irqrestore(&tty->ctrl_lock, flags);
            spin_unlock_irq(&p->sighand->siglock);
        } while_each_pid_task(tty->session, PIDTYPE_SID, p);
    }
    read_unlock(&tasklist_lock);

    spin_lock_irqsave(&tty->ctrl_lock, flags);
    clear_bit(TTY_THROTTLED, &tty->flags);
    clear_bit(TTY_PUSH, &tty->flags);
    clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
    put_pid(tty->session);
    put_pid(tty->pgrp);
    tty->session = NULL;
    tty->pgrp = NULL;
    tty->ctrl_status = 0;
    spin_unlock_irqrestore(&tty->ctrl_lock, flags);

    /* Account for the p->signal references we killed */
    while (refs--)
        tty_kref_put(tty);

    /*
     * If one of the devices matches a console pointer, we
     * cannot just call hangup() because that will cause
     * tty->count and state->count to go out of sync.
     * So we just call close() the right number of times.
     */
    if (cons_filp) {
        if (tty->ops->close)
            for (n = 0; n < closecount; n++)
                tty->ops->close(tty, cons_filp);
    } else if (tty->ops->hangup)
        (tty->ops->hangup)(tty);
    /*
     * We don't want to have driver/ldisc interactions beyond
     * the ones we did here. The driver layer expects no
     * calls after ->hangup() from the ldisc side. However we
     * can't yet guarantee all that.
     */
    set_bit(TTY_HUPPED, &tty->flags);
    clear_bit(TTY_HUPPING, &tty->flags);
    tty_ldisc_enable(tty);

    tty_unlock(tty);

    if (f)
        fput(f);
}

static void do_tty_hangup(struct work_struct *work)
{
    struct tty_struct *tty =
        container_of(work, struct tty_struct, hangup_work);

    __tty_hangup(tty);
}

void tty_hangup(struct tty_struct *tty)
{
#ifdef TTY_DEBUG_HANGUP
    char    buf[64];
    printk(KERN_DEBUG "%s hangup...\n", tty_name(tty, buf));
#endif
    schedule_work(&tty->hangup_work);
}

EXPORT_SYMBOL(tty_hangup);

void tty_vhangup(struct tty_struct *tty)
{
#ifdef TTY_DEBUG_HANGUP
    char    buf[64];

    printk(KERN_DEBUG "%s vhangup...\n", tty_name(tty, buf));
#endif
    __tty_hangup(tty);
}

EXPORT_SYMBOL(tty_vhangup);


void tty_vhangup_self(void)
{
    struct tty_struct *tty;

    tty = get_current_tty();
    if (tty) {
        tty_vhangup(tty);
        tty_kref_put(tty);
    }
}

int tty_hung_up_p(struct file *filp)
{
    return (filp->f_op == &hung_up_tty_fops);
}

EXPORT_SYMBOL(tty_hung_up_p);

static void session_clear_tty(struct pid *session)
{
    struct task_struct *p;
    do_each_pid_task(session, PIDTYPE_SID, p) {
        proc_clear_tty(p);
    } while_each_pid_task(session, PIDTYPE_SID, p);
}

void disassociate_ctty(int on_exit)
{
    struct tty_struct *tty;

    if (!current->signal->leader)
        return;

    tty = get_current_tty();
    if (tty) {
        struct pid *tty_pgrp = get_pid(tty->pgrp);
        if (on_exit) {
            if (tty->driver->type != TTY_DRIVER_TYPE_PTY)
                tty_vhangup(tty);
        }
        tty_kref_put(tty);
        if (tty_pgrp) {
            kill_pgrp(tty_pgrp, SIGHUP, on_exit);
            if (!on_exit)
                kill_pgrp(tty_pgrp, SIGCONT, on_exit);
            put_pid(tty_pgrp);
        }
    } else if (on_exit) {
        struct pid *old_pgrp;
        spin_lock_irq(&current->sighand->siglock);
        old_pgrp = current->signal->tty_old_pgrp;
        current->signal->tty_old_pgrp = NULL;
        spin_unlock_irq(&current->sighand->siglock);
        if (old_pgrp) {
            kill_pgrp(old_pgrp, SIGHUP, on_exit);
            kill_pgrp(old_pgrp, SIGCONT, on_exit);
            put_pid(old_pgrp);
        }
        return;
    }

    spin_lock_irq(&current->sighand->siglock);
    put_pid(current->signal->tty_old_pgrp);
    current->signal->tty_old_pgrp = NULL;
    spin_unlock_irq(&current->sighand->siglock);

    tty = get_current_tty();
    if (tty) {
        unsigned long flags;
        spin_lock_irqsave(&tty->ctrl_lock, flags);
        put_pid(tty->session);
        put_pid(tty->pgrp);
        tty->session = NULL;
        tty->pgrp = NULL;
        spin_unlock_irqrestore(&tty->ctrl_lock, flags);
        tty_kref_put(tty);
    } else {
#ifdef TTY_DEBUG_HANGUP
        printk(KERN_DEBUG "error attempted to write to tty [0x%p]"
               " = NULL", tty);
#endif
    }

    /* Now clear signal->tty under the lock */
    read_lock(&tasklist_lock);
    session_clear_tty(task_session(current));
    read_unlock(&tasklist_lock);
}

void no_tty(void)
{
    /* FIXME: Review locking here. The tty_lock never covered any race
       between a new association and proc_clear_tty but possible we need
       to protect against this anyway */
    struct task_struct *tsk = current;
    disassociate_ctty(0);
    proc_clear_tty(tsk);
}


void stop_tty(struct tty_struct *tty)
{
    unsigned long flags;
    spin_lock_irqsave(&tty->ctrl_lock, flags);
    if (tty->stopped) {
        spin_unlock_irqrestore(&tty->ctrl_lock, flags);
        return;
    }
    tty->stopped = 1;
    if (tty->link && tty->link->packet) {
        tty->ctrl_status &= ~TIOCPKT_START;
        tty->ctrl_status |= TIOCPKT_STOP;
        wake_up_interruptible_poll(&tty->link->read_wait, POLLIN);
    }
    spin_unlock_irqrestore(&tty->ctrl_lock, flags);
    if (tty->ops->stop)
        (tty->ops->stop)(tty);
}

EXPORT_SYMBOL(stop_tty);

void start_tty(struct tty_struct *tty)
{
    unsigned long flags;
    spin_lock_irqsave(&tty->ctrl_lock, flags);
    if (!tty->stopped || tty->flow_stopped) {
        spin_unlock_irqrestore(&tty->ctrl_lock, flags);
        return;
    }
    tty->stopped = 0;
    if (tty->link && tty->link->packet) {
        tty->ctrl_status &= ~TIOCPKT_STOP;
        tty->ctrl_status |= TIOCPKT_START;
        wake_up_interruptible_poll(&tty->link->read_wait, POLLIN);
    }
    spin_unlock_irqrestore(&tty->ctrl_lock, flags);
    if (tty->ops->start)
        (tty->ops->start)(tty);
    /* If we have a running line discipline it may need kicking */
    tty_wakeup(tty);
}

EXPORT_SYMBOL(start_tty);

static ssize_t tty_read(struct file *file, char __user *buf, size_t count,
            loff_t *ppos)
{
    int i;
    struct inode *inode = file->f_path.dentry->d_inode;
    struct tty_struct *tty = file_tty(file);
    struct tty_ldisc *ld;

    if (tty_paranoia_check(tty, inode, "tty_read"))
        return -EIO;
    if (!tty || (test_bit(TTY_IO_ERROR, &tty->flags)))
        return -EIO;

    /* We want to wait for the line discipline to sort out in this
       situation */
    ld = tty_ldisc_ref_wait(tty);
    if (ld->ops->read)
        i = (ld->ops->read)(tty, file, buf, count);
    else
        i = -EIO;
    tty_ldisc_deref(ld);
    if (i > 0)
        inode->i_atime = current_fs_time(inode->i_sb);
    return i;
}

void tty_write_unlock(struct tty_struct *tty)
    __releases(&tty->atomic_write_lock)
{
    mutex_unlock(&tty->atomic_write_lock);
    wake_up_interruptible_poll(&tty->write_wait, POLLOUT);
}

int tty_write_lock(struct tty_struct *tty, int ndelay)
    __acquires(&tty->atomic_write_lock)
{
    if (!mutex_trylock(&tty->atomic_write_lock)) {
        if (ndelay)
            return -EAGAIN;
        if (mutex_lock_interruptible(&tty->atomic_write_lock))
            return -ERESTARTSYS;
    }
    return 0;
}

/*
 * Split writes up in sane blocksizes to avoid
 * denial-of-service type attacks
 */
static inline ssize_t do_tty_write(
    ssize_t (*write)(struct tty_struct *, struct file *, const unsigned char *, size_t),
    struct tty_struct *tty,
    struct file *file,
    const char __user *buf,
    size_t count)
{
    ssize_t ret, written = 0;
    unsigned int chunk;

    ret = tty_write_lock(tty, file->f_flags & O_NDELAY);
    if (ret < 0)
        return ret;

    /*
     * We chunk up writes into a temporary buffer. This
     * simplifies low-level drivers immensely, since they
     * don't have locking issues and user mode accesses.
     *
     * But if TTY_NO_WRITE_SPLIT is set, we should use a
     * big chunk-size..
     *
     * The default chunk-size is 2kB, because the NTTY
     * layer has problems with bigger chunks. It will
     * claim to be able to handle more characters than
     * it actually does.
     *
     * FIXME: This can probably go away now except that 64K chunks
     * are too likely to fail unless switched to vmalloc...
     */
    chunk = 2048;
    if (test_bit(TTY_NO_WRITE_SPLIT, &tty->flags))
        chunk = 65536;
    if (count < chunk)
        chunk = count;

    /* write_buf/write_cnt is protected by the atomic_write_lock mutex */
    if (tty->write_cnt < chunk) {
        unsigned char *buf_chunk;

        if (chunk < 1024)
            chunk = 1024;

        buf_chunk = kmalloc(chunk, GFP_KERNEL);
        if (!buf_chunk) {
            ret = -ENOMEM;
            goto out;
        }
        kfree(tty->write_buf);
        tty->write_cnt = chunk;
        tty->write_buf = buf_chunk;
    }

    /* Do the write .. */
    for (;;) {
        size_t size = count;
        if (size > chunk)
            size = chunk;
        ret = -EFAULT;
        if (copy_from_user(tty->write_buf, buf, size))
            break;
        ret = write(tty, file, tty->write_buf, size);
        if (ret <= 0)
            break;
        written += ret;
        buf += ret;
        count -= ret;
        if (!count)
            break;
        ret = -ERESTARTSYS;
        if (signal_pending(current))
            break;
        cond_resched();
    }
    if (written) {
        struct inode *inode = file->f_path.dentry->d_inode;
        inode->i_mtime = current_fs_time(inode->i_sb);
        ret = written;
    }
out:
    tty_write_unlock(tty);
    return ret;
}

void tty_write_message(struct tty_struct *tty, char *msg)
{
    if (tty) {
        mutex_lock(&tty->atomic_write_lock);
        tty_lock(tty);
        if (tty->ops->write && !test_bit(TTY_CLOSING, &tty->flags)) {
            tty_unlock(tty);
            tty->ops->write(tty, msg, strlen(msg));
        } else
            tty_unlock(tty);
        tty_write_unlock(tty);
    }
    return;
}


static ssize_t tty_write(struct file *file, const char __user *buf,
                        size_t count, loff_t *ppos)
{
    struct inode *inode = file->f_path.dentry->d_inode;
    struct tty_struct *tty = file_tty(file);
    struct tty_ldisc *ld;
    ssize_t ret;

    if (tty_paranoia_check(tty, inode, "tty_write"))
        return -EIO;
    if (!tty || !tty->ops->write ||
        (test_bit(TTY_IO_ERROR, &tty->flags)))
            return -EIO;
    /* Short term debug to catch buggy drivers */
    if (tty->ops->write_room == NULL)
        printk(KERN_ERR "tty driver %s lacks a write_room method.\n",
            tty->driver->name);
    ld = tty_ldisc_ref_wait(tty);
    if (!ld->ops->write)
        ret = -EIO;
    else
        ret = do_tty_write(ld->ops->write, tty, file, buf, count);
    tty_ldisc_deref(ld);
    return ret;
}

ssize_t redirected_tty_write(struct file *file, const char __user *buf,
                        size_t count, loff_t *ppos)
{
    struct file *p = NULL;

    spin_lock(&redirect_lock);
    if (redirect)
        p = get_file(redirect);
    spin_unlock(&redirect_lock);

    if (p) {
        ssize_t res;
        res = vfs_write(p, buf, count, &p->f_pos);
        fput(p);
        return res;
    }
    return tty_write(file, buf, count, ppos);
}

static char ptychar[] = "pqrstuvwxyzabcde";

static void pty_line_name(struct tty_driver *driver, int index, char *p)
{
    int i = index + driver->name_base;
    /* ->name is initialized to "ttyp", but "tty" is expected */
    sprintf(p, "%s%c%x",
        driver->subtype == PTY_TYPE_SLAVE ? "tty" : driver->name,
        ptychar[i >> 4 & 0xf], i & 0xf);
}

static void tty_line_name(struct tty_driver *driver, int index, char *p)
{
    if (driver->flags & TTY_DRIVER_UNNUMBERED_NODE)
        strcpy(p, driver->name);
    else
        sprintf(p, "%s%d", driver->name, index + driver->name_base);
}

static struct tty_struct *tty_driver_lookup_tty(struct tty_driver *driver,
        struct inode *inode, int idx)
{
    if (driver->ops->lookup)
        return driver->ops->lookup(driver, inode, idx);

    return driver->ttys[idx];
}

int tty_init_termios(struct tty_struct *tty)
{
    struct ktermios *tp;
    int idx = tty->index;

    if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS)
        tty->termios = tty->driver->init_termios;
    else {
        /* Check for lazy saved data */
        tp = tty->driver->termios[idx];
        if (tp != NULL)
            tty->termios = *tp;
        else
            tty->termios = tty->driver->init_termios;
    }
    /* Compatibility until drivers always set this */
    tty->termios.c_ispeed = tty_termios_input_baud_rate(&tty->termios);
    tty->termios.c_ospeed = tty_termios_baud_rate(&tty->termios);
    return 0;
}
EXPORT_SYMBOL_GPL(tty_init_termios);

int tty_standard_install(struct tty_driver *driver, struct tty_struct *tty)
{
    int ret = tty_init_termios(tty);
    if (ret)
        return ret;

    tty_driver_kref_get(driver);
    tty->count++;
    driver->ttys[tty->index] = tty;
    return 0;
}
EXPORT_SYMBOL_GPL(tty_standard_install);

static int tty_driver_install_tty(struct tty_driver *driver,
                        struct tty_struct *tty)
{
    return driver->ops->install ? driver->ops->install(driver, tty) :
        tty_standard_install(driver, tty);
}

void tty_driver_remove_tty(struct tty_driver *driver, struct tty_struct *tty)
{
    if (driver->ops->remove)
        driver->ops->remove(driver, tty);
    else
        driver->ttys[tty->index] = NULL;
}

/*
 *  tty_reopen()    - fast re-open of an open tty
 *  @tty    - the tty to open
 *
 *  Return 0 on success, -errno on error.
 *
 *  Locking: tty_mutex must be held from the time the tty was found
 *       till this open completes.
 */
static int tty_reopen(struct tty_struct *tty)
{
    struct tty_driver *driver = tty->driver;

    if (test_bit(TTY_CLOSING, &tty->flags) ||
            test_bit(TTY_HUPPING, &tty->flags) ||
            test_bit(TTY_LDISC_CHANGING, &tty->flags))
        return -EIO;

    if (driver->type == TTY_DRIVER_TYPE_PTY &&
        driver->subtype == PTY_TYPE_MASTER) {
        /*
         * special case for PTY masters: only one open permitted,
         * and the slave side open count is incremented as well.
         */
        if (tty->count)
            return -EIO;

        tty->link->count++;
    }
    tty->count++;

    mutex_lock(&tty->ldisc_mutex);
    WARN_ON(!test_bit(TTY_LDISC, &tty->flags));
    mutex_unlock(&tty->ldisc_mutex);

    return 0;
}

struct tty_struct *tty_init_dev(struct tty_driver *driver, int idx)
{
    struct tty_struct *tty;
    int retval;

    /*
     * First time open is complex, especially for PTY devices.
     * This code guarantees that either everything succeeds and the
     * TTY is ready for operation, or else the table slots are vacated
     * and the allocated memory released.  (Except that the termios
     * and locked termios may be retained.)
     */

    if (!try_module_get(driver->owner))
        return ERR_PTR(-ENODEV);

    tty = alloc_tty_struct();
    if (!tty) {
        retval = -ENOMEM;
        goto err_module_put;
    }
    initialize_tty_struct(tty, driver, idx);

    tty_lock(tty);
    retval = tty_driver_install_tty(driver, tty);
    if (retval < 0)
        goto err_deinit_tty;

    if (!tty->port)
        tty->port = driver->ports[idx];

    WARN_RATELIMIT(!tty->port,
            "%s: %s driver does not set tty->port. This will crash the kernel later. Fix the driver!\n",
            __func__, tty->driver->name);

    /*
     * Structures all installed ... call the ldisc open routines.
     * If we fail here just call release_tty to clean up.  No need
     * to decrement the use counts, as release_tty doesn't care.
     */
    retval = tty_ldisc_setup(tty, tty->link);
    if (retval)
        goto err_release_tty;
    /* Return the tty locked so that it cannot vanish under the caller */
    return tty;

err_deinit_tty:
    tty_unlock(tty);
    deinitialize_tty_struct(tty);
    free_tty_struct(tty);
err_module_put:
    module_put(driver->owner);
    return ERR_PTR(retval);

    /* call the tty release_tty routine to clean out this slot */
err_release_tty:
    tty_unlock(tty);
    printk_ratelimited(KERN_INFO "tty_init_dev: ldisc open failed, "
                 "clearing slot %d\n", idx);
    release_tty(tty, idx);
    return ERR_PTR(retval);
}

void tty_free_termios(struct tty_struct *tty)
{
    struct ktermios *tp;
    int idx = tty->index;

    /* If the port is going to reset then it has no termios to save */
    if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS)
        return;

    /* Stash the termios data */
    tp = tty->driver->termios[idx];
    if (tp == NULL) {
        tp = kmalloc(sizeof(struct ktermios), GFP_KERNEL);
        if (tp == NULL) {
            pr_warn("tty: no memory to save termios state.\n");
            return;
        }
        tty->driver->termios[idx] = tp;
    }
    *tp = tty->termios;
}
EXPORT_SYMBOL(tty_free_termios);


static void release_one_tty(struct work_struct *work)
{
    struct tty_struct *tty =
        container_of(work, struct tty_struct, hangup_work);
    struct tty_driver *driver = tty->driver;

    if (tty->ops->cleanup)
        tty->ops->cleanup(tty);

    tty->magic = 0;
    tty_driver_kref_put(driver);
    module_put(driver->owner);

    spin_lock(&tty_files_lock);
    list_del_init(&tty->tty_files);
    spin_unlock(&tty_files_lock);

    put_pid(tty->pgrp);
    put_pid(tty->session);
    free_tty_struct(tty);
}

static void queue_release_one_tty(struct kref *kref)
{
    struct tty_struct *tty = container_of(kref, struct tty_struct, kref);

    /* The hangup queue is now free so we can reuse it rather than
       waste a chunk of memory for each port */
    INIT_WORK(&tty->hangup_work, release_one_tty);
    schedule_work(&tty->hangup_work);
}

void tty_kref_put(struct tty_struct *tty)
{
    if (tty)
        kref_put(&tty->kref, queue_release_one_tty);
}
EXPORT_SYMBOL(tty_kref_put);

static void release_tty(struct tty_struct *tty, int idx)
{
    /* This should always be true but check for the moment */
    WARN_ON(tty->index != idx);
    WARN_ON(!mutex_is_locked(&tty_mutex));
    if (tty->ops->shutdown)
        tty->ops->shutdown(tty);
    tty_free_termios(tty);
    tty_driver_remove_tty(tty->driver, tty);

    if (tty->link)
        tty_kref_put(tty->link);
    tty_kref_put(tty);
}

static int tty_release_checks(struct tty_struct *tty, struct tty_struct *o_tty,
        int idx)
{
#ifdef TTY_PARANOIA_CHECK
    if (idx < 0 || idx >= tty->driver->num) {
        printk(KERN_DEBUG "%s: bad idx when trying to free (%s)\n",
                __func__, tty->name);
        return -1;
    }

    /* not much to check for devpts */
    if (tty->driver->flags & TTY_DRIVER_DEVPTS_MEM)
        return 0;

    if (tty != tty->driver->ttys[idx]) {
        printk(KERN_DEBUG "%s: driver.table[%d] not tty for (%s)\n",
                __func__, idx, tty->name);
        return -1;
    }
    if (tty->driver->other) {
        if (o_tty != tty->driver->other->ttys[idx]) {
            printk(KERN_DEBUG "%s: other->table[%d] not o_tty for (%s)\n",
                    __func__, idx, tty->name);
            return -1;
        }
        if (o_tty->link != tty) {
            printk(KERN_DEBUG "%s: bad pty pointers\n", __func__);
            return -1;
        }
    }
#endif
    return 0;
}

int tty_release(struct inode *inode, struct file *filp)
{
    struct tty_struct *tty = file_tty(filp);
    struct tty_struct *o_tty;
    int pty_master, tty_closing, o_tty_closing, do_sleep;
    int devpts;
    int idx;
    char    buf[64];

    if (tty_paranoia_check(tty, inode, __func__))
        return 0;

    tty_lock(tty);
    check_tty_count(tty, __func__);

    __tty_fasync(-1, filp, 0);

    idx = tty->index;
    pty_master = (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
              tty->driver->subtype == PTY_TYPE_MASTER);
    devpts = (tty->driver->flags & TTY_DRIVER_DEVPTS_MEM) != 0;
    /* Review: parallel close */
    o_tty = tty->link;

    if (tty_release_checks(tty, o_tty, idx)) {
        tty_unlock(tty);
        return 0;
    }

#ifdef TTY_DEBUG_HANGUP
    printk(KERN_DEBUG "%s: %s (tty count=%d)...\n", __func__,
            tty_name(tty, buf), tty->count);
#endif

    if (tty->ops->close)
        tty->ops->close(tty, filp);

    tty_unlock(tty);
    /*
     * Sanity check: if tty->count is going to zero, there shouldn't be
     * any waiters on tty->read_wait or tty->write_wait.  We test the
     * wait queues and kick everyone out _before_ actually starting to
     * close.  This ensures that we won't block while releasing the tty
     * structure.
     *
     * The test for the o_tty closing is necessary, since the master and
     * slave sides may close in any order.  If the slave side closes out
     * first, its count will be one, since the master side holds an open.
     * Thus this test wouldn't be triggered at the time the slave closes,
     * so we do it now.
     *
     * Note that it's possible for the tty to be opened again while we're
     * flushing out waiters.  By recalculating the closing flags before
     * each iteration we avoid any problems.
     */
    while (1) {
        /* Guard against races with tty->count changes elsewhere and
           opens on /dev/tty */

        mutex_lock(&tty_mutex);
        tty_lock_pair(tty, o_tty);
        tty_closing = tty->count <= 1;
        o_tty_closing = o_tty &&
            (o_tty->count <= (pty_master ? 1 : 0));
        do_sleep = 0;

        if (tty_closing) {
            if (waitqueue_active(&tty->read_wait)) {
                wake_up_poll(&tty->read_wait, POLLIN);
                do_sleep++;
            }
            if (waitqueue_active(&tty->write_wait)) {
                wake_up_poll(&tty->write_wait, POLLOUT);
                do_sleep++;
            }
        }
        if (o_tty_closing) {
            if (waitqueue_active(&o_tty->read_wait)) {
                wake_up_poll(&o_tty->read_wait, POLLIN);
                do_sleep++;
            }
            if (waitqueue_active(&o_tty->write_wait)) {
                wake_up_poll(&o_tty->write_wait, POLLOUT);
                do_sleep++;
            }
        }
        if (!do_sleep)
            break;

        printk(KERN_WARNING "%s: %s: read/write wait queue active!\n",
                __func__, tty_name(tty, buf));
        tty_unlock_pair(tty, o_tty);
        mutex_unlock(&tty_mutex);
        schedule();
    }

    /*
     * The closing flags are now consistent with the open counts on
     * both sides, and we've completed the last operation that could
     * block, so it's safe to proceed with closing.
     *
     * We must *not* drop the tty_mutex until we ensure that a further
     * entry into tty_open can not pick up this tty.
     */
    if (pty_master) {
        if (--o_tty->count < 0) {
            printk(KERN_WARNING "%s: bad pty slave count (%d) for %s\n",
                __func__, o_tty->count, tty_name(o_tty, buf));
            o_tty->count = 0;
        }
    }
    if (--tty->count < 0) {
        printk(KERN_WARNING "%s: bad tty->count (%d) for %s\n",
                __func__, tty->count, tty_name(tty, buf));
        tty->count = 0;
    }

    /*
     * We've decremented tty->count, so we need to remove this file
     * descriptor off the tty->tty_files list; this serves two
     * purposes:
     *  - check_tty_count sees the correct number of file descriptors
     *    associated with this tty.
     *  - do_tty_hangup no longer sees this file descriptor as
     *    something that needs to be handled for hangups.
     */
    tty_del_file(filp);

    /*
     * Perform some housekeeping before deciding whether to return.
     *
     * Set the TTY_CLOSING flag if this was the last open.  In the
     * case of a pty we may have to wait around for the other side
     * to close, and TTY_CLOSING makes sure we can't be reopened.
     */
    if (tty_closing)
        set_bit(TTY_CLOSING, &tty->flags);
    if (o_tty_closing)
        set_bit(TTY_CLOSING, &o_tty->flags);

    /*
     * If _either_ side is closing, make sure there aren't any
     * processes that still think tty or o_tty is their controlling
     * tty.
     */
    if (tty_closing || o_tty_closing) {
        read_lock(&tasklist_lock);
        session_clear_tty(tty->session);
        if (o_tty)
            session_clear_tty(o_tty->session);
        read_unlock(&tasklist_lock);
    }

    mutex_unlock(&tty_mutex);
    tty_unlock_pair(tty, o_tty);
    /* At this point the TTY_CLOSING flag should ensure a dead tty
       cannot be re-opened by a racing opener */

    /* check whether both sides are closing ... */
    if (!tty_closing || (o_tty && !o_tty_closing))
        return 0;

#ifdef TTY_DEBUG_HANGUP
    printk(KERN_DEBUG "%s: freeing tty structure...\n", __func__);
#endif
    /*
     * Ask the line discipline code to release its structures
     */
    tty_ldisc_release(tty, o_tty);
    /*
     * The release_tty function takes care of the details of clearing
     * the slots and preserving the termios structure. The tty_unlock_pair
     * should be safe as we keep a kref while the tty is locked (so the
     * unlock never unlocks a freed tty).
     */
    mutex_lock(&tty_mutex);
    release_tty(tty, idx);
    mutex_unlock(&tty_mutex);

    /* Make this pty number available for reallocation */
    if (devpts)
        devpts_kill_index(inode, idx);
    return 0;
}

static struct tty_struct *tty_open_current_tty(dev_t device, struct file *filp)
{
    struct tty_struct *tty;

    if (device != MKDEV(TTYAUX_MAJOR, 0))
        return NULL;

    tty = get_current_tty();
    if (!tty)
        return ERR_PTR(-ENXIO);

    filp->f_flags |= O_NONBLOCK; /* Don't let /dev/tty block */
    /* noctty = 1; */
    tty_kref_put(tty);
    /* FIXME: we put a reference and return a TTY! */
    /* This is only safe because the caller holds tty_mutex */
    return tty;
}

static struct tty_driver *tty_lookup_driver(dev_t device, struct file *filp,
        int *noctty, int *index)
{
    struct tty_driver *driver;

    switch (device) {
#ifdef CONFIG_VT
    case MKDEV(TTY_MAJOR, 0): {
        extern struct tty_driver *console_driver;
        driver = tty_driver_kref_get(console_driver);
        *index = fg_console;
        *noctty = 1;
        break;
    }
#endif
    case MKDEV(TTYAUX_MAJOR, 1): {
        struct tty_driver *console_driver = console_device(index);
        if (console_driver) {
            driver = tty_driver_kref_get(console_driver);
            if (driver) {
                /* Don't let /dev/console block */
                filp->f_flags |= O_NONBLOCK;
                *noctty = 1;
                break;
            }
        }
        return ERR_PTR(-ENODEV);
    }
    default:
        driver = get_tty_driver(device, index);
        if (!driver)
            return ERR_PTR(-ENODEV);
        break;
    }
    return driver;
}

static int tty_open(struct inode *inode, struct file *filp)
{
    struct tty_struct *tty;
    int noctty, retval;
    struct tty_driver *driver = NULL;
    int index;
    dev_t device = inode->i_rdev;
    unsigned saved_flags = filp->f_flags;

    nonseekable_open(inode, filp);

retry_open:
    retval = tty_alloc_file(filp);
    if (retval)
        return -ENOMEM;

    noctty = filp->f_flags & O_NOCTTY;
    index  = -1;
    retval = 0;

    mutex_lock(&tty_mutex);
    /* This is protected by the tty_mutex */
    tty = tty_open_current_tty(device, filp);
    if (IS_ERR(tty)) {
        retval = PTR_ERR(tty);
        goto err_unlock;
    } else if (!tty) {
        driver = tty_lookup_driver(device, filp, &noctty, &index);
        if (IS_ERR(driver)) {
            retval = PTR_ERR(driver);
            goto err_unlock;
        }

        /* check whether we're reopening an existing tty */
        tty = tty_driver_lookup_tty(driver, inode, index);
        if (IS_ERR(tty)) {
            retval = PTR_ERR(tty);
            goto err_unlock;
        }
    }

    if (tty) {
        tty_lock(tty);
        retval = tty_reopen(tty);
        if (retval < 0) {
            tty_unlock(tty);
            tty = ERR_PTR(retval);
        }
    } else  /* Returns with the tty_lock held for now */
        tty = tty_init_dev(driver, index);

    mutex_unlock(&tty_mutex);
    if (driver)
        tty_driver_kref_put(driver);
    if (IS_ERR(tty)) {
        retval = PTR_ERR(tty);
        goto err_file;
    }

    tty_add_file(tty, filp);

    check_tty_count(tty, __func__);
    if (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
        tty->driver->subtype == PTY_TYPE_MASTER)
        noctty = 1;
#ifdef TTY_DEBUG_HANGUP
    printk(KERN_DEBUG "%s: opening %s...\n", __func__, tty->name);
#endif
    if (tty->ops->open)
        retval = tty->ops->open(tty, filp);
    else
        retval = -ENODEV;
    filp->f_flags = saved_flags;

    if (!retval && test_bit(TTY_EXCLUSIVE, &tty->flags) &&
                        !capable(CAP_SYS_ADMIN))
        retval = -EBUSY;

    if (retval) {
#ifdef TTY_DEBUG_HANGUP
        printk(KERN_DEBUG "%s: error %d in opening %s...\n", __func__,
                retval, tty->name);
#endif
        tty_unlock(tty); /* need to call tty_release without BTM */
        tty_release(inode, filp);
        if (retval != -ERESTARTSYS)
            return retval;

        if (signal_pending(current))
            return retval;

        schedule();
        /*
         * Need to reset f_op in case a hangup happened.
         */
        if (filp->f_op == &hung_up_tty_fops)
            filp->f_op = &tty_fops;
        goto retry_open;
    }
    tty_unlock(tty);


    mutex_lock(&tty_mutex);
    tty_lock(tty);
    spin_lock_irq(&current->sighand->siglock);
    if (!noctty &&
        current->signal->leader &&
        !current->signal->tty &&
        tty->session == NULL)
        __proc_set_tty(current, tty);
    spin_unlock_irq(&current->sighand->siglock);
    tty_unlock(tty);
    mutex_unlock(&tty_mutex);
    return 0;
err_unlock:
    mutex_unlock(&tty_mutex);
    /* after locks to avoid deadlock */
    if (!IS_ERR_OR_NULL(driver))
        tty_driver_kref_put(driver);
err_file:
    tty_free_file(filp);
    return retval;
}



static unsigned int tty_poll(struct file *filp, poll_table *wait)
{
    struct tty_struct *tty = file_tty(filp);
    struct tty_ldisc *ld;
    int ret = 0;

    if (tty_paranoia_check(tty, filp->f_path.dentry->d_inode, "tty_poll"))
        return 0;

    ld = tty_ldisc_ref_wait(tty);
    if (ld->ops->poll)
        ret = (ld->ops->poll)(tty, filp, wait);
    tty_ldisc_deref(ld);
    return ret;
}

static int __tty_fasync(int fd, struct file *filp, int on)
{
    struct tty_struct *tty = file_tty(filp);
    unsigned long flags;
    int retval = 0;

    if (tty_paranoia_check(tty, filp->f_path.dentry->d_inode, "tty_fasync"))
        goto out;

    retval = fasync_helper(fd, filp, on, &tty->fasync);
    if (retval <= 0)
        goto out;

    if (on) {
        enum pid_type type;
        struct pid *pid;
        if (!waitqueue_active(&tty->read_wait))
            tty->minimum_to_wake = 1;
        spin_lock_irqsave(&tty->ctrl_lock, flags);
        if (tty->pgrp) {
            pid = tty->pgrp;
            type = PIDTYPE_PGID;
        } else {
            pid = task_pid(current);
            type = PIDTYPE_PID;
        }
        get_pid(pid);
        spin_unlock_irqrestore(&tty->ctrl_lock, flags);
        retval = __f_setown(filp, pid, type, 0);
        put_pid(pid);
        if (retval)
            goto out;
    } else {
        if (!tty->fasync && !waitqueue_active(&tty->read_wait))
            tty->minimum_to_wake = N_TTY_BUF_SIZE;
    }
    retval = 0;
out:
    return retval;
}

static int tty_fasync(int fd, struct file *filp, int on)
{
    struct tty_struct *tty = file_tty(filp);
    int retval;

    tty_lock(tty);
    retval = __tty_fasync(fd, filp, on);
    tty_unlock(tty);

    return retval;
}

static int tiocsti(struct tty_struct *tty, char __user *p)
{
    char ch, mbz = 0;
    struct tty_ldisc *ld;

    if ((current->signal->tty != tty) && !capable(CAP_SYS_ADMIN))
        return -EPERM;
    if (get_user(ch, p))
        return -EFAULT;
    tty_audit_tiocsti(tty, ch);
    ld = tty_ldisc_ref_wait(tty);
    ld->ops->receive_buf(tty, &ch, &mbz, 1);
    tty_ldisc_deref(ld);
    return 0;
}

static int tiocgwinsz(struct tty_struct *tty, struct winsize __user *arg)
{
    int err;

    mutex_lock(&tty->termios_mutex);
    err = copy_to_user(arg, &tty->winsize, sizeof(*arg));
    mutex_unlock(&tty->termios_mutex);

    return err ? -EFAULT: 0;
}

int tty_do_resize(struct tty_struct *tty, struct winsize *ws)
{
    struct pid *pgrp;
    unsigned long flags;

    /* Lock the tty */
    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 */
    spin_lock_irqsave(&tty->ctrl_lock, flags);
    pgrp = get_pid(tty->pgrp);
    spin_unlock_irqrestore(&tty->ctrl_lock, flags);

    if (pgrp)
        kill_pgrp(pgrp, SIGWINCH, 1);
    put_pid(pgrp);

    tty->winsize = *ws;
done:
    mutex_unlock(&tty->termios_mutex);
    return 0;
}

static int tiocswinsz(struct tty_struct *tty, struct winsize __user *arg)
{
    struct winsize tmp_ws;
    if (copy_from_user(&tmp_ws, arg, sizeof(*arg)))
        return -EFAULT;

    if (tty->ops->resize)
        return tty->ops->resize(tty, &tmp_ws);
    else
        return tty_do_resize(tty, &tmp_ws);
}

static int tioccons(struct file *file)
{
    if (!capable(CAP_SYS_ADMIN))
        return -EPERM;
    if (file->f_op->write == redirected_tty_write) {
        struct file *f;
        spin_lock(&redirect_lock);
        f = redirect;
        redirect = NULL;
        spin_unlock(&redirect_lock);
        if (f)
            fput(f);
        return 0;
    }
    spin_lock(&redirect_lock);
    if (redirect) {
        spin_unlock(&redirect_lock);
        return -EBUSY;
    }
    redirect = get_file(file);
    spin_unlock(&redirect_lock);
    return 0;
}

static int fionbio(struct file *file, int __user *p)
{
    int nonblock;

    if (get_user(nonblock, p))
        return -EFAULT;

    spin_lock(&file->f_lock);
    if (nonblock)
        file->f_flags |= O_NONBLOCK;
    else
        file->f_flags &= ~O_NONBLOCK;
    spin_unlock(&file->f_lock);
    return 0;
}

static int tiocsctty(struct tty_struct *tty, int arg)
{
    int ret = 0;
    if (current->signal->leader && (task_session(current) == tty->session))
        return ret;

    mutex_lock(&tty_mutex);
    /*
     * The process must be a session leader and
     * not have a controlling tty already.
     */
    if (!current->signal->leader || current->signal->tty) {
        ret = -EPERM;
        goto unlock;
    }

    if (tty->session) {
        /*
         * This tty is already the controlling
         * tty for another session group!
         */
        if (arg == 1 && capable(CAP_SYS_ADMIN)) {
            /*
             * Steal it away
             */
            read_lock(&tasklist_lock);
            session_clear_tty(tty->session);
            read_unlock(&tasklist_lock);
        } else {
            ret = -EPERM;
            goto unlock;
        }
    }
    proc_set_tty(current, tty);
unlock:
    mutex_unlock(&tty_mutex);
    return ret;
}

struct pid *tty_get_pgrp(struct tty_struct *tty)
{
    unsigned long flags;
    struct pid *pgrp;

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

    return pgrp;
}
EXPORT_SYMBOL_GPL(tty_get_pgrp);

static int tiocgpgrp(struct tty_struct *tty, struct tty_struct *real_tty, pid_t __user *p)
{
    struct pid *pid;
    int ret;
    /*
     * (tty == real_tty) is a cheap way of
     * testing if the tty is NOT a master pty.
     */
    if (tty == real_tty && current->signal->tty != real_tty)
        return -ENOTTY;
    pid = tty_get_pgrp(real_tty);
    ret =  put_user(pid_vnr(pid), p);
    put_pid(pid);
    return ret;
}

static int tiocspgrp(struct tty_struct *tty, struct tty_struct *real_tty, pid_t __user *p)
{
    struct pid *pgrp;
    pid_t pgrp_nr;
    int retval = tty_check_change(real_tty);
    unsigned long flags;

    if (retval == -EIO)
        return -ENOTTY;
    if (retval)
        return retval;
    if (!current->signal->tty ||
        (current->signal->tty != real_tty) ||
        (real_tty->session != task_session(current)))
        return -ENOTTY;
    if (get_user(pgrp_nr, p))
        return -EFAULT;
    if (pgrp_nr < 0)
        return -EINVAL;
    rcu_read_lock();
    pgrp = find_vpid(pgrp_nr);
    retval = -ESRCH;
    if (!pgrp)
        goto out_unlock;
    retval = -EPERM;
    if (session_of_pgrp(pgrp) != task_session(current))
        goto out_unlock;
    retval = 0;
    spin_lock_irqsave(&tty->ctrl_lock, flags);
    put_pid(real_tty->pgrp);
    real_tty->pgrp = get_pid(pgrp);
    spin_unlock_irqrestore(&tty->ctrl_lock, flags);
out_unlock:
    rcu_read_unlock();
    return retval;
}

static int tiocgsid(struct tty_struct *tty, struct tty_struct *real_tty, pid_t __user *p)
{
    /*
     * (tty == real_tty) is a cheap way of
     * testing if the tty is NOT a master pty.
    */
    if (tty == real_tty && current->signal->tty != real_tty)
        return -ENOTTY;
    if (!real_tty->session)
        return -ENOTTY;
    return put_user(pid_vnr(real_tty->session), p);
}

static int tiocsetd(struct tty_struct *tty, int __user *p)
{
    int ldisc;
    int ret;

    if (get_user(ldisc, p))
        return -EFAULT;

    ret = tty_set_ldisc(tty, ldisc);

    return ret;
}

static int send_break(struct tty_struct *tty, unsigned int duration)
{
    int retval;

    if (tty->ops->break_ctl == NULL)
        return 0;

    if (tty->driver->flags & TTY_DRIVER_HARDWARE_BREAK)
        retval = tty->ops->break_ctl(tty, duration);
    else {
        /* Do the work ourselves */
        if (tty_write_lock(tty, 0) < 0)
            return -EINTR;
        retval = tty->ops->break_ctl(tty, -1);
        if (retval)
            goto out;
        if (!signal_pending(current))
            msleep_interruptible(duration);
        retval = tty->ops->break_ctl(tty, 0);
out:
        tty_write_unlock(tty);
        if (signal_pending(current))
            retval = -EINTR;
    }
    return retval;
}

static int tty_tiocmget(struct tty_struct *tty, int __user *p)
{
    int retval = -EINVAL;

    if (tty->ops->tiocmget) {
        retval = tty->ops->tiocmget(tty);

        if (retval >= 0)
            retval = put_user(retval, p);
    }
    return retval;
}

static int tty_tiocmset(struct tty_struct *tty, unsigned int cmd,
         unsigned __user *p)
{
    int retval;
    unsigned int set, clear, val;

    if (tty->ops->tiocmset == NULL)
        return -EINVAL;

    retval = get_user(val, p);
    if (retval)
        return retval;
    set = clear = 0;
    switch (cmd) {
    case TIOCMBIS:
        set = val;
        break;
    case TIOCMBIC:
        clear = val;
        break;
    case TIOCMSET:
        set = val;
        clear = ~val;
        break;
    }
    set &= TIOCM_DTR|TIOCM_RTS|TIOCM_OUT1|TIOCM_OUT2|TIOCM_LOOP;
    clear &= TIOCM_DTR|TIOCM_RTS|TIOCM_OUT1|TIOCM_OUT2|TIOCM_LOOP;
    return tty->ops->tiocmset(tty, set, clear);
}

static int tty_tiocgicount(struct tty_struct *tty, void __user *arg)
{
    int retval = -EINVAL;
    struct serial_icounter_struct icount;
    memset(&icount, 0, sizeof(icount));
    if (tty->ops->get_icount)
        retval = tty->ops->get_icount(tty, &icount);
    if (retval != 0)
        return retval;
    if (copy_to_user(arg, &icount, sizeof(icount)))
        return -EFAULT;
    return 0;
}

struct tty_struct *tty_pair_get_tty(struct tty_struct *tty)
{
    if (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
        tty->driver->subtype == PTY_TYPE_MASTER)
        tty = tty->link;
    return tty;
}
EXPORT_SYMBOL(tty_pair_get_tty);

struct tty_struct *tty_pair_get_pty(struct tty_struct *tty)
{
    if (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
        tty->driver->subtype == PTY_TYPE_MASTER)
        return tty;
    return tty->link;
}
EXPORT_SYMBOL(tty_pair_get_pty);

/*
 * Split this up, as gcc can choke on it otherwise..
 */
long tty_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
    struct tty_struct *tty = file_tty(file);
    struct tty_struct *real_tty;
    void __user *p = (void __user *)arg;
    int retval;
    struct tty_ldisc *ld;
    struct inode *inode = file->f_dentry->d_inode;

    if (tty_paranoia_check(tty, inode, "tty_ioctl"))
        return -EINVAL;

    real_tty = tty_pair_get_tty(tty);

    /*
     * Factor out some common prep work
     */
    switch (cmd) {
    case TIOCSETD:
    case TIOCSBRK:
    case TIOCCBRK:
    case TCSBRK:
    case TCSBRKP:
        retval = tty_check_change(tty);
        if (retval)
            return retval;
        if (cmd != TIOCCBRK) {
            tty_wait_until_sent(tty, 0);
            if (signal_pending(current))
                return -EINTR;
        }
        break;
    }

    /*
     *  Now do the stuff.
     */
    switch (cmd) {
    case TIOCSTI:
        return tiocsti(tty, p);
    case TIOCGWINSZ:
        return tiocgwinsz(real_tty, p);
    case TIOCSWINSZ:
        return tiocswinsz(real_tty, p);
    case TIOCCONS:
        return real_tty != tty ? -EINVAL : tioccons(file);
    case FIONBIO:
        return fionbio(file, p);
    case TIOCEXCL:
        set_bit(TTY_EXCLUSIVE, &tty->flags);
        return 0;
    case TIOCNXCL:
        clear_bit(TTY_EXCLUSIVE, &tty->flags);
        return 0;
    case TIOCNOTTY:
        if (current->signal->tty != tty)
            return -ENOTTY;
        no_tty();
        return 0;
    case TIOCSCTTY:
        return tiocsctty(tty, arg);
    case TIOCGPGRP:
        return tiocgpgrp(tty, real_tty, p);
    case TIOCSPGRP:
        return tiocspgrp(tty, real_tty, p);
    case TIOCGSID:
        return tiocgsid(tty, real_tty, p);
    case TIOCGETD:
        return put_user(tty->ldisc->ops->num, (int __user *)p);
    case TIOCSETD:
        return tiocsetd(tty, p);
    case TIOCVHANGUP:
        if (!capable(CAP_SYS_ADMIN))
            return -EPERM;
        tty_vhangup(tty);
        return 0;
    case TIOCGDEV:
    {
        unsigned int ret = new_encode_dev(tty_devnum(real_tty));
        return put_user(ret, (unsigned int __user *)p);
    }
    /*
     * Break handling
     */
    case TIOCSBRK:  /* Turn break on, unconditionally */
        if (tty->ops->break_ctl)
            return tty->ops->break_ctl(tty, -1);
        return 0;
    case TIOCCBRK:  /* Turn break off, unconditionally */
        if (tty->ops->break_ctl)
            return tty->ops->break_ctl(tty, 0);
        return 0;
    case TCSBRK:   /* SVID version: non-zero arg --> no break */
        /* non-zero arg means wait for all output data
         * to be sent (performed above) but don't send break.
         * This is used by the tcdrain() termios function.
         */
        if (!arg)
            return send_break(tty, 250);
        return 0;
    case TCSBRKP:   /* support for POSIX tcsendbreak() */
        return send_break(tty, arg ? arg*100 : 250);

    case TIOCMGET:
        return tty_tiocmget(tty, p);
    case TIOCMSET:
    case TIOCMBIC:
    case TIOCMBIS:
        return tty_tiocmset(tty, cmd, p);
    case TIOCGICOUNT:
        retval = tty_tiocgicount(tty, p);
        /* For the moment allow fall through to the old method */
            if (retval != -EINVAL)
            return retval;
        break;
    case TCFLSH:
        switch (arg) {
        case TCIFLUSH:
        case TCIOFLUSH:
        /* flush tty buffer and allow ldisc to process ioctl */
            tty_buffer_flush(tty);
            break;
        }
        break;
    }
    if (tty->ops->ioctl) {
        retval = (tty->ops->ioctl)(tty, cmd, arg);
        if (retval != -ENOIOCTLCMD)
            return retval;
    }
    ld = tty_ldisc_ref_wait(tty);
    retval = -EINVAL;
    if (ld->ops->ioctl) {
        retval = ld->ops->ioctl(tty, file, cmd, arg);
        if (retval == -ENOIOCTLCMD)
            retval = -ENOTTY;
    }
    tty_ldisc_deref(ld);
    return retval;
}

#ifdef CONFIG_COMPAT
static long tty_compat_ioctl(struct file *file, unsigned int cmd,
                unsigned long arg)
{
    struct inode *inode = file->f_dentry->d_inode;
    struct tty_struct *tty = file_tty(file);
    struct tty_ldisc *ld;
    int retval = -ENOIOCTLCMD;

    if (tty_paranoia_check(tty, inode, "tty_ioctl"))
        return -EINVAL;

    if (tty->ops->compat_ioctl) {
        retval = (tty->ops->compat_ioctl)(tty, cmd, arg);
        if (retval != -ENOIOCTLCMD)
            return retval;
    }

    ld = tty_ldisc_ref_wait(tty);
    if (ld->ops->compat_ioctl)
        retval = ld->ops->compat_ioctl(tty, file, cmd, arg);
    else
        retval = n_tty_compat_ioctl_helper(tty, file, cmd, arg);
    tty_ldisc_deref(ld);

    return retval;
}
#endif

static int this_tty(const void *t, struct file *file, unsigned fd)
{
    if (likely(file->f_op->read != tty_read))
        return 0;
    return file_tty(file) != t ? 0 : fd + 1;
}
    
/*
 * This implements the "Secure Attention Key" ---  the idea is to
 * prevent trojan horses by killing all processes associated with this
 * tty when the user hits the "Secure Attention Key".  Required for
 * super-paranoid applications --- see the Orange Book for more details.
 *
 * This code could be nicer; ideally it should send a HUP, wait a few
 * seconds, then send a INT, and then a KILL signal.  But you then
 * have to coordinate with the init process, since all processes associated
 * with the current tty must be dead before the new getty is allowed
 * to spawn.
 *
 * Now, if it would be correct ;-/ The current code has a nasty hole -
 * it doesn't catch files in flight. We may send the descriptor to ourselves
 * via AF_UNIX socket, close it and later fetch from socket. FIXME.
 *
 * Nasty bug: do_SAK is being called in interrupt context.  This can
 * deadlock.  We punt it up to process context.  AKPM - 16Mar2001
 */
void __do_SAK(struct tty_struct *tty)
{
#ifdef TTY_SOFT_SAK
    tty_hangup(tty);
#else
    struct task_struct *g, *p;
    struct pid *session;
    int     i;

    if (!tty)
        return;
    session = tty->session;

    tty_ldisc_flush(tty);

    tty_driver_flush_buffer(tty);

    read_lock(&tasklist_lock);
    /* Kill the entire session */
    do_each_pid_task(session, PIDTYPE_SID, p) {
        printk(KERN_NOTICE "SAK: killed process %d"
            " (%s): task_session(p)==tty->session\n",
            task_pid_nr(p), p->comm);
        send_sig(SIGKILL, p, 1);
    } while_each_pid_task(session, PIDTYPE_SID, p);
    /* Now kill any processes that happen to have the
     * tty open.
     */
    do_each_thread(g, p) {
        if (p->signal->tty == tty) {
            printk(KERN_NOTICE "SAK: killed process %d"
                " (%s): task_session(p)==tty->session\n",
                task_pid_nr(p), p->comm);
            send_sig(SIGKILL, p, 1);
            continue;
        }
        task_lock(p);
        i = iterate_fd(p->files, 0, this_tty, tty);
        if (i != 0) {
            printk(KERN_NOTICE "SAK: killed process %d"
                " (%s): fd#%d opened to the tty\n",
                    task_pid_nr(p), p->comm, i - 1);
            force_sig(SIGKILL, p);
        }
        task_unlock(p);
    } while_each_thread(g, p);
    read_unlock(&tasklist_lock);
#endif
}

static void do_SAK_work(struct work_struct *work)
{
    struct tty_struct *tty =
        container_of(work, struct tty_struct, SAK_work);
    __do_SAK(tty);
}

/*
 * The tq handling here is a little racy - tty->SAK_work may already be queued.
 * Fortunately we don't need to worry, because if ->SAK_work is already queued,
 * the values which we write to it will be identical to the values which it
 * already has. --akpm
 */
void do_SAK(struct tty_struct *tty)
{
    if (!tty)
        return;
    schedule_work(&tty->SAK_work);
}

EXPORT_SYMBOL(do_SAK);

static int dev_match_devt(struct device *dev, void *data)
{
    dev_t *devt = data;
    return dev->devt == *devt;
}

/* Must put_device() after it's unused! */
static struct device *tty_get_device(struct tty_struct *tty)
{
    dev_t devt = tty_devnum(tty);
    return class_find_device(tty_class, NULL, &devt, dev_match_devt);
}


void initialize_tty_struct(struct tty_struct *tty,
        struct tty_driver *driver, int idx)
{
    memset(tty, 0, sizeof(struct tty_struct));
    kref_init(&tty->kref);
    tty->magic = TTY_MAGIC;
    tty_ldisc_init(tty);
    tty->session = NULL;
    tty->pgrp = NULL;
    tty->overrun_time = jiffies;
    tty_buffer_init(tty);
    mutex_init(&tty->legacy_mutex);
    mutex_init(&tty->termios_mutex);
    mutex_init(&tty->ldisc_mutex);
    init_waitqueue_head(&tty->write_wait);
    init_waitqueue_head(&tty->read_wait);
    INIT_WORK(&tty->hangup_work, do_tty_hangup);
    mutex_init(&tty->atomic_read_lock);
    mutex_init(&tty->atomic_write_lock);
    mutex_init(&tty->output_lock);
    mutex_init(&tty->echo_lock);
    spin_lock_init(&tty->read_lock);
    spin_lock_init(&tty->ctrl_lock);
    INIT_LIST_HEAD(&tty->tty_files);
    INIT_WORK(&tty->SAK_work, do_SAK_work);

    tty->driver = driver;
    tty->ops = driver->ops;
    tty->index = idx;
    tty_line_name(driver, idx, tty->name);
    tty->dev = tty_get_device(tty);
}

void deinitialize_tty_struct(struct tty_struct *tty)
{
    tty_ldisc_deinit(tty);
}

int tty_put_char(struct tty_struct *tty, unsigned char ch)
{
    if (tty->ops->put_char)
        return tty->ops->put_char(tty, ch);
    return tty->ops->write(tty, &ch, 1);
}
EXPORT_SYMBOL_GPL(tty_put_char);

struct class *tty_class;

static int tty_cdev_add(struct tty_driver *driver, dev_t dev,
        unsigned int index, unsigned int count)
{
    /* init here, since reused cdevs cause crashes */
    cdev_init(&driver->cdevs[index], &tty_fops);
    driver->cdevs[index].owner = driver->owner;
    return cdev_add(&driver->cdevs[index], dev, count);
}

struct device *tty_register_device(struct tty_driver *driver, unsigned index,
                   struct device *device)
{
    return tty_register_device_attr(driver, index, device, NULL, NULL);
}
EXPORT_SYMBOL(tty_register_device);

static void tty_device_create_release(struct device *dev)
{
    pr_debug("device: '%s': %s\n", dev_name(dev), __func__);
    kfree(dev);
}

struct device *tty_register_device_attr(struct tty_driver *driver,
                   unsigned index, struct device *device,
                   void *drvdata,
                   const struct attribute_group **attr_grp)
{
    char name[64];
    dev_t devt = MKDEV(driver->major, driver->minor_start) + index;
    struct device *dev = NULL;
    int retval = -ENODEV;
    bool cdev = false;

    if (index >= driver->num) {
        printk(KERN_ERR "Attempt to register invalid tty line number "
               " (%d).\n", index);
        return ERR_PTR(-EINVAL);
    }

    if (driver->type == TTY_DRIVER_TYPE_PTY)
        pty_line_name(driver, index, name);
    else
        tty_line_name(driver, index, name);

    if (!(driver->flags & TTY_DRIVER_DYNAMIC_ALLOC)) {
        retval = tty_cdev_add(driver, devt, index, 1);
        if (retval)
            goto error;
        cdev = true;
    }

    dev = kzalloc(sizeof(*dev), GFP_KERNEL);
    if (!dev) {
        retval = -ENOMEM;
        goto error;
    }

    dev->devt = devt;
    dev->class = tty_class;
    dev->parent = device;
    dev->release = tty_device_create_release;
    dev_set_name(dev, "%s", name);
    dev->groups = attr_grp;
    dev_set_drvdata(dev, drvdata);

    retval = device_register(dev);
    if (retval)
        goto error;

    return dev;

error:
    put_device(dev);
    if (cdev)
        cdev_del(&driver->cdevs[index]);
    return ERR_PTR(retval);
}
EXPORT_SYMBOL_GPL(tty_register_device_attr);

void tty_unregister_device(struct tty_driver *driver, unsigned index)
{
    device_destroy(tty_class,
        MKDEV(driver->major, driver->minor_start) + index);
    if (!(driver->flags & TTY_DRIVER_DYNAMIC_ALLOC))
        cdev_del(&driver->cdevs[index]);
}
EXPORT_SYMBOL(tty_unregister_device);

struct tty_driver *__tty_alloc_driver(unsigned int lines, struct module *owner,
        unsigned long flags)
{
    struct tty_driver *driver;
    unsigned int cdevs = 1;
    int err;

    if (!lines || (flags & TTY_DRIVER_UNNUMBERED_NODE && lines > 1))
        return ERR_PTR(-EINVAL);

    driver = kzalloc(sizeof(struct tty_driver), GFP_KERNEL);
    if (!driver)
        return ERR_PTR(-ENOMEM);

    kref_init(&driver->kref);
    driver->magic = TTY_DRIVER_MAGIC;
    driver->num = lines;
    driver->owner = owner;
    driver->flags = flags;

    if (!(flags & TTY_DRIVER_DEVPTS_MEM)) {
        driver->ttys = kcalloc(lines, sizeof(*driver->ttys),
                GFP_KERNEL);
        driver->termios = kcalloc(lines, sizeof(*driver->termios),
                GFP_KERNEL);
        if (!driver->ttys || !driver->termios) {
            err = -ENOMEM;
            goto err_free_all;
        }
    }

    if (!(flags & TTY_DRIVER_DYNAMIC_ALLOC)) {
        driver->ports = kcalloc(lines, sizeof(*driver->ports),
                GFP_KERNEL);
        if (!driver->ports) {
            err = -ENOMEM;
            goto err_free_all;
        }
        cdevs = lines;
    }

    driver->cdevs = kcalloc(cdevs, sizeof(*driver->cdevs), GFP_KERNEL);
    if (!driver->cdevs) {
        err = -ENOMEM;
        goto err_free_all;
    }

    return driver;
err_free_all:
    kfree(driver->ports);
    kfree(driver->ttys);
    kfree(driver->termios);
    kfree(driver);
    return ERR_PTR(err);
}
EXPORT_SYMBOL(__tty_alloc_driver);

static void destruct_tty_driver(struct kref *kref)
{
    struct tty_driver *driver = container_of(kref, struct tty_driver, kref);
    int i;
    struct ktermios *tp;

    if (driver->flags & TTY_DRIVER_INSTALLED) {
        /*
         * Free the termios and termios_locked structures because
         * we don't want to get memory leaks when modular tty
         * drivers are removed from the kernel.
         */
        for (i = 0; i < driver->num; i++) {
            tp = driver->termios[i];
            if (tp) {
                driver->termios[i] = NULL;
                kfree(tp);
            }
            if (!(driver->flags & TTY_DRIVER_DYNAMIC_DEV))
                tty_unregister_device(driver, i);
        }
        proc_tty_unregister_driver(driver);
        if (driver->flags & TTY_DRIVER_DYNAMIC_ALLOC)
            cdev_del(&driver->cdevs[0]);
    }
    kfree(driver->cdevs);
    kfree(driver->ports);
    kfree(driver->termios);
    kfree(driver->ttys);
    kfree(driver);
}

void tty_driver_kref_put(struct tty_driver *driver)
{
    kref_put(&driver->kref, destruct_tty_driver);
}
EXPORT_SYMBOL(tty_driver_kref_put);

void tty_set_operations(struct tty_driver *driver,
            const struct tty_operations *op)
{
    driver->ops = op;
};
EXPORT_SYMBOL(tty_set_operations);

void put_tty_driver(struct tty_driver *d)
{
    tty_driver_kref_put(d);
}
EXPORT_SYMBOL(put_tty_driver);

/*
 * Called by a tty driver to register itself.
 */
int tty_register_driver(struct tty_driver *driver)
{
    int error;
    int i;
    dev_t dev;
    struct device *d;

    if (!driver->major) {
        error = alloc_chrdev_region(&dev, driver->minor_start,
                        driver->num, driver->name);
        if (!error) {
            driver->major = MAJOR(dev);
            driver->minor_start = MINOR(dev);
        }
    } else {
        dev = MKDEV(driver->major, driver->minor_start);
        error = register_chrdev_region(dev, driver->num, driver->name);
    }
    if (error < 0)
        goto err;

    if (driver->flags & TTY_DRIVER_DYNAMIC_ALLOC) {
        error = tty_cdev_add(driver, dev, 0, driver->num);
        if (error)
            goto err_unreg_char;
    }

    mutex_lock(&tty_mutex);
    list_add(&driver->tty_drivers, &tty_drivers);
    mutex_unlock(&tty_mutex);

    if (!(driver->flags & TTY_DRIVER_DYNAMIC_DEV)) {
        for (i = 0; i < driver->num; i++) {
            d = tty_register_device(driver, i, NULL);
            if (IS_ERR(d)) {
                error = PTR_ERR(d);
                goto err_unreg_devs;
            }
        }
    }
    proc_tty_register_driver(driver);
    driver->flags |= TTY_DRIVER_INSTALLED;
    return 0;

err_unreg_devs:
    for (i--; i >= 0; i--)
        tty_unregister_device(driver, i);

    mutex_lock(&tty_mutex);
    list_del(&driver->tty_drivers);
    mutex_unlock(&tty_mutex);

err_unreg_char:
    unregister_chrdev_region(dev, driver->num);
err:
    return error;
}
EXPORT_SYMBOL(tty_register_driver);

/*
 * Called by a tty driver to unregister itself.
 */
int tty_unregister_driver(struct tty_driver *driver)
{
#if 0
    /* FIXME */
    if (driver->refcount)
        return -EBUSY;
#endif
    unregister_chrdev_region(MKDEV(driver->major, driver->minor_start),
                driver->num);
    mutex_lock(&tty_mutex);
    list_del(&driver->tty_drivers);
    mutex_unlock(&tty_mutex);
    return 0;
}

EXPORT_SYMBOL(tty_unregister_driver);

dev_t tty_devnum(struct tty_struct *tty)
{
    return MKDEV(tty->driver->major, tty->driver->minor_start) + tty->index;
}
EXPORT_SYMBOL(tty_devnum);

void proc_clear_tty(struct task_struct *p)
{
    unsigned long flags;
    struct tty_struct *tty;
    spin_lock_irqsave(&p->sighand->siglock, flags);
    tty = p->signal->tty;
    p->signal->tty = NULL;
    spin_unlock_irqrestore(&p->sighand->siglock, flags);
    tty_kref_put(tty);
}

/* Called under the sighand lock */

static void __proc_set_tty(struct task_struct *tsk, struct tty_struct *tty)
{
    if (tty) {
        unsigned long flags;
        /* We should not have a session or pgrp to put here but.... */
        spin_lock_irqsave(&tty->ctrl_lock, flags);
        put_pid(tty->session);
        put_pid(tty->pgrp);
        tty->pgrp = get_pid(task_pgrp(tsk));
        spin_unlock_irqrestore(&tty->ctrl_lock, flags);
        tty->session = get_pid(task_session(tsk));
        if (tsk->signal->tty) {
            printk(KERN_DEBUG "tty not NULL!!\n");
            tty_kref_put(tsk->signal->tty);
        }
    }
    put_pid(tsk->signal->tty_old_pgrp);
    tsk->signal->tty = tty_kref_get(tty);
    tsk->signal->tty_old_pgrp = NULL;
}

static void proc_set_tty(struct task_struct *tsk, struct tty_struct *tty)
{
    spin_lock_irq(&tsk->sighand->siglock);
    __proc_set_tty(tsk, tty);
    spin_unlock_irq(&tsk->sighand->siglock);
}

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

    spin_lock_irqsave(&current->sighand->siglock, flags);
    tty = tty_kref_get(current->signal->tty);
    spin_unlock_irqrestore(&current->sighand->siglock, flags);
    return tty;
}
EXPORT_SYMBOL_GPL(get_current_tty);

void tty_default_fops(struct file_operations *fops)
{
    *fops = tty_fops;
}

/*
 * Initialize the console device. This is called *early*, so
 * we can't necessarily depend on lots of kernel help here.
 * Just do some early initializations, and do the complex setup
 * later.
 */
void __init console_init(void)
{
    initcall_t *call;

    /* Setup the default TTY line discipline. */
    tty_ldisc_begin();

    /*
     * set up the console device so that later boot sequences can
     * inform about problems etc..
     */
    call = __con_initcall_start;
    while (call < __con_initcall_end) {
        (*call)();
        call++;
    }
}

static char *tty_devnode(struct device *dev, umode_t *mode)
{
    if (!mode)
        return NULL;
    if (dev->devt == MKDEV(TTYAUX_MAJOR, 0) ||
        dev->devt == MKDEV(TTYAUX_MAJOR, 2))
        *mode = 0666;
    return NULL;
}

static int __init tty_class_init(void)
{
    tty_class = class_create(THIS_MODULE, "tty");
    if (IS_ERR(tty_class))
        return PTR_ERR(tty_class);
    tty_class->devnode = tty_devnode;
    return 0;
}

postcore_initcall(tty_class_init);

/* 3/2004 jmc: why do these devices exist? */
static struct cdev tty_cdev, console_cdev;

static ssize_t show_cons_active(struct device *dev,
                struct device_attribute *attr, char *buf)
{
    struct console *cs[16];
    int i = 0;
    struct console *c;
    ssize_t count = 0;

    console_lock();
    for_each_console(c) {
        if (!c->device)
            continue;
        if (!c->write)
            continue;
        if ((c->flags & CON_ENABLED) == 0)
            continue;
        cs[i++] = c;
        if (i >= ARRAY_SIZE(cs))
            break;
    }
    while (i--)
        count += sprintf(buf + count, "%s%d%c",
                 cs[i]->name, cs[i]->index, i ? ' ':'\n');
    console_unlock();

    return count;
}
static DEVICE_ATTR(active, S_IRUGO, show_cons_active, NULL);

static struct device *consdev;

void console_sysfs_notify(void)
{
    if (consdev)
        sysfs_notify(&consdev->kobj, NULL, "active");
}

/*
 * Ok, now we can initialize the rest of the tty devices and can count
 * on memory allocations, interrupts etc..
 */
int __init tty_init(void)
{
    cdev_init(&tty_cdev, &tty_fops);
    if (cdev_add(&tty_cdev, MKDEV(TTYAUX_MAJOR, 0), 1) ||
        register_chrdev_region(MKDEV(TTYAUX_MAJOR, 0), 1, "/dev/tty") < 0)
        panic("Couldn't register /dev/tty driver\n");
    device_create(tty_class, NULL, MKDEV(TTYAUX_MAJOR, 0), NULL, "tty");

    cdev_init(&console_cdev, &console_fops);
    if (cdev_add(&console_cdev, MKDEV(TTYAUX_MAJOR, 1), 1) ||
        register_chrdev_region(MKDEV(TTYAUX_MAJOR, 1), 1, "/dev/console") < 0)
        panic("Couldn't register /dev/console driver\n");
    consdev = device_create(tty_class, NULL, MKDEV(TTYAUX_MAJOR, 1), NULL,
                  "console");
    if (IS_ERR(consdev))
        consdev = NULL;
    else
        WARN_ON(device_create_file(consdev, &dev_attr_active) < 0);

#ifdef CONFIG_VT
    vty_init(&console_fops);
#endif
    return 0;
}