tty: rewrite the ldisc locking

[mirror_ubuntu-zesty-kernel.git] / drivers / char / tty_io.c

/*
 *  linux/drivers/char/tty_io.c
 *
 *  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 <alfie@dcs.warwick.ac.uk>, 27th May 1993.
 *
 * Rewrote canonical mode and added more termios flags.
 *      -- julian@uhunix.uhcc.hawaii.edu (J. Cowley), 13Jan94
 *
 * Reorganized FASYNC support so mouse code can share it.
 *      -- ctm@ardi.com, 9Sep95
 *
 * New TIOCLINUX variants added.
 *      -- mj@k332.feld.cvut.cz, 19-Nov-95
 *
 * Restrict vt switching via ioctl()
 *      -- grif@cs.ucr.edu, 5-Dec-95
 *
 * Move console and virtual terminal code to more appropriate files,
 * implement CONFIG_VT and generalize console device interface.
 *      -- Marko Kohtala <Marko.Kohtala@hut.fi>, March 97
 *
 * Rewrote tty_init_dev and tty_release_dev to eliminate races.
 *      -- Bill Hawes <whawes@star.net>, June 97
 *
 * Added devfs support.
 *      -- C. Scott Ananian <cananian@alumni.princeton.edu>, 13-Jan-1998
 *
 * Added support for a Unix98-style ptmx device.
 *      -- C. Scott Ananian <cananian@alumni.princeton.edu>, 14-Jan-1998
 *
 * Reduced memory usage for older ARM systems
 *      -- Russell King <rmk@arm.linux.org.uk>
 *
 * Move do_SAK() into process context.  Less stack use in devfs functions.
 * alloc_tty_struct() always uses kmalloc()
 *                       -- Andrew Morton <andrewm@uow.edu.eu> 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/smp_lock.h>
#include <linux/device.h>
#include <linux/wait.h>
#include <linux/bitops.h>
#include <linux/delay.h>
#include <linux/seq_file.h>

#include <linux/uaccess.h>
#include <asm/system.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);

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 *);
static int tty_release(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 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);

/**
 *      alloc_tty_struct        -       allocate a tty object
 *
 *      Return a new empty tty structure. The data fields have not
 *      been initialized in any way but has been zeroed
 *
 *      Locking: none
 */

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

/**
 *      free_tty_struct         -       free a disused tty
 *      @tty: tty struct to free
 *
 *      Free the write buffers, tty queue and tty memory itself.
 *
 *      Locking: none. Must be called after tty is definitely unused
 */

void free_tty_struct(struct tty_struct *tty)
{
        kfree(tty->write_buf);
        tty_buffer_free_all(tty);
        kfree(tty);
}

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

/**
 *      tty_name        -       return tty naming
 *      @tty: tty structure
 *      @buf: buffer for output
 *
 *      Convert a tty structure into a name. The name reflects the kernel
 *      naming policy and if udev is in use may not reflect user space
 *
 *      Locking: none
 */

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;

        file_list_lock();
        list_for_each(p, &tty->tty_files) {
                count++;
        }
        file_list_unlock();
        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;
}

/**
 *      get_tty_driver          -       find device of a tty
 *      @dev_t: device identifier
 *      @index: returns the index of the tty
 *
 *      This routine returns a tty driver structure, given a device number
 *      and also passes back the index number.
 *
 *      Locking: caller must hold tty_mutex
 */

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

/**
 *      tty_find_polling_driver -       find device of a polled tty
 *      @name: name string to match
 *      @line: pointer to resulting tty line nr
 *
 *      This routine returns a tty driver structure, given a name
 *      and the condition that the tty driver is capable of polled
 *      operation.
 */
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

/**
 *      tty_check_change        -       check for POSIX terminal changes
 *      @tty: tty to check
 *
 *      If we try to write to, or set the state of, a terminal and we're
 *      not in the foreground, send a SIGTTOU.  If the signal is blocked or
 *      ignored, go ahead and perform the operation.  (POSIX 7.2)
 *
 *      Locking: ctrl_lock
 */

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;

/**
 *      tty_wakeup      -       request more data
 *      @tty: terminal
 *
 *      Internal and external helper for wakeups of tty. This function
 *      informs the line discipline if present that the driver is ready
 *      to receive more output data.
 */

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);

/**
 *      tty_ldisc_flush -       flush line discipline queue
 *      @tty: tty
 *
 *      Flush the line discipline queue (if any) for this tty. If there
 *      is no line discipline active this is a no-op.
 */

void tty_ldisc_flush(struct tty_struct *tty)
{
        struct tty_ldisc *ld = tty_ldisc_ref(tty);
        if (ld) {
                if (ld->ops->flush_buffer)
                        ld->ops->flush_buffer(tty);
                tty_ldisc_deref(ld);
        }
        tty_buffer_flush(tty);
}

EXPORT_SYMBOL_GPL(tty_ldisc_flush);

/**
 *      do_tty_hangup           -       actual handler for hangup events
 *      @work: tty device
 *
 *      This can be called by the "eventd" kernel thread.  That is process
 *      synchronous but doesn't hold any locks, so we need to make sure we
 *      have the appropriate locks for what we're doing.
 *
 *      The hangup event clears any pending redirections onto the hung up
 *      device. It ensures future writes will error and it does the needed
 *      line discipline hangup and signal delivery. The tty object itself
 *      remains intact.
 *
 *      Locking:
 *              BKL
 *                redirect lock for undoing redirection
 *                file list lock for manipulating list of ttys
 *                tty_ldisc_lock from called functions
 *                termios_mutex resetting termios data
 *                tasklist_lock to walk task list for hangup event
 *                  ->siglock to protect ->signal/->sighand
 */
static void do_tty_hangup(struct work_struct *work)
{
        struct tty_struct *tty =
                container_of(work, struct tty_struct, hangup_work);
        struct file *cons_filp = NULL;
        struct file *filp, *f = NULL;
        struct task_struct *p;
        int    closecount = 0, n;
        unsigned long flags;
        int refs = 0;

        if (!tty)
                return;

        /* inuse_filps is protected by the single kernel lock */
        lock_kernel();

        spin_lock(&redirect_lock);
        if (redirect && redirect->private_data == tty) {
                f = redirect;
                redirect = NULL;
        }
        spin_unlock(&redirect_lock);

        check_tty_count(tty, "do_tty_hangup");
        file_list_lock();
        /* This breaks for file handles being sent over AF_UNIX sockets ? */
        list_for_each_entry(filp, &tty->tty_files, f_u.fu_list) {
                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;
        }
        file_list_unlock();

        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;
        set_bit(TTY_HUPPED, &tty->flags);
        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);
        tty_ldisc_enable(tty);
        unlock_kernel();
        if (f)
                fput(f);
}

/**
 *      tty_hangup              -       trigger a hangup event
 *      @tty: tty to hangup
 *
 *      A carrier loss (virtual or otherwise) has occurred on this like
 *      schedule a hangup sequence to run after this event.
 */

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);

/**
 *      tty_vhangup             -       process vhangup
 *      @tty: tty to hangup
 *
 *      The user has asked via system call for the terminal to be hung up.
 *      We do this synchronously so that when the syscall returns the process
 *      is complete. That guarantee is necessary for security reasons.
 */

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
        do_tty_hangup(&tty->hangup_work);
}

EXPORT_SYMBOL(tty_vhangup);

/**
 *      tty_vhangup_self        -       process vhangup for own ctty
 *
 *      Perform a vhangup on the current controlling tty
 */

void tty_vhangup_self(void)
{
        struct tty_struct *tty;

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

/**
 *      tty_hung_up_p           -       was tty hung up
 *      @filp: file pointer of tty
 *
 *      Return true if the tty has been subject to a vhangup or a carrier
 *      loss
 */

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);
}

/**
 *      disassociate_ctty       -       disconnect controlling tty
 *      @on_exit: true if exiting so need to "hang up" the session
 *
 *      This function is typically called only by the session leader, when
 *      it wants to disassociate itself from its controlling tty.
 *
 *      It performs the following functions:
 *      (1)  Sends a SIGHUP and SIGCONT to the foreground process group
 *      (2)  Clears the tty from being controlling the session
 *      (3)  Clears the controlling tty for all processes in the
 *              session group.
 *
 *      The argument on_exit is set to 1 if called when a process is
 *      exiting; it is 0 if called by the ioctl TIOCNOTTY.
 *
 *      Locking:
 *              BKL is taken for hysterical raisins
 *                tty_mutex is taken to protect tty
 *                ->siglock is taken to protect ->signal/->sighand
 *                tasklist_lock is taken to walk process list for sessions
 *                  ->siglock is taken to protect ->signal/->sighand
 */

void disassociate_ctty(int on_exit)
{
        struct tty_struct *tty;
        struct pid *tty_pgrp = NULL;


        tty = get_current_tty();
        if (tty) {
                tty_pgrp = get_pid(tty->pgrp);
                lock_kernel();
                if (on_exit && tty->driver->type != TTY_DRIVER_TYPE_PTY)
                        tty_vhangup(tty);
                unlock_kernel();
                tty_kref_put(tty);
        } 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;
        }
        if (tty_pgrp) {
                kill_pgrp(tty_pgrp, SIGHUP, on_exit);
                if (!on_exit)
                        kill_pgrp(tty_pgrp, SIGCONT, on_exit);
                put_pid(tty_pgrp);
        }

        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);
}

/**
 *
 *      no_tty  - Ensure the current process does not have a controlling tty
 */
void no_tty(void)
{
        struct task_struct *tsk = current;
        lock_kernel();
        if (tsk->signal->leader)
                disassociate_ctty(0);
        unlock_kernel();
        proc_clear_tty(tsk);
}


/**
 *      stop_tty        -       propagate flow control
 *      @tty: tty to stop
 *
 *      Perform flow control to the driver. For PTY/TTY pairs we
 *      must also propagate the TIOCKPKT status. May be called
 *      on an already stopped device and will not re-call the driver
 *      method.
 *
 *      This functionality is used by both the line disciplines for
 *      halting incoming flow and by the driver. It may therefore be
 *      called from any context, may be under the tty atomic_write_lock
 *      but not always.
 *
 *      Locking:
 *              Uses the tty control lock internally
 */

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);

/**
 *      start_tty       -       propagate flow control
 *      @tty: tty to start
 *
 *      Start a tty that has been stopped if at all possible. Perform
 *      any necessary wakeups and propagate the TIOCPKT status. If this
 *      is the tty was previous stopped and is being started then the
 *      driver start method is invoked and the line discipline woken.
 *
 *      Locking:
 *              ctrl_lock
 */

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);

/**
 *      tty_read        -       read method for tty device files
 *      @file: pointer to tty file
 *      @buf: user buffer
 *      @count: size of user buffer
 *      @ppos: unused
 *
 *      Perform the read system call function on this terminal device. Checks
 *      for hung up devices before calling the line discipline method.
 *
 *      Locking:
 *              Locks the line discipline internally while needed. Multiple
 *      read calls may be outstanding in parallel.
 */

static ssize_t tty_read(struct file *file, char __user *buf, size_t count,
                        loff_t *ppos)
{
        int i;
        struct tty_struct *tty;
        struct inode *inode;
        struct tty_ldisc *ld;

        tty = (struct tty_struct *)file->private_data;
        inode = file->f_path.dentry->d_inode;
        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)
{
        mutex_unlock(&tty->atomic_write_lock);
        wake_up_interruptible_poll(&tty->write_wait, POLLOUT);
}

int tty_write_lock(struct tty_struct *tty, int ndelay)
{
        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;
}

/**
 * tty_write_message - write a message to a certain tty, not just the console.
 * @tty: the destination tty_struct
 * @msg: the message to write
 *
 * This is used for messages that need to be redirected to a specific tty.
 * We don't put it into the syslog queue right now maybe in the future if
 * really needed.
 *
 * We must still hold the BKL and test the CLOSING flag for the moment.
 */

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


/**
 *      tty_write               -       write method for tty device file
 *      @file: tty file pointer
 *      @buf: user data to write
 *      @count: bytes to write
 *      @ppos: unused
 *
 *      Write data to a tty device via the line discipline.
 *
 *      Locking:
 *              Locks the line discipline as required
 *              Writes to the tty driver are serialized by the atomic_write_lock
 *      and are then processed in chunks to the device. The line discipline
 *      write method will not be invoked in parallel for each device.
 */

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

        tty = (struct tty_struct *)file->private_data;
        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) {
                get_file(redirect);
                p = 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";

/**
 *      pty_line_name   -       generate name for a pty
 *      @driver: the tty driver in use
 *      @index: the minor number
 *      @p: output buffer of at least 6 bytes
 *
 *      Generate a name from a driver reference and write it to the output
 *      buffer.
 *
 *      Locking: None
 */
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);
}

/**
 *      tty_line_name   -       generate name for a tty
 *      @driver: the tty driver in use
 *      @index: the minor number
 *      @p: output buffer of at least 7 bytes
 *
 *      Generate a name from a driver reference and write it to the output
 *      buffer.
 *
 *      Locking: None
 */
static void tty_line_name(struct tty_driver *driver, int index, char *p)
{
        sprintf(p, "%s%d", driver->name, index + driver->name_base);
}

/**
 *      tty_driver_lookup_tty() - find an existing tty, if any
 *      @driver: the driver for the tty
 *      @idx:    the minor number
 *
 *      Return the tty, if found or ERR_PTR() otherwise.
 *
 *      Locking: tty_mutex must be held. If tty is found, the mutex must
 *      be held until the 'fast-open' is also done. Will change once we
 *      have refcounting in the driver and per driver locking
 */
static struct tty_struct *tty_driver_lookup_tty(struct tty_driver *driver,
                struct inode *inode, int idx)
{
        struct tty_struct *tty;

        if (driver->ops->lookup)
                return driver->ops->lookup(driver, inode, idx);

        tty = driver->ttys[idx];
        return tty;
}

/**
 *      tty_init_termios        -  helper for termios setup
 *      @tty: the tty to set up
 *
 *      Initialise the termios structures for this tty. Thus runs under
 *      the tty_mutex currently so we can be relaxed about ordering.
 */

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

        tp = tty->driver->termios[idx];
        if (tp == NULL) {
                tp = kzalloc(sizeof(struct ktermios[2]), GFP_KERNEL);
                if (tp == NULL)
                        return -ENOMEM;
                memcpy(tp, &tty->driver->init_termios,
                                                sizeof(struct ktermios));
                tty->driver->termios[idx] = tp;
        }
        tty->termios = tp;
        tty->termios_locked = tp + 1;

        /* 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;
}

/**
 *      tty_driver_install_tty() - install a tty entry in the driver
 *      @driver: the driver for the tty
 *      @tty: the tty
 *
 *      Install a tty object into the driver tables. The tty->index field
 *      will be set by the time this is called. This method is responsible
 *      for ensuring any need additional structures are allocated and
 *      configured.
 *
 *      Locking: tty_mutex for now
 */
static int tty_driver_install_tty(struct tty_driver *driver,
                                                struct tty_struct *tty)
{
        int idx = tty->index;

        if (driver->ops->install)
                return driver->ops->install(driver, tty);

        if (tty_init_termios(tty) == 0) {
                tty_driver_kref_get(driver);
                tty->count++;
                driver->ttys[idx] = tty;
                return 0;
        }
        return -ENOMEM;
}

/**
 *      tty_driver_remove_tty() - remove a tty from the driver tables
 *      @driver: the driver for the tty
 *      @idx:    the minor number
 *
 *      Remvoe a tty object from the driver tables. The tty->index field
 *      will be set by the time this is called.
 *
 *      Locking: tty_mutex for now
 */
static 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))
                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++;
        tty->driver = driver; /* N.B. why do this every time?? */

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

        return 0;
}

/**
 *      tty_init_dev            -       initialise a tty device
 *      @driver: tty driver we are opening a device on
 *      @idx: device index
 *      @ret_tty: returned tty structure
 *      @first_ok: ok to open a new device (used by ptmx)
 *
 *      Prepare a tty device. This may not be a "new" clean device but
 *      could also be an active device. The pty drivers require special
 *      handling because of this.
 *
 *      Locking:
 *              The function is called under the tty_mutex, which
 *      protects us from the tty struct or driver itself going away.
 *
 *      On exit the tty device has the line discipline attached and
 *      a reference count of 1. If a pair was created for pty/tty use
 *      and the other was a pty master then it too has a reference count of 1.
 *
 * WSH 06/09/97: Rewritten to remove races and properly clean up after a
 * failed open.  The new code protects the open with a mutex, so it's
 * really quite straightforward.  The mutex locking can probably be
 * relaxed for the (most common) case of reopening a tty.
 */

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

        /* Check if pty master is being opened multiple times */
        if (driver->subtype == PTY_TYPE_MASTER &&
                (driver->flags & TTY_DRIVER_DEVPTS_MEM) && !first_ok)
                return ERR_PTR(-EIO);

        /*
         * 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)
                goto fail_no_mem;
        initialize_tty_struct(tty, driver, idx);

        retval = tty_driver_install_tty(driver, tty);
        if (retval < 0) {
                free_tty_struct(tty);
                module_put(driver->owner);
                return ERR_PTR(retval);
        }

        /*
         * 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 release_mem_out;
        return tty;

fail_no_mem:
        module_put(driver->owner);
        return ERR_PTR(-ENOMEM);

        /* call the tty release_tty routine to clean out this slot */
release_mem_out:
        if (printk_ratelimit())
                printk(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;
        /* Kill this flag and push into drivers for locking etc */
        if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS) {
                /* FIXME: Locking on ->termios array */
                tp = tty->termios;
                tty->driver->termios[idx] = NULL;
                kfree(tp);
        }
}
EXPORT_SYMBOL(tty_free_termios);

void tty_shutdown(struct tty_struct *tty)
{
        tty_driver_remove_tty(tty->driver, tty);
        tty_free_termios(tty);
}
EXPORT_SYMBOL(tty_shutdown);

/**
 *      release_one_tty         -       release tty structure memory
 *      @kref: kref of tty we are obliterating
 *
 *      Releases memory associated with a tty structure, and clears out the
 *      driver table slots. This function is called when a device is no longer
 *      in use. It also gets called when setup of a device fails.
 *
 *      Locking:
 *              tty_mutex - sometimes only
 *              takes the file list lock internally when working on the list
 *      of ttys that the driver keeps.
 */
static void release_one_tty(struct kref *kref)
{
        struct tty_struct *tty = container_of(kref, struct tty_struct, kref);
        struct tty_driver *driver = tty->driver;

        if (tty->ops->shutdown)
                tty->ops->shutdown(tty);
        else
                tty_shutdown(tty);
        tty->magic = 0;
        tty_driver_kref_put(driver);
        module_put(driver->owner);

        file_list_lock();
        list_del_init(&tty->tty_files);
        file_list_unlock();

        free_tty_struct(tty);
}

/**
 *      tty_kref_put            -       release a tty kref
 *      @tty: tty device
 *
 *      Release a reference to a tty device and if need be let the kref
 *      layer destruct the object for us
 */

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

/**
 *      release_tty             -       release tty structure memory
 *
 *      Release both @tty and a possible linked partner (think pty pair),
 *      and decrement the refcount of the backing module.
 *
 *      Locking:
 *              tty_mutex - sometimes only
 *              takes the file list lock internally when working on the list
 *      of ttys that the driver keeps.
 *              FIXME: should we require tty_mutex is held here ??
 *
 */
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);

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

/*
 * Even releasing the tty structures is a tricky business.. We have
 * to be very careful that the structures are all released at the
 * same time, as interrupts might otherwise get the wrong pointers.
 *
 * WSH 09/09/97: rewritten to avoid some nasty race conditions that could
 * lead to double frees or releasing memory still in use.
 */
void tty_release_dev(struct file *filp)
{
        struct tty_struct *tty, *o_tty;
        int     pty_master, tty_closing, o_tty_closing, do_sleep;
        int     devpts;
        int     idx;
        char    buf[64];
        struct  inode *inode;

        inode = filp->f_path.dentry->d_inode;
        tty = (struct tty_struct *)filp->private_data;
        if (tty_paranoia_check(tty, inode, "tty_release_dev"))
                return;

        check_tty_count(tty, "tty_release_dev");

        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;
        o_tty = tty->link;

#ifdef TTY_PARANOIA_CHECK
        if (idx < 0 || idx >= tty->driver->num) {
                printk(KERN_DEBUG "tty_release_dev: bad idx when trying to "
                                  "free (%s)\n", tty->name);
                return;
        }
        if (!devpts) {
                if (tty != tty->driver->ttys[idx]) {
                        printk(KERN_DEBUG "tty_release_dev: driver.table[%d] not tty "
                               "for (%s)\n", idx, tty->name);
                        return;
                }
                if (tty->termios != tty->driver->termios[idx]) {
                        printk(KERN_DEBUG "tty_release_dev: driver.termios[%d] not termios "
                               "for (%s)\n",
                               idx, tty->name);
                        return;
                }
        }
#endif

#ifdef TTY_DEBUG_HANGUP
        printk(KERN_DEBUG "tty_release_dev of %s (tty count=%d)...",
               tty_name(tty, buf), tty->count);
#endif

#ifdef TTY_PARANOIA_CHECK
        if (tty->driver->other &&
             !(tty->driver->flags & TTY_DRIVER_DEVPTS_MEM)) {
                if (o_tty != tty->driver->other->ttys[idx]) {
                        printk(KERN_DEBUG "tty_release_dev: other->table[%d] "
                                          "not o_tty for (%s)\n",
                               idx, tty->name);
                        return;
                }
                if (o_tty->termios != tty->driver->other->termios[idx]) {
                        printk(KERN_DEBUG "tty_release_dev: other->termios[%d] "
                                          "not o_termios for (%s)\n",
                               idx, tty->name);
                        return;
                }
                if (o_tty->link != tty) {
                        printk(KERN_DEBUG "tty_release_dev: bad pty pointers\n");
                        return;
                }
        }
#endif
        if (tty->ops->close)
                tty->ops->close(tty, filp);

        /*
         * 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_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 "tty_release_dev: %s: read/write wait queue "
                                    "active!\n", tty_name(tty, buf));
                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.
         */
        if (pty_master) {
                if (--o_tty->count < 0) {
                        printk(KERN_WARNING "tty_release_dev: bad pty slave count "
                                            "(%d) for %s\n",
                               o_tty->count, tty_name(o_tty, buf));
                        o_tty->count = 0;
                }
        }
        if (--tty->count < 0) {
                printk(KERN_WARNING "tty_release_dev: bad tty->count (%d) for %s\n",
                       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.
         */
        file_kill(filp);
        filp->private_data = NULL;

        /*
         * 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);

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

#ifdef TTY_DEBUG_HANGUP
        printk(KERN_DEBUG "freeing tty structure...");
#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.
         */
        release_tty(tty, idx);

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

/**
 *      __tty_open              -       open a tty device
 *      @inode: inode of device file
 *      @filp: file pointer to tty
 *
 *      tty_open and tty_release keep up the tty count that contains the
 *      number of opens done on a tty. We cannot use the inode-count, as
 *      different inodes might point to the same tty.
 *
 *      Open-counting is needed for pty masters, as well as for keeping
 *      track of serial lines: DTR is dropped when the last close happens.
 *      (This is not done solely through tty->count, now.  - Ted 1/27/92)
 *
 *      The termios state of a pty is reset on first open so that
 *      settings don't persist across reuse.
 *
 *      Locking: tty_mutex protects tty, get_tty_driver and tty_init_dev work.
 *               tty->count should protect the rest.
 *               ->siglock protects ->signal/->sighand
 */

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

        nonseekable_open(inode, filp);

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

        mutex_lock(&tty_mutex);

        if (device == MKDEV(TTYAUX_MAJOR, 0)) {
                tty = get_current_tty();
                if (!tty) {
                        mutex_unlock(&tty_mutex);
                        return -ENXIO;
                }
                driver = tty_driver_kref_get(tty->driver);
                index = tty->index;
                filp->f_flags |= O_NONBLOCK; /* Don't let /dev/tty block */
                /* noctty = 1; */
                /* FIXME: Should we take a driver reference ? */
                tty_kref_put(tty);
                goto got_driver;
        }
#ifdef CONFIG_VT
        if (device == MKDEV(TTY_MAJOR, 0)) {
                extern struct tty_driver *console_driver;
                driver = tty_driver_kref_get(console_driver);
                index = fg_console;
                noctty = 1;
                goto got_driver;
        }
#endif
        if (device == 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;
                                goto got_driver;
                        }
                }
                mutex_unlock(&tty_mutex);
                return -ENODEV;
        }

        driver = get_tty_driver(device, &index);
        if (!driver) {
                mutex_unlock(&tty_mutex);
                return -ENODEV;
        }
got_driver:
        if (!tty) {
                /* check whether we're reopening an existing tty */
                tty = tty_driver_lookup_tty(driver, inode, index);

                if (IS_ERR(tty)) {
                        mutex_unlock(&tty_mutex);
                        return PTR_ERR(tty);
                }
        }

        if (tty) {
                retval = tty_reopen(tty);
                if (retval)
                        tty = ERR_PTR(retval);
        } else
                tty = tty_init_dev(driver, index, 0);

        mutex_unlock(&tty_mutex);
        tty_driver_kref_put(driver);
        if (IS_ERR(tty))
                return PTR_ERR(tty);

        filp->private_data = tty;
        file_move(filp, &tty->tty_files);
        check_tty_count(tty, "tty_open");
        if (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
            tty->driver->subtype == PTY_TYPE_MASTER)
                noctty = 1;
#ifdef TTY_DEBUG_HANGUP
        printk(KERN_DEBUG "opening %s...", tty->name);
#endif
        if (!retval) {
                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 "error %d in opening %s...", retval,
                       tty->name);
#endif
                tty_release_dev(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;
        }

        mutex_lock(&tty_mutex);
        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);
        mutex_unlock(&tty_mutex);
        return 0;
}

/* BKL pushdown: scary code avoidance wrapper */
static int tty_open(struct inode *inode, struct file *filp)
{
        int ret;

        lock_kernel();
        ret = __tty_open(inode, filp);
        unlock_kernel();
        return ret;
}




/**
 *      tty_release             -       vfs callback for close
 *      @inode: inode of tty
 *      @filp: file pointer for handle to tty
 *
 *      Called the last time each file handle is closed that references
 *      this tty. There may however be several such references.
 *
 *      Locking:
 *              Takes bkl. See tty_release_dev
 */

static int tty_release(struct inode *inode, struct file *filp)
{
        lock_kernel();
        tty_release_dev(filp);
        unlock_kernel();
        return 0;
}

/**
 *      tty_poll        -       check tty status
 *      @filp: file being polled
 *      @wait: poll wait structures to update
 *
 *      Call the line discipline polling method to obtain the poll
 *      status of the device.
 *
 *      Locking: locks called line discipline but ldisc poll method
 *      may be re-entered freely by other callers.
 */

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

        tty = (struct tty_struct *)filp->private_data;
        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;
        unsigned long flags;
        int retval = 0;

        lock_kernel();
        tty = (struct tty_struct *)filp->private_data;
        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;
                }
                spin_unlock_irqrestore(&tty->ctrl_lock, flags);
                retval = __f_setown(filp, pid, type, 0);
                if (retval)
                        goto out;
        } else {
                if (!tty->fasync && !waitqueue_active(&tty->read_wait))
                        tty->minimum_to_wake = N_TTY_BUF_SIZE;
        }
        retval = 0;
out:
        unlock_kernel();
        return retval;
}

/**
 *      tiocsti                 -       fake input character
 *      @tty: tty to fake input into
 *      @p: pointer to character
 *
 *      Fake input to a tty device. Does the necessary locking and
 *      input management.
 *
 *      FIXME: does not honour flow control ??
 *
 *      Locking:
 *              Called functions take tty_ldisc_lock
 *              current->signal->tty check is safe without locks
 *
 *      FIXME: may race normal receive processing
 */

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;
}

/**
 *      tiocgwinsz              -       implement window query ioctl
 *      @tty; tty
 *      @arg: user buffer for result
 *
 *      Copies the kernel idea of the window size into the user buffer.
 *
 *      Locking: tty->termios_mutex is taken to ensure the winsize data
 *              is consistent.
 */

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;
}

/**
 *      tty_do_resize           -       resize event
 *      @tty: tty being resized
 *      @rows: rows (character)
 *      @cols: cols (character)
 *
 *      Update the termios variables and send the neccessary signals to
 *      peform a terminal resize correctly
 */

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;
}

/**
 *      tiocswinsz              -       implement window size set ioctl
 *      @tty; tty side of tty
 *      @arg: user buffer for result
 *
 *      Copies the user idea of the window size to the kernel. Traditionally
 *      this is just advisory information but for the Linux console it
 *      actually has driver level meaning and triggers a VC resize.
 *
 *      Locking:
 *              Driver dependant. The default do_resize method takes the
 *      tty termios mutex and ctrl_lock. The console takes its own lock
 *      then calls into the default method.
 */

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);
}

/**
 *      tioccons        -       allow admin to move logical console
 *      @file: the file to become console
 *
 *      Allow the adminstrator to move the redirected console device
 *
 *      Locking: uses redirect_lock to guard the redirect information
 */

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;
        }
        get_file(file);
        redirect = file;
        spin_unlock(&redirect_lock);
        return 0;
}

/**
 *      fionbio         -       non blocking ioctl
 *      @file: file to set blocking value
 *      @p: user parameter
 *
 *      Historical tty interfaces had a blocking control ioctl before
 *      the generic functionality existed. This piece of history is preserved
 *      in the expected tty API of posix OS's.
 *
 *      Locking: none, the open fle handle ensures it won't go away.
 */

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;
}

/**
 *      tiocsctty       -       set controlling tty
 *      @tty: tty structure
 *      @arg: user argument
 *
 *      This ioctl is used to manage job control. It permits a session
 *      leader to set this tty as the controlling tty for the session.
 *
 *      Locking:
 *              Takes tty_mutex() to protect tty instance
 *              Takes tasklist_lock internally to walk sessions
 *              Takes ->siglock() when updating signal->tty
 */

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;
}

/**
 *      tty_get_pgrp    -       return a ref counted pgrp pid
 *      @tty: tty to read
 *
 *      Returns a refcounted instance of the pid struct for the process
 *      group controlling the tty.
 */

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);

/**
 *      tiocgpgrp               -       get process group
 *      @tty: tty passed by user
 *      @real_tty: tty side of the tty pased by the user if a pty else the tty
 *      @p: returned pid
 *
 *      Obtain the process group of the tty. If there is no process group
 *      return an error.
 *
 *      Locking: none. Reference to current->signal->tty is safe.
 */

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;
}

/**
 *      tiocspgrp               -       attempt to set process group
 *      @tty: tty passed by user
 *      @real_tty: tty side device matching tty passed by user
 *      @p: pid pointer
 *
 *      Set the process group of the tty to the session passed. Only
 *      permitted where the tty session is our session.
 *
 *      Locking: RCU, ctrl lock
 */

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;
}

/**
 *      tiocgsid                -       get session id
 *      @tty: tty passed by user
 *      @real_tty: tty side of the tty pased by the user if a pty else the tty
 *      @p: pointer to returned session id
 *
 *      Obtain the session id of the tty. If there is no session
 *      return an error.
 *
 *      Locking: none. Reference to current->signal->tty is safe.
 */

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);
}

/**
 *      tiocsetd        -       set line discipline
 *      @tty: tty device
 *      @p: pointer to user data
 *
 *      Set the line discipline according to user request.
 *
 *      Locking: see tty_set_ldisc, this function is just a helper
 */

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

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

        lock_kernel();
        ret = tty_set_ldisc(tty, ldisc);
        unlock_kernel();

        return ret;
}

/**
 *      send_break      -       performed time break
 *      @tty: device to break on
 *      @duration: timeout in mS
 *
 *      Perform a timed break on hardware that lacks its own driver level
 *      timed break functionality.
 *
 *      Locking:
 *              atomic_write_lock serializes
 *
 */

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;
}

/**
 *      tty_tiocmget            -       get modem status
 *      @tty: tty device
 *      @file: user file pointer
 *      @p: pointer to result
 *
 *      Obtain the modem status bits from the tty driver if the feature
 *      is supported. Return -EINVAL if it is not available.
 *
 *      Locking: none (up to the driver)
 */

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

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

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

/**
 *      tty_tiocmset            -       set modem status
 *      @tty: tty device
 *      @file: user file pointer
 *      @cmd: command - clear bits, set bits or set all
 *      @p: pointer to desired bits
 *
 *      Set the modem status bits from the tty driver if the feature
 *      is supported. Return -EINVAL if it is not available.
 *
 *      Locking: none (up to the driver)
 */

static int tty_tiocmset(struct tty_struct *tty, struct file *file, 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, file, set, clear);
}

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, *real_tty;
        void __user *p = (void __user *)arg;
        int retval;
        struct tty_ldisc *ld;
        struct inode *inode = file->f_dentry->d_inode;

        tty = (struct tty_struct *)file->private_data;
        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);
        /*
         * 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, file, p);
        case TIOCMSET:
        case TIOCMBIC:
        case TIOCMBIS:
                return tty_tiocmset(tty, file, cmd, p);
        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, file, 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 = -EINVAL;
        }
        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->private_data;
        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, file, 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);
        tty_ldisc_deref(ld);

        return retval;
}
#endif

/*
 * 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;
        struct file     *filp;
        struct fdtable *fdt;

        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);
                if (p->files) {
                        /*
                         * We don't take a ref to the file, so we must
                         * hold ->file_lock instead.
                         */
                        spin_lock(&p->files->file_lock);
                        fdt = files_fdtable(p->files);
                        for (i = 0; i < fdt->max_fds; i++) {
                                filp = fcheck_files(p->files, i);
                                if (!filp)
                                        continue;
                                if (filp->f_op->read == tty_read &&
                                    filp->private_data == tty) {
                                        printk(KERN_NOTICE "SAK: killed process %d"
                                            " (%s): fd#%d opened to the tty\n",
                                            task_pid_nr(p), p->comm, i);
                                        force_sig(SIGKILL, p);
                                        break;
                                }
                        }
                        spin_unlock(&p->files->file_lock);
                }
                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);

/**
 *      initialize_tty_struct
 *      @tty: tty to initialize
 *
 *      This subroutine initializes a tty structure that has been newly
 *      allocated.
 *
 *      Locking: none - tty in question must not be exposed at this point
 */

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->buf.head = tty->buf.tail = NULL;
        tty_buffer_init(tty);
        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_put_char    -       write one character to a tty
 *      @tty: tty
 *      @ch: character
 *
 *      Write one byte to the tty using the provided put_char method
 *      if present. Returns the number of characters successfully output.
 *
 *      Note: the specific put_char operation in the driver layer may go
 *      away soon. Don't call it directly, use this method
 */

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;

/**
 *      tty_register_device - register a tty device
 *      @driver: the tty driver that describes the tty device
 *      @index: the index in the tty driver for this tty device
 *      @device: a struct device that is associated with this tty device.
 *              This field is optional, if there is no known struct device
 *              for this tty device it can be set to NULL safely.
 *
 *      Returns a pointer to the struct device for this tty device
 *      (or ERR_PTR(-EFOO) on error).
 *
 *      This call is required to be made to register an individual tty device
 *      if the tty driver's flags have the TTY_DRIVER_DYNAMIC_DEV bit set.  If
 *      that bit is not set, this function should not be called by a tty
 *      driver.
 *
 *      Locking: ??
 */

struct device *tty_register_device(struct tty_driver *driver, unsigned index,
                                   struct device *device)
{
        char name[64];
        dev_t dev = MKDEV(driver->major, driver->minor_start) + index;

        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);

        return device_create(tty_class, device, dev, NULL, name);
}
EXPORT_SYMBOL(tty_register_device);

/**
 *      tty_unregister_device - unregister a tty device
 *      @driver: the tty driver that describes the tty device
 *      @index: the index in the tty driver for this tty device
 *
 *      If a tty device is registered with a call to tty_register_device() then
 *      this function must be called when the tty device is gone.
 *
 *      Locking: ??
 */

void tty_unregister_device(struct tty_driver *driver, unsigned index)
{
        device_destroy(tty_class,
                MKDEV(driver->major, driver->minor_start) + index);
}
EXPORT_SYMBOL(tty_unregister_device);

struct tty_driver *alloc_tty_driver(int lines)
{
        struct tty_driver *driver;

        driver = kzalloc(sizeof(struct tty_driver), GFP_KERNEL);
        if (driver) {
                kref_init(&driver->kref);
                driver->magic = TTY_DRIVER_MAGIC;
                driver->num = lines;
                /* later we'll move allocation of tables here */
        }
        return driver;
}
EXPORT_SYMBOL(alloc_tty_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;
        void *p;

        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);
                }
                p = driver->ttys;
                proc_tty_unregister_driver(driver);
                driver->ttys = NULL;
                driver->termios = NULL;
                kfree(p);
                cdev_del(&driver->cdev);
        }
        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;
        void **p = NULL;

        if (!(driver->flags & TTY_DRIVER_DEVPTS_MEM) && driver->num) {
                p = kzalloc(driver->num * 2 * sizeof(void *), GFP_KERNEL);
                if (!p)
                        return -ENOMEM;
        }

        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) {
                kfree(p);
                return error;
        }

        if (p) {
                driver->ttys = (struct tty_struct **)p;
                driver->termios = (struct ktermios **)(p + driver->num);
        } else {
                driver->ttys = NULL;
                driver->termios = NULL;
        }

        cdev_init(&driver->cdev, &tty_fops);
        driver->cdev.owner = driver->owner;
        error = cdev_add(&driver->cdev, dev, driver->num);
        if (error) {
                unregister_chrdev_region(dev, driver->num);
                driver->ttys = NULL;
                driver->termios = NULL;
                kfree(p);
                return error;
        }

        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++)
                    tty_register_device(driver, i, NULL);
        }
        proc_tty_register_driver(driver);
        driver->flags |= TTY_DRIVER_INSTALLED;
        return 0;
}

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

postcore_initcall(tty_class_init);

/* 3/2004 jmc: why do these devices exist? */

static struct cdev tty_cdev, console_cdev;

/*
 * Ok, now we can initialize the rest of the tty devices and can count
 * on memory allocations, interrupts etc..
 */
static 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");
        device_create(tty_class, NULL, MKDEV(TTYAUX_MAJOR, 1), NULL,
                              "console");

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