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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);

/**
 *    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?? */

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

      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);

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