Cross-Referenced Linux and Device Driver Code

   /*
    *  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 init_dev and 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/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/idr.h>
  #include <linux/wait.h>
  #include <linux/bitops.h>
  #include <linux/delay.h>
  
  #include <asm/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);
 
 #ifdef CONFIG_UNIX98_PTYS
 extern struct tty_driver *ptm_driver;   /* Unix98 pty masters; for /dev/ptmx */
 extern int pty_limit;                   /* Config limit on Unix98 ptys */
 static DEFINE_IDR(allocated_ptys);
 static DEFINE_MUTEX(allocated_ptys_lock);
 static int ptmx_open(struct inode *, struct file *);
 #endif
 
 static void initialize_tty_struct(struct tty_struct *tty);
 
 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 *);
 int tty_ioctl(struct inode *inode, 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
  */
 
 static struct tty_struct *alloc_tty_struct(void)
 {
         return kzalloc(sizeof(struct tty_struct), GFP_KERNEL);
 }
 
 static void tty_buffer_free_all(struct tty_struct *);
 
 /**
  *      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
  */
 
 static inline 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 file *filp;
         int count = 0;
 
         percpu_list_fold(&tty->tty_files);
         lock_list_for_each_entry(filp, percpu_list_head(&tty->tty_files), f_u.fu_llist)
                 count++;
 
         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);
                 dump_stack();
                 return count;
         }
 #endif
         return 0;
 }
 
 /*
  * Tty buffer allocation management
  */
 
 /**
  *      tty_buffer_free_all             -       free buffers used by a tty
  *      @tty: tty to free from
  *
  *      Remove all the buffers pending on a tty whether queued with data
  *      or in the free ring. Must be called when the tty is no longer in use
  *
  *      Locking: none
  */
 
 static void tty_buffer_free_all(struct tty_struct *tty)
 {
         struct tty_buffer *thead;
         while ((thead = tty->buf.head) != NULL) {
                 tty->buf.head = thead->next;
                 kfree(thead);
         }
         while ((thead = tty->buf.free) != NULL) {
                 tty->buf.free = thead->next;
                 kfree(thead);
         }
         tty->buf.tail = NULL;
         tty->buf.memory_used = 0;
 }
 
 /**
  *      tty_buffer_init         -       prepare a tty buffer structure
  *      @tty: tty to initialise
  *
  *      Set up the initial state of the buffer management for a tty device.
  *      Must be called before the other tty buffer functions are used.
  *
  *      Locking: none
  */
 
 static void tty_buffer_init(struct tty_struct *tty)
 {
         spin_lock_init(&tty->buf.lock);
         tty->buf.head = NULL;
         tty->buf.tail = NULL;
         tty->buf.free = NULL;
         tty->buf.memory_used = 0;
 }
 
 /**
  *      tty_buffer_alloc        -       allocate a tty buffer
  *      @tty: tty device
  *      @size: desired size (characters)
  *
  *      Allocate a new tty buffer to hold the desired number of characters.
  *      Return NULL if out of memory or the allocation would exceed the
  *      per device queue
  *
  *      Locking: Caller must hold tty->buf.lock
  */
 
 static struct tty_buffer *tty_buffer_alloc(struct tty_struct *tty, size_t size)
 {
         struct tty_buffer *p;
 
         if (tty->buf.memory_used + size > 65536)
                 return NULL;
         p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
         if (p == NULL)
                 return NULL;
         p->used = 0;
         p->size = size;
         p->next = NULL;
         p->commit = 0;
         p->read = 0;
         p->char_buf_ptr = (char *)(p->data);
         p->flag_buf_ptr = (unsigned char *)p->char_buf_ptr + size;
         tty->buf.memory_used += size;
         return p;
 }
 
 /**
  *      tty_buffer_free         -       free a tty buffer
  *      @tty: tty owning the buffer
  *      @b: the buffer to free
  *
  *      Free a tty buffer, or add it to the free list according to our
  *      internal strategy
  *
  *      Locking: Caller must hold tty->buf.lock
  */
 
 static void tty_buffer_free(struct tty_struct *tty, struct tty_buffer *b)
 {
         /* Dumb strategy for now - should keep some stats */
         tty->buf.memory_used -= b->size;
         WARN_ON(tty->buf.memory_used < 0);
 
         if (b->size >= 512)
                 kfree(b);
         else {
                 b->next = tty->buf.free;
                 tty->buf.free = b;
         }
 }
 
 /**
  *      __tty_buffer_flush              -       flush full tty buffers
  *      @tty: tty to flush
  *
  *      flush all the buffers containing receive data. Caller must
  *      hold the buffer lock and must have ensured no parallel flush to
  *      ldisc is running.
  *
  *      Locking: Caller must hold tty->buf.lock
  */
 
 static void __tty_buffer_flush(struct tty_struct *tty)
 {
         struct tty_buffer *thead;
 
         while ((thead = tty->buf.head) != NULL) {
                 tty->buf.head = thead->next;
                 tty_buffer_free(tty, thead);
         }
         tty->buf.tail = NULL;
 }
 
 /**
  *      tty_buffer_flush                -       flush full tty buffers
  *      @tty: tty to flush
  *
  *      flush all the buffers containing receive data. If the buffer is
  *      being processed by flush_to_ldisc then we defer the processing
  *      to that function
  *
  *      Locking: none
  */
 
 static void tty_buffer_flush(struct tty_struct *tty)
 {
         unsigned long flags;
         spin_lock_irqsave(&tty->buf.lock, flags);
 
         /* If the data is being pushed to the tty layer then we can't
            process it here. Instead set a flag and the flush_to_ldisc
            path will process the flush request before it exits */
         if (test_bit(TTY_FLUSHING, &tty->flags)) {
                 set_bit(TTY_FLUSHPENDING, &tty->flags);
                 spin_unlock_irqrestore(&tty->buf.lock, flags);
                 wait_event(tty->read_wait,
                                 test_bit(TTY_FLUSHPENDING, &tty->flags) == 0);
                 return;
         } else
                 __tty_buffer_flush(tty);
         spin_unlock_irqrestore(&tty->buf.lock, flags);
 }
 
 /**
  *      tty_buffer_find         -       find a free tty buffer
  *      @tty: tty owning the buffer
  *      @size: characters wanted
  *
  *      Locate an existing suitable tty buffer or if we are lacking one then
  *      allocate a new one. We round our buffers off in 256 character chunks
  *      to get better allocation behaviour.
  *
  *      Locking: Caller must hold tty->buf.lock
  */
 
 static struct tty_buffer *tty_buffer_find(struct tty_struct *tty, size_t size)
 {
         struct tty_buffer **tbh = &tty->buf.free;
         while ((*tbh) != NULL) {
                 struct tty_buffer *t = *tbh;
                 if (t->size >= size) {
                         *tbh = t->next;
                         t->next = NULL;
                         t->used = 0;
                         t->commit = 0;
                         t->read = 0;
                         tty->buf.memory_used += t->size;
                         return t;
                 }
                 tbh = &((*tbh)->next);
         }
         /* Round the buffer size out */
         size = (size + 0xFF) & ~0xFF;
         return tty_buffer_alloc(tty, size);
         /* Should possibly check if this fails for the largest buffer we
            have queued and recycle that ? */
 }
 
 /**
  *      tty_buffer_request_room         -       grow tty buffer if needed
  *      @tty: tty structure
  *      @size: size desired
  *
  *      Make at least size bytes of linear space available for the tty
  *      buffer. If we fail return the size we managed to find.
  *
  *      Locking: Takes tty->buf.lock
  */
 int tty_buffer_request_room(struct tty_struct *tty, size_t size)
 {
         struct tty_buffer *b, *n;
         int left;
         unsigned long flags;
 
         spin_lock_irqsave(&tty->buf.lock, flags);
 
         /* OPTIMISATION: We could keep a per tty "zero" sized buffer to
            remove this conditional if its worth it. This would be invisible
            to the callers */
         if ((b = tty->buf.tail) != NULL)
                 left = b->size - b->used;
         else
                 left = 0;
 
         if (left < size) {
                 /* This is the slow path - looking for new buffers to use */
                 if ((n = tty_buffer_find(tty, size)) != NULL) {
                         if (b != NULL) {
                                 b->next = n;
                                 b->commit = b->used;
                         } else
                                 tty->buf.head = n;
                         tty->buf.tail = n;
                 } else
                         size = left;
         }
 
         spin_unlock_irqrestore(&tty->buf.lock, flags);
         return size;
 }
 EXPORT_SYMBOL_GPL(tty_buffer_request_room);
 
 /**
  *      tty_insert_flip_string  -       Add characters to the tty buffer
  *      @tty: tty structure
  *      @chars: characters
  *      @size: size
  *
  *      Queue a series of bytes to the tty buffering. All the characters
  *      passed are marked as without error. Returns the number added.
  *
  *      Locking: Called functions may take tty->buf.lock
  */
 
 int tty_insert_flip_string(struct tty_struct *tty, const unsigned char *chars,
                                 size_t size)
 {
         int copied = 0;
         do {
                 int space = tty_buffer_request_room(tty, size - copied);
                 struct tty_buffer *tb = tty->buf.tail;
                 /* If there is no space then tb may be NULL */
                 if (unlikely(space == 0))
                         break;
                 memcpy(tb->char_buf_ptr + tb->used, chars, space);
                 memset(tb->flag_buf_ptr + tb->used, TTY_NORMAL, space);
                 tb->used += space;
                 copied += space;
                 chars += space;
                 /* There is a small chance that we need to split the data over
                    several buffers. If this is the case we must loop */
         } while (unlikely(size > copied));
         return copied;
 }
 EXPORT_SYMBOL(tty_insert_flip_string);
 
 /**
  *      tty_insert_flip_string_flags    -       Add characters to the tty buffer
  *      @tty: tty structure
  *      @chars: characters
  *      @flags: flag bytes
  *      @size: size
  *
  *      Queue a series of bytes to the tty buffering. For each character
  *      the flags array indicates the status of the character. Returns the
  *      number added.
  *
  *      Locking: Called functions may take tty->buf.lock
  */
 
 int tty_insert_flip_string_flags(struct tty_struct *tty,
                 const unsigned char *chars, const char *flags, size_t size)
 {
         int copied = 0;
         do {
                 int space = tty_buffer_request_room(tty, size - copied);
                 struct tty_buffer *tb = tty->buf.tail;
                 /* If there is no space then tb may be NULL */
                 if (unlikely(space == 0))
                         break;
                 memcpy(tb->char_buf_ptr + tb->used, chars, space);
                 memcpy(tb->flag_buf_ptr + tb->used, flags, space);
                 tb->used += space;
                 copied += space;
                 chars += space;
                 flags += space;
                 /* There is a small chance that we need to split the data over
                    several buffers. If this is the case we must loop */
         } while (unlikely(size > copied));
         return copied;
 }
 EXPORT_SYMBOL(tty_insert_flip_string_flags);
 
 /**
  *      tty_schedule_flip       -       push characters to ldisc
  *      @tty: tty to push from
  *
  *      Takes any pending buffers and transfers their ownership to the
  *      ldisc side of the queue. It then schedules those characters for
  *      processing by the line discipline.
  *
  *      Locking: Takes tty->buf.lock
  */
 
 void tty_schedule_flip(struct tty_struct *tty)
 {
         unsigned long flags;
         spin_lock_irqsave(&tty->buf.lock, flags);
         if (tty->buf.tail != NULL)
                 tty->buf.tail->commit = tty->buf.tail->used;
         spin_unlock_irqrestore(&tty->buf.lock, flags);
         schedule_delayed_work(&tty->buf.work, 1);
 }
 EXPORT_SYMBOL(tty_schedule_flip);
 
 /**
  *      tty_prepare_flip_string         -       make room for characters
  *      @tty: tty
  *      @chars: return pointer for character write area
  *      @size: desired size
  *
  *      Prepare a block of space in the buffer for data. Returns the length
  *      available and buffer pointer to the space which is now allocated and
  *      accounted for as ready for normal characters. This is used for drivers
  *      that need their own block copy routines into the buffer. There is no
  *      guarantee the buffer is a DMA target!
  *
  *      Locking: May call functions taking tty->buf.lock
  */
 
 int tty_prepare_flip_string(struct tty_struct *tty, unsigned char **chars,
                                                                 size_t size)
 {
         int space = tty_buffer_request_room(tty, size);
         if (likely(space)) {
                 struct tty_buffer *tb = tty->buf.tail;
                 *chars = tb->char_buf_ptr + tb->used;
                 memset(tb->flag_buf_ptr + tb->used, TTY_NORMAL, space);
                 tb->used += space;
         }
         return space;
 }
 
 EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
 
 /**
  *      tty_prepare_flip_string_flags   -       make room for characters
  *      @tty: tty
  *      @chars: return pointer for character write area
  *      @flags: return pointer for status flag write area
  *      @size: desired size
  *
  *      Prepare a block of space in the buffer for data. Returns the length
  *      available and buffer pointer to the space which is now allocated and
  *      accounted for as ready for characters. This is used for drivers
  *      that need their own block copy routines into the buffer. There is no
  *      guarantee the buffer is a DMA target!
  *
  *      Locking: May call functions taking tty->buf.lock
  */
 
 int tty_prepare_flip_string_flags(struct tty_struct *tty,
                         unsigned char **chars, char **flags, size_t size)
 {
         int space = tty_buffer_request_room(tty, size);
         if (likely(space)) {
                 struct tty_buffer *tb = tty->buf.tail;
                 *chars = tb->char_buf_ptr + tb->used;
                 *flags = tb->flag_buf_ptr + tb->used;
                 tb->used += space;
         }
         return space;
 }
 
 EXPORT_SYMBOL_GPL(tty_prepare_flip_string_flags);
 
 
 
 /**
  *      tty_set_termios_ldisc           -       set ldisc field
  *      @tty: tty structure
  *      @num: line discipline number
  *
  *      This is probably overkill for real world processors but
  *      they are not on hot paths so a little discipline won't do
  *      any harm.
  *
  *      Locking: takes termios_mutex
  */
 
 static void tty_set_termios_ldisc(struct tty_struct *tty, int num)
 {
         mutex_lock(&tty->termios_mutex);
         tty->termios->c_line = num;
         mutex_unlock(&tty->termios_mutex);
 }
 
 /*
  *      This guards the refcounted line discipline lists. The lock
  *      must be taken with irqs off because there are hangup path
  *      callers who will do ldisc lookups and cannot sleep.
  */
 
 static DEFINE_SPINLOCK(tty_ldisc_lock);
 static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_wait);
 /* Line disc dispatch table */
 static struct tty_ldisc tty_ldiscs[NR_LDISCS];
 
 /**
  *      tty_register_ldisc      -       install a line discipline
  *      @disc: ldisc number
  *      @new_ldisc: pointer to the ldisc object
  *
  *      Installs a new line discipline into the kernel. The discipline
  *      is set up as unreferenced and then made available to the kernel
  *      from this point onwards.
  *
  *      Locking:
  *              takes tty_ldisc_lock to guard against ldisc races
  */
 
 int tty_register_ldisc(int disc, struct tty_ldisc *new_ldisc)
 {
         unsigned long flags;
         int ret = 0;
 
         if (disc < N_TTY || disc >= NR_LDISCS)
                 return -EINVAL;
 
         spin_lock_irqsave(&tty_ldisc_lock, flags);
         tty_ldiscs[disc] = *new_ldisc;
         tty_ldiscs[disc].num = disc;
         tty_ldiscs[disc].flags |= LDISC_FLAG_DEFINED;
         tty_ldiscs[disc].refcount = 0;
         spin_unlock_irqrestore(&tty_ldisc_lock, flags);
 
         return ret;
 }
 EXPORT_SYMBOL(tty_register_ldisc);
 
 /**
  *      tty_unregister_ldisc    -       unload a line discipline
  *      @disc: ldisc number
  *      @new_ldisc: pointer to the ldisc object
  *
  *      Remove a line discipline from the kernel providing it is not
  *      currently in use.
  *
  *      Locking:
  *              takes tty_ldisc_lock to guard against ldisc races
  */
 
 int tty_unregister_ldisc(int disc)
 {
         unsigned long flags;
         int ret = 0;
 
         if (disc < N_TTY || disc >= NR_LDISCS)
                 return -EINVAL;
 
         spin_lock_irqsave(&tty_ldisc_lock, flags);
         if (tty_ldiscs[disc].refcount)
                 ret = -EBUSY;
         else
                 tty_ldiscs[disc].flags &= ~LDISC_FLAG_DEFINED;
         spin_unlock_irqrestore(&tty_ldisc_lock, flags);
 
         return ret;
 }
 EXPORT_SYMBOL(tty_unregister_ldisc);
 
 /**
  *      tty_ldisc_get           -       take a reference to an ldisc
  *      @disc: ldisc number
  *
  *      Takes a reference to a line discipline. Deals with refcounts and
  *      module locking counts. Returns NULL if the discipline is not available.
  *      Returns a pointer to the discipline and bumps the ref count if it is
  *      available
  *
  *      Locking:
  *              takes tty_ldisc_lock to guard against ldisc races
  */
 
 struct tty_ldisc *tty_ldisc_get(int disc)
 {
         unsigned long flags;
         struct tty_ldisc *ld;
 
         if (disc < N_TTY || disc >= NR_LDISCS)
                 return NULL;
 
         spin_lock_irqsave(&tty_ldisc_lock, flags);
 
         ld = &tty_ldiscs[disc];
         /* Check the entry is defined */
         if (ld->flags & LDISC_FLAG_DEFINED) {
                 /* If the module is being unloaded we can't use it */
                 if (!try_module_get(ld->owner))
                         ld = NULL;
                 else /* lock it */
                         ld->refcount++;
         } else
                 ld = NULL;
         spin_unlock_irqrestore(&tty_ldisc_lock, flags);
         return ld;
 }
 
 EXPORT_SYMBOL_GPL(tty_ldisc_get);
 
 /**
  *      tty_ldisc_put           -       drop ldisc reference
  *      @disc: ldisc number
  *
  *      Drop a reference to a line discipline. Manage refcounts and
  *      module usage counts
  *
  *      Locking:
  *              takes tty_ldisc_lock to guard against ldisc races
  */
 
 void tty_ldisc_put(int disc)
 {
         struct tty_ldisc *ld;
         unsigned long flags;
 
         BUG_ON(disc < N_TTY || disc >= NR_LDISCS);
 
         spin_lock_irqsave(&tty_ldisc_lock, flags);
         ld = &tty_ldiscs[disc];
         BUG_ON(ld->refcount == 0);
         ld->refcount--;
         module_put(ld->owner);
         spin_unlock_irqrestore(&tty_ldisc_lock, flags);
 }
 
 EXPORT_SYMBOL_GPL(tty_ldisc_put);
 
 /**
  *      tty_ldisc_assign        -       set ldisc on a tty
  *      @tty: tty to assign
  *      @ld: line discipline
  *
  *      Install an instance of a line discipline into a tty structure. The
  *      ldisc must have a reference count above zero to ensure it remains/
  *      The tty instance refcount starts at zero.
  *
  *      Locking:
  *              Caller must hold references
  */
 
 static void tty_ldisc_assign(struct tty_struct *tty, struct tty_ldisc *ld)
 {
         tty->ldisc = *ld;
         tty->ldisc.refcount = 0;
 }
 
 /**
  *      tty_ldisc_try           -       internal helper
  *      @tty: the tty
  *
  *      Make a single attempt to grab and bump the refcount on
  *      the tty ldisc. Return 0 on failure or 1 on success. This is
  *      used to implement both the waiting and non waiting versions
  *      of tty_ldisc_ref
  *
  *      Locking: takes tty_ldisc_lock
  */
 
 static int tty_ldisc_try(struct tty_struct *tty)
 {
         unsigned long flags;
         struct tty_ldisc *ld;
         int ret = 0;
 
         spin_lock_irqsave(&tty_ldisc_lock, flags);
         ld = &tty->ldisc;
         if (test_bit(TTY_LDISC, &tty->flags)) {
                 ld->refcount++;
                 ret = 1;
         }
         spin_unlock_irqrestore(&tty_ldisc_lock, flags);
         return ret;
 }
 
 /**
  *      tty_ldisc_ref_wait      -       wait for the tty ldisc
  *      @tty: tty device
  *
  *      Dereference the line discipline for the terminal and take a
  *      reference to it. If the line discipline is in flux then
  *      wait patiently until it changes.
  *
  *      Note: Must not be called from an IRQ/timer context. The caller
  *      must also be careful not to hold other locks that will deadlock
  *      against a discipline change, such as an existing ldisc reference
  *      (which we check for)
  *
  *      Locking: call functions take tty_ldisc_lock
  */
 
 struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
 {
         /* wait_event is a macro */
         wait_event(tty_ldisc_wait, tty_ldisc_try(tty));
         if (tty->ldisc.refcount == 0)
                 printk(KERN_ERR "tty_ldisc_ref_wait\n");
         return &tty->ldisc;
 }
 
 EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
 
 /**
  *      tty_ldisc_ref           -       get the tty ldisc
  *      @tty: tty device
  *
  *      Dereference the line discipline for the terminal and take a
  *      reference to it. If the line discipline is in flux then
  *      return NULL. Can be called from IRQ and timer functions.
  *
  *      Locking: called functions take tty_ldisc_lock
  */
 
 struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
 {
         if (tty_ldisc_try(tty))
                 return &tty->ldisc;
         return NULL;
 }
 
 EXPORT_SYMBOL_GPL(tty_ldisc_ref);
 
 /**
  *      tty_ldisc_deref         -       free a tty ldisc reference
  *      @ld: reference to free up
  *
  *      Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May
  *      be called in IRQ context.
  *
  *      Locking: takes tty_ldisc_lock
  */
 
 void tty_ldisc_deref(struct tty_ldisc *ld)
 {
         unsigned long flags;
 
         BUG_ON(ld == NULL);
 
         spin_lock_irqsave(&tty_ldisc_lock, flags);
         if (ld->refcount == 0)
                 printk(KERN_ERR "tty_ldisc_deref: no references.\n");
         else
                 ld->refcount--;
         if (ld->refcount == 0)
                 wake_up(&tty_ldisc_wait);
         spin_unlock_irqrestore(&tty_ldisc_lock, flags);
 }
 
 EXPORT_SYMBOL_GPL(tty_ldisc_deref);
 
 /**
  *      tty_ldisc_enable        -       allow ldisc use
  *      @tty: terminal to activate ldisc on
  *
  *      Set the TTY_LDISC flag when the line discipline can be called
  *      again. Do necessary wakeups for existing sleepers.
  *
  *      Note: nobody should set this bit except via this function. Clearing
  *      directly is allowed.
  */
 
 static void tty_ldisc_enable(struct tty_struct *tty)
 {
         set_bit(TTY_LDISC, &tty->flags);
         wake_up(&tty_ldisc_wait);
 }
 
 /**
  *      tty_set_ldisc           -       set line discipline
  *      @tty: the terminal to set
  *      @ldisc: the line discipline
  *
  *      Set the discipline of a tty line. Must be called from a process
  *      context.
  *
  *      Locking: takes tty_ldisc_lock.
  *               called functions take termios_mutex
  */
 
 static int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 {
         int retval = 0;
         struct tty_ldisc o_ldisc;
         char buf[64];
         int work;
         unsigned long flags;
         struct tty_ldisc *ld;
         struct tty_struct *o_tty;
 
         if ((ldisc < N_TTY) || (ldisc >= NR_LDISCS))
                 return -EINVAL;
 
 restart:
 
         ld = tty_ldisc_get(ldisc);
         /* Eduardo Blanco <ejbs@cs.cs.com.uy> */
         /* Cyrus Durgin <cider@speakeasy.org> */
         if (ld == NULL) {
                 request_module("tty-ldisc-%d", ldisc);
                 ld = tty_ldisc_get(ldisc);
         }
         if (ld == NULL)
                 return -EINVAL;
 
         /*
          *      Problem: What do we do if this blocks ?
          */
 
         tty_wait_until_sent(tty, 0);
 
         if (tty->ldisc.num == ldisc) {
                 tty_ldisc_put(ldisc);
                 return 0;
         }
 
         /*
          *      No more input please, we are switching. The new ldisc
          *      will update this value in the ldisc open function
          */
 
         tty->receive_room = 0;
 
         o_ldisc = tty->ldisc;
         o_tty = tty->link;
 
         /*
          *      Make sure we don't change while someone holds a
          *      reference to the line discipline. The TTY_LDISC bit
          *      prevents anyone taking a reference once it is clear.
          *      We need the lock to avoid racing reference takers.
          */
 
         spin_lock_irqsave(&tty_ldisc_lock, flags);
         if (tty->ldisc.refcount || (o_tty && o_tty->ldisc.refcount)) {
                 if (tty->ldisc.refcount) {
                         /* Free the new ldisc we grabbed. Must drop the lock
                            first. */
                         spin_unlock_irqrestore(&tty_ldisc_lock, flags);
                         tty_ldisc_put(ldisc);
                         /*
                          * There are several reasons we may be busy, including
                          * random momentary I/O traffic. We must therefore
                          * retry. We could distinguish between blocking ops
                          * and retries if we made tty_ldisc_wait() smarter.
                          * That is up for discussion.
                          */
                         if (wait_event_interruptible(tty_ldisc_wait, tty->ldisc.refcount == 0) < 0)
                                 return -ERESTARTSYS;
                         goto restart;
                 }
                 if (o_tty && o_tty->ldisc.refcount) {
                         spin_unlock_irqrestore(&tty_ldisc_lock, flags);
                         tty_ldisc_put(ldisc);
                         if (wait_event_interruptible(tty_ldisc_wait, o_tty->ldisc.refcount == 0) < 0)
                                 return -ERESTARTSYS;
                         goto restart;
                 }
         }
         /*
          *      If the TTY_LDISC bit is set, then we are racing against
          *      another ldisc change
          */
         if (!test_bit(TTY_LDISC, &tty->flags)) {
                 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
                 tty_ldisc_put(ldisc);
                 ld = tty_ldisc_ref_wait(tty);
                 tty_ldisc_deref(ld);
                 goto restart;
         }
 
         clear_bit(TTY_LDISC, &tty->flags);
         if (o_tty)
                 clear_bit(TTY_LDISC, &o_tty->flags);
         spin_unlock_irqrestore(&tty_ldisc_lock, flags);
 
         /*
          *      From this point on we know nobody has an ldisc
          *      usage reference, nor can they obtain one until
          *      we say so later on.
          */
 
         work = cancel_delayed_work(&tty->buf.work);
         /*
          * Wait for ->hangup_work and ->buf.work handlers to terminate
          */
         flush_scheduled_work();
         /* Shutdown the current discipline. */
         if (tty->ldisc.close)
                 (tty->ldisc.close)(tty);
 
         /* Now set up the new line discipline. */
         tty_ldisc_assign(tty, ld);
         tty_set_termios_ldisc(tty, ldisc);
         if (tty->ldisc.open)
                 retval = (tty->ldisc.open)(tty);
         if (retval < 0) {
                 tty_ldisc_put(ldisc);
                 /* There is an outstanding reference here so this is safe */
                 tty_ldisc_assign(tty, tty_ldisc_get(o_ldisc.num));
                 tty_set_termios_ldisc(tty, tty->ldisc.num);
                 if (tty->ldisc.open && (tty->ldisc.open(tty) < 0)) {
                         tty_ldisc_put(o_ldisc.num);
                         /* This driver is always present */
                         tty_ldisc_assign(tty, tty_ldisc_get(N_TTY));
                         tty_set_termios_ldisc(tty, N_TTY);
                         if (tty->ldisc.open) {
                                 int r = tty->ldisc.open(tty);
 
                                 if (r < 0)
                                         panic("Couldn't open N_TTY ldisc for "
                                               "%s --- error %d.",
                                               tty_name(tty, buf), r);
                         }
                 }
         }
         /* At this point we hold a reference to the new ldisc and a
            a reference to the old ldisc. If we ended up flipping back
            to the existing ldisc we have two references to it */
 
         if (tty->ldisc.num != o_ldisc.num && tty->driver->set_ldisc)
                 tty->driver->set_ldisc(tty);
 
         tty_ldisc_put(o_ldisc.num);
 
         /*
          *      Allow ldisc referencing to occur as soon as the driver
          *      ldisc callback completes.
          */
 
         tty_ldisc_enable(tty);
         if (o_tty)
                 tty_ldisc_enable(o_tty);
 
         /* Restart it in case no characters kick it off. Safe if
            already running */
         if (work)
                 schedule_delayed_work(&tty->buf.work, 1);
         return retval;
 }
 
 /**
  *      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 p;
         }
         return NULL;
 }
 
 /**
  *      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: none
  */
 
 int tty_check_change(struct tty_struct *tty)
 {
         if (current->signal->tty != tty)
                 return 0;
         if (!tty->pgrp) {
                 printk(KERN_WARNING "tty_check_change: tty->pgrp == NULL!\n");
                 return 0;
         }
         if (task_pgrp(current) == tty->pgrp)
                 return 0;
         if (is_ignored(SIGTTOU))
                 return 0;
         if (is_current_pgrp_orphaned())
                 return -EIO;
         kill_pgrp(task_pgrp(current), SIGTTOU, 1);
         set_thread_flag(TIF_SIGPENDING);
         return -ERESTARTSYS;
 }
 
 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 int hung_up_tty_ioctl(struct inode *inode, 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,
         .ioctl          = tty_ioctl,
         .compat_ioctl   = tty_compat_ioctl,
         .open           = tty_open,
         .release        = tty_release,
         .fasync         = tty_fasync,
 };
 
 #ifdef CONFIG_UNIX98_PTYS
 static const struct file_operations ptmx_fops = {
         .llseek         = no_llseek,
         .read           = tty_read,
         .write          = tty_write,
         .poll           = tty_poll,
         .ioctl          = tty_ioctl,
         .compat_ioctl   = tty_compat_ioctl,
         .open           = ptmx_open,
         .release        = tty_release,
         .fasync         = tty_fasync,
 };
 #endif
 
 static const struct file_operations console_fops = {
         .llseek         = no_llseek,
         .read           = tty_read,
         .write          = redirected_tty_write,
         .poll           = tty_poll,
         .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,
         .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->write_wakeup)
                                 ld->write_wakeup(tty);
                         tty_ldisc_deref(ld);
                 }
         }
         wake_up_interruptible(&tty->write_wait);
 }
 
 EXPORT_SYMBOL_GPL(tty_wakeup);
 
 /**
  *      tty_ldisc_flush -       flush line discipline queue
  *      @tty: tty
  *
  *      Flush the line discipline queue (if any) for this tty. If there
  *      is no line discipline active this is a no-op.
  */
 
 void tty_ldisc_flush(struct tty_struct *tty)
 {
         struct tty_ldisc *ld = tty_ldisc_ref(tty);
         if (ld) {
                 if (ld->flush_buffer)
                         ld->flush_buffer(tty);
                 tty_ldisc_deref(ld);
         }
         tty_buffer_flush(tty);
 }
 
 EXPORT_SYMBOL_GPL(tty_ldisc_flush);
 
 /**
  *      tty_reset_termios       -       reset terminal state
  *      @tty: tty to reset
  *
  *      Restore a terminal to the driver default state
  */
 
 static void tty_reset_termios(struct tty_struct *tty)
 {
         mutex_lock(&tty->termios_mutex);
         *tty->termios = tty->driver->init_termios;
         tty->termios->c_ispeed = tty_termios_input_baud_rate(tty->termios);
         tty->termios->c_ospeed = tty_termios_baud_rate(tty->termios);
         mutex_unlock(&tty->termios_mutex);
 }
 
 /**
  *      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;
         struct tty_ldisc *ld;
         int    closecount = 0, n;
 
         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");
         /* This breaks for file handles being sent over AF_UNIX sockets ? */
         lock_list_for_each_entry(filp, percpu_list_head(&tty->tty_files), f_u.fu_llist) {
                 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;
         }
         /*
          * FIXME! What are the locking issues here? This may me overdoing
          * things... This question is especially important now that we've
          * removed the irqlock.
          */
         ld = tty_ldisc_ref(tty);
         if (ld != NULL) {
                 /* We may have no line discipline at this point */
                 if (ld->flush_buffer)
                         ld->flush_buffer(tty);
                 if (tty->driver->flush_buffer)
                         tty->driver->flush_buffer(tty);
                 if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
                     ld->write_wakeup)
                         ld->write_wakeup(tty);
                 if (ld->hangup)
                         ld->hangup(tty);
         }
         /*
          * FIXME: Once we trust the LDISC code better we can wait here for
          * ldisc completion and fix the driver call race
          */
         wake_up_interruptible(&tty->write_wait);
         wake_up_interruptible(&tty->read_wait);
         /*
          * Shutdown the current line discipline, and reset it to
          * N_TTY.
          */
         if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS)
                 tty_reset_termios(tty);
         /* Defer ldisc switch */
         /* tty_deferred_ldisc_switch(N_TTY);
 
           This should get done automatically when the port closes and
           tty_release is called */
 
         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;
                         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 */
                         if (tty->pgrp)
                                 p->signal->tty_old_pgrp = get_pid(tty->pgrp);
                         spin_unlock_irq(&p->sighand->siglock);
                 } while_each_pid_task(tty->session, PIDTYPE_SID, p);
         }
         read_unlock(&tasklist_lock);
 
         tty->flags = 0;
         put_pid(tty->session);
         put_pid(tty->pgrp);
         tty->session = NULL;
         tty->pgrp = NULL;
         tty->ctrl_status = 0;
         /*
          * 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->driver->close)
                         for (n = 0; n < closecount; n++)
                                 tty->driver->close(tty, cons_filp);
         } else if (tty->driver->hangup)
                 (tty->driver->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);
         if (ld) {
                 tty_ldisc_enable(tty);
                 tty_ldisc_deref(ld);
         }
         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_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);
 
 /**
  *      is_tty  -       checker whether file is a TTY
  *      @filp:          file handle that may be a tty
  *
  *      Check if the file handle is a tty handle.
  */
 
 int is_tty(struct file *filp)
 {
         return filp->f_op->read == tty_read
                 || filp->f_op->read == hung_up_tty_read;
 }
 
 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;
 
         lock_kernel();
 
         mutex_lock(&tty_mutex);
         tty = get_current_tty();
         if (tty) {
                 tty_pgrp = get_pid(tty->pgrp);
                 mutex_unlock(&tty_mutex);
                 /* XXX: here we race, there is nothing protecting tty */
                 if (on_exit && tty->driver->type != TTY_DRIVER_TYPE_PTY)
                         tty_vhangup(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);
                 }
                 mutex_unlock(&tty_mutex);
                 unlock_kernel();
                 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);
 
         mutex_lock(&tty_mutex);
         /* It is possible that do_tty_hangup has free'd this tty */
         tty = get_current_tty();
         if (tty) {
                 put_pid(tty->session);
                 put_pid(tty->pgrp);
                 tty->session = NULL;
                 tty->pgrp = NULL;
         } else {
 #ifdef TTY_DEBUG_HANGUP
                 printk(KERN_DEBUG "error attempted to write to tty [0x%p]"
                        " = NULL", tty);
 #endif
         }
         mutex_unlock(&tty_mutex);
 
         /* Now clear signal->tty under the lock */
         read_lock(&tasklist_lock);
         session_clear_tty(task_session(current));
         read_unlock(&tasklist_lock);
         unlock_kernel();
 }
 
 /**
  *
  *      no_tty  - Ensure the current process does not have a controlling tty
  */
 void no_tty(void)
 {
         struct task_struct *tsk = current;
         if (tsk->signal->leader)
                 disassociate_ctty(0);
         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:
  *              Broken. Relies on BKL which is unsafe here.
  */
 
 void stop_tty(struct tty_struct *tty)
 {
         if (tty->stopped)
                 return;
         tty->stopped = 1;
         if (tty->link && tty->link->packet) {
                 tty->ctrl_status &= ~TIOCPKT_START;
                 tty->ctrl_status |= TIOCPKT_STOP;
                 wake_up_interruptible(&tty->link->read_wait);
         }
         if (tty->driver->stop)
                 (tty->driver->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:
  *              Broken. Relies on BKL which is unsafe here.
  */
 
 void start_tty(struct tty_struct *tty)
 {
         if (!tty->stopped || tty->flow_stopped)
                 return;
         tty->stopped = 0;
         if (tty->link && tty->link->packet) {
                 tty->ctrl_status &= ~TIOCPKT_STOP;
                 tty->ctrl_status |= TIOCPKT_START;
                 wake_up_interruptible(&tty->link->read_wait);
         }
         if (tty->driver->start)
                 (tty->driver->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
  *              For historical reasons the line discipline read method is
  *      invoked under the BKL. This will go away in time so do not rely on it
  *      in new code. 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);
         lock_kernel();
         if (ld->read)
                 i = (ld->read)(tty, file, buf, count);
         else
                 i = -EIO;
         tty_ldisc_deref(ld);
         unlock_kernel();
         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(&tty->write_wait);
 }
 
 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;
 
                 if (chunk < 1024)
                         chunk = 1024;
 
                 buf = kmalloc(chunk, GFP_KERNEL);
                 if (!buf) {
                         ret = -ENOMEM;
                         goto out;
                 }
                 kfree(tty->write_buf);
                 tty->write_cnt = chunk;
                 tty->write_buf = buf;
         }
 
         /* 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;
                 lock_kernel();
                 ret = write(tty, file, tty->write_buf, size);
                 unlock_kernel();
                 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               -       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 involked in parallel for each device
  *              The line discipline write method is called under the big
  *      kernel lock for historical reasons. New code should not rely on this.
  */
 
 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->driver->write ||
                 (test_bit(TTY_IO_ERROR, &tty->flags)))
                         return -EIO;
 
         ld = tty_ldisc_ref_wait(tty);
         if (!ld->write)
                 ret = -EIO;
         else
                 ret = do_tty_write(ld->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);
 }
 
 /**
  *      pty_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);
 }
 
 /**
  *      init_dev                -       initialise a tty device
  *      @driver: tty driver we are opening a device on
  *      @idx: device index
  *      @tty: returned tty structure
  *
  *      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.
  */
 
 static int init_dev(struct tty_driver *driver, int idx,
         struct tty_struct **ret_tty)
 {
         struct tty_struct *tty, *o_tty;
         struct ktermios *tp, **tp_loc, *o_tp, **o_tp_loc;
         struct ktermios *ltp, **ltp_loc, *o_ltp, **o_ltp_loc;
         int retval = 0;
 
         /* check whether we're reopening an existing tty */
         if (driver->flags & TTY_DRIVER_DEVPTS_MEM) {
                 tty = devpts_get_tty(idx);
                 /*
                  * If we don't have a tty here on a slave open, it's because
                  * the master already started the close process and there's
                  * no relation between devpts file and tty anymore.
                  */
                 if (!tty && driver->subtype == PTY_TYPE_SLAVE) {
                         retval = -EIO;
                         goto end_init;
                 }
                 /*
                  * It's safe from now on because init_dev() is called with
                  * tty_mutex held and release_dev() won't change tty->count
                  * or tty->flags without having to grab tty_mutex
                  */
                 if (tty && driver->subtype == PTY_TYPE_MASTER)
                         tty = tty->link;
         } else {
                 tty = driver->ttys[idx];
         }
         if (tty) goto fast_track;
 
         /*
          * 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)) {
                 retval = -ENODEV;
                 goto end_init;
         }
 
         o_tty = NULL;
         tp = o_tp = NULL;
         ltp = o_ltp = NULL;
 
         tty = alloc_tty_struct();
         if (!tty)
                 goto fail_no_mem;
         initialize_tty_struct(tty);
         tty->driver = driver;
         tty->index = idx;
         tty_line_name(driver, idx, tty->name);
 
         if (driver->flags & TTY_DRIVER_DEVPTS_MEM) {
                 tp_loc = &tty->termios;
                 ltp_loc = &tty->termios_locked;
         } else {
                 tp_loc = &driver->termios[idx];
                 ltp_loc = &driver->termios_locked[idx];
         }
 
         if (!*tp_loc) {
                 tp = kmalloc(sizeof(struct ktermios), GFP_KERNEL);
                 if (!tp)
                         goto free_mem_out;
                 *tp = driver->init_termios;
         }
 
         if (!*ltp_loc) {
                 ltp = kzalloc(sizeof(struct ktermios), GFP_KERNEL);
                 if (!ltp)
                         goto free_mem_out;
         }
 
         if (driver->type == TTY_DRIVER_TYPE_PTY) {
                 o_tty = alloc_tty_struct();
                 if (!o_tty)
                         goto free_mem_out;
                 initialize_tty_struct(o_tty);
                 o_tty->driver = driver->other;
                 o_tty->index = idx;
                 tty_line_name(driver->other, idx, o_tty->name);
 
                 if (driver->flags & TTY_DRIVER_DEVPTS_MEM) {
                         o_tp_loc = &o_tty->termios;
                         o_ltp_loc = &o_tty->termios_locked;
                 } else {
                         o_tp_loc = &driver->other->termios[idx];
                         o_ltp_loc = &driver->other->termios_locked[idx];
                 }
 
                 if (!*o_tp_loc) {
                         o_tp = kmalloc(sizeof(struct ktermios), GFP_KERNEL);
                         if (!o_tp)
                                 goto free_mem_out;
                         *o_tp = driver->other->init_termios;
                 }
 
                 if (!*o_ltp_loc) {
                         o_ltp = kzalloc(sizeof(struct ktermios), GFP_KERNEL);
                         if (!o_ltp)
                                 goto free_mem_out;
                 }
 
                 /*
                  * Everything allocated ... set up the o_tty structure.
                  */
                 if (!(driver->other->flags & TTY_DRIVER_DEVPTS_MEM))
                         driver->other->ttys[idx] = o_tty;
                 if (!*o_tp_loc)
                         *o_tp_loc = o_tp;
                 if (!*o_ltp_loc)
                         *o_ltp_loc = o_ltp;
                 o_tty->termios = *o_tp_loc;
                 o_tty->termios_locked = *o_ltp_loc;
                 driver->other->refcount++;
                 if (driver->subtype == PTY_TYPE_MASTER)
                         o_tty->count++;
 
                 /* Establish the links in both directions */
                 tty->link   = o_tty;
                 o_tty->link = tty;
         }
 
         /*
          * All structures have been allocated, so now we install them.
          * Failures after this point use release_tty to clean up, so
          * there's no need to null out the local pointers.
          */
         if (!(driver->flags & TTY_DRIVER_DEVPTS_MEM))
                 driver->ttys[idx] = tty;
 
         if (!*tp_loc)
                 *tp_loc = tp;
         if (!*ltp_loc)
                 *ltp_loc = ltp;
         tty->termios = *tp_loc;
         tty->termios_locked = *ltp_loc;
         /* 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);
         driver->refcount++;
         tty->count++;
 
         /*
          * 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.
          */
 
         if (tty->ldisc.open) {
                 retval = (tty->ldisc.open)(tty);
                 if (retval)
                         goto release_mem_out;
         }
         if (o_tty && o_tty->ldisc.open) {
                 retval = (o_tty->ldisc.open)(o_tty);
                 if (retval) {
                         if (tty->ldisc.close)
                                 (tty->ldisc.close)(tty);
                         goto release_mem_out;
                 }
                 tty_ldisc_enable(o_tty);
         }
         tty_ldisc_enable(tty);
         goto success;
 
         /*
          * This fast open can be used if the tty is already open.
          * No memory is allocated, and the only failures are from
          * attempting to open a closing tty or attempting multiple
          * opens on a pty master.
          */
 fast_track:
         if (test_bit(TTY_CLOSING, &tty->flags)) {
                 retval = -EIO;
                 goto end_init;
         }
         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) {
                         retval = -EIO;
                         goto end_init;
                 }
                 tty->link->count++;
         }
         tty->count++;
         tty->driver = driver; /* N.B. why do this every time?? */
 
         /* FIXME */
         if (!test_bit(TTY_LDISC, &tty->flags))
                 printk(KERN_ERR "init_dev but no ldisc\n");
 success:
         *ret_tty = tty;
 
         /* All paths come through here to release the mutex */
 end_init:
         return retval;
 
         /* Release locally allocated memory ... nothing placed in slots */
 free_mem_out:
         kfree(o_tp);
         if (o_tty)
                 free_tty_struct(o_tty);
         kfree(ltp);
         kfree(tp);
         free_tty_struct(tty);
 
 fail_no_mem:
         module_put(driver->owner);
         retval = -ENOMEM;
         goto end_init;
 
         /* call the tty release_tty routine to clean out this slot */
 release_mem_out:
         if (printk_ratelimit())
                 printk(KERN_INFO "init_dev: ldisc open failed, "
                                  "clearing slot %d\n", idx);
         release_tty(tty, idx);
         goto end_init;
 }
 
 /**
  *      release_one_tty         -       release tty structure memory
  *
  *      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.
  *              FIXME: should we require tty_mutex is held here ??
  */
 static void release_one_tty(struct tty_struct *tty, int idx)
 {
         int devpts = tty->driver->flags & TTY_DRIVER_DEVPTS_MEM;
         struct ktermios *tp;
 
         if (!devpts)
                 tty->driver->ttys[idx] = NULL;
 
         if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS) {
                 tp = tty->termios;
                 if (!devpts)
                         tty->driver->termios[idx] = NULL;
                 kfree(tp);
 
                 tp = tty->termios_locked;
                 if (!devpts)
                         tty->driver->termios_locked[idx] = NULL;
                 kfree(tp);
         }
 
 
         tty->magic = 0;
         tty->driver->refcount--;
 
         percpu_list_fold(&tty->tty_files);
         lock_list_del_init(percpu_list_head(&tty->tty_files));
         percpu_list_destroy(&tty->tty_files);
 
         free_tty_struct(tty);
 }
 
 /**
  *      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)
 {
         struct tty_driver *driver = tty->driver;
 
         if (tty->link)
                 release_one_tty(tty->link, idx);
         release_one_tty(tty, idx);
         module_put(driver->owner);
 }
 
 /*
  * 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.
  */
 static void 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];
         unsigned long flags;
 
         tty = (struct tty_struct *)filp->private_data;
         if (tty_paranoia_check(tty, filp->f_path.dentry->d_inode,
                                                         "release_dev"))
                 return;
 
         check_tty_count(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 "release_dev: bad idx when trying to "
                                   "free (%s)\n", tty->name);
                 return;
         }
         if (!(tty->driver->flags & TTY_DRIVER_DEVPTS_MEM)) {
                 if (tty != tty->driver->ttys[idx]) {
                         printk(KERN_DEBUG "release_dev: driver.table[%d] not tty "
                                "for (%s)\n", idx, tty->name);
                         return;
                 }
                 if (tty->termios != tty->driver->termios[idx]) {
                         printk(KERN_DEBUG "release_dev: driver.termios[%d] not termios "
                                "for (%s)\n",
                                idx, tty->name);
                         return;
                 }
                 if (tty->termios_locked != tty->driver->termios_locked[idx]) {
                         printk(KERN_DEBUG "release_dev: driver.termios_locked[%d] not "
                                "termios_locked for (%s)\n",
                                idx, tty->name);
                         return;
                 }
         }
 #endif
 
 #ifdef TTY_DEBUG_HANGUP
         printk(KERN_DEBUG "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 "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 "release_dev: other->termios[%d] "
                                           "not o_termios for (%s)\n",
                                idx, tty->name);
                         return;
                 }
                 if (o_tty->termios_locked !=
                       tty->driver->other->termios_locked[idx]) {
                         printk(KERN_DEBUG "release_dev: other->termios_locked["
                                           "%d] not o_termios_locked for (%s)\n",
                                idx, tty->name);
                         return;
                 }
                 if (o_tty->link != tty) {
                         printk(KERN_DEBUG "release_dev: bad pty pointers\n");
                         return;
                 }
         }
 #endif
         if (tty->driver->close)
                 tty->driver->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(&tty->read_wait);
                                 do_sleep++;
                         }
                         if (waitqueue_active(&tty->write_wait)) {
                                 wake_up(&tty->write_wait);
                                 do_sleep++;
                         }
                 }
                 if (o_tty_closing) {
                         if (waitqueue_active(&o_tty->read_wait)) {
                                 wake_up(&o_tty->read_wait);
                                 do_sleep++;
                         }
                         if (waitqueue_active(&o_tty->write_wait)) {
                                 wake_up(&o_tty->write_wait);
                                 do_sleep++;
                         }
                 }
                 if (!do_sleep)
                         break;
 
                 printk(KERN_WARNING "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 "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 "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
         /*
          * Prevent flush_to_ldisc() from rescheduling the work for later.  Then
          * kill any delayed work. As this is the final close it does not
          * race with the set_ldisc code path.
          */
         clear_bit(TTY_LDISC, &tty->flags);
         cancel_delayed_work(&tty->buf.work);
 
         /*
          * Wait for ->hangup_work and ->buf.work handlers to terminate
          */
 
         flush_scheduled_work();
 
         /*
          * Wait for any short term users (we know they are just driver
          * side waiters as the file is closing so user count on the file
          * side is zero.
          */
         spin_lock_irqsave(&tty_ldisc_lock, flags);
         while (tty->ldisc.refcount) {
                 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
                 wait_event(tty_ldisc_wait, tty->ldisc.refcount == 0);
                 spin_lock_irqsave(&tty_ldisc_lock, flags);
         }
         spin_unlock_irqrestore(&tty_ldisc_lock, flags);
         /*
          * Shutdown the current line discipline, and reset it to N_TTY.
          * N.B. why reset ldisc when we're releasing the memory??
          *
          * FIXME: this MUST get fixed for the new reflocking
          */
         if (tty->ldisc.close)
                 (tty->ldisc.close)(tty);
         tty_ldisc_put(tty->ldisc.num);
 
         /*
          *      Switch the line discipline back
          */
         tty_ldisc_assign(tty, tty_ldisc_get(N_TTY));
         tty_set_termios_ldisc(tty, N_TTY);
         if (o_tty) {
                 /* FIXME: could o_tty be in setldisc here ? */
                 clear_bit(TTY_LDISC, &o_tty->flags);
                 if (o_tty->ldisc.close)
                         (o_tty->ldisc.close)(o_tty);
                 tty_ldisc_put(o_tty->ldisc.num);
                 tty_ldisc_assign(o_tty, tty_ldisc_get(N_TTY));
                 tty_set_termios_ldisc(o_tty, N_TTY);
         }
         /*
          * The release_tty function takes care of the details of clearing
          * the slots and preserving the termios structure.
          */
         release_tty(tty, idx);
 
 #ifdef CONFIG_UNIX98_PTYS
         /* Make this pty number available for reallocation */
         if (devpts) {
                 mutex_lock(&allocated_ptys_lock);
                 idr_remove(&allocated_ptys, idx);
                 mutex_unlock(&allocated_ptys_lock);
         }
 #endif
 
 }
 
 /**
  *      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 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;
         int noctty, retval;
         struct tty_driver *driver;
         int index;
         dev_t device = inode->i_rdev;
         unsigned short 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;
                 index = tty->index;
                 filp->f_flags |= O_NONBLOCK; /* Don't let /dev/tty block */
                 /* noctty = 1; */
                 goto got_driver;
         }
 #ifdef CONFIG_VT
         if (device == MKDEV(TTY_MAJOR, 0)) {
                 extern struct tty_driver *console_driver;
                 driver = console_driver;
                 index = fg_console;
                 noctty = 1;
                 goto got_driver;
         }
 #endif
         if (device == MKDEV(TTYAUX_MAJOR, 1)) {
                 driver = console_device(&index);
                 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:
         retval = init_dev(driver, index, &tty);
         mutex_unlock(&tty_mutex);
         if (retval)
                 return retval;
 
         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->driver->open)
                         retval = tty->driver->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
                 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);
         tty_audit_opening();
         return 0;
 }
 
 #ifdef CONFIG_UNIX98_PTYS
 /**
  *      ptmx_open               -       open a unix 98 pty master
  *      @inode: inode of device file
  *      @filp: file pointer to tty
  *
  *      Allocate a unix98 pty master device from the ptmx driver.
  *
  *      Locking: tty_mutex protects theinit_dev work. tty->count should
  *              protect the rest.
  *              allocated_ptys_lock handles the list of free pty numbers
  */
 
 static int ptmx_open(struct inode *inode, struct file *filp)
 {
         struct tty_struct *tty;
         int retval;
         int index;
         int idr_ret;
 
         nonseekable_open(inode, filp);
 
         /* find a device that is not in use. */
         mutex_lock(&allocated_ptys_lock);
         if (!idr_pre_get(&allocated_ptys, GFP_KERNEL)) {
                 mutex_unlock(&allocated_ptys_lock);
                 return -ENOMEM;
         }
         idr_ret = idr_get_new(&allocated_ptys, NULL, &index);
         if (idr_ret < 0) {
                 mutex_unlock(&allocated_ptys_lock);
                 if (idr_ret == -EAGAIN)
                         return -ENOMEM;
                 return -EIO;
         }
         if (index >= pty_limit) {
                 idr_remove(&allocated_ptys, index);
                 mutex_unlock(&allocated_ptys_lock);
                 return -EIO;
         }
         mutex_unlock(&allocated_ptys_lock);
 
         mutex_lock(&tty_mutex);
         retval = init_dev(ptm_driver, index, &tty);
         mutex_unlock(&tty_mutex);
 
         if (retval)
                 goto out;
 
         set_bit(TTY_PTY_LOCK, &tty->flags); /* LOCK THE SLAVE */
         filp->private_data = tty;
         file_move(filp, &tty->tty_files);
 
         retval = -ENOMEM;
         if (devpts_pty_new(tty->link))
                 goto out1;
 
         check_tty_count(tty, "tty_open");
         retval = ptm_driver->open(tty, filp);
         if (!retval) {
                 tty_audit_opening();
                 return 0;
         }
 out1:
         release_dev(filp);
         return retval;
 out:
         mutex_lock(&allocated_ptys_lock);
         idr_remove(&allocated_ptys, index);
         mutex_unlock(&allocated_ptys_lock);
         return retval;
 }
 #endif
 
 /**
  *      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 release_dev
  */
 
 static int tty_release(struct inode *inode, struct file *filp)
 {
         lock_kernel();
         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->poll)
                 ret = (ld->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;
         int retval;
 
         tty = (struct tty_struct *)filp->private_data;
         if (tty_paranoia_check(tty, filp->f_path.dentry->d_inode, "tty_fasync"))
                 return 0;
 
         retval = fasync_helper(fd, filp, on, &tty->fasync);
         if (retval <= 0)
                 return retval;
 
         if (on) {
                 enum pid_type type;
                 struct pid *pid;
                 if (!waitqueue_active(&tty->read_wait))
                         tty->minimum_to_wake = 1;
                 if (tty->pgrp) {
                         pid = tty->pgrp;
                         type = PIDTYPE_PGID;
                 } else {
                         pid = task_pid(current);
                         type = PIDTYPE_PID;
                 }
                 retval = __f_setown(filp, pid, type, 0);
                 if (retval)
                         return retval;
         } else {
                 if (!tty->fasync && !waitqueue_active(&tty->read_wait))
                         tty->minimum_to_wake = N_TTY_BUF_SIZE;
         }
         return 0;
 }
 
 /**
  *      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;
         ld = tty_ldisc_ref_wait(tty);
         ld->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;
 }
 
 /**
  *      tiocswinsz              -       implement window size set ioctl
  *      @tty; 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:
  *              Called function use the console_sem is used to ensure we do
  *      not try and resize the console twice at once.
  *              The tty->termios_mutex is used to ensure we don't double
  *      resize and get confused. Lock order - tty->termios_mutex before
  *      console sem
  */
 
 static int tiocswinsz(struct tty_struct *tty, struct tty_struct *real_tty,
         struct winsize __user *arg)
 {
         struct winsize tmp_ws;
 
         if (copy_from_user(&tmp_ws, arg, sizeof(*arg)))
                 return -EFAULT;
 
         mutex_lock(&tty->termios_mutex);
         if (!memcmp(&tmp_ws, &tty->winsize, sizeof(*arg)))
                 goto done;
 
 #ifdef CONFIG_VT
         if (tty->driver->type == TTY_DRIVER_TYPE_CONSOLE) {
                 if (vc_lock_resize(tty->driver_data, tmp_ws.ws_col,
                                         tmp_ws.ws_row)) {
                         mutex_unlock(&tty->termios_mutex);
                         return -ENXIO;
                 }
         }
 #endif
         if (tty->pgrp)
                 kill_pgrp(tty->pgrp, SIGWINCH, 1);
         if ((real_tty->pgrp != tty->pgrp) && real_tty->pgrp)
                 kill_pgrp(real_tty->pgrp, SIGWINCH, 1);
         tty->winsize = tmp_ws;
         real_tty->winsize = tmp_ws;
 done:
         mutex_unlock(&tty->termios_mutex);
         return 0;
 }
 
 /**
  *      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;
 
         if (nonblock)
                 file->f_flags |= O_NONBLOCK;
         else
                 file->f_flags &= ~O_NONBLOCK;
         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;
 }
 
 /**
  *      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)
 {
         /*
          * (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;
         return put_user(pid_vnr(real_tty->pgrp), p);
 }
 
 /**
  *      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: None
  */
 
 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);
 
         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;
         put_pid(real_tty->pgrp);
         real_tty->pgrp = get_pid(pgrp);
 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;
 
         if (get_user(ldisc, p))
                 return -EFAULT;
         return tty_set_ldisc(tty, ldisc);
 }
 
 /**
  *      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)
 {
         if (tty_write_lock(tty, 0) < 0)
                 return -EINTR;
         tty->driver->break_ctl(tty, -1);
         if (!signal_pending(current))
                 msleep_interruptible(duration);
         tty->driver->break_ctl(tty, 0);
         tty_write_unlock(tty);
         if (signal_pending(current))
                 return -EINTR;
         return 0;
 }
 
 /**
  *      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->driver->tiocmget) {
                 retval = tty->driver->tiocmget(tty, file);
 
                 if (retval >= 0)
                         retval = put_user(retval, p);
         }
         return retval;
 }
 
 /**
  *      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 = -EINVAL;
 
         if (tty->driver->tiocmset) {
                 unsigned int set, clear, val;
 
                 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;
 
                 retval = tty->driver->tiocmset(tty, file, set, clear);
         }
         return retval;
 }
 
 /*
  * Split this up, as gcc can choke on it otherwise..
  */
 int tty_ioctl(struct inode *inode, 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;
 
         tty = (struct tty_struct *)file->private_data;
         if (tty_paranoia_check(tty, inode, "tty_ioctl"))
                 return -EINVAL;
 
         /* CHECKME: is this safe as one end closes ? */
 
         real_tty = tty;
         if (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
             tty->driver->subtype == PTY_TYPE_MASTER)
                 real_tty = tty->link;
 
         /*
          * Break handling by driver
          */
         if (!tty->driver->break_ctl) {
                 switch (cmd) {
                 case TIOCSBRK:
                 case TIOCCBRK:
                         if (tty->driver->ioctl)
                                 return tty->driver->ioctl(tty, file, cmd, arg);
                         return -EINVAL;
 
                 /* These two ioctl's always return success; even if */
                 /* the driver doesn't support them. */
                 case TCSBRK:
                 case TCSBRKP:
                         if (!tty->driver->ioctl)
                                 return 0;
                         retval = tty->driver->ioctl(tty, file, cmd, arg);
                         if (retval == -ENOIOCTLCMD)
                                 retval = 0;
                         return retval;
                 }
         }
 
         /*
          * 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;
         }
 
         switch (cmd) {
         case TIOCSTI:
                 return tiocsti(tty, p);
         case TIOCGWINSZ:
                 return tiocgwinsz(tty, p);
         case TIOCSWINSZ:
                 return tiocswinsz(tty, 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:
                 /* FIXME: check this is ok */
                 return put_user(tty->ldisc.num, (int __user *)p);
         case TIOCSETD:
                 return tiocsetd(tty, p);
 #ifdef CONFIG_VT
         case TIOCLINUX:
                 return tioclinux(tty, arg);
 #endif
         /*
          * Break handling
          */
         case TIOCSBRK:  /* Turn break on, unconditionally */
                 tty->driver->break_ctl(tty, -1);
                 return 0;
 
         case TIOCCBRK:  /* Turn break off, unconditionally */
                 tty->driver->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->driver->ioctl) {
                 retval = (tty->driver->ioctl)(tty, file, cmd, arg);
                 if (retval != -ENOIOCTLCMD)
                         return retval;
         }
         ld = tty_ldisc_ref_wait(tty);
         retval = -EINVAL;
         if (ld->ioctl) {
                 retval = ld->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->driver->compat_ioctl) {
                 retval = (tty->driver->compat_ioctl)(tty, file, cmd, arg);
                 if (retval != -ENOIOCTLCMD)
                         return retval;
         }
 
         ld = tty_ldisc_ref_wait(tty);
         if (ld->compat_ioctl)
                 retval = ld->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);
 
         if (tty->driver->flush_buffer)
                 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_nr(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_nr(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);
 
 /**
  *      flush_to_ldisc
  *      @work: tty structure passed from work queue.
  *
  *      This routine is called out of the software interrupt to flush data
  *      from the buffer chain to the line discipline.
  *
  *      Locking: holds tty->buf.lock to guard buffer list. Drops the lock
  *      while invoking the line discipline receive_buf method. The
  *      receive_buf method is single threaded for each tty instance.
  */
 
 static void flush_to_ldisc(struct work_struct *work)
 {
         struct tty_struct *tty =
                 container_of(work, struct tty_struct, buf.work.work);
         unsigned long   flags;
         struct tty_ldisc *disc;
         struct tty_buffer *tbuf, *head;
         char *char_buf;
         unsigned char *flag_buf;
 
         disc = tty_ldisc_ref(tty);
         if (disc == NULL)       /*  !TTY_LDISC */
                 return;
 
         spin_lock_irqsave(&tty->buf.lock, flags);
         /* So we know a flush is running */
         set_bit(TTY_FLUSHING, &tty->flags);
         head = tty->buf.head;
         if (head != NULL) {
                 tty->buf.head = NULL;
                 for (;;) {
                         int count = head->commit - head->read;
                         if (!count) {
                                 if (head->next == NULL)
                                         break;
                                 tbuf = head;
                                 head = head->next;
                                 tty_buffer_free(tty, tbuf);
                                 continue;
                         }
                         /* Ldisc or user is trying to flush the buffers
                            we are feeding to the ldisc, stop feeding the
                            line discipline as we want to empty the queue */
                         if (test_bit(TTY_FLUSHPENDING, &tty->flags))
                                 break;
                         if (!tty->receive_room) {
                                 schedule_delayed_work(&tty->buf.work, 1);
                                 break;
                         }
                         if (count > tty->receive_room)
                                 count = tty->receive_room;
                         char_buf = head->char_buf_ptr + head->read;
                         flag_buf = head->flag_buf_ptr + head->read;
                         head->read += count;
                         spin_unlock_irqrestore(&tty->buf.lock, flags);
                         disc->receive_buf(tty, char_buf, flag_buf, count);
                         spin_lock_irqsave(&tty->buf.lock, flags);
                 }
                 /* Restore the queue head */
                 tty->buf.head = head;
         }
         /* We may have a deferred request to flush the input buffer,
            if so pull the chain under the lock and empty the queue */
         if (test_bit(TTY_FLUSHPENDING, &tty->flags)) {
                 __tty_buffer_flush(tty);
                 clear_bit(TTY_FLUSHPENDING, &tty->flags);
                 wake_up(&tty->read_wait);
         }
         clear_bit(TTY_FLUSHING, &tty->flags);
         spin_unlock_irqrestore(&tty->buf.lock, flags);
 
         tty_ldisc_deref(disc);
 }
 
 /**
  *      tty_flip_buffer_push    -       terminal
  *      @tty: tty to push
  *
  *      Queue a push of the terminal flip buffers to the line discipline. This
  *      function must not be called from IRQ context if tty->low_latency is set.
  *
  *      In the event of the queue being busy for flipping the work will be
  *      held off and retried later.
  *
  *      Locking: tty buffer lock. Driver locks in low latency mode.
  */
 
 void tty_flip_buffer_push(struct tty_struct *tty)
 {
         unsigned long flags;
         spin_lock_irqsave(&tty->buf.lock, flags);
         if (tty->buf.tail != NULL)
                 tty->buf.tail->commit = tty->buf.tail->used;
         spin_unlock_irqrestore(&tty->buf.lock, flags);
 
 #ifndef CONFIG_PREEMPT_RT
         if (tty->low_latency)
                 flush_to_ldisc(&tty->buf.work.work);
         else
                 schedule_delayed_work(&tty->buf.work, 1);
 #else
         flush_to_ldisc(&tty->buf.work.work);
 #endif
 }
 
 EXPORT_SYMBOL(tty_flip_buffer_push);
 
 
 /**
  *      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
  */
 
 static void initialize_tty_struct(struct tty_struct *tty)
 {
         memset(tty, 0, sizeof(struct tty_struct));
         tty->magic = TTY_MAGIC;
         tty_ldisc_assign(tty, tty_ldisc_get(N_TTY));
         tty->session = NULL;
         tty->pgrp = NULL;
         tty->overrun_time = jiffies;
         tty->buf.head = tty->buf.tail = NULL;
         tty_buffer_init(tty);
         INIT_DELAYED_WORK(&tty->buf.work, flush_to_ldisc);
         mutex_init(&tty->termios_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);
         spin_lock_init(&tty->read_lock);
         percpu_list_init(&tty->tty_files);
         INIT_WORK(&tty->SAK_work, do_SAK_work);
 }
 
 /*
  * The default put_char routine if the driver did not define one.
  */
 
 static void tty_default_put_char(struct tty_struct *tty, unsigned char ch)
 {
         tty->driver->write(tty, &ch, 1);
 }
 
 static 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, name);
 }
 
 /**
  *      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_register_device);
 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) {
                 driver->magic = TTY_DRIVER_MAGIC;
                 driver->num = lines;
                 /* later we'll move allocation of tables here */
         }
         return driver;
 }
 
 void put_tty_driver(struct tty_driver *driver)
 {
         kfree(driver);
 }
 
 void tty_set_operations(struct tty_driver *driver,
                         const struct tty_operations *op)
 {
         driver->open = op->open;
         driver->close = op->close;
         driver->write = op->write;
         driver->put_char = op->put_char;
         driver->flush_chars = op->flush_chars;
         driver->write_room = op->write_room;
         driver->chars_in_buffer = op->chars_in_buffer;
         driver->ioctl = op->ioctl;
         driver->compat_ioctl = op->compat_ioctl;
         driver->set_termios = op->set_termios;
         driver->throttle = op->throttle;
         driver->unthrottle = op->unthrottle;
         driver->stop = op->stop;
         driver->start = op->start;
         driver->hangup = op->hangup;
         driver->break_ctl = op->break_ctl;
         driver->flush_buffer = op->flush_buffer;
         driver->set_ldisc = op->set_ldisc;
         driver->wait_until_sent = op->wait_until_sent;
         driver->send_xchar = op->send_xchar;
         driver->read_proc = op->read_proc;
         driver->write_proc = op->write_proc;
         driver->tiocmget = op->tiocmget;
         driver->tiocmset = op->tiocmset;
 }
 
 
 EXPORT_SYMBOL(alloc_tty_driver);
 EXPORT_SYMBOL(put_tty_driver);
 EXPORT_SYMBOL(tty_set_operations);
 
 /*
  * 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_INSTALLED)
                 return 0;
 
         if (!(driver->flags & TTY_DRIVER_DEVPTS_MEM) && driver->num) {
                 p = kzalloc(driver->num * 3 * 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);
                 driver->termios_locked = (struct ktermios **)
                                                         (p + driver->num * 2);
         } else {
                 driver->ttys = NULL;
                 driver->termios = NULL;
                 driver->termios_locked = 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 = driver->termios_locked = NULL;
                 kfree(p);
                 return error;
         }
 
         if (!driver->put_char)
                 driver->put_char = tty_default_put_char;
 
         mutex_lock(&tty_mutex);
         list_add(&driver->tty_drivers, &tty_drivers);
         mutex_unlock(&tty_mutex);
 
         if (!(driver->flags & TTY_DRIVER_DYNAMIC_DEV)) {
                 for (i = 0; i < driver->num; i++)
                     tty_register_device(driver, i, NULL);
         }
         proc_tty_register_driver(driver);
         return 0;
 }
 
 EXPORT_SYMBOL(tty_register_driver);
 
 /*
  * Called by a tty driver to unregister itself.
  */
 int tty_unregister_driver(struct tty_driver *driver)
 {
         int i;
         struct ktermios *tp;
         void *p;
 
         if (driver->refcount)
                 return -EBUSY;
 
         unregister_chrdev_region(MKDEV(driver->major, driver->minor_start),
                                 driver->num);
         mutex_lock(&tty_mutex);
         list_del(&driver->tty_drivers);
         mutex_unlock(&tty_mutex);
 
         /*
          * 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);
                 }
                 tp = driver->termios_locked[i];
                 if (tp) {
                         driver->termios_locked[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 = driver->termios_locked = NULL;
         kfree(p);
         cdev_del(&driver->cdev);
         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)
 {
         spin_lock_irq(&p->sighand->siglock);
         p->signal->tty = NULL;
         spin_unlock_irq(&p->sighand->siglock);
 }
 EXPORT_SYMBOL(proc_clear_tty);
 
 static void __proc_set_tty(struct task_struct *tsk, struct tty_struct *tty)
 {
         if (tty) {
                 /* We should not have a session or pgrp to here but.... */
                 put_pid(tty->session);
                 put_pid(tty->pgrp);
                 tty->session = get_pid(task_session(tsk));
                 tty->pgrp = get_pid(task_pgrp(tsk));
         }
         put_pid(tsk->signal->tty_old_pgrp);
         tsk->signal->tty = 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;
         WARN_ON_ONCE(!mutex_is_locked(&tty_mutex));
         tty = current->signal->tty;
         /*
          * session->tty can be changed/cleared from under us, make sure we
          * issue the load. The obtained pointer, when not NULL, is valid as
          * long as we hold tty_mutex.
          */
         barrier();
         return tty;
 }
 EXPORT_SYMBOL_GPL(get_current_tty);
 
 /*
  * 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. */
         (void) tty_register_ldisc(N_TTY, &tty_ldisc_N_TTY);
 
         /*
          * 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;
 #ifdef CONFIG_UNIX98_PTYS
 static struct cdev ptmx_cdev;
 #endif
 #ifdef CONFIG_VT
 static struct cdev vc0_cdev;
 #endif
 
 /*
  * 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), "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), "console");
 
 #ifdef CONFIG_UNIX98_PTYS
         cdev_init(&ptmx_cdev, &ptmx_fops);
         if (cdev_add(&ptmx_cdev, MKDEV(TTYAUX_MAJOR, 2), 1) ||
             register_chrdev_region(MKDEV(TTYAUX_MAJOR, 2), 1, "/dev/ptmx") < 0)
                 panic("Couldn't register /dev/ptmx driver\n");
         device_create(tty_class, NULL, MKDEV(TTYAUX_MAJOR, 2), "ptmx");
 #endif
 
 #ifdef CONFIG_VT
         cdev_init(&vc0_cdev, &console_fops);
         if (cdev_add(&vc0_cdev, MKDEV(TTY_MAJOR, 0), 1) ||
             register_chrdev_region(MKDEV(TTY_MAJOR, 0), 1, "/dev/vc/0") < 0)
                 panic("Couldn't register /dev/tty0 driver\n");
         device_create(tty_class, NULL, MKDEV(TTY_MAJOR, 0), "tty0");
 
         vty_init();
 #endif
         return 0;
 }
 module_init(tty_init);