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pty.c

/*
 *  linux/drivers/char/pty.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  Added support for a Unix98-style ptmx device.
 *    -- C. Scott Ananian <cananian@alumni.princeton.edu>, 14-Jan-1998
 *  Added TTY_DO_WRITE_WAKEUP to enable n_tty to send POLL_OUT to
 *      waiting writers -- Sapan Bhatia <sapan@corewars.org>
 *
 *
 */

#include <linux/module.h>     /* For EXPORT_SYMBOL */

#include <linux/errno.h>
#include <linux/interrupt.h>
#include <linux/tty.h>
#include <linux/tty_flip.h>
#include <linux/fcntl.h>
#include <linux/string.h>
#include <linux/major.h>
#include <linux/mm.h>
#include <linux/init.h>
#include <linux/sysctl.h>

#include <asm/uaccess.h>
#include <asm/system.h>
#include <linux/bitops.h>
#include <linux/devpts_fs.h>

/* These are global because they are accessed in tty_io.c */
#ifdef CONFIG_UNIX98_PTYS
struct tty_driver *ptm_driver;
static struct tty_driver *pts_driver;
#endif

static void pty_close(struct tty_struct * tty, struct file * filp)
{
      if (!tty)
            return;
      if (tty->driver->subtype == PTY_TYPE_MASTER) {
            if (tty->count > 1)
                  printk("master pty_close: count = %d!!\n", tty->count);
      } else {
            if (tty->count > 2)
                  return;
      }
      wake_up_interruptible(&tty->read_wait);
      wake_up_interruptible(&tty->write_wait);
      tty->packet = 0;
      if (!tty->link)
            return;
      tty->link->packet = 0;
      set_bit(TTY_OTHER_CLOSED, &tty->link->flags);
      wake_up_interruptible(&tty->link->read_wait);
      wake_up_interruptible(&tty->link->write_wait);
      if (tty->driver->subtype == PTY_TYPE_MASTER) {
            set_bit(TTY_OTHER_CLOSED, &tty->flags);
#ifdef CONFIG_UNIX98_PTYS
            if (tty->driver == ptm_driver)
                  devpts_pty_kill(tty->index);
#endif
            tty_vhangup(tty->link);
      }
}

/*
 * The unthrottle routine is called by the line discipline to signal
 * that it can receive more characters.  For PTY's, the TTY_THROTTLED
 * flag is always set, to force the line discipline to always call the
 * unthrottle routine when there are fewer than TTY_THRESHOLD_UNTHROTTLE 
 * characters in the queue.  This is necessary since each time this
 * happens, we need to wake up any sleeping processes that could be
 * (1) trying to send data to the pty, or (2) waiting in wait_until_sent()
 * for the pty buffer to be drained.
 */
static void pty_unthrottle(struct tty_struct * tty)
{
      struct tty_struct *o_tty = tty->link;

      if (!o_tty)
            return;

      tty_wakeup(o_tty);
      set_bit(TTY_THROTTLED, &tty->flags);
}

/*
 * WSH 05/24/97: modified to 
 *   (1) use space in tty->flip instead of a shared temp buffer
 *     The flip buffers aren't being used for a pty, so there's lots
 *     of space available.  The buffer is protected by a per-pty
 *     semaphore that should almost never come under contention.
 *   (2) avoid redundant copying for cases where count >> receive_room
 * N.B. Calls from user space may now return an error code instead of
 * a count.
 *
 * FIXME: Our pty_write method is called with our ldisc lock held but
 * not our partners. We can't just take the other one blindly without
 * risking deadlocks.
 */
static int pty_write(struct tty_struct * tty, const unsigned char *buf, int count)
{
      struct tty_struct *to = tty->link;
      int   c;

      if (!to || tty->stopped)
            return 0;

      c = to->receive_room;
      if (c > count)
            c = count;
      to->ldisc.receive_buf(to, buf, NULL, c);
      
      return c;
}

static int pty_write_room(struct tty_struct *tty)
{
      struct tty_struct *to = tty->link;

      if (!to || tty->stopped)
            return 0;

      return to->receive_room;
}

/*
 *    WSH 05/24/97:  Modified for asymmetric MASTER/SLAVE behavior
 *    The chars_in_buffer() value is used by the ldisc select() function 
 *    to hold off writing when chars_in_buffer > WAKEUP_CHARS (== 256).
 *    The pty driver chars_in_buffer() Master/Slave must behave differently:
 *
 *      The Master side needs to allow typed-ahead commands to accumulate
 *      while being canonicalized, so we report "our buffer" as empty until
 *    some threshold is reached, and then report the count. (Any count >
 *    WAKEUP_CHARS is regarded by select() as "full".)  To avoid deadlock 
 *    the count returned must be 0 if no canonical data is available to be 
 *    read. (The N_TTY ldisc.chars_in_buffer now knows this.)
 *  
 *    The Slave side passes all characters in raw mode to the Master side's
 *    buffer where they can be read immediately, so in this case we can
 *    return the true count in the buffer.
 */
static int pty_chars_in_buffer(struct tty_struct *tty)
{
      struct tty_struct *to = tty->link;
      int count;

      /* We should get the line discipline lock for "tty->link" */
      if (!to || !to->ldisc.chars_in_buffer)
            return 0;

      /* The ldisc must report 0 if no characters available to be read */
      count = to->ldisc.chars_in_buffer(to);

      if (tty->driver->subtype == PTY_TYPE_SLAVE) return count;

      /* Master side driver ... if the other side's read buffer is less than 
       * half full, return 0 to allow writers to proceed; otherwise return
       * the count.  This leaves a comfortable margin to avoid overflow, 
       * and still allows half a buffer's worth of typed-ahead commands.
       */
      return ((count < N_TTY_BUF_SIZE/2) ? 0 : count);
}

/* Set the lock flag on a pty */
static int pty_set_lock(struct tty_struct *tty, int __user * arg)
{
      int val;
      if (get_user(val,arg))
            return -EFAULT;
      if (val)
            set_bit(TTY_PTY_LOCK, &tty->flags);
      else
            clear_bit(TTY_PTY_LOCK, &tty->flags);
      return 0;
}

static void pty_flush_buffer(struct tty_struct *tty)
{
      struct tty_struct *to = tty->link;
      
      if (!to)
            return;
      
      if (to->ldisc.flush_buffer)
            to->ldisc.flush_buffer(to);
      
      if (to->packet) {
            tty->ctrl_status |= TIOCPKT_FLUSHWRITE;
            wake_up_interruptible(&to->read_wait);
      }
}

static int pty_open(struct tty_struct *tty, struct file * filp)
{
      int   retval = -ENODEV;

      if (!tty || !tty->link)
            goto out;

      retval = -EIO;
      if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
            goto out;
      if (test_bit(TTY_PTY_LOCK, &tty->link->flags))
            goto out;
      if (tty->link->count != 1)
            goto out;

      clear_bit(TTY_OTHER_CLOSED, &tty->link->flags);
      set_bit(TTY_THROTTLED, &tty->flags);
      set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
      retval = 0;
out:
      return retval;
}

static void pty_set_termios(struct tty_struct *tty, struct ktermios *old_termios)
{
        tty->termios->c_cflag &= ~(CSIZE | PARENB);
        tty->termios->c_cflag |= (CS8 | CREAD);
}

static const struct tty_operations pty_ops = {
      .open = pty_open,
      .close = pty_close,
      .write = pty_write,
      .write_room = pty_write_room,
      .flush_buffer = pty_flush_buffer,
      .chars_in_buffer = pty_chars_in_buffer,
      .unthrottle = pty_unthrottle,
      .set_termios = pty_set_termios,
};

/* Traditional BSD devices */
#ifdef CONFIG_LEGACY_PTYS
static struct tty_driver *pty_driver, *pty_slave_driver;

static int pty_bsd_ioctl(struct tty_struct *tty, struct file *file,
                   unsigned int cmd, unsigned long arg)
{
      switch (cmd) {
      case TIOCSPTLCK: /* Set PT Lock (disallow slave open) */
            return pty_set_lock(tty, (int __user *) arg);
      }
      return -ENOIOCTLCMD;
}

static int legacy_count = CONFIG_LEGACY_PTY_COUNT;
module_param(legacy_count, int, 0);

static void __init legacy_pty_init(void)
{
      if (legacy_count <= 0)
            return;

      pty_driver = alloc_tty_driver(legacy_count);
      if (!pty_driver)
            panic("Couldn't allocate pty driver");

      pty_slave_driver = alloc_tty_driver(legacy_count);
      if (!pty_slave_driver)
            panic("Couldn't allocate pty slave driver");

      pty_driver->owner = THIS_MODULE;
      pty_driver->driver_name = "pty_master";
      pty_driver->name = "pty";
      pty_driver->major = PTY_MASTER_MAJOR;
      pty_driver->minor_start = 0;
      pty_driver->type = TTY_DRIVER_TYPE_PTY;
      pty_driver->subtype = PTY_TYPE_MASTER;
      pty_driver->init_termios = tty_std_termios;
      pty_driver->init_termios.c_iflag = 0;
      pty_driver->init_termios.c_oflag = 0;
      pty_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
      pty_driver->init_termios.c_lflag = 0;
      pty_driver->init_termios.c_ispeed = 38400;
      pty_driver->init_termios.c_ospeed = 38400;
      pty_driver->flags = TTY_DRIVER_RESET_TERMIOS | TTY_DRIVER_REAL_RAW;
      pty_driver->other = pty_slave_driver;
      tty_set_operations(pty_driver, &pty_ops);
      pty_driver->ioctl = pty_bsd_ioctl;

      pty_slave_driver->owner = THIS_MODULE;
      pty_slave_driver->driver_name = "pty_slave";
      pty_slave_driver->name = "ttyp";
      pty_slave_driver->major = PTY_SLAVE_MAJOR;
      pty_slave_driver->minor_start = 0;
      pty_slave_driver->type = TTY_DRIVER_TYPE_PTY;
      pty_slave_driver->subtype = PTY_TYPE_SLAVE;
      pty_slave_driver->init_termios = tty_std_termios;
      pty_slave_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
      pty_slave_driver->init_termios.c_ispeed = 38400;
      pty_slave_driver->init_termios.c_ospeed = 38400;
      pty_slave_driver->flags = TTY_DRIVER_RESET_TERMIOS |
                              TTY_DRIVER_REAL_RAW;
      pty_slave_driver->other = pty_driver;
      tty_set_operations(pty_slave_driver, &pty_ops);

      if (tty_register_driver(pty_driver))
            panic("Couldn't register pty driver");
      if (tty_register_driver(pty_slave_driver))
            panic("Couldn't register pty slave driver");
}
#else
static inline void legacy_pty_init(void) { }
#endif

/* Unix98 devices */
#ifdef CONFIG_UNIX98_PTYS
/*
 * sysctl support for setting limits on the number of Unix98 ptys allocated.
 * Otherwise one can eat up all kernel memory by opening /dev/ptmx repeatedly.
 */
int pty_limit = NR_UNIX98_PTY_DEFAULT;
static int pty_limit_min = 0;
static int pty_limit_max = NR_UNIX98_PTY_MAX;

static struct ctl_table pty_table[] = {
      {
            .ctl_name   = PTY_MAX,
            .procname   = "max",
            .maxlen           = sizeof(int),
            .mode       = 0644,
            .data       = &pty_limit,
            .proc_handler     = &proc_dointvec_minmax,
            .strategy   = &sysctl_intvec,
            .extra1           = &pty_limit_min,
            .extra2           = &pty_limit_max,
      }, {
            .ctl_name   = PTY_NR,
            .procname   = "nr",
            .maxlen           = sizeof(int),
            .mode       = 0444,
            .proc_handler     = &proc_dointvec,
      }, {
            .ctl_name   = 0
      }
};

static struct ctl_table pty_kern_table[] = {
      {
            .ctl_name   = KERN_PTY,
            .procname   = "pty",
            .mode       = 0555,
            .child            = pty_table,
      },
      {}
};

static struct ctl_table pty_root_table[] = {
      {
            .ctl_name   = CTL_KERN,
            .procname   = "kernel",
            .mode       = 0555,
            .child            = pty_kern_table,
      },
      {}
};


static int pty_unix98_ioctl(struct tty_struct *tty, struct file *file,
                      unsigned int cmd, unsigned long arg)
{
      switch (cmd) {
      case TIOCSPTLCK: /* Set PT Lock (disallow slave open) */
            return pty_set_lock(tty, (int __user *)arg);
      case TIOCGPTN: /* Get PT Number */
            return put_user(tty->index, (unsigned int __user *)arg);
      }

      return -ENOIOCTLCMD;
}

static void __init unix98_pty_init(void)
{
      ptm_driver = alloc_tty_driver(NR_UNIX98_PTY_MAX);
      if (!ptm_driver)
            panic("Couldn't allocate Unix98 ptm driver");
      pts_driver = alloc_tty_driver(NR_UNIX98_PTY_MAX);
      if (!pts_driver)
            panic("Couldn't allocate Unix98 pts driver");

      ptm_driver->owner = THIS_MODULE;
      ptm_driver->driver_name = "pty_master";
      ptm_driver->name = "ptm";
      ptm_driver->major = UNIX98_PTY_MASTER_MAJOR;
      ptm_driver->minor_start = 0;
      ptm_driver->type = TTY_DRIVER_TYPE_PTY;
      ptm_driver->subtype = PTY_TYPE_MASTER;
      ptm_driver->init_termios = tty_std_termios;
      ptm_driver->init_termios.c_iflag = 0;
      ptm_driver->init_termios.c_oflag = 0;
      ptm_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
      ptm_driver->init_termios.c_lflag = 0;
      ptm_driver->init_termios.c_ispeed = 38400;
      ptm_driver->init_termios.c_ospeed = 38400;
      ptm_driver->flags = TTY_DRIVER_RESET_TERMIOS | TTY_DRIVER_REAL_RAW |
            TTY_DRIVER_DYNAMIC_DEV | TTY_DRIVER_DEVPTS_MEM;
      ptm_driver->other = pts_driver;
      tty_set_operations(ptm_driver, &pty_ops);
      ptm_driver->ioctl = pty_unix98_ioctl;

      pts_driver->owner = THIS_MODULE;
      pts_driver->driver_name = "pty_slave";
      pts_driver->name = "pts";
      pts_driver->major = UNIX98_PTY_SLAVE_MAJOR;
      pts_driver->minor_start = 0;
      pts_driver->type = TTY_DRIVER_TYPE_PTY;
      pts_driver->subtype = PTY_TYPE_SLAVE;
      pts_driver->init_termios = tty_std_termios;
      pts_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
      pts_driver->init_termios.c_ispeed = 38400;
      pts_driver->init_termios.c_ospeed = 38400;
      pts_driver->flags = TTY_DRIVER_RESET_TERMIOS | TTY_DRIVER_REAL_RAW |
            TTY_DRIVER_DYNAMIC_DEV | TTY_DRIVER_DEVPTS_MEM;
      pts_driver->other = ptm_driver;
      tty_set_operations(pts_driver, &pty_ops);
      
      if (tty_register_driver(ptm_driver))
            panic("Couldn't register Unix98 ptm driver");
      if (tty_register_driver(pts_driver))
            panic("Couldn't register Unix98 pts driver");

      pty_table[1].data = &ptm_driver->refcount;
      register_sysctl_table(pty_root_table);
}
#else
static inline void unix98_pty_init(void) { }
#endif

static int __init pty_init(void)
{
      legacy_pty_init();
      unix98_pty_init();
      return 0;
}
module_init(pty_init);

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