linux/drivers/char/pty.c
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   1/*
   2 *  linux/drivers/char/pty.c
   3 *
   4 *  Copyright (C) 1991, 1992  Linus Torvalds
   5 *
   6 *  Added support for a Unix98-style ptmx device.
   7 *    -- C. Scott Ananian <cananian@alumni.princeton.edu>, 14-Jan-1998
   8 *  Added TTY_DO_WRITE_WAKEUP to enable n_tty to send POLL_OUT to
   9 *      waiting writers -- Sapan Bhatia <sapan@corewars.org>
  10 *
  11 *
  12 */
  13
  14#include <linux/module.h>       /* For EXPORT_SYMBOL */
  15
  16#include <linux/errno.h>
  17#include <linux/interrupt.h>
  18#include <linux/tty.h>
  19#include <linux/tty_flip.h>
  20#include <linux/fcntl.h>
  21#include <linux/string.h>
  22#include <linux/major.h>
  23#include <linux/mm.h>
  24#include <linux/init.h>
  25#include <linux/sysctl.h>
  26
  27#include <asm/uaccess.h>
  28#include <asm/system.h>
  29#include <linux/bitops.h>
  30#include <linux/devpts_fs.h>
  31
  32/* These are global because they are accessed in tty_io.c */
  33#ifdef CONFIG_UNIX98_PTYS
  34struct tty_driver *ptm_driver;
  35static struct tty_driver *pts_driver;
  36#endif
  37
  38static void pty_close(struct tty_struct * tty, struct file * filp)
  39{
  40        if (!tty)
  41                return;
  42        if (tty->driver->subtype == PTY_TYPE_MASTER) {
  43                if (tty->count > 1)
  44                        printk("master pty_close: count = %d!!\n", tty->count);
  45        } else {
  46                if (tty->count > 2)
  47                        return;
  48        }
  49        wake_up_interruptible(&tty->read_wait);
  50        wake_up_interruptible(&tty->write_wait);
  51        tty->packet = 0;
  52        if (!tty->link)
  53                return;
  54        tty->link->packet = 0;
  55        set_bit(TTY_OTHER_CLOSED, &tty->link->flags);
  56        wake_up_interruptible(&tty->link->read_wait);
  57        wake_up_interruptible(&tty->link->write_wait);
  58        if (tty->driver->subtype == PTY_TYPE_MASTER) {
  59                set_bit(TTY_OTHER_CLOSED, &tty->flags);
  60#ifdef CONFIG_UNIX98_PTYS
  61                if (tty->driver == ptm_driver)
  62                        devpts_pty_kill(tty->index);
  63#endif
  64                tty_vhangup(tty->link);
  65        }
  66}
  67
  68/*
  69 * The unthrottle routine is called by the line discipline to signal
  70 * that it can receive more characters.  For PTY's, the TTY_THROTTLED
  71 * flag is always set, to force the line discipline to always call the
  72 * unthrottle routine when there are fewer than TTY_THRESHOLD_UNTHROTTLE 
  73 * characters in the queue.  This is necessary since each time this
  74 * happens, we need to wake up any sleeping processes that could be
  75 * (1) trying to send data to the pty, or (2) waiting in wait_until_sent()
  76 * for the pty buffer to be drained.
  77 */
  78static void pty_unthrottle(struct tty_struct * tty)
  79{
  80        struct tty_struct *o_tty = tty->link;
  81
  82        if (!o_tty)
  83                return;
  84
  85        tty_wakeup(o_tty);
  86        set_bit(TTY_THROTTLED, &tty->flags);
  87}
  88
  89/*
  90 * WSH 05/24/97: modified to 
  91 *   (1) use space in tty->flip instead of a shared temp buffer
  92 *       The flip buffers aren't being used for a pty, so there's lots
  93 *       of space available.  The buffer is protected by a per-pty
  94 *       semaphore that should almost never come under contention.
  95 *   (2) avoid redundant copying for cases where count >> receive_room
  96 * N.B. Calls from user space may now return an error code instead of
  97 * a count.
  98 *
  99 * FIXME: Our pty_write method is called with our ldisc lock held but
 100 * not our partners. We can't just take the other one blindly without
 101 * risking deadlocks.
 102 */
 103static int pty_write(struct tty_struct * tty, const unsigned char *buf, int count)
 104{
 105        struct tty_struct *to = tty->link;
 106        int     c;
 107
 108        if (!to || tty->stopped)
 109                return 0;
 110
 111        c = to->receive_room;
 112        if (c > count)
 113                c = count;
 114        to->ldisc.receive_buf(to, buf, NULL, c);
 115        
 116        return c;
 117}
 118
 119static int pty_write_room(struct tty_struct *tty)
 120{
 121        struct tty_struct *to = tty->link;
 122
 123        if (!to || tty->stopped)
 124                return 0;
 125
 126        return to->receive_room;
 127}
 128
 129/*
 130 *      WSH 05/24/97:  Modified for asymmetric MASTER/SLAVE behavior
 131 *      The chars_in_buffer() value is used by the ldisc select() function 
 132 *      to hold off writing when chars_in_buffer > WAKEUP_CHARS (== 256).
 133 *      The pty driver chars_in_buffer() Master/Slave must behave differently:
 134 *
 135 *      The Master side needs to allow typed-ahead commands to accumulate
 136 *      while being canonicalized, so we report "our buffer" as empty until
 137 *      some threshold is reached, and then report the count. (Any count >
 138 *      WAKEUP_CHARS is regarded by select() as "full".)  To avoid deadlock 
 139 *      the count returned must be 0 if no canonical data is available to be 
 140 *      read. (The N_TTY ldisc.chars_in_buffer now knows this.)
 141 *  
 142 *      The Slave side passes all characters in raw mode to the Master side's
 143 *      buffer where they can be read immediately, so in this case we can
 144 *      return the true count in the buffer.
 145 */
 146static int pty_chars_in_buffer(struct tty_struct *tty)
 147{
 148        struct tty_struct *to = tty->link;
 149        int count;
 150
 151        /* We should get the line discipline lock for "tty->link" */
 152        if (!to || !to->ldisc.chars_in_buffer)
 153                return 0;
 154
 155        /* The ldisc must report 0 if no characters available to be read */
 156        count = to->ldisc.chars_in_buffer(to);
 157
 158        if (tty->driver->subtype == PTY_TYPE_SLAVE) return count;
 159
 160        /* Master side driver ... if the other side's read buffer is less than 
 161         * half full, return 0 to allow writers to proceed; otherwise return
 162         * the count.  This leaves a comfortable margin to avoid overflow, 
 163         * and still allows half a buffer's worth of typed-ahead commands.
 164         */
 165        return ((count < N_TTY_BUF_SIZE/2) ? 0 : count);
 166}
 167
 168/* Set the lock flag on a pty */
 169static int pty_set_lock(struct tty_struct *tty, int __user * arg)
 170{
 171        int val;
 172        if (get_user(val,arg))
 173                return -EFAULT;
 174        if (val)
 175                set_bit(TTY_PTY_LOCK, &tty->flags);
 176        else
 177                clear_bit(TTY_PTY_LOCK, &tty->flags);
 178        return 0;
 179}
 180
 181static void pty_flush_buffer(struct tty_struct *tty)
 182{
 183        struct tty_struct *to = tty->link;
 184        
 185        if (!to)
 186                return;
 187        
 188        if (to->ldisc.flush_buffer)
 189                to->ldisc.flush_buffer(to);
 190        
 191        if (to->packet) {
 192                tty->ctrl_status |= TIOCPKT_FLUSHWRITE;
 193                wake_up_interruptible(&to->read_wait);
 194        }
 195}
 196
 197static int pty_open(struct tty_struct *tty, struct file * filp)
 198{
 199        int     retval = -ENODEV;
 200
 201        if (!tty || !tty->link)
 202                goto out;
 203
 204        retval = -EIO;
 205        if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
 206                goto out;
 207        if (test_bit(TTY_PTY_LOCK, &tty->link->flags))
 208                goto out;
 209        if (tty->link->count != 1)
 210                goto out;
 211
 212        clear_bit(TTY_OTHER_CLOSED, &tty->link->flags);
 213        set_bit(TTY_THROTTLED, &tty->flags);
 214        set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 215        retval = 0;
 216out:
 217        return retval;
 218}
 219
 220static void pty_set_termios(struct tty_struct *tty, struct ktermios *old_termios)
 221{
 222        tty->termios->c_cflag &= ~(CSIZE | PARENB);
 223        tty->termios->c_cflag |= (CS8 | CREAD);
 224}
 225
 226static const struct tty_operations pty_ops = {
 227        .open = pty_open,
 228        .close = pty_close,
 229        .write = pty_write,
 230        .write_room = pty_write_room,
 231        .flush_buffer = pty_flush_buffer,
 232        .chars_in_buffer = pty_chars_in_buffer,
 233        .unthrottle = pty_unthrottle,
 234        .set_termios = pty_set_termios,
 235};
 236
 237/* Traditional BSD devices */
 238#ifdef CONFIG_LEGACY_PTYS
 239static struct tty_driver *pty_driver, *pty_slave_driver;
 240
 241static int pty_bsd_ioctl(struct tty_struct *tty, struct file *file,
 242                         unsigned int cmd, unsigned long arg)
 243{
 244        switch (cmd) {
 245        case TIOCSPTLCK: /* Set PT Lock (disallow slave open) */
 246                return pty_set_lock(tty, (int __user *) arg);
 247        }
 248        return -ENOIOCTLCMD;
 249}
 250
 251static int legacy_count = CONFIG_LEGACY_PTY_COUNT;
 252module_param(legacy_count, int, 0);
 253
 254static void __init legacy_pty_init(void)
 255{
 256        if (legacy_count <= 0)
 257                return;
 258
 259        pty_driver = alloc_tty_driver(legacy_count);
 260        if (!pty_driver)
 261                panic("Couldn't allocate pty driver");
 262
 263        pty_slave_driver = alloc_tty_driver(legacy_count);
 264        if (!pty_slave_driver)
 265                panic("Couldn't allocate pty slave driver");
 266
 267        pty_driver->owner = THIS_MODULE;
 268        pty_driver->driver_name = "pty_master";
 269        pty_driver->name = "pty";
 270        pty_driver->major = PTY_MASTER_MAJOR;
 271        pty_driver->minor_start = 0;
 272        pty_driver->type = TTY_DRIVER_TYPE_PTY;
 273        pty_driver->subtype = PTY_TYPE_MASTER;
 274        pty_driver->init_termios = tty_std_termios;
 275        pty_driver->init_termios.c_iflag = 0;
 276        pty_driver->init_termios.c_oflag = 0;
 277        pty_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
 278        pty_driver->init_termios.c_lflag = 0;
 279        pty_driver->init_termios.c_ispeed = 38400;
 280        pty_driver->init_termios.c_ospeed = 38400;
 281        pty_driver->flags = TTY_DRIVER_RESET_TERMIOS | TTY_DRIVER_REAL_RAW;
 282        pty_driver->other = pty_slave_driver;
 283        tty_set_operations(pty_driver, &pty_ops);
 284        pty_driver->ioctl = pty_bsd_ioctl;
 285
 286        pty_slave_driver->owner = THIS_MODULE;
 287        pty_slave_driver->driver_name = "pty_slave";
 288        pty_slave_driver->name = "ttyp";
 289        pty_slave_driver->major = PTY_SLAVE_MAJOR;
 290        pty_slave_driver->minor_start = 0;
 291        pty_slave_driver->type = TTY_DRIVER_TYPE_PTY;
 292        pty_slave_driver->subtype = PTY_TYPE_SLAVE;
 293        pty_slave_driver->init_termios = tty_std_termios;
 294        pty_slave_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
 295        pty_slave_driver->init_termios.c_ispeed = 38400;
 296        pty_slave_driver->init_termios.c_ospeed = 38400;
 297        pty_slave_driver->flags = TTY_DRIVER_RESET_TERMIOS |
 298                                        TTY_DRIVER_REAL_RAW;
 299        pty_slave_driver->other = pty_driver;
 300        tty_set_operations(pty_slave_driver, &pty_ops);
 301
 302        if (tty_register_driver(pty_driver))
 303                panic("Couldn't register pty driver");
 304        if (tty_register_driver(pty_slave_driver))
 305                panic("Couldn't register pty slave driver");
 306}
 307#else
 308static inline void legacy_pty_init(void) { }
 309#endif
 310
 311/* Unix98 devices */
 312#ifdef CONFIG_UNIX98_PTYS
 313/*
 314 * sysctl support for setting limits on the number of Unix98 ptys allocated.
 315 * Otherwise one can eat up all kernel memory by opening /dev/ptmx repeatedly.
 316 */
 317int pty_limit = NR_UNIX98_PTY_DEFAULT;
 318static int pty_limit_min = 0;
 319static int pty_limit_max = NR_UNIX98_PTY_MAX;
 320
 321static struct ctl_table pty_table[] = {
 322        {
 323                .ctl_name       = PTY_MAX,
 324                .procname       = "max",
 325                .maxlen         = sizeof(int),
 326                .mode           = 0644,
 327                .data           = &pty_limit,
 328                .proc_handler   = &proc_dointvec_minmax,
 329                .strategy       = &sysctl_intvec,
 330                .extra1         = &pty_limit_min,
 331                .extra2         = &pty_limit_max,
 332        }, {
 333                .ctl_name       = PTY_NR,
 334                .procname       = "nr",
 335                .maxlen         = sizeof(int),
 336                .mode           = 0444,
 337                .proc_handler   = &proc_dointvec,
 338        }, {
 339                .ctl_name       = 0
 340        }
 341};
 342
 343static struct ctl_table pty_kern_table[] = {
 344        {
 345                .ctl_name       = KERN_PTY,
 346                .procname       = "pty",
 347                .mode           = 0555,
 348                .child          = pty_table,
 349        },
 350        {}
 351};
 352
 353static struct ctl_table pty_root_table[] = {
 354        {
 355                .ctl_name       = CTL_KERN,
 356                .procname       = "kernel",
 357                .mode           = 0555,
 358                .child          = pty_kern_table,
 359        },
 360        {}
 361};
 362
 363
 364static int pty_unix98_ioctl(struct tty_struct *tty, struct file *file,
 365                            unsigned int cmd, unsigned long arg)
 366{
 367        switch (cmd) {
 368        case TIOCSPTLCK: /* Set PT Lock (disallow slave open) */
 369                return pty_set_lock(tty, (int __user *)arg);
 370        case TIOCGPTN: /* Get PT Number */
 371                return put_user(tty->index, (unsigned int __user *)arg);
 372        }
 373
 374        return -ENOIOCTLCMD;
 375}
 376
 377static void __init unix98_pty_init(void)
 378{
 379        ptm_driver = alloc_tty_driver(NR_UNIX98_PTY_MAX);
 380        if (!ptm_driver)
 381                panic("Couldn't allocate Unix98 ptm driver");
 382        pts_driver = alloc_tty_driver(NR_UNIX98_PTY_MAX);
 383        if (!pts_driver)
 384                panic("Couldn't allocate Unix98 pts driver");
 385
 386        ptm_driver->owner = THIS_MODULE;
 387        ptm_driver->driver_name = "pty_master";
 388        ptm_driver->name = "ptm";
 389        ptm_driver->major = UNIX98_PTY_MASTER_MAJOR;
 390        ptm_driver->minor_start = 0;
 391        ptm_driver->type = TTY_DRIVER_TYPE_PTY;
 392        ptm_driver->subtype = PTY_TYPE_MASTER;
 393        ptm_driver->init_termios = tty_std_termios;
 394        ptm_driver->init_termios.c_iflag = 0;
 395        ptm_driver->init_termios.c_oflag = 0;
 396        ptm_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
 397        ptm_driver->init_termios.c_lflag = 0;
 398        ptm_driver->init_termios.c_ispeed = 38400;
 399        ptm_driver->init_termios.c_ospeed = 38400;
 400        ptm_driver->flags = TTY_DRIVER_RESET_TERMIOS | TTY_DRIVER_REAL_RAW |
 401                TTY_DRIVER_DYNAMIC_DEV | TTY_DRIVER_DEVPTS_MEM;
 402        ptm_driver->other = pts_driver;
 403        tty_set_operations(ptm_driver, &pty_ops);
 404        ptm_driver->ioctl = pty_unix98_ioctl;
 405
 406        pts_driver->owner = THIS_MODULE;
 407        pts_driver->driver_name = "pty_slave";
 408        pts_driver->name = "pts";
 409        pts_driver->major = UNIX98_PTY_SLAVE_MAJOR;
 410        pts_driver->minor_start = 0;
 411        pts_driver->type = TTY_DRIVER_TYPE_PTY;
 412        pts_driver->subtype = PTY_TYPE_SLAVE;
 413        pts_driver->init_termios = tty_std_termios;
 414        pts_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
 415        pts_driver->init_termios.c_ispeed = 38400;
 416        pts_driver->init_termios.c_ospeed = 38400;
 417        pts_driver->flags = TTY_DRIVER_RESET_TERMIOS | TTY_DRIVER_REAL_RAW |
 418                TTY_DRIVER_DYNAMIC_DEV | TTY_DRIVER_DEVPTS_MEM;
 419        pts_driver->other = ptm_driver;
 420        tty_set_operations(pts_driver, &pty_ops);
 421        
 422        if (tty_register_driver(ptm_driver))
 423                panic("Couldn't register Unix98 ptm driver");
 424        if (tty_register_driver(pts_driver))
 425                panic("Couldn't register Unix98 pts driver");
 426
 427        pty_table[1].data = &ptm_driver->refcount;
 428        register_sysctl_table(pty_root_table);
 429}
 430#else
 431static inline void unix98_pty_init(void) { }
 432#endif
 433
 434static int __init pty_init(void)
 435{
 436        legacy_pty_init();
 437        unix98_pty_init();
 438        return 0;
 439}
 440module_init(pty_init);
 441
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