drivers/char/pty.c

   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 #include <linux/device.h>
  27
  28 #include <asm/uaccess.h>
  29 #include <asm/system.h>
  30 #include <linux/bitops.h>
  31 #include <linux/devpts_fs.h>
  32
  33 /* These are global because they are accessed in tty_io.c */
  34 #ifdef CONFIG_UNIX98_PTYS
  35 struct tty_driver *ptm_driver;
  36 static struct tty_driver *pts_driver;
  37 #endif
  38
  39 static void pty_close(struct tty_struct * tty, struct file * filp)
  40 {
  41         if (!tty)
  42                 return;
  43         if (tty->driver->subtype == PTY_TYPE_MASTER) {
  44                 if (tty->count > 1)
  45                         printk("master pty_close: count = %d!!\n", tty->count);
  46         } else {
  47                 if (tty->count > 2)
  48                         return;
  49         }
  50         wake_up_interruptible(&tty->read_wait);
  51         wake_up_interruptible(&tty->write_wait);
  52         tty->packet = 0;
  53         if (!tty->link)
  54                 return;
  55         tty->link->packet = 0;
  56         set_bit(TTY_OTHER_CLOSED, &tty->link->flags);
  57         wake_up_interruptible(&tty->link->read_wait);
  58         wake_up_interruptible(&tty->link->write_wait);
  59         if (tty->driver->subtype == PTY_TYPE_MASTER) {
  60                 set_bit(TTY_OTHER_CLOSED, &tty->flags);
  61 #ifdef CONFIG_UNIX98_PTYS
  62                 if (tty->driver == ptm_driver)
  63                         devpts_pty_kill(tty->index);
  64 #endif
  65                 tty_vhangup(tty->link);
  66         }
  67 }
  68
  69 /*
  70  * The unthrottle routine is called by the line discipline to signal
  71  * that it can receive more characters.  For PTY's, the TTY_THROTTLED
  72  * flag is always set, to force the line discipline to always call the
  73  * unthrottle routine when there are fewer than TTY_THRESHOLD_UNTHROTTLE
  74  * characters in the queue.  This is necessary since each time this
  75  * happens, we need to wake up any sleeping processes that could be
  76  * (1) trying to send data to the pty, or (2) waiting in wait_until_sent()
  77  * for the pty buffer to be drained.
  78  */
  79 static void pty_unthrottle(struct tty_struct * tty)
  80 {
  81         struct tty_struct *o_tty = tty->link;
  82
  83         if (!o_tty)
  84                 return;
  85
  86         tty_wakeup(o_tty);
  87         set_bit(TTY_THROTTLED, &tty->flags);
  88 }
  89
  90 /*
  91  * WSH 05/24/97: modified to
  92  *   (1) use space in tty->flip instead of a shared temp buffer
  93  *       The flip buffers aren't being used for a pty, so there's lots
  94  *       of space available.  The buffer is protected by a per-pty
  95  *       semaphore that should almost never come under contention.
  96  *   (2) avoid redundant copying for cases where count >> receive_room
  97  * N.B. Calls from user space may now return an error code instead of
  98  * a count.
  99  *
 100  * FIXME: Our pty_write method is called with our ldisc lock held but
 101  * not our partners. We can't just take the other one blindly without
 102  * risking deadlocks.
 103  */
 104 static int pty_write(struct tty_struct * tty, const unsigned char *buf, int count)
 105 {
 106         struct tty_struct *to = tty->link;
 107         int     c;
 108
 109         if (!to || tty->stopped)
 110                 return 0;
 111
 112         c = to->receive_room;
 113         if (c > count)
 114                 c = count;
 115         to->ldisc.ops->receive_buf(to, buf, NULL, c);
 116
 117         return c;
 118 }
 119
 120 static int pty_write_room(struct tty_struct *tty)
 121 {
 122         struct tty_struct *to = tty->link;
 123
 124         if (!to || tty->stopped)
 125                 return 0;
 126
 127         return to->receive_room;
 128 }
 129
 130 /*
 131  *      WSH 05/24/97:  Modified for asymmetric MASTER/SLAVE behavior
 132  *      The chars_in_buffer() value is used by the ldisc select() function
 133  *      to hold off writing when chars_in_buffer > WAKEUP_CHARS (== 256).
 134  *      The pty driver chars_in_buffer() Master/Slave must behave differently:
 135  *
 136  *      The Master side needs to allow typed-ahead commands to accumulate
 137  *      while being canonicalized, so we report "our buffer" as empty until
 138  *      some threshold is reached, and then report the count. (Any count >
 139  *      WAKEUP_CHARS is regarded by select() as "full".)  To avoid deadlock
 140  *      the count returned must be 0 if no canonical data is available to be
 141  *      read. (The N_TTY ldisc.chars_in_buffer now knows this.)
 142  *
 143  *      The Slave side passes all characters in raw mode to the Master side's
 144  *      buffer where they can be read immediately, so in this case we can
 145  *      return the true count in the buffer.
 146  */
 147 static int pty_chars_in_buffer(struct tty_struct *tty)
 148 {
 149         struct tty_struct *to = tty->link;
 150         int count;
 151
 152         /* We should get the line discipline lock for "tty->link" */
 153         if (!to || !to->ldisc.ops->chars_in_buffer)
 154                 return 0;
 155
 156         /* The ldisc must report 0 if no characters available to be read */
 157         count = to->ldisc.ops->chars_in_buffer(to);
 158
 159         if (tty->driver->subtype == PTY_TYPE_SLAVE) return count;
 160
 161         /* Master side driver ... if the other side's read buffer is less than
 162          * half full, return 0 to allow writers to proceed; otherwise return
 163          * the count.  This leaves a comfortable margin to avoid overflow,
 164          * and still allows half a buffer's worth of typed-ahead commands.
 165          */
 166         return ((count < N_TTY_BUF_SIZE/2) ? 0 : count);
 167 }
 168
 169 /* Set the lock flag on a pty */
 170 static int pty_set_lock(struct tty_struct *tty, int __user * arg)
 171 {
 172         int val;
 173         if (get_user(val,arg))
 174                 return -EFAULT;
 175         if (val)
 176                 set_bit(TTY_PTY_LOCK, &tty->flags);
 177         else
 178                 clear_bit(TTY_PTY_LOCK, &tty->flags);
 179         return 0;
 180 }
 181
 182 static void pty_flush_buffer(struct tty_struct *tty)
 183 {
 184         struct tty_struct *to = tty->link;
 185         unsigned long flags;
 186
 187         if (!to)
 188                 return;
 189
 190         if (to->ldisc.ops->flush_buffer)
 191                 to->ldisc.ops->flush_buffer(to);
 192
 193         if (to->packet) {
 194                 spin_lock_irqsave(&tty->ctrl_lock, flags);
 195                 tty->ctrl_status |= TIOCPKT_FLUSHWRITE;
 196                 wake_up_interruptible(&to->read_wait);
 197                 spin_unlock_irqrestore(&tty->ctrl_lock, flags);
 198         }
 199 }
 200
 201 static int pty_open(struct tty_struct *tty, struct file * filp)
 202 {
 203         int     retval = -ENODEV;
 204
 205         if (!tty || !tty->link)
 206                 goto out;
 207
 208         retval = -EIO;
 209         if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
 210                 goto out;
 211         if (test_bit(TTY_PTY_LOCK, &tty->link->flags))
 212                 goto out;
 213         if (tty->link->count != 1)
 214                 goto out;
 215
 216         clear_bit(TTY_OTHER_CLOSED, &tty->link->flags);
 217         set_bit(TTY_THROTTLED, &tty->flags);
 218         set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 219         retval = 0;
 220 out:
 221         return retval;
 222 }
 223
 224 static void pty_set_termios(struct tty_struct *tty, struct ktermios *old_termios)
 225 {
 226         tty->termios->c_cflag &= ~(CSIZE | PARENB);
 227         tty->termios->c_cflag |= (CS8 | CREAD);
 228 }
 229
 230 static const struct tty_operations pty_ops = {
 231         .open = pty_open,
 232         .close = pty_close,
 233         .write = pty_write,
 234         .write_room = pty_write_room,
 235         .flush_buffer = pty_flush_buffer,
 236         .chars_in_buffer = pty_chars_in_buffer,
 237         .unthrottle = pty_unthrottle,
 238         .set_termios = pty_set_termios,
 239 };
 240
 241 /* Traditional BSD devices */
 242 #ifdef CONFIG_LEGACY_PTYS
 243 static struct tty_driver *pty_driver, *pty_slave_driver;
 244
 245 static int pty_bsd_ioctl(struct tty_struct *tty, struct file *file,
 246                          unsigned int cmd, unsigned long arg)
 247 {
 248         switch (cmd) {
 249         case TIOCSPTLCK: /* Set PT Lock (disallow slave open) */
 250                 return pty_set_lock(tty, (int __user *) arg);
 251         }
 252         return -ENOIOCTLCMD;
 253 }
 254
 255 static int legacy_count = CONFIG_LEGACY_PTY_COUNT;
 256 module_param(legacy_count, int, 0);
 257
 258 static const struct tty_operations pty_ops_bsd = {
 259         .open = pty_open,
 260         .close = pty_close,
 261         .write = pty_write,
 262         .write_room = pty_write_room,
 263         .flush_buffer = pty_flush_buffer,
 264         .chars_in_buffer = pty_chars_in_buffer,
 265         .unthrottle = pty_unthrottle,
 266         .set_termios = pty_set_termios,
 267         .ioctl = pty_bsd_ioctl,
 268 };
 269
 270 static void __init legacy_pty_init(void)
 271 {
 272         if (legacy_count <= 0)
 273                 return;
 274
 275         pty_driver = alloc_tty_driver(legacy_count);
 276         if (!pty_driver)
 277                 panic("Couldn't allocate pty driver");
 278
 279         pty_slave_driver = alloc_tty_driver(legacy_count);
 280         if (!pty_slave_driver)
 281                 panic("Couldn't allocate pty slave driver");
 282
 283         pty_driver->owner = THIS_MODULE;
 284         pty_driver->driver_name = "pty_master";
 285         pty_driver->name = "pty";
 286         pty_driver->major = PTY_MASTER_MAJOR;
 287         pty_driver->minor_start = 0;
 288         pty_driver->type = TTY_DRIVER_TYPE_PTY;
 289         pty_driver->subtype = PTY_TYPE_MASTER;
 290         pty_driver->init_termios = tty_std_termios;
 291         pty_driver->init_termios.c_iflag = 0;
 292         pty_driver->init_termios.c_oflag = 0;
 293         pty_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
 294         pty_driver->init_termios.c_lflag = 0;
 295         pty_driver->init_termios.c_ispeed = 38400;
 296         pty_driver->init_termios.c_ospeed = 38400;
 297         pty_driver->flags = TTY_DRIVER_RESET_TERMIOS | TTY_DRIVER_REAL_RAW;
 298         pty_driver->other = pty_slave_driver;
 299         tty_set_operations(pty_driver, &pty_ops);
 300
 301         pty_slave_driver->owner = THIS_MODULE;
 302         pty_slave_driver->driver_name = "pty_slave";
 303         pty_slave_driver->name = "ttyp";
 304         pty_slave_driver->major = PTY_SLAVE_MAJOR;
 305         pty_slave_driver->minor_start = 0;
 306         pty_slave_driver->type = TTY_DRIVER_TYPE_PTY;
 307         pty_slave_driver->subtype = PTY_TYPE_SLAVE;
 308         pty_slave_driver->init_termios = tty_std_termios;
 309         pty_slave_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
 310         pty_slave_driver->init_termios.c_ispeed = 38400;
 311         pty_slave_driver->init_termios.c_ospeed = 38400;
 312         pty_slave_driver->flags = TTY_DRIVER_RESET_TERMIOS |
 313                                         TTY_DRIVER_REAL_RAW;
 314         pty_slave_driver->other = pty_driver;
 315         tty_set_operations(pty_slave_driver, &pty_ops);
 316
 317         if (tty_register_driver(pty_driver))
 318                 panic("Couldn't register pty driver");
 319         if (tty_register_driver(pty_slave_driver))
 320                 panic("Couldn't register pty slave driver");
 321 }
 322 #else
 323 static inline void legacy_pty_init(void) { }
 324 #endif
 325
 326 /* Unix98 devices */
 327 #ifdef CONFIG_UNIX98_PTYS
 328 /*
 329  * sysctl support for setting limits on the number of Unix98 ptys allocated.
 330  * Otherwise one can eat up all kernel memory by opening /dev/ptmx repeatedly.
 331  */
 332 int pty_limit = NR_UNIX98_PTY_DEFAULT;
 333 static int pty_limit_min = 0;
 334 static int pty_limit_max = NR_UNIX98_PTY_MAX;
 335
 336 static struct cdev ptmx_cdev;
 337
 338 static struct ctl_table pty_table[] = {
 339         {
 340                 .ctl_name       = PTY_MAX,
 341                 .procname       = "max",
 342                 .maxlen         = sizeof(int),
 343                 .mode           = 0644,
 344                 .data           = &pty_limit,
 345                 .proc_handler   = &proc_dointvec_minmax,
 346                 .strategy       = &sysctl_intvec,
 347                 .extra1         = &pty_limit_min,
 348                 .extra2         = &pty_limit_max,
 349         }, {
 350                 .ctl_name       = PTY_NR,
 351                 .procname       = "nr",
 352                 .maxlen         = sizeof(int),
 353                 .mode           = 0444,
 354                 .proc_handler   = &proc_dointvec,
 355         }, {
 356                 .ctl_name       = 0
 357         }
 358 };
 359
 360 static struct ctl_table pty_kern_table[] = {
 361         {
 362                 .ctl_name       = KERN_PTY,
 363                 .procname       = "pty",
 364                 .mode           = 0555,
 365                 .child          = pty_table,
 366         },
 367         {}
 368 };
 369
 370 static struct ctl_table pty_root_table[] = {
 371         {
 372                 .ctl_name       = CTL_KERN,
 373                 .procname       = "kernel",
 374                 .mode           = 0555,
 375                 .child          = pty_kern_table,
 376         },
 377         {}
 378 };
 379
 380
 381 static int pty_unix98_ioctl(struct tty_struct *tty, struct file *file,
 382                             unsigned int cmd, unsigned long arg)
 383 {
 384         switch (cmd) {
 385         case TIOCSPTLCK: /* Set PT Lock (disallow slave open) */
 386                 return pty_set_lock(tty, (int __user *)arg);
 387         case TIOCGPTN: /* Get PT Number */
 388                 return put_user(tty->index, (unsigned int __user *)arg);
 389         }
 390
 391         return -ENOIOCTLCMD;
 392 }
 393
 394 /**
 395  *      ptm_unix98_lookup       -       find a pty master
 396  *      @driver: ptm driver
 397  *      @idx: tty index
 398  *
 399  *      Look up a pty master device. Called under the tty_mutex for now.
 400  *      This provides our locking.
 401  */
 402
 403 static struct tty_struct *ptm_unix98_lookup(struct tty_driver *driver, int idx)
 404 {
 405         struct tty_struct *tty = devpts_get_tty(idx);
 406         if (tty)
 407                 tty = tty->link;
 408         return tty;
 409 }
 410
 411 /**
 412  *      pts_unix98_lookup       -       find a pty slave
 413  *      @driver: pts driver
 414  *      @idx: tty index
 415  *
 416  *      Look up a pty master device. Called under the tty_mutex for now.
 417  *      This provides our locking.
 418  */
 419
 420 static struct tty_struct *pts_unix98_lookup(struct tty_driver *driver, int idx)
 421 {
 422         struct tty_struct *tty = devpts_get_tty(idx);
 423         /* Master must be open before slave */
 424         if (!tty)
 425                 return ERR_PTR(-EIO);
 426         return tty;
 427 }
 428
 429 static void pty_shutdown(struct tty_struct *tty)
 430 {
 431         /* We have our own method as we don't use the tty index */
 432         kfree(tty->termios);
 433         kfree(tty->termios_locked);
 434 }
 435
 436 /* We have no need to install and remove our tty objects as devpts does all
 437    the work for us */
 438
 439 static int pty_install(struct tty_driver *driver, struct tty_struct *tty)
 440 {
 441         return 0;
 442 }
 443
 444 static void pty_remove(struct tty_driver *driver, struct tty_struct *tty)
 445 {
 446 }
 447
 448 static const struct tty_operations ptm_unix98_ops = {
 449         .lookup = ptm_unix98_lookup,
 450         .install = pty_install,
 451         .remove = pty_remove,
 452         .open = pty_open,
 453         .close = pty_close,
 454         .write = pty_write,
 455         .write_room = pty_write_room,
 456         .flush_buffer = pty_flush_buffer,
 457         .chars_in_buffer = pty_chars_in_buffer,
 458         .unthrottle = pty_unthrottle,
 459         .set_termios = pty_set_termios,
 460         .ioctl = pty_unix98_ioctl,
 461         .shutdown = pty_shutdown
 462 };
 463
 464 static const struct tty_operations pty_unix98_ops = {
 465         .lookup = pts_unix98_lookup,
 466         .install = pty_install,
 467         .remove = pty_remove,
 468         .open = pty_open,
 469         .close = pty_close,
 470         .write = pty_write,
 471         .write_room = pty_write_room,
 472         .flush_buffer = pty_flush_buffer,
 473         .chars_in_buffer = pty_chars_in_buffer,
 474         .unthrottle = pty_unthrottle,
 475         .set_termios = pty_set_termios,
 476 };
 477
 478 /**
 479  *      ptmx_open               -       open a unix 98 pty master
 480  *      @inode: inode of device file
 481  *      @filp: file pointer to tty
 482  *
 483  *      Allocate a unix98 pty master device from the ptmx driver.
 484  *
 485  *      Locking: tty_mutex protects the init_dev work. tty->count should
 486  *              protect the rest.
 487  *              allocated_ptys_lock handles the list of free pty numbers
 488  */
 489
 490 static int __ptmx_open(struct inode *inode, struct file *filp)
 491 {
 492         struct tty_struct *tty;
 493         int retval;
 494         int index;
 495
 496         nonseekable_open(inode, filp);
 497
 498         /* find a device that is not in use. */
 499         index = devpts_new_index();
 500         if (index < 0)
 501                 return index;
 502
 503         mutex_lock(&tty_mutex);
 504         retval = tty_init_dev(ptm_driver, index, &tty, 1);
 505         mutex_unlock(&tty_mutex);
 506
 507         if (retval)
 508                 goto out;
 509
 510         set_bit(TTY_PTY_LOCK, &tty->flags); /* LOCK THE SLAVE */
 511         filp->private_data = tty;
 512         file_move(filp, &tty->tty_files);
 513
 514         retval = devpts_pty_new(tty->link);
 515         if (retval)
 516                 goto out1;
 517
 518         retval = ptm_driver->ops->open(tty, filp);
 519         if (!retval)
 520                 return 0;
 521 out1:
 522         tty_release_dev(filp);
 523         return retval;
 524 out:
 525         devpts_kill_index(index);
 526         return retval;
 527 }
 528
 529 static int ptmx_open(struct inode *inode, struct file *filp)
 530 {
 531         int ret;
 532
 533         lock_kernel();
 534         ret = __ptmx_open(inode, filp);
 535         unlock_kernel();
 536         return ret;
 537 }
 538
 539 static struct file_operations ptmx_fops;
 540
 541 static void __init unix98_pty_init(void)
 542 {
 543         ptm_driver = alloc_tty_driver(NR_UNIX98_PTY_MAX);
 544         if (!ptm_driver)
 545                 panic("Couldn't allocate Unix98 ptm driver");
 546         pts_driver = alloc_tty_driver(NR_UNIX98_PTY_MAX);
 547         if (!pts_driver)
 548                 panic("Couldn't allocate Unix98 pts driver");
 549
 550         ptm_driver->owner = THIS_MODULE;
 551         ptm_driver->driver_name = "pty_master";
 552         ptm_driver->name = "ptm";
 553         ptm_driver->major = UNIX98_PTY_MASTER_MAJOR;
 554         ptm_driver->minor_start = 0;
 555         ptm_driver->type = TTY_DRIVER_TYPE_PTY;
 556         ptm_driver->subtype = PTY_TYPE_MASTER;
 557         ptm_driver->init_termios = tty_std_termios;
 558         ptm_driver->init_termios.c_iflag = 0;
 559         ptm_driver->init_termios.c_oflag = 0;
 560         ptm_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
 561         ptm_driver->init_termios.c_lflag = 0;
 562         ptm_driver->init_termios.c_ispeed = 38400;
 563         ptm_driver->init_termios.c_ospeed = 38400;
 564         ptm_driver->flags = TTY_DRIVER_RESET_TERMIOS | TTY_DRIVER_REAL_RAW |
 565                 TTY_DRIVER_DYNAMIC_DEV | TTY_DRIVER_DEVPTS_MEM;
 566         ptm_driver->other = pts_driver;
 567         tty_set_operations(ptm_driver, &ptm_unix98_ops);
 568
 569         pts_driver->owner = THIS_MODULE;
 570         pts_driver->driver_name = "pty_slave";
 571         pts_driver->name = "pts";
 572         pts_driver->major = UNIX98_PTY_SLAVE_MAJOR;
 573         pts_driver->minor_start = 0;
 574         pts_driver->type = TTY_DRIVER_TYPE_PTY;
 575         pts_driver->subtype = PTY_TYPE_SLAVE;
 576         pts_driver->init_termios = tty_std_termios;
 577         pts_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
 578         pts_driver->init_termios.c_ispeed = 38400;
 579         pts_driver->init_termios.c_ospeed = 38400;
 580         pts_driver->flags = TTY_DRIVER_RESET_TERMIOS | TTY_DRIVER_REAL_RAW |
 581                 TTY_DRIVER_DYNAMIC_DEV | TTY_DRIVER_DEVPTS_MEM;
 582         pts_driver->other = ptm_driver;
 583         tty_set_operations(pts_driver, &pty_unix98_ops);
 584
 585         if (tty_register_driver(ptm_driver))
 586                 panic("Couldn't register Unix98 ptm driver");
 587         if (tty_register_driver(pts_driver))
 588                 panic("Couldn't register Unix98 pts driver");
 589
 590         /* FIXME: WTF */
 591 #if 0
 592         pty_table[1].data = &ptm_driver->refcount;
 593 #endif
 594         register_sysctl_table(pty_root_table);
 595
 596         /* Now create the /dev/ptmx special device */
 597         tty_default_fops(&ptmx_fops);
 598         ptmx_fops.open = ptmx_open;
 599
 600         cdev_init(&ptmx_cdev, &ptmx_fops);
 601         if (cdev_add(&ptmx_cdev, MKDEV(TTYAUX_MAJOR, 2), 1) ||
 602             register_chrdev_region(MKDEV(TTYAUX_MAJOR, 2), 1, "/dev/ptmx") < 0)
 603                 panic("Couldn't register /dev/ptmx driver\n");
 604         device_create(tty_class, NULL, MKDEV(TTYAUX_MAJOR, 2), NULL, "ptmx");
 605 }
 606
 607 #else
 608 static inline void unix98_pty_init(void) { }
 609 #endif
 610
 611 static int __init pty_init(void)
 612 {
 613         legacy_pty_init();
 614         unix98_pty_init();
 615         return 0;
 616 }
 617 module_init(pty_init);