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
  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
  34 struct tty_driver *ptm_driver;
  35 static struct tty_driver *pts_driver;
  36 #endif
  37
  38 static 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  */
  78 static 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  */
 103 static 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
 119 static 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  */
 146 static 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 */
 169 static 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
 181 static void pty_flush_buffer(struct tty_struct *tty)
 182 {
 183         struct tty_struct *to = tty->link;
 184         unsigned long flags;
 185
 186         if (!to)
 187                 return;
 188
 189         if (to->ldisc.flush_buffer)
 190                 to->ldisc.flush_buffer(to);
 191
 192         if (to->packet) {
 193                 spin_lock_irqsave(&tty->ctrl_lock, flags);
 194                 tty->ctrl_status |= TIOCPKT_FLUSHWRITE;
 195                 wake_up_interruptible(&to->read_wait);
 196                 spin_unlock_irqrestore(&tty->ctrl_lock, flags);
 197         }
 198 }
 199
 200 static int pty_open(struct tty_struct *tty, struct file * filp)
 201 {
 202         int     retval = -ENODEV;
 203
 204         if (!tty || !tty->link)
 205                 goto out;
 206
 207         retval = -EIO;
 208         if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
 209                 goto out;
 210         if (test_bit(TTY_PTY_LOCK, &tty->link->flags))
 211                 goto out;
 212         if (tty->link->count != 1)
 213                 goto out;
 214
 215         clear_bit(TTY_OTHER_CLOSED, &tty->link->flags);
 216         set_bit(TTY_THROTTLED, &tty->flags);
 217         set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 218         retval = 0;
 219 out:
 220         return retval;
 221 }
 222
 223 static void pty_set_termios(struct tty_struct *tty, struct ktermios *old_termios)
 224 {
 225         tty->termios->c_cflag &= ~(CSIZE | PARENB);
 226         tty->termios->c_cflag |= (CS8 | CREAD);
 227 }
 228
 229 static const struct tty_operations pty_ops = {
 230         .open = pty_open,
 231         .close = pty_close,
 232         .write = pty_write,
 233         .write_room = pty_write_room,
 234         .flush_buffer = pty_flush_buffer,
 235         .chars_in_buffer = pty_chars_in_buffer,
 236         .unthrottle = pty_unthrottle,
 237         .set_termios = pty_set_termios,
 238 };
 239
 240 /* Traditional BSD devices */
 241 #ifdef CONFIG_LEGACY_PTYS
 242 static struct tty_driver *pty_driver, *pty_slave_driver;
 243
 244 static int pty_bsd_ioctl(struct tty_struct *tty, struct file *file,
 245                          unsigned int cmd, unsigned long arg)
 246 {
 247         switch (cmd) {
 248         case TIOCSPTLCK: /* Set PT Lock (disallow slave open) */
 249                 return pty_set_lock(tty, (int __user *) arg);
 250         }
 251         return -ENOIOCTLCMD;
 252 }
 253
 254 static int legacy_count = CONFIG_LEGACY_PTY_COUNT;
 255 module_param(legacy_count, int, 0);
 256
 257 static void __init legacy_pty_init(void)
 258 {
 259         if (legacy_count <= 0)
 260                 return;
 261
 262         pty_driver = alloc_tty_driver(legacy_count);
 263         if (!pty_driver)
 264                 panic("Couldn't allocate pty driver");
 265
 266         pty_slave_driver = alloc_tty_driver(legacy_count);
 267         if (!pty_slave_driver)
 268                 panic("Couldn't allocate pty slave driver");
 269
 270         pty_driver->owner = THIS_MODULE;
 271         pty_driver->driver_name = "pty_master";
 272         pty_driver->name = "pty";
 273         pty_driver->major = PTY_MASTER_MAJOR;
 274         pty_driver->minor_start = 0;
 275         pty_driver->type = TTY_DRIVER_TYPE_PTY;
 276         pty_driver->subtype = PTY_TYPE_MASTER;
 277         pty_driver->init_termios = tty_std_termios;
 278         pty_driver->init_termios.c_iflag = 0;
 279         pty_driver->init_termios.c_oflag = 0;
 280         pty_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
 281         pty_driver->init_termios.c_lflag = 0;
 282         pty_driver->init_termios.c_ispeed = 38400;
 283         pty_driver->init_termios.c_ospeed = 38400;
 284         pty_driver->flags = TTY_DRIVER_RESET_TERMIOS | TTY_DRIVER_REAL_RAW;
 285         pty_driver->other = pty_slave_driver;
 286         tty_set_operations(pty_driver, &pty_ops);
 287         pty_driver->ioctl = pty_bsd_ioctl;
 288
 289         pty_slave_driver->owner = THIS_MODULE;
 290         pty_slave_driver->driver_name = "pty_slave";
 291         pty_slave_driver->name = "ttyp";
 292         pty_slave_driver->major = PTY_SLAVE_MAJOR;
 293         pty_slave_driver->minor_start = 0;
 294         pty_slave_driver->type = TTY_DRIVER_TYPE_PTY;
 295         pty_slave_driver->subtype = PTY_TYPE_SLAVE;
 296         pty_slave_driver->init_termios = tty_std_termios;
 297         pty_slave_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
 298         pty_slave_driver->init_termios.c_ispeed = 38400;
 299         pty_slave_driver->init_termios.c_ospeed = 38400;
 300         pty_slave_driver->flags = TTY_DRIVER_RESET_TERMIOS |
 301                                         TTY_DRIVER_REAL_RAW;
 302         pty_slave_driver->other = pty_driver;
 303         tty_set_operations(pty_slave_driver, &pty_ops);
 304
 305         if (tty_register_driver(pty_driver))
 306                 panic("Couldn't register pty driver");
 307         if (tty_register_driver(pty_slave_driver))
 308                 panic("Couldn't register pty slave driver");
 309 }
 310 #else
 311 static inline void legacy_pty_init(void) { }
 312 #endif
 313
 314 /* Unix98 devices */
 315 #ifdef CONFIG_UNIX98_PTYS
 316 /*
 317  * sysctl support for setting limits on the number of Unix98 ptys allocated.
 318  * Otherwise one can eat up all kernel memory by opening /dev/ptmx repeatedly.
 319  */
 320 int pty_limit = NR_UNIX98_PTY_DEFAULT;
 321 static int pty_limit_min = 0;
 322 static int pty_limit_max = NR_UNIX98_PTY_MAX;
 323
 324 static struct ctl_table pty_table[] = {
 325         {
 326                 .ctl_name       = PTY_MAX,
 327                 .procname       = "max",
 328                 .maxlen         = sizeof(int),
 329                 .mode           = 0644,
 330                 .data           = &pty_limit,
 331                 .proc_handler   = &proc_dointvec_minmax,
 332                 .strategy       = &sysctl_intvec,
 333                 .extra1         = &pty_limit_min,
 334                 .extra2         = &pty_limit_max,
 335         }, {
 336                 .ctl_name       = PTY_NR,
 337                 .procname       = "nr",
 338                 .maxlen         = sizeof(int),
 339                 .mode           = 0444,
 340                 .proc_handler   = &proc_dointvec,
 341         }, {
 342                 .ctl_name       = 0
 343         }
 344 };
 345
 346 static struct ctl_table pty_kern_table[] = {
 347         {
 348                 .ctl_name       = KERN_PTY,
 349                 .procname       = "pty",
 350                 .mode           = 0555,
 351                 .child          = pty_table,
 352         },
 353         {}
 354 };
 355
 356 static struct ctl_table pty_root_table[] = {
 357         {
 358                 .ctl_name       = CTL_KERN,
 359                 .procname       = "kernel",
 360                 .mode           = 0555,
 361                 .child          = pty_kern_table,
 362         },
 363         {}
 364 };
 365
 366
 367 static int pty_unix98_ioctl(struct tty_struct *tty, struct file *file,
 368                             unsigned int cmd, unsigned long arg)
 369 {
 370         switch (cmd) {
 371         case TIOCSPTLCK: /* Set PT Lock (disallow slave open) */
 372                 return pty_set_lock(tty, (int __user *)arg);
 373         case TIOCGPTN: /* Get PT Number */
 374                 return put_user(tty->index, (unsigned int __user *)arg);
 375         }
 376
 377         return -ENOIOCTLCMD;
 378 }
 379
 380 static void __init unix98_pty_init(void)
 381 {
 382         ptm_driver = alloc_tty_driver(NR_UNIX98_PTY_MAX);
 383         if (!ptm_driver)
 384                 panic("Couldn't allocate Unix98 ptm driver");
 385         pts_driver = alloc_tty_driver(NR_UNIX98_PTY_MAX);
 386         if (!pts_driver)
 387                 panic("Couldn't allocate Unix98 pts driver");
 388
 389         ptm_driver->owner = THIS_MODULE;
 390         ptm_driver->driver_name = "pty_master";
 391         ptm_driver->name = "ptm";
 392         ptm_driver->major = UNIX98_PTY_MASTER_MAJOR;
 393         ptm_driver->minor_start = 0;
 394         ptm_driver->type = TTY_DRIVER_TYPE_PTY;
 395         ptm_driver->subtype = PTY_TYPE_MASTER;
 396         ptm_driver->init_termios = tty_std_termios;
 397         ptm_driver->init_termios.c_iflag = 0;
 398         ptm_driver->init_termios.c_oflag = 0;
 399         ptm_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
 400         ptm_driver->init_termios.c_lflag = 0;
 401         ptm_driver->init_termios.c_ispeed = 38400;
 402         ptm_driver->init_termios.c_ospeed = 38400;
 403         ptm_driver->flags = TTY_DRIVER_RESET_TERMIOS | TTY_DRIVER_REAL_RAW |
 404                 TTY_DRIVER_DYNAMIC_DEV | TTY_DRIVER_DEVPTS_MEM;
 405         ptm_driver->other = pts_driver;
 406         tty_set_operations(ptm_driver, &pty_ops);
 407         ptm_driver->ioctl = pty_unix98_ioctl;
 408
 409         pts_driver->owner = THIS_MODULE;
 410         pts_driver->driver_name = "pty_slave";
 411         pts_driver->name = "pts";
 412         pts_driver->major = UNIX98_PTY_SLAVE_MAJOR;
 413         pts_driver->minor_start = 0;
 414         pts_driver->type = TTY_DRIVER_TYPE_PTY;
 415         pts_driver->subtype = PTY_TYPE_SLAVE;
 416         pts_driver->init_termios = tty_std_termios;
 417         pts_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
 418         pts_driver->init_termios.c_ispeed = 38400;
 419         pts_driver->init_termios.c_ospeed = 38400;
 420         pts_driver->flags = TTY_DRIVER_RESET_TERMIOS | TTY_DRIVER_REAL_RAW |
 421                 TTY_DRIVER_DYNAMIC_DEV | TTY_DRIVER_DEVPTS_MEM;
 422         pts_driver->other = ptm_driver;
 423         tty_set_operations(pts_driver, &pty_ops);
 424
 425         if (tty_register_driver(ptm_driver))
 426                 panic("Couldn't register Unix98 ptm driver");
 427         if (tty_register_driver(pts_driver))
 428                 panic("Couldn't register Unix98 pts driver");
 429
 430         pty_table[1].data = &ptm_driver->refcount;
 431         register_sysctl_table(pty_root_table);
 432 }
 433 #else
 434 static inline void unix98_pty_init(void) { }
 435 #endif
 436
 437 static int __init pty_init(void)
 438 {
 439         legacy_pty_init();
 440         unix98_pty_init();
 441         return 0;
 442 }
 443 module_init(pty_init);