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
 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
 197 static 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;
 216 out:
 217         return retval;
 218 }
 219
 220 static 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
 226 static 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
 239 static struct tty_driver *pty_driver, *pty_slave_driver;
 240
 241 static 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
 251 static int legacy_count = CONFIG_LEGACY_PTY_COUNT;
 252 module_param(legacy_count, int, 0);
 253
 254 static 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
 308 static 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  */
 317 int pty_limit = NR_UNIX98_PTY_DEFAULT;
 318 static int pty_limit_min = 0;
 319 static int pty_limit_max = NR_UNIX98_PTY_MAX;
 320
 321 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
 343 static int pty_unix98_ioctl(struct tty_struct *tty, struct file *file,
 344                             unsigned int cmd, unsigned long arg)
 345 {
 346         switch (cmd) {
 347         case TIOCSPTLCK: /* Set PT Lock (disallow slave open) */
 348                 return pty_set_lock(tty, (int __user *)arg);
 349         case TIOCGPTN: /* Get PT Number */
 350                 return put_user(tty->index, (unsigned int __user *)arg);
 351         }
 352
 353         return -ENOIOCTLCMD;
 354 }
 355
 356 static void __init unix98_pty_init(void)
 357 {
 358         ptm_driver = alloc_tty_driver(NR_UNIX98_PTY_MAX);
 359         if (!ptm_driver)
 360                 panic("Couldn't allocate Unix98 ptm driver");
 361         pts_driver = alloc_tty_driver(NR_UNIX98_PTY_MAX);
 362         if (!pts_driver)
 363                 panic("Couldn't allocate Unix98 pts driver");
 364
 365         ptm_driver->owner = THIS_MODULE;
 366         ptm_driver->driver_name = "pty_master";
 367         ptm_driver->name = "ptm";
 368         ptm_driver->major = UNIX98_PTY_MASTER_MAJOR;
 369         ptm_driver->minor_start = 0;
 370         ptm_driver->type = TTY_DRIVER_TYPE_PTY;
 371         ptm_driver->subtype = PTY_TYPE_MASTER;
 372         ptm_driver->init_termios = tty_std_termios;
 373         ptm_driver->init_termios.c_iflag = 0;
 374         ptm_driver->init_termios.c_oflag = 0;
 375         ptm_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
 376         ptm_driver->init_termios.c_lflag = 0;
 377         ptm_driver->init_termios.c_ispeed = 38400;
 378         ptm_driver->init_termios.c_ospeed = 38400;
 379         ptm_driver->flags = TTY_DRIVER_RESET_TERMIOS | TTY_DRIVER_REAL_RAW |
 380                 TTY_DRIVER_DYNAMIC_DEV | TTY_DRIVER_DEVPTS_MEM;
 381         ptm_driver->other = pts_driver;
 382         tty_set_operations(ptm_driver, &pty_ops);
 383         ptm_driver->ioctl = pty_unix98_ioctl;
 384
 385         pts_driver->owner = THIS_MODULE;
 386         pts_driver->driver_name = "pty_slave";
 387         pts_driver->name = "pts";
 388         pts_driver->major = UNIX98_PTY_SLAVE_MAJOR;
 389         pts_driver->minor_start = 0;
 390         pts_driver->type = TTY_DRIVER_TYPE_PTY;
 391         pts_driver->subtype = PTY_TYPE_SLAVE;
 392         pts_driver->init_termios = tty_std_termios;
 393         pts_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
 394         pts_driver->init_termios.c_ispeed = 38400;
 395         pts_driver->init_termios.c_ospeed = 38400;
 396         pts_driver->flags = TTY_DRIVER_RESET_TERMIOS | TTY_DRIVER_REAL_RAW |
 397                 TTY_DRIVER_DYNAMIC_DEV | TTY_DRIVER_DEVPTS_MEM;
 398         pts_driver->other = ptm_driver;
 399         tty_set_operations(pts_driver, &pty_ops);
 400
 401         if (tty_register_driver(ptm_driver))
 402                 panic("Couldn't register Unix98 ptm driver");
 403         if (tty_register_driver(pts_driver))
 404                 panic("Couldn't register Unix98 pts driver");
 405
 406         pty_table[1].data = &ptm_driver->refcount;
 407 }
 408 #else
 409 static inline void unix98_pty_init(void) { }
 410 #endif
 411
 412 static int __init pty_init(void)
 413 {
 414         legacy_pty_init();
 415         unix98_pty_init();
 416         return 0;
 417 }
 418 module_init(pty_init);