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/sched.h>
  18 #include <linux/interrupt.h>
  19 #include <linux/tty.h>
  20 #include <linux/tty_flip.h>
  21 #include <linux/fcntl.h>
  22 #include <linux/string.h>
  23 #include <linux/major.h>
  24 #include <linux/mm.h>
  25 #include <linux/init.h>
  26 #include <linux/sysctl.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.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.chars_in_buffer)
 154                 return 0;
 155
 156         /* The ldisc must report 0 if no characters available to be read */
 157         count = to->ldisc.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
 186         if (!to)
 187                 return;
 188
 189         if (to->ldisc.flush_buffer)
 190                 to->ldisc.flush_buffer(to);
 191
 192         if (to->packet) {
 193                 tty->ctrl_status |= TIOCPKT_FLUSHWRITE;
 194                 wake_up_interruptible(&to->read_wait);
 195         }
 196 }
 197
 198 static int pty_open(struct tty_struct *tty, struct file * filp)
 199 {
 200         int     retval = -ENODEV;
 201
 202         if (!tty || !tty->link)
 203                 goto out;
 204
 205         retval = -EIO;
 206         if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
 207                 goto out;
 208         if (test_bit(TTY_PTY_LOCK, &tty->link->flags))
 209                 goto out;
 210         if (tty->link->count != 1)
 211                 goto out;
 212
 213         clear_bit(TTY_OTHER_CLOSED, &tty->link->flags);
 214         set_bit(TTY_THROTTLED, &tty->flags);
 215         set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 216         retval = 0;
 217 out:
 218         return retval;
 219 }
 220
 221 static void pty_set_termios(struct tty_struct *tty, struct ktermios *old_termios)
 222 {
 223         tty->termios->c_cflag &= ~(CSIZE | PARENB);
 224         tty->termios->c_cflag |= (CS8 | CREAD);
 225 }
 226
 227 static const struct tty_operations pty_ops = {
 228         .open = pty_open,
 229         .close = pty_close,
 230         .write = pty_write,
 231         .write_room = pty_write_room,
 232         .flush_buffer = pty_flush_buffer,
 233         .chars_in_buffer = pty_chars_in_buffer,
 234         .unthrottle = pty_unthrottle,
 235         .set_termios = pty_set_termios,
 236 };
 237
 238 /* Traditional BSD devices */
 239 #ifdef CONFIG_LEGACY_PTYS
 240 static struct tty_driver *pty_driver, *pty_slave_driver;
 241
 242 static int pty_bsd_ioctl(struct tty_struct *tty, struct file *file,
 243                          unsigned int cmd, unsigned long arg)
 244 {
 245         switch (cmd) {
 246         case TIOCSPTLCK: /* Set PT Lock (disallow slave open) */
 247                 return pty_set_lock(tty, (int __user *) arg);
 248         }
 249         return -ENOIOCTLCMD;
 250 }
 251
 252 static void __init legacy_pty_init(void)
 253 {
 254
 255         pty_driver = alloc_tty_driver(NR_PTYS);
 256         if (!pty_driver)
 257                 panic("Couldn't allocate pty driver");
 258
 259         pty_slave_driver = alloc_tty_driver(NR_PTYS);
 260         if (!pty_slave_driver)
 261                 panic("Couldn't allocate pty slave driver");
 262
 263         pty_driver->owner = THIS_MODULE;
 264         pty_driver->driver_name = "pty_master";
 265         pty_driver->name = "pty";
 266         pty_driver->major = PTY_MASTER_MAJOR;
 267         pty_driver->minor_start = 0;
 268         pty_driver->type = TTY_DRIVER_TYPE_PTY;
 269         pty_driver->subtype = PTY_TYPE_MASTER;
 270         pty_driver->init_termios = tty_std_termios;
 271         pty_driver->init_termios.c_iflag = 0;
 272         pty_driver->init_termios.c_oflag = 0;
 273         pty_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
 274         pty_driver->init_termios.c_lflag = 0;
 275         pty_driver->init_termios.c_ispeed = 38400;
 276         pty_driver->init_termios.c_ospeed = 38400;
 277         pty_driver->flags = TTY_DRIVER_RESET_TERMIOS | TTY_DRIVER_REAL_RAW;
 278         pty_driver->other = pty_slave_driver;
 279         tty_set_operations(pty_driver, &pty_ops);
 280         pty_driver->ioctl = pty_bsd_ioctl;
 281
 282         pty_slave_driver->owner = THIS_MODULE;
 283         pty_slave_driver->driver_name = "pty_slave";
 284         pty_slave_driver->name = "ttyp";
 285         pty_slave_driver->major = PTY_SLAVE_MAJOR;
 286         pty_slave_driver->minor_start = 0;
 287         pty_slave_driver->type = TTY_DRIVER_TYPE_PTY;
 288         pty_slave_driver->subtype = PTY_TYPE_SLAVE;
 289         pty_slave_driver->init_termios = tty_std_termios;
 290         pty_slave_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
 291         pty_slave_driver->init_termios.c_ispeed = 38400;
 292         pty_slave_driver->init_termios.c_ospeed = 38400;
 293         pty_slave_driver->flags = TTY_DRIVER_RESET_TERMIOS |
 294                                         TTY_DRIVER_REAL_RAW;
 295         pty_slave_driver->other = pty_driver;
 296         tty_set_operations(pty_slave_driver, &pty_ops);
 297
 298         if (tty_register_driver(pty_driver))
 299                 panic("Couldn't register pty driver");
 300         if (tty_register_driver(pty_slave_driver))
 301                 panic("Couldn't register pty slave driver");
 302 }
 303 #else
 304 static inline void legacy_pty_init(void) { }
 305 #endif
 306
 307 /* Unix98 devices */
 308 #ifdef CONFIG_UNIX98_PTYS
 309 /*
 310  * sysctl support for setting limits on the number of Unix98 ptys allocated.
 311  * Otherwise one can eat up all kernel memory by opening /dev/ptmx repeatedly.
 312  */
 313 int pty_limit = NR_UNIX98_PTY_DEFAULT;
 314 static int pty_limit_min = 0;
 315 static int pty_limit_max = NR_UNIX98_PTY_MAX;
 316
 317 ctl_table pty_table[] = {
 318         {
 319                 .ctl_name       = PTY_MAX,
 320                 .procname       = "max",
 321                 .maxlen         = sizeof(int),
 322                 .mode           = 0644,
 323                 .data           = &pty_limit,
 324                 .proc_handler   = &proc_dointvec_minmax,
 325                 .strategy       = &sysctl_intvec,
 326                 .extra1         = &pty_limit_min,
 327                 .extra2         = &pty_limit_max,
 328         }, {
 329                 .ctl_name       = PTY_NR,
 330                 .procname       = "nr",
 331                 .maxlen         = sizeof(int),
 332                 .mode           = 0444,
 333                 .proc_handler   = &proc_dointvec,
 334         }, {
 335                 .ctl_name       = 0
 336         }
 337 };
 338
 339 static int pty_unix98_ioctl(struct tty_struct *tty, struct file *file,
 340                             unsigned int cmd, unsigned long arg)
 341 {
 342         switch (cmd) {
 343         case TIOCSPTLCK: /* Set PT Lock (disallow slave open) */
 344                 return pty_set_lock(tty, (int __user *)arg);
 345         case TIOCGPTN: /* Get PT Number */
 346                 return put_user(tty->index, (unsigned int __user *)arg);
 347         }
 348
 349         return -ENOIOCTLCMD;
 350 }
 351
 352 static void __init unix98_pty_init(void)
 353 {
 354         ptm_driver = alloc_tty_driver(NR_UNIX98_PTY_MAX);
 355         if (!ptm_driver)
 356                 panic("Couldn't allocate Unix98 ptm driver");
 357         pts_driver = alloc_tty_driver(NR_UNIX98_PTY_MAX);
 358         if (!pts_driver)
 359                 panic("Couldn't allocate Unix98 pts driver");
 360
 361         ptm_driver->owner = THIS_MODULE;
 362         ptm_driver->driver_name = "pty_master";
 363         ptm_driver->name = "ptm";
 364         ptm_driver->major = UNIX98_PTY_MASTER_MAJOR;
 365         ptm_driver->minor_start = 0;
 366         ptm_driver->type = TTY_DRIVER_TYPE_PTY;
 367         ptm_driver->subtype = PTY_TYPE_MASTER;
 368         ptm_driver->init_termios = tty_std_termios;
 369         ptm_driver->init_termios.c_iflag = 0;
 370         ptm_driver->init_termios.c_oflag = 0;
 371         ptm_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
 372         ptm_driver->init_termios.c_lflag = 0;
 373         ptm_driver->init_termios.c_ispeed = 38400;
 374         ptm_driver->init_termios.c_ospeed = 38400;
 375         ptm_driver->flags = TTY_DRIVER_RESET_TERMIOS | TTY_DRIVER_REAL_RAW |
 376                 TTY_DRIVER_DYNAMIC_DEV | TTY_DRIVER_DEVPTS_MEM;
 377         ptm_driver->other = pts_driver;
 378         tty_set_operations(ptm_driver, &pty_ops);
 379         ptm_driver->ioctl = pty_unix98_ioctl;
 380
 381         pts_driver->owner = THIS_MODULE;
 382         pts_driver->driver_name = "pty_slave";
 383         pts_driver->name = "pts";
 384         pts_driver->major = UNIX98_PTY_SLAVE_MAJOR;
 385         pts_driver->minor_start = 0;
 386         pts_driver->type = TTY_DRIVER_TYPE_PTY;
 387         pts_driver->subtype = PTY_TYPE_SLAVE;
 388         pts_driver->init_termios = tty_std_termios;
 389         pts_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
 390         pts_driver->init_termios.c_ispeed = 38400;
 391         pts_driver->init_termios.c_ospeed = 38400;
 392         pts_driver->flags = TTY_DRIVER_RESET_TERMIOS | TTY_DRIVER_REAL_RAW |
 393                 TTY_DRIVER_DYNAMIC_DEV | TTY_DRIVER_DEVPTS_MEM;
 394         pts_driver->other = ptm_driver;
 395         tty_set_operations(pts_driver, &pty_ops);
 396
 397         if (tty_register_driver(ptm_driver))
 398                 panic("Couldn't register Unix98 ptm driver");
 399         if (tty_register_driver(pts_driver))
 400                 panic("Couldn't register Unix98 pts driver");
 401
 402         pty_table[1].data = &ptm_driver->refcount;
 403 }
 404 #else
 405 static inline void unix98_pty_init(void) { }
 406 #endif
 407
 408 static int __init pty_init(void)
 409 {
 410         legacy_pty_init();
 411         unix98_pty_init();
 412         return 0;
 413 }
 414 module_init(pty_init);