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