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/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/devfs_fs_kernel.h>
  28 #include <linux/sysctl.h>
  29
  30 #include <asm/uaccess.h>
  31 #include <asm/system.h>
  32 #include <asm/bitops.h>
  33 #include <linux/devpts_fs.h>
  34
  35 /* These are global because they are accessed in tty_io.c */
  36 #ifdef CONFIG_UNIX98_PTYS
  37 struct tty_driver *ptm_driver;
  38 struct tty_driver *pts_driver;
  39 #endif
  40
  41 static void pty_close(struct tty_struct * tty, struct file * filp)
  42 {
  43         if (!tty)
  44                 return;
  45         if (tty->driver->subtype == PTY_TYPE_MASTER) {
  46                 if (tty->count > 1)
  47                         printk("master pty_close: count = %d!!\n", tty->count);
  48         } else {
  49                 if (tty->count > 2)
  50                         return;
  51         }
  52         wake_up_interruptible(&tty->read_wait);
  53         wake_up_interruptible(&tty->write_wait);
  54         tty->packet = 0;
  55         if (!tty->link)
  56                 return;
  57         tty->link->packet = 0;
  58         wake_up_interruptible(&tty->link->read_wait);
  59         wake_up_interruptible(&tty->link->write_wait);
  60         set_bit(TTY_OTHER_CLOSED, &tty->link->flags);
  61         if (tty->driver->subtype == PTY_TYPE_MASTER) {
  62                 set_bit(TTY_OTHER_CLOSED, &tty->flags);
  63 #ifdef CONFIG_UNIX98_PTYS
  64                 if (tty->driver == ptm_driver)
  65                         devpts_pty_kill(tty->index);
  66 #endif
  67                 tty_vhangup(tty->link);
  68         }
  69 }
  70
  71 /*
  72  * The unthrottle routine is called by the line discipline to signal
  73  * that it can receive more characters.  For PTY's, the TTY_THROTTLED
  74  * flag is always set, to force the line discipline to always call the
  75  * unthrottle routine when there are fewer than TTY_THRESHOLD_UNTHROTTLE
  76  * characters in the queue.  This is necessary since each time this
  77  * happens, we need to wake up any sleeping processes that could be
  78  * (1) trying to send data to the pty, or (2) waiting in wait_until_sent()
  79  * for the pty buffer to be drained.
  80  */
  81 static void pty_unthrottle(struct tty_struct * tty)
  82 {
  83         struct tty_struct *o_tty = tty->link;
  84
  85         if (!o_tty)
  86                 return;
  87
  88         tty_wakeup(o_tty);
  89         set_bit(TTY_THROTTLED, &tty->flags);
  90 }
  91
  92 /*
  93  * WSH 05/24/97: modified to
  94  *   (1) use space in tty->flip instead of a shared temp buffer
  95  *       The flip buffers aren't being used for a pty, so there's lots
  96  *       of space available.  The buffer is protected by a per-pty
  97  *       semaphore that should almost never come under contention.
  98  *   (2) avoid redundant copying for cases where count >> receive_room
  99  * N.B. Calls from user space may now return an error code instead of
 100  * a count.
 101  *
 102  * FIXME: Our pty_write method is called with our ldisc lock held but
 103  * not our partners. We can't just take the other one blindly without
 104  * risking deadlocks.  There is also the small matter of TTY_DONT_FLIP
 105  */
 106 static int pty_write(struct tty_struct * tty, int from_user,
 107                        const unsigned char *buf, int count)
 108 {
 109         struct tty_struct *to = tty->link;
 110         int     c=0, n, room;
 111         char    *temp_buffer;
 112
 113         if (!to || tty->stopped)
 114                 return 0;
 115
 116         if (from_user) {
 117                 down(&tty->flip.pty_sem);
 118                 temp_buffer = &tty->flip.char_buf[0];
 119                 while (count > 0) {
 120                         /* check space so we don't copy needlessly */
 121                         n = to->ldisc.receive_room(to);
 122                         if (n > count)
 123                                 n = count;
 124                         if (!n) break;
 125
 126                         n  = min(n, PTY_BUF_SIZE);
 127                         n -= copy_from_user(temp_buffer, buf, n);
 128                         if (!n) {
 129                                 if (!c)
 130                                         c = -EFAULT;
 131                                 break;
 132                         }
 133
 134                         /* check again in case the buffer filled up */
 135                         room = to->ldisc.receive_room(to);
 136                         if (n > room)
 137                                 n = room;
 138                         if (!n) break;
 139                         buf   += n;
 140                         c     += n;
 141                         count -= n;
 142                         to->ldisc.receive_buf(to, temp_buffer, NULL, n);
 143                 }
 144                 up(&tty->flip.pty_sem);
 145         } else {
 146                 c = to->ldisc.receive_room(to);
 147                 if (c > count)
 148                         c = count;
 149                 to->ldisc.receive_buf(to, buf, NULL, c);
 150         }
 151
 152         return c;
 153 }
 154
 155 static int pty_write_room(struct tty_struct *tty)
 156 {
 157         struct tty_struct *to = tty->link;
 158
 159         if (!to || tty->stopped)
 160                 return 0;
 161
 162         return to->ldisc.receive_room(to);
 163 }
 164
 165 /*
 166  *      WSH 05/24/97:  Modified for asymmetric MASTER/SLAVE behavior
 167  *      The chars_in_buffer() value is used by the ldisc select() function
 168  *      to hold off writing when chars_in_buffer > WAKEUP_CHARS (== 256).
 169  *      The pty driver chars_in_buffer() Master/Slave must behave differently:
 170  *
 171  *      The Master side needs to allow typed-ahead commands to accumulate
 172  *      while being canonicalized, so we report "our buffer" as empty until
 173  *      some threshold is reached, and then report the count. (Any count >
 174  *      WAKEUP_CHARS is regarded by select() as "full".)  To avoid deadlock
 175  *      the count returned must be 0 if no canonical data is available to be
 176  *      read. (The N_TTY ldisc.chars_in_buffer now knows this.)
 177  *
 178  *      The Slave side passes all characters in raw mode to the Master side's
 179  *      buffer where they can be read immediately, so in this case we can
 180  *      return the true count in the buffer.
 181  */
 182 static int pty_chars_in_buffer(struct tty_struct *tty)
 183 {
 184         struct tty_struct *to = tty->link;
 185         int count;
 186
 187         if (!to || !to->ldisc.chars_in_buffer)
 188                 return 0;
 189
 190         /* The ldisc must report 0 if no characters available to be read */
 191         count = to->ldisc.chars_in_buffer(to);
 192
 193         if (tty->driver->subtype == PTY_TYPE_SLAVE) return count;
 194
 195         /* Master side driver ... if the other side's read buffer is less than
 196          * half full, return 0 to allow writers to proceed; otherwise return
 197          * the count.  This leaves a comfortable margin to avoid overflow,
 198          * and still allows half a buffer's worth of typed-ahead commands.
 199          */
 200         return ((count < N_TTY_BUF_SIZE/2) ? 0 : count);
 201 }
 202
 203 /* Set the lock flag on a pty */
 204 static int pty_set_lock(struct tty_struct *tty, int __user * arg)
 205 {
 206         int val;
 207         if (get_user(val,arg))
 208                 return -EFAULT;
 209         if (val)
 210                 set_bit(TTY_PTY_LOCK, &tty->flags);
 211         else
 212                 clear_bit(TTY_PTY_LOCK, &tty->flags);
 213         return 0;
 214 }
 215
 216 static void pty_flush_buffer(struct tty_struct *tty)
 217 {
 218         struct tty_struct *to = tty->link;
 219
 220         if (!to)
 221                 return;
 222
 223         if (to->ldisc.flush_buffer)
 224                 to->ldisc.flush_buffer(to);
 225
 226         if (to->packet) {
 227                 tty->ctrl_status |= TIOCPKT_FLUSHWRITE;
 228                 wake_up_interruptible(&to->read_wait);
 229         }
 230 }
 231
 232 static int pty_open(struct tty_struct *tty, struct file * filp)
 233 {
 234         int     retval = -ENODEV;
 235
 236         if (!tty || !tty->link)
 237                 goto out;
 238
 239         retval = -EIO;
 240         if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
 241                 goto out;
 242         if (test_bit(TTY_PTY_LOCK, &tty->link->flags))
 243                 goto out;
 244         if (tty->link->count != 1)
 245                 goto out;
 246
 247         clear_bit(TTY_OTHER_CLOSED, &tty->link->flags);
 248         set_bit(TTY_THROTTLED, &tty->flags);
 249         set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 250         retval = 0;
 251 out:
 252         return retval;
 253 }
 254
 255 static void pty_set_termios(struct tty_struct *tty, struct termios *old_termios)
 256 {
 257         tty->termios->c_cflag &= ~(CSIZE | PARENB);
 258         tty->termios->c_cflag |= (CS8 | CREAD);
 259 }
 260
 261 static struct tty_operations pty_ops = {
 262         .open = pty_open,
 263         .close = pty_close,
 264         .write = pty_write,
 265         .write_room = pty_write_room,
 266         .flush_buffer = pty_flush_buffer,
 267         .chars_in_buffer = pty_chars_in_buffer,
 268         .unthrottle = pty_unthrottle,
 269         .set_termios = pty_set_termios,
 270 };
 271
 272 /* Traditional BSD devices */
 273 #ifdef CONFIG_LEGACY_PTYS
 274 static struct tty_driver *pty_driver, *pty_slave_driver;
 275
 276 static int pty_bsd_ioctl(struct tty_struct *tty, struct file *file,
 277                          unsigned int cmd, unsigned long arg)
 278 {
 279         switch (cmd) {
 280         case TIOCSPTLCK: /* Set PT Lock (disallow slave open) */
 281                 return pty_set_lock(tty, (int __user *) arg);
 282         }
 283         return -ENOIOCTLCMD;
 284 }
 285
 286 static void __init legacy_pty_init(void)
 287 {
 288
 289         pty_driver = alloc_tty_driver(NR_PTYS);
 290         if (!pty_driver)
 291                 panic("Couldn't allocate pty driver");
 292
 293         pty_slave_driver = alloc_tty_driver(NR_PTYS);
 294         if (!pty_slave_driver)
 295                 panic("Couldn't allocate pty slave driver");
 296
 297         pty_driver->owner = THIS_MODULE;
 298         pty_driver->driver_name = "pty_master";
 299         pty_driver->name = "pty";
 300         pty_driver->devfs_name = "pty/m";
 301         pty_driver->major = PTY_MASTER_MAJOR;
 302         pty_driver->minor_start = 0;
 303         pty_driver->type = TTY_DRIVER_TYPE_PTY;
 304         pty_driver->subtype = PTY_TYPE_MASTER;
 305         pty_driver->init_termios = tty_std_termios;
 306         pty_driver->init_termios.c_iflag = 0;
 307         pty_driver->init_termios.c_oflag = 0;
 308         pty_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
 309         pty_driver->init_termios.c_lflag = 0;
 310         pty_driver->flags = TTY_DRIVER_RESET_TERMIOS | TTY_DRIVER_REAL_RAW;
 311         pty_driver->other = pty_slave_driver;
 312         tty_set_operations(pty_driver, &pty_ops);
 313         pty_driver->ioctl = pty_bsd_ioctl;
 314
 315         pty_slave_driver->owner = THIS_MODULE;
 316         pty_slave_driver->driver_name = "pty_slave";
 317         pty_slave_driver->name = "ttyp";
 318         pty_slave_driver->devfs_name = "pty/s";
 319         pty_slave_driver->major = PTY_SLAVE_MAJOR;
 320         pty_slave_driver->minor_start = 0;
 321         pty_slave_driver->type = TTY_DRIVER_TYPE_PTY;
 322         pty_slave_driver->subtype = PTY_TYPE_SLAVE;
 323         pty_slave_driver->init_termios = tty_std_termios;
 324         pty_slave_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
 325         pty_slave_driver->flags = TTY_DRIVER_RESET_TERMIOS |
 326                                         TTY_DRIVER_REAL_RAW;
 327         pty_slave_driver->other = pty_driver;
 328         tty_set_operations(pty_slave_driver, &pty_ops);
 329
 330         if (tty_register_driver(pty_driver))
 331                 panic("Couldn't register pty driver");
 332         if (tty_register_driver(pty_slave_driver))
 333                 panic("Couldn't register pty slave driver");
 334 }
 335 #else
 336 static inline void legacy_pty_init(void) { }
 337 #endif
 338
 339 /* Unix98 devices */
 340 #ifdef CONFIG_UNIX98_PTYS
 341 /*
 342  * sysctl support for setting limits on the number of Unix98 ptys allocated.
 343  * Otherwise one can eat up all kernel memory by opening /dev/ptmx repeatedly.
 344  */
 345 int pty_limit = NR_UNIX98_PTY_DEFAULT;
 346 static int pty_limit_min = 0;
 347 static int pty_limit_max = NR_UNIX98_PTY_MAX;
 348
 349 ctl_table pty_table[] = {
 350         {
 351                 .ctl_name       = PTY_MAX,
 352                 .procname       = "max",
 353                 .maxlen         = sizeof(int),
 354                 .mode           = 0644,
 355                 .data           = &pty_limit,
 356                 .proc_handler   = &proc_dointvec_minmax,
 357                 .strategy       = &sysctl_intvec,
 358                 .extra1         = &pty_limit_min,
 359                 .extra2         = &pty_limit_max,
 360         }, {
 361                 .ctl_name       = PTY_NR,
 362                 .procname       = "nr",
 363                 .maxlen         = sizeof(int),
 364                 .mode           = 0444,
 365                 .proc_handler   = &proc_dointvec,
 366         }, {
 367                 .ctl_name       = 0
 368         }
 369 };
 370
 371 static int pty_unix98_ioctl(struct tty_struct *tty, struct file *file,
 372                             unsigned int cmd, unsigned long arg)
 373 {
 374         switch (cmd) {
 375         case TIOCSPTLCK: /* Set PT Lock (disallow slave open) */
 376                 return pty_set_lock(tty, (int __user *)arg);
 377         case TIOCGPTN: /* Get PT Number */
 378                 return put_user(tty->index, (unsigned int __user *)arg);
 379         }
 380
 381         return -ENOIOCTLCMD;
 382 }
 383
 384 static void __init unix98_pty_init(void)
 385 {
 386         devfs_mk_dir("pts");
 387         ptm_driver = alloc_tty_driver(NR_UNIX98_PTY_MAX);
 388         if (!ptm_driver)
 389                 panic("Couldn't allocate Unix98 ptm driver");
 390         pts_driver = alloc_tty_driver(NR_UNIX98_PTY_MAX);
 391         if (!pts_driver)
 392                 panic("Couldn't allocate Unix98 pts driver");
 393
 394         ptm_driver->owner = THIS_MODULE;
 395         ptm_driver->driver_name = "pty_master";
 396         ptm_driver->name = "ptm";
 397         ptm_driver->major = UNIX98_PTY_MASTER_MAJOR;
 398         ptm_driver->minor_start = 0;
 399         ptm_driver->type = TTY_DRIVER_TYPE_PTY;
 400         ptm_driver->subtype = PTY_TYPE_MASTER;
 401         ptm_driver->init_termios = tty_std_termios;
 402         ptm_driver->init_termios.c_iflag = 0;
 403         ptm_driver->init_termios.c_oflag = 0;
 404         ptm_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
 405         ptm_driver->init_termios.c_lflag = 0;
 406         ptm_driver->flags = TTY_DRIVER_RESET_TERMIOS | TTY_DRIVER_REAL_RAW |
 407                 TTY_DRIVER_NO_DEVFS | TTY_DRIVER_DEVPTS_MEM;
 408         ptm_driver->other = pts_driver;
 409         tty_set_operations(ptm_driver, &pty_ops);
 410         ptm_driver->ioctl = pty_unix98_ioctl;
 411
 412         pts_driver->owner = THIS_MODULE;
 413         pts_driver->driver_name = "pty_slave";
 414         pts_driver->name = "pts";
 415         pts_driver->major = UNIX98_PTY_SLAVE_MAJOR;
 416         pts_driver->minor_start = 0;
 417         pts_driver->type = TTY_DRIVER_TYPE_PTY;
 418         pts_driver->subtype = PTY_TYPE_SLAVE;
 419         pts_driver->init_termios = tty_std_termios;
 420         pts_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
 421         pts_driver->flags = TTY_DRIVER_RESET_TERMIOS | TTY_DRIVER_REAL_RAW |
 422                 TTY_DRIVER_NO_DEVFS | TTY_DRIVER_DEVPTS_MEM;
 423         pts_driver->other = ptm_driver;
 424         tty_set_operations(pts_driver, &pty_ops);
 425
 426         if (tty_register_driver(ptm_driver))
 427                 panic("Couldn't register Unix98 ptm driver");
 428         if (tty_register_driver(pts_driver))
 429                 panic("Couldn't register Unix98 pts driver");
 430
 431         pty_table[1].data = &ptm_driver->refcount;
 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);