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 <linux/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 static 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         set_bit(TTY_OTHER_CLOSED, &tty->link->flags);
  59         wake_up_interruptible(&tty->link->read_wait);
  60         wake_up_interruptible(&tty->link->write_wait);
  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, const unsigned char *buf, int count)
 107 {
 108         struct tty_struct *to = tty->link;
 109         int     c;
 110
 111         if (!to || tty->stopped)
 112                 return 0;
 113
 114         c = to->ldisc.receive_room(to);
 115         if (c > count)
 116                 c = count;
 117         to->ldisc.receive_buf(to, buf, NULL, c);
 118
 119         return c;
 120 }
 121
 122 static int pty_write_room(struct tty_struct *tty)
 123 {
 124         struct tty_struct *to = tty->link;
 125
 126         if (!to || tty->stopped)
 127                 return 0;
 128
 129         return to->ldisc.receive_room(to);
 130 }
 131
 132 /*
 133  *      WSH 05/24/97:  Modified for asymmetric MASTER/SLAVE behavior
 134  *      The chars_in_buffer() value is used by the ldisc select() function
 135  *      to hold off writing when chars_in_buffer > WAKEUP_CHARS (== 256).
 136  *      The pty driver chars_in_buffer() Master/Slave must behave differently:
 137  *
 138  *      The Master side needs to allow typed-ahead commands to accumulate
 139  *      while being canonicalized, so we report "our buffer" as empty until
 140  *      some threshold is reached, and then report the count. (Any count >
 141  *      WAKEUP_CHARS is regarded by select() as "full".)  To avoid deadlock
 142  *      the count returned must be 0 if no canonical data is available to be
 143  *      read. (The N_TTY ldisc.chars_in_buffer now knows this.)
 144  *
 145  *      The Slave side passes all characters in raw mode to the Master side's
 146  *      buffer where they can be read immediately, so in this case we can
 147  *      return the true count in the buffer.
 148  */
 149 static int pty_chars_in_buffer(struct tty_struct *tty)
 150 {
 151         struct tty_struct *to = tty->link;
 152         ssize_t (*chars_in_buffer)(struct tty_struct *);
 153         int count;
 154
 155         /* We should get the line discipline lock for "tty->link" */
 156         if (!to || !(chars_in_buffer = to->ldisc.chars_in_buffer))
 157                 return 0;
 158
 159         /* The ldisc must report 0 if no characters available to be read */
 160         count = chars_in_buffer(to);
 161
 162         if (tty->driver->subtype == PTY_TYPE_SLAVE) return count;
 163
 164         /* Master side driver ... if the other side's read buffer is less than
 165          * half full, return 0 to allow writers to proceed; otherwise return
 166          * the count.  This leaves a comfortable margin to avoid overflow,
 167          * and still allows half a buffer's worth of typed-ahead commands.
 168          */
 169         return ((count < N_TTY_BUF_SIZE/2) ? 0 : count);
 170 }
 171
 172 /* Set the lock flag on a pty */
 173 static int pty_set_lock(struct tty_struct *tty, int __user * arg)
 174 {
 175         int val;
 176         if (get_user(val,arg))
 177                 return -EFAULT;
 178         if (val)
 179                 set_bit(TTY_PTY_LOCK, &tty->flags);
 180         else
 181                 clear_bit(TTY_PTY_LOCK, &tty->flags);
 182         return 0;
 183 }
 184
 185 static void pty_flush_buffer(struct tty_struct *tty)
 186 {
 187         struct tty_struct *to = tty->link;
 188
 189         if (!to)
 190                 return;
 191
 192         if (to->ldisc.flush_buffer)
 193                 to->ldisc.flush_buffer(to);
 194
 195         if (to->packet) {
 196                 tty->ctrl_status |= TIOCPKT_FLUSHWRITE;
 197                 wake_up_interruptible(&to->read_wait);
 198         }
 199 }
 200
 201 static int pty_open(struct tty_struct *tty, struct file * filp)
 202 {
 203         int     retval = -ENODEV;
 204
 205         if (!tty || !tty->link)
 206                 goto out;
 207
 208         retval = -EIO;
 209         if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
 210                 goto out;
 211         if (test_bit(TTY_PTY_LOCK, &tty->link->flags))
 212                 goto out;
 213         if (tty->link->count != 1)
 214                 goto out;
 215
 216         clear_bit(TTY_OTHER_CLOSED, &tty->link->flags);
 217         set_bit(TTY_THROTTLED, &tty->flags);
 218         set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 219         retval = 0;
 220 out:
 221         return retval;
 222 }
 223
 224 static void pty_set_termios(struct tty_struct *tty, struct termios *old_termios)
 225 {
 226         tty->termios->c_cflag &= ~(CSIZE | PARENB);
 227         tty->termios->c_cflag |= (CS8 | CREAD);
 228 }
 229
 230 static struct tty_operations pty_ops = {
 231         .open = pty_open,
 232         .close = pty_close,
 233         .write = pty_write,
 234         .write_room = pty_write_room,
 235         .flush_buffer = pty_flush_buffer,
 236         .chars_in_buffer = pty_chars_in_buffer,
 237         .unthrottle = pty_unthrottle,
 238         .set_termios = pty_set_termios,
 239 };
 240
 241 /* Traditional BSD devices */
 242 #ifdef CONFIG_LEGACY_PTYS
 243 static struct tty_driver *pty_driver, *pty_slave_driver;
 244
 245 static int pty_bsd_ioctl(struct tty_struct *tty, struct file *file,
 246                          unsigned int cmd, unsigned long arg)
 247 {
 248         switch (cmd) {
 249         case TIOCSPTLCK: /* Set PT Lock (disallow slave open) */
 250                 return pty_set_lock(tty, (int __user *) arg);
 251         }
 252         return -ENOIOCTLCMD;
 253 }
 254
 255 static void __init legacy_pty_init(void)
 256 {
 257
 258         pty_driver = alloc_tty_driver(NR_PTYS);
 259         if (!pty_driver)
 260                 panic("Couldn't allocate pty driver");
 261
 262         pty_slave_driver = alloc_tty_driver(NR_PTYS);
 263         if (!pty_slave_driver)
 264                 panic("Couldn't allocate pty slave driver");
 265
 266         pty_driver->owner = THIS_MODULE;
 267         pty_driver->driver_name = "pty_master";
 268         pty_driver->name = "pty";
 269         pty_driver->devfs_name = "pty/m";
 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->flags = TTY_DRIVER_RESET_TERMIOS | TTY_DRIVER_REAL_RAW;
 280         pty_driver->other = pty_slave_driver;
 281         tty_set_operations(pty_driver, &pty_ops);
 282         pty_driver->ioctl = pty_bsd_ioctl;
 283
 284         pty_slave_driver->owner = THIS_MODULE;
 285         pty_slave_driver->driver_name = "pty_slave";
 286         pty_slave_driver->name = "ttyp";
 287         pty_slave_driver->devfs_name = "pty/s";
 288         pty_slave_driver->major = PTY_SLAVE_MAJOR;
 289         pty_slave_driver->minor_start = 0;
 290         pty_slave_driver->type = TTY_DRIVER_TYPE_PTY;
 291         pty_slave_driver->subtype = PTY_TYPE_SLAVE;
 292         pty_slave_driver->init_termios = tty_std_termios;
 293         pty_slave_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
 294         pty_slave_driver->flags = TTY_DRIVER_RESET_TERMIOS |
 295                                         TTY_DRIVER_REAL_RAW;
 296         pty_slave_driver->other = pty_driver;
 297         tty_set_operations(pty_slave_driver, &pty_ops);
 298
 299         if (tty_register_driver(pty_driver))
 300                 panic("Couldn't register pty driver");
 301         if (tty_register_driver(pty_slave_driver))
 302                 panic("Couldn't register pty slave driver");
 303 }
 304 #else
 305 static inline void legacy_pty_init(void) { }
 306 #endif
 307
 308 /* Unix98 devices */
 309 #ifdef CONFIG_UNIX98_PTYS
 310 /*
 311  * sysctl support for setting limits on the number of Unix98 ptys allocated.
 312  * Otherwise one can eat up all kernel memory by opening /dev/ptmx repeatedly.
 313  */
 314 int pty_limit = NR_UNIX98_PTY_DEFAULT;
 315 static int pty_limit_min = 0;
 316 static int pty_limit_max = NR_UNIX98_PTY_MAX;
 317
 318 ctl_table pty_table[] = {
 319         {
 320                 .ctl_name       = PTY_MAX,
 321                 .procname       = "max",
 322                 .maxlen         = sizeof(int),
 323                 .mode           = 0644,
 324                 .data           = &pty_limit,
 325                 .proc_handler   = &proc_dointvec_minmax,
 326                 .strategy       = &sysctl_intvec,
 327                 .extra1         = &pty_limit_min,
 328                 .extra2         = &pty_limit_max,
 329         }, {
 330                 .ctl_name       = PTY_NR,
 331                 .procname       = "nr",
 332                 .maxlen         = sizeof(int),
 333                 .mode           = 0444,
 334                 .proc_handler   = &proc_dointvec,
 335         }, {
 336                 .ctl_name       = 0
 337         }
 338 };
 339
 340 static int pty_unix98_ioctl(struct tty_struct *tty, struct file *file,
 341                             unsigned int cmd, unsigned long arg)
 342 {
 343         switch (cmd) {
 344         case TIOCSPTLCK: /* Set PT Lock (disallow slave open) */
 345                 return pty_set_lock(tty, (int __user *)arg);
 346         case TIOCGPTN: /* Get PT Number */
 347                 return put_user(tty->index, (unsigned int __user *)arg);
 348         }
 349
 350         return -ENOIOCTLCMD;
 351 }
 352
 353 static void __init unix98_pty_init(void)
 354 {
 355         devfs_mk_dir("pts");
 356         ptm_driver = alloc_tty_driver(NR_UNIX98_PTY_MAX);
 357         if (!ptm_driver)
 358                 panic("Couldn't allocate Unix98 ptm driver");
 359         pts_driver = alloc_tty_driver(NR_UNIX98_PTY_MAX);
 360         if (!pts_driver)
 361                 panic("Couldn't allocate Unix98 pts driver");
 362
 363         ptm_driver->owner = THIS_MODULE;
 364         ptm_driver->driver_name = "pty_master";
 365         ptm_driver->name = "ptm";
 366         ptm_driver->major = UNIX98_PTY_MASTER_MAJOR;
 367         ptm_driver->minor_start = 0;
 368         ptm_driver->type = TTY_DRIVER_TYPE_PTY;
 369         ptm_driver->subtype = PTY_TYPE_MASTER;
 370         ptm_driver->init_termios = tty_std_termios;
 371         ptm_driver->init_termios.c_iflag = 0;
 372         ptm_driver->init_termios.c_oflag = 0;
 373         ptm_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
 374         ptm_driver->init_termios.c_lflag = 0;
 375         ptm_driver->flags = TTY_DRIVER_RESET_TERMIOS | TTY_DRIVER_REAL_RAW |
 376                 TTY_DRIVER_NO_DEVFS | 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->flags = TTY_DRIVER_RESET_TERMIOS | TTY_DRIVER_REAL_RAW |
 391                 TTY_DRIVER_NO_DEVFS | TTY_DRIVER_DEVPTS_MEM;
 392         pts_driver->other = ptm_driver;
 393         tty_set_operations(pts_driver, &pty_ops);
 394
 395         if (tty_register_driver(ptm_driver))
 396                 panic("Couldn't register Unix98 ptm driver");
 397         if (tty_register_driver(pts_driver))
 398                 panic("Couldn't register Unix98 pts driver");
 399
 400         pty_table[1].data = &ptm_driver->refcount;
 401 }
 402 #else
 403 static inline void unix98_pty_init(void) { }
 404 #endif
 405
 406 static int __init pty_init(void)
 407 {
 408         legacy_pty_init();
 409         unix98_pty_init();
 410         return 0;
 411 }
 412 module_init(pty_init);