drivers/char/n_tty.c

   1 /*
   2  * n_tty.c --- implements the N_TTY line discipline.
   3  *
   4  * This code used to be in tty_io.c, but things are getting hairy
   5  * enough that it made sense to split things off.  (The N_TTY
   6  * processing has changed so much that it's hardly recognizable,
   7  * anyway...)
   8  *
   9  * Note that the open routine for N_TTY is guaranteed never to return
  10  * an error.  This is because Linux will fall back to setting a line
  11  * to N_TTY if it can not switch to any other line discipline.
  12  *
  13  * Written by Theodore Ts'o, Copyright 1994.
  14  *
  15  * This file also contains code originally written by Linus Torvalds,
  16  * Copyright 1991, 1992, 1993, and by Julian Cowley, Copyright 1994.
  17  *
  18  * This file may be redistributed under the terms of the GNU General Public
  19  * License.
  20  *
  21  * Reduced memory usage for older ARM systems  - Russell King.
  22  *
  23  * 2000/01/20   Fixed SMP locking on put_tty_queue using bits of
  24  *              the patch by Andrew J. Kroll <ag784@freenet.buffalo.edu>
  25  *              who actually finally proved there really was a race.
  26  *
  27  * 2002/03/18   Implemented n_tty_wakeup to send SIGIO POLL_OUTs to
  28  *              waiting writing processes-Sapan Bhatia <sapan@corewars.org>.
  29  *              Also fixed a bug in BLOCKING mode where write_chan returns
  30  *              EAGAIN
  31  */
  32
  33 #include <linux/types.h>
  34 #include <linux/major.h>
  35 #include <linux/errno.h>
  36 #include <linux/signal.h>
  37 #include <linux/fcntl.h>
  38 #include <linux/sched.h>
  39 #include <linux/interrupt.h>
  40 #include <linux/tty.h>
  41 #include <linux/timer.h>
  42 #include <linux/ctype.h>
  43 #include <linux/mm.h>
  44 #include <linux/string.h>
  45 #include <linux/slab.h>
  46 #include <linux/poll.h>
  47 #include <linux/bitops.h>
  48
  49 #include <asm/uaccess.h>
  50 #include <asm/system.h>
  51
  52 /* number of characters left in xmit buffer before select has we have room */
  53 #define WAKEUP_CHARS 256
  54
  55 /*
  56  * This defines the low- and high-watermarks for throttling and
  57  * unthrottling the TTY driver.  These watermarks are used for
  58  * controlling the space in the read buffer.
  59  */
  60 #define TTY_THRESHOLD_THROTTLE          128 /* now based on remaining room */
  61 #define TTY_THRESHOLD_UNTHROTTLE        128
  62
  63 static inline unsigned char *alloc_buf(void)
  64 {
  65         gfp_t prio = in_interrupt() ? GFP_ATOMIC : GFP_KERNEL;
  66
  67         if (PAGE_SIZE != N_TTY_BUF_SIZE)
  68                 return kmalloc(N_TTY_BUF_SIZE, prio);
  69         else
  70                 return (unsigned char *)__get_free_page(prio);
  71 }
  72
  73 static inline void free_buf(unsigned char *buf)
  74 {
  75         if (PAGE_SIZE != N_TTY_BUF_SIZE)
  76                 kfree(buf);
  77         else
  78                 free_page((unsigned long) buf);
  79 }
  80
  81 static inline void put_tty_queue_nolock(unsigned char c, struct tty_struct *tty)
  82 {
  83         if (tty->read_cnt < N_TTY_BUF_SIZE) {
  84                 tty->read_buf[tty->read_head] = c;
  85                 tty->read_head = (tty->read_head + 1) & (N_TTY_BUF_SIZE-1);
  86                 tty->read_cnt++;
  87         }
  88 }
  89
  90 static inline void put_tty_queue(unsigned char c, struct tty_struct *tty)
  91 {
  92         unsigned long flags;
  93         /*
  94          *      The problem of stomping on the buffers ends here.
  95          *      Why didn't anyone see this one coming? --AJK
  96         */
  97         spin_lock_irqsave(&tty->read_lock, flags);
  98         put_tty_queue_nolock(c, tty);
  99         spin_unlock_irqrestore(&tty->read_lock, flags);
 100 }
 101
 102 /**
 103  *      check_unthrottle        -       allow new receive data
 104  *      @tty; tty device
 105  *
 106  *      Check whether to call the driver.unthrottle function.
 107  *      We test the TTY_THROTTLED bit first so that it always
 108  *      indicates the current state. The decision about whether
 109  *      it is worth allowing more input has been taken by the caller.
 110  *      Can sleep, may be called under the atomic_read semaphore but
 111  *      this is not guaranteed.
 112  */
 113
 114 static void check_unthrottle(struct tty_struct * tty)
 115 {
 116         if (tty->count &&
 117             test_and_clear_bit(TTY_THROTTLED, &tty->flags) &&
 118             tty->driver->unthrottle)
 119                 tty->driver->unthrottle(tty);
 120 }
 121
 122 /**
 123  *      reset_buffer_flags      -       reset buffer state
 124  *      @tty: terminal to reset
 125  *
 126  *      Reset the read buffer counters, clear the flags,
 127  *      and make sure the driver is unthrottled. Called
 128  *      from n_tty_open() and n_tty_flush_buffer().
 129  */
 130 static void reset_buffer_flags(struct tty_struct *tty)
 131 {
 132         unsigned long flags;
 133
 134         spin_lock_irqsave(&tty->read_lock, flags);
 135         tty->read_head = tty->read_tail = tty->read_cnt = 0;
 136         spin_unlock_irqrestore(&tty->read_lock, flags);
 137         tty->canon_head = tty->canon_data = tty->erasing = 0;
 138         memset(&tty->read_flags, 0, sizeof tty->read_flags);
 139         check_unthrottle(tty);
 140 }
 141
 142 /**
 143  *      n_tty_flush_buffer      -       clean input queue
 144  *      @tty:   terminal device
 145  *
 146  *      Flush the input buffer. Called when the line discipline is
 147  *      being closed, when the tty layer wants the buffer flushed (eg
 148  *      at hangup) or when the N_TTY line discipline internally has to
 149  *      clean the pending queue (for example some signals).
 150  *
 151  *      FIXME: tty->ctrl_status is not spinlocked and relies on
 152  *      lock_kernel() still.
 153  */
 154
 155 static void n_tty_flush_buffer(struct tty_struct * tty)
 156 {
 157         /* clear everything and unthrottle the driver */
 158         reset_buffer_flags(tty);
 159
 160         if (!tty->link)
 161                 return;
 162
 163         if (tty->link->packet) {
 164                 tty->ctrl_status |= TIOCPKT_FLUSHREAD;
 165                 wake_up_interruptible(&tty->link->read_wait);
 166         }
 167 }
 168
 169 /**
 170  *      n_tty_chars_in_buffer   -       report available bytes
 171  *      @tty: tty device
 172  *
 173  *      Report the number of characters buffered to be delivered to user
 174  *      at this instant in time.
 175  */
 176
 177 static ssize_t n_tty_chars_in_buffer(struct tty_struct *tty)
 178 {
 179         unsigned long flags;
 180         ssize_t n = 0;
 181
 182         spin_lock_irqsave(&tty->read_lock, flags);
 183         if (!tty->icanon) {
 184                 n = tty->read_cnt;
 185         } else if (tty->canon_data) {
 186                 n = (tty->canon_head > tty->read_tail) ?
 187                         tty->canon_head - tty->read_tail :
 188                         tty->canon_head + (N_TTY_BUF_SIZE - tty->read_tail);
 189         }
 190         spin_unlock_irqrestore(&tty->read_lock, flags);
 191         return n;
 192 }
 193
 194 /**
 195  *      is_utf8_continuation    -       utf8 multibyte check
 196  *      @c: byte to check
 197  *
 198  *      Returns true if the utf8 character 'c' is a multibyte continuation
 199  *      character. We use this to correctly compute the on screen size
 200  *      of the character when printing
 201  */
 202
 203 static inline int is_utf8_continuation(unsigned char c)
 204 {
 205         return (c & 0xc0) == 0x80;
 206 }
 207
 208 /**
 209  *      is_continuation         -       multibyte check
 210  *      @c: byte to check
 211  *
 212  *      Returns true if the utf8 character 'c' is a multibyte continuation
 213  *      character and the terminal is in unicode mode.
 214  */
 215
 216 static inline int is_continuation(unsigned char c, struct tty_struct *tty)
 217 {
 218         return I_IUTF8(tty) && is_utf8_continuation(c);
 219 }
 220
 221 /**
 222  *      opost                   -       output post processor
 223  *      @c: character (or partial unicode symbol)
 224  *      @tty: terminal device
 225  *
 226  *      Perform OPOST processing.  Returns -1 when the output device is
 227  *      full and the character must be retried. Note that Linux currently
 228  *      ignores TABDLY, CRDLY, VTDLY, FFDLY and NLDLY. They simply aren't
 229  *      relevant in the world today. If you ever need them, add them here.
 230  *
 231  *      Called from both the receive and transmit sides and can be called
 232  *      re-entrantly. Relies on lock_kernel() still.
 233  */
 234
 235 static int opost(unsigned char c, struct tty_struct *tty)
 236 {
 237         int     space, spaces;
 238
 239         space = tty->driver->write_room(tty);
 240         if (!space)
 241                 return -1;
 242
 243         if (O_OPOST(tty)) {
 244                 switch (c) {
 245                 case '\n':
 246                         if (O_ONLRET(tty))
 247                                 tty->column = 0;
 248                         if (O_ONLCR(tty)) {
 249                                 if (space < 2)
 250                                         return -1;
 251                                 tty->driver->put_char(tty, '\r');
 252                                 tty->column = 0;
 253                         }
 254                         tty->canon_column = tty->column;
 255                         break;
 256                 case '\r':
 257                         if (O_ONOCR(tty) && tty->column == 0)
 258                                 return 0;
 259                         if (O_OCRNL(tty)) {
 260                                 c = '\n';
 261                                 if (O_ONLRET(tty))
 262                                         tty->canon_column = tty->column = 0;
 263                                 break;
 264                         }
 265                         tty->canon_column = tty->column = 0;
 266                         break;
 267                 case '\t':
 268                         spaces = 8 - (tty->column & 7);
 269                         if (O_TABDLY(tty) == XTABS) {
 270                                 if (space < spaces)
 271                                         return -1;
 272                                 tty->column += spaces;
 273                                 tty->driver->write(tty, "        ", spaces);
 274                                 return 0;
 275                         }
 276                         tty->column += spaces;
 277                         break;
 278                 case '\b':
 279                         if (tty->column > 0)
 280                                 tty->column--;
 281                         break;
 282                 default:
 283                         if (O_OLCUC(tty))
 284                                 c = toupper(c);
 285                         if (!iscntrl(c) && !is_continuation(c, tty))
 286                                 tty->column++;
 287                         break;
 288                 }
 289         }
 290         tty->driver->put_char(tty, c);
 291         return 0;
 292 }
 293
 294 /**
 295  *      opost_block             -       block postprocess
 296  *      @tty: terminal device
 297  *      @inbuf: user buffer
 298  *      @nr: number of bytes
 299  *
 300  *      This path is used to speed up block console writes, among other
 301  *      things when processing blocks of output data. It handles only
 302  *      the simple cases normally found and helps to generate blocks of
 303  *      symbols for the console driver and thus improve performance.
 304  *
 305  *      Called from write_chan under the tty layer write lock.
 306  */
 307
 308 static ssize_t opost_block(struct tty_struct * tty,
 309                        const unsigned char * buf, unsigned int nr)
 310 {
 311         int     space;
 312         int     i;
 313         const unsigned char *cp;
 314
 315         space = tty->driver->write_room(tty);
 316         if (!space)
 317                 return 0;
 318         if (nr > space)
 319                 nr = space;
 320
 321         for (i = 0, cp = buf; i < nr; i++, cp++) {
 322                 switch (*cp) {
 323                 case '\n':
 324                         if (O_ONLRET(tty))
 325                                 tty->column = 0;
 326                         if (O_ONLCR(tty))
 327                                 goto break_out;
 328                         tty->canon_column = tty->column;
 329                         break;
 330                 case '\r':
 331                         if (O_ONOCR(tty) && tty->column == 0)
 332                                 goto break_out;
 333                         if (O_OCRNL(tty))
 334                                 goto break_out;
 335                         tty->canon_column = tty->column = 0;
 336                         break;
 337                 case '\t':
 338                         goto break_out;
 339                 case '\b':
 340                         if (tty->column > 0)
 341                                 tty->column--;
 342                         break;
 343                 default:
 344                         if (O_OLCUC(tty))
 345                                 goto break_out;
 346                         if (!iscntrl(*cp))
 347                                 tty->column++;
 348                         break;
 349                 }
 350         }
 351 break_out:
 352         if (tty->driver->flush_chars)
 353                 tty->driver->flush_chars(tty);
 354         i = tty->driver->write(tty, buf, i);
 355         return i;
 356 }
 357
 358
 359 /**
 360  *      put_char        -       write character to driver
 361  *      @c: character (or part of unicode symbol)
 362  *      @tty: terminal device
 363  *
 364  *      Queue a byte to the driver layer for output
 365  */
 366
 367 static inline void put_char(unsigned char c, struct tty_struct *tty)
 368 {
 369         tty->driver->put_char(tty, c);
 370 }
 371
 372 /**
 373  *      echo_char       -       echo characters
 374  *      @c: unicode byte to echo
 375  *      @tty: terminal device
 376  *
 377  *      Echo user input back onto the screen. This must be called only when
 378  *      L_ECHO(tty) is true. Called from the driver receive_buf path.
 379  */
 380
 381 static void echo_char(unsigned char c, struct tty_struct *tty)
 382 {
 383         if (L_ECHOCTL(tty) && iscntrl(c) && c != '\t') {
 384                 put_char('^', tty);
 385                 put_char(c ^ 0100, tty);
 386                 tty->column += 2;
 387         } else
 388                 opost(c, tty);
 389 }
 390
 391 static inline void finish_erasing(struct tty_struct *tty)
 392 {
 393         if (tty->erasing) {
 394                 put_char('/', tty);
 395                 tty->column++;
 396                 tty->erasing = 0;
 397         }
 398 }
 399
 400 /**
 401  *      eraser          -       handle erase function
 402  *      @c: character input
 403  *      @tty: terminal device
 404  *
 405  *      Perform erase and neccessary output when an erase character is
 406  *      present in the stream from the driver layer. Handles the complexities
 407  *      of UTF-8 multibyte symbols.
 408  */
 409
 410 static void eraser(unsigned char c, struct tty_struct *tty)
 411 {
 412         enum { ERASE, WERASE, KILL } kill_type;
 413         int head, seen_alnums, cnt;
 414         unsigned long flags;
 415
 416         if (tty->read_head == tty->canon_head) {
 417                 /* opost('\a', tty); */         /* what do you think? */
 418                 return;
 419         }
 420         if (c == ERASE_CHAR(tty))
 421                 kill_type = ERASE;
 422         else if (c == WERASE_CHAR(tty))
 423                 kill_type = WERASE;
 424         else {
 425                 if (!L_ECHO(tty)) {
 426                         spin_lock_irqsave(&tty->read_lock, flags);
 427                         tty->read_cnt -= ((tty->read_head - tty->canon_head) &
 428                                           (N_TTY_BUF_SIZE - 1));
 429                         tty->read_head = tty->canon_head;
 430                         spin_unlock_irqrestore(&tty->read_lock, flags);
 431                         return;
 432                 }
 433                 if (!L_ECHOK(tty) || !L_ECHOKE(tty) || !L_ECHOE(tty)) {
 434                         spin_lock_irqsave(&tty->read_lock, flags);
 435                         tty->read_cnt -= ((tty->read_head - tty->canon_head) &
 436                                           (N_TTY_BUF_SIZE - 1));
 437                         tty->read_head = tty->canon_head;
 438                         spin_unlock_irqrestore(&tty->read_lock, flags);
 439                         finish_erasing(tty);
 440                         echo_char(KILL_CHAR(tty), tty);
 441                         /* Add a newline if ECHOK is on and ECHOKE is off. */
 442                         if (L_ECHOK(tty))
 443                                 opost('\n', tty);
 444                         return;
 445                 }
 446                 kill_type = KILL;
 447         }
 448
 449         seen_alnums = 0;
 450         while (tty->read_head != tty->canon_head) {
 451                 head = tty->read_head;
 452
 453                 /* erase a single possibly multibyte character */
 454                 do {
 455                         head = (head - 1) & (N_TTY_BUF_SIZE-1);
 456                         c = tty->read_buf[head];
 457                 } while (is_continuation(c, tty) && head != tty->canon_head);
 458
 459                 /* do not partially erase */
 460                 if (is_continuation(c, tty))
 461                         break;
 462
 463                 if (kill_type == WERASE) {
 464                         /* Equivalent to BSD's ALTWERASE. */
 465                         if (isalnum(c) || c == '_')
 466                                 seen_alnums++;
 467                         else if (seen_alnums)
 468                                 break;
 469                 }
 470                 cnt = (tty->read_head - head) & (N_TTY_BUF_SIZE-1);
 471                 spin_lock_irqsave(&tty->read_lock, flags);
 472                 tty->read_head = head;
 473                 tty->read_cnt -= cnt;
 474                 spin_unlock_irqrestore(&tty->read_lock, flags);
 475                 if (L_ECHO(tty)) {
 476                         if (L_ECHOPRT(tty)) {
 477                                 if (!tty->erasing) {
 478                                         put_char('\\', tty);
 479                                         tty->column++;
 480                                         tty->erasing = 1;
 481                                 }
 482                                 /* if cnt > 1, output a multi-byte character */
 483                                 echo_char(c, tty);
 484                                 while (--cnt > 0) {
 485                                         head = (head+1) & (N_TTY_BUF_SIZE-1);
 486                                         put_char(tty->read_buf[head], tty);
 487                                 }
 488                         } else if (kill_type == ERASE && !L_ECHOE(tty)) {
 489                                 echo_char(ERASE_CHAR(tty), tty);
 490                         } else if (c == '\t') {
 491                                 unsigned int col = tty->canon_column;
 492                                 unsigned long tail = tty->canon_head;
 493
 494                                 /* Find the column of the last char. */
 495                                 while (tail != tty->read_head) {
 496                                         c = tty->read_buf[tail];
 497                                         if (c == '\t')
 498                                                 col = (col | 7) + 1;
 499                                         else if (iscntrl(c)) {
 500                                                 if (L_ECHOCTL(tty))
 501                                                         col += 2;
 502                                         } else if (!is_continuation(c, tty))
 503                                                 col++;
 504                                         tail = (tail+1) & (N_TTY_BUF_SIZE-1);
 505                                 }
 506
 507                                 /* should never happen */
 508                                 if (tty->column > 0x80000000)
 509                                         tty->column = 0;
 510
 511                                 /* Now backup to that column. */
 512                                 while (tty->column > col) {
 513                                         /* Can't use opost here. */
 514                                         put_char('\b', tty);
 515                                         if (tty->column > 0)
 516                                                 tty->column--;
 517                                 }
 518                         } else {
 519                                 if (iscntrl(c) && L_ECHOCTL(tty)) {
 520                                         put_char('\b', tty);
 521                                         put_char(' ', tty);
 522                                         put_char('\b', tty);
 523                                         if (tty->column > 0)
 524                                                 tty->column--;
 525                                 }
 526                                 if (!iscntrl(c) || L_ECHOCTL(tty)) {
 527                                         put_char('\b', tty);
 528                                         put_char(' ', tty);
 529                                         put_char('\b', tty);
 530                                         if (tty->column > 0)
 531                                                 tty->column--;
 532                                 }
 533                         }
 534                 }
 535                 if (kill_type == ERASE)
 536                         break;
 537         }
 538         if (tty->read_head == tty->canon_head)
 539                 finish_erasing(tty);
 540 }
 541
 542 /**
 543  *      isig            -       handle the ISIG optio
 544  *      @sig: signal
 545  *      @tty: terminal
 546  *      @flush: force flush
 547  *
 548  *      Called when a signal is being sent due to terminal input. This
 549  *      may caus terminal flushing to take place according to the termios
 550  *      settings and character used. Called from the driver receive_buf
 551  *      path so serialized.
 552  */
 553
 554 static inline void isig(int sig, struct tty_struct *tty, int flush)
 555 {
 556         if (tty->pgrp > 0)
 557                 kill_pg(tty->pgrp, sig, 1);
 558         if (flush || !L_NOFLSH(tty)) {
 559                 n_tty_flush_buffer(tty);
 560                 if (tty->driver->flush_buffer)
 561                         tty->driver->flush_buffer(tty);
 562         }
 563 }
 564
 565 /**
 566  *      n_tty_receive_break     -       handle break
 567  *      @tty: terminal
 568  *
 569  *      An RS232 break event has been hit in the incoming bitstream. This
 570  *      can cause a variety of events depending upon the termios settings.
 571  *
 572  *      Called from the receive_buf path so single threaded.
 573  */
 574
 575 static inline void n_tty_receive_break(struct tty_struct *tty)
 576 {
 577         if (I_IGNBRK(tty))
 578                 return;
 579         if (I_BRKINT(tty)) {
 580                 isig(SIGINT, tty, 1);
 581                 return;
 582         }
 583         if (I_PARMRK(tty)) {
 584                 put_tty_queue('\377', tty);
 585                 put_tty_queue('\0', tty);
 586         }
 587         put_tty_queue('\0', tty);
 588         wake_up_interruptible(&tty->read_wait);
 589 }
 590
 591 /**
 592  *      n_tty_receive_overrun   -       handle overrun reporting
 593  *      @tty: terminal
 594  *
 595  *      Data arrived faster than we could process it. While the tty
 596  *      driver has flagged this the bits that were missed are gone
 597  *      forever.
 598  *
 599  *      Called from the receive_buf path so single threaded. Does not
 600  *      need locking as num_overrun and overrun_time are function
 601  *      private.
 602  */
 603
 604 static inline void n_tty_receive_overrun(struct tty_struct *tty)
 605 {
 606         char buf[64];
 607
 608         tty->num_overrun++;
 609         if (time_before(tty->overrun_time, jiffies - HZ) ||
 610                         time_after(tty->overrun_time, jiffies)) {
 611                 printk(KERN_WARNING "%s: %d input overrun(s)\n",
 612                         tty_name(tty, buf),
 613                         tty->num_overrun);
 614                 tty->overrun_time = jiffies;
 615                 tty->num_overrun = 0;
 616         }
 617 }
 618
 619 /**
 620  *      n_tty_receive_parity_error      -       error notifier
 621  *      @tty: terminal device
 622  *      @c: character
 623  *
 624  *      Process a parity error and queue the right data to indicate
 625  *      the error case if neccessary. Locking as per n_tty_receive_buf.
 626  */
 627 static inline void n_tty_receive_parity_error(struct tty_struct *tty,
 628                                               unsigned char c)
 629 {
 630         if (I_IGNPAR(tty)) {
 631                 return;
 632         }
 633         if (I_PARMRK(tty)) {
 634                 put_tty_queue('\377', tty);
 635                 put_tty_queue('\0', tty);
 636                 put_tty_queue(c, tty);
 637         } else  if (I_INPCK(tty))
 638                 put_tty_queue('\0', tty);
 639         else
 640                 put_tty_queue(c, tty);
 641         wake_up_interruptible(&tty->read_wait);
 642 }
 643
 644 /**
 645  *      n_tty_receive_char      -       perform processing
 646  *      @tty: terminal device
 647  *      @c: character
 648  *
 649  *      Process an individual character of input received from the driver.
 650  *      This is serialized with respect to itself by the rules for the
 651  *      driver above.
 652  */
 653
 654 static inline void n_tty_receive_char(struct tty_struct *tty, unsigned char c)
 655 {
 656         unsigned long flags;
 657
 658         if (tty->raw) {
 659                 put_tty_queue(c, tty);
 660                 return;
 661         }
 662
 663         if (tty->stopped && !tty->flow_stopped &&
 664             I_IXON(tty) && I_IXANY(tty)) {
 665                 start_tty(tty);
 666                 return;
 667         }
 668
 669         if (I_ISTRIP(tty))
 670                 c &= 0x7f;
 671         if (I_IUCLC(tty) && L_IEXTEN(tty))
 672                 c=tolower(c);
 673
 674         if (tty->closing) {
 675                 if (I_IXON(tty)) {
 676                         if (c == START_CHAR(tty))
 677                                 start_tty(tty);
 678                         else if (c == STOP_CHAR(tty))
 679                                 stop_tty(tty);
 680                 }
 681                 return;
 682         }
 683
 684         /*
 685          * If the previous character was LNEXT, or we know that this
 686          * character is not one of the characters that we'll have to
 687          * handle specially, do shortcut processing to speed things
 688          * up.
 689          */
 690         if (!test_bit(c, tty->process_char_map) || tty->lnext) {
 691                 finish_erasing(tty);
 692                 tty->lnext = 0;
 693                 if (L_ECHO(tty)) {
 694                         if (tty->read_cnt >= N_TTY_BUF_SIZE-1) {
 695                                 put_char('\a', tty); /* beep if no space */
 696                                 return;
 697                         }
 698                         /* Record the column of first canon char. */
 699                         if (tty->canon_head == tty->read_head)
 700                                 tty->canon_column = tty->column;
 701                         echo_char(c, tty);
 702                 }
 703                 if (I_PARMRK(tty) && c == (unsigned char) '\377')
 704                         put_tty_queue(c, tty);
 705                 put_tty_queue(c, tty);
 706                 return;
 707         }
 708
 709         if (c == '\r') {
 710                 if (I_IGNCR(tty))
 711                         return;
 712                 if (I_ICRNL(tty))
 713                         c = '\n';
 714         } else if (c == '\n' && I_INLCR(tty))
 715                 c = '\r';
 716         if (I_IXON(tty)) {
 717                 if (c == START_CHAR(tty)) {
 718                         start_tty(tty);
 719                         return;
 720                 }
 721                 if (c == STOP_CHAR(tty)) {
 722                         stop_tty(tty);
 723                         return;
 724                 }
 725         }
 726         if (L_ISIG(tty)) {
 727                 int signal;
 728                 signal = SIGINT;
 729                 if (c == INTR_CHAR(tty))
 730                         goto send_signal;
 731                 signal = SIGQUIT;
 732                 if (c == QUIT_CHAR(tty))
 733                         goto send_signal;
 734                 signal = SIGTSTP;
 735                 if (c == SUSP_CHAR(tty)) {
 736 send_signal:
 737                         isig(signal, tty, 0);
 738                         return;
 739                 }
 740         }
 741         if (tty->icanon) {
 742                 if (c == ERASE_CHAR(tty) || c == KILL_CHAR(tty) ||
 743                     (c == WERASE_CHAR(tty) && L_IEXTEN(tty))) {
 744                         eraser(c, tty);
 745                         return;
 746                 }
 747                 if (c == LNEXT_CHAR(tty) && L_IEXTEN(tty)) {
 748                         tty->lnext = 1;
 749                         if (L_ECHO(tty)) {
 750                                 finish_erasing(tty);
 751                                 if (L_ECHOCTL(tty)) {
 752                                         put_char('^', tty);
 753                                         put_char('\b', tty);
 754                                 }
 755                         }
 756                         return;
 757                 }
 758                 if (c == REPRINT_CHAR(tty) && L_ECHO(tty) &&
 759                     L_IEXTEN(tty)) {
 760                         unsigned long tail = tty->canon_head;
 761
 762                         finish_erasing(tty);
 763                         echo_char(c, tty);
 764                         opost('\n', tty);
 765                         while (tail != tty->read_head) {
 766                                 echo_char(tty->read_buf[tail], tty);
 767                                 tail = (tail+1) & (N_TTY_BUF_SIZE-1);
 768                         }
 769                         return;
 770                 }
 771                 if (c == '\n') {
 772                         if (L_ECHO(tty) || L_ECHONL(tty)) {
 773                                 if (tty->read_cnt >= N_TTY_BUF_SIZE-1)
 774                                         put_char('\a', tty);
 775                                 opost('\n', tty);
 776                         }
 777                         goto handle_newline;
 778                 }
 779                 if (c == EOF_CHAR(tty)) {
 780                         if (tty->canon_head != tty->read_head)
 781                                 set_bit(TTY_PUSH, &tty->flags);
 782                         c = __DISABLED_CHAR;
 783                         goto handle_newline;
 784                 }
 785                 if ((c == EOL_CHAR(tty)) ||
 786                     (c == EOL2_CHAR(tty) && L_IEXTEN(tty))) {
 787                         /*
 788                          * XXX are EOL_CHAR and EOL2_CHAR echoed?!?
 789                          */
 790                         if (L_ECHO(tty)) {
 791                                 if (tty->read_cnt >= N_TTY_BUF_SIZE-1)
 792                                         put_char('\a', tty);
 793                                 /* Record the column of first canon char. */
 794                                 if (tty->canon_head == tty->read_head)
 795                                         tty->canon_column = tty->column;
 796                                 echo_char(c, tty);
 797                         }
 798                         /*
 799                          * XXX does PARMRK doubling happen for
 800                          * EOL_CHAR and EOL2_CHAR?
 801                          */
 802                         if (I_PARMRK(tty) && c == (unsigned char) '\377')
 803                                 put_tty_queue(c, tty);
 804
 805                 handle_newline:
 806                         spin_lock_irqsave(&tty->read_lock, flags);
 807                         set_bit(tty->read_head, tty->read_flags);
 808                         put_tty_queue_nolock(c, tty);
 809                         tty->canon_head = tty->read_head;
 810                         tty->canon_data++;
 811                         spin_unlock_irqrestore(&tty->read_lock, flags);
 812                         kill_fasync(&tty->fasync, SIGIO, POLL_IN);
 813                         if (waitqueue_active(&tty->read_wait))
 814                                 wake_up_interruptible(&tty->read_wait);
 815                         return;
 816                 }
 817         }
 818
 819         finish_erasing(tty);
 820         if (L_ECHO(tty)) {
 821                 if (tty->read_cnt >= N_TTY_BUF_SIZE-1) {
 822                         put_char('\a', tty); /* beep if no space */
 823                         return;
 824                 }
 825                 if (c == '\n')
 826                         opost('\n', tty);
 827                 else {
 828                         /* Record the column of first canon char. */
 829                         if (tty->canon_head == tty->read_head)
 830                                 tty->canon_column = tty->column;
 831                         echo_char(c, tty);
 832                 }
 833         }
 834
 835         if (I_PARMRK(tty) && c == (unsigned char) '\377')
 836                 put_tty_queue(c, tty);
 837
 838         put_tty_queue(c, tty);
 839 }
 840
 841 /**
 842  *      n_tty_receive_room      -       receive space
 843  *      @tty: terminal
 844  *
 845  *      Called by the driver to find out how much data it is
 846  *      permitted to feed to the line discipline without any being lost
 847  *      and thus to manage flow control. Not serialized. Answers for the
 848  *      "instant".
 849  */
 850
 851 static int n_tty_receive_room(struct tty_struct *tty)
 852 {
 853         int     left = N_TTY_BUF_SIZE - tty->read_cnt - 1;
 854
 855         /*
 856          * If we are doing input canonicalization, and there are no
 857          * pending newlines, let characters through without limit, so
 858          * that erase characters will be handled.  Other excess
 859          * characters will be beeped.
 860          */
 861         if (left <= 0)
 862                 left = tty->icanon && !tty->canon_data;
 863         return left;
 864 }
 865
 866 /**
 867  *      n_tty_write_wakeup      -       asynchronous I/O notifier
 868  *      @tty: tty device
 869  *
 870  *      Required for the ptys, serial driver etc. since processes
 871  *      that attach themselves to the master and rely on ASYNC
 872  *      IO must be woken up
 873  */
 874
 875 static void n_tty_write_wakeup(struct tty_struct *tty)
 876 {
 877         if (tty->fasync)
 878         {
 879                 set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 880                 kill_fasync(&tty->fasync, SIGIO, POLL_OUT);
 881         }
 882         return;
 883 }
 884
 885 /**
 886  *      n_tty_receive_buf       -       data receive
 887  *      @tty: terminal device
 888  *      @cp: buffer
 889  *      @fp: flag buffer
 890  *      @count: characters
 891  *
 892  *      Called by the terminal driver when a block of characters has
 893  *      been received. This function must be called from soft contexts
 894  *      not from interrupt context. The driver is responsible for making
 895  *      calls one at a time and in order (or using flush_to_ldisc)
 896  */
 897
 898 static void n_tty_receive_buf(struct tty_struct *tty, const unsigned char *cp,
 899                               char *fp, int count)
 900 {
 901         const unsigned char *p;
 902         char *f, flags = TTY_NORMAL;
 903         int     i;
 904         char    buf[64];
 905         unsigned long cpuflags;
 906
 907         if (!tty->read_buf)
 908                 return;
 909
 910         if (tty->real_raw) {
 911                 spin_lock_irqsave(&tty->read_lock, cpuflags);
 912                 i = min(N_TTY_BUF_SIZE - tty->read_cnt,
 913                         N_TTY_BUF_SIZE - tty->read_head);
 914                 i = min(count, i);
 915                 memcpy(tty->read_buf + tty->read_head, cp, i);
 916                 tty->read_head = (tty->read_head + i) & (N_TTY_BUF_SIZE-1);
 917                 tty->read_cnt += i;
 918                 cp += i;
 919                 count -= i;
 920
 921                 i = min(N_TTY_BUF_SIZE - tty->read_cnt,
 922                         N_TTY_BUF_SIZE - tty->read_head);
 923                 i = min(count, i);
 924                 memcpy(tty->read_buf + tty->read_head, cp, i);
 925                 tty->read_head = (tty->read_head + i) & (N_TTY_BUF_SIZE-1);
 926                 tty->read_cnt += i;
 927                 spin_unlock_irqrestore(&tty->read_lock, cpuflags);
 928         } else {
 929                 for (i=count, p = cp, f = fp; i; i--, p++) {
 930                         if (f)
 931                                 flags = *f++;
 932                         switch (flags) {
 933                         case TTY_NORMAL:
 934                                 n_tty_receive_char(tty, *p);
 935                                 break;
 936                         case TTY_BREAK:
 937                                 n_tty_receive_break(tty);
 938                                 break;
 939                         case TTY_PARITY:
 940                         case TTY_FRAME:
 941                                 n_tty_receive_parity_error(tty, *p);
 942                                 break;
 943                         case TTY_OVERRUN:
 944                                 n_tty_receive_overrun(tty);
 945                                 break;
 946                         default:
 947                                 printk("%s: unknown flag %d\n",
 948                                        tty_name(tty, buf), flags);
 949                                 break;
 950                         }
 951                 }
 952                 if (tty->driver->flush_chars)
 953                         tty->driver->flush_chars(tty);
 954         }
 955
 956         if (!tty->icanon && (tty->read_cnt >= tty->minimum_to_wake)) {
 957                 kill_fasync(&tty->fasync, SIGIO, POLL_IN);
 958                 if (waitqueue_active(&tty->read_wait))
 959                         wake_up_interruptible(&tty->read_wait);
 960         }
 961
 962         /*
 963          * Check the remaining room for the input canonicalization
 964          * mode.  We don't want to throttle the driver if we're in
 965          * canonical mode and don't have a newline yet!
 966          */
 967         if (n_tty_receive_room(tty) < TTY_THRESHOLD_THROTTLE) {
 968                 /* check TTY_THROTTLED first so it indicates our state */
 969                 if (!test_and_set_bit(TTY_THROTTLED, &tty->flags) &&
 970                     tty->driver->throttle)
 971                         tty->driver->throttle(tty);
 972         }
 973 }
 974
 975 int is_ignored(int sig)
 976 {
 977         return (sigismember(&current->blocked, sig) ||
 978                 current->sighand->action[sig-1].sa.sa_handler == SIG_IGN);
 979 }
 980
 981 /**
 982  *      n_tty_set_termios       -       termios data changed
 983  *      @tty: terminal
 984  *      @old: previous data
 985  *
 986  *      Called by the tty layer when the user changes termios flags so
 987  *      that the line discipline can plan ahead. This function cannot sleep
 988  *      and is protected from re-entry by the tty layer. The user is
 989  *      guaranteed that this function will not be re-entered or in progress
 990  *      when the ldisc is closed.
 991  */
 992
 993 static void n_tty_set_termios(struct tty_struct *tty, struct termios * old)
 994 {
 995         if (!tty)
 996                 return;
 997
 998         tty->icanon = (L_ICANON(tty) != 0);
 999         if (test_bit(TTY_HW_COOK_IN, &tty->flags)) {
1000                 tty->raw = 1;
1001                 tty->real_raw = 1;
1002                 return;
1003         }
1004         if (I_ISTRIP(tty) || I_IUCLC(tty) || I_IGNCR(tty) ||
1005             I_ICRNL(tty) || I_INLCR(tty) || L_ICANON(tty) ||
1006             I_IXON(tty) || L_ISIG(tty) || L_ECHO(tty) ||
1007             I_PARMRK(tty)) {
1008                 memset(tty->process_char_map, 0, 256/8);
1009
1010                 if (I_IGNCR(tty) || I_ICRNL(tty))
1011                         set_bit('\r', tty->process_char_map);
1012                 if (I_INLCR(tty))
1013                         set_bit('\n', tty->process_char_map);
1014
1015                 if (L_ICANON(tty)) {
1016                         set_bit(ERASE_CHAR(tty), tty->process_char_map);
1017                         set_bit(KILL_CHAR(tty), tty->process_char_map);
1018                         set_bit(EOF_CHAR(tty), tty->process_char_map);
1019                         set_bit('\n', tty->process_char_map);
1020                         set_bit(EOL_CHAR(tty), tty->process_char_map);
1021                         if (L_IEXTEN(tty)) {
1022                                 set_bit(WERASE_CHAR(tty),
1023                                         tty->process_char_map);
1024                                 set_bit(LNEXT_CHAR(tty),
1025                                         tty->process_char_map);
1026                                 set_bit(EOL2_CHAR(tty),
1027                                         tty->process_char_map);
1028                                 if (L_ECHO(tty))
1029                                         set_bit(REPRINT_CHAR(tty),
1030                                                 tty->process_char_map);
1031                         }
1032                 }
1033                 if (I_IXON(tty)) {
1034                         set_bit(START_CHAR(tty), tty->process_char_map);
1035                         set_bit(STOP_CHAR(tty), tty->process_char_map);
1036                 }
1037                 if (L_ISIG(tty)) {
1038                         set_bit(INTR_CHAR(tty), tty->process_char_map);
1039                         set_bit(QUIT_CHAR(tty), tty->process_char_map);
1040                         set_bit(SUSP_CHAR(tty), tty->process_char_map);
1041                 }
1042                 clear_bit(__DISABLED_CHAR, tty->process_char_map);
1043                 tty->raw = 0;
1044                 tty->real_raw = 0;
1045         } else {
1046                 tty->raw = 1;
1047                 if ((I_IGNBRK(tty) || (!I_BRKINT(tty) && !I_PARMRK(tty))) &&
1048                     (I_IGNPAR(tty) || !I_INPCK(tty)) &&
1049                     (tty->driver->flags & TTY_DRIVER_REAL_RAW))
1050                         tty->real_raw = 1;
1051                 else
1052                         tty->real_raw = 0;
1053         }
1054 }
1055
1056 /**
1057  *      n_tty_close             -       close the ldisc for this tty
1058  *      @tty: device
1059  *
1060  *      Called from the terminal layer when this line discipline is
1061  *      being shut down, either because of a close or becsuse of a
1062  *      discipline change. The function will not be called while other
1063  *      ldisc methods are in progress.
1064  */
1065
1066 static void n_tty_close(struct tty_struct *tty)
1067 {
1068         n_tty_flush_buffer(tty);
1069         if (tty->read_buf) {
1070                 free_buf(tty->read_buf);
1071                 tty->read_buf = NULL;
1072         }
1073 }
1074
1075 /**
1076  *      n_tty_open              -       open an ldisc
1077  *      @tty: terminal to open
1078  *
1079  *      Called when this line discipline is being attached to the
1080  *      terminal device. Can sleep. Called serialized so that no
1081  *      other events will occur in parallel. No further open will occur
1082  *      until a close.
1083  */
1084
1085 static int n_tty_open(struct tty_struct *tty)
1086 {
1087         if (!tty)
1088                 return -EINVAL;
1089
1090         /* This one is ugly. Currently a malloc failure here can panic */
1091         if (!tty->read_buf) {
1092                 tty->read_buf = alloc_buf();
1093                 if (!tty->read_buf)
1094                         return -ENOMEM;
1095         }
1096         memset(tty->read_buf, 0, N_TTY_BUF_SIZE);
1097         reset_buffer_flags(tty);
1098         tty->column = 0;
1099         n_tty_set_termios(tty, NULL);
1100         tty->minimum_to_wake = 1;
1101         tty->closing = 0;
1102         return 0;
1103 }
1104
1105 static inline int input_available_p(struct tty_struct *tty, int amt)
1106 {
1107         if (tty->icanon) {
1108                 if (tty->canon_data)
1109                         return 1;
1110         } else if (tty->read_cnt >= (amt ? amt : 1))
1111                 return 1;
1112
1113         return 0;
1114 }
1115
1116 /**
1117  *      copy_from_read_buf      -       copy read data directly
1118  *      @tty: terminal device
1119  *      @b: user data
1120  *      @nr: size of data
1121  *
1122  *      Helper function to speed up read_chan.  It is only called when
1123  *      ICANON is off; it copies characters straight from the tty queue to
1124  *      user space directly.  It can be profitably called twice; once to
1125  *      drain the space from the tail pointer to the (physical) end of the
1126  *      buffer, and once to drain the space from the (physical) beginning of
1127  *      the buffer to head pointer.
1128  *
1129  *      Called under the tty->atomic_read sem and with TTY_DONT_FLIP set
1130  *
1131  */
1132
1133 static inline int copy_from_read_buf(struct tty_struct *tty,
1134                                       unsigned char __user **b,
1135                                       size_t *nr)
1136
1137 {
1138         int retval;
1139         size_t n;
1140         unsigned long flags;
1141
1142         retval = 0;
1143         spin_lock_irqsave(&tty->read_lock, flags);
1144         n = min(tty->read_cnt, N_TTY_BUF_SIZE - tty->read_tail);
1145         n = min(*nr, n);
1146         spin_unlock_irqrestore(&tty->read_lock, flags);
1147         if (n) {
1148                 mb();
1149                 retval = copy_to_user(*b, &tty->read_buf[tty->read_tail], n);
1150                 n -= retval;
1151                 spin_lock_irqsave(&tty->read_lock, flags);
1152                 tty->read_tail = (tty->read_tail + n) & (N_TTY_BUF_SIZE-1);
1153                 tty->read_cnt -= n;
1154                 spin_unlock_irqrestore(&tty->read_lock, flags);
1155                 *b += n;
1156                 *nr -= n;
1157         }
1158         return retval;
1159 }
1160
1161 extern ssize_t redirected_tty_write(struct file *,const char *,size_t,loff_t *);
1162
1163 /**
1164  *      job_control             -       check job control
1165  *      @tty: tty
1166  *      @file: file handle
1167  *
1168  *      Perform job control management checks on this file/tty descriptor
1169  *      and if appropriate send any needed signals and return a negative
1170  *      error code if action should be taken.
1171  */
1172
1173 static int job_control(struct tty_struct *tty, struct file *file)
1174 {
1175         /* Job control check -- must be done at start and after
1176            every sleep (POSIX.1 7.1.1.4). */
1177         /* NOTE: not yet done after every sleep pending a thorough
1178            check of the logic of this change. -- jlc */
1179         /* don't stop on /dev/console */
1180         if (file->f_op->write != redirected_tty_write &&
1181             current->signal->tty == tty) {
1182                 if (tty->pgrp <= 0)
1183                         printk("read_chan: tty->pgrp <= 0!\n");
1184                 else if (process_group(current) != tty->pgrp) {
1185                         if (is_ignored(SIGTTIN) ||
1186                             is_orphaned_pgrp(process_group(current)))
1187                                 return -EIO;
1188                         kill_pg(process_group(current), SIGTTIN, 1);
1189                         return -ERESTARTSYS;
1190                 }
1191         }
1192         return 0;
1193 }
1194
1195
1196 /**
1197  *      read_chan               -       read function for tty
1198  *      @tty: tty device
1199  *      @file: file object
1200  *      @buf: userspace buffer pointer
1201  *      @nr: size of I/O
1202  *
1203  *      Perform reads for the line discipline. We are guaranteed that the
1204  *      line discipline will not be closed under us but we may get multiple
1205  *      parallel readers and must handle this ourselves. We may also get
1206  *      a hangup. Always called in user context, may sleep.
1207  *
1208  *      This code must be sure never to sleep through a hangup.
1209  */
1210
1211 static ssize_t read_chan(struct tty_struct *tty, struct file *file,
1212                          unsigned char __user *buf, size_t nr)
1213 {
1214         unsigned char __user *b = buf;
1215         DECLARE_WAITQUEUE(wait, current);
1216         int c;
1217         int minimum, time;
1218         ssize_t retval = 0;
1219         ssize_t size;
1220         long timeout;
1221         unsigned long flags;
1222
1223 do_it_again:
1224
1225         if (!tty->read_buf) {
1226                 printk("n_tty_read_chan: called with read_buf == NULL?!?\n");
1227                 return -EIO;
1228         }
1229
1230         c = job_control(tty, file);
1231         if(c < 0)
1232                 return c;
1233
1234         minimum = time = 0;
1235         timeout = MAX_SCHEDULE_TIMEOUT;
1236         if (!tty->icanon) {
1237                 time = (HZ / 10) * TIME_CHAR(tty);
1238                 minimum = MIN_CHAR(tty);
1239                 if (minimum) {
1240                         if (time)
1241                                 tty->minimum_to_wake = 1;
1242                         else if (!waitqueue_active(&tty->read_wait) ||
1243                                  (tty->minimum_to_wake > minimum))
1244                                 tty->minimum_to_wake = minimum;
1245                 } else {
1246                         timeout = 0;
1247                         if (time) {
1248                                 timeout = time;
1249                                 time = 0;
1250                         }
1251                         tty->minimum_to_wake = minimum = 1;
1252                 }
1253         }
1254
1255         /*
1256          *      Internal serialization of reads.
1257          */
1258         if (file->f_flags & O_NONBLOCK) {
1259                 if (down_trylock(&tty->atomic_read))
1260                         return -EAGAIN;
1261         }
1262         else {
1263                 if (down_interruptible(&tty->atomic_read))
1264                         return -ERESTARTSYS;
1265         }
1266
1267         add_wait_queue(&tty->read_wait, &wait);
1268         set_bit(TTY_DONT_FLIP, &tty->flags);
1269         while (nr) {
1270                 /* First test for status change. */
1271                 if (tty->packet && tty->link->ctrl_status) {
1272                         unsigned char cs;
1273                         if (b != buf)
1274                                 break;
1275                         cs = tty->link->ctrl_status;
1276                         tty->link->ctrl_status = 0;
1277                         if (put_user(cs, b++)) {
1278                                 retval = -EFAULT;
1279                                 b--;
1280                                 break;
1281                         }
1282                         nr--;
1283                         break;
1284                 }
1285                 /* This statement must be first before checking for input
1286                    so that any interrupt will set the state back to
1287                    TASK_RUNNING. */
1288                 set_current_state(TASK_INTERRUPTIBLE);
1289
1290                 if (((minimum - (b - buf)) < tty->minimum_to_wake) &&
1291                     ((minimum - (b - buf)) >= 1))
1292                         tty->minimum_to_wake = (minimum - (b - buf));
1293
1294                 if (!input_available_p(tty, 0)) {
1295                         if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
1296                                 retval = -EIO;
1297                                 break;
1298                         }
1299                         if (tty_hung_up_p(file))
1300                                 break;
1301                         if (!timeout)
1302                                 break;
1303                         if (file->f_flags & O_NONBLOCK) {
1304                                 retval = -EAGAIN;
1305                                 break;
1306                         }
1307                         if (signal_pending(current)) {
1308                                 retval = -ERESTARTSYS;
1309                                 break;
1310                         }
1311                         clear_bit(TTY_DONT_FLIP, &tty->flags);
1312                         timeout = schedule_timeout(timeout);
1313                         set_bit(TTY_DONT_FLIP, &tty->flags);
1314                         continue;
1315                 }
1316                 __set_current_state(TASK_RUNNING);
1317
1318                 /* Deal with packet mode. */
1319                 if (tty->packet && b == buf) {
1320                         if (put_user(TIOCPKT_DATA, b++)) {
1321                                 retval = -EFAULT;
1322                                 b--;
1323                                 break;
1324                         }
1325                         nr--;
1326                 }
1327
1328                 if (tty->icanon) {
1329                         /* N.B. avoid overrun if nr == 0 */
1330                         while (nr && tty->read_cnt) {
1331                                 int eol;
1332
1333                                 eol = test_and_clear_bit(tty->read_tail,
1334                                                 tty->read_flags);
1335                                 c = tty->read_buf[tty->read_tail];
1336                                 spin_lock_irqsave(&tty->read_lock, flags);
1337                                 tty->read_tail = ((tty->read_tail+1) &
1338                                                   (N_TTY_BUF_SIZE-1));
1339                                 tty->read_cnt--;
1340                                 if (eol) {
1341                                         /* this test should be redundant:
1342                                          * we shouldn't be reading data if
1343                                          * canon_data is 0
1344                                          */
1345                                         if (--tty->canon_data < 0)
1346                                                 tty->canon_data = 0;
1347                                 }
1348                                 spin_unlock_irqrestore(&tty->read_lock, flags);
1349
1350                                 if (!eol || (c != __DISABLED_CHAR)) {
1351                                         if (put_user(c, b++)) {
1352                                                 retval = -EFAULT;
1353                                                 b--;
1354                                                 break;
1355                                         }
1356                                         nr--;
1357                                 }
1358                                 if (eol)
1359                                         break;
1360                         }
1361                         if (retval)
1362                                 break;
1363                 } else {
1364                         int uncopied;
1365                         uncopied = copy_from_read_buf(tty, &b, &nr);
1366                         uncopied += copy_from_read_buf(tty, &b, &nr);
1367                         if (uncopied) {
1368                                 retval = -EFAULT;
1369                                 break;
1370                         }
1371                 }
1372
1373                 /* If there is enough space in the read buffer now, let the
1374                  * low-level driver know. We use n_tty_chars_in_buffer() to
1375                  * check the buffer, as it now knows about canonical mode.
1376                  * Otherwise, if the driver is throttled and the line is
1377                  * longer than TTY_THRESHOLD_UNTHROTTLE in canonical mode,
1378                  * we won't get any more characters.
1379                  */
1380                 if (n_tty_chars_in_buffer(tty) <= TTY_THRESHOLD_UNTHROTTLE)
1381                         check_unthrottle(tty);
1382
1383                 if (b - buf >= minimum)
1384                         break;
1385                 if (time)
1386                         timeout = time;
1387         }
1388         clear_bit(TTY_DONT_FLIP, &tty->flags);
1389         up(&tty->atomic_read);
1390         remove_wait_queue(&tty->read_wait, &wait);
1391
1392         if (!waitqueue_active(&tty->read_wait))
1393                 tty->minimum_to_wake = minimum;
1394
1395         __set_current_state(TASK_RUNNING);
1396         size = b - buf;
1397         if (size) {
1398                 retval = size;
1399                 if (nr)
1400                         clear_bit(TTY_PUSH, &tty->flags);
1401         } else if (test_and_clear_bit(TTY_PUSH, &tty->flags))
1402                  goto do_it_again;
1403
1404         return retval;
1405 }
1406
1407 /**
1408  *      write_chan              -       write function for tty
1409  *      @tty: tty device
1410  *      @file: file object
1411  *      @buf: userspace buffer pointer
1412  *      @nr: size of I/O
1413  *
1414  *      Write function of the terminal device. This is serialized with
1415  *      respect to other write callers but not to termios changes, reads
1416  *      and other such events. We must be careful with N_TTY as the receive
1417  *      code will echo characters, thus calling driver write methods.
1418  *
1419  *      This code must be sure never to sleep through a hangup.
1420  */
1421
1422 static ssize_t write_chan(struct tty_struct * tty, struct file * file,
1423                           const unsigned char * buf, size_t nr)
1424 {
1425         const unsigned char *b = buf;
1426         DECLARE_WAITQUEUE(wait, current);
1427         int c;
1428         ssize_t retval = 0;
1429
1430         /* Job control check -- must be done at start (POSIX.1 7.1.1.4). */
1431         if (L_TOSTOP(tty) && file->f_op->write != redirected_tty_write) {
1432                 retval = tty_check_change(tty);
1433                 if (retval)
1434                         return retval;
1435         }
1436
1437         add_wait_queue(&tty->write_wait, &wait);
1438         while (1) {
1439                 set_current_state(TASK_INTERRUPTIBLE);
1440                 if (signal_pending(current)) {
1441                         retval = -ERESTARTSYS;
1442                         break;
1443                 }
1444                 if (tty_hung_up_p(file) || (tty->link && !tty->link->count)) {
1445                         retval = -EIO;
1446                         break;
1447                 }
1448                 if (O_OPOST(tty) && !(test_bit(TTY_HW_COOK_OUT, &tty->flags))) {
1449                         while (nr > 0) {
1450                                 ssize_t num = opost_block(tty, b, nr);
1451                                 if (num < 0) {
1452                                         if (num == -EAGAIN)
1453                                                 break;
1454                                         retval = num;
1455                                         goto break_out;
1456                                 }
1457                                 b += num;
1458                                 nr -= num;
1459                                 if (nr == 0)
1460                                         break;
1461                                 c = *b;
1462                                 if (opost(c, tty) < 0)
1463                                         break;
1464                                 b++; nr--;
1465                         }
1466                         if (tty->driver->flush_chars)
1467                                 tty->driver->flush_chars(tty);
1468                 } else {
1469                         while (nr > 0) {
1470                                 c = tty->driver->write(tty, b, nr);
1471                                 if (c < 0) {
1472                                         retval = c;
1473                                         goto break_out;
1474                                 }
1475                                 if (!c)
1476                                         break;
1477                                 b += c;
1478                                 nr -= c;
1479                         }
1480                 }
1481                 if (!nr)
1482                         break;
1483                 if (file->f_flags & O_NONBLOCK) {
1484                         retval = -EAGAIN;
1485                         break;
1486                 }
1487                 schedule();
1488         }
1489 break_out:
1490         __set_current_state(TASK_RUNNING);
1491         remove_wait_queue(&tty->write_wait, &wait);
1492         return (b - buf) ? b - buf : retval;
1493 }
1494
1495 /**
1496  *      normal_poll             -       poll method for N_TTY
1497  *      @tty: terminal device
1498  *      @file: file accessing it
1499  *      @wait: poll table
1500  *
1501  *      Called when the line discipline is asked to poll() for data or
1502  *      for special events. This code is not serialized with respect to
1503  *      other events save open/close.
1504  *
1505  *      This code must be sure never to sleep through a hangup.
1506  *      Called without the kernel lock held - fine
1507  *
1508  *      FIXME: if someone changes the VMIN or discipline settings for the
1509  *      terminal while another process is in poll() the poll does not
1510  *      recompute the new limits. Possibly set_termios should issue
1511  *      a read wakeup to fix this bug.
1512  */
1513
1514 static unsigned int normal_poll(struct tty_struct * tty, struct file * file, poll_table *wait)
1515 {
1516         unsigned int mask = 0;
1517
1518         poll_wait(file, &tty->read_wait, wait);
1519         poll_wait(file, &tty->write_wait, wait);
1520         if (input_available_p(tty, TIME_CHAR(tty) ? 0 : MIN_CHAR(tty)))
1521                 mask |= POLLIN | POLLRDNORM;
1522         if (tty->packet && tty->link->ctrl_status)
1523                 mask |= POLLPRI | POLLIN | POLLRDNORM;
1524         if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
1525                 mask |= POLLHUP;
1526         if (tty_hung_up_p(file))
1527                 mask |= POLLHUP;
1528         if (!(mask & (POLLHUP | POLLIN | POLLRDNORM))) {
1529                 if (MIN_CHAR(tty) && !TIME_CHAR(tty))
1530                         tty->minimum_to_wake = MIN_CHAR(tty);
1531                 else
1532                         tty->minimum_to_wake = 1;
1533         }
1534         if (tty->driver->chars_in_buffer(tty) < WAKEUP_CHARS &&
1535                         tty->driver->write_room(tty) > 0)
1536                 mask |= POLLOUT | POLLWRNORM;
1537         return mask;
1538 }
1539
1540 struct tty_ldisc tty_ldisc_N_TTY = {
1541         TTY_LDISC_MAGIC,        /* magic */
1542         "n_tty",                /* name */
1543         0,                      /* num */
1544         0,                      /* flags */
1545         n_tty_open,             /* open */
1546         n_tty_close,            /* close */
1547         n_tty_flush_buffer,     /* flush_buffer */
1548         n_tty_chars_in_buffer,  /* chars_in_buffer */
1549         read_chan,              /* read */
1550         write_chan,             /* write */
1551         n_tty_ioctl,            /* ioctl */
1552         n_tty_set_termios,      /* set_termios */
1553         normal_poll,            /* poll */
1554         NULL,                   /* hangup */
1555         n_tty_receive_buf,      /* receive_buf */
1556         n_tty_receive_room,     /* receive_room */
1557         n_tty_write_wakeup      /* write_wakeup */
1558 };
1559