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         int 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                 printk(KERN_WARNING "%s: %d input overrun(s)\n", tty_name(tty, buf),
 611                        tty->num_overrun);
 612                 tty->overrun_time = jiffies;
 613                 tty->num_overrun = 0;
 614         }
 615 }
 616
 617 /**
 618  *      n_tty_receive_parity_error      -       error notifier
 619  *      @tty: terminal device
 620  *      @c: character
 621  *
 622  *      Process a parity error and queue the right data to indicate
 623  *      the error case if neccessary. Locking as per n_tty_receive_buf.
 624  */
 625 static inline void n_tty_receive_parity_error(struct tty_struct *tty,
 626                                               unsigned char c)
 627 {
 628         if (I_IGNPAR(tty)) {
 629                 return;
 630         }
 631         if (I_PARMRK(tty)) {
 632                 put_tty_queue('\377', tty);
 633                 put_tty_queue('\0', tty);
 634                 put_tty_queue(c, tty);
 635         } else  if (I_INPCK(tty))
 636                 put_tty_queue('\0', tty);
 637         else
 638                 put_tty_queue(c, tty);
 639         wake_up_interruptible(&tty->read_wait);
 640 }
 641
 642 /**
 643  *      n_tty_receive_char      -       perform processing
 644  *      @tty: terminal device
 645  *      @c: character
 646  *
 647  *      Process an individual character of input received from the driver.
 648  *      This is serialized with respect to itself by the rules for the
 649  *      driver above.
 650  */
 651
 652 static inline void n_tty_receive_char(struct tty_struct *tty, unsigned char c)
 653 {
 654         unsigned long flags;
 655
 656         if (tty->raw) {
 657                 put_tty_queue(c, tty);
 658                 return;
 659         }
 660
 661         if (tty->stopped && !tty->flow_stopped &&
 662             I_IXON(tty) && I_IXANY(tty)) {
 663                 start_tty(tty);
 664                 return;
 665         }
 666
 667         if (I_ISTRIP(tty))
 668                 c &= 0x7f;
 669         if (I_IUCLC(tty) && L_IEXTEN(tty))
 670                 c=tolower(c);
 671
 672         if (tty->closing) {
 673                 if (I_IXON(tty)) {
 674                         if (c == START_CHAR(tty))
 675                                 start_tty(tty);
 676                         else if (c == STOP_CHAR(tty))
 677                                 stop_tty(tty);
 678                 }
 679                 return;
 680         }
 681
 682         /*
 683          * If the previous character was LNEXT, or we know that this
 684          * character is not one of the characters that we'll have to
 685          * handle specially, do shortcut processing to speed things
 686          * up.
 687          */
 688         if (!test_bit(c, tty->process_char_map) || tty->lnext) {
 689                 finish_erasing(tty);
 690                 tty->lnext = 0;
 691                 if (L_ECHO(tty)) {
 692                         if (tty->read_cnt >= N_TTY_BUF_SIZE-1) {
 693                                 put_char('\a', tty); /* beep if no space */
 694                                 return;
 695                         }
 696                         /* Record the column of first canon char. */
 697                         if (tty->canon_head == tty->read_head)
 698                                 tty->canon_column = tty->column;
 699                         echo_char(c, tty);
 700                 }
 701                 if (I_PARMRK(tty) && c == (unsigned char) '\377')
 702                         put_tty_queue(c, tty);
 703                 put_tty_queue(c, tty);
 704                 return;
 705         }
 706
 707         if (c == '\r') {
 708                 if (I_IGNCR(tty))
 709                         return;
 710                 if (I_ICRNL(tty))
 711                         c = '\n';
 712         } else if (c == '\n' && I_INLCR(tty))
 713                 c = '\r';
 714         if (I_IXON(tty)) {
 715                 if (c == START_CHAR(tty)) {
 716                         start_tty(tty);
 717                         return;
 718                 }
 719                 if (c == STOP_CHAR(tty)) {
 720                         stop_tty(tty);
 721                         return;
 722                 }
 723         }
 724         if (L_ISIG(tty)) {
 725                 int signal;
 726                 signal = SIGINT;
 727                 if (c == INTR_CHAR(tty))
 728                         goto send_signal;
 729                 signal = SIGQUIT;
 730                 if (c == QUIT_CHAR(tty))
 731                         goto send_signal;
 732                 signal = SIGTSTP;
 733                 if (c == SUSP_CHAR(tty)) {
 734 send_signal:
 735                         isig(signal, tty, 0);
 736                         return;
 737                 }
 738         }
 739         if (tty->icanon) {
 740                 if (c == ERASE_CHAR(tty) || c == KILL_CHAR(tty) ||
 741                     (c == WERASE_CHAR(tty) && L_IEXTEN(tty))) {
 742                         eraser(c, tty);
 743                         return;
 744                 }
 745                 if (c == LNEXT_CHAR(tty) && L_IEXTEN(tty)) {
 746                         tty->lnext = 1;
 747                         if (L_ECHO(tty)) {
 748                                 finish_erasing(tty);
 749                                 if (L_ECHOCTL(tty)) {
 750                                         put_char('^', tty);
 751                                         put_char('\b', tty);
 752                                 }
 753                         }
 754                         return;
 755                 }
 756                 if (c == REPRINT_CHAR(tty) && L_ECHO(tty) &&
 757                     L_IEXTEN(tty)) {
 758                         unsigned long tail = tty->canon_head;
 759
 760                         finish_erasing(tty);
 761                         echo_char(c, tty);
 762                         opost('\n', tty);
 763                         while (tail != tty->read_head) {
 764                                 echo_char(tty->read_buf[tail], tty);
 765                                 tail = (tail+1) & (N_TTY_BUF_SIZE-1);
 766                         }
 767                         return;
 768                 }
 769                 if (c == '\n') {
 770                         if (L_ECHO(tty) || L_ECHONL(tty)) {
 771                                 if (tty->read_cnt >= N_TTY_BUF_SIZE-1) {
 772                                         put_char('\a', tty);
 773                                         return;
 774                                 }
 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                                         return;
 794                                 }
 795                                 /* Record the column of first canon char. */
 796                                 if (tty->canon_head == tty->read_head)
 797                                         tty->canon_column = tty->column;
 798                                 echo_char(c, tty);
 799                         }
 800                         /*
 801                          * XXX does PARMRK doubling happen for
 802                          * EOL_CHAR and EOL2_CHAR?
 803                          */
 804                         if (I_PARMRK(tty) && c == (unsigned char) '\377')
 805                                 put_tty_queue(c, tty);
 806
 807                 handle_newline:
 808                         spin_lock_irqsave(&tty->read_lock, flags);
 809                         set_bit(tty->read_head, tty->read_flags);
 810                         put_tty_queue_nolock(c, tty);
 811                         tty->canon_head = tty->read_head;
 812                         tty->canon_data++;
 813                         spin_unlock_irqrestore(&tty->read_lock, flags);
 814                         kill_fasync(&tty->fasync, SIGIO, POLL_IN);
 815                         if (waitqueue_active(&tty->read_wait))
 816                                 wake_up_interruptible(&tty->read_wait);
 817                         return;
 818                 }
 819         }
 820
 821         finish_erasing(tty);
 822         if (L_ECHO(tty)) {
 823                 if (tty->read_cnt >= N_TTY_BUF_SIZE-1) {
 824                         put_char('\a', tty); /* beep if no space */
 825                         return;
 826                 }
 827                 if (c == '\n')
 828                         opost('\n', tty);
 829                 else {
 830                         /* Record the column of first canon char. */
 831                         if (tty->canon_head == tty->read_head)
 832                                 tty->canon_column = tty->column;
 833                         echo_char(c, tty);
 834                 }
 835         }
 836
 837         if (I_PARMRK(tty) && c == (unsigned char) '\377')
 838                 put_tty_queue(c, tty);
 839
 840         put_tty_queue(c, tty);
 841 }
 842
 843 /**
 844  *      n_tty_receive_room      -       receive space
 845  *      @tty: terminal
 846  *
 847  *      Called by the driver to find out how much data it is
 848  *      permitted to feed to the line discipline without any being lost
 849  *      and thus to manage flow control. Not serialized. Answers for the
 850  *      "instant".
 851  */
 852
 853 static int n_tty_receive_room(struct tty_struct *tty)
 854 {
 855         int     left = N_TTY_BUF_SIZE - tty->read_cnt - 1;
 856
 857         /*
 858          * If we are doing input canonicalization, and there are no
 859          * pending newlines, let characters through without limit, so
 860          * that erase characters will be handled.  Other excess
 861          * characters will be beeped.
 862          */
 863         if (tty->icanon && !tty->canon_data)
 864                 return N_TTY_BUF_SIZE;
 865
 866         if (left > 0)
 867                 return left;
 868         return 0;
 869 }
 870
 871 /**
 872  *      n_tty_write_wakeup      -       asynchronous I/O notifier
 873  *      @tty: tty device
 874  *
 875  *      Required for the ptys, serial driver etc. since processes
 876  *      that attach themselves to the master and rely on ASYNC
 877  *      IO must be woken up
 878  */
 879
 880 static void n_tty_write_wakeup(struct tty_struct *tty)
 881 {
 882         if (tty->fasync)
 883         {
 884                 set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 885                 kill_fasync(&tty->fasync, SIGIO, POLL_OUT);
 886         }
 887         return;
 888 }
 889
 890 /**
 891  *      n_tty_receive_buf       -       data receive
 892  *      @tty: terminal device
 893  *      @cp: buffer
 894  *      @fp: flag buffer
 895  *      @count: characters
 896  *
 897  *      Called by the terminal driver when a block of characters has
 898  *      been received. This function must be called from soft contexts
 899  *      not from interrupt context. The driver is responsible for making
 900  *      calls one at a time and in order (or using flush_to_ldisc)
 901  */
 902
 903 static void n_tty_receive_buf(struct tty_struct *tty, const unsigned char *cp,
 904                               char *fp, int count)
 905 {
 906         const unsigned char *p;
 907         char *f, flags = TTY_NORMAL;
 908         int     i;
 909         char    buf[64];
 910         unsigned long cpuflags;
 911
 912         if (!tty->read_buf)
 913                 return;
 914
 915         if (tty->real_raw) {
 916                 spin_lock_irqsave(&tty->read_lock, cpuflags);
 917                 i = min(N_TTY_BUF_SIZE - tty->read_cnt,
 918                         N_TTY_BUF_SIZE - tty->read_head);
 919                 i = min(count, i);
 920                 memcpy(tty->read_buf + tty->read_head, cp, i);
 921                 tty->read_head = (tty->read_head + i) & (N_TTY_BUF_SIZE-1);
 922                 tty->read_cnt += i;
 923                 cp += i;
 924                 count -= i;
 925
 926                 i = min(N_TTY_BUF_SIZE - tty->read_cnt,
 927                         N_TTY_BUF_SIZE - tty->read_head);
 928                 i = min(count, i);
 929                 memcpy(tty->read_buf + tty->read_head, cp, i);
 930                 tty->read_head = (tty->read_head + i) & (N_TTY_BUF_SIZE-1);
 931                 tty->read_cnt += i;
 932                 spin_unlock_irqrestore(&tty->read_lock, cpuflags);
 933         } else {
 934                 for (i=count, p = cp, f = fp; i; i--, p++) {
 935                         if (f)
 936                                 flags = *f++;
 937                         switch (flags) {
 938                         case TTY_NORMAL:
 939                                 n_tty_receive_char(tty, *p);
 940                                 break;
 941                         case TTY_BREAK:
 942                                 n_tty_receive_break(tty);
 943                                 break;
 944                         case TTY_PARITY:
 945                         case TTY_FRAME:
 946                                 n_tty_receive_parity_error(tty, *p);
 947                                 break;
 948                         case TTY_OVERRUN:
 949                                 n_tty_receive_overrun(tty);
 950                                 break;
 951                         default:
 952                                 printk("%s: unknown flag %d\n",
 953                                        tty_name(tty, buf), flags);
 954                                 break;
 955                         }
 956                 }
 957                 if (tty->driver->flush_chars)
 958                         tty->driver->flush_chars(tty);
 959         }
 960
 961         if (!tty->icanon && (tty->read_cnt >= tty->minimum_to_wake)) {
 962                 kill_fasync(&tty->fasync, SIGIO, POLL_IN);
 963                 if (waitqueue_active(&tty->read_wait))
 964                         wake_up_interruptible(&tty->read_wait);
 965         }
 966
 967         /*
 968          * Check the remaining room for the input canonicalization
 969          * mode.  We don't want to throttle the driver if we're in
 970          * canonical mode and don't have a newline yet!
 971          */
 972         if (n_tty_receive_room(tty) < TTY_THRESHOLD_THROTTLE) {
 973                 /* check TTY_THROTTLED first so it indicates our state */
 974                 if (!test_and_set_bit(TTY_THROTTLED, &tty->flags) &&
 975                     tty->driver->throttle)
 976                         tty->driver->throttle(tty);
 977         }
 978 }
 979
 980 int is_ignored(int sig)
 981 {
 982         return (sigismember(&current->blocked, sig) ||
 983                 current->sighand->action[sig-1].sa.sa_handler == SIG_IGN);
 984 }
 985
 986 /**
 987  *      n_tty_set_termios       -       termios data changed
 988  *      @tty: terminal
 989  *      @old: previous data
 990  *
 991  *      Called by the tty layer when the user changes termios flags so
 992  *      that the line discipline can plan ahead. This function cannot sleep
 993  *      and is protected from re-entry by the tty layer. The user is
 994  *      guaranteed that this function will not be re-entered or in progress
 995  *      when the ldisc is closed.
 996  */
 997
 998 static void n_tty_set_termios(struct tty_struct *tty, struct termios * old)
 999 {
1000         if (!tty)
1001                 return;
1002
1003         tty->icanon = (L_ICANON(tty) != 0);
1004         if (test_bit(TTY_HW_COOK_IN, &tty->flags)) {
1005                 tty->raw = 1;
1006                 tty->real_raw = 1;
1007                 return;
1008         }
1009         if (I_ISTRIP(tty) || I_IUCLC(tty) || I_IGNCR(tty) ||
1010             I_ICRNL(tty) || I_INLCR(tty) || L_ICANON(tty) ||
1011             I_IXON(tty) || L_ISIG(tty) || L_ECHO(tty) ||
1012             I_PARMRK(tty)) {
1013                 memset(tty->process_char_map, 0, 256/8);
1014
1015                 if (I_IGNCR(tty) || I_ICRNL(tty))
1016                         set_bit('\r', tty->process_char_map);
1017                 if (I_INLCR(tty))
1018                         set_bit('\n', tty->process_char_map);
1019
1020                 if (L_ICANON(tty)) {
1021                         set_bit(ERASE_CHAR(tty), tty->process_char_map);
1022                         set_bit(KILL_CHAR(tty), tty->process_char_map);
1023                         set_bit(EOF_CHAR(tty), tty->process_char_map);
1024                         set_bit('\n', tty->process_char_map);
1025                         set_bit(EOL_CHAR(tty), tty->process_char_map);
1026                         if (L_IEXTEN(tty)) {
1027                                 set_bit(WERASE_CHAR(tty),
1028                                         tty->process_char_map);
1029                                 set_bit(LNEXT_CHAR(tty),
1030                                         tty->process_char_map);
1031                                 set_bit(EOL2_CHAR(tty),
1032                                         tty->process_char_map);
1033                                 if (L_ECHO(tty))
1034                                         set_bit(REPRINT_CHAR(tty),
1035                                                 tty->process_char_map);
1036                         }
1037                 }
1038                 if (I_IXON(tty)) {
1039                         set_bit(START_CHAR(tty), tty->process_char_map);
1040                         set_bit(STOP_CHAR(tty), tty->process_char_map);
1041                 }
1042                 if (L_ISIG(tty)) {
1043                         set_bit(INTR_CHAR(tty), tty->process_char_map);
1044                         set_bit(QUIT_CHAR(tty), tty->process_char_map);
1045                         set_bit(SUSP_CHAR(tty), tty->process_char_map);
1046                 }
1047                 clear_bit(__DISABLED_CHAR, tty->process_char_map);
1048                 tty->raw = 0;
1049                 tty->real_raw = 0;
1050         } else {
1051                 tty->raw = 1;
1052                 if ((I_IGNBRK(tty) || (!I_BRKINT(tty) && !I_PARMRK(tty))) &&
1053                     (I_IGNPAR(tty) || !I_INPCK(tty)) &&
1054                     (tty->driver->flags & TTY_DRIVER_REAL_RAW))
1055                         tty->real_raw = 1;
1056                 else
1057                         tty->real_raw = 0;
1058         }
1059 }
1060
1061 /**
1062  *      n_tty_close             -       close the ldisc for this tty
1063  *      @tty: device
1064  *
1065  *      Called from the terminal layer when this line discipline is
1066  *      being shut down, either because of a close or becsuse of a
1067  *      discipline change. The function will not be called while other
1068  *      ldisc methods are in progress.
1069  */
1070
1071 static void n_tty_close(struct tty_struct *tty)
1072 {
1073         n_tty_flush_buffer(tty);
1074         if (tty->read_buf) {
1075                 free_buf(tty->read_buf);
1076                 tty->read_buf = NULL;
1077         }
1078 }
1079
1080 /**
1081  *      n_tty_open              -       open an ldisc
1082  *      @tty: terminal to open
1083  *
1084  *      Called when this line discipline is being attached to the
1085  *      terminal device. Can sleep. Called serialized so that no
1086  *      other events will occur in parallel. No further open will occur
1087  *      until a close.
1088  */
1089
1090 static int n_tty_open(struct tty_struct *tty)
1091 {
1092         if (!tty)
1093                 return -EINVAL;
1094
1095         /* This one is ugly. Currently a malloc failure here can panic */
1096         if (!tty->read_buf) {
1097                 tty->read_buf = alloc_buf();
1098                 if (!tty->read_buf)
1099                         return -ENOMEM;
1100         }
1101         memset(tty->read_buf, 0, N_TTY_BUF_SIZE);
1102         reset_buffer_flags(tty);
1103         tty->column = 0;
1104         n_tty_set_termios(tty, NULL);
1105         tty->minimum_to_wake = 1;
1106         tty->closing = 0;
1107         return 0;
1108 }
1109
1110 static inline int input_available_p(struct tty_struct *tty, int amt)
1111 {
1112         if (tty->icanon) {
1113                 if (tty->canon_data)
1114                         return 1;
1115         } else if (tty->read_cnt >= (amt ? amt : 1))
1116                 return 1;
1117
1118         return 0;
1119 }
1120
1121 /**
1122  *      copy_from_read_buf      -       copy read data directly
1123  *      @tty: terminal device
1124  *      @b: user data
1125  *      @nr: size of data
1126  *
1127  *      Helper function to speed up read_chan.  It is only called when
1128  *      ICANON is off; it copies characters straight from the tty queue to
1129  *      user space directly.  It can be profitably called twice; once to
1130  *      drain the space from the tail pointer to the (physical) end of the
1131  *      buffer, and once to drain the space from the (physical) beginning of
1132  *      the buffer to head pointer.
1133  *
1134  *      Called under the tty->atomic_read sem and with TTY_DONT_FLIP set
1135  *
1136  */
1137
1138 static inline int copy_from_read_buf(struct tty_struct *tty,
1139                                       unsigned char __user **b,
1140                                       size_t *nr)
1141
1142 {
1143         int retval;
1144         size_t n;
1145         unsigned long flags;
1146
1147         retval = 0;
1148         spin_lock_irqsave(&tty->read_lock, flags);
1149         n = min(tty->read_cnt, N_TTY_BUF_SIZE - tty->read_tail);
1150         n = min(*nr, n);
1151         spin_unlock_irqrestore(&tty->read_lock, flags);
1152         if (n) {
1153                 mb();
1154                 retval = copy_to_user(*b, &tty->read_buf[tty->read_tail], n);
1155                 n -= retval;
1156                 spin_lock_irqsave(&tty->read_lock, flags);
1157                 tty->read_tail = (tty->read_tail + n) & (N_TTY_BUF_SIZE-1);
1158                 tty->read_cnt -= n;
1159                 spin_unlock_irqrestore(&tty->read_lock, flags);
1160                 *b += n;
1161                 *nr -= n;
1162         }
1163         return retval;
1164 }
1165
1166 extern ssize_t redirected_tty_write(struct file *,const char *,size_t,loff_t *);
1167
1168 /**
1169  *      job_control             -       check job control
1170  *      @tty: tty
1171  *      @file: file handle
1172  *
1173  *      Perform job control management checks on this file/tty descriptor
1174  *      and if appropriate send any needed signals and return a negative
1175  *      error code if action should be taken.
1176  */
1177
1178 static int job_control(struct tty_struct *tty, struct file *file)
1179 {
1180         /* Job control check -- must be done at start and after
1181            every sleep (POSIX.1 7.1.1.4). */
1182         /* NOTE: not yet done after every sleep pending a thorough
1183            check of the logic of this change. -- jlc */
1184         /* don't stop on /dev/console */
1185         if (file->f_op->write != redirected_tty_write &&
1186             current->signal->tty == tty) {
1187                 if (tty->pgrp <= 0)
1188                         printk("read_chan: tty->pgrp <= 0!\n");
1189                 else if (process_group(current) != tty->pgrp) {
1190                         if (is_ignored(SIGTTIN) ||
1191                             is_orphaned_pgrp(process_group(current)))
1192                                 return -EIO;
1193                         kill_pg(process_group(current), SIGTTIN, 1);
1194                         return -ERESTARTSYS;
1195                 }
1196         }
1197         return 0;
1198 }
1199
1200
1201 /**
1202  *      read_chan               -       read function for tty
1203  *      @tty: tty device
1204  *      @file: file object
1205  *      @buf: userspace buffer pointer
1206  *      @nr: size of I/O
1207  *
1208  *      Perform reads for the line discipline. We are guaranteed that the
1209  *      line discipline will not be closed under us but we may get multiple
1210  *      parallel readers and must handle this ourselves. We may also get
1211  *      a hangup. Always called in user context, may sleep.
1212  *
1213  *      This code must be sure never to sleep through a hangup.
1214  */
1215
1216 static ssize_t read_chan(struct tty_struct *tty, struct file *file,
1217                          unsigned char __user *buf, size_t nr)
1218 {
1219         unsigned char __user *b = buf;
1220         DECLARE_WAITQUEUE(wait, current);
1221         int c;
1222         int minimum, time;
1223         ssize_t retval = 0;
1224         ssize_t size;
1225         long timeout;
1226         unsigned long flags;
1227
1228 do_it_again:
1229
1230         if (!tty->read_buf) {
1231                 printk("n_tty_read_chan: called with read_buf == NULL?!?\n");
1232                 return -EIO;
1233         }
1234
1235         c = job_control(tty, file);
1236         if(c < 0)
1237                 return c;
1238
1239         minimum = time = 0;
1240         timeout = MAX_SCHEDULE_TIMEOUT;
1241         if (!tty->icanon) {
1242                 time = (HZ / 10) * TIME_CHAR(tty);
1243                 minimum = MIN_CHAR(tty);
1244                 if (minimum) {
1245                         if (time)
1246                                 tty->minimum_to_wake = 1;
1247                         else if (!waitqueue_active(&tty->read_wait) ||
1248                                  (tty->minimum_to_wake > minimum))
1249                                 tty->minimum_to_wake = minimum;
1250                 } else {
1251                         timeout = 0;
1252                         if (time) {
1253                                 timeout = time;
1254                                 time = 0;
1255                         }
1256                         tty->minimum_to_wake = minimum = 1;
1257                 }
1258         }
1259
1260         /*
1261          *      Internal serialization of reads.
1262          */
1263         if (file->f_flags & O_NONBLOCK) {
1264                 if (down_trylock(&tty->atomic_read))
1265                         return -EAGAIN;
1266         }
1267         else {
1268                 if (down_interruptible(&tty->atomic_read))
1269                         return -ERESTARTSYS;
1270         }
1271
1272         add_wait_queue(&tty->read_wait, &wait);
1273         set_bit(TTY_DONT_FLIP, &tty->flags);
1274         while (nr) {
1275                 /* First test for status change. */
1276                 if (tty->packet && tty->link->ctrl_status) {
1277                         unsigned char cs;
1278                         if (b != buf)
1279                                 break;
1280                         cs = tty->link->ctrl_status;
1281                         tty->link->ctrl_status = 0;
1282                         if (put_user(cs, b++)) {
1283                                 retval = -EFAULT;
1284                                 b--;
1285                                 break;
1286                         }
1287                         nr--;
1288                         break;
1289                 }
1290                 /* This statement must be first before checking for input
1291                    so that any interrupt will set the state back to
1292                    TASK_RUNNING. */
1293                 set_current_state(TASK_INTERRUPTIBLE);
1294
1295                 if (((minimum - (b - buf)) < tty->minimum_to_wake) &&
1296                     ((minimum - (b - buf)) >= 1))
1297                         tty->minimum_to_wake = (minimum - (b - buf));
1298
1299                 if (!input_available_p(tty, 0)) {
1300                         if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
1301                                 retval = -EIO;
1302                                 break;
1303                         }
1304                         if (tty_hung_up_p(file))
1305                                 break;
1306                         if (!timeout)
1307                                 break;
1308                         if (file->f_flags & O_NONBLOCK) {
1309                                 retval = -EAGAIN;
1310                                 break;
1311                         }
1312                         if (signal_pending(current)) {
1313                                 retval = -ERESTARTSYS;
1314                                 break;
1315                         }
1316                         clear_bit(TTY_DONT_FLIP, &tty->flags);
1317                         timeout = schedule_timeout(timeout);
1318                         set_bit(TTY_DONT_FLIP, &tty->flags);
1319                         continue;
1320                 }
1321                 __set_current_state(TASK_RUNNING);
1322
1323                 /* Deal with packet mode. */
1324                 if (tty->packet && b == buf) {
1325                         if (put_user(TIOCPKT_DATA, b++)) {
1326                                 retval = -EFAULT;
1327                                 b--;
1328                                 break;
1329                         }
1330                         nr--;
1331                 }
1332
1333                 if (tty->icanon) {
1334                         /* N.B. avoid overrun if nr == 0 */
1335                         while (nr && tty->read_cnt) {
1336                                 int eol;
1337
1338                                 eol = test_and_clear_bit(tty->read_tail,
1339                                                 tty->read_flags);
1340                                 c = tty->read_buf[tty->read_tail];
1341                                 spin_lock_irqsave(&tty->read_lock, flags);
1342                                 tty->read_tail = ((tty->read_tail+1) &
1343                                                   (N_TTY_BUF_SIZE-1));
1344                                 tty->read_cnt--;
1345                                 if (eol) {
1346                                         /* this test should be redundant:
1347                                          * we shouldn't be reading data if
1348                                          * canon_data is 0
1349                                          */
1350                                         if (--tty->canon_data < 0)
1351                                                 tty->canon_data = 0;
1352                                 }
1353                                 spin_unlock_irqrestore(&tty->read_lock, flags);
1354
1355                                 if (!eol || (c != __DISABLED_CHAR)) {
1356                                         if (put_user(c, b++)) {
1357                                                 retval = -EFAULT;
1358                                                 b--;
1359                                                 break;
1360                                         }
1361                                         nr--;
1362                                 }
1363                                 if (eol)
1364                                         break;
1365                         }
1366                         if (retval)
1367                                 break;
1368                 } else {
1369                         int uncopied;
1370                         uncopied = copy_from_read_buf(tty, &b, &nr);
1371                         uncopied += copy_from_read_buf(tty, &b, &nr);
1372                         if (uncopied) {
1373                                 retval = -EFAULT;
1374                                 break;
1375                         }
1376                 }
1377
1378                 /* If there is enough space in the read buffer now, let the
1379                  * low-level driver know. We use n_tty_chars_in_buffer() to
1380                  * check the buffer, as it now knows about canonical mode.
1381                  * Otherwise, if the driver is throttled and the line is
1382                  * longer than TTY_THRESHOLD_UNTHROTTLE in canonical mode,
1383                  * we won't get any more characters.
1384                  */
1385                 if (n_tty_chars_in_buffer(tty) <= TTY_THRESHOLD_UNTHROTTLE)
1386                         check_unthrottle(tty);
1387
1388                 if (b - buf >= minimum)
1389                         break;
1390                 if (time)
1391                         timeout = time;
1392         }
1393         clear_bit(TTY_DONT_FLIP, &tty->flags);
1394         up(&tty->atomic_read);
1395         remove_wait_queue(&tty->read_wait, &wait);
1396
1397         if (!waitqueue_active(&tty->read_wait))
1398                 tty->minimum_to_wake = minimum;
1399
1400         __set_current_state(TASK_RUNNING);
1401         size = b - buf;
1402         if (size) {
1403                 retval = size;
1404                 if (nr)
1405                         clear_bit(TTY_PUSH, &tty->flags);
1406         } else if (test_and_clear_bit(TTY_PUSH, &tty->flags))
1407                  goto do_it_again;
1408
1409         return retval;
1410 }
1411
1412 /**
1413  *      write_chan              -       write function for tty
1414  *      @tty: tty device
1415  *      @file: file object
1416  *      @buf: userspace buffer pointer
1417  *      @nr: size of I/O
1418  *
1419  *      Write function of the terminal device. This is serialized with
1420  *      respect to other write callers but not to termios changes, reads
1421  *      and other such events. We must be careful with N_TTY as the receive
1422  *      code will echo characters, thus calling driver write methods.
1423  *
1424  *      This code must be sure never to sleep through a hangup.
1425  */
1426
1427 static ssize_t write_chan(struct tty_struct * tty, struct file * file,
1428                           const unsigned char * buf, size_t nr)
1429 {
1430         const unsigned char *b = buf;
1431         DECLARE_WAITQUEUE(wait, current);
1432         int c;
1433         ssize_t retval = 0;
1434
1435         /* Job control check -- must be done at start (POSIX.1 7.1.1.4). */
1436         if (L_TOSTOP(tty) && file->f_op->write != redirected_tty_write) {
1437                 retval = tty_check_change(tty);
1438                 if (retval)
1439                         return retval;
1440         }
1441
1442         add_wait_queue(&tty->write_wait, &wait);
1443         while (1) {
1444                 set_current_state(TASK_INTERRUPTIBLE);
1445                 if (signal_pending(current)) {
1446                         retval = -ERESTARTSYS;
1447                         break;
1448                 }
1449                 if (tty_hung_up_p(file) || (tty->link && !tty->link->count)) {
1450                         retval = -EIO;
1451                         break;
1452                 }
1453                 if (O_OPOST(tty) && !(test_bit(TTY_HW_COOK_OUT, &tty->flags))) {
1454                         while (nr > 0) {
1455                                 ssize_t num = opost_block(tty, b, nr);
1456                                 if (num < 0) {
1457                                         if (num == -EAGAIN)
1458                                                 break;
1459                                         retval = num;
1460                                         goto break_out;
1461                                 }
1462                                 b += num;
1463                                 nr -= num;
1464                                 if (nr == 0)
1465                                         break;
1466                                 c = *b;
1467                                 if (opost(c, tty) < 0)
1468                                         break;
1469                                 b++; nr--;
1470                         }
1471                         if (tty->driver->flush_chars)
1472                                 tty->driver->flush_chars(tty);
1473                 } else {
1474                         c = tty->driver->write(tty, b, nr);
1475                         if (c < 0) {
1476                                 retval = c;
1477                                 goto break_out;
1478                         }
1479                         b += c;
1480                         nr -= c;
1481                 }
1482                 if (!nr)
1483                         break;
1484                 if (file->f_flags & O_NONBLOCK) {
1485                         retval = -EAGAIN;
1486                         break;
1487                 }
1488                 schedule();
1489         }
1490 break_out:
1491         __set_current_state(TASK_RUNNING);
1492         remove_wait_queue(&tty->write_wait, &wait);
1493         return (b - buf) ? b - buf : retval;
1494 }
1495
1496 /**
1497  *      normal_poll             -       poll method for N_TTY
1498  *      @tty: terminal device
1499  *      @file: file accessing it
1500  *      @wait: poll table
1501  *
1502  *      Called when the line discipline is asked to poll() for data or
1503  *      for special events. This code is not serialized with respect to
1504  *      other events save open/close.
1505  *
1506  *      This code must be sure never to sleep through a hangup.
1507  *      Called without the kernel lock held - fine
1508  *
1509  *      FIXME: if someone changes the VMIN or discipline settings for the
1510  *      terminal while another process is in poll() the poll does not
1511  *      recompute the new limits. Possibly set_termios should issue
1512  *      a read wakeup to fix this bug.
1513  */
1514
1515 static unsigned int normal_poll(struct tty_struct * tty, struct file * file, poll_table *wait)
1516 {
1517         unsigned int mask = 0;
1518
1519         poll_wait(file, &tty->read_wait, wait);
1520         poll_wait(file, &tty->write_wait, wait);
1521         if (input_available_p(tty, TIME_CHAR(tty) ? 0 : MIN_CHAR(tty)))
1522                 mask |= POLLIN | POLLRDNORM;
1523         if (tty->packet && tty->link->ctrl_status)
1524                 mask |= POLLPRI | POLLIN | POLLRDNORM;
1525         if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
1526                 mask |= POLLHUP;
1527         if (tty_hung_up_p(file))
1528                 mask |= POLLHUP;
1529         if (!(mask & (POLLHUP | POLLIN | POLLRDNORM))) {
1530                 if (MIN_CHAR(tty) && !TIME_CHAR(tty))
1531                         tty->minimum_to_wake = MIN_CHAR(tty);
1532                 else
1533                         tty->minimum_to_wake = 1;
1534         }
1535         if (tty->driver->chars_in_buffer(tty) < WAKEUP_CHARS &&
1536                         tty->driver->write_room(tty) > 0)
1537                 mask |= POLLOUT | POLLWRNORM;
1538         return mask;
1539 }
1540
1541 struct tty_ldisc tty_ldisc_N_TTY = {
1542         TTY_LDISC_MAGIC,        /* magic */
1543         "n_tty",                /* name */
1544         0,                      /* num */
1545         0,                      /* flags */
1546         n_tty_open,             /* open */
1547         n_tty_close,            /* close */
1548         n_tty_flush_buffer,     /* flush_buffer */
1549         n_tty_chars_in_buffer,  /* chars_in_buffer */
1550         read_chan,              /* read */
1551         write_chan,             /* write */
1552         n_tty_ioctl,            /* ioctl */
1553         n_tty_set_termios,      /* set_termios */
1554         normal_poll,            /* poll */
1555         NULL,                   /* hangup */
1556         n_tty_receive_buf,      /* receive_buf */
1557         n_tty_receive_room,     /* receive_room */
1558         n_tty_write_wakeup      /* write_wakeup */
1559 };
1560