drivers/tty/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 n_tty_write 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 #include <linux/audit.h>
  49 #include <linux/file.h>
  50 #include <linux/uaccess.h>
  51 #include <linux/module.h>
  52
  53 #include <asm/system.h>
  54
  55 /* number of characters left in xmit buffer before select has we have room */
  56 #define WAKEUP_CHARS 256
  57
  58 /*
  59  * This defines the low- and high-watermarks for throttling and
  60  * unthrottling the TTY driver.  These watermarks are used for
  61  * controlling the space in the read buffer.
  62  */
  63 #define TTY_THRESHOLD_THROTTLE          128 /* now based on remaining room */
  64 #define TTY_THRESHOLD_UNTHROTTLE        128
  65
  66 /*
  67  * Special byte codes used in the echo buffer to represent operations
  68  * or special handling of characters.  Bytes in the echo buffer that
  69  * are not part of such special blocks are treated as normal character
  70  * codes.
  71  */
  72 #define ECHO_OP_START 0xff
  73 #define ECHO_OP_MOVE_BACK_COL 0x80
  74 #define ECHO_OP_SET_CANON_COL 0x81
  75 #define ECHO_OP_ERASE_TAB 0x82
  76
  77 static inline int tty_put_user(struct tty_struct *tty, unsigned char x,
  78                                unsigned char __user *ptr)
  79 {
  80         tty_audit_add_data(tty, &x, 1);
  81         return put_user(x, ptr);
  82 }
  83
  84 static void put_tty_queue_nolock(unsigned char c, struct tty_struct *tty)
  85 {
  86         if (tty->read_cnt < N_TTY_BUF_SIZE) {
  87                 tty->read_buf[tty->read_head] = c;
  88                 tty->read_head = (tty->read_head + 1) & (N_TTY_BUF_SIZE-1);
  89                 tty->read_cnt++;
  90         }
  91 }
  92
  93 /**
  94  *      put_tty_queue           -       add character to tty
  95  *      @c: character
  96  *      @tty: tty device
  97  *
  98  *      Add a character to the tty read_buf queue. This is done under the
  99  *      read_lock to serialize character addition and also to protect us
 100  *      against parallel reads or flushes
 101  */
 102
 103 static void put_tty_queue(unsigned char c, struct tty_struct *tty)
 104 {
 105         unsigned long flags;
 106         /*
 107          *      The problem of stomping on the buffers ends here.
 108          *      Why didn't anyone see this one coming? --AJK
 109         */
 110         spin_lock_irqsave(&tty->read_lock, flags);
 111         put_tty_queue_nolock(c, tty);
 112         spin_unlock_irqrestore(&tty->read_lock, flags);
 113 }
 114
 115 /**
 116  *      check_unthrottle        -       allow new receive data
 117  *      @tty; tty device
 118  *
 119  *      Check whether to call the driver unthrottle functions
 120  *
 121  *      Can sleep, may be called under the atomic_read_lock mutex but
 122  *      this is not guaranteed.
 123  */
 124 static void check_unthrottle(struct tty_struct *tty)
 125 {
 126         if (tty->count)
 127                 tty_unthrottle(tty);
 128 }
 129
 130 /**
 131  *      reset_buffer_flags      -       reset buffer state
 132  *      @tty: terminal to reset
 133  *
 134  *      Reset the read buffer counters, clear the flags,
 135  *      and make sure the driver is unthrottled. Called
 136  *      from n_tty_open() and n_tty_flush_buffer().
 137  *
 138  *      Locking: tty_read_lock for read fields.
 139  */
 140
 141 static void reset_buffer_flags(struct tty_struct *tty)
 142 {
 143         unsigned long flags;
 144
 145         spin_lock_irqsave(&tty->read_lock, flags);
 146         tty->read_head = tty->read_tail = tty->read_cnt = 0;
 147         spin_unlock_irqrestore(&tty->read_lock, flags);
 148
 149         mutex_lock(&tty->echo_lock);
 150         tty->echo_pos = tty->echo_cnt = tty->echo_overrun = 0;
 151         mutex_unlock(&tty->echo_lock);
 152
 153         tty->canon_head = tty->canon_data = tty->erasing = 0;
 154         memset(&tty->read_flags, 0, sizeof tty->read_flags);
 155         check_unthrottle(tty);
 156 }
 157
 158 /**
 159  *      n_tty_flush_buffer      -       clean input queue
 160  *      @tty:   terminal device
 161  *
 162  *      Flush the input buffer. Called when the line discipline is
 163  *      being closed, when the tty layer wants the buffer flushed (eg
 164  *      at hangup) or when the N_TTY line discipline internally has to
 165  *      clean the pending queue (for example some signals).
 166  *
 167  *      Locking: ctrl_lock, read_lock.
 168  */
 169
 170 static void n_tty_flush_buffer(struct tty_struct *tty)
 171 {
 172         unsigned long flags;
 173         /* clear everything and unthrottle the driver */
 174         reset_buffer_flags(tty);
 175
 176         if (!tty->link)
 177                 return;
 178
 179         spin_lock_irqsave(&tty->ctrl_lock, flags);
 180         if (tty->link->packet) {
 181                 tty->ctrl_status |= TIOCPKT_FLUSHREAD;
 182                 wake_up_interruptible(&tty->link->read_wait);
 183         }
 184         spin_unlock_irqrestore(&tty->ctrl_lock, flags);
 185 }
 186
 187 /**
 188  *      n_tty_chars_in_buffer   -       report available bytes
 189  *      @tty: tty device
 190  *
 191  *      Report the number of characters buffered to be delivered to user
 192  *      at this instant in time.
 193  *
 194  *      Locking: read_lock
 195  */
 196
 197 static ssize_t n_tty_chars_in_buffer(struct tty_struct *tty)
 198 {
 199         unsigned long flags;
 200         ssize_t n = 0;
 201
 202         spin_lock_irqsave(&tty->read_lock, flags);
 203         if (!tty->icanon) {
 204                 n = tty->read_cnt;
 205         } else if (tty->canon_data) {
 206                 n = (tty->canon_head > tty->read_tail) ?
 207                         tty->canon_head - tty->read_tail :
 208                         tty->canon_head + (N_TTY_BUF_SIZE - tty->read_tail);
 209         }
 210         spin_unlock_irqrestore(&tty->read_lock, flags);
 211         return n;
 212 }
 213
 214 /**
 215  *      is_utf8_continuation    -       utf8 multibyte check
 216  *      @c: byte to check
 217  *
 218  *      Returns true if the utf8 character 'c' is a multibyte continuation
 219  *      character. We use this to correctly compute the on screen size
 220  *      of the character when printing
 221  */
 222
 223 static inline int is_utf8_continuation(unsigned char c)
 224 {
 225         return (c & 0xc0) == 0x80;
 226 }
 227
 228 /**
 229  *      is_continuation         -       multibyte check
 230  *      @c: byte to check
 231  *
 232  *      Returns true if the utf8 character 'c' is a multibyte continuation
 233  *      character and the terminal is in unicode mode.
 234  */
 235
 236 static inline int is_continuation(unsigned char c, struct tty_struct *tty)
 237 {
 238         return I_IUTF8(tty) && is_utf8_continuation(c);
 239 }
 240
 241 /**
 242  *      do_output_char                  -       output one character
 243  *      @c: character (or partial unicode symbol)
 244  *      @tty: terminal device
 245  *      @space: space available in tty driver write buffer
 246  *
 247  *      This is a helper function that handles one output character
 248  *      (including special characters like TAB, CR, LF, etc.),
 249  *      doing OPOST processing and putting the results in the
 250  *      tty driver's write buffer.
 251  *
 252  *      Note that Linux currently ignores TABDLY, CRDLY, VTDLY, FFDLY
 253  *      and NLDLY.  They simply aren't relevant in the world today.
 254  *      If you ever need them, add them here.
 255  *
 256  *      Returns the number of bytes of buffer space used or -1 if
 257  *      no space left.
 258  *
 259  *      Locking: should be called under the output_lock to protect
 260  *               the column state and space left in the buffer
 261  */
 262
 263 static int do_output_char(unsigned char c, struct tty_struct *tty, int space)
 264 {
 265         int     spaces;
 266
 267         if (!space)
 268                 return -1;
 269
 270         switch (c) {
 271         case '\n':
 272                 if (O_ONLRET(tty))
 273                         tty->column = 0;
 274                 if (O_ONLCR(tty)) {
 275                         if (space < 2)
 276                                 return -1;
 277                         tty->canon_column = tty->column = 0;
 278                         tty->ops->write(tty, "\r\n", 2);
 279                         return 2;
 280                 }
 281                 tty->canon_column = tty->column;
 282                 break;
 283         case '\r':
 284                 if (O_ONOCR(tty) && tty->column == 0)
 285                         return 0;
 286                 if (O_OCRNL(tty)) {
 287                         c = '\n';
 288                         if (O_ONLRET(tty))
 289                                 tty->canon_column = tty->column = 0;
 290                         break;
 291                 }
 292                 tty->canon_column = tty->column = 0;
 293                 break;
 294         case '\t':
 295                 spaces = 8 - (tty->column & 7);
 296                 if (O_TABDLY(tty) == XTABS) {
 297                         if (space < spaces)
 298                                 return -1;
 299                         tty->column += spaces;
 300                         tty->ops->write(tty, "        ", spaces);
 301                         return spaces;
 302                 }
 303                 tty->column += spaces;
 304                 break;
 305         case '\b':
 306                 if (tty->column > 0)
 307                         tty->column--;
 308                 break;
 309         default:
 310                 if (!iscntrl(c)) {
 311                         if (O_OLCUC(tty))
 312                                 c = toupper(c);
 313                         if (!is_continuation(c, tty))
 314                                 tty->column++;
 315                 }
 316                 break;
 317         }
 318
 319         tty_put_char(tty, c);
 320         return 1;
 321 }
 322
 323 /**
 324  *      process_output                  -       output post processor
 325  *      @c: character (or partial unicode symbol)
 326  *      @tty: terminal device
 327  *
 328  *      Output one character with OPOST processing.
 329  *      Returns -1 when the output device is full and the character
 330  *      must be retried.
 331  *
 332  *      Locking: output_lock to protect column state and space left
 333  *               (also, this is called from n_tty_write under the
 334  *                tty layer write lock)
 335  */
 336
 337 static int process_output(unsigned char c, struct tty_struct *tty)
 338 {
 339         int     space, retval;
 340
 341         mutex_lock(&tty->output_lock);
 342
 343         space = tty_write_room(tty);
 344         retval = do_output_char(c, tty, space);
 345
 346         mutex_unlock(&tty->output_lock);
 347         if (retval < 0)
 348                 return -1;
 349         else
 350                 return 0;
 351 }
 352
 353 /**
 354  *      process_output_block            -       block post processor
 355  *      @tty: terminal device
 356  *      @buf: character buffer
 357  *      @nr: number of bytes to output
 358  *
 359  *      Output a block of characters with OPOST processing.
 360  *      Returns the number of characters output.
 361  *
 362  *      This path is used to speed up block console writes, among other
 363  *      things when processing blocks of output data. It handles only
 364  *      the simple cases normally found and helps to generate blocks of
 365  *      symbols for the console driver and thus improve performance.
 366  *
 367  *      Locking: output_lock to protect column state and space left
 368  *               (also, this is called from n_tty_write under the
 369  *                tty layer write lock)
 370  */
 371
 372 static ssize_t process_output_block(struct tty_struct *tty,
 373                                     const unsigned char *buf, unsigned int nr)
 374 {
 375         int     space;
 376         int     i;
 377         const unsigned char *cp;
 378
 379         mutex_lock(&tty->output_lock);
 380
 381         space = tty_write_room(tty);
 382         if (!space) {
 383                 mutex_unlock(&tty->output_lock);
 384                 return 0;
 385         }
 386         if (nr > space)
 387                 nr = space;
 388
 389         for (i = 0, cp = buf; i < nr; i++, cp++) {
 390                 unsigned char c = *cp;
 391
 392                 switch (c) {
 393                 case '\n':
 394                         if (O_ONLRET(tty))
 395                                 tty->column = 0;
 396                         if (O_ONLCR(tty))
 397                                 goto break_out;
 398                         tty->canon_column = tty->column;
 399                         break;
 400                 case '\r':
 401                         if (O_ONOCR(tty) && tty->column == 0)
 402                                 goto break_out;
 403                         if (O_OCRNL(tty))
 404                                 goto break_out;
 405                         tty->canon_column = tty->column = 0;
 406                         break;
 407                 case '\t':
 408                         goto break_out;
 409                 case '\b':
 410                         if (tty->column > 0)
 411                                 tty->column--;
 412                         break;
 413                 default:
 414                         if (!iscntrl(c)) {
 415                                 if (O_OLCUC(tty))
 416                                         goto break_out;
 417                                 if (!is_continuation(c, tty))
 418                                         tty->column++;
 419                         }
 420                         break;
 421                 }
 422         }
 423 break_out:
 424         i = tty->ops->write(tty, buf, i);
 425
 426         mutex_unlock(&tty->output_lock);
 427         return i;
 428 }
 429
 430 /**
 431  *      process_echoes  -       write pending echo characters
 432  *      @tty: terminal device
 433  *
 434  *      Write previously buffered echo (and other ldisc-generated)
 435  *      characters to the tty.
 436  *
 437  *      Characters generated by the ldisc (including echoes) need to
 438  *      be buffered because the driver's write buffer can fill during
 439  *      heavy program output.  Echoing straight to the driver will
 440  *      often fail under these conditions, causing lost characters and
 441  *      resulting mismatches of ldisc state information.
 442  *
 443  *      Since the ldisc state must represent the characters actually sent
 444  *      to the driver at the time of the write, operations like certain
 445  *      changes in column state are also saved in the buffer and executed
 446  *      here.
 447  *
 448  *      A circular fifo buffer is used so that the most recent characters
 449  *      are prioritized.  Also, when control characters are echoed with a
 450  *      prefixed "^", the pair is treated atomically and thus not separated.
 451  *
 452  *      Locking: output_lock to protect column state and space left,
 453  *               echo_lock to protect the echo buffer
 454  */
 455
 456 static void process_echoes(struct tty_struct *tty)
 457 {
 458         int     space, nr;
 459         unsigned char c;
 460         unsigned char *cp, *buf_end;
 461
 462         if (!tty->echo_cnt)
 463                 return;
 464
 465         mutex_lock(&tty->output_lock);
 466         mutex_lock(&tty->echo_lock);
 467
 468         space = tty_write_room(tty);
 469
 470         buf_end = tty->echo_buf + N_TTY_BUF_SIZE;
 471         cp = tty->echo_buf + tty->echo_pos;
 472         nr = tty->echo_cnt;
 473         while (nr > 0) {
 474                 c = *cp;
 475                 if (c == ECHO_OP_START) {
 476                         unsigned char op;
 477                         unsigned char *opp;
 478                         int no_space_left = 0;
 479
 480                         /*
 481                          * If the buffer byte is the start of a multi-byte
 482                          * operation, get the next byte, which is either the
 483                          * op code or a control character value.
 484                          */
 485                         opp = cp + 1;
 486                         if (opp == buf_end)
 487                                 opp -= N_TTY_BUF_SIZE;
 488                         op = *opp;
 489
 490                         switch (op) {
 491                                 unsigned int num_chars, num_bs;
 492
 493                         case ECHO_OP_ERASE_TAB:
 494                                 if (++opp == buf_end)
 495                                         opp -= N_TTY_BUF_SIZE;
 496                                 num_chars = *opp;
 497
 498                                 /*
 499                                  * Determine how many columns to go back
 500                                  * in order to erase the tab.
 501                                  * This depends on the number of columns
 502                                  * used by other characters within the tab
 503                                  * area.  If this (modulo 8) count is from
 504                                  * the start of input rather than from a
 505                                  * previous tab, we offset by canon column.
 506                                  * Otherwise, tab spacing is normal.
 507                                  */
 508                                 if (!(num_chars & 0x80))
 509                                         num_chars += tty->canon_column;
 510                                 num_bs = 8 - (num_chars & 7);
 511
 512                                 if (num_bs > space) {
 513                                         no_space_left = 1;
 514                                         break;
 515                                 }
 516                                 space -= num_bs;
 517                                 while (num_bs--) {
 518                                         tty_put_char(tty, '\b');
 519                                         if (tty->column > 0)
 520                                                 tty->column--;
 521                                 }
 522                                 cp += 3;
 523                                 nr -= 3;
 524                                 break;
 525
 526                         case ECHO_OP_SET_CANON_COL:
 527                                 tty->canon_column = tty->column;
 528                                 cp += 2;
 529                                 nr -= 2;
 530                                 break;
 531
 532                         case ECHO_OP_MOVE_BACK_COL:
 533                                 if (tty->column > 0)
 534                                         tty->column--;
 535                                 cp += 2;
 536                                 nr -= 2;
 537                                 break;
 538
 539                         case ECHO_OP_START:
 540                                 /* This is an escaped echo op start code */
 541                                 if (!space) {
 542                                         no_space_left = 1;
 543                                         break;
 544                                 }
 545                                 tty_put_char(tty, ECHO_OP_START);
 546                                 tty->column++;
 547                                 space--;
 548                                 cp += 2;
 549                                 nr -= 2;
 550                                 break;
 551
 552                         default:
 553                                 /*
 554                                  * If the op is not a special byte code,
 555                                  * it is a ctrl char tagged to be echoed
 556                                  * as "^X" (where X is the letter
 557                                  * representing the control char).
 558                                  * Note that we must ensure there is
 559                                  * enough space for the whole ctrl pair.
 560                                  *
 561                                  */
 562                                 if (space < 2) {
 563                                         no_space_left = 1;
 564                                         break;
 565                                 }
 566                                 tty_put_char(tty, '^');
 567                                 tty_put_char(tty, op ^ 0100);
 568                                 tty->column += 2;
 569                                 space -= 2;
 570                                 cp += 2;
 571                                 nr -= 2;
 572                         }
 573
 574                         if (no_space_left)
 575                                 break;
 576                 } else {
 577                         if (O_OPOST(tty) &&
 578                             !(test_bit(TTY_HW_COOK_OUT, &tty->flags))) {
 579                                 int retval = do_output_char(c, tty, space);
 580                                 if (retval < 0)
 581                                         break;
 582                                 space -= retval;
 583                         } else {
 584                                 if (!space)
 585                                         break;
 586                                 tty_put_char(tty, c);
 587                                 space -= 1;
 588                         }
 589                         cp += 1;
 590                         nr -= 1;
 591                 }
 592
 593                 /* When end of circular buffer reached, wrap around */
 594                 if (cp >= buf_end)
 595                         cp -= N_TTY_BUF_SIZE;
 596         }
 597
 598         if (nr == 0) {
 599                 tty->echo_pos = 0;
 600                 tty->echo_cnt = 0;
 601                 tty->echo_overrun = 0;
 602         } else {
 603                 int num_processed = tty->echo_cnt - nr;
 604                 tty->echo_pos += num_processed;
 605                 tty->echo_pos &= N_TTY_BUF_SIZE - 1;
 606                 tty->echo_cnt = nr;
 607                 if (num_processed > 0)
 608                         tty->echo_overrun = 0;
 609         }
 610
 611         mutex_unlock(&tty->echo_lock);
 612         mutex_unlock(&tty->output_lock);
 613
 614         if (tty->ops->flush_chars)
 615                 tty->ops->flush_chars(tty);
 616 }
 617
 618 /**
 619  *      add_echo_byte   -       add a byte to the echo buffer
 620  *      @c: unicode byte to echo
 621  *      @tty: terminal device
 622  *
 623  *      Add a character or operation byte to the echo buffer.
 624  *
 625  *      Should be called under the echo lock to protect the echo buffer.
 626  */
 627
 628 static void add_echo_byte(unsigned char c, struct tty_struct *tty)
 629 {
 630         int     new_byte_pos;
 631
 632         if (tty->echo_cnt == N_TTY_BUF_SIZE) {
 633                 /* Circular buffer is already at capacity */
 634                 new_byte_pos = tty->echo_pos;
 635
 636                 /*
 637                  * Since the buffer start position needs to be advanced,
 638                  * be sure to step by a whole operation byte group.
 639                  */
 640                 if (tty->echo_buf[tty->echo_pos] == ECHO_OP_START) {
 641                         if (tty->echo_buf[(tty->echo_pos + 1) &
 642                                           (N_TTY_BUF_SIZE - 1)] ==
 643                                                 ECHO_OP_ERASE_TAB) {
 644                                 tty->echo_pos += 3;
 645                                 tty->echo_cnt -= 2;
 646                         } else {
 647                                 tty->echo_pos += 2;
 648                                 tty->echo_cnt -= 1;
 649                         }
 650                 } else {
 651                         tty->echo_pos++;
 652                 }
 653                 tty->echo_pos &= N_TTY_BUF_SIZE - 1;
 654
 655                 tty->echo_overrun = 1;
 656         } else {
 657                 new_byte_pos = tty->echo_pos + tty->echo_cnt;
 658                 new_byte_pos &= N_TTY_BUF_SIZE - 1;
 659                 tty->echo_cnt++;
 660         }
 661
 662         tty->echo_buf[new_byte_pos] = c;
 663 }
 664
 665 /**
 666  *      echo_move_back_col      -       add operation to move back a column
 667  *      @tty: terminal device
 668  *
 669  *      Add an operation to the echo buffer to move back one column.
 670  *
 671  *      Locking: echo_lock to protect the echo buffer
 672  */
 673
 674 static void echo_move_back_col(struct tty_struct *tty)
 675 {
 676         mutex_lock(&tty->echo_lock);
 677
 678         add_echo_byte(ECHO_OP_START, tty);
 679         add_echo_byte(ECHO_OP_MOVE_BACK_COL, tty);
 680
 681         mutex_unlock(&tty->echo_lock);
 682 }
 683
 684 /**
 685  *      echo_set_canon_col      -       add operation to set the canon column
 686  *      @tty: terminal device
 687  *
 688  *      Add an operation to the echo buffer to set the canon column
 689  *      to the current column.
 690  *
 691  *      Locking: echo_lock to protect the echo buffer
 692  */
 693
 694 static void echo_set_canon_col(struct tty_struct *tty)
 695 {
 696         mutex_lock(&tty->echo_lock);
 697
 698         add_echo_byte(ECHO_OP_START, tty);
 699         add_echo_byte(ECHO_OP_SET_CANON_COL, tty);
 700
 701         mutex_unlock(&tty->echo_lock);
 702 }
 703
 704 /**
 705  *      echo_erase_tab  -       add operation to erase a tab
 706  *      @num_chars: number of character columns already used
 707  *      @after_tab: true if num_chars starts after a previous tab
 708  *      @tty: terminal device
 709  *
 710  *      Add an operation to the echo buffer to erase a tab.
 711  *
 712  *      Called by the eraser function, which knows how many character
 713  *      columns have been used since either a previous tab or the start
 714  *      of input.  This information will be used later, along with
 715  *      canon column (if applicable), to go back the correct number
 716  *      of columns.
 717  *
 718  *      Locking: echo_lock to protect the echo buffer
 719  */
 720
 721 static void echo_erase_tab(unsigned int num_chars, int after_tab,
 722                            struct tty_struct *tty)
 723 {
 724         mutex_lock(&tty->echo_lock);
 725
 726         add_echo_byte(ECHO_OP_START, tty);
 727         add_echo_byte(ECHO_OP_ERASE_TAB, tty);
 728
 729         /* We only need to know this modulo 8 (tab spacing) */
 730         num_chars &= 7;
 731
 732         /* Set the high bit as a flag if num_chars is after a previous tab */
 733         if (after_tab)
 734                 num_chars |= 0x80;
 735
 736         add_echo_byte(num_chars, tty);
 737
 738         mutex_unlock(&tty->echo_lock);
 739 }
 740
 741 /**
 742  *      echo_char_raw   -       echo a character raw
 743  *      @c: unicode byte to echo
 744  *      @tty: terminal device
 745  *
 746  *      Echo user input back onto the screen. This must be called only when
 747  *      L_ECHO(tty) is true. Called from the driver receive_buf path.
 748  *
 749  *      This variant does not treat control characters specially.
 750  *
 751  *      Locking: echo_lock to protect the echo buffer
 752  */
 753
 754 static void echo_char_raw(unsigned char c, struct tty_struct *tty)
 755 {
 756         mutex_lock(&tty->echo_lock);
 757
 758         if (c == ECHO_OP_START) {
 759                 add_echo_byte(ECHO_OP_START, tty);
 760                 add_echo_byte(ECHO_OP_START, tty);
 761         } else {
 762                 add_echo_byte(c, tty);
 763         }
 764
 765         mutex_unlock(&tty->echo_lock);
 766 }
 767
 768 /**
 769  *      echo_char       -       echo a character
 770  *      @c: unicode byte to echo
 771  *      @tty: terminal device
 772  *
 773  *      Echo user input back onto the screen. This must be called only when
 774  *      L_ECHO(tty) is true. Called from the driver receive_buf path.
 775  *
 776  *      This variant tags control characters to be echoed as "^X"
 777  *      (where X is the letter representing the control char).
 778  *
 779  *      Locking: echo_lock to protect the echo buffer
 780  */
 781
 782 static void echo_char(unsigned char c, struct tty_struct *tty)
 783 {
 784         mutex_lock(&tty->echo_lock);
 785
 786         if (c == ECHO_OP_START) {
 787                 add_echo_byte(ECHO_OP_START, tty);
 788                 add_echo_byte(ECHO_OP_START, tty);
 789         } else {
 790                 if (L_ECHOCTL(tty) && iscntrl(c) && c != '\t')
 791                         add_echo_byte(ECHO_OP_START, tty);
 792                 add_echo_byte(c, tty);
 793         }
 794
 795         mutex_unlock(&tty->echo_lock);
 796 }
 797
 798 /**
 799  *      finish_erasing          -       complete erase
 800  *      @tty: tty doing the erase
 801  */
 802
 803 static inline void finish_erasing(struct tty_struct *tty)
 804 {
 805         if (tty->erasing) {
 806                 echo_char_raw('/', tty);
 807                 tty->erasing = 0;
 808         }
 809 }
 810
 811 /**
 812  *      eraser          -       handle erase function
 813  *      @c: character input
 814  *      @tty: terminal device
 815  *
 816  *      Perform erase and necessary output when an erase character is
 817  *      present in the stream from the driver layer. Handles the complexities
 818  *      of UTF-8 multibyte symbols.
 819  *
 820  *      Locking: read_lock for tty buffers
 821  */
 822
 823 static void eraser(unsigned char c, struct tty_struct *tty)
 824 {
 825         enum { ERASE, WERASE, KILL } kill_type;
 826         int head, seen_alnums, cnt;
 827         unsigned long flags;
 828
 829         /* FIXME: locking needed ? */
 830         if (tty->read_head == tty->canon_head) {
 831                 /* process_output('\a', tty); */ /* what do you think? */
 832                 return;
 833         }
 834         if (c == ERASE_CHAR(tty))
 835                 kill_type = ERASE;
 836         else if (c == WERASE_CHAR(tty))
 837                 kill_type = WERASE;
 838         else {
 839                 if (!L_ECHO(tty)) {
 840                         spin_lock_irqsave(&tty->read_lock, flags);
 841                         tty->read_cnt -= ((tty->read_head - tty->canon_head) &
 842                                           (N_TTY_BUF_SIZE - 1));
 843                         tty->read_head = tty->canon_head;
 844                         spin_unlock_irqrestore(&tty->read_lock, flags);
 845                         return;
 846                 }
 847                 if (!L_ECHOK(tty) || !L_ECHOKE(tty) || !L_ECHOE(tty)) {
 848                         spin_lock_irqsave(&tty->read_lock, flags);
 849                         tty->read_cnt -= ((tty->read_head - tty->canon_head) &
 850                                           (N_TTY_BUF_SIZE - 1));
 851                         tty->read_head = tty->canon_head;
 852                         spin_unlock_irqrestore(&tty->read_lock, flags);
 853                         finish_erasing(tty);
 854                         echo_char(KILL_CHAR(tty), tty);
 855                         /* Add a newline if ECHOK is on and ECHOKE is off. */
 856                         if (L_ECHOK(tty))
 857                                 echo_char_raw('\n', tty);
 858                         return;
 859                 }
 860                 kill_type = KILL;
 861         }
 862
 863         seen_alnums = 0;
 864         /* FIXME: Locking ?? */
 865         while (tty->read_head != tty->canon_head) {
 866                 head = tty->read_head;
 867
 868                 /* erase a single possibly multibyte character */
 869                 do {
 870                         head = (head - 1) & (N_TTY_BUF_SIZE-1);
 871                         c = tty->read_buf[head];
 872                 } while (is_continuation(c, tty) && head != tty->canon_head);
 873
 874                 /* do not partially erase */
 875                 if (is_continuation(c, tty))
 876                         break;
 877
 878                 if (kill_type == WERASE) {
 879                         /* Equivalent to BSD's ALTWERASE. */
 880                         if (isalnum(c) || c == '_')
 881                                 seen_alnums++;
 882                         else if (seen_alnums)
 883                                 break;
 884                 }
 885                 cnt = (tty->read_head - head) & (N_TTY_BUF_SIZE-1);
 886                 spin_lock_irqsave(&tty->read_lock, flags);
 887                 tty->read_head = head;
 888                 tty->read_cnt -= cnt;
 889                 spin_unlock_irqrestore(&tty->read_lock, flags);
 890                 if (L_ECHO(tty)) {
 891                         if (L_ECHOPRT(tty)) {
 892                                 if (!tty->erasing) {
 893                                         echo_char_raw('\\', tty);
 894                                         tty->erasing = 1;
 895                                 }
 896                                 /* if cnt > 1, output a multi-byte character */
 897                                 echo_char(c, tty);
 898                                 while (--cnt > 0) {
 899                                         head = (head+1) & (N_TTY_BUF_SIZE-1);
 900                                         echo_char_raw(tty->read_buf[head], tty);
 901                                         echo_move_back_col(tty);
 902                                 }
 903                         } else if (kill_type == ERASE && !L_ECHOE(tty)) {
 904                                 echo_char(ERASE_CHAR(tty), tty);
 905                         } else if (c == '\t') {
 906                                 unsigned int num_chars = 0;
 907                                 int after_tab = 0;
 908                                 unsigned long tail = tty->read_head;
 909
 910                                 /*
 911                                  * Count the columns used for characters
 912                                  * since the start of input or after a
 913                                  * previous tab.
 914                                  * This info is used to go back the correct
 915                                  * number of columns.
 916                                  */
 917                                 while (tail != tty->canon_head) {
 918                                         tail = (tail-1) & (N_TTY_BUF_SIZE-1);
 919                                         c = tty->read_buf[tail];
 920                                         if (c == '\t') {
 921                                                 after_tab = 1;
 922                                                 break;
 923                                         } else if (iscntrl(c)) {
 924                                                 if (L_ECHOCTL(tty))
 925                                                         num_chars += 2;
 926                                         } else if (!is_continuation(c, tty)) {
 927                                                 num_chars++;
 928                                         }
 929                                 }
 930                                 echo_erase_tab(num_chars, after_tab, tty);
 931                         } else {
 932                                 if (iscntrl(c) && L_ECHOCTL(tty)) {
 933                                         echo_char_raw('\b', tty);
 934                                         echo_char_raw(' ', tty);
 935                                         echo_char_raw('\b', tty);
 936                                 }
 937                                 if (!iscntrl(c) || L_ECHOCTL(tty)) {
 938                                         echo_char_raw('\b', tty);
 939                                         echo_char_raw(' ', tty);
 940                                         echo_char_raw('\b', tty);
 941                                 }
 942                         }
 943                 }
 944                 if (kill_type == ERASE)
 945                         break;
 946         }
 947         if (tty->read_head == tty->canon_head && L_ECHO(tty))
 948                 finish_erasing(tty);
 949 }
 950
 951 /**
 952  *      isig            -       handle the ISIG optio
 953  *      @sig: signal
 954  *      @tty: terminal
 955  *      @flush: force flush
 956  *
 957  *      Called when a signal is being sent due to terminal input. This
 958  *      may caus terminal flushing to take place according to the termios
 959  *      settings and character used. Called from the driver receive_buf
 960  *      path so serialized.
 961  *
 962  *      Locking: ctrl_lock, read_lock (both via flush buffer)
 963  */
 964
 965 static inline void isig(int sig, struct tty_struct *tty, int flush)
 966 {
 967         if (tty->pgrp)
 968                 kill_pgrp(tty->pgrp, sig, 1);
 969         if (flush || !L_NOFLSH(tty)) {
 970                 n_tty_flush_buffer(tty);
 971                 tty_driver_flush_buffer(tty);
 972         }
 973 }
 974
 975 /**
 976  *      n_tty_receive_break     -       handle break
 977  *      @tty: terminal
 978  *
 979  *      An RS232 break event has been hit in the incoming bitstream. This
 980  *      can cause a variety of events depending upon the termios settings.
 981  *
 982  *      Called from the receive_buf path so single threaded.
 983  */
 984
 985 static inline void n_tty_receive_break(struct tty_struct *tty)
 986 {
 987         if (I_IGNBRK(tty))
 988                 return;
 989         if (I_BRKINT(tty)) {
 990                 isig(SIGINT, tty, 1);
 991                 return;
 992         }
 993         if (I_PARMRK(tty)) {
 994                 put_tty_queue('\377', tty);
 995                 put_tty_queue('\0', tty);
 996         }
 997         put_tty_queue('\0', tty);
 998         wake_up_interruptible(&tty->read_wait);
 999 }
1000
1001 /**
1002  *      n_tty_receive_overrun   -       handle overrun reporting
1003  *      @tty: terminal
1004  *
1005  *      Data arrived faster than we could process it. While the tty
1006  *      driver has flagged this the bits that were missed are gone
1007  *      forever.
1008  *
1009  *      Called from the receive_buf path so single threaded. Does not
1010  *      need locking as num_overrun and overrun_time are function
1011  *      private.
1012  */
1013
1014 static inline void n_tty_receive_overrun(struct tty_struct *tty)
1015 {
1016         char buf[64];
1017
1018         tty->num_overrun++;
1019         if (time_before(tty->overrun_time, jiffies - HZ) ||
1020                         time_after(tty->overrun_time, jiffies)) {
1021                 printk(KERN_WARNING "%s: %d input overrun(s)\n",
1022                         tty_name(tty, buf),
1023                         tty->num_overrun);
1024                 tty->overrun_time = jiffies;
1025                 tty->num_overrun = 0;
1026         }
1027 }
1028
1029 /**
1030  *      n_tty_receive_parity_error      -       error notifier
1031  *      @tty: terminal device
1032  *      @c: character
1033  *
1034  *      Process a parity error and queue the right data to indicate
1035  *      the error case if necessary. Locking as per n_tty_receive_buf.
1036  */
1037 static inline void n_tty_receive_parity_error(struct tty_struct *tty,
1038                                               unsigned char c)
1039 {
1040         if (I_IGNPAR(tty))
1041                 return;
1042         if (I_PARMRK(tty)) {
1043                 put_tty_queue('\377', tty);
1044                 put_tty_queue('\0', tty);
1045                 put_tty_queue(c, tty);
1046         } else  if (I_INPCK(tty))
1047                 put_tty_queue('\0', tty);
1048         else
1049                 put_tty_queue(c, tty);
1050         wake_up_interruptible(&tty->read_wait);
1051 }
1052
1053 /**
1054  *      n_tty_receive_char      -       perform processing
1055  *      @tty: terminal device
1056  *      @c: character
1057  *
1058  *      Process an individual character of input received from the driver.
1059  *      This is serialized with respect to itself by the rules for the
1060  *      driver above.
1061  */
1062
1063 static inline void n_tty_receive_char(struct tty_struct *tty, unsigned char c)
1064 {
1065         unsigned long flags;
1066         int parmrk;
1067
1068         if (tty->raw) {
1069                 put_tty_queue(c, tty);
1070                 return;
1071         }
1072
1073         if (I_ISTRIP(tty))
1074                 c &= 0x7f;
1075         if (I_IUCLC(tty) && L_IEXTEN(tty))
1076                 c = tolower(c);
1077
1078         if (L_EXTPROC(tty)) {
1079                 put_tty_queue(c, tty);
1080                 return;
1081         }
1082
1083         if (tty->stopped && !tty->flow_stopped && I_IXON(tty) &&
1084             I_IXANY(tty) && c != START_CHAR(tty) && c != STOP_CHAR(tty) &&
1085             c != INTR_CHAR(tty) && c != QUIT_CHAR(tty) && c != SUSP_CHAR(tty)) {
1086                 start_tty(tty);
1087                 process_echoes(tty);
1088         }
1089
1090         if (tty->closing) {
1091                 if (I_IXON(tty)) {
1092                         if (c == START_CHAR(tty)) {
1093                                 start_tty(tty);
1094                                 process_echoes(tty);
1095                         } else if (c == STOP_CHAR(tty))
1096                                 stop_tty(tty);
1097                 }
1098                 return;
1099         }
1100
1101         /*
1102          * If the previous character was LNEXT, or we know that this
1103          * character is not one of the characters that we'll have to
1104          * handle specially, do shortcut processing to speed things
1105          * up.
1106          */
1107         if (!test_bit(c, tty->process_char_map) || tty->lnext) {
1108                 tty->lnext = 0;
1109                 parmrk = (c == (unsigned char) '\377' && I_PARMRK(tty)) ? 1 : 0;
1110                 if (tty->read_cnt >= (N_TTY_BUF_SIZE - parmrk - 1)) {
1111                         /* beep if no space */
1112                         if (L_ECHO(tty))
1113                                 process_output('\a', tty);
1114                         return;
1115                 }
1116                 if (L_ECHO(tty)) {
1117                         finish_erasing(tty);
1118                         /* Record the column of first canon char. */
1119                         if (tty->canon_head == tty->read_head)
1120                                 echo_set_canon_col(tty);
1121                         echo_char(c, tty);
1122                         process_echoes(tty);
1123                 }
1124                 if (parmrk)
1125                         put_tty_queue(c, tty);
1126                 put_tty_queue(c, tty);
1127                 return;
1128         }
1129
1130         if (I_IXON(tty)) {
1131                 if (c == START_CHAR(tty)) {
1132                         start_tty(tty);
1133                         process_echoes(tty);
1134                         return;
1135                 }
1136                 if (c == STOP_CHAR(tty)) {
1137                         stop_tty(tty);
1138                         return;
1139                 }
1140         }
1141
1142         if (L_ISIG(tty)) {
1143                 int signal;
1144                 signal = SIGINT;
1145                 if (c == INTR_CHAR(tty))
1146                         goto send_signal;
1147                 signal = SIGQUIT;
1148                 if (c == QUIT_CHAR(tty))
1149                         goto send_signal;
1150                 signal = SIGTSTP;
1151                 if (c == SUSP_CHAR(tty)) {
1152 send_signal:
1153                         /*
1154                          * Note that we do not use isig() here because we want
1155                          * the order to be:
1156                          * 1) flush, 2) echo, 3) signal
1157                          */
1158                         if (!L_NOFLSH(tty)) {
1159                                 n_tty_flush_buffer(tty);
1160                                 tty_driver_flush_buffer(tty);
1161                         }
1162                         if (I_IXON(tty))
1163                                 start_tty(tty);
1164                         if (L_ECHO(tty)) {
1165                                 echo_char(c, tty);
1166                                 process_echoes(tty);
1167                         }
1168                         if (tty->pgrp)
1169                                 kill_pgrp(tty->pgrp, signal, 1);
1170                         return;
1171                 }
1172         }
1173
1174         if (c == '\r') {
1175                 if (I_IGNCR(tty))
1176                         return;
1177                 if (I_ICRNL(tty))
1178                         c = '\n';
1179         } else if (c == '\n' && I_INLCR(tty))
1180                 c = '\r';
1181
1182         if (tty->icanon) {
1183                 if (c == ERASE_CHAR(tty) || c == KILL_CHAR(tty) ||
1184                     (c == WERASE_CHAR(tty) && L_IEXTEN(tty))) {
1185                         eraser(c, tty);
1186                         process_echoes(tty);
1187                         return;
1188                 }
1189                 if (c == LNEXT_CHAR(tty) && L_IEXTEN(tty)) {
1190                         tty->lnext = 1;
1191                         if (L_ECHO(tty)) {
1192                                 finish_erasing(tty);
1193                                 if (L_ECHOCTL(tty)) {
1194                                         echo_char_raw('^', tty);
1195                                         echo_char_raw('\b', tty);
1196                                         process_echoes(tty);
1197                                 }
1198                         }
1199                         return;
1200                 }
1201                 if (c == REPRINT_CHAR(tty) && L_ECHO(tty) &&
1202                     L_IEXTEN(tty)) {
1203                         unsigned long tail = tty->canon_head;
1204
1205                         finish_erasing(tty);
1206                         echo_char(c, tty);
1207                         echo_char_raw('\n', tty);
1208                         while (tail != tty->read_head) {
1209                                 echo_char(tty->read_buf[tail], tty);
1210                                 tail = (tail+1) & (N_TTY_BUF_SIZE-1);
1211                         }
1212                         process_echoes(tty);
1213                         return;
1214                 }
1215                 if (c == '\n') {
1216                         if (tty->read_cnt >= N_TTY_BUF_SIZE) {
1217                                 if (L_ECHO(tty))
1218                                         process_output('\a', tty);
1219                                 return;
1220                         }
1221                         if (L_ECHO(tty) || L_ECHONL(tty)) {
1222                                 echo_char_raw('\n', tty);
1223                                 process_echoes(tty);
1224                         }
1225                         goto handle_newline;
1226                 }
1227                 if (c == EOF_CHAR(tty)) {
1228                         if (tty->read_cnt >= N_TTY_BUF_SIZE)
1229                                 return;
1230                         if (tty->canon_head != tty->read_head)
1231                                 set_bit(TTY_PUSH, &tty->flags);
1232                         c = __DISABLED_CHAR;
1233                         goto handle_newline;
1234                 }
1235                 if ((c == EOL_CHAR(tty)) ||
1236                     (c == EOL2_CHAR(tty) && L_IEXTEN(tty))) {
1237                         parmrk = (c == (unsigned char) '\377' && I_PARMRK(tty))
1238                                  ? 1 : 0;
1239                         if (tty->read_cnt >= (N_TTY_BUF_SIZE - parmrk)) {
1240                                 if (L_ECHO(tty))
1241                                         process_output('\a', tty);
1242                                 return;
1243                         }
1244                         /*
1245                          * XXX are EOL_CHAR and EOL2_CHAR echoed?!?
1246                          */
1247                         if (L_ECHO(tty)) {
1248                                 /* Record the column of first canon char. */
1249                                 if (tty->canon_head == tty->read_head)
1250                                         echo_set_canon_col(tty);
1251                                 echo_char(c, tty);
1252                                 process_echoes(tty);
1253                         }
1254                         /*
1255                          * XXX does PARMRK doubling happen for
1256                          * EOL_CHAR and EOL2_CHAR?
1257                          */
1258                         if (parmrk)
1259                                 put_tty_queue(c, tty);
1260
1261 handle_newline:
1262                         spin_lock_irqsave(&tty->read_lock, flags);
1263                         set_bit(tty->read_head, tty->read_flags);
1264                         put_tty_queue_nolock(c, tty);
1265                         tty->canon_head = tty->read_head;
1266                         tty->canon_data++;
1267                         spin_unlock_irqrestore(&tty->read_lock, flags);
1268                         kill_fasync(&tty->fasync, SIGIO, POLL_IN);
1269                         if (waitqueue_active(&tty->read_wait))
1270                                 wake_up_interruptible(&tty->read_wait);
1271                         return;
1272                 }
1273         }
1274
1275         parmrk = (c == (unsigned char) '\377' && I_PARMRK(tty)) ? 1 : 0;
1276         if (tty->read_cnt >= (N_TTY_BUF_SIZE - parmrk - 1)) {
1277                 /* beep if no space */
1278                 if (L_ECHO(tty))
1279                         process_output('\a', tty);
1280                 return;
1281         }
1282         if (L_ECHO(tty)) {
1283                 finish_erasing(tty);
1284                 if (c == '\n')
1285                         echo_char_raw('\n', tty);
1286                 else {
1287                         /* Record the column of first canon char. */
1288                         if (tty->canon_head == tty->read_head)
1289                                 echo_set_canon_col(tty);
1290                         echo_char(c, tty);
1291                 }
1292                 process_echoes(tty);
1293         }
1294
1295         if (parmrk)
1296                 put_tty_queue(c, tty);
1297
1298         put_tty_queue(c, tty);
1299 }
1300
1301
1302 /**
1303  *      n_tty_write_wakeup      -       asynchronous I/O notifier
1304  *      @tty: tty device
1305  *
1306  *      Required for the ptys, serial driver etc. since processes
1307  *      that attach themselves to the master and rely on ASYNC
1308  *      IO must be woken up
1309  */
1310
1311 static void n_tty_write_wakeup(struct tty_struct *tty)
1312 {
1313         if (tty->fasync && test_and_clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags))
1314                 kill_fasync(&tty->fasync, SIGIO, POLL_OUT);
1315 }
1316
1317 /**
1318  *      n_tty_receive_buf       -       data receive
1319  *      @tty: terminal device
1320  *      @cp: buffer
1321  *      @fp: flag buffer
1322  *      @count: characters
1323  *
1324  *      Called by the terminal driver when a block of characters has
1325  *      been received. This function must be called from soft contexts
1326  *      not from interrupt context. The driver is responsible for making
1327  *      calls one at a time and in order (or using flush_to_ldisc)
1328  */
1329
1330 static unsigned int n_tty_receive_buf(struct tty_struct *tty,
1331                 const unsigned char *cp, char *fp, int count)
1332 {
1333         const unsigned char *p;
1334         char *f, flags = TTY_NORMAL;
1335         int     i;
1336         char    buf[64];
1337         unsigned long cpuflags;
1338         int left;
1339         int ret = 0;
1340
1341         if (!tty->read_buf)
1342                 return 0;
1343
1344         if (tty->real_raw) {
1345                 spin_lock_irqsave(&tty->read_lock, cpuflags);
1346                 i = min(N_TTY_BUF_SIZE - tty->read_cnt,
1347                         N_TTY_BUF_SIZE - tty->read_head);
1348                 i = min(count, i);
1349                 memcpy(tty->read_buf + tty->read_head, cp, i);
1350                 tty->read_head = (tty->read_head + i) & (N_TTY_BUF_SIZE-1);
1351                 tty->read_cnt += i;
1352                 ret += i;
1353                 cp += i;
1354                 count -= i;
1355
1356                 i = min(N_TTY_BUF_SIZE - tty->read_cnt,
1357                         N_TTY_BUF_SIZE - tty->read_head);
1358                 i = min(count, i);
1359                 memcpy(tty->read_buf + tty->read_head, cp, i);
1360                 tty->read_head = (tty->read_head + i) & (N_TTY_BUF_SIZE-1);
1361                 tty->read_cnt += i;
1362                 ret += i;
1363                 spin_unlock_irqrestore(&tty->read_lock, cpuflags);
1364         } else {
1365                 ret = count;
1366                 for (i = count, p = cp, f = fp; i; i--, p++) {
1367                         if (f)
1368                                 flags = *f++;
1369                         switch (flags) {
1370                         case TTY_NORMAL:
1371                                 n_tty_receive_char(tty, *p);
1372                                 break;
1373                         case TTY_BREAK:
1374                                 n_tty_receive_break(tty);
1375                                 break;
1376                         case TTY_PARITY:
1377                         case TTY_FRAME:
1378                                 n_tty_receive_parity_error(tty, *p);
1379                                 break;
1380                         case TTY_OVERRUN:
1381                                 n_tty_receive_overrun(tty);
1382                                 break;
1383                         default:
1384                                 printk(KERN_ERR "%s: unknown flag %d\n",
1385                                        tty_name(tty, buf), flags);
1386                                 break;
1387                         }
1388                 }
1389                 if (tty->ops->flush_chars)
1390                         tty->ops->flush_chars(tty);
1391         }
1392
1393         if ((!tty->icanon && (tty->read_cnt >= tty->minimum_to_wake)) ||
1394                 L_EXTPROC(tty)) {
1395                 kill_fasync(&tty->fasync, SIGIO, POLL_IN);
1396                 if (waitqueue_active(&tty->read_wait))
1397                         wake_up_interruptible(&tty->read_wait);
1398         }
1399
1400         /*
1401          * Check the remaining room for the input canonicalization
1402          * mode.  We don't want to throttle the driver if we're in
1403          * canonical mode and don't have a newline yet!
1404          */
1405         left = N_TTY_BUF_SIZE - tty->read_cnt - 1;
1406
1407         if (left < TTY_THRESHOLD_THROTTLE)
1408                 tty_throttle(tty);
1409
1410         return ret;
1411 }
1412
1413 int is_ignored(int sig)
1414 {
1415         return (sigismember(&current->blocked, sig) ||
1416                 current->sighand->action[sig-1].sa.sa_handler == SIG_IGN);
1417 }
1418
1419 /**
1420  *      n_tty_set_termios       -       termios data changed
1421  *      @tty: terminal
1422  *      @old: previous data
1423  *
1424  *      Called by the tty layer when the user changes termios flags so
1425  *      that the line discipline can plan ahead. This function cannot sleep
1426  *      and is protected from re-entry by the tty layer. The user is
1427  *      guaranteed that this function will not be re-entered or in progress
1428  *      when the ldisc is closed.
1429  *
1430  *      Locking: Caller holds tty->termios_mutex
1431  */
1432
1433 static void n_tty_set_termios(struct tty_struct *tty, struct ktermios *old)
1434 {
1435         int canon_change = 1;
1436         BUG_ON(!tty);
1437
1438         if (old)
1439                 canon_change = (old->c_lflag ^ tty->termios->c_lflag) & ICANON;
1440         if (canon_change) {
1441                 memset(&tty->read_flags, 0, sizeof tty->read_flags);
1442                 tty->canon_head = tty->read_tail;
1443                 tty->canon_data = 0;
1444                 tty->erasing = 0;
1445         }
1446
1447         if (canon_change && !L_ICANON(tty) && tty->read_cnt)
1448                 wake_up_interruptible(&tty->read_wait);
1449
1450         tty->icanon = (L_ICANON(tty) != 0);
1451         if (test_bit(TTY_HW_COOK_IN, &tty->flags)) {
1452                 tty->raw = 1;
1453                 tty->real_raw = 1;
1454                 return;
1455         }
1456         if (I_ISTRIP(tty) || I_IUCLC(tty) || I_IGNCR(tty) ||
1457             I_ICRNL(tty) || I_INLCR(tty) || L_ICANON(tty) ||
1458             I_IXON(tty) || L_ISIG(tty) || L_ECHO(tty) ||
1459             I_PARMRK(tty)) {
1460                 memset(tty->process_char_map, 0, 256/8);
1461
1462                 if (I_IGNCR(tty) || I_ICRNL(tty))
1463                         set_bit('\r', tty->process_char_map);
1464                 if (I_INLCR(tty))
1465                         set_bit('\n', tty->process_char_map);
1466
1467                 if (L_ICANON(tty)) {
1468                         set_bit(ERASE_CHAR(tty), tty->process_char_map);
1469                         set_bit(KILL_CHAR(tty), tty->process_char_map);
1470                         set_bit(EOF_CHAR(tty), tty->process_char_map);
1471                         set_bit('\n', tty->process_char_map);
1472                         set_bit(EOL_CHAR(tty), tty->process_char_map);
1473                         if (L_IEXTEN(tty)) {
1474                                 set_bit(WERASE_CHAR(tty),
1475                                         tty->process_char_map);
1476                                 set_bit(LNEXT_CHAR(tty),
1477                                         tty->process_char_map);
1478                                 set_bit(EOL2_CHAR(tty),
1479                                         tty->process_char_map);
1480                                 if (L_ECHO(tty))
1481                                         set_bit(REPRINT_CHAR(tty),
1482                                                 tty->process_char_map);
1483                         }
1484                 }
1485                 if (I_IXON(tty)) {
1486                         set_bit(START_CHAR(tty), tty->process_char_map);
1487                         set_bit(STOP_CHAR(tty), tty->process_char_map);
1488                 }
1489                 if (L_ISIG(tty)) {
1490                         set_bit(INTR_CHAR(tty), tty->process_char_map);
1491                         set_bit(QUIT_CHAR(tty), tty->process_char_map);
1492                         set_bit(SUSP_CHAR(tty), tty->process_char_map);
1493                 }
1494                 clear_bit(__DISABLED_CHAR, tty->process_char_map);
1495                 tty->raw = 0;
1496                 tty->real_raw = 0;
1497         } else {
1498                 tty->raw = 1;
1499                 if ((I_IGNBRK(tty) || (!I_BRKINT(tty) && !I_PARMRK(tty))) &&
1500                     (I_IGNPAR(tty) || !I_INPCK(tty)) &&
1501                     (tty->driver->flags & TTY_DRIVER_REAL_RAW))
1502                         tty->real_raw = 1;
1503                 else
1504                         tty->real_raw = 0;
1505         }
1506         /* The termios change make the tty ready for I/O */
1507         wake_up_interruptible(&tty->write_wait);
1508         wake_up_interruptible(&tty->read_wait);
1509 }
1510
1511 /**
1512  *      n_tty_close             -       close the ldisc for this tty
1513  *      @tty: device
1514  *
1515  *      Called from the terminal layer when this line discipline is
1516  *      being shut down, either because of a close or becsuse of a
1517  *      discipline change. The function will not be called while other
1518  *      ldisc methods are in progress.
1519  */
1520
1521 static void n_tty_close(struct tty_struct *tty)
1522 {
1523         n_tty_flush_buffer(tty);
1524         if (tty->read_buf) {
1525                 kfree(tty->read_buf);
1526                 tty->read_buf = NULL;
1527         }
1528         if (tty->echo_buf) {
1529                 kfree(tty->echo_buf);
1530                 tty->echo_buf = NULL;
1531         }
1532 }
1533
1534 /**
1535  *      n_tty_open              -       open an ldisc
1536  *      @tty: terminal to open
1537  *
1538  *      Called when this line discipline is being attached to the
1539  *      terminal device. Can sleep. Called serialized so that no
1540  *      other events will occur in parallel. No further open will occur
1541  *      until a close.
1542  */
1543
1544 static int n_tty_open(struct tty_struct *tty)
1545 {
1546         if (!tty)
1547                 return -EINVAL;
1548
1549         /* These are ugly. Currently a malloc failure here can panic */
1550         if (!tty->read_buf) {
1551                 tty->read_buf = kzalloc(N_TTY_BUF_SIZE, GFP_KERNEL);
1552                 if (!tty->read_buf)
1553                         return -ENOMEM;
1554         }
1555         if (!tty->echo_buf) {
1556                 tty->echo_buf = kzalloc(N_TTY_BUF_SIZE, GFP_KERNEL);
1557
1558                 if (!tty->echo_buf)
1559                         return -ENOMEM;
1560         }
1561         reset_buffer_flags(tty);
1562         tty->column = 0;
1563         n_tty_set_termios(tty, NULL);
1564         tty->minimum_to_wake = 1;
1565         tty->closing = 0;
1566         return 0;
1567 }
1568
1569 static inline int input_available_p(struct tty_struct *tty, int amt)
1570 {
1571         tty_flush_to_ldisc(tty);
1572         if (tty->icanon && !L_EXTPROC(tty)) {
1573                 if (tty->canon_data)
1574                         return 1;
1575         } else if (tty->read_cnt >= (amt ? amt : 1))
1576                 return 1;
1577
1578         return 0;
1579 }
1580
1581 /**
1582  *      copy_from_read_buf      -       copy read data directly
1583  *      @tty: terminal device
1584  *      @b: user data
1585  *      @nr: size of data
1586  *
1587  *      Helper function to speed up n_tty_read.  It is only called when
1588  *      ICANON is off; it copies characters straight from the tty queue to
1589  *      user space directly.  It can be profitably called twice; once to
1590  *      drain the space from the tail pointer to the (physical) end of the
1591  *      buffer, and once to drain the space from the (physical) beginning of
1592  *      the buffer to head pointer.
1593  *
1594  *      Called under the tty->atomic_read_lock sem
1595  *
1596  */
1597
1598 static int copy_from_read_buf(struct tty_struct *tty,
1599                                       unsigned char __user **b,
1600                                       size_t *nr)
1601
1602 {
1603         int retval;
1604         size_t n;
1605         unsigned long flags;
1606
1607         retval = 0;
1608         spin_lock_irqsave(&tty->read_lock, flags);
1609         n = min(tty->read_cnt, N_TTY_BUF_SIZE - tty->read_tail);
1610         n = min(*nr, n);
1611         spin_unlock_irqrestore(&tty->read_lock, flags);
1612         if (n) {
1613                 retval = copy_to_user(*b, &tty->read_buf[tty->read_tail], n);
1614                 n -= retval;
1615                 tty_audit_add_data(tty, &tty->read_buf[tty->read_tail], n);
1616                 spin_lock_irqsave(&tty->read_lock, flags);
1617                 tty->read_tail = (tty->read_tail + n) & (N_TTY_BUF_SIZE-1);
1618                 tty->read_cnt -= n;
1619                 /* Turn single EOF into zero-length read */
1620                 if (L_EXTPROC(tty) && tty->icanon && n == 1) {
1621                         if (!tty->read_cnt && (*b)[n-1] == EOF_CHAR(tty))
1622                                 n--;
1623                 }
1624                 spin_unlock_irqrestore(&tty->read_lock, flags);
1625                 *b += n;
1626                 *nr -= n;
1627         }
1628         return retval;
1629 }
1630
1631 extern ssize_t redirected_tty_write(struct file *, const char __user *,
1632                                                         size_t, loff_t *);
1633
1634 /**
1635  *      job_control             -       check job control
1636  *      @tty: tty
1637  *      @file: file handle
1638  *
1639  *      Perform job control management checks on this file/tty descriptor
1640  *      and if appropriate send any needed signals and return a negative
1641  *      error code if action should be taken.
1642  *
1643  *      FIXME:
1644  *      Locking: None - redirected write test is safe, testing
1645  *      current->signal should possibly lock current->sighand
1646  *      pgrp locking ?
1647  */
1648
1649 static int job_control(struct tty_struct *tty, struct file *file)
1650 {
1651         /* Job control check -- must be done at start and after
1652            every sleep (POSIX.1 7.1.1.4). */
1653         /* NOTE: not yet done after every sleep pending a thorough
1654            check of the logic of this change. -- jlc */
1655         /* don't stop on /dev/console */
1656         if (file->f_op->write != redirected_tty_write &&
1657             current->signal->tty == tty) {
1658                 if (!tty->pgrp)
1659                         printk(KERN_ERR "n_tty_read: no tty->pgrp!\n");
1660                 else if (task_pgrp(current) != tty->pgrp) {
1661                         if (is_ignored(SIGTTIN) ||
1662                             is_current_pgrp_orphaned())
1663                                 return -EIO;
1664                         kill_pgrp(task_pgrp(current), SIGTTIN, 1);
1665                         set_thread_flag(TIF_SIGPENDING);
1666                         return -ERESTARTSYS;
1667                 }
1668         }
1669         return 0;
1670 }
1671
1672
1673 /**
1674  *      n_tty_read              -       read function for tty
1675  *      @tty: tty device
1676  *      @file: file object
1677  *      @buf: userspace buffer pointer
1678  *      @nr: size of I/O
1679  *
1680  *      Perform reads for the line discipline. We are guaranteed that the
1681  *      line discipline will not be closed under us but we may get multiple
1682  *      parallel readers and must handle this ourselves. We may also get
1683  *      a hangup. Always called in user context, may sleep.
1684  *
1685  *      This code must be sure never to sleep through a hangup.
1686  */
1687
1688 static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
1689                          unsigned char __user *buf, size_t nr)
1690 {
1691         unsigned char __user *b = buf;
1692         DECLARE_WAITQUEUE(wait, current);
1693         int c;
1694         int minimum, time;
1695         ssize_t retval = 0;
1696         ssize_t size;
1697         long timeout;
1698         unsigned long flags;
1699         int packet;
1700
1701 do_it_again:
1702
1703         BUG_ON(!tty->read_buf);
1704
1705         c = job_control(tty, file);
1706         if (c < 0)
1707                 return c;
1708
1709         minimum = time = 0;
1710         timeout = MAX_SCHEDULE_TIMEOUT;
1711         if (!tty->icanon) {
1712                 time = (HZ / 10) * TIME_CHAR(tty);
1713                 minimum = MIN_CHAR(tty);
1714                 if (minimum) {
1715                         if (time)
1716                                 tty->minimum_to_wake = 1;
1717                         else if (!waitqueue_active(&tty->read_wait) ||
1718                                  (tty->minimum_to_wake > minimum))
1719                                 tty->minimum_to_wake = minimum;
1720                 } else {
1721                         timeout = 0;
1722                         if (time) {
1723                                 timeout = time;
1724                                 time = 0;
1725                         }
1726                         tty->minimum_to_wake = minimum = 1;
1727                 }
1728         }
1729
1730         /*
1731          *      Internal serialization of reads.
1732          */
1733         if (file->f_flags & O_NONBLOCK) {
1734                 if (!mutex_trylock(&tty->atomic_read_lock))
1735                         return -EAGAIN;
1736         } else {
1737                 if (mutex_lock_interruptible(&tty->atomic_read_lock))
1738                         return -ERESTARTSYS;
1739         }
1740         packet = tty->packet;
1741
1742         add_wait_queue(&tty->read_wait, &wait);
1743         while (nr) {
1744                 /* First test for status change. */
1745                 if (packet && tty->link->ctrl_status) {
1746                         unsigned char cs;
1747                         if (b != buf)
1748                                 break;
1749                         spin_lock_irqsave(&tty->link->ctrl_lock, flags);
1750                         cs = tty->link->ctrl_status;
1751                         tty->link->ctrl_status = 0;
1752                         spin_unlock_irqrestore(&tty->link->ctrl_lock, flags);
1753                         if (tty_put_user(tty, cs, b++)) {
1754                                 retval = -EFAULT;
1755                                 b--;
1756                                 break;
1757                         }
1758                         nr--;
1759                         break;
1760                 }
1761                 /* This statement must be first before checking for input
1762                    so that any interrupt will set the state back to
1763                    TASK_RUNNING. */
1764                 set_current_state(TASK_INTERRUPTIBLE);
1765
1766                 if (((minimum - (b - buf)) < tty->minimum_to_wake) &&
1767                     ((minimum - (b - buf)) >= 1))
1768                         tty->minimum_to_wake = (minimum - (b - buf));
1769
1770                 if (!input_available_p(tty, 0)) {
1771                         if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
1772                                 retval = -EIO;
1773                                 break;
1774                         }
1775                         if (tty_hung_up_p(file))
1776                                 break;
1777                         if (!timeout)
1778                                 break;
1779                         if (file->f_flags & O_NONBLOCK) {
1780                                 retval = -EAGAIN;
1781                                 break;
1782                         }
1783                         if (signal_pending(current)) {
1784                                 retval = -ERESTARTSYS;
1785                                 break;
1786                         }
1787                         timeout = schedule_timeout(timeout);
1788                         continue;
1789                 }
1790                 __set_current_state(TASK_RUNNING);
1791
1792                 /* Deal with packet mode. */
1793                 if (packet && b == buf) {
1794                         if (tty_put_user(tty, TIOCPKT_DATA, b++)) {
1795                                 retval = -EFAULT;
1796                                 b--;
1797                                 break;
1798                         }
1799                         nr--;
1800                 }
1801
1802                 if (tty->icanon && !L_EXTPROC(tty)) {
1803                         /* N.B. avoid overrun if nr == 0 */
1804                         while (nr && tty->read_cnt) {
1805                                 int eol;
1806
1807                                 eol = test_and_clear_bit(tty->read_tail,
1808                                                 tty->read_flags);
1809                                 c = tty->read_buf[tty->read_tail];
1810                                 spin_lock_irqsave(&tty->read_lock, flags);
1811                                 tty->read_tail = ((tty->read_tail+1) &
1812                                                   (N_TTY_BUF_SIZE-1));
1813                                 tty->read_cnt--;
1814                                 if (eol) {
1815                                         /* this test should be redundant:
1816                                          * we shouldn't be reading data if
1817                                          * canon_data is 0
1818                                          */
1819                                         if (--tty->canon_data < 0)
1820                                                 tty->canon_data = 0;
1821                                 }
1822                                 spin_unlock_irqrestore(&tty->read_lock, flags);
1823
1824                                 if (!eol || (c != __DISABLED_CHAR)) {
1825                                         if (tty_put_user(tty, c, b++)) {
1826                                                 retval = -EFAULT;
1827                                                 b--;
1828                                                 break;
1829                                         }
1830                                         nr--;
1831                                 }
1832                                 if (eol) {
1833                                         tty_audit_push(tty);
1834                                         break;
1835                                 }
1836                         }
1837                         if (retval)
1838                                 break;
1839                 } else {
1840                         int uncopied;
1841                         /* The copy function takes the read lock and handles
1842                            locking internally for this case */
1843                         uncopied = copy_from_read_buf(tty, &b, &nr);
1844                         uncopied += copy_from_read_buf(tty, &b, &nr);
1845                         if (uncopied) {
1846                                 retval = -EFAULT;
1847                                 break;
1848                         }
1849                 }
1850
1851                 /* If there is enough space in the read buffer now, let the
1852                  * low-level driver know. We use n_tty_chars_in_buffer() to
1853                  * check the buffer, as it now knows about canonical mode.
1854                  * Otherwise, if the driver is throttled and the line is
1855                  * longer than TTY_THRESHOLD_UNTHROTTLE in canonical mode,
1856                  * we won't get any more characters.
1857                  */
1858                 if (n_tty_chars_in_buffer(tty) <= TTY_THRESHOLD_UNTHROTTLE)
1859                         check_unthrottle(tty);
1860
1861                 if (b - buf >= minimum)
1862                         break;
1863                 if (time)
1864                         timeout = time;
1865         }
1866         mutex_unlock(&tty->atomic_read_lock);
1867         remove_wait_queue(&tty->read_wait, &wait);
1868
1869         if (!waitqueue_active(&tty->read_wait))
1870                 tty->minimum_to_wake = minimum;
1871
1872         __set_current_state(TASK_RUNNING);
1873         size = b - buf;
1874         if (size) {
1875                 retval = size;
1876                 if (nr)
1877                         clear_bit(TTY_PUSH, &tty->flags);
1878         } else if (test_and_clear_bit(TTY_PUSH, &tty->flags))
1879                  goto do_it_again;
1880
1881         return retval;
1882 }
1883
1884 /**
1885  *      n_tty_write             -       write function for tty
1886  *      @tty: tty device
1887  *      @file: file object
1888  *      @buf: userspace buffer pointer
1889  *      @nr: size of I/O
1890  *
1891  *      Write function of the terminal device.  This is serialized with
1892  *      respect to other write callers but not to termios changes, reads
1893  *      and other such events.  Since the receive code will echo characters,
1894  *      thus calling driver write methods, the output_lock is used in
1895  *      the output processing functions called here as well as in the
1896  *      echo processing function to protect the column state and space
1897  *      left in the buffer.
1898  *
1899  *      This code must be sure never to sleep through a hangup.
1900  *
1901  *      Locking: output_lock to protect column state and space left
1902  *               (note that the process_output*() functions take this
1903  *                lock themselves)
1904  */
1905
1906 static ssize_t n_tty_write(struct tty_struct *tty, struct file *file,
1907                            const unsigned char *buf, size_t nr)
1908 {
1909         const unsigned char *b = buf;
1910         DECLARE_WAITQUEUE(wait, current);
1911         int c;
1912         ssize_t retval = 0;
1913
1914         /* Job control check -- must be done at start (POSIX.1 7.1.1.4). */
1915         if (L_TOSTOP(tty) && file->f_op->write != redirected_tty_write) {
1916                 retval = tty_check_change(tty);
1917                 if (retval)
1918                         return retval;
1919         }
1920
1921         /* Write out any echoed characters that are still pending */
1922         process_echoes(tty);
1923
1924         add_wait_queue(&tty->write_wait, &wait);
1925         while (1) {
1926                 set_current_state(TASK_INTERRUPTIBLE);
1927                 if (signal_pending(current)) {
1928                         retval = -ERESTARTSYS;
1929                         break;
1930                 }
1931                 if (tty_hung_up_p(file) || (tty->link && !tty->link->count)) {
1932                         retval = -EIO;
1933                         break;
1934                 }
1935                 if (O_OPOST(tty) && !(test_bit(TTY_HW_COOK_OUT, &tty->flags))) {
1936                         while (nr > 0) {
1937                                 ssize_t num = process_output_block(tty, b, nr);
1938                                 if (num < 0) {
1939                                         if (num == -EAGAIN)
1940                                                 break;
1941                                         retval = num;
1942                                         goto break_out;
1943                                 }
1944                                 b += num;
1945                                 nr -= num;
1946                                 if (nr == 0)
1947                                         break;
1948                                 c = *b;
1949                                 if (process_output(c, tty) < 0)
1950                                         break;
1951                                 b++; nr--;
1952                         }
1953                         if (tty->ops->flush_chars)
1954                                 tty->ops->flush_chars(tty);
1955                 } else {
1956                         while (nr > 0) {
1957                                 c = tty->ops->write(tty, b, nr);
1958                                 if (c < 0) {
1959                                         retval = c;
1960                                         goto break_out;
1961                                 }
1962                                 if (!c)
1963                                         break;
1964                                 b += c;
1965                                 nr -= c;
1966                         }
1967                 }
1968                 if (!nr)
1969                         break;
1970                 if (file->f_flags & O_NONBLOCK) {
1971                         retval = -EAGAIN;
1972                         break;
1973                 }
1974                 schedule();
1975         }
1976 break_out:
1977         __set_current_state(TASK_RUNNING);
1978         remove_wait_queue(&tty->write_wait, &wait);
1979         if (b - buf != nr && tty->fasync)
1980                 set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
1981         return (b - buf) ? b - buf : retval;
1982 }
1983
1984 /**
1985  *      n_tty_poll              -       poll method for N_TTY
1986  *      @tty: terminal device
1987  *      @file: file accessing it
1988  *      @wait: poll table
1989  *
1990  *      Called when the line discipline is asked to poll() for data or
1991  *      for special events. This code is not serialized with respect to
1992  *      other events save open/close.
1993  *
1994  *      This code must be sure never to sleep through a hangup.
1995  *      Called without the kernel lock held - fine
1996  */
1997
1998 static unsigned int n_tty_poll(struct tty_struct *tty, struct file *file,
1999                                                         poll_table *wait)
2000 {
2001         unsigned int mask = 0;
2002
2003         poll_wait(file, &tty->read_wait, wait);
2004         poll_wait(file, &tty->write_wait, wait);
2005         if (input_available_p(tty, TIME_CHAR(tty) ? 0 : MIN_CHAR(tty)))
2006                 mask |= POLLIN | POLLRDNORM;
2007         if (tty->packet && tty->link->ctrl_status)
2008                 mask |= POLLPRI | POLLIN | POLLRDNORM;
2009         if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
2010                 mask |= POLLHUP;
2011         if (tty_hung_up_p(file))
2012                 mask |= POLLHUP;
2013         if (!(mask & (POLLHUP | POLLIN | POLLRDNORM))) {
2014                 if (MIN_CHAR(tty) && !TIME_CHAR(tty))
2015                         tty->minimum_to_wake = MIN_CHAR(tty);
2016                 else
2017                         tty->minimum_to_wake = 1;
2018         }
2019         if (tty->ops->write && !tty_is_writelocked(tty) &&
2020                         tty_chars_in_buffer(tty) < WAKEUP_CHARS &&
2021                         tty_write_room(tty) > 0)
2022                 mask |= POLLOUT | POLLWRNORM;
2023         return mask;
2024 }
2025
2026 static unsigned long inq_canon(struct tty_struct *tty)
2027 {
2028         int nr, head, tail;
2029
2030         if (!tty->canon_data)
2031                 return 0;
2032         head = tty->canon_head;
2033         tail = tty->read_tail;
2034         nr = (head - tail) & (N_TTY_BUF_SIZE-1);
2035         /* Skip EOF-chars.. */
2036         while (head != tail) {
2037                 if (test_bit(tail, tty->read_flags) &&
2038                     tty->read_buf[tail] == __DISABLED_CHAR)
2039                         nr--;
2040                 tail = (tail+1) & (N_TTY_BUF_SIZE-1);
2041         }
2042         return nr;
2043 }
2044
2045 static int n_tty_ioctl(struct tty_struct *tty, struct file *file,
2046                        unsigned int cmd, unsigned long arg)
2047 {
2048         int retval;
2049
2050         switch (cmd) {
2051         case TIOCOUTQ:
2052                 return put_user(tty_chars_in_buffer(tty), (int __user *) arg);
2053         case TIOCINQ:
2054                 /* FIXME: Locking */
2055                 retval = tty->read_cnt;
2056                 if (L_ICANON(tty))
2057                         retval = inq_canon(tty);
2058                 return put_user(retval, (unsigned int __user *) arg);
2059         default:
2060                 return n_tty_ioctl_helper(tty, file, cmd, arg);
2061         }
2062 }
2063
2064 struct tty_ldisc_ops tty_ldisc_N_TTY = {
2065         .magic           = TTY_LDISC_MAGIC,
2066         .name            = "n_tty",
2067         .open            = n_tty_open,
2068         .close           = n_tty_close,
2069         .flush_buffer    = n_tty_flush_buffer,
2070         .chars_in_buffer = n_tty_chars_in_buffer,
2071         .read            = n_tty_read,
2072         .write           = n_tty_write,
2073         .ioctl           = n_tty_ioctl,
2074         .set_termios     = n_tty_set_termios,
2075         .poll            = n_tty_poll,
2076         .receive_buf     = n_tty_receive_buf,
2077         .write_wakeup    = n_tty_write_wakeup
2078 };
2079
2080 /**
2081  *      n_tty_inherit_ops       -       inherit N_TTY methods
2082  *      @ops: struct tty_ldisc_ops where to save N_TTY methods
2083  *
2084  *      Used by a generic struct tty_ldisc_ops to easily inherit N_TTY
2085  *      methods.
2086  */
2087
2088 void n_tty_inherit_ops(struct tty_ldisc_ops *ops)
2089 {
2090         *ops = tty_ldisc_N_TTY;
2091         ops->owner = NULL;
2092         ops->refcount = ops->flags = 0;
2093 }
2094 EXPORT_SYMBOL_GPL(n_tty_inherit_ops);