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 /**
  85  *      n_tty_set__room -       receive space
  86  *      @tty: terminal
  87  *
  88  *      Called by the driver to find out how much data it is
  89  *      permitted to feed to the line discipline without any being lost
  90  *      and thus to manage flow control. Not serialized. Answers for the
  91  *      "instant".
  92  */
  93
  94 static void n_tty_set_room(struct tty_struct *tty)
  95 {
  96         /* tty->read_cnt is not read locked ? */
  97         int     left = N_TTY_BUF_SIZE - tty->read_cnt - 1;
  98         int old_left;
  99
 100         /*
 101          * If we are doing input canonicalization, and there are no
 102          * pending newlines, let characters through without limit, so
 103          * that erase characters will be handled.  Other excess
 104          * characters will be beeped.
 105          */
 106         if (left <= 0)
 107                 left = tty->icanon && !tty->canon_data;
 108         old_left = tty->receive_room;
 109         tty->receive_room = left;
 110
 111         /* Did this open up the receive buffer? We may need to flip */
 112         if (left && !old_left)
 113                 schedule_work(&tty->buf.work);
 114 }
 115
 116 static void put_tty_queue_nolock(unsigned char c, struct tty_struct *tty)
 117 {
 118         if (tty->read_cnt < N_TTY_BUF_SIZE) {
 119                 tty->read_buf[tty->read_head] = c;
 120                 tty->read_head = (tty->read_head + 1) & (N_TTY_BUF_SIZE-1);
 121                 tty->read_cnt++;
 122         }
 123 }
 124
 125 /**
 126  *      put_tty_queue           -       add character to tty
 127  *      @c: character
 128  *      @tty: tty device
 129  *
 130  *      Add a character to the tty read_buf queue. This is done under the
 131  *      read_lock to serialize character addition and also to protect us
 132  *      against parallel reads or flushes
 133  */
 134
 135 static void put_tty_queue(unsigned char c, struct tty_struct *tty)
 136 {
 137         unsigned long flags;
 138         /*
 139          *      The problem of stomping on the buffers ends here.
 140          *      Why didn't anyone see this one coming? --AJK
 141         */
 142         spin_lock_irqsave(&tty->read_lock, flags);
 143         put_tty_queue_nolock(c, tty);
 144         spin_unlock_irqrestore(&tty->read_lock, flags);
 145 }
 146
 147 /**
 148  *      check_unthrottle        -       allow new receive data
 149  *      @tty; tty device
 150  *
 151  *      Check whether to call the driver unthrottle functions
 152  *
 153  *      Can sleep, may be called under the atomic_read_lock mutex but
 154  *      this is not guaranteed.
 155  */
 156 static void check_unthrottle(struct tty_struct *tty)
 157 {
 158         if (tty->count)
 159                 tty_unthrottle(tty);
 160 }
 161
 162 /**
 163  *      reset_buffer_flags      -       reset buffer state
 164  *      @tty: terminal to reset
 165  *
 166  *      Reset the read buffer counters, clear the flags,
 167  *      and make sure the driver is unthrottled. Called
 168  *      from n_tty_open() and n_tty_flush_buffer().
 169  *
 170  *      Locking: tty_read_lock for read fields.
 171  */
 172
 173 static void reset_buffer_flags(struct tty_struct *tty)
 174 {
 175         unsigned long flags;
 176
 177         spin_lock_irqsave(&tty->read_lock, flags);
 178         tty->read_head = tty->read_tail = tty->read_cnt = 0;
 179         spin_unlock_irqrestore(&tty->read_lock, flags);
 180
 181         mutex_lock(&tty->echo_lock);
 182         tty->echo_pos = tty->echo_cnt = tty->echo_overrun = 0;
 183         mutex_unlock(&tty->echo_lock);
 184
 185         tty->canon_head = tty->canon_data = tty->erasing = 0;
 186         memset(&tty->read_flags, 0, sizeof tty->read_flags);
 187         n_tty_set_room(tty);
 188 }
 189
 190 /**
 191  *      n_tty_flush_buffer      -       clean input queue
 192  *      @tty:   terminal device
 193  *
 194  *      Flush the input buffer. Called when the line discipline is
 195  *      being closed, when the tty layer wants the buffer flushed (eg
 196  *      at hangup) or when the N_TTY line discipline internally has to
 197  *      clean the pending queue (for example some signals).
 198  *
 199  *      Locking: ctrl_lock, read_lock.
 200  */
 201
 202 static void n_tty_flush_buffer(struct tty_struct *tty)
 203 {
 204         unsigned long flags;
 205         /* clear everything and unthrottle the driver */
 206         reset_buffer_flags(tty);
 207
 208         if (!tty->link)
 209                 return;
 210
 211         spin_lock_irqsave(&tty->ctrl_lock, flags);
 212         if (tty->link->packet) {
 213                 tty->ctrl_status |= TIOCPKT_FLUSHREAD;
 214                 wake_up_interruptible(&tty->link->read_wait);
 215         }
 216         spin_unlock_irqrestore(&tty->ctrl_lock, flags);
 217 }
 218
 219 /**
 220  *      n_tty_chars_in_buffer   -       report available bytes
 221  *      @tty: tty device
 222  *
 223  *      Report the number of characters buffered to be delivered to user
 224  *      at this instant in time.
 225  *
 226  *      Locking: read_lock
 227  */
 228
 229 static ssize_t n_tty_chars_in_buffer(struct tty_struct *tty)
 230 {
 231         unsigned long flags;
 232         ssize_t n = 0;
 233
 234         spin_lock_irqsave(&tty->read_lock, flags);
 235         if (!tty->icanon) {
 236                 n = tty->read_cnt;
 237         } else if (tty->canon_data) {
 238                 n = (tty->canon_head > tty->read_tail) ?
 239                         tty->canon_head - tty->read_tail :
 240                         tty->canon_head + (N_TTY_BUF_SIZE - tty->read_tail);
 241         }
 242         spin_unlock_irqrestore(&tty->read_lock, flags);
 243         return n;
 244 }
 245
 246 /**
 247  *      is_utf8_continuation    -       utf8 multibyte check
 248  *      @c: byte to check
 249  *
 250  *      Returns true if the utf8 character 'c' is a multibyte continuation
 251  *      character. We use this to correctly compute the on screen size
 252  *      of the character when printing
 253  */
 254
 255 static inline int is_utf8_continuation(unsigned char c)
 256 {
 257         return (c & 0xc0) == 0x80;
 258 }
 259
 260 /**
 261  *      is_continuation         -       multibyte check
 262  *      @c: byte to check
 263  *
 264  *      Returns true if the utf8 character 'c' is a multibyte continuation
 265  *      character and the terminal is in unicode mode.
 266  */
 267
 268 static inline int is_continuation(unsigned char c, struct tty_struct *tty)
 269 {
 270         return I_IUTF8(tty) && is_utf8_continuation(c);
 271 }
 272
 273 /**
 274  *      do_output_char                  -       output one character
 275  *      @c: character (or partial unicode symbol)
 276  *      @tty: terminal device
 277  *      @space: space available in tty driver write buffer
 278  *
 279  *      This is a helper function that handles one output character
 280  *      (including special characters like TAB, CR, LF, etc.),
 281  *      doing OPOST processing and putting the results in the
 282  *      tty driver's write buffer.
 283  *
 284  *      Note that Linux currently ignores TABDLY, CRDLY, VTDLY, FFDLY
 285  *      and NLDLY.  They simply aren't relevant in the world today.
 286  *      If you ever need them, add them here.
 287  *
 288  *      Returns the number of bytes of buffer space used or -1 if
 289  *      no space left.
 290  *
 291  *      Locking: should be called under the output_lock to protect
 292  *               the column state and space left in the buffer
 293  */
 294
 295 static int do_output_char(unsigned char c, struct tty_struct *tty, int space)
 296 {
 297         int     spaces;
 298
 299         if (!space)
 300                 return -1;
 301
 302         switch (c) {
 303         case '\n':
 304                 if (O_ONLRET(tty))
 305                         tty->column = 0;
 306                 if (O_ONLCR(tty)) {
 307                         if (space < 2)
 308                                 return -1;
 309                         tty->canon_column = tty->column = 0;
 310                         tty->ops->write(tty, "\r\n", 2);
 311                         return 2;
 312                 }
 313                 tty->canon_column = tty->column;
 314                 break;
 315         case '\r':
 316                 if (O_ONOCR(tty) && tty->column == 0)
 317                         return 0;
 318                 if (O_OCRNL(tty)) {
 319                         c = '\n';
 320                         if (O_ONLRET(tty))
 321                                 tty->canon_column = tty->column = 0;
 322                         break;
 323                 }
 324                 tty->canon_column = tty->column = 0;
 325                 break;
 326         case '\t':
 327                 spaces = 8 - (tty->column & 7);
 328                 if (O_TABDLY(tty) == XTABS) {
 329                         if (space < spaces)
 330                                 return -1;
 331                         tty->column += spaces;
 332                         tty->ops->write(tty, "        ", spaces);
 333                         return spaces;
 334                 }
 335                 tty->column += spaces;
 336                 break;
 337         case '\b':
 338                 if (tty->column > 0)
 339                         tty->column--;
 340                 break;
 341         default:
 342                 if (!iscntrl(c)) {
 343                         if (O_OLCUC(tty))
 344                                 c = toupper(c);
 345                         if (!is_continuation(c, tty))
 346                                 tty->column++;
 347                 }
 348                 break;
 349         }
 350
 351         tty_put_char(tty, c);
 352         return 1;
 353 }
 354
 355 /**
 356  *      process_output                  -       output post processor
 357  *      @c: character (or partial unicode symbol)
 358  *      @tty: terminal device
 359  *
 360  *      Output one character with OPOST processing.
 361  *      Returns -1 when the output device is full and the character
 362  *      must be retried.
 363  *
 364  *      Locking: output_lock to protect column state and space left
 365  *               (also, this is called from n_tty_write under the
 366  *                tty layer write lock)
 367  */
 368
 369 static int process_output(unsigned char c, struct tty_struct *tty)
 370 {
 371         int     space, retval;
 372
 373         mutex_lock(&tty->output_lock);
 374
 375         space = tty_write_room(tty);
 376         retval = do_output_char(c, tty, space);
 377
 378         mutex_unlock(&tty->output_lock);
 379         if (retval < 0)
 380                 return -1;
 381         else
 382                 return 0;
 383 }
 384
 385 /**
 386  *      process_output_block            -       block post processor
 387  *      @tty: terminal device
 388  *      @buf: character buffer
 389  *      @nr: number of bytes to output
 390  *
 391  *      Output a block of characters with OPOST processing.
 392  *      Returns the number of characters output.
 393  *
 394  *      This path is used to speed up block console writes, among other
 395  *      things when processing blocks of output data. It handles only
 396  *      the simple cases normally found and helps to generate blocks of
 397  *      symbols for the console driver and thus improve performance.
 398  *
 399  *      Locking: output_lock to protect column state and space left
 400  *               (also, this is called from n_tty_write under the
 401  *                tty layer write lock)
 402  */
 403
 404 static ssize_t process_output_block(struct tty_struct *tty,
 405                                     const unsigned char *buf, unsigned int nr)
 406 {
 407         int     space;
 408         int     i;
 409         const unsigned char *cp;
 410
 411         mutex_lock(&tty->output_lock);
 412
 413         space = tty_write_room(tty);
 414         if (!space) {
 415                 mutex_unlock(&tty->output_lock);
 416                 return 0;
 417         }
 418         if (nr > space)
 419                 nr = space;
 420
 421         for (i = 0, cp = buf; i < nr; i++, cp++) {
 422                 unsigned char c = *cp;
 423
 424                 switch (c) {
 425                 case '\n':
 426                         if (O_ONLRET(tty))
 427                                 tty->column = 0;
 428                         if (O_ONLCR(tty))
 429                                 goto break_out;
 430                         tty->canon_column = tty->column;
 431                         break;
 432                 case '\r':
 433                         if (O_ONOCR(tty) && tty->column == 0)
 434                                 goto break_out;
 435                         if (O_OCRNL(tty))
 436                                 goto break_out;
 437                         tty->canon_column = tty->column = 0;
 438                         break;
 439                 case '\t':
 440                         goto break_out;
 441                 case '\b':
 442                         if (tty->column > 0)
 443                                 tty->column--;
 444                         break;
 445                 default:
 446                         if (!iscntrl(c)) {
 447                                 if (O_OLCUC(tty))
 448                                         goto break_out;
 449                                 if (!is_continuation(c, tty))
 450                                         tty->column++;
 451                         }
 452                         break;
 453                 }
 454         }
 455 break_out:
 456         i = tty->ops->write(tty, buf, i);
 457
 458         mutex_unlock(&tty->output_lock);
 459         return i;
 460 }
 461
 462 /**
 463  *      process_echoes  -       write pending echo characters
 464  *      @tty: terminal device
 465  *
 466  *      Write previously buffered echo (and other ldisc-generated)
 467  *      characters to the tty.
 468  *
 469  *      Characters generated by the ldisc (including echoes) need to
 470  *      be buffered because the driver's write buffer can fill during
 471  *      heavy program output.  Echoing straight to the driver will
 472  *      often fail under these conditions, causing lost characters and
 473  *      resulting mismatches of ldisc state information.
 474  *
 475  *      Since the ldisc state must represent the characters actually sent
 476  *      to the driver at the time of the write, operations like certain
 477  *      changes in column state are also saved in the buffer and executed
 478  *      here.
 479  *
 480  *      A circular fifo buffer is used so that the most recent characters
 481  *      are prioritized.  Also, when control characters are echoed with a
 482  *      prefixed "^", the pair is treated atomically and thus not separated.
 483  *
 484  *      Locking: output_lock to protect column state and space left,
 485  *               echo_lock to protect the echo buffer
 486  */
 487
 488 static void process_echoes(struct tty_struct *tty)
 489 {
 490         int     space, nr;
 491         unsigned char c;
 492         unsigned char *cp, *buf_end;
 493
 494         if (!tty->echo_cnt)
 495                 return;
 496
 497         mutex_lock(&tty->output_lock);
 498         mutex_lock(&tty->echo_lock);
 499
 500         space = tty_write_room(tty);
 501
 502         buf_end = tty->echo_buf + N_TTY_BUF_SIZE;
 503         cp = tty->echo_buf + tty->echo_pos;
 504         nr = tty->echo_cnt;
 505         while (nr > 0) {
 506                 c = *cp;
 507                 if (c == ECHO_OP_START) {
 508                         unsigned char op;
 509                         unsigned char *opp;
 510                         int no_space_left = 0;
 511
 512                         /*
 513                          * If the buffer byte is the start of a multi-byte
 514                          * operation, get the next byte, which is either the
 515                          * op code or a control character value.
 516                          */
 517                         opp = cp + 1;
 518                         if (opp == buf_end)
 519                                 opp -= N_TTY_BUF_SIZE;
 520                         op = *opp;
 521
 522                         switch (op) {
 523                                 unsigned int num_chars, num_bs;
 524
 525                         case ECHO_OP_ERASE_TAB:
 526                                 if (++opp == buf_end)
 527                                         opp -= N_TTY_BUF_SIZE;
 528                                 num_chars = *opp;
 529
 530                                 /*
 531                                  * Determine how many columns to go back
 532                                  * in order to erase the tab.
 533                                  * This depends on the number of columns
 534                                  * used by other characters within the tab
 535                                  * area.  If this (modulo 8) count is from
 536                                  * the start of input rather than from a
 537                                  * previous tab, we offset by canon column.
 538                                  * Otherwise, tab spacing is normal.
 539                                  */
 540                                 if (!(num_chars & 0x80))
 541                                         num_chars += tty->canon_column;
 542                                 num_bs = 8 - (num_chars & 7);
 543
 544                                 if (num_bs > space) {
 545                                         no_space_left = 1;
 546                                         break;
 547                                 }
 548                                 space -= num_bs;
 549                                 while (num_bs--) {
 550                                         tty_put_char(tty, '\b');
 551                                         if (tty->column > 0)
 552                                                 tty->column--;
 553                                 }
 554                                 cp += 3;
 555                                 nr -= 3;
 556                                 break;
 557
 558                         case ECHO_OP_SET_CANON_COL:
 559                                 tty->canon_column = tty->column;
 560                                 cp += 2;
 561                                 nr -= 2;
 562                                 break;
 563
 564                         case ECHO_OP_MOVE_BACK_COL:
 565                                 if (tty->column > 0)
 566                                         tty->column--;
 567                                 cp += 2;
 568                                 nr -= 2;
 569                                 break;
 570
 571                         case ECHO_OP_START:
 572                                 /* This is an escaped echo op start code */
 573                                 if (!space) {
 574                                         no_space_left = 1;
 575                                         break;
 576                                 }
 577                                 tty_put_char(tty, ECHO_OP_START);
 578                                 tty->column++;
 579                                 space--;
 580                                 cp += 2;
 581                                 nr -= 2;
 582                                 break;
 583
 584                         default:
 585                                 /*
 586                                  * If the op is not a special byte code,
 587                                  * it is a ctrl char tagged to be echoed
 588                                  * as "^X" (where X is the letter
 589                                  * representing the control char).
 590                                  * Note that we must ensure there is
 591                                  * enough space for the whole ctrl pair.
 592                                  *
 593                                  */
 594                                 if (space < 2) {
 595                                         no_space_left = 1;
 596                                         break;
 597                                 }
 598                                 tty_put_char(tty, '^');
 599                                 tty_put_char(tty, op ^ 0100);
 600                                 tty->column += 2;
 601                                 space -= 2;
 602                                 cp += 2;
 603                                 nr -= 2;
 604                         }
 605
 606                         if (no_space_left)
 607                                 break;
 608                 } else {
 609                         if (O_OPOST(tty) &&
 610                             !(test_bit(TTY_HW_COOK_OUT, &tty->flags))) {
 611                                 int retval = do_output_char(c, tty, space);
 612                                 if (retval < 0)
 613                                         break;
 614                                 space -= retval;
 615                         } else {
 616                                 if (!space)
 617                                         break;
 618                                 tty_put_char(tty, c);
 619                                 space -= 1;
 620                         }
 621                         cp += 1;
 622                         nr -= 1;
 623                 }
 624
 625                 /* When end of circular buffer reached, wrap around */
 626                 if (cp >= buf_end)
 627                         cp -= N_TTY_BUF_SIZE;
 628         }
 629
 630         if (nr == 0) {
 631                 tty->echo_pos = 0;
 632                 tty->echo_cnt = 0;
 633                 tty->echo_overrun = 0;
 634         } else {
 635                 int num_processed = tty->echo_cnt - nr;
 636                 tty->echo_pos += num_processed;
 637                 tty->echo_pos &= N_TTY_BUF_SIZE - 1;
 638                 tty->echo_cnt = nr;
 639                 if (num_processed > 0)
 640                         tty->echo_overrun = 0;
 641         }
 642
 643         mutex_unlock(&tty->echo_lock);
 644         mutex_unlock(&tty->output_lock);
 645
 646         if (tty->ops->flush_chars)
 647                 tty->ops->flush_chars(tty);
 648 }
 649
 650 /**
 651  *      add_echo_byte   -       add a byte to the echo buffer
 652  *      @c: unicode byte to echo
 653  *      @tty: terminal device
 654  *
 655  *      Add a character or operation byte to the echo buffer.
 656  *
 657  *      Should be called under the echo lock to protect the echo buffer.
 658  */
 659
 660 static void add_echo_byte(unsigned char c, struct tty_struct *tty)
 661 {
 662         int     new_byte_pos;
 663
 664         if (tty->echo_cnt == N_TTY_BUF_SIZE) {
 665                 /* Circular buffer is already at capacity */
 666                 new_byte_pos = tty->echo_pos;
 667
 668                 /*
 669                  * Since the buffer start position needs to be advanced,
 670                  * be sure to step by a whole operation byte group.
 671                  */
 672                 if (tty->echo_buf[tty->echo_pos] == ECHO_OP_START) {
 673                         if (tty->echo_buf[(tty->echo_pos + 1) &
 674                                           (N_TTY_BUF_SIZE - 1)] ==
 675                                                 ECHO_OP_ERASE_TAB) {
 676                                 tty->echo_pos += 3;
 677                                 tty->echo_cnt -= 2;
 678                         } else {
 679                                 tty->echo_pos += 2;
 680                                 tty->echo_cnt -= 1;
 681                         }
 682                 } else {
 683                         tty->echo_pos++;
 684                 }
 685                 tty->echo_pos &= N_TTY_BUF_SIZE - 1;
 686
 687                 tty->echo_overrun = 1;
 688         } else {
 689                 new_byte_pos = tty->echo_pos + tty->echo_cnt;
 690                 new_byte_pos &= N_TTY_BUF_SIZE - 1;
 691                 tty->echo_cnt++;
 692         }
 693
 694         tty->echo_buf[new_byte_pos] = c;
 695 }
 696
 697 /**
 698  *      echo_move_back_col      -       add operation to move back a column
 699  *      @tty: terminal device
 700  *
 701  *      Add an operation to the echo buffer to move back one column.
 702  *
 703  *      Locking: echo_lock to protect the echo buffer
 704  */
 705
 706 static void echo_move_back_col(struct tty_struct *tty)
 707 {
 708         mutex_lock(&tty->echo_lock);
 709
 710         add_echo_byte(ECHO_OP_START, tty);
 711         add_echo_byte(ECHO_OP_MOVE_BACK_COL, tty);
 712
 713         mutex_unlock(&tty->echo_lock);
 714 }
 715
 716 /**
 717  *      echo_set_canon_col      -       add operation to set the canon column
 718  *      @tty: terminal device
 719  *
 720  *      Add an operation to the echo buffer to set the canon column
 721  *      to the current column.
 722  *
 723  *      Locking: echo_lock to protect the echo buffer
 724  */
 725
 726 static void echo_set_canon_col(struct tty_struct *tty)
 727 {
 728         mutex_lock(&tty->echo_lock);
 729
 730         add_echo_byte(ECHO_OP_START, tty);
 731         add_echo_byte(ECHO_OP_SET_CANON_COL, tty);
 732
 733         mutex_unlock(&tty->echo_lock);
 734 }
 735
 736 /**
 737  *      echo_erase_tab  -       add operation to erase a tab
 738  *      @num_chars: number of character columns already used
 739  *      @after_tab: true if num_chars starts after a previous tab
 740  *      @tty: terminal device
 741  *
 742  *      Add an operation to the echo buffer to erase a tab.
 743  *
 744  *      Called by the eraser function, which knows how many character
 745  *      columns have been used since either a previous tab or the start
 746  *      of input.  This information will be used later, along with
 747  *      canon column (if applicable), to go back the correct number
 748  *      of columns.
 749  *
 750  *      Locking: echo_lock to protect the echo buffer
 751  */
 752
 753 static void echo_erase_tab(unsigned int num_chars, int after_tab,
 754                            struct tty_struct *tty)
 755 {
 756         mutex_lock(&tty->echo_lock);
 757
 758         add_echo_byte(ECHO_OP_START, tty);
 759         add_echo_byte(ECHO_OP_ERASE_TAB, tty);
 760
 761         /* We only need to know this modulo 8 (tab spacing) */
 762         num_chars &= 7;
 763
 764         /* Set the high bit as a flag if num_chars is after a previous tab */
 765         if (after_tab)
 766                 num_chars |= 0x80;
 767
 768         add_echo_byte(num_chars, tty);
 769
 770         mutex_unlock(&tty->echo_lock);
 771 }
 772
 773 /**
 774  *      echo_char_raw   -       echo a character raw
 775  *      @c: unicode byte to echo
 776  *      @tty: terminal device
 777  *
 778  *      Echo user input back onto the screen. This must be called only when
 779  *      L_ECHO(tty) is true. Called from the driver receive_buf path.
 780  *
 781  *      This variant does not treat control characters specially.
 782  *
 783  *      Locking: echo_lock to protect the echo buffer
 784  */
 785
 786 static void echo_char_raw(unsigned char c, struct tty_struct *tty)
 787 {
 788         mutex_lock(&tty->echo_lock);
 789
 790         if (c == ECHO_OP_START) {
 791                 add_echo_byte(ECHO_OP_START, tty);
 792                 add_echo_byte(ECHO_OP_START, tty);
 793         } else {
 794                 add_echo_byte(c, tty);
 795         }
 796
 797         mutex_unlock(&tty->echo_lock);
 798 }
 799
 800 /**
 801  *      echo_char       -       echo a character
 802  *      @c: unicode byte to echo
 803  *      @tty: terminal device
 804  *
 805  *      Echo user input back onto the screen. This must be called only when
 806  *      L_ECHO(tty) is true. Called from the driver receive_buf path.
 807  *
 808  *      This variant tags control characters to be echoed as "^X"
 809  *      (where X is the letter representing the control char).
 810  *
 811  *      Locking: echo_lock to protect the echo buffer
 812  */
 813
 814 static void echo_char(unsigned char c, struct tty_struct *tty)
 815 {
 816         mutex_lock(&tty->echo_lock);
 817
 818         if (c == ECHO_OP_START) {
 819                 add_echo_byte(ECHO_OP_START, tty);
 820                 add_echo_byte(ECHO_OP_START, tty);
 821         } else {
 822                 if (L_ECHOCTL(tty) && iscntrl(c) && c != '\t')
 823                         add_echo_byte(ECHO_OP_START, tty);
 824                 add_echo_byte(c, tty);
 825         }
 826
 827         mutex_unlock(&tty->echo_lock);
 828 }
 829
 830 /**
 831  *      finish_erasing          -       complete erase
 832  *      @tty: tty doing the erase
 833  */
 834
 835 static inline void finish_erasing(struct tty_struct *tty)
 836 {
 837         if (tty->erasing) {
 838                 echo_char_raw('/', tty);
 839                 tty->erasing = 0;
 840         }
 841 }
 842
 843 /**
 844  *      eraser          -       handle erase function
 845  *      @c: character input
 846  *      @tty: terminal device
 847  *
 848  *      Perform erase and necessary output when an erase character is
 849  *      present in the stream from the driver layer. Handles the complexities
 850  *      of UTF-8 multibyte symbols.
 851  *
 852  *      Locking: read_lock for tty buffers
 853  */
 854
 855 static void eraser(unsigned char c, struct tty_struct *tty)
 856 {
 857         enum { ERASE, WERASE, KILL } kill_type;
 858         int head, seen_alnums, cnt;
 859         unsigned long flags;
 860
 861         /* FIXME: locking needed ? */
 862         if (tty->read_head == tty->canon_head) {
 863                 /* process_output('\a', tty); */ /* what do you think? */
 864                 return;
 865         }
 866         if (c == ERASE_CHAR(tty))
 867                 kill_type = ERASE;
 868         else if (c == WERASE_CHAR(tty))
 869                 kill_type = WERASE;
 870         else {
 871                 if (!L_ECHO(tty)) {
 872                         spin_lock_irqsave(&tty->read_lock, flags);
 873                         tty->read_cnt -= ((tty->read_head - tty->canon_head) &
 874                                           (N_TTY_BUF_SIZE - 1));
 875                         tty->read_head = tty->canon_head;
 876                         spin_unlock_irqrestore(&tty->read_lock, flags);
 877                         return;
 878                 }
 879                 if (!L_ECHOK(tty) || !L_ECHOKE(tty) || !L_ECHOE(tty)) {
 880                         spin_lock_irqsave(&tty->read_lock, flags);
 881                         tty->read_cnt -= ((tty->read_head - tty->canon_head) &
 882                                           (N_TTY_BUF_SIZE - 1));
 883                         tty->read_head = tty->canon_head;
 884                         spin_unlock_irqrestore(&tty->read_lock, flags);
 885                         finish_erasing(tty);
 886                         echo_char(KILL_CHAR(tty), tty);
 887                         /* Add a newline if ECHOK is on and ECHOKE is off. */
 888                         if (L_ECHOK(tty))
 889                                 echo_char_raw('\n', tty);
 890                         return;
 891                 }
 892                 kill_type = KILL;
 893         }
 894
 895         seen_alnums = 0;
 896         /* FIXME: Locking ?? */
 897         while (tty->read_head != tty->canon_head) {
 898                 head = tty->read_head;
 899
 900                 /* erase a single possibly multibyte character */
 901                 do {
 902                         head = (head - 1) & (N_TTY_BUF_SIZE-1);
 903                         c = tty->read_buf[head];
 904                 } while (is_continuation(c, tty) && head != tty->canon_head);
 905
 906                 /* do not partially erase */
 907                 if (is_continuation(c, tty))
 908                         break;
 909
 910                 if (kill_type == WERASE) {
 911                         /* Equivalent to BSD's ALTWERASE. */
 912                         if (isalnum(c) || c == '_')
 913                                 seen_alnums++;
 914                         else if (seen_alnums)
 915                                 break;
 916                 }
 917                 cnt = (tty->read_head - head) & (N_TTY_BUF_SIZE-1);
 918                 spin_lock_irqsave(&tty->read_lock, flags);
 919                 tty->read_head = head;
 920                 tty->read_cnt -= cnt;
 921                 spin_unlock_irqrestore(&tty->read_lock, flags);
 922                 if (L_ECHO(tty)) {
 923                         if (L_ECHOPRT(tty)) {
 924                                 if (!tty->erasing) {
 925                                         echo_char_raw('\\', tty);
 926                                         tty->erasing = 1;
 927                                 }
 928                                 /* if cnt > 1, output a multi-byte character */
 929                                 echo_char(c, tty);
 930                                 while (--cnt > 0) {
 931                                         head = (head+1) & (N_TTY_BUF_SIZE-1);
 932                                         echo_char_raw(tty->read_buf[head], tty);
 933                                         echo_move_back_col(tty);
 934                                 }
 935                         } else if (kill_type == ERASE && !L_ECHOE(tty)) {
 936                                 echo_char(ERASE_CHAR(tty), tty);
 937                         } else if (c == '\t') {
 938                                 unsigned int num_chars = 0;
 939                                 int after_tab = 0;
 940                                 unsigned long tail = tty->read_head;
 941
 942                                 /*
 943                                  * Count the columns used for characters
 944                                  * since the start of input or after a
 945                                  * previous tab.
 946                                  * This info is used to go back the correct
 947                                  * number of columns.
 948                                  */
 949                                 while (tail != tty->canon_head) {
 950                                         tail = (tail-1) & (N_TTY_BUF_SIZE-1);
 951                                         c = tty->read_buf[tail];
 952                                         if (c == '\t') {
 953                                                 after_tab = 1;
 954                                                 break;
 955                                         } else if (iscntrl(c)) {
 956                                                 if (L_ECHOCTL(tty))
 957                                                         num_chars += 2;
 958                                         } else if (!is_continuation(c, tty)) {
 959                                                 num_chars++;
 960                                         }
 961                                 }
 962                                 echo_erase_tab(num_chars, after_tab, tty);
 963                         } else {
 964                                 if (iscntrl(c) && L_ECHOCTL(tty)) {
 965                                         echo_char_raw('\b', tty);
 966                                         echo_char_raw(' ', tty);
 967                                         echo_char_raw('\b', tty);
 968                                 }
 969                                 if (!iscntrl(c) || L_ECHOCTL(tty)) {
 970                                         echo_char_raw('\b', tty);
 971                                         echo_char_raw(' ', tty);
 972                                         echo_char_raw('\b', tty);
 973                                 }
 974                         }
 975                 }
 976                 if (kill_type == ERASE)
 977                         break;
 978         }
 979         if (tty->read_head == tty->canon_head && L_ECHO(tty))
 980                 finish_erasing(tty);
 981 }
 982
 983 /**
 984  *      isig            -       handle the ISIG optio
 985  *      @sig: signal
 986  *      @tty: terminal
 987  *      @flush: force flush
 988  *
 989  *      Called when a signal is being sent due to terminal input. This
 990  *      may caus terminal flushing to take place according to the termios
 991  *      settings and character used. Called from the driver receive_buf
 992  *      path so serialized.
 993  *
 994  *      Locking: ctrl_lock, read_lock (both via flush buffer)
 995  */
 996
 997 static inline void isig(int sig, struct tty_struct *tty, int flush)
 998 {
 999         if (tty->pgrp)
1000                 kill_pgrp(tty->pgrp, sig, 1);
1001         if (flush || !L_NOFLSH(tty)) {
1002                 n_tty_flush_buffer(tty);
1003                 tty_driver_flush_buffer(tty);
1004         }
1005 }
1006
1007 /**
1008  *      n_tty_receive_break     -       handle break
1009  *      @tty: terminal
1010  *
1011  *      An RS232 break event has been hit in the incoming bitstream. This
1012  *      can cause a variety of events depending upon the termios settings.
1013  *
1014  *      Called from the receive_buf path so single threaded.
1015  */
1016
1017 static inline void n_tty_receive_break(struct tty_struct *tty)
1018 {
1019         if (I_IGNBRK(tty))
1020                 return;
1021         if (I_BRKINT(tty)) {
1022                 isig(SIGINT, tty, 1);
1023                 return;
1024         }
1025         if (I_PARMRK(tty)) {
1026                 put_tty_queue('\377', tty);
1027                 put_tty_queue('\0', tty);
1028         }
1029         put_tty_queue('\0', tty);
1030         wake_up_interruptible(&tty->read_wait);
1031 }
1032
1033 /**
1034  *      n_tty_receive_overrun   -       handle overrun reporting
1035  *      @tty: terminal
1036  *
1037  *      Data arrived faster than we could process it. While the tty
1038  *      driver has flagged this the bits that were missed are gone
1039  *      forever.
1040  *
1041  *      Called from the receive_buf path so single threaded. Does not
1042  *      need locking as num_overrun and overrun_time are function
1043  *      private.
1044  */
1045
1046 static inline void n_tty_receive_overrun(struct tty_struct *tty)
1047 {
1048         char buf[64];
1049
1050         tty->num_overrun++;
1051         if (time_before(tty->overrun_time, jiffies - HZ) ||
1052                         time_after(tty->overrun_time, jiffies)) {
1053                 printk(KERN_WARNING "%s: %d input overrun(s)\n",
1054                         tty_name(tty, buf),
1055                         tty->num_overrun);
1056                 tty->overrun_time = jiffies;
1057                 tty->num_overrun = 0;
1058         }
1059 }
1060
1061 /**
1062  *      n_tty_receive_parity_error      -       error notifier
1063  *      @tty: terminal device
1064  *      @c: character
1065  *
1066  *      Process a parity error and queue the right data to indicate
1067  *      the error case if necessary. Locking as per n_tty_receive_buf.
1068  */
1069 static inline void n_tty_receive_parity_error(struct tty_struct *tty,
1070                                               unsigned char c)
1071 {
1072         if (I_IGNPAR(tty))
1073                 return;
1074         if (I_PARMRK(tty)) {
1075                 put_tty_queue('\377', tty);
1076                 put_tty_queue('\0', tty);
1077                 put_tty_queue(c, tty);
1078         } else  if (I_INPCK(tty))
1079                 put_tty_queue('\0', tty);
1080         else
1081                 put_tty_queue(c, tty);
1082         wake_up_interruptible(&tty->read_wait);
1083 }
1084
1085 /**
1086  *      n_tty_receive_char      -       perform processing
1087  *      @tty: terminal device
1088  *      @c: character
1089  *
1090  *      Process an individual character of input received from the driver.
1091  *      This is serialized with respect to itself by the rules for the
1092  *      driver above.
1093  */
1094
1095 static inline void n_tty_receive_char(struct tty_struct *tty, unsigned char c)
1096 {
1097         unsigned long flags;
1098         int parmrk;
1099
1100         if (tty->raw) {
1101                 put_tty_queue(c, tty);
1102                 return;
1103         }
1104
1105         if (I_ISTRIP(tty))
1106                 c &= 0x7f;
1107         if (I_IUCLC(tty) && L_IEXTEN(tty))
1108                 c = tolower(c);
1109
1110         if (L_EXTPROC(tty)) {
1111                 put_tty_queue(c, tty);
1112                 return;
1113         }
1114
1115         if (tty->stopped && !tty->flow_stopped && I_IXON(tty) &&
1116             I_IXANY(tty) && c != START_CHAR(tty) && c != STOP_CHAR(tty) &&
1117             c != INTR_CHAR(tty) && c != QUIT_CHAR(tty) && c != SUSP_CHAR(tty)) {
1118                 start_tty(tty);
1119                 process_echoes(tty);
1120         }
1121
1122         if (tty->closing) {
1123                 if (I_IXON(tty)) {
1124                         if (c == START_CHAR(tty)) {
1125                                 start_tty(tty);
1126                                 process_echoes(tty);
1127                         } else if (c == STOP_CHAR(tty))
1128                                 stop_tty(tty);
1129                 }
1130                 return;
1131         }
1132
1133         /*
1134          * If the previous character was LNEXT, or we know that this
1135          * character is not one of the characters that we'll have to
1136          * handle specially, do shortcut processing to speed things
1137          * up.
1138          */
1139         if (!test_bit(c, tty->process_char_map) || tty->lnext) {
1140                 tty->lnext = 0;
1141                 parmrk = (c == (unsigned char) '\377' && I_PARMRK(tty)) ? 1 : 0;
1142                 if (tty->read_cnt >= (N_TTY_BUF_SIZE - parmrk - 1)) {
1143                         /* beep if no space */
1144                         if (L_ECHO(tty))
1145                                 process_output('\a', tty);
1146                         return;
1147                 }
1148                 if (L_ECHO(tty)) {
1149                         finish_erasing(tty);
1150                         /* Record the column of first canon char. */
1151                         if (tty->canon_head == tty->read_head)
1152                                 echo_set_canon_col(tty);
1153                         echo_char(c, tty);
1154                         process_echoes(tty);
1155                 }
1156                 if (parmrk)
1157                         put_tty_queue(c, tty);
1158                 put_tty_queue(c, tty);
1159                 return;
1160         }
1161
1162         if (I_IXON(tty)) {
1163                 if (c == START_CHAR(tty)) {
1164                         start_tty(tty);
1165                         process_echoes(tty);
1166                         return;
1167                 }
1168                 if (c == STOP_CHAR(tty)) {
1169                         stop_tty(tty);
1170                         return;
1171                 }
1172         }
1173
1174         if (L_ISIG(tty)) {
1175                 int signal;
1176                 signal = SIGINT;
1177                 if (c == INTR_CHAR(tty))
1178                         goto send_signal;
1179                 signal = SIGQUIT;
1180                 if (c == QUIT_CHAR(tty))
1181                         goto send_signal;
1182                 signal = SIGTSTP;
1183                 if (c == SUSP_CHAR(tty)) {
1184 send_signal:
1185                         /*
1186                          * Note that we do not use isig() here because we want
1187                          * the order to be:
1188                          * 1) flush, 2) echo, 3) signal
1189                          */
1190                         if (!L_NOFLSH(tty)) {
1191                                 n_tty_flush_buffer(tty);
1192                                 tty_driver_flush_buffer(tty);
1193                         }
1194                         if (I_IXON(tty))
1195                                 start_tty(tty);
1196                         if (L_ECHO(tty)) {
1197                                 echo_char(c, tty);
1198                                 process_echoes(tty);
1199                         }
1200                         if (tty->pgrp)
1201                                 kill_pgrp(tty->pgrp, signal, 1);
1202                         return;
1203                 }
1204         }
1205
1206         if (c == '\r') {
1207                 if (I_IGNCR(tty))
1208                         return;
1209                 if (I_ICRNL(tty))
1210                         c = '\n';
1211         } else if (c == '\n' && I_INLCR(tty))
1212                 c = '\r';
1213
1214         if (tty->icanon) {
1215                 if (c == ERASE_CHAR(tty) || c == KILL_CHAR(tty) ||
1216                     (c == WERASE_CHAR(tty) && L_IEXTEN(tty))) {
1217                         eraser(c, tty);
1218                         process_echoes(tty);
1219                         return;
1220                 }
1221                 if (c == LNEXT_CHAR(tty) && L_IEXTEN(tty)) {
1222                         tty->lnext = 1;
1223                         if (L_ECHO(tty)) {
1224                                 finish_erasing(tty);
1225                                 if (L_ECHOCTL(tty)) {
1226                                         echo_char_raw('^', tty);
1227                                         echo_char_raw('\b', tty);
1228                                         process_echoes(tty);
1229                                 }
1230                         }
1231                         return;
1232                 }
1233                 if (c == REPRINT_CHAR(tty) && L_ECHO(tty) &&
1234                     L_IEXTEN(tty)) {
1235                         unsigned long tail = tty->canon_head;
1236
1237                         finish_erasing(tty);
1238                         echo_char(c, tty);
1239                         echo_char_raw('\n', tty);
1240                         while (tail != tty->read_head) {
1241                                 echo_char(tty->read_buf[tail], tty);
1242                                 tail = (tail+1) & (N_TTY_BUF_SIZE-1);
1243                         }
1244                         process_echoes(tty);
1245                         return;
1246                 }
1247                 if (c == '\n') {
1248                         if (tty->read_cnt >= N_TTY_BUF_SIZE) {
1249                                 if (L_ECHO(tty))
1250                                         process_output('\a', tty);
1251                                 return;
1252                         }
1253                         if (L_ECHO(tty) || L_ECHONL(tty)) {
1254                                 echo_char_raw('\n', tty);
1255                                 process_echoes(tty);
1256                         }
1257                         goto handle_newline;
1258                 }
1259                 if (c == EOF_CHAR(tty)) {
1260                         if (tty->read_cnt >= N_TTY_BUF_SIZE)
1261                                 return;
1262                         if (tty->canon_head != tty->read_head)
1263                                 set_bit(TTY_PUSH, &tty->flags);
1264                         c = __DISABLED_CHAR;
1265                         goto handle_newline;
1266                 }
1267                 if ((c == EOL_CHAR(tty)) ||
1268                     (c == EOL2_CHAR(tty) && L_IEXTEN(tty))) {
1269                         parmrk = (c == (unsigned char) '\377' && I_PARMRK(tty))
1270                                  ? 1 : 0;
1271                         if (tty->read_cnt >= (N_TTY_BUF_SIZE - parmrk)) {
1272                                 if (L_ECHO(tty))
1273                                         process_output('\a', tty);
1274                                 return;
1275                         }
1276                         /*
1277                          * XXX are EOL_CHAR and EOL2_CHAR echoed?!?
1278                          */
1279                         if (L_ECHO(tty)) {
1280                                 /* Record the column of first canon char. */
1281                                 if (tty->canon_head == tty->read_head)
1282                                         echo_set_canon_col(tty);
1283                                 echo_char(c, tty);
1284                                 process_echoes(tty);
1285                         }
1286                         /*
1287                          * XXX does PARMRK doubling happen for
1288                          * EOL_CHAR and EOL2_CHAR?
1289                          */
1290                         if (parmrk)
1291                                 put_tty_queue(c, tty);
1292
1293 handle_newline:
1294                         spin_lock_irqsave(&tty->read_lock, flags);
1295                         set_bit(tty->read_head, tty->read_flags);
1296                         put_tty_queue_nolock(c, tty);
1297                         tty->canon_head = tty->read_head;
1298                         tty->canon_data++;
1299                         spin_unlock_irqrestore(&tty->read_lock, flags);
1300                         kill_fasync(&tty->fasync, SIGIO, POLL_IN);
1301                         wake_up_interruptible(&tty->read_wait);
1302                         return;
1303                 }
1304         }
1305
1306         parmrk = (c == (unsigned char) '\377' && I_PARMRK(tty)) ? 1 : 0;
1307         if (tty->read_cnt >= (N_TTY_BUF_SIZE - parmrk - 1)) {
1308                 /* beep if no space */
1309                 if (L_ECHO(tty))
1310                         process_output('\a', tty);
1311                 return;
1312         }
1313         if (L_ECHO(tty)) {
1314                 finish_erasing(tty);
1315                 if (c == '\n')
1316                         echo_char_raw('\n', tty);
1317                 else {
1318                         /* Record the column of first canon char. */
1319                         if (tty->canon_head == tty->read_head)
1320                                 echo_set_canon_col(tty);
1321                         echo_char(c, tty);
1322                 }
1323                 process_echoes(tty);
1324         }
1325
1326         if (parmrk)
1327                 put_tty_queue(c, tty);
1328
1329         put_tty_queue(c, tty);
1330 }
1331
1332
1333 /**
1334  *      n_tty_write_wakeup      -       asynchronous I/O notifier
1335  *      @tty: tty device
1336  *
1337  *      Required for the ptys, serial driver etc. since processes
1338  *      that attach themselves to the master and rely on ASYNC
1339  *      IO must be woken up
1340  */
1341
1342 static void n_tty_write_wakeup(struct tty_struct *tty)
1343 {
1344         if (tty->fasync && test_and_clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags))
1345                 kill_fasync(&tty->fasync, SIGIO, POLL_OUT);
1346 }
1347
1348 /**
1349  *      n_tty_receive_buf       -       data receive
1350  *      @tty: terminal device
1351  *      @cp: buffer
1352  *      @fp: flag buffer
1353  *      @count: characters
1354  *
1355  *      Called by the terminal driver when a block of characters has
1356  *      been received. This function must be called from soft contexts
1357  *      not from interrupt context. The driver is responsible for making
1358  *      calls one at a time and in order (or using flush_to_ldisc)
1359  */
1360
1361 static void n_tty_receive_buf(struct tty_struct *tty, const unsigned char *cp,
1362                               char *fp, int count)
1363 {
1364         const unsigned char *p;
1365         char *f, flags = TTY_NORMAL;
1366         int     i;
1367         char    buf[64];
1368         unsigned long cpuflags;
1369
1370         if (!tty->read_buf)
1371                 return;
1372
1373         if (tty->real_raw) {
1374                 spin_lock_irqsave(&tty->read_lock, cpuflags);
1375                 i = min(N_TTY_BUF_SIZE - tty->read_cnt,
1376                         N_TTY_BUF_SIZE - tty->read_head);
1377                 i = min(count, i);
1378                 memcpy(tty->read_buf + tty->read_head, cp, i);
1379                 tty->read_head = (tty->read_head + i) & (N_TTY_BUF_SIZE-1);
1380                 tty->read_cnt += i;
1381                 cp += i;
1382                 count -= i;
1383
1384                 i = min(N_TTY_BUF_SIZE - tty->read_cnt,
1385                         N_TTY_BUF_SIZE - tty->read_head);
1386                 i = min(count, i);
1387                 memcpy(tty->read_buf + tty->read_head, cp, i);
1388                 tty->read_head = (tty->read_head + i) & (N_TTY_BUF_SIZE-1);
1389                 tty->read_cnt += i;
1390                 spin_unlock_irqrestore(&tty->read_lock, cpuflags);
1391         } else {
1392                 for (i = count, p = cp, f = fp; i; i--, p++) {
1393                         if (f)
1394                                 flags = *f++;
1395                         switch (flags) {
1396                         case TTY_NORMAL:
1397                                 n_tty_receive_char(tty, *p);
1398                                 break;
1399                         case TTY_BREAK:
1400                                 n_tty_receive_break(tty);
1401                                 break;
1402                         case TTY_PARITY:
1403                         case TTY_FRAME:
1404                                 n_tty_receive_parity_error(tty, *p);
1405                                 break;
1406                         case TTY_OVERRUN:
1407                                 n_tty_receive_overrun(tty);
1408                                 break;
1409                         default:
1410                                 printk(KERN_ERR "%s: unknown flag %d\n",
1411                                        tty_name(tty, buf), flags);
1412                                 break;
1413                         }
1414                 }
1415                 if (tty->ops->flush_chars)
1416                         tty->ops->flush_chars(tty);
1417         }
1418
1419         n_tty_set_room(tty);
1420
1421         if ((!tty->icanon && (tty->read_cnt >= tty->minimum_to_wake)) ||
1422                 L_EXTPROC(tty)) {
1423                 kill_fasync(&tty->fasync, SIGIO, POLL_IN);
1424                 wake_up_interruptible(&tty->read_wait);
1425         }
1426
1427         /*
1428          * Check the remaining room for the input canonicalization
1429          * mode.  We don't want to throttle the driver if we're in
1430          * canonical mode and don't have a newline yet!
1431          */
1432         if (tty->receive_room < TTY_THRESHOLD_THROTTLE)
1433                 tty_throttle(tty);
1434 }
1435
1436 int is_ignored(int sig)
1437 {
1438         return (sigismember(&current->blocked, sig) ||
1439                 current->sighand->action[sig-1].sa.sa_handler == SIG_IGN);
1440 }
1441
1442 /**
1443  *      n_tty_set_termios       -       termios data changed
1444  *      @tty: terminal
1445  *      @old: previous data
1446  *
1447  *      Called by the tty layer when the user changes termios flags so
1448  *      that the line discipline can plan ahead. This function cannot sleep
1449  *      and is protected from re-entry by the tty layer. The user is
1450  *      guaranteed that this function will not be re-entered or in progress
1451  *      when the ldisc is closed.
1452  *
1453  *      Locking: Caller holds tty->termios_mutex
1454  */
1455
1456 static void n_tty_set_termios(struct tty_struct *tty, struct ktermios *old)
1457 {
1458         int canon_change = 1;
1459         BUG_ON(!tty);
1460
1461         if (old)
1462                 canon_change = (old->c_lflag ^ tty->termios->c_lflag) & (ICANON | EXTPROC);
1463         if (canon_change) {
1464                 memset(&tty->read_flags, 0, sizeof tty->read_flags);
1465                 tty->canon_head = tty->read_tail;
1466                 tty->canon_data = 0;
1467                 tty->erasing = 0;
1468         }
1469
1470         if (canon_change && !L_ICANON(tty) && tty->read_cnt)
1471                 wake_up_interruptible(&tty->read_wait);
1472
1473         tty->icanon = (L_ICANON(tty) != 0);
1474         if (test_bit(TTY_HW_COOK_IN, &tty->flags)) {
1475                 tty->raw = 1;
1476                 tty->real_raw = 1;
1477                 n_tty_set_room(tty);
1478                 return;
1479         }
1480         if (I_ISTRIP(tty) || I_IUCLC(tty) || I_IGNCR(tty) ||
1481             I_ICRNL(tty) || I_INLCR(tty) || L_ICANON(tty) ||
1482             I_IXON(tty) || L_ISIG(tty) || L_ECHO(tty) ||
1483             I_PARMRK(tty)) {
1484                 memset(tty->process_char_map, 0, 256/8);
1485
1486                 if (I_IGNCR(tty) || I_ICRNL(tty))
1487                         set_bit('\r', tty->process_char_map);
1488                 if (I_INLCR(tty))
1489                         set_bit('\n', tty->process_char_map);
1490
1491                 if (L_ICANON(tty)) {
1492                         set_bit(ERASE_CHAR(tty), tty->process_char_map);
1493                         set_bit(KILL_CHAR(tty), tty->process_char_map);
1494                         set_bit(EOF_CHAR(tty), tty->process_char_map);
1495                         set_bit('\n', tty->process_char_map);
1496                         set_bit(EOL_CHAR(tty), tty->process_char_map);
1497                         if (L_IEXTEN(tty)) {
1498                                 set_bit(WERASE_CHAR(tty),
1499                                         tty->process_char_map);
1500                                 set_bit(LNEXT_CHAR(tty),
1501                                         tty->process_char_map);
1502                                 set_bit(EOL2_CHAR(tty),
1503                                         tty->process_char_map);
1504                                 if (L_ECHO(tty))
1505                                         set_bit(REPRINT_CHAR(tty),
1506                                                 tty->process_char_map);
1507                         }
1508                 }
1509                 if (I_IXON(tty)) {
1510                         set_bit(START_CHAR(tty), tty->process_char_map);
1511                         set_bit(STOP_CHAR(tty), tty->process_char_map);
1512                 }
1513                 if (L_ISIG(tty)) {
1514                         set_bit(INTR_CHAR(tty), tty->process_char_map);
1515                         set_bit(QUIT_CHAR(tty), tty->process_char_map);
1516                         set_bit(SUSP_CHAR(tty), tty->process_char_map);
1517                 }
1518                 clear_bit(__DISABLED_CHAR, tty->process_char_map);
1519                 tty->raw = 0;
1520                 tty->real_raw = 0;
1521         } else {
1522                 tty->raw = 1;
1523                 if ((I_IGNBRK(tty) || (!I_BRKINT(tty) && !I_PARMRK(tty))) &&
1524                     (I_IGNPAR(tty) || !I_INPCK(tty)) &&
1525                     (tty->driver->flags & TTY_DRIVER_REAL_RAW))
1526                         tty->real_raw = 1;
1527                 else
1528                         tty->real_raw = 0;
1529         }
1530         n_tty_set_room(tty);
1531         /*
1532          * Fix tty hang when I_IXON(tty) is cleared, but the tty
1533          * been stopped by STOP_CHAR(tty) before it.
1534          */
1535         if (!I_IXON(tty) && old && (old->c_iflag & IXON) && !tty->flow_stopped) {
1536                 start_tty(tty);
1537         }
1538
1539         /* The termios change make the tty ready for I/O */
1540         wake_up_interruptible(&tty->write_wait);
1541         wake_up_interruptible(&tty->read_wait);
1542 }
1543
1544 /**
1545  *      n_tty_close             -       close the ldisc for this tty
1546  *      @tty: device
1547  *
1548  *      Called from the terminal layer when this line discipline is
1549  *      being shut down, either because of a close or becsuse of a
1550  *      discipline change. The function will not be called while other
1551  *      ldisc methods are in progress.
1552  */
1553
1554 static void n_tty_close(struct tty_struct *tty)
1555 {
1556         n_tty_flush_buffer(tty);
1557         if (tty->read_buf) {
1558                 kfree(tty->read_buf);
1559                 tty->read_buf = NULL;
1560         }
1561         if (tty->echo_buf) {
1562                 kfree(tty->echo_buf);
1563                 tty->echo_buf = NULL;
1564         }
1565 }
1566
1567 /**
1568  *      n_tty_open              -       open an ldisc
1569  *      @tty: terminal to open
1570  *
1571  *      Called when this line discipline is being attached to the
1572  *      terminal device. Can sleep. Called serialized so that no
1573  *      other events will occur in parallel. No further open will occur
1574  *      until a close.
1575  */
1576
1577 static int n_tty_open(struct tty_struct *tty)
1578 {
1579         if (!tty)
1580                 return -EINVAL;
1581
1582         /* These are ugly. Currently a malloc failure here can panic */
1583         if (!tty->read_buf) {
1584                 tty->read_buf = kzalloc(N_TTY_BUF_SIZE, GFP_KERNEL);
1585                 if (!tty->read_buf)
1586                         return -ENOMEM;
1587         }
1588         if (!tty->echo_buf) {
1589                 tty->echo_buf = kzalloc(N_TTY_BUF_SIZE, GFP_KERNEL);
1590
1591                 if (!tty->echo_buf)
1592                         return -ENOMEM;
1593         }
1594         reset_buffer_flags(tty);
1595         tty_unthrottle(tty);
1596         tty->column = 0;
1597         n_tty_set_termios(tty, NULL);
1598         tty->minimum_to_wake = 1;
1599         tty->closing = 0;
1600         return 0;
1601 }
1602
1603 static inline int input_available_p(struct tty_struct *tty, int amt)
1604 {
1605         tty_flush_to_ldisc(tty);
1606         if (tty->icanon && !L_EXTPROC(tty)) {
1607                 if (tty->canon_data)
1608                         return 1;
1609         } else if (tty->read_cnt >= (amt ? amt : 1))
1610                 return 1;
1611
1612         return 0;
1613 }
1614
1615 /**
1616  *      copy_from_read_buf      -       copy read data directly
1617  *      @tty: terminal device
1618  *      @b: user data
1619  *      @nr: size of data
1620  *
1621  *      Helper function to speed up n_tty_read.  It is only called when
1622  *      ICANON is off; it copies characters straight from the tty queue to
1623  *      user space directly.  It can be profitably called twice; once to
1624  *      drain the space from the tail pointer to the (physical) end of the
1625  *      buffer, and once to drain the space from the (physical) beginning of
1626  *      the buffer to head pointer.
1627  *
1628  *      Called under the tty->atomic_read_lock sem
1629  *
1630  */
1631
1632 static int copy_from_read_buf(struct tty_struct *tty,
1633                                       unsigned char __user **b,
1634                                       size_t *nr)
1635
1636 {
1637         int retval;
1638         size_t n;
1639         unsigned long flags;
1640
1641         retval = 0;
1642         spin_lock_irqsave(&tty->read_lock, flags);
1643         n = min(tty->read_cnt, N_TTY_BUF_SIZE - tty->read_tail);
1644         n = min(*nr, n);
1645         spin_unlock_irqrestore(&tty->read_lock, flags);
1646         if (n) {
1647                 retval = copy_to_user(*b, &tty->read_buf[tty->read_tail], n);
1648                 n -= retval;
1649                 tty_audit_add_data(tty, &tty->read_buf[tty->read_tail], n);
1650                 spin_lock_irqsave(&tty->read_lock, flags);
1651                 tty->read_tail = (tty->read_tail + n) & (N_TTY_BUF_SIZE-1);
1652                 tty->read_cnt -= n;
1653                 /* Turn single EOF into zero-length read */
1654                 if (L_EXTPROC(tty) && tty->icanon && n == 1) {
1655                         if (!tty->read_cnt && (*b)[n-1] == EOF_CHAR(tty))
1656                                 n--;
1657                 }
1658                 spin_unlock_irqrestore(&tty->read_lock, flags);
1659                 *b += n;
1660                 *nr -= n;
1661         }
1662         return retval;
1663 }
1664
1665 extern ssize_t redirected_tty_write(struct file *, const char __user *,
1666                                                         size_t, loff_t *);
1667
1668 /**
1669  *      job_control             -       check job control
1670  *      @tty: tty
1671  *      @file: file handle
1672  *
1673  *      Perform job control management checks on this file/tty descriptor
1674  *      and if appropriate send any needed signals and return a negative
1675  *      error code if action should be taken.
1676  *
1677  *      FIXME:
1678  *      Locking: None - redirected write test is safe, testing
1679  *      current->signal should possibly lock current->sighand
1680  *      pgrp locking ?
1681  */
1682
1683 static int job_control(struct tty_struct *tty, struct file *file)
1684 {
1685         /* Job control check -- must be done at start and after
1686            every sleep (POSIX.1 7.1.1.4). */
1687         /* NOTE: not yet done after every sleep pending a thorough
1688            check of the logic of this change. -- jlc */
1689         /* don't stop on /dev/console */
1690         if (file->f_op->write != redirected_tty_write &&
1691             current->signal->tty == tty) {
1692                 if (!tty->pgrp)
1693                         printk(KERN_ERR "n_tty_read: no tty->pgrp!\n");
1694                 else if (task_pgrp(current) != tty->pgrp) {
1695                         if (is_ignored(SIGTTIN) ||
1696                             is_current_pgrp_orphaned())
1697                                 return -EIO;
1698                         kill_pgrp(task_pgrp(current), SIGTTIN, 1);
1699                         set_thread_flag(TIF_SIGPENDING);
1700                         return -ERESTARTSYS;
1701                 }
1702         }
1703         return 0;
1704 }
1705
1706
1707 /**
1708  *      n_tty_read              -       read function for tty
1709  *      @tty: tty device
1710  *      @file: file object
1711  *      @buf: userspace buffer pointer
1712  *      @nr: size of I/O
1713  *
1714  *      Perform reads for the line discipline. We are guaranteed that the
1715  *      line discipline will not be closed under us but we may get multiple
1716  *      parallel readers and must handle this ourselves. We may also get
1717  *      a hangup. Always called in user context, may sleep.
1718  *
1719  *      This code must be sure never to sleep through a hangup.
1720  */
1721
1722 static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
1723                          unsigned char __user *buf, size_t nr)
1724 {
1725         unsigned char __user *b = buf;
1726         DECLARE_WAITQUEUE(wait, current);
1727         int c;
1728         int minimum, time;
1729         ssize_t retval = 0;
1730         ssize_t size;
1731         long timeout;
1732         unsigned long flags;
1733         int packet;
1734
1735 do_it_again:
1736
1737         if (WARN_ON(!tty->read_buf))
1738                 return -EAGAIN;
1739
1740         c = job_control(tty, file);
1741         if (c < 0)
1742                 return c;
1743
1744         minimum = time = 0;
1745         timeout = MAX_SCHEDULE_TIMEOUT;
1746         if (!tty->icanon) {
1747                 time = (HZ / 10) * TIME_CHAR(tty);
1748                 minimum = MIN_CHAR(tty);
1749                 if (minimum) {
1750                         if (time)
1751                                 tty->minimum_to_wake = 1;
1752                         else if (!waitqueue_active(&tty->read_wait) ||
1753                                  (tty->minimum_to_wake > minimum))
1754                                 tty->minimum_to_wake = minimum;
1755                 } else {
1756                         timeout = 0;
1757                         if (time) {
1758                                 timeout = time;
1759                                 time = 0;
1760                         }
1761                         tty->minimum_to_wake = minimum = 1;
1762                 }
1763         }
1764
1765         /*
1766          *      Internal serialization of reads.
1767          */
1768         if (file->f_flags & O_NONBLOCK) {
1769                 if (!mutex_trylock(&tty->atomic_read_lock))
1770                         return -EAGAIN;
1771         } else {
1772                 if (mutex_lock_interruptible(&tty->atomic_read_lock))
1773                         return -ERESTARTSYS;
1774         }
1775         packet = tty->packet;
1776
1777         add_wait_queue(&tty->read_wait, &wait);
1778         while (nr) {
1779                 /* First test for status change. */
1780                 if (packet && tty->link->ctrl_status) {
1781                         unsigned char cs;
1782                         if (b != buf)
1783                                 break;
1784                         spin_lock_irqsave(&tty->link->ctrl_lock, flags);
1785                         cs = tty->link->ctrl_status;
1786                         tty->link->ctrl_status = 0;
1787                         spin_unlock_irqrestore(&tty->link->ctrl_lock, flags);
1788                         if (tty_put_user(tty, cs, b++)) {
1789                                 retval = -EFAULT;
1790                                 b--;
1791                                 break;
1792                         }
1793                         nr--;
1794                         break;
1795                 }
1796                 /* This statement must be first before checking for input
1797                    so that any interrupt will set the state back to
1798                    TASK_RUNNING. */
1799                 set_current_state(TASK_INTERRUPTIBLE);
1800
1801                 if (((minimum - (b - buf)) < tty->minimum_to_wake) &&
1802                     ((minimum - (b - buf)) >= 1))
1803                         tty->minimum_to_wake = (minimum - (b - buf));
1804
1805                 if (!input_available_p(tty, 0)) {
1806                         if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
1807                                 retval = -EIO;
1808                                 break;
1809                         }
1810                         if (tty_hung_up_p(file))
1811                                 break;
1812                         /*
1813                          * Abort readers for ttys which never actually
1814                          * get hung up.  See __tty_hangup().
1815                          */
1816                         if (test_bit(TTY_HUPPING, &tty->flags))
1817                                 break;
1818                         if (!timeout)
1819                                 break;
1820                         if (file->f_flags & O_NONBLOCK) {
1821                                 retval = -EAGAIN;
1822                                 break;
1823                         }
1824                         if (signal_pending(current)) {
1825                                 retval = -ERESTARTSYS;
1826                                 break;
1827                         }
1828                         /* FIXME: does n_tty_set_room need locking ? */
1829                         n_tty_set_room(tty);
1830                         timeout = schedule_timeout(timeout);
1831                         BUG_ON(!tty->read_buf);
1832                         continue;
1833                 }
1834                 __set_current_state(TASK_RUNNING);
1835
1836                 /* Deal with packet mode. */
1837                 if (packet && b == buf) {
1838                         if (tty_put_user(tty, TIOCPKT_DATA, b++)) {
1839                                 retval = -EFAULT;
1840                                 b--;
1841                                 break;
1842                         }
1843                         nr--;
1844                 }
1845
1846                 if (tty->icanon && !L_EXTPROC(tty)) {
1847                         /* N.B. avoid overrun if nr == 0 */
1848                         while (nr && tty->read_cnt) {
1849                                 int eol;
1850
1851                                 eol = test_and_clear_bit(tty->read_tail,
1852                                                 tty->read_flags);
1853                                 c = tty->read_buf[tty->read_tail];
1854                                 spin_lock_irqsave(&tty->read_lock, flags);
1855                                 tty->read_tail = ((tty->read_tail+1) &
1856                                                   (N_TTY_BUF_SIZE-1));
1857                                 tty->read_cnt--;
1858                                 if (eol) {
1859                                         /* this test should be redundant:
1860                                          * we shouldn't be reading data if
1861                                          * canon_data is 0
1862                                          */
1863                                         if (--tty->canon_data < 0)
1864                                                 tty->canon_data = 0;
1865                                 }
1866                                 spin_unlock_irqrestore(&tty->read_lock, flags);
1867
1868                                 if (!eol || (c != __DISABLED_CHAR)) {
1869                                         if (tty_put_user(tty, c, b++)) {
1870                                                 retval = -EFAULT;
1871                                                 b--;
1872                                                 break;
1873                                         }
1874                                         nr--;
1875                                 }
1876                                 if (eol) {
1877                                         tty_audit_push(tty);
1878                                         break;
1879                                 }
1880                         }
1881                         if (retval)
1882                                 break;
1883                 } else {
1884                         int uncopied;
1885                         /* The copy function takes the read lock and handles
1886                            locking internally for this case */
1887                         uncopied = copy_from_read_buf(tty, &b, &nr);
1888                         uncopied += copy_from_read_buf(tty, &b, &nr);
1889                         if (uncopied) {
1890                                 retval = -EFAULT;
1891                                 break;
1892                         }
1893                 }
1894
1895                 /* If there is enough space in the read buffer now, let the
1896                  * low-level driver know. We use n_tty_chars_in_buffer() to
1897                  * check the buffer, as it now knows about canonical mode.
1898                  * Otherwise, if the driver is throttled and the line is
1899                  * longer than TTY_THRESHOLD_UNTHROTTLE in canonical mode,
1900                  * we won't get any more characters.
1901                  */
1902                 if (n_tty_chars_in_buffer(tty) <= TTY_THRESHOLD_UNTHROTTLE) {
1903                         n_tty_set_room(tty);
1904                         check_unthrottle(tty);
1905                 }
1906
1907                 if (b - buf >= minimum)
1908                         break;
1909                 if (time)
1910                         timeout = time;
1911         }
1912         mutex_unlock(&tty->atomic_read_lock);
1913         remove_wait_queue(&tty->read_wait, &wait);
1914
1915         if (!waitqueue_active(&tty->read_wait))
1916                 tty->minimum_to_wake = minimum;
1917
1918         __set_current_state(TASK_RUNNING);
1919         size = b - buf;
1920         if (size) {
1921                 retval = size;
1922                 if (nr)
1923                         clear_bit(TTY_PUSH, &tty->flags);
1924         } else if (test_and_clear_bit(TTY_PUSH, &tty->flags))
1925                  goto do_it_again;
1926
1927         n_tty_set_room(tty);
1928         return retval;
1929 }
1930
1931 /**
1932  *      n_tty_write             -       write function for tty
1933  *      @tty: tty device
1934  *      @file: file object
1935  *      @buf: userspace buffer pointer
1936  *      @nr: size of I/O
1937  *
1938  *      Write function of the terminal device.  This is serialized with
1939  *      respect to other write callers but not to termios changes, reads
1940  *      and other such events.  Since the receive code will echo characters,
1941  *      thus calling driver write methods, the output_lock is used in
1942  *      the output processing functions called here as well as in the
1943  *      echo processing function to protect the column state and space
1944  *      left in the buffer.
1945  *
1946  *      This code must be sure never to sleep through a hangup.
1947  *
1948  *      Locking: output_lock to protect column state and space left
1949  *               (note that the process_output*() functions take this
1950  *                lock themselves)
1951  */
1952
1953 static ssize_t n_tty_write(struct tty_struct *tty, struct file *file,
1954                            const unsigned char *buf, size_t nr)
1955 {
1956         const unsigned char *b = buf;
1957         DECLARE_WAITQUEUE(wait, current);
1958         int c;
1959         ssize_t retval = 0;
1960
1961         /* Job control check -- must be done at start (POSIX.1 7.1.1.4). */
1962         if (L_TOSTOP(tty) && file->f_op->write != redirected_tty_write) {
1963                 retval = tty_check_change(tty);
1964                 if (retval)
1965                         return retval;
1966         }
1967
1968         /* Write out any echoed characters that are still pending */
1969         process_echoes(tty);
1970
1971         add_wait_queue(&tty->write_wait, &wait);
1972         while (1) {
1973                 set_current_state(TASK_INTERRUPTIBLE);
1974                 if (signal_pending(current)) {
1975                         retval = -ERESTARTSYS;
1976                         break;
1977                 }
1978                 if (tty_hung_up_p(file) || (tty->link && !tty->link->count)) {
1979                         retval = -EIO;
1980                         break;
1981                 }
1982                 if (O_OPOST(tty) && !(test_bit(TTY_HW_COOK_OUT, &tty->flags))) {
1983                         while (nr > 0) {
1984                                 ssize_t num = process_output_block(tty, b, nr);
1985                                 if (num < 0) {
1986                                         if (num == -EAGAIN)
1987                                                 break;
1988                                         retval = num;
1989                                         goto break_out;
1990                                 }
1991                                 b += num;
1992                                 nr -= num;
1993                                 if (nr == 0)
1994                                         break;
1995                                 c = *b;
1996                                 if (process_output(c, tty) < 0)
1997                                         break;
1998                                 b++; nr--;
1999                         }
2000                         if (tty->ops->flush_chars)
2001                                 tty->ops->flush_chars(tty);
2002                 } else {
2003                         while (nr > 0) {
2004                                 mutex_lock(&tty->output_lock);
2005                                 c = tty->ops->write(tty, b, nr);
2006                                 mutex_unlock(&tty->output_lock);
2007                                 if (c < 0) {
2008                                         retval = c;
2009                                         goto break_out;
2010                                 }
2011                                 if (!c)
2012                                         break;
2013                                 b += c;
2014                                 nr -= c;
2015                         }
2016                 }
2017                 if (!nr)
2018                         break;
2019                 if (file->f_flags & O_NONBLOCK) {
2020                         retval = -EAGAIN;
2021                         break;
2022                 }
2023                 schedule();
2024         }
2025 break_out:
2026         __set_current_state(TASK_RUNNING);
2027         remove_wait_queue(&tty->write_wait, &wait);
2028         if (b - buf != nr && tty->fasync)
2029                 set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
2030         return (b - buf) ? b - buf : retval;
2031 }
2032
2033 /**
2034  *      n_tty_poll              -       poll method for N_TTY
2035  *      @tty: terminal device
2036  *      @file: file accessing it
2037  *      @wait: poll table
2038  *
2039  *      Called when the line discipline is asked to poll() for data or
2040  *      for special events. This code is not serialized with respect to
2041  *      other events save open/close.
2042  *
2043  *      This code must be sure never to sleep through a hangup.
2044  *      Called without the kernel lock held - fine
2045  */
2046
2047 static unsigned int n_tty_poll(struct tty_struct *tty, struct file *file,
2048                                                         poll_table *wait)
2049 {
2050         unsigned int mask = 0;
2051
2052         poll_wait(file, &tty->read_wait, wait);
2053         poll_wait(file, &tty->write_wait, wait);
2054         if (input_available_p(tty, TIME_CHAR(tty) ? 0 : MIN_CHAR(tty)))
2055                 mask |= POLLIN | POLLRDNORM;
2056         if (tty->packet && tty->link->ctrl_status)
2057                 mask |= POLLPRI | POLLIN | POLLRDNORM;
2058         if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
2059                 mask |= POLLHUP;
2060         if (tty_hung_up_p(file))
2061                 mask |= POLLHUP;
2062         if (!(mask & (POLLHUP | POLLIN | POLLRDNORM))) {
2063                 if (MIN_CHAR(tty) && !TIME_CHAR(tty))
2064                         tty->minimum_to_wake = MIN_CHAR(tty);
2065                 else
2066                         tty->minimum_to_wake = 1;
2067         }
2068         if (tty->ops->write && !tty_is_writelocked(tty) &&
2069                         tty_chars_in_buffer(tty) < WAKEUP_CHARS &&
2070                         tty_write_room(tty) > 0)
2071                 mask |= POLLOUT | POLLWRNORM;
2072         return mask;
2073 }
2074
2075 static unsigned long inq_canon(struct tty_struct *tty)
2076 {
2077         int nr, head, tail;
2078
2079         if (!tty->canon_data)
2080                 return 0;
2081         head = tty->canon_head;
2082         tail = tty->read_tail;
2083         nr = (head - tail) & (N_TTY_BUF_SIZE-1);
2084         /* Skip EOF-chars.. */
2085         while (head != tail) {
2086                 if (test_bit(tail, tty->read_flags) &&
2087                     tty->read_buf[tail] == __DISABLED_CHAR)
2088                         nr--;
2089                 tail = (tail+1) & (N_TTY_BUF_SIZE-1);
2090         }
2091         return nr;
2092 }
2093
2094 static int n_tty_ioctl(struct tty_struct *tty, struct file *file,
2095                        unsigned int cmd, unsigned long arg)
2096 {
2097         int retval;
2098
2099         switch (cmd) {
2100         case TIOCOUTQ:
2101                 return put_user(tty_chars_in_buffer(tty), (int __user *) arg);
2102         case TIOCINQ:
2103                 /* FIXME: Locking */
2104                 retval = tty->read_cnt;
2105                 if (L_ICANON(tty) && !L_EXTPROC(tty))
2106                         retval = inq_canon(tty);
2107                 return put_user(retval, (unsigned int __user *) arg);
2108         default:
2109                 return n_tty_ioctl_helper(tty, file, cmd, arg);
2110         }
2111 }
2112
2113 struct tty_ldisc_ops tty_ldisc_N_TTY = {
2114         .magic           = TTY_LDISC_MAGIC,
2115         .name            = "n_tty",
2116         .open            = n_tty_open,
2117         .close           = n_tty_close,
2118         .flush_buffer    = n_tty_flush_buffer,
2119         .chars_in_buffer = n_tty_chars_in_buffer,
2120         .read            = n_tty_read,
2121         .write           = n_tty_write,
2122         .ioctl           = n_tty_ioctl,
2123         .set_termios     = n_tty_set_termios,
2124         .poll            = n_tty_poll,
2125         .receive_buf     = n_tty_receive_buf,
2126         .write_wakeup    = n_tty_write_wakeup
2127 };
2128
2129 /**
2130  *      n_tty_inherit_ops       -       inherit N_TTY methods
2131  *      @ops: struct tty_ldisc_ops where to save N_TTY methods
2132  *
2133  *      Used by a generic struct tty_ldisc_ops to easily inherit N_TTY
2134  *      methods.
2135  */
2136
2137 void n_tty_inherit_ops(struct tty_ldisc_ops *ops)
2138 {
2139         *ops = tty_ldisc_N_TTY;
2140         ops->owner = NULL;
2141         ops->refcount = ops->flags = 0;
2142 }
2143 EXPORT_SYMBOL_GPL(n_tty_inherit_ops);