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 <[email protected]>
  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 <[email protected]>.
  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 #include <linux/ratelimit.h>
  53
  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 struct n_tty_data {
  78         unsigned int column;
  79         unsigned long overrun_time;
  80         int num_overrun;
  81
  82         unsigned char lnext:1, erasing:1, raw:1, real_raw:1, icanon:1;
  83         unsigned char echo_overrun:1;
  84
  85         DECLARE_BITMAP(process_char_map, 256);
  86         DECLARE_BITMAP(read_flags, N_TTY_BUF_SIZE);
  87
  88         char *read_buf;
  89         int read_head;
  90         int read_tail;
  91         int read_cnt;
  92
  93         unsigned char *echo_buf;
  94         unsigned int echo_pos;
  95         unsigned int echo_cnt;
  96
  97         int canon_data;
  98         unsigned long canon_head;
  99         unsigned int canon_column;
 100
 101         struct mutex atomic_read_lock;
 102         struct mutex output_lock;
 103         struct mutex echo_lock;
 104         raw_spinlock_t read_lock;
 105 };
 106
 107 static inline int tty_put_user(struct tty_struct *tty, unsigned char x,
 108                                unsigned char __user *ptr)
 109 {
 110         struct n_tty_data *ldata = tty->disc_data;
 111
 112         tty_audit_add_data(tty, &x, 1, ldata->icanon);
 113         return put_user(x, ptr);
 114 }
 115
 116 /**
 117  *      n_tty_set__room -       receive space
 118  *      @tty: terminal
 119  *
 120  *      Called by the driver to find out how much data it is
 121  *      permitted to feed to the line discipline without any being lost
 122  *      and thus to manage flow control. Not serialized. Answers for the
 123  *      "instant".
 124  */
 125
 126 static void n_tty_set_room(struct tty_struct *tty)
 127 {
 128         struct n_tty_data *ldata = tty->disc_data;
 129         int left;
 130         int old_left;
 131
 132         /* ldata->read_cnt is not read locked ? */
 133         if (I_PARMRK(tty)) {
 134                 /* Multiply read_cnt by 3, since each byte might take up to
 135                  * three times as many spaces when PARMRK is set (depending on
 136                  * its flags, e.g. parity error). */
 137                 left = N_TTY_BUF_SIZE - ldata->read_cnt * 3 - 1;
 138         } else
 139                 left = N_TTY_BUF_SIZE - ldata->read_cnt - 1;
 140
 141         /*
 142          * If we are doing input canonicalization, and there are no
 143          * pending newlines, let characters through without limit, so
 144          * that erase characters will be handled.  Other excess
 145          * characters will be beeped.
 146          */
 147         if (left <= 0)
 148                 left = ldata->icanon && !ldata->canon_data;
 149         old_left = tty->receive_room;
 150         tty->receive_room = left;
 151
 152         /* Did this open up the receive buffer? We may need to flip */
 153         if (left && !old_left) {
 154                 WARN_RATELIMIT(tty->port->itty == NULL,
 155                                 "scheduling with invalid itty\n");
 156                 schedule_work(&tty->port->buf.work);
 157         }
 158 }
 159
 160 static void put_tty_queue_nolock(unsigned char c, struct n_tty_data *ldata)
 161 {
 162         if (ldata->read_cnt < N_TTY_BUF_SIZE) {
 163                 ldata->read_buf[ldata->read_head] = c;
 164                 ldata->read_head = (ldata->read_head + 1) & (N_TTY_BUF_SIZE-1);
 165                 ldata->read_cnt++;
 166         }
 167 }
 168
 169 /**
 170  *      put_tty_queue           -       add character to tty
 171  *      @c: character
 172  *      @ldata: n_tty data
 173  *
 174  *      Add a character to the tty read_buf queue. This is done under the
 175  *      read_lock to serialize character addition and also to protect us
 176  *      against parallel reads or flushes
 177  */
 178
 179 static void put_tty_queue(unsigned char c, struct n_tty_data *ldata)
 180 {
 181         unsigned long flags;
 182         /*
 183          *      The problem of stomping on the buffers ends here.
 184          *      Why didn't anyone see this one coming? --AJK
 185         */
 186         raw_spin_lock_irqsave(&ldata->read_lock, flags);
 187         put_tty_queue_nolock(c, ldata);
 188         raw_spin_unlock_irqrestore(&ldata->read_lock, flags);
 189 }
 190
 191 /**
 192  *      check_unthrottle        -       allow new receive data
 193  *      @tty; tty device
 194  *
 195  *      Check whether to call the driver unthrottle functions
 196  *
 197  *      Can sleep, may be called under the atomic_read_lock mutex but
 198  *      this is not guaranteed.
 199  */
 200 static void check_unthrottle(struct tty_struct *tty)
 201 {
 202         if (tty->count)
 203                 tty_unthrottle(tty);
 204 }
 205
 206 /**
 207  *      reset_buffer_flags      -       reset buffer state
 208  *      @tty: terminal to reset
 209  *
 210  *      Reset the read buffer counters, clear the flags,
 211  *      and make sure the driver is unthrottled. Called
 212  *      from n_tty_open() and n_tty_flush_buffer().
 213  *
 214  *      Locking: tty_read_lock for read fields.
 215  */
 216
 217 static void reset_buffer_flags(struct tty_struct *tty)
 218 {
 219         struct n_tty_data *ldata = tty->disc_data;
 220         unsigned long flags;
 221
 222         raw_spin_lock_irqsave(&ldata->read_lock, flags);
 223         ldata->read_head = ldata->read_tail = ldata->read_cnt = 0;
 224         raw_spin_unlock_irqrestore(&ldata->read_lock, flags);
 225
 226         mutex_lock(&ldata->echo_lock);
 227         ldata->echo_pos = ldata->echo_cnt = ldata->echo_overrun = 0;
 228         mutex_unlock(&ldata->echo_lock);
 229
 230         ldata->canon_head = ldata->canon_data = ldata->erasing = 0;
 231         bitmap_zero(ldata->read_flags, N_TTY_BUF_SIZE);
 232         n_tty_set_room(tty);
 233 }
 234
 235 /**
 236  *      n_tty_flush_buffer      -       clean input queue
 237  *      @tty:   terminal device
 238  *
 239  *      Flush the input buffer. Called when the line discipline is
 240  *      being closed, when the tty layer wants the buffer flushed (eg
 241  *      at hangup) or when the N_TTY line discipline internally has to
 242  *      clean the pending queue (for example some signals).
 243  *
 244  *      Locking: ctrl_lock, read_lock.
 245  */
 246
 247 static void n_tty_flush_buffer(struct tty_struct *tty)
 248 {
 249         unsigned long flags;
 250         /* clear everything and unthrottle the driver */
 251         reset_buffer_flags(tty);
 252
 253         if (!tty->link)
 254                 return;
 255
 256         spin_lock_irqsave(&tty->ctrl_lock, flags);
 257         if (tty->link->packet) {
 258                 tty->ctrl_status |= TIOCPKT_FLUSHREAD;
 259                 wake_up_interruptible(&tty->link->read_wait);
 260         }
 261         spin_unlock_irqrestore(&tty->ctrl_lock, flags);
 262 }
 263
 264 /**
 265  *      n_tty_chars_in_buffer   -       report available bytes
 266  *      @tty: tty device
 267  *
 268  *      Report the number of characters buffered to be delivered to user
 269  *      at this instant in time.
 270  *
 271  *      Locking: read_lock
 272  */
 273
 274 static ssize_t n_tty_chars_in_buffer(struct tty_struct *tty)
 275 {
 276         struct n_tty_data *ldata = tty->disc_data;
 277         unsigned long flags;
 278         ssize_t n = 0;
 279
 280         raw_spin_lock_irqsave(&ldata->read_lock, flags);
 281         if (!ldata->icanon) {
 282                 n = ldata->read_cnt;
 283         } else if (ldata->canon_data) {
 284                 n = (ldata->canon_head > ldata->read_tail) ?
 285                         ldata->canon_head - ldata->read_tail :
 286                         ldata->canon_head + (N_TTY_BUF_SIZE - ldata->read_tail);
 287         }
 288         raw_spin_unlock_irqrestore(&ldata->read_lock, flags);
 289         return n;
 290 }
 291
 292 /**
 293  *      is_utf8_continuation    -       utf8 multibyte check
 294  *      @c: byte to check
 295  *
 296  *      Returns true if the utf8 character 'c' is a multibyte continuation
 297  *      character. We use this to correctly compute the on screen size
 298  *      of the character when printing
 299  */
 300
 301 static inline int is_utf8_continuation(unsigned char c)
 302 {
 303         return (c & 0xc0) == 0x80;
 304 }
 305
 306 /**
 307  *      is_continuation         -       multibyte check
 308  *      @c: byte to check
 309  *
 310  *      Returns true if the utf8 character 'c' is a multibyte continuation
 311  *      character and the terminal is in unicode mode.
 312  */
 313
 314 static inline int is_continuation(unsigned char c, struct tty_struct *tty)
 315 {
 316         return I_IUTF8(tty) && is_utf8_continuation(c);
 317 }
 318
 319 /**
 320  *      do_output_char                  -       output one character
 321  *      @c: character (or partial unicode symbol)
 322  *      @tty: terminal device
 323  *      @space: space available in tty driver write buffer
 324  *
 325  *      This is a helper function that handles one output character
 326  *      (including special characters like TAB, CR, LF, etc.),
 327  *      doing OPOST processing and putting the results in the
 328  *      tty driver's write buffer.
 329  *
 330  *      Note that Linux currently ignores TABDLY, CRDLY, VTDLY, FFDLY
 331  *      and NLDLY.  They simply aren't relevant in the world today.
 332  *      If you ever need them, add them here.
 333  *
 334  *      Returns the number of bytes of buffer space used or -1 if
 335  *      no space left.
 336  *
 337  *      Locking: should be called under the output_lock to protect
 338  *               the column state and space left in the buffer
 339  */
 340
 341 static int do_output_char(unsigned char c, struct tty_struct *tty, int space)
 342 {
 343         struct n_tty_data *ldata = tty->disc_data;
 344         int     spaces;
 345
 346         if (!space)
 347                 return -1;
 348
 349         switch (c) {
 350         case '\n':
 351                 if (O_ONLRET(tty))
 352                         ldata->column = 0;
 353                 if (O_ONLCR(tty)) {
 354                         if (space < 2)
 355                                 return -1;
 356                         ldata->canon_column = ldata->column = 0;
 357                         tty->ops->write(tty, "\r\n", 2);
 358                         return 2;
 359                 }
 360                 ldata->canon_column = ldata->column;
 361                 break;
 362         case '\r':
 363                 if (O_ONOCR(tty) && ldata->column == 0)
 364                         return 0;
 365                 if (O_OCRNL(tty)) {
 366                         c = '\n';
 367                         if (O_ONLRET(tty))
 368                                 ldata->canon_column = ldata->column = 0;
 369                         break;
 370                 }
 371                 ldata->canon_column = ldata->column = 0;
 372                 break;
 373         case '\t':
 374                 spaces = 8 - (ldata->column & 7);
 375                 if (O_TABDLY(tty) == XTABS) {
 376                         if (space < spaces)
 377                                 return -1;
 378                         ldata->column += spaces;
 379                         tty->ops->write(tty, "        ", spaces);
 380                         return spaces;
 381                 }
 382                 ldata->column += spaces;
 383                 break;
 384         case '\b':
 385                 if (ldata->column > 0)
 386                         ldata->column--;
 387                 break;
 388         default:
 389                 if (!iscntrl(c)) {
 390                         if (O_OLCUC(tty))
 391                                 c = toupper(c);
 392                         if (!is_continuation(c, tty))
 393                                 ldata->column++;
 394                 }
 395                 break;
 396         }
 397
 398         tty_put_char(tty, c);
 399         return 1;
 400 }
 401
 402 /**
 403  *      process_output                  -       output post processor
 404  *      @c: character (or partial unicode symbol)
 405  *      @tty: terminal device
 406  *
 407  *      Output one character with OPOST processing.
 408  *      Returns -1 when the output device is full and the character
 409  *      must be retried.
 410  *
 411  *      Locking: output_lock to protect column state and space left
 412  *               (also, this is called from n_tty_write under the
 413  *                tty layer write lock)
 414  */
 415
 416 static int process_output(unsigned char c, struct tty_struct *tty)
 417 {
 418         struct n_tty_data *ldata = tty->disc_data;
 419         int     space, retval;
 420
 421         mutex_lock(&ldata->output_lock);
 422
 423         space = tty_write_room(tty);
 424         retval = do_output_char(c, tty, space);
 425
 426         mutex_unlock(&ldata->output_lock);
 427         if (retval < 0)
 428                 return -1;
 429         else
 430                 return 0;
 431 }
 432
 433 /**
 434  *      process_output_block            -       block post processor
 435  *      @tty: terminal device
 436  *      @buf: character buffer
 437  *      @nr: number of bytes to output
 438  *
 439  *      Output a block of characters with OPOST processing.
 440  *      Returns the number of characters output.
 441  *
 442  *      This path is used to speed up block console writes, among other
 443  *      things when processing blocks of output data. It handles only
 444  *      the simple cases normally found and helps to generate blocks of
 445  *      symbols for the console driver and thus improve performance.
 446  *
 447  *      Locking: output_lock to protect column state and space left
 448  *               (also, this is called from n_tty_write under the
 449  *                tty layer write lock)
 450  */
 451
 452 static ssize_t process_output_block(struct tty_struct *tty,
 453                                     const unsigned char *buf, unsigned int nr)
 454 {
 455         struct n_tty_data *ldata = tty->disc_data;
 456         int     space;
 457         int     i;
 458         const unsigned char *cp;
 459
 460         mutex_lock(&ldata->output_lock);
 461
 462         space = tty_write_room(tty);
 463         if (!space) {
 464                 mutex_unlock(&ldata->output_lock);
 465                 return 0;
 466         }
 467         if (nr > space)
 468                 nr = space;
 469
 470         for (i = 0, cp = buf; i < nr; i++, cp++) {
 471                 unsigned char c = *cp;
 472
 473                 switch (c) {
 474                 case '\n':
 475                         if (O_ONLRET(tty))
 476                                 ldata->column = 0;
 477                         if (O_ONLCR(tty))
 478                                 goto break_out;
 479                         ldata->canon_column = ldata->column;
 480                         break;
 481                 case '\r':
 482                         if (O_ONOCR(tty) && ldata->column == 0)
 483                                 goto break_out;
 484                         if (O_OCRNL(tty))
 485                                 goto break_out;
 486                         ldata->canon_column = ldata->column = 0;
 487                         break;
 488                 case '\t':
 489                         goto break_out;
 490                 case '\b':
 491                         if (ldata->column > 0)
 492                                 ldata->column--;
 493                         break;
 494                 default:
 495                         if (!iscntrl(c)) {
 496                                 if (O_OLCUC(tty))
 497                                         goto break_out;
 498                                 if (!is_continuation(c, tty))
 499                                         ldata->column++;
 500                         }
 501                         break;
 502                 }
 503         }
 504 break_out:
 505         i = tty->ops->write(tty, buf, i);
 506
 507         mutex_unlock(&ldata->output_lock);
 508         return i;
 509 }
 510
 511 /**
 512  *      process_echoes  -       write pending echo characters
 513  *      @tty: terminal device
 514  *
 515  *      Write previously buffered echo (and other ldisc-generated)
 516  *      characters to the tty.
 517  *
 518  *      Characters generated by the ldisc (including echoes) need to
 519  *      be buffered because the driver's write buffer can fill during
 520  *      heavy program output.  Echoing straight to the driver will
 521  *      often fail under these conditions, causing lost characters and
 522  *      resulting mismatches of ldisc state information.
 523  *
 524  *      Since the ldisc state must represent the characters actually sent
 525  *      to the driver at the time of the write, operations like certain
 526  *      changes in column state are also saved in the buffer and executed
 527  *      here.
 528  *
 529  *      A circular fifo buffer is used so that the most recent characters
 530  *      are prioritized.  Also, when control characters are echoed with a
 531  *      prefixed "^", the pair is treated atomically and thus not separated.
 532  *
 533  *      Locking: output_lock to protect column state and space left,
 534  *               echo_lock to protect the echo buffer
 535  */
 536
 537 static void process_echoes(struct tty_struct *tty)
 538 {
 539         struct n_tty_data *ldata = tty->disc_data;
 540         int     space, nr;
 541         unsigned char c;
 542         unsigned char *cp, *buf_end;
 543
 544         if (!ldata->echo_cnt)
 545                 return;
 546
 547         mutex_lock(&ldata->output_lock);
 548         mutex_lock(&ldata->echo_lock);
 549
 550         space = tty_write_room(tty);
 551
 552         buf_end = ldata->echo_buf + N_TTY_BUF_SIZE;
 553         cp = ldata->echo_buf + ldata->echo_pos;
 554         nr = ldata->echo_cnt;
 555         while (nr > 0) {
 556                 c = *cp;
 557                 if (c == ECHO_OP_START) {
 558                         unsigned char op;
 559                         unsigned char *opp;
 560                         int no_space_left = 0;
 561
 562                         /*
 563                          * If the buffer byte is the start of a multi-byte
 564                          * operation, get the next byte, which is either the
 565                          * op code or a control character value.
 566                          */
 567                         opp = cp + 1;
 568                         if (opp == buf_end)
 569                                 opp -= N_TTY_BUF_SIZE;
 570                         op = *opp;
 571
 572                         switch (op) {
 573                                 unsigned int num_chars, num_bs;
 574
 575                         case ECHO_OP_ERASE_TAB:
 576                                 if (++opp == buf_end)
 577                                         opp -= N_TTY_BUF_SIZE;
 578                                 num_chars = *opp;
 579
 580                                 /*
 581                                  * Determine how many columns to go back
 582                                  * in order to erase the tab.
 583                                  * This depends on the number of columns
 584                                  * used by other characters within the tab
 585                                  * area.  If this (modulo 8) count is from
 586                                  * the start of input rather than from a
 587                                  * previous tab, we offset by canon column.
 588                                  * Otherwise, tab spacing is normal.
 589                                  */
 590                                 if (!(num_chars & 0x80))
 591                                         num_chars += ldata->canon_column;
 592                                 num_bs = 8 - (num_chars & 7);
 593
 594                                 if (num_bs > space) {
 595                                         no_space_left = 1;
 596                                         break;
 597                                 }
 598                                 space -= num_bs;
 599                                 while (num_bs--) {
 600                                         tty_put_char(tty, '\b');
 601                                         if (ldata->column > 0)
 602                                                 ldata->column--;
 603                                 }
 604                                 cp += 3;
 605                                 nr -= 3;
 606                                 break;
 607
 608                         case ECHO_OP_SET_CANON_COL:
 609                                 ldata->canon_column = ldata->column;
 610                                 cp += 2;
 611                                 nr -= 2;
 612                                 break;
 613
 614                         case ECHO_OP_MOVE_BACK_COL:
 615                                 if (ldata->column > 0)
 616                                         ldata->column--;
 617                                 cp += 2;
 618                                 nr -= 2;
 619                                 break;
 620
 621                         case ECHO_OP_START:
 622                                 /* This is an escaped echo op start code */
 623                                 if (!space) {
 624                                         no_space_left = 1;
 625                                         break;
 626                                 }
 627                                 tty_put_char(tty, ECHO_OP_START);
 628                                 ldata->column++;
 629                                 space--;
 630                                 cp += 2;
 631                                 nr -= 2;
 632                                 break;
 633
 634                         default:
 635                                 /*
 636                                  * If the op is not a special byte code,
 637                                  * it is a ctrl char tagged to be echoed
 638                                  * as "^X" (where X is the letter
 639                                  * representing the control char).
 640                                  * Note that we must ensure there is
 641                                  * enough space for the whole ctrl pair.
 642                                  *
 643                                  */
 644                                 if (space < 2) {
 645                                         no_space_left = 1;
 646                                         break;
 647                                 }
 648                                 tty_put_char(tty, '^');
 649                                 tty_put_char(tty, op ^ 0100);
 650                                 ldata->column += 2;
 651                                 space -= 2;
 652                                 cp += 2;
 653                                 nr -= 2;
 654                         }
 655
 656                         if (no_space_left)
 657                                 break;
 658                 } else {
 659                         if (O_OPOST(tty) &&
 660                             !(test_bit(TTY_HW_COOK_OUT, &tty->flags))) {
 661                                 int retval = do_output_char(c, tty, space);
 662                                 if (retval < 0)
 663                                         break;
 664                                 space -= retval;
 665                         } else {
 666                                 if (!space)
 667                                         break;
 668                                 tty_put_char(tty, c);
 669                                 space -= 1;
 670                         }
 671                         cp += 1;
 672                         nr -= 1;
 673                 }
 674
 675                 /* When end of circular buffer reached, wrap around */
 676                 if (cp >= buf_end)
 677                         cp -= N_TTY_BUF_SIZE;
 678         }
 679
 680         if (nr == 0) {
 681                 ldata->echo_pos = 0;
 682                 ldata->echo_cnt = 0;
 683                 ldata->echo_overrun = 0;
 684         } else {
 685                 int num_processed = ldata->echo_cnt - nr;
 686                 ldata->echo_pos += num_processed;
 687                 ldata->echo_pos &= N_TTY_BUF_SIZE - 1;
 688                 ldata->echo_cnt = nr;
 689                 if (num_processed > 0)
 690                         ldata->echo_overrun = 0;
 691         }
 692
 693         mutex_unlock(&ldata->echo_lock);
 694         mutex_unlock(&ldata->output_lock);
 695
 696         if (tty->ops->flush_chars)
 697                 tty->ops->flush_chars(tty);
 698 }
 699
 700 /**
 701  *      add_echo_byte   -       add a byte to the echo buffer
 702  *      @c: unicode byte to echo
 703  *      @ldata: n_tty data
 704  *
 705  *      Add a character or operation byte to the echo buffer.
 706  *
 707  *      Should be called under the echo lock to protect the echo buffer.
 708  */
 709
 710 static void add_echo_byte(unsigned char c, struct n_tty_data *ldata)
 711 {
 712         int     new_byte_pos;
 713
 714         if (ldata->echo_cnt == N_TTY_BUF_SIZE) {
 715                 /* Circular buffer is already at capacity */
 716                 new_byte_pos = ldata->echo_pos;
 717
 718                 /*
 719                  * Since the buffer start position needs to be advanced,
 720                  * be sure to step by a whole operation byte group.
 721                  */
 722                 if (ldata->echo_buf[ldata->echo_pos] == ECHO_OP_START) {
 723                         if (ldata->echo_buf[(ldata->echo_pos + 1) &
 724                                           (N_TTY_BUF_SIZE - 1)] ==
 725                                                 ECHO_OP_ERASE_TAB) {
 726                                 ldata->echo_pos += 3;
 727                                 ldata->echo_cnt -= 2;
 728                         } else {
 729                                 ldata->echo_pos += 2;
 730                                 ldata->echo_cnt -= 1;
 731                         }
 732                 } else {
 733                         ldata->echo_pos++;
 734                 }
 735                 ldata->echo_pos &= N_TTY_BUF_SIZE - 1;
 736
 737                 ldata->echo_overrun = 1;
 738         } else {
 739                 new_byte_pos = ldata->echo_pos + ldata->echo_cnt;
 740                 new_byte_pos &= N_TTY_BUF_SIZE - 1;
 741                 ldata->echo_cnt++;
 742         }
 743
 744         ldata->echo_buf[new_byte_pos] = c;
 745 }
 746
 747 /**
 748  *      echo_move_back_col      -       add operation to move back a column
 749  *      @ldata: n_tty data
 750  *
 751  *      Add an operation to the echo buffer to move back one column.
 752  *
 753  *      Locking: echo_lock to protect the echo buffer
 754  */
 755
 756 static void echo_move_back_col(struct n_tty_data *ldata)
 757 {
 758         mutex_lock(&ldata->echo_lock);
 759         add_echo_byte(ECHO_OP_START, ldata);
 760         add_echo_byte(ECHO_OP_MOVE_BACK_COL, ldata);
 761         mutex_unlock(&ldata->echo_lock);
 762 }
 763
 764 /**
 765  *      echo_set_canon_col      -       add operation to set the canon column
 766  *      @ldata: n_tty data
 767  *
 768  *      Add an operation to the echo buffer to set the canon column
 769  *      to the current column.
 770  *
 771  *      Locking: echo_lock to protect the echo buffer
 772  */
 773
 774 static void echo_set_canon_col(struct n_tty_data *ldata)
 775 {
 776         mutex_lock(&ldata->echo_lock);
 777         add_echo_byte(ECHO_OP_START, ldata);
 778         add_echo_byte(ECHO_OP_SET_CANON_COL, ldata);
 779         mutex_unlock(&ldata->echo_lock);
 780 }
 781
 782 /**
 783  *      echo_erase_tab  -       add operation to erase a tab
 784  *      @num_chars: number of character columns already used
 785  *      @after_tab: true if num_chars starts after a previous tab
 786  *      @ldata: n_tty data
 787  *
 788  *      Add an operation to the echo buffer to erase a tab.
 789  *
 790  *      Called by the eraser function, which knows how many character
 791  *      columns have been used since either a previous tab or the start
 792  *      of input.  This information will be used later, along with
 793  *      canon column (if applicable), to go back the correct number
 794  *      of columns.
 795  *
 796  *      Locking: echo_lock to protect the echo buffer
 797  */
 798
 799 static void echo_erase_tab(unsigned int num_chars, int after_tab,
 800                            struct n_tty_data *ldata)
 801 {
 802         mutex_lock(&ldata->echo_lock);
 803
 804         add_echo_byte(ECHO_OP_START, ldata);
 805         add_echo_byte(ECHO_OP_ERASE_TAB, ldata);
 806
 807         /* We only need to know this modulo 8 (tab spacing) */
 808         num_chars &= 7;
 809
 810         /* Set the high bit as a flag if num_chars is after a previous tab */
 811         if (after_tab)
 812                 num_chars |= 0x80;
 813
 814         add_echo_byte(num_chars, ldata);
 815
 816         mutex_unlock(&ldata->echo_lock);
 817 }
 818
 819 /**
 820  *      echo_char_raw   -       echo a character raw
 821  *      @c: unicode byte to echo
 822  *      @tty: terminal device
 823  *
 824  *      Echo user input back onto the screen. This must be called only when
 825  *      L_ECHO(tty) is true. Called from the driver receive_buf path.
 826  *
 827  *      This variant does not treat control characters specially.
 828  *
 829  *      Locking: echo_lock to protect the echo buffer
 830  */
 831
 832 static void echo_char_raw(unsigned char c, struct n_tty_data *ldata)
 833 {
 834         mutex_lock(&ldata->echo_lock);
 835         if (c == ECHO_OP_START) {
 836                 add_echo_byte(ECHO_OP_START, ldata);
 837                 add_echo_byte(ECHO_OP_START, ldata);
 838         } else {
 839                 add_echo_byte(c, ldata);
 840         }
 841         mutex_unlock(&ldata->echo_lock);
 842 }
 843
 844 /**
 845  *      echo_char       -       echo a character
 846  *      @c: unicode byte to echo
 847  *      @tty: terminal device
 848  *
 849  *      Echo user input back onto the screen. This must be called only when
 850  *      L_ECHO(tty) is true. Called from the driver receive_buf path.
 851  *
 852  *      This variant tags control characters to be echoed as "^X"
 853  *      (where X is the letter representing the control char).
 854  *
 855  *      Locking: echo_lock to protect the echo buffer
 856  */
 857
 858 static void echo_char(unsigned char c, struct tty_struct *tty)
 859 {
 860         struct n_tty_data *ldata = tty->disc_data;
 861
 862         mutex_lock(&ldata->echo_lock);
 863
 864         if (c == ECHO_OP_START) {
 865                 add_echo_byte(ECHO_OP_START, ldata);
 866                 add_echo_byte(ECHO_OP_START, ldata);
 867         } else {
 868                 if (L_ECHOCTL(tty) && iscntrl(c) && c != '\t')
 869                         add_echo_byte(ECHO_OP_START, ldata);
 870                 add_echo_byte(c, ldata);
 871         }
 872
 873         mutex_unlock(&ldata->echo_lock);
 874 }
 875
 876 /**
 877  *      finish_erasing          -       complete erase
 878  *      @ldata: n_tty data
 879  */
 880
 881 static inline void finish_erasing(struct n_tty_data *ldata)
 882 {
 883         if (ldata->erasing) {
 884                 echo_char_raw('/', ldata);
 885                 ldata->erasing = 0;
 886         }
 887 }
 888
 889 /**
 890  *      eraser          -       handle erase function
 891  *      @c: character input
 892  *      @tty: terminal device
 893  *
 894  *      Perform erase and necessary output when an erase character is
 895  *      present in the stream from the driver layer. Handles the complexities
 896  *      of UTF-8 multibyte symbols.
 897  *
 898  *      Locking: read_lock for tty buffers
 899  */
 900
 901 static void eraser(unsigned char c, struct tty_struct *tty)
 902 {
 903         struct n_tty_data *ldata = tty->disc_data;
 904         enum { ERASE, WERASE, KILL } kill_type;
 905         int head, seen_alnums, cnt;
 906         unsigned long flags;
 907
 908         /* FIXME: locking needed ? */
 909         if (ldata->read_head == ldata->canon_head) {
 910                 /* process_output('\a', tty); */ /* what do you think? */
 911                 return;
 912         }
 913         if (c == ERASE_CHAR(tty))
 914                 kill_type = ERASE;
 915         else if (c == WERASE_CHAR(tty))
 916                 kill_type = WERASE;
 917         else {
 918                 if (!L_ECHO(tty)) {
 919                         raw_spin_lock_irqsave(&ldata->read_lock, flags);
 920                         ldata->read_cnt -= ((ldata->read_head - ldata->canon_head) &
 921                                           (N_TTY_BUF_SIZE - 1));
 922                         ldata->read_head = ldata->canon_head;
 923                         raw_spin_unlock_irqrestore(&ldata->read_lock, flags);
 924                         return;
 925                 }
 926                 if (!L_ECHOK(tty) || !L_ECHOKE(tty) || !L_ECHOE(tty)) {
 927                         raw_spin_lock_irqsave(&ldata->read_lock, flags);
 928                         ldata->read_cnt -= ((ldata->read_head - ldata->canon_head) &
 929                                           (N_TTY_BUF_SIZE - 1));
 930                         ldata->read_head = ldata->canon_head;
 931                         raw_spin_unlock_irqrestore(&ldata->read_lock, flags);
 932                         finish_erasing(ldata);
 933                         echo_char(KILL_CHAR(tty), tty);
 934                         /* Add a newline if ECHOK is on and ECHOKE is off. */
 935                         if (L_ECHOK(tty))
 936                                 echo_char_raw('\n', ldata);
 937                         return;
 938                 }
 939                 kill_type = KILL;
 940         }
 941
 942         seen_alnums = 0;
 943         /* FIXME: Locking ?? */
 944         while (ldata->read_head != ldata->canon_head) {
 945                 head = ldata->read_head;
 946
 947                 /* erase a single possibly multibyte character */
 948                 do {
 949                         head = (head - 1) & (N_TTY_BUF_SIZE-1);
 950                         c = ldata->read_buf[head];
 951                 } while (is_continuation(c, tty) && head != ldata->canon_head);
 952
 953                 /* do not partially erase */
 954                 if (is_continuation(c, tty))
 955                         break;
 956
 957                 if (kill_type == WERASE) {
 958                         /* Equivalent to BSD's ALTWERASE. */
 959                         if (isalnum(c) || c == '_')
 960                                 seen_alnums++;
 961                         else if (seen_alnums)
 962                                 break;
 963                 }
 964                 cnt = (ldata->read_head - head) & (N_TTY_BUF_SIZE-1);
 965                 raw_spin_lock_irqsave(&ldata->read_lock, flags);
 966                 ldata->read_head = head;
 967                 ldata->read_cnt -= cnt;
 968                 raw_spin_unlock_irqrestore(&ldata->read_lock, flags);
 969                 if (L_ECHO(tty)) {
 970                         if (L_ECHOPRT(tty)) {
 971                                 if (!ldata->erasing) {
 972                                         echo_char_raw('\\', ldata);
 973                                         ldata->erasing = 1;
 974                                 }
 975                                 /* if cnt > 1, output a multi-byte character */
 976                                 echo_char(c, tty);
 977                                 while (--cnt > 0) {
 978                                         head = (head+1) & (N_TTY_BUF_SIZE-1);
 979                                         echo_char_raw(ldata->read_buf[head],
 980                                                         ldata);
 981                                         echo_move_back_col(ldata);
 982                                 }
 983                         } else if (kill_type == ERASE && !L_ECHOE(tty)) {
 984                                 echo_char(ERASE_CHAR(tty), tty);
 985                         } else if (c == '\t') {
 986                                 unsigned int num_chars = 0;
 987                                 int after_tab = 0;
 988                                 unsigned long tail = ldata->read_head;
 989
 990                                 /*
 991                                  * Count the columns used for characters
 992                                  * since the start of input or after a
 993                                  * previous tab.
 994                                  * This info is used to go back the correct
 995                                  * number of columns.
 996                                  */
 997                                 while (tail != ldata->canon_head) {
 998                                         tail = (tail-1) & (N_TTY_BUF_SIZE-1);
 999                                         c = ldata->read_buf[tail];
1000                                         if (c == '\t') {
1001                                                 after_tab = 1;
1002                                                 break;
1003                                         } else if (iscntrl(c)) {
1004                                                 if (L_ECHOCTL(tty))
1005                                                         num_chars += 2;
1006                                         } else if (!is_continuation(c, tty)) {
1007                                                 num_chars++;
1008                                         }
1009                                 }
1010                                 echo_erase_tab(num_chars, after_tab, ldata);
1011                         } else {
1012                                 if (iscntrl(c) && L_ECHOCTL(tty)) {
1013                                         echo_char_raw('\b', ldata);
1014                                         echo_char_raw(' ', ldata);
1015                                         echo_char_raw('\b', ldata);
1016                                 }
1017                                 if (!iscntrl(c) || L_ECHOCTL(tty)) {
1018                                         echo_char_raw('\b', ldata);
1019                                         echo_char_raw(' ', ldata);
1020                                         echo_char_raw('\b', ldata);
1021                                 }
1022                         }
1023                 }
1024                 if (kill_type == ERASE)
1025                         break;
1026         }
1027         if (ldata->read_head == ldata->canon_head && L_ECHO(tty))
1028                 finish_erasing(ldata);
1029 }
1030
1031 /**
1032  *      isig            -       handle the ISIG optio
1033  *      @sig: signal
1034  *      @tty: terminal
1035  *      @flush: force flush
1036  *
1037  *      Called when a signal is being sent due to terminal input. This
1038  *      may caus terminal flushing to take place according to the termios
1039  *      settings and character used. Called from the driver receive_buf
1040  *      path so serialized.
1041  *
1042  *      Locking: ctrl_lock, read_lock (both via flush buffer)
1043  */
1044
1045 static inline void isig(int sig, struct tty_struct *tty, int flush)
1046 {
1047         if (tty->pgrp)
1048                 kill_pgrp(tty->pgrp, sig, 1);
1049         if (flush || !L_NOFLSH(tty)) {
1050                 n_tty_flush_buffer(tty);
1051                 tty_driver_flush_buffer(tty);
1052         }
1053 }
1054
1055 /**
1056  *      n_tty_receive_break     -       handle break
1057  *      @tty: terminal
1058  *
1059  *      An RS232 break event has been hit in the incoming bitstream. This
1060  *      can cause a variety of events depending upon the termios settings.
1061  *
1062  *      Called from the receive_buf path so single threaded.
1063  */
1064
1065 static inline void n_tty_receive_break(struct tty_struct *tty)
1066 {
1067         struct n_tty_data *ldata = tty->disc_data;
1068
1069         if (I_IGNBRK(tty))
1070                 return;
1071         if (I_BRKINT(tty)) {
1072                 isig(SIGINT, tty, 1);
1073                 return;
1074         }
1075         if (I_PARMRK(tty)) {
1076                 put_tty_queue('\377', ldata);
1077                 put_tty_queue('\0', ldata);
1078         }
1079         put_tty_queue('\0', ldata);
1080         wake_up_interruptible(&tty->read_wait);
1081 }
1082
1083 /**
1084  *      n_tty_receive_overrun   -       handle overrun reporting
1085  *      @tty: terminal
1086  *
1087  *      Data arrived faster than we could process it. While the tty
1088  *      driver has flagged this the bits that were missed are gone
1089  *      forever.
1090  *
1091  *      Called from the receive_buf path so single threaded. Does not
1092  *      need locking as num_overrun and overrun_time are function
1093  *      private.
1094  */
1095
1096 static inline void n_tty_receive_overrun(struct tty_struct *tty)
1097 {
1098         struct n_tty_data *ldata = tty->disc_data;
1099         char buf[64];
1100
1101         ldata->num_overrun++;
1102         if (time_after(jiffies, ldata->overrun_time + HZ) ||
1103                         time_after(ldata->overrun_time, jiffies)) {
1104                 printk(KERN_WARNING "%s: %d input overrun(s)\n",
1105                         tty_name(tty, buf),
1106                         ldata->num_overrun);
1107                 ldata->overrun_time = jiffies;
1108                 ldata->num_overrun = 0;
1109         }
1110 }
1111
1112 /**
1113  *      n_tty_receive_parity_error      -       error notifier
1114  *      @tty: terminal device
1115  *      @c: character
1116  *
1117  *      Process a parity error and queue the right data to indicate
1118  *      the error case if necessary. Locking as per n_tty_receive_buf.
1119  */
1120 static inline void n_tty_receive_parity_error(struct tty_struct *tty,
1121                                               unsigned char c)
1122 {
1123         struct n_tty_data *ldata = tty->disc_data;
1124
1125         if (I_IGNPAR(tty))
1126                 return;
1127         if (I_PARMRK(tty)) {
1128                 put_tty_queue('\377', ldata);
1129                 put_tty_queue('\0', ldata);
1130                 put_tty_queue(c, ldata);
1131         } else  if (I_INPCK(tty))
1132                 put_tty_queue('\0', ldata);
1133         else
1134                 put_tty_queue(c, ldata);
1135         wake_up_interruptible(&tty->read_wait);
1136 }
1137
1138 /**
1139  *      n_tty_receive_char      -       perform processing
1140  *      @tty: terminal device
1141  *      @c: character
1142  *
1143  *      Process an individual character of input received from the driver.
1144  *      This is serialized with respect to itself by the rules for the
1145  *      driver above.
1146  */
1147
1148 static inline void n_tty_receive_char(struct tty_struct *tty, unsigned char c)
1149 {
1150         struct n_tty_data *ldata = tty->disc_data;
1151         unsigned long flags;
1152         int parmrk;
1153
1154         if (ldata->raw) {
1155                 put_tty_queue(c, ldata);
1156                 return;
1157         }
1158
1159         if (I_ISTRIP(tty))
1160                 c &= 0x7f;
1161         if (I_IUCLC(tty) && L_IEXTEN(tty))
1162                 c = tolower(c);
1163
1164         if (L_EXTPROC(tty)) {
1165                 put_tty_queue(c, ldata);
1166                 return;
1167         }
1168
1169         if (tty->stopped && !tty->flow_stopped && I_IXON(tty) &&
1170             I_IXANY(tty) && c != START_CHAR(tty) && c != STOP_CHAR(tty) &&
1171             c != INTR_CHAR(tty) && c != QUIT_CHAR(tty) && c != SUSP_CHAR(tty)) {
1172                 start_tty(tty);
1173                 process_echoes(tty);
1174         }
1175
1176         if (tty->closing) {
1177                 if (I_IXON(tty)) {
1178                         if (c == START_CHAR(tty)) {
1179                                 start_tty(tty);
1180                                 process_echoes(tty);
1181                         } else if (c == STOP_CHAR(tty))
1182                                 stop_tty(tty);
1183                 }
1184                 return;
1185         }
1186
1187         /*
1188          * If the previous character was LNEXT, or we know that this
1189          * character is not one of the characters that we'll have to
1190          * handle specially, do shortcut processing to speed things
1191          * up.
1192          */
1193         if (!test_bit(c, ldata->process_char_map) || ldata->lnext) {
1194                 ldata->lnext = 0;
1195                 parmrk = (c == (unsigned char) '\377' && I_PARMRK(tty)) ? 1 : 0;
1196                 if (ldata->read_cnt >= (N_TTY_BUF_SIZE - parmrk - 1)) {
1197                         /* beep if no space */
1198                         if (L_ECHO(tty))
1199                                 process_output('\a', tty);
1200                         return;
1201                 }
1202                 if (L_ECHO(tty)) {
1203                         finish_erasing(ldata);
1204                         /* Record the column of first canon char. */
1205                         if (ldata->canon_head == ldata->read_head)
1206                                 echo_set_canon_col(ldata);
1207                         echo_char(c, tty);
1208                         process_echoes(tty);
1209                 }
1210                 if (parmrk)
1211                         put_tty_queue(c, ldata);
1212                 put_tty_queue(c, ldata);
1213                 return;
1214         }
1215
1216         if (I_IXON(tty)) {
1217                 if (c == START_CHAR(tty)) {
1218                         start_tty(tty);
1219                         process_echoes(tty);
1220                         return;
1221                 }
1222                 if (c == STOP_CHAR(tty)) {
1223                         stop_tty(tty);
1224                         return;
1225                 }
1226         }
1227
1228         if (L_ISIG(tty)) {
1229                 int signal;
1230                 signal = SIGINT;
1231                 if (c == INTR_CHAR(tty))
1232                         goto send_signal;
1233                 signal = SIGQUIT;
1234                 if (c == QUIT_CHAR(tty))
1235                         goto send_signal;
1236                 signal = SIGTSTP;
1237                 if (c == SUSP_CHAR(tty)) {
1238 send_signal:
1239                         /*
1240                          * Note that we do not use isig() here because we want
1241                          * the order to be:
1242                          * 1) flush, 2) echo, 3) signal
1243                          */
1244                         if (!L_NOFLSH(tty)) {
1245                                 n_tty_flush_buffer(tty);
1246                                 tty_driver_flush_buffer(tty);
1247                         }
1248                         if (I_IXON(tty))
1249                                 start_tty(tty);
1250                         if (L_ECHO(tty)) {
1251                                 echo_char(c, tty);
1252                                 process_echoes(tty);
1253                         }
1254                         if (tty->pgrp)
1255                                 kill_pgrp(tty->pgrp, signal, 1);
1256                         return;
1257                 }
1258         }
1259
1260         if (c == '\r') {
1261                 if (I_IGNCR(tty))
1262                         return;
1263                 if (I_ICRNL(tty))
1264                         c = '\n';
1265         } else if (c == '\n' && I_INLCR(tty))
1266                 c = '\r';
1267
1268         if (ldata->icanon) {
1269                 if (c == ERASE_CHAR(tty) || c == KILL_CHAR(tty) ||
1270                     (c == WERASE_CHAR(tty) && L_IEXTEN(tty))) {
1271                         eraser(c, tty);
1272                         process_echoes(tty);
1273                         return;
1274                 }
1275                 if (c == LNEXT_CHAR(tty) && L_IEXTEN(tty)) {
1276                         ldata->lnext = 1;
1277                         if (L_ECHO(tty)) {
1278                                 finish_erasing(ldata);
1279                                 if (L_ECHOCTL(tty)) {
1280                                         echo_char_raw('^', ldata);
1281                                         echo_char_raw('\b', ldata);
1282                                         process_echoes(tty);
1283                                 }
1284                         }
1285                         return;
1286                 }
1287                 if (c == REPRINT_CHAR(tty) && L_ECHO(tty) &&
1288                     L_IEXTEN(tty)) {
1289                         unsigned long tail = ldata->canon_head;
1290
1291                         finish_erasing(ldata);
1292                         echo_char(c, tty);
1293                         echo_char_raw('\n', ldata);
1294                         while (tail != ldata->read_head) {
1295                                 echo_char(ldata->read_buf[tail], tty);
1296                                 tail = (tail+1) & (N_TTY_BUF_SIZE-1);
1297                         }
1298                         process_echoes(tty);
1299                         return;
1300                 }
1301                 if (c == '\n') {
1302                         if (ldata->read_cnt >= N_TTY_BUF_SIZE) {
1303                                 if (L_ECHO(tty))
1304                                         process_output('\a', tty);
1305                                 return;
1306                         }
1307                         if (L_ECHO(tty) || L_ECHONL(tty)) {
1308                                 echo_char_raw('\n', ldata);
1309                                 process_echoes(tty);
1310                         }
1311                         goto handle_newline;
1312                 }
1313                 if (c == EOF_CHAR(tty)) {
1314                         if (ldata->read_cnt >= N_TTY_BUF_SIZE)
1315                                 return;
1316                         if (ldata->canon_head != ldata->read_head)
1317                                 set_bit(TTY_PUSH, &tty->flags);
1318                         c = __DISABLED_CHAR;
1319                         goto handle_newline;
1320                 }
1321                 if ((c == EOL_CHAR(tty)) ||
1322                     (c == EOL2_CHAR(tty) && L_IEXTEN(tty))) {
1323                         parmrk = (c == (unsigned char) '\377' && I_PARMRK(tty))
1324                                  ? 1 : 0;
1325                         if (ldata->read_cnt >= (N_TTY_BUF_SIZE - parmrk)) {
1326                                 if (L_ECHO(tty))
1327                                         process_output('\a', tty);
1328                                 return;
1329                         }
1330                         /*
1331                          * XXX are EOL_CHAR and EOL2_CHAR echoed?!?
1332                          */
1333                         if (L_ECHO(tty)) {
1334                                 /* Record the column of first canon char. */
1335                                 if (ldata->canon_head == ldata->read_head)
1336                                         echo_set_canon_col(ldata);
1337                                 echo_char(c, tty);
1338                                 process_echoes(tty);
1339                         }
1340                         /*
1341                          * XXX does PARMRK doubling happen for
1342                          * EOL_CHAR and EOL2_CHAR?
1343                          */
1344                         if (parmrk)
1345                                 put_tty_queue(c, ldata);
1346
1347 handle_newline:
1348                         raw_spin_lock_irqsave(&ldata->read_lock, flags);
1349                         set_bit(ldata->read_head, ldata->read_flags);
1350                         put_tty_queue_nolock(c, ldata);
1351                         ldata->canon_head = ldata->read_head;
1352                         ldata->canon_data++;
1353                         raw_spin_unlock_irqrestore(&ldata->read_lock, flags);
1354                         kill_fasync(&tty->fasync, SIGIO, POLL_IN);
1355                         if (waitqueue_active(&tty->read_wait))
1356                                 wake_up_interruptible(&tty->read_wait);
1357                         return;
1358                 }
1359         }
1360
1361         parmrk = (c == (unsigned char) '\377' && I_PARMRK(tty)) ? 1 : 0;
1362         if (ldata->read_cnt >= (N_TTY_BUF_SIZE - parmrk - 1)) {
1363                 /* beep if no space */
1364                 if (L_ECHO(tty))
1365                         process_output('\a', tty);
1366                 return;
1367         }
1368         if (L_ECHO(tty)) {
1369                 finish_erasing(ldata);
1370                 if (c == '\n')
1371                         echo_char_raw('\n', ldata);
1372                 else {
1373                         /* Record the column of first canon char. */
1374                         if (ldata->canon_head == ldata->read_head)
1375                                 echo_set_canon_col(ldata);
1376                         echo_char(c, tty);
1377                 }
1378                 process_echoes(tty);
1379         }
1380
1381         if (parmrk)
1382                 put_tty_queue(c, ldata);
1383
1384         put_tty_queue(c, ldata);
1385 }
1386
1387
1388 /**
1389  *      n_tty_write_wakeup      -       asynchronous I/O notifier
1390  *      @tty: tty device
1391  *
1392  *      Required for the ptys, serial driver etc. since processes
1393  *      that attach themselves to the master and rely on ASYNC
1394  *      IO must be woken up
1395  */
1396
1397 static void n_tty_write_wakeup(struct tty_struct *tty)
1398 {
1399         if (tty->fasync && test_and_clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags))
1400                 kill_fasync(&tty->fasync, SIGIO, POLL_OUT);
1401 }
1402
1403 /**
1404  *      n_tty_receive_buf       -       data receive
1405  *      @tty: terminal device
1406  *      @cp: buffer
1407  *      @fp: flag buffer
1408  *      @count: characters
1409  *
1410  *      Called by the terminal driver when a block of characters has
1411  *      been received. This function must be called from soft contexts
1412  *      not from interrupt context. The driver is responsible for making
1413  *      calls one at a time and in order (or using flush_to_ldisc)
1414  */
1415
1416 static void n_tty_receive_buf(struct tty_struct *tty, const unsigned char *cp,
1417                               char *fp, int count)
1418 {
1419         struct n_tty_data *ldata = tty->disc_data;
1420         const unsigned char *p;
1421         char *f, flags = TTY_NORMAL;
1422         int     i;
1423         char    buf[64];
1424         unsigned long cpuflags;
1425
1426         if (ldata->real_raw) {
1427                 raw_spin_lock_irqsave(&ldata->read_lock, cpuflags);
1428                 i = min(N_TTY_BUF_SIZE - ldata->read_cnt,
1429                         N_TTY_BUF_SIZE - ldata->read_head);
1430                 i = min(count, i);
1431                 memcpy(ldata->read_buf + ldata->read_head, cp, i);
1432                 ldata->read_head = (ldata->read_head + i) & (N_TTY_BUF_SIZE-1);
1433                 ldata->read_cnt += i;
1434                 cp += i;
1435                 count -= i;
1436
1437                 i = min(N_TTY_BUF_SIZE - ldata->read_cnt,
1438                         N_TTY_BUF_SIZE - ldata->read_head);
1439                 i = min(count, i);
1440                 memcpy(ldata->read_buf + ldata->read_head, cp, i);
1441                 ldata->read_head = (ldata->read_head + i) & (N_TTY_BUF_SIZE-1);
1442                 ldata->read_cnt += i;
1443                 raw_spin_unlock_irqrestore(&ldata->read_lock, cpuflags);
1444         } else {
1445                 for (i = count, p = cp, f = fp; i; i--, p++) {
1446                         if (f)
1447                                 flags = *f++;
1448                         switch (flags) {
1449                         case TTY_NORMAL:
1450                                 n_tty_receive_char(tty, *p);
1451                                 break;
1452                         case TTY_BREAK:
1453                                 n_tty_receive_break(tty);
1454                                 break;
1455                         case TTY_PARITY:
1456                         case TTY_FRAME:
1457                                 n_tty_receive_parity_error(tty, *p);
1458                                 break;
1459                         case TTY_OVERRUN:
1460                                 n_tty_receive_overrun(tty);
1461                                 break;
1462                         default:
1463                                 printk(KERN_ERR "%s: unknown flag %d\n",
1464                                        tty_name(tty, buf), flags);
1465                                 break;
1466                         }
1467                 }
1468                 if (tty->ops->flush_chars)
1469                         tty->ops->flush_chars(tty);
1470         }
1471
1472         n_tty_set_room(tty);
1473
1474         if ((!ldata->icanon && (ldata->read_cnt >= tty->minimum_to_wake)) ||
1475                 L_EXTPROC(tty)) {
1476                 kill_fasync(&tty->fasync, SIGIO, POLL_IN);
1477                 if (waitqueue_active(&tty->read_wait))
1478                         wake_up_interruptible(&tty->read_wait);
1479         }
1480
1481         /*
1482          * Check the remaining room for the input canonicalization
1483          * mode.  We don't want to throttle the driver if we're in
1484          * canonical mode and don't have a newline yet!
1485          */
1486         if (tty->receive_room < TTY_THRESHOLD_THROTTLE)
1487                 tty_throttle(tty);
1488
1489         /* FIXME: there is a tiny race here if the receive room check runs
1490            before the other work executes and empties the buffer (upping
1491            the receiving room and unthrottling. We then throttle and get
1492            stuck. This has been observed and traced down by Vincent Pillet/
1493            We need to address this when we sort out out the rx path locking */
1494 }
1495
1496 int is_ignored(int sig)
1497 {
1498         return (sigismember(&current->blocked, sig) ||
1499                 current->sighand->action[sig-1].sa.sa_handler == SIG_IGN);
1500 }
1501
1502 /**
1503  *      n_tty_set_termios       -       termios data changed
1504  *      @tty: terminal
1505  *      @old: previous data
1506  *
1507  *      Called by the tty layer when the user changes termios flags so
1508  *      that the line discipline can plan ahead. This function cannot sleep
1509  *      and is protected from re-entry by the tty layer. The user is
1510  *      guaranteed that this function will not be re-entered or in progress
1511  *      when the ldisc is closed.
1512  *
1513  *      Locking: Caller holds tty->termios_mutex
1514  */
1515
1516 static void n_tty_set_termios(struct tty_struct *tty, struct ktermios *old)
1517 {
1518         struct n_tty_data *ldata = tty->disc_data;
1519         int canon_change = 1;
1520
1521         if (old)
1522                 canon_change = (old->c_lflag ^ tty->termios.c_lflag) & ICANON;
1523         if (canon_change) {
1524                 bitmap_zero(ldata->read_flags, N_TTY_BUF_SIZE);
1525                 ldata->canon_head = ldata->read_tail;
1526                 ldata->canon_data = 0;
1527                 ldata->erasing = 0;
1528         }
1529
1530         if (canon_change && !L_ICANON(tty) && ldata->read_cnt)
1531                 wake_up_interruptible(&tty->read_wait);
1532
1533         ldata->icanon = (L_ICANON(tty) != 0);
1534         if (test_bit(TTY_HW_COOK_IN, &tty->flags)) {
1535                 ldata->raw = 1;
1536                 ldata->real_raw = 1;
1537                 n_tty_set_room(tty);
1538                 return;
1539         }
1540         if (I_ISTRIP(tty) || I_IUCLC(tty) || I_IGNCR(tty) ||
1541             I_ICRNL(tty) || I_INLCR(tty) || L_ICANON(tty) ||
1542             I_IXON(tty) || L_ISIG(tty) || L_ECHO(tty) ||
1543             I_PARMRK(tty)) {
1544                 bitmap_zero(ldata->process_char_map, 256);
1545
1546                 if (I_IGNCR(tty) || I_ICRNL(tty))
1547                         set_bit('\r', ldata->process_char_map);
1548                 if (I_INLCR(tty))
1549                         set_bit('\n', ldata->process_char_map);
1550
1551                 if (L_ICANON(tty)) {
1552                         set_bit(ERASE_CHAR(tty), ldata->process_char_map);
1553                         set_bit(KILL_CHAR(tty), ldata->process_char_map);
1554                         set_bit(EOF_CHAR(tty), ldata->process_char_map);
1555                         set_bit('\n', ldata->process_char_map);
1556                         set_bit(EOL_CHAR(tty), ldata->process_char_map);
1557                         if (L_IEXTEN(tty)) {
1558                                 set_bit(WERASE_CHAR(tty),
1559                                         ldata->process_char_map);
1560                                 set_bit(LNEXT_CHAR(tty),
1561                                         ldata->process_char_map);
1562                                 set_bit(EOL2_CHAR(tty),
1563                                         ldata->process_char_map);
1564                                 if (L_ECHO(tty))
1565                                         set_bit(REPRINT_CHAR(tty),
1566                                                 ldata->process_char_map);
1567                         }
1568                 }
1569                 if (I_IXON(tty)) {
1570                         set_bit(START_CHAR(tty), ldata->process_char_map);
1571                         set_bit(STOP_CHAR(tty), ldata->process_char_map);
1572                 }
1573                 if (L_ISIG(tty)) {
1574                         set_bit(INTR_CHAR(tty), ldata->process_char_map);
1575                         set_bit(QUIT_CHAR(tty), ldata->process_char_map);
1576                         set_bit(SUSP_CHAR(tty), ldata->process_char_map);
1577                 }
1578                 clear_bit(__DISABLED_CHAR, ldata->process_char_map);
1579                 ldata->raw = 0;
1580                 ldata->real_raw = 0;
1581         } else {
1582                 ldata->raw = 1;
1583                 if ((I_IGNBRK(tty) || (!I_BRKINT(tty) && !I_PARMRK(tty))) &&
1584                     (I_IGNPAR(tty) || !I_INPCK(tty)) &&
1585                     (tty->driver->flags & TTY_DRIVER_REAL_RAW))
1586                         ldata->real_raw = 1;
1587                 else
1588                         ldata->real_raw = 0;
1589         }
1590         n_tty_set_room(tty);
1591         /* The termios change make the tty ready for I/O */
1592         wake_up_interruptible(&tty->write_wait);
1593         wake_up_interruptible(&tty->read_wait);
1594 }
1595
1596 /**
1597  *      n_tty_close             -       close the ldisc for this tty
1598  *      @tty: device
1599  *
1600  *      Called from the terminal layer when this line discipline is
1601  *      being shut down, either because of a close or becsuse of a
1602  *      discipline change. The function will not be called while other
1603  *      ldisc methods are in progress.
1604  */
1605
1606 static void n_tty_close(struct tty_struct *tty)
1607 {
1608         struct n_tty_data *ldata = tty->disc_data;
1609
1610         n_tty_flush_buffer(tty);
1611         kfree(ldata->read_buf);
1612         kfree(ldata->echo_buf);
1613         kfree(ldata);
1614         tty->disc_data = NULL;
1615 }
1616
1617 /**
1618  *      n_tty_open              -       open an ldisc
1619  *      @tty: terminal to open
1620  *
1621  *      Called when this line discipline is being attached to the
1622  *      terminal device. Can sleep. Called serialized so that no
1623  *      other events will occur in parallel. No further open will occur
1624  *      until a close.
1625  */
1626
1627 static int n_tty_open(struct tty_struct *tty)
1628 {
1629         struct n_tty_data *ldata;
1630
1631         ldata = kzalloc(sizeof(*ldata), GFP_KERNEL);
1632         if (!ldata)
1633                 goto err;
1634
1635         ldata->overrun_time = jiffies;
1636         mutex_init(&ldata->atomic_read_lock);
1637         mutex_init(&ldata->output_lock);
1638         mutex_init(&ldata->echo_lock);
1639         raw_spin_lock_init(&ldata->read_lock);
1640
1641         /* These are ugly. Currently a malloc failure here can panic */
1642         ldata->read_buf = kzalloc(N_TTY_BUF_SIZE, GFP_KERNEL);
1643         ldata->echo_buf = kzalloc(N_TTY_BUF_SIZE, GFP_KERNEL);
1644         if (!ldata->read_buf || !ldata->echo_buf)
1645                 goto err_free_bufs;
1646
1647         tty->disc_data = ldata;
1648         reset_buffer_flags(tty);
1649         tty_unthrottle(tty);
1650         ldata->column = 0;
1651         n_tty_set_termios(tty, NULL);
1652         tty->minimum_to_wake = 1;
1653         tty->closing = 0;
1654
1655         return 0;
1656 err_free_bufs:
1657         kfree(ldata->read_buf);
1658         kfree(ldata->echo_buf);
1659         kfree(ldata);
1660 err:
1661         return -ENOMEM;
1662 }
1663
1664 static inline int input_available_p(struct tty_struct *tty, int amt)
1665 {
1666         struct n_tty_data *ldata = tty->disc_data;
1667
1668         tty_flush_to_ldisc(tty);
1669         if (ldata->icanon && !L_EXTPROC(tty)) {
1670                 if (ldata->canon_data)
1671                         return 1;
1672         } else if (ldata->read_cnt >= (amt ? amt : 1))
1673                 return 1;
1674
1675         return 0;
1676 }
1677
1678 /**
1679  *      copy_from_read_buf      -       copy read data directly
1680  *      @tty: terminal device
1681  *      @b: user data
1682  *      @nr: size of data
1683  *
1684  *      Helper function to speed up n_tty_read.  It is only called when
1685  *      ICANON is off; it copies characters straight from the tty queue to
1686  *      user space directly.  It can be profitably called twice; once to
1687  *      drain the space from the tail pointer to the (physical) end of the
1688  *      buffer, and once to drain the space from the (physical) beginning of
1689  *      the buffer to head pointer.
1690  *
1691  *      Called under the ldata->atomic_read_lock sem
1692  *
1693  */
1694
1695 static int copy_from_read_buf(struct tty_struct *tty,
1696                                       unsigned char __user **b,
1697                                       size_t *nr)
1698
1699 {
1700         struct n_tty_data *ldata = tty->disc_data;
1701         int retval;
1702         size_t n;
1703         unsigned long flags;
1704         bool is_eof;
1705
1706         retval = 0;
1707         raw_spin_lock_irqsave(&ldata->read_lock, flags);
1708         n = min(ldata->read_cnt, N_TTY_BUF_SIZE - ldata->read_tail);
1709         n = min(*nr, n);
1710         raw_spin_unlock_irqrestore(&ldata->read_lock, flags);
1711         if (n) {
1712                 retval = copy_to_user(*b, &ldata->read_buf[ldata->read_tail], n);
1713                 n -= retval;
1714                 is_eof = n == 1 &&
1715                         ldata->read_buf[ldata->read_tail] == EOF_CHAR(tty);
1716                 tty_audit_add_data(tty, &ldata->read_buf[ldata->read_tail], n,
1717                                 ldata->icanon);
1718                 raw_spin_lock_irqsave(&ldata->read_lock, flags);
1719                 ldata->read_tail = (ldata->read_tail + n) & (N_TTY_BUF_SIZE-1);
1720                 ldata->read_cnt -= n;
1721                 /* Turn single EOF into zero-length read */
1722                 if (L_EXTPROC(tty) && ldata->icanon && is_eof && !ldata->read_cnt)
1723                         n = 0;
1724                 raw_spin_unlock_irqrestore(&ldata->read_lock, flags);
1725                 *b += n;
1726                 *nr -= n;
1727         }
1728         return retval;
1729 }
1730
1731 extern ssize_t redirected_tty_write(struct file *, const char __user *,
1732                                                         size_t, loff_t *);
1733
1734 /**
1735  *      job_control             -       check job control
1736  *      @tty: tty
1737  *      @file: file handle
1738  *
1739  *      Perform job control management checks on this file/tty descriptor
1740  *      and if appropriate send any needed signals and return a negative
1741  *      error code if action should be taken.
1742  *
1743  *      FIXME:
1744  *      Locking: None - redirected write test is safe, testing
1745  *      current->signal should possibly lock current->sighand
1746  *      pgrp locking ?
1747  */
1748
1749 static int job_control(struct tty_struct *tty, struct file *file)
1750 {
1751         /* Job control check -- must be done at start and after
1752            every sleep (POSIX.1 7.1.1.4). */
1753         /* NOTE: not yet done after every sleep pending a thorough
1754            check of the logic of this change. -- jlc */
1755         /* don't stop on /dev/console */
1756         if (file->f_op->write != redirected_tty_write &&
1757             current->signal->tty == tty) {
1758                 if (!tty->pgrp)
1759                         printk(KERN_ERR "n_tty_read: no tty->pgrp!\n");
1760                 else if (task_pgrp(current) != tty->pgrp) {
1761                         if (is_ignored(SIGTTIN) ||
1762                             is_current_pgrp_orphaned())
1763                                 return -EIO;
1764                         kill_pgrp(task_pgrp(current), SIGTTIN, 1);
1765                         set_thread_flag(TIF_SIGPENDING);
1766                         return -ERESTARTSYS;
1767                 }
1768         }
1769         return 0;
1770 }
1771
1772
1773 /**
1774  *      n_tty_read              -       read function for tty
1775  *      @tty: tty device
1776  *      @file: file object
1777  *      @buf: userspace buffer pointer
1778  *      @nr: size of I/O
1779  *
1780  *      Perform reads for the line discipline. We are guaranteed that the
1781  *      line discipline will not be closed under us but we may get multiple
1782  *      parallel readers and must handle this ourselves. We may also get
1783  *      a hangup. Always called in user context, may sleep.
1784  *
1785  *      This code must be sure never to sleep through a hangup.
1786  */
1787
1788 static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
1789                          unsigned char __user *buf, size_t nr)
1790 {
1791         struct n_tty_data *ldata = tty->disc_data;
1792         unsigned char __user *b = buf;
1793         DECLARE_WAITQUEUE(wait, current);
1794         int c;
1795         int minimum, time;
1796         ssize_t retval = 0;
1797         ssize_t size;
1798         long timeout;
1799         unsigned long flags;
1800         int packet;
1801
1802 do_it_again:
1803         c = job_control(tty, file);
1804         if (c < 0)
1805                 return c;
1806
1807         minimum = time = 0;
1808         timeout = MAX_SCHEDULE_TIMEOUT;
1809         if (!ldata->icanon) {
1810                 time = (HZ / 10) * TIME_CHAR(tty);
1811                 minimum = MIN_CHAR(tty);
1812                 if (minimum) {
1813                         if (time)
1814                                 tty->minimum_to_wake = 1;
1815                         else if (!waitqueue_active(&tty->read_wait) ||
1816                                  (tty->minimum_to_wake > minimum))
1817                                 tty->minimum_to_wake = minimum;
1818                 } else {
1819                         timeout = 0;
1820                         if (time) {
1821                                 timeout = time;
1822                                 time = 0;
1823                         }
1824                         tty->minimum_to_wake = minimum = 1;
1825                 }
1826         }
1827
1828         /*
1829          *      Internal serialization of reads.
1830          */
1831         if (file->f_flags & O_NONBLOCK) {
1832                 if (!mutex_trylock(&ldata->atomic_read_lock))
1833                         return -EAGAIN;
1834         } else {
1835                 if (mutex_lock_interruptible(&ldata->atomic_read_lock))
1836                         return -ERESTARTSYS;
1837         }
1838         packet = tty->packet;
1839
1840         add_wait_queue(&tty->read_wait, &wait);
1841         while (nr) {
1842                 /* First test for status change. */
1843                 if (packet && tty->link->ctrl_status) {
1844                         unsigned char cs;
1845                         if (b != buf)
1846                                 break;
1847                         spin_lock_irqsave(&tty->link->ctrl_lock, flags);
1848                         cs = tty->link->ctrl_status;
1849                         tty->link->ctrl_status = 0;
1850                         spin_unlock_irqrestore(&tty->link->ctrl_lock, flags);
1851                         if (tty_put_user(tty, cs, b++)) {
1852                                 retval = -EFAULT;
1853                                 b--;
1854                                 break;
1855                         }
1856                         nr--;
1857                         break;
1858                 }
1859                 /* This statement must be first before checking for input
1860                    so that any interrupt will set the state back to
1861                    TASK_RUNNING. */
1862                 set_current_state(TASK_INTERRUPTIBLE);
1863
1864                 if (((minimum - (b - buf)) < tty->minimum_to_wake) &&
1865                     ((minimum - (b - buf)) >= 1))
1866                         tty->minimum_to_wake = (minimum - (b - buf));
1867
1868                 if (!input_available_p(tty, 0)) {
1869                         if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
1870                                 retval = -EIO;
1871                                 break;
1872                         }
1873                         if (tty_hung_up_p(file))
1874                                 break;
1875                         if (!timeout)
1876                                 break;
1877                         if (file->f_flags & O_NONBLOCK) {
1878                                 retval = -EAGAIN;
1879                                 break;
1880                         }
1881                         if (signal_pending(current)) {
1882                                 retval = -ERESTARTSYS;
1883                                 break;
1884                         }
1885                         /* FIXME: does n_tty_set_room need locking ? */
1886                         n_tty_set_room(tty);
1887                         timeout = schedule_timeout(timeout);
1888                         continue;
1889                 }
1890                 __set_current_state(TASK_RUNNING);
1891
1892                 /* Deal with packet mode. */
1893                 if (packet && b == buf) {
1894                         if (tty_put_user(tty, TIOCPKT_DATA, b++)) {
1895                                 retval = -EFAULT;
1896                                 b--;
1897                                 break;
1898                         }
1899                         nr--;
1900                 }
1901
1902                 if (ldata->icanon && !L_EXTPROC(tty)) {
1903                         /* N.B. avoid overrun if nr == 0 */
1904                         raw_spin_lock_irqsave(&ldata->read_lock, flags);
1905                         while (nr && ldata->read_cnt) {
1906                                 int eol;
1907
1908                                 eol = test_and_clear_bit(ldata->read_tail,
1909                                                 ldata->read_flags);
1910                                 c = ldata->read_buf[ldata->read_tail];
1911                                 ldata->read_tail = ((ldata->read_tail+1) &
1912                                                   (N_TTY_BUF_SIZE-1));
1913                                 ldata->read_cnt--;
1914                                 if (eol) {
1915                                         /* this test should be redundant:
1916                                          * we shouldn't be reading data if
1917                                          * canon_data is 0
1918                                          */
1919                                         if (--ldata->canon_data < 0)
1920                                                 ldata->canon_data = 0;
1921                                 }
1922                                 raw_spin_unlock_irqrestore(&ldata->read_lock, flags);
1923
1924                                 if (!eol || (c != __DISABLED_CHAR)) {
1925                                         if (tty_put_user(tty, c, b++)) {
1926                                                 retval = -EFAULT;
1927                                                 b--;
1928                                                 raw_spin_lock_irqsave(&ldata->read_lock, flags);
1929                                                 break;
1930                                         }
1931                                         nr--;
1932                                 }
1933                                 if (eol) {
1934                                         tty_audit_push(tty);
1935                                         raw_spin_lock_irqsave(&ldata->read_lock, flags);
1936                                         break;
1937                                 }
1938                                 raw_spin_lock_irqsave(&ldata->read_lock, flags);
1939                         }
1940                         raw_spin_unlock_irqrestore(&ldata->read_lock, flags);
1941                         if (retval)
1942                                 break;
1943                 } else {
1944                         int uncopied;
1945                         /* The copy function takes the read lock and handles
1946                            locking internally for this case */
1947                         uncopied = copy_from_read_buf(tty, &b, &nr);
1948                         uncopied += copy_from_read_buf(tty, &b, &nr);
1949                         if (uncopied) {
1950                                 retval = -EFAULT;
1951                                 break;
1952                         }
1953                 }
1954
1955                 /* If there is enough space in the read buffer now, let the
1956                  * low-level driver know. We use n_tty_chars_in_buffer() to
1957                  * check the buffer, as it now knows about canonical mode.
1958                  * Otherwise, if the driver is throttled and the line is
1959                  * longer than TTY_THRESHOLD_UNTHROTTLE in canonical mode,
1960                  * we won't get any more characters.
1961                  */
1962                 if (n_tty_chars_in_buffer(tty) <= TTY_THRESHOLD_UNTHROTTLE) {
1963                         n_tty_set_room(tty);
1964                         check_unthrottle(tty);
1965                 }
1966
1967                 if (b - buf >= minimum)
1968                         break;
1969                 if (time)
1970                         timeout = time;
1971         }
1972         mutex_unlock(&ldata->atomic_read_lock);
1973         remove_wait_queue(&tty->read_wait, &wait);
1974
1975         if (!waitqueue_active(&tty->read_wait))
1976                 tty->minimum_to_wake = minimum;
1977
1978         __set_current_state(TASK_RUNNING);
1979         size = b - buf;
1980         if (size) {
1981                 retval = size;
1982                 if (nr)
1983                         clear_bit(TTY_PUSH, &tty->flags);
1984         } else if (test_and_clear_bit(TTY_PUSH, &tty->flags))
1985                 goto do_it_again;
1986
1987         n_tty_set_room(tty);
1988         return retval;
1989 }
1990
1991 /**
1992  *      n_tty_write             -       write function for tty
1993  *      @tty: tty device
1994  *      @file: file object
1995  *      @buf: userspace buffer pointer
1996  *      @nr: size of I/O
1997  *
1998  *      Write function of the terminal device.  This is serialized with
1999  *      respect to other write callers but not to termios changes, reads
2000  *      and other such events.  Since the receive code will echo characters,
2001  *      thus calling driver write methods, the output_lock is used in
2002  *      the output processing functions called here as well as in the
2003  *      echo processing function to protect the column state and space
2004  *      left in the buffer.
2005  *
2006  *      This code must be sure never to sleep through a hangup.
2007  *
2008  *      Locking: output_lock to protect column state and space left
2009  *               (note that the process_output*() functions take this
2010  *                lock themselves)
2011  */
2012
2013 static ssize_t n_tty_write(struct tty_struct *tty, struct file *file,
2014                            const unsigned char *buf, size_t nr)
2015 {
2016         const unsigned char *b = buf;
2017         DECLARE_WAITQUEUE(wait, current);
2018         int c;
2019         ssize_t retval = 0;
2020
2021         /* Job control check -- must be done at start (POSIX.1 7.1.1.4). */
2022         if (L_TOSTOP(tty) && file->f_op->write != redirected_tty_write) {
2023                 retval = tty_check_change(tty);
2024                 if (retval)
2025                         return retval;
2026         }
2027
2028         /* Write out any echoed characters that are still pending */
2029         process_echoes(tty);
2030
2031         add_wait_queue(&tty->write_wait, &wait);
2032         while (1) {
2033                 set_current_state(TASK_INTERRUPTIBLE);
2034                 if (signal_pending(current)) {
2035                         retval = -ERESTARTSYS;
2036                         break;
2037                 }
2038                 if (tty_hung_up_p(file) || (tty->link && !tty->link->count)) {
2039                         retval = -EIO;
2040                         break;
2041                 }
2042                 if (O_OPOST(tty) && !(test_bit(TTY_HW_COOK_OUT, &tty->flags))) {
2043                         while (nr > 0) {
2044                                 ssize_t num = process_output_block(tty, b, nr);
2045                                 if (num < 0) {
2046                                         if (num == -EAGAIN)
2047                                                 break;
2048                                         retval = num;
2049                                         goto break_out;
2050                                 }
2051                                 b += num;
2052                                 nr -= num;
2053                                 if (nr == 0)
2054                                         break;
2055                                 c = *b;
2056                                 if (process_output(c, tty) < 0)
2057                                         break;
2058                                 b++; nr--;
2059                         }
2060                         if (tty->ops->flush_chars)
2061                                 tty->ops->flush_chars(tty);
2062                 } else {
2063                         while (nr > 0) {
2064                                 c = tty->ops->write(tty, b, nr);
2065                                 if (c < 0) {
2066                                         retval = c;
2067                                         goto break_out;
2068                                 }
2069                                 if (!c)
2070                                         break;
2071                                 b += c;
2072                                 nr -= c;
2073                         }
2074                 }
2075                 if (!nr)
2076                         break;
2077                 if (file->f_flags & O_NONBLOCK) {
2078                         retval = -EAGAIN;
2079                         break;
2080                 }
2081                 schedule();
2082         }
2083 break_out:
2084         __set_current_state(TASK_RUNNING);
2085         remove_wait_queue(&tty->write_wait, &wait);
2086         if (b - buf != nr && tty->fasync)
2087                 set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
2088         return (b - buf) ? b - buf : retval;
2089 }
2090
2091 /**
2092  *      n_tty_poll              -       poll method for N_TTY
2093  *      @tty: terminal device
2094  *      @file: file accessing it
2095  *      @wait: poll table
2096  *
2097  *      Called when the line discipline is asked to poll() for data or
2098  *      for special events. This code is not serialized with respect to
2099  *      other events save open/close.
2100  *
2101  *      This code must be sure never to sleep through a hangup.
2102  *      Called without the kernel lock held - fine
2103  */
2104
2105 static unsigned int n_tty_poll(struct tty_struct *tty, struct file *file,
2106                                                         poll_table *wait)
2107 {
2108         unsigned int mask = 0;
2109
2110         poll_wait(file, &tty->read_wait, wait);
2111         poll_wait(file, &tty->write_wait, wait);
2112         if (input_available_p(tty, TIME_CHAR(tty) ? 0 : MIN_CHAR(tty)))
2113                 mask |= POLLIN | POLLRDNORM;
2114         if (tty->packet && tty->link->ctrl_status)
2115                 mask |= POLLPRI | POLLIN | POLLRDNORM;
2116         if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
2117                 mask |= POLLHUP;
2118         if (tty_hung_up_p(file))
2119                 mask |= POLLHUP;
2120         if (!(mask & (POLLHUP | POLLIN | POLLRDNORM))) {
2121                 if (MIN_CHAR(tty) && !TIME_CHAR(tty))
2122                         tty->minimum_to_wake = MIN_CHAR(tty);
2123                 else
2124                         tty->minimum_to_wake = 1;
2125         }
2126         if (tty->ops->write && !tty_is_writelocked(tty) &&
2127                         tty_chars_in_buffer(tty) < WAKEUP_CHARS &&
2128                         tty_write_room(tty) > 0)
2129                 mask |= POLLOUT | POLLWRNORM;
2130         return mask;
2131 }
2132
2133 static unsigned long inq_canon(struct n_tty_data *ldata)
2134 {
2135         int nr, head, tail;
2136
2137         if (!ldata->canon_data)
2138                 return 0;
2139         head = ldata->canon_head;
2140         tail = ldata->read_tail;
2141         nr = (head - tail) & (N_TTY_BUF_SIZE-1);
2142         /* Skip EOF-chars.. */
2143         while (head != tail) {
2144                 if (test_bit(tail, ldata->read_flags) &&
2145                     ldata->read_buf[tail] == __DISABLED_CHAR)
2146                         nr--;
2147                 tail = (tail+1) & (N_TTY_BUF_SIZE-1);
2148         }
2149         return nr;
2150 }
2151
2152 static int n_tty_ioctl(struct tty_struct *tty, struct file *file,
2153                        unsigned int cmd, unsigned long arg)
2154 {
2155         struct n_tty_data *ldata = tty->disc_data;
2156         int retval;
2157
2158         switch (cmd) {
2159         case TIOCOUTQ:
2160                 return put_user(tty_chars_in_buffer(tty), (int __user *) arg);
2161         case TIOCINQ:
2162                 /* FIXME: Locking */
2163                 retval = ldata->read_cnt;
2164                 if (L_ICANON(tty))
2165                         retval = inq_canon(ldata);
2166                 return put_user(retval, (unsigned int __user *) arg);
2167         default:
2168                 return n_tty_ioctl_helper(tty, file, cmd, arg);
2169         }
2170 }
2171
2172 struct tty_ldisc_ops tty_ldisc_N_TTY = {
2173         .magic           = TTY_LDISC_MAGIC,
2174         .name            = "n_tty",
2175         .open            = n_tty_open,
2176         .close           = n_tty_close,
2177         .flush_buffer    = n_tty_flush_buffer,
2178         .chars_in_buffer = n_tty_chars_in_buffer,
2179         .read            = n_tty_read,
2180         .write           = n_tty_write,
2181         .ioctl           = n_tty_ioctl,
2182         .set_termios     = n_tty_set_termios,
2183         .poll            = n_tty_poll,
2184         .receive_buf     = n_tty_receive_buf,
2185         .write_wakeup    = n_tty_write_wakeup
2186 };
2187
2188 /**
2189  *      n_tty_inherit_ops       -       inherit N_TTY methods
2190  *      @ops: struct tty_ldisc_ops where to save N_TTY methods
2191  *
2192  *      Enables a 'subclass' line discipline to 'inherit' N_TTY
2193  *      methods.
2194  */
2195
2196 void n_tty_inherit_ops(struct tty_ldisc_ops *ops)
2197 {
2198         *ops = tty_ldisc_N_TTY;
2199         ops->owner = NULL;
2200         ops->refcount = ops->flags = 0;
2201 }
2202 EXPORT_SYMBOL_GPL(n_tty_inherit_ops);