drivers/char/n_tty.c

   1 /*
   2  * n_tty.c --- implements the N_TTY line discipline.
   3  *
   4  * This code used to be in tty_io.c, but things are getting hairy
   5  * enough that it made sense to split things off.  (The N_TTY
   6  * processing has changed so much that it's hardly recognizable,
   7  * anyway...)
   8  *
   9  * Note that the open routine for N_TTY is guaranteed never to return
  10  * an error.  This is because Linux will fall back to setting a line
  11  * to N_TTY if it can not switch to any other line discipline.
  12  *
  13  * Written by Theodore Ts'o, Copyright 1994.
  14  *
  15  * This file also contains code originally written by Linus Torvalds,
  16  * Copyright 1991, 1992, 1993, and by Julian Cowley, Copyright 1994.
  17  *
  18  * This file may be redistributed under the terms of the GNU General Public
  19  * License.
  20  *
  21  * Reduced memory usage for older ARM systems  - Russell King.
  22  *
  23  * 2000/01/20   Fixed SMP locking on put_tty_queue using bits of
  24  *              the patch by Andrew J. Kroll <ag784@freenet.buffalo.edu>
  25  *              who actually finally proved there really was a race.
  26  *
  27  * 2002/03/18   Implemented n_tty_wakeup to send SIGIO POLL_OUTs to
  28  *              waiting writing processes-Sapan Bhatia <sapan@corewars.org>.
  29  *              Also fixed a bug in BLOCKING mode where write_chan returns
  30  *              EAGAIN
  31  */
  32
  33 #include <linux/types.h>
  34 #include <linux/major.h>
  35 #include <linux/errno.h>
  36 #include <linux/signal.h>
  37 #include <linux/fcntl.h>
  38 #include <linux/sched.h>
  39 #include <linux/interrupt.h>
  40 #include <linux/tty.h>
  41 #include <linux/timer.h>
  42 #include <linux/ctype.h>
  43 #include <linux/mm.h>
  44 #include <linux/string.h>
  45 #include <linux/slab.h>
  46 #include <linux/poll.h>
  47 #include <linux/bitops.h>
  48 #include <linux/audit.h>
  49 #include <linux/file.h>
  50
  51 #include <asm/uaccess.h>
  52 #include <asm/system.h>
  53
  54 /* number of characters left in xmit buffer before select has we have room */
  55 #define WAKEUP_CHARS 256
  56
  57 /*
  58  * This defines the low- and high-watermarks for throttling and
  59  * unthrottling the TTY driver.  These watermarks are used for
  60  * controlling the space in the read buffer.
  61  */
  62 #define TTY_THRESHOLD_THROTTLE          128 /* now based on remaining room */
  63 #define TTY_THRESHOLD_UNTHROTTLE        128
  64
  65 static inline unsigned char *alloc_buf(void)
  66 {
  67         gfp_t prio = in_interrupt() ? GFP_ATOMIC : GFP_KERNEL;
  68
  69         if (PAGE_SIZE != N_TTY_BUF_SIZE)
  70                 return kmalloc(N_TTY_BUF_SIZE, prio);
  71         else
  72                 return (unsigned char *)__get_free_page(prio);
  73 }
  74
  75 static inline void free_buf(unsigned char *buf)
  76 {
  77         if (PAGE_SIZE != N_TTY_BUF_SIZE)
  78                 kfree(buf);
  79         else
  80                 free_page((unsigned long) buf);
  81 }
  82
  83 static inline int tty_put_user(struct tty_struct *tty, unsigned char x,
  84                                unsigned char __user *ptr)
  85 {
  86         tty_audit_add_data(tty, &x, 1);
  87         return put_user(x, ptr);
  88 }
  89
  90 /**
  91  *      n_tty_set__room -       receive space
  92  *      @tty: terminal
  93  *
  94  *      Called by the driver to find out how much data it is
  95  *      permitted to feed to the line discipline without any being lost
  96  *      and thus to manage flow control. Not serialized. Answers for the
  97  *      "instant".
  98  */
  99
 100 static void n_tty_set_room(struct tty_struct *tty)
 101 {
 102         int     left = N_TTY_BUF_SIZE - tty->read_cnt - 1;
 103
 104         /*
 105          * If we are doing input canonicalization, and there are no
 106          * pending newlines, let characters through without limit, so
 107          * that erase characters will be handled.  Other excess
 108          * characters will be beeped.
 109          */
 110         if (left <= 0)
 111                 left = tty->icanon && !tty->canon_data;
 112         tty->receive_room = left;
 113 }
 114
 115 static void put_tty_queue_nolock(unsigned char c, struct tty_struct *tty)
 116 {
 117         if (tty->read_cnt < N_TTY_BUF_SIZE) {
 118                 tty->read_buf[tty->read_head] = c;
 119                 tty->read_head = (tty->read_head + 1) & (N_TTY_BUF_SIZE-1);
 120                 tty->read_cnt++;
 121         }
 122 }
 123
 124 static void put_tty_queue(unsigned char c, struct tty_struct *tty)
 125 {
 126         unsigned long flags;
 127         /*
 128          *      The problem of stomping on the buffers ends here.
 129          *      Why didn't anyone see this one coming? --AJK
 130         */
 131         spin_lock_irqsave(&tty->read_lock, flags);
 132         put_tty_queue_nolock(c, tty);
 133         spin_unlock_irqrestore(&tty->read_lock, flags);
 134 }
 135
 136 /**
 137  *      check_unthrottle        -       allow new receive data
 138  *      @tty; tty device
 139  *
 140  *      Check whether to call the driver.unthrottle function.
 141  *      We test the TTY_THROTTLED bit first so that it always
 142  *      indicates the current state. The decision about whether
 143  *      it is worth allowing more input has been taken by the caller.
 144  *      Can sleep, may be called under the atomic_read_lock mutex but
 145  *      this is not guaranteed.
 146  */
 147
 148 static void check_unthrottle(struct tty_struct *tty)
 149 {
 150         if (tty->count &&
 151             test_and_clear_bit(TTY_THROTTLED, &tty->flags) &&
 152             tty->driver->unthrottle)
 153                 tty->driver->unthrottle(tty);
 154 }
 155
 156 /**
 157  *      reset_buffer_flags      -       reset buffer state
 158  *      @tty: terminal to reset
 159  *
 160  *      Reset the read buffer counters, clear the flags,
 161  *      and make sure the driver is unthrottled. Called
 162  *      from n_tty_open() and n_tty_flush_buffer().
 163  */
 164 static void reset_buffer_flags(struct tty_struct *tty)
 165 {
 166         unsigned long flags;
 167
 168         spin_lock_irqsave(&tty->read_lock, flags);
 169         tty->read_head = tty->read_tail = tty->read_cnt = 0;
 170         spin_unlock_irqrestore(&tty->read_lock, flags);
 171         tty->canon_head = tty->canon_data = tty->erasing = 0;
 172         memset(&tty->read_flags, 0, sizeof tty->read_flags);
 173         n_tty_set_room(tty);
 174         check_unthrottle(tty);
 175 }
 176
 177 /**
 178  *      n_tty_flush_buffer      -       clean input queue
 179  *      @tty:   terminal device
 180  *
 181  *      Flush the input buffer. Called when the line discipline is
 182  *      being closed, when the tty layer wants the buffer flushed (eg
 183  *      at hangup) or when the N_TTY line discipline internally has to
 184  *      clean the pending queue (for example some signals).
 185  *
 186  *      Locking: ctrl_lock
 187  */
 188
 189 static void n_tty_flush_buffer(struct tty_struct *tty)
 190 {
 191         unsigned long flags;
 192         /* clear everything and unthrottle the driver */
 193         reset_buffer_flags(tty);
 194
 195         if (!tty->link)
 196                 return;
 197
 198         spin_lock_irqsave(&tty->ctrl_lock, flags);
 199         if (tty->link->packet) {
 200                 tty->ctrl_status |= TIOCPKT_FLUSHREAD;
 201                 wake_up_interruptible(&tty->link->read_wait);
 202         }
 203         spin_unlock_irqrestore(&tty->ctrl_lock, flags);
 204 }
 205
 206 /**
 207  *      n_tty_chars_in_buffer   -       report available bytes
 208  *      @tty: tty device
 209  *
 210  *      Report the number of characters buffered to be delivered to user
 211  *      at this instant in time.
 212  */
 213
 214 static ssize_t n_tty_chars_in_buffer(struct tty_struct *tty)
 215 {
 216         unsigned long flags;
 217         ssize_t n = 0;
 218
 219         spin_lock_irqsave(&tty->read_lock, flags);
 220         if (!tty->icanon) {
 221                 n = tty->read_cnt;
 222         } else if (tty->canon_data) {
 223                 n = (tty->canon_head > tty->read_tail) ?
 224                         tty->canon_head - tty->read_tail :
 225                         tty->canon_head + (N_TTY_BUF_SIZE - tty->read_tail);
 226         }
 227         spin_unlock_irqrestore(&tty->read_lock, flags);
 228         return n;
 229 }
 230
 231 /**
 232  *      is_utf8_continuation    -       utf8 multibyte check
 233  *      @c: byte to check
 234  *
 235  *      Returns true if the utf8 character 'c' is a multibyte continuation
 236  *      character. We use this to correctly compute the on screen size
 237  *      of the character when printing
 238  */
 239
 240 static inline int is_utf8_continuation(unsigned char c)
 241 {
 242         return (c & 0xc0) == 0x80;
 243 }
 244
 245 /**
 246  *      is_continuation         -       multibyte check
 247  *      @c: byte to check
 248  *
 249  *      Returns true if the utf8 character 'c' is a multibyte continuation
 250  *      character and the terminal is in unicode mode.
 251  */
 252
 253 static inline int is_continuation(unsigned char c, struct tty_struct *tty)
 254 {
 255         return I_IUTF8(tty) && is_utf8_continuation(c);
 256 }
 257
 258 /**
 259  *      opost                   -       output post processor
 260  *      @c: character (or partial unicode symbol)
 261  *      @tty: terminal device
 262  *
 263  *      Perform OPOST processing.  Returns -1 when the output device is
 264  *      full and the character must be retried. Note that Linux currently
 265  *      ignores TABDLY, CRDLY, VTDLY, FFDLY and NLDLY. They simply aren't
 266  *      relevant in the world today. If you ever need them, add them here.
 267  *
 268  *      Called from both the receive and transmit sides and can be called
 269  *      re-entrantly. Relies on lock_kernel() for tty->column state.
 270  */
 271
 272 static int opost(unsigned char c, struct tty_struct *tty)
 273 {
 274         int     space, spaces;
 275
 276         space = tty->driver->write_room(tty);
 277         if (!space)
 278                 return -1;
 279
 280         lock_kernel();
 281         if (O_OPOST(tty)) {
 282                 switch (c) {
 283                 case '\n':
 284                         if (O_ONLRET(tty))
 285                                 tty->column = 0;
 286                         if (O_ONLCR(tty)) {
 287                                 if (space < 2)
 288                                         return -1;
 289                                 tty->driver->put_char(tty, '\r');
 290                                 tty->column = 0;
 291                         }
 292                         tty->canon_column = tty->column;
 293                         break;
 294                 case '\r':
 295                         if (O_ONOCR(tty) && tty->column == 0)
 296                                 return 0;
 297                         if (O_OCRNL(tty)) {
 298                                 c = '\n';
 299                                 if (O_ONLRET(tty))
 300                                         tty->canon_column = tty->column = 0;
 301                                 break;
 302                         }
 303                         tty->canon_column = tty->column = 0;
 304                         break;
 305                 case '\t':
 306                         spaces = 8 - (tty->column & 7);
 307                         if (O_TABDLY(tty) == XTABS) {
 308                                 if (space < spaces)
 309                                         return -1;
 310                                 tty->column += spaces;
 311                                 tty->driver->write(tty, "        ", spaces);
 312                                 return 0;
 313                         }
 314                         tty->column += spaces;
 315                         break;
 316                 case '\b':
 317                         if (tty->column > 0)
 318                                 tty->column--;
 319                         break;
 320                 default:
 321                         if (O_OLCUC(tty))
 322                                 c = toupper(c);
 323                         if (!iscntrl(c) && !is_continuation(c, tty))
 324                                 tty->column++;
 325                         break;
 326                 }
 327         }
 328         tty->driver->put_char(tty, c);
 329         unlock_kernel();
 330         return 0;
 331 }
 332
 333 /**
 334  *      opost_block             -       block postprocess
 335  *      @tty: terminal device
 336  *      @inbuf: user buffer
 337  *      @nr: number of bytes
 338  *
 339  *      This path is used to speed up block console writes, among other
 340  *      things when processing blocks of output data. It handles only
 341  *      the simple cases normally found and helps to generate blocks of
 342  *      symbols for the console driver and thus improve performance.
 343  *
 344  *      Called from write_chan under the tty layer write lock. Relies
 345  *      on lock_kernel for the tty->column state.
 346  */
 347
 348 static ssize_t opost_block(struct tty_struct *tty,
 349                        const unsigned char *buf, unsigned int nr)
 350 {
 351         int     space;
 352         int     i;
 353         const unsigned char *cp;
 354
 355         space = tty->driver->write_room(tty);
 356         if (!space)
 357                 return 0;
 358         if (nr > space)
 359                 nr = space;
 360
 361         lock_kernel();
 362         for (i = 0, cp = buf; i < nr; i++, cp++) {
 363                 switch (*cp) {
 364                 case '\n':
 365                         if (O_ONLRET(tty))
 366                                 tty->column = 0;
 367                         if (O_ONLCR(tty))
 368                                 goto break_out;
 369                         tty->canon_column = tty->column;
 370                         break;
 371                 case '\r':
 372                         if (O_ONOCR(tty) && tty->column == 0)
 373                                 goto break_out;
 374                         if (O_OCRNL(tty))
 375                                 goto break_out;
 376                         tty->canon_column = tty->column = 0;
 377                         break;
 378                 case '\t':
 379                         goto break_out;
 380                 case '\b':
 381                         if (tty->column > 0)
 382                                 tty->column--;
 383                         break;
 384                 default:
 385                         if (O_OLCUC(tty))
 386                                 goto break_out;
 387                         if (!iscntrl(*cp))
 388                                 tty->column++;
 389                         break;
 390                 }
 391         }
 392 break_out:
 393         if (tty->driver->flush_chars)
 394                 tty->driver->flush_chars(tty);
 395         i = tty->driver->write(tty, buf, i);
 396         unlock_kernel();
 397         return i;
 398 }
 399
 400
 401 /**
 402  *      put_char        -       write character to driver
 403  *      @c: character (or part of unicode symbol)
 404  *      @tty: terminal device
 405  *
 406  *      Queue a byte to the driver layer for output
 407  */
 408
 409 static inline void put_char(unsigned char c, struct tty_struct *tty)
 410 {
 411         tty->driver->put_char(tty, c);
 412 }
 413
 414 /**
 415  *      echo_char       -       echo characters
 416  *      @c: unicode byte to echo
 417  *      @tty: terminal device
 418  *
 419  *      Echo user input back onto the screen. This must be called only when
 420  *      L_ECHO(tty) is true. Called from the driver receive_buf path.
 421  */
 422
 423 static void echo_char(unsigned char c, struct tty_struct *tty)
 424 {
 425         if (L_ECHOCTL(tty) && iscntrl(c) && c != '\t') {
 426                 put_char('^', tty);
 427                 put_char(c ^ 0100, tty);
 428                 tty->column += 2;
 429         } else
 430                 opost(c, tty);
 431 }
 432
 433 static inline void finish_erasing(struct tty_struct *tty)
 434 {
 435         if (tty->erasing) {
 436                 put_char('/', tty);
 437                 tty->column++;
 438                 tty->erasing = 0;
 439         }
 440 }
 441
 442 /**
 443  *      eraser          -       handle erase function
 444  *      @c: character input
 445  *      @tty: terminal device
 446  *
 447  *      Perform erase and necessary output when an erase character is
 448  *      present in the stream from the driver layer. Handles the complexities
 449  *      of UTF-8 multibyte symbols.
 450  */
 451
 452 static void eraser(unsigned char c, struct tty_struct *tty)
 453 {
 454         enum { ERASE, WERASE, KILL } kill_type;
 455         int head, seen_alnums, cnt;
 456         unsigned long flags;
 457
 458         if (tty->read_head == tty->canon_head) {
 459                 /* opost('\a', tty); */         /* what do you think? */
 460                 return;
 461         }
 462         if (c == ERASE_CHAR(tty))
 463                 kill_type = ERASE;
 464         else if (c == WERASE_CHAR(tty))
 465                 kill_type = WERASE;
 466         else {
 467                 if (!L_ECHO(tty)) {
 468                         spin_lock_irqsave(&tty->read_lock, flags);
 469                         tty->read_cnt -= ((tty->read_head - tty->canon_head) &
 470                                           (N_TTY_BUF_SIZE - 1));
 471                         tty->read_head = tty->canon_head;
 472                         spin_unlock_irqrestore(&tty->read_lock, flags);
 473                         return;
 474                 }
 475                 if (!L_ECHOK(tty) || !L_ECHOKE(tty) || !L_ECHOE(tty)) {
 476                         spin_lock_irqsave(&tty->read_lock, flags);
 477                         tty->read_cnt -= ((tty->read_head - tty->canon_head) &
 478                                           (N_TTY_BUF_SIZE - 1));
 479                         tty->read_head = tty->canon_head;
 480                         spin_unlock_irqrestore(&tty->read_lock, flags);
 481                         finish_erasing(tty);
 482                         echo_char(KILL_CHAR(tty), tty);
 483                         /* Add a newline if ECHOK is on and ECHOKE is off. */
 484                         if (L_ECHOK(tty))
 485                                 opost('\n', tty);
 486                         return;
 487                 }
 488                 kill_type = KILL;
 489         }
 490
 491         seen_alnums = 0;
 492         while (tty->read_head != tty->canon_head) {
 493                 head = tty->read_head;
 494
 495                 /* erase a single possibly multibyte character */
 496                 do {
 497                         head = (head - 1) & (N_TTY_BUF_SIZE-1);
 498                         c = tty->read_buf[head];
 499                 } while (is_continuation(c, tty) && head != tty->canon_head);
 500
 501                 /* do not partially erase */
 502                 if (is_continuation(c, tty))
 503                         break;
 504
 505                 if (kill_type == WERASE) {
 506                         /* Equivalent to BSD's ALTWERASE. */
 507                         if (isalnum(c) || c == '_')
 508                                 seen_alnums++;
 509                         else if (seen_alnums)
 510                                 break;
 511                 }
 512                 cnt = (tty->read_head - head) & (N_TTY_BUF_SIZE-1);
 513                 spin_lock_irqsave(&tty->read_lock, flags);
 514                 tty->read_head = head;
 515                 tty->read_cnt -= cnt;
 516                 spin_unlock_irqrestore(&tty->read_lock, flags);
 517                 if (L_ECHO(tty)) {
 518                         if (L_ECHOPRT(tty)) {
 519                                 if (!tty->erasing) {
 520                                         put_char('\\', tty);
 521                                         tty->column++;
 522                                         tty->erasing = 1;
 523                                 }
 524                                 /* if cnt > 1, output a multi-byte character */
 525                                 echo_char(c, tty);
 526                                 while (--cnt > 0) {
 527                                         head = (head+1) & (N_TTY_BUF_SIZE-1);
 528                                         put_char(tty->read_buf[head], tty);
 529                                 }
 530                         } else if (kill_type == ERASE && !L_ECHOE(tty)) {
 531                                 echo_char(ERASE_CHAR(tty), tty);
 532                         } else if (c == '\t') {
 533                                 unsigned int col = tty->canon_column;
 534                                 unsigned long tail = tty->canon_head;
 535
 536                                 /* Find the column of the last char. */
 537                                 while (tail != tty->read_head) {
 538                                         c = tty->read_buf[tail];
 539                                         if (c == '\t')
 540                                                 col = (col | 7) + 1;
 541                                         else if (iscntrl(c)) {
 542                                                 if (L_ECHOCTL(tty))
 543                                                         col += 2;
 544                                         } else if (!is_continuation(c, tty))
 545                                                 col++;
 546                                         tail = (tail+1) & (N_TTY_BUF_SIZE-1);
 547                                 }
 548
 549                                 /* should never happen */
 550                                 if (tty->column > 0x80000000)
 551                                         tty->column = 0;
 552
 553                                 /* Now backup to that column. */
 554                                 while (tty->column > col) {
 555                                         /* Can't use opost here. */
 556                                         put_char('\b', tty);
 557                                         if (tty->column > 0)
 558                                                 tty->column--;
 559                                 }
 560                         } else {
 561                                 if (iscntrl(c) && L_ECHOCTL(tty)) {
 562                                         put_char('\b', tty);
 563                                         put_char(' ', tty);
 564                                         put_char('\b', tty);
 565                                         if (tty->column > 0)
 566                                                 tty->column--;
 567                                 }
 568                                 if (!iscntrl(c) || L_ECHOCTL(tty)) {
 569                                         put_char('\b', tty);
 570                                         put_char(' ', tty);
 571                                         put_char('\b', tty);
 572                                         if (tty->column > 0)
 573                                                 tty->column--;
 574                                 }
 575                         }
 576                 }
 577                 if (kill_type == ERASE)
 578                         break;
 579         }
 580         if (tty->read_head == tty->canon_head)
 581                 finish_erasing(tty);
 582 }
 583
 584 /**
 585  *      isig            -       handle the ISIG optio
 586  *      @sig: signal
 587  *      @tty: terminal
 588  *      @flush: force flush
 589  *
 590  *      Called when a signal is being sent due to terminal input. This
 591  *      may caus terminal flushing to take place according to the termios
 592  *      settings and character used. Called from the driver receive_buf
 593  *      path so serialized.
 594  */
 595
 596 static inline void isig(int sig, struct tty_struct *tty, int flush)
 597 {
 598         if (tty->pgrp)
 599                 kill_pgrp(tty->pgrp, sig, 1);
 600         if (flush || !L_NOFLSH(tty)) {
 601                 n_tty_flush_buffer(tty);
 602                 if (tty->driver->flush_buffer)
 603                         tty->driver->flush_buffer(tty);
 604         }
 605 }
 606
 607 /**
 608  *      n_tty_receive_break     -       handle break
 609  *      @tty: terminal
 610  *
 611  *      An RS232 break event has been hit in the incoming bitstream. This
 612  *      can cause a variety of events depending upon the termios settings.
 613  *
 614  *      Called from the receive_buf path so single threaded.
 615  */
 616
 617 static inline void n_tty_receive_break(struct tty_struct *tty)
 618 {
 619         if (I_IGNBRK(tty))
 620                 return;
 621         if (I_BRKINT(tty)) {
 622                 isig(SIGINT, tty, 1);
 623                 return;
 624         }
 625         if (I_PARMRK(tty)) {
 626                 put_tty_queue('\377', tty);
 627                 put_tty_queue('\0', tty);
 628         }
 629         put_tty_queue('\0', tty);
 630         wake_up_interruptible(&tty->read_wait);
 631 }
 632
 633 /**
 634  *      n_tty_receive_overrun   -       handle overrun reporting
 635  *      @tty: terminal
 636  *
 637  *      Data arrived faster than we could process it. While the tty
 638  *      driver has flagged this the bits that were missed are gone
 639  *      forever.
 640  *
 641  *      Called from the receive_buf path so single threaded. Does not
 642  *      need locking as num_overrun and overrun_time are function
 643  *      private.
 644  */
 645
 646 static inline void n_tty_receive_overrun(struct tty_struct *tty)
 647 {
 648         char buf[64];
 649
 650         tty->num_overrun++;
 651         if (time_before(tty->overrun_time, jiffies - HZ) ||
 652                         time_after(tty->overrun_time, jiffies)) {
 653                 printk(KERN_WARNING "%s: %d input overrun(s)\n",
 654                         tty_name(tty, buf),
 655                         tty->num_overrun);
 656                 tty->overrun_time = jiffies;
 657                 tty->num_overrun = 0;
 658         }
 659 }
 660
 661 /**
 662  *      n_tty_receive_parity_error      -       error notifier
 663  *      @tty: terminal device
 664  *      @c: character
 665  *
 666  *      Process a parity error and queue the right data to indicate
 667  *      the error case if necessary. Locking as per n_tty_receive_buf.
 668  */
 669 static inline void n_tty_receive_parity_error(struct tty_struct *tty,
 670                                               unsigned char c)
 671 {
 672         if (I_IGNPAR(tty))
 673                 return;
 674         if (I_PARMRK(tty)) {
 675                 put_tty_queue('\377', tty);
 676                 put_tty_queue('\0', tty);
 677                 put_tty_queue(c, tty);
 678         } else  if (I_INPCK(tty))
 679                 put_tty_queue('\0', tty);
 680         else
 681                 put_tty_queue(c, tty);
 682         wake_up_interruptible(&tty->read_wait);
 683 }
 684
 685 /**
 686  *      n_tty_receive_char      -       perform processing
 687  *      @tty: terminal device
 688  *      @c: character
 689  *
 690  *      Process an individual character of input received from the driver.
 691  *      This is serialized with respect to itself by the rules for the
 692  *      driver above.
 693  */
 694
 695 static inline void n_tty_receive_char(struct tty_struct *tty, unsigned char c)
 696 {
 697         unsigned long flags;
 698
 699         if (tty->raw) {
 700                 put_tty_queue(c, tty);
 701                 return;
 702         }
 703
 704         if (I_ISTRIP(tty))
 705                 c &= 0x7f;
 706         if (I_IUCLC(tty) && L_IEXTEN(tty))
 707                 c=tolower(c);
 708
 709         if (tty->stopped && !tty->flow_stopped && I_IXON(tty) &&
 710             ((I_IXANY(tty) && c != START_CHAR(tty) && c != STOP_CHAR(tty)) ||
 711              c == INTR_CHAR(tty) || c == QUIT_CHAR(tty)))
 712                 start_tty(tty);
 713
 714         if (tty->closing) {
 715                 if (I_IXON(tty)) {
 716                         if (c == START_CHAR(tty))
 717                                 start_tty(tty);
 718                         else if (c == STOP_CHAR(tty))
 719                                 stop_tty(tty);
 720                 }
 721                 return;
 722         }
 723
 724         /*
 725          * If the previous character was LNEXT, or we know that this
 726          * character is not one of the characters that we'll have to
 727          * handle specially, do shortcut processing to speed things
 728          * up.
 729          */
 730         if (!test_bit(c, tty->process_char_map) || tty->lnext) {
 731                 finish_erasing(tty);
 732                 tty->lnext = 0;
 733                 if (L_ECHO(tty)) {
 734                         if (tty->read_cnt >= N_TTY_BUF_SIZE-1) {
 735                                 put_char('\a', tty); /* beep if no space */
 736                                 return;
 737                         }
 738                         /* Record the column of first canon char. */
 739                         if (tty->canon_head == tty->read_head)
 740                                 tty->canon_column = tty->column;
 741                         echo_char(c, tty);
 742                 }
 743                 if (I_PARMRK(tty) && c == (unsigned char) '\377')
 744                         put_tty_queue(c, tty);
 745                 put_tty_queue(c, tty);
 746                 return;
 747         }
 748
 749         if (c == '\r') {
 750                 if (I_IGNCR(tty))
 751                         return;
 752                 if (I_ICRNL(tty))
 753                         c = '\n';
 754         } else if (c == '\n' && I_INLCR(tty))
 755                 c = '\r';
 756         if (I_IXON(tty)) {
 757                 if (c == START_CHAR(tty)) {
 758                         start_tty(tty);
 759                         return;
 760                 }
 761                 if (c == STOP_CHAR(tty)) {
 762                         stop_tty(tty);
 763                         return;
 764                 }
 765         }
 766         if (L_ISIG(tty)) {
 767                 int signal;
 768                 signal = SIGINT;
 769                 if (c == INTR_CHAR(tty))
 770                         goto send_signal;
 771                 signal = SIGQUIT;
 772                 if (c == QUIT_CHAR(tty))
 773                         goto send_signal;
 774                 signal = SIGTSTP;
 775                 if (c == SUSP_CHAR(tty)) {
 776 send_signal:
 777                         /*
 778                          * Echo character, and then send the signal.
 779                          * Note that we do not use isig() here because we want
 780                          * the order to be:
 781                          * 1) flush, 2) echo, 3) signal
 782                          */
 783                         if (!L_NOFLSH(tty)) {
 784                                 n_tty_flush_buffer(tty);
 785                                 if (tty->driver->flush_buffer)
 786                                         tty->driver->flush_buffer(tty);
 787                         }
 788                         if (L_ECHO(tty))
 789                                 echo_char(c, tty);
 790                         if (tty->pgrp)
 791                                 kill_pgrp(tty->pgrp, signal, 1);
 792                         return;
 793                 }
 794         }
 795         if (tty->icanon) {
 796                 if (c == ERASE_CHAR(tty) || c == KILL_CHAR(tty) ||
 797                     (c == WERASE_CHAR(tty) && L_IEXTEN(tty))) {
 798                         eraser(c, tty);
 799                         return;
 800                 }
 801                 if (c == LNEXT_CHAR(tty) && L_IEXTEN(tty)) {
 802                         tty->lnext = 1;
 803                         if (L_ECHO(tty)) {
 804                                 finish_erasing(tty);
 805                                 if (L_ECHOCTL(tty)) {
 806                                         put_char('^', tty);
 807                                         put_char('\b', tty);
 808                                 }
 809                         }
 810                         return;
 811                 }
 812                 if (c == REPRINT_CHAR(tty) && L_ECHO(tty) &&
 813                     L_IEXTEN(tty)) {
 814                         unsigned long tail = tty->canon_head;
 815
 816                         finish_erasing(tty);
 817                         echo_char(c, tty);
 818                         opost('\n', tty);
 819                         while (tail != tty->read_head) {
 820                                 echo_char(tty->read_buf[tail], tty);
 821                                 tail = (tail+1) & (N_TTY_BUF_SIZE-1);
 822                         }
 823                         return;
 824                 }
 825                 if (c == '\n') {
 826                         if (L_ECHO(tty) || L_ECHONL(tty)) {
 827                                 if (tty->read_cnt >= N_TTY_BUF_SIZE-1)
 828                                         put_char('\a', tty);
 829                                 opost('\n', tty);
 830                         }
 831                         goto handle_newline;
 832                 }
 833                 if (c == EOF_CHAR(tty)) {
 834                         if (tty->canon_head != tty->read_head)
 835                                 set_bit(TTY_PUSH, &tty->flags);
 836                         c = __DISABLED_CHAR;
 837                         goto handle_newline;
 838                 }
 839                 if ((c == EOL_CHAR(tty)) ||
 840                     (c == EOL2_CHAR(tty) && L_IEXTEN(tty))) {
 841                         /*
 842                          * XXX are EOL_CHAR and EOL2_CHAR echoed?!?
 843                          */
 844                         if (L_ECHO(tty)) {
 845                                 if (tty->read_cnt >= N_TTY_BUF_SIZE-1)
 846                                         put_char('\a', tty);
 847                                 /* Record the column of first canon char. */
 848                                 if (tty->canon_head == tty->read_head)
 849                                         tty->canon_column = tty->column;
 850                                 echo_char(c, tty);
 851                         }
 852                         /*
 853                          * XXX does PARMRK doubling happen for
 854                          * EOL_CHAR and EOL2_CHAR?
 855                          */
 856                         if (I_PARMRK(tty) && c == (unsigned char) '\377')
 857                                 put_tty_queue(c, tty);
 858
 859 handle_newline:
 860                         spin_lock_irqsave(&tty->read_lock, flags);
 861                         set_bit(tty->read_head, tty->read_flags);
 862                         put_tty_queue_nolock(c, tty);
 863                         tty->canon_head = tty->read_head;
 864                         tty->canon_data++;
 865                         spin_unlock_irqrestore(&tty->read_lock, flags);
 866                         kill_fasync(&tty->fasync, SIGIO, POLL_IN);
 867                         if (waitqueue_active(&tty->read_wait))
 868                                 wake_up_interruptible(&tty->read_wait);
 869                         return;
 870                 }
 871         }
 872
 873         finish_erasing(tty);
 874         if (L_ECHO(tty)) {
 875                 if (tty->read_cnt >= N_TTY_BUF_SIZE-1) {
 876                         put_char('\a', tty); /* beep if no space */
 877                         return;
 878                 }
 879                 if (c == '\n')
 880                         opost('\n', tty);
 881                 else {
 882                         /* Record the column of first canon char. */
 883                         if (tty->canon_head == tty->read_head)
 884                                 tty->canon_column = tty->column;
 885                         echo_char(c, tty);
 886                 }
 887         }
 888
 889         if (I_PARMRK(tty) && c == (unsigned char) '\377')
 890                 put_tty_queue(c, tty);
 891
 892         put_tty_queue(c, tty);
 893 }
 894
 895
 896 /**
 897  *      n_tty_write_wakeup      -       asynchronous I/O notifier
 898  *      @tty: tty device
 899  *
 900  *      Required for the ptys, serial driver etc. since processes
 901  *      that attach themselves to the master and rely on ASYNC
 902  *      IO must be woken up
 903  */
 904
 905 static void n_tty_write_wakeup(struct tty_struct *tty)
 906 {
 907         if (tty->fasync) {
 908                 set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 909                 kill_fasync(&tty->fasync, SIGIO, POLL_OUT);
 910         }
 911 }
 912
 913 /**
 914  *      n_tty_receive_buf       -       data receive
 915  *      @tty: terminal device
 916  *      @cp: buffer
 917  *      @fp: flag buffer
 918  *      @count: characters
 919  *
 920  *      Called by the terminal driver when a block of characters has
 921  *      been received. This function must be called from soft contexts
 922  *      not from interrupt context. The driver is responsible for making
 923  *      calls one at a time and in order (or using flush_to_ldisc)
 924  */
 925
 926 static void n_tty_receive_buf(struct tty_struct *tty, const unsigned char *cp,
 927                               char *fp, int count)
 928 {
 929         const unsigned char *p;
 930         char *f, flags = TTY_NORMAL;
 931         int     i;
 932         char    buf[64];
 933         unsigned long cpuflags;
 934
 935         if (!tty->read_buf)
 936                 return;
 937
 938         if (tty->real_raw) {
 939                 spin_lock_irqsave(&tty->read_lock, cpuflags);
 940                 i = min(N_TTY_BUF_SIZE - tty->read_cnt,
 941                         N_TTY_BUF_SIZE - tty->read_head);
 942                 i = min(count, i);
 943                 memcpy(tty->read_buf + tty->read_head, cp, i);
 944                 tty->read_head = (tty->read_head + i) & (N_TTY_BUF_SIZE-1);
 945                 tty->read_cnt += i;
 946                 cp += i;
 947                 count -= i;
 948
 949                 i = min(N_TTY_BUF_SIZE - tty->read_cnt,
 950                         N_TTY_BUF_SIZE - tty->read_head);
 951                 i = min(count, i);
 952                 memcpy(tty->read_buf + tty->read_head, cp, i);
 953                 tty->read_head = (tty->read_head + i) & (N_TTY_BUF_SIZE-1);
 954                 tty->read_cnt += i;
 955                 spin_unlock_irqrestore(&tty->read_lock, cpuflags);
 956         } else {
 957                 for (i = count, p = cp, f = fp; i; i--, p++) {
 958                         if (f)
 959                                 flags = *f++;
 960                         switch (flags) {
 961                         case TTY_NORMAL:
 962                                 n_tty_receive_char(tty, *p);
 963                                 break;
 964                         case TTY_BREAK:
 965                                 n_tty_receive_break(tty);
 966                                 break;
 967                         case TTY_PARITY:
 968                         case TTY_FRAME:
 969                                 n_tty_receive_parity_error(tty, *p);
 970                                 break;
 971                         case TTY_OVERRUN:
 972                                 n_tty_receive_overrun(tty);
 973                                 break;
 974                         default:
 975                                 printk(KERN_ERR "%s: unknown flag %d\n",
 976                                        tty_name(tty, buf), flags);
 977                                 break;
 978                         }
 979                 }
 980                 if (tty->driver->flush_chars)
 981                         tty->driver->flush_chars(tty);
 982         }
 983
 984         n_tty_set_room(tty);
 985
 986         if (!tty->icanon && (tty->read_cnt >= tty->minimum_to_wake)) {
 987                 kill_fasync(&tty->fasync, SIGIO, POLL_IN);
 988                 if (waitqueue_active(&tty->read_wait))
 989                         wake_up_interruptible(&tty->read_wait);
 990         }
 991
 992         /*
 993          * Check the remaining room for the input canonicalization
 994          * mode.  We don't want to throttle the driver if we're in
 995          * canonical mode and don't have a newline yet!
 996          */
 997         if (tty->receive_room < TTY_THRESHOLD_THROTTLE) {
 998                 /* check TTY_THROTTLED first so it indicates our state */
 999                 if (!test_and_set_bit(TTY_THROTTLED, &tty->flags) &&
1000                     tty->driver->throttle)
1001                         tty->driver->throttle(tty);
1002         }
1003 }
1004
1005 int is_ignored(int sig)
1006 {
1007         return (sigismember(&current->blocked, sig) ||
1008                 current->sighand->action[sig-1].sa.sa_handler == SIG_IGN);
1009 }
1010
1011 /**
1012  *      n_tty_set_termios       -       termios data changed
1013  *      @tty: terminal
1014  *      @old: previous data
1015  *
1016  *      Called by the tty layer when the user changes termios flags so
1017  *      that the line discipline can plan ahead. This function cannot sleep
1018  *      and is protected from re-entry by the tty layer. The user is
1019  *      guaranteed that this function will not be re-entered or in progress
1020  *      when the ldisc is closed.
1021  */
1022
1023 static void n_tty_set_termios(struct tty_struct *tty, struct ktermios *old)
1024 {
1025         if (!tty)
1026                 return;
1027
1028         tty->icanon = (L_ICANON(tty) != 0);
1029         if (test_bit(TTY_HW_COOK_IN, &tty->flags)) {
1030                 tty->raw = 1;
1031                 tty->real_raw = 1;
1032                 n_tty_set_room(tty);
1033                 return;
1034         }
1035         if (I_ISTRIP(tty) || I_IUCLC(tty) || I_IGNCR(tty) ||
1036             I_ICRNL(tty) || I_INLCR(tty) || L_ICANON(tty) ||
1037             I_IXON(tty) || L_ISIG(tty) || L_ECHO(tty) ||
1038             I_PARMRK(tty)) {
1039                 memset(tty->process_char_map, 0, 256/8);
1040
1041                 if (I_IGNCR(tty) || I_ICRNL(tty))
1042                         set_bit('\r', tty->process_char_map);
1043                 if (I_INLCR(tty))
1044                         set_bit('\n', tty->process_char_map);
1045
1046                 if (L_ICANON(tty)) {
1047                         set_bit(ERASE_CHAR(tty), tty->process_char_map);
1048                         set_bit(KILL_CHAR(tty), tty->process_char_map);
1049                         set_bit(EOF_CHAR(tty), tty->process_char_map);
1050                         set_bit('\n', tty->process_char_map);
1051                         set_bit(EOL_CHAR(tty), tty->process_char_map);
1052                         if (L_IEXTEN(tty)) {
1053                                 set_bit(WERASE_CHAR(tty),
1054                                         tty->process_char_map);
1055                                 set_bit(LNEXT_CHAR(tty),
1056                                         tty->process_char_map);
1057                                 set_bit(EOL2_CHAR(tty),
1058                                         tty->process_char_map);
1059                                 if (L_ECHO(tty))
1060                                         set_bit(REPRINT_CHAR(tty),
1061                                                 tty->process_char_map);
1062                         }
1063                 }
1064                 if (I_IXON(tty)) {
1065                         set_bit(START_CHAR(tty), tty->process_char_map);
1066                         set_bit(STOP_CHAR(tty), tty->process_char_map);
1067                 }
1068                 if (L_ISIG(tty)) {
1069                         set_bit(INTR_CHAR(tty), tty->process_char_map);
1070                         set_bit(QUIT_CHAR(tty), tty->process_char_map);
1071                         set_bit(SUSP_CHAR(tty), tty->process_char_map);
1072                 }
1073                 clear_bit(__DISABLED_CHAR, tty->process_char_map);
1074                 tty->raw = 0;
1075                 tty->real_raw = 0;
1076         } else {
1077                 tty->raw = 1;
1078                 if ((I_IGNBRK(tty) || (!I_BRKINT(tty) && !I_PARMRK(tty))) &&
1079                     (I_IGNPAR(tty) || !I_INPCK(tty)) &&
1080                     (tty->driver->flags & TTY_DRIVER_REAL_RAW))
1081                         tty->real_raw = 1;
1082                 else
1083                         tty->real_raw = 0;
1084         }
1085         n_tty_set_room(tty);
1086 }
1087
1088 /**
1089  *      n_tty_close             -       close the ldisc for this tty
1090  *      @tty: device
1091  *
1092  *      Called from the terminal layer when this line discipline is
1093  *      being shut down, either because of a close or becsuse of a
1094  *      discipline change. The function will not be called while other
1095  *      ldisc methods are in progress.
1096  */
1097
1098 static void n_tty_close(struct tty_struct *tty)
1099 {
1100         n_tty_flush_buffer(tty);
1101         if (tty->read_buf) {
1102                 free_buf(tty->read_buf);
1103                 tty->read_buf = NULL;
1104         }
1105 }
1106
1107 /**
1108  *      n_tty_open              -       open an ldisc
1109  *      @tty: terminal to open
1110  *
1111  *      Called when this line discipline is being attached to the
1112  *      terminal device. Can sleep. Called serialized so that no
1113  *      other events will occur in parallel. No further open will occur
1114  *      until a close.
1115  */
1116
1117 static int n_tty_open(struct tty_struct *tty)
1118 {
1119         if (!tty)
1120                 return -EINVAL;
1121
1122         /* This one is ugly. Currently a malloc failure here can panic */
1123         if (!tty->read_buf) {
1124                 tty->read_buf = alloc_buf();
1125                 if (!tty->read_buf)
1126                         return -ENOMEM;
1127         }
1128         memset(tty->read_buf, 0, N_TTY_BUF_SIZE);
1129         reset_buffer_flags(tty);
1130         tty->column = 0;
1131         n_tty_set_termios(tty, NULL);
1132         tty->minimum_to_wake = 1;
1133         tty->closing = 0;
1134         return 0;
1135 }
1136
1137 static inline int input_available_p(struct tty_struct *tty, int amt)
1138 {
1139         if (tty->icanon) {
1140                 if (tty->canon_data)
1141                         return 1;
1142         } else if (tty->read_cnt >= (amt ? amt : 1))
1143                 return 1;
1144
1145         return 0;
1146 }
1147
1148 /**
1149  *      copy_from_read_buf      -       copy read data directly
1150  *      @tty: terminal device
1151  *      @b: user data
1152  *      @nr: size of data
1153  *
1154  *      Helper function to speed up read_chan.  It is only called when
1155  *      ICANON is off; it copies characters straight from the tty queue to
1156  *      user space directly.  It can be profitably called twice; once to
1157  *      drain the space from the tail pointer to the (physical) end of the
1158  *      buffer, and once to drain the space from the (physical) beginning of
1159  *      the buffer to head pointer.
1160  *
1161  *      Called under the tty->atomic_read_lock sem
1162  *
1163  */
1164
1165 static int copy_from_read_buf(struct tty_struct *tty,
1166                                       unsigned char __user **b,
1167                                       size_t *nr)
1168
1169 {
1170         int retval;
1171         size_t n;
1172         unsigned long flags;
1173
1174         retval = 0;
1175         spin_lock_irqsave(&tty->read_lock, flags);
1176         n = min(tty->read_cnt, N_TTY_BUF_SIZE - tty->read_tail);
1177         n = min(*nr, n);
1178         spin_unlock_irqrestore(&tty->read_lock, flags);
1179         if (n) {
1180                 retval = copy_to_user(*b, &tty->read_buf[tty->read_tail], n);
1181                 n -= retval;
1182                 tty_audit_add_data(tty, &tty->read_buf[tty->read_tail], n);
1183                 spin_lock_irqsave(&tty->read_lock, flags);
1184                 tty->read_tail = (tty->read_tail + n) & (N_TTY_BUF_SIZE-1);
1185                 tty->read_cnt -= n;
1186                 spin_unlock_irqrestore(&tty->read_lock, flags);
1187                 *b += n;
1188                 *nr -= n;
1189         }
1190         return retval;
1191 }
1192
1193 extern ssize_t redirected_tty_write(struct file *, const char __user *,
1194                                                         size_t, loff_t *);
1195
1196 /**
1197  *      job_control             -       check job control
1198  *      @tty: tty
1199  *      @file: file handle
1200  *
1201  *      Perform job control management checks on this file/tty descriptor
1202  *      and if appropriate send any needed signals and return a negative
1203  *      error code if action should be taken.
1204  *
1205  *      FIXME:
1206  *      Locking: None - redirected write test is safe, testing
1207  *      current->signal should possibly lock current->sighand
1208  *      pgrp locking ?
1209  */
1210
1211 static int job_control(struct tty_struct *tty, struct file *file)
1212 {
1213         /* Job control check -- must be done at start and after
1214            every sleep (POSIX.1 7.1.1.4). */
1215         /* NOTE: not yet done after every sleep pending a thorough
1216            check of the logic of this change. -- jlc */
1217         /* don't stop on /dev/console */
1218         if (file->f_op->write != redirected_tty_write &&
1219             current->signal->tty == tty) {
1220                 if (!tty->pgrp)
1221                         printk(KERN_ERR "read_chan: no tty->pgrp!\n");
1222                 else if (task_pgrp(current) != tty->pgrp) {
1223                         if (is_ignored(SIGTTIN) ||
1224                             is_current_pgrp_orphaned())
1225                                 return -EIO;
1226                         kill_pgrp(task_pgrp(current), SIGTTIN, 1);
1227                         set_thread_flag(TIF_SIGPENDING);
1228                         return -ERESTARTSYS;
1229                 }
1230         }
1231         return 0;
1232 }
1233
1234
1235 /**
1236  *      read_chan               -       read function for tty
1237  *      @tty: tty device
1238  *      @file: file object
1239  *      @buf: userspace buffer pointer
1240  *      @nr: size of I/O
1241  *
1242  *      Perform reads for the line discipline. We are guaranteed that the
1243  *      line discipline will not be closed under us but we may get multiple
1244  *      parallel readers and must handle this ourselves. We may also get
1245  *      a hangup. Always called in user context, may sleep.
1246  *
1247  *      This code must be sure never to sleep through a hangup.
1248  */
1249
1250 static ssize_t read_chan(struct tty_struct *tty, struct file *file,
1251                          unsigned char __user *buf, size_t nr)
1252 {
1253         unsigned char __user *b = buf;
1254         DECLARE_WAITQUEUE(wait, current);
1255         int c;
1256         int minimum, time;
1257         ssize_t retval = 0;
1258         ssize_t size;
1259         long timeout;
1260         unsigned long flags;
1261         int packet;
1262
1263 do_it_again:
1264
1265         if (!tty->read_buf) {
1266                 printk(KERN_ERR "n_tty_read_chan: read_buf == NULL?!?\n");
1267                 return -EIO;
1268         }
1269
1270         c = job_control(tty, file);
1271         if (c < 0)
1272                 return c;
1273
1274         minimum = time = 0;
1275         timeout = MAX_SCHEDULE_TIMEOUT;
1276         if (!tty->icanon) {
1277                 time = (HZ / 10) * TIME_CHAR(tty);
1278                 minimum = MIN_CHAR(tty);
1279                 if (minimum) {
1280                         if (time)
1281                                 tty->minimum_to_wake = 1;
1282                         else if (!waitqueue_active(&tty->read_wait) ||
1283                                  (tty->minimum_to_wake > minimum))
1284                                 tty->minimum_to_wake = minimum;
1285                 } else {
1286                         timeout = 0;
1287                         if (time) {
1288                                 timeout = time;
1289                                 time = 0;
1290                         }
1291                         tty->minimum_to_wake = minimum = 1;
1292                 }
1293         }
1294
1295         /*
1296          *      Internal serialization of reads.
1297          */
1298         if (file->f_flags & O_NONBLOCK) {
1299                 if (!mutex_trylock(&tty->atomic_read_lock))
1300                         return -EAGAIN;
1301         } else {
1302                 if (mutex_lock_interruptible(&tty->atomic_read_lock))
1303                         return -ERESTARTSYS;
1304         }
1305         packet = tty->packet;
1306
1307         add_wait_queue(&tty->read_wait, &wait);
1308         while (nr) {
1309                 /* First test for status change. */
1310                 if (packet && tty->link->ctrl_status) {
1311                         unsigned char cs;
1312                         if (b != buf)
1313                                 break;
1314                         spin_lock_irqsave(&tty->link->ctrl_lock, flags);
1315                         cs = tty->link->ctrl_status;
1316                         tty->link->ctrl_status = 0;
1317                         spin_unlock_irqrestore(&tty->link->ctrl_lock, flags);
1318                         if (tty_put_user(tty, cs, b++)) {
1319                                 retval = -EFAULT;
1320                                 b--;
1321                                 break;
1322                         }
1323                         nr--;
1324                         break;
1325                 }
1326                 /* This statement must be first before checking for input
1327                    so that any interrupt will set the state back to
1328                    TASK_RUNNING. */
1329                 set_current_state(TASK_INTERRUPTIBLE);
1330
1331                 if (((minimum - (b - buf)) < tty->minimum_to_wake) &&
1332                     ((minimum - (b - buf)) >= 1))
1333                         tty->minimum_to_wake = (minimum - (b - buf));
1334
1335                 if (!input_available_p(tty, 0)) {
1336                         if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
1337                                 retval = -EIO;
1338                                 break;
1339                         }
1340                         if (tty_hung_up_p(file))
1341                                 break;
1342                         if (!timeout)
1343                                 break;
1344                         if (file->f_flags & O_NONBLOCK) {
1345                                 retval = -EAGAIN;
1346                                 break;
1347                         }
1348                         if (signal_pending(current)) {
1349                                 retval = -ERESTARTSYS;
1350                                 break;
1351                         }
1352                         /* FIXME: does n_tty_set_room need locking ? */
1353                         n_tty_set_room(tty);
1354                         timeout = schedule_timeout(timeout);
1355                         continue;
1356                 }
1357                 __set_current_state(TASK_RUNNING);
1358
1359                 /* Deal with packet mode. */
1360                 if (packet && b == buf) {
1361                         if (tty_put_user(tty, TIOCPKT_DATA, b++)) {
1362                                 retval = -EFAULT;
1363                                 b--;
1364                                 break;
1365                         }
1366                         nr--;
1367                 }
1368
1369                 if (tty->icanon) {
1370                         /* N.B. avoid overrun if nr == 0 */
1371                         while (nr && tty->read_cnt) {
1372                                 int eol;
1373
1374                                 eol = test_and_clear_bit(tty->read_tail,
1375                                                 tty->read_flags);
1376                                 c = tty->read_buf[tty->read_tail];
1377                                 spin_lock_irqsave(&tty->read_lock, flags);
1378                                 tty->read_tail = ((tty->read_tail+1) &
1379                                                   (N_TTY_BUF_SIZE-1));
1380                                 tty->read_cnt--;
1381                                 if (eol) {
1382                                         /* this test should be redundant:
1383                                          * we shouldn't be reading data if
1384                                          * canon_data is 0
1385                                          */
1386                                         if (--tty->canon_data < 0)
1387                                                 tty->canon_data = 0;
1388                                 }
1389                                 spin_unlock_irqrestore(&tty->read_lock, flags);
1390
1391                                 if (!eol || (c != __DISABLED_CHAR)) {
1392                                         if (tty_put_user(tty, c, b++)) {
1393                                                 retval = -EFAULT;
1394                                                 b--;
1395                                                 break;
1396                                         }
1397                                         nr--;
1398                                 }
1399                                 if (eol) {
1400                                         tty_audit_push(tty);
1401                                         break;
1402                                 }
1403                         }
1404                         if (retval)
1405                                 break;
1406                 } else {
1407                         int uncopied;
1408                         /* The copy function takes the read lock and handles
1409                            locking internally for this case */
1410                         uncopied = copy_from_read_buf(tty, &b, &nr);
1411                         uncopied += copy_from_read_buf(tty, &b, &nr);
1412                         if (uncopied) {
1413                                 retval = -EFAULT;
1414                                 break;
1415                         }
1416                 }
1417
1418                 /* If there is enough space in the read buffer now, let the
1419                  * low-level driver know. We use n_tty_chars_in_buffer() to
1420                  * check the buffer, as it now knows about canonical mode.
1421                  * Otherwise, if the driver is throttled and the line is
1422                  * longer than TTY_THRESHOLD_UNTHROTTLE in canonical mode,
1423                  * we won't get any more characters.
1424                  */
1425                 if (n_tty_chars_in_buffer(tty) <= TTY_THRESHOLD_UNTHROTTLE) {
1426                         n_tty_set_room(tty);
1427                         check_unthrottle(tty);
1428                 }
1429
1430                 if (b - buf >= minimum)
1431                         break;
1432                 if (time)
1433                         timeout = time;
1434         }
1435         mutex_unlock(&tty->atomic_read_lock);
1436         remove_wait_queue(&tty->read_wait, &wait);
1437
1438         if (!waitqueue_active(&tty->read_wait))
1439                 tty->minimum_to_wake = minimum;
1440
1441         __set_current_state(TASK_RUNNING);
1442         size = b - buf;
1443         if (size) {
1444                 retval = size;
1445                 if (nr)
1446                         clear_bit(TTY_PUSH, &tty->flags);
1447         } else if (test_and_clear_bit(TTY_PUSH, &tty->flags))
1448                  goto do_it_again;
1449
1450         n_tty_set_room(tty);
1451         return retval;
1452 }
1453
1454 /**
1455  *      write_chan              -       write function for tty
1456  *      @tty: tty device
1457  *      @file: file object
1458  *      @buf: userspace buffer pointer
1459  *      @nr: size of I/O
1460  *
1461  *      Write function of the terminal device. This is serialized with
1462  *      respect to other write callers but not to termios changes, reads
1463  *      and other such events. We must be careful with N_TTY as the receive
1464  *      code will echo characters, thus calling driver write methods.
1465  *
1466  *      This code must be sure never to sleep through a hangup.
1467  */
1468
1469 static ssize_t write_chan(struct tty_struct *tty, struct file *file,
1470                           const unsigned char *buf, size_t nr)
1471 {
1472         const unsigned char *b = buf;
1473         DECLARE_WAITQUEUE(wait, current);
1474         int c;
1475         ssize_t retval = 0;
1476
1477         /* Job control check -- must be done at start (POSIX.1 7.1.1.4). */
1478         if (L_TOSTOP(tty) && file->f_op->write != redirected_tty_write) {
1479                 retval = tty_check_change(tty);
1480                 if (retval)
1481                         return retval;
1482         }
1483
1484         add_wait_queue(&tty->write_wait, &wait);
1485         while (1) {
1486                 set_current_state(TASK_INTERRUPTIBLE);
1487                 if (signal_pending(current)) {
1488                         retval = -ERESTARTSYS;
1489                         break;
1490                 }
1491                 if (tty_hung_up_p(file) || (tty->link && !tty->link->count)) {
1492                         retval = -EIO;
1493                         break;
1494                 }
1495                 if (O_OPOST(tty) && !(test_bit(TTY_HW_COOK_OUT, &tty->flags))) {
1496                         while (nr > 0) {
1497                                 ssize_t num = opost_block(tty, b, nr);
1498                                 if (num < 0) {
1499                                         if (num == -EAGAIN)
1500                                                 break;
1501                                         retval = num;
1502                                         goto break_out;
1503                                 }
1504                                 b += num;
1505                                 nr -= num;
1506                                 if (nr == 0)
1507                                         break;
1508                                 c = *b;
1509                                 if (opost(c, tty) < 0)
1510                                         break;
1511                                 b++; nr--;
1512                         }
1513                         if (tty->driver->flush_chars)
1514                                 tty->driver->flush_chars(tty);
1515                 } else {
1516                         while (nr > 0) {
1517                                 c = tty->driver->write(tty, b, nr);
1518                                 if (c < 0) {
1519                                         retval = c;
1520                                         goto break_out;
1521                                 }
1522                                 if (!c)
1523                                         break;
1524                                 b += c;
1525                                 nr -= c;
1526                         }
1527                 }
1528                 if (!nr)
1529                         break;
1530                 if (file->f_flags & O_NONBLOCK) {
1531                         retval = -EAGAIN;
1532                         break;
1533                 }
1534                 schedule();
1535         }
1536 break_out:
1537         __set_current_state(TASK_RUNNING);
1538         remove_wait_queue(&tty->write_wait, &wait);
1539         return (b - buf) ? b - buf : retval;
1540 }
1541
1542 /**
1543  *      normal_poll             -       poll method for N_TTY
1544  *      @tty: terminal device
1545  *      @file: file accessing it
1546  *      @wait: poll table
1547  *
1548  *      Called when the line discipline is asked to poll() for data or
1549  *      for special events. This code is not serialized with respect to
1550  *      other events save open/close.
1551  *
1552  *      This code must be sure never to sleep through a hangup.
1553  *      Called without the kernel lock held - fine
1554  *
1555  *      FIXME: if someone changes the VMIN or discipline settings for the
1556  *      terminal while another process is in poll() the poll does not
1557  *      recompute the new limits. Possibly set_termios should issue
1558  *      a read wakeup to fix this bug.
1559  */
1560
1561 static unsigned int normal_poll(struct tty_struct *tty, struct file *file,
1562                                                         poll_table *wait)
1563 {
1564         unsigned int mask = 0;
1565
1566         poll_wait(file, &tty->read_wait, wait);
1567         poll_wait(file, &tty->write_wait, wait);
1568         if (input_available_p(tty, TIME_CHAR(tty) ? 0 : MIN_CHAR(tty)))
1569                 mask |= POLLIN | POLLRDNORM;
1570         if (tty->packet && tty->link->ctrl_status)
1571                 mask |= POLLPRI | POLLIN | POLLRDNORM;
1572         if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
1573                 mask |= POLLHUP;
1574         if (tty_hung_up_p(file))
1575                 mask |= POLLHUP;
1576         if (!(mask & (POLLHUP | POLLIN | POLLRDNORM))) {
1577                 if (MIN_CHAR(tty) && !TIME_CHAR(tty))
1578                         tty->minimum_to_wake = MIN_CHAR(tty);
1579                 else
1580                         tty->minimum_to_wake = 1;
1581         }
1582         if (!tty_is_writelocked(tty) &&
1583                         tty->driver->chars_in_buffer(tty) < WAKEUP_CHARS &&
1584                         tty->driver->write_room(tty) > 0)
1585                 mask |= POLLOUT | POLLWRNORM;
1586         return mask;
1587 }
1588
1589 struct tty_ldisc tty_ldisc_N_TTY = {
1590         .magic           = TTY_LDISC_MAGIC,
1591         .name            = "n_tty",
1592         .open            = n_tty_open,
1593         .close           = n_tty_close,
1594         .flush_buffer    = n_tty_flush_buffer,
1595         .chars_in_buffer = n_tty_chars_in_buffer,
1596         .read            = read_chan,
1597         .write           = write_chan,
1598         .ioctl           = n_tty_ioctl,
1599         .set_termios     = n_tty_set_termios,
1600         .poll            = normal_poll,
1601         .receive_buf     = n_tty_receive_buf,
1602         .write_wakeup    = n_tty_write_wakeup
1603 };
1604