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->ops->unthrottle)
 153                 tty->ops->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_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_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->ops->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_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_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->ops->flush_chars)
 394                 tty->ops->flush_chars(tty);
 395         i = tty->ops->write(tty, buf, i);
 396         unlock_kernel();
 397         return i;
 398 }
 399
 400
 401 /**
 402  *      echo_char       -       echo characters
 403  *      @c: unicode byte to echo
 404  *      @tty: terminal device
 405  *
 406  *      Echo user input back onto the screen. This must be called only when
 407  *      L_ECHO(tty) is true. Called from the driver receive_buf path.
 408  */
 409
 410 static void echo_char(unsigned char c, struct tty_struct *tty)
 411 {
 412         if (L_ECHOCTL(tty) && iscntrl(c) && c != '\t') {
 413                 tty_put_char(tty, '^');
 414                 tty_put_char(tty, c ^ 0100);
 415                 tty->column += 2;
 416         } else
 417                 opost(c, tty);
 418 }
 419
 420 static inline void finish_erasing(struct tty_struct *tty)
 421 {
 422         if (tty->erasing) {
 423                 tty_put_char(tty, '/');
 424                 tty->column++;
 425                 tty->erasing = 0;
 426         }
 427 }
 428
 429 /**
 430  *      eraser          -       handle erase function
 431  *      @c: character input
 432  *      @tty: terminal device
 433  *
 434  *      Perform erase and necessary output when an erase character is
 435  *      present in the stream from the driver layer. Handles the complexities
 436  *      of UTF-8 multibyte symbols.
 437  */
 438
 439 static void eraser(unsigned char c, struct tty_struct *tty)
 440 {
 441         enum { ERASE, WERASE, KILL } kill_type;
 442         int head, seen_alnums, cnt;
 443         unsigned long flags;
 444
 445         if (tty->read_head == tty->canon_head) {
 446                 /* opost('\a', tty); */         /* what do you think? */
 447                 return;
 448         }
 449         if (c == ERASE_CHAR(tty))
 450                 kill_type = ERASE;
 451         else if (c == WERASE_CHAR(tty))
 452                 kill_type = WERASE;
 453         else {
 454                 if (!L_ECHO(tty)) {
 455                         spin_lock_irqsave(&tty->read_lock, flags);
 456                         tty->read_cnt -= ((tty->read_head - tty->canon_head) &
 457                                           (N_TTY_BUF_SIZE - 1));
 458                         tty->read_head = tty->canon_head;
 459                         spin_unlock_irqrestore(&tty->read_lock, flags);
 460                         return;
 461                 }
 462                 if (!L_ECHOK(tty) || !L_ECHOKE(tty) || !L_ECHOE(tty)) {
 463                         spin_lock_irqsave(&tty->read_lock, flags);
 464                         tty->read_cnt -= ((tty->read_head - tty->canon_head) &
 465                                           (N_TTY_BUF_SIZE - 1));
 466                         tty->read_head = tty->canon_head;
 467                         spin_unlock_irqrestore(&tty->read_lock, flags);
 468                         finish_erasing(tty);
 469                         echo_char(KILL_CHAR(tty), tty);
 470                         /* Add a newline if ECHOK is on and ECHOKE is off. */
 471                         if (L_ECHOK(tty))
 472                                 opost('\n', tty);
 473                         return;
 474                 }
 475                 kill_type = KILL;
 476         }
 477
 478         seen_alnums = 0;
 479         while (tty->read_head != tty->canon_head) {
 480                 head = tty->read_head;
 481
 482                 /* erase a single possibly multibyte character */
 483                 do {
 484                         head = (head - 1) & (N_TTY_BUF_SIZE-1);
 485                         c = tty->read_buf[head];
 486                 } while (is_continuation(c, tty) && head != tty->canon_head);
 487
 488                 /* do not partially erase */
 489                 if (is_continuation(c, tty))
 490                         break;
 491
 492                 if (kill_type == WERASE) {
 493                         /* Equivalent to BSD's ALTWERASE. */
 494                         if (isalnum(c) || c == '_')
 495                                 seen_alnums++;
 496                         else if (seen_alnums)
 497                                 break;
 498                 }
 499                 cnt = (tty->read_head - head) & (N_TTY_BUF_SIZE-1);
 500                 spin_lock_irqsave(&tty->read_lock, flags);
 501                 tty->read_head = head;
 502                 tty->read_cnt -= cnt;
 503                 spin_unlock_irqrestore(&tty->read_lock, flags);
 504                 if (L_ECHO(tty)) {
 505                         if (L_ECHOPRT(tty)) {
 506                                 if (!tty->erasing) {
 507                                         tty_put_char(tty, '\\');
 508                                         tty->column++;
 509                                         tty->erasing = 1;
 510                                 }
 511                                 /* if cnt > 1, output a multi-byte character */
 512                                 echo_char(c, tty);
 513                                 while (--cnt > 0) {
 514                                         head = (head+1) & (N_TTY_BUF_SIZE-1);
 515                                         tty_put_char(tty, tty->read_buf[head]);
 516                                 }
 517                         } else if (kill_type == ERASE && !L_ECHOE(tty)) {
 518                                 echo_char(ERASE_CHAR(tty), tty);
 519                         } else if (c == '\t') {
 520                                 unsigned int col = tty->canon_column;
 521                                 unsigned long tail = tty->canon_head;
 522
 523                                 /* Find the column of the last char. */
 524                                 while (tail != tty->read_head) {
 525                                         c = tty->read_buf[tail];
 526                                         if (c == '\t')
 527                                                 col = (col | 7) + 1;
 528                                         else if (iscntrl(c)) {
 529                                                 if (L_ECHOCTL(tty))
 530                                                         col += 2;
 531                                         } else if (!is_continuation(c, tty))
 532                                                 col++;
 533                                         tail = (tail+1) & (N_TTY_BUF_SIZE-1);
 534                                 }
 535
 536                                 /* should never happen */
 537                                 if (tty->column > 0x80000000)
 538                                         tty->column = 0;
 539
 540                                 /* Now backup to that column. */
 541                                 while (tty->column > col) {
 542                                         /* Can't use opost here. */
 543                                         tty_put_char(tty, '\b');
 544                                         if (tty->column > 0)
 545                                                 tty->column--;
 546                                 }
 547                         } else {
 548                                 if (iscntrl(c) && L_ECHOCTL(tty)) {
 549                                         tty_put_char(tty, '\b');
 550                                         tty_put_char(tty, ' ');
 551                                         tty_put_char(tty, '\b');
 552                                         if (tty->column > 0)
 553                                                 tty->column--;
 554                                 }
 555                                 if (!iscntrl(c) || L_ECHOCTL(tty)) {
 556                                         tty_put_char(tty, '\b');
 557                                         tty_put_char(tty, ' ');
 558                                         tty_put_char(tty, '\b');
 559                                         if (tty->column > 0)
 560                                                 tty->column--;
 561                                 }
 562                         }
 563                 }
 564                 if (kill_type == ERASE)
 565                         break;
 566         }
 567         if (tty->read_head == tty->canon_head)
 568                 finish_erasing(tty);
 569 }
 570
 571 /**
 572  *      isig            -       handle the ISIG optio
 573  *      @sig: signal
 574  *      @tty: terminal
 575  *      @flush: force flush
 576  *
 577  *      Called when a signal is being sent due to terminal input. This
 578  *      may caus terminal flushing to take place according to the termios
 579  *      settings and character used. Called from the driver receive_buf
 580  *      path so serialized.
 581  */
 582
 583 static inline void isig(int sig, struct tty_struct *tty, int flush)
 584 {
 585         if (tty->pgrp)
 586                 kill_pgrp(tty->pgrp, sig, 1);
 587         if (flush || !L_NOFLSH(tty)) {
 588                 n_tty_flush_buffer(tty);
 589                 tty_driver_flush_buffer(tty);
 590         }
 591 }
 592
 593 /**
 594  *      n_tty_receive_break     -       handle break
 595  *      @tty: terminal
 596  *
 597  *      An RS232 break event has been hit in the incoming bitstream. This
 598  *      can cause a variety of events depending upon the termios settings.
 599  *
 600  *      Called from the receive_buf path so single threaded.
 601  */
 602
 603 static inline void n_tty_receive_break(struct tty_struct *tty)
 604 {
 605         if (I_IGNBRK(tty))
 606                 return;
 607         if (I_BRKINT(tty)) {
 608                 isig(SIGINT, tty, 1);
 609                 return;
 610         }
 611         if (I_PARMRK(tty)) {
 612                 put_tty_queue('\377', tty);
 613                 put_tty_queue('\0', tty);
 614         }
 615         put_tty_queue('\0', tty);
 616         wake_up_interruptible(&tty->read_wait);
 617 }
 618
 619 /**
 620  *      n_tty_receive_overrun   -       handle overrun reporting
 621  *      @tty: terminal
 622  *
 623  *      Data arrived faster than we could process it. While the tty
 624  *      driver has flagged this the bits that were missed are gone
 625  *      forever.
 626  *
 627  *      Called from the receive_buf path so single threaded. Does not
 628  *      need locking as num_overrun and overrun_time are function
 629  *      private.
 630  */
 631
 632 static inline void n_tty_receive_overrun(struct tty_struct *tty)
 633 {
 634         char buf[64];
 635
 636         tty->num_overrun++;
 637         if (time_before(tty->overrun_time, jiffies - HZ) ||
 638                         time_after(tty->overrun_time, jiffies)) {
 639                 printk(KERN_WARNING "%s: %d input overrun(s)\n",
 640                         tty_name(tty, buf),
 641                         tty->num_overrun);
 642                 tty->overrun_time = jiffies;
 643                 tty->num_overrun = 0;
 644         }
 645 }
 646
 647 /**
 648  *      n_tty_receive_parity_error      -       error notifier
 649  *      @tty: terminal device
 650  *      @c: character
 651  *
 652  *      Process a parity error and queue the right data to indicate
 653  *      the error case if necessary. Locking as per n_tty_receive_buf.
 654  */
 655 static inline void n_tty_receive_parity_error(struct tty_struct *tty,
 656                                               unsigned char c)
 657 {
 658         if (I_IGNPAR(tty))
 659                 return;
 660         if (I_PARMRK(tty)) {
 661                 put_tty_queue('\377', tty);
 662                 put_tty_queue('\0', tty);
 663                 put_tty_queue(c, tty);
 664         } else  if (I_INPCK(tty))
 665                 put_tty_queue('\0', tty);
 666         else
 667                 put_tty_queue(c, tty);
 668         wake_up_interruptible(&tty->read_wait);
 669 }
 670
 671 /**
 672  *      n_tty_receive_char      -       perform processing
 673  *      @tty: terminal device
 674  *      @c: character
 675  *
 676  *      Process an individual character of input received from the driver.
 677  *      This is serialized with respect to itself by the rules for the
 678  *      driver above.
 679  */
 680
 681 static inline void n_tty_receive_char(struct tty_struct *tty, unsigned char c)
 682 {
 683         unsigned long flags;
 684
 685         if (tty->raw) {
 686                 put_tty_queue(c, tty);
 687                 return;
 688         }
 689
 690         if (I_ISTRIP(tty))
 691                 c &= 0x7f;
 692         if (I_IUCLC(tty) && L_IEXTEN(tty))
 693                 c=tolower(c);
 694
 695         if (tty->stopped && !tty->flow_stopped && I_IXON(tty) &&
 696             ((I_IXANY(tty) && c != START_CHAR(tty) && c != STOP_CHAR(tty)) ||
 697              c == INTR_CHAR(tty) || c == QUIT_CHAR(tty) || c == SUSP_CHAR(tty)))
 698                 start_tty(tty);
 699
 700         if (tty->closing) {
 701                 if (I_IXON(tty)) {
 702                         if (c == START_CHAR(tty))
 703                                 start_tty(tty);
 704                         else if (c == STOP_CHAR(tty))
 705                                 stop_tty(tty);
 706                 }
 707                 return;
 708         }
 709
 710         /*
 711          * If the previous character was LNEXT, or we know that this
 712          * character is not one of the characters that we'll have to
 713          * handle specially, do shortcut processing to speed things
 714          * up.
 715          */
 716         if (!test_bit(c, tty->process_char_map) || tty->lnext) {
 717                 finish_erasing(tty);
 718                 tty->lnext = 0;
 719                 if (L_ECHO(tty)) {
 720                         if (tty->read_cnt >= N_TTY_BUF_SIZE-1) {
 721                                 tty_put_char(tty, '\a'); /* beep if no space */
 722                                 return;
 723                         }
 724                         /* Record the column of first canon char. */
 725                         if (tty->canon_head == tty->read_head)
 726                                 tty->canon_column = tty->column;
 727                         echo_char(c, tty);
 728                 }
 729                 if (I_PARMRK(tty) && c == (unsigned char) '\377')
 730                         put_tty_queue(c, tty);
 731                 put_tty_queue(c, tty);
 732                 return;
 733         }
 734
 735         if (I_IXON(tty)) {
 736                 if (c == START_CHAR(tty)) {
 737                         start_tty(tty);
 738                         return;
 739                 }
 740                 if (c == STOP_CHAR(tty)) {
 741                         stop_tty(tty);
 742                         return;
 743                 }
 744         }
 745
 746         if (L_ISIG(tty)) {
 747                 int signal;
 748                 signal = SIGINT;
 749                 if (c == INTR_CHAR(tty))
 750                         goto send_signal;
 751                 signal = SIGQUIT;
 752                 if (c == QUIT_CHAR(tty))
 753                         goto send_signal;
 754                 signal = SIGTSTP;
 755                 if (c == SUSP_CHAR(tty)) {
 756 send_signal:
 757                         /*
 758                          * Echo character, and then send the signal.
 759                          * Note that we do not use isig() here because we want
 760                          * the order to be:
 761                          * 1) flush, 2) echo, 3) signal
 762                          */
 763                         if (!L_NOFLSH(tty)) {
 764                                 n_tty_flush_buffer(tty);
 765                                 tty_driver_flush_buffer(tty);
 766                         }
 767                         if (L_ECHO(tty))
 768                                 echo_char(c, tty);
 769                         if (tty->pgrp)
 770                                 kill_pgrp(tty->pgrp, signal, 1);
 771                         return;
 772                 }
 773         }
 774
 775         if (c == '\r') {
 776                 if (I_IGNCR(tty))
 777                         return;
 778                 if (I_ICRNL(tty))
 779                         c = '\n';
 780         } else if (c == '\n' && I_INLCR(tty))
 781                 c = '\r';
 782
 783         if (tty->icanon) {
 784                 if (c == ERASE_CHAR(tty) || c == KILL_CHAR(tty) ||
 785                     (c == WERASE_CHAR(tty) && L_IEXTEN(tty))) {
 786                         eraser(c, tty);
 787                         return;
 788                 }
 789                 if (c == LNEXT_CHAR(tty) && L_IEXTEN(tty)) {
 790                         tty->lnext = 1;
 791                         if (L_ECHO(tty)) {
 792                                 finish_erasing(tty);
 793                                 if (L_ECHOCTL(tty)) {
 794                                         tty_put_char(tty, '^');
 795                                         tty_put_char(tty, '\b');
 796                                 }
 797                         }
 798                         return;
 799                 }
 800                 if (c == REPRINT_CHAR(tty) && L_ECHO(tty) &&
 801                     L_IEXTEN(tty)) {
 802                         unsigned long tail = tty->canon_head;
 803
 804                         finish_erasing(tty);
 805                         echo_char(c, tty);
 806                         opost('\n', tty);
 807                         while (tail != tty->read_head) {
 808                                 echo_char(tty->read_buf[tail], tty);
 809                                 tail = (tail+1) & (N_TTY_BUF_SIZE-1);
 810                         }
 811                         return;
 812                 }
 813                 if (c == '\n') {
 814                         if (L_ECHO(tty) || L_ECHONL(tty)) {
 815                                 if (tty->read_cnt >= N_TTY_BUF_SIZE-1)
 816                                         tty_put_char(tty, '\a');
 817                                 opost('\n', tty);
 818                         }
 819                         goto handle_newline;
 820                 }
 821                 if (c == EOF_CHAR(tty)) {
 822                         if (tty->canon_head != tty->read_head)
 823                                 set_bit(TTY_PUSH, &tty->flags);
 824                         c = __DISABLED_CHAR;
 825                         goto handle_newline;
 826                 }
 827                 if ((c == EOL_CHAR(tty)) ||
 828                     (c == EOL2_CHAR(tty) && L_IEXTEN(tty))) {
 829                         /*
 830                          * XXX are EOL_CHAR and EOL2_CHAR echoed?!?
 831                          */
 832                         if (L_ECHO(tty)) {
 833                                 if (tty->read_cnt >= N_TTY_BUF_SIZE-1)
 834                                         tty_put_char(tty, '\a');
 835                                 /* Record the column of first canon char. */
 836                                 if (tty->canon_head == tty->read_head)
 837                                         tty->canon_column = tty->column;
 838                                 echo_char(c, tty);
 839                         }
 840                         /*
 841                          * XXX does PARMRK doubling happen for
 842                          * EOL_CHAR and EOL2_CHAR?
 843                          */
 844                         if (I_PARMRK(tty) && c == (unsigned char) '\377')
 845                                 put_tty_queue(c, tty);
 846
 847 handle_newline:
 848                         spin_lock_irqsave(&tty->read_lock, flags);
 849                         set_bit(tty->read_head, tty->read_flags);
 850                         put_tty_queue_nolock(c, tty);
 851                         tty->canon_head = tty->read_head;
 852                         tty->canon_data++;
 853                         spin_unlock_irqrestore(&tty->read_lock, flags);
 854                         kill_fasync(&tty->fasync, SIGIO, POLL_IN);
 855                         if (waitqueue_active(&tty->read_wait))
 856                                 wake_up_interruptible(&tty->read_wait);
 857                         return;
 858                 }
 859         }
 860
 861         finish_erasing(tty);
 862         if (L_ECHO(tty)) {
 863                 if (tty->read_cnt >= N_TTY_BUF_SIZE-1) {
 864                         tty_put_char(tty, '\a'); /* beep if no space */
 865                         return;
 866                 }
 867                 if (c == '\n')
 868                         opost('\n', tty);
 869                 else {
 870                         /* Record the column of first canon char. */
 871                         if (tty->canon_head == tty->read_head)
 872                                 tty->canon_column = tty->column;
 873                         echo_char(c, tty);
 874                 }
 875         }
 876
 877         if (I_PARMRK(tty) && c == (unsigned char) '\377')
 878                 put_tty_queue(c, tty);
 879
 880         put_tty_queue(c, tty);
 881 }
 882
 883
 884 /**
 885  *      n_tty_write_wakeup      -       asynchronous I/O notifier
 886  *      @tty: tty device
 887  *
 888  *      Required for the ptys, serial driver etc. since processes
 889  *      that attach themselves to the master and rely on ASYNC
 890  *      IO must be woken up
 891  */
 892
 893 static void n_tty_write_wakeup(struct tty_struct *tty)
 894 {
 895         if (tty->fasync) {
 896                 set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 897                 kill_fasync(&tty->fasync, SIGIO, POLL_OUT);
 898         }
 899 }
 900
 901 /**
 902  *      n_tty_receive_buf       -       data receive
 903  *      @tty: terminal device
 904  *      @cp: buffer
 905  *      @fp: flag buffer
 906  *      @count: characters
 907  *
 908  *      Called by the terminal driver when a block of characters has
 909  *      been received. This function must be called from soft contexts
 910  *      not from interrupt context. The driver is responsible for making
 911  *      calls one at a time and in order (or using flush_to_ldisc)
 912  */
 913
 914 static void n_tty_receive_buf(struct tty_struct *tty, const unsigned char *cp,
 915                               char *fp, int count)
 916 {
 917         const unsigned char *p;
 918         char *f, flags = TTY_NORMAL;
 919         int     i;
 920         char    buf[64];
 921         unsigned long cpuflags;
 922
 923         if (!tty->read_buf)
 924                 return;
 925
 926         if (tty->real_raw) {
 927                 spin_lock_irqsave(&tty->read_lock, cpuflags);
 928                 i = min(N_TTY_BUF_SIZE - tty->read_cnt,
 929                         N_TTY_BUF_SIZE - tty->read_head);
 930                 i = min(count, i);
 931                 memcpy(tty->read_buf + tty->read_head, cp, i);
 932                 tty->read_head = (tty->read_head + i) & (N_TTY_BUF_SIZE-1);
 933                 tty->read_cnt += i;
 934                 cp += i;
 935                 count -= i;
 936
 937                 i = min(N_TTY_BUF_SIZE - tty->read_cnt,
 938                         N_TTY_BUF_SIZE - tty->read_head);
 939                 i = min(count, i);
 940                 memcpy(tty->read_buf + tty->read_head, cp, i);
 941                 tty->read_head = (tty->read_head + i) & (N_TTY_BUF_SIZE-1);
 942                 tty->read_cnt += i;
 943                 spin_unlock_irqrestore(&tty->read_lock, cpuflags);
 944         } else {
 945                 for (i = count, p = cp, f = fp; i; i--, p++) {
 946                         if (f)
 947                                 flags = *f++;
 948                         switch (flags) {
 949                         case TTY_NORMAL:
 950                                 n_tty_receive_char(tty, *p);
 951                                 break;
 952                         case TTY_BREAK:
 953                                 n_tty_receive_break(tty);
 954                                 break;
 955                         case TTY_PARITY:
 956                         case TTY_FRAME:
 957                                 n_tty_receive_parity_error(tty, *p);
 958                                 break;
 959                         case TTY_OVERRUN:
 960                                 n_tty_receive_overrun(tty);
 961                                 break;
 962                         default:
 963                                 printk(KERN_ERR "%s: unknown flag %d\n",
 964                                        tty_name(tty, buf), flags);
 965                                 break;
 966                         }
 967                 }
 968                 if (tty->ops->flush_chars)
 969                         tty->ops->flush_chars(tty);
 970         }
 971
 972         n_tty_set_room(tty);
 973
 974         if (!tty->icanon && (tty->read_cnt >= tty->minimum_to_wake)) {
 975                 kill_fasync(&tty->fasync, SIGIO, POLL_IN);
 976                 if (waitqueue_active(&tty->read_wait))
 977                         wake_up_interruptible(&tty->read_wait);
 978         }
 979
 980         /*
 981          * Check the remaining room for the input canonicalization
 982          * mode.  We don't want to throttle the driver if we're in
 983          * canonical mode and don't have a newline yet!
 984          */
 985         if (tty->receive_room < TTY_THRESHOLD_THROTTLE) {
 986                 /* check TTY_THROTTLED first so it indicates our state */
 987                 if (!test_and_set_bit(TTY_THROTTLED, &tty->flags) &&
 988                     tty->ops->throttle)
 989                         tty->ops->throttle(tty);
 990         }
 991 }
 992
 993 int is_ignored(int sig)
 994 {
 995         return (sigismember(&current->blocked, sig) ||
 996                 current->sighand->action[sig-1].sa.sa_handler == SIG_IGN);
 997 }
 998
 999 /**
1000  *      n_tty_set_termios       -       termios data changed
1001  *      @tty: terminal
1002  *      @old: previous data
1003  *
1004  *      Called by the tty layer when the user changes termios flags so
1005  *      that the line discipline can plan ahead. This function cannot sleep
1006  *      and is protected from re-entry by the tty layer. The user is
1007  *      guaranteed that this function will not be re-entered or in progress
1008  *      when the ldisc is closed.
1009  */
1010
1011 static void n_tty_set_termios(struct tty_struct *tty, struct ktermios *old)
1012 {
1013         if (!tty)
1014                 return;
1015
1016         tty->icanon = (L_ICANON(tty) != 0);
1017         if (test_bit(TTY_HW_COOK_IN, &tty->flags)) {
1018                 tty->raw = 1;
1019                 tty->real_raw = 1;
1020                 n_tty_set_room(tty);
1021                 return;
1022         }
1023         if (I_ISTRIP(tty) || I_IUCLC(tty) || I_IGNCR(tty) ||
1024             I_ICRNL(tty) || I_INLCR(tty) || L_ICANON(tty) ||
1025             I_IXON(tty) || L_ISIG(tty) || L_ECHO(tty) ||
1026             I_PARMRK(tty)) {
1027                 memset(tty->process_char_map, 0, 256/8);
1028
1029                 if (I_IGNCR(tty) || I_ICRNL(tty))
1030                         set_bit('\r', tty->process_char_map);
1031                 if (I_INLCR(tty))
1032                         set_bit('\n', tty->process_char_map);
1033
1034                 if (L_ICANON(tty)) {
1035                         set_bit(ERASE_CHAR(tty), tty->process_char_map);
1036                         set_bit(KILL_CHAR(tty), tty->process_char_map);
1037                         set_bit(EOF_CHAR(tty), tty->process_char_map);
1038                         set_bit('\n', tty->process_char_map);
1039                         set_bit(EOL_CHAR(tty), tty->process_char_map);
1040                         if (L_IEXTEN(tty)) {
1041                                 set_bit(WERASE_CHAR(tty),
1042                                         tty->process_char_map);
1043                                 set_bit(LNEXT_CHAR(tty),
1044                                         tty->process_char_map);
1045                                 set_bit(EOL2_CHAR(tty),
1046                                         tty->process_char_map);
1047                                 if (L_ECHO(tty))
1048                                         set_bit(REPRINT_CHAR(tty),
1049                                                 tty->process_char_map);
1050                         }
1051                 }
1052                 if (I_IXON(tty)) {
1053                         set_bit(START_CHAR(tty), tty->process_char_map);
1054                         set_bit(STOP_CHAR(tty), tty->process_char_map);
1055                 }
1056                 if (L_ISIG(tty)) {
1057                         set_bit(INTR_CHAR(tty), tty->process_char_map);
1058                         set_bit(QUIT_CHAR(tty), tty->process_char_map);
1059                         set_bit(SUSP_CHAR(tty), tty->process_char_map);
1060                 }
1061                 clear_bit(__DISABLED_CHAR, tty->process_char_map);
1062                 tty->raw = 0;
1063                 tty->real_raw = 0;
1064         } else {
1065                 tty->raw = 1;
1066                 if ((I_IGNBRK(tty) || (!I_BRKINT(tty) && !I_PARMRK(tty))) &&
1067                     (I_IGNPAR(tty) || !I_INPCK(tty)) &&
1068                     (tty->driver->flags & TTY_DRIVER_REAL_RAW))
1069                         tty->real_raw = 1;
1070                 else
1071                         tty->real_raw = 0;
1072         }
1073         n_tty_set_room(tty);
1074         /* The termios change make the tty ready for I/O */
1075         wake_up_interruptible(&tty->write_wait);
1076         wake_up_interruptible(&tty->read_wait);
1077 }
1078
1079 /**
1080  *      n_tty_close             -       close the ldisc for this tty
1081  *      @tty: device
1082  *
1083  *      Called from the terminal layer when this line discipline is
1084  *      being shut down, either because of a close or becsuse of a
1085  *      discipline change. The function will not be called while other
1086  *      ldisc methods are in progress.
1087  */
1088
1089 static void n_tty_close(struct tty_struct *tty)
1090 {
1091         n_tty_flush_buffer(tty);
1092         if (tty->read_buf) {
1093                 free_buf(tty->read_buf);
1094                 tty->read_buf = NULL;
1095         }
1096 }
1097
1098 /**
1099  *      n_tty_open              -       open an ldisc
1100  *      @tty: terminal to open
1101  *
1102  *      Called when this line discipline is being attached to the
1103  *      terminal device. Can sleep. Called serialized so that no
1104  *      other events will occur in parallel. No further open will occur
1105  *      until a close.
1106  */
1107
1108 static int n_tty_open(struct tty_struct *tty)
1109 {
1110         if (!tty)
1111                 return -EINVAL;
1112
1113         /* This one is ugly. Currently a malloc failure here can panic */
1114         if (!tty->read_buf) {
1115                 tty->read_buf = alloc_buf();
1116                 if (!tty->read_buf)
1117                         return -ENOMEM;
1118         }
1119         memset(tty->read_buf, 0, N_TTY_BUF_SIZE);
1120         reset_buffer_flags(tty);
1121         tty->column = 0;
1122         n_tty_set_termios(tty, NULL);
1123         tty->minimum_to_wake = 1;
1124         tty->closing = 0;
1125         return 0;
1126 }
1127
1128 static inline int input_available_p(struct tty_struct *tty, int amt)
1129 {
1130         if (tty->icanon) {
1131                 if (tty->canon_data)
1132                         return 1;
1133         } else if (tty->read_cnt >= (amt ? amt : 1))
1134                 return 1;
1135
1136         return 0;
1137 }
1138
1139 /**
1140  *      copy_from_read_buf      -       copy read data directly
1141  *      @tty: terminal device
1142  *      @b: user data
1143  *      @nr: size of data
1144  *
1145  *      Helper function to speed up read_chan.  It is only called when
1146  *      ICANON is off; it copies characters straight from the tty queue to
1147  *      user space directly.  It can be profitably called twice; once to
1148  *      drain the space from the tail pointer to the (physical) end of the
1149  *      buffer, and once to drain the space from the (physical) beginning of
1150  *      the buffer to head pointer.
1151  *
1152  *      Called under the tty->atomic_read_lock sem
1153  *
1154  */
1155
1156 static int copy_from_read_buf(struct tty_struct *tty,
1157                                       unsigned char __user **b,
1158                                       size_t *nr)
1159
1160 {
1161         int retval;
1162         size_t n;
1163         unsigned long flags;
1164
1165         retval = 0;
1166         spin_lock_irqsave(&tty->read_lock, flags);
1167         n = min(tty->read_cnt, N_TTY_BUF_SIZE - tty->read_tail);
1168         n = min(*nr, n);
1169         spin_unlock_irqrestore(&tty->read_lock, flags);
1170         if (n) {
1171                 retval = copy_to_user(*b, &tty->read_buf[tty->read_tail], n);
1172                 n -= retval;
1173                 tty_audit_add_data(tty, &tty->read_buf[tty->read_tail], n);
1174                 spin_lock_irqsave(&tty->read_lock, flags);
1175                 tty->read_tail = (tty->read_tail + n) & (N_TTY_BUF_SIZE-1);
1176                 tty->read_cnt -= n;
1177                 spin_unlock_irqrestore(&tty->read_lock, flags);
1178                 *b += n;
1179                 *nr -= n;
1180         }
1181         return retval;
1182 }
1183
1184 extern ssize_t redirected_tty_write(struct file *, const char __user *,
1185                                                         size_t, loff_t *);
1186
1187 /**
1188  *      job_control             -       check job control
1189  *      @tty: tty
1190  *      @file: file handle
1191  *
1192  *      Perform job control management checks on this file/tty descriptor
1193  *      and if appropriate send any needed signals and return a negative
1194  *      error code if action should be taken.
1195  *
1196  *      FIXME:
1197  *      Locking: None - redirected write test is safe, testing
1198  *      current->signal should possibly lock current->sighand
1199  *      pgrp locking ?
1200  */
1201
1202 static int job_control(struct tty_struct *tty, struct file *file)
1203 {
1204         /* Job control check -- must be done at start and after
1205            every sleep (POSIX.1 7.1.1.4). */
1206         /* NOTE: not yet done after every sleep pending a thorough
1207            check of the logic of this change. -- jlc */
1208         /* don't stop on /dev/console */
1209         if (file->f_op->write != redirected_tty_write &&
1210             current->signal->tty == tty) {
1211                 if (!tty->pgrp)
1212                         printk(KERN_ERR "read_chan: no tty->pgrp!\n");
1213                 else if (task_pgrp(current) != tty->pgrp) {
1214                         if (is_ignored(SIGTTIN) ||
1215                             is_current_pgrp_orphaned())
1216                                 return -EIO;
1217                         kill_pgrp(task_pgrp(current), SIGTTIN, 1);
1218                         set_thread_flag(TIF_SIGPENDING);
1219                         return -ERESTARTSYS;
1220                 }
1221         }
1222         return 0;
1223 }
1224
1225
1226 /**
1227  *      read_chan               -       read function for tty
1228  *      @tty: tty device
1229  *      @file: file object
1230  *      @buf: userspace buffer pointer
1231  *      @nr: size of I/O
1232  *
1233  *      Perform reads for the line discipline. We are guaranteed that the
1234  *      line discipline will not be closed under us but we may get multiple
1235  *      parallel readers and must handle this ourselves. We may also get
1236  *      a hangup. Always called in user context, may sleep.
1237  *
1238  *      This code must be sure never to sleep through a hangup.
1239  */
1240
1241 static ssize_t read_chan(struct tty_struct *tty, struct file *file,
1242                          unsigned char __user *buf, size_t nr)
1243 {
1244         unsigned char __user *b = buf;
1245         DECLARE_WAITQUEUE(wait, current);
1246         int c;
1247         int minimum, time;
1248         ssize_t retval = 0;
1249         ssize_t size;
1250         long timeout;
1251         unsigned long flags;
1252         int packet;
1253
1254 do_it_again:
1255
1256         if (!tty->read_buf) {
1257                 printk(KERN_ERR "n_tty_read_chan: read_buf == NULL?!?\n");
1258                 return -EIO;
1259         }
1260
1261         c = job_control(tty, file);
1262         if (c < 0)
1263                 return c;
1264
1265         minimum = time = 0;
1266         timeout = MAX_SCHEDULE_TIMEOUT;
1267         if (!tty->icanon) {
1268                 time = (HZ / 10) * TIME_CHAR(tty);
1269                 minimum = MIN_CHAR(tty);
1270                 if (minimum) {
1271                         if (time)
1272                                 tty->minimum_to_wake = 1;
1273                         else if (!waitqueue_active(&tty->read_wait) ||
1274                                  (tty->minimum_to_wake > minimum))
1275                                 tty->minimum_to_wake = minimum;
1276                 } else {
1277                         timeout = 0;
1278                         if (time) {
1279                                 timeout = time;
1280                                 time = 0;
1281                         }
1282                         tty->minimum_to_wake = minimum = 1;
1283                 }
1284         }
1285
1286         /*
1287          *      Internal serialization of reads.
1288          */
1289         if (file->f_flags & O_NONBLOCK) {
1290                 if (!mutex_trylock(&tty->atomic_read_lock))
1291                         return -EAGAIN;
1292         } else {
1293                 if (mutex_lock_interruptible(&tty->atomic_read_lock))
1294                         return -ERESTARTSYS;
1295         }
1296         packet = tty->packet;
1297
1298         add_wait_queue(&tty->read_wait, &wait);
1299         while (nr) {
1300                 /* First test for status change. */
1301                 if (packet && tty->link->ctrl_status) {
1302                         unsigned char cs;
1303                         if (b != buf)
1304                                 break;
1305                         spin_lock_irqsave(&tty->link->ctrl_lock, flags);
1306                         cs = tty->link->ctrl_status;
1307                         tty->link->ctrl_status = 0;
1308                         spin_unlock_irqrestore(&tty->link->ctrl_lock, flags);
1309                         if (tty_put_user(tty, cs, b++)) {
1310                                 retval = -EFAULT;
1311                                 b--;
1312                                 break;
1313                         }
1314                         nr--;
1315                         break;
1316                 }
1317                 /* This statement must be first before checking for input
1318                    so that any interrupt will set the state back to
1319                    TASK_RUNNING. */
1320                 set_current_state(TASK_INTERRUPTIBLE);
1321
1322                 if (((minimum - (b - buf)) < tty->minimum_to_wake) &&
1323                     ((minimum - (b - buf)) >= 1))
1324                         tty->minimum_to_wake = (minimum - (b - buf));
1325
1326                 if (!input_available_p(tty, 0)) {
1327                         if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
1328                                 retval = -EIO;
1329                                 break;
1330                         }
1331                         if (tty_hung_up_p(file))
1332                                 break;
1333                         if (!timeout)
1334                                 break;
1335                         if (file->f_flags & O_NONBLOCK) {
1336                                 retval = -EAGAIN;
1337                                 break;
1338                         }
1339                         if (signal_pending(current)) {
1340                                 retval = -ERESTARTSYS;
1341                                 break;
1342                         }
1343                         /* FIXME: does n_tty_set_room need locking ? */
1344                         n_tty_set_room(tty);
1345                         timeout = schedule_timeout(timeout);
1346                         continue;
1347                 }
1348                 __set_current_state(TASK_RUNNING);
1349
1350                 /* Deal with packet mode. */
1351                 if (packet && b == buf) {
1352                         if (tty_put_user(tty, TIOCPKT_DATA, b++)) {
1353                                 retval = -EFAULT;
1354                                 b--;
1355                                 break;
1356                         }
1357                         nr--;
1358                 }
1359
1360                 if (tty->icanon) {
1361                         /* N.B. avoid overrun if nr == 0 */
1362                         while (nr && tty->read_cnt) {
1363                                 int eol;
1364
1365                                 eol = test_and_clear_bit(tty->read_tail,
1366                                                 tty->read_flags);
1367                                 c = tty->read_buf[tty->read_tail];
1368                                 spin_lock_irqsave(&tty->read_lock, flags);
1369                                 tty->read_tail = ((tty->read_tail+1) &
1370                                                   (N_TTY_BUF_SIZE-1));
1371                                 tty->read_cnt--;
1372                                 if (eol) {
1373                                         /* this test should be redundant:
1374                                          * we shouldn't be reading data if
1375                                          * canon_data is 0
1376                                          */
1377                                         if (--tty->canon_data < 0)
1378                                                 tty->canon_data = 0;
1379                                 }
1380                                 spin_unlock_irqrestore(&tty->read_lock, flags);
1381
1382                                 if (!eol || (c != __DISABLED_CHAR)) {
1383                                         if (tty_put_user(tty, c, b++)) {
1384                                                 retval = -EFAULT;
1385                                                 b--;
1386                                                 break;
1387                                         }
1388                                         nr--;
1389                                 }
1390                                 if (eol) {
1391                                         tty_audit_push(tty);
1392                                         break;
1393                                 }
1394                         }
1395                         if (retval)
1396                                 break;
1397                 } else {
1398                         int uncopied;
1399                         /* The copy function takes the read lock and handles
1400                            locking internally for this case */
1401                         uncopied = copy_from_read_buf(tty, &b, &nr);
1402                         uncopied += copy_from_read_buf(tty, &b, &nr);
1403                         if (uncopied) {
1404                                 retval = -EFAULT;
1405                                 break;
1406                         }
1407                 }
1408
1409                 /* If there is enough space in the read buffer now, let the
1410                  * low-level driver know. We use n_tty_chars_in_buffer() to
1411                  * check the buffer, as it now knows about canonical mode.
1412                  * Otherwise, if the driver is throttled and the line is
1413                  * longer than TTY_THRESHOLD_UNTHROTTLE in canonical mode,
1414                  * we won't get any more characters.
1415                  */
1416                 if (n_tty_chars_in_buffer(tty) <= TTY_THRESHOLD_UNTHROTTLE) {
1417                         n_tty_set_room(tty);
1418                         check_unthrottle(tty);
1419                 }
1420
1421                 if (b - buf >= minimum)
1422                         break;
1423                 if (time)
1424                         timeout = time;
1425         }
1426         mutex_unlock(&tty->atomic_read_lock);
1427         remove_wait_queue(&tty->read_wait, &wait);
1428
1429         if (!waitqueue_active(&tty->read_wait))
1430                 tty->minimum_to_wake = minimum;
1431
1432         __set_current_state(TASK_RUNNING);
1433         size = b - buf;
1434         if (size) {
1435                 retval = size;
1436                 if (nr)
1437                         clear_bit(TTY_PUSH, &tty->flags);
1438         } else if (test_and_clear_bit(TTY_PUSH, &tty->flags))
1439                  goto do_it_again;
1440
1441         n_tty_set_room(tty);
1442         return retval;
1443 }
1444
1445 /**
1446  *      write_chan              -       write function for tty
1447  *      @tty: tty device
1448  *      @file: file object
1449  *      @buf: userspace buffer pointer
1450  *      @nr: size of I/O
1451  *
1452  *      Write function of the terminal device. This is serialized with
1453  *      respect to other write callers but not to termios changes, reads
1454  *      and other such events. We must be careful with N_TTY as the receive
1455  *      code will echo characters, thus calling driver write methods.
1456  *
1457  *      This code must be sure never to sleep through a hangup.
1458  */
1459
1460 static ssize_t write_chan(struct tty_struct *tty, struct file *file,
1461                           const unsigned char *buf, size_t nr)
1462 {
1463         const unsigned char *b = buf;
1464         DECLARE_WAITQUEUE(wait, current);
1465         int c;
1466         ssize_t retval = 0;
1467
1468         /* Job control check -- must be done at start (POSIX.1 7.1.1.4). */
1469         if (L_TOSTOP(tty) && file->f_op->write != redirected_tty_write) {
1470                 retval = tty_check_change(tty);
1471                 if (retval)
1472                         return retval;
1473         }
1474
1475         add_wait_queue(&tty->write_wait, &wait);
1476         while (1) {
1477                 set_current_state(TASK_INTERRUPTIBLE);
1478                 if (signal_pending(current)) {
1479                         retval = -ERESTARTSYS;
1480                         break;
1481                 }
1482                 if (tty_hung_up_p(file) || (tty->link && !tty->link->count)) {
1483                         retval = -EIO;
1484                         break;
1485                 }
1486                 if (O_OPOST(tty) && !(test_bit(TTY_HW_COOK_OUT, &tty->flags))) {
1487                         while (nr > 0) {
1488                                 ssize_t num = opost_block(tty, b, nr);
1489                                 if (num < 0) {
1490                                         if (num == -EAGAIN)
1491                                                 break;
1492                                         retval = num;
1493                                         goto break_out;
1494                                 }
1495                                 b += num;
1496                                 nr -= num;
1497                                 if (nr == 0)
1498                                         break;
1499                                 c = *b;
1500                                 if (opost(c, tty) < 0)
1501                                         break;
1502                                 b++; nr--;
1503                         }
1504                         if (tty->ops->flush_chars)
1505                                 tty->ops->flush_chars(tty);
1506                 } else {
1507                         while (nr > 0) {
1508                                 c = tty->ops->write(tty, b, nr);
1509                                 if (c < 0) {
1510                                         retval = c;
1511                                         goto break_out;
1512                                 }
1513                                 if (!c)
1514                                         break;
1515                                 b += c;
1516                                 nr -= c;
1517                         }
1518                 }
1519                 if (!nr)
1520                         break;
1521                 if (file->f_flags & O_NONBLOCK) {
1522                         retval = -EAGAIN;
1523                         break;
1524                 }
1525                 schedule();
1526         }
1527 break_out:
1528         __set_current_state(TASK_RUNNING);
1529         remove_wait_queue(&tty->write_wait, &wait);
1530         return (b - buf) ? b - buf : retval;
1531 }
1532
1533 /**
1534  *      normal_poll             -       poll method for N_TTY
1535  *      @tty: terminal device
1536  *      @file: file accessing it
1537  *      @wait: poll table
1538  *
1539  *      Called when the line discipline is asked to poll() for data or
1540  *      for special events. This code is not serialized with respect to
1541  *      other events save open/close.
1542  *
1543  *      This code must be sure never to sleep through a hangup.
1544  *      Called without the kernel lock held - fine
1545  */
1546
1547 static unsigned int normal_poll(struct tty_struct *tty, struct file *file,
1548                                                         poll_table *wait)
1549 {
1550         unsigned int mask = 0;
1551
1552         poll_wait(file, &tty->read_wait, wait);
1553         poll_wait(file, &tty->write_wait, wait);
1554         if (input_available_p(tty, TIME_CHAR(tty) ? 0 : MIN_CHAR(tty)))
1555                 mask |= POLLIN | POLLRDNORM;
1556         if (tty->packet && tty->link->ctrl_status)
1557                 mask |= POLLPRI | POLLIN | POLLRDNORM;
1558         if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
1559                 mask |= POLLHUP;
1560         if (tty_hung_up_p(file))
1561                 mask |= POLLHUP;
1562         if (!(mask & (POLLHUP | POLLIN | POLLRDNORM))) {
1563                 if (MIN_CHAR(tty) && !TIME_CHAR(tty))
1564                         tty->minimum_to_wake = MIN_CHAR(tty);
1565                 else
1566                         tty->minimum_to_wake = 1;
1567         }
1568         if (tty->ops->write && !tty_is_writelocked(tty) &&
1569                         tty_chars_in_buffer(tty) < WAKEUP_CHARS &&
1570                         tty_write_room(tty) > 0)
1571                 mask |= POLLOUT | POLLWRNORM;
1572         return mask;
1573 }
1574
1575 struct tty_ldisc tty_ldisc_N_TTY = {
1576         .magic           = TTY_LDISC_MAGIC,
1577         .name            = "n_tty",
1578         .open            = n_tty_open,
1579         .close           = n_tty_close,
1580         .flush_buffer    = n_tty_flush_buffer,
1581         .chars_in_buffer = n_tty_chars_in_buffer,
1582         .read            = read_chan,
1583         .write           = write_chan,
1584         .ioctl           = n_tty_ioctl,
1585         .set_termios     = n_tty_set_termios,
1586         .poll            = normal_poll,
1587         .receive_buf     = n_tty_receive_buf,
1588         .write_wakeup    = n_tty_write_wakeup
1589 };
1590