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