drivers/char/n_tty.c

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