drivers/tty/n_tty.c

   1 // SPDX-License-Identifier: GPL-1.0+
   2 /*
   3  * n_tty.c --- implements the N_TTY line discipline.
   4  *
   5  * This code used to be in tty_io.c, but things are getting hairy
   6  * enough that it made sense to split things off.  (The N_TTY
   7  * processing has changed so much that it's hardly recognizable,
   8  * anyway...)
   9  *
  10  * Note that the open routine for N_TTY is guaranteed never to return
  11  * an error.  This is because Linux will fall back to setting a line
  12  * to N_TTY if it can not switch to any other line discipline.
  13  *
  14  * Written by Theodore Ts'o, Copyright 1994.
  15  *
  16  * This file also contains code originally written by Linus Torvalds,
  17  * Copyright 1991, 1992, 1993, and by Julian Cowley, Copyright 1994.
  18  *
  19  * Reduced memory usage for older ARM systems  - Russell King.
  20  *
  21  * 2000/01/20   Fixed SMP locking on put_tty_queue using bits of
  22  *              the patch by Andrew J. Kroll <ag784@freenet.buffalo.edu>
  23  *              who actually finally proved there really was a race.
  24  *
  25  * 2002/03/18   Implemented n_tty_wakeup to send SIGIO POLL_OUTs to
  26  *              waiting writing processes-Sapan Bhatia <sapan@corewars.org>.
  27  *              Also fixed a bug in BLOCKING mode where n_tty_write returns
  28  *              EAGAIN
  29  */
  30
  31 #include <linux/types.h>
  32 #include <linux/major.h>
  33 #include <linux/errno.h>
  34 #include <linux/signal.h>
  35 #include <linux/fcntl.h>
  36 #include <linux/sched.h>
  37 #include <linux/interrupt.h>
  38 #include <linux/tty.h>
  39 #include <linux/timer.h>
  40 #include <linux/ctype.h>
  41 #include <linux/mm.h>
  42 #include <linux/string.h>
  43 #include <linux/slab.h>
  44 #include <linux/poll.h>
  45 #include <linux/bitops.h>
  46 #include <linux/audit.h>
  47 #include <linux/file.h>
  48 #include <linux/uaccess.h>
  49 #include <linux/module.h>
  50 #include <linux/ratelimit.h>
  51 #include <linux/vmalloc.h>
  52 #include "tty.h"
  53
  54 /*
  55  * Until this number of characters is queued in the xmit buffer, select will
  56  * return "we have room for writes".
  57  */
  58 #define WAKEUP_CHARS 256
  59
  60 /*
  61  * This defines the low- and high-watermarks for throttling and
  62  * unthrottling the TTY driver.  These watermarks are used for
  63  * controlling the space in the read buffer.
  64  */
  65 #define TTY_THRESHOLD_THROTTLE          128 /* now based on remaining room */
  66 #define TTY_THRESHOLD_UNTHROTTLE        128
  67
  68 /*
  69  * Special byte codes used in the echo buffer to represent operations
  70  * or special handling of characters.  Bytes in the echo buffer that
  71  * are not part of such special blocks are treated as normal character
  72  * codes.
  73  */
  74 #define ECHO_OP_START 0xff
  75 #define ECHO_OP_MOVE_BACK_COL 0x80
  76 #define ECHO_OP_SET_CANON_COL 0x81
  77 #define ECHO_OP_ERASE_TAB 0x82
  78
  79 #define ECHO_COMMIT_WATERMARK   256
  80 #define ECHO_BLOCK              256
  81 #define ECHO_DISCARD_WATERMARK  N_TTY_BUF_SIZE - (ECHO_BLOCK + 32)
  82
  83
  84 #undef N_TTY_TRACE
  85 #ifdef N_TTY_TRACE
  86 # define n_tty_trace(f, args...)        trace_printk(f, ##args)
  87 #else
  88 # define n_tty_trace(f, args...)        no_printk(f, ##args)
  89 #endif
  90
  91 struct n_tty_data {
  92         /* producer-published */
  93         size_t read_head;
  94         size_t commit_head;
  95         size_t canon_head;
  96         size_t echo_head;
  97         size_t echo_commit;
  98         size_t echo_mark;
  99         DECLARE_BITMAP(char_map, 256);
 100
 101         /* private to n_tty_receive_overrun (single-threaded) */
 102         unsigned long overrun_time;
 103         int num_overrun;
 104
 105         /* non-atomic */
 106         bool no_room;
 107
 108         /* must hold exclusive termios_rwsem to reset these */
 109         unsigned char lnext:1, erasing:1, raw:1, real_raw:1, icanon:1;
 110         unsigned char push:1;
 111
 112         /* shared by producer and consumer */
 113         char read_buf[N_TTY_BUF_SIZE];
 114         DECLARE_BITMAP(read_flags, N_TTY_BUF_SIZE);
 115         unsigned char echo_buf[N_TTY_BUF_SIZE];
 116
 117         /* consumer-published */
 118         size_t read_tail;
 119         size_t line_start;
 120
 121         /* protected by output lock */
 122         unsigned int column;
 123         unsigned int canon_column;
 124         size_t echo_tail;
 125
 126         struct mutex atomic_read_lock;
 127         struct mutex output_lock;
 128 };
 129
 130 #define MASK(x) ((x) & (N_TTY_BUF_SIZE - 1))
 131
 132 static inline size_t read_cnt(struct n_tty_data *ldata)
 133 {
 134         return ldata->read_head - ldata->read_tail;
 135 }
 136
 137 static inline unsigned char read_buf(struct n_tty_data *ldata, size_t i)
 138 {
 139         return ldata->read_buf[i & (N_TTY_BUF_SIZE - 1)];
 140 }
 141
 142 static inline unsigned char *read_buf_addr(struct n_tty_data *ldata, size_t i)
 143 {
 144         return &ldata->read_buf[i & (N_TTY_BUF_SIZE - 1)];
 145 }
 146
 147 static inline unsigned char echo_buf(struct n_tty_data *ldata, size_t i)
 148 {
 149         smp_rmb(); /* Matches smp_wmb() in add_echo_byte(). */
 150         return ldata->echo_buf[i & (N_TTY_BUF_SIZE - 1)];
 151 }
 152
 153 static inline unsigned char *echo_buf_addr(struct n_tty_data *ldata, size_t i)
 154 {
 155         return &ldata->echo_buf[i & (N_TTY_BUF_SIZE - 1)];
 156 }
 157
 158 /* If we are not echoing the data, perhaps this is a secret so erase it */
 159 static void zero_buffer(struct tty_struct *tty, u8 *buffer, int size)
 160 {
 161         bool icanon = !!L_ICANON(tty);
 162         bool no_echo = !L_ECHO(tty);
 163
 164         if (icanon && no_echo)
 165                 memset(buffer, 0x00, size);
 166 }
 167
 168 static void tty_copy(struct tty_struct *tty, void *to, size_t tail, size_t n)
 169 {
 170         struct n_tty_data *ldata = tty->disc_data;
 171         size_t size = N_TTY_BUF_SIZE - tail;
 172         void *from = read_buf_addr(ldata, tail);
 173
 174         if (n > size) {
 175                 tty_audit_add_data(tty, from, size);
 176                 memcpy(to, from, size);
 177                 zero_buffer(tty, from, size);
 178                 to += size;
 179                 n -= size;
 180                 from = ldata->read_buf;
 181         }
 182
 183         tty_audit_add_data(tty, from, n);
 184         memcpy(to, from, n);
 185         zero_buffer(tty, from, n);
 186 }
 187
 188 /**
 189  * n_tty_kick_worker - start input worker (if required)
 190  * @tty: terminal
 191  *
 192  * Re-schedules the flip buffer work if it may have stopped.
 193  *
 194  * Locking:
 195  *  * Caller holds exclusive %termios_rwsem, or
 196  *  * n_tty_read()/consumer path:
 197  *      holds non-exclusive %termios_rwsem
 198  */
 199 static void n_tty_kick_worker(struct tty_struct *tty)
 200 {
 201         struct n_tty_data *ldata = tty->disc_data;
 202
 203         /* Did the input worker stop? Restart it */
 204         if (unlikely(ldata->no_room)) {
 205                 ldata->no_room = 0;
 206
 207                 WARN_RATELIMIT(tty->port->itty == NULL,
 208                                 "scheduling with invalid itty\n");
 209                 /* see if ldisc has been killed - if so, this means that
 210                  * even though the ldisc has been halted and ->buf.work
 211                  * cancelled, ->buf.work is about to be rescheduled
 212                  */
 213                 WARN_RATELIMIT(test_bit(TTY_LDISC_HALTED, &tty->flags),
 214                                "scheduling buffer work for halted ldisc\n");
 215                 tty_buffer_restart_work(tty->port);
 216         }
 217 }
 218
 219 static ssize_t chars_in_buffer(struct tty_struct *tty)
 220 {
 221         struct n_tty_data *ldata = tty->disc_data;
 222         ssize_t n = 0;
 223
 224         if (!ldata->icanon)
 225                 n = ldata->commit_head - ldata->read_tail;
 226         else
 227                 n = ldata->canon_head - ldata->read_tail;
 228         return n;
 229 }
 230
 231 /**
 232  * n_tty_write_wakeup   -       asynchronous I/O notifier
 233  * @tty: tty device
 234  *
 235  * Required for the ptys, serial driver etc. since processes that attach
 236  * themselves to the master and rely on ASYNC IO must be woken up.
 237  */
 238 static void n_tty_write_wakeup(struct tty_struct *tty)
 239 {
 240         clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 241         kill_fasync(&tty->fasync, SIGIO, POLL_OUT);
 242 }
 243
 244 static void n_tty_check_throttle(struct tty_struct *tty)
 245 {
 246         struct n_tty_data *ldata = tty->disc_data;
 247
 248         /*
 249          * Check the remaining room for the input canonicalization
 250          * mode.  We don't want to throttle the driver if we're in
 251          * canonical mode and don't have a newline yet!
 252          */
 253         if (ldata->icanon && ldata->canon_head == ldata->read_tail)
 254                 return;
 255
 256         while (1) {
 257                 int throttled;
 258                 tty_set_flow_change(tty, TTY_THROTTLE_SAFE);
 259                 if (N_TTY_BUF_SIZE - read_cnt(ldata) >= TTY_THRESHOLD_THROTTLE)
 260                         break;
 261                 throttled = tty_throttle_safe(tty);
 262                 if (!throttled)
 263                         break;
 264         }
 265         __tty_set_flow_change(tty, 0);
 266 }
 267
 268 static void n_tty_check_unthrottle(struct tty_struct *tty)
 269 {
 270         if (tty->driver->type == TTY_DRIVER_TYPE_PTY) {
 271                 if (chars_in_buffer(tty) > TTY_THRESHOLD_UNTHROTTLE)
 272                         return;
 273                 n_tty_kick_worker(tty);
 274                 tty_wakeup(tty->link);
 275                 return;
 276         }
 277
 278         /* If there is enough space in the read buffer now, let the
 279          * low-level driver know. We use chars_in_buffer() to
 280          * check the buffer, as it now knows about canonical mode.
 281          * Otherwise, if the driver is throttled and the line is
 282          * longer than TTY_THRESHOLD_UNTHROTTLE in canonical mode,
 283          * we won't get any more characters.
 284          */
 285
 286         while (1) {
 287                 int unthrottled;
 288                 tty_set_flow_change(tty, TTY_UNTHROTTLE_SAFE);
 289                 if (chars_in_buffer(tty) > TTY_THRESHOLD_UNTHROTTLE)
 290                         break;
 291                 n_tty_kick_worker(tty);
 292                 unthrottled = tty_unthrottle_safe(tty);
 293                 if (!unthrottled)
 294                         break;
 295         }
 296         __tty_set_flow_change(tty, 0);
 297 }
 298
 299 /**
 300  * put_tty_queue                -       add character to tty
 301  * @c: character
 302  * @ldata: n_tty data
 303  *
 304  * Add a character to the tty read_buf queue.
 305  *
 306  * Locking:
 307  *  * n_tty_receive_buf()/producer path:
 308  *      caller holds non-exclusive %termios_rwsem
 309  */
 310 static inline void put_tty_queue(unsigned char c, struct n_tty_data *ldata)
 311 {
 312         *read_buf_addr(ldata, ldata->read_head) = c;
 313         ldata->read_head++;
 314 }
 315
 316 /**
 317  * reset_buffer_flags   -       reset buffer state
 318  * @ldata: line disc data to reset
 319  *
 320  * Reset the read buffer counters and clear the flags. Called from
 321  * n_tty_open() and n_tty_flush_buffer().
 322  *
 323  * Locking:
 324  *  * caller holds exclusive %termios_rwsem, or
 325  *  * (locking is not required)
 326  */
 327 static void reset_buffer_flags(struct n_tty_data *ldata)
 328 {
 329         ldata->read_head = ldata->canon_head = ldata->read_tail = 0;
 330         ldata->commit_head = 0;
 331         ldata->line_start = 0;
 332
 333         ldata->erasing = 0;
 334         bitmap_zero(ldata->read_flags, N_TTY_BUF_SIZE);
 335         ldata->push = 0;
 336 }
 337
 338 static void n_tty_packet_mode_flush(struct tty_struct *tty)
 339 {
 340         unsigned long flags;
 341
 342         if (tty->link->ctrl.packet) {
 343                 spin_lock_irqsave(&tty->ctrl.lock, flags);
 344                 tty->ctrl.pktstatus |= TIOCPKT_FLUSHREAD;
 345                 spin_unlock_irqrestore(&tty->ctrl.lock, flags);
 346                 wake_up_interruptible(&tty->link->read_wait);
 347         }
 348 }
 349
 350 /**
 351  * n_tty_flush_buffer   -       clean input queue
 352  * @tty: terminal device
 353  *
 354  * Flush the input buffer. Called when the tty layer wants the buffer flushed
 355  * (eg at hangup) or when the %N_TTY line discipline internally has to clean
 356  * the pending queue (for example some signals).
 357  *
 358  * Holds %termios_rwsem to exclude producer/consumer while buffer indices are
 359  * reset.
 360  *
 361  * Locking: %ctrl.lock, exclusive %termios_rwsem
 362  */
 363 static void n_tty_flush_buffer(struct tty_struct *tty)
 364 {
 365         down_write(&tty->termios_rwsem);
 366         reset_buffer_flags(tty->disc_data);
 367         n_tty_kick_worker(tty);
 368
 369         if (tty->link)
 370                 n_tty_packet_mode_flush(tty);
 371         up_write(&tty->termios_rwsem);
 372 }
 373
 374 /**
 375  * is_utf8_continuation -       utf8 multibyte check
 376  * @c: byte to check
 377  *
 378  * Returns: true if the utf8 character @c is a multibyte continuation
 379  * character. We use this to correctly compute the on-screen size of the
 380  * character when printing.
 381  */
 382 static inline int is_utf8_continuation(unsigned char c)
 383 {
 384         return (c & 0xc0) == 0x80;
 385 }
 386
 387 /**
 388  * is_continuation      -       multibyte check
 389  * @c: byte to check
 390  * @tty: terminal device
 391  *
 392  * Returns: true if the utf8 character @c is a multibyte continuation character
 393  * and the terminal is in unicode mode.
 394  */
 395 static inline int is_continuation(unsigned char c, struct tty_struct *tty)
 396 {
 397         return I_IUTF8(tty) && is_utf8_continuation(c);
 398 }
 399
 400 /**
 401  * do_output_char       -       output one character
 402  * @c: character (or partial unicode symbol)
 403  * @tty: terminal device
 404  * @space: space available in tty driver write buffer
 405  *
 406  * This is a helper function that handles one output character (including
 407  * special characters like TAB, CR, LF, etc.), doing OPOST processing and
 408  * putting the results in the tty driver's write buffer.
 409  *
 410  * Note that Linux currently ignores TABDLY, CRDLY, VTDLY, FFDLY and NLDLY.
 411  * They simply aren't relevant in the world today. If you ever need them, add
 412  * them here.
 413  *
 414  * Returns: the number of bytes of buffer space used or -1 if no space left.
 415  *
 416  * Locking: should be called under the %output_lock to protect the column state
 417  * and space left in the buffer.
 418  */
 419 static int do_output_char(unsigned char c, struct tty_struct *tty, int space)
 420 {
 421         struct n_tty_data *ldata = tty->disc_data;
 422         int     spaces;
 423
 424         if (!space)
 425                 return -1;
 426
 427         switch (c) {
 428         case '\n':
 429                 if (O_ONLRET(tty))
 430                         ldata->column = 0;
 431                 if (O_ONLCR(tty)) {
 432                         if (space < 2)
 433                                 return -1;
 434                         ldata->canon_column = ldata->column = 0;
 435                         tty->ops->write(tty, "\r\n", 2);
 436                         return 2;
 437                 }
 438                 ldata->canon_column = ldata->column;
 439                 break;
 440         case '\r':
 441                 if (O_ONOCR(tty) && ldata->column == 0)
 442                         return 0;
 443                 if (O_OCRNL(tty)) {
 444                         c = '\n';
 445                         if (O_ONLRET(tty))
 446                                 ldata->canon_column = ldata->column = 0;
 447                         break;
 448                 }
 449                 ldata->canon_column = ldata->column = 0;
 450                 break;
 451         case '\t':
 452                 spaces = 8 - (ldata->column & 7);
 453                 if (O_TABDLY(tty) == XTABS) {
 454                         if (space < spaces)
 455                                 return -1;
 456                         ldata->column += spaces;
 457                         tty->ops->write(tty, "        ", spaces);
 458                         return spaces;
 459                 }
 460                 ldata->column += spaces;
 461                 break;
 462         case '\b':
 463                 if (ldata->column > 0)
 464                         ldata->column--;
 465                 break;
 466         default:
 467                 if (!iscntrl(c)) {
 468                         if (O_OLCUC(tty))
 469                                 c = toupper(c);
 470                         if (!is_continuation(c, tty))
 471                                 ldata->column++;
 472                 }
 473                 break;
 474         }
 475
 476         tty_put_char(tty, c);
 477         return 1;
 478 }
 479
 480 /**
 481  * process_output       -       output post processor
 482  * @c: character (or partial unicode symbol)
 483  * @tty: terminal device
 484  *
 485  * Output one character with OPOST processing.
 486  *
 487  * Returns: -1 when the output device is full and the character must be
 488  * retried.
 489  *
 490  * Locking: %output_lock to protect column state and space left (also, this is
 491  *called from n_tty_write() under the tty layer write lock).
 492  */
 493 static int process_output(unsigned char c, struct tty_struct *tty)
 494 {
 495         struct n_tty_data *ldata = tty->disc_data;
 496         int     space, retval;
 497
 498         mutex_lock(&ldata->output_lock);
 499
 500         space = tty_write_room(tty);
 501         retval = do_output_char(c, tty, space);
 502
 503         mutex_unlock(&ldata->output_lock);
 504         if (retval < 0)
 505                 return -1;
 506         else
 507                 return 0;
 508 }
 509
 510 /**
 511  * process_output_block -       block post processor
 512  * @tty: terminal device
 513  * @buf: character buffer
 514  * @nr: number of bytes to output
 515  *
 516  * Output a block of characters with OPOST processing.
 517  *
 518  * This path is used to speed up block console writes, among other things when
 519  * processing blocks of output data. It handles only the simple cases normally
 520  * found and helps to generate blocks of symbols for the console driver and
 521  * thus improve performance.
 522  *
 523  * Returns: the number of characters output.
 524  *
 525  * Locking: %output_lock to protect column state and space left (also, this is
 526  * called from n_tty_write() under the tty layer write lock).
 527  */
 528 static ssize_t process_output_block(struct tty_struct *tty,
 529                                     const unsigned char *buf, unsigned int nr)
 530 {
 531         struct n_tty_data *ldata = tty->disc_data;
 532         int     space;
 533         int     i;
 534         const unsigned char *cp;
 535
 536         mutex_lock(&ldata->output_lock);
 537
 538         space = tty_write_room(tty);
 539         if (space <= 0) {
 540                 mutex_unlock(&ldata->output_lock);
 541                 return space;
 542         }
 543         if (nr > space)
 544                 nr = space;
 545
 546         for (i = 0, cp = buf; i < nr; i++, cp++) {
 547                 unsigned char c = *cp;
 548
 549                 switch (c) {
 550                 case '\n':
 551                         if (O_ONLRET(tty))
 552                                 ldata->column = 0;
 553                         if (O_ONLCR(tty))
 554                                 goto break_out;
 555                         ldata->canon_column = ldata->column;
 556                         break;
 557                 case '\r':
 558                         if (O_ONOCR(tty) && ldata->column == 0)
 559                                 goto break_out;
 560                         if (O_OCRNL(tty))
 561                                 goto break_out;
 562                         ldata->canon_column = ldata->column = 0;
 563                         break;
 564                 case '\t':
 565                         goto break_out;
 566                 case '\b':
 567                         if (ldata->column > 0)
 568                                 ldata->column--;
 569                         break;
 570                 default:
 571                         if (!iscntrl(c)) {
 572                                 if (O_OLCUC(tty))
 573                                         goto break_out;
 574                                 if (!is_continuation(c, tty))
 575                                         ldata->column++;
 576                         }
 577                         break;
 578                 }
 579         }
 580 break_out:
 581         i = tty->ops->write(tty, buf, i);
 582
 583         mutex_unlock(&ldata->output_lock);
 584         return i;
 585 }
 586
 587 /**
 588  * __process_echoes     -       write pending echo characters
 589  * @tty: terminal device
 590  *
 591  * Write previously buffered echo (and other ldisc-generated) characters to the
 592  * tty.
 593  *
 594  * Characters generated by the ldisc (including echoes) need to be buffered
 595  * because the driver's write buffer can fill during heavy program output.
 596  * Echoing straight to the driver will often fail under these conditions,
 597  * causing lost characters and resulting mismatches of ldisc state information.
 598  *
 599  * Since the ldisc state must represent the characters actually sent to the
 600  * driver at the time of the write, operations like certain changes in column
 601  * state are also saved in the buffer and executed here.
 602  *
 603  * A circular fifo buffer is used so that the most recent characters are
 604  * prioritized. Also, when control characters are echoed with a prefixed "^",
 605  * the pair is treated atomically and thus not separated.
 606  *
 607  * Locking: callers must hold %output_lock.
 608  */
 609 static size_t __process_echoes(struct tty_struct *tty)
 610 {
 611         struct n_tty_data *ldata = tty->disc_data;
 612         int     space, old_space;
 613         size_t tail;
 614         unsigned char c;
 615
 616         old_space = space = tty_write_room(tty);
 617
 618         tail = ldata->echo_tail;
 619         while (MASK(ldata->echo_commit) != MASK(tail)) {
 620                 c = echo_buf(ldata, tail);
 621                 if (c == ECHO_OP_START) {
 622                         unsigned char op;
 623                         int no_space_left = 0;
 624
 625                         /*
 626                          * Since add_echo_byte() is called without holding
 627                          * output_lock, we might see only portion of multi-byte
 628                          * operation.
 629                          */
 630                         if (MASK(ldata->echo_commit) == MASK(tail + 1))
 631                                 goto not_yet_stored;
 632                         /*
 633                          * If the buffer byte is the start of a multi-byte
 634                          * operation, get the next byte, which is either the
 635                          * op code or a control character value.
 636                          */
 637                         op = echo_buf(ldata, tail + 1);
 638
 639                         switch (op) {
 640                         case ECHO_OP_ERASE_TAB: {
 641                                 unsigned int num_chars, num_bs;
 642
 643                                 if (MASK(ldata->echo_commit) == MASK(tail + 2))
 644                                         goto not_yet_stored;
 645                                 num_chars = echo_buf(ldata, tail + 2);
 646
 647                                 /*
 648                                  * Determine how many columns to go back
 649                                  * in order to erase the tab.
 650                                  * This depends on the number of columns
 651                                  * used by other characters within the tab
 652                                  * area.  If this (modulo 8) count is from
 653                                  * the start of input rather than from a
 654                                  * previous tab, we offset by canon column.
 655                                  * Otherwise, tab spacing is normal.
 656                                  */
 657                                 if (!(num_chars & 0x80))
 658                                         num_chars += ldata->canon_column;
 659                                 num_bs = 8 - (num_chars & 7);
 660
 661                                 if (num_bs > space) {
 662                                         no_space_left = 1;
 663                                         break;
 664                                 }
 665                                 space -= num_bs;
 666                                 while (num_bs--) {
 667                                         tty_put_char(tty, '\b');
 668                                         if (ldata->column > 0)
 669                                                 ldata->column--;
 670                                 }
 671                                 tail += 3;
 672                                 break;
 673                         }
 674                         case ECHO_OP_SET_CANON_COL:
 675                                 ldata->canon_column = ldata->column;
 676                                 tail += 2;
 677                                 break;
 678
 679                         case ECHO_OP_MOVE_BACK_COL:
 680                                 if (ldata->column > 0)
 681                                         ldata->column--;
 682                                 tail += 2;
 683                                 break;
 684
 685                         case ECHO_OP_START:
 686                                 /* This is an escaped echo op start code */
 687                                 if (!space) {
 688                                         no_space_left = 1;
 689                                         break;
 690                                 }
 691                                 tty_put_char(tty, ECHO_OP_START);
 692                                 ldata->column++;
 693                                 space--;
 694                                 tail += 2;
 695                                 break;
 696
 697                         default:
 698                                 /*
 699                                  * If the op is not a special byte code,
 700                                  * it is a ctrl char tagged to be echoed
 701                                  * as "^X" (where X is the letter
 702                                  * representing the control char).
 703                                  * Note that we must ensure there is
 704                                  * enough space for the whole ctrl pair.
 705                                  *
 706                                  */
 707                                 if (space < 2) {
 708                                         no_space_left = 1;
 709                                         break;
 710                                 }
 711                                 tty_put_char(tty, '^');
 712                                 tty_put_char(tty, op ^ 0100);
 713                                 ldata->column += 2;
 714                                 space -= 2;
 715                                 tail += 2;
 716                         }
 717
 718                         if (no_space_left)
 719                                 break;
 720                 } else {
 721                         if (O_OPOST(tty)) {
 722                                 int retval = do_output_char(c, tty, space);
 723                                 if (retval < 0)
 724                                         break;
 725                                 space -= retval;
 726                         } else {
 727                                 if (!space)
 728                                         break;
 729                                 tty_put_char(tty, c);
 730                                 space -= 1;
 731                         }
 732                         tail += 1;
 733                 }
 734         }
 735
 736         /* If the echo buffer is nearly full (so that the possibility exists
 737          * of echo overrun before the next commit), then discard enough
 738          * data at the tail to prevent a subsequent overrun */
 739         while (ldata->echo_commit > tail &&
 740                ldata->echo_commit - tail >= ECHO_DISCARD_WATERMARK) {
 741                 if (echo_buf(ldata, tail) == ECHO_OP_START) {
 742                         if (echo_buf(ldata, tail + 1) == ECHO_OP_ERASE_TAB)
 743                                 tail += 3;
 744                         else
 745                                 tail += 2;
 746                 } else
 747                         tail++;
 748         }
 749
 750  not_yet_stored:
 751         ldata->echo_tail = tail;
 752         return old_space - space;
 753 }
 754
 755 static void commit_echoes(struct tty_struct *tty)
 756 {
 757         struct n_tty_data *ldata = tty->disc_data;
 758         size_t nr, old, echoed;
 759         size_t head;
 760
 761         mutex_lock(&ldata->output_lock);
 762         head = ldata->echo_head;
 763         ldata->echo_mark = head;
 764         old = ldata->echo_commit - ldata->echo_tail;
 765
 766         /* Process committed echoes if the accumulated # of bytes
 767          * is over the threshold (and try again each time another
 768          * block is accumulated) */
 769         nr = head - ldata->echo_tail;
 770         if (nr < ECHO_COMMIT_WATERMARK ||
 771             (nr % ECHO_BLOCK > old % ECHO_BLOCK)) {
 772                 mutex_unlock(&ldata->output_lock);
 773                 return;
 774         }
 775
 776         ldata->echo_commit = head;
 777         echoed = __process_echoes(tty);
 778         mutex_unlock(&ldata->output_lock);
 779
 780         if (echoed && tty->ops->flush_chars)
 781                 tty->ops->flush_chars(tty);
 782 }
 783
 784 static void process_echoes(struct tty_struct *tty)
 785 {
 786         struct n_tty_data *ldata = tty->disc_data;
 787         size_t echoed;
 788
 789         if (ldata->echo_mark == ldata->echo_tail)
 790                 return;
 791
 792         mutex_lock(&ldata->output_lock);
 793         ldata->echo_commit = ldata->echo_mark;
 794         echoed = __process_echoes(tty);
 795         mutex_unlock(&ldata->output_lock);
 796
 797         if (echoed && tty->ops->flush_chars)
 798                 tty->ops->flush_chars(tty);
 799 }
 800
 801 /* NB: echo_mark and echo_head should be equivalent here */
 802 static void flush_echoes(struct tty_struct *tty)
 803 {
 804         struct n_tty_data *ldata = tty->disc_data;
 805
 806         if ((!L_ECHO(tty) && !L_ECHONL(tty)) ||
 807             ldata->echo_commit == ldata->echo_head)
 808                 return;
 809
 810         mutex_lock(&ldata->output_lock);
 811         ldata->echo_commit = ldata->echo_head;
 812         __process_echoes(tty);
 813         mutex_unlock(&ldata->output_lock);
 814 }
 815
 816 /**
 817  * add_echo_byte        -       add a byte to the echo buffer
 818  * @c: unicode byte to echo
 819  * @ldata: n_tty data
 820  *
 821  * Add a character or operation byte to the echo buffer.
 822  */
 823 static inline void add_echo_byte(unsigned char c, struct n_tty_data *ldata)
 824 {
 825         *echo_buf_addr(ldata, ldata->echo_head) = c;
 826         smp_wmb(); /* Matches smp_rmb() in echo_buf(). */
 827         ldata->echo_head++;
 828 }
 829
 830 /**
 831  * echo_move_back_col   -       add operation to move back a column
 832  * @ldata: n_tty data
 833  *
 834  * Add an operation to the echo buffer to move back one column.
 835  */
 836 static void echo_move_back_col(struct n_tty_data *ldata)
 837 {
 838         add_echo_byte(ECHO_OP_START, ldata);
 839         add_echo_byte(ECHO_OP_MOVE_BACK_COL, ldata);
 840 }
 841
 842 /**
 843  * echo_set_canon_col   -       add operation to set the canon column
 844  * @ldata: n_tty data
 845  *
 846  * Add an operation to the echo buffer to set the canon column to the current
 847  * column.
 848  */
 849 static void echo_set_canon_col(struct n_tty_data *ldata)
 850 {
 851         add_echo_byte(ECHO_OP_START, ldata);
 852         add_echo_byte(ECHO_OP_SET_CANON_COL, ldata);
 853 }
 854
 855 /**
 856  * echo_erase_tab       -       add operation to erase a tab
 857  * @num_chars: number of character columns already used
 858  * @after_tab: true if num_chars starts after a previous tab
 859  * @ldata: n_tty data
 860  *
 861  * Add an operation to the echo buffer to erase a tab.
 862  *
 863  * Called by the eraser function, which knows how many character columns have
 864  * been used since either a previous tab or the start of input. This
 865  * information will be used later, along with canon column (if applicable), to
 866  * go back the correct number of columns.
 867  */
 868 static void echo_erase_tab(unsigned int num_chars, int after_tab,
 869                            struct n_tty_data *ldata)
 870 {
 871         add_echo_byte(ECHO_OP_START, ldata);
 872         add_echo_byte(ECHO_OP_ERASE_TAB, ldata);
 873
 874         /* We only need to know this modulo 8 (tab spacing) */
 875         num_chars &= 7;
 876
 877         /* Set the high bit as a flag if num_chars is after a previous tab */
 878         if (after_tab)
 879                 num_chars |= 0x80;
 880
 881         add_echo_byte(num_chars, ldata);
 882 }
 883
 884 /**
 885  * echo_char_raw        -       echo a character raw
 886  * @c: unicode byte to echo
 887  * @ldata: line disc data
 888  *
 889  * Echo user input back onto the screen. This must be called only when
 890  * L_ECHO(tty) is true. Called from the &tty_driver.receive_buf() path.
 891  *
 892  * This variant does not treat control characters specially.
 893  */
 894 static void echo_char_raw(unsigned char c, struct n_tty_data *ldata)
 895 {
 896         if (c == ECHO_OP_START) {
 897                 add_echo_byte(ECHO_OP_START, ldata);
 898                 add_echo_byte(ECHO_OP_START, ldata);
 899         } else {
 900                 add_echo_byte(c, ldata);
 901         }
 902 }
 903
 904 /**
 905  * echo_char            -       echo a character
 906  * @c: unicode byte to echo
 907  * @tty: terminal device
 908  *
 909  * Echo user input back onto the screen. This must be called only when
 910  * L_ECHO(tty) is true. Called from the &tty_driver.receive_buf() path.
 911  *
 912  * This variant tags control characters to be echoed as "^X" (where X is the
 913  * letter representing the control char).
 914  */
 915 static void echo_char(unsigned char c, struct tty_struct *tty)
 916 {
 917         struct n_tty_data *ldata = tty->disc_data;
 918
 919         if (c == ECHO_OP_START) {
 920                 add_echo_byte(ECHO_OP_START, ldata);
 921                 add_echo_byte(ECHO_OP_START, ldata);
 922         } else {
 923                 if (L_ECHOCTL(tty) && iscntrl(c) && c != '\t')
 924                         add_echo_byte(ECHO_OP_START, ldata);
 925                 add_echo_byte(c, ldata);
 926         }
 927 }
 928
 929 /**
 930  * finish_erasing       -       complete erase
 931  * @ldata: n_tty data
 932  */
 933 static inline void finish_erasing(struct n_tty_data *ldata)
 934 {
 935         if (ldata->erasing) {
 936                 echo_char_raw('/', ldata);
 937                 ldata->erasing = 0;
 938         }
 939 }
 940
 941 /**
 942  * eraser               -       handle erase function
 943  * @c: character input
 944  * @tty: terminal device
 945  *
 946  * Perform erase and necessary output when an erase character is present in the
 947  * stream from the driver layer. Handles the complexities of UTF-8 multibyte
 948  * symbols.
 949  *
 950  * Locking: n_tty_receive_buf()/producer path:
 951  *      caller holds non-exclusive %termios_rwsem
 952  */
 953 static void eraser(unsigned char c, struct tty_struct *tty)
 954 {
 955         struct n_tty_data *ldata = tty->disc_data;
 956         enum { ERASE, WERASE, KILL } kill_type;
 957         size_t head;
 958         size_t cnt;
 959         int seen_alnums;
 960
 961         if (ldata->read_head == ldata->canon_head) {
 962                 /* process_output('\a', tty); */ /* what do you think? */
 963                 return;
 964         }
 965         if (c == ERASE_CHAR(tty))
 966                 kill_type = ERASE;
 967         else if (c == WERASE_CHAR(tty))
 968                 kill_type = WERASE;
 969         else {
 970                 if (!L_ECHO(tty)) {
 971                         ldata->read_head = ldata->canon_head;
 972                         return;
 973                 }
 974                 if (!L_ECHOK(tty) || !L_ECHOKE(tty) || !L_ECHOE(tty)) {
 975                         ldata->read_head = ldata->canon_head;
 976                         finish_erasing(ldata);
 977                         echo_char(KILL_CHAR(tty), tty);
 978                         /* Add a newline if ECHOK is on and ECHOKE is off. */
 979                         if (L_ECHOK(tty))
 980                                 echo_char_raw('\n', ldata);
 981                         return;
 982                 }
 983                 kill_type = KILL;
 984         }
 985
 986         seen_alnums = 0;
 987         while (MASK(ldata->read_head) != MASK(ldata->canon_head)) {
 988                 head = ldata->read_head;
 989
 990                 /* erase a single possibly multibyte character */
 991                 do {
 992                         head--;
 993                         c = read_buf(ldata, head);
 994                 } while (is_continuation(c, tty) &&
 995                          MASK(head) != MASK(ldata->canon_head));
 996
 997                 /* do not partially erase */
 998                 if (is_continuation(c, tty))
 999                         break;
1000
1001                 if (kill_type == WERASE) {
1002                         /* Equivalent to BSD's ALTWERASE. */
1003                         if (isalnum(c) || c == '_')
1004                                 seen_alnums++;
1005                         else if (seen_alnums)
1006                                 break;
1007                 }
1008                 cnt = ldata->read_head - head;
1009                 ldata->read_head = head;
1010                 if (L_ECHO(tty)) {
1011                         if (L_ECHOPRT(tty)) {
1012                                 if (!ldata->erasing) {
1013                                         echo_char_raw('\\', ldata);
1014                                         ldata->erasing = 1;
1015                                 }
1016                                 /* if cnt > 1, output a multi-byte character */
1017                                 echo_char(c, tty);
1018                                 while (--cnt > 0) {
1019                                         head++;
1020                                         echo_char_raw(read_buf(ldata, head), ldata);
1021                                         echo_move_back_col(ldata);
1022                                 }
1023                         } else if (kill_type == ERASE && !L_ECHOE(tty)) {
1024                                 echo_char(ERASE_CHAR(tty), tty);
1025                         } else if (c == '\t') {
1026                                 unsigned int num_chars = 0;
1027                                 int after_tab = 0;
1028                                 size_t tail = ldata->read_head;
1029
1030                                 /*
1031                                  * Count the columns used for characters
1032                                  * since the start of input or after a
1033                                  * previous tab.
1034                                  * This info is used to go back the correct
1035                                  * number of columns.
1036                                  */
1037                                 while (MASK(tail) != MASK(ldata->canon_head)) {
1038                                         tail--;
1039                                         c = read_buf(ldata, tail);
1040                                         if (c == '\t') {
1041                                                 after_tab = 1;
1042                                                 break;
1043                                         } else if (iscntrl(c)) {
1044                                                 if (L_ECHOCTL(tty))
1045                                                         num_chars += 2;
1046                                         } else if (!is_continuation(c, tty)) {
1047                                                 num_chars++;
1048                                         }
1049                                 }
1050                                 echo_erase_tab(num_chars, after_tab, ldata);
1051                         } else {
1052                                 if (iscntrl(c) && L_ECHOCTL(tty)) {
1053                                         echo_char_raw('\b', ldata);
1054                                         echo_char_raw(' ', ldata);
1055                                         echo_char_raw('\b', ldata);
1056                                 }
1057                                 if (!iscntrl(c) || L_ECHOCTL(tty)) {
1058                                         echo_char_raw('\b', ldata);
1059                                         echo_char_raw(' ', ldata);
1060                                         echo_char_raw('\b', ldata);
1061                                 }
1062                         }
1063                 }
1064                 if (kill_type == ERASE)
1065                         break;
1066         }
1067         if (ldata->read_head == ldata->canon_head && L_ECHO(tty))
1068                 finish_erasing(ldata);
1069 }
1070
1071
1072 static void __isig(int sig, struct tty_struct *tty)
1073 {
1074         struct pid *tty_pgrp = tty_get_pgrp(tty);
1075         if (tty_pgrp) {
1076                 kill_pgrp(tty_pgrp, sig, 1);
1077                 put_pid(tty_pgrp);
1078         }
1079 }
1080
1081 /**
1082  * isig                 -       handle the ISIG optio
1083  * @sig: signal
1084  * @tty: terminal
1085  *
1086  * Called when a signal is being sent due to terminal input. Called from the
1087  * &tty_driver.receive_buf() path, so serialized.
1088  *
1089  * Performs input and output flush if !NOFLSH. In this context, the echo
1090  * buffer is 'output'. The signal is processed first to alert any current
1091  * readers or writers to discontinue and exit their i/o loops.
1092  *
1093  * Locking: %ctrl.lock
1094  */
1095 static void isig(int sig, struct tty_struct *tty)
1096 {
1097         struct n_tty_data *ldata = tty->disc_data;
1098
1099         if (L_NOFLSH(tty)) {
1100                 /* signal only */
1101                 __isig(sig, tty);
1102
1103         } else { /* signal and flush */
1104                 up_read(&tty->termios_rwsem);
1105                 down_write(&tty->termios_rwsem);
1106
1107                 __isig(sig, tty);
1108
1109                 /* clear echo buffer */
1110                 mutex_lock(&ldata->output_lock);
1111                 ldata->echo_head = ldata->echo_tail = 0;
1112                 ldata->echo_mark = ldata->echo_commit = 0;
1113                 mutex_unlock(&ldata->output_lock);
1114
1115                 /* clear output buffer */
1116                 tty_driver_flush_buffer(tty);
1117
1118                 /* clear input buffer */
1119                 reset_buffer_flags(tty->disc_data);
1120
1121                 /* notify pty master of flush */
1122                 if (tty->link)
1123                         n_tty_packet_mode_flush(tty);
1124
1125                 up_write(&tty->termios_rwsem);
1126                 down_read(&tty->termios_rwsem);
1127         }
1128 }
1129
1130 /**
1131  * n_tty_receive_break  -       handle break
1132  * @tty: terminal
1133  *
1134  * An RS232 break event has been hit in the incoming bitstream. This can cause
1135  * a variety of events depending upon the termios settings.
1136  *
1137  * Locking: n_tty_receive_buf()/producer path:
1138  *      caller holds non-exclusive termios_rwsem
1139  *
1140  * Note: may get exclusive %termios_rwsem if flushing input buffer
1141  */
1142 static void n_tty_receive_break(struct tty_struct *tty)
1143 {
1144         struct n_tty_data *ldata = tty->disc_data;
1145
1146         if (I_IGNBRK(tty))
1147                 return;
1148         if (I_BRKINT(tty)) {
1149                 isig(SIGINT, tty);
1150                 return;
1151         }
1152         if (I_PARMRK(tty)) {
1153                 put_tty_queue('\377', ldata);
1154                 put_tty_queue('\0', ldata);
1155         }
1156         put_tty_queue('\0', ldata);
1157 }
1158
1159 /**
1160  * n_tty_receive_overrun        -       handle overrun reporting
1161  * @tty: terminal
1162  *
1163  * Data arrived faster than we could process it. While the tty driver has
1164  * flagged this the bits that were missed are gone forever.
1165  *
1166  * Called from the receive_buf path so single threaded. Does not need locking
1167  * as num_overrun and overrun_time are function private.
1168  */
1169 static void n_tty_receive_overrun(struct tty_struct *tty)
1170 {
1171         struct n_tty_data *ldata = tty->disc_data;
1172
1173         ldata->num_overrun++;
1174         if (time_after(jiffies, ldata->overrun_time + HZ) ||
1175                         time_after(ldata->overrun_time, jiffies)) {
1176                 tty_warn(tty, "%d input overrun(s)\n", ldata->num_overrun);
1177                 ldata->overrun_time = jiffies;
1178                 ldata->num_overrun = 0;
1179         }
1180 }
1181
1182 /**
1183  * n_tty_receive_parity_error   -       error notifier
1184  * @tty: terminal device
1185  * @c: character
1186  *
1187  * Process a parity error and queue the right data to indicate the error case
1188  * if necessary.
1189  *
1190  * Locking: n_tty_receive_buf()/producer path:
1191  *      caller holds non-exclusive %termios_rwsem
1192  */
1193 static void n_tty_receive_parity_error(struct tty_struct *tty, unsigned char c)
1194 {
1195         struct n_tty_data *ldata = tty->disc_data;
1196
1197         if (I_INPCK(tty)) {
1198                 if (I_IGNPAR(tty))
1199                         return;
1200                 if (I_PARMRK(tty)) {
1201                         put_tty_queue('\377', ldata);
1202                         put_tty_queue('\0', ldata);
1203                         put_tty_queue(c, ldata);
1204                 } else
1205                         put_tty_queue('\0', ldata);
1206         } else
1207                 put_tty_queue(c, ldata);
1208 }
1209
1210 static void
1211 n_tty_receive_signal_char(struct tty_struct *tty, int signal, unsigned char c)
1212 {
1213         isig(signal, tty);
1214         if (I_IXON(tty))
1215                 start_tty(tty);
1216         if (L_ECHO(tty)) {
1217                 echo_char(c, tty);
1218                 commit_echoes(tty);
1219         } else
1220                 process_echoes(tty);
1221 }
1222
1223 static bool n_tty_is_char_flow_ctrl(struct tty_struct *tty, unsigned char c)
1224 {
1225         return c == START_CHAR(tty) || c == STOP_CHAR(tty);
1226 }
1227
1228 /* Returns true if c is consumed as flow-control character */
1229 static bool n_tty_receive_char_flow_ctrl(struct tty_struct *tty, unsigned char c)
1230 {
1231         if (!n_tty_is_char_flow_ctrl(tty, c))
1232                 return false;
1233
1234         if (c == START_CHAR(tty)) {
1235                 start_tty(tty);
1236                 process_echoes(tty);
1237                 return true;
1238         }
1239
1240         /* STOP_CHAR */
1241         stop_tty(tty);
1242         return true;
1243 }
1244
1245 static void n_tty_receive_char_special(struct tty_struct *tty, unsigned char c)
1246 {
1247         struct n_tty_data *ldata = tty->disc_data;
1248
1249         if (I_IXON(tty) && n_tty_receive_char_flow_ctrl(tty, c))
1250                 return;
1251
1252         if (L_ISIG(tty)) {
1253                 if (c == INTR_CHAR(tty)) {
1254                         n_tty_receive_signal_char(tty, SIGINT, c);
1255                         return;
1256                 } else if (c == QUIT_CHAR(tty)) {
1257                         n_tty_receive_signal_char(tty, SIGQUIT, c);
1258                         return;
1259                 } else if (c == SUSP_CHAR(tty)) {
1260                         n_tty_receive_signal_char(tty, SIGTSTP, c);
1261                         return;
1262                 }
1263         }
1264
1265         if (tty->flow.stopped && !tty->flow.tco_stopped && I_IXON(tty) && I_IXANY(tty)) {
1266                 start_tty(tty);
1267                 process_echoes(tty);
1268         }
1269
1270         if (c == '\r') {
1271                 if (I_IGNCR(tty))
1272                         return;
1273                 if (I_ICRNL(tty))
1274                         c = '\n';
1275         } else if (c == '\n' && I_INLCR(tty))
1276                 c = '\r';
1277
1278         if (ldata->icanon) {
1279                 if (c == ERASE_CHAR(tty) || c == KILL_CHAR(tty) ||
1280                     (c == WERASE_CHAR(tty) && L_IEXTEN(tty))) {
1281                         eraser(c, tty);
1282                         commit_echoes(tty);
1283                         return;
1284                 }
1285                 if (c == LNEXT_CHAR(tty) && L_IEXTEN(tty)) {
1286                         ldata->lnext = 1;
1287                         if (L_ECHO(tty)) {
1288                                 finish_erasing(ldata);
1289                                 if (L_ECHOCTL(tty)) {
1290                                         echo_char_raw('^', ldata);
1291                                         echo_char_raw('\b', ldata);
1292                                         commit_echoes(tty);
1293                                 }
1294                         }
1295                         return;
1296                 }
1297                 if (c == REPRINT_CHAR(tty) && L_ECHO(tty) && L_IEXTEN(tty)) {
1298                         size_t tail = ldata->canon_head;
1299
1300                         finish_erasing(ldata);
1301                         echo_char(c, tty);
1302                         echo_char_raw('\n', ldata);
1303                         while (MASK(tail) != MASK(ldata->read_head)) {
1304                                 echo_char(read_buf(ldata, tail), tty);
1305                                 tail++;
1306                         }
1307                         commit_echoes(tty);
1308                         return;
1309                 }
1310                 if (c == '\n') {
1311                         if (L_ECHO(tty) || L_ECHONL(tty)) {
1312                                 echo_char_raw('\n', ldata);
1313                                 commit_echoes(tty);
1314                         }
1315                         goto handle_newline;
1316                 }
1317                 if (c == EOF_CHAR(tty)) {
1318                         c = __DISABLED_CHAR;
1319                         goto handle_newline;
1320                 }
1321                 if ((c == EOL_CHAR(tty)) ||
1322                     (c == EOL2_CHAR(tty) && L_IEXTEN(tty))) {
1323                         /*
1324                          * XXX are EOL_CHAR and EOL2_CHAR echoed?!?
1325                          */
1326                         if (L_ECHO(tty)) {
1327                                 /* Record the column of first canon char. */
1328                                 if (ldata->canon_head == ldata->read_head)
1329                                         echo_set_canon_col(ldata);
1330                                 echo_char(c, tty);
1331                                 commit_echoes(tty);
1332                         }
1333                         /*
1334                          * XXX does PARMRK doubling happen for
1335                          * EOL_CHAR and EOL2_CHAR?
1336                          */
1337                         if (c == (unsigned char) '\377' && I_PARMRK(tty))
1338                                 put_tty_queue(c, ldata);
1339
1340 handle_newline:
1341                         set_bit(ldata->read_head & (N_TTY_BUF_SIZE - 1), ldata->read_flags);
1342                         put_tty_queue(c, ldata);
1343                         smp_store_release(&ldata->canon_head, ldata->read_head);
1344                         kill_fasync(&tty->fasync, SIGIO, POLL_IN);
1345                         wake_up_interruptible_poll(&tty->read_wait, EPOLLIN | EPOLLRDNORM);
1346                         return;
1347                 }
1348         }
1349
1350         if (L_ECHO(tty)) {
1351                 finish_erasing(ldata);
1352                 if (c == '\n')
1353                         echo_char_raw('\n', ldata);
1354                 else {
1355                         /* Record the column of first canon char. */
1356                         if (ldata->canon_head == ldata->read_head)
1357                                 echo_set_canon_col(ldata);
1358                         echo_char(c, tty);
1359                 }
1360                 commit_echoes(tty);
1361         }
1362
1363         /* PARMRK doubling check */
1364         if (c == (unsigned char) '\377' && I_PARMRK(tty))
1365                 put_tty_queue(c, ldata);
1366
1367         put_tty_queue(c, ldata);
1368 }
1369
1370 /**
1371  * n_tty_receive_char   -       perform processing
1372  * @tty: terminal device
1373  * @c: character
1374  *
1375  * Process an individual character of input received from the driver.  This is
1376  * serialized with respect to itself by the rules for the driver above.
1377  *
1378  * Locking: n_tty_receive_buf()/producer path:
1379  *      caller holds non-exclusive %termios_rwsem
1380  *      publishes canon_head if canonical mode is active
1381  */
1382 static void n_tty_receive_char(struct tty_struct *tty, unsigned char c)
1383 {
1384         struct n_tty_data *ldata = tty->disc_data;
1385
1386         if (tty->flow.stopped && !tty->flow.tco_stopped && I_IXON(tty) && I_IXANY(tty)) {
1387                 start_tty(tty);
1388                 process_echoes(tty);
1389         }
1390         if (L_ECHO(tty)) {
1391                 finish_erasing(ldata);
1392                 /* Record the column of first canon char. */
1393                 if (ldata->canon_head == ldata->read_head)
1394                         echo_set_canon_col(ldata);
1395                 echo_char(c, tty);
1396                 commit_echoes(tty);
1397         }
1398         /* PARMRK doubling check */
1399         if (c == (unsigned char) '\377' && I_PARMRK(tty))
1400                 put_tty_queue(c, ldata);
1401         put_tty_queue(c, ldata);
1402 }
1403
1404 static void n_tty_receive_char_closing(struct tty_struct *tty, unsigned char c)
1405 {
1406         if (I_ISTRIP(tty))
1407                 c &= 0x7f;
1408         if (I_IUCLC(tty) && L_IEXTEN(tty))
1409                 c = tolower(c);
1410
1411         if (I_IXON(tty)) {
1412                 if (c == STOP_CHAR(tty))
1413                         stop_tty(tty);
1414                 else if (c == START_CHAR(tty) ||
1415                          (tty->flow.stopped && !tty->flow.tco_stopped && I_IXANY(tty) &&
1416                           c != INTR_CHAR(tty) && c != QUIT_CHAR(tty) &&
1417                           c != SUSP_CHAR(tty))) {
1418                         start_tty(tty);
1419                         process_echoes(tty);
1420                 }
1421         }
1422 }
1423
1424 static void
1425 n_tty_receive_char_flagged(struct tty_struct *tty, unsigned char c, char flag)
1426 {
1427         switch (flag) {
1428         case TTY_BREAK:
1429                 n_tty_receive_break(tty);
1430                 break;
1431         case TTY_PARITY:
1432         case TTY_FRAME:
1433                 n_tty_receive_parity_error(tty, c);
1434                 break;
1435         case TTY_OVERRUN:
1436                 n_tty_receive_overrun(tty);
1437                 break;
1438         default:
1439                 tty_err(tty, "unknown flag %d\n", flag);
1440                 break;
1441         }
1442 }
1443
1444 static void
1445 n_tty_receive_char_lnext(struct tty_struct *tty, unsigned char c, char flag)
1446 {
1447         struct n_tty_data *ldata = tty->disc_data;
1448
1449         ldata->lnext = 0;
1450         if (likely(flag == TTY_NORMAL)) {
1451                 if (I_ISTRIP(tty))
1452                         c &= 0x7f;
1453                 if (I_IUCLC(tty) && L_IEXTEN(tty))
1454                         c = tolower(c);
1455                 n_tty_receive_char(tty, c);
1456         } else
1457                 n_tty_receive_char_flagged(tty, c, flag);
1458 }
1459
1460 static void
1461 n_tty_receive_buf_real_raw(struct tty_struct *tty, const unsigned char *cp,
1462                            const char *fp, int count)
1463 {
1464         struct n_tty_data *ldata = tty->disc_data;
1465         size_t n, head;
1466
1467         head = ldata->read_head & (N_TTY_BUF_SIZE - 1);
1468         n = min_t(size_t, count, N_TTY_BUF_SIZE - head);
1469         memcpy(read_buf_addr(ldata, head), cp, n);
1470         ldata->read_head += n;
1471         cp += n;
1472         count -= n;
1473
1474         head = ldata->read_head & (N_TTY_BUF_SIZE - 1);
1475         n = min_t(size_t, count, N_TTY_BUF_SIZE - head);
1476         memcpy(read_buf_addr(ldata, head), cp, n);
1477         ldata->read_head += n;
1478 }
1479
1480 static void
1481 n_tty_receive_buf_raw(struct tty_struct *tty, const unsigned char *cp,
1482                       const char *fp, int count)
1483 {
1484         struct n_tty_data *ldata = tty->disc_data;
1485         char flag = TTY_NORMAL;
1486
1487         while (count--) {
1488                 if (fp)
1489                         flag = *fp++;
1490                 if (likely(flag == TTY_NORMAL))
1491                         put_tty_queue(*cp++, ldata);
1492                 else
1493                         n_tty_receive_char_flagged(tty, *cp++, flag);
1494         }
1495 }
1496
1497 static void
1498 n_tty_receive_buf_closing(struct tty_struct *tty, const unsigned char *cp,
1499                           const char *fp, int count)
1500 {
1501         char flag = TTY_NORMAL;
1502
1503         while (count--) {
1504                 if (fp)
1505                         flag = *fp++;
1506                 if (likely(flag == TTY_NORMAL))
1507                         n_tty_receive_char_closing(tty, *cp++);
1508         }
1509 }
1510
1511 static void n_tty_receive_buf_standard(struct tty_struct *tty,
1512                 const unsigned char *cp, const char *fp, int count)
1513 {
1514         struct n_tty_data *ldata = tty->disc_data;
1515         char flag = TTY_NORMAL;
1516
1517         while (count--) {
1518                 unsigned char c = *cp++;
1519
1520                 if (fp)
1521                         flag = *fp++;
1522
1523                 if (ldata->lnext) {
1524                         n_tty_receive_char_lnext(tty, c, flag);
1525                         continue;
1526                 }
1527
1528                 if (unlikely(flag != TTY_NORMAL)) {
1529                         n_tty_receive_char_flagged(tty, c, flag);
1530                         continue;
1531                 }
1532
1533                 if (I_ISTRIP(tty))
1534                         c &= 0x7f;
1535                 if (I_IUCLC(tty) && L_IEXTEN(tty))
1536                         c = tolower(c);
1537                 if (L_EXTPROC(tty)) {
1538                         put_tty_queue(c, ldata);
1539                         continue;
1540                 }
1541
1542                 if (test_bit(c, ldata->char_map))
1543                         n_tty_receive_char_special(tty, c);
1544                 else
1545                         n_tty_receive_char(tty, c);
1546         }
1547 }
1548
1549 static void __receive_buf(struct tty_struct *tty, const unsigned char *cp,
1550                           const char *fp, int count)
1551 {
1552         struct n_tty_data *ldata = tty->disc_data;
1553         bool preops = I_ISTRIP(tty) || (I_IUCLC(tty) && L_IEXTEN(tty));
1554
1555         if (ldata->real_raw)
1556                 n_tty_receive_buf_real_raw(tty, cp, fp, count);
1557         else if (ldata->raw || (L_EXTPROC(tty) && !preops))
1558                 n_tty_receive_buf_raw(tty, cp, fp, count);
1559         else if (tty->closing && !L_EXTPROC(tty))
1560                 n_tty_receive_buf_closing(tty, cp, fp, count);
1561         else {
1562                 n_tty_receive_buf_standard(tty, cp, fp, count);
1563
1564                 flush_echoes(tty);
1565                 if (tty->ops->flush_chars)
1566                         tty->ops->flush_chars(tty);
1567         }
1568
1569         if (ldata->icanon && !L_EXTPROC(tty))
1570                 return;
1571
1572         /* publish read_head to consumer */
1573         smp_store_release(&ldata->commit_head, ldata->read_head);
1574
1575         if (read_cnt(ldata)) {
1576                 kill_fasync(&tty->fasync, SIGIO, POLL_IN);
1577                 wake_up_interruptible_poll(&tty->read_wait, EPOLLIN | EPOLLRDNORM);
1578         }
1579 }
1580
1581 /**
1582  * n_tty_receive_buf_common     -       process input
1583  * @tty: device to receive input
1584  * @cp: input chars
1585  * @fp: flags for each char (if %NULL, all chars are %TTY_NORMAL)
1586  * @count: number of input chars in @cp
1587  * @flow: enable flow control
1588  *
1589  * Called by the terminal driver when a block of characters has been received.
1590  * This function must be called from soft contexts not from interrupt context.
1591  * The driver is responsible for making calls one at a time and in order (or
1592  * using flush_to_ldisc()).
1593  *
1594  * Returns: the # of input chars from @cp which were processed.
1595  *
1596  * In canonical mode, the maximum line length is 4096 chars (including the line
1597  * termination char); lines longer than 4096 chars are truncated. After 4095
1598  * chars, input data is still processed but not stored. Overflow processing
1599  * ensures the tty can always receive more input until at least one line can be
1600  * read.
1601  *
1602  * In non-canonical mode, the read buffer will only accept 4095 chars; this
1603  * provides the necessary space for a newline char if the input mode is
1604  * switched to canonical.
1605  *
1606  * Note it is possible for the read buffer to _contain_ 4096 chars in
1607  * non-canonical mode: the read buffer could already contain the maximum canon
1608  * line of 4096 chars when the mode is switched to non-canonical.
1609  *
1610  * Locking: n_tty_receive_buf()/producer path:
1611  *      claims non-exclusive %termios_rwsem
1612  *      publishes commit_head or canon_head
1613  */
1614 static int
1615 n_tty_receive_buf_common(struct tty_struct *tty, const unsigned char *cp,
1616                          const char *fp, int count, int flow)
1617 {
1618         struct n_tty_data *ldata = tty->disc_data;
1619         int room, n, rcvd = 0, overflow;
1620
1621         down_read(&tty->termios_rwsem);
1622
1623         do {
1624                 /*
1625                  * When PARMRK is set, each input char may take up to 3 chars
1626                  * in the read buf; reduce the buffer space avail by 3x
1627                  *
1628                  * If we are doing input canonicalization, and there are no
1629                  * pending newlines, let characters through without limit, so
1630                  * that erase characters will be handled.  Other excess
1631                  * characters will be beeped.
1632                  *
1633                  * paired with store in *_copy_from_read_buf() -- guarantees
1634                  * the consumer has loaded the data in read_buf up to the new
1635                  * read_tail (so this producer will not overwrite unread data)
1636                  */
1637                 size_t tail = smp_load_acquire(&ldata->read_tail);
1638
1639                 room = N_TTY_BUF_SIZE - (ldata->read_head - tail);
1640                 if (I_PARMRK(tty))
1641                         room = (room + 2) / 3;
1642                 room--;
1643                 if (room <= 0) {
1644                         overflow = ldata->icanon && ldata->canon_head == tail;
1645                         if (overflow && room < 0)
1646                                 ldata->read_head--;
1647                         room = overflow;
1648                         ldata->no_room = flow && !room;
1649                 } else
1650                         overflow = 0;
1651
1652                 n = min(count, room);
1653                 if (!n)
1654                         break;
1655
1656                 /* ignore parity errors if handling overflow */
1657                 if (!overflow || !fp || *fp != TTY_PARITY)
1658                         __receive_buf(tty, cp, fp, n);
1659
1660                 cp += n;
1661                 if (fp)
1662                         fp += n;
1663                 count -= n;
1664                 rcvd += n;
1665         } while (!test_bit(TTY_LDISC_CHANGING, &tty->flags));
1666
1667         tty->receive_room = room;
1668
1669         /* Unthrottle if handling overflow on pty */
1670         if (tty->driver->type == TTY_DRIVER_TYPE_PTY) {
1671                 if (overflow) {
1672                         tty_set_flow_change(tty, TTY_UNTHROTTLE_SAFE);
1673                         tty_unthrottle_safe(tty);
1674                         __tty_set_flow_change(tty, 0);
1675                 }
1676         } else
1677                 n_tty_check_throttle(tty);
1678
1679         up_read(&tty->termios_rwsem);
1680
1681         return rcvd;
1682 }
1683
1684 static void n_tty_receive_buf(struct tty_struct *tty, const unsigned char *cp,
1685                               const char *fp, int count)
1686 {
1687         n_tty_receive_buf_common(tty, cp, fp, count, 0);
1688 }
1689
1690 static int n_tty_receive_buf2(struct tty_struct *tty, const unsigned char *cp,
1691                               const char *fp, int count)
1692 {
1693         return n_tty_receive_buf_common(tty, cp, fp, count, 1);
1694 }
1695
1696 /**
1697  * n_tty_set_termios    -       termios data changed
1698  * @tty: terminal
1699  * @old: previous data
1700  *
1701  * Called by the tty layer when the user changes termios flags so that the line
1702  * discipline can plan ahead. This function cannot sleep and is protected from
1703  * re-entry by the tty layer. The user is guaranteed that this function will
1704  * not be re-entered or in progress when the ldisc is closed.
1705  *
1706  * Locking: Caller holds @tty->termios_rwsem
1707  */
1708 static void n_tty_set_termios(struct tty_struct *tty, struct ktermios *old)
1709 {
1710         struct n_tty_data *ldata = tty->disc_data;
1711
1712         if (!old || (old->c_lflag ^ tty->termios.c_lflag) & (ICANON | EXTPROC)) {
1713                 bitmap_zero(ldata->read_flags, N_TTY_BUF_SIZE);
1714                 ldata->line_start = ldata->read_tail;
1715                 if (!L_ICANON(tty) || !read_cnt(ldata)) {
1716                         ldata->canon_head = ldata->read_tail;
1717                         ldata->push = 0;
1718                 } else {
1719                         set_bit((ldata->read_head - 1) & (N_TTY_BUF_SIZE - 1),
1720                                 ldata->read_flags);
1721                         ldata->canon_head = ldata->read_head;
1722                         ldata->push = 1;
1723                 }
1724                 ldata->commit_head = ldata->read_head;
1725                 ldata->erasing = 0;
1726                 ldata->lnext = 0;
1727         }
1728
1729         ldata->icanon = (L_ICANON(tty) != 0);
1730
1731         if (I_ISTRIP(tty) || I_IUCLC(tty) || I_IGNCR(tty) ||
1732             I_ICRNL(tty) || I_INLCR(tty) || L_ICANON(tty) ||
1733             I_IXON(tty) || L_ISIG(tty) || L_ECHO(tty) ||
1734             I_PARMRK(tty)) {
1735                 bitmap_zero(ldata->char_map, 256);
1736
1737                 if (I_IGNCR(tty) || I_ICRNL(tty))
1738                         set_bit('\r', ldata->char_map);
1739                 if (I_INLCR(tty))
1740                         set_bit('\n', ldata->char_map);
1741
1742                 if (L_ICANON(tty)) {
1743                         set_bit(ERASE_CHAR(tty), ldata->char_map);
1744                         set_bit(KILL_CHAR(tty), ldata->char_map);
1745                         set_bit(EOF_CHAR(tty), ldata->char_map);
1746                         set_bit('\n', ldata->char_map);
1747                         set_bit(EOL_CHAR(tty), ldata->char_map);
1748                         if (L_IEXTEN(tty)) {
1749                                 set_bit(WERASE_CHAR(tty), ldata->char_map);
1750                                 set_bit(LNEXT_CHAR(tty), ldata->char_map);
1751                                 set_bit(EOL2_CHAR(tty), ldata->char_map);
1752                                 if (L_ECHO(tty))
1753                                         set_bit(REPRINT_CHAR(tty),
1754                                                 ldata->char_map);
1755                         }
1756                 }
1757                 if (I_IXON(tty)) {
1758                         set_bit(START_CHAR(tty), ldata->char_map);
1759                         set_bit(STOP_CHAR(tty), ldata->char_map);
1760                 }
1761                 if (L_ISIG(tty)) {
1762                         set_bit(INTR_CHAR(tty), ldata->char_map);
1763                         set_bit(QUIT_CHAR(tty), ldata->char_map);
1764                         set_bit(SUSP_CHAR(tty), ldata->char_map);
1765                 }
1766                 clear_bit(__DISABLED_CHAR, ldata->char_map);
1767                 ldata->raw = 0;
1768                 ldata->real_raw = 0;
1769         } else {
1770                 ldata->raw = 1;
1771                 if ((I_IGNBRK(tty) || (!I_BRKINT(tty) && !I_PARMRK(tty))) &&
1772                     (I_IGNPAR(tty) || !I_INPCK(tty)) &&
1773                     (tty->driver->flags & TTY_DRIVER_REAL_RAW))
1774                         ldata->real_raw = 1;
1775                 else
1776                         ldata->real_raw = 0;
1777         }
1778         /*
1779          * Fix tty hang when I_IXON(tty) is cleared, but the tty
1780          * been stopped by STOP_CHAR(tty) before it.
1781          */
1782         if (!I_IXON(tty) && old && (old->c_iflag & IXON) && !tty->flow.tco_stopped) {
1783                 start_tty(tty);
1784                 process_echoes(tty);
1785         }
1786
1787         /* The termios change make the tty ready for I/O */
1788         wake_up_interruptible(&tty->write_wait);
1789         wake_up_interruptible(&tty->read_wait);
1790 }
1791
1792 /**
1793  * n_tty_close          -       close the ldisc for this tty
1794  * @tty: device
1795  *
1796  * Called from the terminal layer when this line discipline is being shut down,
1797  * either because of a close or becsuse of a discipline change. The function
1798  * will not be called while other ldisc methods are in progress.
1799  */
1800 static void n_tty_close(struct tty_struct *tty)
1801 {
1802         struct n_tty_data *ldata = tty->disc_data;
1803
1804         if (tty->link)
1805                 n_tty_packet_mode_flush(tty);
1806
1807         down_write(&tty->termios_rwsem);
1808         vfree(ldata);
1809         tty->disc_data = NULL;
1810         up_write(&tty->termios_rwsem);
1811 }
1812
1813 /**
1814  * n_tty_open           -       open an ldisc
1815  * @tty: terminal to open
1816  *
1817  * Called when this line discipline is being attached to the terminal device.
1818  * Can sleep. Called serialized so that no other events will occur in parallel.
1819  * No further open will occur until a close.
1820  */
1821 static int n_tty_open(struct tty_struct *tty)
1822 {
1823         struct n_tty_data *ldata;
1824
1825         /* Currently a malloc failure here can panic */
1826         ldata = vzalloc(sizeof(*ldata));
1827         if (!ldata)
1828                 return -ENOMEM;
1829
1830         ldata->overrun_time = jiffies;
1831         mutex_init(&ldata->atomic_read_lock);
1832         mutex_init(&ldata->output_lock);
1833
1834         tty->disc_data = ldata;
1835         tty->closing = 0;
1836         /* indicate buffer work may resume */
1837         clear_bit(TTY_LDISC_HALTED, &tty->flags);
1838         n_tty_set_termios(tty, NULL);
1839         tty_unthrottle(tty);
1840         return 0;
1841 }
1842
1843 static inline int input_available_p(struct tty_struct *tty, int poll)
1844 {
1845         struct n_tty_data *ldata = tty->disc_data;
1846         int amt = poll && !TIME_CHAR(tty) && MIN_CHAR(tty) ? MIN_CHAR(tty) : 1;
1847
1848         if (ldata->icanon && !L_EXTPROC(tty))
1849                 return ldata->canon_head != ldata->read_tail;
1850         else
1851                 return ldata->commit_head - ldata->read_tail >= amt;
1852 }
1853
1854 /**
1855  * copy_from_read_buf   -       copy read data directly
1856  * @tty: terminal device
1857  * @kbp: data
1858  * @nr: size of data
1859  *
1860  * Helper function to speed up n_tty_read(). It is only called when %ICANON is
1861  * off; it copies characters straight from the tty queue.
1862  *
1863  * Returns: true if it successfully copied data, but there is still more data
1864  * to be had.
1865  *
1866  * Locking:
1867  *  * called under the @ldata->atomic_read_lock sem
1868  *  * n_tty_read()/consumer path:
1869  *              caller holds non-exclusive %termios_rwsem;
1870  *              read_tail published
1871  */
1872 static bool copy_from_read_buf(struct tty_struct *tty,
1873                                       unsigned char **kbp,
1874                                       size_t *nr)
1875
1876 {
1877         struct n_tty_data *ldata = tty->disc_data;
1878         size_t n;
1879         bool is_eof;
1880         size_t head = smp_load_acquire(&ldata->commit_head);
1881         size_t tail = ldata->read_tail & (N_TTY_BUF_SIZE - 1);
1882
1883         n = min(head - ldata->read_tail, N_TTY_BUF_SIZE - tail);
1884         n = min(*nr, n);
1885         if (n) {
1886                 unsigned char *from = read_buf_addr(ldata, tail);
1887                 memcpy(*kbp, from, n);
1888                 is_eof = n == 1 && *from == EOF_CHAR(tty);
1889                 tty_audit_add_data(tty, from, n);
1890                 zero_buffer(tty, from, n);
1891                 smp_store_release(&ldata->read_tail, ldata->read_tail + n);
1892                 /* Turn single EOF into zero-length read */
1893                 if (L_EXTPROC(tty) && ldata->icanon && is_eof &&
1894                     (head == ldata->read_tail))
1895                         return false;
1896                 *kbp += n;
1897                 *nr -= n;
1898
1899                 /* If we have more to copy, let the caller know */
1900                 return head != ldata->read_tail;
1901         }
1902         return false;
1903 }
1904
1905 /**
1906  * canon_copy_from_read_buf     -       copy read data in canonical mode
1907  * @tty: terminal device
1908  * @kbp: data
1909  * @nr: size of data
1910  *
1911  * Helper function for n_tty_read(). It is only called when %ICANON is on; it
1912  * copies one line of input up to and including the line-delimiting character
1913  * into the result buffer.
1914  *
1915  * Note: When termios is changed from non-canonical to canonical mode and the
1916  * read buffer contains data, n_tty_set_termios() simulates an EOF push (as if
1917  * C-d were input) _without_ the %DISABLED_CHAR in the buffer. This causes data
1918  * already processed as input to be immediately available as input although a
1919  * newline has not been received.
1920  *
1921  * Locking:
1922  *  * called under the %atomic_read_lock mutex
1923  *  * n_tty_read()/consumer path:
1924  *      caller holds non-exclusive %termios_rwsem;
1925  *      read_tail published
1926  */
1927 static bool canon_copy_from_read_buf(struct tty_struct *tty,
1928                                      unsigned char **kbp,
1929                                      size_t *nr)
1930 {
1931         struct n_tty_data *ldata = tty->disc_data;
1932         size_t n, size, more, c;
1933         size_t eol;
1934         size_t tail, canon_head;
1935         int found = 0;
1936
1937         /* N.B. avoid overrun if nr == 0 */
1938         if (!*nr)
1939                 return false;
1940
1941         canon_head = smp_load_acquire(&ldata->canon_head);
1942         n = min(*nr, canon_head - ldata->read_tail);
1943
1944         tail = ldata->read_tail & (N_TTY_BUF_SIZE - 1);
1945         size = min_t(size_t, tail + n, N_TTY_BUF_SIZE);
1946
1947         n_tty_trace("%s: nr:%zu tail:%zu n:%zu size:%zu\n",
1948                     __func__, *nr, tail, n, size);
1949
1950         eol = find_next_bit(ldata->read_flags, size, tail);
1951         more = n - (size - tail);
1952         if (eol == N_TTY_BUF_SIZE && more) {
1953                 /* scan wrapped without finding set bit */
1954                 eol = find_first_bit(ldata->read_flags, more);
1955                 found = eol != more;
1956         } else
1957                 found = eol != size;
1958
1959         n = eol - tail;
1960         if (n > N_TTY_BUF_SIZE)
1961                 n += N_TTY_BUF_SIZE;
1962         c = n + found;
1963
1964         if (!found || read_buf(ldata, eol) != __DISABLED_CHAR)
1965                 n = c;
1966
1967         n_tty_trace("%s: eol:%zu found:%d n:%zu c:%zu tail:%zu more:%zu\n",
1968                     __func__, eol, found, n, c, tail, more);
1969
1970         tty_copy(tty, *kbp, tail, n);
1971         *kbp += n;
1972         *nr -= n;
1973
1974         if (found)
1975                 clear_bit(eol, ldata->read_flags);
1976         smp_store_release(&ldata->read_tail, ldata->read_tail + c);
1977
1978         if (found) {
1979                 if (!ldata->push)
1980                         ldata->line_start = ldata->read_tail;
1981                 else
1982                         ldata->push = 0;
1983                 tty_audit_push();
1984                 return false;
1985         }
1986
1987         /* No EOL found - do a continuation retry if there is more data */
1988         return ldata->read_tail != canon_head;
1989 }
1990
1991 /*
1992  * If we finished a read at the exact location of an
1993  * EOF (special EOL character that's a __DISABLED_CHAR)
1994  * in the stream, silently eat the EOF.
1995  */
1996 static void canon_skip_eof(struct tty_struct *tty)
1997 {
1998         struct n_tty_data *ldata = tty->disc_data;
1999         size_t tail, canon_head;
2000
2001         canon_head = smp_load_acquire(&ldata->canon_head);
2002         tail = ldata->read_tail;
2003
2004         // No data?
2005         if (tail == canon_head)
2006                 return;
2007
2008         // See if the tail position is EOF in the circular buffer
2009         tail &= (N_TTY_BUF_SIZE - 1);
2010         if (!test_bit(tail, ldata->read_flags))
2011                 return;
2012         if (read_buf(ldata, tail) != __DISABLED_CHAR)
2013                 return;
2014
2015         // Clear the EOL bit, skip the EOF char.
2016         clear_bit(tail, ldata->read_flags);
2017         smp_store_release(&ldata->read_tail, ldata->read_tail + 1);
2018 }
2019
2020 /**
2021  * job_control          -       check job control
2022  * @tty: tty
2023  * @file: file handle
2024  *
2025  * Perform job control management checks on this @file/@tty descriptor and if
2026  * appropriate send any needed signals and return a negative error code if
2027  * action should be taken.
2028  *
2029  * Locking:
2030  *  * redirected write test is safe
2031  *  * current->signal->tty check is safe
2032  *  * ctrl.lock to safely reference @tty->ctrl.pgrp
2033  */
2034 static int job_control(struct tty_struct *tty, struct file *file)
2035 {
2036         /* Job control check -- must be done at start and after
2037            every sleep (POSIX.1 7.1.1.4). */
2038         /* NOTE: not yet done after every sleep pending a thorough
2039            check of the logic of this change. -- jlc */
2040         /* don't stop on /dev/console */
2041         if (file->f_op->write_iter == redirected_tty_write)
2042                 return 0;
2043
2044         return __tty_check_change(tty, SIGTTIN);
2045 }
2046
2047
2048 /**
2049  * n_tty_read           -       read function for tty
2050  * @tty: tty device
2051  * @file: file object
2052  * @kbuf: kernelspace buffer pointer
2053  * @nr: size of I/O
2054  * @cookie: if non-%NULL, this is a continuation read
2055  * @offset: where to continue reading from (unused in n_tty)
2056  *
2057  * Perform reads for the line discipline. We are guaranteed that the line
2058  * discipline will not be closed under us but we may get multiple parallel
2059  * readers and must handle this ourselves. We may also get a hangup. Always
2060  * called in user context, may sleep.
2061  *
2062  * This code must be sure never to sleep through a hangup.
2063  *
2064  * Locking: n_tty_read()/consumer path:
2065  *      claims non-exclusive termios_rwsem;
2066  *      publishes read_tail
2067  */
2068 static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
2069                           unsigned char *kbuf, size_t nr,
2070                           void **cookie, unsigned long offset)
2071 {
2072         struct n_tty_data *ldata = tty->disc_data;
2073         unsigned char *kb = kbuf;
2074         DEFINE_WAIT_FUNC(wait, woken_wake_function);
2075         int c;
2076         int minimum, time;
2077         ssize_t retval = 0;
2078         long timeout;
2079         bool packet;
2080         size_t tail;
2081
2082         /*
2083          * Is this a continuation of a read started earler?
2084          *
2085          * If so, we still hold the atomic_read_lock and the
2086          * termios_rwsem, and can just continue to copy data.
2087          */
2088         if (*cookie) {
2089                 if (ldata->icanon && !L_EXTPROC(tty)) {
2090                         /*
2091                          * If we have filled the user buffer, see
2092                          * if we should skip an EOF character before
2093                          * releasing the lock and returning done.
2094                          */
2095                         if (!nr)
2096                                 canon_skip_eof(tty);
2097                         else if (canon_copy_from_read_buf(tty, &kb, &nr))
2098                                 return kb - kbuf;
2099                 } else {
2100                         if (copy_from_read_buf(tty, &kb, &nr))
2101                                 return kb - kbuf;
2102                 }
2103
2104                 /* No more data - release locks and stop retries */
2105                 n_tty_kick_worker(tty);
2106                 n_tty_check_unthrottle(tty);
2107                 up_read(&tty->termios_rwsem);
2108                 mutex_unlock(&ldata->atomic_read_lock);
2109                 *cookie = NULL;
2110                 return kb - kbuf;
2111         }
2112
2113         c = job_control(tty, file);
2114         if (c < 0)
2115                 return c;
2116
2117         /*
2118          *      Internal serialization of reads.
2119          */
2120         if (file->f_flags & O_NONBLOCK) {
2121                 if (!mutex_trylock(&ldata->atomic_read_lock))
2122                         return -EAGAIN;
2123         } else {
2124                 if (mutex_lock_interruptible(&ldata->atomic_read_lock))
2125                         return -ERESTARTSYS;
2126         }
2127
2128         down_read(&tty->termios_rwsem);
2129
2130         minimum = time = 0;
2131         timeout = MAX_SCHEDULE_TIMEOUT;
2132         if (!ldata->icanon) {
2133                 minimum = MIN_CHAR(tty);
2134                 if (minimum) {
2135                         time = (HZ / 10) * TIME_CHAR(tty);
2136                 } else {
2137                         timeout = (HZ / 10) * TIME_CHAR(tty);
2138                         minimum = 1;
2139                 }
2140         }
2141
2142         packet = tty->ctrl.packet;
2143         tail = ldata->read_tail;
2144
2145         add_wait_queue(&tty->read_wait, &wait);
2146         while (nr) {
2147                 /* First test for status change. */
2148                 if (packet && tty->link->ctrl.pktstatus) {
2149                         unsigned char cs;
2150                         if (kb != kbuf)
2151                                 break;
2152                         spin_lock_irq(&tty->link->ctrl.lock);
2153                         cs = tty->link->ctrl.pktstatus;
2154                         tty->link->ctrl.pktstatus = 0;
2155                         spin_unlock_irq(&tty->link->ctrl.lock);
2156                         *kb++ = cs;
2157                         nr--;
2158                         break;
2159                 }
2160
2161                 if (!input_available_p(tty, 0)) {
2162                         up_read(&tty->termios_rwsem);
2163                         tty_buffer_flush_work(tty->port);
2164                         down_read(&tty->termios_rwsem);
2165                         if (!input_available_p(tty, 0)) {
2166                                 if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
2167                                         retval = -EIO;
2168                                         break;
2169                                 }
2170                                 if (tty_hung_up_p(file))
2171                                         break;
2172                                 /*
2173                                  * Abort readers for ttys which never actually
2174                                  * get hung up.  See __tty_hangup().
2175                                  */
2176                                 if (test_bit(TTY_HUPPING, &tty->flags))
2177                                         break;
2178                                 if (!timeout)
2179                                         break;
2180                                 if (tty_io_nonblock(tty, file)) {
2181                                         retval = -EAGAIN;
2182                                         break;
2183                                 }
2184                                 if (signal_pending(current)) {
2185                                         retval = -ERESTARTSYS;
2186                                         break;
2187                                 }
2188                                 up_read(&tty->termios_rwsem);
2189
2190                                 timeout = wait_woken(&wait, TASK_INTERRUPTIBLE,
2191                                                 timeout);
2192
2193                                 down_read(&tty->termios_rwsem);
2194                                 continue;
2195                         }
2196                 }
2197
2198                 if (ldata->icanon && !L_EXTPROC(tty)) {
2199                         if (canon_copy_from_read_buf(tty, &kb, &nr))
2200                                 goto more_to_be_read;
2201                 } else {
2202                         /* Deal with packet mode. */
2203                         if (packet && kb == kbuf) {
2204                                 *kb++ = TIOCPKT_DATA;
2205                                 nr--;
2206                         }
2207
2208                         /*
2209                          * Copy data, and if there is more to be had
2210                          * and we have nothing more to wait for, then
2211                          * let's mark us for retries.
2212                          *
2213                          * NOTE! We return here with both the termios_sem
2214                          * and atomic_read_lock still held, the retries
2215                          * will release them when done.
2216                          */
2217                         if (copy_from_read_buf(tty, &kb, &nr) && kb - kbuf >= minimum) {
2218 more_to_be_read:
2219                                 remove_wait_queue(&tty->read_wait, &wait);
2220                                 *cookie = cookie;
2221                                 return kb - kbuf;
2222                         }
2223                 }
2224
2225                 n_tty_check_unthrottle(tty);
2226
2227                 if (kb - kbuf >= minimum)
2228                         break;
2229                 if (time)
2230                         timeout = time;
2231         }
2232         if (tail != ldata->read_tail)
2233                 n_tty_kick_worker(tty);
2234         up_read(&tty->termios_rwsem);
2235
2236         remove_wait_queue(&tty->read_wait, &wait);
2237         mutex_unlock(&ldata->atomic_read_lock);
2238
2239         if (kb - kbuf)
2240                 retval = kb - kbuf;
2241
2242         return retval;
2243 }
2244
2245 /**
2246  * n_tty_write          -       write function for tty
2247  * @tty: tty device
2248  * @file: file object
2249  * @buf: userspace buffer pointer
2250  * @nr: size of I/O
2251  *
2252  * Write function of the terminal device. This is serialized with respect to
2253  * other write callers but not to termios changes, reads and other such events.
2254  * Since the receive code will echo characters, thus calling driver write
2255  * methods, the %output_lock is used in the output processing functions called
2256  * here as well as in the echo processing function to protect the column state
2257  * and space left in the buffer.
2258  *
2259  * This code must be sure never to sleep through a hangup.
2260  *
2261  * Locking: output_lock to protect column state and space left
2262  *       (note that the process_output*() functions take this lock themselves)
2263  */
2264
2265 static ssize_t n_tty_write(struct tty_struct *tty, struct file *file,
2266                            const unsigned char *buf, size_t nr)
2267 {
2268         const unsigned char *b = buf;
2269         DEFINE_WAIT_FUNC(wait, woken_wake_function);
2270         int c;
2271         ssize_t retval = 0;
2272
2273         /* Job control check -- must be done at start (POSIX.1 7.1.1.4). */
2274         if (L_TOSTOP(tty) && file->f_op->write_iter != redirected_tty_write) {
2275                 retval = tty_check_change(tty);
2276                 if (retval)
2277                         return retval;
2278         }
2279
2280         down_read(&tty->termios_rwsem);
2281
2282         /* Write out any echoed characters that are still pending */
2283         process_echoes(tty);
2284
2285         add_wait_queue(&tty->write_wait, &wait);
2286         while (1) {
2287                 if (signal_pending(current)) {
2288                         retval = -ERESTARTSYS;
2289                         break;
2290                 }
2291                 if (tty_hung_up_p(file) || (tty->link && !tty->link->count)) {
2292                         retval = -EIO;
2293                         break;
2294                 }
2295                 if (O_OPOST(tty)) {
2296                         while (nr > 0) {
2297                                 ssize_t num = process_output_block(tty, b, nr);
2298                                 if (num < 0) {
2299                                         if (num == -EAGAIN)
2300                                                 break;
2301                                         retval = num;
2302                                         goto break_out;
2303                                 }
2304                                 b += num;
2305                                 nr -= num;
2306                                 if (nr == 0)
2307                                         break;
2308                                 c = *b;
2309                                 if (process_output(c, tty) < 0)
2310                                         break;
2311                                 b++; nr--;
2312                         }
2313                         if (tty->ops->flush_chars)
2314                                 tty->ops->flush_chars(tty);
2315                 } else {
2316                         struct n_tty_data *ldata = tty->disc_data;
2317
2318                         while (nr > 0) {
2319                                 mutex_lock(&ldata->output_lock);
2320                                 c = tty->ops->write(tty, b, nr);
2321                                 mutex_unlock(&ldata->output_lock);
2322                                 if (c < 0) {
2323                                         retval = c;
2324                                         goto break_out;
2325                                 }
2326                                 if (!c)
2327                                         break;
2328                                 b += c;
2329                                 nr -= c;
2330                         }
2331                 }
2332                 if (!nr)
2333                         break;
2334                 if (tty_io_nonblock(tty, file)) {
2335                         retval = -EAGAIN;
2336                         break;
2337                 }
2338                 up_read(&tty->termios_rwsem);
2339
2340                 wait_woken(&wait, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
2341
2342                 down_read(&tty->termios_rwsem);
2343         }
2344 break_out:
2345         remove_wait_queue(&tty->write_wait, &wait);
2346         if (nr && tty->fasync)
2347                 set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
2348         up_read(&tty->termios_rwsem);
2349         return (b - buf) ? b - buf : retval;
2350 }
2351
2352 /**
2353  * n_tty_poll           -       poll method for N_TTY
2354  * @tty: terminal device
2355  * @file: file accessing it
2356  * @wait: poll table
2357  *
2358  * Called when the line discipline is asked to poll() for data or for special
2359  * events. This code is not serialized with respect to other events save
2360  * open/close.
2361  *
2362  * This code must be sure never to sleep through a hangup.
2363  *
2364  * Locking: called without the kernel lock held -- fine.
2365  */
2366 static __poll_t n_tty_poll(struct tty_struct *tty, struct file *file,
2367                                                         poll_table *wait)
2368 {
2369         __poll_t mask = 0;
2370
2371         poll_wait(file, &tty->read_wait, wait);
2372         poll_wait(file, &tty->write_wait, wait);
2373         if (input_available_p(tty, 1))
2374                 mask |= EPOLLIN | EPOLLRDNORM;
2375         else {
2376                 tty_buffer_flush_work(tty->port);
2377                 if (input_available_p(tty, 1))
2378                         mask |= EPOLLIN | EPOLLRDNORM;
2379         }
2380         if (tty->ctrl.packet && tty->link->ctrl.pktstatus)
2381                 mask |= EPOLLPRI | EPOLLIN | EPOLLRDNORM;
2382         if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
2383                 mask |= EPOLLHUP;
2384         if (tty_hung_up_p(file))
2385                 mask |= EPOLLHUP;
2386         if (tty->ops->write && !tty_is_writelocked(tty) &&
2387                         tty_chars_in_buffer(tty) < WAKEUP_CHARS &&
2388                         tty_write_room(tty) > 0)
2389                 mask |= EPOLLOUT | EPOLLWRNORM;
2390         return mask;
2391 }
2392
2393 static unsigned long inq_canon(struct n_tty_data *ldata)
2394 {
2395         size_t nr, head, tail;
2396
2397         if (ldata->canon_head == ldata->read_tail)
2398                 return 0;
2399         head = ldata->canon_head;
2400         tail = ldata->read_tail;
2401         nr = head - tail;
2402         /* Skip EOF-chars.. */
2403         while (MASK(head) != MASK(tail)) {
2404                 if (test_bit(tail & (N_TTY_BUF_SIZE - 1), ldata->read_flags) &&
2405                     read_buf(ldata, tail) == __DISABLED_CHAR)
2406                         nr--;
2407                 tail++;
2408         }
2409         return nr;
2410 }
2411
2412 static int n_tty_ioctl(struct tty_struct *tty, unsigned int cmd,
2413                        unsigned long arg)
2414 {
2415         struct n_tty_data *ldata = tty->disc_data;
2416         int retval;
2417
2418         switch (cmd) {
2419         case TIOCOUTQ:
2420                 return put_user(tty_chars_in_buffer(tty), (int __user *) arg);
2421         case TIOCINQ:
2422                 down_write(&tty->termios_rwsem);
2423                 if (L_ICANON(tty) && !L_EXTPROC(tty))
2424                         retval = inq_canon(ldata);
2425                 else
2426                         retval = read_cnt(ldata);
2427                 up_write(&tty->termios_rwsem);
2428                 return put_user(retval, (unsigned int __user *) arg);
2429         default:
2430                 return n_tty_ioctl_helper(tty, cmd, arg);
2431         }
2432 }
2433
2434 static struct tty_ldisc_ops n_tty_ops = {
2435         .owner           = THIS_MODULE,
2436         .num             = N_TTY,
2437         .name            = "n_tty",
2438         .open            = n_tty_open,
2439         .close           = n_tty_close,
2440         .flush_buffer    = n_tty_flush_buffer,
2441         .read            = n_tty_read,
2442         .write           = n_tty_write,
2443         .ioctl           = n_tty_ioctl,
2444         .set_termios     = n_tty_set_termios,
2445         .poll            = n_tty_poll,
2446         .receive_buf     = n_tty_receive_buf,
2447         .write_wakeup    = n_tty_write_wakeup,
2448         .receive_buf2    = n_tty_receive_buf2,
2449 };
2450
2451 /**
2452  *      n_tty_inherit_ops       -       inherit N_TTY methods
2453  *      @ops: struct tty_ldisc_ops where to save N_TTY methods
2454  *
2455  *      Enables a 'subclass' line discipline to 'inherit' N_TTY methods.
2456  */
2457
2458 void n_tty_inherit_ops(struct tty_ldisc_ops *ops)
2459 {
2460         *ops = n_tty_ops;
2461         ops->owner = NULL;
2462 }
2463 EXPORT_SYMBOL_GPL(n_tty_inherit_ops);
2464
2465 void __init n_tty_init(void)
2466 {
2467         tty_register_ldisc(&n_tty_ops);
2468 }