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         /* # of chars looked ahead (to find software flow control chars) */
 122         size_t lookahead_count;
 123
 124         /* protected by output lock */
 125         unsigned int column;
 126         unsigned int canon_column;
 127         size_t echo_tail;
 128
 129         struct mutex atomic_read_lock;
 130         struct mutex output_lock;
 131 };
 132
 133 #define MASK(x) ((x) & (N_TTY_BUF_SIZE - 1))
 134
 135 static inline size_t read_cnt(struct n_tty_data *ldata)
 136 {
 137         return ldata->read_head - ldata->read_tail;
 138 }
 139
 140 static inline unsigned char read_buf(struct n_tty_data *ldata, size_t i)
 141 {
 142         return ldata->read_buf[i & (N_TTY_BUF_SIZE - 1)];
 143 }
 144
 145 static inline unsigned char *read_buf_addr(struct n_tty_data *ldata, size_t i)
 146 {
 147         return &ldata->read_buf[i & (N_TTY_BUF_SIZE - 1)];
 148 }
 149
 150 static inline unsigned char echo_buf(struct n_tty_data *ldata, size_t i)
 151 {
 152         smp_rmb(); /* Matches smp_wmb() in add_echo_byte(). */
 153         return ldata->echo_buf[i & (N_TTY_BUF_SIZE - 1)];
 154 }
 155
 156 static inline unsigned char *echo_buf_addr(struct n_tty_data *ldata, size_t i)
 157 {
 158         return &ldata->echo_buf[i & (N_TTY_BUF_SIZE - 1)];
 159 }
 160
 161 /* If we are not echoing the data, perhaps this is a secret so erase it */
 162 static void zero_buffer(struct tty_struct *tty, u8 *buffer, int size)
 163 {
 164         bool icanon = !!L_ICANON(tty);
 165         bool no_echo = !L_ECHO(tty);
 166
 167         if (icanon && no_echo)
 168                 memset(buffer, 0x00, size);
 169 }
 170
 171 static void tty_copy(struct tty_struct *tty, void *to, size_t tail, size_t n)
 172 {
 173         struct n_tty_data *ldata = tty->disc_data;
 174         size_t size = N_TTY_BUF_SIZE - tail;
 175         void *from = read_buf_addr(ldata, tail);
 176
 177         if (n > size) {
 178                 tty_audit_add_data(tty, from, size);
 179                 memcpy(to, from, size);
 180                 zero_buffer(tty, from, size);
 181                 to += size;
 182                 n -= size;
 183                 from = ldata->read_buf;
 184         }
 185
 186         tty_audit_add_data(tty, from, n);
 187         memcpy(to, from, n);
 188         zero_buffer(tty, from, n);
 189 }
 190
 191 /**
 192  * n_tty_kick_worker - start input worker (if required)
 193  * @tty: terminal
 194  *
 195  * Re-schedules the flip buffer work if it may have stopped.
 196  *
 197  * Locking:
 198  *  * Caller holds exclusive %termios_rwsem, or
 199  *  * n_tty_read()/consumer path:
 200  *      holds non-exclusive %termios_rwsem
 201  */
 202 static void n_tty_kick_worker(struct tty_struct *tty)
 203 {
 204         struct n_tty_data *ldata = tty->disc_data;
 205
 206         /* Did the input worker stop? Restart it */
 207         if (unlikely(READ_ONCE(ldata->no_room))) {
 208                 WRITE_ONCE(ldata->no_room, 0);
 209
 210                 WARN_RATELIMIT(tty->port->itty == NULL,
 211                                 "scheduling with invalid itty\n");
 212                 /* see if ldisc has been killed - if so, this means that
 213                  * even though the ldisc has been halted and ->buf.work
 214                  * cancelled, ->buf.work is about to be rescheduled
 215                  */
 216                 WARN_RATELIMIT(test_bit(TTY_LDISC_HALTED, &tty->flags),
 217                                "scheduling buffer work for halted ldisc\n");
 218                 tty_buffer_restart_work(tty->port);
 219         }
 220 }
 221
 222 static ssize_t chars_in_buffer(struct tty_struct *tty)
 223 {
 224         struct n_tty_data *ldata = tty->disc_data;
 225         ssize_t n = 0;
 226
 227         if (!ldata->icanon)
 228                 n = ldata->commit_head - ldata->read_tail;
 229         else
 230                 n = ldata->canon_head - ldata->read_tail;
 231         return n;
 232 }
 233
 234 /**
 235  * n_tty_write_wakeup   -       asynchronous I/O notifier
 236  * @tty: tty device
 237  *
 238  * Required for the ptys, serial driver etc. since processes that attach
 239  * themselves to the master and rely on ASYNC IO must be woken up.
 240  */
 241 static void n_tty_write_wakeup(struct tty_struct *tty)
 242 {
 243         clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 244         kill_fasync(&tty->fasync, SIGIO, POLL_OUT);
 245 }
 246
 247 static void n_tty_check_throttle(struct tty_struct *tty)
 248 {
 249         struct n_tty_data *ldata = tty->disc_data;
 250
 251         /*
 252          * Check the remaining room for the input canonicalization
 253          * mode.  We don't want to throttle the driver if we're in
 254          * canonical mode and don't have a newline yet!
 255          */
 256         if (ldata->icanon && ldata->canon_head == ldata->read_tail)
 257                 return;
 258
 259         while (1) {
 260                 int throttled;
 261                 tty_set_flow_change(tty, TTY_THROTTLE_SAFE);
 262                 if (N_TTY_BUF_SIZE - read_cnt(ldata) >= TTY_THRESHOLD_THROTTLE)
 263                         break;
 264                 throttled = tty_throttle_safe(tty);
 265                 if (!throttled)
 266                         break;
 267         }
 268         __tty_set_flow_change(tty, 0);
 269 }
 270
 271 static void n_tty_check_unthrottle(struct tty_struct *tty)
 272 {
 273         if (tty->driver->type == TTY_DRIVER_TYPE_PTY) {
 274                 if (chars_in_buffer(tty) > TTY_THRESHOLD_UNTHROTTLE)
 275                         return;
 276                 n_tty_kick_worker(tty);
 277                 tty_wakeup(tty->link);
 278                 return;
 279         }
 280
 281         /* If there is enough space in the read buffer now, let the
 282          * low-level driver know. We use chars_in_buffer() to
 283          * check the buffer, as it now knows about canonical mode.
 284          * Otherwise, if the driver is throttled and the line is
 285          * longer than TTY_THRESHOLD_UNTHROTTLE in canonical mode,
 286          * we won't get any more characters.
 287          */
 288
 289         while (1) {
 290                 int unthrottled;
 291                 tty_set_flow_change(tty, TTY_UNTHROTTLE_SAFE);
 292                 if (chars_in_buffer(tty) > TTY_THRESHOLD_UNTHROTTLE)
 293                         break;
 294                 n_tty_kick_worker(tty);
 295                 unthrottled = tty_unthrottle_safe(tty);
 296                 if (!unthrottled)
 297                         break;
 298         }
 299         __tty_set_flow_change(tty, 0);
 300 }
 301
 302 /**
 303  * put_tty_queue                -       add character to tty
 304  * @c: character
 305  * @ldata: n_tty data
 306  *
 307  * Add a character to the tty read_buf queue.
 308  *
 309  * Locking:
 310  *  * n_tty_receive_buf()/producer path:
 311  *      caller holds non-exclusive %termios_rwsem
 312  */
 313 static inline void put_tty_queue(unsigned char c, struct n_tty_data *ldata)
 314 {
 315         *read_buf_addr(ldata, ldata->read_head) = c;
 316         ldata->read_head++;
 317 }
 318
 319 /**
 320  * reset_buffer_flags   -       reset buffer state
 321  * @ldata: line disc data to reset
 322  *
 323  * Reset the read buffer counters and clear the flags. Called from
 324  * n_tty_open() and n_tty_flush_buffer().
 325  *
 326  * Locking:
 327  *  * caller holds exclusive %termios_rwsem, or
 328  *  * (locking is not required)
 329  */
 330 static void reset_buffer_flags(struct n_tty_data *ldata)
 331 {
 332         ldata->read_head = ldata->canon_head = ldata->read_tail = 0;
 333         ldata->commit_head = 0;
 334         ldata->line_start = 0;
 335
 336         ldata->erasing = 0;
 337         bitmap_zero(ldata->read_flags, N_TTY_BUF_SIZE);
 338         ldata->push = 0;
 339
 340         ldata->lookahead_count = 0;
 341 }
 342
 343 static void n_tty_packet_mode_flush(struct tty_struct *tty)
 344 {
 345         unsigned long flags;
 346
 347         if (tty->link->ctrl.packet) {
 348                 spin_lock_irqsave(&tty->ctrl.lock, flags);
 349                 tty->ctrl.pktstatus |= TIOCPKT_FLUSHREAD;
 350                 spin_unlock_irqrestore(&tty->ctrl.lock, flags);
 351                 wake_up_interruptible(&tty->link->read_wait);
 352         }
 353 }
 354
 355 /**
 356  * n_tty_flush_buffer   -       clean input queue
 357  * @tty: terminal device
 358  *
 359  * Flush the input buffer. Called when the tty layer wants the buffer flushed
 360  * (eg at hangup) or when the %N_TTY line discipline internally has to clean
 361  * the pending queue (for example some signals).
 362  *
 363  * Holds %termios_rwsem to exclude producer/consumer while buffer indices are
 364  * reset.
 365  *
 366  * Locking: %ctrl.lock, exclusive %termios_rwsem
 367  */
 368 static void n_tty_flush_buffer(struct tty_struct *tty)
 369 {
 370         down_write(&tty->termios_rwsem);
 371         reset_buffer_flags(tty->disc_data);
 372         n_tty_kick_worker(tty);
 373
 374         if (tty->link)
 375                 n_tty_packet_mode_flush(tty);
 376         up_write(&tty->termios_rwsem);
 377 }
 378
 379 /**
 380  * is_utf8_continuation -       utf8 multibyte check
 381  * @c: byte to check
 382  *
 383  * Returns: true if the utf8 character @c is a multibyte continuation
 384  * character. We use this to correctly compute the on-screen size of the
 385  * character when printing.
 386  */
 387 static inline int is_utf8_continuation(unsigned char c)
 388 {
 389         return (c & 0xc0) == 0x80;
 390 }
 391
 392 /**
 393  * is_continuation      -       multibyte check
 394  * @c: byte to check
 395  * @tty: terminal device
 396  *
 397  * Returns: true if the utf8 character @c is a multibyte continuation character
 398  * and the terminal is in unicode mode.
 399  */
 400 static inline int is_continuation(unsigned char c, struct tty_struct *tty)
 401 {
 402         return I_IUTF8(tty) && is_utf8_continuation(c);
 403 }
 404
 405 /**
 406  * do_output_char       -       output one character
 407  * @c: character (or partial unicode symbol)
 408  * @tty: terminal device
 409  * @space: space available in tty driver write buffer
 410  *
 411  * This is a helper function that handles one output character (including
 412  * special characters like TAB, CR, LF, etc.), doing OPOST processing and
 413  * putting the results in the tty driver's write buffer.
 414  *
 415  * Note that Linux currently ignores TABDLY, CRDLY, VTDLY, FFDLY and NLDLY.
 416  * They simply aren't relevant in the world today. If you ever need them, add
 417  * them here.
 418  *
 419  * Returns: the number of bytes of buffer space used or -1 if no space left.
 420  *
 421  * Locking: should be called under the %output_lock to protect the column state
 422  * and space left in the buffer.
 423  */
 424 static int do_output_char(unsigned char c, struct tty_struct *tty, int space)
 425 {
 426         struct n_tty_data *ldata = tty->disc_data;
 427         int     spaces;
 428
 429         if (!space)
 430                 return -1;
 431
 432         switch (c) {
 433         case '\n':
 434                 if (O_ONLRET(tty))
 435                         ldata->column = 0;
 436                 if (O_ONLCR(tty)) {
 437                         if (space < 2)
 438                                 return -1;
 439                         ldata->canon_column = ldata->column = 0;
 440                         tty->ops->write(tty, "\r\n", 2);
 441                         return 2;
 442                 }
 443                 ldata->canon_column = ldata->column;
 444                 break;
 445         case '\r':
 446                 if (O_ONOCR(tty) && ldata->column == 0)
 447                         return 0;
 448                 if (O_OCRNL(tty)) {
 449                         c = '\n';
 450                         if (O_ONLRET(tty))
 451                                 ldata->canon_column = ldata->column = 0;
 452                         break;
 453                 }
 454                 ldata->canon_column = ldata->column = 0;
 455                 break;
 456         case '\t':
 457                 spaces = 8 - (ldata->column & 7);
 458                 if (O_TABDLY(tty) == XTABS) {
 459                         if (space < spaces)
 460                                 return -1;
 461                         ldata->column += spaces;
 462                         tty->ops->write(tty, "        ", spaces);
 463                         return spaces;
 464                 }
 465                 ldata->column += spaces;
 466                 break;
 467         case '\b':
 468                 if (ldata->column > 0)
 469                         ldata->column--;
 470                 break;
 471         default:
 472                 if (!iscntrl(c)) {
 473                         if (O_OLCUC(tty))
 474                                 c = toupper(c);
 475                         if (!is_continuation(c, tty))
 476                                 ldata->column++;
 477                 }
 478                 break;
 479         }
 480
 481         tty_put_char(tty, c);
 482         return 1;
 483 }
 484
 485 /**
 486  * process_output       -       output post processor
 487  * @c: character (or partial unicode symbol)
 488  * @tty: terminal device
 489  *
 490  * Output one character with OPOST processing.
 491  *
 492  * Returns: -1 when the output device is full and the character must be
 493  * retried.
 494  *
 495  * Locking: %output_lock to protect column state and space left (also, this is
 496  *called from n_tty_write() under the tty layer write lock).
 497  */
 498 static int process_output(unsigned char c, struct tty_struct *tty)
 499 {
 500         struct n_tty_data *ldata = tty->disc_data;
 501         int     space, retval;
 502
 503         mutex_lock(&ldata->output_lock);
 504
 505         space = tty_write_room(tty);
 506         retval = do_output_char(c, tty, space);
 507
 508         mutex_unlock(&ldata->output_lock);
 509         if (retval < 0)
 510                 return -1;
 511         else
 512                 return 0;
 513 }
 514
 515 /**
 516  * process_output_block -       block post processor
 517  * @tty: terminal device
 518  * @buf: character buffer
 519  * @nr: number of bytes to output
 520  *
 521  * Output a block of characters with OPOST processing.
 522  *
 523  * This path is used to speed up block console writes, among other things when
 524  * processing blocks of output data. It handles only the simple cases normally
 525  * found and helps to generate blocks of symbols for the console driver and
 526  * thus improve performance.
 527  *
 528  * Returns: the number of characters output.
 529  *
 530  * Locking: %output_lock to protect column state and space left (also, this is
 531  * called from n_tty_write() under the tty layer write lock).
 532  */
 533 static ssize_t process_output_block(struct tty_struct *tty,
 534                                     const unsigned char *buf, unsigned int nr)
 535 {
 536         struct n_tty_data *ldata = tty->disc_data;
 537         int     space;
 538         int     i;
 539         const unsigned char *cp;
 540
 541         mutex_lock(&ldata->output_lock);
 542
 543         space = tty_write_room(tty);
 544         if (space <= 0) {
 545                 mutex_unlock(&ldata->output_lock);
 546                 return space;
 547         }
 548         if (nr > space)
 549                 nr = space;
 550
 551         for (i = 0, cp = buf; i < nr; i++, cp++) {
 552                 unsigned char c = *cp;
 553
 554                 switch (c) {
 555                 case '\n':
 556                         if (O_ONLRET(tty))
 557                                 ldata->column = 0;
 558                         if (O_ONLCR(tty))
 559                                 goto break_out;
 560                         ldata->canon_column = ldata->column;
 561                         break;
 562                 case '\r':
 563                         if (O_ONOCR(tty) && ldata->column == 0)
 564                                 goto break_out;
 565                         if (O_OCRNL(tty))
 566                                 goto break_out;
 567                         ldata->canon_column = ldata->column = 0;
 568                         break;
 569                 case '\t':
 570                         goto break_out;
 571                 case '\b':
 572                         if (ldata->column > 0)
 573                                 ldata->column--;
 574                         break;
 575                 default:
 576                         if (!iscntrl(c)) {
 577                                 if (O_OLCUC(tty))
 578                                         goto break_out;
 579                                 if (!is_continuation(c, tty))
 580                                         ldata->column++;
 581                         }
 582                         break;
 583                 }
 584         }
 585 break_out:
 586         i = tty->ops->write(tty, buf, i);
 587
 588         mutex_unlock(&ldata->output_lock);
 589         return i;
 590 }
 591
 592 /**
 593  * __process_echoes     -       write pending echo characters
 594  * @tty: terminal device
 595  *
 596  * Write previously buffered echo (and other ldisc-generated) characters to the
 597  * tty.
 598  *
 599  * Characters generated by the ldisc (including echoes) need to be buffered
 600  * because the driver's write buffer can fill during heavy program output.
 601  * Echoing straight to the driver will often fail under these conditions,
 602  * causing lost characters and resulting mismatches of ldisc state information.
 603  *
 604  * Since the ldisc state must represent the characters actually sent to the
 605  * driver at the time of the write, operations like certain changes in column
 606  * state are also saved in the buffer and executed here.
 607  *
 608  * A circular fifo buffer is used so that the most recent characters are
 609  * prioritized. Also, when control characters are echoed with a prefixed "^",
 610  * the pair is treated atomically and thus not separated.
 611  *
 612  * Locking: callers must hold %output_lock.
 613  */
 614 static size_t __process_echoes(struct tty_struct *tty)
 615 {
 616         struct n_tty_data *ldata = tty->disc_data;
 617         int     space, old_space;
 618         size_t tail;
 619         unsigned char c;
 620
 621         old_space = space = tty_write_room(tty);
 622
 623         tail = ldata->echo_tail;
 624         while (MASK(ldata->echo_commit) != MASK(tail)) {
 625                 c = echo_buf(ldata, tail);
 626                 if (c == ECHO_OP_START) {
 627                         unsigned char op;
 628                         int no_space_left = 0;
 629
 630                         /*
 631                          * Since add_echo_byte() is called without holding
 632                          * output_lock, we might see only portion of multi-byte
 633                          * operation.
 634                          */
 635                         if (MASK(ldata->echo_commit) == MASK(tail + 1))
 636                                 goto not_yet_stored;
 637                         /*
 638                          * If the buffer byte is the start of a multi-byte
 639                          * operation, get the next byte, which is either the
 640                          * op code or a control character value.
 641                          */
 642                         op = echo_buf(ldata, tail + 1);
 643
 644                         switch (op) {
 645                         case ECHO_OP_ERASE_TAB: {
 646                                 unsigned int num_chars, num_bs;
 647
 648                                 if (MASK(ldata->echo_commit) == MASK(tail + 2))
 649                                         goto not_yet_stored;
 650                                 num_chars = echo_buf(ldata, tail + 2);
 651
 652                                 /*
 653                                  * Determine how many columns to go back
 654                                  * in order to erase the tab.
 655                                  * This depends on the number of columns
 656                                  * used by other characters within the tab
 657                                  * area.  If this (modulo 8) count is from
 658                                  * the start of input rather than from a
 659                                  * previous tab, we offset by canon column.
 660                                  * Otherwise, tab spacing is normal.
 661                                  */
 662                                 if (!(num_chars & 0x80))
 663                                         num_chars += ldata->canon_column;
 664                                 num_bs = 8 - (num_chars & 7);
 665
 666                                 if (num_bs > space) {
 667                                         no_space_left = 1;
 668                                         break;
 669                                 }
 670                                 space -= num_bs;
 671                                 while (num_bs--) {
 672                                         tty_put_char(tty, '\b');
 673                                         if (ldata->column > 0)
 674                                                 ldata->column--;
 675                                 }
 676                                 tail += 3;
 677                                 break;
 678                         }
 679                         case ECHO_OP_SET_CANON_COL:
 680                                 ldata->canon_column = ldata->column;
 681                                 tail += 2;
 682                                 break;
 683
 684                         case ECHO_OP_MOVE_BACK_COL:
 685                                 if (ldata->column > 0)
 686                                         ldata->column--;
 687                                 tail += 2;
 688                                 break;
 689
 690                         case ECHO_OP_START:
 691                                 /* This is an escaped echo op start code */
 692                                 if (!space) {
 693                                         no_space_left = 1;
 694                                         break;
 695                                 }
 696                                 tty_put_char(tty, ECHO_OP_START);
 697                                 ldata->column++;
 698                                 space--;
 699                                 tail += 2;
 700                                 break;
 701
 702                         default:
 703                                 /*
 704                                  * If the op is not a special byte code,
 705                                  * it is a ctrl char tagged to be echoed
 706                                  * as "^X" (where X is the letter
 707                                  * representing the control char).
 708                                  * Note that we must ensure there is
 709                                  * enough space for the whole ctrl pair.
 710                                  *
 711                                  */
 712                                 if (space < 2) {
 713                                         no_space_left = 1;
 714                                         break;
 715                                 }
 716                                 tty_put_char(tty, '^');
 717                                 tty_put_char(tty, op ^ 0100);
 718                                 ldata->column += 2;
 719                                 space -= 2;
 720                                 tail += 2;
 721                         }
 722
 723                         if (no_space_left)
 724                                 break;
 725                 } else {
 726                         if (O_OPOST(tty)) {
 727                                 int retval = do_output_char(c, tty, space);
 728                                 if (retval < 0)
 729                                         break;
 730                                 space -= retval;
 731                         } else {
 732                                 if (!space)
 733                                         break;
 734                                 tty_put_char(tty, c);
 735                                 space -= 1;
 736                         }
 737                         tail += 1;
 738                 }
 739         }
 740
 741         /* If the echo buffer is nearly full (so that the possibility exists
 742          * of echo overrun before the next commit), then discard enough
 743          * data at the tail to prevent a subsequent overrun */
 744         while (ldata->echo_commit > tail &&
 745                ldata->echo_commit - tail >= ECHO_DISCARD_WATERMARK) {
 746                 if (echo_buf(ldata, tail) == ECHO_OP_START) {
 747                         if (echo_buf(ldata, tail + 1) == ECHO_OP_ERASE_TAB)
 748                                 tail += 3;
 749                         else
 750                                 tail += 2;
 751                 } else
 752                         tail++;
 753         }
 754
 755  not_yet_stored:
 756         ldata->echo_tail = tail;
 757         return old_space - space;
 758 }
 759
 760 static void commit_echoes(struct tty_struct *tty)
 761 {
 762         struct n_tty_data *ldata = tty->disc_data;
 763         size_t nr, old, echoed;
 764         size_t head;
 765
 766         mutex_lock(&ldata->output_lock);
 767         head = ldata->echo_head;
 768         ldata->echo_mark = head;
 769         old = ldata->echo_commit - ldata->echo_tail;
 770
 771         /* Process committed echoes if the accumulated # of bytes
 772          * is over the threshold (and try again each time another
 773          * block is accumulated) */
 774         nr = head - ldata->echo_tail;
 775         if (nr < ECHO_COMMIT_WATERMARK ||
 776             (nr % ECHO_BLOCK > old % ECHO_BLOCK)) {
 777                 mutex_unlock(&ldata->output_lock);
 778                 return;
 779         }
 780
 781         ldata->echo_commit = head;
 782         echoed = __process_echoes(tty);
 783         mutex_unlock(&ldata->output_lock);
 784
 785         if (echoed && tty->ops->flush_chars)
 786                 tty->ops->flush_chars(tty);
 787 }
 788
 789 static void process_echoes(struct tty_struct *tty)
 790 {
 791         struct n_tty_data *ldata = tty->disc_data;
 792         size_t echoed;
 793
 794         if (ldata->echo_mark == ldata->echo_tail)
 795                 return;
 796
 797         mutex_lock(&ldata->output_lock);
 798         ldata->echo_commit = ldata->echo_mark;
 799         echoed = __process_echoes(tty);
 800         mutex_unlock(&ldata->output_lock);
 801
 802         if (echoed && tty->ops->flush_chars)
 803                 tty->ops->flush_chars(tty);
 804 }
 805
 806 /* NB: echo_mark and echo_head should be equivalent here */
 807 static void flush_echoes(struct tty_struct *tty)
 808 {
 809         struct n_tty_data *ldata = tty->disc_data;
 810
 811         if ((!L_ECHO(tty) && !L_ECHONL(tty)) ||
 812             ldata->echo_commit == ldata->echo_head)
 813                 return;
 814
 815         mutex_lock(&ldata->output_lock);
 816         ldata->echo_commit = ldata->echo_head;
 817         __process_echoes(tty);
 818         mutex_unlock(&ldata->output_lock);
 819 }
 820
 821 /**
 822  * add_echo_byte        -       add a byte to the echo buffer
 823  * @c: unicode byte to echo
 824  * @ldata: n_tty data
 825  *
 826  * Add a character or operation byte to the echo buffer.
 827  */
 828 static inline void add_echo_byte(unsigned char c, struct n_tty_data *ldata)
 829 {
 830         *echo_buf_addr(ldata, ldata->echo_head) = c;
 831         smp_wmb(); /* Matches smp_rmb() in echo_buf(). */
 832         ldata->echo_head++;
 833 }
 834
 835 /**
 836  * echo_move_back_col   -       add operation to move back a column
 837  * @ldata: n_tty data
 838  *
 839  * Add an operation to the echo buffer to move back one column.
 840  */
 841 static void echo_move_back_col(struct n_tty_data *ldata)
 842 {
 843         add_echo_byte(ECHO_OP_START, ldata);
 844         add_echo_byte(ECHO_OP_MOVE_BACK_COL, ldata);
 845 }
 846
 847 /**
 848  * echo_set_canon_col   -       add operation to set the canon column
 849  * @ldata: n_tty data
 850  *
 851  * Add an operation to the echo buffer to set the canon column to the current
 852  * column.
 853  */
 854 static void echo_set_canon_col(struct n_tty_data *ldata)
 855 {
 856         add_echo_byte(ECHO_OP_START, ldata);
 857         add_echo_byte(ECHO_OP_SET_CANON_COL, ldata);
 858 }
 859
 860 /**
 861  * echo_erase_tab       -       add operation to erase a tab
 862  * @num_chars: number of character columns already used
 863  * @after_tab: true if num_chars starts after a previous tab
 864  * @ldata: n_tty data
 865  *
 866  * Add an operation to the echo buffer to erase a tab.
 867  *
 868  * Called by the eraser function, which knows how many character columns have
 869  * been used since either a previous tab or the start of input. This
 870  * information will be used later, along with canon column (if applicable), to
 871  * go back the correct number of columns.
 872  */
 873 static void echo_erase_tab(unsigned int num_chars, int after_tab,
 874                            struct n_tty_data *ldata)
 875 {
 876         add_echo_byte(ECHO_OP_START, ldata);
 877         add_echo_byte(ECHO_OP_ERASE_TAB, ldata);
 878
 879         /* We only need to know this modulo 8 (tab spacing) */
 880         num_chars &= 7;
 881
 882         /* Set the high bit as a flag if num_chars is after a previous tab */
 883         if (after_tab)
 884                 num_chars |= 0x80;
 885
 886         add_echo_byte(num_chars, ldata);
 887 }
 888
 889 /**
 890  * echo_char_raw        -       echo a character raw
 891  * @c: unicode byte to echo
 892  * @ldata: line disc data
 893  *
 894  * Echo user input back onto the screen. This must be called only when
 895  * L_ECHO(tty) is true. Called from the &tty_driver.receive_buf() path.
 896  *
 897  * This variant does not treat control characters specially.
 898  */
 899 static void echo_char_raw(unsigned char c, struct n_tty_data *ldata)
 900 {
 901         if (c == ECHO_OP_START) {
 902                 add_echo_byte(ECHO_OP_START, ldata);
 903                 add_echo_byte(ECHO_OP_START, ldata);
 904         } else {
 905                 add_echo_byte(c, ldata);
 906         }
 907 }
 908
 909 /**
 910  * echo_char            -       echo a character
 911  * @c: unicode byte to echo
 912  * @tty: terminal device
 913  *
 914  * Echo user input back onto the screen. This must be called only when
 915  * L_ECHO(tty) is true. Called from the &tty_driver.receive_buf() path.
 916  *
 917  * This variant tags control characters to be echoed as "^X" (where X is the
 918  * letter representing the control char).
 919  */
 920 static void echo_char(unsigned char c, struct tty_struct *tty)
 921 {
 922         struct n_tty_data *ldata = tty->disc_data;
 923
 924         if (c == ECHO_OP_START) {
 925                 add_echo_byte(ECHO_OP_START, ldata);
 926                 add_echo_byte(ECHO_OP_START, ldata);
 927         } else {
 928                 if (L_ECHOCTL(tty) && iscntrl(c) && c != '\t')
 929                         add_echo_byte(ECHO_OP_START, ldata);
 930                 add_echo_byte(c, ldata);
 931         }
 932 }
 933
 934 /**
 935  * finish_erasing       -       complete erase
 936  * @ldata: n_tty data
 937  */
 938 static inline void finish_erasing(struct n_tty_data *ldata)
 939 {
 940         if (ldata->erasing) {
 941                 echo_char_raw('/', ldata);
 942                 ldata->erasing = 0;
 943         }
 944 }
 945
 946 /**
 947  * eraser               -       handle erase function
 948  * @c: character input
 949  * @tty: terminal device
 950  *
 951  * Perform erase and necessary output when an erase character is present in the
 952  * stream from the driver layer. Handles the complexities of UTF-8 multibyte
 953  * symbols.
 954  *
 955  * Locking: n_tty_receive_buf()/producer path:
 956  *      caller holds non-exclusive %termios_rwsem
 957  */
 958 static void eraser(unsigned char c, struct tty_struct *tty)
 959 {
 960         struct n_tty_data *ldata = tty->disc_data;
 961         enum { ERASE, WERASE, KILL } kill_type;
 962         size_t head;
 963         size_t cnt;
 964         int seen_alnums;
 965
 966         if (ldata->read_head == ldata->canon_head) {
 967                 /* process_output('\a', tty); */ /* what do you think? */
 968                 return;
 969         }
 970         if (c == ERASE_CHAR(tty))
 971                 kill_type = ERASE;
 972         else if (c == WERASE_CHAR(tty))
 973                 kill_type = WERASE;
 974         else {
 975                 if (!L_ECHO(tty)) {
 976                         ldata->read_head = ldata->canon_head;
 977                         return;
 978                 }
 979                 if (!L_ECHOK(tty) || !L_ECHOKE(tty) || !L_ECHOE(tty)) {
 980                         ldata->read_head = ldata->canon_head;
 981                         finish_erasing(ldata);
 982                         echo_char(KILL_CHAR(tty), tty);
 983                         /* Add a newline if ECHOK is on and ECHOKE is off. */
 984                         if (L_ECHOK(tty))
 985                                 echo_char_raw('\n', ldata);
 986                         return;
 987                 }
 988                 kill_type = KILL;
 989         }
 990
 991         seen_alnums = 0;
 992         while (MASK(ldata->read_head) != MASK(ldata->canon_head)) {
 993                 head = ldata->read_head;
 994
 995                 /* erase a single possibly multibyte character */
 996                 do {
 997                         head--;
 998                         c = read_buf(ldata, head);
 999                 } while (is_continuation(c, tty) &&
1000                          MASK(head) != MASK(ldata->canon_head));
1001
1002                 /* do not partially erase */
1003                 if (is_continuation(c, tty))
1004                         break;
1005
1006                 if (kill_type == WERASE) {
1007                         /* Equivalent to BSD's ALTWERASE. */
1008                         if (isalnum(c) || c == '_')
1009                                 seen_alnums++;
1010                         else if (seen_alnums)
1011                                 break;
1012                 }
1013                 cnt = ldata->read_head - head;
1014                 ldata->read_head = head;
1015                 if (L_ECHO(tty)) {
1016                         if (L_ECHOPRT(tty)) {
1017                                 if (!ldata->erasing) {
1018                                         echo_char_raw('\\', ldata);
1019                                         ldata->erasing = 1;
1020                                 }
1021                                 /* if cnt > 1, output a multi-byte character */
1022                                 echo_char(c, tty);
1023                                 while (--cnt > 0) {
1024                                         head++;
1025                                         echo_char_raw(read_buf(ldata, head), ldata);
1026                                         echo_move_back_col(ldata);
1027                                 }
1028                         } else if (kill_type == ERASE && !L_ECHOE(tty)) {
1029                                 echo_char(ERASE_CHAR(tty), tty);
1030                         } else if (c == '\t') {
1031                                 unsigned int num_chars = 0;
1032                                 int after_tab = 0;
1033                                 size_t tail = ldata->read_head;
1034
1035                                 /*
1036                                  * Count the columns used for characters
1037                                  * since the start of input or after a
1038                                  * previous tab.
1039                                  * This info is used to go back the correct
1040                                  * number of columns.
1041                                  */
1042                                 while (MASK(tail) != MASK(ldata->canon_head)) {
1043                                         tail--;
1044                                         c = read_buf(ldata, tail);
1045                                         if (c == '\t') {
1046                                                 after_tab = 1;
1047                                                 break;
1048                                         } else if (iscntrl(c)) {
1049                                                 if (L_ECHOCTL(tty))
1050                                                         num_chars += 2;
1051                                         } else if (!is_continuation(c, tty)) {
1052                                                 num_chars++;
1053                                         }
1054                                 }
1055                                 echo_erase_tab(num_chars, after_tab, ldata);
1056                         } else {
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                                 if (!iscntrl(c) || L_ECHOCTL(tty)) {
1063                                         echo_char_raw('\b', ldata);
1064                                         echo_char_raw(' ', ldata);
1065                                         echo_char_raw('\b', ldata);
1066                                 }
1067                         }
1068                 }
1069                 if (kill_type == ERASE)
1070                         break;
1071         }
1072         if (ldata->read_head == ldata->canon_head && L_ECHO(tty))
1073                 finish_erasing(ldata);
1074 }
1075
1076
1077 static void __isig(int sig, struct tty_struct *tty)
1078 {
1079         struct pid *tty_pgrp = tty_get_pgrp(tty);
1080         if (tty_pgrp) {
1081                 kill_pgrp(tty_pgrp, sig, 1);
1082                 put_pid(tty_pgrp);
1083         }
1084 }
1085
1086 /**
1087  * isig                 -       handle the ISIG optio
1088  * @sig: signal
1089  * @tty: terminal
1090  *
1091  * Called when a signal is being sent due to terminal input. Called from the
1092  * &tty_driver.receive_buf() path, so serialized.
1093  *
1094  * Performs input and output flush if !NOFLSH. In this context, the echo
1095  * buffer is 'output'. The signal is processed first to alert any current
1096  * readers or writers to discontinue and exit their i/o loops.
1097  *
1098  * Locking: %ctrl.lock
1099  */
1100 static void isig(int sig, struct tty_struct *tty)
1101 {
1102         struct n_tty_data *ldata = tty->disc_data;
1103
1104         if (L_NOFLSH(tty)) {
1105                 /* signal only */
1106                 __isig(sig, tty);
1107
1108         } else { /* signal and flush */
1109                 up_read(&tty->termios_rwsem);
1110                 down_write(&tty->termios_rwsem);
1111
1112                 __isig(sig, tty);
1113
1114                 /* clear echo buffer */
1115                 mutex_lock(&ldata->output_lock);
1116                 ldata->echo_head = ldata->echo_tail = 0;
1117                 ldata->echo_mark = ldata->echo_commit = 0;
1118                 mutex_unlock(&ldata->output_lock);
1119
1120                 /* clear output buffer */
1121                 tty_driver_flush_buffer(tty);
1122
1123                 /* clear input buffer */
1124                 reset_buffer_flags(tty->disc_data);
1125
1126                 /* notify pty master of flush */
1127                 if (tty->link)
1128                         n_tty_packet_mode_flush(tty);
1129
1130                 up_write(&tty->termios_rwsem);
1131                 down_read(&tty->termios_rwsem);
1132         }
1133 }
1134
1135 /**
1136  * n_tty_receive_break  -       handle break
1137  * @tty: terminal
1138  *
1139  * An RS232 break event has been hit in the incoming bitstream. This can cause
1140  * a variety of events depending upon the termios settings.
1141  *
1142  * Locking: n_tty_receive_buf()/producer path:
1143  *      caller holds non-exclusive termios_rwsem
1144  *
1145  * Note: may get exclusive %termios_rwsem if flushing input buffer
1146  */
1147 static void n_tty_receive_break(struct tty_struct *tty)
1148 {
1149         struct n_tty_data *ldata = tty->disc_data;
1150
1151         if (I_IGNBRK(tty))
1152                 return;
1153         if (I_BRKINT(tty)) {
1154                 isig(SIGINT, tty);
1155                 return;
1156         }
1157         if (I_PARMRK(tty)) {
1158                 put_tty_queue('\377', ldata);
1159                 put_tty_queue('\0', ldata);
1160         }
1161         put_tty_queue('\0', ldata);
1162 }
1163
1164 /**
1165  * n_tty_receive_overrun        -       handle overrun reporting
1166  * @tty: terminal
1167  *
1168  * Data arrived faster than we could process it. While the tty driver has
1169  * flagged this the bits that were missed are gone forever.
1170  *
1171  * Called from the receive_buf path so single threaded. Does not need locking
1172  * as num_overrun and overrun_time are function private.
1173  */
1174 static void n_tty_receive_overrun(struct tty_struct *tty)
1175 {
1176         struct n_tty_data *ldata = tty->disc_data;
1177
1178         ldata->num_overrun++;
1179         if (time_after(jiffies, ldata->overrun_time + HZ) ||
1180                         time_after(ldata->overrun_time, jiffies)) {
1181                 tty_warn(tty, "%d input overrun(s)\n", ldata->num_overrun);
1182                 ldata->overrun_time = jiffies;
1183                 ldata->num_overrun = 0;
1184         }
1185 }
1186
1187 /**
1188  * n_tty_receive_parity_error   -       error notifier
1189  * @tty: terminal device
1190  * @c: character
1191  *
1192  * Process a parity error and queue the right data to indicate the error case
1193  * if necessary.
1194  *
1195  * Locking: n_tty_receive_buf()/producer path:
1196  *      caller holds non-exclusive %termios_rwsem
1197  */
1198 static void n_tty_receive_parity_error(struct tty_struct *tty, unsigned char c)
1199 {
1200         struct n_tty_data *ldata = tty->disc_data;
1201
1202         if (I_INPCK(tty)) {
1203                 if (I_IGNPAR(tty))
1204                         return;
1205                 if (I_PARMRK(tty)) {
1206                         put_tty_queue('\377', ldata);
1207                         put_tty_queue('\0', ldata);
1208                         put_tty_queue(c, ldata);
1209                 } else
1210                         put_tty_queue('\0', ldata);
1211         } else
1212                 put_tty_queue(c, ldata);
1213 }
1214
1215 static void
1216 n_tty_receive_signal_char(struct tty_struct *tty, int signal, unsigned char c)
1217 {
1218         isig(signal, tty);
1219         if (I_IXON(tty))
1220                 start_tty(tty);
1221         if (L_ECHO(tty)) {
1222                 echo_char(c, tty);
1223                 commit_echoes(tty);
1224         } else
1225                 process_echoes(tty);
1226 }
1227
1228 static bool n_tty_is_char_flow_ctrl(struct tty_struct *tty, unsigned char c)
1229 {
1230         return c == START_CHAR(tty) || c == STOP_CHAR(tty);
1231 }
1232
1233 /**
1234  * n_tty_receive_char_flow_ctrl - receive flow control chars
1235  * @tty: terminal device
1236  * @c: character
1237  * @lookahead_done: lookahead has processed this character already
1238  *
1239  * Receive and process flow control character actions.
1240  *
1241  * In case lookahead for flow control chars already handled the character in
1242  * advance to the normal receive, the actions are skipped during normal
1243  * receive.
1244  *
1245  * Returns true if @c is consumed as flow-control character, the character
1246  * must not be treated as normal character.
1247  */
1248 static bool n_tty_receive_char_flow_ctrl(struct tty_struct *tty, unsigned char c,
1249                                          bool lookahead_done)
1250 {
1251         if (!n_tty_is_char_flow_ctrl(tty, c))
1252                 return false;
1253
1254         if (lookahead_done)
1255                 return true;
1256
1257         if (c == START_CHAR(tty)) {
1258                 start_tty(tty);
1259                 process_echoes(tty);
1260                 return true;
1261         }
1262
1263         /* STOP_CHAR */
1264         stop_tty(tty);
1265         return true;
1266 }
1267
1268 static void n_tty_receive_char_special(struct tty_struct *tty, unsigned char c,
1269                                        bool lookahead_done)
1270 {
1271         struct n_tty_data *ldata = tty->disc_data;
1272
1273         if (I_IXON(tty) && n_tty_receive_char_flow_ctrl(tty, c, lookahead_done))
1274                 return;
1275
1276         if (L_ISIG(tty)) {
1277                 if (c == INTR_CHAR(tty)) {
1278                         n_tty_receive_signal_char(tty, SIGINT, c);
1279                         return;
1280                 } else if (c == QUIT_CHAR(tty)) {
1281                         n_tty_receive_signal_char(tty, SIGQUIT, c);
1282                         return;
1283                 } else if (c == SUSP_CHAR(tty)) {
1284                         n_tty_receive_signal_char(tty, SIGTSTP, c);
1285                         return;
1286                 }
1287         }
1288
1289         if (tty->flow.stopped && !tty->flow.tco_stopped && I_IXON(tty) && I_IXANY(tty)) {
1290                 start_tty(tty);
1291                 process_echoes(tty);
1292         }
1293
1294         if (c == '\r') {
1295                 if (I_IGNCR(tty))
1296                         return;
1297                 if (I_ICRNL(tty))
1298                         c = '\n';
1299         } else if (c == '\n' && I_INLCR(tty))
1300                 c = '\r';
1301
1302         if (ldata->icanon) {
1303                 if (c == ERASE_CHAR(tty) || c == KILL_CHAR(tty) ||
1304                     (c == WERASE_CHAR(tty) && L_IEXTEN(tty))) {
1305                         eraser(c, tty);
1306                         commit_echoes(tty);
1307                         return;
1308                 }
1309                 if (c == LNEXT_CHAR(tty) && L_IEXTEN(tty)) {
1310                         ldata->lnext = 1;
1311                         if (L_ECHO(tty)) {
1312                                 finish_erasing(ldata);
1313                                 if (L_ECHOCTL(tty)) {
1314                                         echo_char_raw('^', ldata);
1315                                         echo_char_raw('\b', ldata);
1316                                         commit_echoes(tty);
1317                                 }
1318                         }
1319                         return;
1320                 }
1321                 if (c == REPRINT_CHAR(tty) && L_ECHO(tty) && L_IEXTEN(tty)) {
1322                         size_t tail = ldata->canon_head;
1323
1324                         finish_erasing(ldata);
1325                         echo_char(c, tty);
1326                         echo_char_raw('\n', ldata);
1327                         while (MASK(tail) != MASK(ldata->read_head)) {
1328                                 echo_char(read_buf(ldata, tail), tty);
1329                                 tail++;
1330                         }
1331                         commit_echoes(tty);
1332                         return;
1333                 }
1334                 if (c == '\n') {
1335                         if (L_ECHO(tty) || L_ECHONL(tty)) {
1336                                 echo_char_raw('\n', ldata);
1337                                 commit_echoes(tty);
1338                         }
1339                         goto handle_newline;
1340                 }
1341                 if (c == EOF_CHAR(tty)) {
1342                         c = __DISABLED_CHAR;
1343                         goto handle_newline;
1344                 }
1345                 if ((c == EOL_CHAR(tty)) ||
1346                     (c == EOL2_CHAR(tty) && L_IEXTEN(tty))) {
1347                         /*
1348                          * XXX are EOL_CHAR and EOL2_CHAR echoed?!?
1349                          */
1350                         if (L_ECHO(tty)) {
1351                                 /* Record the column of first canon char. */
1352                                 if (ldata->canon_head == ldata->read_head)
1353                                         echo_set_canon_col(ldata);
1354                                 echo_char(c, tty);
1355                                 commit_echoes(tty);
1356                         }
1357                         /*
1358                          * XXX does PARMRK doubling happen for
1359                          * EOL_CHAR and EOL2_CHAR?
1360                          */
1361                         if (c == (unsigned char) '\377' && I_PARMRK(tty))
1362                                 put_tty_queue(c, ldata);
1363
1364 handle_newline:
1365                         set_bit(ldata->read_head & (N_TTY_BUF_SIZE - 1), ldata->read_flags);
1366                         put_tty_queue(c, ldata);
1367                         smp_store_release(&ldata->canon_head, ldata->read_head);
1368                         kill_fasync(&tty->fasync, SIGIO, POLL_IN);
1369                         wake_up_interruptible_poll(&tty->read_wait, EPOLLIN | EPOLLRDNORM);
1370                         return;
1371                 }
1372         }
1373
1374         if (L_ECHO(tty)) {
1375                 finish_erasing(ldata);
1376                 if (c == '\n')
1377                         echo_char_raw('\n', ldata);
1378                 else {
1379                         /* Record the column of first canon char. */
1380                         if (ldata->canon_head == ldata->read_head)
1381                                 echo_set_canon_col(ldata);
1382                         echo_char(c, tty);
1383                 }
1384                 commit_echoes(tty);
1385         }
1386
1387         /* PARMRK doubling check */
1388         if (c == (unsigned char) '\377' && I_PARMRK(tty))
1389                 put_tty_queue(c, ldata);
1390
1391         put_tty_queue(c, ldata);
1392 }
1393
1394 /**
1395  * n_tty_receive_char   -       perform processing
1396  * @tty: terminal device
1397  * @c: character
1398  *
1399  * Process an individual character of input received from the driver.  This is
1400  * serialized with respect to itself by the rules for the driver above.
1401  *
1402  * Locking: n_tty_receive_buf()/producer path:
1403  *      caller holds non-exclusive %termios_rwsem
1404  *      publishes canon_head if canonical mode is active
1405  */
1406 static void n_tty_receive_char(struct tty_struct *tty, unsigned char c)
1407 {
1408         struct n_tty_data *ldata = tty->disc_data;
1409
1410         if (tty->flow.stopped && !tty->flow.tco_stopped && I_IXON(tty) && I_IXANY(tty)) {
1411                 start_tty(tty);
1412                 process_echoes(tty);
1413         }
1414         if (L_ECHO(tty)) {
1415                 finish_erasing(ldata);
1416                 /* Record the column of first canon char. */
1417                 if (ldata->canon_head == ldata->read_head)
1418                         echo_set_canon_col(ldata);
1419                 echo_char(c, tty);
1420                 commit_echoes(tty);
1421         }
1422         /* PARMRK doubling check */
1423         if (c == (unsigned char) '\377' && I_PARMRK(tty))
1424                 put_tty_queue(c, ldata);
1425         put_tty_queue(c, ldata);
1426 }
1427
1428 static void n_tty_receive_char_closing(struct tty_struct *tty, unsigned char c,
1429                                        bool lookahead_done)
1430 {
1431         if (I_ISTRIP(tty))
1432                 c &= 0x7f;
1433         if (I_IUCLC(tty) && L_IEXTEN(tty))
1434                 c = tolower(c);
1435
1436         if (I_IXON(tty)) {
1437                 if (!n_tty_receive_char_flow_ctrl(tty, c, lookahead_done) &&
1438                     tty->flow.stopped && !tty->flow.tco_stopped && I_IXANY(tty) &&
1439                     c != INTR_CHAR(tty) && c != QUIT_CHAR(tty) &&
1440                     c != SUSP_CHAR(tty)) {
1441                         start_tty(tty);
1442                         process_echoes(tty);
1443                 }
1444         }
1445 }
1446
1447 static void
1448 n_tty_receive_char_flagged(struct tty_struct *tty, unsigned char c, char flag)
1449 {
1450         switch (flag) {
1451         case TTY_BREAK:
1452                 n_tty_receive_break(tty);
1453                 break;
1454         case TTY_PARITY:
1455         case TTY_FRAME:
1456                 n_tty_receive_parity_error(tty, c);
1457                 break;
1458         case TTY_OVERRUN:
1459                 n_tty_receive_overrun(tty);
1460                 break;
1461         default:
1462                 tty_err(tty, "unknown flag %d\n", flag);
1463                 break;
1464         }
1465 }
1466
1467 static void
1468 n_tty_receive_char_lnext(struct tty_struct *tty, unsigned char c, char flag)
1469 {
1470         struct n_tty_data *ldata = tty->disc_data;
1471
1472         ldata->lnext = 0;
1473         if (likely(flag == TTY_NORMAL)) {
1474                 if (I_ISTRIP(tty))
1475                         c &= 0x7f;
1476                 if (I_IUCLC(tty) && L_IEXTEN(tty))
1477                         c = tolower(c);
1478                 n_tty_receive_char(tty, c);
1479         } else
1480                 n_tty_receive_char_flagged(tty, c, flag);
1481 }
1482
1483 /* Caller must ensure count > 0 */
1484 static void n_tty_lookahead_flow_ctrl(struct tty_struct *tty, const unsigned char *cp,
1485                                       const unsigned char *fp, unsigned int count)
1486 {
1487         struct n_tty_data *ldata = tty->disc_data;
1488         unsigned char flag = TTY_NORMAL;
1489
1490         ldata->lookahead_count += count;
1491
1492         if (!I_IXON(tty))
1493                 return;
1494
1495         while (count--) {
1496                 if (fp)
1497                         flag = *fp++;
1498                 if (likely(flag == TTY_NORMAL))
1499                         n_tty_receive_char_flow_ctrl(tty, *cp, false);
1500                 cp++;
1501         }
1502 }
1503
1504 static void
1505 n_tty_receive_buf_real_raw(struct tty_struct *tty, const unsigned char *cp,
1506                            const char *fp, int count)
1507 {
1508         struct n_tty_data *ldata = tty->disc_data;
1509         size_t n, head;
1510
1511         head = ldata->read_head & (N_TTY_BUF_SIZE - 1);
1512         n = min_t(size_t, count, N_TTY_BUF_SIZE - head);
1513         memcpy(read_buf_addr(ldata, head), cp, n);
1514         ldata->read_head += n;
1515         cp += n;
1516         count -= n;
1517
1518         head = ldata->read_head & (N_TTY_BUF_SIZE - 1);
1519         n = min_t(size_t, count, N_TTY_BUF_SIZE - head);
1520         memcpy(read_buf_addr(ldata, head), cp, n);
1521         ldata->read_head += n;
1522 }
1523
1524 static void
1525 n_tty_receive_buf_raw(struct tty_struct *tty, const unsigned char *cp,
1526                       const char *fp, int count)
1527 {
1528         struct n_tty_data *ldata = tty->disc_data;
1529         char flag = TTY_NORMAL;
1530
1531         while (count--) {
1532                 if (fp)
1533                         flag = *fp++;
1534                 if (likely(flag == TTY_NORMAL))
1535                         put_tty_queue(*cp++, ldata);
1536                 else
1537                         n_tty_receive_char_flagged(tty, *cp++, flag);
1538         }
1539 }
1540
1541 static void
1542 n_tty_receive_buf_closing(struct tty_struct *tty, const unsigned char *cp,
1543                           const char *fp, int count, bool lookahead_done)
1544 {
1545         char flag = TTY_NORMAL;
1546
1547         while (count--) {
1548                 if (fp)
1549                         flag = *fp++;
1550                 if (likely(flag == TTY_NORMAL))
1551                         n_tty_receive_char_closing(tty, *cp++, lookahead_done);
1552         }
1553 }
1554
1555 static void n_tty_receive_buf_standard(struct tty_struct *tty,
1556                 const unsigned char *cp, const char *fp, int count, bool lookahead_done)
1557 {
1558         struct n_tty_data *ldata = tty->disc_data;
1559         char flag = TTY_NORMAL;
1560
1561         while (count--) {
1562                 unsigned char c = *cp++;
1563
1564                 if (fp)
1565                         flag = *fp++;
1566
1567                 if (ldata->lnext) {
1568                         n_tty_receive_char_lnext(tty, c, flag);
1569                         continue;
1570                 }
1571
1572                 if (unlikely(flag != TTY_NORMAL)) {
1573                         n_tty_receive_char_flagged(tty, c, flag);
1574                         continue;
1575                 }
1576
1577                 if (I_ISTRIP(tty))
1578                         c &= 0x7f;
1579                 if (I_IUCLC(tty) && L_IEXTEN(tty))
1580                         c = tolower(c);
1581                 if (L_EXTPROC(tty)) {
1582                         put_tty_queue(c, ldata);
1583                         continue;
1584                 }
1585
1586                 if (test_bit(c, ldata->char_map))
1587                         n_tty_receive_char_special(tty, c, lookahead_done);
1588                 else
1589                         n_tty_receive_char(tty, c);
1590         }
1591 }
1592
1593 static void __receive_buf(struct tty_struct *tty, const unsigned char *cp,
1594                           const char *fp, int count)
1595 {
1596         struct n_tty_data *ldata = tty->disc_data;
1597         bool preops = I_ISTRIP(tty) || (I_IUCLC(tty) && L_IEXTEN(tty));
1598         size_t la_count = min_t(size_t, ldata->lookahead_count, count);
1599
1600         if (ldata->real_raw)
1601                 n_tty_receive_buf_real_raw(tty, cp, fp, count);
1602         else if (ldata->raw || (L_EXTPROC(tty) && !preops))
1603                 n_tty_receive_buf_raw(tty, cp, fp, count);
1604         else if (tty->closing && !L_EXTPROC(tty)) {
1605                 if (la_count > 0)
1606                         n_tty_receive_buf_closing(tty, cp, fp, la_count, true);
1607                 if (count > la_count)
1608                         n_tty_receive_buf_closing(tty, cp, fp, count - la_count, false);
1609         } else {
1610                 if (la_count > 0)
1611                         n_tty_receive_buf_standard(tty, cp, fp, la_count, true);
1612                 if (count > la_count)
1613                         n_tty_receive_buf_standard(tty, cp, fp, count - la_count, false);
1614
1615                 flush_echoes(tty);
1616                 if (tty->ops->flush_chars)
1617                         tty->ops->flush_chars(tty);
1618         }
1619
1620         ldata->lookahead_count -= la_count;
1621
1622         if (ldata->icanon && !L_EXTPROC(tty))
1623                 return;
1624
1625         /* publish read_head to consumer */
1626         smp_store_release(&ldata->commit_head, ldata->read_head);
1627
1628         if (read_cnt(ldata)) {
1629                 kill_fasync(&tty->fasync, SIGIO, POLL_IN);
1630                 wake_up_interruptible_poll(&tty->read_wait, EPOLLIN | EPOLLRDNORM);
1631         }
1632 }
1633
1634 /**
1635  * n_tty_receive_buf_common     -       process input
1636  * @tty: device to receive input
1637  * @cp: input chars
1638  * @fp: flags for each char (if %NULL, all chars are %TTY_NORMAL)
1639  * @count: number of input chars in @cp
1640  * @flow: enable flow control
1641  *
1642  * Called by the terminal driver when a block of characters has been received.
1643  * This function must be called from soft contexts not from interrupt context.
1644  * The driver is responsible for making calls one at a time and in order (or
1645  * using flush_to_ldisc()).
1646  *
1647  * Returns: the # of input chars from @cp which were processed.
1648  *
1649  * In canonical mode, the maximum line length is 4096 chars (including the line
1650  * termination char); lines longer than 4096 chars are truncated. After 4095
1651  * chars, input data is still processed but not stored. Overflow processing
1652  * ensures the tty can always receive more input until at least one line can be
1653  * read.
1654  *
1655  * In non-canonical mode, the read buffer will only accept 4095 chars; this
1656  * provides the necessary space for a newline char if the input mode is
1657  * switched to canonical.
1658  *
1659  * Note it is possible for the read buffer to _contain_ 4096 chars in
1660  * non-canonical mode: the read buffer could already contain the maximum canon
1661  * line of 4096 chars when the mode is switched to non-canonical.
1662  *
1663  * Locking: n_tty_receive_buf()/producer path:
1664  *      claims non-exclusive %termios_rwsem
1665  *      publishes commit_head or canon_head
1666  */
1667 static int
1668 n_tty_receive_buf_common(struct tty_struct *tty, const unsigned char *cp,
1669                          const char *fp, int count, int flow)
1670 {
1671         struct n_tty_data *ldata = tty->disc_data;
1672         int room, n, rcvd = 0, overflow;
1673
1674         down_read(&tty->termios_rwsem);
1675
1676         do {
1677                 /*
1678                  * When PARMRK is set, each input char may take up to 3 chars
1679                  * in the read buf; reduce the buffer space avail by 3x
1680                  *
1681                  * If we are doing input canonicalization, and there are no
1682                  * pending newlines, let characters through without limit, so
1683                  * that erase characters will be handled.  Other excess
1684                  * characters will be beeped.
1685                  *
1686                  * paired with store in *_copy_from_read_buf() -- guarantees
1687                  * the consumer has loaded the data in read_buf up to the new
1688                  * read_tail (so this producer will not overwrite unread data)
1689                  */
1690                 size_t tail = smp_load_acquire(&ldata->read_tail);
1691
1692                 room = N_TTY_BUF_SIZE - (ldata->read_head - tail);
1693                 if (I_PARMRK(tty))
1694                         room = (room + 2) / 3;
1695                 room--;
1696                 if (room <= 0) {
1697                         overflow = ldata->icanon && ldata->canon_head == tail;
1698                         if (overflow && room < 0)
1699                                 ldata->read_head--;
1700                         room = overflow;
1701                         WRITE_ONCE(ldata->no_room, flow && !room);
1702                 } else
1703                         overflow = 0;
1704
1705                 n = min(count, room);
1706                 if (!n)
1707                         break;
1708
1709                 /* ignore parity errors if handling overflow */
1710                 if (!overflow || !fp || *fp != TTY_PARITY)
1711                         __receive_buf(tty, cp, fp, n);
1712
1713                 cp += n;
1714                 if (fp)
1715                         fp += n;
1716                 count -= n;
1717                 rcvd += n;
1718         } while (!test_bit(TTY_LDISC_CHANGING, &tty->flags));
1719
1720         tty->receive_room = room;
1721
1722         /* Unthrottle if handling overflow on pty */
1723         if (tty->driver->type == TTY_DRIVER_TYPE_PTY) {
1724                 if (overflow) {
1725                         tty_set_flow_change(tty, TTY_UNTHROTTLE_SAFE);
1726                         tty_unthrottle_safe(tty);
1727                         __tty_set_flow_change(tty, 0);
1728                 }
1729         } else
1730                 n_tty_check_throttle(tty);
1731
1732         if (unlikely(ldata->no_room)) {
1733                 /*
1734                  * Barrier here is to ensure to read the latest read_tail in
1735                  * chars_in_buffer() and to make sure that read_tail is not loaded
1736                  * before ldata->no_room is set.
1737                  */
1738                 smp_mb();
1739                 if (!chars_in_buffer(tty))
1740                         n_tty_kick_worker(tty);
1741         }
1742
1743         up_read(&tty->termios_rwsem);
1744
1745         return rcvd;
1746 }
1747
1748 static void n_tty_receive_buf(struct tty_struct *tty, const unsigned char *cp,
1749                               const char *fp, int count)
1750 {
1751         n_tty_receive_buf_common(tty, cp, fp, count, 0);
1752 }
1753
1754 static int n_tty_receive_buf2(struct tty_struct *tty, const unsigned char *cp,
1755                               const char *fp, int count)
1756 {
1757         return n_tty_receive_buf_common(tty, cp, fp, count, 1);
1758 }
1759
1760 /**
1761  * n_tty_set_termios    -       termios data changed
1762  * @tty: terminal
1763  * @old: previous data
1764  *
1765  * Called by the tty layer when the user changes termios flags so that the line
1766  * discipline can plan ahead. This function cannot sleep and is protected from
1767  * re-entry by the tty layer. The user is guaranteed that this function will
1768  * not be re-entered or in progress when the ldisc is closed.
1769  *
1770  * Locking: Caller holds @tty->termios_rwsem
1771  */
1772 static void n_tty_set_termios(struct tty_struct *tty, const struct ktermios *old)
1773 {
1774         struct n_tty_data *ldata = tty->disc_data;
1775
1776         if (!old || (old->c_lflag ^ tty->termios.c_lflag) & (ICANON | EXTPROC)) {
1777                 bitmap_zero(ldata->read_flags, N_TTY_BUF_SIZE);
1778                 ldata->line_start = ldata->read_tail;
1779                 if (!L_ICANON(tty) || !read_cnt(ldata)) {
1780                         ldata->canon_head = ldata->read_tail;
1781                         ldata->push = 0;
1782                 } else {
1783                         set_bit((ldata->read_head - 1) & (N_TTY_BUF_SIZE - 1),
1784                                 ldata->read_flags);
1785                         ldata->canon_head = ldata->read_head;
1786                         ldata->push = 1;
1787                 }
1788                 ldata->commit_head = ldata->read_head;
1789                 ldata->erasing = 0;
1790                 ldata->lnext = 0;
1791         }
1792
1793         ldata->icanon = (L_ICANON(tty) != 0);
1794
1795         if (I_ISTRIP(tty) || I_IUCLC(tty) || I_IGNCR(tty) ||
1796             I_ICRNL(tty) || I_INLCR(tty) || L_ICANON(tty) ||
1797             I_IXON(tty) || L_ISIG(tty) || L_ECHO(tty) ||
1798             I_PARMRK(tty)) {
1799                 bitmap_zero(ldata->char_map, 256);
1800
1801                 if (I_IGNCR(tty) || I_ICRNL(tty))
1802                         set_bit('\r', ldata->char_map);
1803                 if (I_INLCR(tty))
1804                         set_bit('\n', ldata->char_map);
1805
1806                 if (L_ICANON(tty)) {
1807                         set_bit(ERASE_CHAR(tty), ldata->char_map);
1808                         set_bit(KILL_CHAR(tty), ldata->char_map);
1809                         set_bit(EOF_CHAR(tty), ldata->char_map);
1810                         set_bit('\n', ldata->char_map);
1811                         set_bit(EOL_CHAR(tty), ldata->char_map);
1812                         if (L_IEXTEN(tty)) {
1813                                 set_bit(WERASE_CHAR(tty), ldata->char_map);
1814                                 set_bit(LNEXT_CHAR(tty), ldata->char_map);
1815                                 set_bit(EOL2_CHAR(tty), ldata->char_map);
1816                                 if (L_ECHO(tty))
1817                                         set_bit(REPRINT_CHAR(tty),
1818                                                 ldata->char_map);
1819                         }
1820                 }
1821                 if (I_IXON(tty)) {
1822                         set_bit(START_CHAR(tty), ldata->char_map);
1823                         set_bit(STOP_CHAR(tty), ldata->char_map);
1824                 }
1825                 if (L_ISIG(tty)) {
1826                         set_bit(INTR_CHAR(tty), ldata->char_map);
1827                         set_bit(QUIT_CHAR(tty), ldata->char_map);
1828                         set_bit(SUSP_CHAR(tty), ldata->char_map);
1829                 }
1830                 clear_bit(__DISABLED_CHAR, ldata->char_map);
1831                 ldata->raw = 0;
1832                 ldata->real_raw = 0;
1833         } else {
1834                 ldata->raw = 1;
1835                 if ((I_IGNBRK(tty) || (!I_BRKINT(tty) && !I_PARMRK(tty))) &&
1836                     (I_IGNPAR(tty) || !I_INPCK(tty)) &&
1837                     (tty->driver->flags & TTY_DRIVER_REAL_RAW))
1838                         ldata->real_raw = 1;
1839                 else
1840                         ldata->real_raw = 0;
1841         }
1842         /*
1843          * Fix tty hang when I_IXON(tty) is cleared, but the tty
1844          * been stopped by STOP_CHAR(tty) before it.
1845          */
1846         if (!I_IXON(tty) && old && (old->c_iflag & IXON) && !tty->flow.tco_stopped) {
1847                 start_tty(tty);
1848                 process_echoes(tty);
1849         }
1850
1851         /* The termios change make the tty ready for I/O */
1852         wake_up_interruptible(&tty->write_wait);
1853         wake_up_interruptible(&tty->read_wait);
1854 }
1855
1856 /**
1857  * n_tty_close          -       close the ldisc for this tty
1858  * @tty: device
1859  *
1860  * Called from the terminal layer when this line discipline is being shut down,
1861  * either because of a close or becsuse of a discipline change. The function
1862  * will not be called while other ldisc methods are in progress.
1863  */
1864 static void n_tty_close(struct tty_struct *tty)
1865 {
1866         struct n_tty_data *ldata = tty->disc_data;
1867
1868         if (tty->link)
1869                 n_tty_packet_mode_flush(tty);
1870
1871         down_write(&tty->termios_rwsem);
1872         vfree(ldata);
1873         tty->disc_data = NULL;
1874         up_write(&tty->termios_rwsem);
1875 }
1876
1877 /**
1878  * n_tty_open           -       open an ldisc
1879  * @tty: terminal to open
1880  *
1881  * Called when this line discipline is being attached to the terminal device.
1882  * Can sleep. Called serialized so that no other events will occur in parallel.
1883  * No further open will occur until a close.
1884  */
1885 static int n_tty_open(struct tty_struct *tty)
1886 {
1887         struct n_tty_data *ldata;
1888
1889         /* Currently a malloc failure here can panic */
1890         ldata = vzalloc(sizeof(*ldata));
1891         if (!ldata)
1892                 return -ENOMEM;
1893
1894         ldata->overrun_time = jiffies;
1895         mutex_init(&ldata->atomic_read_lock);
1896         mutex_init(&ldata->output_lock);
1897
1898         tty->disc_data = ldata;
1899         tty->closing = 0;
1900         /* indicate buffer work may resume */
1901         clear_bit(TTY_LDISC_HALTED, &tty->flags);
1902         n_tty_set_termios(tty, NULL);
1903         tty_unthrottle(tty);
1904         return 0;
1905 }
1906
1907 static inline int input_available_p(struct tty_struct *tty, int poll)
1908 {
1909         struct n_tty_data *ldata = tty->disc_data;
1910         int amt = poll && !TIME_CHAR(tty) && MIN_CHAR(tty) ? MIN_CHAR(tty) : 1;
1911
1912         if (ldata->icanon && !L_EXTPROC(tty))
1913                 return ldata->canon_head != ldata->read_tail;
1914         else
1915                 return ldata->commit_head - ldata->read_tail >= amt;
1916 }
1917
1918 /**
1919  * copy_from_read_buf   -       copy read data directly
1920  * @tty: terminal device
1921  * @kbp: data
1922  * @nr: size of data
1923  *
1924  * Helper function to speed up n_tty_read(). It is only called when %ICANON is
1925  * off; it copies characters straight from the tty queue.
1926  *
1927  * Returns: true if it successfully copied data, but there is still more data
1928  * to be had.
1929  *
1930  * Locking:
1931  *  * called under the @ldata->atomic_read_lock sem
1932  *  * n_tty_read()/consumer path:
1933  *              caller holds non-exclusive %termios_rwsem;
1934  *              read_tail published
1935  */
1936 static bool copy_from_read_buf(struct tty_struct *tty,
1937                                       unsigned char **kbp,
1938                                       size_t *nr)
1939
1940 {
1941         struct n_tty_data *ldata = tty->disc_data;
1942         size_t n;
1943         bool is_eof;
1944         size_t head = smp_load_acquire(&ldata->commit_head);
1945         size_t tail = ldata->read_tail & (N_TTY_BUF_SIZE - 1);
1946
1947         n = min(head - ldata->read_tail, N_TTY_BUF_SIZE - tail);
1948         n = min(*nr, n);
1949         if (n) {
1950                 unsigned char *from = read_buf_addr(ldata, tail);
1951                 memcpy(*kbp, from, n);
1952                 is_eof = n == 1 && *from == EOF_CHAR(tty);
1953                 tty_audit_add_data(tty, from, n);
1954                 zero_buffer(tty, from, n);
1955                 smp_store_release(&ldata->read_tail, ldata->read_tail + n);
1956                 /* Turn single EOF into zero-length read */
1957                 if (L_EXTPROC(tty) && ldata->icanon && is_eof &&
1958                     (head == ldata->read_tail))
1959                         return false;
1960                 *kbp += n;
1961                 *nr -= n;
1962
1963                 /* If we have more to copy, let the caller know */
1964                 return head != ldata->read_tail;
1965         }
1966         return false;
1967 }
1968
1969 /**
1970  * canon_copy_from_read_buf     -       copy read data in canonical mode
1971  * @tty: terminal device
1972  * @kbp: data
1973  * @nr: size of data
1974  *
1975  * Helper function for n_tty_read(). It is only called when %ICANON is on; it
1976  * copies one line of input up to and including the line-delimiting character
1977  * into the result buffer.
1978  *
1979  * Note: When termios is changed from non-canonical to canonical mode and the
1980  * read buffer contains data, n_tty_set_termios() simulates an EOF push (as if
1981  * C-d were input) _without_ the %DISABLED_CHAR in the buffer. This causes data
1982  * already processed as input to be immediately available as input although a
1983  * newline has not been received.
1984  *
1985  * Locking:
1986  *  * called under the %atomic_read_lock mutex
1987  *  * n_tty_read()/consumer path:
1988  *      caller holds non-exclusive %termios_rwsem;
1989  *      read_tail published
1990  */
1991 static bool canon_copy_from_read_buf(struct tty_struct *tty,
1992                                      unsigned char **kbp,
1993                                      size_t *nr)
1994 {
1995         struct n_tty_data *ldata = tty->disc_data;
1996         size_t n, size, more, c;
1997         size_t eol;
1998         size_t tail, canon_head;
1999         int found = 0;
2000
2001         /* N.B. avoid overrun if nr == 0 */
2002         if (!*nr)
2003                 return false;
2004
2005         canon_head = smp_load_acquire(&ldata->canon_head);
2006         n = min(*nr, canon_head - ldata->read_tail);
2007
2008         tail = ldata->read_tail & (N_TTY_BUF_SIZE - 1);
2009         size = min_t(size_t, tail + n, N_TTY_BUF_SIZE);
2010
2011         n_tty_trace("%s: nr:%zu tail:%zu n:%zu size:%zu\n",
2012                     __func__, *nr, tail, n, size);
2013
2014         eol = find_next_bit(ldata->read_flags, size, tail);
2015         more = n - (size - tail);
2016         if (eol == N_TTY_BUF_SIZE && more) {
2017                 /* scan wrapped without finding set bit */
2018                 eol = find_first_bit(ldata->read_flags, more);
2019                 found = eol != more;
2020         } else
2021                 found = eol != size;
2022
2023         n = eol - tail;
2024         if (n > N_TTY_BUF_SIZE)
2025                 n += N_TTY_BUF_SIZE;
2026         c = n + found;
2027
2028         if (!found || read_buf(ldata, eol) != __DISABLED_CHAR)
2029                 n = c;
2030
2031         n_tty_trace("%s: eol:%zu found:%d n:%zu c:%zu tail:%zu more:%zu\n",
2032                     __func__, eol, found, n, c, tail, more);
2033
2034         tty_copy(tty, *kbp, tail, n);
2035         *kbp += n;
2036         *nr -= n;
2037
2038         if (found)
2039                 clear_bit(eol, ldata->read_flags);
2040         smp_store_release(&ldata->read_tail, ldata->read_tail + c);
2041
2042         if (found) {
2043                 if (!ldata->push)
2044                         ldata->line_start = ldata->read_tail;
2045                 else
2046                         ldata->push = 0;
2047                 tty_audit_push();
2048                 return false;
2049         }
2050
2051         /* No EOL found - do a continuation retry if there is more data */
2052         return ldata->read_tail != canon_head;
2053 }
2054
2055 /*
2056  * If we finished a read at the exact location of an
2057  * EOF (special EOL character that's a __DISABLED_CHAR)
2058  * in the stream, silently eat the EOF.
2059  */
2060 static void canon_skip_eof(struct tty_struct *tty)
2061 {
2062         struct n_tty_data *ldata = tty->disc_data;
2063         size_t tail, canon_head;
2064
2065         canon_head = smp_load_acquire(&ldata->canon_head);
2066         tail = ldata->read_tail;
2067
2068         // No data?
2069         if (tail == canon_head)
2070                 return;
2071
2072         // See if the tail position is EOF in the circular buffer
2073         tail &= (N_TTY_BUF_SIZE - 1);
2074         if (!test_bit(tail, ldata->read_flags))
2075                 return;
2076         if (read_buf(ldata, tail) != __DISABLED_CHAR)
2077                 return;
2078
2079         // Clear the EOL bit, skip the EOF char.
2080         clear_bit(tail, ldata->read_flags);
2081         smp_store_release(&ldata->read_tail, ldata->read_tail + 1);
2082 }
2083
2084 /**
2085  * job_control          -       check job control
2086  * @tty: tty
2087  * @file: file handle
2088  *
2089  * Perform job control management checks on this @file/@tty descriptor and if
2090  * appropriate send any needed signals and return a negative error code if
2091  * action should be taken.
2092  *
2093  * Locking:
2094  *  * redirected write test is safe
2095  *  * current->signal->tty check is safe
2096  *  * ctrl.lock to safely reference @tty->ctrl.pgrp
2097  */
2098 static int job_control(struct tty_struct *tty, struct file *file)
2099 {
2100         /* Job control check -- must be done at start and after
2101            every sleep (POSIX.1 7.1.1.4). */
2102         /* NOTE: not yet done after every sleep pending a thorough
2103            check of the logic of this change. -- jlc */
2104         /* don't stop on /dev/console */
2105         if (file->f_op->write_iter == redirected_tty_write)
2106                 return 0;
2107
2108         return __tty_check_change(tty, SIGTTIN);
2109 }
2110
2111
2112 /**
2113  * n_tty_read           -       read function for tty
2114  * @tty: tty device
2115  * @file: file object
2116  * @kbuf: kernelspace buffer pointer
2117  * @nr: size of I/O
2118  * @cookie: if non-%NULL, this is a continuation read
2119  * @offset: where to continue reading from (unused in n_tty)
2120  *
2121  * Perform reads for the line discipline. We are guaranteed that the line
2122  * discipline will not be closed under us but we may get multiple parallel
2123  * readers and must handle this ourselves. We may also get a hangup. Always
2124  * called in user context, may sleep.
2125  *
2126  * This code must be sure never to sleep through a hangup.
2127  *
2128  * Locking: n_tty_read()/consumer path:
2129  *      claims non-exclusive termios_rwsem;
2130  *      publishes read_tail
2131  */
2132 static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
2133                           unsigned char *kbuf, size_t nr,
2134                           void **cookie, unsigned long offset)
2135 {
2136         struct n_tty_data *ldata = tty->disc_data;
2137         unsigned char *kb = kbuf;
2138         DEFINE_WAIT_FUNC(wait, woken_wake_function);
2139         int c;
2140         int minimum, time;
2141         ssize_t retval = 0;
2142         long timeout;
2143         bool packet;
2144         size_t old_tail;
2145
2146         /*
2147          * Is this a continuation of a read started earler?
2148          *
2149          * If so, we still hold the atomic_read_lock and the
2150          * termios_rwsem, and can just continue to copy data.
2151          */
2152         if (*cookie) {
2153                 if (ldata->icanon && !L_EXTPROC(tty)) {
2154                         /*
2155                          * If we have filled the user buffer, see
2156                          * if we should skip an EOF character before
2157                          * releasing the lock and returning done.
2158                          */
2159                         if (!nr)
2160                                 canon_skip_eof(tty);
2161                         else if (canon_copy_from_read_buf(tty, &kb, &nr))
2162                                 return kb - kbuf;
2163                 } else {
2164                         if (copy_from_read_buf(tty, &kb, &nr))
2165                                 return kb - kbuf;
2166                 }
2167
2168                 /* No more data - release locks and stop retries */
2169                 n_tty_kick_worker(tty);
2170                 n_tty_check_unthrottle(tty);
2171                 up_read(&tty->termios_rwsem);
2172                 mutex_unlock(&ldata->atomic_read_lock);
2173                 *cookie = NULL;
2174                 return kb - kbuf;
2175         }
2176
2177         c = job_control(tty, file);
2178         if (c < 0)
2179                 return c;
2180
2181         /*
2182          *      Internal serialization of reads.
2183          */
2184         if (file->f_flags & O_NONBLOCK) {
2185                 if (!mutex_trylock(&ldata->atomic_read_lock))
2186                         return -EAGAIN;
2187         } else {
2188                 if (mutex_lock_interruptible(&ldata->atomic_read_lock))
2189                         return -ERESTARTSYS;
2190         }
2191
2192         down_read(&tty->termios_rwsem);
2193
2194         minimum = time = 0;
2195         timeout = MAX_SCHEDULE_TIMEOUT;
2196         if (!ldata->icanon) {
2197                 minimum = MIN_CHAR(tty);
2198                 if (minimum) {
2199                         time = (HZ / 10) * TIME_CHAR(tty);
2200                 } else {
2201                         timeout = (HZ / 10) * TIME_CHAR(tty);
2202                         minimum = 1;
2203                 }
2204         }
2205
2206         packet = tty->ctrl.packet;
2207         old_tail = ldata->read_tail;
2208
2209         add_wait_queue(&tty->read_wait, &wait);
2210         while (nr) {
2211                 /* First test for status change. */
2212                 if (packet && tty->link->ctrl.pktstatus) {
2213                         unsigned char cs;
2214                         if (kb != kbuf)
2215                                 break;
2216                         spin_lock_irq(&tty->link->ctrl.lock);
2217                         cs = tty->link->ctrl.pktstatus;
2218                         tty->link->ctrl.pktstatus = 0;
2219                         spin_unlock_irq(&tty->link->ctrl.lock);
2220                         *kb++ = cs;
2221                         nr--;
2222                         break;
2223                 }
2224
2225                 if (!input_available_p(tty, 0)) {
2226                         up_read(&tty->termios_rwsem);
2227                         tty_buffer_flush_work(tty->port);
2228                         down_read(&tty->termios_rwsem);
2229                         if (!input_available_p(tty, 0)) {
2230                                 if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
2231                                         retval = -EIO;
2232                                         break;
2233                                 }
2234                                 if (tty_hung_up_p(file))
2235                                         break;
2236                                 /*
2237                                  * Abort readers for ttys which never actually
2238                                  * get hung up.  See __tty_hangup().
2239                                  */
2240                                 if (test_bit(TTY_HUPPING, &tty->flags))
2241                                         break;
2242                                 if (!timeout)
2243                                         break;
2244                                 if (tty_io_nonblock(tty, file)) {
2245                                         retval = -EAGAIN;
2246                                         break;
2247                                 }
2248                                 if (signal_pending(current)) {
2249                                         retval = -ERESTARTSYS;
2250                                         break;
2251                                 }
2252                                 up_read(&tty->termios_rwsem);
2253
2254                                 timeout = wait_woken(&wait, TASK_INTERRUPTIBLE,
2255                                                 timeout);
2256
2257                                 down_read(&tty->termios_rwsem);
2258                                 continue;
2259                         }
2260                 }
2261
2262                 if (ldata->icanon && !L_EXTPROC(tty)) {
2263                         if (canon_copy_from_read_buf(tty, &kb, &nr))
2264                                 goto more_to_be_read;
2265                 } else {
2266                         /* Deal with packet mode. */
2267                         if (packet && kb == kbuf) {
2268                                 *kb++ = TIOCPKT_DATA;
2269                                 nr--;
2270                         }
2271
2272                         /*
2273                          * Copy data, and if there is more to be had
2274                          * and we have nothing more to wait for, then
2275                          * let's mark us for retries.
2276                          *
2277                          * NOTE! We return here with both the termios_sem
2278                          * and atomic_read_lock still held, the retries
2279                          * will release them when done.
2280                          */
2281                         if (copy_from_read_buf(tty, &kb, &nr) && kb - kbuf >= minimum) {
2282 more_to_be_read:
2283                                 remove_wait_queue(&tty->read_wait, &wait);
2284                                 *cookie = cookie;
2285                                 return kb - kbuf;
2286                         }
2287                 }
2288
2289                 n_tty_check_unthrottle(tty);
2290
2291                 if (kb - kbuf >= minimum)
2292                         break;
2293                 if (time)
2294                         timeout = time;
2295         }
2296         if (old_tail != ldata->read_tail) {
2297                 /*
2298                  * Make sure no_room is not read in n_tty_kick_worker()
2299                  * before setting ldata->read_tail in copy_from_read_buf().
2300                  */
2301                 smp_mb();
2302                 n_tty_kick_worker(tty);
2303         }
2304         up_read(&tty->termios_rwsem);
2305
2306         remove_wait_queue(&tty->read_wait, &wait);
2307         mutex_unlock(&ldata->atomic_read_lock);
2308
2309         if (kb - kbuf)
2310                 retval = kb - kbuf;
2311
2312         return retval;
2313 }
2314
2315 /**
2316  * n_tty_write          -       write function for tty
2317  * @tty: tty device
2318  * @file: file object
2319  * @buf: userspace buffer pointer
2320  * @nr: size of I/O
2321  *
2322  * Write function of the terminal device. This is serialized with respect to
2323  * other write callers but not to termios changes, reads and other such events.
2324  * Since the receive code will echo characters, thus calling driver write
2325  * methods, the %output_lock is used in the output processing functions called
2326  * here as well as in the echo processing function to protect the column state
2327  * and space left in the buffer.
2328  *
2329  * This code must be sure never to sleep through a hangup.
2330  *
2331  * Locking: output_lock to protect column state and space left
2332  *       (note that the process_output*() functions take this lock themselves)
2333  */
2334
2335 static ssize_t n_tty_write(struct tty_struct *tty, struct file *file,
2336                            const unsigned char *buf, size_t nr)
2337 {
2338         const unsigned char *b = buf;
2339         DEFINE_WAIT_FUNC(wait, woken_wake_function);
2340         int c;
2341         ssize_t retval = 0;
2342
2343         /* Job control check -- must be done at start (POSIX.1 7.1.1.4). */
2344         if (L_TOSTOP(tty) && file->f_op->write_iter != redirected_tty_write) {
2345                 retval = tty_check_change(tty);
2346                 if (retval)
2347                         return retval;
2348         }
2349
2350         down_read(&tty->termios_rwsem);
2351
2352         /* Write out any echoed characters that are still pending */
2353         process_echoes(tty);
2354
2355         add_wait_queue(&tty->write_wait, &wait);
2356         while (1) {
2357                 if (signal_pending(current)) {
2358                         retval = -ERESTARTSYS;
2359                         break;
2360                 }
2361                 if (tty_hung_up_p(file) || (tty->link && !tty->link->count)) {
2362                         retval = -EIO;
2363                         break;
2364                 }
2365                 if (O_OPOST(tty)) {
2366                         while (nr > 0) {
2367                                 ssize_t num = process_output_block(tty, b, nr);
2368                                 if (num < 0) {
2369                                         if (num == -EAGAIN)
2370                                                 break;
2371                                         retval = num;
2372                                         goto break_out;
2373                                 }
2374                                 b += num;
2375                                 nr -= num;
2376                                 if (nr == 0)
2377                                         break;
2378                                 c = *b;
2379                                 if (process_output(c, tty) < 0)
2380                                         break;
2381                                 b++; nr--;
2382                         }
2383                         if (tty->ops->flush_chars)
2384                                 tty->ops->flush_chars(tty);
2385                 } else {
2386                         struct n_tty_data *ldata = tty->disc_data;
2387
2388                         while (nr > 0) {
2389                                 mutex_lock(&ldata->output_lock);
2390                                 c = tty->ops->write(tty, b, nr);
2391                                 mutex_unlock(&ldata->output_lock);
2392                                 if (c < 0) {
2393                                         retval = c;
2394                                         goto break_out;
2395                                 }
2396                                 if (!c)
2397                                         break;
2398                                 b += c;
2399                                 nr -= c;
2400                         }
2401                 }
2402                 if (!nr)
2403                         break;
2404                 if (tty_io_nonblock(tty, file)) {
2405                         retval = -EAGAIN;
2406                         break;
2407                 }
2408                 up_read(&tty->termios_rwsem);
2409
2410                 wait_woken(&wait, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
2411
2412                 down_read(&tty->termios_rwsem);
2413         }
2414 break_out:
2415         remove_wait_queue(&tty->write_wait, &wait);
2416         if (nr && tty->fasync)
2417                 set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
2418         up_read(&tty->termios_rwsem);
2419         return (b - buf) ? b - buf : retval;
2420 }
2421
2422 /**
2423  * n_tty_poll           -       poll method for N_TTY
2424  * @tty: terminal device
2425  * @file: file accessing it
2426  * @wait: poll table
2427  *
2428  * Called when the line discipline is asked to poll() for data or for special
2429  * events. This code is not serialized with respect to other events save
2430  * open/close.
2431  *
2432  * This code must be sure never to sleep through a hangup.
2433  *
2434  * Locking: called without the kernel lock held -- fine.
2435  */
2436 static __poll_t n_tty_poll(struct tty_struct *tty, struct file *file,
2437                                                         poll_table *wait)
2438 {
2439         __poll_t mask = 0;
2440
2441         poll_wait(file, &tty->read_wait, wait);
2442         poll_wait(file, &tty->write_wait, wait);
2443         if (input_available_p(tty, 1))
2444                 mask |= EPOLLIN | EPOLLRDNORM;
2445         else {
2446                 tty_buffer_flush_work(tty->port);
2447                 if (input_available_p(tty, 1))
2448                         mask |= EPOLLIN | EPOLLRDNORM;
2449         }
2450         if (tty->ctrl.packet && tty->link->ctrl.pktstatus)
2451                 mask |= EPOLLPRI | EPOLLIN | EPOLLRDNORM;
2452         if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
2453                 mask |= EPOLLHUP;
2454         if (tty_hung_up_p(file))
2455                 mask |= EPOLLHUP;
2456         if (tty->ops->write && !tty_is_writelocked(tty) &&
2457                         tty_chars_in_buffer(tty) < WAKEUP_CHARS &&
2458                         tty_write_room(tty) > 0)
2459                 mask |= EPOLLOUT | EPOLLWRNORM;
2460         return mask;
2461 }
2462
2463 static unsigned long inq_canon(struct n_tty_data *ldata)
2464 {
2465         size_t nr, head, tail;
2466
2467         if (ldata->canon_head == ldata->read_tail)
2468                 return 0;
2469         head = ldata->canon_head;
2470         tail = ldata->read_tail;
2471         nr = head - tail;
2472         /* Skip EOF-chars.. */
2473         while (MASK(head) != MASK(tail)) {
2474                 if (test_bit(tail & (N_TTY_BUF_SIZE - 1), ldata->read_flags) &&
2475                     read_buf(ldata, tail) == __DISABLED_CHAR)
2476                         nr--;
2477                 tail++;
2478         }
2479         return nr;
2480 }
2481
2482 static int n_tty_ioctl(struct tty_struct *tty, unsigned int cmd,
2483                        unsigned long arg)
2484 {
2485         struct n_tty_data *ldata = tty->disc_data;
2486         int retval;
2487
2488         switch (cmd) {
2489         case TIOCOUTQ:
2490                 return put_user(tty_chars_in_buffer(tty), (int __user *) arg);
2491         case TIOCINQ:
2492                 down_write(&tty->termios_rwsem);
2493                 if (L_ICANON(tty) && !L_EXTPROC(tty))
2494                         retval = inq_canon(ldata);
2495                 else
2496                         retval = read_cnt(ldata);
2497                 up_write(&tty->termios_rwsem);
2498                 return put_user(retval, (unsigned int __user *) arg);
2499         default:
2500                 return n_tty_ioctl_helper(tty, cmd, arg);
2501         }
2502 }
2503
2504 static struct tty_ldisc_ops n_tty_ops = {
2505         .owner           = THIS_MODULE,
2506         .num             = N_TTY,
2507         .name            = "n_tty",
2508         .open            = n_tty_open,
2509         .close           = n_tty_close,
2510         .flush_buffer    = n_tty_flush_buffer,
2511         .read            = n_tty_read,
2512         .write           = n_tty_write,
2513         .ioctl           = n_tty_ioctl,
2514         .set_termios     = n_tty_set_termios,
2515         .poll            = n_tty_poll,
2516         .receive_buf     = n_tty_receive_buf,
2517         .write_wakeup    = n_tty_write_wakeup,
2518         .receive_buf2    = n_tty_receive_buf2,
2519         .lookahead_buf   = n_tty_lookahead_flow_ctrl,
2520 };
2521
2522 /**
2523  *      n_tty_inherit_ops       -       inherit N_TTY methods
2524  *      @ops: struct tty_ldisc_ops where to save N_TTY methods
2525  *
2526  *      Enables a 'subclass' line discipline to 'inherit' N_TTY methods.
2527  */
2528
2529 void n_tty_inherit_ops(struct tty_ldisc_ops *ops)
2530 {
2531         *ops = n_tty_ops;
2532         ops->owner = NULL;
2533 }
2534 EXPORT_SYMBOL_GPL(n_tty_inherit_ops);
2535
2536 void __init n_tty_init(void)
2537 {
2538         tty_register_ldisc(&n_tty_ops);
2539 }