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/bitmap.h>
  32#include <linux/bitops.h>
  33#include <linux/ctype.h>
  34#include <linux/errno.h>
  35#include <linux/export.h>
  36#include <linux/fcntl.h>
  37#include <linux/file.h>
  38#include <linux/jiffies.h>
  39#include <linux/math.h>
  40#include <linux/poll.h>
  41#include <linux/ratelimit.h>
  42#include <linux/sched.h>
  43#include <linux/signal.h>
  44#include <linux/slab.h>
  45#include <linux/string.h>
  46#include <linux/tty.h>
  47#include <linux/types.h>
  48#include <linux/uaccess.h>
  49#include <linux/vmalloc.h>
  50
  51#include "tty.h"
  52
  53/*
  54 * Until this number of characters is queued in the xmit buffer, select will
  55 * return "we have room for writes".
  56 */
  57#define WAKEUP_CHARS 256
  58
  59#define N_TTY_BUF_SIZE 4096
  60
  61/*
  62 * This defines the low- and high-watermarks for throttling and
  63 * unthrottling the TTY driver.  These watermarks are used for
  64 * controlling the space in the read buffer.
  65 */
  66#define TTY_THRESHOLD_THROTTLE		128 /* now based on remaining room */
  67#define TTY_THRESHOLD_UNTHROTTLE	128
  68
  69/*
  70 * Special byte codes used in the echo buffer to represent operations
  71 * or special handling of characters.  Bytes in the echo buffer that
  72 * are not part of such special blocks are treated as normal character
  73 * codes.
  74 */
  75#define ECHO_OP_START 0xff
  76#define ECHO_OP_MOVE_BACK_COL 0x80
  77#define ECHO_OP_SET_CANON_COL 0x81
  78#define ECHO_OP_ERASE_TAB 0x82
  79
  80#define ECHO_COMMIT_WATERMARK	256
  81#define ECHO_BLOCK		256
  82#define ECHO_DISCARD_WATERMARK	N_TTY_BUF_SIZE - (ECHO_BLOCK + 32)
  83
  84struct n_tty_data {
  85	/* producer-published */
  86	size_t read_head;
  87	size_t commit_head;
  88	size_t canon_head;
  89	size_t echo_head;
  90	size_t echo_commit;
  91	size_t echo_mark;
  92	DECLARE_BITMAP(char_map, 256);
  93
  94	/* private to n_tty_receive_overrun (single-threaded) */
  95	unsigned long overrun_time;
  96	unsigned int num_overrun;
  97
  98	/* non-atomic */
  99	bool no_room;
 100
 101	/* must hold exclusive termios_rwsem to reset these */
 102	unsigned char lnext:1, erasing:1, raw:1, real_raw:1, icanon:1;
 103	unsigned char push:1;
 104
 105	/* shared by producer and consumer */
 106	u8 read_buf[N_TTY_BUF_SIZE];
 107	DECLARE_BITMAP(read_flags, N_TTY_BUF_SIZE);
 108	u8 echo_buf[N_TTY_BUF_SIZE];
 109
 110	/* consumer-published */
 111	size_t read_tail;
 112	size_t line_start;
 113
 114	/* # of chars looked ahead (to find software flow control chars) */
 115	size_t lookahead_count;
 116
 117	/* protected by output lock */
 118	unsigned int column;
 119	unsigned int canon_column;
 120	size_t echo_tail;
 121
 122	struct mutex atomic_read_lock;
 123	struct mutex output_lock;
 124};
 125
 126#define MASK(x) ((x) & (N_TTY_BUF_SIZE - 1))
 127
 128static inline size_t read_cnt(struct n_tty_data *ldata)
 129{
 130	return ldata->read_head - ldata->read_tail;
 131}
 132
 133static inline u8 read_buf(struct n_tty_data *ldata, size_t i)
 134{
 135	return ldata->read_buf[MASK(i)];
 136}
 137
 138static inline u8 *read_buf_addr(struct n_tty_data *ldata, size_t i)
 139{
 140	return &ldata->read_buf[MASK(i)];
 141}
 142
 143static inline u8 echo_buf(struct n_tty_data *ldata, size_t i)
 144{
 145	smp_rmb(); /* Matches smp_wmb() in add_echo_byte(). */
 146	return ldata->echo_buf[MASK(i)];
 147}
 148
 149static inline u8 *echo_buf_addr(struct n_tty_data *ldata, size_t i)
 150{
 151	return &ldata->echo_buf[MASK(i)];
 152}
 153
 154/* If we are not echoing the data, perhaps this is a secret so erase it */
 155static void zero_buffer(const struct tty_struct *tty, u8 *buffer, size_t size)
 156{
 157	if (L_ICANON(tty) && !L_ECHO(tty))
 158		memset(buffer, 0, size);
 159}
 160
 161static void tty_copy(const struct tty_struct *tty, void *to, size_t tail,
 162		     size_t n)
 163{
 164	struct n_tty_data *ldata = tty->disc_data;
 165	size_t size = N_TTY_BUF_SIZE - tail;
 166	void *from = read_buf_addr(ldata, tail);
 167
 168	if (n > size) {
 169		tty_audit_add_data(tty, from, size);
 170		memcpy(to, from, size);
 171		zero_buffer(tty, from, size);
 172		to += size;
 173		n -= size;
 174		from = ldata->read_buf;
 175	}
 176
 177	tty_audit_add_data(tty, from, n);
 178	memcpy(to, from, n);
 179	zero_buffer(tty, from, n);
 180}
 181
 182/**
 183 * n_tty_kick_worker - start input worker (if required)
 184 * @tty: terminal
 185 *
 186 * Re-schedules the flip buffer work if it may have stopped.
 187 *
 188 * Locking:
 189 *  * Caller holds exclusive %termios_rwsem, or
 190 *  * n_tty_read()/consumer path:
 191 *	holds non-exclusive %termios_rwsem
 192 */
 193static void n_tty_kick_worker(const struct tty_struct *tty)
 194{
 195	struct n_tty_data *ldata = tty->disc_data;
 196
 197	/* Did the input worker stop? Restart it */
 198	if (unlikely(READ_ONCE(ldata->no_room))) {
 199		WRITE_ONCE(ldata->no_room, 0);
 200
 201		WARN_RATELIMIT(tty->port->itty == NULL,
 202				"scheduling with invalid itty\n");
 203		/* see if ldisc has been killed - if so, this means that
 204		 * even though the ldisc has been halted and ->buf.work
 205		 * cancelled, ->buf.work is about to be rescheduled
 206		 */
 207		WARN_RATELIMIT(test_bit(TTY_LDISC_HALTED, &tty->flags),
 208			       "scheduling buffer work for halted ldisc\n");
 209		tty_buffer_restart_work(tty->port);
 210	}
 211}
 212
 213static ssize_t chars_in_buffer(const struct tty_struct *tty)
 214{
 215	const struct n_tty_data *ldata = tty->disc_data;
 216	size_t head = ldata->icanon ? ldata->canon_head : ldata->commit_head;
 217
 218	return head - ldata->read_tail;
 219}
 220
 221/**
 222 * n_tty_write_wakeup	-	asynchronous I/O notifier
 223 * @tty: tty device
 224 *
 225 * Required for the ptys, serial driver etc. since processes that attach
 226 * themselves to the master and rely on ASYNC IO must be woken up.
 227 */
 228static void n_tty_write_wakeup(struct tty_struct *tty)
 229{
 230	clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 231	kill_fasync(&tty->fasync, SIGIO, POLL_OUT);
 232}
 233
 234static void n_tty_check_throttle(struct tty_struct *tty)
 235{
 236	struct n_tty_data *ldata = tty->disc_data;
 237
 238	/*
 239	 * Check the remaining room for the input canonicalization
 240	 * mode.  We don't want to throttle the driver if we're in
 241	 * canonical mode and don't have a newline yet!
 242	 */
 243	if (ldata->icanon && ldata->canon_head == ldata->read_tail)
 244		return;
 245
 246	do {
 247		tty_set_flow_change(tty, TTY_THROTTLE_SAFE);
 248		if (N_TTY_BUF_SIZE - read_cnt(ldata) >= TTY_THRESHOLD_THROTTLE)
 249			break;
 250	} while (!tty_throttle_safe(tty));
 251
 252	__tty_set_flow_change(tty, 0);
 253}
 254
 255static void n_tty_check_unthrottle(struct tty_struct *tty)
 256{
 257	if (tty->driver->type == TTY_DRIVER_TYPE_PTY) {
 258		if (chars_in_buffer(tty) > TTY_THRESHOLD_UNTHROTTLE)
 259			return;
 260		n_tty_kick_worker(tty);
 261		tty_wakeup(tty->link);
 262		return;
 263	}
 264
 265	/* If there is enough space in the read buffer now, let the
 266	 * low-level driver know. We use chars_in_buffer() to
 267	 * check the buffer, as it now knows about canonical mode.
 268	 * Otherwise, if the driver is throttled and the line is
 269	 * longer than TTY_THRESHOLD_UNTHROTTLE in canonical mode,
 270	 * we won't get any more characters.
 271	 */
 272
 273	do {
 274		tty_set_flow_change(tty, TTY_UNTHROTTLE_SAFE);
 275		if (chars_in_buffer(tty) > TTY_THRESHOLD_UNTHROTTLE)
 276			break;
 277
 278		n_tty_kick_worker(tty);
 279	} while (!tty_unthrottle_safe(tty));
 280
 281	__tty_set_flow_change(tty, 0);
 282}
 283
 284/**
 285 * put_tty_queue		-	add character to tty
 286 * @c: character
 287 * @ldata: n_tty data
 288 *
 289 * Add a character to the tty read_buf queue.
 290 *
 291 * Locking:
 292 *  * n_tty_receive_buf()/producer path:
 293 *	caller holds non-exclusive %termios_rwsem
 294 */
 295static inline void put_tty_queue(u8 c, struct n_tty_data *ldata)
 296{
 297	*read_buf_addr(ldata, ldata->read_head) = c;
 298	ldata->read_head++;
 299}
 300
 301/**
 302 * reset_buffer_flags	-	reset buffer state
 303 * @ldata: line disc data to reset
 304 *
 305 * Reset the read buffer counters and clear the flags. Called from
 306 * n_tty_open() and n_tty_flush_buffer().
 307 *
 308 * Locking:
 309 *  * caller holds exclusive %termios_rwsem, or
 310 *  * (locking is not required)
 311 */
 312static void reset_buffer_flags(struct n_tty_data *ldata)
 313{
 314	ldata->read_head = ldata->canon_head = ldata->read_tail = 0;
 315	ldata->commit_head = 0;
 316	ldata->line_start = 0;
 317
 318	ldata->erasing = 0;
 319	bitmap_zero(ldata->read_flags, N_TTY_BUF_SIZE);
 320	ldata->push = 0;
 321
 322	ldata->lookahead_count = 0;
 323}
 324
 325static void n_tty_packet_mode_flush(struct tty_struct *tty)
 326{
 327	if (tty->link->ctrl.packet) {
 328		scoped_guard(spinlock_irqsave, &tty->ctrl.lock)
 329			tty->ctrl.pktstatus |= TIOCPKT_FLUSHREAD;
 330		wake_up_interruptible(&tty->link->read_wait);
 331	}
 332}
 333
 334/**
 335 * n_tty_flush_buffer	-	clean input queue
 336 * @tty: terminal device
 337 *
 338 * Flush the input buffer. Called when the tty layer wants the buffer flushed
 339 * (eg at hangup) or when the %N_TTY line discipline internally has to clean
 340 * the pending queue (for example some signals).
 341 *
 342 * Holds %termios_rwsem to exclude producer/consumer while buffer indices are
 343 * reset.
 344 *
 345 * Locking: %ctrl.lock, exclusive %termios_rwsem
 346 */
 347static void n_tty_flush_buffer(struct tty_struct *tty)
 348{
 349	guard(rwsem_write)(&tty->termios_rwsem);
 350	reset_buffer_flags(tty->disc_data);
 351	n_tty_kick_worker(tty);
 352
 353	if (tty->link)
 354		n_tty_packet_mode_flush(tty);
 355}
 356
 357/**
 358 * is_utf8_continuation	-	utf8 multibyte check
 359 * @c: byte to check
 360 *
 361 * Returns: true if the utf8 character @c is a multibyte continuation
 362 * character. We use this to correctly compute the on-screen size of the
 363 * character when printing.
 364 */
 365static inline int is_utf8_continuation(u8 c)
 366{
 367	return (c & 0xc0) == 0x80;
 368}
 369
 370/**
 371 * is_continuation	-	multibyte check
 372 * @c: byte to check
 373 * @tty: terminal device
 374 *
 375 * Returns: true if the utf8 character @c is a multibyte continuation character
 376 * and the terminal is in unicode mode.
 377 */
 378static inline int is_continuation(u8 c, const struct tty_struct *tty)
 379{
 380	return I_IUTF8(tty) && is_utf8_continuation(c);
 381}
 382
 383/**
 384 * do_output_char	-	output one character
 385 * @c: character (or partial unicode symbol)
 386 * @tty: terminal device
 387 * @space: space available in tty driver write buffer
 388 *
 389 * This is a helper function that handles one output character (including
 390 * special characters like TAB, CR, LF, etc.), doing OPOST processing and
 391 * putting the results in the tty driver's write buffer.
 392 *
 393 * Note that Linux currently ignores TABDLY, CRDLY, VTDLY, FFDLY and NLDLY.
 394 * They simply aren't relevant in the world today. If you ever need them, add
 395 * them here.
 396 *
 397 * Returns: the number of bytes of buffer space used or -1 if no space left.
 398 *
 399 * Locking: should be called under the %output_lock to protect the column state
 400 * and space left in the buffer.
 401 */
 402static int do_output_char(u8 c, struct tty_struct *tty, int space)
 403{
 404	struct n_tty_data *ldata = tty->disc_data;
 405	int	spaces;
 406
 407	if (!space)
 408		return -1;
 409
 410	switch (c) {
 411	case '\n':
 412		if (O_ONLRET(tty))
 413			ldata->column = 0;
 414		if (O_ONLCR(tty)) {
 415			if (space < 2)
 416				return -1;
 417			ldata->canon_column = ldata->column = 0;
 418			tty->ops->write(tty, "\r\n", 2);
 419			return 2;
 420		}
 421		ldata->canon_column = ldata->column;
 422		break;
 423	case '\r':
 424		if (O_ONOCR(tty) && ldata->column == 0)
 425			return 0;
 426		if (O_OCRNL(tty)) {
 427			c = '\n';
 428			if (O_ONLRET(tty))
 429				ldata->canon_column = ldata->column = 0;
 430			break;
 431		}
 432		ldata->canon_column = ldata->column = 0;
 433		break;
 434	case '\t':
 435		spaces = 8 - (ldata->column & 7);
 436		if (O_TABDLY(tty) == XTABS) {
 437			if (space < spaces)
 438				return -1;
 439			ldata->column += spaces;
 440			tty->ops->write(tty, "        ", spaces);
 441			return spaces;
 442		}
 443		ldata->column += spaces;
 444		break;
 445	case '\b':
 446		if (ldata->column > 0)
 447			ldata->column--;
 448		break;
 449	default:
 450		if (!iscntrl(c)) {
 451			if (O_OLCUC(tty))
 452				c = toupper(c);
 453			if (!is_continuation(c, tty))
 454				ldata->column++;
 455		}
 456		break;
 457	}
 458
 459	tty_put_char(tty, c);
 460	return 1;
 461}
 462
 463/**
 464 * process_output	-	output post processor
 465 * @c: character (or partial unicode symbol)
 466 * @tty: terminal device
 467 *
 468 * Output one character with OPOST processing.
 469 *
 470 * Returns: -1 when the output device is full and the character must be
 471 * retried.
 472 *
 473 * Locking: %output_lock to protect column state and space left (also, this is
 474 *called from n_tty_write() under the tty layer write lock).
 475 */
 476static int process_output(u8 c, struct tty_struct *tty)
 477{
 478	struct n_tty_data *ldata = tty->disc_data;
 479
 480	guard(mutex)(&ldata->output_lock);
 481
 482	if (do_output_char(c, tty, tty_write_room(tty)) < 0)
 483		return -1;
 484
 485	return 0;
 486}
 487
 488/**
 489 * process_output_block	-	block post processor
 490 * @tty: terminal device
 491 * @buf: character buffer
 492 * @nr: number of bytes to output
 493 *
 494 * Output a block of characters with OPOST processing.
 495 *
 496 * This path is used to speed up block console writes, among other things when
 497 * processing blocks of output data. It handles only the simple cases normally
 498 * found and helps to generate blocks of symbols for the console driver and
 499 * thus improve performance.
 500 *
 501 * Returns: the number of characters output.
 502 *
 503 * Locking: %output_lock to protect column state and space left (also, this is
 504 * called from n_tty_write() under the tty layer write lock).
 505 */
 506static ssize_t process_output_block(struct tty_struct *tty,
 507				    const u8 *buf, unsigned int nr)
 508{
 509	struct n_tty_data *ldata = tty->disc_data;
 510	unsigned int space, i;
 511	const u8 *cp;
 512
 513	guard(mutex)(&ldata->output_lock);
 514
 515	space = tty_write_room(tty);
 516	if (space == 0)
 517		return 0;
 518
 519	if (nr > space)
 520		nr = space;
 521
 522	for (i = 0, cp = buf; i < nr; i++, cp++) {
 523		u8 c = *cp;
 524
 525		switch (c) {
 526		case '\n':
 527			if (O_ONLRET(tty))
 528				ldata->column = 0;
 529			if (O_ONLCR(tty))
 530				goto do_write;
 531			ldata->canon_column = ldata->column;
 532			break;
 533		case '\r':
 534			if (O_ONOCR(tty) && ldata->column == 0)
 535				goto do_write;
 536			if (O_OCRNL(tty))
 537				goto do_write;
 538			ldata->canon_column = ldata->column = 0;
 539			break;
 540		case '\t':
 541			goto do_write;
 542		case '\b':
 543			if (ldata->column > 0)
 544				ldata->column--;
 545			break;
 546		default:
 547			if (!iscntrl(c)) {
 548				if (O_OLCUC(tty))
 549					goto do_write;
 550				if (!is_continuation(c, tty))
 551					ldata->column++;
 552			}
 553			break;
 554		}
 555	}
 556do_write:
 557	return tty->ops->write(tty, buf, i);
 558}
 559
 560static int n_tty_process_echo_ops(struct tty_struct *tty, size_t *tail,
 561				  int space)
 562{
 563	struct n_tty_data *ldata = tty->disc_data;
 564	u8 op;
 565
 566	/*
 567	 * Since add_echo_byte() is called without holding output_lock, we
 568	 * might see only portion of multi-byte operation.
 569	 */
 570	if (MASK(ldata->echo_commit) == MASK(*tail + 1))
 571		return -ENODATA;
 572
 573	/*
 574	 * If the buffer byte is the start of a multi-byte operation, get the
 575	 * next byte, which is either the op code or a control character value.
 576	 */
 577	op = echo_buf(ldata, *tail + 1);
 578
 579	switch (op) {
 580	case ECHO_OP_ERASE_TAB: {
 581		unsigned int num_chars, num_bs;
 582
 583		if (MASK(ldata->echo_commit) == MASK(*tail + 2))
 584			return -ENODATA;
 585
 586		num_chars = echo_buf(ldata, *tail + 2);
 587
 588		/*
 589		 * Determine how many columns to go back in order to erase the
 590		 * tab. This depends on the number of columns used by other
 591		 * characters within the tab area. If this (modulo 8) count is
 592		 * from the start of input rather than from a previous tab, we
 593		 * offset by canon column. Otherwise, tab spacing is normal.
 594		 */
 595		if (!(num_chars & 0x80))
 596			num_chars += ldata->canon_column;
 597		num_bs = 8 - (num_chars & 7);
 598
 599		if (num_bs > space)
 600			return -ENOSPC;
 601
 602		space -= num_bs;
 603		while (num_bs--) {
 604			tty_put_char(tty, '\b');
 605			if (ldata->column > 0)
 606				ldata->column--;
 607		}
 608		*tail += 3;
 609		break;
 610	}
 611	case ECHO_OP_SET_CANON_COL:
 612		ldata->canon_column = ldata->column;
 613		*tail += 2;
 614		break;
 615
 616	case ECHO_OP_MOVE_BACK_COL:
 617		if (ldata->column > 0)
 618			ldata->column--;
 619		*tail += 2;
 620		break;
 621
 622	case ECHO_OP_START:
 623		/* This is an escaped echo op start code */
 624		if (!space)
 625			return -ENOSPC;
 626
 627		tty_put_char(tty, ECHO_OP_START);
 628		ldata->column++;
 629		space--;
 630		*tail += 2;
 631		break;
 632
 633	default:
 634		/*
 635		 * If the op is not a special byte code, it is a ctrl char
 636		 * tagged to be echoed as "^X" (where X is the letter
 637		 * representing the control char). Note that we must ensure
 638		 * there is enough space for the whole ctrl pair.
 639		 */
 640		if (space < 2)
 641			return -ENOSPC;
 642
 643		tty_put_char(tty, '^');
 644		tty_put_char(tty, op ^ 0100);
 645		ldata->column += 2;
 646		space -= 2;
 647		*tail += 2;
 648		break;
 649	}
 650
 651	return space;
 652}
 653
 654/**
 655 * __process_echoes	-	write pending echo characters
 656 * @tty: terminal device
 657 *
 658 * Write previously buffered echo (and other ldisc-generated) characters to the
 659 * tty.
 660 *
 661 * Characters generated by the ldisc (including echoes) need to be buffered
 662 * because the driver's write buffer can fill during heavy program output.
 663 * Echoing straight to the driver will often fail under these conditions,
 664 * causing lost characters and resulting mismatches of ldisc state information.
 665 *
 666 * Since the ldisc state must represent the characters actually sent to the
 667 * driver at the time of the write, operations like certain changes in column
 668 * state are also saved in the buffer and executed here.
 669 *
 670 * A circular fifo buffer is used so that the most recent characters are
 671 * prioritized. Also, when control characters are echoed with a prefixed "^",
 672 * the pair is treated atomically and thus not separated.
 673 *
 674 * Locking: callers must hold %output_lock.
 675 */
 676static size_t __process_echoes(struct tty_struct *tty)
 677{
 678	struct n_tty_data *ldata = tty->disc_data;
 679	unsigned int space, old_space;
 680	size_t tail;
 681	u8 c;
 682
 683	old_space = space = tty_write_room(tty);
 684
 685	tail = ldata->echo_tail;
 686	while (MASK(ldata->echo_commit) != MASK(tail)) {
 687		c = echo_buf(ldata, tail);
 688		if (c == ECHO_OP_START) {
 689			int ret = n_tty_process_echo_ops(tty, &tail, space);
 690			if (ret == -ENODATA)
 691				goto not_yet_stored;
 692			if (ret < 0)
 693				break;
 694			space = ret;
 695		} else {
 696			if (O_OPOST(tty)) {
 697				int retval = do_output_char(c, tty, space);
 698				if (retval < 0)
 699					break;
 700				space -= retval;
 701			} else {
 702				if (!space)
 703					break;
 704				tty_put_char(tty, c);
 705				space -= 1;
 706			}
 707			tail += 1;
 708		}
 709	}
 710
 711	/* If the echo buffer is nearly full (so that the possibility exists
 712	 * of echo overrun before the next commit), then discard enough
 713	 * data at the tail to prevent a subsequent overrun */
 714	while (ldata->echo_commit > tail &&
 715	       ldata->echo_commit - tail >= ECHO_DISCARD_WATERMARK) {
 716		if (echo_buf(ldata, tail) == ECHO_OP_START) {
 717			if (echo_buf(ldata, tail + 1) == ECHO_OP_ERASE_TAB)
 718				tail += 3;
 719			else
 720				tail += 2;
 721		} else
 722			tail++;
 723	}
 724
 725 not_yet_stored:
 726	ldata->echo_tail = tail;
 727	return old_space - space;
 728}
 729
 730static void commit_echoes(struct tty_struct *tty)
 731{
 732	struct n_tty_data *ldata = tty->disc_data;
 733	size_t nr, old, echoed;
 734	size_t head;
 735
 736	scoped_guard(mutex, &ldata->output_lock) {
 737		head = ldata->echo_head;
 738		ldata->echo_mark = head;
 739		old = ldata->echo_commit - ldata->echo_tail;
 740
 741		/*
 742		 * Process committed echoes if the accumulated # of bytes is over the threshold
 743		 * (and try again each time another block is accumulated)
 744		 */
 745		nr = head - ldata->echo_tail;
 746		if (nr < ECHO_COMMIT_WATERMARK || (nr % ECHO_BLOCK > old % ECHO_BLOCK))
 747			return;
 748
 749		ldata->echo_commit = head;
 750		echoed = __process_echoes(tty);
 751	}
 752
 753	if (echoed && tty->ops->flush_chars)
 754		tty->ops->flush_chars(tty);
 755}
 756
 757static void process_echoes(struct tty_struct *tty)
 758{
 759	struct n_tty_data *ldata = tty->disc_data;
 760	size_t echoed;
 761
 762	if (ldata->echo_mark == ldata->echo_tail)
 763		return;
 764
 765	scoped_guard(mutex, &ldata->output_lock) {
 766		ldata->echo_commit = ldata->echo_mark;
 767		echoed = __process_echoes(tty);
 768	}
 769
 770	if (echoed && tty->ops->flush_chars)
 771		tty->ops->flush_chars(tty);
 772}
 773
 774/* NB: echo_mark and echo_head should be equivalent here */
 775static void flush_echoes(struct tty_struct *tty)
 776{
 777	struct n_tty_data *ldata = tty->disc_data;
 778
 779	if ((!L_ECHO(tty) && !L_ECHONL(tty)) ||
 780	    ldata->echo_commit == ldata->echo_head)
 781		return;
 782
 783	guard(mutex)(&ldata->output_lock);
 784	ldata->echo_commit = ldata->echo_head;
 785	__process_echoes(tty);
 786}
 787
 788/**
 789 * add_echo_byte	-	add a byte to the echo buffer
 790 * @c: unicode byte to echo
 791 * @ldata: n_tty data
 792 *
 793 * Add a character or operation byte to the echo buffer.
 794 */
 795static inline void add_echo_byte(u8 c, struct n_tty_data *ldata)
 796{
 797	*echo_buf_addr(ldata, ldata->echo_head) = c;
 798	smp_wmb(); /* Matches smp_rmb() in echo_buf(). */
 799	ldata->echo_head++;
 800}
 801
 802/**
 803 * echo_move_back_col	-	add operation to move back a column
 804 * @ldata: n_tty data
 805 *
 806 * Add an operation to the echo buffer to move back one column.
 807 */
 808static void echo_move_back_col(struct n_tty_data *ldata)
 809{
 810	add_echo_byte(ECHO_OP_START, ldata);
 811	add_echo_byte(ECHO_OP_MOVE_BACK_COL, ldata);
 812}
 813
 814/**
 815 * echo_set_canon_col	-	add operation to set the canon column
 816 * @ldata: n_tty data
 817 *
 818 * Add an operation to the echo buffer to set the canon column to the current
 819 * column.
 820 */
 821static void echo_set_canon_col(struct n_tty_data *ldata)
 822{
 823	add_echo_byte(ECHO_OP_START, ldata);
 824	add_echo_byte(ECHO_OP_SET_CANON_COL, ldata);
 825}
 826
 827/**
 828 * echo_erase_tab	-	add operation to erase a tab
 829 * @num_chars: number of character columns already used
 830 * @after_tab: true if num_chars starts after a previous tab
 831 * @ldata: n_tty data
 832 *
 833 * Add an operation to the echo buffer to erase a tab.
 834 *
 835 * Called by the eraser function, which knows how many character columns have
 836 * been used since either a previous tab or the start of input. This
 837 * information will be used later, along with canon column (if applicable), to
 838 * go back the correct number of columns.
 839 */
 840static void echo_erase_tab(unsigned int num_chars, int after_tab,
 841			   struct n_tty_data *ldata)
 842{
 843	add_echo_byte(ECHO_OP_START, ldata);
 844	add_echo_byte(ECHO_OP_ERASE_TAB, ldata);
 845
 846	/* We only need to know this modulo 8 (tab spacing) */
 847	num_chars &= 7;
 848
 849	/* Set the high bit as a flag if num_chars is after a previous tab */
 850	if (after_tab)
 851		num_chars |= 0x80;
 852
 853	add_echo_byte(num_chars, ldata);
 854}
 855
 856/**
 857 * echo_char_raw	-	echo a character raw
 858 * @c: unicode byte to echo
 859 * @ldata: line disc data
 860 *
 861 * Echo user input back onto the screen. This must be called only when
 862 * L_ECHO(tty) is true. Called from the &tty_driver.receive_buf() path.
 863 *
 864 * This variant does not treat control characters specially.
 865 */
 866static void echo_char_raw(u8 c, struct n_tty_data *ldata)
 867{
 868	if (c == ECHO_OP_START) {
 869		add_echo_byte(ECHO_OP_START, ldata);
 870		add_echo_byte(ECHO_OP_START, ldata);
 871	} else {
 872		add_echo_byte(c, ldata);
 873	}
 874}
 875
 876/**
 877 * echo_char		-	echo a character
 878 * @c: unicode byte to echo
 879 * @tty: terminal device
 880 *
 881 * Echo user input back onto the screen. This must be called only when
 882 * L_ECHO(tty) is true. Called from the &tty_driver.receive_buf() path.
 883 *
 884 * This variant tags control characters to be echoed as "^X" (where X is the
 885 * letter representing the control char).
 886 */
 887static void echo_char(u8 c, const struct tty_struct *tty)
 888{
 889	struct n_tty_data *ldata = tty->disc_data;
 890
 891	if (c == ECHO_OP_START) {
 892		add_echo_byte(ECHO_OP_START, ldata);
 893		add_echo_byte(ECHO_OP_START, ldata);
 894	} else {
 895		if (L_ECHOCTL(tty) && iscntrl(c) && c != '\t')
 896			add_echo_byte(ECHO_OP_START, ldata);
 897		add_echo_byte(c, ldata);
 898	}
 899}
 900
 901/**
 902 * finish_erasing	-	complete erase
 903 * @ldata: n_tty data
 904 */
 905static inline void finish_erasing(struct n_tty_data *ldata)
 906{
 907	if (ldata->erasing) {
 908		echo_char_raw('/', ldata);
 909		ldata->erasing = 0;
 910	}
 911}
 912
 913/**
 914 * eraser		-	handle erase function
 915 * @c: character input
 916 * @tty: terminal device
 917 *
 918 * Perform erase and necessary output when an erase character is present in the
 919 * stream from the driver layer. Handles the complexities of UTF-8 multibyte
 920 * symbols.
 921 *
 922 * Locking: n_tty_receive_buf()/producer path:
 923 *	caller holds non-exclusive %termios_rwsem
 924 */
 925static void eraser(u8 c, const struct tty_struct *tty)
 926{
 927	struct n_tty_data *ldata = tty->disc_data;
 928	enum { ERASE, WERASE, KILL } kill_type;
 929	size_t head;
 930	size_t cnt;
 931	int seen_alnums;
 932
 933	if (ldata->read_head == ldata->canon_head) {
 934		/* process_output('\a', tty); */ /* what do you think? */
 935		return;
 936	}
 937	if (c == ERASE_CHAR(tty))
 938		kill_type = ERASE;
 939	else if (c == WERASE_CHAR(tty))
 940		kill_type = WERASE;
 941	else {
 942		if (!L_ECHO(tty)) {
 943			ldata->read_head = ldata->canon_head;
 944			return;
 945		}
 946		if (!L_ECHOK(tty) || !L_ECHOKE(tty) || !L_ECHOE(tty)) {
 947			ldata->read_head = ldata->canon_head;
 948			finish_erasing(ldata);
 949			echo_char(KILL_CHAR(tty), tty);
 950			/* Add a newline if ECHOK is on and ECHOKE is off. */
 951			if (L_ECHOK(tty))
 952				echo_char_raw('\n', ldata);
 953			return;
 954		}
 955		kill_type = KILL;
 956	}
 957
 958	seen_alnums = 0;
 959	while (MASK(ldata->read_head) != MASK(ldata->canon_head)) {
 960		head = ldata->read_head;
 961
 962		/* erase a single possibly multibyte character */
 963		do {
 964			head--;
 965			c = read_buf(ldata, head);
 966		} while (is_continuation(c, tty) &&
 967			 MASK(head) != MASK(ldata->canon_head));
 968
 969		/* do not partially erase */
 970		if (is_continuation(c, tty))
 971			break;
 972
 973		if (kill_type == WERASE) {
 974			/* Equivalent to BSD's ALTWERASE. */
 975			if (isalnum(c) || c == '_')
 976				seen_alnums++;
 977			else if (seen_alnums)
 978				break;
 979		}
 980		cnt = ldata->read_head - head;
 981		ldata->read_head = head;
 982		if (L_ECHO(tty)) {
 983			if (L_ECHOPRT(tty)) {
 984				if (!ldata->erasing) {
 985					echo_char_raw('\\', ldata);
 986					ldata->erasing = 1;
 987				}
 988				/* if cnt > 1, output a multi-byte character */
 989				echo_char(c, tty);
 990				while (--cnt > 0) {
 991					head++;
 992					echo_char_raw(read_buf(ldata, head), ldata);
 993					echo_move_back_col(ldata);
 994				}
 995			} else if (kill_type == ERASE && !L_ECHOE(tty)) {
 996				echo_char(ERASE_CHAR(tty), tty);
 997			} else if (c == '\t') {
 998				unsigned int num_chars = 0;
 999				int after_tab = 0;
1000				size_t tail = ldata->read_head;
1001
1002				/*
1003				 * Count the columns used for characters
1004				 * since the start of input or after a
1005				 * previous tab.
1006				 * This info is used to go back the correct
1007				 * number of columns.
1008				 */
1009				while (MASK(tail) != MASK(ldata->canon_head)) {
1010					tail--;
1011					c = read_buf(ldata, tail);
1012					if (c == '\t') {
1013						after_tab = 1;
1014						break;
1015					} else if (iscntrl(c)) {
1016						if (L_ECHOCTL(tty))
1017							num_chars += 2;
1018					} else if (!is_continuation(c, tty)) {
1019						num_chars++;
1020					}
1021				}
1022				echo_erase_tab(num_chars, after_tab, ldata);
1023			} else {
1024				if (iscntrl(c) && L_ECHOCTL(tty)) {
1025					echo_char_raw('\b', ldata);
1026					echo_char_raw(' ', ldata);
1027					echo_char_raw('\b', ldata);
1028				}
1029				if (!iscntrl(c) || L_ECHOCTL(tty)) {
1030					echo_char_raw('\b', ldata);
1031					echo_char_raw(' ', ldata);
1032					echo_char_raw('\b', ldata);
1033				}
1034			}
1035		}
1036		if (kill_type == ERASE)
1037			break;
1038	}
1039	if (ldata->read_head == ldata->canon_head && L_ECHO(tty))
1040		finish_erasing(ldata);
1041}
1042
1043
1044static void __isig(int sig, struct tty_struct *tty)
1045{
1046	struct pid *tty_pgrp = tty_get_pgrp(tty);
1047	if (tty_pgrp) {
1048		kill_pgrp(tty_pgrp, sig, 1);
1049		put_pid(tty_pgrp);
1050	}
1051}
1052
1053/**
1054 * isig			-	handle the ISIG optio
1055 * @sig: signal
1056 * @tty: terminal
1057 *
1058 * Called when a signal is being sent due to terminal input. Called from the
1059 * &tty_driver.receive_buf() path, so serialized.
1060 *
1061 * Performs input and output flush if !NOFLSH. In this context, the echo
1062 * buffer is 'output'. The signal is processed first to alert any current
1063 * readers or writers to discontinue and exit their i/o loops.
1064 *
1065 * Locking: %ctrl.lock
1066 */
1067static void isig(int sig, struct tty_struct *tty)
1068{
1069	struct n_tty_data *ldata = tty->disc_data;
1070
1071	if (L_NOFLSH(tty)) {
1072		/* signal only */
1073		__isig(sig, tty);
1074		return;
1075	}
1076
1077	/* signal and flush */
1078	up_read(&tty->termios_rwsem);
1079	scoped_guard(rwsem_write, &tty->termios_rwsem) {
1080		__isig(sig, tty);
1081
1082		/* clear echo buffer */
1083		scoped_guard(mutex, &ldata->output_lock) {
1084			ldata->echo_head = ldata->echo_tail = 0;
1085			ldata->echo_mark = ldata->echo_commit = 0;
1086		}
1087
1088		/* clear output buffer */
1089		tty_driver_flush_buffer(tty);
1090
1091		/* clear input buffer */
1092		reset_buffer_flags(tty->disc_data);
1093
1094		/* notify pty master of flush */
1095		if (tty->link)
1096			n_tty_packet_mode_flush(tty);
1097	}
1098	down_read(&tty->termios_rwsem);
1099}
1100
1101/**
1102 * n_tty_receive_break	-	handle break
1103 * @tty: terminal
1104 *
1105 * An RS232 break event has been hit in the incoming bitstream. This can cause
1106 * a variety of events depending upon the termios settings.
1107 *
1108 * Locking: n_tty_receive_buf()/producer path:
1109 *	caller holds non-exclusive termios_rwsem
1110 *
1111 * Note: may get exclusive %termios_rwsem if flushing input buffer
1112 */
1113static void n_tty_receive_break(struct tty_struct *tty)
1114{
1115	struct n_tty_data *ldata = tty->disc_data;
1116
1117	if (I_IGNBRK(tty))
1118		return;
1119	if (I_BRKINT(tty)) {
1120		isig(SIGINT, tty);
1121		return;
1122	}
1123	if (I_PARMRK(tty)) {
1124		put_tty_queue('\377', ldata);
1125		put_tty_queue('\0', ldata);
1126	}
1127	put_tty_queue('\0', ldata);
1128}
1129
1130/**
1131 * n_tty_receive_overrun	-	handle overrun reporting
1132 * @tty: terminal
1133 *
1134 * Data arrived faster than we could process it. While the tty driver has
1135 * flagged this the bits that were missed are gone forever.
1136 *
1137 * Called from the receive_buf path so single threaded. Does not need locking
1138 * as num_overrun and overrun_time are function private.
1139 */
1140static void n_tty_receive_overrun(const struct tty_struct *tty)
1141{
1142	struct n_tty_data *ldata = tty->disc_data;
1143
1144	ldata->num_overrun++;
1145	if (time_is_before_jiffies(ldata->overrun_time + HZ)) {
1146		tty_warn(tty, "%u input overrun(s)\n", ldata->num_overrun);
1147		ldata->overrun_time = jiffies;
1148		ldata->num_overrun = 0;
1149	}
1150}
1151
1152/**
1153 * n_tty_receive_parity_error	-	error notifier
1154 * @tty: terminal device
1155 * @c: character
1156 *
1157 * Process a parity error and queue the right data to indicate the error case
1158 * if necessary.
1159 *
1160 * Locking: n_tty_receive_buf()/producer path:
1161 * 	caller holds non-exclusive %termios_rwsem
1162 */
1163static void n_tty_receive_parity_error(const struct tty_struct *tty,
1164				       u8 c)
1165{
1166	struct n_tty_data *ldata = tty->disc_data;
1167
1168	if (I_INPCK(tty)) {
1169		if (I_IGNPAR(tty))
1170			return;
1171		if (I_PARMRK(tty)) {
1172			put_tty_queue('\377', ldata);
1173			put_tty_queue('\0', ldata);
1174			put_tty_queue(c, ldata);
1175		} else
1176			put_tty_queue('\0', ldata);
1177	} else
1178		put_tty_queue(c, ldata);
1179}
1180
1181static void
1182n_tty_receive_signal_char(struct tty_struct *tty, int signal, u8 c)
1183{
1184	isig(signal, tty);
1185	if (I_IXON(tty))
1186		start_tty(tty);
1187	if (L_ECHO(tty)) {
1188		echo_char(c, tty);
1189		commit_echoes(tty);
1190	} else
1191		process_echoes(tty);
1192}
1193
1194static bool n_tty_is_char_flow_ctrl(struct tty_struct *tty, u8 c)
1195{
1196	return c == START_CHAR(tty) || c == STOP_CHAR(tty);
1197}
1198
1199/**
1200 * n_tty_receive_char_flow_ctrl - receive flow control chars
1201 * @tty: terminal device
1202 * @c: character
1203 * @lookahead_done: lookahead has processed this character already
1204 *
1205 * Receive and process flow control character actions.
1206 *
1207 * In case lookahead for flow control chars already handled the character in
1208 * advance to the normal receive, the actions are skipped during normal
1209 * receive.
1210 *
1211 * Returns true if @c is consumed as flow-control character, the character
1212 * must not be treated as normal character.
1213 */
1214static bool n_tty_receive_char_flow_ctrl(struct tty_struct *tty, u8 c,
1215					 bool lookahead_done)
1216{
1217	if (!n_tty_is_char_flow_ctrl(tty, c))
1218		return false;
1219
1220	if (lookahead_done)
1221		return true;
1222
1223	if (c == START_CHAR(tty)) {
1224		start_tty(tty);
1225		process_echoes(tty);
1226		return true;
1227	}
1228
1229	/* STOP_CHAR */
1230	stop_tty(tty);
1231	return true;
1232}
1233
1234static void n_tty_receive_handle_newline(struct tty_struct *tty, u8 c)
1235{
1236	struct n_tty_data *ldata = tty->disc_data;
1237
1238	set_bit(MASK(ldata->read_head), ldata->read_flags);
1239	put_tty_queue(c, ldata);
1240	smp_store_release(&ldata->canon_head, ldata->read_head);
1241	kill_fasync(&tty->fasync, SIGIO, POLL_IN);
1242	wake_up_interruptible_poll(&tty->read_wait, EPOLLIN | EPOLLRDNORM);
1243}
1244
1245static bool n_tty_receive_char_canon(struct tty_struct *tty, u8 c)
1246{
1247	struct n_tty_data *ldata = tty->disc_data;
1248
1249	if (c == ERASE_CHAR(tty) || c == KILL_CHAR(tty) ||
1250	    (c == WERASE_CHAR(tty) && L_IEXTEN(tty))) {
1251		eraser(c, tty);
1252		commit_echoes(tty);
1253
1254		return true;
1255	}
1256
1257	if (c == LNEXT_CHAR(tty) && L_IEXTEN(tty)) {
1258		ldata->lnext = 1;
1259		if (L_ECHO(tty)) {
1260			finish_erasing(ldata);
1261			if (L_ECHOCTL(tty)) {
1262				echo_char_raw('^', ldata);
1263				echo_char_raw('\b', ldata);
1264				commit_echoes(tty);
1265			}
1266		}
1267
1268		return true;
1269	}
1270
1271	if (c == REPRINT_CHAR(tty) && L_ECHO(tty) && L_IEXTEN(tty)) {
1272		size_t tail = ldata->canon_head;
1273
1274		finish_erasing(ldata);
1275		echo_char(c, tty);
1276		echo_char_raw('\n', ldata);
1277		while (MASK(tail) != MASK(ldata->read_head)) {
1278			echo_char(read_buf(ldata, tail), tty);
1279			tail++;
1280		}
1281		commit_echoes(tty);
1282
1283		return true;
1284	}
1285
1286	if (c == '\n') {
1287		if (L_ECHO(tty) || L_ECHONL(tty)) {
1288			echo_char_raw('\n', ldata);
1289			commit_echoes(tty);
1290		}
1291		n_tty_receive_handle_newline(tty, c);
1292
1293		return true;
1294	}
1295
1296	if (c == EOF_CHAR(tty)) {
1297		c = __DISABLED_CHAR;
1298		n_tty_receive_handle_newline(tty, c);
1299
1300		return true;
1301	}
1302
1303	if ((c == EOL_CHAR(tty)) ||
1304	    (c == EOL2_CHAR(tty) && L_IEXTEN(tty))) {
1305		/*
1306		 * XXX are EOL_CHAR and EOL2_CHAR echoed?!?
1307		 */
1308		if (L_ECHO(tty)) {
1309			/* Record the column of first canon char. */
1310			if (ldata->canon_head == ldata->read_head)
1311				echo_set_canon_col(ldata);
1312			echo_char(c, tty);
1313			commit_echoes(tty);
1314		}
1315		/*
1316		 * XXX does PARMRK doubling happen for
1317		 * EOL_CHAR and EOL2_CHAR?
1318		 */
1319		if (c == '\377' && I_PARMRK(tty))
1320			put_tty_queue(c, ldata);
1321
1322		n_tty_receive_handle_newline(tty, c);
1323
1324		return true;
1325	}
1326
1327	return false;
1328}
1329
1330static void n_tty_receive_char_special(struct tty_struct *tty, u8 c,
1331				       bool lookahead_done)
1332{
1333	struct n_tty_data *ldata = tty->disc_data;
1334
1335	if (I_IXON(tty) && n_tty_receive_char_flow_ctrl(tty, c, lookahead_done))
1336		return;
1337
1338	if (L_ISIG(tty)) {
1339		if (c == INTR_CHAR(tty)) {
1340			n_tty_receive_signal_char(tty, SIGINT, c);
1341			return;
1342		} else if (c == QUIT_CHAR(tty)) {
1343			n_tty_receive_signal_char(tty, SIGQUIT, c);
1344			return;
1345		} else if (c == SUSP_CHAR(tty)) {
1346			n_tty_receive_signal_char(tty, SIGTSTP, c);
1347			return;
1348		}
1349	}
1350
1351	if (tty->flow.stopped && !tty->flow.tco_stopped && I_IXON(tty) && I_IXANY(tty)) {
1352		start_tty(tty);
1353		process_echoes(tty);
1354	}
1355
1356	if (c == '\r') {
1357		if (I_IGNCR(tty))
1358			return;
1359		if (I_ICRNL(tty))
1360			c = '\n';
1361	} else if (c == '\n' && I_INLCR(tty))
1362		c = '\r';
1363
1364	if (ldata->icanon && n_tty_receive_char_canon(tty, c))
1365		return;
1366
1367	if (L_ECHO(tty)) {
1368		finish_erasing(ldata);
1369		if (c == '\n')
1370			echo_char_raw('\n', ldata);
1371		else {
1372			/* Record the column of first canon char. */
1373			if (ldata->canon_head == ldata->read_head)
1374				echo_set_canon_col(ldata);
1375			echo_char(c, tty);
1376		}
1377		commit_echoes(tty);
1378	}
1379
1380	/* PARMRK doubling check */
1381	if (c == '\377' && I_PARMRK(tty))
1382		put_tty_queue(c, ldata);
1383
1384	put_tty_queue(c, ldata);
1385}
1386
1387/**
1388 * n_tty_receive_char	-	perform processing
1389 * @tty: terminal device
1390 * @c: character
1391 *
1392 * Process an individual character of input received from the driver.  This is
1393 * serialized with respect to itself by the rules for the driver above.
1394 *
1395 * Locking: n_tty_receive_buf()/producer path:
1396 *	caller holds non-exclusive %termios_rwsem
1397 *	publishes canon_head if canonical mode is active
1398 */
1399static void n_tty_receive_char(struct tty_struct *tty, u8 c)
1400{
1401	struct n_tty_data *ldata = tty->disc_data;
1402
1403	if (tty->flow.stopped && !tty->flow.tco_stopped && I_IXON(tty) && I_IXANY(tty)) {
1404		start_tty(tty);
1405		process_echoes(tty);
1406	}
1407	if (L_ECHO(tty)) {
1408		finish_erasing(ldata);
1409		/* Record the column of first canon char. */
1410		if (ldata->canon_head == ldata->read_head)
1411			echo_set_canon_col(ldata);
1412		echo_char(c, tty);
1413		commit_echoes(tty);
1414	}
1415	/* PARMRK doubling check */
1416	if (c == '\377' && I_PARMRK(tty))
1417		put_tty_queue(c, ldata);
1418	put_tty_queue(c, ldata);
1419}
1420
1421static void n_tty_receive_char_closing(struct tty_struct *tty, u8 c,
1422				       bool lookahead_done)
1423{
1424	if (I_ISTRIP(tty))
1425		c &= 0x7f;
1426	if (I_IUCLC(tty) && L_IEXTEN(tty))
1427		c = tolower(c);
1428
1429	if (I_IXON(tty)) {
1430		if (!n_tty_receive_char_flow_ctrl(tty, c, lookahead_done) &&
1431		    tty->flow.stopped && !tty->flow.tco_stopped && I_IXANY(tty) &&
1432		    c != INTR_CHAR(tty) && c != QUIT_CHAR(tty) &&
1433		    c != SUSP_CHAR(tty)) {
1434			start_tty(tty);
1435			process_echoes(tty);
1436		}
1437	}
1438}
1439
1440static void
1441n_tty_receive_char_flagged(struct tty_struct *tty, u8 c, u8 flag)
1442{
1443	switch (flag) {
1444	case TTY_BREAK:
1445		n_tty_receive_break(tty);
1446		break;
1447	case TTY_PARITY:
1448	case TTY_FRAME:
1449		n_tty_receive_parity_error(tty, c);
1450		break;
1451	case TTY_OVERRUN:
1452		n_tty_receive_overrun(tty);
1453		break;
1454	default:
1455		tty_err(tty, "unknown flag %u\n", flag);
1456		break;
1457	}
1458}
1459
1460static void
1461n_tty_receive_char_lnext(struct tty_struct *tty, u8 c, u8 flag)
1462{
1463	struct n_tty_data *ldata = tty->disc_data;
1464
1465	ldata->lnext = 0;
1466	if (likely(flag == TTY_NORMAL)) {
1467		if (I_ISTRIP(tty))
1468			c &= 0x7f;
1469		if (I_IUCLC(tty) && L_IEXTEN(tty))
1470			c = tolower(c);
1471		n_tty_receive_char(tty, c);
1472	} else
1473		n_tty_receive_char_flagged(tty, c, flag);
1474}
1475
1476/* Caller must ensure count > 0 */
1477static void n_tty_lookahead_flow_ctrl(struct tty_struct *tty, const u8 *cp,
1478				      const u8 *fp, size_t count)
1479{
1480	struct n_tty_data *ldata = tty->disc_data;
1481	u8 flag = TTY_NORMAL;
1482
1483	ldata->lookahead_count += count;
1484
1485	if (!I_IXON(tty))
1486		return;
1487
1488	while (count--) {
1489		if (fp)
1490			flag = *fp++;
1491		if (likely(flag == TTY_NORMAL))
1492			n_tty_receive_char_flow_ctrl(tty, *cp, false);
1493		cp++;
1494	}
1495}
1496
1497static void
1498n_tty_receive_buf_real_raw(const struct tty_struct *tty, const u8 *cp,
1499			   size_t count)
1500{
1501	struct n_tty_data *ldata = tty->disc_data;
1502
1503	/* handle buffer wrap-around by a loop */
1504	for (unsigned int i = 0; i < 2; i++) {
1505		size_t head = MASK(ldata->read_head);
1506		size_t n = min(count, N_TTY_BUF_SIZE - head);
1507
1508		memcpy(read_buf_addr(ldata, head), cp, n);
1509
1510		ldata->read_head += n;
1511		cp += n;
1512		count -= n;
1513	}
1514}
1515
1516static void
1517n_tty_receive_buf_raw(struct tty_struct *tty, const u8 *cp, const u8 *fp,
1518		      size_t count)
1519{
1520	struct n_tty_data *ldata = tty->disc_data;
1521	u8 flag = TTY_NORMAL;
1522
1523	while (count--) {
1524		if (fp)
1525			flag = *fp++;
1526		if (likely(flag == TTY_NORMAL))
1527			put_tty_queue(*cp++, ldata);
1528		else
1529			n_tty_receive_char_flagged(tty, *cp++, flag);
1530	}
1531}
1532
1533static void
1534n_tty_receive_buf_closing(struct tty_struct *tty, const u8 *cp, const u8 *fp,
1535			  size_t count, bool lookahead_done)
1536{
1537	u8 flag = TTY_NORMAL;
1538
1539	while (count--) {
1540		if (fp)
1541			flag = *fp++;
1542		if (likely(flag == TTY_NORMAL))
1543			n_tty_receive_char_closing(tty, *cp++, lookahead_done);
1544	}
1545}
1546
1547static void n_tty_receive_buf_standard(struct tty_struct *tty, const u8 *cp,
1548				       const u8 *fp, size_t count,
1549				       bool lookahead_done)
1550{
1551	struct n_tty_data *ldata = tty->disc_data;
1552	u8 flag = TTY_NORMAL;
1553
1554	while (count--) {
1555		u8 c = *cp++;
1556
1557		if (fp)
1558			flag = *fp++;
1559
1560		if (ldata->lnext) {
1561			n_tty_receive_char_lnext(tty, c, flag);
1562			continue;
1563		}
1564
1565		if (unlikely(flag != TTY_NORMAL)) {
1566			n_tty_receive_char_flagged(tty, c, flag);
1567			continue;
1568		}
1569
1570		if (I_ISTRIP(tty))
1571			c &= 0x7f;
1572		if (I_IUCLC(tty) && L_IEXTEN(tty))
1573			c = tolower(c);
1574		if (L_EXTPROC(tty)) {
1575			put_tty_queue(c, ldata);
1576			continue;
1577		}
1578
1579		if (test_bit(c, ldata->char_map))
1580			n_tty_receive_char_special(tty, c, lookahead_done);
1581		else
1582			n_tty_receive_char(tty, c);
1583	}
1584}
1585
1586static void __receive_buf(struct tty_struct *tty, const u8 *cp, const u8 *fp,
1587			  size_t count)
1588{
1589	struct n_tty_data *ldata = tty->disc_data;
1590	bool preops = I_ISTRIP(tty) || (I_IUCLC(tty) && L_IEXTEN(tty));
1591	size_t la_count = min(ldata->lookahead_count, count);
1592
1593	if (ldata->real_raw)
1594		n_tty_receive_buf_real_raw(tty, cp, count);
1595	else if (ldata->raw || (L_EXTPROC(tty) && !preops))
1596		n_tty_receive_buf_raw(tty, cp, fp, count);
1597	else if (tty->closing && !L_EXTPROC(tty)) {
1598		if (la_count > 0) {
1599			n_tty_receive_buf_closing(tty, cp, fp, la_count, true);
1600			cp += la_count;
1601			if (fp)
1602				fp += la_count;
1603			count -= la_count;
1604		}
1605		if (count > 0)
1606			n_tty_receive_buf_closing(tty, cp, fp, count, false);
1607	} else {
1608		if (la_count > 0) {
1609			n_tty_receive_buf_standard(tty, cp, fp, la_count, true);
1610			cp += la_count;
1611			if (fp)
1612				fp += la_count;
1613			count -= la_count;
1614		}
1615		if (count > 0)
1616			n_tty_receive_buf_standard(tty, cp, fp, count, false);
1617
1618		flush_echoes(tty);
1619		if (tty->ops->flush_chars)
1620			tty->ops->flush_chars(tty);
1621	}
1622
1623	ldata->lookahead_count -= la_count;
1624
1625	if (ldata->icanon && !L_EXTPROC(tty))
1626		return;
1627
1628	/* publish read_head to consumer */
1629	smp_store_release(&ldata->commit_head, ldata->read_head);
1630
1631	if (read_cnt(ldata)) {
1632		kill_fasync(&tty->fasync, SIGIO, POLL_IN);
1633		wake_up_interruptible_poll(&tty->read_wait, EPOLLIN | EPOLLRDNORM);
1634	}
1635}
1636
1637/**
1638 * n_tty_receive_buf_common	-	process input
1639 * @tty: device to receive input
1640 * @cp: input chars
1641 * @fp: flags for each char (if %NULL, all chars are %TTY_NORMAL)
1642 * @count: number of input chars in @cp
1643 * @flow: enable flow control
1644 *
1645 * Called by the terminal driver when a block of characters has been received.
1646 * This function must be called from soft contexts not from interrupt context.
1647 * The driver is responsible for making calls one at a time and in order (or
1648 * using flush_to_ldisc()).
1649 *
1650 * Returns: the # of input chars from @cp which were processed.
1651 *
1652 * In canonical mode, the maximum line length is 4096 chars (including the line
1653 * termination char); lines longer than 4096 chars are truncated. After 4095
1654 * chars, input data is still processed but not stored. Overflow processing
1655 * ensures the tty can always receive more input until at least one line can be
1656 * read.
1657 *
1658 * In non-canonical mode, the read buffer will only accept 4095 chars; this
1659 * provides the necessary space for a newline char if the input mode is
1660 * switched to canonical.
1661 *
1662 * Note it is possible for the read buffer to _contain_ 4096 chars in
1663 * non-canonical mode: the read buffer could already contain the maximum canon
1664 * line of 4096 chars when the mode is switched to non-canonical.
1665 *
1666 * Locking: n_tty_receive_buf()/producer path:
1667 *	claims non-exclusive %termios_rwsem
1668 *	publishes commit_head or canon_head
1669 */
1670static size_t
1671n_tty_receive_buf_common(struct tty_struct *tty, const u8 *cp, const u8 *fp,
1672			 size_t count, bool flow)
1673{
1674	struct n_tty_data *ldata = tty->disc_data;
1675	size_t n, rcvd = 0;
1676	int room, overflow;
1677
1678	guard(rwsem_read)(&tty->termios_rwsem);
1679
1680	do {
1681		/*
1682		 * When PARMRK is set, each input char may take up to 3 chars
1683		 * in the read buf; reduce the buffer space avail by 3x
1684		 *
1685		 * If we are doing input canonicalization, and there are no
1686		 * pending newlines, let characters through without limit, so
1687		 * that erase characters will be handled.  Other excess
1688		 * characters will be beeped.
1689		 *
1690		 * paired with store in *_copy_from_read_buf() -- guarantees
1691		 * the consumer has loaded the data in read_buf up to the new
1692		 * read_tail (so this producer will not overwrite unread data)
1693		 */
1694		size_t tail = smp_load_acquire(&ldata->read_tail);
1695
1696		room = N_TTY_BUF_SIZE - (ldata->read_head - tail);
1697		if (I_PARMRK(tty))
1698			room = DIV_ROUND_UP(room, 3);
1699		room--;
1700		if (room <= 0) {
1701			overflow = ldata->icanon && ldata->canon_head == tail;
1702			if (overflow && room < 0)
1703				ldata->read_head--;
1704			room = overflow;
1705			WRITE_ONCE(ldata->no_room, flow && !room);
1706		} else
1707			overflow = 0;
1708
1709		n = min_t(size_t, count, room);
1710		if (!n)
1711			break;
1712
1713		/* ignore parity errors if handling overflow */
1714		if (!overflow || !fp || *fp != TTY_PARITY)
1715			__receive_buf(tty, cp, fp, n);
1716
1717		cp += n;
1718		if (fp)
1719			fp += n;
1720		count -= n;
1721		rcvd += n;
1722	} while (!test_bit(TTY_LDISC_CHANGING, &tty->flags));
1723
1724	tty->receive_room = room;
1725
1726	/* Unthrottle if handling overflow on pty */
1727	if (tty->driver->type == TTY_DRIVER_TYPE_PTY) {
1728		if (overflow) {
1729			tty_set_flow_change(tty, TTY_UNTHROTTLE_SAFE);
1730			tty_unthrottle_safe(tty);
1731			__tty_set_flow_change(tty, 0);
1732		}
1733	} else
1734		n_tty_check_throttle(tty);
1735
1736	if (unlikely(ldata->no_room)) {
1737		/*
1738		 * Barrier here is to ensure to read the latest read_tail in
1739		 * chars_in_buffer() and to make sure that read_tail is not loaded
1740		 * before ldata->no_room is set.
1741		 */
1742		smp_mb();
1743		if (!chars_in_buffer(tty))
1744			n_tty_kick_worker(tty);
1745	}
1746
1747	return rcvd;
1748}
1749
1750static void n_tty_receive_buf(struct tty_struct *tty, const u8 *cp,
1751			      const u8 *fp, size_t count)
1752{
1753	n_tty_receive_buf_common(tty, cp, fp, count, false);
1754}
1755
1756static size_t n_tty_receive_buf2(struct tty_struct *tty, const u8 *cp,
1757				 const u8 *fp, size_t count)
1758{
1759	return n_tty_receive_buf_common(tty, cp, fp, count, true);
1760}
1761
1762/**
1763 * n_tty_set_termios	-	termios data changed
1764 * @tty: terminal
1765 * @old: previous data
1766 *
1767 * Called by the tty layer when the user changes termios flags so that the line
1768 * discipline can plan ahead. This function cannot sleep and is protected from
1769 * re-entry by the tty layer. The user is guaranteed that this function will
1770 * not be re-entered or in progress when the ldisc is closed.
1771 *
1772 * Locking: Caller holds @tty->termios_rwsem
1773 */
1774static void n_tty_set_termios(struct tty_struct *tty, const struct ktermios *old)
1775{
1776	struct n_tty_data *ldata = tty->disc_data;
1777
1778	if (!old || (old->c_lflag ^ tty->termios.c_lflag) & (ICANON | EXTPROC)) {
1779		bitmap_zero(ldata->read_flags, N_TTY_BUF_SIZE);
1780		ldata->line_start = ldata->read_tail;
1781		if (!L_ICANON(tty) || !read_cnt(ldata)) {
1782			ldata->canon_head = ldata->read_tail;
1783			ldata->push = 0;
1784		} else {
1785			set_bit(MASK(ldata->read_head - 1), ldata->read_flags);
1786			ldata->canon_head = ldata->read_head;
1787			ldata->push = 1;
1788		}
1789		ldata->commit_head = ldata->read_head;
1790		ldata->erasing = 0;
1791		ldata->lnext = 0;
1792	}
1793
1794	ldata->icanon = (L_ICANON(tty) != 0);
1795
1796	if (I_ISTRIP(tty) || I_IUCLC(tty) || I_IGNCR(tty) ||
1797	    I_ICRNL(tty) || I_INLCR(tty) || L_ICANON(tty) ||
1798	    I_IXON(tty) || L_ISIG(tty) || L_ECHO(tty) ||
1799	    I_PARMRK(tty)) {
1800		bitmap_zero(ldata->char_map, 256);
1801
1802		if (I_IGNCR(tty) || I_ICRNL(tty))
1803			set_bit('\r', ldata->char_map);
1804		if (I_INLCR(tty))
1805			set_bit('\n', ldata->char_map);
1806
1807		if (L_ICANON(tty)) {
1808			set_bit(ERASE_CHAR(tty), ldata->char_map);
1809			set_bit(KILL_CHAR(tty), ldata->char_map);
1810			set_bit(EOF_CHAR(tty), ldata->char_map);
1811			set_bit('\n', ldata->char_map);
1812			set_bit(EOL_CHAR(tty), ldata->char_map);
1813			if (L_IEXTEN(tty)) {
1814				set_bit(WERASE_CHAR(tty), ldata->char_map);
1815				set_bit(LNEXT_CHAR(tty), ldata->char_map);
1816				set_bit(EOL2_CHAR(tty), ldata->char_map);
1817				if (L_ECHO(tty))
1818					set_bit(REPRINT_CHAR(tty),
1819						ldata->char_map);
1820			}
1821		}
1822		if (I_IXON(tty)) {
1823			set_bit(START_CHAR(tty), ldata->char_map);
1824			set_bit(STOP_CHAR(tty), ldata->char_map);
1825		}
1826		if (L_ISIG(tty)) {
1827			set_bit(INTR_CHAR(tty), ldata->char_map);
1828			set_bit(QUIT_CHAR(tty), ldata->char_map);
1829			set_bit(SUSP_CHAR(tty), ldata->char_map);
1830		}
1831		clear_bit(__DISABLED_CHAR, ldata->char_map);
1832		ldata->raw = 0;
1833		ldata->real_raw = 0;
1834	} else {
1835		ldata->raw = 1;
1836		if ((I_IGNBRK(tty) || (!I_BRKINT(tty) && !I_PARMRK(tty))) &&
1837		    (I_IGNPAR(tty) || !I_INPCK(tty)) &&
1838		    (tty->driver->flags & TTY_DRIVER_REAL_RAW))
1839			ldata->real_raw = 1;
1840		else
1841			ldata->real_raw = 0;
1842	}
1843	/*
1844	 * Fix tty hang when I_IXON(tty) is cleared, but the tty
1845	 * been stopped by STOP_CHAR(tty) before it.
1846	 */
1847	if (!I_IXON(tty) && old && (old->c_iflag & IXON) && !tty->flow.tco_stopped) {
1848		start_tty(tty);
1849		process_echoes(tty);
1850	}
1851
1852	/* The termios change make the tty ready for I/O */
1853	wake_up_interruptible(&tty->write_wait);
1854	wake_up_interruptible(&tty->read_wait);
1855}
1856
1857/**
1858 * n_tty_close		-	close the ldisc for this tty
1859 * @tty: device
1860 *
1861 * Called from the terminal layer when this line discipline is being shut down,
1862 * either because of a close or becsuse of a discipline change. The function
1863 * will not be called while other ldisc methods are in progress.
1864 */
1865static void n_tty_close(struct tty_struct *tty)
1866{
1867	struct n_tty_data *ldata = tty->disc_data;
1868
1869	if (tty->link)
1870		n_tty_packet_mode_flush(tty);
1871
1872	guard(rwsem_write)(&tty->termios_rwsem);
1873	vfree(ldata);
1874	tty->disc_data = NULL;
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 */
1885static 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
1907static inline int input_available_p(const struct tty_struct *tty, int poll)
1908{
1909	const 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 */
1936static bool copy_from_read_buf(const struct tty_struct *tty, u8 **kbp,
1937			       size_t *nr)
1938
1939{
1940	struct n_tty_data *ldata = tty->disc_data;
1941	size_t n;
1942	bool is_eof;
1943	size_t head = smp_load_acquire(&ldata->commit_head);
1944	size_t tail = MASK(ldata->read_tail);
1945
1946	n = min3(head - ldata->read_tail, N_TTY_BUF_SIZE - tail, *nr);
1947	if (!n)
1948		return false;
1949
1950	u8 *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
1957	/* Turn single EOF into zero-length read */
1958	if (L_EXTPROC(tty) && ldata->icanon && is_eof &&
1959	    head == ldata->read_tail)
1960		return false;
1961
1962	*kbp += n;
1963	*nr -= n;
1964
1965	/* If we have more to copy, let the caller know */
1966	return head != ldata->read_tail;
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 */
1991static bool canon_copy_from_read_buf(const struct tty_struct *tty, u8 **kbp,
1992				     size_t *nr)
1993{
1994	struct n_tty_data *ldata = tty->disc_data;
1995	size_t n, size, more, c;
1996	size_t eol;
1997	size_t tail, canon_head;
1998	int found = 0;
1999
2000	/* N.B. avoid overrun if nr == 0 */
2001	if (!*nr)
2002		return false;
2003
2004	canon_head = smp_load_acquire(&ldata->canon_head);
2005	n = min(*nr, canon_head - ldata->read_tail);
2006
2007	tail = MASK(ldata->read_tail);
2008	size = min_t(size_t, tail + n, N_TTY_BUF_SIZE);
2009
2010	eol = find_next_bit(ldata->read_flags, size, tail);
2011	more = n - (size - tail);
2012	if (eol == N_TTY_BUF_SIZE && more) {
2013		/* scan wrapped without finding set bit */
2014		eol = find_first_bit(ldata->read_flags, more);
2015		found = eol != more;
2016	} else
2017		found = eol != size;
2018
2019	n = eol - tail;
2020	if (n > N_TTY_BUF_SIZE)
2021		n += N_TTY_BUF_SIZE;
2022	c = n + found;
2023
2024	if (!found || read_buf(ldata, eol) != __DISABLED_CHAR)
2025		n = c;
2026
2027	tty_copy(tty, *kbp, tail, n);
2028	*kbp += n;
2029	*nr -= n;
2030
2031	if (found)
2032		clear_bit(eol, ldata->read_flags);
2033	smp_store_release(&ldata->read_tail, ldata->read_tail + c);
2034
2035	if (found) {
2036		if (!ldata->push)
2037			ldata->line_start = ldata->read_tail;
2038		else
2039			ldata->push = 0;
2040		tty_audit_push();
2041		return false;
2042	}
2043
2044	/* No EOL found - do a continuation retry if there is more data */
2045	return ldata->read_tail != canon_head;
2046}
2047
2048/*
2049 * If we finished a read at the exact location of an
2050 * EOF (special EOL character that's a __DISABLED_CHAR)
2051 * in the stream, silently eat the EOF.
2052 */
2053static void canon_skip_eof(struct n_tty_data *ldata)
2054{
2055	size_t tail, canon_head;
2056
2057	canon_head = smp_load_acquire(&ldata->canon_head);
2058	tail = ldata->read_tail;
2059
2060	// No data?
2061	if (tail == canon_head)
2062		return;
2063
2064	// See if the tail position is EOF in the circular buffer
2065	tail &= (N_TTY_BUF_SIZE - 1);
2066	if (!test_bit(tail, ldata->read_flags))
2067		return;
2068	if (read_buf(ldata, tail) != __DISABLED_CHAR)
2069		return;
2070
2071	// Clear the EOL bit, skip the EOF char.
2072	clear_bit(tail, ldata->read_flags);
2073	smp_store_release(&ldata->read_tail, ldata->read_tail + 1);
2074}
2075
2076/**
2077 * job_control		-	check job control
2078 * @tty: tty
2079 * @file: file handle
2080 *
2081 * Perform job control management checks on this @file/@tty descriptor and if
2082 * appropriate send any needed signals and return a negative error code if
2083 * action should be taken.
2084 *
2085 * Locking:
2086 *  * redirected write test is safe
2087 *  * current->signal->tty check is safe
2088 *  * ctrl.lock to safely reference @tty->ctrl.pgrp
2089 */
2090static int job_control(struct tty_struct *tty, struct file *file)
2091{
2092	/* Job control check -- must be done at start and after
2093	   every sleep (POSIX.1 7.1.1.4). */
2094	/* NOTE: not yet done after every sleep pending a thorough
2095	   check of the logic of this change. -- jlc */
2096	/* don't stop on /dev/console */
2097	if (file->f_op->write_iter == redirected_tty_write)
2098		return 0;
2099
2100	return __tty_check_change(tty, SIGTTIN);
2101}
2102
2103/*
2104 * We still hold the atomic_read_lock and the termios_rwsem, and can just
2105 * continue to copy data.
2106 */
2107static ssize_t n_tty_continue_cookie(struct tty_struct *tty, u8 *kbuf,
2108				   size_t nr, void **cookie)
2109{
2110	struct n_tty_data *ldata = tty->disc_data;
2111	u8 *kb = kbuf;
2112
2113	if (ldata->icanon && !L_EXTPROC(tty)) {
2114		/*
2115		 * If we have filled the user buffer, see if we should skip an
2116		 * EOF character before releasing the lock and returning done.
2117		 */
2118		if (!nr)
2119			canon_skip_eof(ldata);
2120		else if (canon_copy_from_read_buf(tty, &kb, &nr))
2121			return kb - kbuf;
2122	} else {
2123		if (copy_from_read_buf(tty, &kb, &nr))
2124			return kb - kbuf;
2125	}
2126
2127	/* No more data - release locks and stop retries */
2128	n_tty_kick_worker(tty);
2129	n_tty_check_unthrottle(tty);
2130	up_read(&tty->termios_rwsem);
2131	mutex_unlock(&ldata->atomic_read_lock);
2132	*cookie = NULL;
2133
2134	return kb - kbuf;
2135}
2136
2137static int n_tty_wait_for_input(struct tty_struct *tty, struct file *file,
2138				struct wait_queue_entry *wait, long *timeout)
2139{
2140	if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
2141		return -EIO;
2142	if (tty_hung_up_p(file))
2143		return 0;
2144	/*
2145	 * Abort readers for ttys which never actually get hung up.
2146	 * See __tty_hangup().
2147	 */
2148	if (test_bit(TTY_HUPPING, &tty->flags))
2149		return 0;
2150	if (!*timeout)
2151		return 0;
2152	if (tty_io_nonblock(tty, file))
2153		return -EAGAIN;
2154	if (signal_pending(current))
2155		return -ERESTARTSYS;
2156
2157	up_read(&tty->termios_rwsem);
2158	*timeout = wait_woken(wait, TASK_INTERRUPTIBLE, *timeout);
2159	down_read(&tty->termios_rwsem);
2160
2161	return 1;
2162}
2163
2164/**
2165 * n_tty_read		-	read function for tty
2166 * @tty: tty device
2167 * @file: file object
2168 * @kbuf: kernelspace buffer pointer
2169 * @nr: size of I/O
2170 * @cookie: if non-%NULL, this is a continuation read
2171 * @offset: where to continue reading from (unused in n_tty)
2172 *
2173 * Perform reads for the line discipline. We are guaranteed that the line
2174 * discipline will not be closed under us but we may get multiple parallel
2175 * readers and must handle this ourselves. We may also get a hangup. Always
2176 * called in user context, may sleep.
2177 *
2178 * This code must be sure never to sleep through a hangup.
2179 *
2180 * Locking: n_tty_read()/consumer path:
2181 *	claims non-exclusive termios_rwsem;
2182 *	publishes read_tail
2183 */
2184static ssize_t n_tty_read(struct tty_struct *tty, struct file *file, u8 *kbuf,
2185			  size_t nr, void **cookie, unsigned long offset)
2186{
2187	struct n_tty_data *ldata = tty->disc_data;
2188	u8 *kb = kbuf;
2189	DEFINE_WAIT_FUNC(wait, woken_wake_function);
2190	int minimum, time;
2191	ssize_t retval;
2192	long timeout;
2193	bool packet;
2194	size_t old_tail;
2195
2196	/* Is this a continuation of a read started earlier? */
2197	if (*cookie)
2198		return n_tty_continue_cookie(tty, kbuf, nr, cookie);
2199
2200	retval = job_control(tty, file);
2201	if (retval < 0)
2202		return retval;
2203
2204	/*
2205	 *	Internal serialization of reads.
2206	 */
2207	if (file->f_flags & O_NONBLOCK) {
2208		if (!mutex_trylock(&ldata->atomic_read_lock))
2209			return -EAGAIN;
2210	} else {
2211		if (mutex_lock_interruptible(&ldata->atomic_read_lock))
2212			return -ERESTARTSYS;
2213	}
2214
2215	down_read(&tty->termios_rwsem);
2216
2217	minimum = time = 0;
2218	timeout = MAX_SCHEDULE_TIMEOUT;
2219	if (!ldata->icanon) {
2220		minimum = MIN_CHAR(tty);
2221		if (minimum) {
2222			time = (HZ / 10) * TIME_CHAR(tty);
2223		} else {
2224			timeout = (HZ / 10) * TIME_CHAR(tty);
2225			minimum = 1;
2226		}
2227	}
2228
2229	packet = tty->ctrl.packet;
2230	old_tail = ldata->read_tail;
2231
2232	add_wait_queue(&tty->read_wait, &wait);
2233	while (nr) {
2234		/* First test for status change. */
2235		if (packet && tty->link->ctrl.pktstatus) {
2236			u8 cs;
2237			if (kb != kbuf)
2238				break;
2239			scoped_guard(spinlock_irq, &tty->link->ctrl.lock) {
2240				cs = tty->link->ctrl.pktstatus;
2241				tty->link->ctrl.pktstatus = 0;
2242			}
2243			*kb++ = cs;
2244			nr--;
2245			break;
2246		}
2247
2248		if (!input_available_p(tty, 0)) {
2249			up_read(&tty->termios_rwsem);
2250			tty_buffer_flush_work(tty->port);
2251			down_read(&tty->termios_rwsem);
2252			if (!input_available_p(tty, 0)) {
2253				int ret = n_tty_wait_for_input(tty, file, &wait,
2254							       &timeout);
2255				if (ret <= 0) {
2256					retval = ret;
2257					break;
2258				}
2259				continue;
2260			}
2261		}
2262
2263		if (ldata->icanon && !L_EXTPROC(tty)) {
2264			if (canon_copy_from_read_buf(tty, &kb, &nr))
2265				goto more_to_be_read;
2266		} else {
2267			/* Deal with packet mode. */
2268			if (packet && kb == kbuf) {
2269				*kb++ = TIOCPKT_DATA;
2270				nr--;
2271			}
2272
2273			if (copy_from_read_buf(tty, &kb, &nr) && kb - kbuf >= minimum)
2274				goto more_to_be_read;
2275		}
2276
2277		n_tty_check_unthrottle(tty);
2278
2279		if (kb - kbuf >= minimum)
2280			break;
2281		if (time)
2282			timeout = time;
2283	}
2284	if (old_tail != ldata->read_tail) {
2285		/*
2286		 * Make sure no_room is not read in n_tty_kick_worker()
2287		 * before setting ldata->read_tail in copy_from_read_buf().
2288		 */
2289		smp_mb();
2290		n_tty_kick_worker(tty);
2291	}
2292	up_read(&tty->termios_rwsem);
2293
2294	remove_wait_queue(&tty->read_wait, &wait);
2295	mutex_unlock(&ldata->atomic_read_lock);
2296
2297	if (kb - kbuf)
2298		retval = kb - kbuf;
2299
2300	return retval;
2301more_to_be_read:
2302	/*
2303	 * There is more to be had and we have nothing more to wait for, so
2304	 * let's mark us for retries.
2305	 *
2306	 * NOTE! We return here with both the termios_sem and atomic_read_lock
2307	 * still held, the retries will release them when done.
2308	 */
2309	remove_wait_queue(&tty->read_wait, &wait);
2310	*cookie = cookie;
2311
2312	return kb - kbuf;
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
2335static ssize_t n_tty_write(struct tty_struct *tty, struct file *file,
2336			   const u8 *buf, size_t nr)
2337{
2338	const u8 *b = buf;
2339	DEFINE_WAIT_FUNC(wait, woken_wake_function);
2340	ssize_t num, retval = 0;
2341
2342	/* Job control check -- must be done at start (POSIX.1 7.1.1.4). */
2343	if (L_TOSTOP(tty) && file->f_op->write_iter != redirected_tty_write) {
2344		retval = tty_check_change(tty);
2345		if (retval)
2346			return retval;
2347	}
2348
2349	guard(rwsem_read)(&tty->termios_rwsem);
2350
2351	/* Write out any echoed characters that are still pending */
2352	process_echoes(tty);
2353
2354	add_wait_queue(&tty->write_wait, &wait);
2355	while (1) {
2356		if (signal_pending(current)) {
2357			retval = -ERESTARTSYS;
2358			break;
2359		}
2360		if (tty_hung_up_p(file) || (tty->link && !tty->link->count)) {
2361			retval = -EIO;
2362			break;
2363		}
2364		if (O_OPOST(tty)) {
2365			while (nr > 0) {
2366				num = process_output_block(tty, b, nr);
2367				if (num < 0) {
2368					if (num == -EAGAIN)
2369						break;
2370					retval = num;
2371					goto break_out;
2372				}
2373				b += num;
2374				nr -= num;
2375				if (nr == 0)
2376					break;
2377				if (process_output(*b, tty) < 0)
2378					break;
2379				b++; nr--;
2380			}
2381			if (tty->ops->flush_chars)
2382				tty->ops->flush_chars(tty);
2383		} else {
2384			struct n_tty_data *ldata = tty->disc_data;
2385
2386			while (nr > 0) {
2387				scoped_guard(mutex, &ldata->output_lock)
2388					num = tty->ops->write(tty, b, nr);
2389				if (num < 0) {
2390					retval = num;
2391					goto break_out;
2392				}
2393				if (!num)
2394					break;
2395				b += num;
2396				nr -= num;
2397			}
2398		}
2399		if (!nr)
2400			break;
2401		if (tty_io_nonblock(tty, file)) {
2402			retval = -EAGAIN;
2403			break;
2404		}
2405		up_read(&tty->termios_rwsem);
2406
2407		wait_woken(&wait, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
2408
2409		down_read(&tty->termios_rwsem);
2410	}
2411break_out:
2412	remove_wait_queue(&tty->write_wait, &wait);
2413	if (nr && tty->fasync)
2414		set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
2415
2416	return (b - buf) ? b - buf : retval;
2417}
2418
2419/**
2420 * n_tty_poll		-	poll method for N_TTY
2421 * @tty: terminal device
2422 * @file: file accessing it
2423 * @wait: poll table
2424 *
2425 * Called when the line discipline is asked to poll() for data or for special
2426 * events. This code is not serialized with respect to other events save
2427 * open/close.
2428 *
2429 * This code must be sure never to sleep through a hangup.
2430 *
2431 * Locking: called without the kernel lock held -- fine.
2432 */
2433static __poll_t n_tty_poll(struct tty_struct *tty, struct file *file,
2434							poll_table *wait)
2435{
2436	__poll_t mask = 0;
2437
2438	poll_wait(file, &tty->read_wait, wait);
2439	poll_wait(file, &tty->write_wait, wait);
2440	if (input_available_p(tty, 1))
2441		mask |= EPOLLIN | EPOLLRDNORM;
2442	else {
2443		tty_buffer_flush_work(tty->port);
2444		if (input_available_p(tty, 1))
2445			mask |= EPOLLIN | EPOLLRDNORM;
2446	}
2447	if (tty->ctrl.packet && tty->link->ctrl.pktstatus)
2448		mask |= EPOLLPRI | EPOLLIN | EPOLLRDNORM;
2449	if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
2450		mask |= EPOLLHUP;
2451	if (tty_hung_up_p(file))
2452		mask |= EPOLLHUP;
2453	if (tty->ops->write && !tty_is_writelocked(tty) &&
2454			tty_chars_in_buffer(tty) < WAKEUP_CHARS &&
2455			tty_write_room(tty) > 0)
2456		mask |= EPOLLOUT | EPOLLWRNORM;
2457	return mask;
2458}
2459
2460static unsigned long inq_canon(struct n_tty_data *ldata)
2461{
2462	size_t nr, head, tail;
2463
2464	if (ldata->canon_head == ldata->read_tail)
2465		return 0;
2466	head = ldata->canon_head;
2467	tail = ldata->read_tail;
2468	nr = head - tail;
2469	/* Skip EOF-chars.. */
2470	while (MASK(head) != MASK(tail)) {
2471		if (test_bit(MASK(tail), ldata->read_flags) &&
2472		    read_buf(ldata, tail) == __DISABLED_CHAR)
2473			nr--;
2474		tail++;
2475	}
2476	return nr;
2477}
2478
2479static int n_tty_ioctl(struct tty_struct *tty, unsigned int cmd,
2480		       unsigned long arg)
2481{
2482	struct n_tty_data *ldata = tty->disc_data;
2483	unsigned int num;
2484
2485	switch (cmd) {
2486	case TIOCOUTQ:
2487		return put_user(tty_chars_in_buffer(tty), (int __user *) arg);
2488	case TIOCINQ:
2489		scoped_guard(rwsem_write, &tty->termios_rwsem)
2490			if (L_ICANON(tty) && !L_EXTPROC(tty))
2491				num = inq_canon(ldata);
2492			else
2493				num = read_cnt(ldata);
2494		return put_user(num, (unsigned int __user *) arg);
2495	default:
2496		return n_tty_ioctl_helper(tty, cmd, arg);
2497	}
2498}
2499
2500static struct tty_ldisc_ops n_tty_ops = {
2501	.owner		 = THIS_MODULE,
2502	.num		 = N_TTY,
2503	.name            = "n_tty",
2504	.open            = n_tty_open,
2505	.close           = n_tty_close,
2506	.flush_buffer    = n_tty_flush_buffer,
2507	.read            = n_tty_read,
2508	.write           = n_tty_write,
2509	.ioctl           = n_tty_ioctl,
2510	.set_termios     = n_tty_set_termios,
2511	.poll            = n_tty_poll,
2512	.receive_buf     = n_tty_receive_buf,
2513	.write_wakeup    = n_tty_write_wakeup,
2514	.receive_buf2	 = n_tty_receive_buf2,
2515	.lookahead_buf	 = n_tty_lookahead_flow_ctrl,
2516};
2517
2518/**
2519 *	n_tty_inherit_ops	-	inherit N_TTY methods
2520 *	@ops: struct tty_ldisc_ops where to save N_TTY methods
2521 *
2522 *	Enables a 'subclass' line discipline to 'inherit' N_TTY methods.
2523 */
2524
2525void n_tty_inherit_ops(struct tty_ldisc_ops *ops)
2526{
2527	*ops = n_tty_ops;
2528	ops->owner = NULL;
2529}
2530EXPORT_SYMBOL_GPL(n_tty_inherit_ops);
2531
2532void __init n_tty_init(void)
2533{
2534	tty_register_ldisc(&n_tty_ops);
2535}