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
  91struct 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
 135static inline size_t read_cnt(struct n_tty_data *ldata)
 136{
 137	return ldata->read_head - ldata->read_tail;
 138}
 139
 140static 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
 145static 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
 150static 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
 156static 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 */
 162static 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
 171static 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 */
 
 202static 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(ldata->no_room)) {
 208		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
 222static 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 */
 
 241static 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
 247static 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
 271static 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 */
 
 313static 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 */
 
 330static 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
 343static 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 */
 
 368static 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 */
 
 387static 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 */
 
 400static 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 */
 
 424static 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 */
 
 498static 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 */
 
 533static 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	}
 585break_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 */
 
 614static 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
 760static 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
 789static 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 */
 807static 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 */
 
 828static 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 */
 
 841static 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 */
 
 854static 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 */
 
 873static 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 */
 
 899static 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 */
 
 920static 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 */
 
 938static 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 */
 
 958static 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
1077static 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 */
1100static 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 */
 
1147static 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 */
 
1174static 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 */
1198static 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
1215static void
1216n_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
1228static 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 */
1248static 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
1268static 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
1364handle_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 */
1406static 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
1428static 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
1447static void
1448n_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
1467static void
1468n_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 */
1484static 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
1504static void
1505n_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
1524static void
1525n_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
1541static void
1542n_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
1555static 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
1593static 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 */
1667static int
1668n_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			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	up_read(&tty->termios_rwsem);
1733
1734	return rcvd;
1735}
1736
1737static void n_tty_receive_buf(struct tty_struct *tty, const unsigned char *cp,
1738			      const char *fp, int count)
1739{
1740	n_tty_receive_buf_common(tty, cp, fp, count, 0);
1741}
1742
1743static int n_tty_receive_buf2(struct tty_struct *tty, const unsigned char *cp,
1744			      const char *fp, int count)
1745{
1746	return n_tty_receive_buf_common(tty, cp, fp, count, 1);
1747}
1748
1749/**
1750 * n_tty_set_termios	-	termios data changed
1751 * @tty: terminal
1752 * @old: previous data
1753 *
1754 * Called by the tty layer when the user changes termios flags so that the line
1755 * discipline can plan ahead. This function cannot sleep and is protected from
1756 * re-entry by the tty layer. The user is guaranteed that this function will
1757 * not be re-entered or in progress when the ldisc is closed.
 
1758 *
1759 * Locking: Caller holds @tty->termios_rwsem
1760 */
1761static void n_tty_set_termios(struct tty_struct *tty, const struct ktermios *old)
 
1762{
1763	struct n_tty_data *ldata = tty->disc_data;
1764
1765	if (!old || (old->c_lflag ^ tty->termios.c_lflag) & (ICANON | EXTPROC)) {
1766		bitmap_zero(ldata->read_flags, N_TTY_BUF_SIZE);
1767		ldata->line_start = ldata->read_tail;
1768		if (!L_ICANON(tty) || !read_cnt(ldata)) {
1769			ldata->canon_head = ldata->read_tail;
1770			ldata->push = 0;
1771		} else {
1772			set_bit((ldata->read_head - 1) & (N_TTY_BUF_SIZE - 1),
1773				ldata->read_flags);
1774			ldata->canon_head = ldata->read_head;
1775			ldata->push = 1;
1776		}
1777		ldata->commit_head = ldata->read_head;
1778		ldata->erasing = 0;
1779		ldata->lnext = 0;
1780	}
1781
1782	ldata->icanon = (L_ICANON(tty) != 0);
1783
1784	if (I_ISTRIP(tty) || I_IUCLC(tty) || I_IGNCR(tty) ||
1785	    I_ICRNL(tty) || I_INLCR(tty) || L_ICANON(tty) ||
1786	    I_IXON(tty) || L_ISIG(tty) || L_ECHO(tty) ||
1787	    I_PARMRK(tty)) {
1788		bitmap_zero(ldata->char_map, 256);
1789
1790		if (I_IGNCR(tty) || I_ICRNL(tty))
1791			set_bit('\r', ldata->char_map);
1792		if (I_INLCR(tty))
1793			set_bit('\n', ldata->char_map);
1794
1795		if (L_ICANON(tty)) {
1796			set_bit(ERASE_CHAR(tty), ldata->char_map);
1797			set_bit(KILL_CHAR(tty), ldata->char_map);
1798			set_bit(EOF_CHAR(tty), ldata->char_map);
1799			set_bit('\n', ldata->char_map);
1800			set_bit(EOL_CHAR(tty), ldata->char_map);
1801			if (L_IEXTEN(tty)) {
1802				set_bit(WERASE_CHAR(tty), ldata->char_map);
1803				set_bit(LNEXT_CHAR(tty), ldata->char_map);
1804				set_bit(EOL2_CHAR(tty), ldata->char_map);
1805				if (L_ECHO(tty))
1806					set_bit(REPRINT_CHAR(tty),
1807						ldata->char_map);
1808			}
1809		}
1810		if (I_IXON(tty)) {
1811			set_bit(START_CHAR(tty), ldata->char_map);
1812			set_bit(STOP_CHAR(tty), ldata->char_map);
1813		}
1814		if (L_ISIG(tty)) {
1815			set_bit(INTR_CHAR(tty), ldata->char_map);
1816			set_bit(QUIT_CHAR(tty), ldata->char_map);
1817			set_bit(SUSP_CHAR(tty), ldata->char_map);
1818		}
1819		clear_bit(__DISABLED_CHAR, ldata->char_map);
1820		ldata->raw = 0;
1821		ldata->real_raw = 0;
1822	} else {
1823		ldata->raw = 1;
1824		if ((I_IGNBRK(tty) || (!I_BRKINT(tty) && !I_PARMRK(tty))) &&
1825		    (I_IGNPAR(tty) || !I_INPCK(tty)) &&
1826		    (tty->driver->flags & TTY_DRIVER_REAL_RAW))
1827			ldata->real_raw = 1;
1828		else
1829			ldata->real_raw = 0;
1830	}
1831	/*
1832	 * Fix tty hang when I_IXON(tty) is cleared, but the tty
1833	 * been stopped by STOP_CHAR(tty) before it.
1834	 */
1835	if (!I_IXON(tty) && old && (old->c_iflag & IXON) && !tty->flow.tco_stopped) {
1836		start_tty(tty);
1837		process_echoes(tty);
1838	}
1839
1840	/* The termios change make the tty ready for I/O */
1841	wake_up_interruptible(&tty->write_wait);
1842	wake_up_interruptible(&tty->read_wait);
1843}
1844
1845/**
1846 * n_tty_close		-	close the ldisc for this tty
1847 * @tty: device
1848 *
1849 * Called from the terminal layer when this line discipline is being shut down,
1850 * either because of a close or becsuse of a discipline change. The function
1851 * will not be called while other ldisc methods are in progress.
 
1852 */
 
1853static void n_tty_close(struct tty_struct *tty)
1854{
1855	struct n_tty_data *ldata = tty->disc_data;
1856
1857	if (tty->link)
1858		n_tty_packet_mode_flush(tty);
1859
1860	down_write(&tty->termios_rwsem);
1861	vfree(ldata);
1862	tty->disc_data = NULL;
1863	up_write(&tty->termios_rwsem);
1864}
1865
1866/**
1867 * n_tty_open		-	open an ldisc
1868 * @tty: terminal to open
1869 *
1870 * Called when this line discipline is being attached to the terminal device.
1871 * Can sleep. Called serialized so that no other events will occur in parallel.
1872 * No further open will occur until a close.
 
1873 */
 
1874static int n_tty_open(struct tty_struct *tty)
1875{
1876	struct n_tty_data *ldata;
1877
1878	/* Currently a malloc failure here can panic */
1879	ldata = vzalloc(sizeof(*ldata));
1880	if (!ldata)
1881		return -ENOMEM;
1882
1883	ldata->overrun_time = jiffies;
1884	mutex_init(&ldata->atomic_read_lock);
1885	mutex_init(&ldata->output_lock);
1886
1887	tty->disc_data = ldata;
1888	tty->closing = 0;
1889	/* indicate buffer work may resume */
1890	clear_bit(TTY_LDISC_HALTED, &tty->flags);
1891	n_tty_set_termios(tty, NULL);
1892	tty_unthrottle(tty);
1893	return 0;
1894}
1895
1896static inline int input_available_p(struct tty_struct *tty, int poll)
1897{
1898	struct n_tty_data *ldata = tty->disc_data;
1899	int amt = poll && !TIME_CHAR(tty) && MIN_CHAR(tty) ? MIN_CHAR(tty) : 1;
1900
1901	if (ldata->icanon && !L_EXTPROC(tty))
1902		return ldata->canon_head != ldata->read_tail;
1903	else
1904		return ldata->commit_head - ldata->read_tail >= amt;
1905}
1906
1907/**
1908 * copy_from_read_buf	-	copy read data directly
1909 * @tty: terminal device
1910 * @kbp: data
1911 * @nr: size of data
1912 *
1913 * Helper function to speed up n_tty_read(). It is only called when %ICANON is
1914 * off; it copies characters straight from the tty queue.
1915 *
1916 * Returns: true if it successfully copied data, but there is still more data
1917 * to be had.
1918 *
1919 * Locking:
1920 *  * called under the @ldata->atomic_read_lock sem
1921 *  * n_tty_read()/consumer path:
1922 *		caller holds non-exclusive %termios_rwsem;
1923 *		read_tail published
1924 */
 
1925static bool copy_from_read_buf(struct tty_struct *tty,
1926				      unsigned char **kbp,
1927				      size_t *nr)
1928
1929{
1930	struct n_tty_data *ldata = tty->disc_data;
1931	size_t n;
1932	bool is_eof;
1933	size_t head = smp_load_acquire(&ldata->commit_head);
1934	size_t tail = ldata->read_tail & (N_TTY_BUF_SIZE - 1);
1935
1936	n = min(head - ldata->read_tail, N_TTY_BUF_SIZE - tail);
1937	n = min(*nr, n);
1938	if (n) {
1939		unsigned char *from = read_buf_addr(ldata, tail);
1940		memcpy(*kbp, from, n);
1941		is_eof = n == 1 && *from == EOF_CHAR(tty);
1942		tty_audit_add_data(tty, from, n);
1943		zero_buffer(tty, from, n);
1944		smp_store_release(&ldata->read_tail, ldata->read_tail + n);
1945		/* Turn single EOF into zero-length read */
1946		if (L_EXTPROC(tty) && ldata->icanon && is_eof &&
1947		    (head == ldata->read_tail))
1948			return false;
1949		*kbp += n;
1950		*nr -= n;
1951
1952		/* If we have more to copy, let the caller know */
1953		return head != ldata->read_tail;
1954	}
1955	return false;
1956}
1957
1958/**
1959 * canon_copy_from_read_buf	-	copy read data in canonical mode
1960 * @tty: terminal device
1961 * @kbp: data
1962 * @nr: size of data
1963 *
1964 * Helper function for n_tty_read(). It is only called when %ICANON is on; it
1965 * copies one line of input up to and including the line-delimiting character
1966 * into the result buffer.
1967 *
1968 * Note: When termios is changed from non-canonical to canonical mode and the
1969 * read buffer contains data, n_tty_set_termios() simulates an EOF push (as if
1970 * C-d were input) _without_ the %DISABLED_CHAR in the buffer. This causes data
1971 * already processed as input to be immediately available as input although a
1972 * newline has not been received.
1973 *
1974 * Locking:
1975 *  * called under the %atomic_read_lock mutex
1976 *  * n_tty_read()/consumer path:
1977 *	caller holds non-exclusive %termios_rwsem;
1978 *	read_tail published
1979 */
 
1980static bool canon_copy_from_read_buf(struct tty_struct *tty,
1981				     unsigned char **kbp,
1982				     size_t *nr)
1983{
1984	struct n_tty_data *ldata = tty->disc_data;
1985	size_t n, size, more, c;
1986	size_t eol;
1987	size_t tail, canon_head;
1988	int found = 0;
1989
1990	/* N.B. avoid overrun if nr == 0 */
1991	if (!*nr)
1992		return false;
1993
1994	canon_head = smp_load_acquire(&ldata->canon_head);
1995	n = min(*nr, canon_head - ldata->read_tail);
1996
1997	tail = ldata->read_tail & (N_TTY_BUF_SIZE - 1);
1998	size = min_t(size_t, tail + n, N_TTY_BUF_SIZE);
1999
2000	n_tty_trace("%s: nr:%zu tail:%zu n:%zu size:%zu\n",
2001		    __func__, *nr, tail, n, size);
2002
2003	eol = find_next_bit(ldata->read_flags, size, tail);
2004	more = n - (size - tail);
2005	if (eol == N_TTY_BUF_SIZE && more) {
2006		/* scan wrapped without finding set bit */
2007		eol = find_first_bit(ldata->read_flags, more);
2008		found = eol != more;
2009	} else
2010		found = eol != size;
2011
2012	n = eol - tail;
2013	if (n > N_TTY_BUF_SIZE)
2014		n += N_TTY_BUF_SIZE;
2015	c = n + found;
2016
2017	if (!found || read_buf(ldata, eol) != __DISABLED_CHAR)
 
2018		n = c;
 
2019
2020	n_tty_trace("%s: eol:%zu found:%d n:%zu c:%zu tail:%zu more:%zu\n",
2021		    __func__, eol, found, n, c, tail, more);
2022
2023	tty_copy(tty, *kbp, tail, n);
2024	*kbp += n;
2025	*nr -= n;
2026
2027	if (found)
2028		clear_bit(eol, ldata->read_flags);
2029	smp_store_release(&ldata->read_tail, ldata->read_tail + c);
2030
2031	if (found) {
2032		if (!ldata->push)
2033			ldata->line_start = ldata->read_tail;
2034		else
2035			ldata->push = 0;
2036		tty_audit_push();
2037		return false;
2038	}
2039
2040	/* No EOL found - do a continuation retry if there is more data */
2041	return ldata->read_tail != canon_head;
2042}
2043
2044/*
2045 * If we finished a read at the exact location of an
2046 * EOF (special EOL character that's a __DISABLED_CHAR)
2047 * in the stream, silently eat the EOF.
2048 */
2049static void canon_skip_eof(struct tty_struct *tty)
2050{
2051	struct n_tty_data *ldata = tty->disc_data;
2052	size_t tail, canon_head;
2053
2054	canon_head = smp_load_acquire(&ldata->canon_head);
2055	tail = ldata->read_tail;
2056
2057	// No data?
2058	if (tail == canon_head)
2059		return;
2060
2061	// See if the tail position is EOF in the circular buffer
2062	tail &= (N_TTY_BUF_SIZE - 1);
2063	if (!test_bit(tail, ldata->read_flags))
2064		return;
2065	if (read_buf(ldata, tail) != __DISABLED_CHAR)
2066		return;
2067
2068	// Clear the EOL bit, skip the EOF char.
2069	clear_bit(tail, ldata->read_flags);
2070	smp_store_release(&ldata->read_tail, ldata->read_tail + 1);
2071}
2072
2073/**
2074 * job_control		-	check job control
2075 * @tty: tty
2076 * @file: file handle
2077 *
2078 * Perform job control management checks on this @file/@tty descriptor and if
2079 * appropriate send any needed signals and return a negative error code if
2080 * action should be taken.
2081 *
2082 * Locking:
2083 *  * redirected write test is safe
2084 *  * current->signal->tty check is safe
2085 *  * ctrl.lock to safely reference @tty->ctrl.pgrp
2086 */
 
2087static int job_control(struct tty_struct *tty, struct file *file)
2088{
2089	/* Job control check -- must be done at start and after
2090	   every sleep (POSIX.1 7.1.1.4). */
2091	/* NOTE: not yet done after every sleep pending a thorough
2092	   check of the logic of this change. -- jlc */
2093	/* don't stop on /dev/console */
2094	if (file->f_op->write_iter == redirected_tty_write)
2095		return 0;
2096
2097	return __tty_check_change(tty, SIGTTIN);
2098}
2099
2100
2101/**
2102 * n_tty_read		-	read function for tty
2103 * @tty: tty device
2104 * @file: file object
2105 * @kbuf: kernelspace buffer pointer
2106 * @nr: size of I/O
2107 * @cookie: if non-%NULL, this is a continuation read
2108 * @offset: where to continue reading from (unused in n_tty)
2109 *
2110 * Perform reads for the line discipline. We are guaranteed that the line
2111 * discipline will not be closed under us but we may get multiple parallel
2112 * readers and must handle this ourselves. We may also get a hangup. Always
2113 * called in user context, may sleep.
2114 *
2115 * This code must be sure never to sleep through a hangup.
2116 *
2117 * Locking: n_tty_read()/consumer path:
2118 *	claims non-exclusive termios_rwsem;
2119 *	publishes read_tail
2120 */
 
2121static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
2122			  unsigned char *kbuf, size_t nr,
2123			  void **cookie, unsigned long offset)
2124{
2125	struct n_tty_data *ldata = tty->disc_data;
2126	unsigned char *kb = kbuf;
2127	DEFINE_WAIT_FUNC(wait, woken_wake_function);
2128	int c;
2129	int minimum, time;
2130	ssize_t retval = 0;
2131	long timeout;
2132	bool packet;
2133	size_t old_tail;
2134
2135	/*
2136	 * Is this a continuation of a read started earler?
2137	 *
2138	 * If so, we still hold the atomic_read_lock and the
2139	 * termios_rwsem, and can just continue to copy data.
2140	 */
2141	if (*cookie) {
2142		if (ldata->icanon && !L_EXTPROC(tty)) {
2143			/*
2144			 * If we have filled the user buffer, see
2145			 * if we should skip an EOF character before
2146			 * releasing the lock and returning done.
2147			 */
2148			if (!nr)
2149				canon_skip_eof(tty);
2150			else if (canon_copy_from_read_buf(tty, &kb, &nr))
2151				return kb - kbuf;
2152		} else {
2153			if (copy_from_read_buf(tty, &kb, &nr))
2154				return kb - kbuf;
2155		}
2156
2157		/* No more data - release locks and stop retries */
2158		n_tty_kick_worker(tty);
2159		n_tty_check_unthrottle(tty);
2160		up_read(&tty->termios_rwsem);
2161		mutex_unlock(&ldata->atomic_read_lock);
2162		*cookie = NULL;
2163		return kb - kbuf;
2164	}
2165
2166	c = job_control(tty, file);
2167	if (c < 0)
2168		return c;
2169
2170	/*
2171	 *	Internal serialization of reads.
2172	 */
2173	if (file->f_flags & O_NONBLOCK) {
2174		if (!mutex_trylock(&ldata->atomic_read_lock))
2175			return -EAGAIN;
2176	} else {
2177		if (mutex_lock_interruptible(&ldata->atomic_read_lock))
2178			return -ERESTARTSYS;
2179	}
2180
2181	down_read(&tty->termios_rwsem);
2182
2183	minimum = time = 0;
2184	timeout = MAX_SCHEDULE_TIMEOUT;
2185	if (!ldata->icanon) {
2186		minimum = MIN_CHAR(tty);
2187		if (minimum) {
2188			time = (HZ / 10) * TIME_CHAR(tty);
2189		} else {
2190			timeout = (HZ / 10) * TIME_CHAR(tty);
2191			minimum = 1;
2192		}
2193	}
2194
2195	packet = tty->ctrl.packet;
2196	old_tail = ldata->read_tail;
2197
2198	add_wait_queue(&tty->read_wait, &wait);
2199	while (nr) {
2200		/* First test for status change. */
2201		if (packet && tty->link->ctrl.pktstatus) {
2202			unsigned char cs;
2203			if (kb != kbuf)
2204				break;
2205			spin_lock_irq(&tty->link->ctrl.lock);
2206			cs = tty->link->ctrl.pktstatus;
2207			tty->link->ctrl.pktstatus = 0;
2208			spin_unlock_irq(&tty->link->ctrl.lock);
2209			*kb++ = cs;
2210			nr--;
2211			break;
2212		}
2213
2214		if (!input_available_p(tty, 0)) {
2215			up_read(&tty->termios_rwsem);
2216			tty_buffer_flush_work(tty->port);
2217			down_read(&tty->termios_rwsem);
2218			if (!input_available_p(tty, 0)) {
2219				if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
2220					retval = -EIO;
2221					break;
2222				}
2223				if (tty_hung_up_p(file))
2224					break;
2225				/*
2226				 * Abort readers for ttys which never actually
2227				 * get hung up.  See __tty_hangup().
2228				 */
2229				if (test_bit(TTY_HUPPING, &tty->flags))
2230					break;
2231				if (!timeout)
2232					break;
2233				if (tty_io_nonblock(tty, file)) {
2234					retval = -EAGAIN;
2235					break;
2236				}
2237				if (signal_pending(current)) {
2238					retval = -ERESTARTSYS;
2239					break;
2240				}
2241				up_read(&tty->termios_rwsem);
2242
2243				timeout = wait_woken(&wait, TASK_INTERRUPTIBLE,
2244						timeout);
2245
2246				down_read(&tty->termios_rwsem);
2247				continue;
2248			}
2249		}
2250
2251		if (ldata->icanon && !L_EXTPROC(tty)) {
2252			if (canon_copy_from_read_buf(tty, &kb, &nr))
2253				goto more_to_be_read;
2254		} else {
2255			/* Deal with packet mode. */
2256			if (packet && kb == kbuf) {
2257				*kb++ = TIOCPKT_DATA;
2258				nr--;
2259			}
2260
2261			/*
2262			 * Copy data, and if there is more to be had
2263			 * and we have nothing more to wait for, then
2264			 * let's mark us for retries.
2265			 *
2266			 * NOTE! We return here with both the termios_sem
2267			 * and atomic_read_lock still held, the retries
2268			 * will release them when done.
2269			 */
2270			if (copy_from_read_buf(tty, &kb, &nr) && kb - kbuf >= minimum) {
2271more_to_be_read:
2272				remove_wait_queue(&tty->read_wait, &wait);
2273				*cookie = cookie;
2274				return kb - kbuf;
2275			}
2276		}
2277
2278		n_tty_check_unthrottle(tty);
2279
2280		if (kb - kbuf >= minimum)
2281			break;
2282		if (time)
2283			timeout = time;
2284	}
2285	if (old_tail != ldata->read_tail)
2286		n_tty_kick_worker(tty);
2287	up_read(&tty->termios_rwsem);
2288
2289	remove_wait_queue(&tty->read_wait, &wait);
2290	mutex_unlock(&ldata->atomic_read_lock);
2291
2292	if (kb - kbuf)
2293		retval = kb - kbuf;
2294
2295	return retval;
2296}
2297
2298/**
2299 * n_tty_write		-	write function for tty
2300 * @tty: tty device
2301 * @file: file object
2302 * @buf: userspace buffer pointer
2303 * @nr: size of I/O
2304 *
2305 * Write function of the terminal device. This is serialized with respect to
2306 * other write callers but not to termios changes, reads and other such events.
2307 * Since the receive code will echo characters, thus calling driver write
2308 * methods, the %output_lock is used in the output processing functions called
2309 * here as well as in the echo processing function to protect the column state
2310 * and space left in the buffer.
2311 *
2312 * This code must be sure never to sleep through a hangup.
2313 *
2314 * Locking: output_lock to protect column state and space left
2315 *	 (note that the process_output*() functions take this lock themselves)
 
 
2316 */
2317
2318static ssize_t n_tty_write(struct tty_struct *tty, struct file *file,
2319			   const unsigned char *buf, size_t nr)
2320{
2321	const unsigned char *b = buf;
2322	DEFINE_WAIT_FUNC(wait, woken_wake_function);
2323	int c;
2324	ssize_t retval = 0;
2325
2326	/* Job control check -- must be done at start (POSIX.1 7.1.1.4). */
2327	if (L_TOSTOP(tty) && file->f_op->write_iter != redirected_tty_write) {
2328		retval = tty_check_change(tty);
2329		if (retval)
2330			return retval;
2331	}
2332
2333	down_read(&tty->termios_rwsem);
2334
2335	/* Write out any echoed characters that are still pending */
2336	process_echoes(tty);
2337
2338	add_wait_queue(&tty->write_wait, &wait);
2339	while (1) {
2340		if (signal_pending(current)) {
2341			retval = -ERESTARTSYS;
2342			break;
2343		}
2344		if (tty_hung_up_p(file) || (tty->link && !tty->link->count)) {
2345			retval = -EIO;
2346			break;
2347		}
2348		if (O_OPOST(tty)) {
2349			while (nr > 0) {
2350				ssize_t num = process_output_block(tty, b, nr);
2351				if (num < 0) {
2352					if (num == -EAGAIN)
2353						break;
2354					retval = num;
2355					goto break_out;
2356				}
2357				b += num;
2358				nr -= num;
2359				if (nr == 0)
2360					break;
2361				c = *b;
2362				if (process_output(c, tty) < 0)
2363					break;
2364				b++; nr--;
2365			}
2366			if (tty->ops->flush_chars)
2367				tty->ops->flush_chars(tty);
2368		} else {
2369			struct n_tty_data *ldata = tty->disc_data;
2370
2371			while (nr > 0) {
2372				mutex_lock(&ldata->output_lock);
2373				c = tty->ops->write(tty, b, nr);
2374				mutex_unlock(&ldata->output_lock);
2375				if (c < 0) {
2376					retval = c;
2377					goto break_out;
2378				}
2379				if (!c)
2380					break;
2381				b += c;
2382				nr -= c;
2383			}
2384		}
2385		if (!nr)
2386			break;
2387		if (tty_io_nonblock(tty, file)) {
2388			retval = -EAGAIN;
2389			break;
2390		}
2391		up_read(&tty->termios_rwsem);
2392
2393		wait_woken(&wait, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
2394
2395		down_read(&tty->termios_rwsem);
2396	}
2397break_out:
2398	remove_wait_queue(&tty->write_wait, &wait);
2399	if (nr && tty->fasync)
2400		set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
2401	up_read(&tty->termios_rwsem);
2402	return (b - buf) ? b - buf : retval;
2403}
2404
2405/**
2406 * n_tty_poll		-	poll method for N_TTY
2407 * @tty: terminal device
2408 * @file: file accessing it
2409 * @wait: poll table
2410 *
2411 * Called when the line discipline is asked to poll() for data or for special
2412 * events. This code is not serialized with respect to other events save
2413 * open/close.
2414 *
2415 * This code must be sure never to sleep through a hangup.
2416 *
2417 * Locking: called without the kernel lock held -- fine.
 
2418 */
 
2419static __poll_t n_tty_poll(struct tty_struct *tty, struct file *file,
2420							poll_table *wait)
2421{
2422	__poll_t mask = 0;
2423
2424	poll_wait(file, &tty->read_wait, wait);
2425	poll_wait(file, &tty->write_wait, wait);
2426	if (input_available_p(tty, 1))
2427		mask |= EPOLLIN | EPOLLRDNORM;
2428	else {
2429		tty_buffer_flush_work(tty->port);
2430		if (input_available_p(tty, 1))
2431			mask |= EPOLLIN | EPOLLRDNORM;
2432	}
2433	if (tty->ctrl.packet && tty->link->ctrl.pktstatus)
2434		mask |= EPOLLPRI | EPOLLIN | EPOLLRDNORM;
2435	if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
2436		mask |= EPOLLHUP;
2437	if (tty_hung_up_p(file))
2438		mask |= EPOLLHUP;
2439	if (tty->ops->write && !tty_is_writelocked(tty) &&
2440			tty_chars_in_buffer(tty) < WAKEUP_CHARS &&
2441			tty_write_room(tty) > 0)
2442		mask |= EPOLLOUT | EPOLLWRNORM;
2443	return mask;
2444}
2445
2446static unsigned long inq_canon(struct n_tty_data *ldata)
2447{
2448	size_t nr, head, tail;
2449
2450	if (ldata->canon_head == ldata->read_tail)
2451		return 0;
2452	head = ldata->canon_head;
2453	tail = ldata->read_tail;
2454	nr = head - tail;
2455	/* Skip EOF-chars.. */
2456	while (MASK(head) != MASK(tail)) {
2457		if (test_bit(tail & (N_TTY_BUF_SIZE - 1), ldata->read_flags) &&
2458		    read_buf(ldata, tail) == __DISABLED_CHAR)
2459			nr--;
2460		tail++;
2461	}
2462	return nr;
2463}
2464
2465static int n_tty_ioctl(struct tty_struct *tty, unsigned int cmd,
2466		       unsigned long arg)
2467{
2468	struct n_tty_data *ldata = tty->disc_data;
2469	int retval;
2470
2471	switch (cmd) {
2472	case TIOCOUTQ:
2473		return put_user(tty_chars_in_buffer(tty), (int __user *) arg);
2474	case TIOCINQ:
2475		down_write(&tty->termios_rwsem);
2476		if (L_ICANON(tty) && !L_EXTPROC(tty))
2477			retval = inq_canon(ldata);
2478		else
2479			retval = read_cnt(ldata);
2480		up_write(&tty->termios_rwsem);
2481		return put_user(retval, (unsigned int __user *) arg);
2482	default:
2483		return n_tty_ioctl_helper(tty, cmd, arg);
2484	}
2485}
2486
2487static struct tty_ldisc_ops n_tty_ops = {
2488	.owner		 = THIS_MODULE,
2489	.num		 = N_TTY,
2490	.name            = "n_tty",
2491	.open            = n_tty_open,
2492	.close           = n_tty_close,
2493	.flush_buffer    = n_tty_flush_buffer,
2494	.read            = n_tty_read,
2495	.write           = n_tty_write,
2496	.ioctl           = n_tty_ioctl,
2497	.set_termios     = n_tty_set_termios,
2498	.poll            = n_tty_poll,
2499	.receive_buf     = n_tty_receive_buf,
2500	.write_wakeup    = n_tty_write_wakeup,
2501	.receive_buf2	 = n_tty_receive_buf2,
2502	.lookahead_buf	 = n_tty_lookahead_flow_ctrl,
2503};
2504
2505/**
2506 *	n_tty_inherit_ops	-	inherit N_TTY methods
2507 *	@ops: struct tty_ldisc_ops where to save N_TTY methods
2508 *
2509 *	Enables a 'subclass' line discipline to 'inherit' N_TTY methods.
2510 */
2511
2512void n_tty_inherit_ops(struct tty_ldisc_ops *ops)
2513{
2514	*ops = n_tty_ops;
2515	ops->owner = NULL;
 
2516}
2517EXPORT_SYMBOL_GPL(n_tty_inherit_ops);
2518
2519void __init n_tty_init(void)
2520{
2521	tty_register_ldisc(&n_tty_ops);
2522}