ASoC: Merge dropped fixes from v5.18
[platform/kernel/linux-starfive.git] / drivers / tty / n_tty.c
1 // SPDX-License-Identifier: GPL-1.0+
2 /*
3  * n_tty.c --- implements the N_TTY line discipline.
4  *
5  * This code used to be in tty_io.c, but things are getting hairy
6  * enough that it made sense to split things off.  (The N_TTY
7  * processing has changed so much that it's hardly recognizable,
8  * anyway...)
9  *
10  * Note that the open routine for N_TTY is guaranteed never to return
11  * an error.  This is because Linux will fall back to setting a line
12  * to N_TTY if it can not switch to any other line discipline.
13  *
14  * Written by Theodore Ts'o, Copyright 1994.
15  *
16  * This file also contains code originally written by Linus Torvalds,
17  * Copyright 1991, 1992, 1993, and by Julian Cowley, Copyright 1994.
18  *
19  * Reduced memory usage for older ARM systems  - Russell King.
20  *
21  * 2000/01/20   Fixed SMP locking on put_tty_queue using bits of
22  *              the patch by Andrew J. Kroll <ag784@freenet.buffalo.edu>
23  *              who actually finally proved there really was a race.
24  *
25  * 2002/03/18   Implemented n_tty_wakeup to send SIGIO POLL_OUTs to
26  *              waiting writing processes-Sapan Bhatia <sapan@corewars.org>.
27  *              Also fixed a bug in BLOCKING mode where n_tty_write returns
28  *              EAGAIN
29  */
30
31 #include <linux/types.h>
32 #include <linux/major.h>
33 #include <linux/errno.h>
34 #include <linux/signal.h>
35 #include <linux/fcntl.h>
36 #include <linux/sched.h>
37 #include <linux/interrupt.h>
38 #include <linux/tty.h>
39 #include <linux/timer.h>
40 #include <linux/ctype.h>
41 #include <linux/mm.h>
42 #include <linux/string.h>
43 #include <linux/slab.h>
44 #include <linux/poll.h>
45 #include <linux/bitops.h>
46 #include <linux/audit.h>
47 #include <linux/file.h>
48 #include <linux/uaccess.h>
49 #include <linux/module.h>
50 #include <linux/ratelimit.h>
51 #include <linux/vmalloc.h>
52 #include "tty.h"
53
54 /*
55  * Until this number of characters is queued in the xmit buffer, select will
56  * return "we have room for writes".
57  */
58 #define WAKEUP_CHARS 256
59
60 /*
61  * This defines the low- and high-watermarks for throttling and
62  * unthrottling the TTY driver.  These watermarks are used for
63  * controlling the space in the read buffer.
64  */
65 #define TTY_THRESHOLD_THROTTLE          128 /* now based on remaining room */
66 #define TTY_THRESHOLD_UNTHROTTLE        128
67
68 /*
69  * Special byte codes used in the echo buffer to represent operations
70  * or special handling of characters.  Bytes in the echo buffer that
71  * are not part of such special blocks are treated as normal character
72  * codes.
73  */
74 #define ECHO_OP_START 0xff
75 #define ECHO_OP_MOVE_BACK_COL 0x80
76 #define ECHO_OP_SET_CANON_COL 0x81
77 #define ECHO_OP_ERASE_TAB 0x82
78
79 #define ECHO_COMMIT_WATERMARK   256
80 #define ECHO_BLOCK              256
81 #define ECHO_DISCARD_WATERMARK  N_TTY_BUF_SIZE - (ECHO_BLOCK + 32)
82
83
84 #undef N_TTY_TRACE
85 #ifdef N_TTY_TRACE
86 # define n_tty_trace(f, args...)        trace_printk(f, ##args)
87 #else
88 # define n_tty_trace(f, args...)        no_printk(f, ##args)
89 #endif
90
91 struct n_tty_data {
92         /* producer-published */
93         size_t read_head;
94         size_t commit_head;
95         size_t canon_head;
96         size_t echo_head;
97         size_t echo_commit;
98         size_t echo_mark;
99         DECLARE_BITMAP(char_map, 256);
100
101         /* private to n_tty_receive_overrun (single-threaded) */
102         unsigned long overrun_time;
103         int num_overrun;
104
105         /* non-atomic */
106         bool no_room;
107
108         /* must hold exclusive termios_rwsem to reset these */
109         unsigned char lnext:1, erasing:1, raw:1, real_raw:1, icanon:1;
110         unsigned char push:1;
111
112         /* shared by producer and consumer */
113         char read_buf[N_TTY_BUF_SIZE];
114         DECLARE_BITMAP(read_flags, N_TTY_BUF_SIZE);
115         unsigned char echo_buf[N_TTY_BUF_SIZE];
116
117         /* consumer-published */
118         size_t read_tail;
119         size_t line_start;
120
121         /* # of chars looked ahead (to find software flow control chars) */
122         size_t lookahead_count;
123
124         /* protected by output lock */
125         unsigned int column;
126         unsigned int canon_column;
127         size_t echo_tail;
128
129         struct mutex atomic_read_lock;
130         struct mutex output_lock;
131 };
132
133 #define MASK(x) ((x) & (N_TTY_BUF_SIZE - 1))
134
135 static inline size_t read_cnt(struct n_tty_data *ldata)
136 {
137         return ldata->read_head - ldata->read_tail;
138 }
139
140 static inline unsigned char read_buf(struct n_tty_data *ldata, size_t i)
141 {
142         return ldata->read_buf[i & (N_TTY_BUF_SIZE - 1)];
143 }
144
145 static inline unsigned char *read_buf_addr(struct n_tty_data *ldata, size_t i)
146 {
147         return &ldata->read_buf[i & (N_TTY_BUF_SIZE - 1)];
148 }
149
150 static inline unsigned char echo_buf(struct n_tty_data *ldata, size_t i)
151 {
152         smp_rmb(); /* Matches smp_wmb() in add_echo_byte(). */
153         return ldata->echo_buf[i & (N_TTY_BUF_SIZE - 1)];
154 }
155
156 static inline unsigned char *echo_buf_addr(struct n_tty_data *ldata, size_t i)
157 {
158         return &ldata->echo_buf[i & (N_TTY_BUF_SIZE - 1)];
159 }
160
161 /* If we are not echoing the data, perhaps this is a secret so erase it */
162 static void zero_buffer(struct tty_struct *tty, u8 *buffer, int size)
163 {
164         bool icanon = !!L_ICANON(tty);
165         bool no_echo = !L_ECHO(tty);
166
167         if (icanon && no_echo)
168                 memset(buffer, 0x00, size);
169 }
170
171 static void tty_copy(struct tty_struct *tty, void *to, size_t tail, size_t n)
172 {
173         struct n_tty_data *ldata = tty->disc_data;
174         size_t size = N_TTY_BUF_SIZE - tail;
175         void *from = read_buf_addr(ldata, tail);
176
177         if (n > size) {
178                 tty_audit_add_data(tty, from, size);
179                 memcpy(to, from, size);
180                 zero_buffer(tty, from, size);
181                 to += size;
182                 n -= size;
183                 from = ldata->read_buf;
184         }
185
186         tty_audit_add_data(tty, from, n);
187         memcpy(to, from, n);
188         zero_buffer(tty, from, n);
189 }
190
191 /**
192  * n_tty_kick_worker - start input worker (if required)
193  * @tty: terminal
194  *
195  * Re-schedules the flip buffer work if it may have stopped.
196  *
197  * Locking:
198  *  * Caller holds exclusive %termios_rwsem, or
199  *  * n_tty_read()/consumer path:
200  *      holds non-exclusive %termios_rwsem
201  */
202 static void n_tty_kick_worker(struct tty_struct *tty)
203 {
204         struct n_tty_data *ldata = tty->disc_data;
205
206         /* Did the input worker stop? Restart it */
207         if (unlikely(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
222 static ssize_t chars_in_buffer(struct tty_struct *tty)
223 {
224         struct n_tty_data *ldata = tty->disc_data;
225         ssize_t n = 0;
226
227         if (!ldata->icanon)
228                 n = ldata->commit_head - ldata->read_tail;
229         else
230                 n = ldata->canon_head - ldata->read_tail;
231         return n;
232 }
233
234 /**
235  * n_tty_write_wakeup   -       asynchronous I/O notifier
236  * @tty: tty device
237  *
238  * Required for the ptys, serial driver etc. since processes that attach
239  * themselves to the master and rely on ASYNC IO must be woken up.
240  */
241 static void n_tty_write_wakeup(struct tty_struct *tty)
242 {
243         clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
244         kill_fasync(&tty->fasync, SIGIO, POLL_OUT);
245 }
246
247 static void n_tty_check_throttle(struct tty_struct *tty)
248 {
249         struct n_tty_data *ldata = tty->disc_data;
250
251         /*
252          * Check the remaining room for the input canonicalization
253          * mode.  We don't want to throttle the driver if we're in
254          * canonical mode and don't have a newline yet!
255          */
256         if (ldata->icanon && ldata->canon_head == ldata->read_tail)
257                 return;
258
259         while (1) {
260                 int throttled;
261                 tty_set_flow_change(tty, TTY_THROTTLE_SAFE);
262                 if (N_TTY_BUF_SIZE - read_cnt(ldata) >= TTY_THRESHOLD_THROTTLE)
263                         break;
264                 throttled = tty_throttle_safe(tty);
265                 if (!throttled)
266                         break;
267         }
268         __tty_set_flow_change(tty, 0);
269 }
270
271 static void n_tty_check_unthrottle(struct tty_struct *tty)
272 {
273         if (tty->driver->type == TTY_DRIVER_TYPE_PTY) {
274                 if (chars_in_buffer(tty) > TTY_THRESHOLD_UNTHROTTLE)
275                         return;
276                 n_tty_kick_worker(tty);
277                 tty_wakeup(tty->link);
278                 return;
279         }
280
281         /* If there is enough space in the read buffer now, let the
282          * low-level driver know. We use chars_in_buffer() to
283          * check the buffer, as it now knows about canonical mode.
284          * Otherwise, if the driver is throttled and the line is
285          * longer than TTY_THRESHOLD_UNTHROTTLE in canonical mode,
286          * we won't get any more characters.
287          */
288
289         while (1) {
290                 int unthrottled;
291                 tty_set_flow_change(tty, TTY_UNTHROTTLE_SAFE);
292                 if (chars_in_buffer(tty) > TTY_THRESHOLD_UNTHROTTLE)
293                         break;
294                 n_tty_kick_worker(tty);
295                 unthrottled = tty_unthrottle_safe(tty);
296                 if (!unthrottled)
297                         break;
298         }
299         __tty_set_flow_change(tty, 0);
300 }
301
302 /**
303  * put_tty_queue                -       add character to tty
304  * @c: character
305  * @ldata: n_tty data
306  *
307  * Add a character to the tty read_buf queue.
308  *
309  * Locking:
310  *  * n_tty_receive_buf()/producer path:
311  *      caller holds non-exclusive %termios_rwsem
312  */
313 static inline void put_tty_queue(unsigned char c, struct n_tty_data *ldata)
314 {
315         *read_buf_addr(ldata, ldata->read_head) = c;
316         ldata->read_head++;
317 }
318
319 /**
320  * reset_buffer_flags   -       reset buffer state
321  * @ldata: line disc data to reset
322  *
323  * Reset the read buffer counters and clear the flags. Called from
324  * n_tty_open() and n_tty_flush_buffer().
325  *
326  * Locking:
327  *  * caller holds exclusive %termios_rwsem, or
328  *  * (locking is not required)
329  */
330 static void reset_buffer_flags(struct n_tty_data *ldata)
331 {
332         ldata->read_head = ldata->canon_head = ldata->read_tail = 0;
333         ldata->commit_head = 0;
334         ldata->line_start = 0;
335
336         ldata->erasing = 0;
337         bitmap_zero(ldata->read_flags, N_TTY_BUF_SIZE);
338         ldata->push = 0;
339
340         ldata->lookahead_count = 0;
341 }
342
343 static void n_tty_packet_mode_flush(struct tty_struct *tty)
344 {
345         unsigned long flags;
346
347         if (tty->link->ctrl.packet) {
348                 spin_lock_irqsave(&tty->ctrl.lock, flags);
349                 tty->ctrl.pktstatus |= TIOCPKT_FLUSHREAD;
350                 spin_unlock_irqrestore(&tty->ctrl.lock, flags);
351                 wake_up_interruptible(&tty->link->read_wait);
352         }
353 }
354
355 /**
356  * n_tty_flush_buffer   -       clean input queue
357  * @tty: terminal device
358  *
359  * Flush the input buffer. Called when the tty layer wants the buffer flushed
360  * (eg at hangup) or when the %N_TTY line discipline internally has to clean
361  * the pending queue (for example some signals).
362  *
363  * Holds %termios_rwsem to exclude producer/consumer while buffer indices are
364  * reset.
365  *
366  * Locking: %ctrl.lock, exclusive %termios_rwsem
367  */
368 static void n_tty_flush_buffer(struct tty_struct *tty)
369 {
370         down_write(&tty->termios_rwsem);
371         reset_buffer_flags(tty->disc_data);
372         n_tty_kick_worker(tty);
373
374         if (tty->link)
375                 n_tty_packet_mode_flush(tty);
376         up_write(&tty->termios_rwsem);
377 }
378
379 /**
380  * is_utf8_continuation -       utf8 multibyte check
381  * @c: byte to check
382  *
383  * Returns: true if the utf8 character @c is a multibyte continuation
384  * character. We use this to correctly compute the on-screen size of the
385  * character when printing.
386  */
387 static inline int is_utf8_continuation(unsigned char c)
388 {
389         return (c & 0xc0) == 0x80;
390 }
391
392 /**
393  * is_continuation      -       multibyte check
394  * @c: byte to check
395  * @tty: terminal device
396  *
397  * Returns: true if the utf8 character @c is a multibyte continuation character
398  * and the terminal is in unicode mode.
399  */
400 static inline int is_continuation(unsigned char c, struct tty_struct *tty)
401 {
402         return I_IUTF8(tty) && is_utf8_continuation(c);
403 }
404
405 /**
406  * do_output_char       -       output one character
407  * @c: character (or partial unicode symbol)
408  * @tty: terminal device
409  * @space: space available in tty driver write buffer
410  *
411  * This is a helper function that handles one output character (including
412  * special characters like TAB, CR, LF, etc.), doing OPOST processing and
413  * putting the results in the tty driver's write buffer.
414  *
415  * Note that Linux currently ignores TABDLY, CRDLY, VTDLY, FFDLY and NLDLY.
416  * They simply aren't relevant in the world today. If you ever need them, add
417  * them here.
418  *
419  * Returns: the number of bytes of buffer space used or -1 if no space left.
420  *
421  * Locking: should be called under the %output_lock to protect the column state
422  * and space left in the buffer.
423  */
424 static int do_output_char(unsigned char c, struct tty_struct *tty, int space)
425 {
426         struct n_tty_data *ldata = tty->disc_data;
427         int     spaces;
428
429         if (!space)
430                 return -1;
431
432         switch (c) {
433         case '\n':
434                 if (O_ONLRET(tty))
435                         ldata->column = 0;
436                 if (O_ONLCR(tty)) {
437                         if (space < 2)
438                                 return -1;
439                         ldata->canon_column = ldata->column = 0;
440                         tty->ops->write(tty, "\r\n", 2);
441                         return 2;
442                 }
443                 ldata->canon_column = ldata->column;
444                 break;
445         case '\r':
446                 if (O_ONOCR(tty) && ldata->column == 0)
447                         return 0;
448                 if (O_OCRNL(tty)) {
449                         c = '\n';
450                         if (O_ONLRET(tty))
451                                 ldata->canon_column = ldata->column = 0;
452                         break;
453                 }
454                 ldata->canon_column = ldata->column = 0;
455                 break;
456         case '\t':
457                 spaces = 8 - (ldata->column & 7);
458                 if (O_TABDLY(tty) == XTABS) {
459                         if (space < spaces)
460                                 return -1;
461                         ldata->column += spaces;
462                         tty->ops->write(tty, "        ", spaces);
463                         return spaces;
464                 }
465                 ldata->column += spaces;
466                 break;
467         case '\b':
468                 if (ldata->column > 0)
469                         ldata->column--;
470                 break;
471         default:
472                 if (!iscntrl(c)) {
473                         if (O_OLCUC(tty))
474                                 c = toupper(c);
475                         if (!is_continuation(c, tty))
476                                 ldata->column++;
477                 }
478                 break;
479         }
480
481         tty_put_char(tty, c);
482         return 1;
483 }
484
485 /**
486  * process_output       -       output post processor
487  * @c: character (or partial unicode symbol)
488  * @tty: terminal device
489  *
490  * Output one character with OPOST processing.
491  *
492  * Returns: -1 when the output device is full and the character must be
493  * retried.
494  *
495  * Locking: %output_lock to protect column state and space left (also, this is
496  *called from n_tty_write() under the tty layer write lock).
497  */
498 static int process_output(unsigned char c, struct tty_struct *tty)
499 {
500         struct n_tty_data *ldata = tty->disc_data;
501         int     space, retval;
502
503         mutex_lock(&ldata->output_lock);
504
505         space = tty_write_room(tty);
506         retval = do_output_char(c, tty, space);
507
508         mutex_unlock(&ldata->output_lock);
509         if (retval < 0)
510                 return -1;
511         else
512                 return 0;
513 }
514
515 /**
516  * process_output_block -       block post processor
517  * @tty: terminal device
518  * @buf: character buffer
519  * @nr: number of bytes to output
520  *
521  * Output a block of characters with OPOST processing.
522  *
523  * This path is used to speed up block console writes, among other things when
524  * processing blocks of output data. It handles only the simple cases normally
525  * found and helps to generate blocks of symbols for the console driver and
526  * thus improve performance.
527  *
528  * Returns: the number of characters output.
529  *
530  * Locking: %output_lock to protect column state and space left (also, this is
531  * called from n_tty_write() under the tty layer write lock).
532  */
533 static ssize_t process_output_block(struct tty_struct *tty,
534                                     const unsigned char *buf, unsigned int nr)
535 {
536         struct n_tty_data *ldata = tty->disc_data;
537         int     space;
538         int     i;
539         const unsigned char *cp;
540
541         mutex_lock(&ldata->output_lock);
542
543         space = tty_write_room(tty);
544         if (space <= 0) {
545                 mutex_unlock(&ldata->output_lock);
546                 return space;
547         }
548         if (nr > space)
549                 nr = space;
550
551         for (i = 0, cp = buf; i < nr; i++, cp++) {
552                 unsigned char c = *cp;
553
554                 switch (c) {
555                 case '\n':
556                         if (O_ONLRET(tty))
557                                 ldata->column = 0;
558                         if (O_ONLCR(tty))
559                                 goto break_out;
560                         ldata->canon_column = ldata->column;
561                         break;
562                 case '\r':
563                         if (O_ONOCR(tty) && ldata->column == 0)
564                                 goto break_out;
565                         if (O_OCRNL(tty))
566                                 goto break_out;
567                         ldata->canon_column = ldata->column = 0;
568                         break;
569                 case '\t':
570                         goto break_out;
571                 case '\b':
572                         if (ldata->column > 0)
573                                 ldata->column--;
574                         break;
575                 default:
576                         if (!iscntrl(c)) {
577                                 if (O_OLCUC(tty))
578                                         goto break_out;
579                                 if (!is_continuation(c, tty))
580                                         ldata->column++;
581                         }
582                         break;
583                 }
584         }
585 break_out:
586         i = tty->ops->write(tty, buf, i);
587
588         mutex_unlock(&ldata->output_lock);
589         return i;
590 }
591
592 /**
593  * __process_echoes     -       write pending echo characters
594  * @tty: terminal device
595  *
596  * Write previously buffered echo (and other ldisc-generated) characters to the
597  * tty.
598  *
599  * Characters generated by the ldisc (including echoes) need to be buffered
600  * because the driver's write buffer can fill during heavy program output.
601  * Echoing straight to the driver will often fail under these conditions,
602  * causing lost characters and resulting mismatches of ldisc state information.
603  *
604  * Since the ldisc state must represent the characters actually sent to the
605  * driver at the time of the write, operations like certain changes in column
606  * state are also saved in the buffer and executed here.
607  *
608  * A circular fifo buffer is used so that the most recent characters are
609  * prioritized. Also, when control characters are echoed with a prefixed "^",
610  * the pair is treated atomically and thus not separated.
611  *
612  * Locking: callers must hold %output_lock.
613  */
614 static size_t __process_echoes(struct tty_struct *tty)
615 {
616         struct n_tty_data *ldata = tty->disc_data;
617         int     space, old_space;
618         size_t tail;
619         unsigned char c;
620
621         old_space = space = tty_write_room(tty);
622
623         tail = ldata->echo_tail;
624         while (MASK(ldata->echo_commit) != MASK(tail)) {
625                 c = echo_buf(ldata, tail);
626                 if (c == ECHO_OP_START) {
627                         unsigned char op;
628                         int no_space_left = 0;
629
630                         /*
631                          * Since add_echo_byte() is called without holding
632                          * output_lock, we might see only portion of multi-byte
633                          * operation.
634                          */
635                         if (MASK(ldata->echo_commit) == MASK(tail + 1))
636                                 goto not_yet_stored;
637                         /*
638                          * If the buffer byte is the start of a multi-byte
639                          * operation, get the next byte, which is either the
640                          * op code or a control character value.
641                          */
642                         op = echo_buf(ldata, tail + 1);
643
644                         switch (op) {
645                         case ECHO_OP_ERASE_TAB: {
646                                 unsigned int num_chars, num_bs;
647
648                                 if (MASK(ldata->echo_commit) == MASK(tail + 2))
649                                         goto not_yet_stored;
650                                 num_chars = echo_buf(ldata, tail + 2);
651
652                                 /*
653                                  * Determine how many columns to go back
654                                  * in order to erase the tab.
655                                  * This depends on the number of columns
656                                  * used by other characters within the tab
657                                  * area.  If this (modulo 8) count is from
658                                  * the start of input rather than from a
659                                  * previous tab, we offset by canon column.
660                                  * Otherwise, tab spacing is normal.
661                                  */
662                                 if (!(num_chars & 0x80))
663                                         num_chars += ldata->canon_column;
664                                 num_bs = 8 - (num_chars & 7);
665
666                                 if (num_bs > space) {
667                                         no_space_left = 1;
668                                         break;
669                                 }
670                                 space -= num_bs;
671                                 while (num_bs--) {
672                                         tty_put_char(tty, '\b');
673                                         if (ldata->column > 0)
674                                                 ldata->column--;
675                                 }
676                                 tail += 3;
677                                 break;
678                         }
679                         case ECHO_OP_SET_CANON_COL:
680                                 ldata->canon_column = ldata->column;
681                                 tail += 2;
682                                 break;
683
684                         case ECHO_OP_MOVE_BACK_COL:
685                                 if (ldata->column > 0)
686                                         ldata->column--;
687                                 tail += 2;
688                                 break;
689
690                         case ECHO_OP_START:
691                                 /* This is an escaped echo op start code */
692                                 if (!space) {
693                                         no_space_left = 1;
694                                         break;
695                                 }
696                                 tty_put_char(tty, ECHO_OP_START);
697                                 ldata->column++;
698                                 space--;
699                                 tail += 2;
700                                 break;
701
702                         default:
703                                 /*
704                                  * If the op is not a special byte code,
705                                  * it is a ctrl char tagged to be echoed
706                                  * as "^X" (where X is the letter
707                                  * representing the control char).
708                                  * Note that we must ensure there is
709                                  * enough space for the whole ctrl pair.
710                                  *
711                                  */
712                                 if (space < 2) {
713                                         no_space_left = 1;
714                                         break;
715                                 }
716                                 tty_put_char(tty, '^');
717                                 tty_put_char(tty, op ^ 0100);
718                                 ldata->column += 2;
719                                 space -= 2;
720                                 tail += 2;
721                         }
722
723                         if (no_space_left)
724                                 break;
725                 } else {
726                         if (O_OPOST(tty)) {
727                                 int retval = do_output_char(c, tty, space);
728                                 if (retval < 0)
729                                         break;
730                                 space -= retval;
731                         } else {
732                                 if (!space)
733                                         break;
734                                 tty_put_char(tty, c);
735                                 space -= 1;
736                         }
737                         tail += 1;
738                 }
739         }
740
741         /* If the echo buffer is nearly full (so that the possibility exists
742          * of echo overrun before the next commit), then discard enough
743          * data at the tail to prevent a subsequent overrun */
744         while (ldata->echo_commit > tail &&
745                ldata->echo_commit - tail >= ECHO_DISCARD_WATERMARK) {
746                 if (echo_buf(ldata, tail) == ECHO_OP_START) {
747                         if (echo_buf(ldata, tail + 1) == ECHO_OP_ERASE_TAB)
748                                 tail += 3;
749                         else
750                                 tail += 2;
751                 } else
752                         tail++;
753         }
754
755  not_yet_stored:
756         ldata->echo_tail = tail;
757         return old_space - space;
758 }
759
760 static void commit_echoes(struct tty_struct *tty)
761 {
762         struct n_tty_data *ldata = tty->disc_data;
763         size_t nr, old, echoed;
764         size_t head;
765
766         mutex_lock(&ldata->output_lock);
767         head = ldata->echo_head;
768         ldata->echo_mark = head;
769         old = ldata->echo_commit - ldata->echo_tail;
770
771         /* Process committed echoes if the accumulated # of bytes
772          * is over the threshold (and try again each time another
773          * block is accumulated) */
774         nr = head - ldata->echo_tail;
775         if (nr < ECHO_COMMIT_WATERMARK ||
776             (nr % ECHO_BLOCK > old % ECHO_BLOCK)) {
777                 mutex_unlock(&ldata->output_lock);
778                 return;
779         }
780
781         ldata->echo_commit = head;
782         echoed = __process_echoes(tty);
783         mutex_unlock(&ldata->output_lock);
784
785         if (echoed && tty->ops->flush_chars)
786                 tty->ops->flush_chars(tty);
787 }
788
789 static void process_echoes(struct tty_struct *tty)
790 {
791         struct n_tty_data *ldata = tty->disc_data;
792         size_t echoed;
793
794         if (ldata->echo_mark == ldata->echo_tail)
795                 return;
796
797         mutex_lock(&ldata->output_lock);
798         ldata->echo_commit = ldata->echo_mark;
799         echoed = __process_echoes(tty);
800         mutex_unlock(&ldata->output_lock);
801
802         if (echoed && tty->ops->flush_chars)
803                 tty->ops->flush_chars(tty);
804 }
805
806 /* NB: echo_mark and echo_head should be equivalent here */
807 static void flush_echoes(struct tty_struct *tty)
808 {
809         struct n_tty_data *ldata = tty->disc_data;
810
811         if ((!L_ECHO(tty) && !L_ECHONL(tty)) ||
812             ldata->echo_commit == ldata->echo_head)
813                 return;
814
815         mutex_lock(&ldata->output_lock);
816         ldata->echo_commit = ldata->echo_head;
817         __process_echoes(tty);
818         mutex_unlock(&ldata->output_lock);
819 }
820
821 /**
822  * add_echo_byte        -       add a byte to the echo buffer
823  * @c: unicode byte to echo
824  * @ldata: n_tty data
825  *
826  * Add a character or operation byte to the echo buffer.
827  */
828 static inline void add_echo_byte(unsigned char c, struct n_tty_data *ldata)
829 {
830         *echo_buf_addr(ldata, ldata->echo_head) = c;
831         smp_wmb(); /* Matches smp_rmb() in echo_buf(). */
832         ldata->echo_head++;
833 }
834
835 /**
836  * echo_move_back_col   -       add operation to move back a column
837  * @ldata: n_tty data
838  *
839  * Add an operation to the echo buffer to move back one column.
840  */
841 static void echo_move_back_col(struct n_tty_data *ldata)
842 {
843         add_echo_byte(ECHO_OP_START, ldata);
844         add_echo_byte(ECHO_OP_MOVE_BACK_COL, ldata);
845 }
846
847 /**
848  * echo_set_canon_col   -       add operation to set the canon column
849  * @ldata: n_tty data
850  *
851  * Add an operation to the echo buffer to set the canon column to the current
852  * column.
853  */
854 static void echo_set_canon_col(struct n_tty_data *ldata)
855 {
856         add_echo_byte(ECHO_OP_START, ldata);
857         add_echo_byte(ECHO_OP_SET_CANON_COL, ldata);
858 }
859
860 /**
861  * echo_erase_tab       -       add operation to erase a tab
862  * @num_chars: number of character columns already used
863  * @after_tab: true if num_chars starts after a previous tab
864  * @ldata: n_tty data
865  *
866  * Add an operation to the echo buffer to erase a tab.
867  *
868  * Called by the eraser function, which knows how many character columns have
869  * been used since either a previous tab or the start of input. This
870  * information will be used later, along with canon column (if applicable), to
871  * go back the correct number of columns.
872  */
873 static void echo_erase_tab(unsigned int num_chars, int after_tab,
874                            struct n_tty_data *ldata)
875 {
876         add_echo_byte(ECHO_OP_START, ldata);
877         add_echo_byte(ECHO_OP_ERASE_TAB, ldata);
878
879         /* We only need to know this modulo 8 (tab spacing) */
880         num_chars &= 7;
881
882         /* Set the high bit as a flag if num_chars is after a previous tab */
883         if (after_tab)
884                 num_chars |= 0x80;
885
886         add_echo_byte(num_chars, ldata);
887 }
888
889 /**
890  * echo_char_raw        -       echo a character raw
891  * @c: unicode byte to echo
892  * @ldata: line disc data
893  *
894  * Echo user input back onto the screen. This must be called only when
895  * L_ECHO(tty) is true. Called from the &tty_driver.receive_buf() path.
896  *
897  * This variant does not treat control characters specially.
898  */
899 static void echo_char_raw(unsigned char c, struct n_tty_data *ldata)
900 {
901         if (c == ECHO_OP_START) {
902                 add_echo_byte(ECHO_OP_START, ldata);
903                 add_echo_byte(ECHO_OP_START, ldata);
904         } else {
905                 add_echo_byte(c, ldata);
906         }
907 }
908
909 /**
910  * echo_char            -       echo a character
911  * @c: unicode byte to echo
912  * @tty: terminal device
913  *
914  * Echo user input back onto the screen. This must be called only when
915  * L_ECHO(tty) is true. Called from the &tty_driver.receive_buf() path.
916  *
917  * This variant tags control characters to be echoed as "^X" (where X is the
918  * letter representing the control char).
919  */
920 static void echo_char(unsigned char c, struct tty_struct *tty)
921 {
922         struct n_tty_data *ldata = tty->disc_data;
923
924         if (c == ECHO_OP_START) {
925                 add_echo_byte(ECHO_OP_START, ldata);
926                 add_echo_byte(ECHO_OP_START, ldata);
927         } else {
928                 if (L_ECHOCTL(tty) && iscntrl(c) && c != '\t')
929                         add_echo_byte(ECHO_OP_START, ldata);
930                 add_echo_byte(c, ldata);
931         }
932 }
933
934 /**
935  * finish_erasing       -       complete erase
936  * @ldata: n_tty data
937  */
938 static inline void finish_erasing(struct n_tty_data *ldata)
939 {
940         if (ldata->erasing) {
941                 echo_char_raw('/', ldata);
942                 ldata->erasing = 0;
943         }
944 }
945
946 /**
947  * eraser               -       handle erase function
948  * @c: character input
949  * @tty: terminal device
950  *
951  * Perform erase and necessary output when an erase character is present in the
952  * stream from the driver layer. Handles the complexities of UTF-8 multibyte
953  * symbols.
954  *
955  * Locking: n_tty_receive_buf()/producer path:
956  *      caller holds non-exclusive %termios_rwsem
957  */
958 static void eraser(unsigned char c, struct tty_struct *tty)
959 {
960         struct n_tty_data *ldata = tty->disc_data;
961         enum { ERASE, WERASE, KILL } kill_type;
962         size_t head;
963         size_t cnt;
964         int seen_alnums;
965
966         if (ldata->read_head == ldata->canon_head) {
967                 /* process_output('\a', tty); */ /* what do you think? */
968                 return;
969         }
970         if (c == ERASE_CHAR(tty))
971                 kill_type = ERASE;
972         else if (c == WERASE_CHAR(tty))
973                 kill_type = WERASE;
974         else {
975                 if (!L_ECHO(tty)) {
976                         ldata->read_head = ldata->canon_head;
977                         return;
978                 }
979                 if (!L_ECHOK(tty) || !L_ECHOKE(tty) || !L_ECHOE(tty)) {
980                         ldata->read_head = ldata->canon_head;
981                         finish_erasing(ldata);
982                         echo_char(KILL_CHAR(tty), tty);
983                         /* Add a newline if ECHOK is on and ECHOKE is off. */
984                         if (L_ECHOK(tty))
985                                 echo_char_raw('\n', ldata);
986                         return;
987                 }
988                 kill_type = KILL;
989         }
990
991         seen_alnums = 0;
992         while (MASK(ldata->read_head) != MASK(ldata->canon_head)) {
993                 head = ldata->read_head;
994
995                 /* erase a single possibly multibyte character */
996                 do {
997                         head--;
998                         c = read_buf(ldata, head);
999                 } while (is_continuation(c, tty) &&
1000                          MASK(head) != MASK(ldata->canon_head));
1001
1002                 /* do not partially erase */
1003                 if (is_continuation(c, tty))
1004                         break;
1005
1006                 if (kill_type == WERASE) {
1007                         /* Equivalent to BSD's ALTWERASE. */
1008                         if (isalnum(c) || c == '_')
1009                                 seen_alnums++;
1010                         else if (seen_alnums)
1011                                 break;
1012                 }
1013                 cnt = ldata->read_head - head;
1014                 ldata->read_head = head;
1015                 if (L_ECHO(tty)) {
1016                         if (L_ECHOPRT(tty)) {
1017                                 if (!ldata->erasing) {
1018                                         echo_char_raw('\\', ldata);
1019                                         ldata->erasing = 1;
1020                                 }
1021                                 /* if cnt > 1, output a multi-byte character */
1022                                 echo_char(c, tty);
1023                                 while (--cnt > 0) {
1024                                         head++;
1025                                         echo_char_raw(read_buf(ldata, head), ldata);
1026                                         echo_move_back_col(ldata);
1027                                 }
1028                         } else if (kill_type == ERASE && !L_ECHOE(tty)) {
1029                                 echo_char(ERASE_CHAR(tty), tty);
1030                         } else if (c == '\t') {
1031                                 unsigned int num_chars = 0;
1032                                 int after_tab = 0;
1033                                 size_t tail = ldata->read_head;
1034
1035                                 /*
1036                                  * Count the columns used for characters
1037                                  * since the start of input or after a
1038                                  * previous tab.
1039                                  * This info is used to go back the correct
1040                                  * number of columns.
1041                                  */
1042                                 while (MASK(tail) != MASK(ldata->canon_head)) {
1043                                         tail--;
1044                                         c = read_buf(ldata, tail);
1045                                         if (c == '\t') {
1046                                                 after_tab = 1;
1047                                                 break;
1048                                         } else if (iscntrl(c)) {
1049                                                 if (L_ECHOCTL(tty))
1050                                                         num_chars += 2;
1051                                         } else if (!is_continuation(c, tty)) {
1052                                                 num_chars++;
1053                                         }
1054                                 }
1055                                 echo_erase_tab(num_chars, after_tab, ldata);
1056                         } else {
1057                                 if (iscntrl(c) && L_ECHOCTL(tty)) {
1058                                         echo_char_raw('\b', ldata);
1059                                         echo_char_raw(' ', ldata);
1060                                         echo_char_raw('\b', ldata);
1061                                 }
1062                                 if (!iscntrl(c) || L_ECHOCTL(tty)) {
1063                                         echo_char_raw('\b', ldata);
1064                                         echo_char_raw(' ', ldata);
1065                                         echo_char_raw('\b', ldata);
1066                                 }
1067                         }
1068                 }
1069                 if (kill_type == ERASE)
1070                         break;
1071         }
1072         if (ldata->read_head == ldata->canon_head && L_ECHO(tty))
1073                 finish_erasing(ldata);
1074 }
1075
1076
1077 static void __isig(int sig, struct tty_struct *tty)
1078 {
1079         struct pid *tty_pgrp = tty_get_pgrp(tty);
1080         if (tty_pgrp) {
1081                 kill_pgrp(tty_pgrp, sig, 1);
1082                 put_pid(tty_pgrp);
1083         }
1084 }
1085
1086 /**
1087  * isig                 -       handle the ISIG optio
1088  * @sig: signal
1089  * @tty: terminal
1090  *
1091  * Called when a signal is being sent due to terminal input. Called from the
1092  * &tty_driver.receive_buf() path, so serialized.
1093  *
1094  * Performs input and output flush if !NOFLSH. In this context, the echo
1095  * buffer is 'output'. The signal is processed first to alert any current
1096  * readers or writers to discontinue and exit their i/o loops.
1097  *
1098  * Locking: %ctrl.lock
1099  */
1100 static void isig(int sig, struct tty_struct *tty)
1101 {
1102         struct n_tty_data *ldata = tty->disc_data;
1103
1104         if (L_NOFLSH(tty)) {
1105                 /* signal only */
1106                 __isig(sig, tty);
1107
1108         } else { /* signal and flush */
1109                 up_read(&tty->termios_rwsem);
1110                 down_write(&tty->termios_rwsem);
1111
1112                 __isig(sig, tty);
1113
1114                 /* clear echo buffer */
1115                 mutex_lock(&ldata->output_lock);
1116                 ldata->echo_head = ldata->echo_tail = 0;
1117                 ldata->echo_mark = ldata->echo_commit = 0;
1118                 mutex_unlock(&ldata->output_lock);
1119
1120                 /* clear output buffer */
1121                 tty_driver_flush_buffer(tty);
1122
1123                 /* clear input buffer */
1124                 reset_buffer_flags(tty->disc_data);
1125
1126                 /* notify pty master of flush */
1127                 if (tty->link)
1128                         n_tty_packet_mode_flush(tty);
1129
1130                 up_write(&tty->termios_rwsem);
1131                 down_read(&tty->termios_rwsem);
1132         }
1133 }
1134
1135 /**
1136  * n_tty_receive_break  -       handle break
1137  * @tty: terminal
1138  *
1139  * An RS232 break event has been hit in the incoming bitstream. This can cause
1140  * a variety of events depending upon the termios settings.
1141  *
1142  * Locking: n_tty_receive_buf()/producer path:
1143  *      caller holds non-exclusive termios_rwsem
1144  *
1145  * Note: may get exclusive %termios_rwsem if flushing input buffer
1146  */
1147 static void n_tty_receive_break(struct tty_struct *tty)
1148 {
1149         struct n_tty_data *ldata = tty->disc_data;
1150
1151         if (I_IGNBRK(tty))
1152                 return;
1153         if (I_BRKINT(tty)) {
1154                 isig(SIGINT, tty);
1155                 return;
1156         }
1157         if (I_PARMRK(tty)) {
1158                 put_tty_queue('\377', ldata);
1159                 put_tty_queue('\0', ldata);
1160         }
1161         put_tty_queue('\0', ldata);
1162 }
1163
1164 /**
1165  * n_tty_receive_overrun        -       handle overrun reporting
1166  * @tty: terminal
1167  *
1168  * Data arrived faster than we could process it. While the tty driver has
1169  * flagged this the bits that were missed are gone forever.
1170  *
1171  * Called from the receive_buf path so single threaded. Does not need locking
1172  * as num_overrun and overrun_time are function private.
1173  */
1174 static void n_tty_receive_overrun(struct tty_struct *tty)
1175 {
1176         struct n_tty_data *ldata = tty->disc_data;
1177
1178         ldata->num_overrun++;
1179         if (time_after(jiffies, ldata->overrun_time + HZ) ||
1180                         time_after(ldata->overrun_time, jiffies)) {
1181                 tty_warn(tty, "%d input overrun(s)\n", ldata->num_overrun);
1182                 ldata->overrun_time = jiffies;
1183                 ldata->num_overrun = 0;
1184         }
1185 }
1186
1187 /**
1188  * n_tty_receive_parity_error   -       error notifier
1189  * @tty: terminal device
1190  * @c: character
1191  *
1192  * Process a parity error and queue the right data to indicate the error case
1193  * if necessary.
1194  *
1195  * Locking: n_tty_receive_buf()/producer path:
1196  *      caller holds non-exclusive %termios_rwsem
1197  */
1198 static void n_tty_receive_parity_error(struct tty_struct *tty, unsigned char c)
1199 {
1200         struct n_tty_data *ldata = tty->disc_data;
1201
1202         if (I_INPCK(tty)) {
1203                 if (I_IGNPAR(tty))
1204                         return;
1205                 if (I_PARMRK(tty)) {
1206                         put_tty_queue('\377', ldata);
1207                         put_tty_queue('\0', ldata);
1208                         put_tty_queue(c, ldata);
1209                 } else
1210                         put_tty_queue('\0', ldata);
1211         } else
1212                 put_tty_queue(c, ldata);
1213 }
1214
1215 static void
1216 n_tty_receive_signal_char(struct tty_struct *tty, int signal, unsigned char c)
1217 {
1218         isig(signal, tty);
1219         if (I_IXON(tty))
1220                 start_tty(tty);
1221         if (L_ECHO(tty)) {
1222                 echo_char(c, tty);
1223                 commit_echoes(tty);
1224         } else
1225                 process_echoes(tty);
1226 }
1227
1228 static bool n_tty_is_char_flow_ctrl(struct tty_struct *tty, unsigned char c)
1229 {
1230         return c == START_CHAR(tty) || c == STOP_CHAR(tty);
1231 }
1232
1233 /**
1234  * n_tty_receive_char_flow_ctrl - receive flow control chars
1235  * @tty: terminal device
1236  * @c: character
1237  * @lookahead_done: lookahead has processed this character already
1238  *
1239  * Receive and process flow control character actions.
1240  *
1241  * In case lookahead for flow control chars already handled the character in
1242  * advance to the normal receive, the actions are skipped during normal
1243  * receive.
1244  *
1245  * Returns true if @c is consumed as flow-control character, the character
1246  * must not be treated as normal character.
1247  */
1248 static bool n_tty_receive_char_flow_ctrl(struct tty_struct *tty, unsigned char c,
1249                                          bool lookahead_done)
1250 {
1251         if (!n_tty_is_char_flow_ctrl(tty, c))
1252                 return false;
1253
1254         if (lookahead_done)
1255                 return true;
1256
1257         if (c == START_CHAR(tty)) {
1258                 start_tty(tty);
1259                 process_echoes(tty);
1260                 return true;
1261         }
1262
1263         /* STOP_CHAR */
1264         stop_tty(tty);
1265         return true;
1266 }
1267
1268 static void n_tty_receive_char_special(struct tty_struct *tty, unsigned char c,
1269                                        bool lookahead_done)
1270 {
1271         struct n_tty_data *ldata = tty->disc_data;
1272
1273         if (I_IXON(tty) && n_tty_receive_char_flow_ctrl(tty, c, lookahead_done))
1274                 return;
1275
1276         if (L_ISIG(tty)) {
1277                 if (c == INTR_CHAR(tty)) {
1278                         n_tty_receive_signal_char(tty, SIGINT, c);
1279                         return;
1280                 } else if (c == QUIT_CHAR(tty)) {
1281                         n_tty_receive_signal_char(tty, SIGQUIT, c);
1282                         return;
1283                 } else if (c == SUSP_CHAR(tty)) {
1284                         n_tty_receive_signal_char(tty, SIGTSTP, c);
1285                         return;
1286                 }
1287         }
1288
1289         if (tty->flow.stopped && !tty->flow.tco_stopped && I_IXON(tty) && I_IXANY(tty)) {
1290                 start_tty(tty);
1291                 process_echoes(tty);
1292         }
1293
1294         if (c == '\r') {
1295                 if (I_IGNCR(tty))
1296                         return;
1297                 if (I_ICRNL(tty))
1298                         c = '\n';
1299         } else if (c == '\n' && I_INLCR(tty))
1300                 c = '\r';
1301
1302         if (ldata->icanon) {
1303                 if (c == ERASE_CHAR(tty) || c == KILL_CHAR(tty) ||
1304                     (c == WERASE_CHAR(tty) && L_IEXTEN(tty))) {
1305                         eraser(c, tty);
1306                         commit_echoes(tty);
1307                         return;
1308                 }
1309                 if (c == LNEXT_CHAR(tty) && L_IEXTEN(tty)) {
1310                         ldata->lnext = 1;
1311                         if (L_ECHO(tty)) {
1312                                 finish_erasing(ldata);
1313                                 if (L_ECHOCTL(tty)) {
1314                                         echo_char_raw('^', ldata);
1315                                         echo_char_raw('\b', ldata);
1316                                         commit_echoes(tty);
1317                                 }
1318                         }
1319                         return;
1320                 }
1321                 if (c == REPRINT_CHAR(tty) && L_ECHO(tty) && L_IEXTEN(tty)) {
1322                         size_t tail = ldata->canon_head;
1323
1324                         finish_erasing(ldata);
1325                         echo_char(c, tty);
1326                         echo_char_raw('\n', ldata);
1327                         while (MASK(tail) != MASK(ldata->read_head)) {
1328                                 echo_char(read_buf(ldata, tail), tty);
1329                                 tail++;
1330                         }
1331                         commit_echoes(tty);
1332                         return;
1333                 }
1334                 if (c == '\n') {
1335                         if (L_ECHO(tty) || L_ECHONL(tty)) {
1336                                 echo_char_raw('\n', ldata);
1337                                 commit_echoes(tty);
1338                         }
1339                         goto handle_newline;
1340                 }
1341                 if (c == EOF_CHAR(tty)) {
1342                         c = __DISABLED_CHAR;
1343                         goto handle_newline;
1344                 }
1345                 if ((c == EOL_CHAR(tty)) ||
1346                     (c == EOL2_CHAR(tty) && L_IEXTEN(tty))) {
1347                         /*
1348                          * XXX are EOL_CHAR and EOL2_CHAR echoed?!?
1349                          */
1350                         if (L_ECHO(tty)) {
1351                                 /* Record the column of first canon char. */
1352                                 if (ldata->canon_head == ldata->read_head)
1353                                         echo_set_canon_col(ldata);
1354                                 echo_char(c, tty);
1355                                 commit_echoes(tty);
1356                         }
1357                         /*
1358                          * XXX does PARMRK doubling happen for
1359                          * EOL_CHAR and EOL2_CHAR?
1360                          */
1361                         if (c == (unsigned char) '\377' && I_PARMRK(tty))
1362                                 put_tty_queue(c, ldata);
1363
1364 handle_newline:
1365                         set_bit(ldata->read_head & (N_TTY_BUF_SIZE - 1), ldata->read_flags);
1366                         put_tty_queue(c, ldata);
1367                         smp_store_release(&ldata->canon_head, ldata->read_head);
1368                         kill_fasync(&tty->fasync, SIGIO, POLL_IN);
1369                         wake_up_interruptible_poll(&tty->read_wait, EPOLLIN | EPOLLRDNORM);
1370                         return;
1371                 }
1372         }
1373
1374         if (L_ECHO(tty)) {
1375                 finish_erasing(ldata);
1376                 if (c == '\n')
1377                         echo_char_raw('\n', ldata);
1378                 else {
1379                         /* Record the column of first canon char. */
1380                         if (ldata->canon_head == ldata->read_head)
1381                                 echo_set_canon_col(ldata);
1382                         echo_char(c, tty);
1383                 }
1384                 commit_echoes(tty);
1385         }
1386
1387         /* PARMRK doubling check */
1388         if (c == (unsigned char) '\377' && I_PARMRK(tty))
1389                 put_tty_queue(c, ldata);
1390
1391         put_tty_queue(c, ldata);
1392 }
1393
1394 /**
1395  * n_tty_receive_char   -       perform processing
1396  * @tty: terminal device
1397  * @c: character
1398  *
1399  * Process an individual character of input received from the driver.  This is
1400  * serialized with respect to itself by the rules for the driver above.
1401  *
1402  * Locking: n_tty_receive_buf()/producer path:
1403  *      caller holds non-exclusive %termios_rwsem
1404  *      publishes canon_head if canonical mode is active
1405  */
1406 static void n_tty_receive_char(struct tty_struct *tty, unsigned char c)
1407 {
1408         struct n_tty_data *ldata = tty->disc_data;
1409
1410         if (tty->flow.stopped && !tty->flow.tco_stopped && I_IXON(tty) && I_IXANY(tty)) {
1411                 start_tty(tty);
1412                 process_echoes(tty);
1413         }
1414         if (L_ECHO(tty)) {
1415                 finish_erasing(ldata);
1416                 /* Record the column of first canon char. */
1417                 if (ldata->canon_head == ldata->read_head)
1418                         echo_set_canon_col(ldata);
1419                 echo_char(c, tty);
1420                 commit_echoes(tty);
1421         }
1422         /* PARMRK doubling check */
1423         if (c == (unsigned char) '\377' && I_PARMRK(tty))
1424                 put_tty_queue(c, ldata);
1425         put_tty_queue(c, ldata);
1426 }
1427
1428 static void n_tty_receive_char_closing(struct tty_struct *tty, unsigned char c,
1429                                        bool lookahead_done)
1430 {
1431         if (I_ISTRIP(tty))
1432                 c &= 0x7f;
1433         if (I_IUCLC(tty) && L_IEXTEN(tty))
1434                 c = tolower(c);
1435
1436         if (I_IXON(tty)) {
1437                 if (!n_tty_receive_char_flow_ctrl(tty, c, lookahead_done) &&
1438                     tty->flow.stopped && !tty->flow.tco_stopped && I_IXANY(tty) &&
1439                     c != INTR_CHAR(tty) && c != QUIT_CHAR(tty) &&
1440                     c != SUSP_CHAR(tty)) {
1441                         start_tty(tty);
1442                         process_echoes(tty);
1443                 }
1444         }
1445 }
1446
1447 static void
1448 n_tty_receive_char_flagged(struct tty_struct *tty, unsigned char c, char flag)
1449 {
1450         switch (flag) {
1451         case TTY_BREAK:
1452                 n_tty_receive_break(tty);
1453                 break;
1454         case TTY_PARITY:
1455         case TTY_FRAME:
1456                 n_tty_receive_parity_error(tty, c);
1457                 break;
1458         case TTY_OVERRUN:
1459                 n_tty_receive_overrun(tty);
1460                 break;
1461         default:
1462                 tty_err(tty, "unknown flag %d\n", flag);
1463                 break;
1464         }
1465 }
1466
1467 static void
1468 n_tty_receive_char_lnext(struct tty_struct *tty, unsigned char c, char flag)
1469 {
1470         struct n_tty_data *ldata = tty->disc_data;
1471
1472         ldata->lnext = 0;
1473         if (likely(flag == TTY_NORMAL)) {
1474                 if (I_ISTRIP(tty))
1475                         c &= 0x7f;
1476                 if (I_IUCLC(tty) && L_IEXTEN(tty))
1477                         c = tolower(c);
1478                 n_tty_receive_char(tty, c);
1479         } else
1480                 n_tty_receive_char_flagged(tty, c, flag);
1481 }
1482
1483 /* Caller must ensure count > 0 */
1484 static void n_tty_lookahead_flow_ctrl(struct tty_struct *tty, const unsigned char *cp,
1485                                       const unsigned char *fp, unsigned int count)
1486 {
1487         struct n_tty_data *ldata = tty->disc_data;
1488         unsigned char flag = TTY_NORMAL;
1489
1490         ldata->lookahead_count += count;
1491
1492         if (!I_IXON(tty))
1493                 return;
1494
1495         while (count--) {
1496                 if (fp)
1497                         flag = *fp++;
1498                 if (likely(flag == TTY_NORMAL))
1499                         n_tty_receive_char_flow_ctrl(tty, *cp, false);
1500                 cp++;
1501         }
1502 }
1503
1504 static void
1505 n_tty_receive_buf_real_raw(struct tty_struct *tty, const unsigned char *cp,
1506                            const char *fp, int count)
1507 {
1508         struct n_tty_data *ldata = tty->disc_data;
1509         size_t n, head;
1510
1511         head = ldata->read_head & (N_TTY_BUF_SIZE - 1);
1512         n = min_t(size_t, count, N_TTY_BUF_SIZE - head);
1513         memcpy(read_buf_addr(ldata, head), cp, n);
1514         ldata->read_head += n;
1515         cp += n;
1516         count -= n;
1517
1518         head = ldata->read_head & (N_TTY_BUF_SIZE - 1);
1519         n = min_t(size_t, count, N_TTY_BUF_SIZE - head);
1520         memcpy(read_buf_addr(ldata, head), cp, n);
1521         ldata->read_head += n;
1522 }
1523
1524 static void
1525 n_tty_receive_buf_raw(struct tty_struct *tty, const unsigned char *cp,
1526                       const char *fp, int count)
1527 {
1528         struct n_tty_data *ldata = tty->disc_data;
1529         char flag = TTY_NORMAL;
1530
1531         while (count--) {
1532                 if (fp)
1533                         flag = *fp++;
1534                 if (likely(flag == TTY_NORMAL))
1535                         put_tty_queue(*cp++, ldata);
1536                 else
1537                         n_tty_receive_char_flagged(tty, *cp++, flag);
1538         }
1539 }
1540
1541 static void
1542 n_tty_receive_buf_closing(struct tty_struct *tty, const unsigned char *cp,
1543                           const char *fp, int count, bool lookahead_done)
1544 {
1545         char flag = TTY_NORMAL;
1546
1547         while (count--) {
1548                 if (fp)
1549                         flag = *fp++;
1550                 if (likely(flag == TTY_NORMAL))
1551                         n_tty_receive_char_closing(tty, *cp++, lookahead_done);
1552         }
1553 }
1554
1555 static void n_tty_receive_buf_standard(struct tty_struct *tty,
1556                 const unsigned char *cp, const char *fp, int count, bool lookahead_done)
1557 {
1558         struct n_tty_data *ldata = tty->disc_data;
1559         char flag = TTY_NORMAL;
1560
1561         while (count--) {
1562                 unsigned char c = *cp++;
1563
1564                 if (fp)
1565                         flag = *fp++;
1566
1567                 if (ldata->lnext) {
1568                         n_tty_receive_char_lnext(tty, c, flag);
1569                         continue;
1570                 }
1571
1572                 if (unlikely(flag != TTY_NORMAL)) {
1573                         n_tty_receive_char_flagged(tty, c, flag);
1574                         continue;
1575                 }
1576
1577                 if (I_ISTRIP(tty))
1578                         c &= 0x7f;
1579                 if (I_IUCLC(tty) && L_IEXTEN(tty))
1580                         c = tolower(c);
1581                 if (L_EXTPROC(tty)) {
1582                         put_tty_queue(c, ldata);
1583                         continue;
1584                 }
1585
1586                 if (test_bit(c, ldata->char_map))
1587                         n_tty_receive_char_special(tty, c, lookahead_done);
1588                 else
1589                         n_tty_receive_char(tty, c);
1590         }
1591 }
1592
1593 static void __receive_buf(struct tty_struct *tty, const unsigned char *cp,
1594                           const char *fp, int count)
1595 {
1596         struct n_tty_data *ldata = tty->disc_data;
1597         bool preops = I_ISTRIP(tty) || (I_IUCLC(tty) && L_IEXTEN(tty));
1598         size_t la_count = min_t(size_t, ldata->lookahead_count, count);
1599
1600         if (ldata->real_raw)
1601                 n_tty_receive_buf_real_raw(tty, cp, fp, count);
1602         else if (ldata->raw || (L_EXTPROC(tty) && !preops))
1603                 n_tty_receive_buf_raw(tty, cp, fp, count);
1604         else if (tty->closing && !L_EXTPROC(tty)) {
1605                 if (la_count > 0)
1606                         n_tty_receive_buf_closing(tty, cp, fp, la_count, true);
1607                 if (count > la_count)
1608                         n_tty_receive_buf_closing(tty, cp, fp, count - la_count, false);
1609         } else {
1610                 if (la_count > 0)
1611                         n_tty_receive_buf_standard(tty, cp, fp, la_count, true);
1612                 if (count > la_count)
1613                         n_tty_receive_buf_standard(tty, cp, fp, count - la_count, false);
1614
1615                 flush_echoes(tty);
1616                 if (tty->ops->flush_chars)
1617                         tty->ops->flush_chars(tty);
1618         }
1619
1620         ldata->lookahead_count -= la_count;
1621
1622         if (ldata->icanon && !L_EXTPROC(tty))
1623                 return;
1624
1625         /* publish read_head to consumer */
1626         smp_store_release(&ldata->commit_head, ldata->read_head);
1627
1628         if (read_cnt(ldata)) {
1629                 kill_fasync(&tty->fasync, SIGIO, POLL_IN);
1630                 wake_up_interruptible_poll(&tty->read_wait, EPOLLIN | EPOLLRDNORM);
1631         }
1632 }
1633
1634 /**
1635  * n_tty_receive_buf_common     -       process input
1636  * @tty: device to receive input
1637  * @cp: input chars
1638  * @fp: flags for each char (if %NULL, all chars are %TTY_NORMAL)
1639  * @count: number of input chars in @cp
1640  * @flow: enable flow control
1641  *
1642  * Called by the terminal driver when a block of characters has been received.
1643  * This function must be called from soft contexts not from interrupt context.
1644  * The driver is responsible for making calls one at a time and in order (or
1645  * using flush_to_ldisc()).
1646  *
1647  * Returns: the # of input chars from @cp which were processed.
1648  *
1649  * In canonical mode, the maximum line length is 4096 chars (including the line
1650  * termination char); lines longer than 4096 chars are truncated. After 4095
1651  * chars, input data is still processed but not stored. Overflow processing
1652  * ensures the tty can always receive more input until at least one line can be
1653  * read.
1654  *
1655  * In non-canonical mode, the read buffer will only accept 4095 chars; this
1656  * provides the necessary space for a newline char if the input mode is
1657  * switched to canonical.
1658  *
1659  * Note it is possible for the read buffer to _contain_ 4096 chars in
1660  * non-canonical mode: the read buffer could already contain the maximum canon
1661  * line of 4096 chars when the mode is switched to non-canonical.
1662  *
1663  * Locking: n_tty_receive_buf()/producer path:
1664  *      claims non-exclusive %termios_rwsem
1665  *      publishes commit_head or canon_head
1666  */
1667 static int
1668 n_tty_receive_buf_common(struct tty_struct *tty, const unsigned char *cp,
1669                          const char *fp, int count, int flow)
1670 {
1671         struct n_tty_data *ldata = tty->disc_data;
1672         int room, n, rcvd = 0, overflow;
1673
1674         down_read(&tty->termios_rwsem);
1675
1676         do {
1677                 /*
1678                  * When PARMRK is set, each input char may take up to 3 chars
1679                  * in the read buf; reduce the buffer space avail by 3x
1680                  *
1681                  * If we are doing input canonicalization, and there are no
1682                  * pending newlines, let characters through without limit, so
1683                  * that erase characters will be handled.  Other excess
1684                  * characters will be beeped.
1685                  *
1686                  * paired with store in *_copy_from_read_buf() -- guarantees
1687                  * the consumer has loaded the data in read_buf up to the new
1688                  * read_tail (so this producer will not overwrite unread data)
1689                  */
1690                 size_t tail = smp_load_acquire(&ldata->read_tail);
1691
1692                 room = N_TTY_BUF_SIZE - (ldata->read_head - tail);
1693                 if (I_PARMRK(tty))
1694                         room = (room + 2) / 3;
1695                 room--;
1696                 if (room <= 0) {
1697                         overflow = ldata->icanon && ldata->canon_head == tail;
1698                         if (overflow && room < 0)
1699                                 ldata->read_head--;
1700                         room = overflow;
1701                         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
1737 static 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
1743 static 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  */
1761 static 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  */
1853 static 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  */
1874 static 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
1896 static 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  */
1925 static 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  */
1980 static 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  */
2049 static 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  */
2087 static 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  */
2121 static 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 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         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) {
2271 more_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 (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
2318 static 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         }
2397 break_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  */
2419 static __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
2446 static 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
2465 static 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
2487 static 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
2512 void n_tty_inherit_ops(struct tty_ldisc_ops *ops)
2513 {
2514         *ops = n_tty_ops;
2515         ops->owner = NULL;
2516 }
2517 EXPORT_SYMBOL_GPL(n_tty_inherit_ops);
2518
2519 void __init n_tty_init(void)
2520 {
2521         tty_register_ldisc(&n_tty_ops);
2522 }