tty: remove buffer special casing
[linux-3.10.git] / drivers / char / n_tty.c
1 /*
2  * n_tty.c --- implements the N_TTY line discipline.
3  *
4  * This code used to be in tty_io.c, but things are getting hairy
5  * enough that it made sense to split things off.  (The N_TTY
6  * processing has changed so much that it's hardly recognizable,
7  * anyway...)
8  *
9  * Note that the open routine for N_TTY is guaranteed never to return
10  * an error.  This is because Linux will fall back to setting a line
11  * to N_TTY if it can not switch to any other line discipline.
12  *
13  * Written by Theodore Ts'o, Copyright 1994.
14  *
15  * This file also contains code originally written by Linus Torvalds,
16  * Copyright 1991, 1992, 1993, and by Julian Cowley, Copyright 1994.
17  *
18  * This file may be redistributed under the terms of the GNU General Public
19  * License.
20  *
21  * Reduced memory usage for older ARM systems  - Russell King.
22  *
23  * 2000/01/20   Fixed SMP locking on put_tty_queue using bits of
24  *              the patch by Andrew J. Kroll <ag784@freenet.buffalo.edu>
25  *              who actually finally proved there really was a race.
26  *
27  * 2002/03/18   Implemented n_tty_wakeup to send SIGIO POLL_OUTs to
28  *              waiting writing processes-Sapan Bhatia <sapan@corewars.org>.
29  *              Also fixed a bug in BLOCKING mode where n_tty_write returns
30  *              EAGAIN
31  */
32
33 #include <linux/types.h>
34 #include <linux/major.h>
35 #include <linux/errno.h>
36 #include <linux/signal.h>
37 #include <linux/fcntl.h>
38 #include <linux/sched.h>
39 #include <linux/interrupt.h>
40 #include <linux/tty.h>
41 #include <linux/timer.h>
42 #include <linux/ctype.h>
43 #include <linux/mm.h>
44 #include <linux/string.h>
45 #include <linux/slab.h>
46 #include <linux/poll.h>
47 #include <linux/bitops.h>
48 #include <linux/audit.h>
49 #include <linux/file.h>
50 #include <linux/uaccess.h>
51
52 #include <asm/system.h>
53
54 /* number of characters left in xmit buffer before select has we have room */
55 #define WAKEUP_CHARS 256
56
57 /*
58  * This defines the low- and high-watermarks for throttling and
59  * unthrottling the TTY driver.  These watermarks are used for
60  * controlling the space in the read buffer.
61  */
62 #define TTY_THRESHOLD_THROTTLE          128 /* now based on remaining room */
63 #define TTY_THRESHOLD_UNTHROTTLE        128
64
65 /*
66  * Special byte codes used in the echo buffer to represent operations
67  * or special handling of characters.  Bytes in the echo buffer that
68  * are not part of such special blocks are treated as normal character
69  * codes.
70  */
71 #define ECHO_OP_START 0xff
72 #define ECHO_OP_MOVE_BACK_COL 0x80
73 #define ECHO_OP_SET_CANON_COL 0x81
74 #define ECHO_OP_ERASE_TAB 0x82
75
76 static inline unsigned char *alloc_buf(void)
77 {
78         gfp_t prio = in_interrupt() ? GFP_ATOMIC : GFP_KERNEL;
79         return kmalloc(N_TTY_BUF_SIZE, prio);
80 }
81
82 static inline void free_buf(unsigned char *buf)
83 {
84         kfree(buf);
85 }
86
87 static inline int tty_put_user(struct tty_struct *tty, unsigned char x,
88                                unsigned char __user *ptr)
89 {
90         tty_audit_add_data(tty, &x, 1);
91         return put_user(x, ptr);
92 }
93
94 /**
95  *      n_tty_set__room -       receive space
96  *      @tty: terminal
97  *
98  *      Called by the driver to find out how much data it is
99  *      permitted to feed to the line discipline without any being lost
100  *      and thus to manage flow control. Not serialized. Answers for the
101  *      "instant".
102  */
103
104 static void n_tty_set_room(struct tty_struct *tty)
105 {
106         /* tty->read_cnt is not read locked ? */
107         int     left = N_TTY_BUF_SIZE - tty->read_cnt - 1;
108
109         /*
110          * If we are doing input canonicalization, and there are no
111          * pending newlines, let characters through without limit, so
112          * that erase characters will be handled.  Other excess
113          * characters will be beeped.
114          */
115         if (left <= 0)
116                 left = tty->icanon && !tty->canon_data;
117         tty->receive_room = left;
118 }
119
120 static void put_tty_queue_nolock(unsigned char c, struct tty_struct *tty)
121 {
122         if (tty->read_cnt < N_TTY_BUF_SIZE) {
123                 tty->read_buf[tty->read_head] = c;
124                 tty->read_head = (tty->read_head + 1) & (N_TTY_BUF_SIZE-1);
125                 tty->read_cnt++;
126         }
127 }
128
129 /**
130  *      put_tty_queue           -       add character to tty
131  *      @c: character
132  *      @tty: tty device
133  *
134  *      Add a character to the tty read_buf queue. This is done under the
135  *      read_lock to serialize character addition and also to protect us
136  *      against parallel reads or flushes
137  */
138
139 static void put_tty_queue(unsigned char c, struct tty_struct *tty)
140 {
141         unsigned long flags;
142         /*
143          *      The problem of stomping on the buffers ends here.
144          *      Why didn't anyone see this one coming? --AJK
145         */
146         spin_lock_irqsave(&tty->read_lock, flags);
147         put_tty_queue_nolock(c, tty);
148         spin_unlock_irqrestore(&tty->read_lock, flags);
149 }
150
151 /**
152  *      check_unthrottle        -       allow new receive data
153  *      @tty; tty device
154  *
155  *      Check whether to call the driver unthrottle functions
156  *
157  *      Can sleep, may be called under the atomic_read_lock mutex but
158  *      this is not guaranteed.
159  */
160 static void check_unthrottle(struct tty_struct *tty)
161 {
162         if (tty->count)
163                 tty_unthrottle(tty);
164 }
165
166 /**
167  *      reset_buffer_flags      -       reset buffer state
168  *      @tty: terminal to reset
169  *
170  *      Reset the read buffer counters, clear the flags,
171  *      and make sure the driver is unthrottled. Called
172  *      from n_tty_open() and n_tty_flush_buffer().
173  *
174  *      Locking: tty_read_lock for read fields.
175  */
176
177 static void reset_buffer_flags(struct tty_struct *tty)
178 {
179         unsigned long flags;
180
181         spin_lock_irqsave(&tty->read_lock, flags);
182         tty->read_head = tty->read_tail = tty->read_cnt = 0;
183         spin_unlock_irqrestore(&tty->read_lock, flags);
184
185         mutex_lock(&tty->echo_lock);
186         tty->echo_pos = tty->echo_cnt = tty->echo_overrun = 0;
187         mutex_unlock(&tty->echo_lock);
188
189         tty->canon_head = tty->canon_data = tty->erasing = 0;
190         memset(&tty->read_flags, 0, sizeof tty->read_flags);
191         n_tty_set_room(tty);
192         check_unthrottle(tty);
193 }
194
195 /**
196  *      n_tty_flush_buffer      -       clean input queue
197  *      @tty:   terminal device
198  *
199  *      Flush the input buffer. Called when the line discipline is
200  *      being closed, when the tty layer wants the buffer flushed (eg
201  *      at hangup) or when the N_TTY line discipline internally has to
202  *      clean the pending queue (for example some signals).
203  *
204  *      Locking: ctrl_lock, read_lock.
205  */
206
207 static void n_tty_flush_buffer(struct tty_struct *tty)
208 {
209         unsigned long flags;
210         /* clear everything and unthrottle the driver */
211         reset_buffer_flags(tty);
212
213         if (!tty->link)
214                 return;
215
216         spin_lock_irqsave(&tty->ctrl_lock, flags);
217         if (tty->link->packet) {
218                 tty->ctrl_status |= TIOCPKT_FLUSHREAD;
219                 wake_up_interruptible(&tty->link->read_wait);
220         }
221         spin_unlock_irqrestore(&tty->ctrl_lock, flags);
222 }
223
224 /**
225  *      n_tty_chars_in_buffer   -       report available bytes
226  *      @tty: tty device
227  *
228  *      Report the number of characters buffered to be delivered to user
229  *      at this instant in time.
230  *
231  *      Locking: read_lock
232  */
233
234 static ssize_t n_tty_chars_in_buffer(struct tty_struct *tty)
235 {
236         unsigned long flags;
237         ssize_t n = 0;
238
239         spin_lock_irqsave(&tty->read_lock, flags);
240         if (!tty->icanon) {
241                 n = tty->read_cnt;
242         } else if (tty->canon_data) {
243                 n = (tty->canon_head > tty->read_tail) ?
244                         tty->canon_head - tty->read_tail :
245                         tty->canon_head + (N_TTY_BUF_SIZE - tty->read_tail);
246         }
247         spin_unlock_irqrestore(&tty->read_lock, flags);
248         return n;
249 }
250
251 /**
252  *      is_utf8_continuation    -       utf8 multibyte check
253  *      @c: byte to check
254  *
255  *      Returns true if the utf8 character 'c' is a multibyte continuation
256  *      character. We use this to correctly compute the on screen size
257  *      of the character when printing
258  */
259
260 static inline int is_utf8_continuation(unsigned char c)
261 {
262         return (c & 0xc0) == 0x80;
263 }
264
265 /**
266  *      is_continuation         -       multibyte check
267  *      @c: byte to check
268  *
269  *      Returns true if the utf8 character 'c' is a multibyte continuation
270  *      character and the terminal is in unicode mode.
271  */
272
273 static inline int is_continuation(unsigned char c, struct tty_struct *tty)
274 {
275         return I_IUTF8(tty) && is_utf8_continuation(c);
276 }
277
278 /**
279  *      do_output_char                  -       output one character
280  *      @c: character (or partial unicode symbol)
281  *      @tty: terminal device
282  *      @space: space available in tty driver write buffer
283  *
284  *      This is a helper function that handles one output character
285  *      (including special characters like TAB, CR, LF, etc.),
286  *      putting the results in the tty driver's write buffer.
287  *
288  *      Note that Linux currently ignores TABDLY, CRDLY, VTDLY, FFDLY
289  *      and NLDLY.  They simply aren't relevant in the world today.
290  *      If you ever need them, add them here.
291  *
292  *      Returns the number of bytes of buffer space used or -1 if
293  *      no space left.
294  *
295  *      Locking: should be called under the output_lock to protect
296  *               the column state and space left in the buffer
297  */
298
299 static int do_output_char(unsigned char c, struct tty_struct *tty, int space)
300 {
301         int     spaces;
302
303         if (!space)
304                 return -1;
305
306         switch (c) {
307         case '\n':
308                 if (O_ONLRET(tty))
309                         tty->column = 0;
310                 if (O_ONLCR(tty)) {
311                         if (space < 2)
312                                 return -1;
313                         tty->canon_column = tty->column = 0;
314                         tty_put_char(tty, '\r');
315                         tty_put_char(tty, c);
316                         return 2;
317                 }
318                 tty->canon_column = tty->column;
319                 break;
320         case '\r':
321                 if (O_ONOCR(tty) && tty->column == 0)
322                         return 0;
323                 if (O_OCRNL(tty)) {
324                         c = '\n';
325                         if (O_ONLRET(tty))
326                                 tty->canon_column = tty->column = 0;
327                         break;
328                 }
329                 tty->canon_column = tty->column = 0;
330                 break;
331         case '\t':
332                 spaces = 8 - (tty->column & 7);
333                 if (O_TABDLY(tty) == XTABS) {
334                         if (space < spaces)
335                                 return -1;
336                         tty->column += spaces;
337                         tty->ops->write(tty, "        ", spaces);
338                         return spaces;
339                 }
340                 tty->column += spaces;
341                 break;
342         case '\b':
343                 if (tty->column > 0)
344                         tty->column--;
345                 break;
346         default:
347                 if (!iscntrl(c)) {
348                         if (O_OLCUC(tty))
349                                 c = toupper(c);
350                         if (!is_continuation(c, tty))
351                                 tty->column++;
352                 }
353                 break;
354         }
355
356         tty_put_char(tty, c);
357         return 1;
358 }
359
360 /**
361  *      process_output                  -       output post processor
362  *      @c: character (or partial unicode symbol)
363  *      @tty: terminal device
364  *
365  *      Perform OPOST processing.  Returns -1 when the output device is
366  *      full and the character must be retried.
367  *
368  *      Locking: output_lock to protect column state and space left
369  *               (also, this is called from n_tty_write under the
370  *                tty layer write lock)
371  */
372
373 static int process_output(unsigned char c, struct tty_struct *tty)
374 {
375         int     space, retval;
376
377         mutex_lock(&tty->output_lock);
378
379         space = tty_write_room(tty);
380         retval = do_output_char(c, tty, space);
381
382         mutex_unlock(&tty->output_lock);
383         if (retval < 0)
384                 return -1;
385         else
386                 return 0;
387 }
388
389 /**
390  *      process_output_block            -       block post processor
391  *      @tty: terminal device
392  *      @inbuf: user buffer
393  *      @nr: number of bytes
394  *
395  *      This path is used to speed up block console writes, among other
396  *      things when processing blocks of output data. It handles only
397  *      the simple cases normally found and helps to generate blocks of
398  *      symbols for the console driver and thus improve performance.
399  *
400  *      Locking: output_lock to protect column state and space left
401  *               (also, this is called from n_tty_write under the
402  *                tty layer write lock)
403  */
404
405 static ssize_t process_output_block(struct tty_struct *tty,
406                                     const unsigned char *buf, unsigned int nr)
407 {
408         int     space;
409         int     i;
410         const unsigned char *cp;
411
412         mutex_lock(&tty->output_lock);
413
414         space = tty_write_room(tty);
415         if (!space) {
416                 mutex_unlock(&tty->output_lock);
417                 return 0;
418         }
419         if (nr > space)
420                 nr = space;
421
422         for (i = 0, cp = buf; i < nr; i++, cp++) {
423                 unsigned char c = *cp;
424
425                 switch (c) {
426                 case '\n':
427                         if (O_ONLRET(tty))
428                                 tty->column = 0;
429                         if (O_ONLCR(tty))
430                                 goto break_out;
431                         tty->canon_column = tty->column;
432                         break;
433                 case '\r':
434                         if (O_ONOCR(tty) && tty->column == 0)
435                                 goto break_out;
436                         if (O_OCRNL(tty))
437                                 goto break_out;
438                         tty->canon_column = tty->column = 0;
439                         break;
440                 case '\t':
441                         goto break_out;
442                 case '\b':
443                         if (tty->column > 0)
444                                 tty->column--;
445                         break;
446                 default:
447                         if (!iscntrl(c)) {
448                                 if (O_OLCUC(tty))
449                                         goto break_out;
450                                 if (!is_continuation(c, tty))
451                                         tty->column++;
452                         }
453                         break;
454                 }
455         }
456 break_out:
457         i = tty->ops->write(tty, buf, i);
458
459         mutex_unlock(&tty->output_lock);
460         return i;
461 }
462
463 /**
464  *      process_echoes  -       write pending echo characters
465  *      @tty: terminal device
466  *
467  *      Write previously buffered echo (and other ldisc-generated)
468  *      characters to the tty.
469  *
470  *      Characters generated by the ldisc (including echoes) need to
471  *      be buffered because the driver's write buffer can fill during
472  *      heavy program output.  Echoing straight to the driver will
473  *      often fail under these conditions, causing lost characters and
474  *      resulting mismatches of ldisc state information.
475  *
476  *      Since the ldisc state must represent the characters actually sent
477  *      to the driver at the time of the write, operations like certain
478  *      changes in column state are also saved in the buffer and executed
479  *      here.
480  *
481  *      A circular fifo buffer is used so that the most recent characters
482  *      are prioritized.  Also, when control characters are echoed with a
483  *      prefixed "^", the pair is treated atomically and thus not separated.
484  *
485  *      Locking: output_lock to protect column state and space left,
486  *               echo_lock to protect the echo buffer
487  */
488
489 static void process_echoes(struct tty_struct *tty)
490 {
491         int     space, nr;
492         unsigned char c;
493         unsigned char *cp, *buf_end;
494
495         if (!tty->echo_cnt)
496                 return;
497
498         mutex_lock(&tty->output_lock);
499         mutex_lock(&tty->echo_lock);
500
501         space = tty_write_room(tty);
502
503         buf_end = tty->echo_buf + N_TTY_BUF_SIZE;
504         cp = tty->echo_buf + tty->echo_pos;
505         nr = tty->echo_cnt;
506         while (nr > 0) {
507                 c = *cp;
508                 if (c == ECHO_OP_START) {
509                         unsigned char op;
510                         unsigned char *opp;
511                         int no_space_left = 0;
512
513                         /*
514                          * If the buffer byte is the start of a multi-byte
515                          * operation, get the next byte, which is either the
516                          * op code or a control character value.
517                          */
518                         opp = cp + 1;
519                         if (opp == buf_end)
520                                 opp -= N_TTY_BUF_SIZE;
521                         op = *opp;
522
523                         switch (op) {
524                                 unsigned int num_chars, num_bs;
525
526                         case ECHO_OP_ERASE_TAB:
527                                 if (++opp == buf_end)
528                                         opp -= N_TTY_BUF_SIZE;
529                                 num_chars = *opp;
530
531                                 /*
532                                  * Determine how many columns to go back
533                                  * in order to erase the tab.
534                                  * This depends on the number of columns
535                                  * used by other characters within the tab
536                                  * area.  If this (modulo 8) count is from
537                                  * the start of input rather than from a
538                                  * previous tab, we offset by canon column.
539                                  * Otherwise, tab spacing is normal.
540                                  */
541                                 if (!(num_chars & 0x80))
542                                         num_chars += tty->canon_column;
543                                 num_bs = 8 - (num_chars & 7);
544
545                                 if (num_bs > space) {
546                                         no_space_left = 1;
547                                         break;
548                                 }
549                                 space -= num_bs;
550                                 while (num_bs--) {
551                                         tty_put_char(tty, '\b');
552                                         if (tty->column > 0)
553                                                 tty->column--;
554                                 }
555                                 cp += 3;
556                                 nr -= 3;
557                                 break;
558
559                         case ECHO_OP_SET_CANON_COL:
560                                 tty->canon_column = tty->column;
561                                 cp += 2;
562                                 nr -= 2;
563                                 break;
564
565                         case ECHO_OP_MOVE_BACK_COL:
566                                 if (tty->column > 0)
567                                         tty->column--;
568                                 cp += 2;
569                                 nr -= 2;
570                                 break;
571
572                         case ECHO_OP_START:
573                                 /* This is an escaped echo op start code */
574                                 if (!space) {
575                                         no_space_left = 1;
576                                         break;
577                                 }
578                                 tty_put_char(tty, ECHO_OP_START);
579                                 tty->column++;
580                                 space--;
581                                 cp += 2;
582                                 nr -= 2;
583                                 break;
584
585                         default:
586                                 if (iscntrl(op)) {
587                                         if (L_ECHOCTL(tty)) {
588                                                 /*
589                                                  * Ensure there is enough space
590                                                  * for the whole ctrl pair.
591                                                  */
592                                                 if (space < 2) {
593                                                         no_space_left = 1;
594                                                         break;
595                                                 }
596                                                 tty_put_char(tty, '^');
597                                                 tty_put_char(tty, op ^ 0100);
598                                                 tty->column += 2;
599                                                 space -= 2;
600                                         } else {
601                                                 if (!space) {
602                                                         no_space_left = 1;
603                                                         break;
604                                                 }
605                                                 tty_put_char(tty, op);
606                                                 space--;
607                                         }
608                                 }
609                                 /*
610                                  * If above falls through, this was an
611                                  * undefined op.
612                                  */
613                                 cp += 2;
614                                 nr -= 2;
615                         }
616
617                         if (no_space_left)
618                                 break;
619                 } else {
620                         int retval;
621
622                         retval = do_output_char(c, tty, space);
623                         if (retval < 0)
624                                 break;
625                         space -= retval;
626                         cp += 1;
627                         nr -= 1;
628                 }
629
630                 /* When end of circular buffer reached, wrap around */
631                 if (cp >= buf_end)
632                         cp -= N_TTY_BUF_SIZE;
633         }
634
635         if (nr == 0) {
636                 tty->echo_pos = 0;
637                 tty->echo_cnt = 0;
638                 tty->echo_overrun = 0;
639         } else {
640                 int num_processed = tty->echo_cnt - nr;
641                 tty->echo_pos += num_processed;
642                 tty->echo_pos &= N_TTY_BUF_SIZE - 1;
643                 tty->echo_cnt = nr;
644                 if (num_processed > 0)
645                         tty->echo_overrun = 0;
646         }
647
648         mutex_unlock(&tty->echo_lock);
649         mutex_unlock(&tty->output_lock);
650
651         if (tty->ops->flush_chars)
652                 tty->ops->flush_chars(tty);
653 }
654
655 /**
656  *      add_echo_byte   -       add a byte to the echo buffer
657  *      @c: unicode byte to echo
658  *      @tty: terminal device
659  *
660  *      Add a character or operation byte to the echo buffer.
661  *
662  *      Should be called under the echo lock to protect the echo buffer.
663  */
664
665 static void add_echo_byte(unsigned char c, struct tty_struct *tty)
666 {
667         int     new_byte_pos;
668
669         if (tty->echo_cnt == N_TTY_BUF_SIZE) {
670                 /* Circular buffer is already at capacity */
671                 new_byte_pos = tty->echo_pos;
672
673                 /*
674                  * Since the buffer start position needs to be advanced,
675                  * be sure to step by a whole operation byte group.
676                  */
677                 if (tty->echo_buf[tty->echo_pos] == ECHO_OP_START) {
678                         if (tty->echo_buf[(tty->echo_pos + 1) &
679                                           (N_TTY_BUF_SIZE - 1)] ==
680                                                 ECHO_OP_ERASE_TAB) {
681                                 tty->echo_pos += 3;
682                                 tty->echo_cnt -= 2;
683                         } else {
684                                 tty->echo_pos += 2;
685                                 tty->echo_cnt -= 1;
686                         }
687                 } else {
688                         tty->echo_pos++;
689                 }
690                 tty->echo_pos &= N_TTY_BUF_SIZE - 1;
691
692                 tty->echo_overrun = 1;
693         } else {
694                 new_byte_pos = tty->echo_pos + tty->echo_cnt;
695                 new_byte_pos &= N_TTY_BUF_SIZE - 1;
696                 tty->echo_cnt++;
697         }
698
699         tty->echo_buf[new_byte_pos] = c;
700 }
701
702 /**
703  *      echo_move_back_col      -       add operation to move back a column
704  *      @tty: terminal device
705  *
706  *      Add an operation to the echo buffer to move back one column.
707  *
708  *      Locking: echo_lock to protect the echo buffer
709  */
710
711 static void echo_move_back_col(struct tty_struct *tty)
712 {
713         mutex_lock(&tty->echo_lock);
714
715         add_echo_byte(ECHO_OP_START, tty);
716         add_echo_byte(ECHO_OP_MOVE_BACK_COL, tty);
717
718         mutex_unlock(&tty->echo_lock);
719 }
720
721 /**
722  *      echo_set_canon_col      -       add operation to set the canon column
723  *      @tty: terminal device
724  *
725  *      Add an operation to the echo buffer to set the canon column
726  *      to the current column.
727  *
728  *      Locking: echo_lock to protect the echo buffer
729  */
730
731 static void echo_set_canon_col(struct tty_struct *tty)
732 {
733         mutex_lock(&tty->echo_lock);
734
735         add_echo_byte(ECHO_OP_START, tty);
736         add_echo_byte(ECHO_OP_SET_CANON_COL, tty);
737
738         mutex_unlock(&tty->echo_lock);
739 }
740
741 /**
742  *      echo_erase_tab  -       add operation to erase a tab
743  *      @num_chars: number of character columns already used
744  *      @after_tab: true if num_chars starts after a previous tab
745  *      @tty: terminal device
746  *
747  *      Add an operation to the echo buffer to erase a tab.
748  *
749  *      Called by the eraser function, which knows how many character
750  *      columns have been used since either a previous tab or the start
751  *      of input.  This information will be used later, along with
752  *      canon column (if applicable), to go back the correct number
753  *      of columns.
754  *
755  *      Locking: echo_lock to protect the echo buffer
756  */
757
758 static void echo_erase_tab(unsigned int num_chars, int after_tab,
759                            struct tty_struct *tty)
760 {
761         mutex_lock(&tty->echo_lock);
762
763         add_echo_byte(ECHO_OP_START, tty);
764         add_echo_byte(ECHO_OP_ERASE_TAB, tty);
765
766         /* We only need to know this modulo 8 (tab spacing) */
767         num_chars &= 7;
768
769         /* Set the high bit as a flag if num_chars is after a previous tab */
770         if (after_tab)
771                 num_chars |= 0x80;
772
773         add_echo_byte(num_chars, tty);
774
775         mutex_unlock(&tty->echo_lock);
776 }
777
778 /**
779  *      echo_char_raw   -       echo a character raw
780  *      @c: unicode byte to echo
781  *      @tty: terminal device
782  *
783  *      Echo user input back onto the screen. This must be called only when
784  *      L_ECHO(tty) is true. Called from the driver receive_buf path.
785  *
786  *      This variant does not treat control characters specially.
787  *
788  *      Locking: echo_lock to protect the echo buffer
789  */
790
791 static void echo_char_raw(unsigned char c, struct tty_struct *tty)
792 {
793         mutex_lock(&tty->echo_lock);
794
795         if (c == ECHO_OP_START) {
796                 add_echo_byte(ECHO_OP_START, tty);
797                 add_echo_byte(ECHO_OP_START, tty);
798         } else {
799                 add_echo_byte(c, tty);
800         }
801
802         mutex_unlock(&tty->echo_lock);
803 }
804
805 /**
806  *      echo_char       -       echo a character
807  *      @c: unicode byte to echo
808  *      @tty: terminal device
809  *
810  *      Echo user input back onto the screen. This must be called only when
811  *      L_ECHO(tty) is true. Called from the driver receive_buf path.
812  *
813  *      This variant tags control characters to be possibly echoed as
814  *      as "^X" (where X is the letter representing the control char).
815  *
816  *      Locking: echo_lock to protect the echo buffer
817  */
818
819 static void echo_char(unsigned char c, struct tty_struct *tty)
820 {
821         mutex_lock(&tty->echo_lock);
822
823         if (c == ECHO_OP_START) {
824                 add_echo_byte(ECHO_OP_START, tty);
825                 add_echo_byte(ECHO_OP_START, tty);
826         } else {
827                 if (iscntrl(c) && c != '\t')
828                         add_echo_byte(ECHO_OP_START, tty);
829                 add_echo_byte(c, tty);
830         }
831
832         mutex_unlock(&tty->echo_lock);
833 }
834
835 /**
836  *      finish_erasing          -       complete erase
837  *      @tty: tty doing the erase
838  */
839
840 static inline void finish_erasing(struct tty_struct *tty)
841 {
842         if (tty->erasing) {
843                 echo_char_raw('/', tty);
844                 tty->erasing = 0;
845         }
846 }
847
848 /**
849  *      eraser          -       handle erase function
850  *      @c: character input
851  *      @tty: terminal device
852  *
853  *      Perform erase and necessary output when an erase character is
854  *      present in the stream from the driver layer. Handles the complexities
855  *      of UTF-8 multibyte symbols.
856  *
857  *      Locking: read_lock for tty buffers
858  */
859
860 static void eraser(unsigned char c, struct tty_struct *tty)
861 {
862         enum { ERASE, WERASE, KILL } kill_type;
863         int head, seen_alnums, cnt;
864         unsigned long flags;
865
866         /* FIXME: locking needed ? */
867         if (tty->read_head == tty->canon_head) {
868                 /* process_output('\a', tty); */ /* what do you think? */
869                 return;
870         }
871         if (c == ERASE_CHAR(tty))
872                 kill_type = ERASE;
873         else if (c == WERASE_CHAR(tty))
874                 kill_type = WERASE;
875         else {
876                 if (!L_ECHO(tty)) {
877                         spin_lock_irqsave(&tty->read_lock, flags);
878                         tty->read_cnt -= ((tty->read_head - tty->canon_head) &
879                                           (N_TTY_BUF_SIZE - 1));
880                         tty->read_head = tty->canon_head;
881                         spin_unlock_irqrestore(&tty->read_lock, flags);
882                         return;
883                 }
884                 if (!L_ECHOK(tty) || !L_ECHOKE(tty) || !L_ECHOE(tty)) {
885                         spin_lock_irqsave(&tty->read_lock, flags);
886                         tty->read_cnt -= ((tty->read_head - tty->canon_head) &
887                                           (N_TTY_BUF_SIZE - 1));
888                         tty->read_head = tty->canon_head;
889                         spin_unlock_irqrestore(&tty->read_lock, flags);
890                         finish_erasing(tty);
891                         echo_char(KILL_CHAR(tty), tty);
892                         /* Add a newline if ECHOK is on and ECHOKE is off. */
893                         if (L_ECHOK(tty))
894                                 echo_char_raw('\n', tty);
895                         return;
896                 }
897                 kill_type = KILL;
898         }
899
900         seen_alnums = 0;
901         /* FIXME: Locking ?? */
902         while (tty->read_head != tty->canon_head) {
903                 head = tty->read_head;
904
905                 /* erase a single possibly multibyte character */
906                 do {
907                         head = (head - 1) & (N_TTY_BUF_SIZE-1);
908                         c = tty->read_buf[head];
909                 } while (is_continuation(c, tty) && head != tty->canon_head);
910
911                 /* do not partially erase */
912                 if (is_continuation(c, tty))
913                         break;
914
915                 if (kill_type == WERASE) {
916                         /* Equivalent to BSD's ALTWERASE. */
917                         if (isalnum(c) || c == '_')
918                                 seen_alnums++;
919                         else if (seen_alnums)
920                                 break;
921                 }
922                 cnt = (tty->read_head - head) & (N_TTY_BUF_SIZE-1);
923                 spin_lock_irqsave(&tty->read_lock, flags);
924                 tty->read_head = head;
925                 tty->read_cnt -= cnt;
926                 spin_unlock_irqrestore(&tty->read_lock, flags);
927                 if (L_ECHO(tty)) {
928                         if (L_ECHOPRT(tty)) {
929                                 if (!tty->erasing) {
930                                         echo_char_raw('\\', tty);
931                                         tty->erasing = 1;
932                                 }
933                                 /* if cnt > 1, output a multi-byte character */
934                                 echo_char(c, tty);
935                                 while (--cnt > 0) {
936                                         head = (head+1) & (N_TTY_BUF_SIZE-1);
937                                         echo_char_raw(tty->read_buf[head], tty);
938                                         echo_move_back_col(tty);
939                                 }
940                         } else if (kill_type == ERASE && !L_ECHOE(tty)) {
941                                 echo_char(ERASE_CHAR(tty), tty);
942                         } else if (c == '\t') {
943                                 unsigned int num_chars = 0;
944                                 int after_tab = 0;
945                                 unsigned long tail = tty->read_head;
946
947                                 /*
948                                  * Count the columns used for characters
949                                  * since the start of input or after a
950                                  * previous tab.
951                                  * This info is used to go back the correct
952                                  * number of columns.
953                                  */
954                                 while (tail != tty->canon_head) {
955                                         tail = (tail-1) & (N_TTY_BUF_SIZE-1);
956                                         c = tty->read_buf[tail];
957                                         if (c == '\t') {
958                                                 after_tab = 1;
959                                                 break;
960                                         } else if (iscntrl(c)) {
961                                                 if (L_ECHOCTL(tty))
962                                                         num_chars += 2;
963                                         } else if (!is_continuation(c, tty)) {
964                                                 num_chars++;
965                                         }
966                                 }
967                                 echo_erase_tab(num_chars, after_tab, tty);
968                         } else {
969                                 if (iscntrl(c) && L_ECHOCTL(tty)) {
970                                         echo_char_raw('\b', tty);
971                                         echo_char_raw(' ', tty);
972                                         echo_char_raw('\b', tty);
973                                 }
974                                 if (!iscntrl(c) || L_ECHOCTL(tty)) {
975                                         echo_char_raw('\b', tty);
976                                         echo_char_raw(' ', tty);
977                                         echo_char_raw('\b', tty);
978                                 }
979                         }
980                 }
981                 if (kill_type == ERASE)
982                         break;
983         }
984         if (tty->read_head == tty->canon_head && L_ECHO(tty))
985                 finish_erasing(tty);
986 }
987
988 /**
989  *      isig            -       handle the ISIG optio
990  *      @sig: signal
991  *      @tty: terminal
992  *      @flush: force flush
993  *
994  *      Called when a signal is being sent due to terminal input. This
995  *      may caus terminal flushing to take place according to the termios
996  *      settings and character used. Called from the driver receive_buf
997  *      path so serialized.
998  *
999  *      Locking: ctrl_lock, read_lock (both via flush buffer)
1000  */
1001
1002 static inline void isig(int sig, struct tty_struct *tty, int flush)
1003 {
1004         if (tty->pgrp)
1005                 kill_pgrp(tty->pgrp, sig, 1);
1006         if (flush || !L_NOFLSH(tty)) {
1007                 n_tty_flush_buffer(tty);
1008                 tty_driver_flush_buffer(tty);
1009         }
1010 }
1011
1012 /**
1013  *      n_tty_receive_break     -       handle break
1014  *      @tty: terminal
1015  *
1016  *      An RS232 break event has been hit in the incoming bitstream. This
1017  *      can cause a variety of events depending upon the termios settings.
1018  *
1019  *      Called from the receive_buf path so single threaded.
1020  */
1021
1022 static inline void n_tty_receive_break(struct tty_struct *tty)
1023 {
1024         if (I_IGNBRK(tty))
1025                 return;
1026         if (I_BRKINT(tty)) {
1027                 isig(SIGINT, tty, 1);
1028                 return;
1029         }
1030         if (I_PARMRK(tty)) {
1031                 put_tty_queue('\377', tty);
1032                 put_tty_queue('\0', tty);
1033         }
1034         put_tty_queue('\0', tty);
1035         wake_up_interruptible(&tty->read_wait);
1036 }
1037
1038 /**
1039  *      n_tty_receive_overrun   -       handle overrun reporting
1040  *      @tty: terminal
1041  *
1042  *      Data arrived faster than we could process it. While the tty
1043  *      driver has flagged this the bits that were missed are gone
1044  *      forever.
1045  *
1046  *      Called from the receive_buf path so single threaded. Does not
1047  *      need locking as num_overrun and overrun_time are function
1048  *      private.
1049  */
1050
1051 static inline void n_tty_receive_overrun(struct tty_struct *tty)
1052 {
1053         char buf[64];
1054
1055         tty->num_overrun++;
1056         if (time_before(tty->overrun_time, jiffies - HZ) ||
1057                         time_after(tty->overrun_time, jiffies)) {
1058                 printk(KERN_WARNING "%s: %d input overrun(s)\n",
1059                         tty_name(tty, buf),
1060                         tty->num_overrun);
1061                 tty->overrun_time = jiffies;
1062                 tty->num_overrun = 0;
1063         }
1064 }
1065
1066 /**
1067  *      n_tty_receive_parity_error      -       error notifier
1068  *      @tty: terminal device
1069  *      @c: character
1070  *
1071  *      Process a parity error and queue the right data to indicate
1072  *      the error case if necessary. Locking as per n_tty_receive_buf.
1073  */
1074 static inline void n_tty_receive_parity_error(struct tty_struct *tty,
1075                                               unsigned char c)
1076 {
1077         if (I_IGNPAR(tty))
1078                 return;
1079         if (I_PARMRK(tty)) {
1080                 put_tty_queue('\377', tty);
1081                 put_tty_queue('\0', tty);
1082                 put_tty_queue(c, tty);
1083         } else  if (I_INPCK(tty))
1084                 put_tty_queue('\0', tty);
1085         else
1086                 put_tty_queue(c, tty);
1087         wake_up_interruptible(&tty->read_wait);
1088 }
1089
1090 /**
1091  *      n_tty_receive_char      -       perform processing
1092  *      @tty: terminal device
1093  *      @c: character
1094  *
1095  *      Process an individual character of input received from the driver.
1096  *      This is serialized with respect to itself by the rules for the
1097  *      driver above.
1098  */
1099
1100 static inline void n_tty_receive_char(struct tty_struct *tty, unsigned char c)
1101 {
1102         unsigned long flags;
1103         int parmrk;
1104
1105         if (tty->raw) {
1106                 put_tty_queue(c, tty);
1107                 return;
1108         }
1109
1110         if (I_ISTRIP(tty))
1111                 c &= 0x7f;
1112         if (I_IUCLC(tty) && L_IEXTEN(tty))
1113                 c = tolower(c);
1114
1115         if (tty->stopped && !tty->flow_stopped && I_IXON(tty) &&
1116             I_IXANY(tty) && c != START_CHAR(tty) && c != STOP_CHAR(tty) &&
1117             c != INTR_CHAR(tty) && c != QUIT_CHAR(tty) && c != SUSP_CHAR(tty)) {
1118                 start_tty(tty);
1119                 process_echoes(tty);
1120         }
1121
1122         if (tty->closing) {
1123                 if (I_IXON(tty)) {
1124                         if (c == START_CHAR(tty)) {
1125                                 start_tty(tty);
1126                                 process_echoes(tty);
1127                         } else if (c == STOP_CHAR(tty))
1128                                 stop_tty(tty);
1129                 }
1130                 return;
1131         }
1132
1133         /*
1134          * If the previous character was LNEXT, or we know that this
1135          * character is not one of the characters that we'll have to
1136          * handle specially, do shortcut processing to speed things
1137          * up.
1138          */
1139         if (!test_bit(c, tty->process_char_map) || tty->lnext) {
1140                 tty->lnext = 0;
1141                 parmrk = (c == (unsigned char) '\377' && I_PARMRK(tty)) ? 1 : 0;
1142                 if (tty->read_cnt >= (N_TTY_BUF_SIZE - parmrk - 1)) {
1143                         /* beep if no space */
1144                         if (L_ECHO(tty))
1145                                 process_output('\a', tty);
1146                         return;
1147                 }
1148                 if (L_ECHO(tty)) {
1149                         finish_erasing(tty);
1150                         /* Record the column of first canon char. */
1151                         if (tty->canon_head == tty->read_head)
1152                                 echo_set_canon_col(tty);
1153                         echo_char(c, tty);
1154                         process_echoes(tty);
1155                 }
1156                 if (parmrk)
1157                         put_tty_queue(c, tty);
1158                 put_tty_queue(c, tty);
1159                 return;
1160         }
1161
1162         if (I_IXON(tty)) {
1163                 if (c == START_CHAR(tty)) {
1164                         start_tty(tty);
1165                         process_echoes(tty);
1166                         return;
1167                 }
1168                 if (c == STOP_CHAR(tty)) {
1169                         stop_tty(tty);
1170                         return;
1171                 }
1172         }
1173
1174         if (L_ISIG(tty)) {
1175                 int signal;
1176                 signal = SIGINT;
1177                 if (c == INTR_CHAR(tty))
1178                         goto send_signal;
1179                 signal = SIGQUIT;
1180                 if (c == QUIT_CHAR(tty))
1181                         goto send_signal;
1182                 signal = SIGTSTP;
1183                 if (c == SUSP_CHAR(tty)) {
1184 send_signal:
1185                         /*
1186                          * Note that we do not use isig() here because we want
1187                          * the order to be:
1188                          * 1) flush, 2) echo, 3) signal
1189                          */
1190                         if (!L_NOFLSH(tty)) {
1191                                 n_tty_flush_buffer(tty);
1192                                 tty_driver_flush_buffer(tty);
1193                         }
1194                         if (I_IXON(tty))
1195                                 start_tty(tty);
1196                         if (L_ECHO(tty)) {
1197                                 echo_char(c, tty);
1198                                 process_echoes(tty);
1199                         }
1200                         if (tty->pgrp)
1201                                 kill_pgrp(tty->pgrp, signal, 1);
1202                         return;
1203                 }
1204         }
1205
1206         if (c == '\r') {
1207                 if (I_IGNCR(tty))
1208                         return;
1209                 if (I_ICRNL(tty))
1210                         c = '\n';
1211         } else if (c == '\n' && I_INLCR(tty))
1212                 c = '\r';
1213
1214         if (tty->icanon) {
1215                 if (c == ERASE_CHAR(tty) || c == KILL_CHAR(tty) ||
1216                     (c == WERASE_CHAR(tty) && L_IEXTEN(tty))) {
1217                         eraser(c, tty);
1218                         process_echoes(tty);
1219                         return;
1220                 }
1221                 if (c == LNEXT_CHAR(tty) && L_IEXTEN(tty)) {
1222                         tty->lnext = 1;
1223                         if (L_ECHO(tty)) {
1224                                 finish_erasing(tty);
1225                                 if (L_ECHOCTL(tty)) {
1226                                         echo_char_raw('^', tty);
1227                                         echo_char_raw('\b', tty);
1228                                         process_echoes(tty);
1229                                 }
1230                         }
1231                         return;
1232                 }
1233                 if (c == REPRINT_CHAR(tty) && L_ECHO(tty) &&
1234                     L_IEXTEN(tty)) {
1235                         unsigned long tail = tty->canon_head;
1236
1237                         finish_erasing(tty);
1238                         echo_char(c, tty);
1239                         echo_char_raw('\n', tty);
1240                         while (tail != tty->read_head) {
1241                                 echo_char(tty->read_buf[tail], tty);
1242                                 tail = (tail+1) & (N_TTY_BUF_SIZE-1);
1243                         }
1244                         process_echoes(tty);
1245                         return;
1246                 }
1247                 if (c == '\n') {
1248                         if (tty->read_cnt >= N_TTY_BUF_SIZE) {
1249                                 if (L_ECHO(tty))
1250                                         process_output('\a', tty);
1251                                 return;
1252                         }
1253                         if (L_ECHO(tty) || L_ECHONL(tty)) {
1254                                 echo_char_raw('\n', tty);
1255                                 process_echoes(tty);
1256                         }
1257                         goto handle_newline;
1258                 }
1259                 if (c == EOF_CHAR(tty)) {
1260                         if (tty->read_cnt >= N_TTY_BUF_SIZE)
1261                                 return;
1262                         if (tty->canon_head != tty->read_head)
1263                                 set_bit(TTY_PUSH, &tty->flags);
1264                         c = __DISABLED_CHAR;
1265                         goto handle_newline;
1266                 }
1267                 if ((c == EOL_CHAR(tty)) ||
1268                     (c == EOL2_CHAR(tty) && L_IEXTEN(tty))) {
1269                         parmrk = (c == (unsigned char) '\377' && I_PARMRK(tty))
1270                                  ? 1 : 0;
1271                         if (tty->read_cnt >= (N_TTY_BUF_SIZE - parmrk)) {
1272                                 if (L_ECHO(tty))
1273                                         process_output('\a', tty);
1274                                 return;
1275                         }
1276                         /*
1277                          * XXX are EOL_CHAR and EOL2_CHAR echoed?!?
1278                          */
1279                         if (L_ECHO(tty)) {
1280                                 /* Record the column of first canon char. */
1281                                 if (tty->canon_head == tty->read_head)
1282                                         echo_set_canon_col(tty);
1283                                 echo_char(c, tty);
1284                                 process_echoes(tty);
1285                         }
1286                         /*
1287                          * XXX does PARMRK doubling happen for
1288                          * EOL_CHAR and EOL2_CHAR?
1289                          */
1290                         if (parmrk)
1291                                 put_tty_queue(c, tty);
1292
1293 handle_newline:
1294                         spin_lock_irqsave(&tty->read_lock, flags);
1295                         set_bit(tty->read_head, tty->read_flags);
1296                         put_tty_queue_nolock(c, tty);
1297                         tty->canon_head = tty->read_head;
1298                         tty->canon_data++;
1299                         spin_unlock_irqrestore(&tty->read_lock, flags);
1300                         kill_fasync(&tty->fasync, SIGIO, POLL_IN);
1301                         if (waitqueue_active(&tty->read_wait))
1302                                 wake_up_interruptible(&tty->read_wait);
1303                         return;
1304                 }
1305         }
1306
1307         parmrk = (c == (unsigned char) '\377' && I_PARMRK(tty)) ? 1 : 0;
1308         if (tty->read_cnt >= (N_TTY_BUF_SIZE - parmrk - 1)) {
1309                 /* beep if no space */
1310                 if (L_ECHO(tty))
1311                         process_output('\a', tty);
1312                 return;
1313         }
1314         if (L_ECHO(tty)) {
1315                 finish_erasing(tty);
1316                 if (c == '\n')
1317                         echo_char_raw('\n', tty);
1318                 else {
1319                         /* Record the column of first canon char. */
1320                         if (tty->canon_head == tty->read_head)
1321                                 echo_set_canon_col(tty);
1322                         echo_char(c, tty);
1323                 }
1324                 process_echoes(tty);
1325         }
1326
1327         if (parmrk)
1328                 put_tty_queue(c, tty);
1329
1330         put_tty_queue(c, tty);
1331 }
1332
1333
1334 /**
1335  *      n_tty_write_wakeup      -       asynchronous I/O notifier
1336  *      @tty: tty device
1337  *
1338  *      Required for the ptys, serial driver etc. since processes
1339  *      that attach themselves to the master and rely on ASYNC
1340  *      IO must be woken up
1341  */
1342
1343 static void n_tty_write_wakeup(struct tty_struct *tty)
1344 {
1345         /* Write out any echoed characters that are still pending */
1346         process_echoes(tty);
1347
1348         if (tty->fasync && test_and_clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags))
1349                 kill_fasync(&tty->fasync, SIGIO, POLL_OUT);
1350 }
1351
1352 /**
1353  *      n_tty_receive_buf       -       data receive
1354  *      @tty: terminal device
1355  *      @cp: buffer
1356  *      @fp: flag buffer
1357  *      @count: characters
1358  *
1359  *      Called by the terminal driver when a block of characters has
1360  *      been received. This function must be called from soft contexts
1361  *      not from interrupt context. The driver is responsible for making
1362  *      calls one at a time and in order (or using flush_to_ldisc)
1363  */
1364
1365 static void n_tty_receive_buf(struct tty_struct *tty, const unsigned char *cp,
1366                               char *fp, int count)
1367 {
1368         const unsigned char *p;
1369         char *f, flags = TTY_NORMAL;
1370         int     i;
1371         char    buf[64];
1372         unsigned long cpuflags;
1373
1374         if (!tty->read_buf)
1375                 return;
1376
1377         if (tty->real_raw) {
1378                 spin_lock_irqsave(&tty->read_lock, cpuflags);
1379                 i = min(N_TTY_BUF_SIZE - tty->read_cnt,
1380                         N_TTY_BUF_SIZE - tty->read_head);
1381                 i = min(count, i);
1382                 memcpy(tty->read_buf + tty->read_head, cp, i);
1383                 tty->read_head = (tty->read_head + i) & (N_TTY_BUF_SIZE-1);
1384                 tty->read_cnt += i;
1385                 cp += i;
1386                 count -= i;
1387
1388                 i = min(N_TTY_BUF_SIZE - tty->read_cnt,
1389                         N_TTY_BUF_SIZE - tty->read_head);
1390                 i = min(count, i);
1391                 memcpy(tty->read_buf + tty->read_head, cp, i);
1392                 tty->read_head = (tty->read_head + i) & (N_TTY_BUF_SIZE-1);
1393                 tty->read_cnt += i;
1394                 spin_unlock_irqrestore(&tty->read_lock, cpuflags);
1395         } else {
1396                 for (i = count, p = cp, f = fp; i; i--, p++) {
1397                         if (f)
1398                                 flags = *f++;
1399                         switch (flags) {
1400                         case TTY_NORMAL:
1401                                 n_tty_receive_char(tty, *p);
1402                                 break;
1403                         case TTY_BREAK:
1404                                 n_tty_receive_break(tty);
1405                                 break;
1406                         case TTY_PARITY:
1407                         case TTY_FRAME:
1408                                 n_tty_receive_parity_error(tty, *p);
1409                                 break;
1410                         case TTY_OVERRUN:
1411                                 n_tty_receive_overrun(tty);
1412                                 break;
1413                         default:
1414                                 printk(KERN_ERR "%s: unknown flag %d\n",
1415                                        tty_name(tty, buf), flags);
1416                                 break;
1417                         }
1418                 }
1419                 if (tty->ops->flush_chars)
1420                         tty->ops->flush_chars(tty);
1421         }
1422
1423         n_tty_set_room(tty);
1424
1425         if (!tty->icanon && (tty->read_cnt >= tty->minimum_to_wake)) {
1426                 kill_fasync(&tty->fasync, SIGIO, POLL_IN);
1427                 if (waitqueue_active(&tty->read_wait))
1428                         wake_up_interruptible(&tty->read_wait);
1429         }
1430
1431         /*
1432          * Check the remaining room for the input canonicalization
1433          * mode.  We don't want to throttle the driver if we're in
1434          * canonical mode and don't have a newline yet!
1435          */
1436         if (tty->receive_room < TTY_THRESHOLD_THROTTLE)
1437                 tty_throttle(tty);
1438 }
1439
1440 int is_ignored(int sig)
1441 {
1442         return (sigismember(&current->blocked, sig) ||
1443                 current->sighand->action[sig-1].sa.sa_handler == SIG_IGN);
1444 }
1445
1446 /**
1447  *      n_tty_set_termios       -       termios data changed
1448  *      @tty: terminal
1449  *      @old: previous data
1450  *
1451  *      Called by the tty layer when the user changes termios flags so
1452  *      that the line discipline can plan ahead. This function cannot sleep
1453  *      and is protected from re-entry by the tty layer. The user is
1454  *      guaranteed that this function will not be re-entered or in progress
1455  *      when the ldisc is closed.
1456  *
1457  *      Locking: Caller holds tty->termios_mutex
1458  */
1459
1460 static void n_tty_set_termios(struct tty_struct *tty, struct ktermios *old)
1461 {
1462         int canon_change = 1;
1463         BUG_ON(!tty);
1464
1465         if (old)
1466                 canon_change = (old->c_lflag ^ tty->termios->c_lflag) & ICANON;
1467         if (canon_change) {
1468                 memset(&tty->read_flags, 0, sizeof tty->read_flags);
1469                 tty->canon_head = tty->read_tail;
1470                 tty->canon_data = 0;
1471                 tty->erasing = 0;
1472         }
1473
1474         if (canon_change && !L_ICANON(tty) && tty->read_cnt)
1475                 wake_up_interruptible(&tty->read_wait);
1476
1477         tty->icanon = (L_ICANON(tty) != 0);
1478         if (test_bit(TTY_HW_COOK_IN, &tty->flags)) {
1479                 tty->raw = 1;
1480                 tty->real_raw = 1;
1481                 n_tty_set_room(tty);
1482                 return;
1483         }
1484         if (I_ISTRIP(tty) || I_IUCLC(tty) || I_IGNCR(tty) ||
1485             I_ICRNL(tty) || I_INLCR(tty) || L_ICANON(tty) ||
1486             I_IXON(tty) || L_ISIG(tty) || L_ECHO(tty) ||
1487             I_PARMRK(tty)) {
1488                 memset(tty->process_char_map, 0, 256/8);
1489
1490                 if (I_IGNCR(tty) || I_ICRNL(tty))
1491                         set_bit('\r', tty->process_char_map);
1492                 if (I_INLCR(tty))
1493                         set_bit('\n', tty->process_char_map);
1494
1495                 if (L_ICANON(tty)) {
1496                         set_bit(ERASE_CHAR(tty), tty->process_char_map);
1497                         set_bit(KILL_CHAR(tty), tty->process_char_map);
1498                         set_bit(EOF_CHAR(tty), tty->process_char_map);
1499                         set_bit('\n', tty->process_char_map);
1500                         set_bit(EOL_CHAR(tty), tty->process_char_map);
1501                         if (L_IEXTEN(tty)) {
1502                                 set_bit(WERASE_CHAR(tty),
1503                                         tty->process_char_map);
1504                                 set_bit(LNEXT_CHAR(tty),
1505                                         tty->process_char_map);
1506                                 set_bit(EOL2_CHAR(tty),
1507                                         tty->process_char_map);
1508                                 if (L_ECHO(tty))
1509                                         set_bit(REPRINT_CHAR(tty),
1510                                                 tty->process_char_map);
1511                         }
1512                 }
1513                 if (I_IXON(tty)) {
1514                         set_bit(START_CHAR(tty), tty->process_char_map);
1515                         set_bit(STOP_CHAR(tty), tty->process_char_map);
1516                 }
1517                 if (L_ISIG(tty)) {
1518                         set_bit(INTR_CHAR(tty), tty->process_char_map);
1519                         set_bit(QUIT_CHAR(tty), tty->process_char_map);
1520                         set_bit(SUSP_CHAR(tty), tty->process_char_map);
1521                 }
1522                 clear_bit(__DISABLED_CHAR, tty->process_char_map);
1523                 tty->raw = 0;
1524                 tty->real_raw = 0;
1525         } else {
1526                 tty->raw = 1;
1527                 if ((I_IGNBRK(tty) || (!I_BRKINT(tty) && !I_PARMRK(tty))) &&
1528                     (I_IGNPAR(tty) || !I_INPCK(tty)) &&
1529                     (tty->driver->flags & TTY_DRIVER_REAL_RAW))
1530                         tty->real_raw = 1;
1531                 else
1532                         tty->real_raw = 0;
1533         }
1534         n_tty_set_room(tty);
1535         /* The termios change make the tty ready for I/O */
1536         wake_up_interruptible(&tty->write_wait);
1537         wake_up_interruptible(&tty->read_wait);
1538 }
1539
1540 /**
1541  *      n_tty_close             -       close the ldisc for this tty
1542  *      @tty: device
1543  *
1544  *      Called from the terminal layer when this line discipline is
1545  *      being shut down, either because of a close or becsuse of a
1546  *      discipline change. The function will not be called while other
1547  *      ldisc methods are in progress.
1548  */
1549
1550 static void n_tty_close(struct tty_struct *tty)
1551 {
1552         n_tty_flush_buffer(tty);
1553         if (tty->read_buf) {
1554                 free_buf(tty->read_buf);
1555                 tty->read_buf = NULL;
1556         }
1557         if (tty->echo_buf) {
1558                 free_buf(tty->echo_buf);
1559                 tty->echo_buf = NULL;
1560         }
1561 }
1562
1563 /**
1564  *      n_tty_open              -       open an ldisc
1565  *      @tty: terminal to open
1566  *
1567  *      Called when this line discipline is being attached to the
1568  *      terminal device. Can sleep. Called serialized so that no
1569  *      other events will occur in parallel. No further open will occur
1570  *      until a close.
1571  */
1572
1573 static int n_tty_open(struct tty_struct *tty)
1574 {
1575         if (!tty)
1576                 return -EINVAL;
1577
1578         /* These are ugly. Currently a malloc failure here can panic */
1579         if (!tty->read_buf) {
1580                 tty->read_buf = alloc_buf();
1581                 if (!tty->read_buf)
1582                         return -ENOMEM;
1583         }
1584         if (!tty->echo_buf) {
1585                 tty->echo_buf = alloc_buf();
1586                 if (!tty->echo_buf)
1587                         return -ENOMEM;
1588         }
1589         memset(tty->read_buf, 0, N_TTY_BUF_SIZE);
1590         memset(tty->echo_buf, 0, N_TTY_BUF_SIZE);
1591         reset_buffer_flags(tty);
1592         tty->column = 0;
1593         n_tty_set_termios(tty, NULL);
1594         tty->minimum_to_wake = 1;
1595         tty->closing = 0;
1596         return 0;
1597 }
1598
1599 static inline int input_available_p(struct tty_struct *tty, int amt)
1600 {
1601         if (tty->icanon) {
1602                 if (tty->canon_data)
1603                         return 1;
1604         } else if (tty->read_cnt >= (amt ? amt : 1))
1605                 return 1;
1606
1607         return 0;
1608 }
1609
1610 /**
1611  *      copy_from_read_buf      -       copy read data directly
1612  *      @tty: terminal device
1613  *      @b: user data
1614  *      @nr: size of data
1615  *
1616  *      Helper function to speed up n_tty_read.  It is only called when
1617  *      ICANON is off; it copies characters straight from the tty queue to
1618  *      user space directly.  It can be profitably called twice; once to
1619  *      drain the space from the tail pointer to the (physical) end of the
1620  *      buffer, and once to drain the space from the (physical) beginning of
1621  *      the buffer to head pointer.
1622  *
1623  *      Called under the tty->atomic_read_lock sem
1624  *
1625  */
1626
1627 static int copy_from_read_buf(struct tty_struct *tty,
1628                                       unsigned char __user **b,
1629                                       size_t *nr)
1630
1631 {
1632         int retval;
1633         size_t n;
1634         unsigned long flags;
1635
1636         retval = 0;
1637         spin_lock_irqsave(&tty->read_lock, flags);
1638         n = min(tty->read_cnt, N_TTY_BUF_SIZE - tty->read_tail);
1639         n = min(*nr, n);
1640         spin_unlock_irqrestore(&tty->read_lock, flags);
1641         if (n) {
1642                 retval = copy_to_user(*b, &tty->read_buf[tty->read_tail], n);
1643                 n -= retval;
1644                 tty_audit_add_data(tty, &tty->read_buf[tty->read_tail], n);
1645                 spin_lock_irqsave(&tty->read_lock, flags);
1646                 tty->read_tail = (tty->read_tail + n) & (N_TTY_BUF_SIZE-1);
1647                 tty->read_cnt -= n;
1648                 spin_unlock_irqrestore(&tty->read_lock, flags);
1649                 *b += n;
1650                 *nr -= n;
1651         }
1652         return retval;
1653 }
1654
1655 extern ssize_t redirected_tty_write(struct file *, const char __user *,
1656                                                         size_t, loff_t *);
1657
1658 /**
1659  *      job_control             -       check job control
1660  *      @tty: tty
1661  *      @file: file handle
1662  *
1663  *      Perform job control management checks on this file/tty descriptor
1664  *      and if appropriate send any needed signals and return a negative
1665  *      error code if action should be taken.
1666  *
1667  *      FIXME:
1668  *      Locking: None - redirected write test is safe, testing
1669  *      current->signal should possibly lock current->sighand
1670  *      pgrp locking ?
1671  */
1672
1673 static int job_control(struct tty_struct *tty, struct file *file)
1674 {
1675         /* Job control check -- must be done at start and after
1676            every sleep (POSIX.1 7.1.1.4). */
1677         /* NOTE: not yet done after every sleep pending a thorough
1678            check of the logic of this change. -- jlc */
1679         /* don't stop on /dev/console */
1680         if (file->f_op->write != redirected_tty_write &&
1681             current->signal->tty == tty) {
1682                 if (!tty->pgrp)
1683                         printk(KERN_ERR "n_tty_read: no tty->pgrp!\n");
1684                 else if (task_pgrp(current) != tty->pgrp) {
1685                         if (is_ignored(SIGTTIN) ||
1686                             is_current_pgrp_orphaned())
1687                                 return -EIO;
1688                         kill_pgrp(task_pgrp(current), SIGTTIN, 1);
1689                         set_thread_flag(TIF_SIGPENDING);
1690                         return -ERESTARTSYS;
1691                 }
1692         }
1693         return 0;
1694 }
1695
1696
1697 /**
1698  *      n_tty_read              -       read function for tty
1699  *      @tty: tty device
1700  *      @file: file object
1701  *      @buf: userspace buffer pointer
1702  *      @nr: size of I/O
1703  *
1704  *      Perform reads for the line discipline. We are guaranteed that the
1705  *      line discipline will not be closed under us but we may get multiple
1706  *      parallel readers and must handle this ourselves. We may also get
1707  *      a hangup. Always called in user context, may sleep.
1708  *
1709  *      This code must be sure never to sleep through a hangup.
1710  */
1711
1712 static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
1713                          unsigned char __user *buf, size_t nr)
1714 {
1715         unsigned char __user *b = buf;
1716         DECLARE_WAITQUEUE(wait, current);
1717         int c;
1718         int minimum, time;
1719         ssize_t retval = 0;
1720         ssize_t size;
1721         long timeout;
1722         unsigned long flags;
1723         int packet;
1724
1725 do_it_again:
1726
1727         BUG_ON(!tty->read_buf);
1728
1729         c = job_control(tty, file);
1730         if (c < 0)
1731                 return c;
1732
1733         minimum = time = 0;
1734         timeout = MAX_SCHEDULE_TIMEOUT;
1735         if (!tty->icanon) {
1736                 time = (HZ / 10) * TIME_CHAR(tty);
1737                 minimum = MIN_CHAR(tty);
1738                 if (minimum) {
1739                         if (time)
1740                                 tty->minimum_to_wake = 1;
1741                         else if (!waitqueue_active(&tty->read_wait) ||
1742                                  (tty->minimum_to_wake > minimum))
1743                                 tty->minimum_to_wake = minimum;
1744                 } else {
1745                         timeout = 0;
1746                         if (time) {
1747                                 timeout = time;
1748                                 time = 0;
1749                         }
1750                         tty->minimum_to_wake = minimum = 1;
1751                 }
1752         }
1753
1754         /*
1755          *      Internal serialization of reads.
1756          */
1757         if (file->f_flags & O_NONBLOCK) {
1758                 if (!mutex_trylock(&tty->atomic_read_lock))
1759                         return -EAGAIN;
1760         } else {
1761                 if (mutex_lock_interruptible(&tty->atomic_read_lock))
1762                         return -ERESTARTSYS;
1763         }
1764         packet = tty->packet;
1765
1766         add_wait_queue(&tty->read_wait, &wait);
1767         while (nr) {
1768                 /* First test for status change. */
1769                 if (packet && tty->link->ctrl_status) {
1770                         unsigned char cs;
1771                         if (b != buf)
1772                                 break;
1773                         spin_lock_irqsave(&tty->link->ctrl_lock, flags);
1774                         cs = tty->link->ctrl_status;
1775                         tty->link->ctrl_status = 0;
1776                         spin_unlock_irqrestore(&tty->link->ctrl_lock, flags);
1777                         if (tty_put_user(tty, cs, b++)) {
1778                                 retval = -EFAULT;
1779                                 b--;
1780                                 break;
1781                         }
1782                         nr--;
1783                         break;
1784                 }
1785                 /* This statement must be first before checking for input
1786                    so that any interrupt will set the state back to
1787                    TASK_RUNNING. */
1788                 set_current_state(TASK_INTERRUPTIBLE);
1789
1790                 if (((minimum - (b - buf)) < tty->minimum_to_wake) &&
1791                     ((minimum - (b - buf)) >= 1))
1792                         tty->minimum_to_wake = (minimum - (b - buf));
1793
1794                 if (!input_available_p(tty, 0)) {
1795                         if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
1796                                 retval = -EIO;
1797                                 break;
1798                         }
1799                         if (tty_hung_up_p(file))
1800                                 break;
1801                         if (!timeout)
1802                                 break;
1803                         if (file->f_flags & O_NONBLOCK) {
1804                                 retval = -EAGAIN;
1805                                 break;
1806                         }
1807                         if (signal_pending(current)) {
1808                                 retval = -ERESTARTSYS;
1809                                 break;
1810                         }
1811                         /* FIXME: does n_tty_set_room need locking ? */
1812                         n_tty_set_room(tty);
1813                         timeout = schedule_timeout(timeout);
1814                         continue;
1815                 }
1816                 __set_current_state(TASK_RUNNING);
1817
1818                 /* Deal with packet mode. */
1819                 if (packet && b == buf) {
1820                         if (tty_put_user(tty, TIOCPKT_DATA, b++)) {
1821                                 retval = -EFAULT;
1822                                 b--;
1823                                 break;
1824                         }
1825                         nr--;
1826                 }
1827
1828                 if (tty->icanon) {
1829                         /* N.B. avoid overrun if nr == 0 */
1830                         while (nr && tty->read_cnt) {
1831                                 int eol;
1832
1833                                 eol = test_and_clear_bit(tty->read_tail,
1834                                                 tty->read_flags);
1835                                 c = tty->read_buf[tty->read_tail];
1836                                 spin_lock_irqsave(&tty->read_lock, flags);
1837                                 tty->read_tail = ((tty->read_tail+1) &
1838                                                   (N_TTY_BUF_SIZE-1));
1839                                 tty->read_cnt--;
1840                                 if (eol) {
1841                                         /* this test should be redundant:
1842                                          * we shouldn't be reading data if
1843                                          * canon_data is 0
1844                                          */
1845                                         if (--tty->canon_data < 0)
1846                                                 tty->canon_data = 0;
1847                                 }
1848                                 spin_unlock_irqrestore(&tty->read_lock, flags);
1849
1850                                 if (!eol || (c != __DISABLED_CHAR)) {
1851                                         if (tty_put_user(tty, c, b++)) {
1852                                                 retval = -EFAULT;
1853                                                 b--;
1854                                                 break;
1855                                         }
1856                                         nr--;
1857                                 }
1858                                 if (eol) {
1859                                         tty_audit_push(tty);
1860                                         break;
1861                                 }
1862                         }
1863                         if (retval)
1864                                 break;
1865                 } else {
1866                         int uncopied;
1867                         /* The copy function takes the read lock and handles
1868                            locking internally for this case */
1869                         uncopied = copy_from_read_buf(tty, &b, &nr);
1870                         uncopied += copy_from_read_buf(tty, &b, &nr);
1871                         if (uncopied) {
1872                                 retval = -EFAULT;
1873                                 break;
1874                         }
1875                 }
1876
1877                 /* If there is enough space in the read buffer now, let the
1878                  * low-level driver know. We use n_tty_chars_in_buffer() to
1879                  * check the buffer, as it now knows about canonical mode.
1880                  * Otherwise, if the driver is throttled and the line is
1881                  * longer than TTY_THRESHOLD_UNTHROTTLE in canonical mode,
1882                  * we won't get any more characters.
1883                  */
1884                 if (n_tty_chars_in_buffer(tty) <= TTY_THRESHOLD_UNTHROTTLE) {
1885                         n_tty_set_room(tty);
1886                         check_unthrottle(tty);
1887                 }
1888
1889                 if (b - buf >= minimum)
1890                         break;
1891                 if (time)
1892                         timeout = time;
1893         }
1894         mutex_unlock(&tty->atomic_read_lock);
1895         remove_wait_queue(&tty->read_wait, &wait);
1896
1897         if (!waitqueue_active(&tty->read_wait))
1898                 tty->minimum_to_wake = minimum;
1899
1900         __set_current_state(TASK_RUNNING);
1901         size = b - buf;
1902         if (size) {
1903                 retval = size;
1904                 if (nr)
1905                         clear_bit(TTY_PUSH, &tty->flags);
1906         } else if (test_and_clear_bit(TTY_PUSH, &tty->flags))
1907                  goto do_it_again;
1908
1909         n_tty_set_room(tty);
1910         return retval;
1911 }
1912
1913 /**
1914  *      n_tty_write             -       write function for tty
1915  *      @tty: tty device
1916  *      @file: file object
1917  *      @buf: userspace buffer pointer
1918  *      @nr: size of I/O
1919  *
1920  *      Write function of the terminal device.  This is serialized with
1921  *      respect to other write callers but not to termios changes, reads
1922  *      and other such events.  Since the receive code will echo characters,
1923  *      thus calling driver write methods, the output_lock is used in
1924  *      the output processing functions called here as well as in the
1925  *      echo processing function to protect the column state and space
1926  *      left in the buffer.
1927  *
1928  *      This code must be sure never to sleep through a hangup.
1929  *
1930  *      Locking: output_lock to protect column state and space left
1931  *               (note that the process_output*() functions take this
1932  *                lock themselves)
1933  */
1934
1935 static ssize_t n_tty_write(struct tty_struct *tty, struct file *file,
1936                            const unsigned char *buf, size_t nr)
1937 {
1938         const unsigned char *b = buf;
1939         DECLARE_WAITQUEUE(wait, current);
1940         int c;
1941         ssize_t retval = 0;
1942
1943         /* Job control check -- must be done at start (POSIX.1 7.1.1.4). */
1944         if (L_TOSTOP(tty) && file->f_op->write != redirected_tty_write) {
1945                 retval = tty_check_change(tty);
1946                 if (retval)
1947                         return retval;
1948         }
1949
1950         /* Write out any echoed characters that are still pending */
1951         process_echoes(tty);
1952
1953         add_wait_queue(&tty->write_wait, &wait);
1954         while (1) {
1955                 set_current_state(TASK_INTERRUPTIBLE);
1956                 if (signal_pending(current)) {
1957                         retval = -ERESTARTSYS;
1958                         break;
1959                 }
1960                 if (tty_hung_up_p(file) || (tty->link && !tty->link->count)) {
1961                         retval = -EIO;
1962                         break;
1963                 }
1964                 if (O_OPOST(tty) && !(test_bit(TTY_HW_COOK_OUT, &tty->flags))) {
1965                         while (nr > 0) {
1966                                 ssize_t num = process_output_block(tty, b, nr);
1967                                 if (num < 0) {
1968                                         if (num == -EAGAIN)
1969                                                 break;
1970                                         retval = num;
1971                                         goto break_out;
1972                                 }
1973                                 b += num;
1974                                 nr -= num;
1975                                 if (nr == 0)
1976                                         break;
1977                                 c = *b;
1978                                 if (process_output(c, tty) < 0)
1979                                         break;
1980                                 b++; nr--;
1981                         }
1982                         if (tty->ops->flush_chars)
1983                                 tty->ops->flush_chars(tty);
1984                 } else {
1985                         while (nr > 0) {
1986                                 c = tty->ops->write(tty, b, nr);
1987                                 if (c < 0) {
1988                                         retval = c;
1989                                         goto break_out;
1990                                 }
1991                                 if (!c)
1992                                         break;
1993                                 b += c;
1994                                 nr -= c;
1995                         }
1996                 }
1997                 if (!nr)
1998                         break;
1999                 if (file->f_flags & O_NONBLOCK) {
2000                         retval = -EAGAIN;
2001                         break;
2002                 }
2003                 schedule();
2004         }
2005 break_out:
2006         __set_current_state(TASK_RUNNING);
2007         remove_wait_queue(&tty->write_wait, &wait);
2008         if (b - buf != nr && tty->fasync)
2009                 set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
2010         return (b - buf) ? b - buf : retval;
2011 }
2012
2013 /**
2014  *      n_tty_poll              -       poll method for N_TTY
2015  *      @tty: terminal device
2016  *      @file: file accessing it
2017  *      @wait: poll table
2018  *
2019  *      Called when the line discipline is asked to poll() for data or
2020  *      for special events. This code is not serialized with respect to
2021  *      other events save open/close.
2022  *
2023  *      This code must be sure never to sleep through a hangup.
2024  *      Called without the kernel lock held - fine
2025  */
2026
2027 static unsigned int n_tty_poll(struct tty_struct *tty, struct file *file,
2028                                                         poll_table *wait)
2029 {
2030         unsigned int mask = 0;
2031
2032         poll_wait(file, &tty->read_wait, wait);
2033         poll_wait(file, &tty->write_wait, wait);
2034         if (input_available_p(tty, TIME_CHAR(tty) ? 0 : MIN_CHAR(tty)))
2035                 mask |= POLLIN | POLLRDNORM;
2036         if (tty->packet && tty->link->ctrl_status)
2037                 mask |= POLLPRI | POLLIN | POLLRDNORM;
2038         if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
2039                 mask |= POLLHUP;
2040         if (tty_hung_up_p(file))
2041                 mask |= POLLHUP;
2042         if (!(mask & (POLLHUP | POLLIN | POLLRDNORM))) {
2043                 if (MIN_CHAR(tty) && !TIME_CHAR(tty))
2044                         tty->minimum_to_wake = MIN_CHAR(tty);
2045                 else
2046                         tty->minimum_to_wake = 1;
2047         }
2048         if (tty->ops->write && !tty_is_writelocked(tty) &&
2049                         tty_chars_in_buffer(tty) < WAKEUP_CHARS &&
2050                         tty_write_room(tty) > 0)
2051                 mask |= POLLOUT | POLLWRNORM;
2052         return mask;
2053 }
2054
2055 static unsigned long inq_canon(struct tty_struct *tty)
2056 {
2057         int nr, head, tail;
2058
2059         if (!tty->canon_data)
2060                 return 0;
2061         head = tty->canon_head;
2062         tail = tty->read_tail;
2063         nr = (head - tail) & (N_TTY_BUF_SIZE-1);
2064         /* Skip EOF-chars.. */
2065         while (head != tail) {
2066                 if (test_bit(tail, tty->read_flags) &&
2067                     tty->read_buf[tail] == __DISABLED_CHAR)
2068                         nr--;
2069                 tail = (tail+1) & (N_TTY_BUF_SIZE-1);
2070         }
2071         return nr;
2072 }
2073
2074 static int n_tty_ioctl(struct tty_struct *tty, struct file *file,
2075                        unsigned int cmd, unsigned long arg)
2076 {
2077         int retval;
2078
2079         switch (cmd) {
2080         case TIOCOUTQ:
2081                 return put_user(tty_chars_in_buffer(tty), (int __user *) arg);
2082         case TIOCINQ:
2083                 /* FIXME: Locking */
2084                 retval = tty->read_cnt;
2085                 if (L_ICANON(tty))
2086                         retval = inq_canon(tty);
2087                 return put_user(retval, (unsigned int __user *) arg);
2088         default:
2089                 return n_tty_ioctl_helper(tty, file, cmd, arg);
2090         }
2091 }
2092
2093 struct tty_ldisc_ops tty_ldisc_N_TTY = {
2094         .magic           = TTY_LDISC_MAGIC,
2095         .name            = "n_tty",
2096         .open            = n_tty_open,
2097         .close           = n_tty_close,
2098         .flush_buffer    = n_tty_flush_buffer,
2099         .chars_in_buffer = n_tty_chars_in_buffer,
2100         .read            = n_tty_read,
2101         .write           = n_tty_write,
2102         .ioctl           = n_tty_ioctl,
2103         .set_termios     = n_tty_set_termios,
2104         .poll            = n_tty_poll,
2105         .receive_buf     = n_tty_receive_buf,
2106         .write_wakeup    = n_tty_write_wakeup
2107 };