drivers/char/n_tty.c misannotated prototype
[sfrench/cifs-2.6.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 write_chan 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
51 #include <asm/uaccess.h>
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 static inline unsigned char *alloc_buf(void)
66 {
67         gfp_t prio = in_interrupt() ? GFP_ATOMIC : GFP_KERNEL;
68
69         if (PAGE_SIZE != N_TTY_BUF_SIZE)
70                 return kmalloc(N_TTY_BUF_SIZE, prio);
71         else
72                 return (unsigned char *)__get_free_page(prio);
73 }
74
75 static inline void free_buf(unsigned char *buf)
76 {
77         if (PAGE_SIZE != N_TTY_BUF_SIZE)
78                 kfree(buf);
79         else
80                 free_page((unsigned long) buf);
81 }
82
83 static inline int tty_put_user(struct tty_struct *tty, unsigned char x,
84                                unsigned char __user *ptr)
85 {
86         tty_audit_add_data(tty, &x, 1);
87         return put_user(x, ptr);
88 }
89
90 /**
91  *      n_tty_set__room -       receive space
92  *      @tty: terminal
93  *
94  *      Called by the driver to find out how much data it is
95  *      permitted to feed to the line discipline without any being lost
96  *      and thus to manage flow control. Not serialized. Answers for the
97  *      "instant".
98  */
99
100 static void n_tty_set_room(struct tty_struct *tty)
101 {
102         int     left = N_TTY_BUF_SIZE - tty->read_cnt - 1;
103
104         /*
105          * If we are doing input canonicalization, and there are no
106          * pending newlines, let characters through without limit, so
107          * that erase characters will be handled.  Other excess
108          * characters will be beeped.
109          */
110         if (left <= 0)
111                 left = tty->icanon && !tty->canon_data;
112         tty->receive_room = left;
113 }
114
115 static void put_tty_queue_nolock(unsigned char c, struct tty_struct *tty)
116 {
117         if (tty->read_cnt < N_TTY_BUF_SIZE) {
118                 tty->read_buf[tty->read_head] = c;
119                 tty->read_head = (tty->read_head + 1) & (N_TTY_BUF_SIZE-1);
120                 tty->read_cnt++;
121         }
122 }
123
124 static void put_tty_queue(unsigned char c, struct tty_struct *tty)
125 {
126         unsigned long flags;
127         /*
128          *      The problem of stomping on the buffers ends here.
129          *      Why didn't anyone see this one coming? --AJK
130         */
131         spin_lock_irqsave(&tty->read_lock, flags);
132         put_tty_queue_nolock(c, tty);
133         spin_unlock_irqrestore(&tty->read_lock, flags);
134 }
135
136 /**
137  *      check_unthrottle        -       allow new receive data
138  *      @tty; tty device
139  *
140  *      Check whether to call the driver.unthrottle function.
141  *      We test the TTY_THROTTLED bit first so that it always
142  *      indicates the current state. The decision about whether
143  *      it is worth allowing more input has been taken by the caller.
144  *      Can sleep, may be called under the atomic_read_lock mutex but
145  *      this is not guaranteed.
146  */
147
148 static void check_unthrottle(struct tty_struct *tty)
149 {
150         if (tty->count &&
151             test_and_clear_bit(TTY_THROTTLED, &tty->flags) &&
152             tty->driver->unthrottle)
153                 tty->driver->unthrottle(tty);
154 }
155
156 /**
157  *      reset_buffer_flags      -       reset buffer state
158  *      @tty: terminal to reset
159  *
160  *      Reset the read buffer counters, clear the flags,
161  *      and make sure the driver is unthrottled. Called
162  *      from n_tty_open() and n_tty_flush_buffer().
163  */
164 static void reset_buffer_flags(struct tty_struct *tty)
165 {
166         unsigned long flags;
167
168         spin_lock_irqsave(&tty->read_lock, flags);
169         tty->read_head = tty->read_tail = tty->read_cnt = 0;
170         spin_unlock_irqrestore(&tty->read_lock, flags);
171         tty->canon_head = tty->canon_data = tty->erasing = 0;
172         memset(&tty->read_flags, 0, sizeof tty->read_flags);
173         n_tty_set_room(tty);
174         check_unthrottle(tty);
175 }
176
177 /**
178  *      n_tty_flush_buffer      -       clean input queue
179  *      @tty:   terminal device
180  *
181  *      Flush the input buffer. Called when the line discipline is
182  *      being closed, when the tty layer wants the buffer flushed (eg
183  *      at hangup) or when the N_TTY line discipline internally has to
184  *      clean the pending queue (for example some signals).
185  *
186  *      FIXME: tty->ctrl_status is not spinlocked and relies on
187  *      lock_kernel() still.
188  */
189
190 static void n_tty_flush_buffer(struct tty_struct *tty)
191 {
192         /* clear everything and unthrottle the driver */
193         reset_buffer_flags(tty);
194
195         if (!tty->link)
196                 return;
197
198         if (tty->link->packet) {
199                 tty->ctrl_status |= TIOCPKT_FLUSHREAD;
200                 wake_up_interruptible(&tty->link->read_wait);
201         }
202 }
203
204 /**
205  *      n_tty_chars_in_buffer   -       report available bytes
206  *      @tty: tty device
207  *
208  *      Report the number of characters buffered to be delivered to user
209  *      at this instant in time.
210  */
211
212 static ssize_t n_tty_chars_in_buffer(struct tty_struct *tty)
213 {
214         unsigned long flags;
215         ssize_t n = 0;
216
217         spin_lock_irqsave(&tty->read_lock, flags);
218         if (!tty->icanon) {
219                 n = tty->read_cnt;
220         } else if (tty->canon_data) {
221                 n = (tty->canon_head > tty->read_tail) ?
222                         tty->canon_head - tty->read_tail :
223                         tty->canon_head + (N_TTY_BUF_SIZE - tty->read_tail);
224         }
225         spin_unlock_irqrestore(&tty->read_lock, flags);
226         return n;
227 }
228
229 /**
230  *      is_utf8_continuation    -       utf8 multibyte check
231  *      @c: byte to check
232  *
233  *      Returns true if the utf8 character 'c' is a multibyte continuation
234  *      character. We use this to correctly compute the on screen size
235  *      of the character when printing
236  */
237
238 static inline int is_utf8_continuation(unsigned char c)
239 {
240         return (c & 0xc0) == 0x80;
241 }
242
243 /**
244  *      is_continuation         -       multibyte check
245  *      @c: byte to check
246  *
247  *      Returns true if the utf8 character 'c' is a multibyte continuation
248  *      character and the terminal is in unicode mode.
249  */
250
251 static inline int is_continuation(unsigned char c, struct tty_struct *tty)
252 {
253         return I_IUTF8(tty) && is_utf8_continuation(c);
254 }
255
256 /**
257  *      opost                   -       output post processor
258  *      @c: character (or partial unicode symbol)
259  *      @tty: terminal device
260  *
261  *      Perform OPOST processing.  Returns -1 when the output device is
262  *      full and the character must be retried. Note that Linux currently
263  *      ignores TABDLY, CRDLY, VTDLY, FFDLY and NLDLY. They simply aren't
264  *      relevant in the world today. If you ever need them, add them here.
265  *
266  *      Called from both the receive and transmit sides and can be called
267  *      re-entrantly. Relies on lock_kernel() still.
268  */
269
270 static int opost(unsigned char c, struct tty_struct *tty)
271 {
272         int     space, spaces;
273
274         space = tty->driver->write_room(tty);
275         if (!space)
276                 return -1;
277
278         if (O_OPOST(tty)) {
279                 switch (c) {
280                 case '\n':
281                         if (O_ONLRET(tty))
282                                 tty->column = 0;
283                         if (O_ONLCR(tty)) {
284                                 if (space < 2)
285                                         return -1;
286                                 tty->driver->put_char(tty, '\r');
287                                 tty->column = 0;
288                         }
289                         tty->canon_column = tty->column;
290                         break;
291                 case '\r':
292                         if (O_ONOCR(tty) && tty->column == 0)
293                                 return 0;
294                         if (O_OCRNL(tty)) {
295                                 c = '\n';
296                                 if (O_ONLRET(tty))
297                                         tty->canon_column = tty->column = 0;
298                                 break;
299                         }
300                         tty->canon_column = tty->column = 0;
301                         break;
302                 case '\t':
303                         spaces = 8 - (tty->column & 7);
304                         if (O_TABDLY(tty) == XTABS) {
305                                 if (space < spaces)
306                                         return -1;
307                                 tty->column += spaces;
308                                 tty->driver->write(tty, "        ", spaces);
309                                 return 0;
310                         }
311                         tty->column += spaces;
312                         break;
313                 case '\b':
314                         if (tty->column > 0)
315                                 tty->column--;
316                         break;
317                 default:
318                         if (O_OLCUC(tty))
319                                 c = toupper(c);
320                         if (!iscntrl(c) && !is_continuation(c, tty))
321                                 tty->column++;
322                         break;
323                 }
324         }
325         tty->driver->put_char(tty, c);
326         return 0;
327 }
328
329 /**
330  *      opost_block             -       block postprocess
331  *      @tty: terminal device
332  *      @inbuf: user buffer
333  *      @nr: number of bytes
334  *
335  *      This path is used to speed up block console writes, among other
336  *      things when processing blocks of output data. It handles only
337  *      the simple cases normally found and helps to generate blocks of
338  *      symbols for the console driver and thus improve performance.
339  *
340  *      Called from write_chan under the tty layer write lock.
341  */
342
343 static ssize_t opost_block(struct tty_struct *tty,
344                        const unsigned char *buf, unsigned int nr)
345 {
346         int     space;
347         int     i;
348         const unsigned char *cp;
349
350         space = tty->driver->write_room(tty);
351         if (!space)
352                 return 0;
353         if (nr > space)
354                 nr = space;
355
356         for (i = 0, cp = buf; i < nr; i++, cp++) {
357                 switch (*cp) {
358                 case '\n':
359                         if (O_ONLRET(tty))
360                                 tty->column = 0;
361                         if (O_ONLCR(tty))
362                                 goto break_out;
363                         tty->canon_column = tty->column;
364                         break;
365                 case '\r':
366                         if (O_ONOCR(tty) && tty->column == 0)
367                                 goto break_out;
368                         if (O_OCRNL(tty))
369                                 goto break_out;
370                         tty->canon_column = tty->column = 0;
371                         break;
372                 case '\t':
373                         goto break_out;
374                 case '\b':
375                         if (tty->column > 0)
376                                 tty->column--;
377                         break;
378                 default:
379                         if (O_OLCUC(tty))
380                                 goto break_out;
381                         if (!iscntrl(*cp))
382                                 tty->column++;
383                         break;
384                 }
385         }
386 break_out:
387         if (tty->driver->flush_chars)
388                 tty->driver->flush_chars(tty);
389         i = tty->driver->write(tty, buf, i);
390         return i;
391 }
392
393
394 /**
395  *      put_char        -       write character to driver
396  *      @c: character (or part of unicode symbol)
397  *      @tty: terminal device
398  *
399  *      Queue a byte to the driver layer for output
400  */
401
402 static inline void put_char(unsigned char c, struct tty_struct *tty)
403 {
404         tty->driver->put_char(tty, c);
405 }
406
407 /**
408  *      echo_char       -       echo characters
409  *      @c: unicode byte to echo
410  *      @tty: terminal device
411  *
412  *      Echo user input back onto the screen. This must be called only when
413  *      L_ECHO(tty) is true. Called from the driver receive_buf path.
414  */
415
416 static void echo_char(unsigned char c, struct tty_struct *tty)
417 {
418         if (L_ECHOCTL(tty) && iscntrl(c) && c != '\t') {
419                 put_char('^', tty);
420                 put_char(c ^ 0100, tty);
421                 tty->column += 2;
422         } else
423                 opost(c, tty);
424 }
425
426 static inline void finish_erasing(struct tty_struct *tty)
427 {
428         if (tty->erasing) {
429                 put_char('/', tty);
430                 tty->column++;
431                 tty->erasing = 0;
432         }
433 }
434
435 /**
436  *      eraser          -       handle erase function
437  *      @c: character input
438  *      @tty: terminal device
439  *
440  *      Perform erase and necessary output when an erase character is
441  *      present in the stream from the driver layer. Handles the complexities
442  *      of UTF-8 multibyte symbols.
443  */
444
445 static void eraser(unsigned char c, struct tty_struct *tty)
446 {
447         enum { ERASE, WERASE, KILL } kill_type;
448         int head, seen_alnums, cnt;
449         unsigned long flags;
450
451         if (tty->read_head == tty->canon_head) {
452                 /* opost('\a', tty); */         /* what do you think? */
453                 return;
454         }
455         if (c == ERASE_CHAR(tty))
456                 kill_type = ERASE;
457         else if (c == WERASE_CHAR(tty))
458                 kill_type = WERASE;
459         else {
460                 if (!L_ECHO(tty)) {
461                         spin_lock_irqsave(&tty->read_lock, flags);
462                         tty->read_cnt -= ((tty->read_head - tty->canon_head) &
463                                           (N_TTY_BUF_SIZE - 1));
464                         tty->read_head = tty->canon_head;
465                         spin_unlock_irqrestore(&tty->read_lock, flags);
466                         return;
467                 }
468                 if (!L_ECHOK(tty) || !L_ECHOKE(tty) || !L_ECHOE(tty)) {
469                         spin_lock_irqsave(&tty->read_lock, flags);
470                         tty->read_cnt -= ((tty->read_head - tty->canon_head) &
471                                           (N_TTY_BUF_SIZE - 1));
472                         tty->read_head = tty->canon_head;
473                         spin_unlock_irqrestore(&tty->read_lock, flags);
474                         finish_erasing(tty);
475                         echo_char(KILL_CHAR(tty), tty);
476                         /* Add a newline if ECHOK is on and ECHOKE is off. */
477                         if (L_ECHOK(tty))
478                                 opost('\n', tty);
479                         return;
480                 }
481                 kill_type = KILL;
482         }
483
484         seen_alnums = 0;
485         while (tty->read_head != tty->canon_head) {
486                 head = tty->read_head;
487
488                 /* erase a single possibly multibyte character */
489                 do {
490                         head = (head - 1) & (N_TTY_BUF_SIZE-1);
491                         c = tty->read_buf[head];
492                 } while (is_continuation(c, tty) && head != tty->canon_head);
493
494                 /* do not partially erase */
495                 if (is_continuation(c, tty))
496                         break;
497
498                 if (kill_type == WERASE) {
499                         /* Equivalent to BSD's ALTWERASE. */
500                         if (isalnum(c) || c == '_')
501                                 seen_alnums++;
502                         else if (seen_alnums)
503                                 break;
504                 }
505                 cnt = (tty->read_head - head) & (N_TTY_BUF_SIZE-1);
506                 spin_lock_irqsave(&tty->read_lock, flags);
507                 tty->read_head = head;
508                 tty->read_cnt -= cnt;
509                 spin_unlock_irqrestore(&tty->read_lock, flags);
510                 if (L_ECHO(tty)) {
511                         if (L_ECHOPRT(tty)) {
512                                 if (!tty->erasing) {
513                                         put_char('\\', tty);
514                                         tty->column++;
515                                         tty->erasing = 1;
516                                 }
517                                 /* if cnt > 1, output a multi-byte character */
518                                 echo_char(c, tty);
519                                 while (--cnt > 0) {
520                                         head = (head+1) & (N_TTY_BUF_SIZE-1);
521                                         put_char(tty->read_buf[head], tty);
522                                 }
523                         } else if (kill_type == ERASE && !L_ECHOE(tty)) {
524                                 echo_char(ERASE_CHAR(tty), tty);
525                         } else if (c == '\t') {
526                                 unsigned int col = tty->canon_column;
527                                 unsigned long tail = tty->canon_head;
528
529                                 /* Find the column of the last char. */
530                                 while (tail != tty->read_head) {
531                                         c = tty->read_buf[tail];
532                                         if (c == '\t')
533                                                 col = (col | 7) + 1;
534                                         else if (iscntrl(c)) {
535                                                 if (L_ECHOCTL(tty))
536                                                         col += 2;
537                                         } else if (!is_continuation(c, tty))
538                                                 col++;
539                                         tail = (tail+1) & (N_TTY_BUF_SIZE-1);
540                                 }
541
542                                 /* should never happen */
543                                 if (tty->column > 0x80000000)
544                                         tty->column = 0;
545
546                                 /* Now backup to that column. */
547                                 while (tty->column > col) {
548                                         /* Can't use opost here. */
549                                         put_char('\b', tty);
550                                         if (tty->column > 0)
551                                                 tty->column--;
552                                 }
553                         } else {
554                                 if (iscntrl(c) && L_ECHOCTL(tty)) {
555                                         put_char('\b', tty);
556                                         put_char(' ', tty);
557                                         put_char('\b', tty);
558                                         if (tty->column > 0)
559                                                 tty->column--;
560                                 }
561                                 if (!iscntrl(c) || L_ECHOCTL(tty)) {
562                                         put_char('\b', tty);
563                                         put_char(' ', tty);
564                                         put_char('\b', tty);
565                                         if (tty->column > 0)
566                                                 tty->column--;
567                                 }
568                         }
569                 }
570                 if (kill_type == ERASE)
571                         break;
572         }
573         if (tty->read_head == tty->canon_head)
574                 finish_erasing(tty);
575 }
576
577 /**
578  *      isig            -       handle the ISIG optio
579  *      @sig: signal
580  *      @tty: terminal
581  *      @flush: force flush
582  *
583  *      Called when a signal is being sent due to terminal input. This
584  *      may caus terminal flushing to take place according to the termios
585  *      settings and character used. Called from the driver receive_buf
586  *      path so serialized.
587  */
588
589 static inline void isig(int sig, struct tty_struct *tty, int flush)
590 {
591         if (tty->pgrp)
592                 kill_pgrp(tty->pgrp, sig, 1);
593         if (flush || !L_NOFLSH(tty)) {
594                 n_tty_flush_buffer(tty);
595                 if (tty->driver->flush_buffer)
596                         tty->driver->flush_buffer(tty);
597         }
598 }
599
600 /**
601  *      n_tty_receive_break     -       handle break
602  *      @tty: terminal
603  *
604  *      An RS232 break event has been hit in the incoming bitstream. This
605  *      can cause a variety of events depending upon the termios settings.
606  *
607  *      Called from the receive_buf path so single threaded.
608  */
609
610 static inline void n_tty_receive_break(struct tty_struct *tty)
611 {
612         if (I_IGNBRK(tty))
613                 return;
614         if (I_BRKINT(tty)) {
615                 isig(SIGINT, tty, 1);
616                 return;
617         }
618         if (I_PARMRK(tty)) {
619                 put_tty_queue('\377', tty);
620                 put_tty_queue('\0', tty);
621         }
622         put_tty_queue('\0', tty);
623         wake_up_interruptible(&tty->read_wait);
624 }
625
626 /**
627  *      n_tty_receive_overrun   -       handle overrun reporting
628  *      @tty: terminal
629  *
630  *      Data arrived faster than we could process it. While the tty
631  *      driver has flagged this the bits that were missed are gone
632  *      forever.
633  *
634  *      Called from the receive_buf path so single threaded. Does not
635  *      need locking as num_overrun and overrun_time are function
636  *      private.
637  */
638
639 static inline void n_tty_receive_overrun(struct tty_struct *tty)
640 {
641         char buf[64];
642
643         tty->num_overrun++;
644         if (time_before(tty->overrun_time, jiffies - HZ) ||
645                         time_after(tty->overrun_time, jiffies)) {
646                 printk(KERN_WARNING "%s: %d input overrun(s)\n",
647                         tty_name(tty, buf),
648                         tty->num_overrun);
649                 tty->overrun_time = jiffies;
650                 tty->num_overrun = 0;
651         }
652 }
653
654 /**
655  *      n_tty_receive_parity_error      -       error notifier
656  *      @tty: terminal device
657  *      @c: character
658  *
659  *      Process a parity error and queue the right data to indicate
660  *      the error case if necessary. Locking as per n_tty_receive_buf.
661  */
662 static inline void n_tty_receive_parity_error(struct tty_struct *tty,
663                                               unsigned char c)
664 {
665         if (I_IGNPAR(tty))
666                 return;
667         if (I_PARMRK(tty)) {
668                 put_tty_queue('\377', tty);
669                 put_tty_queue('\0', tty);
670                 put_tty_queue(c, tty);
671         } else  if (I_INPCK(tty))
672                 put_tty_queue('\0', tty);
673         else
674                 put_tty_queue(c, tty);
675         wake_up_interruptible(&tty->read_wait);
676 }
677
678 /**
679  *      n_tty_receive_char      -       perform processing
680  *      @tty: terminal device
681  *      @c: character
682  *
683  *      Process an individual character of input received from the driver.
684  *      This is serialized with respect to itself by the rules for the
685  *      driver above.
686  */
687
688 static inline void n_tty_receive_char(struct tty_struct *tty, unsigned char c)
689 {
690         unsigned long flags;
691
692         if (tty->raw) {
693                 put_tty_queue(c, tty);
694                 return;
695         }
696
697         if (I_ISTRIP(tty))
698                 c &= 0x7f;
699         if (I_IUCLC(tty) && L_IEXTEN(tty))
700                 c=tolower(c);
701
702         if (tty->stopped && !tty->flow_stopped && I_IXON(tty) &&
703             ((I_IXANY(tty) && c != START_CHAR(tty) && c != STOP_CHAR(tty)) ||
704              c == INTR_CHAR(tty) || c == QUIT_CHAR(tty)))
705                 start_tty(tty);
706
707         if (tty->closing) {
708                 if (I_IXON(tty)) {
709                         if (c == START_CHAR(tty))
710                                 start_tty(tty);
711                         else if (c == STOP_CHAR(tty))
712                                 stop_tty(tty);
713                 }
714                 return;
715         }
716
717         /*
718          * If the previous character was LNEXT, or we know that this
719          * character is not one of the characters that we'll have to
720          * handle specially, do shortcut processing to speed things
721          * up.
722          */
723         if (!test_bit(c, tty->process_char_map) || tty->lnext) {
724                 finish_erasing(tty);
725                 tty->lnext = 0;
726                 if (L_ECHO(tty)) {
727                         if (tty->read_cnt >= N_TTY_BUF_SIZE-1) {
728                                 put_char('\a', tty); /* beep if no space */
729                                 return;
730                         }
731                         /* Record the column of first canon char. */
732                         if (tty->canon_head == tty->read_head)
733                                 tty->canon_column = tty->column;
734                         echo_char(c, tty);
735                 }
736                 if (I_PARMRK(tty) && c == (unsigned char) '\377')
737                         put_tty_queue(c, tty);
738                 put_tty_queue(c, tty);
739                 return;
740         }
741
742         if (c == '\r') {
743                 if (I_IGNCR(tty))
744                         return;
745                 if (I_ICRNL(tty))
746                         c = '\n';
747         } else if (c == '\n' && I_INLCR(tty))
748                 c = '\r';
749         if (I_IXON(tty)) {
750                 if (c == START_CHAR(tty)) {
751                         start_tty(tty);
752                         return;
753                 }
754                 if (c == STOP_CHAR(tty)) {
755                         stop_tty(tty);
756                         return;
757                 }
758         }
759         if (L_ISIG(tty)) {
760                 int signal;
761                 signal = SIGINT;
762                 if (c == INTR_CHAR(tty))
763                         goto send_signal;
764                 signal = SIGQUIT;
765                 if (c == QUIT_CHAR(tty))
766                         goto send_signal;
767                 signal = SIGTSTP;
768                 if (c == SUSP_CHAR(tty)) {
769 send_signal:
770                         /*
771                          * Echo character, and then send the signal.
772                          * Note that we do not use isig() here because we want
773                          * the order to be:
774                          * 1) flush, 2) echo, 3) signal
775                          */
776                         if (!L_NOFLSH(tty)) {
777                                 n_tty_flush_buffer(tty);
778                                 if (tty->driver->flush_buffer)
779                                         tty->driver->flush_buffer(tty);
780                         }
781                         if (L_ECHO(tty))
782                                 echo_char(c, tty);
783                         if (tty->pgrp)
784                                 kill_pgrp(tty->pgrp, signal, 1);
785                         return;
786                 }
787         }
788         if (tty->icanon) {
789                 if (c == ERASE_CHAR(tty) || c == KILL_CHAR(tty) ||
790                     (c == WERASE_CHAR(tty) && L_IEXTEN(tty))) {
791                         eraser(c, tty);
792                         return;
793                 }
794                 if (c == LNEXT_CHAR(tty) && L_IEXTEN(tty)) {
795                         tty->lnext = 1;
796                         if (L_ECHO(tty)) {
797                                 finish_erasing(tty);
798                                 if (L_ECHOCTL(tty)) {
799                                         put_char('^', tty);
800                                         put_char('\b', tty);
801                                 }
802                         }
803                         return;
804                 }
805                 if (c == REPRINT_CHAR(tty) && L_ECHO(tty) &&
806                     L_IEXTEN(tty)) {
807                         unsigned long tail = tty->canon_head;
808
809                         finish_erasing(tty);
810                         echo_char(c, tty);
811                         opost('\n', tty);
812                         while (tail != tty->read_head) {
813                                 echo_char(tty->read_buf[tail], tty);
814                                 tail = (tail+1) & (N_TTY_BUF_SIZE-1);
815                         }
816                         return;
817                 }
818                 if (c == '\n') {
819                         if (L_ECHO(tty) || L_ECHONL(tty)) {
820                                 if (tty->read_cnt >= N_TTY_BUF_SIZE-1)
821                                         put_char('\a', tty);
822                                 opost('\n', tty);
823                         }
824                         goto handle_newline;
825                 }
826                 if (c == EOF_CHAR(tty)) {
827                         if (tty->canon_head != tty->read_head)
828                                 set_bit(TTY_PUSH, &tty->flags);
829                         c = __DISABLED_CHAR;
830                         goto handle_newline;
831                 }
832                 if ((c == EOL_CHAR(tty)) ||
833                     (c == EOL2_CHAR(tty) && L_IEXTEN(tty))) {
834                         /*
835                          * XXX are EOL_CHAR and EOL2_CHAR echoed?!?
836                          */
837                         if (L_ECHO(tty)) {
838                                 if (tty->read_cnt >= N_TTY_BUF_SIZE-1)
839                                         put_char('\a', tty);
840                                 /* Record the column of first canon char. */
841                                 if (tty->canon_head == tty->read_head)
842                                         tty->canon_column = tty->column;
843                                 echo_char(c, tty);
844                         }
845                         /*
846                          * XXX does PARMRK doubling happen for
847                          * EOL_CHAR and EOL2_CHAR?
848                          */
849                         if (I_PARMRK(tty) && c == (unsigned char) '\377')
850                                 put_tty_queue(c, tty);
851
852 handle_newline:
853                         spin_lock_irqsave(&tty->read_lock, flags);
854                         set_bit(tty->read_head, tty->read_flags);
855                         put_tty_queue_nolock(c, tty);
856                         tty->canon_head = tty->read_head;
857                         tty->canon_data++;
858                         spin_unlock_irqrestore(&tty->read_lock, flags);
859                         kill_fasync(&tty->fasync, SIGIO, POLL_IN);
860                         if (waitqueue_active(&tty->read_wait))
861                                 wake_up_interruptible(&tty->read_wait);
862                         return;
863                 }
864         }
865
866         finish_erasing(tty);
867         if (L_ECHO(tty)) {
868                 if (tty->read_cnt >= N_TTY_BUF_SIZE-1) {
869                         put_char('\a', tty); /* beep if no space */
870                         return;
871                 }
872                 if (c == '\n')
873                         opost('\n', tty);
874                 else {
875                         /* Record the column of first canon char. */
876                         if (tty->canon_head == tty->read_head)
877                                 tty->canon_column = tty->column;
878                         echo_char(c, tty);
879                 }
880         }
881
882         if (I_PARMRK(tty) && c == (unsigned char) '\377')
883                 put_tty_queue(c, tty);
884
885         put_tty_queue(c, tty);
886 }
887
888
889 /**
890  *      n_tty_write_wakeup      -       asynchronous I/O notifier
891  *      @tty: tty device
892  *
893  *      Required for the ptys, serial driver etc. since processes
894  *      that attach themselves to the master and rely on ASYNC
895  *      IO must be woken up
896  */
897
898 static void n_tty_write_wakeup(struct tty_struct *tty)
899 {
900         if (tty->fasync) {
901                 set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
902                 kill_fasync(&tty->fasync, SIGIO, POLL_OUT);
903         }
904 }
905
906 /**
907  *      n_tty_receive_buf       -       data receive
908  *      @tty: terminal device
909  *      @cp: buffer
910  *      @fp: flag buffer
911  *      @count: characters
912  *
913  *      Called by the terminal driver when a block of characters has
914  *      been received. This function must be called from soft contexts
915  *      not from interrupt context. The driver is responsible for making
916  *      calls one at a time and in order (or using flush_to_ldisc)
917  */
918
919 static void n_tty_receive_buf(struct tty_struct *tty, const unsigned char *cp,
920                               char *fp, int count)
921 {
922         const unsigned char *p;
923         char *f, flags = TTY_NORMAL;
924         int     i;
925         char    buf[64];
926         unsigned long cpuflags;
927
928         if (!tty->read_buf)
929                 return;
930
931         if (tty->real_raw) {
932                 spin_lock_irqsave(&tty->read_lock, cpuflags);
933                 i = min(N_TTY_BUF_SIZE - tty->read_cnt,
934                         N_TTY_BUF_SIZE - tty->read_head);
935                 i = min(count, i);
936                 memcpy(tty->read_buf + tty->read_head, cp, i);
937                 tty->read_head = (tty->read_head + i) & (N_TTY_BUF_SIZE-1);
938                 tty->read_cnt += i;
939                 cp += i;
940                 count -= i;
941
942                 i = min(N_TTY_BUF_SIZE - tty->read_cnt,
943                         N_TTY_BUF_SIZE - tty->read_head);
944                 i = min(count, i);
945                 memcpy(tty->read_buf + tty->read_head, cp, i);
946                 tty->read_head = (tty->read_head + i) & (N_TTY_BUF_SIZE-1);
947                 tty->read_cnt += i;
948                 spin_unlock_irqrestore(&tty->read_lock, cpuflags);
949         } else {
950                 for (i = count, p = cp, f = fp; i; i--, p++) {
951                         if (f)
952                                 flags = *f++;
953                         switch (flags) {
954                         case TTY_NORMAL:
955                                 n_tty_receive_char(tty, *p);
956                                 break;
957                         case TTY_BREAK:
958                                 n_tty_receive_break(tty);
959                                 break;
960                         case TTY_PARITY:
961                         case TTY_FRAME:
962                                 n_tty_receive_parity_error(tty, *p);
963                                 break;
964                         case TTY_OVERRUN:
965                                 n_tty_receive_overrun(tty);
966                                 break;
967                         default:
968                                 printk(KERN_ERR "%s: unknown flag %d\n",
969                                        tty_name(tty, buf), flags);
970                                 break;
971                         }
972                 }
973                 if (tty->driver->flush_chars)
974                         tty->driver->flush_chars(tty);
975         }
976
977         n_tty_set_room(tty);
978
979         if (!tty->icanon && (tty->read_cnt >= tty->minimum_to_wake)) {
980                 kill_fasync(&tty->fasync, SIGIO, POLL_IN);
981                 if (waitqueue_active(&tty->read_wait))
982                         wake_up_interruptible(&tty->read_wait);
983         }
984
985         /*
986          * Check the remaining room for the input canonicalization
987          * mode.  We don't want to throttle the driver if we're in
988          * canonical mode and don't have a newline yet!
989          */
990         if (tty->receive_room < TTY_THRESHOLD_THROTTLE) {
991                 /* check TTY_THROTTLED first so it indicates our state */
992                 if (!test_and_set_bit(TTY_THROTTLED, &tty->flags) &&
993                     tty->driver->throttle)
994                         tty->driver->throttle(tty);
995         }
996 }
997
998 int is_ignored(int sig)
999 {
1000         return (sigismember(&current->blocked, sig) ||
1001                 current->sighand->action[sig-1].sa.sa_handler == SIG_IGN);
1002 }
1003
1004 /**
1005  *      n_tty_set_termios       -       termios data changed
1006  *      @tty: terminal
1007  *      @old: previous data
1008  *
1009  *      Called by the tty layer when the user changes termios flags so
1010  *      that the line discipline can plan ahead. This function cannot sleep
1011  *      and is protected from re-entry by the tty layer. The user is
1012  *      guaranteed that this function will not be re-entered or in progress
1013  *      when the ldisc is closed.
1014  */
1015
1016 static void n_tty_set_termios(struct tty_struct *tty, struct ktermios *old)
1017 {
1018         if (!tty)
1019                 return;
1020
1021         tty->icanon = (L_ICANON(tty) != 0);
1022         if (test_bit(TTY_HW_COOK_IN, &tty->flags)) {
1023                 tty->raw = 1;
1024                 tty->real_raw = 1;
1025                 n_tty_set_room(tty);
1026                 return;
1027         }
1028         if (I_ISTRIP(tty) || I_IUCLC(tty) || I_IGNCR(tty) ||
1029             I_ICRNL(tty) || I_INLCR(tty) || L_ICANON(tty) ||
1030             I_IXON(tty) || L_ISIG(tty) || L_ECHO(tty) ||
1031             I_PARMRK(tty)) {
1032                 memset(tty->process_char_map, 0, 256/8);
1033
1034                 if (I_IGNCR(tty) || I_ICRNL(tty))
1035                         set_bit('\r', tty->process_char_map);
1036                 if (I_INLCR(tty))
1037                         set_bit('\n', tty->process_char_map);
1038
1039                 if (L_ICANON(tty)) {
1040                         set_bit(ERASE_CHAR(tty), tty->process_char_map);
1041                         set_bit(KILL_CHAR(tty), tty->process_char_map);
1042                         set_bit(EOF_CHAR(tty), tty->process_char_map);
1043                         set_bit('\n', tty->process_char_map);
1044                         set_bit(EOL_CHAR(tty), tty->process_char_map);
1045                         if (L_IEXTEN(tty)) {
1046                                 set_bit(WERASE_CHAR(tty),
1047                                         tty->process_char_map);
1048                                 set_bit(LNEXT_CHAR(tty),
1049                                         tty->process_char_map);
1050                                 set_bit(EOL2_CHAR(tty),
1051                                         tty->process_char_map);
1052                                 if (L_ECHO(tty))
1053                                         set_bit(REPRINT_CHAR(tty),
1054                                                 tty->process_char_map);
1055                         }
1056                 }
1057                 if (I_IXON(tty)) {
1058                         set_bit(START_CHAR(tty), tty->process_char_map);
1059                         set_bit(STOP_CHAR(tty), tty->process_char_map);
1060                 }
1061                 if (L_ISIG(tty)) {
1062                         set_bit(INTR_CHAR(tty), tty->process_char_map);
1063                         set_bit(QUIT_CHAR(tty), tty->process_char_map);
1064                         set_bit(SUSP_CHAR(tty), tty->process_char_map);
1065                 }
1066                 clear_bit(__DISABLED_CHAR, tty->process_char_map);
1067                 tty->raw = 0;
1068                 tty->real_raw = 0;
1069         } else {
1070                 tty->raw = 1;
1071                 if ((I_IGNBRK(tty) || (!I_BRKINT(tty) && !I_PARMRK(tty))) &&
1072                     (I_IGNPAR(tty) || !I_INPCK(tty)) &&
1073                     (tty->driver->flags & TTY_DRIVER_REAL_RAW))
1074                         tty->real_raw = 1;
1075                 else
1076                         tty->real_raw = 0;
1077         }
1078         n_tty_set_room(tty);
1079 }
1080
1081 /**
1082  *      n_tty_close             -       close the ldisc for this tty
1083  *      @tty: device
1084  *
1085  *      Called from the terminal layer when this line discipline is
1086  *      being shut down, either because of a close or becsuse of a
1087  *      discipline change. The function will not be called while other
1088  *      ldisc methods are in progress.
1089  */
1090
1091 static void n_tty_close(struct tty_struct *tty)
1092 {
1093         n_tty_flush_buffer(tty);
1094         if (tty->read_buf) {
1095                 free_buf(tty->read_buf);
1096                 tty->read_buf = NULL;
1097         }
1098 }
1099
1100 /**
1101  *      n_tty_open              -       open an ldisc
1102  *      @tty: terminal to open
1103  *
1104  *      Called when this line discipline is being attached to the
1105  *      terminal device. Can sleep. Called serialized so that no
1106  *      other events will occur in parallel. No further open will occur
1107  *      until a close.
1108  */
1109
1110 static int n_tty_open(struct tty_struct *tty)
1111 {
1112         if (!tty)
1113                 return -EINVAL;
1114
1115         /* This one is ugly. Currently a malloc failure here can panic */
1116         if (!tty->read_buf) {
1117                 tty->read_buf = alloc_buf();
1118                 if (!tty->read_buf)
1119                         return -ENOMEM;
1120         }
1121         memset(tty->read_buf, 0, N_TTY_BUF_SIZE);
1122         reset_buffer_flags(tty);
1123         tty->column = 0;
1124         n_tty_set_termios(tty, NULL);
1125         tty->minimum_to_wake = 1;
1126         tty->closing = 0;
1127         return 0;
1128 }
1129
1130 static inline int input_available_p(struct tty_struct *tty, int amt)
1131 {
1132         if (tty->icanon) {
1133                 if (tty->canon_data)
1134                         return 1;
1135         } else if (tty->read_cnt >= (amt ? amt : 1))
1136                 return 1;
1137
1138         return 0;
1139 }
1140
1141 /**
1142  *      copy_from_read_buf      -       copy read data directly
1143  *      @tty: terminal device
1144  *      @b: user data
1145  *      @nr: size of data
1146  *
1147  *      Helper function to speed up read_chan.  It is only called when
1148  *      ICANON is off; it copies characters straight from the tty queue to
1149  *      user space directly.  It can be profitably called twice; once to
1150  *      drain the space from the tail pointer to the (physical) end of the
1151  *      buffer, and once to drain the space from the (physical) beginning of
1152  *      the buffer to head pointer.
1153  *
1154  *      Called under the tty->atomic_read_lock sem
1155  *
1156  */
1157
1158 static int copy_from_read_buf(struct tty_struct *tty,
1159                                       unsigned char __user **b,
1160                                       size_t *nr)
1161
1162 {
1163         int retval;
1164         size_t n;
1165         unsigned long flags;
1166
1167         retval = 0;
1168         spin_lock_irqsave(&tty->read_lock, flags);
1169         n = min(tty->read_cnt, N_TTY_BUF_SIZE - tty->read_tail);
1170         n = min(*nr, n);
1171         spin_unlock_irqrestore(&tty->read_lock, flags);
1172         if (n) {
1173                 retval = copy_to_user(*b, &tty->read_buf[tty->read_tail], n);
1174                 n -= retval;
1175                 tty_audit_add_data(tty, &tty->read_buf[tty->read_tail], n);
1176                 spin_lock_irqsave(&tty->read_lock, flags);
1177                 tty->read_tail = (tty->read_tail + n) & (N_TTY_BUF_SIZE-1);
1178                 tty->read_cnt -= n;
1179                 spin_unlock_irqrestore(&tty->read_lock, flags);
1180                 *b += n;
1181                 *nr -= n;
1182         }
1183         return retval;
1184 }
1185
1186 extern ssize_t redirected_tty_write(struct file *, const char __user *,
1187                                                         size_t, loff_t *);
1188
1189 /**
1190  *      job_control             -       check job control
1191  *      @tty: tty
1192  *      @file: file handle
1193  *
1194  *      Perform job control management checks on this file/tty descriptor
1195  *      and if appropriate send any needed signals and return a negative
1196  *      error code if action should be taken.
1197  */
1198
1199 static int job_control(struct tty_struct *tty, struct file *file)
1200 {
1201         /* Job control check -- must be done at start and after
1202            every sleep (POSIX.1 7.1.1.4). */
1203         /* NOTE: not yet done after every sleep pending a thorough
1204            check of the logic of this change. -- jlc */
1205         /* don't stop on /dev/console */
1206         if (file->f_op->write != redirected_tty_write &&
1207             current->signal->tty == tty) {
1208                 if (!tty->pgrp)
1209                         printk(KERN_ERR "read_chan: no tty->pgrp!\n");
1210                 else if (task_pgrp(current) != tty->pgrp) {
1211                         if (is_ignored(SIGTTIN) ||
1212                             is_current_pgrp_orphaned())
1213                                 return -EIO;
1214                         kill_pgrp(task_pgrp(current), SIGTTIN, 1);
1215                         set_thread_flag(TIF_SIGPENDING);
1216                         return -ERESTARTSYS;
1217                 }
1218         }
1219         return 0;
1220 }
1221
1222
1223 /**
1224  *      read_chan               -       read function for tty
1225  *      @tty: tty device
1226  *      @file: file object
1227  *      @buf: userspace buffer pointer
1228  *      @nr: size of I/O
1229  *
1230  *      Perform reads for the line discipline. We are guaranteed that the
1231  *      line discipline will not be closed under us but we may get multiple
1232  *      parallel readers and must handle this ourselves. We may also get
1233  *      a hangup. Always called in user context, may sleep.
1234  *
1235  *      This code must be sure never to sleep through a hangup.
1236  */
1237
1238 static ssize_t read_chan(struct tty_struct *tty, struct file *file,
1239                          unsigned char __user *buf, size_t nr)
1240 {
1241         unsigned char __user *b = buf;
1242         DECLARE_WAITQUEUE(wait, current);
1243         int c;
1244         int minimum, time;
1245         ssize_t retval = 0;
1246         ssize_t size;
1247         long timeout;
1248         unsigned long flags;
1249
1250 do_it_again:
1251
1252         if (!tty->read_buf) {
1253                 printk(KERN_ERR "n_tty_read_chan: read_buf == NULL?!?\n");
1254                 return -EIO;
1255         }
1256
1257         c = job_control(tty, file);
1258         if (c < 0)
1259                 return c;
1260
1261         minimum = time = 0;
1262         timeout = MAX_SCHEDULE_TIMEOUT;
1263         if (!tty->icanon) {
1264                 time = (HZ / 10) * TIME_CHAR(tty);
1265                 minimum = MIN_CHAR(tty);
1266                 if (minimum) {
1267                         if (time)
1268                                 tty->minimum_to_wake = 1;
1269                         else if (!waitqueue_active(&tty->read_wait) ||
1270                                  (tty->minimum_to_wake > minimum))
1271                                 tty->minimum_to_wake = minimum;
1272                 } else {
1273                         timeout = 0;
1274                         if (time) {
1275                                 timeout = time;
1276                                 time = 0;
1277                         }
1278                         tty->minimum_to_wake = minimum = 1;
1279                 }
1280         }
1281
1282         /*
1283          *      Internal serialization of reads.
1284          */
1285         if (file->f_flags & O_NONBLOCK) {
1286                 if (!mutex_trylock(&tty->atomic_read_lock))
1287                         return -EAGAIN;
1288         } else {
1289                 if (mutex_lock_interruptible(&tty->atomic_read_lock))
1290                         return -ERESTARTSYS;
1291         }
1292
1293         add_wait_queue(&tty->read_wait, &wait);
1294         while (nr) {
1295                 /* First test for status change. */
1296                 if (tty->packet && tty->link->ctrl_status) {
1297                         unsigned char cs;
1298                         if (b != buf)
1299                                 break;
1300                         cs = tty->link->ctrl_status;
1301                         tty->link->ctrl_status = 0;
1302                         if (tty_put_user(tty, cs, b++)) {
1303                                 retval = -EFAULT;
1304                                 b--;
1305                                 break;
1306                         }
1307                         nr--;
1308                         break;
1309                 }
1310                 /* This statement must be first before checking for input
1311                    so that any interrupt will set the state back to
1312                    TASK_RUNNING. */
1313                 set_current_state(TASK_INTERRUPTIBLE);
1314
1315                 if (((minimum - (b - buf)) < tty->minimum_to_wake) &&
1316                     ((minimum - (b - buf)) >= 1))
1317                         tty->minimum_to_wake = (minimum - (b - buf));
1318
1319                 if (!input_available_p(tty, 0)) {
1320                         if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
1321                                 retval = -EIO;
1322                                 break;
1323                         }
1324                         if (tty_hung_up_p(file))
1325                                 break;
1326                         if (!timeout)
1327                                 break;
1328                         if (file->f_flags & O_NONBLOCK) {
1329                                 retval = -EAGAIN;
1330                                 break;
1331                         }
1332                         if (signal_pending(current)) {
1333                                 retval = -ERESTARTSYS;
1334                                 break;
1335                         }
1336                         n_tty_set_room(tty);
1337                         timeout = schedule_timeout(timeout);
1338                         continue;
1339                 }
1340                 __set_current_state(TASK_RUNNING);
1341
1342                 /* Deal with packet mode. */
1343                 if (tty->packet && b == buf) {
1344                         if (tty_put_user(tty, TIOCPKT_DATA, b++)) {
1345                                 retval = -EFAULT;
1346                                 b--;
1347                                 break;
1348                         }
1349                         nr--;
1350                 }
1351
1352                 if (tty->icanon) {
1353                         /* N.B. avoid overrun if nr == 0 */
1354                         while (nr && tty->read_cnt) {
1355                                 int eol;
1356
1357                                 eol = test_and_clear_bit(tty->read_tail,
1358                                                 tty->read_flags);
1359                                 c = tty->read_buf[tty->read_tail];
1360                                 spin_lock_irqsave(&tty->read_lock, flags);
1361                                 tty->read_tail = ((tty->read_tail+1) &
1362                                                   (N_TTY_BUF_SIZE-1));
1363                                 tty->read_cnt--;
1364                                 if (eol) {
1365                                         /* this test should be redundant:
1366                                          * we shouldn't be reading data if
1367                                          * canon_data is 0
1368                                          */
1369                                         if (--tty->canon_data < 0)
1370                                                 tty->canon_data = 0;
1371                                 }
1372                                 spin_unlock_irqrestore(&tty->read_lock, flags);
1373
1374                                 if (!eol || (c != __DISABLED_CHAR)) {
1375                                         if (tty_put_user(tty, c, b++)) {
1376                                                 retval = -EFAULT;
1377                                                 b--;
1378                                                 break;
1379                                         }
1380                                         nr--;
1381                                 }
1382                                 if (eol) {
1383                                         tty_audit_push(tty);
1384                                         break;
1385                                 }
1386                         }
1387                         if (retval)
1388                                 break;
1389                 } else {
1390                         int uncopied;
1391                         uncopied = copy_from_read_buf(tty, &b, &nr);
1392                         uncopied += copy_from_read_buf(tty, &b, &nr);
1393                         if (uncopied) {
1394                                 retval = -EFAULT;
1395                                 break;
1396                         }
1397                 }
1398
1399                 /* If there is enough space in the read buffer now, let the
1400                  * low-level driver know. We use n_tty_chars_in_buffer() to
1401                  * check the buffer, as it now knows about canonical mode.
1402                  * Otherwise, if the driver is throttled and the line is
1403                  * longer than TTY_THRESHOLD_UNTHROTTLE in canonical mode,
1404                  * we won't get any more characters.
1405                  */
1406                 if (n_tty_chars_in_buffer(tty) <= TTY_THRESHOLD_UNTHROTTLE) {
1407                         n_tty_set_room(tty);
1408                         check_unthrottle(tty);
1409                 }
1410
1411                 if (b - buf >= minimum)
1412                         break;
1413                 if (time)
1414                         timeout = time;
1415         }
1416         mutex_unlock(&tty->atomic_read_lock);
1417         remove_wait_queue(&tty->read_wait, &wait);
1418
1419         if (!waitqueue_active(&tty->read_wait))
1420                 tty->minimum_to_wake = minimum;
1421
1422         __set_current_state(TASK_RUNNING);
1423         size = b - buf;
1424         if (size) {
1425                 retval = size;
1426                 if (nr)
1427                         clear_bit(TTY_PUSH, &tty->flags);
1428         } else if (test_and_clear_bit(TTY_PUSH, &tty->flags))
1429                  goto do_it_again;
1430
1431         n_tty_set_room(tty);
1432
1433         return retval;
1434 }
1435
1436 /**
1437  *      write_chan              -       write function for tty
1438  *      @tty: tty device
1439  *      @file: file object
1440  *      @buf: userspace buffer pointer
1441  *      @nr: size of I/O
1442  *
1443  *      Write function of the terminal device. This is serialized with
1444  *      respect to other write callers but not to termios changes, reads
1445  *      and other such events. We must be careful with N_TTY as the receive
1446  *      code will echo characters, thus calling driver write methods.
1447  *
1448  *      This code must be sure never to sleep through a hangup.
1449  */
1450
1451 static ssize_t write_chan(struct tty_struct *tty, struct file *file,
1452                           const unsigned char *buf, size_t nr)
1453 {
1454         const unsigned char *b = buf;
1455         DECLARE_WAITQUEUE(wait, current);
1456         int c;
1457         ssize_t retval = 0;
1458
1459         /* Job control check -- must be done at start (POSIX.1 7.1.1.4). */
1460         if (L_TOSTOP(tty) && file->f_op->write != redirected_tty_write) {
1461                 retval = tty_check_change(tty);
1462                 if (retval)
1463                         return retval;
1464         }
1465
1466         add_wait_queue(&tty->write_wait, &wait);
1467         while (1) {
1468                 set_current_state(TASK_INTERRUPTIBLE);
1469                 if (signal_pending(current)) {
1470                         retval = -ERESTARTSYS;
1471                         break;
1472                 }
1473                 if (tty_hung_up_p(file) || (tty->link && !tty->link->count)) {
1474                         retval = -EIO;
1475                         break;
1476                 }
1477                 if (O_OPOST(tty) && !(test_bit(TTY_HW_COOK_OUT, &tty->flags))) {
1478                         while (nr > 0) {
1479                                 ssize_t num = opost_block(tty, b, nr);
1480                                 if (num < 0) {
1481                                         if (num == -EAGAIN)
1482                                                 break;
1483                                         retval = num;
1484                                         goto break_out;
1485                                 }
1486                                 b += num;
1487                                 nr -= num;
1488                                 if (nr == 0)
1489                                         break;
1490                                 c = *b;
1491                                 if (opost(c, tty) < 0)
1492                                         break;
1493                                 b++; nr--;
1494                         }
1495                         if (tty->driver->flush_chars)
1496                                 tty->driver->flush_chars(tty);
1497                 } else {
1498                         while (nr > 0) {
1499                                 c = tty->driver->write(tty, b, nr);
1500                                 if (c < 0) {
1501                                         retval = c;
1502                                         goto break_out;
1503                                 }
1504                                 if (!c)
1505                                         break;
1506                                 b += c;
1507                                 nr -= c;
1508                         }
1509                 }
1510                 if (!nr)
1511                         break;
1512                 if (file->f_flags & O_NONBLOCK) {
1513                         retval = -EAGAIN;
1514                         break;
1515                 }
1516                 schedule();
1517         }
1518 break_out:
1519         __set_current_state(TASK_RUNNING);
1520         remove_wait_queue(&tty->write_wait, &wait);
1521         return (b - buf) ? b - buf : retval;
1522 }
1523
1524 /**
1525  *      normal_poll             -       poll method for N_TTY
1526  *      @tty: terminal device
1527  *      @file: file accessing it
1528  *      @wait: poll table
1529  *
1530  *      Called when the line discipline is asked to poll() for data or
1531  *      for special events. This code is not serialized with respect to
1532  *      other events save open/close.
1533  *
1534  *      This code must be sure never to sleep through a hangup.
1535  *      Called without the kernel lock held - fine
1536  *
1537  *      FIXME: if someone changes the VMIN or discipline settings for the
1538  *      terminal while another process is in poll() the poll does not
1539  *      recompute the new limits. Possibly set_termios should issue
1540  *      a read wakeup to fix this bug.
1541  */
1542
1543 static unsigned int normal_poll(struct tty_struct *tty, struct file *file,
1544                                                         poll_table *wait)
1545 {
1546         unsigned int mask = 0;
1547
1548         poll_wait(file, &tty->read_wait, wait);
1549         poll_wait(file, &tty->write_wait, wait);
1550         if (input_available_p(tty, TIME_CHAR(tty) ? 0 : MIN_CHAR(tty)))
1551                 mask |= POLLIN | POLLRDNORM;
1552         if (tty->packet && tty->link->ctrl_status)
1553                 mask |= POLLPRI | POLLIN | POLLRDNORM;
1554         if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
1555                 mask |= POLLHUP;
1556         if (tty_hung_up_p(file))
1557                 mask |= POLLHUP;
1558         if (!(mask & (POLLHUP | POLLIN | POLLRDNORM))) {
1559                 if (MIN_CHAR(tty) && !TIME_CHAR(tty))
1560                         tty->minimum_to_wake = MIN_CHAR(tty);
1561                 else
1562                         tty->minimum_to_wake = 1;
1563         }
1564         if (!tty_is_writelocked(tty) &&
1565                         tty->driver->chars_in_buffer(tty) < WAKEUP_CHARS &&
1566                         tty->driver->write_room(tty) > 0)
1567                 mask |= POLLOUT | POLLWRNORM;
1568         return mask;
1569 }
1570
1571 struct tty_ldisc tty_ldisc_N_TTY = {
1572         .magic           = TTY_LDISC_MAGIC,
1573         .name            = "n_tty",
1574         .open            = n_tty_open,
1575         .close           = n_tty_close,
1576         .flush_buffer    = n_tty_flush_buffer,
1577         .chars_in_buffer = n_tty_chars_in_buffer,
1578         .read            = read_chan,
1579         .write           = write_chan,
1580         .ioctl           = n_tty_ioctl,
1581         .set_termios     = n_tty_set_termios,
1582         .poll            = normal_poll,
1583         .receive_buf     = n_tty_receive_buf,
1584         .write_wakeup    = n_tty_write_wakeup
1585 };
1586