Linux-2.6.12-rc2
[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 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
49 #include <asm/uaccess.h>
50 #include <asm/system.h>
51
52 /* number of characters left in xmit buffer before select has we have room */
53 #define WAKEUP_CHARS 256
54
55 /*
56  * This defines the low- and high-watermarks for throttling and
57  * unthrottling the TTY driver.  These watermarks are used for
58  * controlling the space in the read buffer.
59  */
60 #define TTY_THRESHOLD_THROTTLE          128 /* now based on remaining room */
61 #define TTY_THRESHOLD_UNTHROTTLE        128
62
63 static inline unsigned char *alloc_buf(void)
64 {
65         int prio = in_interrupt() ? GFP_ATOMIC : GFP_KERNEL;
66
67         if (PAGE_SIZE != N_TTY_BUF_SIZE)
68                 return kmalloc(N_TTY_BUF_SIZE, prio);
69         else
70                 return (unsigned char *)__get_free_page(prio);
71 }
72
73 static inline void free_buf(unsigned char *buf)
74 {
75         if (PAGE_SIZE != N_TTY_BUF_SIZE)
76                 kfree(buf);
77         else
78                 free_page((unsigned long) buf);
79 }
80
81 static inline void put_tty_queue_nolock(unsigned char c, struct tty_struct *tty)
82 {
83         if (tty->read_cnt < N_TTY_BUF_SIZE) {
84                 tty->read_buf[tty->read_head] = c;
85                 tty->read_head = (tty->read_head + 1) & (N_TTY_BUF_SIZE-1);
86                 tty->read_cnt++;
87         }
88 }
89
90 static inline void put_tty_queue(unsigned char c, struct tty_struct *tty)
91 {
92         unsigned long flags;
93         /*
94          *      The problem of stomping on the buffers ends here.
95          *      Why didn't anyone see this one coming? --AJK
96         */
97         spin_lock_irqsave(&tty->read_lock, flags);
98         put_tty_queue_nolock(c, tty);
99         spin_unlock_irqrestore(&tty->read_lock, flags);
100 }
101
102 /**
103  *      check_unthrottle        -       allow new receive data
104  *      @tty; tty device
105  *
106  *      Check whether to call the driver.unthrottle function.
107  *      We test the TTY_THROTTLED bit first so that it always
108  *      indicates the current state. The decision about whether
109  *      it is worth allowing more input has been taken by the caller.
110  *      Can sleep, may be called under the atomic_read semaphore but
111  *      this is not guaranteed.
112  */
113  
114 static void check_unthrottle(struct tty_struct * tty)
115 {
116         if (tty->count &&
117             test_and_clear_bit(TTY_THROTTLED, &tty->flags) && 
118             tty->driver->unthrottle)
119                 tty->driver->unthrottle(tty);
120 }
121
122 /**
123  *      reset_buffer_flags      -       reset buffer state
124  *      @tty: terminal to reset
125  *
126  *      Reset the read buffer counters, clear the flags, 
127  *      and make sure the driver is unthrottled. Called
128  *      from n_tty_open() and n_tty_flush_buffer().
129  */
130 static void reset_buffer_flags(struct tty_struct *tty)
131 {
132         unsigned long flags;
133
134         spin_lock_irqsave(&tty->read_lock, flags);
135         tty->read_head = tty->read_tail = tty->read_cnt = 0;
136         spin_unlock_irqrestore(&tty->read_lock, flags);
137         tty->canon_head = tty->canon_data = tty->erasing = 0;
138         memset(&tty->read_flags, 0, sizeof tty->read_flags);
139         check_unthrottle(tty);
140 }
141
142 /**
143  *      n_tty_flush_buffer      -       clean input queue
144  *      @tty:   terminal device
145  *
146  *      Flush the input buffer. Called when the line discipline is
147  *      being closed, when the tty layer wants the buffer flushed (eg
148  *      at hangup) or when the N_TTY line discipline internally has to
149  *      clean the pending queue (for example some signals).
150  *
151  *      FIXME: tty->ctrl_status is not spinlocked and relies on
152  *      lock_kernel() still.
153  */
154  
155 static void n_tty_flush_buffer(struct tty_struct * tty)
156 {
157         /* clear everything and unthrottle the driver */
158         reset_buffer_flags(tty);
159         
160         if (!tty->link)
161                 return;
162
163         if (tty->link->packet) {
164                 tty->ctrl_status |= TIOCPKT_FLUSHREAD;
165                 wake_up_interruptible(&tty->link->read_wait);
166         }
167 }
168
169 /**
170  *      n_tty_chars_in_buffer   -       report available bytes
171  *      @tty: tty device
172  *
173  *      Report the number of characters buffered to be delivered to user
174  *      at this instant in time. 
175  */
176  
177 static ssize_t n_tty_chars_in_buffer(struct tty_struct *tty)
178 {
179         unsigned long flags;
180         ssize_t n = 0;
181
182         spin_lock_irqsave(&tty->read_lock, flags);
183         if (!tty->icanon) {
184                 n = tty->read_cnt;
185         } else if (tty->canon_data) {
186                 n = (tty->canon_head > tty->read_tail) ?
187                         tty->canon_head - tty->read_tail :
188                         tty->canon_head + (N_TTY_BUF_SIZE - tty->read_tail);
189         }
190         spin_unlock_irqrestore(&tty->read_lock, flags);
191         return n;
192 }
193
194 /**
195  *      is_utf8_continuation    -       utf8 multibyte check
196  *      @c: byte to check
197  *
198  *      Returns true if the utf8 character 'c' is a multibyte continuation
199  *      character. We use this to correctly compute the on screen size
200  *      of the character when printing
201  */
202  
203 static inline int is_utf8_continuation(unsigned char c)
204 {
205         return (c & 0xc0) == 0x80;
206 }
207
208 /**
209  *      is_continuation         -       multibyte check
210  *      @c: byte to check
211  *
212  *      Returns true if the utf8 character 'c' is a multibyte continuation
213  *      character and the terminal is in unicode mode.
214  */
215  
216 static inline int is_continuation(unsigned char c, struct tty_struct *tty)
217 {
218         return I_IUTF8(tty) && is_utf8_continuation(c);
219 }
220
221 /**
222  *      opost                   -       output post processor
223  *      @c: character (or partial unicode symbol)
224  *      @tty: terminal device
225  *
226  *      Perform OPOST processing.  Returns -1 when the output device is
227  *      full and the character must be retried. Note that Linux currently
228  *      ignores TABDLY, CRDLY, VTDLY, FFDLY and NLDLY. They simply aren't
229  *      relevant in the world today. If you ever need them, add them here.
230  *
231  *      Called from both the receive and transmit sides and can be called
232  *      re-entrantly. Relies on lock_kernel() still.
233  */
234  
235 static int opost(unsigned char c, struct tty_struct *tty)
236 {
237         int     space, spaces;
238
239         space = tty->driver->write_room(tty);
240         if (!space)
241                 return -1;
242
243         if (O_OPOST(tty)) {
244                 switch (c) {
245                 case '\n':
246                         if (O_ONLRET(tty))
247                                 tty->column = 0;
248                         if (O_ONLCR(tty)) {
249                                 if (space < 2)
250                                         return -1;
251                                 tty->driver->put_char(tty, '\r');
252                                 tty->column = 0;
253                         }
254                         tty->canon_column = tty->column;
255                         break;
256                 case '\r':
257                         if (O_ONOCR(tty) && tty->column == 0)
258                                 return 0;
259                         if (O_OCRNL(tty)) {
260                                 c = '\n';
261                                 if (O_ONLRET(tty))
262                                         tty->canon_column = tty->column = 0;
263                                 break;
264                         }
265                         tty->canon_column = tty->column = 0;
266                         break;
267                 case '\t':
268                         spaces = 8 - (tty->column & 7);
269                         if (O_TABDLY(tty) == XTABS) {
270                                 if (space < spaces)
271                                         return -1;
272                                 tty->column += spaces;
273                                 tty->driver->write(tty, "        ", spaces);
274                                 return 0;
275                         }
276                         tty->column += spaces;
277                         break;
278                 case '\b':
279                         if (tty->column > 0)
280                                 tty->column--;
281                         break;
282                 default:
283                         if (O_OLCUC(tty))
284                                 c = toupper(c);
285                         if (!iscntrl(c) && !is_continuation(c, tty))
286                                 tty->column++;
287                         break;
288                 }
289         }
290         tty->driver->put_char(tty, c);
291         return 0;
292 }
293
294 /**
295  *      opost_block             -       block postprocess
296  *      @tty: terminal device
297  *      @inbuf: user buffer
298  *      @nr: number of bytes
299  *
300  *      This path is used to speed up block console writes, among other
301  *      things when processing blocks of output data. It handles only
302  *      the simple cases normally found and helps to generate blocks of
303  *      symbols for the console driver and thus improve performance.
304  *
305  *      Called from write_chan under the tty layer write lock.
306  */
307  
308 static ssize_t opost_block(struct tty_struct * tty,
309                        const unsigned char * buf, unsigned int nr)
310 {
311         int     space;
312         int     i;
313         const unsigned char *cp;
314
315         space = tty->driver->write_room(tty);
316         if (!space)
317                 return 0;
318         if (nr > space)
319                 nr = space;
320
321         for (i = 0, cp = buf; i < nr; i++, cp++) {
322                 switch (*cp) {
323                 case '\n':
324                         if (O_ONLRET(tty))
325                                 tty->column = 0;
326                         if (O_ONLCR(tty))
327                                 goto break_out;
328                         tty->canon_column = tty->column;
329                         break;
330                 case '\r':
331                         if (O_ONOCR(tty) && tty->column == 0)
332                                 goto break_out;
333                         if (O_OCRNL(tty))
334                                 goto break_out;
335                         tty->canon_column = tty->column = 0;
336                         break;
337                 case '\t':
338                         goto break_out;
339                 case '\b':
340                         if (tty->column > 0)
341                                 tty->column--;
342                         break;
343                 default:
344                         if (O_OLCUC(tty))
345                                 goto break_out;
346                         if (!iscntrl(*cp))
347                                 tty->column++;
348                         break;
349                 }
350         }
351 break_out:
352         if (tty->driver->flush_chars)
353                 tty->driver->flush_chars(tty);
354         i = tty->driver->write(tty, buf, i);    
355         return i;
356 }
357
358
359 /**
360  *      put_char        -       write character to driver
361  *      @c: character (or part of unicode symbol)
362  *      @tty: terminal device
363  *
364  *      Queue a byte to the driver layer for output
365  */
366  
367 static inline void put_char(unsigned char c, struct tty_struct *tty)
368 {
369         tty->driver->put_char(tty, c);
370 }
371
372 /**
373  *      echo_char       -       echo characters
374  *      @c: unicode byte to echo
375  *      @tty: terminal device
376  *
377  *      Echo user input back onto the screen. This must be called only when 
378  *      L_ECHO(tty) is true. Called from the driver receive_buf path.
379  */
380
381 static void echo_char(unsigned char c, struct tty_struct *tty)
382 {
383         if (L_ECHOCTL(tty) && iscntrl(c) && c != '\t') {
384                 put_char('^', tty);
385                 put_char(c ^ 0100, tty);
386                 tty->column += 2;
387         } else
388                 opost(c, tty);
389 }
390
391 static inline void finish_erasing(struct tty_struct *tty)
392 {
393         if (tty->erasing) {
394                 put_char('/', tty);
395                 tty->column++;
396                 tty->erasing = 0;
397         }
398 }
399
400 /**
401  *      eraser          -       handle erase function
402  *      @c: character input
403  *      @tty: terminal device
404  *
405  *      Perform erase and neccessary output when an erase character is
406  *      present in the stream from the driver layer. Handles the complexities
407  *      of UTF-8 multibyte symbols.
408  */
409  
410 static void eraser(unsigned char c, struct tty_struct *tty)
411 {
412         enum { ERASE, WERASE, KILL } kill_type;
413         int head, seen_alnums, cnt;
414         unsigned long flags;
415
416         if (tty->read_head == tty->canon_head) {
417                 /* opost('\a', tty); */         /* what do you think? */
418                 return;
419         }
420         if (c == ERASE_CHAR(tty))
421                 kill_type = ERASE;
422         else if (c == WERASE_CHAR(tty))
423                 kill_type = WERASE;
424         else {
425                 if (!L_ECHO(tty)) {
426                         spin_lock_irqsave(&tty->read_lock, flags);
427                         tty->read_cnt -= ((tty->read_head - tty->canon_head) &
428                                           (N_TTY_BUF_SIZE - 1));
429                         tty->read_head = tty->canon_head;
430                         spin_unlock_irqrestore(&tty->read_lock, flags);
431                         return;
432                 }
433                 if (!L_ECHOK(tty) || !L_ECHOKE(tty) || !L_ECHOE(tty)) {
434                         spin_lock_irqsave(&tty->read_lock, flags);
435                         tty->read_cnt -= ((tty->read_head - tty->canon_head) &
436                                           (N_TTY_BUF_SIZE - 1));
437                         tty->read_head = tty->canon_head;
438                         spin_unlock_irqrestore(&tty->read_lock, flags);
439                         finish_erasing(tty);
440                         echo_char(KILL_CHAR(tty), tty);
441                         /* Add a newline if ECHOK is on and ECHOKE is off. */
442                         if (L_ECHOK(tty))
443                                 opost('\n', tty);
444                         return;
445                 }
446                 kill_type = KILL;
447         }
448
449         seen_alnums = 0;
450         while (tty->read_head != tty->canon_head) {
451                 head = tty->read_head;
452
453                 /* erase a single possibly multibyte character */
454                 do {
455                         head = (head - 1) & (N_TTY_BUF_SIZE-1);
456                         c = tty->read_buf[head];
457                 } while (is_continuation(c, tty) && head != tty->canon_head);
458
459                 /* do not partially erase */
460                 if (is_continuation(c, tty))
461                         break;
462
463                 if (kill_type == WERASE) {
464                         /* Equivalent to BSD's ALTWERASE. */
465                         if (isalnum(c) || c == '_')
466                                 seen_alnums++;
467                         else if (seen_alnums)
468                                 break;
469                 }
470                 cnt = (tty->read_head - head) & (N_TTY_BUF_SIZE-1);
471                 spin_lock_irqsave(&tty->read_lock, flags);
472                 tty->read_head = head;
473                 tty->read_cnt -= cnt;
474                 spin_unlock_irqrestore(&tty->read_lock, flags);
475                 if (L_ECHO(tty)) {
476                         if (L_ECHOPRT(tty)) {
477                                 if (!tty->erasing) {
478                                         put_char('\\', tty);
479                                         tty->column++;
480                                         tty->erasing = 1;
481                                 }
482                                 /* if cnt > 1, output a multi-byte character */
483                                 echo_char(c, tty);
484                                 while (--cnt > 0) {
485                                         head = (head+1) & (N_TTY_BUF_SIZE-1);
486                                         put_char(tty->read_buf[head], tty);
487                                 }
488                         } else if (kill_type == ERASE && !L_ECHOE(tty)) {
489                                 echo_char(ERASE_CHAR(tty), tty);
490                         } else if (c == '\t') {
491                                 unsigned int col = tty->canon_column;
492                                 unsigned long tail = tty->canon_head;
493
494                                 /* Find the column of the last char. */
495                                 while (tail != tty->read_head) {
496                                         c = tty->read_buf[tail];
497                                         if (c == '\t')
498                                                 col = (col | 7) + 1;
499                                         else if (iscntrl(c)) {
500                                                 if (L_ECHOCTL(tty))
501                                                         col += 2;
502                                         } else if (!is_continuation(c, tty))
503                                                 col++;
504                                         tail = (tail+1) & (N_TTY_BUF_SIZE-1);
505                                 }
506
507                                 /* should never happen */
508                                 if (tty->column > 0x80000000)
509                                         tty->column = 0; 
510
511                                 /* Now backup to that column. */
512                                 while (tty->column > col) {
513                                         /* Can't use opost here. */
514                                         put_char('\b', tty);
515                                         if (tty->column > 0)
516                                                 tty->column--;
517                                 }
518                         } else {
519                                 if (iscntrl(c) && L_ECHOCTL(tty)) {
520                                         put_char('\b', tty);
521                                         put_char(' ', tty);
522                                         put_char('\b', tty);
523                                         if (tty->column > 0)
524                                                 tty->column--;
525                                 }
526                                 if (!iscntrl(c) || L_ECHOCTL(tty)) {
527                                         put_char('\b', tty);
528                                         put_char(' ', tty);
529                                         put_char('\b', tty);
530                                         if (tty->column > 0)
531                                                 tty->column--;
532                                 }
533                         }
534                 }
535                 if (kill_type == ERASE)
536                         break;
537         }
538         if (tty->read_head == tty->canon_head)
539                 finish_erasing(tty);
540 }
541
542 /**
543  *      isig            -       handle the ISIG optio
544  *      @sig: signal
545  *      @tty: terminal
546  *      @flush: force flush
547  *
548  *      Called when a signal is being sent due to terminal input. This
549  *      may caus terminal flushing to take place according to the termios
550  *      settings and character used. Called from the driver receive_buf
551  *      path so serialized.
552  */
553  
554 static inline void isig(int sig, struct tty_struct *tty, int flush)
555 {
556         if (tty->pgrp > 0)
557                 kill_pg(tty->pgrp, sig, 1);
558         if (flush || !L_NOFLSH(tty)) {
559                 n_tty_flush_buffer(tty);
560                 if (tty->driver->flush_buffer)
561                         tty->driver->flush_buffer(tty);
562         }
563 }
564
565 /**
566  *      n_tty_receive_break     -       handle break
567  *      @tty: terminal
568  *
569  *      An RS232 break event has been hit in the incoming bitstream. This
570  *      can cause a variety of events depending upon the termios settings.
571  *
572  *      Called from the receive_buf path so single threaded.
573  */
574  
575 static inline void n_tty_receive_break(struct tty_struct *tty)
576 {
577         if (I_IGNBRK(tty))
578                 return;
579         if (I_BRKINT(tty)) {
580                 isig(SIGINT, tty, 1);
581                 return;
582         }
583         if (I_PARMRK(tty)) {
584                 put_tty_queue('\377', tty);
585                 put_tty_queue('\0', tty);
586         }
587         put_tty_queue('\0', tty);
588         wake_up_interruptible(&tty->read_wait);
589 }
590
591 /**
592  *      n_tty_receive_overrun   -       handle overrun reporting
593  *      @tty: terminal
594  *
595  *      Data arrived faster than we could process it. While the tty
596  *      driver has flagged this the bits that were missed are gone
597  *      forever.
598  *
599  *      Called from the receive_buf path so single threaded. Does not
600  *      need locking as num_overrun and overrun_time are function
601  *      private.
602  */
603  
604 static inline void n_tty_receive_overrun(struct tty_struct *tty)
605 {
606         char buf[64];
607
608         tty->num_overrun++;
609         if (time_before(tty->overrun_time, jiffies - HZ) ||
610                         time_after(tty->overrun_time, jiffies)) {
611                 printk(KERN_WARNING "%s: %d input overrun(s)\n",
612                         tty_name(tty, buf),
613                         tty->num_overrun);
614                 tty->overrun_time = jiffies;
615                 tty->num_overrun = 0;
616         }
617 }
618
619 /**
620  *      n_tty_receive_parity_error      -       error notifier
621  *      @tty: terminal device
622  *      @c: character
623  *
624  *      Process a parity error and queue the right data to indicate
625  *      the error case if neccessary. Locking as per n_tty_receive_buf.
626  */
627 static inline void n_tty_receive_parity_error(struct tty_struct *tty,
628                                               unsigned char c)
629 {
630         if (I_IGNPAR(tty)) {
631                 return;
632         }
633         if (I_PARMRK(tty)) {
634                 put_tty_queue('\377', tty);
635                 put_tty_queue('\0', tty);
636                 put_tty_queue(c, tty);
637         } else  if (I_INPCK(tty))
638                 put_tty_queue('\0', tty);
639         else
640                 put_tty_queue(c, tty);
641         wake_up_interruptible(&tty->read_wait);
642 }
643
644 /**
645  *      n_tty_receive_char      -       perform processing
646  *      @tty: terminal device
647  *      @c: character
648  *
649  *      Process an individual character of input received from the driver.
650  *      This is serialized with respect to itself by the rules for the 
651  *      driver above.
652  */
653
654 static inline void n_tty_receive_char(struct tty_struct *tty, unsigned char c)
655 {
656         unsigned long flags;
657
658         if (tty->raw) {
659                 put_tty_queue(c, tty);
660                 return;
661         }
662         
663         if (tty->stopped && !tty->flow_stopped &&
664             I_IXON(tty) && I_IXANY(tty)) {
665                 start_tty(tty);
666                 return;
667         }
668         
669         if (I_ISTRIP(tty))
670                 c &= 0x7f;
671         if (I_IUCLC(tty) && L_IEXTEN(tty))
672                 c=tolower(c);
673
674         if (tty->closing) {
675                 if (I_IXON(tty)) {
676                         if (c == START_CHAR(tty))
677                                 start_tty(tty);
678                         else if (c == STOP_CHAR(tty))
679                                 stop_tty(tty);
680                 }
681                 return;
682         }
683
684         /*
685          * If the previous character was LNEXT, or we know that this
686          * character is not one of the characters that we'll have to
687          * handle specially, do shortcut processing to speed things
688          * up.
689          */
690         if (!test_bit(c, tty->process_char_map) || tty->lnext) {
691                 finish_erasing(tty);
692                 tty->lnext = 0;
693                 if (L_ECHO(tty)) {
694                         if (tty->read_cnt >= N_TTY_BUF_SIZE-1) {
695                                 put_char('\a', tty); /* beep if no space */
696                                 return;
697                         }
698                         /* Record the column of first canon char. */
699                         if (tty->canon_head == tty->read_head)
700                                 tty->canon_column = tty->column;
701                         echo_char(c, tty);
702                 }
703                 if (I_PARMRK(tty) && c == (unsigned char) '\377')
704                         put_tty_queue(c, tty);
705                 put_tty_queue(c, tty);
706                 return;
707         }
708                 
709         if (c == '\r') {
710                 if (I_IGNCR(tty))
711                         return;
712                 if (I_ICRNL(tty))
713                         c = '\n';
714         } else if (c == '\n' && I_INLCR(tty))
715                 c = '\r';
716         if (I_IXON(tty)) {
717                 if (c == START_CHAR(tty)) {
718                         start_tty(tty);
719                         return;
720                 }
721                 if (c == STOP_CHAR(tty)) {
722                         stop_tty(tty);
723                         return;
724                 }
725         }
726         if (L_ISIG(tty)) {
727                 int signal;
728                 signal = SIGINT;
729                 if (c == INTR_CHAR(tty))
730                         goto send_signal;
731                 signal = SIGQUIT;
732                 if (c == QUIT_CHAR(tty))
733                         goto send_signal;
734                 signal = SIGTSTP;
735                 if (c == SUSP_CHAR(tty)) {
736 send_signal:
737                         isig(signal, tty, 0);
738                         return;
739                 }
740         }
741         if (tty->icanon) {
742                 if (c == ERASE_CHAR(tty) || c == KILL_CHAR(tty) ||
743                     (c == WERASE_CHAR(tty) && L_IEXTEN(tty))) {
744                         eraser(c, tty);
745                         return;
746                 }
747                 if (c == LNEXT_CHAR(tty) && L_IEXTEN(tty)) {
748                         tty->lnext = 1;
749                         if (L_ECHO(tty)) {
750                                 finish_erasing(tty);
751                                 if (L_ECHOCTL(tty)) {
752                                         put_char('^', tty);
753                                         put_char('\b', tty);
754                                 }
755                         }
756                         return;
757                 }
758                 if (c == REPRINT_CHAR(tty) && L_ECHO(tty) &&
759                     L_IEXTEN(tty)) {
760                         unsigned long tail = tty->canon_head;
761
762                         finish_erasing(tty);
763                         echo_char(c, tty);
764                         opost('\n', tty);
765                         while (tail != tty->read_head) {
766                                 echo_char(tty->read_buf[tail], tty);
767                                 tail = (tail+1) & (N_TTY_BUF_SIZE-1);
768                         }
769                         return;
770                 }
771                 if (c == '\n') {
772                         if (L_ECHO(tty) || L_ECHONL(tty)) {
773                                 if (tty->read_cnt >= N_TTY_BUF_SIZE-1) {
774                                         put_char('\a', tty);
775                                         return;
776                                 }
777                                 opost('\n', tty);
778                         }
779                         goto handle_newline;
780                 }
781                 if (c == EOF_CHAR(tty)) {
782                         if (tty->canon_head != tty->read_head)
783                                 set_bit(TTY_PUSH, &tty->flags);
784                         c = __DISABLED_CHAR;
785                         goto handle_newline;
786                 }
787                 if ((c == EOL_CHAR(tty)) ||
788                     (c == EOL2_CHAR(tty) && L_IEXTEN(tty))) {
789                         /*
790                          * XXX are EOL_CHAR and EOL2_CHAR echoed?!?
791                          */
792                         if (L_ECHO(tty)) {
793                                 if (tty->read_cnt >= N_TTY_BUF_SIZE-1) {
794                                         put_char('\a', tty);
795                                         return;
796                                 }
797                                 /* Record the column of first canon char. */
798                                 if (tty->canon_head == tty->read_head)
799                                         tty->canon_column = tty->column;
800                                 echo_char(c, tty);
801                         }
802                         /*
803                          * XXX does PARMRK doubling happen for
804                          * EOL_CHAR and EOL2_CHAR?
805                          */
806                         if (I_PARMRK(tty) && c == (unsigned char) '\377')
807                                 put_tty_queue(c, tty);
808
809                 handle_newline:
810                         spin_lock_irqsave(&tty->read_lock, flags);
811                         set_bit(tty->read_head, tty->read_flags);
812                         put_tty_queue_nolock(c, tty);
813                         tty->canon_head = tty->read_head;
814                         tty->canon_data++;
815                         spin_unlock_irqrestore(&tty->read_lock, flags);
816                         kill_fasync(&tty->fasync, SIGIO, POLL_IN);
817                         if (waitqueue_active(&tty->read_wait))
818                                 wake_up_interruptible(&tty->read_wait);
819                         return;
820                 }
821         }
822         
823         finish_erasing(tty);
824         if (L_ECHO(tty)) {
825                 if (tty->read_cnt >= N_TTY_BUF_SIZE-1) {
826                         put_char('\a', tty); /* beep if no space */
827                         return;
828                 }
829                 if (c == '\n')
830                         opost('\n', tty);
831                 else {
832                         /* Record the column of first canon char. */
833                         if (tty->canon_head == tty->read_head)
834                                 tty->canon_column = tty->column;
835                         echo_char(c, tty);
836                 }
837         }
838
839         if (I_PARMRK(tty) && c == (unsigned char) '\377')
840                 put_tty_queue(c, tty);
841
842         put_tty_queue(c, tty);
843 }       
844
845 /**
846  *      n_tty_receive_room      -       receive space
847  *      @tty: terminal
848  *
849  *      Called by the driver to find out how much data it is
850  *      permitted to feed to the line discipline without any being lost
851  *      and thus to manage flow control. Not serialized. Answers for the
852  *      "instant".
853  */
854  
855 static int n_tty_receive_room(struct tty_struct *tty)
856 {
857         int     left = N_TTY_BUF_SIZE - tty->read_cnt - 1;
858
859         /*
860          * If we are doing input canonicalization, and there are no
861          * pending newlines, let characters through without limit, so
862          * that erase characters will be handled.  Other excess
863          * characters will be beeped.
864          */
865         if (tty->icanon && !tty->canon_data)
866                 return N_TTY_BUF_SIZE;
867
868         if (left > 0)
869                 return left;
870         return 0;
871 }
872
873 /**
874  *      n_tty_write_wakeup      -       asynchronous I/O notifier
875  *      @tty: tty device
876  *
877  *      Required for the ptys, serial driver etc. since processes
878  *      that attach themselves to the master and rely on ASYNC
879  *      IO must be woken up
880  */
881
882 static void n_tty_write_wakeup(struct tty_struct *tty)
883 {
884         if (tty->fasync)
885         {
886                 set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
887                 kill_fasync(&tty->fasync, SIGIO, POLL_OUT);
888         }
889         return;
890 }
891
892 /**
893  *      n_tty_receive_buf       -       data receive
894  *      @tty: terminal device
895  *      @cp: buffer
896  *      @fp: flag buffer
897  *      @count: characters
898  *
899  *      Called by the terminal driver when a block of characters has
900  *      been received. This function must be called from soft contexts
901  *      not from interrupt context. The driver is responsible for making
902  *      calls one at a time and in order (or using flush_to_ldisc)
903  */
904  
905 static void n_tty_receive_buf(struct tty_struct *tty, const unsigned char *cp,
906                               char *fp, int count)
907 {
908         const unsigned char *p;
909         char *f, flags = TTY_NORMAL;
910         int     i;
911         char    buf[64];
912         unsigned long cpuflags;
913
914         if (!tty->read_buf)
915                 return;
916
917         if (tty->real_raw) {
918                 spin_lock_irqsave(&tty->read_lock, cpuflags);
919                 i = min(N_TTY_BUF_SIZE - tty->read_cnt,
920                         N_TTY_BUF_SIZE - tty->read_head);
921                 i = min(count, i);
922                 memcpy(tty->read_buf + tty->read_head, cp, i);
923                 tty->read_head = (tty->read_head + i) & (N_TTY_BUF_SIZE-1);
924                 tty->read_cnt += i;
925                 cp += i;
926                 count -= i;
927
928                 i = min(N_TTY_BUF_SIZE - tty->read_cnt,
929                         N_TTY_BUF_SIZE - tty->read_head);
930                 i = min(count, i);
931                 memcpy(tty->read_buf + tty->read_head, cp, i);
932                 tty->read_head = (tty->read_head + i) & (N_TTY_BUF_SIZE-1);
933                 tty->read_cnt += i;
934                 spin_unlock_irqrestore(&tty->read_lock, cpuflags);
935         } else {
936                 for (i=count, p = cp, f = fp; i; i--, p++) {
937                         if (f)
938                                 flags = *f++;
939                         switch (flags) {
940                         case TTY_NORMAL:
941                                 n_tty_receive_char(tty, *p);
942                                 break;
943                         case TTY_BREAK:
944                                 n_tty_receive_break(tty);
945                                 break;
946                         case TTY_PARITY:
947                         case TTY_FRAME:
948                                 n_tty_receive_parity_error(tty, *p);
949                                 break;
950                         case TTY_OVERRUN:
951                                 n_tty_receive_overrun(tty);
952                                 break;
953                         default:
954                                 printk("%s: unknown flag %d\n",
955                                        tty_name(tty, buf), flags);
956                                 break;
957                         }
958                 }
959                 if (tty->driver->flush_chars)
960                         tty->driver->flush_chars(tty);
961         }
962
963         if (!tty->icanon && (tty->read_cnt >= tty->minimum_to_wake)) {
964                 kill_fasync(&tty->fasync, SIGIO, POLL_IN);
965                 if (waitqueue_active(&tty->read_wait))
966                         wake_up_interruptible(&tty->read_wait);
967         }
968
969         /*
970          * Check the remaining room for the input canonicalization
971          * mode.  We don't want to throttle the driver if we're in
972          * canonical mode and don't have a newline yet!
973          */
974         if (n_tty_receive_room(tty) < TTY_THRESHOLD_THROTTLE) {
975                 /* check TTY_THROTTLED first so it indicates our state */
976                 if (!test_and_set_bit(TTY_THROTTLED, &tty->flags) &&
977                     tty->driver->throttle)
978                         tty->driver->throttle(tty);
979         }
980 }
981
982 int is_ignored(int sig)
983 {
984         return (sigismember(&current->blocked, sig) ||
985                 current->sighand->action[sig-1].sa.sa_handler == SIG_IGN);
986 }
987
988 /**
989  *      n_tty_set_termios       -       termios data changed
990  *      @tty: terminal
991  *      @old: previous data
992  *
993  *      Called by the tty layer when the user changes termios flags so
994  *      that the line discipline can plan ahead. This function cannot sleep
995  *      and is protected from re-entry by the tty layer. The user is 
996  *      guaranteed that this function will not be re-entered or in progress
997  *      when the ldisc is closed.
998  */
999  
1000 static void n_tty_set_termios(struct tty_struct *tty, struct termios * old)
1001 {
1002         if (!tty)
1003                 return;
1004         
1005         tty->icanon = (L_ICANON(tty) != 0);
1006         if (test_bit(TTY_HW_COOK_IN, &tty->flags)) {
1007                 tty->raw = 1;
1008                 tty->real_raw = 1;
1009                 return;
1010         }
1011         if (I_ISTRIP(tty) || I_IUCLC(tty) || I_IGNCR(tty) ||
1012             I_ICRNL(tty) || I_INLCR(tty) || L_ICANON(tty) ||
1013             I_IXON(tty) || L_ISIG(tty) || L_ECHO(tty) ||
1014             I_PARMRK(tty)) {
1015                 memset(tty->process_char_map, 0, 256/8);
1016
1017                 if (I_IGNCR(tty) || I_ICRNL(tty))
1018                         set_bit('\r', tty->process_char_map);
1019                 if (I_INLCR(tty))
1020                         set_bit('\n', tty->process_char_map);
1021
1022                 if (L_ICANON(tty)) {
1023                         set_bit(ERASE_CHAR(tty), tty->process_char_map);
1024                         set_bit(KILL_CHAR(tty), tty->process_char_map);
1025                         set_bit(EOF_CHAR(tty), tty->process_char_map);
1026                         set_bit('\n', tty->process_char_map);
1027                         set_bit(EOL_CHAR(tty), tty->process_char_map);
1028                         if (L_IEXTEN(tty)) {
1029                                 set_bit(WERASE_CHAR(tty),
1030                                         tty->process_char_map);
1031                                 set_bit(LNEXT_CHAR(tty),
1032                                         tty->process_char_map);
1033                                 set_bit(EOL2_CHAR(tty),
1034                                         tty->process_char_map);
1035                                 if (L_ECHO(tty))
1036                                         set_bit(REPRINT_CHAR(tty),
1037                                                 tty->process_char_map);
1038                         }
1039                 }
1040                 if (I_IXON(tty)) {
1041                         set_bit(START_CHAR(tty), tty->process_char_map);
1042                         set_bit(STOP_CHAR(tty), tty->process_char_map);
1043                 }
1044                 if (L_ISIG(tty)) {
1045                         set_bit(INTR_CHAR(tty), tty->process_char_map);
1046                         set_bit(QUIT_CHAR(tty), tty->process_char_map);
1047                         set_bit(SUSP_CHAR(tty), tty->process_char_map);
1048                 }
1049                 clear_bit(__DISABLED_CHAR, tty->process_char_map);
1050                 tty->raw = 0;
1051                 tty->real_raw = 0;
1052         } else {
1053                 tty->raw = 1;
1054                 if ((I_IGNBRK(tty) || (!I_BRKINT(tty) && !I_PARMRK(tty))) &&
1055                     (I_IGNPAR(tty) || !I_INPCK(tty)) &&
1056                     (tty->driver->flags & TTY_DRIVER_REAL_RAW))
1057                         tty->real_raw = 1;
1058                 else
1059                         tty->real_raw = 0;
1060         }
1061 }
1062
1063 /**
1064  *      n_tty_close             -       close the ldisc for this tty
1065  *      @tty: device
1066  *
1067  *      Called from the terminal layer when this line discipline is 
1068  *      being shut down, either because of a close or becsuse of a 
1069  *      discipline change. The function will not be called while other
1070  *      ldisc methods are in progress.
1071  */
1072  
1073 static void n_tty_close(struct tty_struct *tty)
1074 {
1075         n_tty_flush_buffer(tty);
1076         if (tty->read_buf) {
1077                 free_buf(tty->read_buf);
1078                 tty->read_buf = NULL;
1079         }
1080 }
1081
1082 /**
1083  *      n_tty_open              -       open an ldisc
1084  *      @tty: terminal to open
1085  *
1086  *      Called when this line discipline is being attached to the 
1087  *      terminal device. Can sleep. Called serialized so that no
1088  *      other events will occur in parallel. No further open will occur
1089  *      until a close.
1090  */
1091
1092 static int n_tty_open(struct tty_struct *tty)
1093 {
1094         if (!tty)
1095                 return -EINVAL;
1096
1097         /* This one is ugly. Currently a malloc failure here can panic */
1098         if (!tty->read_buf) {
1099                 tty->read_buf = alloc_buf();
1100                 if (!tty->read_buf)
1101                         return -ENOMEM;
1102         }
1103         memset(tty->read_buf, 0, N_TTY_BUF_SIZE);
1104         reset_buffer_flags(tty);
1105         tty->column = 0;
1106         n_tty_set_termios(tty, NULL);
1107         tty->minimum_to_wake = 1;
1108         tty->closing = 0;
1109         return 0;
1110 }
1111
1112 static inline int input_available_p(struct tty_struct *tty, int amt)
1113 {
1114         if (tty->icanon) {
1115                 if (tty->canon_data)
1116                         return 1;
1117         } else if (tty->read_cnt >= (amt ? amt : 1))
1118                 return 1;
1119
1120         return 0;
1121 }
1122
1123 /**
1124  *      copy_from_read_buf      -       copy read data directly
1125  *      @tty: terminal device
1126  *      @b: user data
1127  *      @nr: size of data
1128  *
1129  *      Helper function to speed up read_chan.  It is only called when
1130  *      ICANON is off; it copies characters straight from the tty queue to
1131  *      user space directly.  It can be profitably called twice; once to
1132  *      drain the space from the tail pointer to the (physical) end of the
1133  *      buffer, and once to drain the space from the (physical) beginning of
1134  *      the buffer to head pointer.
1135  *
1136  *      Called under the tty->atomic_read sem and with TTY_DONT_FLIP set
1137  *
1138  */
1139  
1140 static inline int copy_from_read_buf(struct tty_struct *tty,
1141                                       unsigned char __user **b,
1142                                       size_t *nr)
1143
1144 {
1145         int retval;
1146         size_t n;
1147         unsigned long flags;
1148
1149         retval = 0;
1150         spin_lock_irqsave(&tty->read_lock, flags);
1151         n = min(tty->read_cnt, N_TTY_BUF_SIZE - tty->read_tail);
1152         n = min(*nr, n);
1153         spin_unlock_irqrestore(&tty->read_lock, flags);
1154         if (n) {
1155                 mb();
1156                 retval = copy_to_user(*b, &tty->read_buf[tty->read_tail], n);
1157                 n -= retval;
1158                 spin_lock_irqsave(&tty->read_lock, flags);
1159                 tty->read_tail = (tty->read_tail + n) & (N_TTY_BUF_SIZE-1);
1160                 tty->read_cnt -= n;
1161                 spin_unlock_irqrestore(&tty->read_lock, flags);
1162                 *b += n;
1163                 *nr -= n;
1164         }
1165         return retval;
1166 }
1167
1168 extern ssize_t redirected_tty_write(struct file *,const char *,size_t,loff_t *);
1169
1170 /**
1171  *      job_control             -       check job control
1172  *      @tty: tty
1173  *      @file: file handle
1174  *
1175  *      Perform job control management checks on this file/tty descriptor
1176  *      and if appropriate send any needed signals and return a negative 
1177  *      error code if action should be taken.
1178  */
1179  
1180 static int job_control(struct tty_struct *tty, struct file *file)
1181 {
1182         /* Job control check -- must be done at start and after
1183            every sleep (POSIX.1 7.1.1.4). */
1184         /* NOTE: not yet done after every sleep pending a thorough
1185            check of the logic of this change. -- jlc */
1186         /* don't stop on /dev/console */
1187         if (file->f_op->write != redirected_tty_write &&
1188             current->signal->tty == tty) {
1189                 if (tty->pgrp <= 0)
1190                         printk("read_chan: tty->pgrp <= 0!\n");
1191                 else if (process_group(current) != tty->pgrp) {
1192                         if (is_ignored(SIGTTIN) ||
1193                             is_orphaned_pgrp(process_group(current)))
1194                                 return -EIO;
1195                         kill_pg(process_group(current), SIGTTIN, 1);
1196                         return -ERESTARTSYS;
1197                 }
1198         }
1199         return 0;
1200 }
1201  
1202
1203 /**
1204  *      read_chan               -       read function for tty
1205  *      @tty: tty device
1206  *      @file: file object
1207  *      @buf: userspace buffer pointer
1208  *      @nr: size of I/O
1209  *
1210  *      Perform reads for the line discipline. We are guaranteed that the
1211  *      line discipline will not be closed under us but we may get multiple
1212  *      parallel readers and must handle this ourselves. We may also get
1213  *      a hangup. Always called in user context, may sleep.
1214  *
1215  *      This code must be sure never to sleep through a hangup.
1216  */
1217  
1218 static ssize_t read_chan(struct tty_struct *tty, struct file *file,
1219                          unsigned char __user *buf, size_t nr)
1220 {
1221         unsigned char __user *b = buf;
1222         DECLARE_WAITQUEUE(wait, current);
1223         int c;
1224         int minimum, time;
1225         ssize_t retval = 0;
1226         ssize_t size;
1227         long timeout;
1228         unsigned long flags;
1229
1230 do_it_again:
1231
1232         if (!tty->read_buf) {
1233                 printk("n_tty_read_chan: called with read_buf == NULL?!?\n");
1234                 return -EIO;
1235         }
1236
1237         c = job_control(tty, file);
1238         if(c < 0)
1239                 return c;
1240         
1241         minimum = time = 0;
1242         timeout = MAX_SCHEDULE_TIMEOUT;
1243         if (!tty->icanon) {
1244                 time = (HZ / 10) * TIME_CHAR(tty);
1245                 minimum = MIN_CHAR(tty);
1246                 if (minimum) {
1247                         if (time)
1248                                 tty->minimum_to_wake = 1;
1249                         else if (!waitqueue_active(&tty->read_wait) ||
1250                                  (tty->minimum_to_wake > minimum))
1251                                 tty->minimum_to_wake = minimum;
1252                 } else {
1253                         timeout = 0;
1254                         if (time) {
1255                                 timeout = time;
1256                                 time = 0;
1257                         }
1258                         tty->minimum_to_wake = minimum = 1;
1259                 }
1260         }
1261
1262         /*
1263          *      Internal serialization of reads.
1264          */
1265         if (file->f_flags & O_NONBLOCK) {
1266                 if (down_trylock(&tty->atomic_read))
1267                         return -EAGAIN;
1268         }
1269         else {
1270                 if (down_interruptible(&tty->atomic_read))
1271                         return -ERESTARTSYS;
1272         }
1273
1274         add_wait_queue(&tty->read_wait, &wait);
1275         set_bit(TTY_DONT_FLIP, &tty->flags);
1276         while (nr) {
1277                 /* First test for status change. */
1278                 if (tty->packet && tty->link->ctrl_status) {
1279                         unsigned char cs;
1280                         if (b != buf)
1281                                 break;
1282                         cs = tty->link->ctrl_status;
1283                         tty->link->ctrl_status = 0;
1284                         if (put_user(cs, b++)) {
1285                                 retval = -EFAULT;
1286                                 b--;
1287                                 break;
1288                         }
1289                         nr--;
1290                         break;
1291                 }
1292                 /* This statement must be first before checking for input
1293                    so that any interrupt will set the state back to
1294                    TASK_RUNNING. */
1295                 set_current_state(TASK_INTERRUPTIBLE);
1296                 
1297                 if (((minimum - (b - buf)) < tty->minimum_to_wake) &&
1298                     ((minimum - (b - buf)) >= 1))
1299                         tty->minimum_to_wake = (minimum - (b - buf));
1300                 
1301                 if (!input_available_p(tty, 0)) {
1302                         if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
1303                                 retval = -EIO;
1304                                 break;
1305                         }
1306                         if (tty_hung_up_p(file))
1307                                 break;
1308                         if (!timeout)
1309                                 break;
1310                         if (file->f_flags & O_NONBLOCK) {
1311                                 retval = -EAGAIN;
1312                                 break;
1313                         }
1314                         if (signal_pending(current)) {
1315                                 retval = -ERESTARTSYS;
1316                                 break;
1317                         }
1318                         clear_bit(TTY_DONT_FLIP, &tty->flags);
1319                         timeout = schedule_timeout(timeout);
1320                         set_bit(TTY_DONT_FLIP, &tty->flags);
1321                         continue;
1322                 }
1323                 __set_current_state(TASK_RUNNING);
1324
1325                 /* Deal with packet mode. */
1326                 if (tty->packet && b == buf) {
1327                         if (put_user(TIOCPKT_DATA, b++)) {
1328                                 retval = -EFAULT;
1329                                 b--;
1330                                 break;
1331                         }
1332                         nr--;
1333                 }
1334
1335                 if (tty->icanon) {
1336                         /* N.B. avoid overrun if nr == 0 */
1337                         while (nr && tty->read_cnt) {
1338                                 int eol;
1339
1340                                 eol = test_and_clear_bit(tty->read_tail,
1341                                                 tty->read_flags);
1342                                 c = tty->read_buf[tty->read_tail];
1343                                 spin_lock_irqsave(&tty->read_lock, flags);
1344                                 tty->read_tail = ((tty->read_tail+1) &
1345                                                   (N_TTY_BUF_SIZE-1));
1346                                 tty->read_cnt--;
1347                                 if (eol) {
1348                                         /* this test should be redundant:
1349                                          * we shouldn't be reading data if
1350                                          * canon_data is 0
1351                                          */
1352                                         if (--tty->canon_data < 0)
1353                                                 tty->canon_data = 0;
1354                                 }
1355                                 spin_unlock_irqrestore(&tty->read_lock, flags);
1356
1357                                 if (!eol || (c != __DISABLED_CHAR)) {
1358                                         if (put_user(c, b++)) {
1359                                                 retval = -EFAULT;
1360                                                 b--;
1361                                                 break;
1362                                         }
1363                                         nr--;
1364                                 }
1365                                 if (eol)
1366                                         break;
1367                         }
1368                         if (retval)
1369                                 break;
1370                 } else {
1371                         int uncopied;
1372                         uncopied = copy_from_read_buf(tty, &b, &nr);
1373                         uncopied += copy_from_read_buf(tty, &b, &nr);
1374                         if (uncopied) {
1375                                 retval = -EFAULT;
1376                                 break;
1377                         }
1378                 }
1379
1380                 /* If there is enough space in the read buffer now, let the
1381                  * low-level driver know. We use n_tty_chars_in_buffer() to
1382                  * check the buffer, as it now knows about canonical mode.
1383                  * Otherwise, if the driver is throttled and the line is
1384                  * longer than TTY_THRESHOLD_UNTHROTTLE in canonical mode,
1385                  * we won't get any more characters.
1386                  */
1387                 if (n_tty_chars_in_buffer(tty) <= TTY_THRESHOLD_UNTHROTTLE)
1388                         check_unthrottle(tty);
1389
1390                 if (b - buf >= minimum)
1391                         break;
1392                 if (time)
1393                         timeout = time;
1394         }
1395         clear_bit(TTY_DONT_FLIP, &tty->flags);
1396         up(&tty->atomic_read);
1397         remove_wait_queue(&tty->read_wait, &wait);
1398
1399         if (!waitqueue_active(&tty->read_wait))
1400                 tty->minimum_to_wake = minimum;
1401
1402         __set_current_state(TASK_RUNNING);
1403         size = b - buf;
1404         if (size) {
1405                 retval = size;
1406                 if (nr)
1407                         clear_bit(TTY_PUSH, &tty->flags);
1408         } else if (test_and_clear_bit(TTY_PUSH, &tty->flags))
1409                  goto do_it_again;
1410
1411         return retval;
1412 }
1413
1414 /**
1415  *      write_chan              -       write function for tty
1416  *      @tty: tty device
1417  *      @file: file object
1418  *      @buf: userspace buffer pointer
1419  *      @nr: size of I/O
1420  *
1421  *      Write function of the terminal device. This is serialized with
1422  *      respect to other write callers but not to termios changes, reads
1423  *      and other such events. We must be careful with N_TTY as the receive
1424  *      code will echo characters, thus calling driver write methods.
1425  *
1426  *      This code must be sure never to sleep through a hangup.
1427  */
1428  
1429 static ssize_t write_chan(struct tty_struct * tty, struct file * file,
1430                           const unsigned char * buf, size_t nr)
1431 {
1432         const unsigned char *b = buf;
1433         DECLARE_WAITQUEUE(wait, current);
1434         int c;
1435         ssize_t retval = 0;
1436
1437         /* Job control check -- must be done at start (POSIX.1 7.1.1.4). */
1438         if (L_TOSTOP(tty) && file->f_op->write != redirected_tty_write) {
1439                 retval = tty_check_change(tty);
1440                 if (retval)
1441                         return retval;
1442         }
1443
1444         add_wait_queue(&tty->write_wait, &wait);
1445         while (1) {
1446                 set_current_state(TASK_INTERRUPTIBLE);
1447                 if (signal_pending(current)) {
1448                         retval = -ERESTARTSYS;
1449                         break;
1450                 }
1451                 if (tty_hung_up_p(file) || (tty->link && !tty->link->count)) {
1452                         retval = -EIO;
1453                         break;
1454                 }
1455                 if (O_OPOST(tty) && !(test_bit(TTY_HW_COOK_OUT, &tty->flags))) {
1456                         while (nr > 0) {
1457                                 ssize_t num = opost_block(tty, b, nr);
1458                                 if (num < 0) {
1459                                         if (num == -EAGAIN)
1460                                                 break;
1461                                         retval = num;
1462                                         goto break_out;
1463                                 }
1464                                 b += num;
1465                                 nr -= num;
1466                                 if (nr == 0)
1467                                         break;
1468                                 c = *b;
1469                                 if (opost(c, tty) < 0)
1470                                         break;
1471                                 b++; nr--;
1472                         }
1473                         if (tty->driver->flush_chars)
1474                                 tty->driver->flush_chars(tty);
1475                 } else {
1476                         c = tty->driver->write(tty, b, nr);
1477                         if (c < 0) {
1478                                 retval = c;
1479                                 goto break_out;
1480                         }
1481                         b += c;
1482                         nr -= c;
1483                 }
1484                 if (!nr)
1485                         break;
1486                 if (file->f_flags & O_NONBLOCK) {
1487                         retval = -EAGAIN;
1488                         break;
1489                 }
1490                 schedule();
1491         }
1492 break_out:
1493         __set_current_state(TASK_RUNNING);
1494         remove_wait_queue(&tty->write_wait, &wait);
1495         return (b - buf) ? b - buf : retval;
1496 }
1497
1498 /**
1499  *      normal_poll             -       poll method for N_TTY
1500  *      @tty: terminal device
1501  *      @file: file accessing it
1502  *      @wait: poll table
1503  *
1504  *      Called when the line discipline is asked to poll() for data or
1505  *      for special events. This code is not serialized with respect to
1506  *      other events save open/close.
1507  *
1508  *      This code must be sure never to sleep through a hangup.
1509  *      Called without the kernel lock held - fine
1510  *
1511  *      FIXME: if someone changes the VMIN or discipline settings for the
1512  *      terminal while another process is in poll() the poll does not
1513  *      recompute the new limits. Possibly set_termios should issue
1514  *      a read wakeup to fix this bug.
1515  */
1516  
1517 static unsigned int normal_poll(struct tty_struct * tty, struct file * file, poll_table *wait)
1518 {
1519         unsigned int mask = 0;
1520
1521         poll_wait(file, &tty->read_wait, wait);
1522         poll_wait(file, &tty->write_wait, wait);
1523         if (input_available_p(tty, TIME_CHAR(tty) ? 0 : MIN_CHAR(tty)))
1524                 mask |= POLLIN | POLLRDNORM;
1525         if (tty->packet && tty->link->ctrl_status)
1526                 mask |= POLLPRI | POLLIN | POLLRDNORM;
1527         if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
1528                 mask |= POLLHUP;
1529         if (tty_hung_up_p(file))
1530                 mask |= POLLHUP;
1531         if (!(mask & (POLLHUP | POLLIN | POLLRDNORM))) {
1532                 if (MIN_CHAR(tty) && !TIME_CHAR(tty))
1533                         tty->minimum_to_wake = MIN_CHAR(tty);
1534                 else
1535                         tty->minimum_to_wake = 1;
1536         }
1537         if (tty->driver->chars_in_buffer(tty) < WAKEUP_CHARS &&
1538                         tty->driver->write_room(tty) > 0)
1539                 mask |= POLLOUT | POLLWRNORM;
1540         return mask;
1541 }
1542
1543 struct tty_ldisc tty_ldisc_N_TTY = {
1544         TTY_LDISC_MAGIC,        /* magic */
1545         "n_tty",                /* name */
1546         0,                      /* num */
1547         0,                      /* flags */
1548         n_tty_open,             /* open */
1549         n_tty_close,            /* close */
1550         n_tty_flush_buffer,     /* flush_buffer */
1551         n_tty_chars_in_buffer,  /* chars_in_buffer */
1552         read_chan,              /* read */
1553         write_chan,             /* write */
1554         n_tty_ioctl,            /* ioctl */
1555         n_tty_set_termios,      /* set_termios */
1556         normal_poll,            /* poll */
1557         NULL,                   /* hangup */
1558         n_tty_receive_buf,      /* receive_buf */
1559         n_tty_receive_room,     /* receive_room */
1560         n_tty_write_wakeup      /* write_wakeup */
1561 };
1562