summaryrefslogtreecommitdiffstats
path: root/drivers/char/n_tty.c
blob: b3d4ccc33a47e777d1a391ae9a85bde2f450051e (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
/*
 * n_tty.c --- implements the N_TTY line discipline.
 * 
 * This code used to be in tty_io.c, but things are getting hairy
 * enough that it made sense to split things off.  (The N_TTY
 * processing has changed so much that it's hardly recognizable,
 * anyway...)
 *
 * Note that the open routine for N_TTY is guaranteed never to return
 * an error.  This is because Linux will fall back to setting a line
 * to N_TTY if it can not switch to any other line discipline.  
 *
 * Written by Theodore Ts'o, Copyright 1994.
 * 
 * This file also contains code originally written by Linus Torvalds,
 * Copyright 1991, 1992, 1993, and by Julian Cowley, Copyright 1994.
 * 
 * This file may be redistributed under the terms of the GNU General Public
 * License.
 *
 * Reduced memory usage for older ARM systems  - Russell King.
 *
 * 2000/01/20   Fixed SMP locking on put_tty_queue using bits of 
 *		the patch by Andrew J. Kroll <ag784@freenet.buffalo.edu>
 *		who actually finally proved there really was a race.
 *
 * 2002/03/18   Implemented n_tty_wakeup to send SIGIO POLL_OUTs to
 *		waiting writing processes-Sapan Bhatia <sapan@corewars.org>.
 *		Also fixed a bug in BLOCKING mode where write_chan returns
 *		EAGAIN
 */

#include <linux/types.h>
#include <linux/major.h>
#include <linux/errno.h>
#include <linux/signal.h>
#include <linux/fcntl.h>
#include <linux/sched.h>
#include <linux/interrupt.h>
#include <linux/tty.h>
#include <linux/timer.h>
#include <linux/ctype.h>
#include <linux/mm.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/poll.h>
#include <linux/bitops.h>

#include <asm/uaccess.h>
#include <asm/system.h>

/* number of characters left in xmit buffer before select has we have room */
#define WAKEUP_CHARS 256

/*
 * This defines the low- and high-watermarks for throttling and
 * unthrottling the TTY driver.  These watermarks are used for
 * controlling the space in the read buffer.
 */
#define TTY_THRESHOLD_THROTTLE		128 /* now based on remaining room */
#define TTY_THRESHOLD_UNTHROTTLE 	128

static inline unsigned char *alloc_buf(void)
{
	gfp_t prio = in_interrupt() ? GFP_ATOMIC : GFP_KERNEL;

	if (PAGE_SIZE != N_TTY_BUF_SIZE)
		return kmalloc(N_TTY_BUF_SIZE, prio);
	else
		return (unsigned char *)__get_free_page(prio);
}

static inline void free_buf(unsigned char *buf)
{
	if (PAGE_SIZE != N_TTY_BUF_SIZE)
		kfree(buf);
	else
		free_page((unsigned long) buf);
}

/**
 *	n_tty_set__room	-	receive space
 *	@tty: terminal
 *
 *	Called by the driver to find out how much data it is
 *	permitted to feed to the line discipline without any being lost
 *	and thus to manage flow control. Not serialized. Answers for the
 *	"instant".
 */

static void n_tty_set_room(struct tty_struct *tty)
{
	int	left = N_TTY_BUF_SIZE - tty->read_cnt - 1;

	/*
	 * If we are doing input canonicalization, and there are no
	 * pending newlines, let characters through without limit, so
	 * that erase characters will be handled.  Other excess
	 * characters will be beeped.
	 */
	if (left <= 0)
		left = tty->icanon && !tty->canon_data;
	tty->receive_room = left;
}

static void put_tty_queue_nolock(unsigned char c, struct tty_struct *tty)
{
	if (tty->read_cnt < N_TTY_BUF_SIZE) {
		tty->read_buf[tty->read_head] = c;
		tty->read_head = (tty->read_head + 1) & (N_TTY_BUF_SIZE-1);
		tty->read_cnt++;
	}
}

static void put_tty_queue(unsigned char c, struct tty_struct *tty)
{
	unsigned long flags;
	/*
	 *	The problem of stomping on the buffers ends here.
	 *	Why didn't anyone see this one coming? --AJK
	*/
	spin_lock_irqsave(&tty->read_lock, flags);
	put_tty_queue_nolock(c, tty);
	spin_unlock_irqrestore(&tty->read_lock, flags);
}

/**
 *	check_unthrottle	-	allow new receive data
 *	@tty; tty device
 *
 *	Check whether to call the driver.unthrottle function.
 *	We test the TTY_THROTTLED bit first so that it always
 *	indicates the current state. The decision about whether
 *	it is worth allowing more input has been taken by the caller.
 *	Can sleep, may be called under the atomic_read_lock mutex but
 *	this is not guaranteed.
 */
 
static void check_unthrottle(struct tty_struct * tty)
{
	if (tty->count &&
	    test_and_clear_bit(TTY_THROTTLED, &tty->flags) && 
	    tty->driver->unthrottle)
		tty->driver->unthrottle(tty);
}

/**
 *	reset_buffer_flags	-	reset buffer state
 *	@tty: terminal to reset
 *
 *	Reset the read buffer counters, clear the flags, 
 *	and make sure the driver is unthrottled. Called
 *	from n_tty_open() and n_tty_flush_buffer().
 */
static void reset_buffer_flags(struct tty_struct *tty)
{
	unsigned long flags;

	spin_lock_irqsave(&tty->read_lock, flags);
	tty->read_head = tty->read_tail = tty->read_cnt = 0;
	spin_unlock_irqrestore(&tty->read_lock, flags);
	tty->canon_head = tty->canon_data = tty->erasing = 0;
	memset(&tty->read_flags, 0, sizeof tty->read_flags);
	n_tty_set_room(tty);
	check_unthrottle(tty);
}

/**
 *	n_tty_flush_buffer	-	clean input queue
 *	@tty:	terminal device
 *
 *	Flush the input buffer. Called when the line discipline is
 *	being closed, when the tty layer wants the buffer flushed (eg
 *	at hangup) or when the N_TTY line discipline internally has to
 *	clean the pending queue (for example some signals).
 *
 *	FIXME: tty->ctrl_status is not spinlocked and relies on
 *	lock_kernel() still.
 */
 
static void n_tty_flush_buffer(struct tty_struct * tty)
{
	/* clear everything and unthrottle the driver */
	reset_buffer_flags(tty);
	
	if (!tty->link)
		return;

	if (tty->link->packet) {
		tty->ctrl_status |= TIOCPKT_FLUSHREAD;
		wake_up_interruptible(&tty->link->read_wait);
	}
}

/**
 *	n_tty_chars_in_buffer	-	report available bytes
 *	@tty: tty device
 *
 *	Report the number of characters buffered to be delivered to user
 *	at this instant in time. 
 */
 
static ssize_t n_tty_chars_in_buffer(struct tty_struct *tty)
{
	unsigned long flags;
	ssize_t n = 0;

	spin_lock_irqsave(&tty->read_lock, flags);
	if (!tty->icanon) {
		n = tty->read_cnt;
	} else if (tty->canon_data) {
		n = (tty->canon_head > tty->read_tail) ?
			tty->canon_head - tty->read_tail :
			tty->canon_head + (N_TTY_BUF_SIZE - tty->read_tail);
	}
	spin_unlock_irqrestore(&tty->read_lock, flags);
	return n;
}

/**
 *	is_utf8_continuation	-	utf8 multibyte check
 *	@c: byte to check
 *
 *	Returns true if the utf8 character 'c' is a multibyte continuation
 *	character. We use this to correctly compute the on screen size
 *	of the character when printing
 */
 
static inline int is_utf8_continuation(unsigned char c)
{
	return (c & 0xc0) == 0x80;
}

/**
 *	is_continuation		-	multibyte check
 *	@c: byte to check
 *
 *	Returns true if the utf8 character 'c' is a multibyte continuation
 *	character and the terminal is in unicode mode.
 */
 
static inline int is_continuation(unsigned char c, struct tty_struct *tty)
{
	return I_IUTF8(tty) && is_utf8_continuation(c);
}

/**
 *	opost			-	output post processor
 *	@c: character (or partial unicode symbol)
 *	@tty: terminal device
 *
 *	Perform OPOST processing.  Returns -1 when the output device is
 *	full and the character must be retried. Note that Linux currently
 *	ignores TABDLY, CRDLY, VTDLY, FFDLY and NLDLY. They simply aren't
 *	relevant in the world today. If you ever need them, add them here.
 *
 *	Called from both the receive and transmit sides and can be called
 *	re-entrantly. Relies on lock_kernel() still.
 */
 
static int opost(unsigned char c, struct tty_struct *tty)
{
	int	space, spaces;

	space = tty->driver->write_room(tty);
	if (!space)
		return -1;

	if (O_OPOST(tty)) {
		switch (c) {
		case '\n':
			if (O_ONLRET(tty))
				tty->column = 0;
			if (O_ONLCR(tty)) {
				if (space < 2)
					return -1;
				tty->driver->put_char(tty, '\r');
				tty->column = 0;
			}
			tty->canon_column = tty->column;
			break;
		case '\r':
			if (O_ONOCR(tty) && tty->column == 0)
				return 0;
			if (O_OCRNL(tty)) {
				c = '\n';
				if (O_ONLRET(tty))
					tty->canon_column = tty->column = 0;
				break;
			}
			tty->canon_column = tty->column = 0;
			break;
		case '\t':
			spaces = 8 - (tty->column & 7);
			if (O_TABDLY(tty) == XTABS) {
				if (space < spaces)
					return -1;
				tty->column += spaces;
				tty->driver->write(tty, "        ", spaces);
				return 0;
			}
			tty->column += spaces;
			break;
		case '\b':
			if (tty->column > 0)
				tty->column--;
			break;
		default:
			if (O_OLCUC(tty))
				c = toupper(c);
			if (!iscntrl(c) && !is_continuation(c, tty))
				tty->column++;
			break;
		}
	}
	tty->driver->put_char(tty, c);
	return 0;
}

/**
 *	opost_block		-	block postprocess
 *	@tty: terminal device
 *	@inbuf: user buffer
 *	@nr: number of bytes
 *
 *	This path is used to speed up block console writes, among other
 *	things when processing blocks of output data. It handles only
 *	the simple cases normally found and helps to generate blocks of
 *	symbols for the console driver and thus improve performance.
 *
 *	Called from write_chan under the tty layer write lock.
 */
 
static ssize_t opost_block(struct tty_struct * tty,
		       const unsigned char * buf, unsigned int nr)
{
	int	space;
	int 	i;
	const unsigned char *cp;

	space = tty->driver->write_room(tty);
	if (!space)
		return 0;
	if (nr > space)
		nr = space;

	for (i = 0, cp = buf; i < nr; i++, cp++) {
		switch (*cp) {
		case '\n':
			if (O_ONLRET(tty))
				tty->column = 0;
			if (O_ONLCR(tty))
				goto break_out;
			tty->canon_column = tty->column;
			break;
		case '\r':
			if (O_ONOCR(tty) && tty->column == 0)
				goto break_out;
			if (O_OCRNL(tty))
				goto break_out;
			tty->canon_column = tty->column = 0;
			break;
		case '\t':
			goto break_out;
		case '\b':
			if (tty->column > 0)
				tty->column--;
			break;
		default:
			if (O_OLCUC(tty))
				goto break_out;
			if (!iscntrl(*cp))
				tty->column++;
			break;
		}
	}
break_out:
	if (tty->driver->flush_chars)
		tty->driver->flush_chars(tty);
	i = tty->driver->write(tty, buf, i);	
	return i;
}


/**
 *	put_char	-	write character to driver
 *	@c: character (or part of unicode symbol)
 *	@tty: terminal device
 *
 *	Queue a byte to the driver layer for output
 */
 
static inline void put_char(unsigned char c, struct tty_struct *tty)
{
	tty->driver->put_char(tty, c);
}

/**
 *	echo_char	-	echo characters
 *	@c: unicode byte to echo
 *	@tty: terminal device
 *
 *	Echo user input back onto the screen. This must be called only when 
 *	L_ECHO(tty) is true. Called from the driver receive_buf path.
 */

static void echo_char(unsigned char c, struct tty_struct *tty)
{
	if (L_ECHOCTL(tty) && iscntrl(c) && c != '\t') {
		put_char('^', tty);
		put_char(c ^ 0100, tty);
		tty->column += 2;
	} else
		opost(c, tty);
}

static inline void finish_erasing(struct tty_struct *tty)
{
	if (tty->erasing) {
		put_char('/', tty);
		tty->column++;
		tty->erasing = 0;
	}
}

/**
 *	eraser		-	handle erase function
 *	@c: character input
 *	@tty: terminal device
 *
 *	Perform erase and neccessary output when an erase character is
 *	present in the stream from the driver layer. Handles the complexities
 *	of UTF-8 multibyte symbols.
 */
 
static void eraser(unsigned char c, struct tty_struct *tty)
{
	enum { ERASE, WERASE, KILL } kill_type;
	int head, seen_alnums, cnt;
	unsigned long flags;

	if (tty->read_head == tty->canon_head) {
		/* opost('\a', tty); */		/* what do you think? */
		return;
	}
	if (c == ERASE_CHAR(tty))
		kill_type = ERASE;
	else if (c == WERASE_CHAR(tty))
		kill_type = WERASE;
	else {
		if (!L_ECHO(tty)) {
			spin_lock_irqsave(&tty->read_lock, flags);
			tty->read_cnt -= ((tty->read_head - tty->canon_head) &
					  (N_TTY_BUF_SIZE - 1));
			tty->read_head = tty->canon_head;
			spin_unlock_irqrestore(&tty->read_lock, flags);
			return;
		}
		if (!L_ECHOK(tty) || !L_ECHOKE(tty) || !L_ECHOE(tty)) {
			spin_lock_irqsave(&tty->read_lock, flags);
			tty->read_cnt -= ((tty->read_head - tty->canon_head) &
					  (N_TTY_BUF_SIZE - 1));
			tty->read_head = tty->canon_head;
			spin_unlock_irqrestore(&tty->read_lock, flags);
			finish_erasing(tty);
			echo_char(KILL_CHAR(tty), tty);
			/* Add a newline if ECHOK is on and ECHOKE is off. */
			if (L_ECHOK(tty))
				opost('\n', tty);
			return;
		}
		kill_type = KILL;
	}

	seen_alnums = 0;
	while (tty->read_head != tty->canon_head) {
		head = tty->read_head;

		/* erase a single possibly multibyte character */
		do {
			head = (head - 1) & (N_TTY_BUF_SIZE-1);
			c = tty->read_buf[head];
		} while (is_continuation(c, tty) && head != tty->canon_head);

		/* do not partially erase */
		if (is_continuation(c, tty))
			break;

		if (kill_type == WERASE) {
			/* Equivalent to BSD's ALTWERASE. */
			if (isalnum(c) || c == '_')
				seen_alnums++;
			else if (seen_alnums)
				break;
		}
		cnt = (tty->read_head - head) & (N_TTY_BUF_SIZE-1);
		spin_lock_irqsave(&tty->read_lock, flags);
		tty->read_head = head;
		tty->read_cnt -= cnt;
		spin_unlock_irqrestore(&tty->read_lock, flags);
		if (L_ECHO(tty)) {
			if (L_ECHOPRT(tty)) {
				if (!tty->erasing) {
					put_char('\\', tty);
					tty->column++;
					tty->erasing = 1;
				}
				/* if cnt > 1, output a multi-byte character */
				echo_char(c, tty);
				while (--cnt > 0) {
					head = (head+1) & (N_TTY_BUF_SIZE-1);
					put_char(tty->read_buf[head], tty);
				}
			} else if (kill_type == ERASE && !L_ECHOE(tty)) {
				echo_char(ERASE_CHAR(tty), tty);
			} else if (c == '\t') {
				unsigned int col = tty->canon_column;
				unsigned long tail = tty->canon_head;

				/* Find the column of the last char. */
				while (tail != tty->read_head) {
					c = tty->read_buf[tail];
					if (c == '\t')
						col = (col | 7) + 1;
					else if (iscntrl(c)) {
						if (L_ECHOCTL(tty))
							col += 2;
					} else if (!is_continuation(c, tty))
						col++;
					tail = (tail+1) & (N_TTY_BUF_SIZE-1);
				}

				/* should never happen */
				if (tty->column > 0x80000000)
					tty->column = 0; 

				/* Now backup to that column. */
				while (tty->column > col) {
					/* Can't use opost here. */
					put_char('\b', tty);
					if (tty->column > 0)
						tty->column--;
				}
			} else {
				if (iscntrl(c) && L_ECHOCTL(tty)) {
					put_char('\b', tty);
					put_char(' ', tty);
					put_char('\b', tty);
					if (tty->column > 0)
						tty->column--;
				}
				if (!iscntrl(c) || L_ECHOCTL(tty)) {
					put_char('\b', tty);
					put_char(' ', tty);
					put_char('\b', tty);
					if (tty->column > 0)
						tty->column--;
				}
			}
		}
		if (kill_type == ERASE)
			break;
	}
	if (tty->read_head == tty->canon_head)
		finish_erasing(tty);
}

/**
 *	isig		-	handle the ISIG optio
 *	@sig: signal
 *	@tty: terminal
 *	@flush: force flush
 *
 *	Called when a signal is being sent due to terminal input. This
 *	may caus terminal flushing to take place according to the termios
 *	settings and character used. Called from the driver receive_buf
 *	path so serialized.
 */
 
static inline void isig(int sig, struct tty_struct *tty, int flush)
{
	if (tty->pgrp)
		kill_pgrp(tty->pgrp, sig, 1);
	if (flush || !L_NOFLSH(tty)) {
		n_tty_flush_buffer(tty);
		if (tty->driver->flush_buffer)
			tty->driver->flush_buffer(tty);
	}
}

/**
 *	n_tty_receive_break	-	handle break
 *	@tty: terminal
 *
 *	An RS232 break event has been hit in the incoming bitstream. This
 *	can cause a variety of events depending upon the termios settings.
 *
 *	Called from the receive_buf path so single threaded.
 */
 
static inline void n_tty_receive_break(struct tty_struct *tty)
{
	if (I_IGNBRK(tty))
		return;
	if (I_BRKINT(tty)) {
		isig(SIGINT, tty, 1);
		return;
	}
	if (I_PARMRK(tty)) {
		put_tty_queue('\377', tty);
		put_tty_queue('\0', tty);
	}
	put_tty_queue('\0', tty);
	wake_up_interruptible(&tty->read_wait);
}

/**
 *	n_tty_receive_overrun	-	handle overrun reporting
 *	@tty: terminal
 *
 *	Data arrived faster than we could process it. While the tty
 *	driver has flagged this the bits that were missed are gone
 *	forever.
 *
 *	Called from the receive_buf path so single threaded. Does not
 *	need locking as num_overrun and overrun_time are function
 *	private.
 */
 
static inline void n_tty_receive_overrun(struct tty_struct *tty)
{
	char buf[64];

	tty->num_overrun++;
	if (time_before(tty->overrun_time, jiffies - HZ) ||
			time_after(tty->overrun_time, jiffies)) {
		printk(KERN_WARNING "%s: %d input overrun(s)\n",
			tty_name(tty, buf),
			tty->num_overrun);
		tty->overrun_time = jiffies;
		tty->num_overrun = 0;
	}
}

/**
 *	n_tty_receive_parity_error	-	error notifier
 *	@tty: terminal device
 *	@c: character
 *
 *	Process a parity error and queue the right data to indicate
 *	the error case if neccessary. Locking as per n_tty_receive_buf.
 */
static inline void n_tty_receive_parity_error(struct tty_struct *tty,
					      unsigned char c)
{
	if (I_IGNPAR(tty)) {
		return;
	}
	if (I_PARMRK(tty)) {
		put_tty_queue('\377', tty);
		put_tty_queue('\0', tty);
		put_tty_queue(c, tty);
	} else	if (I_INPCK(tty))
		put_tty_queue('\0', tty);
	else
		put_tty_queue(c, tty);
	wake_up_interruptible(&tty->read_wait);
}

/**
 *	n_tty_receive_char	-	perform processing
 *	@tty: terminal device
 *	@c: character
 *
 *	Process an individual character of input received from the driver.
 *	This is serialized with respect to itself by the rules for the 
 *	driver above.
 */

static inline void n_tty_receive_char(struct tty_struct *tty, unsigned char c)
{
	unsigned long flags;

	if (tty->raw) {
		put_tty_queue(c, tty);
		return;
	}
	
	if (tty->stopped && !tty->flow_stopped &&
	    I_IXON(tty) && I_IXANY(tty)) {
		start_tty(tty);
		return;
	}
	
	if (I_ISTRIP(tty))
		c &= 0x7f;
	if (I_IUCLC(tty) && L_IEXTEN(tty))
		c=tolower(c);

	if (tty->closing) {
		if (I_IXON(tty)) {
			if (c == START_CHAR(tty))
				start_tty(tty);
			else if (c == STOP_CHAR(tty))
				stop_tty(tty);
		}
		return;
	}

	/*
	 * If the previous character was LNEXT, or we know that this
	 * character is not one of the characters that we'll have to
	 * handle specially, do shortcut processing to speed things
	 * up.
	 */
	if (!test_bit(c, tty->process_char_map) || tty->lnext) {
		finish_erasing(tty);
		tty->lnext = 0;
		if (L_ECHO(tty)) {
			if (tty->read_cnt >= N_TTY_BUF_SIZE-1) {
				put_char('\a', tty); /* beep if no space */
				return;
			}
			/* Record the column of first canon char. */
			if (tty->canon_head == tty->read_head)
				tty->canon_column = tty->column;
			echo_char(c, tty);
		}
		if (I_PARMRK(tty) && c == (unsigned char) '\377')
			put_tty_queue(c, tty);
		put_tty_queue(c, tty);
		return;
	}
		
	if (c == '\r') {
		if (I_IGNCR(tty))
			return;
		if (I_ICRNL(tty))
			c = '\n';
	} else if (c == '\n' && I_INLCR(tty))
		c = '\r';
	if (I_IXON(tty)) {
		if (c == START_CHAR(tty)) {
			start_tty(tty);
			return;
		}
		if (c == STOP_CHAR(tty)) {
			stop_tty(tty);
			return;
		}
	}
	if (L_ISIG(tty)) {
		int signal;
		signal = SIGINT;
		if (c == INTR_CHAR(tty))
			goto send_signal;
		signal = SIGQUIT;
		if (c == QUIT_CHAR(tty))
			goto send_signal;
		signal = SIGTSTP;
		if (c == SUSP_CHAR(tty)) {
send_signal:
			isig(signal, tty, 0);
			return;
		}
	}
	if (tty->icanon) {
		if (c == ERASE_CHAR(tty) || c == KILL_CHAR(tty) ||
		    (c == WERASE_CHAR(tty) && L_IEXTEN(tty))) {
			eraser(c, tty);
			return;
		}
		if (c == LNEXT_CHAR(tty) && L_IEXTEN(tty)) {
			tty->lnext = 1;
			if (L_ECHO(tty)) {
				finish_erasing(tty);
				if (L_ECHOCTL(tty)) {
					put_char('^', tty);
					put_char('\b', tty);
				}
			}
			return;
		}
		if (c == REPRINT_CHAR(tty) && L_ECHO(tty) &&
		    L_IEXTEN(tty)) {
			unsigned long tail = tty->canon_head;

			finish_erasing(tty);
			echo_char(c, tty);
			opost('\n', tty);
			while (tail != tty->read_head) {
				echo_char(tty->read_buf[tail], tty);
				tail = (tail+1) & (N_TTY_BUF_SIZE-1);
			}
			return;
		}
		if (c == '\n') {
			if (L_ECHO(tty) || L_ECHONL(tty)) {
				if (tty->read_cnt >= N_TTY_BUF_SIZE-1)
					put_char('\a', tty);
				opost('\n', tty);
			}
			goto handle_newline;
		}
		if (c == EOF_CHAR(tty)) {
		        if (tty->canon_head != tty->read_head)
			        set_bit(TTY_PUSH, &tty->flags);
			c = __DISABLED_CHAR;
			goto handle_newline;
		}
		if ((c == EOL_CHAR(tty)) ||
		    (c == EOL2_CHAR(tty) && L_IEXTEN(tty))) {
			/*
			 * XXX are EOL_CHAR and EOL2_CHAR echoed?!?
			 */
			if (L_ECHO(tty)) {
				if (tty->read_cnt >= N_TTY_BUF_SIZE-1)
					put_char('\a', tty);
				/* Record the column of first canon char. */
				if (tty->canon_head == tty->read_head)
					tty->canon_column = tty->column;
				echo_char(c, tty);
			}
			/*
			 * XXX does PARMRK doubling happen for
			 * EOL_CHAR and EOL2_CHAR?
			 */
			if (I_PARMRK(tty) && c == (unsigned char) '\377')
				put_tty_queue(c, tty);

		handle_newline:
			spin_lock_irqsave(&tty->read_lock, flags);
			set_bit(tty->read_head, tty->read_flags);
			put_tty_queue_nolock(c, tty);
			tty->canon_head = tty->read_head;
			tty->canon_data++;
			spin_unlock_irqrestore(&tty->read_lock, flags);
			kill_fasync(&tty->fasync, SIGIO, POLL_IN);
			if (waitqueue_active(&tty->read_wait))
				wake_up_interruptible(&tty->read_wait);
			return;
		}
	}
	
	finish_erasing(tty);
	if (L_ECHO(tty)) {
		if (tty->read_cnt >= N_TTY_BUF_SIZE-1) {
			put_char('\a', tty); /* beep if no space */
			return;
		}
		if (c == '\n')
			opost('\n', tty);
		else {
			/* Record the column of first canon char. */
			if (tty->canon_head == tty->read_head)
				tty->canon_column = tty->column;
			echo_char(c, tty);
		}
	}

	if (I_PARMRK(tty) && c == (unsigned char) '\377')
		put_tty_queue(c, tty);

	put_tty_queue(c, tty);
}	


/**
 *	n_tty_write_wakeup	-	asynchronous I/O notifier
 *	@tty: tty device
 *
 *	Required for the ptys, serial driver etc. since processes
 *	that attach themselves to the master and rely on ASYNC
 *	IO must be woken up
 */

static void n_tty_write_wakeup(struct tty_struct *tty)
{
	if (tty->fasync)
	{
 		set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
		kill_fasync(&tty->fasync, SIGIO, POLL_OUT);
	}
	return;
}

/**
 *	n_tty_receive_buf	-	data receive
 *	@tty: terminal device
 *	@cp: buffer
 *	@fp: flag buffer
 *	@count: characters
 *
 *	Called by the terminal driver when a block of characters has
 *	been received. This function must be called from soft contexts
 *	not from interrupt context. The driver is responsible for making
 *	calls one at a time and in order (or using flush_to_ldisc)
 */
 
static void n_tty_receive_buf(struct tty_struct *tty, const unsigned char *cp,
			      char *fp, int count)
{
	const unsigned char *p;
	char *f, flags = TTY_NORMAL;
	int	i;
	char	buf[64];
	unsigned long cpuflags;

	if (!tty->read_buf)
		return;

	if (tty->real_raw) {
		spin_lock_irqsave(&tty->read_lock, cpuflags);
		i = min(N_TTY_BUF_SIZE - tty->read_cnt,
			N_TTY_BUF_SIZE - tty->read_head);
		i = min(count, i);
		memcpy(tty->read_buf + tty->read_head, cp, i);
		tty->read_head = (tty->read_head + i) & (N_TTY_BUF_SIZE-1);
		tty->read_cnt += i;
		cp += i;
		count -= i;

		i = min(N_TTY_BUF_SIZE - tty->read_cnt,
			N_TTY_BUF_SIZE - tty->read_head);
		i = min(count, i);
		memcpy(tty->read_buf + tty->read_head, cp, i);
		tty->read_head = (tty->read_head + i) & (N_TTY_BUF_SIZE-1);
		tty->read_cnt += i;
		spin_unlock_irqrestore(&tty->read_lock, cpuflags);
	} else {
		for (i=count, p = cp, f = fp; i; i--, p++) {
			if (f)
				flags = *f++;
			switch (flags) {
			case TTY_NORMAL:
				n_tty_receive_char(tty, *p);
				break;
			case TTY_BREAK:
				n_tty_receive_break(tty);
				break;
			case TTY_PARITY:
			case TTY_FRAME:
				n_tty_receive_parity_error(tty, *p);
				break;
			case TTY_OVERRUN:
				n_tty_receive_overrun(tty);
				break;
			default:
				printk("%s: unknown flag %d\n",
				       tty_name(tty, buf), flags);
				break;
			}
		}
		if (tty->driver->flush_chars)
			tty->driver->flush_chars(tty);
	}

	n_tty_set_room(tty);

	if (!tty->icanon && (tty->read_cnt >= tty->minimum_to_wake)) {
		kill_fasync(&tty->fasync, SIGIO, POLL_IN);
		if (waitqueue_active(&tty->read_wait))
			wake_up_interruptible(&tty->read_wait);
	}

	/*
	 * Check the remaining room for the input canonicalization
	 * mode.  We don't want to throttle the driver if we're in
	 * canonical mode and don't have a newline yet!
	 */
	if (tty->receive_room < TTY_THRESHOLD_THROTTLE) {
		/* check TTY_THROTTLED first so it indicates our state */
		if (!test_and_set_bit(TTY_THROTTLED, &tty->flags) &&
		    tty->driver->throttle)
			tty->driver->throttle(tty);
	}
}

int is_ignored(int sig)
{
	return (sigismember(&current->blocked, sig) ||
	        current->sighand->action[sig-1].sa.sa_handler == SIG_IGN);
}

/**
 *	n_tty_set_termios	-	termios data changed
 *	@tty: terminal
 *	@old: previous data
 *
 *	Called by the tty layer when the user changes termios flags so
 *	that the line discipline can plan ahead. This function cannot sleep
 *	and is protected from re-entry by the tty layer. The user is 
 *	guaranteed that this function will not be re-entered or in progress
 *	when the ldisc is closed.
 */
 
static void n_tty_set_termios(struct tty_struct *tty, struct ktermios * old)
{
	if (!tty)
		return;
	
	tty->icanon = (L_ICANON(tty) != 0);
	if (test_bit(TTY_HW_COOK_IN, &tty->flags)) {
		tty->raw = 1;
		tty->real_raw = 1;
		n_tty_set_room(tty);
		return;
	}
	if (I_ISTRIP(tty) || I_IUCLC(tty) || I_IGNCR(tty) ||
	    I_ICRNL(tty) || I_INLCR(tty) || L_ICANON(tty) ||
	    I_IXON(tty) || L_ISIG(tty) || L_ECHO(tty) ||
	    I_PARMRK(tty)) {
		memset(tty->process_char_map, 0, 256/8);

		if (I_IGNCR(tty) || I_ICRNL(tty))
			set_bit('\r', tty->process_char_map);
		if (I_INLCR(tty))
			set_bit('\n', tty->process_char_map);

		if (L_ICANON(tty)) {
			set_bit(ERASE_CHAR(tty), tty->process_char_map);
			set_bit(KILL_CHAR(tty), tty->process_char_map);
			set_bit(EOF_CHAR(tty), tty->process_char_map);
			set_bit('\n', tty->process_char_map);
			set_bit(EOL_CHAR(tty), tty->process_char_map);
			if (L_IEXTEN(tty)) {
				set_bit(WERASE_CHAR(tty),
					tty->process_char_map);
				set_bit(LNEXT_CHAR(tty),
					tty->process_char_map);
				set_bit(EOL2_CHAR(tty),
					tty->process_char_map);
				if (L_ECHO(tty))
					set_bit(REPRINT_CHAR(tty),
						tty->process_char_map);
			}
		}
		if (I_IXON(tty)) {
			set_bit(START_CHAR(tty), tty->process_char_map);
			set_bit(STOP_CHAR(tty), tty->process_char_map);
		}
		if (L_ISIG(tty)) {
			set_bit(INTR_CHAR(tty), tty->process_char_map);
			set_bit(QUIT_CHAR(tty), tty->process_char_map);
			set_bit(SUSP_CHAR(tty), tty->process_char_map);
		}
		clear_bit(__DISABLED_CHAR, tty->process_char_map);
		tty->raw = 0;
		tty->real_raw = 0;
	} else {
		tty->raw = 1;
		if ((I_IGNBRK(tty) || (!I_BRKINT(tty) && !I_PARMRK(tty))) &&
		    (I_IGNPAR(tty) || !I_INPCK(tty)) &&
		    (tty->driver->flags & TTY_DRIVER_REAL_RAW))
			tty->real_raw = 1;
		else
			tty->real_raw = 0;
	}
	n_tty_set_room(tty);
}

/**
 *	n_tty_close		-	close the ldisc for this tty
 *	@tty: device
 *
 *	Called from the terminal layer when this line discipline is 
 *	being shut down, either because of a close or becsuse of a 
 *	discipline change. The function will not be called while other
 *	ldisc methods are in progress.
 */
 
static void n_tty_close(struct tty_struct *tty)
{
	n_tty_flush_buffer(tty);
	if (tty->read_buf) {
		free_buf(tty->read_buf);
		tty->read_buf = NULL;
	}
}

/**
 *	n_tty_open		-	open an ldisc
 *	@tty: terminal to open
 *
 *	Called when this line discipline is being attached to the 
 *	terminal device. Can sleep. Called serialized so that no
 *	other events will occur in parallel. No further open will occur
 *	until a close.
 */

static int n_tty_open(struct tty_struct *tty)
{
	if (!tty)
		return -EINVAL;

	/* This one is ugly. Currently a malloc failure here can panic */
	if (!tty->read_buf) {
		tty->read_buf = alloc_buf();
		if (!tty->read_buf)
			return -ENOMEM;
	}
	memset(tty->read_buf, 0, N_TTY_BUF_SIZE);
	reset_buffer_flags(tty);
	tty->column = 0;
	n_tty_set_termios(tty, NULL);
	tty->minimum_to_wake = 1;
	tty->closing = 0;
	return 0;
}

static inline int input_available_p(struct tty_struct *tty, int amt)
{
	if (tty->icanon) {
		if (tty->canon_data)
			return 1;
	} else if (tty->read_cnt >= (amt ? amt : 1))
		return 1;

	return 0;
}

/**
 * 	copy_from_read_buf	-	copy read data directly
 *	@tty: terminal device
 *	@b: user data
 *	@nr: size of data
 *
 *	Helper function to speed up read_chan.  It is only called when
 *	ICANON is off; it copies characters straight from the tty queue to
 *	user space directly.  It can be profitably called twice; once to
 *	drain the space from the tail pointer to the (physical) end of the
 *	buffer, and once to drain the space from the (physical) beginning of
 *	the buffer to head pointer.
 *
 *	Called under the tty->atomic_read_lock sem
 *
 */
 
static int copy_from_read_buf(struct tty_struct *tty,
				      unsigned char __user **b,
				      size_t *nr)

{
	int retval;
	size_t n;
	unsigned long flags;

	retval = 0;
	spin_lock_irqsave(&tty->read_lock, flags);
	n = min(tty->read_cnt, N_TTY_BUF_SIZE - tty->read_tail);
	n = min(*nr, n);
	spin_unlock_irqrestore(&tty->read_lock, flags);
	if (n) {
		retval = copy_to_user(*b, &tty->read_buf[tty->read_tail], n);
		n -= retval;
		spin_lock_irqsave(&tty->read_lock, flags);
		tty->read_tail = (tty->read_tail + n) & (N_TTY_BUF_SIZE-1);
		tty->read_cnt -= n;
		spin_unlock_irqrestore(&tty->read_lock, flags);
		*b += n;
		*nr -= n;
	}
	return retval;
}

extern ssize_t redirected_tty_write(struct file *,const char *,size_t,loff_t *);

/**
 *	job_control		-	check job control
 *	@tty: tty
 *	@file: file handle
 *
 *	Perform job control management checks on this file/tty descriptor
 *	and if appropriate send any needed signals and return a negative 
 *	error code if action should be taken.
 */
 
static int job_control(struct tty_struct *tty, struct file *file)
{
	/* Job control check -- must be done at start and after
	   every sleep (POSIX.1 7.1.1.4). */
	/* NOTE: not yet done after every sleep pending a thorough
	   check of the logic of this change. -- jlc */
	/* don't stop on /dev/console */
	if (file->f_op->write != redirected_tty_write &&
	    current->signal->tty == tty) {
		if (!tty->pgrp)
			printk("read_chan: no tty->pgrp!\n");
		else if (task_pgrp(current) != tty->pgrp) {
			if (is_ignored(SIGTTIN) ||
			    is_current_pgrp_orphaned())
				return -EIO;
			kill_pgrp(task_pgrp(current), SIGTTIN, 1);
			return -ERESTARTSYS;
		}
	}
	return 0;
}
 

/**
 *	read_chan		-	read function for tty
 *	@tty: tty device
 *	@file: file object
 *	@buf: userspace buffer pointer
 *	@nr: size of I/O
 *
 *	Perform reads for the line discipline. We are guaranteed that the
 *	line discipline will not be closed under us but we may get multiple
 *	parallel readers and must handle this ourselves. We may also get
 *	a hangup. Always called in user context, may sleep.
 *
 *	This code must be sure never to sleep through a hangup.
 */
 
static ssize_t read_chan(struct tty_struct *tty, struct file *file,
			 unsigned char __user *buf, size_t nr)
{
	unsigned char __user *b = buf;
	DECLARE_WAITQUEUE(wait, current);
	int c;
	int minimum, time;
	ssize_t retval = 0;
	ssize_t size;
	long timeout;
	unsigned long flags;

do_it_again:

	if (!tty->read_buf) {
		printk("n_tty_read_chan: called with read_buf == NULL?!?\n");
		return -EIO;
	}

	c = job_control(tty, file);
	if(c < 0)
		return c;
	
	minimum = time = 0;
	timeout = MAX_SCHEDULE_TIMEOUT;
	if (!tty->icanon) {
		time = (HZ / 10) * TIME_CHAR(tty);
		minimum = MIN_CHAR(tty);
		if (minimum) {
			if (time)
				tty->minimum_to_wake = 1;
			else if (!waitqueue_active(&tty->read_wait) ||
				 (tty->minimum_to_wake > minimum))
				tty->minimum_to_wake = minimum;
		} else {
			timeout = 0;
			if (time) {
				timeout = time;
				time = 0;
			}
			tty->minimum_to_wake = minimum = 1;
		}
	}

	/*
	 *	Internal serialization of reads.
	 */
	if (file->f_flags & O_NONBLOCK) {
		if (!mutex_trylock(&tty->atomic_read_lock))
			return -EAGAIN;
	}
	else {
		if (mutex_lock_interruptible(&tty->atomic_read_lock))
			return -ERESTARTSYS;
	}

	add_wait_queue(&tty->read_wait, &wait);
	while (nr) {
		/* First test for status change. */
		if (tty->packet && tty->link->ctrl_status) {
			unsigned char cs;
			if (b != buf)
				break;
			cs = tty->link->ctrl_status;
			tty->link->ctrl_status = 0;
			if (put_user(cs, b++)) {
				retval = -EFAULT;
				b--;
				break;
			}
			nr--;
			break;
		}
		/* This statement must be first before checking for input
		   so that any interrupt will set the state back to
		   TASK_RUNNING. */
		set_current_state(TASK_INTERRUPTIBLE);
		
		if (((minimum - (b - buf)) < tty->minimum_to_wake) &&
		    ((minimum - (b - buf)) >= 1))
			tty->minimum_to_wake = (minimum - (b - buf));
		
		if (!input_available_p(tty, 0)) {
			if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
				retval = -EIO;
				break;
			}
			if (tty_hung_up_p(file))
				break;
			if (!timeout)
				break;
			if (file->f_flags & O_NONBLOCK) {
				retval = -EAGAIN;
				break;
			}
			if (signal_pending(current)) {
				retval = -ERESTARTSYS;
				break;
			}
			n_tty_set_room(tty);
			timeout = schedule_timeout(timeout);
			continue;
		}
		__set_current_state(TASK_RUNNING);

		/* Deal with packet mode. */
		if (tty->packet && b == buf) {
			if (put_user(TIOCPKT_DATA, b++)) {
				retval = -EFAULT;
				b--;
				break;
			}
			nr--;
		}

		if (tty->icanon) {
			/* N.B. avoid overrun if nr == 0 */
			while (nr && tty->read_cnt) {
 				int eol;

				eol = test_and_clear_bit(tty->read_tail,
						tty->read_flags);
				c = tty->read_buf[tty->read_tail];
				spin_lock_irqsave(&tty->read_lock, flags);
				tty->read_tail = ((tty->read_tail+1) &
						  (N_TTY_BUF_SIZE-1));
				tty->read_cnt--;
				if (eol) {
					/* this test should be redundant:
					 * we shouldn't be reading data if
					 * canon_data is 0
					 */
					if (--tty->canon_data < 0)
						tty->canon_data = 0;
				}
				spin_unlock_irqrestore(&tty->read_lock, flags);

				if (!eol || (c != __DISABLED_CHAR)) {
					if (put_user(c, b++)) {
						retval = -EFAULT;
						b--;
						break;
					}
					nr--;
				}
				if (eol)
					break;
			}
			if (retval)
				break;
		} else {
			int uncopied;
			uncopied = copy_from_read_buf(tty, &b, &nr);
			uncopied += copy_from_read_buf(tty, &b, &nr);
			if (uncopied) {
				retval = -EFAULT;
				break;
			}
		}

		/* If there is enough space in the read buffer now, let the
		 * low-level driver know. We use n_tty_chars_in_buffer() to
		 * check the buffer, as it now knows about canonical mode.
		 * Otherwise, if the driver is throttled and the line is
		 * longer than TTY_THRESHOLD_UNTHROTTLE in canonical mode,
		 * we won't get any more characters.
		 */
		if (n_tty_chars_in_buffer(tty) <= TTY_THRESHOLD_UNTHROTTLE) {
			n_tty_set_room(tty);
			check_unthrottle(tty);
		}

		if (b - buf >= minimum)
			break;
		if (time)
			timeout = time;
	}
	mutex_unlock(&tty->atomic_read_lock);
	remove_wait_queue(&tty->read_wait, &wait);

	if (!waitqueue_active(&tty->read_wait))
		tty->minimum_to_wake = minimum;

	__set_current_state(TASK_RUNNING);
	size = b - buf;
	if (size) {
		retval = size;
		if (nr)
	       		clear_bit(TTY_PUSH, &tty->flags);
	} else if (test_and_clear_bit(TTY_PUSH, &tty->flags))
		 goto do_it_again;

	n_tty_set_room(tty);

	return retval;
}

/**
 *	write_chan		-	write function for tty
 *	@tty: tty device
 *	@file: file object
 *	@buf: userspace buffer pointer
 *	@nr: size of I/O
 *
 *	Write function of the terminal device. This is serialized with
 *	respect to other write callers but not to termios changes, reads
 *	and other such events. We must be careful with N_TTY as the receive
 *	code will echo characters, thus calling driver write methods.
 *
 *	This code must be sure never to sleep through a hangup.
 */
 
static ssize_t write_chan(struct tty_struct * tty, struct file * file,
			  const unsigned char * buf, size_t nr)
{
	const unsigned char *b = buf;
	DECLARE_WAITQUEUE(wait, current);
	int c;
	ssize_t retval = 0;

	/* Job control check -- must be done at start (POSIX.1 7.1.1.4). */
	if (L_TOSTOP(tty) && file->f_op->write != redirected_tty_write) {
		retval = tty_check_change(tty);
		if (retval)
			return retval;
	}

	add_wait_queue(&tty->write_wait, &wait);
	while (1) {
		set_current_state(TASK_INTERRUPTIBLE);
		if (signal_pending(current)) {
			retval = -ERESTARTSYS;
			break;
		}
		if (tty_hung_up_p(file) || (tty->link && !tty->link->count)) {
			retval = -EIO;
			break;
		}
		if (O_OPOST(tty) && !(test_bit(TTY_HW_COOK_OUT, &tty->flags))) {
			while (nr > 0) {
				ssize_t num = opost_block(tty, b, nr);
				if (num < 0) {
					if (num == -EAGAIN)
						break;
					retval = num;
					goto break_out;
				}
				b += num;
				nr -= num;
				if (nr == 0)
					break;
				c = *b;
				if (opost(c, tty) < 0)
					break;
				b++; nr--;
			}
			if (tty->driver->flush_chars)
				tty->driver->flush_chars(tty);
		} else {
			while (nr > 0) {
				c = tty->driver->write(tty, b, nr);
				if (c < 0) {
					retval = c;
					goto break_out;
				}
				if (!c)
					break;
				b += c;
				nr -= c;
			}
		}
		if (!nr)
			break;
		if (file->f_flags & O_NONBLOCK) {
			retval = -EAGAIN;
			break;
		}
		schedule();
	}
break_out:
	__set_current_state(TASK_RUNNING);
	remove_wait_queue(&tty->write_wait, &wait);
	return (b - buf) ? b - buf : retval;
}

/**
 *	normal_poll		-	poll method for N_TTY
 *	@tty: terminal device
 *	@file: file accessing it
 *	@wait: poll table
 *
 *	Called when the line discipline is asked to poll() for data or
 *	for special events. This code is not serialized with respect to
 *	other events save open/close.
 *
 *	This code must be sure never to sleep through a hangup.
 *	Called without the kernel lock held - fine
 *
 *	FIXME: if someone changes the VMIN or discipline settings for the
 *	terminal while another process is in poll() the poll does not
 *	recompute the new limits. Possibly set_termios should issue
 *	a read wakeup to fix this bug.
 */
 
static unsigned int normal_poll(struct tty_struct * tty, struct file * file, poll_table *wait)
{
	unsigned int mask = 0;

	poll_wait(file, &tty->read_wait, wait);
	poll_wait(file, &tty->write_wait, wait);
	if (input_available_p(tty, TIME_CHAR(tty) ? 0 : MIN_CHAR(tty)))
		mask |= POLLIN | POLLRDNORM;
	if (tty->packet && tty->link->ctrl_status)
		mask |= POLLPRI | POLLIN | POLLRDNORM;
	if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
		mask |= POLLHUP;
	if (tty_hung_up_p(file))
		mask |= POLLHUP;
	if (!(mask & (POLLHUP | POLLIN | POLLRDNORM))) {
		if (MIN_CHAR(tty) && !TIME_CHAR(tty))
			tty->minimum_to_wake = MIN_CHAR(tty);
		else
			tty->minimum_to_wake = 1;
	}
	if (tty->driver->chars_in_buffer(tty) < WAKEUP_CHARS &&
			tty->driver->write_room(tty) > 0)
		mask |= POLLOUT | POLLWRNORM;
	return mask;
}

struct tty_ldisc tty_ldisc_N_TTY = {
	.magic           = TTY_LDISC_MAGIC,
	.name            = "n_tty",
	.open            = n_tty_open,
	.close           = n_tty_close,
	.flush_buffer    = n_tty_flush_buffer,
	.chars_in_buffer = n_tty_chars_in_buffer,
	.read            = read_chan,
	.write           = write_chan,
	.ioctl           = n_tty_ioctl,
	.set_termios     = n_tty_set_termios,
	.poll            = normal_poll,
	.receive_buf     = n_tty_receive_buf,
	.write_wakeup    = n_tty_write_wakeup
};

OpenPOWER on IntegriCloud