summaryrefslogtreecommitdiff
path: root/drivers/tty/n_tty.c
blob: 9cdb0fa3c4bf97c6a658a35e5ae3c1fd9784d3f7 (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
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
// SPDX-License-Identifier: GPL-1.0+
/*
 * 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.
 *
 * 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 n_tty_write 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 <linux/audit.h>
#include <linux/file.h>
#include <linux/uaccess.h>
#include <linux/module.h>
#include <linux/ratelimit.h>
#include <linux/vmalloc.h>

/*
 * Until this number of characters is queued in the xmit buffer, select will
 * return "we have room for writes".
 */
#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

/*
 * Special byte codes used in the echo buffer to represent operations
 * or special handling of characters.  Bytes in the echo buffer that
 * are not part of such special blocks are treated as normal character
 * codes.
 */
#define ECHO_OP_START 0xff
#define ECHO_OP_MOVE_BACK_COL 0x80
#define ECHO_OP_SET_CANON_COL 0x81
#define ECHO_OP_ERASE_TAB 0x82

#define ECHO_COMMIT_WATERMARK	256
#define ECHO_BLOCK		256
#define ECHO_DISCARD_WATERMARK	N_TTY_BUF_SIZE - (ECHO_BLOCK + 32)


#undef N_TTY_TRACE
#ifdef N_TTY_TRACE
# define n_tty_trace(f, args...)	trace_printk(f, ##args)
#else
# define n_tty_trace(f, args...)
#endif

struct n_tty_data {
	/* producer-published */
	size_t read_head;
	size_t commit_head;
	size_t canon_head;
	size_t echo_head;
	size_t echo_commit;
	size_t echo_mark;
	DECLARE_BITMAP(char_map, 256);

	/* private to n_tty_receive_overrun (single-threaded) */
	unsigned long overrun_time;
	int num_overrun;

	/* non-atomic */
	bool no_room;

	/* must hold exclusive termios_rwsem to reset these */
	unsigned char lnext:1, erasing:1, raw:1, real_raw:1, icanon:1;
	unsigned char push:1;

	/* shared by producer and consumer */
	char read_buf[N_TTY_BUF_SIZE];
	DECLARE_BITMAP(read_flags, N_TTY_BUF_SIZE);
	unsigned char echo_buf[N_TTY_BUF_SIZE];

	/* consumer-published */
	size_t read_tail;
	size_t line_start;

	/* protected by output lock */
	unsigned int column;
	unsigned int canon_column;
	size_t echo_tail;

	struct mutex atomic_read_lock;
	struct mutex output_lock;
};

#define MASK(x) ((x) & (N_TTY_BUF_SIZE - 1))

static inline size_t read_cnt(struct n_tty_data *ldata)
{
	return ldata->read_head - ldata->read_tail;
}

static inline unsigned char read_buf(struct n_tty_data *ldata, size_t i)
{
	return ldata->read_buf[i & (N_TTY_BUF_SIZE - 1)];
}

static inline unsigned char *read_buf_addr(struct n_tty_data *ldata, size_t i)
{
	return &ldata->read_buf[i & (N_TTY_BUF_SIZE - 1)];
}

static inline unsigned char echo_buf(struct n_tty_data *ldata, size_t i)
{
	smp_rmb(); /* Matches smp_wmb() in add_echo_byte(). */
	return ldata->echo_buf[i & (N_TTY_BUF_SIZE - 1)];
}

static inline unsigned char *echo_buf_addr(struct n_tty_data *ldata, size_t i)
{
	return &ldata->echo_buf[i & (N_TTY_BUF_SIZE - 1)];
}

/* If we are not echoing the data, perhaps this is a secret so erase it */
static void zero_buffer(struct tty_struct *tty, u8 *buffer, int size)
{
	bool icanon = !!L_ICANON(tty);
	bool no_echo = !L_ECHO(tty);

	if (icanon && no_echo)
		memset(buffer, 0x00, size);
}

static int tty_copy_to_user(struct tty_struct *tty, void __user *to,
			    size_t tail, size_t n)
{
	struct n_tty_data *ldata = tty->disc_data;
	size_t size = N_TTY_BUF_SIZE - tail;
	void *from = read_buf_addr(ldata, tail);
	int uncopied;

	if (n > size) {
		tty_audit_add_data(tty, from, size);
		uncopied = copy_to_user(to, from, size);
		zero_buffer(tty, from, size - uncopied);
		if (uncopied)
			return uncopied;
		to += size;
		n -= size;
		from = ldata->read_buf;
	}

	tty_audit_add_data(tty, from, n);
	uncopied = copy_to_user(to, from, n);
	zero_buffer(tty, from, n - uncopied);
	return uncopied;
}

/**
 *	n_tty_kick_worker - start input worker (if required)
 *	@tty: terminal
 *
 *	Re-schedules the flip buffer work if it may have stopped
 *
 *	Caller holds exclusive termios_rwsem
 *	   or
 *	n_tty_read()/consumer path:
 *		holds non-exclusive termios_rwsem
 */

static void n_tty_kick_worker(struct tty_struct *tty)
{
	struct n_tty_data *ldata = tty->disc_data;

	/* Did the input worker stop? Restart it */
	if (unlikely(ldata->no_room)) {
		ldata->no_room = 0;

		WARN_RATELIMIT(tty->port->itty == NULL,
				"scheduling with invalid itty\n");
		/* see if ldisc has been killed - if so, this means that
		 * even though the ldisc has been halted and ->buf.work
		 * cancelled, ->buf.work is about to be rescheduled
		 */
		WARN_RATELIMIT(test_bit(TTY_LDISC_HALTED, &tty->flags),
			       "scheduling buffer work for halted ldisc\n");
		tty_buffer_restart_work(tty->port);
	}
}

static ssize_t chars_in_buffer(struct tty_struct *tty)
{
	struct n_tty_data *ldata = tty->disc_data;
	ssize_t n = 0;

	if (!ldata->icanon)
		n = ldata->commit_head - ldata->read_tail;
	else
		n = ldata->canon_head - ldata->read_tail;
	return n;
}

/**
 *	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)
{
	clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
	kill_fasync(&tty->fasync, SIGIO, POLL_OUT);
}

static void n_tty_check_throttle(struct tty_struct *tty)
{
	struct n_tty_data *ldata = tty->disc_data;

	/*
	 * 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 (ldata->icanon && ldata->canon_head == ldata->read_tail)
		return;

	while (1) {
		int throttled;
		tty_set_flow_change(tty, TTY_THROTTLE_SAFE);
		if (N_TTY_BUF_SIZE - read_cnt(ldata) >= TTY_THRESHOLD_THROTTLE)
			break;
		throttled = tty_throttle_safe(tty);
		if (!throttled)
			break;
	}
	__tty_set_flow_change(tty, 0);
}

static void n_tty_check_unthrottle(struct tty_struct *tty)
{
	if (tty->driver->type == TTY_DRIVER_TYPE_PTY) {
		if (chars_in_buffer(tty) > TTY_THRESHOLD_UNTHROTTLE)
			return;
		n_tty_kick_worker(tty);
		tty_wakeup(tty->link);
		return;
	}

	/* If there is enough space in the read buffer now, let the
	 * low-level driver know. We use 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.
	 */

	while (1) {
		int unthrottled;
		tty_set_flow_change(tty, TTY_UNTHROTTLE_SAFE);
		if (chars_in_buffer(tty) > TTY_THRESHOLD_UNTHROTTLE)
			break;
		n_tty_kick_worker(tty);
		unthrottled = tty_unthrottle_safe(tty);
		if (!unthrottled)
			break;
	}
	__tty_set_flow_change(tty, 0);
}

/**
 *	put_tty_queue		-	add character to tty
 *	@c: character
 *	@ldata: n_tty data
 *
 *	Add a character to the tty read_buf queue.
 *
 *	n_tty_receive_buf()/producer path:
 *		caller holds non-exclusive termios_rwsem
 */

static inline void put_tty_queue(unsigned char c, struct n_tty_data *ldata)
{
	*read_buf_addr(ldata, ldata->read_head) = c;
	ldata->read_head++;
}

/**
 *	reset_buffer_flags	-	reset buffer state
 *	@tty: terminal to reset
 *
 *	Reset the read buffer counters and clear the flags.
 *	Called from n_tty_open() and n_tty_flush_buffer().
 *
 *	Locking: caller holds exclusive termios_rwsem
 *		 (or locking is not required)
 */

static void reset_buffer_flags(struct n_tty_data *ldata)
{
	ldata->read_head = ldata->canon_head = ldata->read_tail = 0;
	ldata->commit_head = 0;
	ldata->line_start = 0;

	ldata->erasing = 0;
	bitmap_zero(ldata->read_flags, N_TTY_BUF_SIZE);
	ldata->push = 0;
}

static void n_tty_packet_mode_flush(struct tty_struct *tty)
{
	unsigned long flags;

	if (tty->link->packet) {
		spin_lock_irqsave(&tty->ctrl_lock, flags);
		tty->ctrl_status |= TIOCPKT_FLUSHREAD;
		spin_unlock_irqrestore(&tty->ctrl_lock, flags);
		wake_up_interruptible(&tty->link->read_wait);
	}
}

/**
 *	n_tty_flush_buffer	-	clean input queue
 *	@tty:	terminal device
 *
 *	Flush the input buffer. Called 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).
 *
 *	Holds termios_rwsem to exclude producer/consumer while
 *	buffer indices are reset.
 *
 *	Locking: ctrl_lock, exclusive termios_rwsem
 */

static void n_tty_flush_buffer(struct tty_struct *tty)
{
	down_write(&tty->termios_rwsem);
	reset_buffer_flags(tty->disc_data);
	n_tty_kick_worker(tty);

	if (tty->link)
		n_tty_packet_mode_flush(tty);
	up_write(&tty->termios_rwsem);
}

/**
 *	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);
}

/**
 *	do_output_char			-	output one character
 *	@c: character (or partial unicode symbol)
 *	@tty: terminal device
 *	@space: space available in tty driver write buffer
 *
 *	This is a helper function that handles one output character
 *	(including special characters like TAB, CR, LF, etc.),
 *	doing OPOST processing and putting the results in the
 *	tty driver's write buffer.
 *
 *	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.
 *
 *	Returns the number of bytes of buffer space used or -1 if
 *	no space left.
 *
 *	Locking: should be called under the output_lock to protect
 *		 the column state and space left in the buffer
 */

static int do_output_char(unsigned char c, struct tty_struct *tty, int space)
{
	struct n_tty_data *ldata = tty->disc_data;
	int	spaces;

	if (!space)
		return -1;

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

	tty_put_char(tty, c);
	return 1;
}

/**
 *	process_output			-	output post processor
 *	@c: character (or partial unicode symbol)
 *	@tty: terminal device
 *
 *	Output one character with OPOST processing.
 *	Returns -1 when the output device is full and the character
 *	must be retried.
 *
 *	Locking: output_lock to protect column state and space left
 *		 (also, this is called from n_tty_write under the
 *		  tty layer write lock)
 */

static int process_output(unsigned char c, struct tty_struct *tty)
{
	struct n_tty_data *ldata = tty->disc_data;
	int	space, retval;

	mutex_lock(&ldata->output_lock);

	space = tty_write_room(tty);
	retval = do_output_char(c, tty, space);

	mutex_unlock(&ldata->output_lock);
	if (retval < 0)
		return -1;
	else
		return 0;
}

/**
 *	process_output_block		-	block post processor
 *	@tty: terminal device
 *	@buf: character buffer
 *	@nr: number of bytes to output
 *
 *	Output a block of characters with OPOST processing.
 *	Returns the number of characters output.
 *
 *	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.
 *
 *	Locking: output_lock to protect column state and space left
 *		 (also, this is called from n_tty_write under the
 *		  tty layer write lock)
 */

static ssize_t process_output_block(struct tty_struct *tty,
				    const unsigned char *buf, unsigned int nr)
{
	struct n_tty_data *ldata = tty->disc_data;
	int	space;
	int	i;
	const unsigned char *cp;

	mutex_lock(&ldata->output_lock);

	space = tty_write_room(tty);
	if (!space) {
		mutex_unlock(&ldata->output_lock);
		return 0;
	}
	if (nr > space)
		nr = space;

	for (i = 0, cp = buf; i < nr; i++, cp++) {
		unsigned char c = *cp;

		switch (c) {
		case '\n':
			if (O_ONLRET(tty))
				ldata->column = 0;
			if (O_ONLCR(tty))
				goto break_out;
			ldata->canon_column = ldata->column;
			break;
		case '\r':
			if (O_ONOCR(tty) && ldata->column == 0)
				goto break_out;
			if (O_OCRNL(tty))
				goto break_out;
			ldata->canon_column = ldata->column = 0;
			break;
		case '\t':
			goto break_out;
		case '\b':
			if (ldata->column > 0)
				ldata->column--;
			break;
		default:
			if (!iscntrl(c)) {
				if (O_OLCUC(tty))
					goto break_out;
				if (!is_continuation(c, tty))
					ldata->column++;
			}
			break;
		}
	}
break_out:
	i = tty->ops->write(tty, buf, i);

	mutex_unlock(&ldata->output_lock);
	return i;
}

/**
 *	process_echoes	-	write pending echo characters
 *	@tty: terminal device
 *
 *	Write previously buffered echo (and other ldisc-generated)
 *	characters to the tty.
 *
 *	Characters generated by the ldisc (including echoes) need to
 *	be buffered because the driver's write buffer can fill during
 *	heavy program output.  Echoing straight to the driver will
 *	often fail under these conditions, causing lost characters and
 *	resulting mismatches of ldisc state information.
 *
 *	Since the ldisc state must represent the characters actually sent
 *	to the driver at the time of the write, operations like certain
 *	changes in column state are also saved in the buffer and executed
 *	here.
 *
 *	A circular fifo buffer is used so that the most recent characters
 *	are prioritized.  Also, when control characters are echoed with a
 *	prefixed "^", the pair is treated atomically and thus not separated.
 *
 *	Locking: callers must hold output_lock
 */

static size_t __process_echoes(struct tty_struct *tty)
{
	struct n_tty_data *ldata = tty->disc_data;
	int	space, old_space;
	size_t tail;
	unsigned char c;

	old_space = space = tty_write_room(tty);

	tail = ldata->echo_tail;
	while (MASK(ldata->echo_commit) != MASK(tail)) {
		c = echo_buf(ldata, tail);
		if (c == ECHO_OP_START) {
			unsigned char op;
			int no_space_left = 0;

			/*
			 * Since add_echo_byte() is called without holding
			 * output_lock, we might see only portion of multi-byte
			 * operation.
			 */
			if (MASK(ldata->echo_commit) == MASK(tail + 1))
				goto not_yet_stored;
			/*
			 * If the buffer byte is the start of a multi-byte
			 * operation, get the next byte, which is either the
			 * op code or a control character value.
			 */
			op = echo_buf(ldata, tail + 1);

			switch (op) {
				unsigned int num_chars, num_bs;

			case ECHO_OP_ERASE_TAB:
				if (MASK(ldata->echo_commit) == MASK(tail + 2))
					goto not_yet_stored;
				num_chars = echo_buf(ldata, tail + 2);

				/*
				 * Determine how many columns to go back
				 * in order to erase the tab.
				 * This depends on the number of columns
				 * used by other characters within the tab
				 * area.  If this (modulo 8) count is from
				 * the start of input rather than from a
				 * previous tab, we offset by canon column.
				 * Otherwise, tab spacing is normal.
				 */
				if (!(num_chars & 0x80))
					num_chars += ldata->canon_column;
				num_bs = 8 - (num_chars & 7);

				if (num_bs > space) {
					no_space_left = 1;
					break;
				}
				space -= num_bs;
				while (num_bs--) {
					tty_put_char(tty, '\b');
					if (ldata->column > 0)
						ldata->column--;
				}
				tail += 3;
				break;

			case ECHO_OP_SET_CANON_COL:
				ldata->canon_column = ldata->column;
				tail += 2;
				break;

			case ECHO_OP_MOVE_BACK_COL:
				if (ldata->column > 0)
					ldata->column--;
				tail += 2;
				break;

			case ECHO_OP_START:
				/* This is an escaped echo op start code */
				if (!space) {
					no_space_left = 1;
					break;
				}
				tty_put_char(tty, ECHO_OP_START);
				ldata->column++;
				space--;
				tail += 2;
				break;

			default:
				/*
				 * If the op is not a special byte code,
				 * it is a ctrl char tagged to be echoed
				 * as "^X" (where X is the letter
				 * representing the control char).
				 * Note that we must ensure there is
				 * enough space for the whole ctrl pair.
				 *
				 */
				if (space < 2) {
					no_space_left = 1;
					break;
				}
				tty_put_char(tty, '^');
				tty_put_char(tty, op ^ 0100);
				ldata->column += 2;
				space -= 2;
				tail += 2;
			}

			if (no_space_left)
				break;
		} else {
			if (O_OPOST(tty)) {
				int retval = do_output_char(c, tty, space);
				if (retval < 0)
					break;
				space -= retval;
			} else {
				if (!space)
					break;
				tty_put_char(tty, c);
				space -= 1;
			}
			tail += 1;
		}
	}

	/* If the echo buffer is nearly full (so that the possibility exists
	 * of echo overrun before the next commit), then discard enough
	 * data at the tail to prevent a subsequent overrun */
	while (ldata->echo_commit > tail &&
	       ldata->echo_commit - tail >= ECHO_DISCARD_WATERMARK) {
		if (echo_buf(ldata, tail) == ECHO_OP_START) {
			if (echo_buf(ldata, tail + 1) == ECHO_OP_ERASE_TAB)
				tail += 3;
			else
				tail += 2;
		} else
			tail++;
	}

 not_yet_stored:
	ldata->echo_tail = tail;
	return old_space - space;
}

static void commit_echoes(struct tty_struct *tty)
{
	struct n_tty_data *ldata = tty->disc_data;
	size_t nr, old, echoed;
	size_t head;

	mutex_lock(&ldata->output_lock);
	head = ldata->echo_head;
	ldata->echo_mark = head;
	old = ldata->echo_commit - ldata->echo_tail;

	/* Process committed echoes if the accumulated # of bytes
	 * is over the threshold (and try again each time another
	 * block is accumulated) */
	nr = head - ldata->echo_tail;
	if (nr < ECHO_COMMIT_WATERMARK ||
	    (nr % ECHO_BLOCK > old % ECHO_BLOCK)) {
		mutex_unlock(&ldata->output_lock);
		return;
	}

	ldata->echo_commit = head;
	echoed = __process_echoes(tty);
	mutex_unlock(&ldata->output_lock);

	if (echoed && tty->ops->flush_chars)
		tty->ops->flush_chars(tty);
}

static void process_echoes(struct tty_struct *tty)
{
	struct n_tty_data *ldata = tty->disc_data;
	size_t echoed;

	if (ldata->echo_mark == ldata->echo_tail)
		return;

	mutex_lock(&ldata->output_lock);
	ldata->echo_commit = ldata->echo_mark;
	echoed = __process_echoes(tty);
	mutex_unlock(&ldata->output_lock);

	if (echoed && tty->ops->flush_chars)
		tty->ops->flush_chars(tty);
}

/* NB: echo_mark and echo_head should be equivalent here */
static void flush_echoes(struct tty_struct *tty)
{
	struct n_tty_data *ldata = tty->disc_data;

	if ((!L_ECHO(tty) && !L_ECHONL(tty)) ||
	    ldata->echo_commit == ldata->echo_head)
		return;

	mutex_lock(&ldata->output_lock);
	ldata->echo_commit = ldata->echo_head;
	__process_echoes(tty);
	mutex_unlock(&ldata->output_lock);
}

/**
 *	add_echo_byte	-	add a byte to the echo buffer
 *	@c: unicode byte to echo
 *	@ldata: n_tty data
 *
 *	Add a character or operation byte to the echo buffer.
 */

static inline void add_echo_byte(unsigned char c, struct n_tty_data *ldata)
{
	*echo_buf_addr(ldata, ldata->echo_head) = c;
	smp_wmb(); /* Matches smp_rmb() in echo_buf(). */
	ldata->echo_head++;
}

/**
 *	echo_move_back_col	-	add operation to move back a column
 *	@ldata: n_tty data
 *
 *	Add an operation to the echo buffer to move back one column.
 */

static void echo_move_back_col(struct n_tty_data *ldata)
{
	add_echo_byte(ECHO_OP_START, ldata);
	add_echo_byte(ECHO_OP_MOVE_BACK_COL, ldata);
}

/**
 *	echo_set_canon_col	-	add operation to set the canon column
 *	@ldata: n_tty data
 *
 *	Add an operation to the echo buffer to set the canon column
 *	to the current column.
 */

static void echo_set_canon_col(struct n_tty_data *ldata)
{
	add_echo_byte(ECHO_OP_START, ldata);
	add_echo_byte(ECHO_OP_SET_CANON_COL, ldata);
}

/**
 *	echo_erase_tab	-	add operation to erase a tab
 *	@num_chars: number of character columns already used
 *	@after_tab: true if num_chars starts after a previous tab
 *	@ldata: n_tty data
 *
 *	Add an operation to the echo buffer to erase a tab.
 *
 *	Called by the eraser function, which knows how many character
 *	columns have been used since either a previous tab or the start
 *	of input.  This information will be used later, along with
 *	canon column (if applicable), to go back the correct number
 *	of columns.
 */

static void echo_erase_tab(unsigned int num_chars, int after_tab,
			   struct n_tty_data *ldata)
{
	add_echo_byte(ECHO_OP_START, ldata);
	add_echo_byte(ECHO_OP_ERASE_TAB, ldata);

	/* We only need to know this modulo 8 (tab spacing) */
	num_chars &= 7;

	/* Set the high bit as a flag if num_chars is after a previous tab */
	if (after_tab)
		num_chars |= 0x80;

	add_echo_byte(num_chars, ldata);
}

/**
 *	echo_char_raw	-	echo a character raw
 *	@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.
 *
 *	This variant does not treat control characters specially.
 */

static void echo_char_raw(unsigned char c, struct n_tty_data *ldata)
{
	if (c == ECHO_OP_START) {
		add_echo_byte(ECHO_OP_START, ldata);
		add_echo_byte(ECHO_OP_START, ldata);
	} else {
		add_echo_byte(c, ldata);
	}
}

/**
 *	echo_char	-	echo a character
 *	@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.
 *
 *	This variant tags control characters to be echoed as "^X"
 *	(where X is the letter representing the control char).
 */

static void echo_char(unsigned char c, struct tty_struct *tty)
{
	struct n_tty_data *ldata = tty->disc_data;

	if (c == ECHO_OP_START) {
		add_echo_byte(ECHO_OP_START, ldata);
		add_echo_byte(ECHO_OP_START, ldata);
	} else {
		if (L_ECHOCTL(tty) && iscntrl(c) && c != '\t')
			add_echo_byte(ECHO_OP_START, ldata);
		add_echo_byte(c, ldata);
	}
}

/**
 *	finish_erasing		-	complete erase
 *	@ldata: n_tty data
 */

static inline void finish_erasing(struct n_tty_data *ldata)
{
	if (ldata->erasing) {
		echo_char_raw('/', ldata);
		ldata->erasing = 0;
	}
}

/**
 *	eraser		-	handle erase function
 *	@c: character input
 *	@tty: terminal device
 *
 *	Perform erase and necessary output when an erase character is
 *	present in the stream from the driver layer. Handles the complexities
 *	of UTF-8 multibyte symbols.
 *
 *	n_tty_receive_buf()/producer path:
 *		caller holds non-exclusive termios_rwsem
 */

static void eraser(unsigned char c, struct tty_struct *tty)
{
	struct n_tty_data *ldata = tty->disc_data;
	enum { ERASE, WERASE, KILL } kill_type;
	size_t head;
	size_t cnt;
	int seen_alnums;

	if (ldata->read_head == ldata->canon_head) {
		/* process_output('\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)) {
			ldata->read_head = ldata->canon_head;
			return;
		}
		if (!L_ECHOK(tty) || !L_ECHOKE(tty) || !L_ECHOE(tty)) {
			ldata->read_head = ldata->canon_head;
			finish_erasing(ldata);
			echo_char(KILL_CHAR(tty), tty);
			/* Add a newline if ECHOK is on and ECHOKE is off. */
			if (L_ECHOK(tty))
				echo_char_raw('\n', ldata);
			return;
		}
		kill_type = KILL;
	}

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

		/* erase a single possibly multibyte character */
		do {
			head--;
			c = read_buf(ldata, head);
		} while (is_continuation(c, tty) &&
			 MASK(head) != MASK(ldata->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 = ldata->read_head - head;
		ldata->read_head = head;
		if (L_ECHO(tty)) {
			if (L_ECHOPRT(tty)) {
				if (!ldata->erasing) {
					echo_char_raw('\\', ldata);
					ldata->erasing = 1;
				}
				/* if cnt > 1, output a multi-byte character */
				echo_char(c, tty);
				while (--cnt > 0) {
					head++;
					echo_char_raw(read_buf(ldata, head), ldata);
					echo_move_back_col(ldata);
				}
			} else if (kill_type == ERASE && !L_ECHOE(tty)) {
				echo_char(ERASE_CHAR(tty), tty);
			} else if (c == '\t') {
				unsigned int num_chars = 0;
				int after_tab = 0;
				size_t tail = ldata->read_head;

				/*
				 * Count the columns used for characters
				 * since the start of input or after a
				 * previous tab.
				 * This info is used to go back the correct
				 * number of columns.
				 */
				while (MASK(tail) != MASK(ldata->canon_head)) {
					tail--;
					c = read_buf(ldata, tail);
					if (c == '\t') {
						after_tab = 1;
						break;
					} else if (iscntrl(c)) {
						if (L_ECHOCTL(tty))
							num_chars += 2;
					} else if (!is_continuation(c, tty)) {
						num_chars++;
					}
				}
				echo_erase_tab(num_chars, after_tab, ldata);
			} else {
				if (iscntrl(c) && L_ECHOCTL(tty)) {
					echo_char_raw('\b', ldata);
					echo_char_raw(' ', ldata);
					echo_char_raw('\b', ldata);
				}
				if (!iscntrl(c) || L_ECHOCTL(tty)) {
					echo_char_raw('\b', ldata);
					echo_char_raw(' ', ldata);
					echo_char_raw('\b', ldata);
				}
			}
		}
		if (kill_type == ERASE)
			break;
	}
	if (ldata->read_head == ldata->canon_head && L_ECHO(tty))
		finish_erasing(ldata);
}

/**
 *	isig		-	handle the ISIG optio
 *	@sig: signal
 *	@tty: terminal
 *
 *	Called when a signal is being sent due to terminal input.
 *	Called from the driver receive_buf path so serialized.
 *
 *	Performs input and output flush if !NOFLSH. In this context, the echo
 *	buffer is 'output'. The signal is processed first to alert any current
 *	readers or writers to discontinue and exit their i/o loops.
 *
 *	Locking: ctrl_lock
 */

static void __isig(int sig, struct tty_struct *tty)
{
	struct pid *tty_pgrp = tty_get_pgrp(tty);
	if (tty_pgrp) {
		kill_pgrp(tty_pgrp, sig, 1);
		put_pid(tty_pgrp);
	}
}

static void isig(int sig, struct tty_struct *tty)
{
	struct n_tty_data *ldata = tty->disc_data;

	if (L_NOFLSH(tty)) {
		/* signal only */
		__isig(sig, tty);

	} else { /* signal and flush */
		up_read(&tty->termios_rwsem);
		down_write(&tty->termios_rwsem);

		__isig(sig, tty);

		/* clear echo buffer */
		mutex_lock(&ldata->output_lock);
		ldata->echo_head = ldata->echo_tail = 0;
		ldata->echo_mark = ldata->echo_commit = 0;
		mutex_unlock(&ldata->output_lock);

		/* clear output buffer */
		tty_driver_flush_buffer(tty);

		/* clear input buffer */
		reset_buffer_flags(tty->disc_data);

		/* notify pty master of flush */
		if (tty->link)
			n_tty_packet_mode_flush(tty);

		up_write(&tty->termios_rwsem);
		down_read(&tty->termios_rwsem);
	}
}

/**
 *	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.
 *
 *	n_tty_receive_buf()/producer path:
 *		caller holds non-exclusive termios_rwsem
 *
 *	Note: may get exclusive termios_rwsem if flushing input buffer
 */

static void n_tty_receive_break(struct tty_struct *tty)
{
	struct n_tty_data *ldata = tty->disc_data;

	if (I_IGNBRK(tty))
		return;
	if (I_BRKINT(tty)) {
		isig(SIGINT, tty);
		return;
	}
	if (I_PARMRK(tty)) {
		put_tty_queue('\377', ldata);
		put_tty_queue('\0', ldata);
	}
	put_tty_queue('\0', ldata);
}

/**
 *	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 void n_tty_receive_overrun(struct tty_struct *tty)
{
	struct n_tty_data *ldata = tty->disc_data;

	ldata->num_overrun++;
	if (time_after(jiffies, ldata->overrun_time + HZ) ||
			time_after(ldata->overrun_time, jiffies)) {
		tty_warn(tty, "%d input overrun(s)\n", ldata->num_overrun);
		ldata->overrun_time = jiffies;
		ldata->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 necessary.
 *
 *	n_tty_receive_buf()/producer path:
 *		caller holds non-exclusive termios_rwsem
 */
static void n_tty_receive_parity_error(struct tty_struct *tty, unsigned char c)
{
	struct n_tty_data *ldata = tty->disc_data;

	if (I_INPCK(tty)) {
		if (I_IGNPAR(tty))
			return;
		if (I_PARMRK(tty)) {
			put_tty_queue('\377', ldata);
			put_tty_queue('\0', ldata);
			put_tty_queue(c, ldata);
		} else
			put_tty_queue('\0', ldata);
	} else
		put_tty_queue(c, ldata);
}

static void
n_tty_receive_signal_char(struct tty_struct *tty, int signal, unsigned char c)
{
	isig(signal, tty);
	if (I_IXON(tty))
		start_tty(tty);
	if (L_ECHO(tty)) {
		echo_char(c, tty);
		commit_echoes(tty);
	} else
		process_echoes(tty);
	return;
}

/**
 *	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.
 *
 *	n_tty_receive_buf()/producer path:
 *		caller holds non-exclusive termios_rwsem
 *		publishes canon_head if canonical mode is active
 *
 *	Returns 1 if LNEXT was received, else returns 0
 */

static int
n_tty_receive_char_special(struct tty_struct *tty, unsigned char c)
{
	struct n_tty_data *ldata = tty->disc_data;

	if (I_IXON(tty)) {
		if (c == START_CHAR(tty)) {
			start_tty(tty);
			process_echoes(tty);
			return 0;
		}
		if (c == STOP_CHAR(tty)) {
			stop_tty(tty);
			return 0;
		}
	}

	if (L_ISIG(tty)) {
		if (c == INTR_CHAR(tty)) {
			n_tty_receive_signal_char(tty, SIGINT, c);
			return 0;
		} else if (c == QUIT_CHAR(tty)) {
			n_tty_receive_signal_char(tty, SIGQUIT, c);
			return 0;
		} else if (c == SUSP_CHAR(tty)) {
			n_tty_receive_signal_char(tty, SIGTSTP, c);
			return 0;
		}
	}

	if (tty->stopped && !tty->flow_stopped && I_IXON(tty) && I_IXANY(tty)) {
		start_tty(tty);
		process_echoes(tty);
	}

	if (c == '\r') {
		if (I_IGNCR(tty))
			return 0;
		if (I_ICRNL(tty))
			c = '\n';
	} else if (c == '\n' && I_INLCR(tty))
		c = '\r';

	if (ldata->icanon) {
		if (c == ERASE_CHAR(tty) || c == KILL_CHAR(tty) ||
		    (c == WERASE_CHAR(tty) && L_IEXTEN(tty))) {
			eraser(c, tty);
			commit_echoes(tty);
			return 0;
		}
		if (c == LNEXT_CHAR(tty) && L_IEXTEN(tty)) {
			ldata->lnext = 1;
			if (L_ECHO(tty)) {
				finish_erasing(ldata);
				if (L_ECHOCTL(tty)) {
					echo_char_raw('^', ldata);
					echo_char_raw('\b', ldata);
					commit_echoes(tty);
				}
			}
			return 1;
		}
		if (c == REPRINT_CHAR(tty) && L_ECHO(tty) && L_IEXTEN(tty)) {
			size_t tail = ldata->canon_head;

			finish_erasing(ldata);
			echo_char(c, tty);
			echo_char_raw('\n', ldata);
			while (MASK(tail) != MASK(ldata->read_head)) {
				echo_char(read_buf(ldata, tail), tty);
				tail++;
			}
			commit_echoes(tty);
			return 0;
		}
		if (c == '\n') {
			if (L_ECHO(tty) || L_ECHONL(tty)) {
				echo_char_raw('\n', ldata);
				commit_echoes(tty);
			}
			goto handle_newline;
		}
		if (c == EOF_CHAR(tty)) {
			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)) {
				/* Record the column of first canon char. */
				if (ldata->canon_head == ldata->read_head)
					echo_set_canon_col(ldata);
				echo_char(c, tty);
				commit_echoes(tty);
			}
			/*
			 * XXX does PARMRK doubling happen for
			 * EOL_CHAR and EOL2_CHAR?
			 */
			if (c == (unsigned char) '\377' && I_PARMRK(tty))
				put_tty_queue(c, ldata);

handle_newline:
			set_bit(ldata->read_head & (N_TTY_BUF_SIZE - 1), ldata->read_flags);
			put_tty_queue(c, ldata);
			smp_store_release(&ldata->canon_head, ldata->read_head);
			kill_fasync(&tty->fasync, SIGIO, POLL_IN);
			wake_up_interruptible_poll(&tty->read_wait, EPOLLIN);
			return 0;
		}
	}

	if (L_ECHO(tty)) {
		finish_erasing(ldata);
		if (c == '\n')
			echo_char_raw('\n', ldata);
		else {
			/* Record the column of first canon char. */
			if (ldata->canon_head == ldata->read_head)
				echo_set_canon_col(ldata);
			echo_char(c, tty);
		}
		commit_echoes(tty);
	}

	/* PARMRK doubling check */
	if (c == (unsigned char) '\377' && I_PARMRK(tty))
		put_tty_queue(c, ldata);

	put_tty_queue(c, ldata);
	return 0;
}

static inline void
n_tty_receive_char_inline(struct tty_struct *tty, unsigned char c)
{
	struct n_tty_data *ldata = tty->disc_data;

	if (tty->stopped && !tty->flow_stopped && I_IXON(tty) && I_IXANY(tty)) {
		start_tty(tty);
		process_echoes(tty);
	}
	if (L_ECHO(tty)) {
		finish_erasing(ldata);
		/* Record the column of first canon char. */
		if (ldata->canon_head == ldata->read_head)
			echo_set_canon_col(ldata);
		echo_char(c, tty);
		commit_echoes(tty);
	}
	/* PARMRK doubling check */
	if (c == (unsigned char) '\377' && I_PARMRK(tty))
		put_tty_queue(c, ldata);
	put_tty_queue(c, ldata);
}

static void n_tty_receive_char(struct tty_struct *tty, unsigned char c)
{
	n_tty_receive_char_inline(tty, c);
}

static inline void
n_tty_receive_char_fast(struct tty_struct *tty, unsigned char c)
{
	struct n_tty_data *ldata = tty->disc_data;

	if (tty->stopped && !tty->flow_stopped && I_IXON(tty) && I_IXANY(tty)) {
		start_tty(tty);
		process_echoes(tty);
	}
	if (L_ECHO(tty)) {
		finish_erasing(ldata);
		/* Record the column of first canon char. */
		if (ldata->canon_head == ldata->read_head)
			echo_set_canon_col(ldata);
		echo_char(c, tty);
		commit_echoes(tty);
	}
	put_tty_queue(c, ldata);
}

static void n_tty_receive_char_closing(struct tty_struct *tty, unsigned char c)
{
	if (I_ISTRIP(tty))
		c &= 0x7f;
	if (I_IUCLC(tty) && L_IEXTEN(tty))
		c = tolower(c);

	if (I_IXON(tty)) {
		if (c == STOP_CHAR(tty))
			stop_tty(tty);
		else if (c == START_CHAR(tty) ||
			 (tty->stopped && !tty->flow_stopped && I_IXANY(tty) &&
			  c != INTR_CHAR(tty) && c != QUIT_CHAR(tty) &&
			  c != SUSP_CHAR(tty))) {
			start_tty(tty);
			process_echoes(tty);
		}
	}
}

static void
n_tty_receive_char_flagged(struct tty_struct *tty, unsigned char c, char flag)
{
	switch (flag) {
	case TTY_BREAK:
		n_tty_receive_break(tty);
		break;
	case TTY_PARITY:
	case TTY_FRAME:
		n_tty_receive_parity_error(tty, c);
		break;
	case TTY_OVERRUN:
		n_tty_receive_overrun(tty);
		break;
	default:
		tty_err(tty, "unknown flag %d\n", flag);
		break;
	}
}

static void
n_tty_receive_char_lnext(struct tty_struct *tty, unsigned char c, char flag)
{
	struct n_tty_data *ldata = tty->disc_data;

	ldata->lnext = 0;
	if (likely(flag == TTY_NORMAL)) {
		if (I_ISTRIP(tty))
			c &= 0x7f;
		if (I_IUCLC(tty) && L_IEXTEN(tty))
			c = tolower(c);
		n_tty_receive_char(tty, c);
	} else
		n_tty_receive_char_flagged(tty, c, flag);
}

static void
n_tty_receive_buf_real_raw(struct tty_struct *tty, const unsigned char *cp,
			   char *fp, int count)
{
	struct n_tty_data *ldata = tty->disc_data;
	size_t n, head;

	head = ldata->read_head & (N_TTY_BUF_SIZE - 1);
	n = min_t(size_t, count, N_TTY_BUF_SIZE - head);
	memcpy(read_buf_addr(ldata, head), cp, n);
	ldata->read_head += n;
	cp += n;
	count -= n;

	head = ldata->read_head & (N_TTY_BUF_SIZE - 1);
	n = min_t(size_t, count, N_TTY_BUF_SIZE - head);
	memcpy(read_buf_addr(ldata, head), cp, n);
	ldata->read_head += n;
}

static void
n_tty_receive_buf_raw(struct tty_struct *tty, const unsigned char *cp,
		      char *fp, int count)
{
	struct n_tty_data *ldata = tty->disc_data;
	char flag = TTY_NORMAL;

	while (count--) {
		if (fp)
			flag = *fp++;
		if (likely(flag == TTY_NORMAL))
			put_tty_queue(*cp++, ldata);
		else
			n_tty_receive_char_flagged(tty, *cp++, flag);
	}
}

static void
n_tty_receive_buf_closing(struct tty_struct *tty, const unsigned char *cp,
			  char *fp, int count)
{
	char flag = TTY_NORMAL;

	while (count--) {
		if (fp)
			flag = *fp++;
		if (likely(flag == TTY_NORMAL))
			n_tty_receive_char_closing(tty, *cp++);
	}
}

static void
n_tty_receive_buf_standard(struct tty_struct *tty, const unsigned char *cp,
			  char *fp, int count)
{
	struct n_tty_data *ldata = tty->disc_data;
	char flag = TTY_NORMAL;

	while (count--) {
		if (fp)
			flag = *fp++;
		if (likely(flag == TTY_NORMAL)) {
			unsigned char c = *cp++;

			if (I_ISTRIP(tty))
				c &= 0x7f;
			if (I_IUCLC(tty) && L_IEXTEN(tty))
				c = tolower(c);
			if (L_EXTPROC(tty)) {
				put_tty_queue(c, ldata);
				continue;
			}
			if (!test_bit(c, ldata->char_map))
				n_tty_receive_char_inline(tty, c);
			else if (n_tty_receive_char_special(tty, c) && count) {
				if (fp)
					flag = *fp++;
				n_tty_receive_char_lnext(tty, *cp++, flag);
				count--;
			}
		} else
			n_tty_receive_char_flagged(tty, *cp++, flag);
	}
}

static void
n_tty_receive_buf_fast(struct tty_struct *tty, const unsigned char *cp,
		       char *fp, int count)
{
	struct n_tty_data *ldata = tty->disc_data;
	char flag = TTY_NORMAL;

	while (count--) {
		if (fp)
			flag = *fp++;
		if (likely(flag == TTY_NORMAL)) {
			unsigned char c = *cp++;

			if (!test_bit(c, ldata->char_map))
				n_tty_receive_char_fast(tty, c);
			else if (n_tty_receive_char_special(tty, c) && count) {
				if (fp)
					flag = *fp++;
				n_tty_receive_char_lnext(tty, *cp++, flag);
				count--;
			}
		} else
			n_tty_receive_char_flagged(tty, *cp++, flag);
	}
}

static void __receive_buf(struct tty_struct *tty, const unsigned char *cp,
			  char *fp, int count)
{
	struct n_tty_data *ldata = tty->disc_data;
	bool preops = I_ISTRIP(tty) || (I_IUCLC(tty) && L_IEXTEN(tty));

	if (ldata->real_raw)
		n_tty_receive_buf_real_raw(tty, cp, fp, count);
	else if (ldata->raw || (L_EXTPROC(tty) && !preops))
		n_tty_receive_buf_raw(tty, cp, fp, count);
	else if (tty->closing && !L_EXTPROC(tty))
		n_tty_receive_buf_closing(tty, cp, fp, count);
	else {
		if (ldata->lnext) {
			char flag = TTY_NORMAL;

			if (fp)
				flag = *fp++;
			n_tty_receive_char_lnext(tty, *cp++, flag);
			count--;
		}

		if (!preops && !I_PARMRK(tty))
			n_tty_receive_buf_fast(tty, cp, fp, count);
		else
			n_tty_receive_buf_standard(tty, cp, fp, count);

		flush_echoes(tty);
		if (tty->ops->flush_chars)
			tty->ops->flush_chars(tty);
	}

	if (ldata->icanon && !L_EXTPROC(tty))
		return;

	/* publish read_head to consumer */
	smp_store_release(&ldata->commit_head, ldata->read_head);

	if (read_cnt(ldata)) {
		kill_fasync(&tty->fasync, SIGIO, POLL_IN);
		wake_up_interruptible_poll(&tty->read_wait, EPOLLIN);
	}
}

/**
 *	n_tty_receive_buf_common	-	process input
 *	@tty: device to receive input
 *	@cp: input chars
 *	@fp: flags for each char (if NULL, all chars are TTY_NORMAL)
 *	@count: number of input chars in @cp
 *
 *	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)
 *
 *	Returns the # of input chars from @cp which were processed.
 *
 *	In canonical mode, the maximum line length is 4096 chars (including
 *	the line termination char); lines longer than 4096 chars are
 *	truncated. After 4095 chars, input data is still processed but
 *	not stored. Overflow processing ensures the tty can always
 *	receive more input until at least one line can be read.
 *
 *	In non-canonical mode, the read buffer will only accept 4095 chars;
 *	this provides the necessary space for a newline char if the input
 *	mode is switched to canonical.
 *
 *	Note it is possible for the read buffer to _contain_ 4096 chars
 *	in non-canonical mode: the read buffer could already contain the
 *	maximum canon line of 4096 chars when the mode is switched to
 *	non-canonical.
 *
 *	n_tty_receive_buf()/producer path:
 *		claims non-exclusive termios_rwsem
 *		publishes commit_head or canon_head
 */
static int
n_tty_receive_buf_common(struct tty_struct *tty, const unsigned char *cp,
			 char *fp, int count, int flow)
{
	struct n_tty_data *ldata = tty->disc_data;
	int room, n, rcvd = 0, overflow;

	down_read(&tty->termios_rwsem);

	do {
		/*
		 * When PARMRK is set, each input char may take up to 3 chars
		 * in the read buf; reduce the buffer space avail by 3x
		 *
		 * 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.
		 *
		 * paired with store in *_copy_from_read_buf() -- guarantees
		 * the consumer has loaded the data in read_buf up to the new
		 * read_tail (so this producer will not overwrite unread data)
		 */
		size_t tail = smp_load_acquire(&ldata->read_tail);

		room = N_TTY_BUF_SIZE - (ldata->read_head - tail);
		if (I_PARMRK(tty))
			room = (room + 2) / 3;
		room--;
		if (room <= 0) {
			overflow = ldata->icanon && ldata->canon_head == tail;
			if (overflow && room < 0)
				ldata->read_head--;
			room = overflow;
			ldata->no_room = flow && !room;
		} else
			overflow = 0;

		n = min(count, room);
		if (!n)
			break;

		/* ignore parity errors if handling overflow */
		if (!overflow || !fp || *fp != TTY_PARITY)
			__receive_buf(tty, cp, fp, n);

		cp += n;
		if (fp)
			fp += n;
		count -= n;
		rcvd += n;
	} while (!test_bit(TTY_LDISC_CHANGING, &tty->flags));

	tty->receive_room = room;

	/* Unthrottle if handling overflow on pty */
	if (tty->driver->type == TTY_DRIVER_TYPE_PTY) {
		if (overflow) {
			tty_set_flow_change(tty, TTY_UNTHROTTLE_SAFE);
			tty_unthrottle_safe(tty);
			__tty_set_flow_change(tty, 0);
		}
	} else
		n_tty_check_throttle(tty);

	up_read(&tty->termios_rwsem);

	return rcvd;
}

static void n_tty_receive_buf(struct tty_struct *tty, const unsigned char *cp,
			      char *fp, int count)
{
	n_tty_receive_buf_common(tty, cp, fp, count, 0);
}

static int n_tty_receive_buf2(struct tty_struct *tty, const unsigned char *cp,
			      char *fp, int count)
{
	return n_tty_receive_buf_common(tty, cp, fp, count, 1);
}

/**
 *	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.
 *
 *	Locking: Caller holds tty->termios_rwsem
 */

static void n_tty_set_termios(struct tty_struct *tty, struct ktermios *old)
{
	struct n_tty_data *ldata = tty->disc_data;

	if (!old || (old->c_lflag ^ tty->termios.c_lflag) & (ICANON | EXTPROC)) {
		bitmap_zero(ldata->read_flags, N_TTY_BUF_SIZE);
		ldata->line_start = ldata->read_tail;
		if (!L_ICANON(tty) || !read_cnt(ldata)) {
			ldata->canon_head = ldata->read_tail;
			ldata->push = 0;
		} else {
			set_bit((ldata->read_head - 1) & (N_TTY_BUF_SIZE - 1),
				ldata->read_flags);
			ldata->canon_head = ldata->read_head;
			ldata->push = 1;
		}
		ldata->commit_head = ldata->read_head;
		ldata->erasing = 0;
		ldata->lnext = 0;
	}

	ldata->icanon = (L_ICANON(tty) != 0);

	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)) {
		bitmap_zero(ldata->char_map, 256);

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

		if (L_ICANON(tty)) {
			set_bit(ERASE_CHAR(tty), ldata->char_map);
			set_bit(KILL_CHAR(tty), ldata->char_map);
			set_bit(EOF_CHAR(tty), ldata->char_map);
			set_bit('\n', ldata->char_map);
			set_bit(EOL_CHAR(tty), ldata->char_map);
			if (L_IEXTEN(tty)) {
				set_bit(WERASE_CHAR(tty), ldata->char_map);
				set_bit(LNEXT_CHAR(tty), ldata->char_map);
				set_bit(EOL2_CHAR(tty), ldata->char_map);
				if (L_ECHO(tty))
					set_bit(REPRINT_CHAR(tty),
						ldata->char_map);
			}
		}
		if (I_IXON(tty)) {
			set_bit(START_CHAR(tty), ldata->char_map);
			set_bit(STOP_CHAR(tty), ldata->char_map);
		}
		if (L_ISIG(tty)) {
			set_bit(INTR_CHAR(tty), ldata->char_map);
			set_bit(QUIT_CHAR(tty), ldata->char_map);
			set_bit(SUSP_CHAR(tty), ldata->char_map);
		}
		clear_bit(__DISABLED_CHAR, ldata->char_map);
		ldata->raw = 0;
		ldata->real_raw = 0;
	} else {
		ldata->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))
			ldata->real_raw = 1;
		else
			ldata->real_raw = 0;
	}
	/*
	 * Fix tty hang when I_IXON(tty) is cleared, but the tty
	 * been stopped by STOP_CHAR(tty) before it.
	 */
	if (!I_IXON(tty) && old && (old->c_iflag & IXON) && !tty->flow_stopped) {
		start_tty(tty);
		process_echoes(tty);
	}

	/* The termios change make the tty ready for I/O */
	wake_up_interruptible(&tty->write_wait);
	wake_up_interruptible(&tty->read_wait);
}

/**
 *	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)
{
	struct n_tty_data *ldata = tty->disc_data;

	if (tty->link)
		n_tty_packet_mode_flush(tty);

	vfree(ldata);
	tty->disc_data = 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)
{
	struct n_tty_data *ldata;

	/* Currently a malloc failure here can panic */
	ldata = vzalloc(sizeof(*ldata));
	if (!ldata)
		return -ENOMEM;

	ldata->overrun_time = jiffies;
	mutex_init(&ldata->atomic_read_lock);
	mutex_init(&ldata->output_lock);

	tty->disc_data = ldata;
	tty->closing = 0;
	/* indicate buffer work may resume */
	clear_bit(TTY_LDISC_HALTED, &tty->flags);
	n_tty_set_termios(tty, NULL);
	tty_unthrottle(tty);
	return 0;
}

static inline int input_available_p(struct tty_struct *tty, int poll)
{
	struct n_tty_data *ldata = tty->disc_data;
	int amt = poll && !TIME_CHAR(tty) && MIN_CHAR(tty) ? MIN_CHAR(tty) : 1;

	if (ldata->icanon && !L_EXTPROC(tty))
		return ldata->canon_head != ldata->read_tail;
	else
		return ldata->commit_head - ldata->read_tail >= amt;
}

/**
 *	copy_from_read_buf	-	copy read data directly
 *	@tty: terminal device
 *	@b: user data
 *	@nr: size of data
 *
 *	Helper function to speed up n_tty_read.  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 ldata->atomic_read_lock sem
 *
 *	n_tty_read()/consumer path:
 *		caller holds non-exclusive termios_rwsem
 *		read_tail published
 */

static int copy_from_read_buf(struct tty_struct *tty,
				      unsigned char __user **b,
				      size_t *nr)

{
	struct n_tty_data *ldata = tty->disc_data;
	int retval;
	size_t n;
	bool is_eof;
	size_t head = smp_load_acquire(&ldata->commit_head);
	size_t tail = ldata->read_tail & (N_TTY_BUF_SIZE - 1);

	retval = 0;
	n = min(head - ldata->read_tail, N_TTY_BUF_SIZE - tail);
	n = min(*nr, n);
	if (n) {
		unsigned char *from = read_buf_addr(ldata, tail);
		retval = copy_to_user(*b, from, n);
		n -= retval;
		is_eof = n == 1 && *from == EOF_CHAR(tty);
		tty_audit_add_data(tty, from, n);
		zero_buffer(tty, from, n);
		smp_store_release(&ldata->read_tail, ldata->read_tail + n);
		/* Turn single EOF into zero-length read */
		if (L_EXTPROC(tty) && ldata->icanon && is_eof &&
		    (head == ldata->read_tail))
			n = 0;
		*b += n;
		*nr -= n;
	}
	return retval;
}

/**
 *	canon_copy_from_read_buf	-	copy read data in canonical mode
 *	@tty: terminal device
 *	@b: user data
 *	@nr: size of data
 *
 *	Helper function for n_tty_read.  It is only called when ICANON is on;
 *	it copies one line of input up to and including the line-delimiting
 *	character into the user-space buffer.
 *
 *	NB: When termios is changed from non-canonical to canonical mode and
 *	the read buffer contains data, n_tty_set_termios() simulates an EOF
 *	push (as if C-d were input) _without_ the DISABLED_CHAR in the buffer.
 *	This causes data already processed as input to be immediately available
 *	as input although a newline has not been received.
 *
 *	Called under the atomic_read_lock mutex
 *
 *	n_tty_read()/consumer path:
 *		caller holds non-exclusive termios_rwsem
 *		read_tail published
 */

static int canon_copy_from_read_buf(struct tty_struct *tty,
				    unsigned char __user **b,
				    size_t *nr)
{
	struct n_tty_data *ldata = tty->disc_data;
	size_t n, size, more, c;
	size_t eol;
	size_t tail;
	int ret, found = 0;

	/* N.B. avoid overrun if nr == 0 */
	if (!*nr)
		return 0;

	n = min(*nr + 1, smp_load_acquire(&ldata->canon_head) - ldata->read_tail);

	tail = ldata->read_tail & (N_TTY_BUF_SIZE - 1);
	size = min_t(size_t, tail + n, N_TTY_BUF_SIZE);

	n_tty_trace("%s: nr:%zu tail:%zu n:%zu size:%zu\n",
		    __func__, *nr, tail, n, size);

	eol = find_next_bit(ldata->read_flags, size, tail);
	more = n - (size - tail);
	if (eol == N_TTY_BUF_SIZE && more) {
		/* scan wrapped without finding set bit */
		eol = find_next_bit(ldata->read_flags, more, 0);
		found = eol != more;
	} else
		found = eol != size;

	n = eol - tail;
	if (n > N_TTY_BUF_SIZE)
		n += N_TTY_BUF_SIZE;
	c = n + found;

	if (!found || read_buf(ldata, eol) != __DISABLED_CHAR) {
		c = min(*nr, c);
		n = c;
	}

	n_tty_trace("%s: eol:%zu found:%d n:%zu c:%zu tail:%zu more:%zu\n",
		    __func__, eol, found, n, c, tail, more);

	ret = tty_copy_to_user(tty, *b, tail, n);
	if (ret)
		return -EFAULT;
	*b += n;
	*nr -= n;

	if (found)
		clear_bit(eol, ldata->read_flags);
	smp_store_release(&ldata->read_tail, ldata->read_tail + c);

	if (found) {
		if (!ldata->push)
			ldata->line_start = ldata->read_tail;
		else
			ldata->push = 0;
		tty_audit_push();
	}
	return 0;
}

extern ssize_t redirected_tty_write(struct file *, const char __user *,
							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.
 *
 *	Locking: redirected write test is safe
 *		 current->signal->tty check is safe
 *		 ctrl_lock to safely reference tty->pgrp
 */

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)
		return 0;

	return __tty_check_change(tty, SIGTTIN);
}


/**
 *	n_tty_read		-	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.
 *
 *	n_tty_read()/consumer path:
 *		claims non-exclusive termios_rwsem
 *		publishes read_tail
 */

static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
			 unsigned char __user *buf, size_t nr)
{
	struct n_tty_data *ldata = tty->disc_data;
	unsigned char __user *b = buf;
	DEFINE_WAIT_FUNC(wait, woken_wake_function);
	int c;
	int minimum, time;
	ssize_t retval = 0;
	long timeout;
	int packet;
	size_t tail;

	c = job_control(tty, file);
	if (c < 0)
		return c;

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

	down_read(&tty->termios_rwsem);

	minimum = time = 0;
	timeout = MAX_SCHEDULE_TIMEOUT;
	if (!ldata->icanon) {
		minimum = MIN_CHAR(tty);
		if (minimum) {
			time = (HZ / 10) * TIME_CHAR(tty);
		} else {
			timeout = (HZ / 10) * TIME_CHAR(tty);
			minimum = 1;
		}
	}

	packet = tty->packet;
	tail = ldata->read_tail;

	add_wait_queue(&tty->read_wait, &wait);
	while (nr) {
		/* First test for status change. */
		if (packet && tty->link->ctrl_status) {
			unsigned char cs;
			if (b != buf)
				break;
			spin_lock_irq(&tty->link->ctrl_lock);
			cs = tty->link->ctrl_status;
			tty->link->ctrl_status = 0;
			spin_unlock_irq(&tty->link->ctrl_lock);
			if (put_user(cs, b)) {
				retval = -EFAULT;
				break;
			}
			b++;
			nr--;
			break;
		}

		if (!input_available_p(tty, 0)) {
			up_read(&tty->termios_rwsem);
			tty_buffer_flush_work(tty->port);
			down_read(&tty->termios_rwsem);
			if (!input_available_p(tty, 0)) {
				if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
					retval = -EIO;
					break;
				}
				if (tty_hung_up_p(file))
					break;
				/*
				 * Abort readers for ttys which never actually
				 * get hung up.  See __tty_hangup().
				 */
				if (test_bit(TTY_HUPPING, &tty->flags))
					break;
				if (!timeout)
					break;
				if (tty_io_nonblock(tty, file)) {
					retval = -EAGAIN;
					break;
				}
				if (signal_pending(current)) {
					retval = -ERESTARTSYS;
					break;
				}
				up_read(&tty->termios_rwsem);

				timeout = wait_woken(&wait, TASK_INTERRUPTIBLE,
						timeout);

				down_read(&tty->termios_rwsem);
				continue;
			}
		}

		if (ldata->icanon && !L_EXTPROC(tty)) {
			retval = canon_copy_from_read_buf(tty, &b, &nr);
			if (retval)
				break;
		} else {
			int uncopied;

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

			uncopied = copy_from_read_buf(tty, &b, &nr);
			uncopied += copy_from_read_buf(tty, &b, &nr);
			if (uncopied) {
				retval = -EFAULT;
				break;
			}
		}

		n_tty_check_unthrottle(tty);

		if (b - buf >= minimum)
			break;
		if (time)
			timeout = time;
	}
	if (tail != ldata->read_tail)
		n_tty_kick_worker(tty);
	up_read(&tty->termios_rwsem);

	remove_wait_queue(&tty->read_wait, &wait);
	mutex_unlock(&ldata->atomic_read_lock);

	if (b - buf)
		retval = b - buf;

	return retval;
}

/**
 *	n_tty_write		-	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.  Since the receive code will echo characters,
 *	thus calling driver write methods, the output_lock is used in
 *	the output processing functions called here as well as in the
 *	echo processing function to protect the column state and space
 *	left in the buffer.
 *
 *	This code must be sure never to sleep through a hangup.
 *
 *	Locking: output_lock to protect column state and space left
 *		 (note that the process_output*() functions take this
 *		  lock themselves)
 */

static ssize_t n_tty_write(struct tty_struct *tty, struct file *file,
			   const unsigned char *buf, size_t nr)
{
	const unsigned char *b = buf;
	DEFINE_WAIT_FUNC(wait, woken_wake_function);
	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;
	}

	down_read(&tty->termios_rwsem);

	/* Write out any echoed characters that are still pending */
	process_echoes(tty);

	add_wait_queue(&tty->write_wait, &wait);
	while (1) {
		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)) {
			while (nr > 0) {
				ssize_t num = process_output_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 (process_output(c, tty) < 0)
					break;
				b++; nr--;
			}
			if (tty->ops->flush_chars)
				tty->ops->flush_chars(tty);
		} else {
			struct n_tty_data *ldata = tty->disc_data;

			while (nr > 0) {
				mutex_lock(&ldata->output_lock);
				c = tty->ops->write(tty, b, nr);
				mutex_unlock(&ldata->output_lock);
				if (c < 0) {
					retval = c;
					goto break_out;
				}
				if (!c)
					break;
				b += c;
				nr -= c;
			}
		}
		if (!nr)
			break;
		if (tty_io_nonblock(tty, file)) {
			retval = -EAGAIN;
			break;
		}
		up_read(&tty->termios_rwsem);

		wait_woken(&wait, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);

		down_read(&tty->termios_rwsem);
	}
break_out:
	remove_wait_queue(&tty->write_wait, &wait);
	if (nr && tty->fasync)
		set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
	up_read(&tty->termios_rwsem);
	return (b - buf) ? b - buf : retval;
}

/**
 *	n_tty_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
 */

static __poll_t n_tty_poll(struct tty_struct *tty, struct file *file,
							poll_table *wait)
{
	__poll_t mask = 0;

	poll_wait(file, &tty->read_wait, wait);
	poll_wait(file, &tty->write_wait, wait);
	if (input_available_p(tty, 1))
		mask |= EPOLLIN | EPOLLRDNORM;
	else {
		tty_buffer_flush_work(tty->port);
		if (input_available_p(tty, 1))
			mask |= EPOLLIN | EPOLLRDNORM;
	}
	if (tty->packet && tty->link->ctrl_status)
		mask |= EPOLLPRI | EPOLLIN | EPOLLRDNORM;
	if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
		mask |= EPOLLHUP;
	if (tty_hung_up_p(file))
		mask |= EPOLLHUP;
	if (tty->ops->write && !tty_is_writelocked(tty) &&
			tty_chars_in_buffer(tty) < WAKEUP_CHARS &&
			tty_write_room(tty) > 0)
		mask |= EPOLLOUT | EPOLLWRNORM;
	return mask;
}

static unsigned long inq_canon(struct n_tty_data *ldata)
{
	size_t nr, head, tail;

	if (ldata->canon_head == ldata->read_tail)
		return 0;
	head = ldata->canon_head;
	tail = ldata->read_tail;
	nr = head - tail;
	/* Skip EOF-chars.. */
	while (MASK(head) != MASK(tail)) {
		if (test_bit(tail & (N_TTY_BUF_SIZE - 1), ldata->read_flags) &&
		    read_buf(ldata, tail) == __DISABLED_CHAR)
			nr--;
		tail++;
	}
	return nr;
}

static int n_tty_ioctl(struct tty_struct *tty, struct file *file,
		       unsigned int cmd, unsigned long arg)
{
	struct n_tty_data *ldata = tty->disc_data;
	int retval;

	switch (cmd) {
	case TIOCOUTQ:
		return put_user(tty_chars_in_buffer(tty), (int __user *) arg);
	case TIOCINQ:
		down_write(&tty->termios_rwsem);
		if (L_ICANON(tty) && !L_EXTPROC(tty))
			retval = inq_canon(ldata);
		else
			retval = read_cnt(ldata);
		up_write(&tty->termios_rwsem);
		return put_user(retval, (unsigned int __user *) arg);
	default:
		return n_tty_ioctl_helper(tty, file, cmd, arg);
	}
}

static struct tty_ldisc_ops n_tty_ops = {
	.magic           = TTY_LDISC_MAGIC,
	.name            = "n_tty",
	.open            = n_tty_open,
	.close           = n_tty_close,
	.flush_buffer    = n_tty_flush_buffer,
	.read            = n_tty_read,
	.write           = n_tty_write,
	.ioctl           = n_tty_ioctl,
	.set_termios     = n_tty_set_termios,
	.poll            = n_tty_poll,
	.receive_buf     = n_tty_receive_buf,
	.write_wakeup    = n_tty_write_wakeup,
	.receive_buf2	 = n_tty_receive_buf2,
};

/**
 *	n_tty_inherit_ops	-	inherit N_TTY methods
 *	@ops: struct tty_ldisc_ops where to save N_TTY methods
 *
 *	Enables a 'subclass' line discipline to 'inherit' N_TTY methods.
 */

void n_tty_inherit_ops(struct tty_ldisc_ops *ops)
{
	*ops = n_tty_ops;
	ops->owner = NULL;
	ops->refcount = ops->flags = 0;
}
EXPORT_SYMBOL_GPL(n_tty_inherit_ops);

void __init n_tty_init(void)
{
	tty_register_ldisc(N_TTY, &n_tty_ops);
}