summaryrefslogtreecommitdiff
path: root/fs/ntfs/aops.c
blob: 2a7cba258cca8c19c24c8f4fd410d77aaca9f351 (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
/**
 * aops.c - NTFS kernel address space operations and page cache handling.
 *	    Part of the Linux-NTFS project.
 *
 * Copyright (c) 2001-2005 Anton Altaparmakov
 * Copyright (c) 2002 Richard Russon
 *
 * This program/include file is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as published
 * by the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program/include file is distributed in the hope that it will be
 * useful, but WITHOUT ANY WARRANTY; without even the implied warranty
 * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program (in the main directory of the Linux-NTFS
 * distribution in the file COPYING); if not, write to the Free Software
 * Foundation,Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#include <linux/errno.h>
#include <linux/mm.h>
#include <linux/pagemap.h>
#include <linux/swap.h>
#include <linux/buffer_head.h>
#include <linux/writeback.h>

#include "aops.h"
#include "attrib.h"
#include "debug.h"
#include "inode.h"
#include "mft.h"
#include "runlist.h"
#include "types.h"
#include "ntfs.h"

/**
 * ntfs_end_buffer_async_read - async io completion for reading attributes
 * @bh:		buffer head on which io is completed
 * @uptodate:	whether @bh is now uptodate or not
 *
 * Asynchronous I/O completion handler for reading pages belonging to the
 * attribute address space of an inode.  The inodes can either be files or
 * directories or they can be fake inodes describing some attribute.
 *
 * If NInoMstProtected(), perform the post read mst fixups when all IO on the
 * page has been completed and mark the page uptodate or set the error bit on
 * the page.  To determine the size of the records that need fixing up, we
 * cheat a little bit by setting the index_block_size in ntfs_inode to the ntfs
 * record size, and index_block_size_bits, to the log(base 2) of the ntfs
 * record size.
 */
static void ntfs_end_buffer_async_read(struct buffer_head *bh, int uptodate)
{
	static DEFINE_SPINLOCK(page_uptodate_lock);
	unsigned long flags;
	struct buffer_head *tmp;
	struct page *page;
	ntfs_inode *ni;
	int page_uptodate = 1;

	page = bh->b_page;
	ni = NTFS_I(page->mapping->host);

	if (likely(uptodate)) {
		s64 file_ofs, initialized_size;

		set_buffer_uptodate(bh);

		file_ofs = ((s64)page->index << PAGE_CACHE_SHIFT) +
				bh_offset(bh);
		read_lock_irqsave(&ni->size_lock, flags);
		initialized_size = ni->initialized_size;
		read_unlock_irqrestore(&ni->size_lock, flags);
		/* Check for the current buffer head overflowing. */
		if (file_ofs + bh->b_size > initialized_size) {
			char *addr;
			int ofs = 0;

			if (file_ofs < initialized_size)
				ofs = initialized_size - file_ofs;
			addr = kmap_atomic(page, KM_BIO_SRC_IRQ);
			memset(addr + bh_offset(bh) + ofs, 0, bh->b_size - ofs);
			flush_dcache_page(page);
			kunmap_atomic(addr, KM_BIO_SRC_IRQ);
		}
	} else {
		clear_buffer_uptodate(bh);
		ntfs_error(ni->vol->sb, "Buffer I/O error, logical block %llu.",
				(unsigned long long)bh->b_blocknr);
		SetPageError(page);
	}
	spin_lock_irqsave(&page_uptodate_lock, flags);
	clear_buffer_async_read(bh);
	unlock_buffer(bh);
	tmp = bh;
	do {
		if (!buffer_uptodate(tmp))
			page_uptodate = 0;
		if (buffer_async_read(tmp)) {
			if (likely(buffer_locked(tmp)))
				goto still_busy;
			/* Async buffers must be locked. */
			BUG();
		}
		tmp = tmp->b_this_page;
	} while (tmp != bh);
	spin_unlock_irqrestore(&page_uptodate_lock, flags);
	/*
	 * If none of the buffers had errors then we can set the page uptodate,
	 * but we first have to perform the post read mst fixups, if the
	 * attribute is mst protected, i.e. if NInoMstProteced(ni) is true.
	 * Note we ignore fixup errors as those are detected when
	 * map_mft_record() is called which gives us per record granularity
	 * rather than per page granularity.
	 */
	if (!NInoMstProtected(ni)) {
		if (likely(page_uptodate && !PageError(page)))
			SetPageUptodate(page);
	} else {
		char *addr;
		unsigned int i, recs;
		u32 rec_size;

		rec_size = ni->itype.index.block_size;
		recs = PAGE_CACHE_SIZE / rec_size;
		/* Should have been verified before we got here... */
		BUG_ON(!recs);
		addr = kmap_atomic(page, KM_BIO_SRC_IRQ);
		for (i = 0; i < recs; i++)
			post_read_mst_fixup((NTFS_RECORD*)(addr +
					i * rec_size), rec_size);
		flush_dcache_page(page);
		kunmap_atomic(addr, KM_BIO_SRC_IRQ);
		if (likely(page_uptodate && !PageError(page)))
			SetPageUptodate(page);
	}
	unlock_page(page);
	return;
still_busy:
	spin_unlock_irqrestore(&page_uptodate_lock, flags);
	return;
}

/**
 * ntfs_read_block - fill a @page of an address space with data
 * @page:	page cache page to fill with data
 *
 * Fill the page @page of the address space belonging to the @page->host inode.
 * We read each buffer asynchronously and when all buffers are read in, our io
 * completion handler ntfs_end_buffer_read_async(), if required, automatically
 * applies the mst fixups to the page before finally marking it uptodate and
 * unlocking it.
 *
 * We only enforce allocated_size limit because i_size is checked for in
 * generic_file_read().
 *
 * Return 0 on success and -errno on error.
 *
 * Contains an adapted version of fs/buffer.c::block_read_full_page().
 */
static int ntfs_read_block(struct page *page)
{
	VCN vcn;
	LCN lcn;
	ntfs_inode *ni;
	ntfs_volume *vol;
	runlist_element *rl;
	struct buffer_head *bh, *head, *arr[MAX_BUF_PER_PAGE];
	sector_t iblock, lblock, zblock;
	unsigned long flags;
	unsigned int blocksize, vcn_ofs;
	int i, nr;
	unsigned char blocksize_bits;

	ni = NTFS_I(page->mapping->host);
	vol = ni->vol;

	/* $MFT/$DATA must have its complete runlist in memory at all times. */
	BUG_ON(!ni->runlist.rl && !ni->mft_no && !NInoAttr(ni));

	blocksize_bits = VFS_I(ni)->i_blkbits;
	blocksize = 1 << blocksize_bits;

	if (!page_has_buffers(page))
		create_empty_buffers(page, blocksize, 0);
	bh = head = page_buffers(page);
	if (unlikely(!bh)) {
		unlock_page(page);
		return -ENOMEM;
	}

	iblock = (s64)page->index << (PAGE_CACHE_SHIFT - blocksize_bits);
	read_lock_irqsave(&ni->size_lock, flags);
	lblock = (ni->allocated_size + blocksize - 1) >> blocksize_bits;
	zblock = (ni->initialized_size + blocksize - 1) >> blocksize_bits;
	read_unlock_irqrestore(&ni->size_lock, flags);

	/* Loop through all the buffers in the page. */
	rl = NULL;
	nr = i = 0;
	do {
		u8 *kaddr;

		if (unlikely(buffer_uptodate(bh)))
			continue;
		if (unlikely(buffer_mapped(bh))) {
			arr[nr++] = bh;
			continue;
		}
		bh->b_bdev = vol->sb->s_bdev;
		/* Is the block within the allowed limits? */
		if (iblock < lblock) {
			BOOL is_retry = FALSE;

			/* Convert iblock into corresponding vcn and offset. */
			vcn = (VCN)iblock << blocksize_bits >>
					vol->cluster_size_bits;
			vcn_ofs = ((VCN)iblock << blocksize_bits) &
					vol->cluster_size_mask;
			if (!rl) {
lock_retry_remap:
				down_read(&ni->runlist.lock);
				rl = ni->runlist.rl;
			}
			if (likely(rl != NULL)) {
				/* Seek to element containing target vcn. */
				while (rl->length && rl[1].vcn <= vcn)
					rl++;
				lcn = ntfs_rl_vcn_to_lcn(rl, vcn);
			} else
				lcn = LCN_RL_NOT_MAPPED;
			/* Successful remap. */
			if (lcn >= 0) {
				/* Setup buffer head to correct block. */
				bh->b_blocknr = ((lcn << vol->cluster_size_bits)
						+ vcn_ofs) >> blocksize_bits;
				set_buffer_mapped(bh);
				/* Only read initialized data blocks. */
				if (iblock < zblock) {
					arr[nr++] = bh;
					continue;
				}
				/* Fully non-initialized data block, zero it. */
				goto handle_zblock;
			}
			/* It is a hole, need to zero it. */
			if (lcn == LCN_HOLE)
				goto handle_hole;
			/* If first try and runlist unmapped, map and retry. */
			if (!is_retry && lcn == LCN_RL_NOT_MAPPED) {
				int err;
				is_retry = TRUE;
				/*
				 * Attempt to map runlist, dropping lock for
				 * the duration.
				 */
				up_read(&ni->runlist.lock);
				err = ntfs_map_runlist(ni, vcn);
				if (likely(!err))
					goto lock_retry_remap;
				rl = NULL;
				lcn = err;
			}
			/* Hard error, zero out region. */
			bh->b_blocknr = -1;
			SetPageError(page);
			ntfs_error(vol->sb, "Failed to read from inode 0x%lx, "
					"attribute type 0x%x, vcn 0x%llx, "
					"offset 0x%x because its location on "
					"disk could not be determined%s "
					"(error code %lli).", ni->mft_no,
					ni->type, (unsigned long long)vcn,
					vcn_ofs, is_retry ? " even after "
					"retrying" : "", (long long)lcn);
		}
		/*
		 * Either iblock was outside lblock limits or
		 * ntfs_rl_vcn_to_lcn() returned error.  Just zero that portion
		 * of the page and set the buffer uptodate.
		 */
handle_hole:
		bh->b_blocknr = -1UL;
		clear_buffer_mapped(bh);
handle_zblock:
		kaddr = kmap_atomic(page, KM_USER0);
		memset(kaddr + i * blocksize, 0, blocksize);
		flush_dcache_page(page);
		kunmap_atomic(kaddr, KM_USER0);
		set_buffer_uptodate(bh);
	} while (i++, iblock++, (bh = bh->b_this_page) != head);

	/* Release the lock if we took it. */
	if (rl)
		up_read(&ni->runlist.lock);

	/* Check we have at least one buffer ready for i/o. */
	if (nr) {
		struct buffer_head *tbh;

		/* Lock the buffers. */
		for (i = 0; i < nr; i++) {
			tbh = arr[i];
			lock_buffer(tbh);
			tbh->b_end_io = ntfs_end_buffer_async_read;
			set_buffer_async_read(tbh);
		}
		/* Finally, start i/o on the buffers. */
		for (i = 0; i < nr; i++) {
			tbh = arr[i];
			if (likely(!buffer_uptodate(tbh)))
				submit_bh(READ, tbh);
			else
				ntfs_end_buffer_async_read(tbh, 1);
		}
		return 0;
	}
	/* No i/o was scheduled on any of the buffers. */
	if (likely(!PageError(page)))
		SetPageUptodate(page);
	else /* Signal synchronous i/o error. */
		nr = -EIO;
	unlock_page(page);
	return nr;
}

/**
 * ntfs_readpage - fill a @page of a @file with data from the device
 * @file:	open file to which the page @page belongs or NULL
 * @page:	page cache page to fill with data
 *
 * For non-resident attributes, ntfs_readpage() fills the @page of the open
 * file @file by calling the ntfs version of the generic block_read_full_page()
 * function, ntfs_read_block(), which in turn creates and reads in the buffers
 * associated with the page asynchronously.
 *
 * For resident attributes, OTOH, ntfs_readpage() fills @page by copying the
 * data from the mft record (which at this stage is most likely in memory) and
 * fills the remainder with zeroes. Thus, in this case, I/O is synchronous, as
 * even if the mft record is not cached at this point in time, we need to wait
 * for it to be read in before we can do the copy.
 *
 * Return 0 on success and -errno on error.
 */
static int ntfs_readpage(struct file *file, struct page *page)
{
	ntfs_inode *ni, *base_ni;
	u8 *kaddr;
	ntfs_attr_search_ctx *ctx;
	MFT_RECORD *mrec;
	unsigned long flags;
	u32 attr_len;
	int err = 0;

	BUG_ON(!PageLocked(page));
	/*
	 * This can potentially happen because we clear PageUptodate() during
	 * ntfs_writepage() of MstProtected() attributes.
	 */
	if (PageUptodate(page)) {
		unlock_page(page);
		return 0;
	}
	ni = NTFS_I(page->mapping->host);

	/* NInoNonResident() == NInoIndexAllocPresent() */
	if (NInoNonResident(ni)) {
		/*
		 * Only unnamed $DATA attributes can be compressed or
		 * encrypted.
		 */
		if (ni->type == AT_DATA && !ni->name_len) {
			/* If file is encrypted, deny access, just like NT4. */
			if (NInoEncrypted(ni)) {
				err = -EACCES;
				goto err_out;
			}
			/* Compressed data streams are handled in compress.c. */
			if (NInoCompressed(ni))
				return ntfs_read_compressed_block(page);
		}
		/* Normal data stream. */
		return ntfs_read_block(page);
	}
	/*
	 * Attribute is resident, implying it is not compressed or encrypted.
	 * This also means the attribute is smaller than an mft record and
	 * hence smaller than a page, so can simply zero out any pages with
	 * index above 0.
	 */
	if (unlikely(page->index > 0)) {
		kaddr = kmap_atomic(page, KM_USER0);
		memset(kaddr, 0, PAGE_CACHE_SIZE);
		flush_dcache_page(page);
		kunmap_atomic(kaddr, KM_USER0);
		goto done;
	}
	if (!NInoAttr(ni))
		base_ni = ni;
	else
		base_ni = ni->ext.base_ntfs_ino;
	/* Map, pin, and lock the mft record. */
	mrec = map_mft_record(base_ni);
	if (IS_ERR(mrec)) {
		err = PTR_ERR(mrec);
		goto err_out;
	}
	ctx = ntfs_attr_get_search_ctx(base_ni, mrec);
	if (unlikely(!ctx)) {
		err = -ENOMEM;
		goto unm_err_out;
	}
	err = ntfs_attr_lookup(ni->type, ni->name, ni->name_len,
			CASE_SENSITIVE, 0, NULL, 0, ctx);
	if (unlikely(err))
		goto put_unm_err_out;
	attr_len = le32_to_cpu(ctx->attr->data.resident.value_length);
	read_lock_irqsave(&ni->size_lock, flags);
	if (unlikely(attr_len > ni->initialized_size))
		attr_len = ni->initialized_size;
	read_unlock_irqrestore(&ni->size_lock, flags);
	kaddr = kmap_atomic(page, KM_USER0);
	/* Copy the data to the page. */
	memcpy(kaddr, (u8*)ctx->attr +
			le16_to_cpu(ctx->attr->data.resident.value_offset),
			attr_len);
	/* Zero the remainder of the page. */
	memset(kaddr + attr_len, 0, PAGE_CACHE_SIZE - attr_len);
	flush_dcache_page(page);
	kunmap_atomic(kaddr, KM_USER0);
put_unm_err_out:
	ntfs_attr_put_search_ctx(ctx);
unm_err_out:
	unmap_mft_record(base_ni);
done:
	SetPageUptodate(page);
err_out:
	unlock_page(page);
	return err;
}

#ifdef NTFS_RW

/**
 * ntfs_write_block - write a @page to the backing store
 * @page:	page cache page to write out
 * @wbc:	writeback control structure
 *
 * This function is for writing pages belonging to non-resident, non-mst
 * protected attributes to their backing store.
 *
 * For a page with buffers, map and write the dirty buffers asynchronously
 * under page writeback. For a page without buffers, create buffers for the
 * page, then proceed as above.
 *
 * If a page doesn't have buffers the page dirty state is definitive. If a page
 * does have buffers, the page dirty state is just a hint, and the buffer dirty
 * state is definitive. (A hint which has rules: dirty buffers against a clean
 * page is illegal. Other combinations are legal and need to be handled. In
 * particular a dirty page containing clean buffers for example.)
 *
 * Return 0 on success and -errno on error.
 *
 * Based on ntfs_read_block() and __block_write_full_page().
 */
static int ntfs_write_block(struct page *page, struct writeback_control *wbc)
{
	VCN vcn;
	LCN lcn;
	s64 initialized_size;
	loff_t i_size;
	sector_t block, dblock, iblock;
	struct inode *vi;
	ntfs_inode *ni;
	ntfs_volume *vol;
	runlist_element *rl;
	struct buffer_head *bh, *head;
	unsigned long flags;
	unsigned int blocksize, vcn_ofs;
	int err;
	BOOL need_end_writeback;
	unsigned char blocksize_bits;

	vi = page->mapping->host;
	ni = NTFS_I(vi);
	vol = ni->vol;

	ntfs_debug("Entering for inode 0x%lx, attribute type 0x%x, page index "
			"0x%lx.", ni->mft_no, ni->type, page->index);

	BUG_ON(!NInoNonResident(ni));
	BUG_ON(NInoMstProtected(ni));

	blocksize_bits = vi->i_blkbits;
	blocksize = 1 << blocksize_bits;

	if (!page_has_buffers(page)) {
		BUG_ON(!PageUptodate(page));
		create_empty_buffers(page, blocksize,
				(1 << BH_Uptodate) | (1 << BH_Dirty));
	}
	bh = head = page_buffers(page);
	if (unlikely(!bh)) {
		ntfs_warning(vol->sb, "Error allocating page buffers. "
				"Redirtying page so we try again later.");
		/*
		 * Put the page back on mapping->dirty_pages, but leave its
		 * buffer's dirty state as-is.
		 */
		redirty_page_for_writepage(wbc, page);
		unlock_page(page);
		return 0;
	}

	/* NOTE: Different naming scheme to ntfs_read_block()! */

	/* The first block in the page. */
	block = (s64)page->index << (PAGE_CACHE_SHIFT - blocksize_bits);

	read_lock_irqsave(&ni->size_lock, flags);
	i_size = i_size_read(vi);
	initialized_size = ni->initialized_size;
	read_unlock_irqrestore(&ni->size_lock, flags);

	/* The first out of bounds block for the data size. */
	dblock = (i_size + blocksize - 1) >> blocksize_bits;

	/* The last (fully or partially) initialized block. */
	iblock = initialized_size >> blocksize_bits;

	/*
	 * Be very careful.  We have no exclusion from __set_page_dirty_buffers
	 * here, and the (potentially unmapped) buffers may become dirty at
	 * any time.  If a buffer becomes dirty here after we've inspected it
	 * then we just miss that fact, and the page stays dirty.
	 *
	 * Buffers outside i_size may be dirtied by __set_page_dirty_buffers;
	 * handle that here by just cleaning them.
	 */

	/*
	 * Loop through all the buffers in the page, mapping all the dirty
	 * buffers to disk addresses and handling any aliases from the
	 * underlying block device's mapping.
	 */
	rl = NULL;
	err = 0;
	do {
		BOOL is_retry = FALSE;

		if (unlikely(block >= dblock)) {
			/*
			 * Mapped buffers outside i_size will occur, because
			 * this page can be outside i_size when there is a
			 * truncate in progress. The contents of such buffers
			 * were zeroed by ntfs_writepage().
			 *
			 * FIXME: What about the small race window where
			 * ntfs_writepage() has not done any clearing because
			 * the page was within i_size but before we get here,
			 * vmtruncate() modifies i_size?
			 */
			clear_buffer_dirty(bh);
			set_buffer_uptodate(bh);
			continue;
		}

		/* Clean buffers are not written out, so no need to map them. */
		if (!buffer_dirty(bh))
			continue;

		/* Make sure we have enough initialized size. */
		if (unlikely((block >= iblock) &&
				(initialized_size < i_size))) {
			/*
			 * If this page is fully outside initialized size, zero
			 * out all pages between the current initialized size
			 * and the current page. Just use ntfs_readpage() to do
			 * the zeroing transparently.
			 */
			if (block > iblock) {
				// TODO:
				// For each page do:
				// - read_cache_page()
				// Again for each page do:
				// - wait_on_page_locked()
				// - Check (PageUptodate(page) &&
				//			!PageError(page))
				// Update initialized size in the attribute and
				// in the inode.
				// Again, for each page do:
				//	__set_page_dirty_buffers();
				// page_cache_release()
				// We don't need to wait on the writes.
				// Update iblock.
			}
			/*
			 * The current page straddles initialized size. Zero
			 * all non-uptodate buffers and set them uptodate (and
			 * dirty?). Note, there aren't any non-uptodate buffers
			 * if the page is uptodate.
			 * FIXME: For an uptodate page, the buffers may need to
			 * be written out because they were not initialized on
			 * disk before.
			 */
			if (!PageUptodate(page)) {
				// TODO:
				// Zero any non-uptodate buffers up to i_size.
				// Set them uptodate and dirty.
			}
			// TODO:
			// Update initialized size in the attribute and in the
			// inode (up to i_size).
			// Update iblock.
			// FIXME: This is inefficient. Try to batch the two
			// size changes to happen in one go.
			ntfs_error(vol->sb, "Writing beyond initialized size "
					"is not supported yet. Sorry.");
			err = -EOPNOTSUPP;
			break;
			// Do NOT set_buffer_new() BUT DO clear buffer range
			// outside write request range.
			// set_buffer_uptodate() on complete buffers as well as
			// set_buffer_dirty().
		}

		/* No need to map buffers that are already mapped. */
		if (buffer_mapped(bh))
			continue;

		/* Unmapped, dirty buffer. Need to map it. */
		bh->b_bdev = vol->sb->s_bdev;

		/* Convert block into corresponding vcn and offset. */
		vcn = (VCN)block << blocksize_bits;
		vcn_ofs = vcn & vol->cluster_size_mask;
		vcn >>= vol->cluster_size_bits;
		if (!rl) {
lock_retry_remap:
			down_read(&ni->runlist.lock);
			rl = ni->runlist.rl;
		}
		if (likely(rl != NULL)) {
			/* Seek to element containing target vcn. */
			while (rl->length && rl[1].vcn <= vcn)
				rl++;
			lcn = ntfs_rl_vcn_to_lcn(rl, vcn);
		} else
			lcn = LCN_RL_NOT_MAPPED;
		/* Successful remap. */
		if (lcn >= 0) {
			/* Setup buffer head to point to correct block. */
			bh->b_blocknr = ((lcn << vol->cluster_size_bits) +
					vcn_ofs) >> blocksize_bits;
			set_buffer_mapped(bh);
			continue;
		}
		/* It is a hole, need to instantiate it. */
		if (lcn == LCN_HOLE) {
			// TODO: Instantiate the hole.
			// clear_buffer_new(bh);
			// unmap_underlying_metadata(bh->b_bdev, bh->b_blocknr);
			ntfs_error(vol->sb, "Writing into sparse regions is "
					"not supported yet. Sorry.");
			err = -EOPNOTSUPP;
			break;
		}
		/* If first try and runlist unmapped, map and retry. */
		if (!is_retry && lcn == LCN_RL_NOT_MAPPED) {
			is_retry = TRUE;
			/*
			 * Attempt to map runlist, dropping lock for
			 * the duration.
			 */
			up_read(&ni->runlist.lock);
			err = ntfs_map_runlist(ni, vcn);
			if (likely(!err))
				goto lock_retry_remap;
			rl = NULL;
			lcn = err;
		}
		/* Failed to map the buffer, even after retrying. */
		bh->b_blocknr = -1;
		ntfs_error(vol->sb, "Failed to write to inode 0x%lx, "
				"attribute type 0x%x, vcn 0x%llx, offset 0x%x "
				"because its location on disk could not be "
				"determined%s (error code %lli).", ni->mft_no,
				ni->type, (unsigned long long)vcn,
				vcn_ofs, is_retry ? " even after "
				"retrying" : "", (long long)lcn);
		if (!err)
			err = -EIO;
		break;
	} while (block++, (bh = bh->b_this_page) != head);

	/* Release the lock if we took it. */
	if (rl)
		up_read(&ni->runlist.lock);

	/* For the error case, need to reset bh to the beginning. */
	bh = head;

	/* Just an optimization, so ->readpage() isn't called later. */
	if (unlikely(!PageUptodate(page))) {
		int uptodate = 1;
		do {
			if (!buffer_uptodate(bh)) {
				uptodate = 0;
				bh = head;
				break;
			}
		} while ((bh = bh->b_this_page) != head);
		if (uptodate)
			SetPageUptodate(page);
	}

	/* Setup all mapped, dirty buffers for async write i/o. */
	do {
		get_bh(bh);
		if (buffer_mapped(bh) && buffer_dirty(bh)) {
			lock_buffer(bh);
			if (test_clear_buffer_dirty(bh)) {
				BUG_ON(!buffer_uptodate(bh));
				mark_buffer_async_write(bh);
			} else
				unlock_buffer(bh);
		} else if (unlikely(err)) {
			/*
			 * For the error case. The buffer may have been set
			 * dirty during attachment to a dirty page.
			 */
			if (err != -ENOMEM)
				clear_buffer_dirty(bh);
		}
	} while ((bh = bh->b_this_page) != head);

	if (unlikely(err)) {
		// TODO: Remove the -EOPNOTSUPP check later on...
		if (unlikely(err == -EOPNOTSUPP))
			err = 0;
		else if (err == -ENOMEM) {
			ntfs_warning(vol->sb, "Error allocating memory. "
					"Redirtying page so we try again "
					"later.");
			/*
			 * Put the page back on mapping->dirty_pages, but
			 * leave its buffer's dirty state as-is.
			 */
			redirty_page_for_writepage(wbc, page);
			err = 0;
		} else
			SetPageError(page);
	}

	BUG_ON(PageWriteback(page));
	set_page_writeback(page);	/* Keeps try_to_free_buffers() away. */
	unlock_page(page);

	/*
	 * Submit the prepared buffers for i/o. Note the page is unlocked,
	 * and the async write i/o completion handler can end_page_writeback()
	 * at any time after the *first* submit_bh(). So the buffers can then
	 * disappear...
	 */
	need_end_writeback = TRUE;
	do {
		struct buffer_head *next = bh->b_this_page;
		if (buffer_async_write(bh)) {
			submit_bh(WRITE, bh);
			need_end_writeback = FALSE;
		}
		put_bh(bh);
		bh = next;
	} while (bh != head);

	/* If no i/o was started, need to end_page_writeback(). */
	if (unlikely(need_end_writeback))
		end_page_writeback(page);

	ntfs_debug("Done.");
	return err;
}

/**
 * ntfs_write_mst_block - write a @page to the backing store
 * @page:	page cache page to write out
 * @wbc:	writeback control structure
 *
 * This function is for writing pages belonging to non-resident, mst protected
 * attributes to their backing store.  The only supported attributes are index
 * allocation and $MFT/$DATA.  Both directory inodes and index inodes are
 * supported for the index allocation case.
 *
 * The page must remain locked for the duration of the write because we apply
 * the mst fixups, write, and then undo the fixups, so if we were to unlock the
 * page before undoing the fixups, any other user of the page will see the
 * page contents as corrupt.
 *
 * We clear the page uptodate flag for the duration of the function to ensure
 * exclusion for the $MFT/$DATA case against someone mapping an mft record we
 * are about to apply the mst fixups to.
 *
 * Return 0 on success and -errno on error.
 *
 * Based on ntfs_write_block(), ntfs_mft_writepage(), and
 * write_mft_record_nolock().
 */
static int ntfs_write_mst_block(struct page *page,
		struct writeback_control *wbc)
{
	sector_t block, dblock, rec_block;
	struct inode *vi = page->mapping->host;
	ntfs_inode *ni = NTFS_I(vi);
	ntfs_volume *vol = ni->vol;
	u8 *kaddr;
	unsigned char bh_size_bits = vi->i_blkbits;
	unsigned int bh_size = 1 << bh_size_bits;
	unsigned int rec_size = ni->itype.index.block_size;
	ntfs_inode *locked_nis[PAGE_CACHE_SIZE / rec_size];
	struct buffer_head *bh, *head, *tbh, *rec_start_bh;
	int max_bhs = PAGE_CACHE_SIZE / bh_size;
	struct buffer_head *bhs[max_bhs];
	runlist_element *rl;
	int i, nr_locked_nis, nr_recs, nr_bhs, bhs_per_rec, err, err2;
	unsigned rec_size_bits;
	BOOL sync, is_mft, page_is_dirty, rec_is_dirty;

	ntfs_debug("Entering for inode 0x%lx, attribute type 0x%x, page index "
			"0x%lx.", vi->i_ino, ni->type, page->index);
	BUG_ON(!NInoNonResident(ni));
	BUG_ON(!NInoMstProtected(ni));
	is_mft = (S_ISREG(vi->i_mode) && !vi->i_ino);
	/*
	 * NOTE: ntfs_write_mst_block() would be called for $MFTMirr if a page
	 * in its page cache were to be marked dirty.  However this should
	 * never happen with the current driver and considering we do not
	 * handle this case here we do want to BUG(), at least for now.
	 */
	BUG_ON(!(is_mft || S_ISDIR(vi->i_mode) ||
			(NInoAttr(ni) && ni->type == AT_INDEX_ALLOCATION)));
	BUG_ON(!max_bhs);

	/* Were we called for sync purposes? */
	sync = (wbc->sync_mode == WB_SYNC_ALL);

	/* Make sure we have mapped buffers. */
	BUG_ON(!page_has_buffers(page));
	bh = head = page_buffers(page);
	BUG_ON(!bh);

	rec_size_bits = ni->itype.index.block_size_bits;
	BUG_ON(!(PAGE_CACHE_SIZE >> rec_size_bits));
	bhs_per_rec = rec_size >> bh_size_bits;
	BUG_ON(!bhs_per_rec);

	/* The first block in the page. */
	rec_block = block = (sector_t)page->index <<
			(PAGE_CACHE_SHIFT - bh_size_bits);

	/* The first out of bounds block for the data size. */
	dblock = (i_size_read(vi) + bh_size - 1) >> bh_size_bits;

	rl = NULL;
	err = err2 = nr_bhs = nr_recs = nr_locked_nis = 0;
	page_is_dirty = rec_is_dirty = FALSE;
	rec_start_bh = NULL;
	do {
		BOOL is_retry = FALSE;

		if (likely(block < rec_block)) {
			if (unlikely(block >= dblock)) {
				clear_buffer_dirty(bh);
				set_buffer_uptodate(bh);
				continue;
			}
			/*
			 * This block is not the first one in the record.  We
			 * ignore the buffer's dirty state because we could
			 * have raced with a parallel mark_ntfs_record_dirty().
			 */
			if (!rec_is_dirty)
				continue;
			if (unlikely(err2)) {
				if (err2 != -ENOMEM)
					clear_buffer_dirty(bh);
				continue;
			}
		} else /* if (block == rec_block) */ {
			BUG_ON(block > rec_block);
			/* This block is the first one in the record. */
			rec_block += bhs_per_rec;
			err2 = 0;
			if (unlikely(block >= dblock)) {
				clear_buffer_dirty(bh);
				continue;
			}
			if (!buffer_dirty(bh)) {
				/* Clean records are not written out. */
				rec_is_dirty = FALSE;
				continue;
			}
			rec_is_dirty = TRUE;
			rec_start_bh = bh;
		}
		/* Need to map the buffer if it is not mapped already. */
		if (unlikely(!buffer_mapped(bh))) {
			VCN vcn;
			LCN lcn;
			unsigned int vcn_ofs;

			/* Obtain the vcn and offset of the current block. */
			vcn = (VCN)block << bh_size_bits;
			vcn_ofs = vcn & vol->cluster_size_mask;
			vcn >>= vol->cluster_size_bits;
			if (!rl) {
lock_retry_remap:
				down_read(&ni->runlist.lock);
				rl = ni->runlist.rl;
			}
			if (likely(rl != NULL)) {
				/* Seek to element containing target vcn. */
				while (rl->length && rl[1].vcn <= vcn)
					rl++;
				lcn = ntfs_rl_vcn_to_lcn(rl, vcn);
			} else
				lcn = LCN_RL_NOT_MAPPED;
			/* Successful remap. */
			if (likely(lcn >= 0)) {
				/* Setup buffer head to correct block. */
				bh->b_blocknr = ((lcn <<
						vol->cluster_size_bits) +
						vcn_ofs) >> bh_size_bits;
				set_buffer_mapped(bh);
			} else {
				/*
				 * Remap failed.  Retry to map the runlist once
				 * unless we are working on $MFT which always
				 * has the whole of its runlist in memory.
				 */
				if (!is_mft && !is_retry &&
						lcn == LCN_RL_NOT_MAPPED) {
					is_retry = TRUE;
					/*
					 * Attempt to map runlist, dropping
					 * lock for the duration.
					 */
					up_read(&ni->runlist.lock);
					err2 = ntfs_map_runlist(ni, vcn);
					if (likely(!err2))
						goto lock_retry_remap;
					if (err2 == -ENOMEM)
						page_is_dirty = TRUE;
					lcn = err2;
				} else
					err2 = -EIO;
				/* Hard error.  Abort writing this record. */
				if (!err || err == -ENOMEM)
					err = err2;
				bh->b_blocknr = -1;
				ntfs_error(vol->sb, "Cannot write ntfs record "
						"0x%llx (inode 0x%lx, "
						"attribute type 0x%x) because "
						"its location on disk could "
						"not be determined (error "
						"code %lli).",
						(long long)block <<
						bh_size_bits >>
						vol->mft_record_size_bits,
						ni->mft_no, ni->type,
						(long long)lcn);
				/*
				 * If this is not the first buffer, remove the
				 * buffers in this record from the list of
				 * buffers to write and clear their dirty bit
				 * if not error -ENOMEM.
				 */
				if (rec_start_bh != bh) {
					while (bhs[--nr_bhs] != rec_start_bh)
						;
					if (err2 != -ENOMEM) {
						do {
							clear_buffer_dirty(
								rec_start_bh);
						} while ((rec_start_bh =
								rec_start_bh->
								b_this_page) !=
								bh);
					}
				}
				continue;
			}
		}
		BUG_ON(!buffer_uptodate(bh));
		BUG_ON(nr_bhs >= max_bhs);
		bhs[nr_bhs++] = bh;
	} while (block++, (bh = bh->b_this_page) != head);
	if (unlikely(rl))
		up_read(&ni->runlist.lock);
	/* If there were no dirty buffers, we are done. */
	if (!nr_bhs)
		goto done;
	/* Map the page so we can access its contents. */
	kaddr = kmap(page);
	/* Clear the page uptodate flag whilst the mst fixups are applied. */
	BUG_ON(!PageUptodate(page));
	ClearPageUptodate(page);
	for (i = 0; i < nr_bhs; i++) {
		unsigned int ofs;

		/* Skip buffers which are not at the beginning of records. */
		if (i % bhs_per_rec)
			continue;
		tbh = bhs[i];
		ofs = bh_offset(tbh);
		if (is_mft) {
			ntfs_inode *tni;
			unsigned long mft_no;

			/* Get the mft record number. */
			mft_no = (((s64)page->index << PAGE_CACHE_SHIFT) + ofs)
					>> rec_size_bits;
			/* Check whether to write this mft record. */
			tni = NULL;
			if (!ntfs_may_write_mft_record(vol, mft_no,
					(MFT_RECORD*)(kaddr + ofs), &tni)) {
				/*
				 * The record should not be written.  This
				 * means we need to redirty the page before
				 * returning.
				 */
				page_is_dirty = TRUE;
				/*
				 * Remove the buffers in this mft record from
				 * the list of buffers to write.
				 */
				do {
					bhs[i] = NULL;
				} while (++i % bhs_per_rec);
				continue;
			}
			/*
			 * The record should be written.  If a locked ntfs
			 * inode was returned, add it to the array of locked
			 * ntfs inodes.
			 */
			if (tni)
				locked_nis[nr_locked_nis++] = tni;
		}
		/* Apply the mst protection fixups. */
		err2 = pre_write_mst_fixup((NTFS_RECORD*)(kaddr + ofs),
				rec_size);
		if (unlikely(err2)) {
			if (!err || err == -ENOMEM)
				err = -EIO;
			ntfs_error(vol->sb, "Failed to apply mst fixups "
					"(inode 0x%lx, attribute type 0x%x, "
					"page index 0x%lx, page offset 0x%x)!"
					"  Unmount and run chkdsk.", vi->i_ino,
					ni->type, page->index, ofs);
			/*
			 * Mark all the buffers in this record clean as we do
			 * not want to write corrupt data to disk.
			 */
			do {
				clear_buffer_dirty(bhs[i]);
				bhs[i] = NULL;
			} while (++i % bhs_per_rec);
			continue;
		}
		nr_recs++;
	}
	/* If no records are to be written out, we are done. */
	if (!nr_recs)
		goto unm_done;
	flush_dcache_page(page);
	/* Lock buffers and start synchronous write i/o on them. */
	for (i = 0; i < nr_bhs; i++) {
		tbh = bhs[i];
		if (!tbh)
			continue;
		if (unlikely(test_set_buffer_locked(tbh)))
			BUG();
		/* The buffer dirty state is now irrelevant, just clean it. */
		clear_buffer_dirty(tbh);
		BUG_ON(!buffer_uptodate(tbh));
		BUG_ON(!buffer_mapped(tbh));
		get_bh(tbh);
		tbh->b_end_io = end_buffer_write_sync;
		submit_bh(WRITE, tbh);
	}
	/* Synchronize the mft mirror now if not @sync. */
	if (is_mft && !sync)
		goto do_mirror;
do_wait:
	/* Wait on i/o completion of buffers. */
	for (i = 0; i < nr_bhs; i++) {
		tbh = bhs[i];
		if (!tbh)
			continue;
		wait_on_buffer(tbh);
		if (unlikely(!buffer_uptodate(tbh))) {
			ntfs_error(vol->sb, "I/O error while writing ntfs "
					"record buffer (inode 0x%lx, "
					"attribute type 0x%x, page index "
					"0x%lx, page offset 0x%lx)!  Unmount "
					"and run chkdsk.", vi->i_ino, ni->type,
					page->index, bh_offset(tbh));
			if (!err || err == -ENOMEM)
				err = -EIO;
			/*
			 * Set the buffer uptodate so the page and buffer
			 * states do not become out of sync.
			 */
			set_buffer_uptodate(tbh);
		}
	}
	/* If @sync, now synchronize the mft mirror. */
	if (is_mft && sync) {
do_mirror:
		for (i = 0; i < nr_bhs; i++) {
			unsigned long mft_no;
			unsigned int ofs;

			/*
			 * Skip buffers which are not at the beginning of
			 * records.
			 */
			if (i % bhs_per_rec)
				continue;
			tbh = bhs[i];
			/* Skip removed buffers (and hence records). */
			if (!tbh)
				continue;
			ofs = bh_offset(tbh);
			/* Get the mft record number. */
			mft_no = (((s64)page->index << PAGE_CACHE_SHIFT) + ofs)
					>> rec_size_bits;
			if (mft_no < vol->mftmirr_size)
				ntfs_sync_mft_mirror(vol, mft_no,
						(MFT_RECORD*)(kaddr + ofs),
						sync);
		}
		if (!sync)
			goto do_wait;
	}
	/* Remove the mst protection fixups again. */
	for (i = 0; i < nr_bhs; i++) {
		if (!(i % bhs_per_rec)) {
			tbh = bhs[i];
			if (!tbh)
				continue;
			post_write_mst_fixup((NTFS_RECORD*)(kaddr +
					bh_offset(tbh)));
		}
	}
	flush_dcache_page(page);
unm_done:
	/* Unlock any locked inodes. */
	while (nr_locked_nis-- > 0) {
		ntfs_inode *tni, *base_tni;
		
		tni = locked_nis[nr_locked_nis];
		/* Get the base inode. */
		down(&tni->extent_lock);
		if (tni->nr_extents >= 0)
			base_tni = tni;
		else {
			base_tni = tni->ext.base_ntfs_ino;
			BUG_ON(!base_tni);
		}
		up(&tni->extent_lock);
		ntfs_debug("Unlocking %s inode 0x%lx.",
				tni == base_tni ? "base" : "extent",
				tni->mft_no);
		up(&tni->mrec_lock);
		atomic_dec(&tni->count);
		iput(VFS_I(base_tni));
	}
	SetPageUptodate(page);
	kunmap(page);
done:
	if (unlikely(err && err != -ENOMEM)) {
		/*
		 * Set page error if there is only one ntfs record in the page.
		 * Otherwise we would loose per-record granularity.
		 */
		if (ni->itype.index.block_size == PAGE_CACHE_SIZE)
			SetPageError(page);
		NVolSetErrors(vol);
	}
	if (page_is_dirty) {
		ntfs_debug("Page still contains one or more dirty ntfs "
				"records.  Redirtying the page starting at "
				"record 0x%lx.", page->index <<
				(PAGE_CACHE_SHIFT - rec_size_bits));
		redirty_page_for_writepage(wbc, page);
		unlock_page(page);
	} else {
		/*
		 * Keep the VM happy.  This must be done otherwise the
		 * radix-tree tag PAGECACHE_TAG_DIRTY remains set even though
		 * the page is clean.
		 */
		BUG_ON(PageWriteback(page));
		set_page_writeback(page);
		unlock_page(page);
		end_page_writeback(page);
	}
	if (likely(!err))
		ntfs_debug("Done.");
	return err;
}

/**
 * ntfs_writepage - write a @page to the backing store
 * @page:	page cache page to write out
 * @wbc:	writeback control structure
 *
 * This is called from the VM when it wants to have a dirty ntfs page cache
 * page cleaned.  The VM has already locked the page and marked it clean.
 *
 * For non-resident attributes, ntfs_writepage() writes the @page by calling
 * the ntfs version of the generic block_write_full_page() function,
 * ntfs_write_block(), which in turn if necessary creates and writes the
 * buffers associated with the page asynchronously.
 *
 * For resident attributes, OTOH, ntfs_writepage() writes the @page by copying
 * the data to the mft record (which at this stage is most likely in memory).
 * The mft record is then marked dirty and written out asynchronously via the
 * vfs inode dirty code path for the inode the mft record belongs to or via the
 * vm page dirty code path for the page the mft record is in.
 *
 * Based on ntfs_readpage() and fs/buffer.c::block_write_full_page().
 *
 * Return 0 on success and -errno on error.
 */
static int ntfs_writepage(struct page *page, struct writeback_control *wbc)
{
	loff_t i_size;
	struct inode *vi = page->mapping->host;
	ntfs_inode *base_ni = NULL, *ni = NTFS_I(vi);
	char *kaddr;
	ntfs_attr_search_ctx *ctx = NULL;
	MFT_RECORD *m = NULL;
	u32 attr_len;
	int err;

	BUG_ON(!PageLocked(page));
	i_size = i_size_read(vi);
	/* Is the page fully outside i_size? (truncate in progress) */
	if (unlikely(page->index >= (i_size + PAGE_CACHE_SIZE - 1) >>
			PAGE_CACHE_SHIFT)) {
		/*
		 * The page may have dirty, unmapped buffers.  Make them
		 * freeable here, so the page does not leak.
		 */
		block_invalidatepage(page, 0);
		unlock_page(page);
		ntfs_debug("Write outside i_size - truncated?");
		return 0;
	}
	/* NInoNonResident() == NInoIndexAllocPresent() */
	if (NInoNonResident(ni)) {
		/*
		 * Only unnamed $DATA attributes can be compressed, encrypted,
		 * and/or sparse.
		 */
		if (ni->type == AT_DATA && !ni->name_len) {
			/* If file is encrypted, deny access, just like NT4. */
			if (NInoEncrypted(ni)) {
				unlock_page(page);
				ntfs_debug("Denying write access to encrypted "
						"file.");
				return -EACCES;
			}
			/* Compressed data streams are handled in compress.c. */
			if (NInoCompressed(ni)) {
				// TODO: Implement and replace this check with
				// return ntfs_write_compressed_block(page);
				unlock_page(page);
				ntfs_error(vi->i_sb, "Writing to compressed "
						"files is not supported yet. "
						"Sorry.");
				return -EOPNOTSUPP;
			}
			// TODO: Implement and remove this check.
			if (NInoSparse(ni)) {
				unlock_page(page);
				ntfs_error(vi->i_sb, "Writing to sparse files "
						"is not supported yet. Sorry.");
				return -EOPNOTSUPP;
			}
		}
		/* We have to zero every time due to mmap-at-end-of-file. */
		if (page->index >= (i_size >> PAGE_CACHE_SHIFT)) {
			/* The page straddles i_size. */
			unsigned int ofs = i_size & ~PAGE_CACHE_MASK;
			kaddr = kmap_atomic(page, KM_USER0);
			memset(kaddr + ofs, 0, PAGE_CACHE_SIZE - ofs);
			flush_dcache_page(page);
			kunmap_atomic(kaddr, KM_USER0);
		}
		/* Handle mst protected attributes. */
		if (NInoMstProtected(ni))
			return ntfs_write_mst_block(page, wbc);
		/* Normal data stream. */
		return ntfs_write_block(page, wbc);
	}
	/*
	 * Attribute is resident, implying it is not compressed, encrypted,
	 * sparse, or mst protected.  This also means the attribute is smaller
	 * than an mft record and hence smaller than a page, so can simply
	 * return error on any pages with index above 0.
	 */
	BUG_ON(page_has_buffers(page));
	BUG_ON(!PageUptodate(page));
	if (unlikely(page->index > 0)) {
		ntfs_error(vi->i_sb, "BUG()! page->index (0x%lx) > 0.  "
				"Aborting write.", page->index);
		BUG_ON(PageWriteback(page));
		set_page_writeback(page);
		unlock_page(page);
		end_page_writeback(page);
		return -EIO;
	}
	if (!NInoAttr(ni))
		base_ni = ni;
	else
		base_ni = ni->ext.base_ntfs_ino;
	/* Map, pin, and lock the mft record. */
	m = map_mft_record(base_ni);
	if (IS_ERR(m)) {
		err = PTR_ERR(m);
		m = NULL;
		ctx = NULL;
		goto err_out;
	}
	ctx = ntfs_attr_get_search_ctx(base_ni, m);
	if (unlikely(!ctx)) {
		err = -ENOMEM;
		goto err_out;
	}
	err = ntfs_attr_lookup(ni->type, ni->name, ni->name_len,
			CASE_SENSITIVE, 0, NULL, 0, ctx);
	if (unlikely(err))
		goto err_out;
	/*
	 * Keep the VM happy.  This must be done otherwise the radix-tree tag
	 * PAGECACHE_TAG_DIRTY remains set even though the page is clean.
	 */
	BUG_ON(PageWriteback(page));
	set_page_writeback(page);
	unlock_page(page);

	/*
	 * Here, we don't need to zero the out of bounds area everytime because
	 * the below memcpy() already takes care of the mmap-at-end-of-file
	 * requirements. If the file is converted to a non-resident one, then
	 * the code path use is switched to the non-resident one where the
	 * zeroing happens on each ntfs_writepage() invocation.
	 *
	 * The above also applies nicely when i_size is decreased.
	 *
	 * When i_size is increased, the memory between the old and new i_size
	 * _must_ be zeroed (or overwritten with new data). Otherwise we will
	 * expose data to userspace/disk which should never have been exposed.
	 *
	 * FIXME: Ensure that i_size increases do the zeroing/overwriting and
	 * if we cannot guarantee that, then enable the zeroing below.  If the
	 * zeroing below is enabled, we MUST move the unlock_page() from above
	 * to after the kunmap_atomic(), i.e. just before the
	 * end_page_writeback().
	 * UPDATE: ntfs_prepare/commit_write() do the zeroing on i_size
	 * increases for resident attributes so those are ok.
	 * TODO: ntfs_truncate(), others?
	 */

	attr_len = le32_to_cpu(ctx->attr->data.resident.value_length);
	i_size = i_size_read(vi);
	if (unlikely(attr_len > i_size)) {
		attr_len = i_size;
		ctx->attr->data.resident.value_length = cpu_to_le32(attr_len);
	}
	kaddr = kmap_atomic(page, KM_USER0);
	/* Copy the data from the page to the mft record. */
	memcpy((u8*)ctx->attr +
			le16_to_cpu(ctx->attr->data.resident.value_offset),
			kaddr, attr_len);
	flush_dcache_mft_record_page(ctx->ntfs_ino);
	/* Zero out of bounds area in the page cache page. */
	memset(kaddr + attr_len, 0, PAGE_CACHE_SIZE - attr_len);
	flush_dcache_page(page);
	kunmap_atomic(kaddr, KM_USER0);

	end_page_writeback(page);

	/* Mark the mft record dirty, so it gets written back. */
	mark_mft_record_dirty(ctx->ntfs_ino);
	ntfs_attr_put_search_ctx(ctx);
	unmap_mft_record(base_ni);
	return 0;
err_out:
	if (err == -ENOMEM) {
		ntfs_warning(vi->i_sb, "Error allocating memory. Redirtying "
				"page so we try again later.");
		/*
		 * Put the page back on mapping->dirty_pages, but leave its
		 * buffers' dirty state as-is.
		 */
		redirty_page_for_writepage(wbc, page);
		err = 0;
	} else {
		ntfs_error(vi->i_sb, "Resident attribute write failed with "
				"error %i.", err);
		SetPageError(page);
		NVolSetErrors(ni->vol);
		make_bad_inode(vi);
	}
	unlock_page(page);
	if (ctx)
		ntfs_attr_put_search_ctx(ctx);
	if (m)
		unmap_mft_record(base_ni);
	return err;
}

/**
 * ntfs_prepare_nonresident_write -
 *
 */
static int ntfs_prepare_nonresident_write(struct page *page,
		unsigned from, unsigned to)
{
	VCN vcn;
	LCN lcn;
	s64 initialized_size;
	loff_t i_size;
	sector_t block, ablock, iblock;
	struct inode *vi;
	ntfs_inode *ni;
	ntfs_volume *vol;
	runlist_element *rl;
	struct buffer_head *bh, *head, *wait[2], **wait_bh = wait;
	unsigned long flags;
	unsigned int vcn_ofs, block_start, block_end, blocksize;
	int err;
	BOOL is_retry;
	unsigned char blocksize_bits;

	vi = page->mapping->host;
	ni = NTFS_I(vi);
	vol = ni->vol;

	ntfs_debug("Entering for inode 0x%lx, attribute type 0x%x, page index "
			"0x%lx, from = %u, to = %u.", ni->mft_no, ni->type,
			page->index, from, to);

	BUG_ON(!NInoNonResident(ni));

	blocksize_bits = vi->i_blkbits;
	blocksize = 1 << blocksize_bits;

	/*
	 * create_empty_buffers() will create uptodate/dirty buffers if the
	 * page is uptodate/dirty.
	 */
	if (!page_has_buffers(page))
		create_empty_buffers(page, blocksize, 0);
	bh = head = page_buffers(page);
	if (unlikely(!bh))
		return -ENOMEM;

	/* The first block in the page. */
	block = (s64)page->index << (PAGE_CACHE_SHIFT - blocksize_bits);

	read_lock_irqsave(&ni->size_lock, flags);
	/*
	 * The first out of bounds block for the allocated size.  No need to
	 * round up as allocated_size is in multiples of cluster size and the
	 * minimum cluster size is 512 bytes, which is equal to the smallest
	 * blocksize.
	 */
	ablock = ni->allocated_size >> blocksize_bits;
	i_size = i_size_read(vi);
	initialized_size = ni->initialized_size;
	read_unlock_irqrestore(&ni->size_lock, flags);

	/* The last (fully or partially) initialized block. */
	iblock = initialized_size >> blocksize_bits;

	/* Loop through all the buffers in the page. */
	block_start = 0;
	rl = NULL;
	err = 0;
	do {
		block_end = block_start + blocksize;
		/*
		 * If buffer @bh is outside the write, just mark it uptodate
		 * if the page is uptodate and continue with the next buffer.
		 */
		if (block_end <= from || block_start >= to) {
			if (PageUptodate(page)) {
				if (!buffer_uptodate(bh))
					set_buffer_uptodate(bh);
			}
			continue;
		}
		/*
		 * @bh is at least partially being written to.
		 * Make sure it is not marked as new.
		 */
		//if (buffer_new(bh))
		//	clear_buffer_new(bh);

		if (block >= ablock) {
			// TODO: block is above allocated_size, need to
			// allocate it. Best done in one go to accommodate not
			// only block but all above blocks up to and including:
			// ((page->index << PAGE_CACHE_SHIFT) + to + blocksize
			// - 1) >> blobksize_bits. Obviously will need to round
			// up to next cluster boundary, too. This should be
			// done with a helper function, so it can be reused.
			ntfs_error(vol->sb, "Writing beyond allocated size "
					"is not supported yet. Sorry.");
			err = -EOPNOTSUPP;
			goto err_out;
			// Need to update ablock.
			// Need to set_buffer_new() on all block bhs that are
			// newly allocated.
		}
		/*
		 * Now we have enough allocated size to fulfill the whole
		 * request, i.e. block < ablock is true.
		 */
		if (unlikely((block >= iblock) &&
				(initialized_size < i_size))) {
			/*
			 * If this page is fully outside initialized size, zero
			 * out all pages between the current initialized size
			 * and the current page. Just use ntfs_readpage() to do
			 * the zeroing transparently.
			 */
			if (block > iblock) {
				// TODO:
				// For each page do:
				// - read_cache_page()
				// Again for each page do:
				// - wait_on_page_locked()
				// - Check (PageUptodate(page) &&
				//			!PageError(page))
				// Update initialized size in the attribute and
				// in the inode.
				// Again, for each page do:
				//	__set_page_dirty_buffers();
				// page_cache_release()
				// We don't need to wait on the writes.
				// Update iblock.
			}
			/*
			 * The current page straddles initialized size. Zero
			 * all non-uptodate buffers and set them uptodate (and
			 * dirty?). Note, there aren't any non-uptodate buffers
			 * if the page is uptodate.
			 * FIXME: For an uptodate page, the buffers may need to
			 * be written out because they were not initialized on
			 * disk before.
			 */
			if (!PageUptodate(page)) {
				// TODO:
				// Zero any non-uptodate buffers up to i_size.
				// Set them uptodate and dirty.
			}
			// TODO:
			// Update initialized size in the attribute and in the
			// inode (up to i_size).
			// Update iblock.
			// FIXME: This is inefficient. Try to batch the two
			// size changes to happen in one go.
			ntfs_error(vol->sb, "Writing beyond initialized size "
					"is not supported yet. Sorry.");
			err = -EOPNOTSUPP;
			goto err_out;
			// Do NOT set_buffer_new() BUT DO clear buffer range
			// outside write request range.
			// set_buffer_uptodate() on complete buffers as well as
			// set_buffer_dirty().
		}

		/* Need to map unmapped buffers. */
		if (!buffer_mapped(bh)) {
			/* Unmapped buffer. Need to map it. */
			bh->b_bdev = vol->sb->s_bdev;

			/* Convert block into corresponding vcn and offset. */
			vcn = (VCN)block << blocksize_bits >>
					vol->cluster_size_bits;
			vcn_ofs = ((VCN)block << blocksize_bits) &
					vol->cluster_size_mask;

			is_retry = FALSE;
			if (!rl) {
lock_retry_remap:
				down_read(&ni->runlist.lock);
				rl = ni->runlist.rl;
			}
			if (likely(rl != NULL)) {
				/* Seek to element containing target vcn. */
				while (rl->length && rl[1].vcn <= vcn)
					rl++;
				lcn = ntfs_rl_vcn_to_lcn(rl, vcn);
			} else
				lcn = LCN_RL_NOT_MAPPED;
			if (unlikely(lcn < 0)) {
				/*
				 * We extended the attribute allocation above.
				 * If we hit an ENOENT here it means that the
				 * allocation was insufficient which is a bug.
				 */
				BUG_ON(lcn == LCN_ENOENT);

				/* It is a hole, need to instantiate it. */
				if (lcn == LCN_HOLE) {
					// TODO: Instantiate the hole.
					// clear_buffer_new(bh);
					// unmap_underlying_metadata(bh->b_bdev,
					//		bh->b_blocknr);
					// For non-uptodate buffers, need to
					// zero out the region outside the
					// request in this bh or all bhs,
					// depending on what we implemented
					// above.
					// Need to flush_dcache_page().
					// Or could use set_buffer_new()
					// instead?
					ntfs_error(vol->sb, "Writing into "
							"sparse regions is "
							"not supported yet. "
							"Sorry.");
					err = -EOPNOTSUPP;
					goto err_out;
				} else if (!is_retry &&
						lcn == LCN_RL_NOT_MAPPED) {
					is_retry = TRUE;
					/*
					 * Attempt to map runlist, dropping
					 * lock for the duration.
					 */
					up_read(&ni->runlist.lock);
					err = ntfs_map_runlist(ni, vcn);
					if (likely(!err))
						goto lock_retry_remap;
					rl = NULL;
					lcn = err;
				}
				/*
				 * Failed to map the buffer, even after
				 * retrying.
				 */
				bh->b_blocknr = -1;
				ntfs_error(vol->sb, "Failed to write to inode "
						"0x%lx, attribute type 0x%x, "
						"vcn 0x%llx, offset 0x%x "
						"because its location on disk "
						"could not be determined%s "
						"(error code %lli).",
						ni->mft_no, ni->type,
						(unsigned long long)vcn,
						vcn_ofs, is_retry ? " even "
						"after retrying" : "",
						(long long)lcn);
				if (!err)
					err = -EIO;
				goto err_out;
			}
			/* We now have a successful remap, i.e. lcn >= 0. */

			/* Setup buffer head to correct block. */
			bh->b_blocknr = ((lcn << vol->cluster_size_bits)
					+ vcn_ofs) >> blocksize_bits;
			set_buffer_mapped(bh);

			// FIXME: Something analogous to this is needed for
			// each newly allocated block, i.e. BH_New.
			// FIXME: Might need to take this out of the
			// if (!buffer_mapped(bh)) {}, depending on how we
			// implement things during the allocated_size and
			// initialized_size extension code above.
			if (buffer_new(bh)) {
				clear_buffer_new(bh);
				unmap_underlying_metadata(bh->b_bdev,
						bh->b_blocknr);
				if (PageUptodate(page)) {
					set_buffer_uptodate(bh);
					continue;
				}
				/*
				 * Page is _not_ uptodate, zero surrounding
				 * region. NOTE: This is how we decide if to
				 * zero or not!
				 */
				if (block_end > to || block_start < from) {
					void *kaddr;

					kaddr = kmap_atomic(page, KM_USER0);
					if (block_end > to)
						memset(kaddr + to, 0,
								block_end - to);
					if (block_start < from)
						memset(kaddr + block_start, 0,
								from -
								block_start);
					flush_dcache_page(page);
					kunmap_atomic(kaddr, KM_USER0);
				}
				continue;
			}
		}
		/* @bh is mapped, set it uptodate if the page is uptodate. */
		if (PageUptodate(page)) {
			if (!buffer_uptodate(bh))
				set_buffer_uptodate(bh);
			continue;
		}
		/*
		 * The page is not uptodate. The buffer is mapped. If it is not
		 * uptodate, and it is only partially being written to, we need
		 * to read the buffer in before the write, i.e. right now.
		 */
		if (!buffer_uptodate(bh) &&
				(block_start < from || block_end > to)) {
			ll_rw_block(READ, 1, &bh);
			*wait_bh++ = bh;
		}
	} while (block++, block_start = block_end,
			(bh = bh->b_this_page) != head);

	/* Release the lock if we took it. */
	if (rl) {
		up_read(&ni->runlist.lock);
		rl = NULL;
	}

	/* If we issued read requests, let them complete. */
	while (wait_bh > wait) {
		wait_on_buffer(*--wait_bh);
		if (!buffer_uptodate(*wait_bh))
			return -EIO;
	}

	ntfs_debug("Done.");
	return 0;
err_out:
	/*
	 * Zero out any newly allocated blocks to avoid exposing stale data.
	 * If BH_New is set, we know that the block was newly allocated in the
	 * above loop.
	 * FIXME: What about initialized_size increments? Have we done all the
	 * required zeroing above? If not this error handling is broken, and
	 * in particular the if (block_end <= from) check is completely bogus.
	 */
	bh = head;
	block_start = 0;
	is_retry = FALSE;
	do {
		block_end = block_start + blocksize;
		if (block_end <= from)
			continue;
		if (block_start >= to)
			break;
		if (buffer_new(bh)) {
			void *kaddr;

			clear_buffer_new(bh);
			kaddr = kmap_atomic(page, KM_USER0);
			memset(kaddr + block_start, 0, bh->b_size);
			kunmap_atomic(kaddr, KM_USER0);
			set_buffer_uptodate(bh);
			mark_buffer_dirty(bh);
			is_retry = TRUE;
		}
	} while (block_start = block_end, (bh = bh->b_this_page) != head);
	if (is_retry)
		flush_dcache_page(page);
	if (rl)
		up_read(&ni->runlist.lock);
	return err;
}

/**
 * ntfs_prepare_write - prepare a page for receiving data
 *
 * This is called from generic_file_write() with i_sem held on the inode
 * (@page->mapping->host).  The @page is locked but not kmap()ped.  The source
 * data has not yet been copied into the @page.
 *
 * Need to extend the attribute/fill in holes if necessary, create blocks and
 * make partially overwritten blocks uptodate,
 *
 * i_size is not to be modified yet.
 *
 * Return 0 on success or -errno on error.
 *
 * Should be using block_prepare_write() [support for sparse files] or
 * cont_prepare_write() [no support for sparse files].  Cannot do that due to
 * ntfs specifics but can look at them for implementation guidance.
 *
 * Note: In the range, @from is inclusive and @to is exclusive, i.e. @from is
 * the first byte in the page that will be written to and @to is the first byte
 * after the last byte that will be written to.
 */
static int ntfs_prepare_write(struct file *file, struct page *page,
		unsigned from, unsigned to)
{
	s64 new_size;
	loff_t i_size;
	struct inode *vi = page->mapping->host;
	ntfs_inode *base_ni = NULL, *ni = NTFS_I(vi);
	ntfs_volume *vol = ni->vol;
	ntfs_attr_search_ctx *ctx = NULL;
	MFT_RECORD *m = NULL;
	ATTR_RECORD *a;
	u8 *kaddr;
	u32 attr_len;
	int err;

	ntfs_debug("Entering for inode 0x%lx, attribute type 0x%x, page index "
			"0x%lx, from = %u, to = %u.", vi->i_ino, ni->type,
			page->index, from, to);
	BUG_ON(!PageLocked(page));
	BUG_ON(from > PAGE_CACHE_SIZE);
	BUG_ON(to > PAGE_CACHE_SIZE);
	BUG_ON(from > to);
	BUG_ON(NInoMstProtected(ni));
	/*
	 * If a previous ntfs_truncate() failed, repeat it and abort if it
	 * fails again.
	 */
	if (unlikely(NInoTruncateFailed(ni))) {
		down_write(&vi->i_alloc_sem);
		err = ntfs_truncate(vi);
		up_write(&vi->i_alloc_sem);
		if (err || NInoTruncateFailed(ni)) {
			if (!err)
				err = -EIO;
			goto err_out;
		}
	}
	/* If the attribute is not resident, deal with it elsewhere. */
	if (NInoNonResident(ni)) {
		/*
		 * Only unnamed $DATA attributes can be compressed, encrypted,
		 * and/or sparse.
		 */
		if (ni->type == AT_DATA && !ni->name_len) {
			/* If file is encrypted, deny access, just like NT4. */
			if (NInoEncrypted(ni)) {
				ntfs_debug("Denying write access to encrypted "
						"file.");
				return -EACCES;
			}
			/* Compressed data streams are handled in compress.c. */
			if (NInoCompressed(ni)) {
				// TODO: Implement and replace this check with
				// return ntfs_write_compressed_block(page);
				ntfs_error(vi->i_sb, "Writing to compressed "
						"files is not supported yet. "
						"Sorry.");
				return -EOPNOTSUPP;
			}
			// TODO: Implement and remove this check.
			if (NInoSparse(ni)) {
				ntfs_error(vi->i_sb, "Writing to sparse files "
						"is not supported yet. Sorry.");
				return -EOPNOTSUPP;
			}
		}
		/* Normal data stream. */
		return ntfs_prepare_nonresident_write(page, from, to);
	}
	/*
	 * Attribute is resident, implying it is not compressed, encrypted, or
	 * sparse.
	 */
	BUG_ON(page_has_buffers(page));
	new_size = ((s64)page->index << PAGE_CACHE_SHIFT) + to;
	/* If we do not need to resize the attribute allocation we are done. */
	if (new_size <= i_size_read(vi))
		goto done;
	/* Map, pin, and lock the (base) mft record. */
	if (!NInoAttr(ni))
		base_ni = ni;
	else
		base_ni = ni->ext.base_ntfs_ino;
	m = map_mft_record(base_ni);
	if (IS_ERR(m)) {
		err = PTR_ERR(m);
		m = NULL;
		ctx = NULL;
		goto err_out;
	}
	ctx = ntfs_attr_get_search_ctx(base_ni, m);
	if (unlikely(!ctx)) {
		err = -ENOMEM;
		goto err_out;
	}
	err = ntfs_attr_lookup(ni->type, ni->name, ni->name_len,
			CASE_SENSITIVE, 0, NULL, 0, ctx);
	if (unlikely(err)) {
		if (err == -ENOENT)
			err = -EIO;
		goto err_out;
	}
	m = ctx->mrec;
	a = ctx->attr;
	/* The total length of the attribute value. */
	attr_len = le32_to_cpu(a->data.resident.value_length);
	/* Fix an eventual previous failure of ntfs_commit_write(). */
	i_size = i_size_read(vi);
	if (unlikely(attr_len > i_size)) {
		attr_len = i_size;
		a->data.resident.value_length = cpu_to_le32(attr_len);
	}
	/* If we do not need to resize the attribute allocation we are done. */
	if (new_size <= attr_len)
		goto done_unm;
	/* Check if new size is allowed in $AttrDef. */
	err = ntfs_attr_size_bounds_check(vol, ni->type, new_size);
	if (unlikely(err)) {
		if (err == -ERANGE) {
			ntfs_error(vol->sb, "Write would cause the inode "
					"0x%lx to exceed the maximum size for "
					"its attribute type (0x%x).  Aborting "
					"write.", vi->i_ino,
					le32_to_cpu(ni->type));
		} else {
			ntfs_error(vol->sb, "Inode 0x%lx has unknown "
					"attribute type 0x%x.  Aborting "
					"write.", vi->i_ino,
					le32_to_cpu(ni->type));
			err = -EIO;
		}
		goto err_out2;
	}
	/*
	 * Extend the attribute record to be able to store the new attribute
	 * size.
	 */
	if (new_size >= vol->mft_record_size || ntfs_attr_record_resize(m, a,
			le16_to_cpu(a->data.resident.value_offset) +
			new_size)) {
		/* Not enough space in the mft record. */
		ntfs_error(vol->sb, "Not enough space in the mft record for "
				"the resized attribute value.  This is not "
				"supported yet.  Aborting write.");
		err = -EOPNOTSUPP;
		goto err_out2;
	}
	/*
	 * We have enough space in the mft record to fit the write.  This
	 * implies the attribute is smaller than the mft record and hence the
	 * attribute must be in a single page and hence page->index must be 0.
	 */
	BUG_ON(page->index);
	/*
	 * If the beginning of the write is past the old size, enlarge the
	 * attribute value up to the beginning of the write and fill it with
	 * zeroes.
	 */
	if (from > attr_len) {
		memset((u8*)a + le16_to_cpu(a->data.resident.value_offset) +
				attr_len, 0, from - attr_len);
		a->data.resident.value_length = cpu_to_le32(from);
		/* Zero the corresponding area in the page as well. */
		if (PageUptodate(page)) {
			kaddr = kmap_atomic(page, KM_USER0);
			memset(kaddr + attr_len, 0, from - attr_len);
			kunmap_atomic(kaddr, KM_USER0);
			flush_dcache_page(page);
		}
	}
	flush_dcache_mft_record_page(ctx->ntfs_ino);
	mark_mft_record_dirty(ctx->ntfs_ino);
done_unm:
	ntfs_attr_put_search_ctx(ctx);
	unmap_mft_record(base_ni);
	/*
	 * Because resident attributes are handled by memcpy() to/from the
	 * corresponding MFT record, and because this form of i/o is byte
	 * aligned rather than block aligned, there is no need to bring the
	 * page uptodate here as in the non-resident case where we need to
	 * bring the buffers straddled by the write uptodate before
	 * generic_file_write() does the copying from userspace.
	 *
	 * We thus defer the uptodate bringing of the page region outside the
	 * region written to to ntfs_commit_write(), which makes the code
	 * simpler and saves one atomic kmap which is good.
	 */
done:
	ntfs_debug("Done.");
	return 0;
err_out:
	if (err == -ENOMEM)
		ntfs_warning(vi->i_sb, "Error allocating memory required to "
				"prepare the write.");
	else {
		ntfs_error(vi->i_sb, "Resident attribute prepare write failed "
				"with error %i.", err);
		NVolSetErrors(vol);
		make_bad_inode(vi);
	}
err_out2:
	if (ctx)
		ntfs_attr_put_search_ctx(ctx);
	if (m)
		unmap_mft_record(base_ni);
	return err;
}

/**
 * ntfs_commit_nonresident_write -
 *
 */
static int ntfs_commit_nonresident_write(struct page *page,
		unsigned from, unsigned to)
{
	s64 pos = ((s64)page->index << PAGE_CACHE_SHIFT) + to;
	struct inode *vi = page->mapping->host;
	struct buffer_head *bh, *head;
	unsigned int block_start, block_end, blocksize;
	BOOL partial;

	ntfs_debug("Entering for inode 0x%lx, attribute type 0x%x, page index "
			"0x%lx, from = %u, to = %u.", vi->i_ino,
			NTFS_I(vi)->type, page->index, from, to);
	blocksize = 1 << vi->i_blkbits;

	// FIXME: We need a whole slew of special cases in here for compressed
	// files for example...
	// For now, we know ntfs_prepare_write() would have failed so we can't
	// get here in any of the cases which we have to special case, so we
	// are just a ripped off, unrolled generic_commit_write().

	bh = head = page_buffers(page);
	block_start = 0;
	partial = FALSE;
	do {
		block_end = block_start + blocksize;
		if (block_end <= from || block_start >= to) {
			if (!buffer_uptodate(bh))
				partial = TRUE;
		} else {
			set_buffer_uptodate(bh);
			mark_buffer_dirty(bh);
		}
	} while (block_start = block_end, (bh = bh->b_this_page) != head);
	/*
	 * If this is a partial write which happened to make all buffers
	 * uptodate then we can optimize away a bogus ->readpage() for the next
	 * read().  Here we 'discover' whether the page went uptodate as a
	 * result of this (potentially partial) write.
	 */
	if (!partial)
		SetPageUptodate(page);
	/*
	 * Not convinced about this at all.  See disparity comment above.  For
	 * now we know ntfs_prepare_write() would have failed in the write
	 * exceeds i_size case, so this will never trigger which is fine.
	 */
	if (pos > i_size_read(vi)) {
		ntfs_error(vi->i_sb, "Writing beyond the existing file size is "
				"not supported yet.  Sorry.");
		return -EOPNOTSUPP;
		// vi->i_size = pos;
		// mark_inode_dirty(vi);
	}
	ntfs_debug("Done.");
	return 0;
}

/**
 * ntfs_commit_write - commit the received data
 *
 * This is called from generic_file_write() with i_sem held on the inode
 * (@page->mapping->host).  The @page is locked but not kmap()ped.  The source
 * data has already been copied into the @page.  ntfs_prepare_write() has been
 * called before the data copied and it returned success so we can take the
 * results of various BUG checks and some error handling for granted.
 *
 * Need to mark modified blocks dirty so they get written out later when
 * ntfs_writepage() is invoked by the VM.
 *
 * Return 0 on success or -errno on error.
 *
 * Should be using generic_commit_write().  This marks buffers uptodate and
 * dirty, sets the page uptodate if all buffers in the page are uptodate, and
 * updates i_size if the end of io is beyond i_size.  In that case, it also
 * marks the inode dirty.
 *
 * Cannot use generic_commit_write() due to ntfs specialities but can look at
 * it for implementation guidance.
 *
 * If things have gone as outlined in ntfs_prepare_write(), then we do not
 * need to do any page content modifications here at all, except in the write
 * to resident attribute case, where we need to do the uptodate bringing here
 * which we combine with the copying into the mft record which means we save
 * one atomic kmap.
 */
static int ntfs_commit_write(struct file *file, struct page *page,
		unsigned from, unsigned to)
{
	struct inode *vi = page->mapping->host;
	ntfs_inode *base_ni, *ni = NTFS_I(vi);
	char *kaddr, *kattr;
	ntfs_attr_search_ctx *ctx;
	MFT_RECORD *m;
	ATTR_RECORD *a;
	u32 attr_len;
	int err;

	ntfs_debug("Entering for inode 0x%lx, attribute type 0x%x, page index "
			"0x%lx, from = %u, to = %u.", vi->i_ino, ni->type,
			page->index, from, to);
	/* If the attribute is not resident, deal with it elsewhere. */
	if (NInoNonResident(ni)) {
		/* Only unnamed $DATA attributes can be compressed/encrypted. */
		if (ni->type == AT_DATA && !ni->name_len) {
			/* Encrypted files need separate handling. */
			if (NInoEncrypted(ni)) {
				// We never get here at present!
				BUG();
			}
			/* Compressed data streams are handled in compress.c. */
			if (NInoCompressed(ni)) {
				// TODO: Implement this!
				// return ntfs_write_compressed_block(page);
				// We never get here at present!
				BUG();
			}
		}
		/* Normal data stream. */
		return ntfs_commit_nonresident_write(page, from, to);
	}
	/*
	 * Attribute is resident, implying it is not compressed, encrypted, or
	 * sparse.
	 */
	if (!NInoAttr(ni))
		base_ni = ni;
	else
		base_ni = ni->ext.base_ntfs_ino;
	/* Map, pin, and lock the mft record. */
	m = map_mft_record(base_ni);
	if (IS_ERR(m)) {
		err = PTR_ERR(m);
		m = NULL;
		ctx = NULL;
		goto err_out;
	}
	ctx = ntfs_attr_get_search_ctx(base_ni, m);
	if (unlikely(!ctx)) {
		err = -ENOMEM;
		goto err_out;
	}
	err = ntfs_attr_lookup(ni->type, ni->name, ni->name_len,
			CASE_SENSITIVE, 0, NULL, 0, ctx);
	if (unlikely(err)) {
		if (err == -ENOENT)
			err = -EIO;
		goto err_out;
	}
	a = ctx->attr;
	/* The total length of the attribute value. */
	attr_len = le32_to_cpu(a->data.resident.value_length);
	BUG_ON(from > attr_len);
	kattr = (u8*)a + le16_to_cpu(a->data.resident.value_offset);
	kaddr = kmap_atomic(page, KM_USER0);
	/* Copy the received data from the page to the mft record. */
	memcpy(kattr + from, kaddr + from, to - from);
	/* Update the attribute length if necessary. */
	if (to > attr_len) {
		attr_len = to;
		a->data.resident.value_length = cpu_to_le32(attr_len);
	}
	/*
	 * If the page is not uptodate, bring the out of bounds area(s)
	 * uptodate by copying data from the mft record to the page.
	 */
	if (!PageUptodate(page)) {
		if (from > 0)
			memcpy(kaddr, kattr, from);
		if (to < attr_len)
			memcpy(kaddr + to, kattr + to, attr_len - to);
		/* Zero the region outside the end of the attribute value. */
		if (attr_len < PAGE_CACHE_SIZE)
			memset(kaddr + attr_len, 0, PAGE_CACHE_SIZE - attr_len);
		/*
		 * The probability of not having done any of the above is
		 * extremely small, so we just flush unconditionally.
		 */
		flush_dcache_page(page);
		SetPageUptodate(page);
	}
	kunmap_atomic(kaddr, KM_USER0);
	/* Update i_size if necessary. */
	if (i_size_read(vi) < attr_len) {
		unsigned long flags;

		write_lock_irqsave(&ni->size_lock, flags);
		ni->allocated_size = ni->initialized_size = attr_len;
		i_size_write(vi, attr_len);
		write_unlock_irqrestore(&ni->size_lock, flags);
	}
	/* Mark the mft record dirty, so it gets written back. */
	flush_dcache_mft_record_page(ctx->ntfs_ino);
	mark_mft_record_dirty(ctx->ntfs_ino);
	ntfs_attr_put_search_ctx(ctx);
	unmap_mft_record(base_ni);
	ntfs_debug("Done.");
	return 0;
err_out:
	if (err == -ENOMEM) {
		ntfs_warning(vi->i_sb, "Error allocating memory required to "
				"commit the write.");
		if (PageUptodate(page)) {
			ntfs_warning(vi->i_sb, "Page is uptodate, setting "
					"dirty so the write will be retried "
					"later on by the VM.");
			/*
			 * Put the page on mapping->dirty_pages, but leave its
			 * buffers' dirty state as-is.
			 */
			__set_page_dirty_nobuffers(page);
			err = 0;
		} else
			ntfs_error(vi->i_sb, "Page is not uptodate.  Written "
					"data has been lost.");
	} else {
		ntfs_error(vi->i_sb, "Resident attribute commit write failed "
				"with error %i.", err);
		NVolSetErrors(ni->vol);
		make_bad_inode(vi);
	}
	if (ctx)
		ntfs_attr_put_search_ctx(ctx);
	if (m)
		unmap_mft_record(base_ni);
	return err;
}

#endif	/* NTFS_RW */

/**
 * ntfs_aops - general address space operations for inodes and attributes
 */
struct address_space_operations ntfs_aops = {
	.readpage	= ntfs_readpage,	/* Fill page with data. */
	.sync_page	= block_sync_page,	/* Currently, just unplugs the
						   disk request queue. */
#ifdef NTFS_RW
	.writepage	= ntfs_writepage,	/* Write dirty page to disk. */
	.prepare_write	= ntfs_prepare_write,	/* Prepare page and buffers
						   ready to receive data. */
	.commit_write	= ntfs_commit_write,	/* Commit received data. */
#endif /* NTFS_RW */
};

/**
 * ntfs_mst_aops - general address space operations for mst protecteed inodes
 *		   and attributes
 */
struct address_space_operations ntfs_mst_aops = {
	.readpage	= ntfs_readpage,	/* Fill page with data. */
	.sync_page	= block_sync_page,	/* Currently, just unplugs the
						   disk request queue. */
#ifdef NTFS_RW
	.writepage	= ntfs_writepage,	/* Write dirty page to disk. */
	.set_page_dirty	= __set_page_dirty_nobuffers,	/* Set the page dirty
						   without touching the buffers
						   belonging to the page. */
#endif /* NTFS_RW */
};

#ifdef NTFS_RW

/**
 * mark_ntfs_record_dirty - mark an ntfs record dirty
 * @page:	page containing the ntfs record to mark dirty
 * @ofs:	byte offset within @page at which the ntfs record begins
 *
 * Set the buffers and the page in which the ntfs record is located dirty.
 *
 * The latter also marks the vfs inode the ntfs record belongs to dirty
 * (I_DIRTY_PAGES only).
 *
 * If the page does not have buffers, we create them and set them uptodate.
 * The page may not be locked which is why we need to handle the buffers under
 * the mapping->private_lock.  Once the buffers are marked dirty we no longer
 * need the lock since try_to_free_buffers() does not free dirty buffers.
 */
void mark_ntfs_record_dirty(struct page *page, const unsigned int ofs) {
	struct address_space *mapping = page->mapping;
	ntfs_inode *ni = NTFS_I(mapping->host);
	struct buffer_head *bh, *head, *buffers_to_free = NULL;
	unsigned int end, bh_size, bh_ofs;

	BUG_ON(!PageUptodate(page));
	end = ofs + ni->itype.index.block_size;
	bh_size = 1 << VFS_I(ni)->i_blkbits;
	spin_lock(&mapping->private_lock);
	if (unlikely(!page_has_buffers(page))) {
		spin_unlock(&mapping->private_lock);
		bh = head = alloc_page_buffers(page, bh_size, 1);
		spin_lock(&mapping->private_lock);
		if (likely(!page_has_buffers(page))) {
			struct buffer_head *tail;

			do {
				set_buffer_uptodate(bh);
				tail = bh;
				bh = bh->b_this_page;
			} while (bh);
			tail->b_this_page = head;
			attach_page_buffers(page, head);
		} else
			buffers_to_free = bh;
	}
	bh = head = page_buffers(page);
	do {
		bh_ofs = bh_offset(bh);
		if (bh_ofs + bh_size <= ofs)
			continue;
		if (unlikely(bh_ofs >= end))
			break;
		set_buffer_dirty(bh);
	} while ((bh = bh->b_this_page) != head);
	spin_unlock(&mapping->private_lock);
	__set_page_dirty_nobuffers(page);
	if (unlikely(buffers_to_free)) {
		do {
			bh = buffers_to_free->b_this_page;
			free_buffer_head(buffers_to_free);
			buffers_to_free = bh;
		} while (buffers_to_free);
	}
}

#endif /* NTFS_RW */