summaryrefslogtreecommitdiff
path: root/drivers/block/drbd/drbd_bitmap.c
blob: 7b976296b564faeed6a676afb22119bb99500174 (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
/*
   drbd_bitmap.c

   This file is part of DRBD by Philipp Reisner and Lars Ellenberg.

   Copyright (C) 2004-2008, LINBIT Information Technologies GmbH.
   Copyright (C) 2004-2008, Philipp Reisner <philipp.reisner@linbit.com>.
   Copyright (C) 2004-2008, Lars Ellenberg <lars.ellenberg@linbit.com>.

   drbd 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, or (at your option)
   any later version.

   drbd 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 drbd; see the file COPYING.  If not, write to
   the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#include <linux/bitops.h>
#include <linux/vmalloc.h>
#include <linux/string.h>
#include <linux/drbd.h>
#include <linux/slab.h>
#include <asm/kmap_types.h>

#include "drbd_int.h"


/* OPAQUE outside this file!
 * interface defined in drbd_int.h

 * convention:
 * function name drbd_bm_... => used elsewhere, "public".
 * function name      bm_... => internal to implementation, "private".
 */


/*
 * LIMITATIONS:
 * We want to support >= peta byte of backend storage, while for now still using
 * a granularity of one bit per 4KiB of storage.
 * 1 << 50		bytes backend storage (1 PiB)
 * 1 << (50 - 12)	bits needed
 *	38 --> we need u64 to index and count bits
 * 1 << (38 - 3)	bitmap bytes needed
 *	35 --> we still need u64 to index and count bytes
 *			(that's 32 GiB of bitmap for 1 PiB storage)
 * 1 << (35 - 2)	32bit longs needed
 *	33 --> we'd even need u64 to index and count 32bit long words.
 * 1 << (35 - 3)	64bit longs needed
 *	32 --> we could get away with a 32bit unsigned int to index and count
 *	64bit long words, but I rather stay with unsigned long for now.
 *	We probably should neither count nor point to bytes or long words
 *	directly, but either by bitnumber, or by page index and offset.
 * 1 << (35 - 12)
 *	22 --> we need that much 4KiB pages of bitmap.
 *	1 << (22 + 3) --> on a 64bit arch,
 *	we need 32 MiB to store the array of page pointers.
 *
 * Because I'm lazy, and because the resulting patch was too large, too ugly
 * and still incomplete, on 32bit we still "only" support 16 TiB (minus some),
 * (1 << 32) bits * 4k storage.
 *

 * bitmap storage and IO:
 *	Bitmap is stored little endian on disk, and is kept little endian in
 *	core memory. Currently we still hold the full bitmap in core as long
 *	as we are "attached" to a local disk, which at 32 GiB for 1PiB storage
 *	seems excessive.
 *
 *	We plan to reduce the amount of in-core bitmap pages by paging them in
 *	and out against their on-disk location as necessary, but need to make
 *	sure we don't cause too much meta data IO, and must not deadlock in
 *	tight memory situations. This needs some more work.
 */

/*
 * NOTE
 *  Access to the *bm_pages is protected by bm_lock.
 *  It is safe to read the other members within the lock.
 *
 *  drbd_bm_set_bits is called from bio_endio callbacks,
 *  We may be called with irq already disabled,
 *  so we need spin_lock_irqsave().
 *  And we need the kmap_atomic.
 */
struct drbd_bitmap {
	struct page **bm_pages;
	spinlock_t bm_lock;

	/* see LIMITATIONS: above */

	unsigned long bm_set;       /* nr of set bits; THINK maybe atomic_t? */
	unsigned long bm_bits;
	size_t   bm_words;
	size_t   bm_number_of_pages;
	sector_t bm_dev_capacity;
	struct mutex bm_change; /* serializes resize operations */

	wait_queue_head_t bm_io_wait; /* used to serialize IO of single pages */

	enum bm_flag bm_flags;

	/* debugging aid, in case we are still racy somewhere */
	char          *bm_why;
	struct task_struct *bm_task;
};

#define bm_print_lock_info(m) __bm_print_lock_info(m, __func__)
static void __bm_print_lock_info(struct drbd_conf *mdev, const char *func)
{
	struct drbd_bitmap *b = mdev->bitmap;
	if (!__ratelimit(&drbd_ratelimit_state))
		return;
	dev_err(DEV, "FIXME %s in %s, bitmap locked for '%s' by %s\n",
	    current == mdev->receiver.task ? "receiver" :
	    current == mdev->asender.task  ? "asender"  :
	    current == mdev->worker.task   ? "worker"   : current->comm,
	    func, b->bm_why ?: "?",
	    b->bm_task == mdev->receiver.task ? "receiver" :
	    b->bm_task == mdev->asender.task  ? "asender"  :
	    b->bm_task == mdev->worker.task   ? "worker"   : "?");
}

void drbd_bm_lock(struct drbd_conf *mdev, char *why, enum bm_flag flags)
{
	struct drbd_bitmap *b = mdev->bitmap;
	int trylock_failed;

	if (!b) {
		dev_err(DEV, "FIXME no bitmap in drbd_bm_lock!?\n");
		return;
	}

	trylock_failed = !mutex_trylock(&b->bm_change);

	if (trylock_failed) {
		dev_warn(DEV, "%s going to '%s' but bitmap already locked for '%s' by %s\n",
		    current == mdev->receiver.task ? "receiver" :
		    current == mdev->asender.task  ? "asender"  :
		    current == mdev->worker.task   ? "worker"   : current->comm,
		    why, b->bm_why ?: "?",
		    b->bm_task == mdev->receiver.task ? "receiver" :
		    b->bm_task == mdev->asender.task  ? "asender"  :
		    b->bm_task == mdev->worker.task   ? "worker"   : "?");
		mutex_lock(&b->bm_change);
	}
	if (BM_LOCKED_MASK & b->bm_flags)
		dev_err(DEV, "FIXME bitmap already locked in bm_lock\n");
	b->bm_flags |= flags & BM_LOCKED_MASK;

	b->bm_why  = why;
	b->bm_task = current;
}

void drbd_bm_unlock(struct drbd_conf *mdev)
{
	struct drbd_bitmap *b = mdev->bitmap;
	if (!b) {
		dev_err(DEV, "FIXME no bitmap in drbd_bm_unlock!?\n");
		return;
	}

	if (!(BM_LOCKED_MASK & mdev->bitmap->bm_flags))
		dev_err(DEV, "FIXME bitmap not locked in bm_unlock\n");

	b->bm_flags &= ~BM_LOCKED_MASK;
	b->bm_why  = NULL;
	b->bm_task = NULL;
	mutex_unlock(&b->bm_change);
}

/* we store some "meta" info about our pages in page->private */
/* at a granularity of 4k storage per bitmap bit:
 * one peta byte storage: 1<<50 byte, 1<<38 * 4k storage blocks
 *  1<<38 bits,
 *  1<<23 4k bitmap pages.
 * Use 24 bits as page index, covers 2 peta byte storage
 * at a granularity of 4k per bit.
 * Used to report the failed page idx on io error from the endio handlers.
 */
#define BM_PAGE_IDX_MASK	((1UL<<24)-1)
/* this page is currently read in, or written back */
#define BM_PAGE_IO_LOCK		31
/* if there has been an IO error for this page */
#define BM_PAGE_IO_ERROR	30
/* this is to be able to intelligently skip disk IO,
 * set if bits have been set since last IO. */
#define BM_PAGE_NEED_WRITEOUT	29
/* to mark for lazy writeout once syncer cleared all clearable bits,
 * we if bits have been cleared since last IO. */
#define BM_PAGE_LAZY_WRITEOUT	28

/* store_page_idx uses non-atomic assignment. It is only used directly after
 * allocating the page.  All other bm_set_page_* and bm_clear_page_* need to
 * use atomic bit manipulation, as set_out_of_sync (and therefore bitmap
 * changes) may happen from various contexts, and wait_on_bit/wake_up_bit
 * requires it all to be atomic as well. */
static void bm_store_page_idx(struct page *page, unsigned long idx)
{
	BUG_ON(0 != (idx & ~BM_PAGE_IDX_MASK));
	page_private(page) |= idx;
}

static unsigned long bm_page_to_idx(struct page *page)
{
	return page_private(page) & BM_PAGE_IDX_MASK;
}

/* As is very unlikely that the same page is under IO from more than one
 * context, we can get away with a bit per page and one wait queue per bitmap.
 */
static void bm_page_lock_io(struct drbd_conf *mdev, int page_nr)
{
	struct drbd_bitmap *b = mdev->bitmap;
	void *addr = &page_private(b->bm_pages[page_nr]);
	wait_event(b->bm_io_wait, !test_and_set_bit(BM_PAGE_IO_LOCK, addr));
}

static void bm_page_unlock_io(struct drbd_conf *mdev, int page_nr)
{
	struct drbd_bitmap *b = mdev->bitmap;
	void *addr = &page_private(b->bm_pages[page_nr]);
	clear_bit(BM_PAGE_IO_LOCK, addr);
	smp_mb__after_clear_bit();
	wake_up(&mdev->bitmap->bm_io_wait);
}

/* set _before_ submit_io, so it may be reset due to being changed
 * while this page is in flight... will get submitted later again */
static void bm_set_page_unchanged(struct page *page)
{
	/* use cmpxchg? */
	clear_bit(BM_PAGE_NEED_WRITEOUT, &page_private(page));
	clear_bit(BM_PAGE_LAZY_WRITEOUT, &page_private(page));
}

static void bm_set_page_need_writeout(struct page *page)
{
	set_bit(BM_PAGE_NEED_WRITEOUT, &page_private(page));
}

static int bm_test_page_unchanged(struct page *page)
{
	volatile const unsigned long *addr = &page_private(page);
	return (*addr & ((1UL<<BM_PAGE_NEED_WRITEOUT)|(1UL<<BM_PAGE_LAZY_WRITEOUT))) == 0;
}

static void bm_set_page_io_err(struct page *page)
{
	set_bit(BM_PAGE_IO_ERROR, &page_private(page));
}

static void bm_clear_page_io_err(struct page *page)
{
	clear_bit(BM_PAGE_IO_ERROR, &page_private(page));
}

static void bm_set_page_lazy_writeout(struct page *page)
{
	set_bit(BM_PAGE_LAZY_WRITEOUT, &page_private(page));
}

static int bm_test_page_lazy_writeout(struct page *page)
{
	return test_bit(BM_PAGE_LAZY_WRITEOUT, &page_private(page));
}

/* on a 32bit box, this would allow for exactly (2<<38) bits. */
static unsigned int bm_word_to_page_idx(struct drbd_bitmap *b, unsigned long long_nr)
{
	/* page_nr = (word*sizeof(long)) >> PAGE_SHIFT; */
	unsigned int page_nr = long_nr >> (PAGE_SHIFT - LN2_BPL + 3);
	BUG_ON(page_nr >= b->bm_number_of_pages);
	return page_nr;
}

static unsigned int bm_bit_to_page_idx(struct drbd_bitmap *b, u64 bitnr)
{
	/* page_nr = (bitnr/8) >> PAGE_SHIFT; */
	unsigned int page_nr = bitnr >> (PAGE_SHIFT + 3);
	BUG_ON(page_nr >= b->bm_number_of_pages);
	return page_nr;
}

static unsigned long *__bm_map_pidx(struct drbd_bitmap *b, unsigned int idx, const enum km_type km)
{
	struct page *page = b->bm_pages[idx];
	return (unsigned long *) kmap_atomic(page, km);
}

static unsigned long *bm_map_pidx(struct drbd_bitmap *b, unsigned int idx)
{
	return __bm_map_pidx(b, idx, KM_IRQ1);
}

static void __bm_unmap(unsigned long *p_addr, const enum km_type km)
{
	kunmap_atomic(p_addr, km);
};

static void bm_unmap(unsigned long *p_addr)
{
	return __bm_unmap(p_addr, KM_IRQ1);
}

/* long word offset of _bitmap_ sector */
#define S2W(s)	((s)<<(BM_EXT_SHIFT-BM_BLOCK_SHIFT-LN2_BPL))
/* word offset from start of bitmap to word number _in_page_
 * modulo longs per page
#define MLPP(X) ((X) % (PAGE_SIZE/sizeof(long))
 hm, well, Philipp thinks gcc might not optimize the % into & (... - 1)
 so do it explicitly:
 */
#define MLPP(X) ((X) & ((PAGE_SIZE/sizeof(long))-1))

/* Long words per page */
#define LWPP (PAGE_SIZE/sizeof(long))

/*
 * actually most functions herein should take a struct drbd_bitmap*, not a
 * struct drbd_conf*, but for the debug macros I like to have the mdev around
 * to be able to report device specific.
 */


static void bm_free_pages(struct page **pages, unsigned long number)
{
	unsigned long i;
	if (!pages)
		return;

	for (i = 0; i < number; i++) {
		if (!pages[i]) {
			printk(KERN_ALERT "drbd: bm_free_pages tried to free "
					  "a NULL pointer; i=%lu n=%lu\n",
					  i, number);
			continue;
		}
		__free_page(pages[i]);
		pages[i] = NULL;
	}
}

static void bm_vk_free(void *ptr, int v)
{
	if (v)
		vfree(ptr);
	else
		kfree(ptr);
}

/*
 * "have" and "want" are NUMBER OF PAGES.
 */
static struct page **bm_realloc_pages(struct drbd_bitmap *b, unsigned long want)
{
	struct page **old_pages = b->bm_pages;
	struct page **new_pages, *page;
	unsigned int i, bytes, vmalloced = 0;
	unsigned long have = b->bm_number_of_pages;

	BUG_ON(have == 0 && old_pages != NULL);
	BUG_ON(have != 0 && old_pages == NULL);

	if (have == want)
		return old_pages;

	/* Trying kmalloc first, falling back to vmalloc.
	 * GFP_KERNEL is ok, as this is done when a lower level disk is
	 * "attached" to the drbd.  Context is receiver thread or cqueue
	 * thread.  As we have no disk yet, we are not in the IO path,
	 * not even the IO path of the peer. */
	bytes = sizeof(struct page *)*want;
	new_pages = kmalloc(bytes, GFP_KERNEL);
	if (!new_pages) {
		new_pages = vmalloc(bytes);
		if (!new_pages)
			return NULL;
		vmalloced = 1;
	}

	memset(new_pages, 0, bytes);
	if (want >= have) {
		for (i = 0; i < have; i++)
			new_pages[i] = old_pages[i];
		for (; i < want; i++) {
			page = alloc_page(GFP_HIGHUSER);
			if (!page) {
				bm_free_pages(new_pages + have, i - have);
				bm_vk_free(new_pages, vmalloced);
				return NULL;
			}
			/* we want to know which page it is
			 * from the endio handlers */
			bm_store_page_idx(page, i);
			new_pages[i] = page;
		}
	} else {
		for (i = 0; i < want; i++)
			new_pages[i] = old_pages[i];
		/* NOT HERE, we are outside the spinlock!
		bm_free_pages(old_pages + want, have - want);
		*/
	}

	if (vmalloced)
		b->bm_flags |= BM_P_VMALLOCED;
	else
		b->bm_flags &= ~BM_P_VMALLOCED;

	return new_pages;
}

/*
 * called on driver init only. TODO call when a device is created.
 * allocates the drbd_bitmap, and stores it in mdev->bitmap.
 */
int drbd_bm_init(struct drbd_conf *mdev)
{
	struct drbd_bitmap *b = mdev->bitmap;
	WARN_ON(b != NULL);
	b = kzalloc(sizeof(struct drbd_bitmap), GFP_KERNEL);
	if (!b)
		return -ENOMEM;
	spin_lock_init(&b->bm_lock);
	mutex_init(&b->bm_change);
	init_waitqueue_head(&b->bm_io_wait);

	mdev->bitmap = b;

	return 0;
}

sector_t drbd_bm_capacity(struct drbd_conf *mdev)
{
	ERR_IF(!mdev->bitmap) return 0;
	return mdev->bitmap->bm_dev_capacity;
}

/* called on driver unload. TODO: call when a device is destroyed.
 */
void drbd_bm_cleanup(struct drbd_conf *mdev)
{
	ERR_IF (!mdev->bitmap) return;
	bm_free_pages(mdev->bitmap->bm_pages, mdev->bitmap->bm_number_of_pages);
	bm_vk_free(mdev->bitmap->bm_pages, (BM_P_VMALLOCED & mdev->bitmap->bm_flags));
	kfree(mdev->bitmap);
	mdev->bitmap = NULL;
}

/*
 * since (b->bm_bits % BITS_PER_LONG) != 0,
 * this masks out the remaining bits.
 * Returns the number of bits cleared.
 */
#define BITS_PER_PAGE		(1UL << (PAGE_SHIFT + 3))
#define BITS_PER_PAGE_MASK	(BITS_PER_PAGE - 1)
#define BITS_PER_LONG_MASK	(BITS_PER_LONG - 1)
static int bm_clear_surplus(struct drbd_bitmap *b)
{
	unsigned long mask;
	unsigned long *p_addr, *bm;
	int tmp;
	int cleared = 0;

	/* number of bits modulo bits per page */
	tmp = (b->bm_bits & BITS_PER_PAGE_MASK);
	/* mask the used bits of the word containing the last bit */
	mask = (1UL << (tmp & BITS_PER_LONG_MASK)) -1;
	/* bitmap is always stored little endian,
	 * on disk and in core memory alike */
	mask = cpu_to_lel(mask);

	p_addr = bm_map_pidx(b, b->bm_number_of_pages - 1);
	bm = p_addr + (tmp/BITS_PER_LONG);
	if (mask) {
		/* If mask != 0, we are not exactly aligned, so bm now points
		 * to the long containing the last bit.
		 * If mask == 0, bm already points to the word immediately
		 * after the last (long word aligned) bit. */
		cleared = hweight_long(*bm & ~mask);
		*bm &= mask;
		bm++;
	}

	if (BITS_PER_LONG == 32 && ((bm - p_addr) & 1) == 1) {
		/* on a 32bit arch, we may need to zero out
		 * a padding long to align with a 64bit remote */
		cleared += hweight_long(*bm);
		*bm = 0;
	}
	bm_unmap(p_addr);
	return cleared;
}

static void bm_set_surplus(struct drbd_bitmap *b)
{
	unsigned long mask;
	unsigned long *p_addr, *bm;
	int tmp;

	/* number of bits modulo bits per page */
	tmp = (b->bm_bits & BITS_PER_PAGE_MASK);
	/* mask the used bits of the word containing the last bit */
	mask = (1UL << (tmp & BITS_PER_LONG_MASK)) -1;
	/* bitmap is always stored little endian,
	 * on disk and in core memory alike */
	mask = cpu_to_lel(mask);

	p_addr = bm_map_pidx(b, b->bm_number_of_pages - 1);
	bm = p_addr + (tmp/BITS_PER_LONG);
	if (mask) {
		/* If mask != 0, we are not exactly aligned, so bm now points
		 * to the long containing the last bit.
		 * If mask == 0, bm already points to the word immediately
		 * after the last (long word aligned) bit. */
		*bm |= ~mask;
		bm++;
	}

	if (BITS_PER_LONG == 32 && ((bm - p_addr) & 1) == 1) {
		/* on a 32bit arch, we may need to zero out
		 * a padding long to align with a 64bit remote */
		*bm = ~0UL;
	}
	bm_unmap(p_addr);
}

/* you better not modify the bitmap while this is running,
 * or its results will be stale */
static unsigned long bm_count_bits(struct drbd_bitmap *b)
{
	unsigned long *p_addr;
	unsigned long bits = 0;
	unsigned long mask = (1UL << (b->bm_bits & BITS_PER_LONG_MASK)) -1;
	int idx, i, last_word;

	/* all but last page */
	for (idx = 0; idx < b->bm_number_of_pages - 1; idx++) {
		p_addr = __bm_map_pidx(b, idx, KM_USER0);
		for (i = 0; i < LWPP; i++)
			bits += hweight_long(p_addr[i]);
		__bm_unmap(p_addr, KM_USER0);
		cond_resched();
	}
	/* last (or only) page */
	last_word = ((b->bm_bits - 1) & BITS_PER_PAGE_MASK) >> LN2_BPL;
	p_addr = __bm_map_pidx(b, idx, KM_USER0);
	for (i = 0; i < last_word; i++)
		bits += hweight_long(p_addr[i]);
	p_addr[last_word] &= cpu_to_lel(mask);
	bits += hweight_long(p_addr[last_word]);
	/* 32bit arch, may have an unused padding long */
	if (BITS_PER_LONG == 32 && (last_word & 1) == 0)
		p_addr[last_word+1] = 0;
	__bm_unmap(p_addr, KM_USER0);
	return bits;
}

/* offset and len in long words.*/
static void bm_memset(struct drbd_bitmap *b, size_t offset, int c, size_t len)
{
	unsigned long *p_addr, *bm;
	unsigned int idx;
	size_t do_now, end;

	end = offset + len;

	if (end > b->bm_words) {
		printk(KERN_ALERT "drbd: bm_memset end > bm_words\n");
		return;
	}

	while (offset < end) {
		do_now = min_t(size_t, ALIGN(offset + 1, LWPP), end) - offset;
		idx = bm_word_to_page_idx(b, offset);
		p_addr = bm_map_pidx(b, idx);
		bm = p_addr + MLPP(offset);
		if (bm+do_now > p_addr + LWPP) {
			printk(KERN_ALERT "drbd: BUG BUG BUG! p_addr:%p bm:%p do_now:%d\n",
			       p_addr, bm, (int)do_now);
		} else
			memset(bm, c, do_now * sizeof(long));
		bm_unmap(p_addr);
		bm_set_page_need_writeout(b->bm_pages[idx]);
		offset += do_now;
	}
}

/*
 * make sure the bitmap has enough room for the attached storage,
 * if necessary, resize.
 * called whenever we may have changed the device size.
 * returns -ENOMEM if we could not allocate enough memory, 0 on success.
 * In case this is actually a resize, we copy the old bitmap into the new one.
 * Otherwise, the bitmap is initialized to all bits set.
 */
int drbd_bm_resize(struct drbd_conf *mdev, sector_t capacity, int set_new_bits)
{
	struct drbd_bitmap *b = mdev->bitmap;
	unsigned long bits, words, owords, obits;
	unsigned long want, have, onpages; /* number of pages */
	struct page **npages, **opages = NULL;
	int err = 0, growing;
	int opages_vmalloced;

	ERR_IF(!b) return -ENOMEM;

	drbd_bm_lock(mdev, "resize", BM_LOCKED_MASK);

	dev_info(DEV, "drbd_bm_resize called with capacity == %llu\n",
			(unsigned long long)capacity);

	if (capacity == b->bm_dev_capacity)
		goto out;

	opages_vmalloced = (BM_P_VMALLOCED & b->bm_flags);

	if (capacity == 0) {
		spin_lock_irq(&b->bm_lock);
		opages = b->bm_pages;
		onpages = b->bm_number_of_pages;
		owords = b->bm_words;
		b->bm_pages = NULL;
		b->bm_number_of_pages =
		b->bm_set   =
		b->bm_bits  =
		b->bm_words =
		b->bm_dev_capacity = 0;
		spin_unlock_irq(&b->bm_lock);
		bm_free_pages(opages, onpages);
		bm_vk_free(opages, opages_vmalloced);
		goto out;
	}
	bits  = BM_SECT_TO_BIT(ALIGN(capacity, BM_SECT_PER_BIT));

	/* if we would use
	   words = ALIGN(bits,BITS_PER_LONG) >> LN2_BPL;
	   a 32bit host could present the wrong number of words
	   to a 64bit host.
	*/
	words = ALIGN(bits, 64) >> LN2_BPL;

	if (get_ldev(mdev)) {
		u64 bits_on_disk = ((u64)mdev->ldev->md.md_size_sect-MD_BM_OFFSET) << 12;
		put_ldev(mdev);
		if (bits > bits_on_disk) {
			dev_info(DEV, "bits = %lu\n", bits);
			dev_info(DEV, "bits_on_disk = %llu\n", bits_on_disk);
			err = -ENOSPC;
			goto out;
		}
	}

	want = ALIGN(words*sizeof(long), PAGE_SIZE) >> PAGE_SHIFT;
	have = b->bm_number_of_pages;
	if (want == have) {
		D_ASSERT(b->bm_pages != NULL);
		npages = b->bm_pages;
	} else {
		if (drbd_insert_fault(mdev, DRBD_FAULT_BM_ALLOC))
			npages = NULL;
		else
			npages = bm_realloc_pages(b, want);
	}

	if (!npages) {
		err = -ENOMEM;
		goto out;
	}

	spin_lock_irq(&b->bm_lock);
	opages = b->bm_pages;
	owords = b->bm_words;
	obits  = b->bm_bits;

	growing = bits > obits;
	if (opages && growing && set_new_bits)
		bm_set_surplus(b);

	b->bm_pages = npages;
	b->bm_number_of_pages = want;
	b->bm_bits  = bits;
	b->bm_words = words;
	b->bm_dev_capacity = capacity;

	if (growing) {
		if (set_new_bits) {
			bm_memset(b, owords, 0xff, words-owords);
			b->bm_set += bits - obits;
		} else
			bm_memset(b, owords, 0x00, words-owords);

	}

	if (want < have) {
		/* implicit: (opages != NULL) && (opages != npages) */
		bm_free_pages(opages + want, have - want);
	}

	(void)bm_clear_surplus(b);

	spin_unlock_irq(&b->bm_lock);
	if (opages != npages)
		bm_vk_free(opages, opages_vmalloced);
	if (!growing)
		b->bm_set = bm_count_bits(b);
	dev_info(DEV, "resync bitmap: bits=%lu words=%lu pages=%lu\n", bits, words, want);

 out:
	drbd_bm_unlock(mdev);
	return err;
}

/* inherently racy:
 * if not protected by other means, return value may be out of date when
 * leaving this function...
 * we still need to lock it, since it is important that this returns
 * bm_set == 0 precisely.
 *
 * maybe bm_set should be atomic_t ?
 */
unsigned long _drbd_bm_total_weight(struct drbd_conf *mdev)
{
	struct drbd_bitmap *b = mdev->bitmap;
	unsigned long s;
	unsigned long flags;

	ERR_IF(!b) return 0;
	ERR_IF(!b->bm_pages) return 0;

	spin_lock_irqsave(&b->bm_lock, flags);
	s = b->bm_set;
	spin_unlock_irqrestore(&b->bm_lock, flags);

	return s;
}

unsigned long drbd_bm_total_weight(struct drbd_conf *mdev)
{
	unsigned long s;
	/* if I don't have a disk, I don't know about out-of-sync status */
	if (!get_ldev_if_state(mdev, D_NEGOTIATING))
		return 0;
	s = _drbd_bm_total_weight(mdev);
	put_ldev(mdev);
	return s;
}

size_t drbd_bm_words(struct drbd_conf *mdev)
{
	struct drbd_bitmap *b = mdev->bitmap;
	ERR_IF(!b) return 0;
	ERR_IF(!b->bm_pages) return 0;

	return b->bm_words;
}

unsigned long drbd_bm_bits(struct drbd_conf *mdev)
{
	struct drbd_bitmap *b = mdev->bitmap;
	ERR_IF(!b) return 0;

	return b->bm_bits;
}

/* merge number words from buffer into the bitmap starting at offset.
 * buffer[i] is expected to be little endian unsigned long.
 * bitmap must be locked by drbd_bm_lock.
 * currently only used from receive_bitmap.
 */
void drbd_bm_merge_lel(struct drbd_conf *mdev, size_t offset, size_t number,
			unsigned long *buffer)
{
	struct drbd_bitmap *b = mdev->bitmap;
	unsigned long *p_addr, *bm;
	unsigned long word, bits;
	unsigned int idx;
	size_t end, do_now;

	end = offset + number;

	ERR_IF(!b) return;
	ERR_IF(!b->bm_pages) return;
	if (number == 0)
		return;
	WARN_ON(offset >= b->bm_words);
	WARN_ON(end    >  b->bm_words);

	spin_lock_irq(&b->bm_lock);
	while (offset < end) {
		do_now = min_t(size_t, ALIGN(offset+1, LWPP), end) - offset;
		idx = bm_word_to_page_idx(b, offset);
		p_addr = bm_map_pidx(b, idx);
		bm = p_addr + MLPP(offset);
		offset += do_now;
		while (do_now--) {
			bits = hweight_long(*bm);
			word = *bm | *buffer++;
			*bm++ = word;
			b->bm_set += hweight_long(word) - bits;
		}
		bm_unmap(p_addr);
		bm_set_page_need_writeout(b->bm_pages[idx]);
	}
	/* with 32bit <-> 64bit cross-platform connect
	 * this is only correct for current usage,
	 * where we _know_ that we are 64 bit aligned,
	 * and know that this function is used in this way, too...
	 */
	if (end == b->bm_words)
		b->bm_set -= bm_clear_surplus(b);
	spin_unlock_irq(&b->bm_lock);
}

/* copy number words from the bitmap starting at offset into the buffer.
 * buffer[i] will be little endian unsigned long.
 */
void drbd_bm_get_lel(struct drbd_conf *mdev, size_t offset, size_t number,
		     unsigned long *buffer)
{
	struct drbd_bitmap *b = mdev->bitmap;
	unsigned long *p_addr, *bm;
	size_t end, do_now;

	end = offset + number;

	ERR_IF(!b) return;
	ERR_IF(!b->bm_pages) return;

	spin_lock_irq(&b->bm_lock);
	if ((offset >= b->bm_words) ||
	    (end    >  b->bm_words) ||
	    (number <= 0))
		dev_err(DEV, "offset=%lu number=%lu bm_words=%lu\n",
			(unsigned long)	offset,
			(unsigned long)	number,
			(unsigned long) b->bm_words);
	else {
		while (offset < end) {
			do_now = min_t(size_t, ALIGN(offset+1, LWPP), end) - offset;
			p_addr = bm_map_pidx(b, bm_word_to_page_idx(b, offset));
			bm = p_addr + MLPP(offset);
			offset += do_now;
			while (do_now--)
				*buffer++ = *bm++;
			bm_unmap(p_addr);
		}
	}
	spin_unlock_irq(&b->bm_lock);
}

/* set all bits in the bitmap */
void drbd_bm_set_all(struct drbd_conf *mdev)
{
	struct drbd_bitmap *b = mdev->bitmap;
	ERR_IF(!b) return;
	ERR_IF(!b->bm_pages) return;

	spin_lock_irq(&b->bm_lock);
	bm_memset(b, 0, 0xff, b->bm_words);
	(void)bm_clear_surplus(b);
	b->bm_set = b->bm_bits;
	spin_unlock_irq(&b->bm_lock);
}

/* clear all bits in the bitmap */
void drbd_bm_clear_all(struct drbd_conf *mdev)
{
	struct drbd_bitmap *b = mdev->bitmap;
	ERR_IF(!b) return;
	ERR_IF(!b->bm_pages) return;

	spin_lock_irq(&b->bm_lock);
	bm_memset(b, 0, 0, b->bm_words);
	b->bm_set = 0;
	spin_unlock_irq(&b->bm_lock);
}

struct bm_aio_ctx {
	struct drbd_conf *mdev;
	atomic_t in_flight;
	struct completion done;
	unsigned flags;
#define BM_AIO_COPY_PAGES	1
	int error;
};

/* bv_page may be a copy, or may be the original */
static void bm_async_io_complete(struct bio *bio, int error)
{
	struct bm_aio_ctx *ctx = bio->bi_private;
	struct drbd_conf *mdev = ctx->mdev;
	struct drbd_bitmap *b = mdev->bitmap;
	unsigned int idx = bm_page_to_idx(bio->bi_io_vec[0].bv_page);
	int uptodate = bio_flagged(bio, BIO_UPTODATE);


	/* strange behavior of some lower level drivers...
	 * fail the request by clearing the uptodate flag,
	 * but do not return any error?!
	 * do we want to WARN() on this? */
	if (!error && !uptodate)
		error = -EIO;

	if ((ctx->flags & BM_AIO_COPY_PAGES) == 0 &&
	    !bm_test_page_unchanged(b->bm_pages[idx]))
		dev_warn(DEV, "bitmap page idx %u changed during IO!\n", idx);

	if (error) {
		/* ctx error will hold the completed-last non-zero error code,
		 * in case error codes differ. */
		ctx->error = error;
		bm_set_page_io_err(b->bm_pages[idx]);
		/* Not identical to on disk version of it.
		 * Is BM_PAGE_IO_ERROR enough? */
		if (__ratelimit(&drbd_ratelimit_state))
			dev_err(DEV, "IO ERROR %d on bitmap page idx %u\n",
					error, idx);
	} else {
		bm_clear_page_io_err(b->bm_pages[idx]);
		dynamic_dev_dbg(DEV, "bitmap page idx %u completed\n", idx);
	}

	bm_page_unlock_io(mdev, idx);

	/* FIXME give back to page pool */
	if (ctx->flags & BM_AIO_COPY_PAGES)
		put_page(bio->bi_io_vec[0].bv_page);

	bio_put(bio);

	if (atomic_dec_and_test(&ctx->in_flight))
		complete(&ctx->done);
}

static void bm_page_io_async(struct bm_aio_ctx *ctx, int page_nr, int rw) __must_hold(local)
{
	/* we are process context. we always get a bio */
	struct bio *bio = bio_alloc(GFP_KERNEL, 1);
	struct drbd_conf *mdev = ctx->mdev;
	struct drbd_bitmap *b = mdev->bitmap;
	struct page *page;
	unsigned int len;

	sector_t on_disk_sector =
		mdev->ldev->md.md_offset + mdev->ldev->md.bm_offset;
	on_disk_sector += ((sector_t)page_nr) << (PAGE_SHIFT-9);

	/* this might happen with very small
	 * flexible external meta data device,
	 * or with PAGE_SIZE > 4k */
	len = min_t(unsigned int, PAGE_SIZE,
		(drbd_md_last_sector(mdev->ldev) - on_disk_sector + 1)<<9);

	/* serialize IO on this page */
	bm_page_lock_io(mdev, page_nr);
	/* before memcpy and submit,
	 * so it can be redirtied any time */
	bm_set_page_unchanged(b->bm_pages[page_nr]);

	if (ctx->flags & BM_AIO_COPY_PAGES) {
		/* FIXME alloc_page is good enough for now, but actually needs
		 * to use pre-allocated page pool */
		void *src, *dest;
		page = alloc_page(__GFP_HIGHMEM|__GFP_WAIT);
		dest = kmap_atomic(page, KM_USER0);
		src = kmap_atomic(b->bm_pages[page_nr], KM_USER1);
		memcpy(dest, src, PAGE_SIZE);
		kunmap_atomic(src, KM_USER1);
		kunmap_atomic(dest, KM_USER0);
		bm_store_page_idx(page, page_nr);
	} else
		page = b->bm_pages[page_nr];

	bio->bi_bdev = mdev->ldev->md_bdev;
	bio->bi_sector = on_disk_sector;
	bio_add_page(bio, page, len, 0);
	bio->bi_private = ctx;
	bio->bi_end_io = bm_async_io_complete;

	if (drbd_insert_fault(mdev, (rw & WRITE) ? DRBD_FAULT_MD_WR : DRBD_FAULT_MD_RD)) {
		bio->bi_rw |= rw;
		bio_endio(bio, -EIO);
	} else {
		submit_bio(rw, bio);
		/* this should not count as user activity and cause the
		 * resync to throttle -- see drbd_rs_should_slow_down(). */
		atomic_add(len >> 9, &mdev->rs_sect_ev);
	}
}

/*
 * bm_rw: read/write the whole bitmap from/to its on disk location.
 */
static int bm_rw(struct drbd_conf *mdev, int rw, unsigned lazy_writeout_upper_idx) __must_hold(local)
{
	struct bm_aio_ctx ctx = {
		.mdev = mdev,
		.in_flight = ATOMIC_INIT(1),
		.done = COMPLETION_INITIALIZER_ONSTACK(ctx.done),
		.flags = lazy_writeout_upper_idx ? BM_AIO_COPY_PAGES : 0,
	};
	struct drbd_bitmap *b = mdev->bitmap;
	int num_pages, i, count = 0;
	unsigned long now;
	char ppb[10];
	int err = 0;

	/*
	 * We are protected against bitmap disappearing/resizing by holding an
	 * ldev reference (caller must have called get_ldev()).
	 * For read/write, we are protected against changes to the bitmap by
	 * the bitmap lock (see drbd_bitmap_io).
	 * For lazy writeout, we don't care for ongoing changes to the bitmap,
	 * as we submit copies of pages anyways.
	 */
	if (!ctx.flags)
		WARN_ON(!(BM_LOCKED_MASK & b->bm_flags));

	num_pages = b->bm_number_of_pages;

	now = jiffies;

	/* let the layers below us try to merge these bios... */
	for (i = 0; i < num_pages; i++) {
		/* ignore completely unchanged pages */
		if (lazy_writeout_upper_idx && i == lazy_writeout_upper_idx)
			break;
		if (rw & WRITE) {
			if (bm_test_page_unchanged(b->bm_pages[i])) {
				dynamic_dev_dbg(DEV, "skipped bm write for idx %u\n", i);
				continue;
			}
			/* during lazy writeout,
			 * ignore those pages not marked for lazy writeout. */
			if (lazy_writeout_upper_idx &&
			    !bm_test_page_lazy_writeout(b->bm_pages[i])) {
				dynamic_dev_dbg(DEV, "skipped bm lazy write for idx %u\n", i);
				continue;
			}
		}
		atomic_inc(&ctx.in_flight);
		bm_page_io_async(&ctx, i, rw);
		++count;
		cond_resched();
	}

	/*
	 * We initialize ctx.in_flight to one to make sure bm_async_io_complete
	 * will not complete() early, and decrement / test it here.  If there
	 * are still some bios in flight, we need to wait for them here.
	 */
	if (!atomic_dec_and_test(&ctx.in_flight))
		wait_for_completion(&ctx.done);
	dev_info(DEV, "bitmap %s of %u pages took %lu jiffies\n",
			rw == WRITE ? "WRITE" : "READ",
			count, jiffies - now);

	if (ctx.error) {
		dev_alert(DEV, "we had at least one MD IO ERROR during bitmap IO\n");
		drbd_chk_io_error(mdev, 1, true);
		err = -EIO; /* ctx.error ? */
	}

	now = jiffies;
	if (rw == WRITE) {
		drbd_md_flush(mdev);
	} else /* rw == READ */ {
		b->bm_set = bm_count_bits(b);
		dev_info(DEV, "recounting of set bits took additional %lu jiffies\n",
		     jiffies - now);
	}
	now = b->bm_set;

	dev_info(DEV, "%s (%lu bits) marked out-of-sync by on disk bit-map.\n",
	     ppsize(ppb, now << (BM_BLOCK_SHIFT-10)), now);

	return err;
}

/**
 * drbd_bm_read() - Read the whole bitmap from its on disk location.
 * @mdev:	DRBD device.
 */
int drbd_bm_read(struct drbd_conf *mdev) __must_hold(local)
{
	return bm_rw(mdev, READ, 0);
}

/**
 * drbd_bm_write() - Write the whole bitmap to its on disk location.
 * @mdev:	DRBD device.
 *
 * Will only write pages that have changed since last IO.
 */
int drbd_bm_write(struct drbd_conf *mdev) __must_hold(local)
{
	return bm_rw(mdev, WRITE, 0);
}

/**
 * drbd_bm_lazy_write_out() - Write bitmap pages 0 to @upper_idx-1, if they have changed.
 * @mdev:	DRBD device.
 * @upper_idx:	0: write all changed pages; +ve: page index to stop scanning for changed pages
 */
int drbd_bm_write_lazy(struct drbd_conf *mdev, unsigned upper_idx) __must_hold(local)
{
	return bm_rw(mdev, WRITE, upper_idx);
}


/**
 * drbd_bm_write_page: Writes a PAGE_SIZE aligned piece of bitmap
 * @mdev:	DRBD device.
 * @idx:	bitmap page index
 *
 * We don't want to special case on logical_block_size of the backend device,
 * so we submit PAGE_SIZE aligned pieces.
 * Note that on "most" systems, PAGE_SIZE is 4k.
 *
 * In case this becomes an issue on systems with larger PAGE_SIZE,
 * we may want to change this again to write 4k aligned 4k pieces.
 */
int drbd_bm_write_page(struct drbd_conf *mdev, unsigned int idx) __must_hold(local)
{
	struct bm_aio_ctx ctx = {
		.mdev = mdev,
		.in_flight = ATOMIC_INIT(1),
		.done = COMPLETION_INITIALIZER_ONSTACK(ctx.done),
		.flags = BM_AIO_COPY_PAGES,
	};

	if (bm_test_page_unchanged(mdev->bitmap->bm_pages[idx])) {
		dynamic_dev_dbg(DEV, "skipped bm page write for idx %u\n", idx);
		return 0;
	}

	bm_page_io_async(&ctx, idx, WRITE_SYNC);
	wait_for_completion(&ctx.done);

	if (ctx.error)
		drbd_chk_io_error(mdev, 1, true);
		/* that should force detach, so the in memory bitmap will be
		 * gone in a moment as well. */

	mdev->bm_writ_cnt++;
	return ctx.error;
}

/* NOTE
 * find_first_bit returns int, we return unsigned long.
 * For this to work on 32bit arch with bitnumbers > (1<<32),
 * we'd need to return u64, and get a whole lot of other places
 * fixed where we still use unsigned long.
 *
 * this returns a bit number, NOT a sector!
 */
static unsigned long __bm_find_next(struct drbd_conf *mdev, unsigned long bm_fo,
	const int find_zero_bit, const enum km_type km)
{
	struct drbd_bitmap *b = mdev->bitmap;
	unsigned long *p_addr;
	unsigned long bit_offset;
	unsigned i;


	if (bm_fo > b->bm_bits) {
		dev_err(DEV, "bm_fo=%lu bm_bits=%lu\n", bm_fo, b->bm_bits);
		bm_fo = DRBD_END_OF_BITMAP;
	} else {
		while (bm_fo < b->bm_bits) {
			/* bit offset of the first bit in the page */
			bit_offset = bm_fo & ~BITS_PER_PAGE_MASK;
			p_addr = __bm_map_pidx(b, bm_bit_to_page_idx(b, bm_fo), km);

			if (find_zero_bit)
				i = find_next_zero_bit_le(p_addr,
						PAGE_SIZE*8, bm_fo & BITS_PER_PAGE_MASK);
			else
				i = find_next_bit_le(p_addr,
						PAGE_SIZE*8, bm_fo & BITS_PER_PAGE_MASK);

			__bm_unmap(p_addr, km);
			if (i < PAGE_SIZE*8) {
				bm_fo = bit_offset + i;
				if (bm_fo >= b->bm_bits)
					break;
				goto found;
			}
			bm_fo = bit_offset + PAGE_SIZE*8;
		}
		bm_fo = DRBD_END_OF_BITMAP;
	}
 found:
	return bm_fo;
}

static unsigned long bm_find_next(struct drbd_conf *mdev,
	unsigned long bm_fo, const int find_zero_bit)
{
	struct drbd_bitmap *b = mdev->bitmap;
	unsigned long i = DRBD_END_OF_BITMAP;

	ERR_IF(!b) return i;
	ERR_IF(!b->bm_pages) return i;

	spin_lock_irq(&b->bm_lock);
	if (BM_DONT_TEST & b->bm_flags)
		bm_print_lock_info(mdev);

	i = __bm_find_next(mdev, bm_fo, find_zero_bit, KM_IRQ1);

	spin_unlock_irq(&b->bm_lock);
	return i;
}

unsigned long drbd_bm_find_next(struct drbd_conf *mdev, unsigned long bm_fo)
{
	return bm_find_next(mdev, bm_fo, 0);
}

#if 0
/* not yet needed for anything. */
unsigned long drbd_bm_find_next_zero(struct drbd_conf *mdev, unsigned long bm_fo)
{
	return bm_find_next(mdev, bm_fo, 1);
}
#endif

/* does not spin_lock_irqsave.
 * you must take drbd_bm_lock() first */
unsigned long _drbd_bm_find_next(struct drbd_conf *mdev, unsigned long bm_fo)
{
	/* WARN_ON(!(BM_DONT_SET & mdev->b->bm_flags)); */
	return __bm_find_next(mdev, bm_fo, 0, KM_USER1);
}

unsigned long _drbd_bm_find_next_zero(struct drbd_conf *mdev, unsigned long bm_fo)
{
	/* WARN_ON(!(BM_DONT_SET & mdev->b->bm_flags)); */
	return __bm_find_next(mdev, bm_fo, 1, KM_USER1);
}

/* returns number of bits actually changed.
 * for val != 0, we change 0 -> 1, return code positive
 * for val == 0, we change 1 -> 0, return code negative
 * wants bitnr, not sector.
 * expected to be called for only a few bits (e - s about BITS_PER_LONG).
 * Must hold bitmap lock already. */
static int __bm_change_bits_to(struct drbd_conf *mdev, const unsigned long s,
	unsigned long e, int val)
{
	struct drbd_bitmap *b = mdev->bitmap;
	unsigned long *p_addr = NULL;
	unsigned long bitnr;
	unsigned int last_page_nr = -1U;
	int c = 0;
	int changed_total = 0;

	if (e >= b->bm_bits) {
		dev_err(DEV, "ASSERT FAILED: bit_s=%lu bit_e=%lu bm_bits=%lu\n",
				s, e, b->bm_bits);
		e = b->bm_bits ? b->bm_bits -1 : 0;
	}
	for (bitnr = s; bitnr <= e; bitnr++) {
		unsigned int page_nr = bm_bit_to_page_idx(b, bitnr);
		if (page_nr != last_page_nr) {
			if (p_addr)
				__bm_unmap(p_addr, KM_IRQ1);
			if (c < 0)
				bm_set_page_lazy_writeout(b->bm_pages[last_page_nr]);
			else if (c > 0)
				bm_set_page_need_writeout(b->bm_pages[last_page_nr]);
			changed_total += c;
			c = 0;
			p_addr = __bm_map_pidx(b, page_nr, KM_IRQ1);
			last_page_nr = page_nr;
		}
		if (val)
			c += (0 == __test_and_set_bit_le(bitnr & BITS_PER_PAGE_MASK, p_addr));
		else
			c -= (0 != __test_and_clear_bit_le(bitnr & BITS_PER_PAGE_MASK, p_addr));
	}
	if (p_addr)
		__bm_unmap(p_addr, KM_IRQ1);
	if (c < 0)
		bm_set_page_lazy_writeout(b->bm_pages[last_page_nr]);
	else if (c > 0)
		bm_set_page_need_writeout(b->bm_pages[last_page_nr]);
	changed_total += c;
	b->bm_set += changed_total;
	return changed_total;
}

/* returns number of bits actually changed.
 * for val != 0, we change 0 -> 1, return code positive
 * for val == 0, we change 1 -> 0, return code negative
 * wants bitnr, not sector */
static int bm_change_bits_to(struct drbd_conf *mdev, const unsigned long s,
	const unsigned long e, int val)
{
	unsigned long flags;
	struct drbd_bitmap *b = mdev->bitmap;
	int c = 0;

	ERR_IF(!b) return 1;
	ERR_IF(!b->bm_pages) return 0;

	spin_lock_irqsave(&b->bm_lock, flags);
	if ((val ? BM_DONT_SET : BM_DONT_CLEAR) & b->bm_flags)
		bm_print_lock_info(mdev);

	c = __bm_change_bits_to(mdev, s, e, val);

	spin_unlock_irqrestore(&b->bm_lock, flags);
	return c;
}

/* returns number of bits changed 0 -> 1 */
int drbd_bm_set_bits(struct drbd_conf *mdev, const unsigned long s, const unsigned long e)
{
	return bm_change_bits_to(mdev, s, e, 1);
}

/* returns number of bits changed 1 -> 0 */
int drbd_bm_clear_bits(struct drbd_conf *mdev, const unsigned long s, const unsigned long e)
{
	return -bm_change_bits_to(mdev, s, e, 0);
}

/* sets all bits in full words,
 * from first_word up to, but not including, last_word */
static inline void bm_set_full_words_within_one_page(struct drbd_bitmap *b,
		int page_nr, int first_word, int last_word)
{
	int i;
	int bits;
	unsigned long *paddr = kmap_atomic(b->bm_pages[page_nr], KM_IRQ1);
	for (i = first_word; i < last_word; i++) {
		bits = hweight_long(paddr[i]);
		paddr[i] = ~0UL;
		b->bm_set += BITS_PER_LONG - bits;
	}
	kunmap_atomic(paddr, KM_IRQ1);
}

/* Same thing as drbd_bm_set_bits,
 * but more efficient for a large bit range.
 * You must first drbd_bm_lock().
 * Can be called to set the whole bitmap in one go.
 * Sets bits from s to e _inclusive_. */
void _drbd_bm_set_bits(struct drbd_conf *mdev, const unsigned long s, const unsigned long e)
{
	/* First set_bit from the first bit (s)
	 * up to the next long boundary (sl),
	 * then assign full words up to the last long boundary (el),
	 * then set_bit up to and including the last bit (e).
	 *
	 * Do not use memset, because we must account for changes,
	 * so we need to loop over the words with hweight() anyways.
	 */
	struct drbd_bitmap *b = mdev->bitmap;
	unsigned long sl = ALIGN(s,BITS_PER_LONG);
	unsigned long el = (e+1) & ~((unsigned long)BITS_PER_LONG-1);
	int first_page;
	int last_page;
	int page_nr;
	int first_word;
	int last_word;

	if (e - s <= 3*BITS_PER_LONG) {
		/* don't bother; el and sl may even be wrong. */
		spin_lock_irq(&b->bm_lock);
		__bm_change_bits_to(mdev, s, e, 1);
		spin_unlock_irq(&b->bm_lock);
		return;
	}

	/* difference is large enough that we can trust sl and el */

	spin_lock_irq(&b->bm_lock);

	/* bits filling the current long */
	if (sl)
		__bm_change_bits_to(mdev, s, sl-1, 1);

	first_page = sl >> (3 + PAGE_SHIFT);
	last_page = el >> (3 + PAGE_SHIFT);

	/* MLPP: modulo longs per page */
	/* LWPP: long words per page */
	first_word = MLPP(sl >> LN2_BPL);
	last_word = LWPP;

	/* first and full pages, unless first page == last page */
	for (page_nr = first_page; page_nr < last_page; page_nr++) {
		bm_set_full_words_within_one_page(mdev->bitmap, page_nr, first_word, last_word);
		spin_unlock_irq(&b->bm_lock);
		cond_resched();
		first_word = 0;
		spin_lock_irq(&b->bm_lock);
	}

	/* last page (respectively only page, for first page == last page) */
	last_word = MLPP(el >> LN2_BPL);
	bm_set_full_words_within_one_page(mdev->bitmap, last_page, first_word, last_word);

	/* possibly trailing bits.
	 * example: (e & 63) == 63, el will be e+1.
	 * if that even was the very last bit,
	 * it would trigger an assert in __bm_change_bits_to()
	 */
	if (el <= e)
		__bm_change_bits_to(mdev, el, e, 1);
	spin_unlock_irq(&b->bm_lock);
}

/* returns bit state
 * wants bitnr, NOT sector.
 * inherently racy... area needs to be locked by means of {al,rs}_lru
 *  1 ... bit set
 *  0 ... bit not set
 * -1 ... first out of bounds access, stop testing for bits!
 */
int drbd_bm_test_bit(struct drbd_conf *mdev, const unsigned long bitnr)
{
	unsigned long flags;
	struct drbd_bitmap *b = mdev->bitmap;
	unsigned long *p_addr;
	int i;

	ERR_IF(!b) return 0;
	ERR_IF(!b->bm_pages) return 0;

	spin_lock_irqsave(&b->bm_lock, flags);
	if (BM_DONT_TEST & b->bm_flags)
		bm_print_lock_info(mdev);
	if (bitnr < b->bm_bits) {
		p_addr = bm_map_pidx(b, bm_bit_to_page_idx(b, bitnr));
		i = test_bit_le(bitnr & BITS_PER_PAGE_MASK, p_addr) ? 1 : 0;
		bm_unmap(p_addr);
	} else if (bitnr == b->bm_bits) {
		i = -1;
	} else { /* (bitnr > b->bm_bits) */
		dev_err(DEV, "bitnr=%lu > bm_bits=%lu\n", bitnr, b->bm_bits);
		i = 0;
	}

	spin_unlock_irqrestore(&b->bm_lock, flags);
	return i;
}

/* returns number of bits set in the range [s, e] */
int drbd_bm_count_bits(struct drbd_conf *mdev, const unsigned long s, const unsigned long e)
{
	unsigned long flags;
	struct drbd_bitmap *b = mdev->bitmap;
	unsigned long *p_addr = NULL;
	unsigned long bitnr;
	unsigned int page_nr = -1U;
	int c = 0;

	/* If this is called without a bitmap, that is a bug.  But just to be
	 * robust in case we screwed up elsewhere, in that case pretend there
	 * was one dirty bit in the requested area, so we won't try to do a
	 * local read there (no bitmap probably implies no disk) */
	ERR_IF(!b) return 1;
	ERR_IF(!b->bm_pages) return 1;

	spin_lock_irqsave(&b->bm_lock, flags);
	if (BM_DONT_TEST & b->bm_flags)
		bm_print_lock_info(mdev);
	for (bitnr = s; bitnr <= e; bitnr++) {
		unsigned int idx = bm_bit_to_page_idx(b, bitnr);
		if (page_nr != idx) {
			page_nr = idx;
			if (p_addr)
				bm_unmap(p_addr);
			p_addr = bm_map_pidx(b, idx);
		}
		ERR_IF (bitnr >= b->bm_bits) {
			dev_err(DEV, "bitnr=%lu bm_bits=%lu\n", bitnr, b->bm_bits);
		} else {
			c += (0 != test_bit_le(bitnr - (page_nr << (PAGE_SHIFT+3)), p_addr));
		}
	}
	if (p_addr)
		bm_unmap(p_addr);
	spin_unlock_irqrestore(&b->bm_lock, flags);
	return c;
}


/* inherently racy...
 * return value may be already out-of-date when this function returns.
 * but the general usage is that this is only use during a cstate when bits are
 * only cleared, not set, and typically only care for the case when the return
 * value is zero, or we already "locked" this "bitmap extent" by other means.
 *
 * enr is bm-extent number, since we chose to name one sector (512 bytes)
 * worth of the bitmap a "bitmap extent".
 *
 * TODO
 * I think since we use it like a reference count, we should use the real
 * reference count of some bitmap extent element from some lru instead...
 *
 */
int drbd_bm_e_weight(struct drbd_conf *mdev, unsigned long enr)
{
	struct drbd_bitmap *b = mdev->bitmap;
	int count, s, e;
	unsigned long flags;
	unsigned long *p_addr, *bm;

	ERR_IF(!b) return 0;
	ERR_IF(!b->bm_pages) return 0;

	spin_lock_irqsave(&b->bm_lock, flags);
	if (BM_DONT_TEST & b->bm_flags)
		bm_print_lock_info(mdev);

	s = S2W(enr);
	e = min((size_t)S2W(enr+1), b->bm_words);
	count = 0;
	if (s < b->bm_words) {
		int n = e-s;
		p_addr = bm_map_pidx(b, bm_word_to_page_idx(b, s));
		bm = p_addr + MLPP(s);
		while (n--)
			count += hweight_long(*bm++);
		bm_unmap(p_addr);
	} else {
		dev_err(DEV, "start offset (%d) too large in drbd_bm_e_weight\n", s);
	}
	spin_unlock_irqrestore(&b->bm_lock, flags);
	return count;
}

/* Set all bits covered by the AL-extent al_enr.
 * Returns number of bits changed. */
unsigned long drbd_bm_ALe_set_all(struct drbd_conf *mdev, unsigned long al_enr)
{
	struct drbd_bitmap *b = mdev->bitmap;
	unsigned long *p_addr, *bm;
	unsigned long weight;
	unsigned long s, e;
	int count, i, do_now;
	ERR_IF(!b) return 0;
	ERR_IF(!b->bm_pages) return 0;

	spin_lock_irq(&b->bm_lock);
	if (BM_DONT_SET & b->bm_flags)
		bm_print_lock_info(mdev);
	weight = b->bm_set;

	s = al_enr * BM_WORDS_PER_AL_EXT;
	e = min_t(size_t, s + BM_WORDS_PER_AL_EXT, b->bm_words);
	/* assert that s and e are on the same page */
	D_ASSERT((e-1) >> (PAGE_SHIFT - LN2_BPL + 3)
	      ==  s    >> (PAGE_SHIFT - LN2_BPL + 3));
	count = 0;
	if (s < b->bm_words) {
		i = do_now = e-s;
		p_addr = bm_map_pidx(b, bm_word_to_page_idx(b, s));
		bm = p_addr + MLPP(s);
		while (i--) {
			count += hweight_long(*bm);
			*bm = -1UL;
			bm++;
		}
		bm_unmap(p_addr);
		b->bm_set += do_now*BITS_PER_LONG - count;
		if (e == b->bm_words)
			b->bm_set -= bm_clear_surplus(b);
	} else {
		dev_err(DEV, "start offset (%lu) too large in drbd_bm_ALe_set_all\n", s);
	}
	weight = b->bm_set - weight;
	spin_unlock_irq(&b->bm_lock);
	return weight;
}