summaryrefslogtreecommitdiffstats
path: root/drivers/block/drbd/drbd_actlog.c
blob: 1318e3217cb0811513c807d09261cdf63d12c682 (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
/*
   drbd_actlog.c

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

   Copyright (C) 2003-2008, LINBIT Information Technologies GmbH.
   Copyright (C) 2003-2008, Philipp Reisner <philipp.reisner@linbit.com>.
   Copyright (C) 2003-2008, 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/slab.h>
#include <linux/crc32c.h>
#include <linux/drbd.h>
#include <linux/drbd_limits.h>
#include <linux/dynamic_debug.h>
#include "drbd_int.h"


enum al_transaction_types {
	AL_TR_UPDATE = 0,
	AL_TR_INITIALIZED = 0xffff
};
/* all fields on disc in big endian */
struct __packed al_transaction_on_disk {
	/* don't we all like magic */
	__be32	magic;

	/* to identify the most recent transaction block
	 * in the on disk ring buffer */
	__be32	tr_number;

	/* checksum on the full 4k block, with this field set to 0. */
	__be32	crc32c;

	/* type of transaction, special transaction types like:
	 * purge-all, set-all-idle, set-all-active, ... to-be-defined
	 * see also enum al_transaction_types */
	__be16	transaction_type;

	/* we currently allow only a few thousand extents,
	 * so 16bit will be enough for the slot number. */

	/* how many updates in this transaction */
	__be16	n_updates;

	/* maximum slot number, "al-extents" in drbd.conf speak.
	 * Having this in each transaction should make reconfiguration
	 * of that parameter easier. */
	__be16	context_size;

	/* slot number the context starts with */
	__be16	context_start_slot_nr;

	/* Some reserved bytes.  Expected usage is a 64bit counter of
	 * sectors-written since device creation, and other data generation tag
	 * supporting usage */
	__be32	__reserved[4];

	/* --- 36 byte used --- */

	/* Reserve space for up to AL_UPDATES_PER_TRANSACTION changes
	 * in one transaction, then use the remaining byte in the 4k block for
	 * context information.  "Flexible" number of updates per transaction
	 * does not help, as we have to account for the case when all update
	 * slots are used anyways, so it would only complicate code without
	 * additional benefit.
	 */
	__be16	update_slot_nr[AL_UPDATES_PER_TRANSACTION];

	/* but the extent number is 32bit, which at an extent size of 4 MiB
	 * allows to cover device sizes of up to 2**54 Byte (16 PiB) */
	__be32	update_extent_nr[AL_UPDATES_PER_TRANSACTION];

	/* --- 420 bytes used (36 + 64*6) --- */

	/* 4096 - 420 = 3676 = 919 * 4 */
	__be32	context[AL_CONTEXT_PER_TRANSACTION];
};

void *drbd_md_get_buffer(struct drbd_device *device, const char *intent)
{
	int r;

	wait_event(device->misc_wait,
		   (r = atomic_cmpxchg(&device->md_io.in_use, 0, 1)) == 0 ||
		   device->state.disk <= D_FAILED);

	if (r)
		return NULL;

	device->md_io.current_use = intent;
	device->md_io.start_jif = jiffies;
	device->md_io.submit_jif = device->md_io.start_jif - 1;
	return page_address(device->md_io.page);
}

void drbd_md_put_buffer(struct drbd_device *device)
{
	if (atomic_dec_and_test(&device->md_io.in_use))
		wake_up(&device->misc_wait);
}

void wait_until_done_or_force_detached(struct drbd_device *device, struct drbd_backing_dev *bdev,
				     unsigned int *done)
{
	long dt;

	rcu_read_lock();
	dt = rcu_dereference(bdev->disk_conf)->disk_timeout;
	rcu_read_unlock();
	dt = dt * HZ / 10;
	if (dt == 0)
		dt = MAX_SCHEDULE_TIMEOUT;

	dt = wait_event_timeout(device->misc_wait,
			*done || test_bit(FORCE_DETACH, &device->flags), dt);
	if (dt == 0) {
		drbd_err(device, "meta-data IO operation timed out\n");
		drbd_chk_io_error(device, 1, DRBD_FORCE_DETACH);
	}
}

static int _drbd_md_sync_page_io(struct drbd_device *device,
				 struct drbd_backing_dev *bdev,
				 sector_t sector, int rw)
{
	struct bio *bio;
	/* we do all our meta data IO in aligned 4k blocks. */
	const int size = 4096;
	int err;

	device->md_io.done = 0;
	device->md_io.error = -ENODEV;

	if ((rw & WRITE) && !test_bit(MD_NO_FUA, &device->flags))
		rw |= REQ_FUA | REQ_FLUSH;
	rw |= REQ_SYNC | REQ_NOIDLE;

	bio = bio_alloc_drbd(GFP_NOIO);
	bio->bi_bdev = bdev->md_bdev;
	bio->bi_iter.bi_sector = sector;
	err = -EIO;
	if (bio_add_page(bio, device->md_io.page, size, 0) != size)
		goto out;
	bio->bi_private = device;
	bio->bi_end_io = drbd_md_endio;
	bio->bi_rw = rw;

	if (!(rw & WRITE) && device->state.disk == D_DISKLESS && device->ldev == NULL)
		/* special case, drbd_md_read() during drbd_adm_attach(): no get_ldev */
		;
	else if (!get_ldev_if_state(device, D_ATTACHING)) {
		/* Corresponding put_ldev in drbd_md_endio() */
		drbd_err(device, "ASSERT FAILED: get_ldev_if_state() == 1 in _drbd_md_sync_page_io()\n");
		err = -ENODEV;
		goto out;
	}

	bio_get(bio); /* one bio_put() is in the completion handler */
	atomic_inc(&device->md_io.in_use); /* drbd_md_put_buffer() is in the completion handler */
	device->md_io.submit_jif = jiffies;
	if (drbd_insert_fault(device, (rw & WRITE) ? DRBD_FAULT_MD_WR : DRBD_FAULT_MD_RD))
		bio_endio(bio, -EIO);
	else
		submit_bio(rw, bio);
	wait_until_done_or_force_detached(device, bdev, &device->md_io.done);
	if (bio_flagged(bio, BIO_UPTODATE))
		err = device->md_io.error;

 out:
	bio_put(bio);
	return err;
}

int drbd_md_sync_page_io(struct drbd_device *device, struct drbd_backing_dev *bdev,
			 sector_t sector, int rw)
{
	int err;
	D_ASSERT(device, atomic_read(&device->md_io.in_use) == 1);

	BUG_ON(!bdev->md_bdev);

	dynamic_drbd_dbg(device, "meta_data io: %s [%d]:%s(,%llus,%s) %pS\n",
	     current->comm, current->pid, __func__,
	     (unsigned long long)sector, (rw & WRITE) ? "WRITE" : "READ",
	     (void*)_RET_IP_ );

	if (sector < drbd_md_first_sector(bdev) ||
	    sector + 7 > drbd_md_last_sector(bdev))
		drbd_alert(device, "%s [%d]:%s(,%llus,%s) out of range md access!\n",
		     current->comm, current->pid, __func__,
		     (unsigned long long)sector, (rw & WRITE) ? "WRITE" : "READ");

	err = _drbd_md_sync_page_io(device, bdev, sector, rw);
	if (err) {
		drbd_err(device, "drbd_md_sync_page_io(,%llus,%s) failed with error %d\n",
		    (unsigned long long)sector, (rw & WRITE) ? "WRITE" : "READ", err);
	}
	return err;
}

static struct bm_extent *find_active_resync_extent(struct drbd_device *device, unsigned int enr)
{
	struct lc_element *tmp;
	tmp = lc_find(device->resync, enr/AL_EXT_PER_BM_SECT);
	if (unlikely(tmp != NULL)) {
		struct bm_extent  *bm_ext = lc_entry(tmp, struct bm_extent, lce);
		if (test_bit(BME_NO_WRITES, &bm_ext->flags))
			return bm_ext;
	}
	return NULL;
}

static struct lc_element *_al_get(struct drbd_device *device, unsigned int enr, bool nonblock)
{
	struct lc_element *al_ext;
	struct bm_extent *bm_ext;
	int wake;

	spin_lock_irq(&device->al_lock);
	bm_ext = find_active_resync_extent(device, enr);
	if (bm_ext) {
		wake = !test_and_set_bit(BME_PRIORITY, &bm_ext->flags);
		spin_unlock_irq(&device->al_lock);
		if (wake)
			wake_up(&device->al_wait);
		return NULL;
	}
	if (nonblock)
		al_ext = lc_try_get(device->act_log, enr);
	else
		al_ext = lc_get(device->act_log, enr);
	spin_unlock_irq(&device->al_lock);
	return al_ext;
}

bool drbd_al_begin_io_fastpath(struct drbd_device *device, struct drbd_interval *i)
{
	/* for bios crossing activity log extent boundaries,
	 * we may need to activate two extents in one go */
	unsigned first = i->sector >> (AL_EXTENT_SHIFT-9);
	unsigned last = i->size == 0 ? first : (i->sector + (i->size >> 9) - 1) >> (AL_EXTENT_SHIFT-9);

	D_ASSERT(device, (unsigned)(last - first) <= 1);
	D_ASSERT(device, atomic_read(&device->local_cnt) > 0);

	/* FIXME figure out a fast path for bios crossing AL extent boundaries */
	if (first != last)
		return false;

	return _al_get(device, first, true);
}

bool drbd_al_begin_io_prepare(struct drbd_device *device, struct drbd_interval *i)
{
	/* for bios crossing activity log extent boundaries,
	 * we may need to activate two extents in one go */
	unsigned first = i->sector >> (AL_EXTENT_SHIFT-9);
	unsigned last = i->size == 0 ? first : (i->sector + (i->size >> 9) - 1) >> (AL_EXTENT_SHIFT-9);
	unsigned enr;
	bool need_transaction = false;

	D_ASSERT(device, first <= last);
	D_ASSERT(device, atomic_read(&device->local_cnt) > 0);

	for (enr = first; enr <= last; enr++) {
		struct lc_element *al_ext;
		wait_event(device->al_wait,
				(al_ext = _al_get(device, enr, false)) != NULL);
		if (al_ext->lc_number != enr)
			need_transaction = true;
	}
	return need_transaction;
}

static int al_write_transaction(struct drbd_device *device);

void drbd_al_begin_io_commit(struct drbd_device *device)
{
	bool locked = false;

	/* Serialize multiple transactions.
	 * This uses test_and_set_bit, memory barrier is implicit.
	 */
	wait_event(device->al_wait,
			device->act_log->pending_changes == 0 ||
			(locked = lc_try_lock_for_transaction(device->act_log)));

	if (locked) {
		/* Double check: it may have been committed by someone else,
		 * while we have been waiting for the lock. */
		if (device->act_log->pending_changes) {
			bool write_al_updates;

			rcu_read_lock();
			write_al_updates = rcu_dereference(device->ldev->disk_conf)->al_updates;
			rcu_read_unlock();

			if (write_al_updates)
				al_write_transaction(device);
			spin_lock_irq(&device->al_lock);
			/* FIXME
			if (err)
				we need an "lc_cancel" here;
			*/
			lc_committed(device->act_log);
			spin_unlock_irq(&device->al_lock);
		}
		lc_unlock(device->act_log);
		wake_up(&device->al_wait);
	}
}

/*
 * @delegate:   delegate activity log I/O to the worker thread
 */
void drbd_al_begin_io(struct drbd_device *device, struct drbd_interval *i)
{
	if (drbd_al_begin_io_prepare(device, i))
		drbd_al_begin_io_commit(device);
}

int drbd_al_begin_io_nonblock(struct drbd_device *device, struct drbd_interval *i)
{
	struct lru_cache *al = device->act_log;
	/* for bios crossing activity log extent boundaries,
	 * we may need to activate two extents in one go */
	unsigned first = i->sector >> (AL_EXTENT_SHIFT-9);
	unsigned last = i->size == 0 ? first : (i->sector + (i->size >> 9) - 1) >> (AL_EXTENT_SHIFT-9);
	unsigned nr_al_extents;
	unsigned available_update_slots;
	unsigned enr;

	D_ASSERT(device, first <= last);

	nr_al_extents = 1 + last - first; /* worst case: all touched extends are cold. */
	available_update_slots = min(al->nr_elements - al->used,
				al->max_pending_changes - al->pending_changes);

	/* We want all necessary updates for a given request within the same transaction
	 * We could first check how many updates are *actually* needed,
	 * and use that instead of the worst-case nr_al_extents */
	if (available_update_slots < nr_al_extents) {
		/* Too many activity log extents are currently "hot".
		 *
		 * If we have accumulated pending changes already,
		 * we made progress.
		 *
		 * If we cannot get even a single pending change through,
		 * stop the fast path until we made some progress,
		 * or requests to "cold" extents could be starved. */
		if (!al->pending_changes)
			__set_bit(__LC_STARVING, &device->act_log->flags);
		return -ENOBUFS;
	}

	/* Is resync active in this area? */
	for (enr = first; enr <= last; enr++) {
		struct lc_element *tmp;
		tmp = lc_find(device->resync, enr/AL_EXT_PER_BM_SECT);
		if (unlikely(tmp != NULL)) {
			struct bm_extent  *bm_ext = lc_entry(tmp, struct bm_extent, lce);
			if (test_bit(BME_NO_WRITES, &bm_ext->flags)) {
				if (!test_and_set_bit(BME_PRIORITY, &bm_ext->flags))
					return -EBUSY;
				return -EWOULDBLOCK;
			}
		}
	}

	/* Checkout the refcounts.
	 * Given that we checked for available elements and update slots above,
	 * this has to be successful. */
	for (enr = first; enr <= last; enr++) {
		struct lc_element *al_ext;
		al_ext = lc_get_cumulative(device->act_log, enr);
		if (!al_ext)
			drbd_info(device, "LOGIC BUG for enr=%u\n", enr);
	}
	return 0;
}

void drbd_al_complete_io(struct drbd_device *device, struct drbd_interval *i)
{
	/* for bios crossing activity log extent boundaries,
	 * we may need to activate two extents in one go */
	unsigned first = i->sector >> (AL_EXTENT_SHIFT-9);
	unsigned last = i->size == 0 ? first : (i->sector + (i->size >> 9) - 1) >> (AL_EXTENT_SHIFT-9);
	unsigned enr;
	struct lc_element *extent;
	unsigned long flags;

	D_ASSERT(device, first <= last);
	spin_lock_irqsave(&device->al_lock, flags);

	for (enr = first; enr <= last; enr++) {
		extent = lc_find(device->act_log, enr);
		if (!extent) {
			drbd_err(device, "al_complete_io() called on inactive extent %u\n", enr);
			continue;
		}
		lc_put(device->act_log, extent);
	}
	spin_unlock_irqrestore(&device->al_lock, flags);
	wake_up(&device->al_wait);
}

#if (PAGE_SHIFT + 3) < (AL_EXTENT_SHIFT - BM_BLOCK_SHIFT)
/* Currently BM_BLOCK_SHIFT, BM_EXT_SHIFT and AL_EXTENT_SHIFT
 * are still coupled, or assume too much about their relation.
 * Code below will not work if this is violated.
 * Will be cleaned up with some followup patch.
 */
# error FIXME
#endif

static unsigned int al_extent_to_bm_page(unsigned int al_enr)
{
	return al_enr >>
		/* bit to page */
		((PAGE_SHIFT + 3) -
		/* al extent number to bit */
		 (AL_EXTENT_SHIFT - BM_BLOCK_SHIFT));
}

static sector_t al_tr_number_to_on_disk_sector(struct drbd_device *device)
{
	const unsigned int stripes = device->ldev->md.al_stripes;
	const unsigned int stripe_size_4kB = device->ldev->md.al_stripe_size_4k;

	/* transaction number, modulo on-disk ring buffer wrap around */
	unsigned int t = device->al_tr_number % (device->ldev->md.al_size_4k);

	/* ... to aligned 4k on disk block */
	t = ((t % stripes) * stripe_size_4kB) + t/stripes;

	/* ... to 512 byte sector in activity log */
	t *= 8;

	/* ... plus offset to the on disk position */
	return device->ldev->md.md_offset + device->ldev->md.al_offset + t;
}

int al_write_transaction(struct drbd_device *device)
{
	struct al_transaction_on_disk *buffer;
	struct lc_element *e;
	sector_t sector;
	int i, mx;
	unsigned extent_nr;
	unsigned crc = 0;
	int err = 0;

	if (!get_ldev(device)) {
		drbd_err(device, "disk is %s, cannot start al transaction\n",
			drbd_disk_str(device->state.disk));
		return -EIO;
	}

	/* The bitmap write may have failed, causing a state change. */
	if (device->state.disk < D_INCONSISTENT) {
		drbd_err(device,
			"disk is %s, cannot write al transaction\n",
			drbd_disk_str(device->state.disk));
		put_ldev(device);
		return -EIO;
	}

	/* protects md_io_buffer, al_tr_cycle, ... */
	buffer = drbd_md_get_buffer(device, __func__);
	if (!buffer) {
		drbd_err(device, "disk failed while waiting for md_io buffer\n");
		put_ldev(device);
		return -ENODEV;
	}

	memset(buffer, 0, sizeof(*buffer));
	buffer->magic = cpu_to_be32(DRBD_AL_MAGIC);
	buffer->tr_number = cpu_to_be32(device->al_tr_number);

	i = 0;

	/* Even though no one can start to change this list
	 * once we set the LC_LOCKED -- from drbd_al_begin_io(),
	 * lc_try_lock_for_transaction() --, someone may still
	 * be in the process of changing it. */
	spin_lock_irq(&device->al_lock);
	list_for_each_entry(e, &device->act_log->to_be_changed, list) {
		if (i == AL_UPDATES_PER_TRANSACTION) {
			i++;
			break;
		}
		buffer->update_slot_nr[i] = cpu_to_be16(e->lc_index);
		buffer->update_extent_nr[i] = cpu_to_be32(e->lc_new_number);
		if (e->lc_number != LC_FREE)
			drbd_bm_mark_for_writeout(device,
					al_extent_to_bm_page(e->lc_number));
		i++;
	}
	spin_unlock_irq(&device->al_lock);
	BUG_ON(i > AL_UPDATES_PER_TRANSACTION);

	buffer->n_updates = cpu_to_be16(i);
	for ( ; i < AL_UPDATES_PER_TRANSACTION; i++) {
		buffer->update_slot_nr[i] = cpu_to_be16(-1);
		buffer->update_extent_nr[i] = cpu_to_be32(LC_FREE);
	}

	buffer->context_size = cpu_to_be16(device->act_log->nr_elements);
	buffer->context_start_slot_nr = cpu_to_be16(device->al_tr_cycle);

	mx = min_t(int, AL_CONTEXT_PER_TRANSACTION,
		   device->act_log->nr_elements - device->al_tr_cycle);
	for (i = 0; i < mx; i++) {
		unsigned idx = device->al_tr_cycle + i;
		extent_nr = lc_element_by_index(device->act_log, idx)->lc_number;
		buffer->context[i] = cpu_to_be32(extent_nr);
	}
	for (; i < AL_CONTEXT_PER_TRANSACTION; i++)
		buffer->context[i] = cpu_to_be32(LC_FREE);

	device->al_tr_cycle += AL_CONTEXT_PER_TRANSACTION;
	if (device->al_tr_cycle >= device->act_log->nr_elements)
		device->al_tr_cycle = 0;

	sector = al_tr_number_to_on_disk_sector(device);

	crc = crc32c(0, buffer, 4096);
	buffer->crc32c = cpu_to_be32(crc);

	if (drbd_bm_write_hinted(device))
		err = -EIO;
	else {
		bool write_al_updates;
		rcu_read_lock();
		write_al_updates = rcu_dereference(device->ldev->disk_conf)->al_updates;
		rcu_read_unlock();
		if (write_al_updates) {
			if (drbd_md_sync_page_io(device, device->ldev, sector, WRITE)) {
				err = -EIO;
				drbd_chk_io_error(device, 1, DRBD_META_IO_ERROR);
			} else {
				device->al_tr_number++;
				device->al_writ_cnt++;
			}
		}
	}

	drbd_md_put_buffer(device);
	put_ldev(device);

	return err;
}

static int _try_lc_del(struct drbd_device *device, struct lc_element *al_ext)
{
	int rv;

	spin_lock_irq(&device->al_lock);
	rv = (al_ext->refcnt == 0);
	if (likely(rv))
		lc_del(device->act_log, al_ext);
	spin_unlock_irq(&device->al_lock);

	return rv;
}

/**
 * drbd_al_shrink() - Removes all active extents form the activity log
 * @device:	DRBD device.
 *
 * Removes all active extents form the activity log, waiting until
 * the reference count of each entry dropped to 0 first, of course.
 *
 * You need to lock device->act_log with lc_try_lock() / lc_unlock()
 */
void drbd_al_shrink(struct drbd_device *device)
{
	struct lc_element *al_ext;
	int i;

	D_ASSERT(device, test_bit(__LC_LOCKED, &device->act_log->flags));

	for (i = 0; i < device->act_log->nr_elements; i++) {
		al_ext = lc_element_by_index(device->act_log, i);
		if (al_ext->lc_number == LC_FREE)
			continue;
		wait_event(device->al_wait, _try_lc_del(device, al_ext));
	}

	wake_up(&device->al_wait);
}

int drbd_initialize_al(struct drbd_device *device, void *buffer)
{
	struct al_transaction_on_disk *al = buffer;
	struct drbd_md *md = &device->ldev->md;
	sector_t al_base = md->md_offset + md->al_offset;
	int al_size_4k = md->al_stripes * md->al_stripe_size_4k;
	int i;

	memset(al, 0, 4096);
	al->magic = cpu_to_be32(DRBD_AL_MAGIC);
	al->transaction_type = cpu_to_be16(AL_TR_INITIALIZED);
	al->crc32c = cpu_to_be32(crc32c(0, al, 4096));

	for (i = 0; i < al_size_4k; i++) {
		int err = drbd_md_sync_page_io(device, device->ldev, al_base + i * 8, WRITE);
		if (err)
			return err;
	}
	return 0;
}

static const char *drbd_change_sync_fname[] = {
	[RECORD_RS_FAILED] = "drbd_rs_failed_io",
	[SET_IN_SYNC] = "drbd_set_in_sync",
	[SET_OUT_OF_SYNC] = "drbd_set_out_of_sync"
};

/* ATTENTION. The AL's extents are 4MB each, while the extents in the
 * resync LRU-cache are 16MB each.
 * The caller of this function has to hold an get_ldev() reference.
 *
 * Adjusts the caching members ->rs_left (success) or ->rs_failed (!success),
 * potentially pulling in (and recounting the corresponding bits)
 * this resync extent into the resync extent lru cache.
 *
 * Returns whether all bits have been cleared for this resync extent,
 * precisely: (rs_left <= rs_failed)
 *
 * TODO will be obsoleted once we have a caching lru of the on disk bitmap
 */
static bool update_rs_extent(struct drbd_device *device,
		unsigned int enr, int count,
		enum update_sync_bits_mode mode)
{
	struct lc_element *e;

	D_ASSERT(device, atomic_read(&device->local_cnt));

	/* When setting out-of-sync bits,
	 * we don't need it cached (lc_find).
	 * But if it is present in the cache,
	 * we should update the cached bit count.
	 * Otherwise, that extent should be in the resync extent lru cache
	 * already -- or we want to pull it in if necessary -- (lc_get),
	 * then update and check rs_left and rs_failed. */
	if (mode == SET_OUT_OF_SYNC)
		e = lc_find(device->resync, enr);
	else
		e = lc_get(device->resync, enr);
	if (e) {
		struct bm_extent *ext = lc_entry(e, struct bm_extent, lce);
		if (ext->lce.lc_number == enr) {
			if (mode == SET_IN_SYNC)
				ext->rs_left -= count;
			else if (mode == SET_OUT_OF_SYNC)
				ext->rs_left += count;
			else
				ext->rs_failed += count;
			if (ext->rs_left < ext->rs_failed) {
				drbd_warn(device, "BAD! enr=%u rs_left=%d "
				    "rs_failed=%d count=%d cstate=%s\n",
				     ext->lce.lc_number, ext->rs_left,
				     ext->rs_failed, count,
				     drbd_conn_str(device->state.conn));

				/* We don't expect to be able to clear more bits
				 * than have been set when we originally counted
				 * the set bits to cache that value in ext->rs_left.
				 * Whatever the reason (disconnect during resync,
				 * delayed local completion of an application write),
				 * try to fix it up by recounting here. */
				ext->rs_left = drbd_bm_e_weight(device, enr);
			}
		} else {
			/* Normally this element should be in the cache,
			 * since drbd_rs_begin_io() pulled it already in.
			 *
			 * But maybe an application write finished, and we set
			 * something outside the resync lru_cache in sync.
			 */
			int rs_left = drbd_bm_e_weight(device, enr);
			if (ext->flags != 0) {
				drbd_warn(device, "changing resync lce: %d[%u;%02lx]"
				     " -> %d[%u;00]\n",
				     ext->lce.lc_number, ext->rs_left,
				     ext->flags, enr, rs_left);
				ext->flags = 0;
			}
			if (ext->rs_failed) {
				drbd_warn(device, "Kicking resync_lru element enr=%u "
				     "out with rs_failed=%d\n",
				     ext->lce.lc_number, ext->rs_failed);
			}
			ext->rs_left = rs_left;
			ext->rs_failed = (mode == RECORD_RS_FAILED) ? count : 0;
			/* we don't keep a persistent log of the resync lru,
			 * we can commit any change right away. */
			lc_committed(device->resync);
		}
		if (mode != SET_OUT_OF_SYNC)
			lc_put(device->resync, &ext->lce);
		/* no race, we are within the al_lock! */

		if (ext->rs_left <= ext->rs_failed) {
			ext->rs_failed = 0;
			return true;
		}
	} else if (mode != SET_OUT_OF_SYNC) {
		/* be quiet if lc_find() did not find it. */
		drbd_err(device, "lc_get() failed! locked=%d/%d flags=%lu\n",
		    device->resync_locked,
		    device->resync->nr_elements,
		    device->resync->flags);
	}
	return false;
}

void drbd_advance_rs_marks(struct drbd_device *device, unsigned long still_to_go)
{
	unsigned long now = jiffies;
	unsigned long last = device->rs_mark_time[device->rs_last_mark];
	int next = (device->rs_last_mark + 1) % DRBD_SYNC_MARKS;
	if (time_after_eq(now, last + DRBD_SYNC_MARK_STEP)) {
		if (device->rs_mark_left[device->rs_last_mark] != still_to_go &&
		    device->state.conn != C_PAUSED_SYNC_T &&
		    device->state.conn != C_PAUSED_SYNC_S) {
			device->rs_mark_time[next] = now;
			device->rs_mark_left[next] = still_to_go;
			device->rs_last_mark = next;
		}
	}
}

/* It is called lazy update, so don't do write-out too often. */
static bool lazy_bitmap_update_due(struct drbd_device *device)
{
	return time_after(jiffies, device->rs_last_bcast + 2*HZ);
}

static void maybe_schedule_on_disk_bitmap_update(struct drbd_device *device, bool rs_done)
{
	if (rs_done)
		set_bit(RS_DONE, &device->flags);
		/* and also set RS_PROGRESS below */
	else if (!lazy_bitmap_update_due(device))
		return;

	drbd_device_post_work(device, RS_PROGRESS);
}

static int update_sync_bits(struct drbd_device *device,
		unsigned long sbnr, unsigned long ebnr,
		enum update_sync_bits_mode mode)
{
	/*
	 * We keep a count of set bits per resync-extent in the ->rs_left
	 * caching member, so we need to loop and work within the resync extent
	 * alignment. Typically this loop will execute exactly once.
	 */
	unsigned long flags;
	unsigned long count = 0;
	unsigned int cleared = 0;
	while (sbnr <= ebnr) {
		/* set temporary boundary bit number to last bit number within
		 * the resync extent of the current start bit number,
		 * but cap at provided end bit number */
		unsigned long tbnr = min(ebnr, sbnr | BM_BLOCKS_PER_BM_EXT_MASK);
		unsigned long c;

		if (mode == RECORD_RS_FAILED)
			/* Only called from drbd_rs_failed_io(), bits
			 * supposedly still set.  Recount, maybe some
			 * of the bits have been successfully cleared
			 * by application IO meanwhile.
			 */
			c = drbd_bm_count_bits(device, sbnr, tbnr);
		else if (mode == SET_IN_SYNC)
			c = drbd_bm_clear_bits(device, sbnr, tbnr);
		else /* if (mode == SET_OUT_OF_SYNC) */
			c = drbd_bm_set_bits(device, sbnr, tbnr);

		if (c) {
			spin_lock_irqsave(&device->al_lock, flags);
			cleared += update_rs_extent(device, BM_BIT_TO_EXT(sbnr), c, mode);
			spin_unlock_irqrestore(&device->al_lock, flags);
			count += c;
		}
		sbnr = tbnr + 1;
	}
	if (count) {
		if (mode == SET_IN_SYNC) {
			unsigned long still_to_go = drbd_bm_total_weight(device);
			bool rs_is_done = (still_to_go <= device->rs_failed);
			drbd_advance_rs_marks(device, still_to_go);
			if (cleared || rs_is_done)
				maybe_schedule_on_disk_bitmap_update(device, rs_is_done);
		} else if (mode == RECORD_RS_FAILED)
			device->rs_failed += count;
		wake_up(&device->al_wait);
	}
	return count;
}

/* clear the bit corresponding to the piece of storage in question:
 * size byte of data starting from sector.  Only clear a bits of the affected
 * one ore more _aligned_ BM_BLOCK_SIZE blocks.
 *
 * called by worker on C_SYNC_TARGET and receiver on SyncSource.
 *
 */
int __drbd_change_sync(struct drbd_device *device, sector_t sector, int size,
		enum update_sync_bits_mode mode)
{
	/* Is called from worker and receiver context _only_ */
	unsigned long sbnr, ebnr, lbnr;
	unsigned long count = 0;
	sector_t esector, nr_sectors;

	/* This would be an empty REQ_FLUSH, be silent. */
	if ((mode == SET_OUT_OF_SYNC) && size == 0)
		return 0;

	if (size <= 0 || !IS_ALIGNED(size, 512) || size > DRBD_MAX_DISCARD_SIZE) {
		drbd_err(device, "%s: sector=%llus size=%d nonsense!\n",
				drbd_change_sync_fname[mode],
				(unsigned long long)sector, size);
		return 0;
	}

	if (!get_ldev(device))
		return 0; /* no disk, no metadata, no bitmap to manipulate bits in */

	nr_sectors = drbd_get_capacity(device->this_bdev);
	esector = sector + (size >> 9) - 1;

	if (!expect(sector < nr_sectors))
		goto out;
	if (!expect(esector < nr_sectors))
		esector = nr_sectors - 1;

	lbnr = BM_SECT_TO_BIT(nr_sectors-1);

	if (mode == SET_IN_SYNC) {
		/* Round up start sector, round down end sector.  We make sure
		 * we only clear full, aligned, BM_BLOCK_SIZE blocks. */
		if (unlikely(esector < BM_SECT_PER_BIT-1))
			goto out;
		if (unlikely(esector == (nr_sectors-1)))
			ebnr = lbnr;
		else
			ebnr = BM_SECT_TO_BIT(esector - (BM_SECT_PER_BIT-1));
		sbnr = BM_SECT_TO_BIT(sector + BM_SECT_PER_BIT-1);
	} else {
		/* We set it out of sync, or record resync failure.
		 * Should not round anything here. */
		sbnr = BM_SECT_TO_BIT(sector);
		ebnr = BM_SECT_TO_BIT(esector);
	}

	count = update_sync_bits(device, sbnr, ebnr, mode);
out:
	put_ldev(device);
	return count;
}

static
struct bm_extent *_bme_get(struct drbd_device *device, unsigned int enr)
{
	struct lc_element *e;
	struct bm_extent *bm_ext;
	int wakeup = 0;
	unsigned long rs_flags;

	spin_lock_irq(&device->al_lock);
	if (device->resync_locked > device->resync->nr_elements/2) {
		spin_unlock_irq(&device->al_lock);
		return NULL;
	}
	e = lc_get(device->resync, enr);
	bm_ext = e ? lc_entry(e, struct bm_extent, lce) : NULL;
	if (bm_ext) {
		if (bm_ext->lce.lc_number != enr) {
			bm_ext->rs_left = drbd_bm_e_weight(device, enr);
			bm_ext->rs_failed = 0;
			lc_committed(device->resync);
			wakeup = 1;
		}
		if (bm_ext->lce.refcnt == 1)
			device->resync_locked++;
		set_bit(BME_NO_WRITES, &bm_ext->flags);
	}
	rs_flags = device->resync->flags;
	spin_unlock_irq(&device->al_lock);
	if (wakeup)
		wake_up(&device->al_wait);

	if (!bm_ext) {
		if (rs_flags & LC_STARVING)
			drbd_warn(device, "Have to wait for element"
			     " (resync LRU too small?)\n");
		BUG_ON(rs_flags & LC_LOCKED);
	}

	return bm_ext;
}

static int _is_in_al(struct drbd_device *device, unsigned int enr)
{
	int rv;

	spin_lock_irq(&device->al_lock);
	rv = lc_is_used(device->act_log, enr);
	spin_unlock_irq(&device->al_lock);

	return rv;
}

/**
 * drbd_rs_begin_io() - Gets an extent in the resync LRU cache and sets it to BME_LOCKED
 * @device:	DRBD device.
 * @sector:	The sector number.
 *
 * This functions sleeps on al_wait. Returns 0 on success, -EINTR if interrupted.
 */
int drbd_rs_begin_io(struct drbd_device *device, sector_t sector)
{
	unsigned int enr = BM_SECT_TO_EXT(sector);
	struct bm_extent *bm_ext;
	int i, sig;
	bool sa;

retry:
	sig = wait_event_interruptible(device->al_wait,
			(bm_ext = _bme_get(device, enr)));
	if (sig)
		return -EINTR;

	if (test_bit(BME_LOCKED, &bm_ext->flags))
		return 0;

	/* step aside only while we are above c-min-rate; unless disabled. */
	sa = drbd_rs_c_min_rate_throttle(device);

	for (i = 0; i < AL_EXT_PER_BM_SECT; i++) {
		sig = wait_event_interruptible(device->al_wait,
					       !_is_in_al(device, enr * AL_EXT_PER_BM_SECT + i) ||
					       (sa && test_bit(BME_PRIORITY, &bm_ext->flags)));

		if (sig || (sa && test_bit(BME_PRIORITY, &bm_ext->flags))) {
			spin_lock_irq(&device->al_lock);
			if (lc_put(device->resync, &bm_ext->lce) == 0) {
				bm_ext->flags = 0; /* clears BME_NO_WRITES and eventually BME_PRIORITY */
				device->resync_locked--;
				wake_up(&device->al_wait);
			}
			spin_unlock_irq(&device->al_lock);
			if (sig)
				return -EINTR;
			if (schedule_timeout_interruptible(HZ/10))
				return -EINTR;
			goto retry;
		}
	}
	set_bit(BME_LOCKED, &bm_ext->flags);
	return 0;
}

/**
 * drbd_try_rs_begin_io() - Gets an extent in the resync LRU cache, does not sleep
 * @device:	DRBD device.
 * @sector:	The sector number.
 *
 * Gets an extent in the resync LRU cache, sets it to BME_NO_WRITES, then
 * tries to set it to BME_LOCKED. Returns 0 upon success, and -EAGAIN
 * if there is still application IO going on in this area.
 */
int drbd_try_rs_begin_io(struct drbd_device *device, sector_t sector)
{
	unsigned int enr = BM_SECT_TO_EXT(sector);
	const unsigned int al_enr = enr*AL_EXT_PER_BM_SECT;
	struct lc_element *e;
	struct bm_extent *bm_ext;
	int i;
	bool throttle = drbd_rs_should_slow_down(device, sector, true);

	/* If we need to throttle, a half-locked (only marked BME_NO_WRITES,
	 * not yet BME_LOCKED) extent needs to be kicked out explicitly if we
	 * need to throttle. There is at most one such half-locked extent,
	 * which is remembered in resync_wenr. */

	if (throttle && device->resync_wenr != enr)
		return -EAGAIN;

	spin_lock_irq(&device->al_lock);
	if (device->resync_wenr != LC_FREE && device->resync_wenr != enr) {
		/* in case you have very heavy scattered io, it may
		 * stall the syncer undefined if we give up the ref count
		 * when we try again and requeue.
		 *
		 * if we don't give up the refcount, but the next time
		 * we are scheduled this extent has been "synced" by new
		 * application writes, we'd miss the lc_put on the
		 * extent we keep the refcount on.
		 * so we remembered which extent we had to try again, and
		 * if the next requested one is something else, we do
		 * the lc_put here...
		 * we also have to wake_up
		 */
		e = lc_find(device->resync, device->resync_wenr);
		bm_ext = e ? lc_entry(e, struct bm_extent, lce) : NULL;
		if (bm_ext) {
			D_ASSERT(device, !test_bit(BME_LOCKED, &bm_ext->flags));
			D_ASSERT(device, test_bit(BME_NO_WRITES, &bm_ext->flags));
			clear_bit(BME_NO_WRITES, &bm_ext->flags);
			device->resync_wenr = LC_FREE;
			if (lc_put(device->resync, &bm_ext->lce) == 0) {
				bm_ext->flags = 0;
				device->resync_locked--;
			}
			wake_up(&device->al_wait);
		} else {
			drbd_alert(device, "LOGIC BUG\n");
		}
	}
	/* TRY. */
	e = lc_try_get(device->resync, enr);
	bm_ext = e ? lc_entry(e, struct bm_extent, lce) : NULL;
	if (bm_ext) {
		if (test_bit(BME_LOCKED, &bm_ext->flags))
			goto proceed;
		if (!test_and_set_bit(BME_NO_WRITES, &bm_ext->flags)) {
			device->resync_locked++;
		} else {
			/* we did set the BME_NO_WRITES,
			 * but then could not set BME_LOCKED,
			 * so we tried again.
			 * drop the extra reference. */
			bm_ext->lce.refcnt--;
			D_ASSERT(device, bm_ext->lce.refcnt > 0);
		}
		goto check_al;
	} else {
		/* do we rather want to try later? */
		if (device->resync_locked > device->resync->nr_elements-3)
			goto try_again;
		/* Do or do not. There is no try. -- Yoda */
		e = lc_get(device->resync, enr);
		bm_ext = e ? lc_entry(e, struct bm_extent, lce) : NULL;
		if (!bm_ext) {
			const unsigned long rs_flags = device->resync->flags;
			if (rs_flags & LC_STARVING)
				drbd_warn(device, "Have to wait for element"
				     " (resync LRU too small?)\n");
			BUG_ON(rs_flags & LC_LOCKED);
			goto try_again;
		}
		if (bm_ext->lce.lc_number != enr) {
			bm_ext->rs_left = drbd_bm_e_weight(device, enr);
			bm_ext->rs_failed = 0;
			lc_committed(device->resync);
			wake_up(&device->al_wait);
			D_ASSERT(device, test_bit(BME_LOCKED, &bm_ext->flags) == 0);
		}
		set_bit(BME_NO_WRITES, &bm_ext->flags);
		D_ASSERT(device, bm_ext->lce.refcnt == 1);
		device->resync_locked++;
		goto check_al;
	}
check_al:
	for (i = 0; i < AL_EXT_PER_BM_SECT; i++) {
		if (lc_is_used(device->act_log, al_enr+i))
			goto try_again;
	}
	set_bit(BME_LOCKED, &bm_ext->flags);
proceed:
	device->resync_wenr = LC_FREE;
	spin_unlock_irq(&device->al_lock);
	return 0;

try_again:
	if (bm_ext) {
		if (throttle) {
			D_ASSERT(device, !test_bit(BME_LOCKED, &bm_ext->flags));
			D_ASSERT(device, test_bit(BME_NO_WRITES, &bm_ext->flags));
			clear_bit(BME_NO_WRITES, &bm_ext->flags);
			device->resync_wenr = LC_FREE;
			if (lc_put(device->resync, &bm_ext->lce) == 0) {
				bm_ext->flags = 0;
				device->resync_locked--;
			}
			wake_up(&device->al_wait);
		} else
			device->resync_wenr = enr;
	}
	spin_unlock_irq(&device->al_lock);
	return -EAGAIN;
}

void drbd_rs_complete_io(struct drbd_device *device, sector_t sector)
{
	unsigned int enr = BM_SECT_TO_EXT(sector);
	struct lc_element *e;
	struct bm_extent *bm_ext;
	unsigned long flags;

	spin_lock_irqsave(&device->al_lock, flags);
	e = lc_find(device->resync, enr);
	bm_ext = e ? lc_entry(e, struct bm_extent, lce) : NULL;
	if (!bm_ext) {
		spin_unlock_irqrestore(&device->al_lock, flags);
		if (__ratelimit(&drbd_ratelimit_state))
			drbd_err(device, "drbd_rs_complete_io() called, but extent not found\n");
		return;
	}

	if (bm_ext->lce.refcnt == 0) {
		spin_unlock_irqrestore(&device->al_lock, flags);
		drbd_err(device, "drbd_rs_complete_io(,%llu [=%u]) called, "
		    "but refcnt is 0!?\n",
		    (unsigned long long)sector, enr);
		return;
	}

	if (lc_put(device->resync, &bm_ext->lce) == 0) {
		bm_ext->flags = 0; /* clear BME_LOCKED, BME_NO_WRITES and BME_PRIORITY */
		device->resync_locked--;
		wake_up(&device->al_wait);
	}

	spin_unlock_irqrestore(&device->al_lock, flags);
}

/**
 * drbd_rs_cancel_all() - Removes all extents from the resync LRU (even BME_LOCKED)
 * @device:	DRBD device.
 */
void drbd_rs_cancel_all(struct drbd_device *device)
{
	spin_lock_irq(&device->al_lock);

	if (get_ldev_if_state(device, D_FAILED)) { /* Makes sure ->resync is there. */
		lc_reset(device->resync);
		put_ldev(device);
	}
	device->resync_locked = 0;
	device->resync_wenr = LC_FREE;
	spin_unlock_irq(&device->al_lock);
	wake_up(&device->al_wait);
}

/**
 * drbd_rs_del_all() - Gracefully remove all extents from the resync LRU
 * @device:	DRBD device.
 *
 * Returns 0 upon success, -EAGAIN if at least one reference count was
 * not zero.
 */
int drbd_rs_del_all(struct drbd_device *device)
{
	struct lc_element *e;
	struct bm_extent *bm_ext;
	int i;

	spin_lock_irq(&device->al_lock);

	if (get_ldev_if_state(device, D_FAILED)) {
		/* ok, ->resync is there. */
		for (i = 0; i < device->resync->nr_elements; i++) {
			e = lc_element_by_index(device->resync, i);
			bm_ext = lc_entry(e, struct bm_extent, lce);
			if (bm_ext->lce.lc_number == LC_FREE)
				continue;
			if (bm_ext->lce.lc_number == device->resync_wenr) {
				drbd_info(device, "dropping %u in drbd_rs_del_all, apparently"
				     " got 'synced' by application io\n",
				     device->resync_wenr);
				D_ASSERT(device, !test_bit(BME_LOCKED, &bm_ext->flags));
				D_ASSERT(device, test_bit(BME_NO_WRITES, &bm_ext->flags));
				clear_bit(BME_NO_WRITES, &bm_ext->flags);
				device->resync_wenr = LC_FREE;
				lc_put(device->resync, &bm_ext->lce);
			}
			if (bm_ext->lce.refcnt != 0) {
				drbd_info(device, "Retrying drbd_rs_del_all() later. "
				     "refcnt=%d\n", bm_ext->lce.refcnt);
				put_ldev(device);
				spin_unlock_irq(&device->al_lock);
				return -EAGAIN;
			}
			D_ASSERT(device, !test_bit(BME_LOCKED, &bm_ext->flags));
			D_ASSERT(device, !test_bit(BME_NO_WRITES, &bm_ext->flags));
			lc_del(device->resync, &bm_ext->lce);
		}
		D_ASSERT(device, device->resync->used == 0);
		put_ldev(device);
	}
	spin_unlock_irq(&device->al_lock);
	wake_up(&device->al_wait);

	return 0;
}