aboutsummaryrefslogblamecommitdiffstats
path: root/drivers/md/raid6main.c
blob: f62ea1a73d0d9d1b87f5f10d7b91a6f6d7f48b0d (plain) (tree)
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



































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































                                                                                                                           
                                  
 












                                                                                 
 
















































                                                                                                  
                                                                                             





















                                                                                   

                                                             













































                                                                                         








































































                                                                                                                    
















































































































                                                                                                    


                                                         














































































































































                                                                                                                     
                                  






























































































                                                                          
/*
 * raid6main.c : Multiple Devices driver for Linux
 *	   Copyright (C) 1996, 1997 Ingo Molnar, Miguel de Icaza, Gadi Oxman
 *	   Copyright (C) 1999, 2000 Ingo Molnar
 *	   Copyright (C) 2002, 2003 H. Peter Anvin
 *
 * RAID-6 management functions.  This code is derived from raid5.c.
 * Last merge from raid5.c bkcvs version 1.79 (kernel 2.6.1).
 *
 * Thanks to Penguin Computing for making the RAID-6 development possible
 * by donating a test server!
 *
 * This program 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.
 *
 * You should have received a copy of the GNU General Public License
 * (for example /usr/src/linux/COPYING); if not, write to the Free
 * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */


#include <linux/config.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/highmem.h>
#include <linux/bitops.h>
#include <asm/atomic.h>
#include "raid6.h"

/*
 * Stripe cache
 */

#define NR_STRIPES		256
#define STRIPE_SIZE		PAGE_SIZE
#define STRIPE_SHIFT		(PAGE_SHIFT - 9)
#define STRIPE_SECTORS		(STRIPE_SIZE>>9)
#define	IO_THRESHOLD		1
#define HASH_PAGES		1
#define HASH_PAGES_ORDER	0
#define NR_HASH			(HASH_PAGES * PAGE_SIZE / sizeof(struct stripe_head *))
#define HASH_MASK		(NR_HASH - 1)

#define stripe_hash(conf, sect)	((conf)->stripe_hashtbl[((sect) >> STRIPE_SHIFT) & HASH_MASK])

/* bio's attached to a stripe+device for I/O are linked together in bi_sector
 * order without overlap.  There may be several bio's per stripe+device, and
 * a bio could span several devices.
 * When walking this list for a particular stripe+device, we must never proceed
 * beyond a bio that extends past this device, as the next bio might no longer
 * be valid.
 * This macro is used to determine the 'next' bio in the list, given the sector
 * of the current stripe+device
 */
#define r5_next_bio(bio, sect) ( ( (bio)->bi_sector + ((bio)->bi_size>>9) < sect + STRIPE_SECTORS) ? (bio)->bi_next : NULL)
/*
 * The following can be used to debug the driver
 */
#define RAID6_DEBUG	0	/* Extremely verbose printk */
#define RAID6_PARANOIA	1	/* Check spinlocks */
#define RAID6_DUMPSTATE 0	/* Include stripe cache state in /proc/mdstat */
#if RAID6_PARANOIA && defined(CONFIG_SMP)
# define CHECK_DEVLOCK() assert_spin_locked(&conf->device_lock)
#else
# define CHECK_DEVLOCK()
#endif

#define PRINTK(x...) ((void)(RAID6_DEBUG && printk(KERN_DEBUG x)))
#if RAID6_DEBUG
#undef inline
#undef __inline__
#define inline
#define __inline__
#endif

#if !RAID6_USE_EMPTY_ZERO_PAGE
/* In .bss so it's zeroed */
const char raid6_empty_zero_page[PAGE_SIZE] __attribute__((aligned(256)));
#endif

static inline int raid6_next_disk(int disk, int raid_disks)
{
	disk++;
	return (disk < raid_disks) ? disk : 0;
}

static void print_raid6_conf (raid6_conf_t *conf);

static inline void __release_stripe(raid6_conf_t *conf, struct stripe_head *sh)
{
	if (atomic_dec_and_test(&sh->count)) {
		if (!list_empty(&sh->lru))
			BUG();
		if (atomic_read(&conf->active_stripes)==0)
			BUG();
		if (test_bit(STRIPE_HANDLE, &sh->state)) {
			if (test_bit(STRIPE_DELAYED, &sh->state))
				list_add_tail(&sh->lru, &conf->delayed_list);
			else
				list_add_tail(&sh->lru, &conf->handle_list);
			md_wakeup_thread(conf->mddev->thread);
		} else {
			if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
				atomic_dec(&conf->preread_active_stripes);
				if (atomic_read(&conf->preread_active_stripes) < IO_THRESHOLD)
					md_wakeup_thread(conf->mddev->thread);
			}
			list_add_tail(&sh->lru, &conf->inactive_list);
			atomic_dec(&conf->active_stripes);
			if (!conf->inactive_blocked ||
			    atomic_read(&conf->active_stripes) < (NR_STRIPES*3/4))
				wake_up(&conf->wait_for_stripe);
		}
	}
}
static void release_stripe(struct stripe_head *sh)
{
	raid6_conf_t *conf = sh->raid_conf;
	unsigned long flags;

	spin_lock_irqsave(&conf->device_lock, flags);
	__release_stripe(conf, sh);
	spin_unlock_irqrestore(&conf->device_lock, flags);
}

static void remove_hash(struct stripe_head *sh)
{
	PRINTK("remove_hash(), stripe %llu\n", (unsigned long long)sh->sector);

	if (sh->hash_pprev) {
		if (sh->hash_next)
			sh->hash_next->hash_pprev = sh->hash_pprev;
		*sh->hash_pprev = sh->hash_next;
		sh->hash_pprev = NULL;
	}
}

static __inline__ void insert_hash(raid6_conf_t *conf, struct stripe_head *sh)
{
	struct stripe_head **shp = &stripe_hash(conf, sh->sector);

	PRINTK("insert_hash(), stripe %llu\n", (unsigned long long)sh->sector);

	CHECK_DEVLOCK();
	if ((sh->hash_next = *shp) != NULL)
		(*shp)->hash_pprev = &sh->hash_next;
	*shp = sh;
	sh->hash_pprev = shp;
}


/* find an idle stripe, make sure it is unhashed, and return it. */
static struct stripe_head *get_free_stripe(raid6_conf_t *conf)
{
	struct stripe_head *sh = NULL;
	struct list_head *first;

	CHECK_DEVLOCK();
	if (list_empty(&conf->inactive_list))
		goto out;
	first = conf->inactive_list.next;
	sh = list_entry(first, struct stripe_head, lru);
	list_del_init(first);
	remove_hash(sh);
	atomic_inc(&conf->active_stripes);
out:
	return sh;
}

static void shrink_buffers(struct stripe_head *sh, int num)
{
	struct page *p;
	int i;

	for (i=0; i<num ; i++) {
		p = sh->dev[i].page;
		if (!p)
			continue;
		sh->dev[i].page = NULL;
		page_cache_release(p);
	}
}

static int grow_buffers(struct stripe_head *sh, int num)
{
	int i;

	for (i=0; i<num; i++) {
		struct page *page;

		if (!(page = alloc_page(GFP_KERNEL))) {
			return 1;
		}
		sh->dev[i].page = page;
	}
	return 0;
}

static void raid6_build_block (struct stripe_head *sh, int i);

static inline void init_stripe(struct stripe_head *sh, sector_t sector, int pd_idx)
{
	raid6_conf_t *conf = sh->raid_conf;
	int disks = conf->raid_disks, i;

	if (atomic_read(&sh->count) != 0)
		BUG();
	if (test_bit(STRIPE_HANDLE, &sh->state))
		BUG();

	CHECK_DEVLOCK();
	PRINTK("init_stripe called, stripe %llu\n",
		(unsigned long long)sh->sector);

	remove_hash(sh);

	sh->sector = sector;
	sh->pd_idx = pd_idx;
	sh->state = 0;

	for (i=disks; i--; ) {
		struct r5dev *dev = &sh->dev[i];

		if (dev->toread || dev->towrite || dev->written ||
		    test_bit(R5_LOCKED, &dev->flags)) {
			PRINTK("sector=%llx i=%d %p %p %p %d\n",
			       (unsigned long long)sh->sector, i, dev->toread,
			       dev->towrite, dev->written,
			       test_bit(R5_LOCKED, &dev->flags));
			BUG();
		}
		dev->flags = 0;
		raid6_build_block(sh, i);
	}
	insert_hash(conf, sh);
}

static struct stripe_head *__find_stripe(raid6_conf_t *conf, sector_t sector)
{
	struct stripe_head *sh;

	CHECK_DEVLOCK();
	PRINTK("__find_stripe, sector %llu\n", (unsigned long long)sector);
	for (sh = stripe_hash(conf, sector); sh; sh = sh->hash_next)
		if (sh->sector == sector)
			return sh;
	PRINTK("__stripe %llu not in cache\n", (unsigned long long)sector);
	return NULL;
}

static void unplug_slaves(mddev_t *mddev);

static struct stripe_head *get_active_stripe(raid6_conf_t *conf, sector_t sector,
					     int pd_idx, int noblock)
{
	struct stripe_head *sh;

	PRINTK("get_stripe, sector %llu\n", (unsigned long long)sector);

	spin_lock_irq(&conf->device_lock);

	do {
		sh = __find_stripe(conf, sector);
		if (!sh) {
			if (!conf->inactive_blocked)
				sh = get_free_stripe(conf);
			if (noblock && sh == NULL)
				break;
			if (!sh) {
				conf->inactive_blocked = 1;
				wait_event_lock_irq(conf->wait_for_stripe,
						    !list_empty(&conf->inactive_list) &&
						    (atomic_read(&conf->active_stripes) < (NR_STRIPES *3/4)
						     || !conf->inactive_blocked),
						    conf->device_lock,
						    unplug_slaves(conf->mddev);
					);
				conf->inactive_blocked = 0;
			} else
				init_stripe(sh, sector, pd_idx);
		} else {
			if (atomic_read(&sh->count)) {
				if (!list_empty(&sh->lru))
					BUG();
			} else {
				if (!test_bit(STRIPE_HANDLE, &sh->state))
					atomic_inc(&conf->active_stripes);
				if (list_empty(&sh->lru))
					BUG();
				list_del_init(&sh->lru);
			}
		}
	} while (sh == NULL);

	if (sh)
		atomic_inc(&sh->count);

	spin_unlock_irq(&conf->device_lock);
	return sh;
}

static int grow_stripes(raid6_conf_t *conf, int num)
{
	struct stripe_head *sh;
	kmem_cache_t *sc;
	int devs = conf->raid_disks;

	sprintf(conf->cache_name, "raid6/%s", mdname(conf->mddev));

	sc = kmem_cache_create(conf->cache_name,
			       sizeof(struct stripe_head)+(devs-1)*sizeof(struct r5dev),
			       0, 0, NULL, NULL);
	if (!sc)
		return 1;
	conf->slab_cache = sc;
	while (num--) {
		sh = kmem_cache_alloc(sc, GFP_KERNEL);
		if (!sh)
			return 1;
		memset(sh, 0, sizeof(*sh) + (devs-1)*sizeof(struct r5dev));
		sh->raid_conf = conf;
		spin_lock_init(&sh->lock);

		if (grow_buffers(sh, conf->raid_disks)) {
			shrink_buffers(sh, conf->raid_disks);
			kmem_cache_free(sc, sh);
			return 1;
		}
		/* we just created an active stripe so... */
		atomic_set(&sh->count, 1);
		atomic_inc(&conf->active_stripes);
		INIT_LIST_HEAD(&sh->lru);
		release_stripe(sh);
	}
	return 0;
}

static void shrink_stripes(raid6_conf_t *conf)
{
	struct stripe_head *sh;

	while (1) {
		spin_lock_irq(&conf->device_lock);
		sh = get_free_stripe(conf);
		spin_unlock_irq(&conf->device_lock);
		if (!sh)
			break;
		if (atomic_read(&sh->count))
			BUG();
		shrink_buffers(sh, conf->raid_disks);
		kmem_cache_free(conf->slab_cache, sh);
		atomic_dec(&conf->active_stripes);
	}
	kmem_cache_destroy(conf->slab_cache);
	conf->slab_cache = NULL;
}

static int raid6_end_read_request (struct bio * bi, unsigned int bytes_done,
				   int error)
{
 	struct stripe_head *sh = bi->bi_private;
	raid6_conf_t *conf = sh->raid_conf;
	int disks = conf->raid_disks, i;
	int uptodate = test_bit(BIO_UPTODATE, &bi->bi_flags);

	if (bi->bi_size)
		return 1;

	for (i=0 ; i<disks; i++)
		if (bi == &sh->dev[i].req)
			break;

	PRINTK("end_read_request %llu/%d, count: %d, uptodate %d.\n",
		(unsigned long long)sh->sector, i, atomic_read(&sh->count),
		uptodate);
	if (i == disks) {
		BUG();
		return 0;
	}

	if (uptodate) {
#if 0
		struct bio *bio;
		unsigned long flags;
		spin_lock_irqsave(&conf->device_lock, flags);
		/* we can return a buffer if we bypassed the cache or
		 * if the top buffer is not in highmem.  If there are
		 * multiple buffers, leave the extra work to
		 * handle_stripe
		 */
		buffer = sh->bh_read[i];
		if (buffer &&
		    (!PageHighMem(buffer->b_page)
		     || buffer->b_page == bh->b_page )
			) {
			sh->bh_read[i] = buffer->b_reqnext;
			buffer->b_reqnext = NULL;
		} else
			buffer = NULL;
		spin_unlock_irqrestore(&conf->device_lock, flags);
		if (sh->bh_page[i]==bh->b_page)
			set_buffer_uptodate(bh);
		if (buffer) {
			if (buffer->b_page != bh->b_page)
				memcpy(buffer->b_data, bh->b_data, bh->b_size);
			buffer->b_end_io(buffer, 1);
		}
#else
		set_bit(R5_UPTODATE, &sh->dev[i].flags);
#endif
	} else {
		md_error(conf->mddev, conf->disks[i].rdev);
		clear_bit(R5_UPTODATE, &sh->dev[i].flags);
	}
	rdev_dec_pending(conf->disks[i].rdev, conf->mddev);
#if 0
	/* must restore b_page before unlocking buffer... */
	if (sh->bh_page[i] != bh->b_page) {
		bh->b_page = sh->bh_page[i];
		bh->b_data = page_address(bh->b_page);
		clear_buffer_uptodate(bh);
	}
#endif
	clear_bit(R5_LOCKED, &sh->dev[i].flags);
	set_bit(STRIPE_HANDLE, &sh->state);
	release_stripe(sh);
	return 0;
}

static int raid6_end_write_request (struct bio *bi, unsigned int bytes_done,
				    int error)
{
 	struct stripe_head *sh = bi->bi_private;
	raid6_conf_t *conf = sh->raid_conf;
	int disks = conf->raid_disks, i;
	unsigned long flags;
	int uptodate = test_bit(BIO_UPTODATE, &bi->bi_flags);

	if (bi->bi_size)
		return 1;

	for (i=0 ; i<disks; i++)
		if (bi == &sh->dev[i].req)
			break;

	PRINTK("end_write_request %llu/%d, count %d, uptodate: %d.\n",
		(unsigned long long)sh->sector, i, atomic_read(&sh->count),
		uptodate);
	if (i == disks) {
		BUG();
		return 0;
	}

	spin_lock_irqsave(&conf->device_lock, flags);
	if (!uptodate)
		md_error(conf->mddev, conf->disks[i].rdev);

	rdev_dec_pending(conf->disks[i].rdev, conf->mddev);

	clear_bit(R5_LOCKED, &sh->dev[i].flags);
	set_bit(STRIPE_HANDLE, &sh->state);
	__release_stripe(conf, sh);
	spin_unlock_irqrestore(&conf->device_lock, flags);
	return 0;
}


static sector_t compute_blocknr(struct stripe_head *sh, int i);

static void raid6_build_block (struct stripe_head *sh, int i)
{
	struct r5dev *dev = &sh->dev[i];
	int pd_idx = sh->pd_idx;
	int qd_idx = raid6_next_disk(pd_idx, sh->raid_conf->raid_disks);

	bio_init(&dev->req);
	dev->req.bi_io_vec = &dev->vec;
	dev->req.bi_vcnt++;
	dev->req.bi_max_vecs++;
	dev->vec.bv_page = dev->page;
	dev->vec.bv_len = STRIPE_SIZE;
	dev->vec.bv_offset = 0;

	dev->req.bi_sector = sh->sector;
	dev->req.bi_private = sh;

	dev->flags = 0;
	if (i != pd_idx && i != qd_idx)
		dev->sector = compute_blocknr(sh, i);
}

static void error(mddev_t *mddev, mdk_rdev_t *rdev)
{
	char b[BDEVNAME_SIZE];
	raid6_conf_t *conf = (raid6_conf_t *) mddev->private;
	PRINTK("raid6: error called\n");

	if (!rdev->faulty) {
		mddev->sb_dirty = 1;
		if (rdev->in_sync) {
			conf->working_disks--;
			mddev->degraded++;
			conf->failed_disks++;
			rdev->in_sync = 0;
			/*
			 * if recovery was running, make sure it aborts.
			 */
			set_bit(MD_RECOVERY_ERR, &mddev->recovery);
		}
		rdev->faulty = 1;
		printk (KERN_ALERT
			"raid6: Disk failure on %s, disabling device."
			" Operation continuing on %d devices\n",
			bdevname(rdev->bdev,b), conf->working_disks);
	}
}

/*
 * Input: a 'big' sector number,
 * Output: index of the data and parity disk, and the sector # in them.
 */
static sector_t raid6_compute_sector(sector_t r_sector, unsigned int raid_disks,
			unsigned int data_disks, unsigned int * dd_idx,
			unsigned int * pd_idx, raid6_conf_t *conf)
{
	long stripe;
	unsigned long chunk_number;
	unsigned int chunk_offset;
	sector_t new_sector;
	int sectors_per_chunk = conf->chunk_size >> 9;

	/* First compute the information on this sector */

	/*
	 * Compute the chunk number and the sector offset inside the chunk
	 */
	chunk_offset = sector_div(r_sector, sectors_per_chunk);
	chunk_number = r_sector;
	if ( r_sector != chunk_number ) {
		printk(KERN_CRIT "raid6: ERROR: r_sector = %llu, chunk_number = %lu\n",
		       (unsigned long long)r_sector, (unsigned long)chunk_number);
		BUG();
	}

	/*
	 * Compute the stripe number
	 */
	stripe = chunk_number / data_disks;

	/*
	 * Compute the data disk and parity disk indexes inside the stripe
	 */
	*dd_idx = chunk_number % data_disks;

	/*
	 * Select the parity disk based on the user selected algorithm.
	 */

	/**** FIX THIS ****/
	switch (conf->algorithm) {
	case ALGORITHM_LEFT_ASYMMETRIC:
		*pd_idx = raid_disks - 1 - (stripe % raid_disks);
		if (*pd_idx == raid_disks-1)
		  	(*dd_idx)++; 	/* Q D D D P */
		else if (*dd_idx >= *pd_idx)
		  	(*dd_idx) += 2; /* D D P Q D */
		break;
	case ALGORITHM_RIGHT_ASYMMETRIC:
		*pd_idx = stripe % raid_disks;
		if (*pd_idx == raid_disks-1)
		  	(*dd_idx)++; 	/* Q D D D P */
		else if (*dd_idx >= *pd_idx)
		  	(*dd_idx) += 2; /* D D P Q D */
		break;
	case ALGORITHM_LEFT_SYMMETRIC:
		*pd_idx = raid_disks - 1 - (stripe % raid_disks);
		*dd_idx = (*pd_idx + 2 + *dd_idx) % raid_disks;
		break;
	case ALGORITHM_RIGHT_SYMMETRIC:
		*pd_idx = stripe % raid_disks;
		*dd_idx = (*pd_idx + 2 + *dd_idx) % raid_disks;
		break;
	default:
		printk (KERN_CRIT "raid6: unsupported algorithm %d\n",
			conf->algorithm);
	}

	PRINTK("raid6: chunk_number = %lu, pd_idx = %u, dd_idx = %u\n",
	       chunk_number, *pd_idx, *dd_idx);

	/*
	 * Finally, compute the new sector number
	 */
	new_sector = (sector_t) stripe * sectors_per_chunk + chunk_offset;
	return new_sector;
}


static sector_t compute_blocknr(struct stripe_head *sh, int i)
{
	raid6_conf_t *conf = sh->raid_conf;
	int raid_disks = conf->raid_disks, data_disks = raid_disks - 2;
	sector_t new_sector = sh->sector, check;
	int sectors_per_chunk = conf->chunk_size >> 9;
	sector_t stripe;
	int chunk_offset;
	int chunk_number, dummy1, dummy2, dd_idx = i;
	sector_t r_sector;
	int i0 = i;

	chunk_offset = sector_div(new_sector, sectors_per_chunk);
	stripe = new_sector;
	if ( new_sector != stripe ) {
		printk(KERN_CRIT "raid6: ERROR: new_sector = %llu, stripe = %lu\n",
		       (unsigned long long)new_sector, (unsigned long)stripe);
		BUG();
	}

	switch (conf->algorithm) {
		case ALGORITHM_LEFT_ASYMMETRIC:
		case ALGORITHM_RIGHT_ASYMMETRIC:
		  	if (sh->pd_idx == raid_disks-1)
				i--; 	/* Q D D D P */
			else if (i > sh->pd_idx)
				i -= 2; /* D D P Q D */
			break;
		case ALGORITHM_LEFT_SYMMETRIC:
		case ALGORITHM_RIGHT_SYMMETRIC:
			if (sh->pd_idx == raid_disks-1)
				i--; /* Q D D D P */
			else {
				/* D D P Q D */
				if (i < sh->pd_idx)
					i += raid_disks;
				i -= (sh->pd_idx + 2);
			}
			break;
		default:
			printk (KERN_CRIT "raid6: unsupported algorithm %d\n",
				conf->algorithm);
	}

	PRINTK("raid6: compute_blocknr: pd_idx = %u, i0 = %u, i = %u\n", sh->pd_idx, i0, i);

	chunk_number = stripe * data_disks + i;
	r_sector = (sector_t)chunk_number * sectors_per_chunk + chunk_offset;

	check = raid6_compute_sector (r_sector, raid_disks, data_disks, &dummy1, &dummy2, conf);
	if (check != sh->sector || dummy1 != dd_idx || dummy2 != sh->pd_idx) {
		printk(KERN_CRIT "raid6: compute_blocknr: map not correct\n");
		return 0;
	}
	return r_sector;
}



/*
 * Copy data between a page in the stripe cache, and one or more bion
 * The page could align with the middle of the bio, or there could be
 * several bion, each with several bio_vecs, which cover part of the page
 * Multiple bion are linked together on bi_next.  There may be extras
 * at the end of this list.  We ignore them.
 */
static void copy_data(int frombio, struct bio *bio,
		     struct page *page,
		     sector_t sector)
{
	char *pa = page_address(page);
	struct bio_vec *bvl;
	int i;
	int page_offset;

	if (bio->bi_sector >= sector)
		page_offset = (signed)(bio->bi_sector - sector) * 512;
	else
		page_offset = (signed)(sector - bio->bi_sector) * -512;
	bio_for_each_segment(bvl, bio, i) {
		int len = bio_iovec_idx(bio,i)->bv_len;
		int clen;
		int b_offset = 0;

		if (page_offset < 0) {
			b_offset = -page_offset;
			page_offset += b_offset;
			len -= b_offset;
		}

		if (len > 0 && page_offset + len > STRIPE_SIZE)
			clen = STRIPE_SIZE - page_offset;
		else clen = len;

		if (clen > 0) {
			char *ba = __bio_kmap_atomic(bio, i, KM_USER0);
			if (frombio)
				memcpy(pa+page_offset, ba+b_offset, clen);
			else
				memcpy(ba+b_offset, pa+page_offset, clen);
			__bio_kunmap_atomic(ba, KM_USER0);
		}
		if (clen < len) /* hit end of page */
			break;
		page_offset +=  len;
	}
}

#define check_xor() 	do { 						\
			   if (count == MAX_XOR_BLOCKS) {		\
				xor_block(count, STRIPE_SIZE, ptr);	\
				count = 1;				\
			   }						\
			} while(0)

/* Compute P and Q syndromes */
static void compute_parity(struct stripe_head *sh, int method)
{
	raid6_conf_t *conf = sh->raid_conf;
	int i, pd_idx = sh->pd_idx, qd_idx, d0_idx, disks = conf->raid_disks, count;
	struct bio *chosen;
	/**** FIX THIS: This could be very bad if disks is close to 256 ****/
	void *ptrs[disks];

	qd_idx = raid6_next_disk(pd_idx, disks);
	d0_idx = raid6_next_disk(qd_idx, disks);

	PRINTK("compute_parity, stripe %llu, method %d\n",
		(unsigned long long)sh->sector, method);

	switch(method) {
	case READ_MODIFY_WRITE:
		BUG();		/* READ_MODIFY_WRITE N/A for RAID-6 */
	case RECONSTRUCT_WRITE:
		for (i= disks; i-- ;)
			if ( i != pd_idx && i != qd_idx && sh->dev[i].towrite ) {
				chosen = sh->dev[i].towrite;
				sh->dev[i].towrite = NULL;

				if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
					wake_up(&conf->wait_for_overlap);

				if (sh->dev[i].written) BUG();
				sh->dev[i].written = chosen;
			}
		break;
	case CHECK_PARITY:
		BUG();		/* Not implemented yet */
	}

	for (i = disks; i--;)
		if (sh->dev[i].written) {
			sector_t sector = sh->dev[i].sector;
			struct bio *wbi = sh->dev[i].written;
			while (wbi && wbi->bi_sector < sector + STRIPE_SECTORS) {
				copy_data(1, wbi, sh->dev[i].page, sector);
				wbi = r5_next_bio(wbi, sector);
			}

			set_bit(R5_LOCKED, &sh->dev[i].flags);
			set_bit(R5_UPTODATE, &sh->dev[i].flags);
		}

//	switch(method) {
//	case RECONSTRUCT_WRITE:
//	case CHECK_PARITY:
//	case UPDATE_PARITY:
		/* Note that unlike RAID-5, the ordering of the disks matters greatly. */
		/* FIX: Is this ordering of drives even remotely optimal? */
		count = 0;
		i = d0_idx;
		do {
			ptrs[count++] = page_address(sh->dev[i].page);
			if (count <= disks-2 && !test_bit(R5_UPTODATE, &sh->dev[i].flags))
				printk("block %d/%d not uptodate on parity calc\n", i,count);
			i = raid6_next_disk(i, disks);
		} while ( i != d0_idx );
//		break;
//	}

	raid6_call.gen_syndrome(disks, STRIPE_SIZE, ptrs);

	switch(method) {
	case RECONSTRUCT_WRITE:
		set_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);
		set_bit(R5_UPTODATE, &sh->dev[qd_idx].flags);
		set_bit(R5_LOCKED,   &sh->dev[pd_idx].flags);
		set_bit(R5_LOCKED,   &sh->dev[qd_idx].flags);
		break;
	case UPDATE_PARITY:
		set_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);
		set_bit(R5_UPTODATE, &sh->dev[qd_idx].flags);
		break;
	}
}

/* Compute one missing block */
static void compute_block_1(struct stripe_head *sh, int dd_idx)
{
	raid6_conf_t *conf = sh->raid_conf;
	int i, count, disks = conf->raid_disks;
	void *ptr[MAX_XOR_BLOCKS], *p;
	int pd_idx = sh->pd_idx;
	int qd_idx = raid6_next_disk(pd_idx, disks);

	PRINTK("compute_block_1, stripe %llu, idx %d\n",
		(unsigned long long)sh->sector, dd_idx);

	if ( dd_idx == qd_idx ) {
		/* We're actually computing the Q drive */
		compute_parity(sh, UPDATE_PARITY);
	} else {
		ptr[0] = page_address(sh->dev[dd_idx].page);
		memset(ptr[0], 0, STRIPE_SIZE);
		count = 1;
		for (i = disks ; i--; ) {
			if (i == dd_idx || i == qd_idx)
				continue;
			p = page_address(sh->dev[i].page);
			if (test_bit(R5_UPTODATE, &sh->dev[i].flags))
				ptr[count++] = p;
			else
				printk("compute_block() %d, stripe %llu, %d"
				       " not present\n", dd_idx,
				       (unsigned long long)sh->sector, i);

			check_xor();
		}
		if (count != 1)
			xor_block(count, STRIPE_SIZE, ptr);
		set_bit(R5_UPTODATE, &sh->dev[dd_idx].flags);
	}
}

/* Compute two missing blocks */
static void compute_block_2(struct stripe_head *sh, int dd_idx1, int dd_idx2)
{
	raid6_conf_t *conf = sh->raid_conf;
	int i, count, disks = conf->raid_disks;
	int pd_idx = sh->pd_idx;
	int qd_idx = raid6_next_disk(pd_idx, disks);
	int d0_idx = raid6_next_disk(qd_idx, disks);
	int faila, failb;

	/* faila and failb are disk numbers relative to d0_idx */
	/* pd_idx become disks-2 and qd_idx become disks-1 */
	faila = (dd_idx1 < d0_idx) ? dd_idx1+(disks-d0_idx) : dd_idx1-d0_idx;
	failb = (dd_idx2 < d0_idx) ? dd_idx2+(disks-d0_idx) : dd_idx2-d0_idx;

	BUG_ON(faila == failb);
	if ( failb < faila ) { int tmp = faila; faila = failb; failb = tmp; }

	PRINTK("compute_block_2, stripe %llu, idx %d,%d (%d,%d)\n",
	       (unsigned long long)sh->sector, dd_idx1, dd_idx2, faila, failb);

	if ( failb == disks-1 ) {
		/* Q disk is one of the missing disks */
		if ( faila == disks-2 ) {
			/* Missing P+Q, just recompute */
			compute_parity(sh, UPDATE_PARITY);
			return;
		} else {
			/* We're missing D+Q; recompute D from P */
			compute_block_1(sh, (dd_idx1 == qd_idx) ? dd_idx2 : dd_idx1);
			compute_parity(sh, UPDATE_PARITY); /* Is this necessary? */
			return;
		}
	}

	/* We're missing D+P or D+D; build pointer table */
	{
		/**** FIX THIS: This could be very bad if disks is close to 256 ****/
		void *ptrs[disks];

		count = 0;
		i = d0_idx;
		do {
			ptrs[count++] = page_address(sh->dev[i].page);
			i = raid6_next_disk(i, disks);
			if (i != dd_idx1 && i != dd_idx2 &&
			    !test_bit(R5_UPTODATE, &sh->dev[i].flags))
				printk("compute_2 with missing block %d/%d\n", count, i);
		} while ( i != d0_idx );

		if ( failb == disks-2 ) {
			/* We're missing D+P. */
			raid6_datap_recov(disks, STRIPE_SIZE, faila, ptrs);
		} else {
			/* We're missing D+D. */
			raid6_2data_recov(disks, STRIPE_SIZE, faila, failb, ptrs);
		}

		/* Both the above update both missing blocks */
		set_bit(R5_UPTODATE, &sh->dev[dd_idx1].flags);
		set_bit(R5_UPTODATE, &sh->dev[dd_idx2].flags);
	}
}


/*
 * Each stripe/dev can have one or more bion attached.
 * toread/towrite point to the first in a chain.
 * The bi_next chain must be in order.
 */
static int add_stripe_bio(struct stripe_head *sh, struct bio *bi, int dd_idx, int forwrite)
{
	struct bio **bip;
	raid6_conf_t *conf = sh->raid_conf;

	PRINTK("adding bh b#%llu to stripe s#%llu\n",
		(unsigned long long)bi->bi_sector,
		(unsigned long long)sh->sector);


	spin_lock(&sh->lock);
	spin_lock_irq(&conf->device_lock);
	if (forwrite)
		bip = &sh->dev[dd_idx].towrite;
	else
		bip = &sh->dev[dd_idx].toread;
	while (*bip && (*bip)->bi_sector < bi->bi_sector) {
		if ((*bip)->bi_sector + ((*bip)->bi_size >> 9) > bi->bi_sector)
			goto overlap;
		bip = &(*bip)->bi_next;
	}
	if (*bip && (*bip)->bi_sector < bi->bi_sector + ((bi->bi_size)>>9))
		goto overlap;

	if (*bip && bi->bi_next && (*bip) != bi->bi_next)
		BUG();
	if (*bip)
		bi->bi_next = *bip;
	*bip = bi;
	bi->bi_phys_segments ++;
	spin_unlock_irq(&conf->device_lock);
	spin_unlock(&sh->lock);

	PRINTK("added bi b#%llu to stripe s#%llu, disk %d.\n",
		(unsigned long long)bi->bi_sector,
		(unsigned long long)sh->sector, dd_idx);

	if (forwrite) {
		/* check if page is covered */
		sector_t sector = sh->dev[dd_idx].sector;
		for (bi=sh->dev[dd_idx].towrite;
		     sector < sh->dev[dd_idx].sector + STRIPE_SECTORS &&
			     bi && bi->bi_sector <= sector;
		     bi = r5_next_bio(bi, sh->dev[dd_idx].sector)) {
			if (bi->bi_sector + (bi->bi_size>>9) >= sector)
				sector = bi->bi_sector + (bi->bi_size>>9);
		}
		if (sector >= sh->dev[dd_idx].sector + STRIPE_SECTORS)
			set_bit(R5_OVERWRITE, &sh->dev[dd_idx].flags);
	}
	return 1;

 overlap:
	set_bit(R5_Overlap, &sh->dev[dd_idx].flags);
	spin_unlock_irq(&conf->device_lock);
	spin_unlock(&sh->lock);
	return 0;
}


/*
 * handle_stripe - do things to a stripe.
 *
 * We lock the stripe and then examine the state of various bits
 * to see what needs to be done.
 * Possible results:
 *    return some read request which now have data
 *    return some write requests which are safely on disc
 *    schedule a read on some buffers
 *    schedule a write of some buffers
 *    return confirmation of parity correctness
 *
 * Parity calculations are done inside the stripe lock
 * buffers are taken off read_list or write_list, and bh_cache buffers
 * get BH_Lock set before the stripe lock is released.
 *
 */

static void handle_stripe(struct stripe_head *sh)
{
	raid6_conf_t *conf = sh->raid_conf;
	int disks = conf->raid_disks;
	struct bio *return_bi= NULL;
	struct bio *bi;
	int i;
	int syncing;
	int locked=0, uptodate=0, to_read=0, to_write=0, failed=0, written=0;
	int non_overwrite = 0;
	int failed_num[2] = {0, 0};
	struct r5dev *dev, *pdev, *qdev;
	int pd_idx = sh->pd_idx;
	int qd_idx = raid6_next_disk(pd_idx, disks);
	int p_failed, q_failed;

	PRINTK("handling stripe %llu, state=%#lx cnt=%d, pd_idx=%d, qd_idx=%d\n",
	       (unsigned long long)sh->sector, sh->state, atomic_read(&sh->count),
	       pd_idx, qd_idx);

	spin_lock(&sh->lock);
	clear_bit(STRIPE_HANDLE, &sh->state);
	clear_bit(STRIPE_DELAYED, &sh->state);

	syncing = test_bit(STRIPE_SYNCING, &sh->state);
	/* Now to look around and see what can be done */

	for (i=disks; i--; ) {
		mdk_rdev_t *rdev;
		dev = &sh->dev[i];
		clear_bit(R5_Insync, &dev->flags);
		clear_bit(R5_Syncio, &dev->flags);

		PRINTK("check %d: state 0x%lx read %p write %p written %p\n",
			i, dev->flags, dev->toread, dev->towrite, dev->written);
		/* maybe we can reply to a read */
		if (test_bit(R5_UPTODATE, &dev->flags) && dev->toread) {
			struct bio *rbi, *rbi2;
			PRINTK("Return read for disc %d\n", i);
			spin_lock_irq(&conf->device_lock);
			rbi = dev->toread;
			dev->toread = NULL;
			if (test_and_clear_bit(R5_Overlap, &dev->flags))
				wake_up(&conf->wait_for_overlap);
			spin_unlock_irq(&conf->device_lock);
			while (rbi && rbi->bi_sector < dev->sector + STRIPE_SECTORS) {
				copy_data(0, rbi, dev->page, dev->sector);
				rbi2 = r5_next_bio(rbi, dev->sector);
				spin_lock_irq(&conf->device_lock);
				if (--rbi->bi_phys_segments == 0) {
					rbi->bi_next = return_bi;
					return_bi = rbi;
				}
				spin_unlock_irq(&conf->device_lock);
				rbi = rbi2;
			}
		}

		/* now count some things */
		if (test_bit(R5_LOCKED, &dev->flags)) locked++;
		if (test_bit(R5_UPTODATE, &dev->flags)) uptodate++;


		if (dev->toread) to_read++;
		if (dev->towrite) {
			to_write++;
			if (!test_bit(R5_OVERWRITE, &dev->flags))
				non_overwrite++;
		}
		if (dev->written) written++;
		rdev = conf->disks[i].rdev; /* FIXME, should I be looking rdev */
		if (!rdev || !rdev->in_sync) {
			if ( failed < 2 )
				failed_num[failed] = i;
			failed++;
		} else
			set_bit(R5_Insync, &dev->flags);
	}
	PRINTK("locked=%d uptodate=%d to_read=%d"
	       " to_write=%d failed=%d failed_num=%d,%d\n",
	       locked, uptodate, to_read, to_write, failed,
	       failed_num[0], failed_num[1]);
	/* check if the array has lost >2 devices and, if so, some requests might
	 * need to be failed
	 */
	if (failed > 2 && to_read+to_write+written) {
		spin_lock_irq(&conf->device_lock);
		for (i=disks; i--; ) {
			/* fail all writes first */
			bi = sh->dev[i].towrite;
			sh->dev[i].towrite = NULL;
			if (bi) to_write--;

			if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
				wake_up(&conf->wait_for_overlap);

			while (bi && bi->bi_sector < sh->dev[i].sector + STRIPE_SECTORS){
				struct bio *nextbi = r5_next_bio(bi, sh->dev[i].sector);
				clear_bit(BIO_UPTODATE, &bi->bi_flags);
				if (--bi->bi_phys_segments == 0) {
					md_write_end(conf->mddev);
					bi->bi_next = return_bi;
					return_bi = bi;
				}
				bi = nextbi;
			}
			/* and fail all 'written' */
			bi = sh->dev[i].written;
			sh->dev[i].written = NULL;
			while (bi && bi->bi_sector < sh->dev[i].sector + STRIPE_SECTORS) {
				struct bio *bi2 = r5_next_bio(bi, sh->dev[i].sector);
				clear_bit(BIO_UPTODATE, &bi->bi_flags);
				if (--bi->bi_phys_segments == 0) {
					md_write_end(conf->mddev);
					bi->bi_next = return_bi;
					return_bi = bi;
				}
				bi = bi2;
			}

			/* fail any reads if this device is non-operational */
			if (!test_bit(R5_Insync, &sh->dev[i].flags)) {
				bi = sh->dev[i].toread;
				sh->dev[i].toread = NULL;
				if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
					wake_up(&conf->wait_for_overlap);
				if (bi) to_read--;
				while (bi && bi->bi_sector < sh->dev[i].sector + STRIPE_SECTORS){
					struct bio *nextbi = r5_next_bio(bi, sh->dev[i].sector);
					clear_bit(BIO_UPTODATE, &bi->bi_flags);
					if (--bi->bi_phys_segments == 0) {
						bi->bi_next = return_bi;
						return_bi = bi;
					}
					bi = nextbi;
				}
			}
		}
		spin_unlock_irq(&conf->device_lock);
	}
	if (failed > 2 && syncing) {
		md_done_sync(conf->mddev, STRIPE_SECTORS,0);
		clear_bit(STRIPE_SYNCING, &sh->state);
		syncing = 0;
	}

	/*
	 * might be able to return some write requests if the parity blocks
	 * are safe, or on a failed drive
	 */
	pdev = &sh->dev[pd_idx];
	p_failed = (failed >= 1 && failed_num[0] == pd_idx)
		|| (failed >= 2 && failed_num[1] == pd_idx);
	qdev = &sh->dev[qd_idx];
	q_failed = (failed >= 1 && failed_num[0] == qd_idx)
		|| (failed >= 2 && failed_num[1] == qd_idx);

	if ( written &&
	     ( p_failed || ((test_bit(R5_Insync, &pdev->flags)
			     && !test_bit(R5_LOCKED, &pdev->flags)
			     && test_bit(R5_UPTODATE, &pdev->flags))) ) &&
	     ( q_failed || ((test_bit(R5_Insync, &qdev->flags)
			     && !test_bit(R5_LOCKED, &qdev->flags)
			     && test_bit(R5_UPTODATE, &qdev->flags))) ) ) {
		/* any written block on an uptodate or failed drive can be
		 * returned.  Note that if we 'wrote' to a failed drive,
		 * it will be UPTODATE, but never LOCKED, so we don't need
		 * to test 'failed' directly.
		 */
		for (i=disks; i--; )
			if (sh->dev[i].written) {
				dev = &sh->dev[i];
				if (!test_bit(R5_LOCKED, &dev->flags) &&
				    test_bit(R5_UPTODATE, &dev->flags) ) {
					/* We can return any write requests */
					struct bio *wbi, *wbi2;
					PRINTK("Return write for stripe %llu disc %d\n",
					       (unsigned long long)sh->sector, i);
					spin_lock_irq(&conf->device_lock);
					wbi = dev->written;
					dev->written = NULL;
					while (wbi && wbi->bi_sector < dev->sector + STRIPE_SECTORS) {
						wbi2 = r5_next_bio(wbi, dev->sector);
						if (--wbi->bi_phys_segments == 0) {
							md_write_end(conf->mddev);
							wbi->bi_next = return_bi;
							return_bi = wbi;
						}
						wbi = wbi2;
					}
					spin_unlock_irq(&conf->device_lock);
				}
			}
	}

	/* Now we might consider reading some blocks, either to check/generate
	 * parity, or to satisfy requests
	 * or to load a block that is being partially written.
	 */
	if (to_read || non_overwrite || (to_write && failed) || (syncing && (uptodate < disks))) {
		for (i=disks; i--;) {
			dev = &sh->dev[i];
			if (!test_bit(R5_LOCKED, &dev->flags) && !test_bit(R5_UPTODATE, &dev->flags) &&
			    (dev->toread ||
			     (dev->towrite && !test_bit(R5_OVERWRITE, &dev->flags)) ||
			     syncing ||
			     (failed >= 1 && (sh->dev[failed_num[0]].toread || to_write)) ||
			     (failed >= 2 && (sh->dev[failed_num[1]].toread || to_write))
				    )
				) {
				/* we would like to get this block, possibly
				 * by computing it, but we might not be able to
				 */
				if (uptodate == disks-1) {
					PRINTK("Computing stripe %llu block %d\n",
					       (unsigned long long)sh->sector, i);
					compute_block_1(sh, i);
					uptodate++;
				} else if ( uptodate == disks-2 && failed >= 2 ) {
					/* Computing 2-failure is *very* expensive; only do it if failed >= 2 */
					int other;
					for (other=disks; other--;) {
						if ( other == i )
							continue;
						if ( !test_bit(R5_UPTODATE, &sh->dev[other].flags) )
							break;
					}
					BUG_ON(other < 0);
					PRINTK("Computing stripe %llu blocks %d,%d\n",
					       (unsigned long long)sh->sector, i, other);
					compute_block_2(sh, i, other);
					uptodate += 2;
				} else if (test_bit(R5_Insync, &dev->flags)) {
					set_bit(R5_LOCKED, &dev->flags);
					set_bit(R5_Wantread, &dev->flags);
#if 0
					/* if I am just reading this block and we don't have
					   a failed drive, or any pending writes then sidestep the cache */
					if (sh->bh_read[i] && !sh->bh_read[i]->b_reqnext &&
					    ! syncing && !failed && !to_write) {
						sh->bh_cache[i]->b_page =  sh->bh_read[i]->b_page;
						sh->bh_cache[i]->b_data =  sh->bh_read[i]->b_data;
					}
#endif
					locked++;
					PRINTK("Reading block %d (sync=%d)\n",
						i, syncing);
					if (syncing)
						md_sync_acct(conf->disks[i].rdev->bdev,
							     STRIPE_SECTORS);
				}
			}
		}
		set_bit(STRIPE_HANDLE, &sh->state);
	}

	/* now to consider writing and what else, if anything should be read */
	if (to_write) {
		int rcw=0, must_compute=0;
		for (i=disks ; i--;) {
			dev = &sh->dev[i];
			/* Would I have to read this buffer for reconstruct_write */
			if (!test_bit(R5_OVERWRITE, &dev->flags)
			    && i != pd_idx && i != qd_idx
			    && (!test_bit(R5_LOCKED, &dev->flags)
#if 0
				|| sh->bh_page[i] != bh->b_page
#endif
				    ) &&
			    !test_bit(R5_UPTODATE, &dev->flags)) {
				if (test_bit(R5_Insync, &dev->flags)) rcw++;
				else {
					PRINTK("raid6: must_compute: disk %d flags=%#lx\n", i, dev->flags);
					must_compute++;
				}
			}
		}
		PRINTK("for sector %llu, rcw=%d, must_compute=%d\n",
		       (unsigned long long)sh->sector, rcw, must_compute);
		set_bit(STRIPE_HANDLE, &sh->state);

		if (rcw > 0)
			/* want reconstruct write, but need to get some data */
			for (i=disks; i--;) {
				dev = &sh->dev[i];
				if (!test_bit(R5_OVERWRITE, &dev->flags)
				    && !(failed == 0 && (i == pd_idx || i == qd_idx))
				    && !test_bit(R5_LOCKED, &dev->flags) && !test_bit(R5_UPTODATE, &dev->flags) &&
				    test_bit(R5_Insync, &dev->flags)) {
					if (test_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
					{
						PRINTK("Read_old stripe %llu block %d for Reconstruct\n",
						       (unsigned long long)sh->sector, i);
						set_bit(R5_LOCKED, &dev->flags);
						set_bit(R5_Wantread, &dev->flags);
						locked++;
					} else {
						PRINTK("Request delayed stripe %llu block %d for Reconstruct\n",
						       (unsigned long long)sh->sector, i);
						set_bit(STRIPE_DELAYED, &sh->state);
						set_bit(STRIPE_HANDLE, &sh->state);
					}
				}
			}
		/* now if nothing is locked, and if we have enough data, we can start a write request */
		if (locked == 0 && rcw == 0) {
			if ( must_compute > 0 ) {
				/* We have failed blocks and need to compute them */
				switch ( failed ) {
				case 0:	BUG();
				case 1: compute_block_1(sh, failed_num[0]); break;
				case 2: compute_block_2(sh, failed_num[0], failed_num[1]); break;
				default: BUG();	/* This request should have been failed? */
				}
			}

			PRINTK("Computing parity for stripe %llu\n", (unsigned long long)sh->sector);
			compute_parity(sh, RECONSTRUCT_WRITE);
			/* now every locked buffer is ready to be written */
			for (i=disks; i--;)
				if (test_bit(R5_LOCKED, &sh->dev[i].flags)) {
					PRINTK("Writing stripe %llu block %d\n",
					       (unsigned long long)sh->sector, i);
					locked++;
					set_bit(R5_Wantwrite, &sh->dev[i].flags);
#if 0 /**** FIX: I don't understand the logic here... ****/
					if (!test_bit(R5_Insync, &sh->dev[i].flags)
					    || ((i==pd_idx || i==qd_idx) && failed == 0)) /* FIX? */
						set_bit(STRIPE_INSYNC, &sh->state);
#endif
				}
			if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
				atomic_dec(&conf->preread_active_stripes);
				if (atomic_read(&conf->preread_active_stripes) < IO_THRESHOLD)
					md_wakeup_thread(conf->mddev->thread);
			}
		}
	}

	/* maybe we need to check and possibly fix the parity for this stripe
	 * Any reads will already have been scheduled, so we just see if enough data
	 * is available
	 */
	if (syncing && locked == 0 &&
	    !test_bit(STRIPE_INSYNC, &sh->state) && failed <= 2) {
		set_bit(STRIPE_HANDLE, &sh->state);
#if 0 /* RAID-6: Don't support CHECK PARITY yet */
		if (failed == 0) {
			char *pagea;
			if (uptodate != disks)
				BUG();
			compute_parity(sh, CHECK_PARITY);
			uptodate--;
			pagea = page_address(sh->dev[pd_idx].page);
			if ((*(u32*)pagea) == 0 &&
			    !memcmp(pagea, pagea+4, STRIPE_SIZE-4)) {
				/* parity is correct (on disc, not in buffer any more) */
				set_bit(STRIPE_INSYNC, &sh->state);
			}
		}
#endif
		if (!test_bit(STRIPE_INSYNC, &sh->state)) {
			int failed_needupdate[2];
			struct r5dev *adev, *bdev;

			if ( failed < 1 )
				failed_num[0] = pd_idx;
			if ( failed < 2 )
				failed_num[1] = (failed_num[0] == qd_idx) ? pd_idx : qd_idx;

			failed_needupdate[0] = !test_bit(R5_UPTODATE, &sh->dev[failed_num[0]].flags);
			failed_needupdate[1] = !test_bit(R5_UPTODATE, &sh->dev[failed_num[1]].flags);

			PRINTK("sync: failed=%d num=%d,%d fnu=%u%u\n",
			       failed, failed_num[0], failed_num[1], failed_needupdate[0], failed_needupdate[1]);

#if 0  /* RAID-6: This code seems to require that CHECK_PARITY destroys the uptodateness of the parity */
			/* should be able to compute the missing block(s) and write to spare */
			if ( failed_needupdate[0] ^ failed_needupdate[1] ) {
				if (uptodate+1 != disks)
					BUG();
				compute_block_1(sh, failed_needupdate[0] ? failed_num[0] : failed_num[1]);
				uptodate++;
			} else if ( failed_needupdate[0] & failed_needupdate[1] ) {
				if (uptodate+2 != disks)
					BUG();
				compute_block_2(sh, failed_num[0], failed_num[1]);
				uptodate += 2;
			}
#else
			compute_block_2(sh, failed_num[0], failed_num[1]);
			uptodate += failed_needupdate[0] + failed_needupdate[1];
#endif

			if (uptodate != disks)
				BUG();

			PRINTK("Marking for sync stripe %llu blocks %d,%d\n",
			       (unsigned long long)sh->sector, failed_num[0], failed_num[1]);

			/**** FIX: Should we really do both of these unconditionally? ****/
			adev = &sh->dev[failed_num[0]];
			locked += !test_bit(R5_LOCKED, &adev->flags);
			set_bit(R5_LOCKED, &adev->flags);
			set_bit(R5_Wantwrite, &adev->flags);
			bdev = &sh->dev[failed_num[1]];
			locked += !test_bit(R5_LOCKED, &bdev->flags);
			set_bit(R5_LOCKED, &bdev->flags);
			set_bit(R5_Wantwrite, &bdev->flags);

			set_bit(STRIPE_INSYNC, &sh->state);
			set_bit(R5_Syncio, &adev->flags);
			set_bit(R5_Syncio, &bdev->flags);
		}
	}
	if (syncing && locked == 0 && test_bit(STRIPE_INSYNC, &sh->state)) {
		md_done_sync(conf->mddev, STRIPE_SECTORS,1);
		clear_bit(STRIPE_SYNCING, &sh->state);
	}

	spin_unlock(&sh->lock);

	while ((bi=return_bi)) {
		int bytes = bi->bi_size;

		return_bi = bi->bi_next;
		bi->bi_next = NULL;
		bi->bi_size = 0;
		bi->bi_end_io(bi, bytes, 0);
	}
	for (i=disks; i-- ;) {
		int rw;
		struct bio *bi;
		mdk_rdev_t *rdev;
		if (test_and_clear_bit(R5_Wantwrite, &sh->dev[i].flags))
			rw = 1;
		else if (test_and_clear_bit(R5_Wantread, &sh->dev[i].flags))
			rw = 0;
		else
			continue;

		bi = &sh->dev[i].req;

		bi->bi_rw = rw;
		if (rw)
			bi->bi_end_io = raid6_end_write_request;
		else
			bi->bi_end_io = raid6_end_read_request;

		rcu_read_lock();
		rdev = conf->disks[i].rdev;
		if (rdev && rdev->faulty)
			rdev = NULL;
		if (rdev)
			atomic_inc(&rdev->nr_pending);
		rcu_read_unlock();

		if (rdev) {
			if (test_bit(R5_Syncio, &sh->dev[i].flags))
				md_sync_acct(rdev->bdev, STRIPE_SECTORS);

			bi->bi_bdev = rdev->bdev;
			PRINTK("for %llu schedule op %ld on disc %d\n",
				(unsigned long long)sh->sector, bi->bi_rw, i);
			atomic_inc(&sh->count);
			bi->bi_sector = sh->sector + rdev->data_offset;
			bi->bi_flags = 1 << BIO_UPTODATE;
			bi->bi_vcnt = 1;
			bi->bi_max_vecs = 1;
			bi->bi_idx = 0;
			bi->bi_io_vec = &sh->dev[i].vec;
			bi->bi_io_vec[0].bv_len = STRIPE_SIZE;
			bi->bi_io_vec[0].bv_offset = 0;
			bi->bi_size = STRIPE_SIZE;
			bi->bi_next = NULL;
			generic_make_request(bi);
		} else {
			PRINTK("skip op %ld on disc %d for sector %llu\n",
				bi->bi_rw, i, (unsigned long long)sh->sector);
			clear_bit(R5_LOCKED, &sh->dev[i].flags);
			set_bit(STRIPE_HANDLE, &sh->state);
		}
	}
}

static inline void raid6_activate_delayed(raid6_conf_t *conf)
{
	if (atomic_read(&conf->preread_active_stripes) < IO_THRESHOLD) {
		while (!list_empty(&conf->delayed_list)) {
			struct list_head *l = conf->delayed_list.next;
			struct stripe_head *sh;
			sh = list_entry(l, struct stripe_head, lru);
			list_del_init(l);
			clear_bit(STRIPE_DELAYED, &sh->state);
			if (!test_and_set_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
				atomic_inc(&conf->preread_active_stripes);
			list_add_tail(&sh->lru, &conf->handle_list);
		}
	}
}

static void unplug_slaves(mddev_t *mddev)
{
	raid6_conf_t *conf = mddev_to_conf(mddev);
	int i;

	rcu_read_lock();
	for (i=0; i<mddev->raid_disks; i++) {
		mdk_rdev_t *rdev = conf->disks[i].rdev;
		if (rdev && !rdev->faulty && atomic_read(&rdev->nr_pending)) {
			request_queue_t *r_queue = bdev_get_queue(rdev->bdev);

			atomic_inc(&rdev->nr_pending);
			rcu_read_unlock();

			if (r_queue->unplug_fn)
				r_queue->unplug_fn(r_queue);

			rdev_dec_pending(rdev, mddev);
			rcu_read_lock();
		}
	}
	rcu_read_unlock();
}

static void raid6_unplug_device(request_queue_t *q)
{
	mddev_t *mddev = q->queuedata;
	raid6_conf_t *conf = mddev_to_conf(mddev);
	unsigned long flags;

	spin_lock_irqsave(&conf->device_lock, flags);

	if (blk_remove_plug(q))
		raid6_activate_delayed(conf);
	md_wakeup_thread(mddev->thread);

	spin_unlock_irqrestore(&conf->device_lock, flags);

	unplug_slaves(mddev);
}

static int raid6_issue_flush(request_queue_t *q, struct gendisk *disk,
			     sector_t *error_sector)
{
	mddev_t *mddev = q->queuedata;
	raid6_conf_t *conf = mddev_to_conf(mddev);
	int i, ret = 0;

	rcu_read_lock();
	for (i=0; i<mddev->raid_disks && ret == 0; i++) {
		mdk_rdev_t *rdev = conf->disks[i].rdev;
		if (rdev && !rdev->faulty) {
			struct block_device *bdev = rdev->bdev;
			request_queue_t *r_queue = bdev_get_queue(bdev);

			if (!r_queue->issue_flush_fn)
				ret = -EOPNOTSUPP;
			else {
				atomic_inc(&rdev->nr_pending);
				rcu_read_unlock();
				ret = r_queue->issue_flush_fn(r_queue, bdev->bd_disk,
							      error_sector);
				rdev_dec_pending(rdev, mddev);
				rcu_read_lock();
			}
		}
	}
	rcu_read_unlock();
	return ret;
}

static inline void raid6_plug_device(raid6_conf_t *conf)
{
	spin_lock_irq(&conf->device_lock);
	blk_plug_device(conf->mddev->queue);
	spin_unlock_irq(&conf->device_lock);
}

static int make_request (request_queue_t *q, struct bio * bi)
{
	mddev_t *mddev = q->queuedata;
	raid6_conf_t *conf = mddev_to_conf(mddev);
	const unsigned int raid_disks = conf->raid_disks;
	const unsigned int data_disks = raid_disks - 2;
	unsigned int dd_idx, pd_idx;
	sector_t new_sector;
	sector_t logical_sector, last_sector;
	struct stripe_head *sh;

	md_write_start(mddev, bi);

	if (bio_data_dir(bi)==WRITE) {
		disk_stat_inc(mddev->gendisk, writes);
		disk_stat_add(mddev->gendisk, write_sectors, bio_sectors(bi));
	} else {
		disk_stat_inc(mddev->gendisk, reads);
		disk_stat_add(mddev->gendisk, read_sectors, bio_sectors(bi));
	}

	logical_sector = bi->bi_sector & ~((sector_t)STRIPE_SECTORS-1);
	last_sector = bi->bi_sector + (bi->bi_size>>9);

	bi->bi_next = NULL;
	bi->bi_phys_segments = 1;	/* over-loaded to count active stripes */

	for (;logical_sector < last_sector; logical_sector += STRIPE_SECTORS) {
		DEFINE_WAIT(w);

		new_sector = raid6_compute_sector(logical_sector,
						  raid_disks, data_disks, &dd_idx, &pd_idx, conf);

		PRINTK("raid6: make_request, sector %llu logical %llu\n",
		       (unsigned long long)new_sector,
		       (unsigned long long)logical_sector);

	retry:
		prepare_to_wait(&conf->wait_for_overlap, &w, TASK_UNINTERRUPTIBLE);
		sh = get_active_stripe(conf, new_sector, pd_idx, (bi->bi_rw&RWA_MASK));
		if (sh) {
			if (!add_stripe_bio(sh, bi, dd_idx, (bi->bi_rw&RW_MASK))) {
				/* Add failed due to overlap.  Flush everything
				 * and wait a while
				 */
				raid6_unplug_device(mddev->queue);
				release_stripe(sh);
				schedule();
				goto retry;
			}
			finish_wait(&conf->wait_for_overlap, &w);
			raid6_plug_device(conf);
			handle_stripe(sh);
			release_stripe(sh);
		} else {
			/* cannot get stripe for read-ahead, just give-up */
			clear_bit(BIO_UPTODATE, &bi->bi_flags);
			finish_wait(&conf->wait_for_overlap, &w);
			break;
		}

	}
	spin_lock_irq(&conf->device_lock);
	if (--bi->bi_phys_segments == 0) {
		int bytes = bi->bi_size;

		if ( bio_data_dir(bi) == WRITE )
			md_write_end(mddev);
		bi->bi_size = 0;
		bi->bi_end_io(bi, bytes, 0);
	}
	spin_unlock_irq(&conf->device_lock);
	return 0;
}

/* FIXME go_faster isn't used */
static sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, int go_faster)
{
	raid6_conf_t *conf = (raid6_conf_t *) mddev->private;
	struct stripe_head *sh;
	int sectors_per_chunk = conf->chunk_size >> 9;
	sector_t x;
	unsigned long stripe;
	int chunk_offset;
	int dd_idx, pd_idx;
	sector_t first_sector;
	int raid_disks = conf->raid_disks;
	int data_disks = raid_disks - 2;

	if (sector_nr >= mddev->size <<1) {
		/* just being told to finish up .. nothing much to do */
		unplug_slaves(mddev);
		return 0;
	}
	/* if there are 2 or more failed drives and we are trying
	 * to resync, then assert that we are finished, because there is
	 * nothing we can do.
	 */
	if (mddev->degraded >= 2 && test_bit(MD_RECOVERY_SYNC, &mddev->recovery)) {
		sector_t rv = (mddev->size << 1) - sector_nr;
		*skipped = 1;
		return rv;
	}

	x = sector_nr;
	chunk_offset = sector_div(x, sectors_per_chunk);
	stripe = x;
	BUG_ON(x != stripe);

	first_sector = raid6_compute_sector((sector_t)stripe*data_disks*sectors_per_chunk
		+ chunk_offset, raid_disks, data_disks, &dd_idx, &pd_idx, conf);
	sh = get_active_stripe(conf, sector_nr, pd_idx, 1);
	if (sh == NULL) {
		sh = get_active_stripe(conf, sector_nr, pd_idx, 0);
		/* make sure we don't swamp the stripe cache if someone else
		 * is trying to get access
		 */
		set_current_state(TASK_UNINTERRUPTIBLE);
		schedule_timeout(1);
	}
	spin_lock(&sh->lock);
	set_bit(STRIPE_SYNCING, &sh->state);
	clear_bit(STRIPE_INSYNC, &sh->state);
	spin_unlock(&sh->lock);

	handle_stripe(sh);
	release_stripe(sh);

	return STRIPE_SECTORS;
}

/*
 * This is our raid6 kernel thread.
 *
 * We scan the hash table for stripes which can be handled now.
 * During the scan, completed stripes are saved for us by the interrupt
 * handler, so that they will not have to wait for our next wakeup.
 */
static void raid6d (mddev_t *mddev)
{
	struct stripe_head *sh;
	raid6_conf_t *conf = mddev_to_conf(mddev);
	int handled;

	PRINTK("+++ raid6d active\n");

	md_check_recovery(mddev);

	handled = 0;
	spin_lock_irq(&conf->device_lock);
	while (1) {
		struct list_head *first;

		if (list_empty(&conf->handle_list) &&
		    atomic_read(&conf->preread_active_stripes) < IO_THRESHOLD &&
		    !blk_queue_plugged(mddev->queue) &&
		    !list_empty(&conf->delayed_list))
			raid6_activate_delayed(conf);

		if (list_empty(&conf->handle_list))
			break;

		first = conf->handle_list.next;
		sh = list_entry(first, struct stripe_head, lru);

		list_del_init(first);
		atomic_inc(&sh->count);
		if (atomic_read(&sh->count)!= 1)
			BUG();
		spin_unlock_irq(&conf->device_lock);

		handled++;
		handle_stripe(sh);
		release_stripe(sh);

		spin_lock_irq(&conf->device_lock);
	}
	PRINTK("%d stripes handled\n", handled);

	spin_unlock_irq(&conf->device_lock);

	unplug_slaves(mddev);

	PRINTK("--- raid6d inactive\n");
}

static int run (mddev_t *mddev)
{
	raid6_conf_t *conf;
	int raid_disk, memory;
	mdk_rdev_t *rdev;
	struct disk_info *disk;
	struct list_head *tmp;

	if (mddev->level != 6) {
		PRINTK("raid6: %s: raid level not set to 6 (%d)\n", mdname(mddev), mddev->level);
		return -EIO;
	}

	mddev->private = kmalloc (sizeof (raid6_conf_t)
				  + mddev->raid_disks * sizeof(struct disk_info),
				  GFP_KERNEL);
	if ((conf = mddev->private) == NULL)
		goto abort;
	memset (conf, 0, sizeof (*conf) + mddev->raid_disks * sizeof(struct disk_info) );
	conf->mddev = mddev;

	if ((conf->stripe_hashtbl = (struct stripe_head **) __get_free_pages(GFP_ATOMIC, HASH_PAGES_ORDER)) == NULL)
		goto abort;
	memset(conf->stripe_hashtbl, 0, HASH_PAGES * PAGE_SIZE);

	spin_lock_init(&conf->device_lock);
	init_waitqueue_head(&conf->wait_for_stripe);
	init_waitqueue_head(&conf->wait_for_overlap);
	INIT_LIST_HEAD(&conf->handle_list);
	INIT_LIST_HEAD(&conf->delayed_list);
	INIT_LIST_HEAD(&conf->inactive_list);
	atomic_set(&conf->active_stripes, 0);
	atomic_set(&conf->preread_active_stripes, 0);

	PRINTK("raid6: run(%s) called.\n", mdname(mddev));

	ITERATE_RDEV(mddev,rdev,tmp) {
		raid_disk = rdev->raid_disk;
		if (raid_disk >= mddev->raid_disks
		    || raid_disk < 0)
			continue;
		disk = conf->disks + raid_disk;

		disk->rdev = rdev;

		if (rdev->in_sync) {
			char b[BDEVNAME_SIZE];
			printk(KERN_INFO "raid6: device %s operational as raid"
			       " disk %d\n", bdevname(rdev->bdev,b),
			       raid_disk);
			conf->working_disks++;
		}
	}

	conf->raid_disks = mddev->raid_disks;

	/*
	 * 0 for a fully functional array, 1 or 2 for a degraded array.
	 */
	mddev->degraded = conf->failed_disks = conf->raid_disks - conf->working_disks;
	conf->mddev = mddev;
	conf->chunk_size = mddev->chunk_size;
	conf->level = mddev->level;
	conf->algorithm = mddev->layout;
	conf->max_nr_stripes = NR_STRIPES;

	/* device size must be a multiple of chunk size */
	mddev->size &= ~(mddev->chunk_size/1024 -1);

	if (conf->raid_disks < 4) {
		printk(KERN_ERR "raid6: not enough configured devices for %s (%d, minimum 4)\n",
		       mdname(mddev), conf->raid_disks);
		goto abort;
	}
	if (!conf->chunk_size || conf->chunk_size % 4) {
		printk(KERN_ERR "raid6: invalid chunk size %d for %s\n",
		       conf->chunk_size, mdname(mddev));
		goto abort;
	}
	if (conf->algorithm > ALGORITHM_RIGHT_SYMMETRIC) {
		printk(KERN_ERR
		       "raid6: unsupported parity algorithm %d for %s\n",
		       conf->algorithm, mdname(mddev));
		goto abort;
	}
	if (mddev->degraded > 2) {
		printk(KERN_ERR "raid6: not enough operational devices for %s"
		       " (%d/%d failed)\n",
		       mdname(mddev), conf->failed_disks, conf->raid_disks);
		goto abort;
	}

#if 0				/* FIX: For now */
	if (mddev->degraded > 0 &&
	    mddev->recovery_cp != MaxSector) {
		printk(KERN_ERR "raid6: cannot start dirty degraded array for %s\n", mdname(mddev));
		goto abort;
	}
#endif

	{
		mddev->thread = md_register_thread(raid6d, mddev, "%s_raid6");
		if (!mddev->thread) {
			printk(KERN_ERR
			       "raid6: couldn't allocate thread for %s\n",
			       mdname(mddev));
			goto abort;
		}
	}

	memory = conf->max_nr_stripes * (sizeof(struct stripe_head) +
		 conf->raid_disks * ((sizeof(struct bio) + PAGE_SIZE))) / 1024;
	if (grow_stripes(conf, conf->max_nr_stripes)) {
		printk(KERN_ERR
		       "raid6: couldn't allocate %dkB for buffers\n", memory);
		shrink_stripes(conf);
		md_unregister_thread(mddev->thread);
		goto abort;
	} else
		printk(KERN_INFO "raid6: allocated %dkB for %s\n",
		       memory, mdname(mddev));

	if (mddev->degraded == 0)
		printk(KERN_INFO "raid6: raid level %d set %s active with %d out of %d"
		       " devices, algorithm %d\n", conf->level, mdname(mddev),
		       mddev->raid_disks-mddev->degraded, mddev->raid_disks,
		       conf->algorithm);
	else
		printk(KERN_ALERT "raid6: raid level %d set %s active with %d"
		       " out of %d devices, algorithm %d\n", conf->level,
		       mdname(mddev), mddev->raid_disks - mddev->degraded,
		       mddev->raid_disks, conf->algorithm);

	print_raid6_conf(conf);

	/* read-ahead size must cover two whole stripes, which is
	 * 2 * (n-2) * chunksize where 'n' is the number of raid devices
	 */
	{
		int stripe = (mddev->raid_disks-2) * mddev->chunk_size
			/ PAGE_CACHE_SIZE;
		if (mddev->queue->backing_dev_info.ra_pages < 2 * stripe)
			mddev->queue->backing_dev_info.ra_pages = 2 * stripe;
	}

	/* Ok, everything is just fine now */
	mddev->array_size =  mddev->size * (mddev->raid_disks - 2);

	mddev->queue->unplug_fn = raid6_unplug_device;
	mddev->queue->issue_flush_fn = raid6_issue_flush;
	return 0;
abort:
	if (conf) {
		print_raid6_conf(conf);
		if (conf->stripe_hashtbl)
			free_pages((unsigned long) conf->stripe_hashtbl,
							HASH_PAGES_ORDER);
		kfree(conf);
	}
	mddev->private = NULL;
	printk(KERN_ALERT "raid6: failed to run raid set %s\n", mdname(mddev));
	return -EIO;
}



static int stop (mddev_t *mddev)
{
	raid6_conf_t *conf = (raid6_conf_t *) mddev->private;

	md_unregister_thread(mddev->thread);
	mddev->thread = NULL;
	shrink_stripes(conf);
	free_pages((unsigned long) conf->stripe_hashtbl, HASH_PAGES_ORDER);
	blk_sync_queue(mddev->queue); /* the unplug fn references 'conf'*/
	kfree(conf);
	mddev->private = NULL;
	return 0;
}

#if RAID6_DUMPSTATE
static void print_sh (struct seq_file *seq, struct stripe_head *sh)
{
	int i;

	seq_printf(seq, "sh %llu, pd_idx %d, state %ld.\n",
		   (unsigned long long)sh->sector, sh->pd_idx, sh->state);
	seq_printf(seq, "sh %llu,  count %d.\n",
		   (unsigned long long)sh->sector, atomic_read(&sh->count));
	seq_printf(seq, "sh %llu, ", (unsigned long long)sh->sector);
	for (i = 0; i < sh->raid_conf->raid_disks; i++) {
		seq_printf(seq, "(cache%d: %p %ld) ",
			   i, sh->dev[i].page, sh->dev[i].flags);
	}
	seq_printf(seq, "\n");
}

static void printall (struct seq_file *seq, raid6_conf_t *conf)
{
	struct stripe_head *sh;
	int i;

	spin_lock_irq(&conf->device_lock);
	for (i = 0; i < NR_HASH; i++) {
		sh = conf->stripe_hashtbl[i];
		for (; sh; sh = sh->hash_next) {
			if (sh->raid_conf != conf)
				continue;
			print_sh(seq, sh);
		}
	}
	spin_unlock_irq(&conf->device_lock);
}
#endif

static void status (struct seq_file *seq, mddev_t *mddev)
{
	raid6_conf_t *conf = (raid6_conf_t *) mddev->private;
	int i;

	seq_printf (seq, " level %d, %dk chunk, algorithm %d", mddev->level, mddev->chunk_size >> 10, mddev->layout);
	seq_printf (seq, " [%d/%d] [", conf->raid_disks, conf->working_disks);
	for (i = 0; i < conf->raid_disks; i++)
 		seq_printf (seq, "%s",
			    conf->disks[i].rdev &&
			    conf->disks[i].rdev->in_sync ? "U" : "_");
	seq_printf (seq, "]");
#if RAID6_DUMPSTATE
	seq_printf (seq, "\n");
	printall(seq, conf);
#endif
}

static void print_raid6_conf (raid6_conf_t *conf)
{
	int i;
	struct disk_info *tmp;

	printk("RAID6 conf printout:\n");
	if (!conf) {
		printk("(conf==NULL)\n");
		return;
	}
	printk(" --- rd:%d wd:%d fd:%d\n", conf->raid_disks,
		 conf->working_disks, conf->failed_disks);

	for (i = 0; i < conf->raid_disks; i++) {
		char b[BDEVNAME_SIZE];
		tmp = conf->disks + i;
		if (tmp->rdev)
		printk(" disk %d, o:%d, dev:%s\n",
			i, !tmp->rdev->faulty,
			bdevname(tmp->rdev->bdev,b));
	}
}

static int raid6_spare_active(mddev_t *mddev)
{
	int i;
	raid6_conf_t *conf = mddev->private;
	struct disk_info *tmp;

	for (i = 0; i < conf->raid_disks; i++) {
		tmp = conf->disks + i;
		if (tmp->rdev
		    && !tmp->rdev->faulty
		    && !tmp->rdev->in_sync) {
			mddev->degraded--;
			conf->failed_disks--;
			conf->working_disks++;
			tmp->rdev->in_sync = 1;
		}
	}
	print_raid6_conf(conf);
	return 0;
}

static int raid6_remove_disk(mddev_t *mddev, int number)
{
	raid6_conf_t *conf = mddev->private;
	int err = 0;
	mdk_rdev_t *rdev;
	struct disk_info *p = conf->disks + number;

	print_raid6_conf(conf);
	rdev = p->rdev;
	if (rdev) {
		if (rdev->in_sync ||
		    atomic_read(&rdev->nr_pending)) {
			err = -EBUSY;
			goto abort;
		}
		p->rdev = NULL;
		synchronize_rcu();
		if (atomic_read(&rdev->nr_pending)) {
			/* lost the race, try later */
			err = -EBUSY;
			p->rdev = rdev;
		}
	}

abort:

	print_raid6_conf(conf);
	return err;
}

static int raid6_add_disk(mddev_t *mddev, mdk_rdev_t *rdev)
{
	raid6_conf_t *conf = mddev->private;
	int found = 0;
	int disk;
	struct disk_info *p;

	if (mddev->degraded > 2)
		/* no point adding a device */
		return 0;
	/*
	 * find the disk ...
	 */
	for (disk=0; disk < mddev->raid_disks; disk++)
		if ((p=conf->disks + disk)->rdev == NULL) {
			rdev->in_sync = 0;
			rdev->raid_disk = disk;
			found = 1;
			p->rdev = rdev;
			break;
		}
	print_raid6_conf(conf);
	return found;
}

static int raid6_resize(mddev_t *mddev, sector_t sectors)
{
	/* no resync is happening, and there is enough space
	 * on all devices, so we can resize.
	 * We need to make sure resync covers any new space.
	 * If the array is shrinking we should possibly wait until
	 * any io in the removed space completes, but it hardly seems
	 * worth it.
	 */
	sectors &= ~((sector_t)mddev->chunk_size/512 - 1);
	mddev->array_size = (sectors * (mddev->raid_disks-2))>>1;
	set_capacity(mddev->gendisk, mddev->array_size << 1);
	mddev->changed = 1;
	if (sectors/2  > mddev->size && mddev->recovery_cp == MaxSector) {
		mddev->recovery_cp = mddev->size << 1;
		set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
	}
	mddev->size = sectors /2;
	return 0;
}

static mdk_personality_t raid6_personality=
{
	.name		= "raid6",
	.owner		= THIS_MODULE,
	.make_request	= make_request,
	.run		= run,
	.stop		= stop,
	.status		= status,
	.error_handler	= error,
	.hot_add_disk	= raid6_add_disk,
	.hot_remove_disk= raid6_remove_disk,
	.spare_active	= raid6_spare_active,
	.sync_request	= sync_request,
	.resize		= raid6_resize,
};

static int __init raid6_init (void)
{
	int e;

	e = raid6_select_algo();
	if ( e )
		return e;

	return register_md_personality (RAID6, &raid6_personality);
}

static void raid6_exit (void)
{
	unregister_md_personality (RAID6);
}

module_init(raid6_init);
module_exit(raid6_exit);
MODULE_LICENSE("GPL");
MODULE_ALIAS("md-personality-8"); /* RAID6 */