summaryrefslogtreecommitdiffstats
path: root/drivers/scsi/device_handler/scsi_dh_alua.c
blob: 29a2865b8e2e1453ac8629cb2de307dc3687efbb (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Generic SCSI-3 ALUA SCSI Device Handler
 *
 * Copyright (C) 2007-2010 Hannes Reinecke, SUSE Linux Products GmbH.
 * All rights reserved.
 */
#include <linux/slab.h>
#include <linux/delay.h>
#include <linux/module.h>
#include <asm/unaligned.h>
#include <scsi/scsi.h>
#include <scsi/scsi_proto.h>
#include <scsi/scsi_dbg.h>
#include <scsi/scsi_eh.h>
#include <scsi/scsi_dh.h>

#define ALUA_DH_NAME "alua"
#define ALUA_DH_VER "2.0"

#define TPGS_SUPPORT_NONE		0x00
#define TPGS_SUPPORT_OPTIMIZED		0x01
#define TPGS_SUPPORT_NONOPTIMIZED	0x02
#define TPGS_SUPPORT_STANDBY		0x04
#define TPGS_SUPPORT_UNAVAILABLE	0x08
#define TPGS_SUPPORT_LBA_DEPENDENT	0x10
#define TPGS_SUPPORT_OFFLINE		0x40
#define TPGS_SUPPORT_TRANSITION		0x80
#define TPGS_SUPPORT_ALL		0xdf

#define RTPG_FMT_MASK			0x70
#define RTPG_FMT_EXT_HDR		0x10

#define TPGS_MODE_UNINITIALIZED		 -1
#define TPGS_MODE_NONE			0x0
#define TPGS_MODE_IMPLICIT		0x1
#define TPGS_MODE_EXPLICIT		0x2

#define ALUA_RTPG_SIZE			128
#define ALUA_FAILOVER_TIMEOUT		60
#define ALUA_FAILOVER_RETRIES		5
#define ALUA_RTPG_DELAY_MSECS		5
#define ALUA_RTPG_RETRY_DELAY		2

/* device handler flags */
#define ALUA_OPTIMIZE_STPG		0x01
#define ALUA_RTPG_EXT_HDR_UNSUPP	0x02
/* State machine flags */
#define ALUA_PG_RUN_RTPG		0x10
#define ALUA_PG_RUN_STPG		0x20
#define ALUA_PG_RUNNING			0x40

static uint optimize_stpg;
module_param(optimize_stpg, uint, S_IRUGO|S_IWUSR);
MODULE_PARM_DESC(optimize_stpg, "Allow use of a non-optimized path, rather than sending a STPG, when implicit TPGS is supported (0=No,1=Yes). Default is 0.");

static LIST_HEAD(port_group_list);
static DEFINE_SPINLOCK(port_group_lock);
static struct workqueue_struct *kaluad_wq;

struct alua_port_group {
	struct kref		kref;
	struct rcu_head		rcu;
	struct list_head	node;
	struct list_head	dh_list;
	unsigned char		device_id_str[256];
	int			device_id_len;
	int			group_id;
	int			tpgs;
	int			state;
	int			pref;
	int			valid_states;
	unsigned		flags; /* used for optimizing STPG */
	unsigned char		transition_tmo;
	unsigned long		expiry;
	unsigned long		interval;
	struct delayed_work	rtpg_work;
	spinlock_t		lock;
	struct list_head	rtpg_list;
	struct scsi_device	*rtpg_sdev;
};

struct alua_dh_data {
	struct list_head	node;
	struct alua_port_group __rcu *pg;
	int			group_id;
	spinlock_t		pg_lock;
	struct scsi_device	*sdev;
	int			init_error;
	struct mutex		init_mutex;
	bool			disabled;
};

struct alua_queue_data {
	struct list_head	entry;
	activate_complete	callback_fn;
	void			*callback_data;
};

#define ALUA_POLICY_SWITCH_CURRENT	0
#define ALUA_POLICY_SWITCH_ALL		1

static void alua_rtpg_work(struct work_struct *work);
static bool alua_rtpg_queue(struct alua_port_group *pg,
			    struct scsi_device *sdev,
			    struct alua_queue_data *qdata, bool force);
static void alua_check(struct scsi_device *sdev, bool force);

static void release_port_group(struct kref *kref)
{
	struct alua_port_group *pg;

	pg = container_of(kref, struct alua_port_group, kref);
	if (pg->rtpg_sdev)
		flush_delayed_work(&pg->rtpg_work);
	spin_lock(&port_group_lock);
	list_del(&pg->node);
	spin_unlock(&port_group_lock);
	kfree_rcu(pg, rcu);
}

/*
 * submit_rtpg - Issue a REPORT TARGET GROUP STATES command
 * @sdev: sdev the command should be sent to
 */
static int submit_rtpg(struct scsi_device *sdev, unsigned char *buff,
		       int bufflen, struct scsi_sense_hdr *sshdr, int flags)
{
	u8 cdb[MAX_COMMAND_SIZE];
	blk_opf_t req_flags = REQ_FAILFAST_DEV | REQ_FAILFAST_TRANSPORT |
		REQ_FAILFAST_DRIVER;

	/* Prepare the command. */
	memset(cdb, 0x0, MAX_COMMAND_SIZE);
	cdb[0] = MAINTENANCE_IN;
	if (!(flags & ALUA_RTPG_EXT_HDR_UNSUPP))
		cdb[1] = MI_REPORT_TARGET_PGS | MI_EXT_HDR_PARAM_FMT;
	else
		cdb[1] = MI_REPORT_TARGET_PGS;
	put_unaligned_be32(bufflen, &cdb[6]);

	return scsi_execute(sdev, cdb, DMA_FROM_DEVICE, buff, bufflen, NULL,
			sshdr, ALUA_FAILOVER_TIMEOUT * HZ,
			ALUA_FAILOVER_RETRIES, req_flags, 0, NULL);
}

/*
 * submit_stpg - Issue a SET TARGET PORT GROUP command
 *
 * Currently we're only setting the current target port group state
 * to 'active/optimized' and let the array firmware figure out
 * the states of the remaining groups.
 */
static int submit_stpg(struct scsi_device *sdev, int group_id,
		       struct scsi_sense_hdr *sshdr)
{
	u8 cdb[MAX_COMMAND_SIZE];
	unsigned char stpg_data[8];
	int stpg_len = 8;
	blk_opf_t req_flags = REQ_FAILFAST_DEV | REQ_FAILFAST_TRANSPORT |
		REQ_FAILFAST_DRIVER;

	/* Prepare the data buffer */
	memset(stpg_data, 0, stpg_len);
	stpg_data[4] = SCSI_ACCESS_STATE_OPTIMAL;
	put_unaligned_be16(group_id, &stpg_data[6]);

	/* Prepare the command. */
	memset(cdb, 0x0, MAX_COMMAND_SIZE);
	cdb[0] = MAINTENANCE_OUT;
	cdb[1] = MO_SET_TARGET_PGS;
	put_unaligned_be32(stpg_len, &cdb[6]);

	return scsi_execute(sdev, cdb, DMA_TO_DEVICE, stpg_data, stpg_len, NULL,
			sshdr, ALUA_FAILOVER_TIMEOUT * HZ,
			ALUA_FAILOVER_RETRIES, req_flags, 0, NULL);
}

static struct alua_port_group *alua_find_get_pg(char *id_str, size_t id_size,
						int group_id)
{
	struct alua_port_group *pg;

	if (!id_str || !id_size || !strlen(id_str))
		return NULL;

	list_for_each_entry(pg, &port_group_list, node) {
		if (pg->group_id != group_id)
			continue;
		if (!pg->device_id_len || pg->device_id_len != id_size)
			continue;
		if (strncmp(pg->device_id_str, id_str, id_size))
			continue;
		if (!kref_get_unless_zero(&pg->kref))
			continue;
		return pg;
	}

	return NULL;
}

/*
 * alua_alloc_pg - Allocate a new port_group structure
 * @sdev: scsi device
 * @group_id: port group id
 * @tpgs: target port group settings
 *
 * Allocate a new port_group structure for a given
 * device.
 */
static struct alua_port_group *alua_alloc_pg(struct scsi_device *sdev,
					     int group_id, int tpgs)
{
	struct alua_port_group *pg, *tmp_pg;

	pg = kzalloc(sizeof(struct alua_port_group), GFP_KERNEL);
	if (!pg)
		return ERR_PTR(-ENOMEM);

	pg->device_id_len = scsi_vpd_lun_id(sdev, pg->device_id_str,
					    sizeof(pg->device_id_str));
	if (pg->device_id_len <= 0) {
		/*
		 * TPGS supported but no device identification found.
		 * Generate private device identification.
		 */
		sdev_printk(KERN_INFO, sdev,
			    "%s: No device descriptors found\n",
			    ALUA_DH_NAME);
		pg->device_id_str[0] = '\0';
		pg->device_id_len = 0;
	}
	pg->group_id = group_id;
	pg->tpgs = tpgs;
	pg->state = SCSI_ACCESS_STATE_OPTIMAL;
	pg->valid_states = TPGS_SUPPORT_ALL;
	if (optimize_stpg)
		pg->flags |= ALUA_OPTIMIZE_STPG;
	kref_init(&pg->kref);
	INIT_DELAYED_WORK(&pg->rtpg_work, alua_rtpg_work);
	INIT_LIST_HEAD(&pg->rtpg_list);
	INIT_LIST_HEAD(&pg->node);
	INIT_LIST_HEAD(&pg->dh_list);
	spin_lock_init(&pg->lock);

	spin_lock(&port_group_lock);
	tmp_pg = alua_find_get_pg(pg->device_id_str, pg->device_id_len,
				  group_id);
	if (tmp_pg) {
		spin_unlock(&port_group_lock);
		kfree(pg);
		return tmp_pg;
	}

	list_add(&pg->node, &port_group_list);
	spin_unlock(&port_group_lock);

	return pg;
}

/*
 * alua_check_tpgs - Evaluate TPGS setting
 * @sdev: device to be checked
 *
 * Examine the TPGS setting of the sdev to find out if ALUA
 * is supported.
 */
static int alua_check_tpgs(struct scsi_device *sdev)
{
	int tpgs = TPGS_MODE_NONE;

	/*
	 * ALUA support for non-disk devices is fraught with
	 * difficulties, so disable it for now.
	 */
	if (sdev->type != TYPE_DISK) {
		sdev_printk(KERN_INFO, sdev,
			    "%s: disable for non-disk devices\n",
			    ALUA_DH_NAME);
		return tpgs;
	}

	tpgs = scsi_device_tpgs(sdev);
	switch (tpgs) {
	case TPGS_MODE_EXPLICIT|TPGS_MODE_IMPLICIT:
		sdev_printk(KERN_INFO, sdev,
			    "%s: supports implicit and explicit TPGS\n",
			    ALUA_DH_NAME);
		break;
	case TPGS_MODE_EXPLICIT:
		sdev_printk(KERN_INFO, sdev, "%s: supports explicit TPGS\n",
			    ALUA_DH_NAME);
		break;
	case TPGS_MODE_IMPLICIT:
		sdev_printk(KERN_INFO, sdev, "%s: supports implicit TPGS\n",
			    ALUA_DH_NAME);
		break;
	case TPGS_MODE_NONE:
		sdev_printk(KERN_INFO, sdev, "%s: not supported\n",
			    ALUA_DH_NAME);
		break;
	default:
		sdev_printk(KERN_INFO, sdev,
			    "%s: unsupported TPGS setting %d\n",
			    ALUA_DH_NAME, tpgs);
		tpgs = TPGS_MODE_NONE;
		break;
	}

	return tpgs;
}

/*
 * alua_check_vpd - Evaluate INQUIRY vpd page 0x83
 * @sdev: device to be checked
 *
 * Extract the relative target port and the target port group
 * descriptor from the list of identificators.
 */
static int alua_check_vpd(struct scsi_device *sdev, struct alua_dh_data *h,
			  int tpgs)
{
	int rel_port = -1, group_id;
	struct alua_port_group *pg, *old_pg = NULL;
	bool pg_updated = false;
	unsigned long flags;

	group_id = scsi_vpd_tpg_id(sdev, &rel_port);
	if (group_id < 0) {
		/*
		 * Internal error; TPGS supported but required
		 * VPD identification descriptors not present.
		 * Disable ALUA support
		 */
		sdev_printk(KERN_INFO, sdev,
			    "%s: No target port descriptors found\n",
			    ALUA_DH_NAME);
		return SCSI_DH_DEV_UNSUPP;
	}

	pg = alua_alloc_pg(sdev, group_id, tpgs);
	if (IS_ERR(pg)) {
		if (PTR_ERR(pg) == -ENOMEM)
			return SCSI_DH_NOMEM;
		return SCSI_DH_DEV_UNSUPP;
	}
	if (pg->device_id_len)
		sdev_printk(KERN_INFO, sdev,
			    "%s: device %s port group %x rel port %x\n",
			    ALUA_DH_NAME, pg->device_id_str,
			    group_id, rel_port);
	else
		sdev_printk(KERN_INFO, sdev,
			    "%s: port group %x rel port %x\n",
			    ALUA_DH_NAME, group_id, rel_port);

	kref_get(&pg->kref);

	/* Check for existing port group references */
	spin_lock(&h->pg_lock);
	old_pg = rcu_dereference_protected(h->pg, lockdep_is_held(&h->pg_lock));
	if (old_pg != pg) {
		/* port group has changed. Update to new port group */
		if (h->pg) {
			spin_lock_irqsave(&old_pg->lock, flags);
			list_del_rcu(&h->node);
			spin_unlock_irqrestore(&old_pg->lock, flags);
		}
		rcu_assign_pointer(h->pg, pg);
		pg_updated = true;
	}

	spin_lock_irqsave(&pg->lock, flags);
	if (pg_updated)
		list_add_rcu(&h->node, &pg->dh_list);
	spin_unlock_irqrestore(&pg->lock, flags);

	spin_unlock(&h->pg_lock);

	alua_rtpg_queue(pg, sdev, NULL, true);
	kref_put(&pg->kref, release_port_group);

	if (old_pg)
		kref_put(&old_pg->kref, release_port_group);

	return SCSI_DH_OK;
}

static char print_alua_state(unsigned char state)
{
	switch (state) {
	case SCSI_ACCESS_STATE_OPTIMAL:
		return 'A';
	case SCSI_ACCESS_STATE_ACTIVE:
		return 'N';
	case SCSI_ACCESS_STATE_STANDBY:
		return 'S';
	case SCSI_ACCESS_STATE_UNAVAILABLE:
		return 'U';
	case SCSI_ACCESS_STATE_LBA:
		return 'L';
	case SCSI_ACCESS_STATE_OFFLINE:
		return 'O';
	case SCSI_ACCESS_STATE_TRANSITIONING:
		return 'T';
	default:
		return 'X';
	}
}

static enum scsi_disposition alua_check_sense(struct scsi_device *sdev,
					      struct scsi_sense_hdr *sense_hdr)
{
	struct alua_dh_data *h = sdev->handler_data;
	struct alua_port_group *pg;

	switch (sense_hdr->sense_key) {
	case NOT_READY:
		if (sense_hdr->asc == 0x04 && sense_hdr->ascq == 0x0a) {
			/*
			 * LUN Not Accessible - ALUA state transition
			 */
			rcu_read_lock();
			pg = rcu_dereference(h->pg);
			if (pg)
				pg->state = SCSI_ACCESS_STATE_TRANSITIONING;
			rcu_read_unlock();
			alua_check(sdev, false);
			return NEEDS_RETRY;
		}
		break;
	case UNIT_ATTENTION:
		if (sense_hdr->asc == 0x29 && sense_hdr->ascq == 0x00) {
			/*
			 * Power On, Reset, or Bus Device Reset.
			 * Might have obscured a state transition,
			 * so schedule a recheck.
			 */
			alua_check(sdev, true);
			return ADD_TO_MLQUEUE;
		}
		if (sense_hdr->asc == 0x29 && sense_hdr->ascq == 0x04)
			/*
			 * Device internal reset
			 */
			return ADD_TO_MLQUEUE;
		if (sense_hdr->asc == 0x2a && sense_hdr->ascq == 0x01)
			/*
			 * Mode Parameters Changed
			 */
			return ADD_TO_MLQUEUE;
		if (sense_hdr->asc == 0x2a && sense_hdr->ascq == 0x06) {
			/*
			 * ALUA state changed
			 */
			alua_check(sdev, true);
			return ADD_TO_MLQUEUE;
		}
		if (sense_hdr->asc == 0x2a && sense_hdr->ascq == 0x07) {
			/*
			 * Implicit ALUA state transition failed
			 */
			alua_check(sdev, true);
			return ADD_TO_MLQUEUE;
		}
		if (sense_hdr->asc == 0x3f && sense_hdr->ascq == 0x03)
			/*
			 * Inquiry data has changed
			 */
			return ADD_TO_MLQUEUE;
		if (sense_hdr->asc == 0x3f && sense_hdr->ascq == 0x0e)
			/*
			 * REPORTED_LUNS_DATA_HAS_CHANGED is reported
			 * when switching controllers on targets like
			 * Intel Multi-Flex. We can just retry.
			 */
			return ADD_TO_MLQUEUE;
		break;
	}

	return SCSI_RETURN_NOT_HANDLED;
}

/*
 * alua_tur - Send a TEST UNIT READY
 * @sdev: device to which the TEST UNIT READY command should be send
 *
 * Send a TEST UNIT READY to @sdev to figure out the device state
 * Returns SCSI_DH_RETRY if the sense code is NOT READY/ALUA TRANSITIONING,
 * SCSI_DH_OK if no error occurred, and SCSI_DH_IO otherwise.
 */
static int alua_tur(struct scsi_device *sdev)
{
	struct scsi_sense_hdr sense_hdr;
	int retval;

	retval = scsi_test_unit_ready(sdev, ALUA_FAILOVER_TIMEOUT * HZ,
				      ALUA_FAILOVER_RETRIES, &sense_hdr);
	if (sense_hdr.sense_key == NOT_READY &&
	    sense_hdr.asc == 0x04 && sense_hdr.ascq == 0x0a)
		return SCSI_DH_RETRY;
	else if (retval)
		return SCSI_DH_IO;
	else
		return SCSI_DH_OK;
}

/*
 * alua_rtpg - Evaluate REPORT TARGET GROUP STATES
 * @sdev: the device to be evaluated.
 *
 * Evaluate the Target Port Group State.
 * Returns SCSI_DH_DEV_OFFLINED if the path is
 * found to be unusable.
 */
static int alua_rtpg(struct scsi_device *sdev, struct alua_port_group *pg)
{
	struct scsi_sense_hdr sense_hdr;
	struct alua_port_group *tmp_pg;
	int len, k, off, bufflen = ALUA_RTPG_SIZE;
	int group_id_old, state_old, pref_old, valid_states_old;
	unsigned char *desc, *buff;
	unsigned err;
	int retval;
	unsigned int tpg_desc_tbl_off;
	unsigned char orig_transition_tmo;
	unsigned long flags;
	bool transitioning_sense = false;

	group_id_old = pg->group_id;
	state_old = pg->state;
	pref_old = pg->pref;
	valid_states_old = pg->valid_states;

	if (!pg->expiry) {
		unsigned long transition_tmo = ALUA_FAILOVER_TIMEOUT * HZ;

		if (pg->transition_tmo)
			transition_tmo = pg->transition_tmo * HZ;

		pg->expiry = round_jiffies_up(jiffies + transition_tmo);
	}

	buff = kzalloc(bufflen, GFP_KERNEL);
	if (!buff)
		return SCSI_DH_DEV_TEMP_BUSY;

 retry:
	err = 0;
	retval = submit_rtpg(sdev, buff, bufflen, &sense_hdr, pg->flags);

	if (retval) {
		/*
		 * Some (broken) implementations have a habit of returning
		 * an error during things like firmware update etc.
		 * But if the target only supports active/optimized there's
		 * not much we can do; it's not that we can switch paths
		 * or anything.
		 * So ignore any errors to avoid spurious failures during
		 * path failover.
		 */
		if ((pg->valid_states & ~TPGS_SUPPORT_OPTIMIZED) == 0) {
			sdev_printk(KERN_INFO, sdev,
				    "%s: ignoring rtpg result %d\n",
				    ALUA_DH_NAME, retval);
			kfree(buff);
			return SCSI_DH_OK;
		}
		if (retval < 0 || !scsi_sense_valid(&sense_hdr)) {
			sdev_printk(KERN_INFO, sdev,
				    "%s: rtpg failed, result %d\n",
				    ALUA_DH_NAME, retval);
			kfree(buff);
			if (retval < 0)
				return SCSI_DH_DEV_TEMP_BUSY;
			if (host_byte(retval) == DID_NO_CONNECT)
				return SCSI_DH_RES_TEMP_UNAVAIL;
			return SCSI_DH_IO;
		}

		/*
		 * submit_rtpg() has failed on existing arrays
		 * when requesting extended header info, and
		 * the array doesn't support extended headers,
		 * even though it shouldn't according to T10.
		 * The retry without rtpg_ext_hdr_req set
		 * handles this.
		 * Note:  some arrays return a sense key of ILLEGAL_REQUEST
		 * with ASC 00h if they don't support the extended header.
		 */
		if (!(pg->flags & ALUA_RTPG_EXT_HDR_UNSUPP) &&
		    sense_hdr.sense_key == ILLEGAL_REQUEST) {
			pg->flags |= ALUA_RTPG_EXT_HDR_UNSUPP;
			goto retry;
		}
		/*
		 * If the array returns with 'ALUA state transition'
		 * sense code here it cannot return RTPG data during
		 * transition. So set the state to 'transitioning' directly.
		 */
		if (sense_hdr.sense_key == NOT_READY &&
		    sense_hdr.asc == 0x04 && sense_hdr.ascq == 0x0a) {
			transitioning_sense = true;
			goto skip_rtpg;
		}
		/*
		 * Retry on any other UNIT ATTENTION occurred.
		 */
		if (sense_hdr.sense_key == UNIT_ATTENTION)
			err = SCSI_DH_RETRY;
		if (err == SCSI_DH_RETRY &&
		    pg->expiry != 0 && time_before(jiffies, pg->expiry)) {
			sdev_printk(KERN_ERR, sdev, "%s: rtpg retry\n",
				    ALUA_DH_NAME);
			scsi_print_sense_hdr(sdev, ALUA_DH_NAME, &sense_hdr);
			kfree(buff);
			return err;
		}
		sdev_printk(KERN_ERR, sdev, "%s: rtpg failed\n",
			    ALUA_DH_NAME);
		scsi_print_sense_hdr(sdev, ALUA_DH_NAME, &sense_hdr);
		kfree(buff);
		pg->expiry = 0;
		return SCSI_DH_IO;
	}

	len = get_unaligned_be32(&buff[0]) + 4;

	if (len > bufflen) {
		/* Resubmit with the correct length */
		kfree(buff);
		bufflen = len;
		buff = kmalloc(bufflen, GFP_KERNEL);
		if (!buff) {
			sdev_printk(KERN_WARNING, sdev,
				    "%s: kmalloc buffer failed\n",__func__);
			/* Temporary failure, bypass */
			pg->expiry = 0;
			return SCSI_DH_DEV_TEMP_BUSY;
		}
		goto retry;
	}

	orig_transition_tmo = pg->transition_tmo;
	if ((buff[4] & RTPG_FMT_MASK) == RTPG_FMT_EXT_HDR && buff[5] != 0)
		pg->transition_tmo = buff[5];
	else
		pg->transition_tmo = ALUA_FAILOVER_TIMEOUT;

	if (orig_transition_tmo != pg->transition_tmo) {
		sdev_printk(KERN_INFO, sdev,
			    "%s: transition timeout set to %d seconds\n",
			    ALUA_DH_NAME, pg->transition_tmo);
		pg->expiry = jiffies + pg->transition_tmo * HZ;
	}

	if ((buff[4] & RTPG_FMT_MASK) == RTPG_FMT_EXT_HDR)
		tpg_desc_tbl_off = 8;
	else
		tpg_desc_tbl_off = 4;

	for (k = tpg_desc_tbl_off, desc = buff + tpg_desc_tbl_off;
	     k < len;
	     k += off, desc += off) {
		u16 group_id = get_unaligned_be16(&desc[2]);

		spin_lock_irqsave(&port_group_lock, flags);
		tmp_pg = alua_find_get_pg(pg->device_id_str, pg->device_id_len,
					  group_id);
		spin_unlock_irqrestore(&port_group_lock, flags);
		if (tmp_pg) {
			if (spin_trylock_irqsave(&tmp_pg->lock, flags)) {
				if ((tmp_pg == pg) ||
				    !(tmp_pg->flags & ALUA_PG_RUNNING)) {
					struct alua_dh_data *h;

					tmp_pg->state = desc[0] & 0x0f;
					tmp_pg->pref = desc[0] >> 7;
					rcu_read_lock();
					list_for_each_entry_rcu(h,
						&tmp_pg->dh_list, node) {
						if (!h->sdev)
							continue;
						h->sdev->access_state = desc[0];
					}
					rcu_read_unlock();
				}
				if (tmp_pg == pg)
					tmp_pg->valid_states = desc[1];
				spin_unlock_irqrestore(&tmp_pg->lock, flags);
			}
			kref_put(&tmp_pg->kref, release_port_group);
		}
		off = 8 + (desc[7] * 4);
	}

 skip_rtpg:
	spin_lock_irqsave(&pg->lock, flags);
	if (transitioning_sense)
		pg->state = SCSI_ACCESS_STATE_TRANSITIONING;

	if (group_id_old != pg->group_id || state_old != pg->state ||
		pref_old != pg->pref || valid_states_old != pg->valid_states)
		sdev_printk(KERN_INFO, sdev,
			"%s: port group %02x state %c %s supports %c%c%c%c%c%c%c\n",
			ALUA_DH_NAME, pg->group_id, print_alua_state(pg->state),
			pg->pref ? "preferred" : "non-preferred",
			pg->valid_states&TPGS_SUPPORT_TRANSITION?'T':'t',
			pg->valid_states&TPGS_SUPPORT_OFFLINE?'O':'o',
			pg->valid_states&TPGS_SUPPORT_LBA_DEPENDENT?'L':'l',
			pg->valid_states&TPGS_SUPPORT_UNAVAILABLE?'U':'u',
			pg->valid_states&TPGS_SUPPORT_STANDBY?'S':'s',
			pg->valid_states&TPGS_SUPPORT_NONOPTIMIZED?'N':'n',
			pg->valid_states&TPGS_SUPPORT_OPTIMIZED?'A':'a');

	switch (pg->state) {
	case SCSI_ACCESS_STATE_TRANSITIONING:
		if (time_before(jiffies, pg->expiry)) {
			/* State transition, retry */
			pg->interval = ALUA_RTPG_RETRY_DELAY;
			err = SCSI_DH_RETRY;
		} else {
			struct alua_dh_data *h;

			/* Transitioning time exceeded, set port to standby */
			err = SCSI_DH_IO;
			pg->state = SCSI_ACCESS_STATE_STANDBY;
			pg->expiry = 0;
			rcu_read_lock();
			list_for_each_entry_rcu(h, &pg->dh_list, node) {
				if (!h->sdev)
					continue;
				h->sdev->access_state =
					(pg->state & SCSI_ACCESS_STATE_MASK);
				if (pg->pref)
					h->sdev->access_state |=
						SCSI_ACCESS_STATE_PREFERRED;
			}
			rcu_read_unlock();
		}
		break;
	case SCSI_ACCESS_STATE_OFFLINE:
		/* Path unusable */
		err = SCSI_DH_DEV_OFFLINED;
		pg->expiry = 0;
		break;
	default:
		/* Useable path if active */
		err = SCSI_DH_OK;
		pg->expiry = 0;
		break;
	}
	spin_unlock_irqrestore(&pg->lock, flags);
	kfree(buff);
	return err;
}

/*
 * alua_stpg - Issue a SET TARGET PORT GROUP command
 *
 * Issue a SET TARGET PORT GROUP command and evaluate the
 * response. Returns SCSI_DH_RETRY per default to trigger
 * a re-evaluation of the target group state or SCSI_DH_OK
 * if no further action needs to be taken.
 */
static unsigned alua_stpg(struct scsi_device *sdev, struct alua_port_group *pg)
{
	int retval;
	struct scsi_sense_hdr sense_hdr;

	if (!(pg->tpgs & TPGS_MODE_EXPLICIT)) {
		/* Only implicit ALUA supported, retry */
		return SCSI_DH_RETRY;
	}
	switch (pg->state) {
	case SCSI_ACCESS_STATE_OPTIMAL:
		return SCSI_DH_OK;
	case SCSI_ACCESS_STATE_ACTIVE:
		if ((pg->flags & ALUA_OPTIMIZE_STPG) &&
		    !pg->pref &&
		    (pg->tpgs & TPGS_MODE_IMPLICIT))
			return SCSI_DH_OK;
		break;
	case SCSI_ACCESS_STATE_STANDBY:
	case SCSI_ACCESS_STATE_UNAVAILABLE:
		break;
	case SCSI_ACCESS_STATE_OFFLINE:
		return SCSI_DH_IO;
	case SCSI_ACCESS_STATE_TRANSITIONING:
		break;
	default:
		sdev_printk(KERN_INFO, sdev,
			    "%s: stpg failed, unhandled TPGS state %d",
			    ALUA_DH_NAME, pg->state);
		return SCSI_DH_NOSYS;
	}
	retval = submit_stpg(sdev, pg->group_id, &sense_hdr);

	if (retval) {
		if (retval < 0 || !scsi_sense_valid(&sense_hdr)) {
			sdev_printk(KERN_INFO, sdev,
				    "%s: stpg failed, result %d",
				    ALUA_DH_NAME, retval);
			if (retval < 0)
				return SCSI_DH_DEV_TEMP_BUSY;
		} else {
			sdev_printk(KERN_INFO, sdev, "%s: stpg failed\n",
				    ALUA_DH_NAME);
			scsi_print_sense_hdr(sdev, ALUA_DH_NAME, &sense_hdr);
		}
	}
	/* Retry RTPG */
	return SCSI_DH_RETRY;
}

/*
 * The caller must call scsi_device_put() on the returned pointer if it is not
 * NULL.
 */
static struct scsi_device * __must_check
alua_rtpg_select_sdev(struct alua_port_group *pg)
{
	struct alua_dh_data *h;
	struct scsi_device *sdev = NULL, *prev_sdev;

	lockdep_assert_held(&pg->lock);
	if (WARN_ON(!pg->rtpg_sdev))
		return NULL;

	/*
	 * RCU protection isn't necessary for dh_list here
	 * as we hold pg->lock, but for access to h->pg.
	 */
	rcu_read_lock();
	list_for_each_entry_rcu(h, &pg->dh_list, node) {
		if (!h->sdev)
			continue;
		if (h->sdev == pg->rtpg_sdev) {
			h->disabled = true;
			continue;
		}
		if (rcu_dereference(h->pg) == pg &&
		    !h->disabled &&
		    !scsi_device_get(h->sdev)) {
			sdev = h->sdev;
			break;
		}
	}
	rcu_read_unlock();

	if (!sdev) {
		pr_warn("%s: no device found for rtpg\n",
			(pg->device_id_len ?
			 (char *)pg->device_id_str : "(nameless PG)"));
		return NULL;
	}

	sdev_printk(KERN_INFO, sdev, "rtpg retry on different device\n");

	prev_sdev = pg->rtpg_sdev;
	pg->rtpg_sdev = sdev;

	return prev_sdev;
}

static void alua_rtpg_work(struct work_struct *work)
{
	struct alua_port_group *pg =
		container_of(work, struct alua_port_group, rtpg_work.work);
	struct scsi_device *sdev, *prev_sdev = NULL;
	LIST_HEAD(qdata_list);
	int err = SCSI_DH_OK;
	struct alua_queue_data *qdata, *tmp;
	struct alua_dh_data *h;
	unsigned long flags;

	spin_lock_irqsave(&pg->lock, flags);
	sdev = pg->rtpg_sdev;
	if (!sdev) {
		WARN_ON(pg->flags & ALUA_PG_RUN_RTPG);
		WARN_ON(pg->flags & ALUA_PG_RUN_STPG);
		spin_unlock_irqrestore(&pg->lock, flags);
		kref_put(&pg->kref, release_port_group);
		return;
	}
	pg->flags |= ALUA_PG_RUNNING;
	if (pg->flags & ALUA_PG_RUN_RTPG) {
		int state = pg->state;

		pg->flags &= ~ALUA_PG_RUN_RTPG;
		spin_unlock_irqrestore(&pg->lock, flags);
		if (state == SCSI_ACCESS_STATE_TRANSITIONING) {
			if (alua_tur(sdev) == SCSI_DH_RETRY) {
				spin_lock_irqsave(&pg->lock, flags);
				pg->flags &= ~ALUA_PG_RUNNING;
				pg->flags |= ALUA_PG_RUN_RTPG;
				if (!pg->interval)
					pg->interval = ALUA_RTPG_RETRY_DELAY;
				spin_unlock_irqrestore(&pg->lock, flags);
				queue_delayed_work(kaluad_wq, &pg->rtpg_work,
						   pg->interval * HZ);
				return;
			}
			/* Send RTPG on failure or if TUR indicates SUCCESS */
		}
		err = alua_rtpg(sdev, pg);
		spin_lock_irqsave(&pg->lock, flags);

		/* If RTPG failed on the current device, try using another */
		if (err == SCSI_DH_RES_TEMP_UNAVAIL &&
		    (prev_sdev = alua_rtpg_select_sdev(pg)))
			err = SCSI_DH_IMM_RETRY;

		if (err == SCSI_DH_RETRY || err == SCSI_DH_IMM_RETRY ||
		    pg->flags & ALUA_PG_RUN_RTPG) {
			pg->flags &= ~ALUA_PG_RUNNING;
			if (err == SCSI_DH_IMM_RETRY)
				pg->interval = 0;
			else if (!pg->interval && !(pg->flags & ALUA_PG_RUN_RTPG))
				pg->interval = ALUA_RTPG_RETRY_DELAY;
			pg->flags |= ALUA_PG_RUN_RTPG;
			spin_unlock_irqrestore(&pg->lock, flags);
			goto queue_rtpg;
		}
		if (err != SCSI_DH_OK)
			pg->flags &= ~ALUA_PG_RUN_STPG;
	}
	if (pg->flags & ALUA_PG_RUN_STPG) {
		pg->flags &= ~ALUA_PG_RUN_STPG;
		spin_unlock_irqrestore(&pg->lock, flags);
		err = alua_stpg(sdev, pg);
		spin_lock_irqsave(&pg->lock, flags);
		if (err == SCSI_DH_RETRY || pg->flags & ALUA_PG_RUN_RTPG) {
			pg->flags |= ALUA_PG_RUN_RTPG;
			pg->interval = 0;
			pg->flags &= ~ALUA_PG_RUNNING;
			spin_unlock_irqrestore(&pg->lock, flags);
			goto queue_rtpg;
		}
	}

	list_splice_init(&pg->rtpg_list, &qdata_list);
	/*
	 * We went through an RTPG, for good or bad.
	 * Re-enable all devices for the next attempt.
	 */
	list_for_each_entry(h, &pg->dh_list, node)
		h->disabled = false;
	pg->rtpg_sdev = NULL;
	spin_unlock_irqrestore(&pg->lock, flags);

	if (prev_sdev)
		scsi_device_put(prev_sdev);

	list_for_each_entry_safe(qdata, tmp, &qdata_list, entry) {
		list_del(&qdata->entry);
		if (qdata->callback_fn)
			qdata->callback_fn(qdata->callback_data, err);
		kfree(qdata);
	}
	spin_lock_irqsave(&pg->lock, flags);
	pg->flags &= ~ALUA_PG_RUNNING;
	spin_unlock_irqrestore(&pg->lock, flags);
	scsi_device_put(sdev);
	kref_put(&pg->kref, release_port_group);
	return;

queue_rtpg:
	if (prev_sdev)
		scsi_device_put(prev_sdev);
	queue_delayed_work(kaluad_wq, &pg->rtpg_work, pg->interval * HZ);
}

/**
 * alua_rtpg_queue() - cause RTPG to be submitted asynchronously
 * @pg: ALUA port group associated with @sdev.
 * @sdev: SCSI device for which to submit an RTPG.
 * @qdata: Information about the callback to invoke after the RTPG.
 * @force: Whether or not to submit an RTPG if a work item that will submit an
 *         RTPG already has been scheduled.
 *
 * Returns true if and only if alua_rtpg_work() will be called asynchronously.
 * That function is responsible for calling @qdata->fn().
 *
 * Context: may be called from atomic context (alua_check()) only if the caller
 *	holds an sdev reference.
 */
static bool alua_rtpg_queue(struct alua_port_group *pg,
			    struct scsi_device *sdev,
			    struct alua_queue_data *qdata, bool force)
{
	int start_queue = 0;
	unsigned long flags;

	if (WARN_ON_ONCE(!pg) || scsi_device_get(sdev))
		return false;

	spin_lock_irqsave(&pg->lock, flags);
	if (qdata) {
		list_add_tail(&qdata->entry, &pg->rtpg_list);
		pg->flags |= ALUA_PG_RUN_STPG;
		force = true;
	}
	if (pg->rtpg_sdev == NULL) {
		struct alua_dh_data *h = sdev->handler_data;

		rcu_read_lock();
		if (h && rcu_dereference(h->pg) == pg) {
			pg->interval = 0;
			pg->flags |= ALUA_PG_RUN_RTPG;
			kref_get(&pg->kref);
			pg->rtpg_sdev = sdev;
			start_queue = 1;
		}
		rcu_read_unlock();
	} else if (!(pg->flags & ALUA_PG_RUN_RTPG) && force) {
		pg->flags |= ALUA_PG_RUN_RTPG;
		/* Do not queue if the worker is already running */
		if (!(pg->flags & ALUA_PG_RUNNING)) {
			kref_get(&pg->kref);
			start_queue = 1;
		}
	}

	spin_unlock_irqrestore(&pg->lock, flags);

	if (start_queue) {
		if (queue_delayed_work(kaluad_wq, &pg->rtpg_work,
				msecs_to_jiffies(ALUA_RTPG_DELAY_MSECS)))
			sdev = NULL;
		else
			kref_put(&pg->kref, release_port_group);
	}
	if (sdev)
		scsi_device_put(sdev);

	return true;
}

/*
 * alua_initialize - Initialize ALUA state
 * @sdev: the device to be initialized
 *
 * For the prep_fn to work correctly we have
 * to initialize the ALUA state for the device.
 */
static int alua_initialize(struct scsi_device *sdev, struct alua_dh_data *h)
{
	int err = SCSI_DH_DEV_UNSUPP, tpgs;

	mutex_lock(&h->init_mutex);
	h->disabled = false;
	tpgs = alua_check_tpgs(sdev);
	if (tpgs != TPGS_MODE_NONE)
		err = alua_check_vpd(sdev, h, tpgs);
	h->init_error = err;
	mutex_unlock(&h->init_mutex);
	return err;
}
/*
 * alua_set_params - set/unset the optimize flag
 * @sdev: device on the path to be activated
 * params - parameters in the following format
 *      "no_of_params\0param1\0param2\0param3\0...\0"
 * For example, to set the flag pass the following parameters
 * from multipath.conf
 *     hardware_handler        "2 alua 1"
 */
static int alua_set_params(struct scsi_device *sdev, const char *params)
{
	struct alua_dh_data *h = sdev->handler_data;
	struct alua_port_group *pg = NULL;
	unsigned int optimize = 0, argc;
	const char *p = params;
	int result = SCSI_DH_OK;
	unsigned long flags;

	if ((sscanf(params, "%u", &argc) != 1) || (argc != 1))
		return -EINVAL;

	while (*p++)
		;
	if ((sscanf(p, "%u", &optimize) != 1) || (optimize > 1))
		return -EINVAL;

	rcu_read_lock();
	pg = rcu_dereference(h->pg);
	if (!pg) {
		rcu_read_unlock();
		return -ENXIO;
	}
	spin_lock_irqsave(&pg->lock, flags);
	if (optimize)
		pg->flags |= ALUA_OPTIMIZE_STPG;
	else
		pg->flags &= ~ALUA_OPTIMIZE_STPG;
	spin_unlock_irqrestore(&pg->lock, flags);
	rcu_read_unlock();

	return result;
}

/*
 * alua_activate - activate a path
 * @sdev: device on the path to be activated
 *
 * We're currently switching the port group to be activated only and
 * let the array figure out the rest.
 * There may be other arrays which require us to switch all port groups
 * based on a certain policy. But until we actually encounter them it
 * should be okay.
 */
static int alua_activate(struct scsi_device *sdev,
			activate_complete fn, void *data)
{
	struct alua_dh_data *h = sdev->handler_data;
	int err = SCSI_DH_OK;
	struct alua_queue_data *qdata;
	struct alua_port_group *pg;

	qdata = kzalloc(sizeof(*qdata), GFP_KERNEL);
	if (!qdata) {
		err = SCSI_DH_RES_TEMP_UNAVAIL;
		goto out;
	}
	qdata->callback_fn = fn;
	qdata->callback_data = data;

	mutex_lock(&h->init_mutex);
	rcu_read_lock();
	pg = rcu_dereference(h->pg);
	if (!pg || !kref_get_unless_zero(&pg->kref)) {
		rcu_read_unlock();
		kfree(qdata);
		err = h->init_error;
		mutex_unlock(&h->init_mutex);
		goto out;
	}
	rcu_read_unlock();
	mutex_unlock(&h->init_mutex);

	if (alua_rtpg_queue(pg, sdev, qdata, true))
		fn = NULL;
	else
		err = SCSI_DH_DEV_OFFLINED;
	kref_put(&pg->kref, release_port_group);
out:
	if (fn)
		fn(data, err);
	return 0;
}

/*
 * alua_check - check path status
 * @sdev: device on the path to be checked
 *
 * Check the device status
 */
static void alua_check(struct scsi_device *sdev, bool force)
{
	struct alua_dh_data *h = sdev->handler_data;
	struct alua_port_group *pg;

	rcu_read_lock();
	pg = rcu_dereference(h->pg);
	if (!pg || !kref_get_unless_zero(&pg->kref)) {
		rcu_read_unlock();
		return;
	}
	rcu_read_unlock();
	alua_rtpg_queue(pg, sdev, NULL, force);
	kref_put(&pg->kref, release_port_group);
}

/*
 * alua_prep_fn - request callback
 *
 * Fail I/O to all paths not in state
 * active/optimized or active/non-optimized.
 */
static blk_status_t alua_prep_fn(struct scsi_device *sdev, struct request *req)
{
	struct alua_dh_data *h = sdev->handler_data;
	struct alua_port_group *pg;
	unsigned char state = SCSI_ACCESS_STATE_OPTIMAL;

	rcu_read_lock();
	pg = rcu_dereference(h->pg);
	if (pg)
		state = pg->state;
	rcu_read_unlock();

	switch (state) {
	case SCSI_ACCESS_STATE_OPTIMAL:
	case SCSI_ACCESS_STATE_ACTIVE:
	case SCSI_ACCESS_STATE_LBA:
	case SCSI_ACCESS_STATE_TRANSITIONING:
		return BLK_STS_OK;
	default:
		req->rq_flags |= RQF_QUIET;
		return BLK_STS_IOERR;
	}
}

static void alua_rescan(struct scsi_device *sdev)
{
	struct alua_dh_data *h = sdev->handler_data;

	alua_initialize(sdev, h);
}

/*
 * alua_bus_attach - Attach device handler
 * @sdev: device to be attached to
 */
static int alua_bus_attach(struct scsi_device *sdev)
{
	struct alua_dh_data *h;
	int err;

	h = kzalloc(sizeof(*h) , GFP_KERNEL);
	if (!h)
		return SCSI_DH_NOMEM;
	spin_lock_init(&h->pg_lock);
	rcu_assign_pointer(h->pg, NULL);
	h->init_error = SCSI_DH_OK;
	h->sdev = sdev;
	INIT_LIST_HEAD(&h->node);

	mutex_init(&h->init_mutex);
	err = alua_initialize(sdev, h);
	if (err != SCSI_DH_OK && err != SCSI_DH_DEV_OFFLINED)
		goto failed;

	sdev->handler_data = h;
	return SCSI_DH_OK;
failed:
	kfree(h);
	return err;
}

/*
 * alua_bus_detach - Detach device handler
 * @sdev: device to be detached from
 */
static void alua_bus_detach(struct scsi_device *sdev)
{
	struct alua_dh_data *h = sdev->handler_data;
	struct alua_port_group *pg;

	spin_lock(&h->pg_lock);
	pg = rcu_dereference_protected(h->pg, lockdep_is_held(&h->pg_lock));
	rcu_assign_pointer(h->pg, NULL);
	spin_unlock(&h->pg_lock);
	if (pg) {
		spin_lock_irq(&pg->lock);
		list_del_rcu(&h->node);
		spin_unlock_irq(&pg->lock);
		kref_put(&pg->kref, release_port_group);
	}
	sdev->handler_data = NULL;
	synchronize_rcu();
	kfree(h);
}

static struct scsi_device_handler alua_dh = {
	.name = ALUA_DH_NAME,
	.module = THIS_MODULE,
	.attach = alua_bus_attach,
	.detach = alua_bus_detach,
	.prep_fn = alua_prep_fn,
	.check_sense = alua_check_sense,
	.activate = alua_activate,
	.rescan = alua_rescan,
	.set_params = alua_set_params,
};

static int __init alua_init(void)
{
	int r;

	kaluad_wq = alloc_workqueue("kaluad", WQ_MEM_RECLAIM, 0);
	if (!kaluad_wq)
		return -ENOMEM;

	r = scsi_register_device_handler(&alua_dh);
	if (r != 0) {
		printk(KERN_ERR "%s: Failed to register scsi device handler",
			ALUA_DH_NAME);
		destroy_workqueue(kaluad_wq);
	}
	return r;
}

static void __exit alua_exit(void)
{
	scsi_unregister_device_handler(&alua_dh);
	destroy_workqueue(kaluad_wq);
}

module_init(alua_init);
module_exit(alua_exit);

MODULE_DESCRIPTION("DM Multipath ALUA support");
MODULE_AUTHOR("Hannes Reinecke <hare@suse.de>");
MODULE_LICENSE("GPL");
MODULE_VERSION(ALUA_DH_VER);