aboutsummaryrefslogtreecommitdiff
path: root/block/quorum.c
blob: ecec3a54071c08eac8bb1d8e20240cc97cdb3759 (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
/*
 * Quorum Block filter
 *
 * Copyright (C) 2012-2014 Nodalink, EURL.
 *
 * Author:
 *   Benoît Canet <benoit.canet@irqsave.net>
 *
 * Based on the design and code of blkverify.c (Copyright (C) 2010 IBM, Corp)
 * and blkmirror.c (Copyright (C) 2011 Red Hat, Inc).
 *
 * This work is licensed under the terms of the GNU GPL, version 2 or later.
 * See the COPYING file in the top-level directory.
 */

#include <gnutls/gnutls.h>
#include <gnutls/crypto.h>
#include "block/block_int.h"
#include "qapi/qmp/qjson.h"

#define HASH_LENGTH 32

#define QUORUM_OPT_VOTE_THRESHOLD "vote-threshold"
#define QUORUM_OPT_BLKVERIFY      "blkverify"

/* This union holds a vote hash value */
typedef union QuorumVoteValue {
    char h[HASH_LENGTH];       /* SHA-256 hash */
    int64_t l;                 /* simpler 64 bits hash */
} QuorumVoteValue;

/* A vote item */
typedef struct QuorumVoteItem {
    int index;
    QLIST_ENTRY(QuorumVoteItem) next;
} QuorumVoteItem;

/* this structure is a vote version. A version is the set of votes sharing the
 * same vote value.
 * The set of votes will be tracked with the items field and its cardinality is
 * vote_count.
 */
typedef struct QuorumVoteVersion {
    QuorumVoteValue value;
    int index;
    int vote_count;
    QLIST_HEAD(, QuorumVoteItem) items;
    QLIST_ENTRY(QuorumVoteVersion) next;
} QuorumVoteVersion;

/* this structure holds a group of vote versions together */
typedef struct QuorumVotes {
    QLIST_HEAD(, QuorumVoteVersion) vote_list;
    bool (*compare)(QuorumVoteValue *a, QuorumVoteValue *b);
} QuorumVotes;

/* the following structure holds the state of one quorum instance */
typedef struct BDRVQuorumState {
    BlockDriverState **bs; /* children BlockDriverStates */
    int num_children;      /* children count */
    int threshold;         /* if less than threshold children reads gave the
                            * same result a quorum error occurs.
                            */
    bool is_blkverify;     /* true if the driver is in blkverify mode
                            * Writes are mirrored on two children devices.
                            * On reads the two children devices' contents are
                            * compared and if a difference is spotted its
                            * location is printed and the code aborts.
                            * It is useful to debug other block drivers by
                            * comparing them with a reference one.
                            */
} BDRVQuorumState;

typedef struct QuorumAIOCB QuorumAIOCB;

/* Quorum will create one instance of the following structure per operation it
 * performs on its children.
 * So for each read/write operation coming from the upper layer there will be
 * $children_count QuorumChildRequest.
 */
typedef struct QuorumChildRequest {
    BlockDriverAIOCB *aiocb;
    QEMUIOVector qiov;
    uint8_t *buf;
    int ret;
    QuorumAIOCB *parent;
} QuorumChildRequest;

/* Quorum will use the following structure to track progress of each read/write
 * operation received by the upper layer.
 * This structure hold pointers to the QuorumChildRequest structures instances
 * used to do operations on each children and track overall progress.
 */
struct QuorumAIOCB {
    BlockDriverAIOCB common;

    /* Request metadata */
    uint64_t sector_num;
    int nb_sectors;

    QEMUIOVector *qiov;         /* calling IOV */

    QuorumChildRequest *qcrs;   /* individual child requests */
    int count;                  /* number of completed AIOCB */
    int success_count;          /* number of successfully completed AIOCB */

    QuorumVotes votes;

    bool is_read;
    int vote_ret;
};

static void quorum_vote(QuorumAIOCB *acb);

static void quorum_aio_cancel(BlockDriverAIOCB *blockacb)
{
    QuorumAIOCB *acb = container_of(blockacb, QuorumAIOCB, common);
    BDRVQuorumState *s = acb->common.bs->opaque;
    int i;

    /* cancel all callbacks */
    for (i = 0; i < s->num_children; i++) {
        bdrv_aio_cancel(acb->qcrs[i].aiocb);
    }

    g_free(acb->qcrs);
    qemu_aio_release(acb);
}

static AIOCBInfo quorum_aiocb_info = {
    .aiocb_size         = sizeof(QuorumAIOCB),
    .cancel             = quorum_aio_cancel,
};

static void quorum_aio_finalize(QuorumAIOCB *acb)
{
    BDRVQuorumState *s = acb->common.bs->opaque;
    int i, ret = 0;

    if (acb->vote_ret) {
        ret = acb->vote_ret;
    }

    acb->common.cb(acb->common.opaque, ret);

    if (acb->is_read) {
        for (i = 0; i < s->num_children; i++) {
            qemu_vfree(acb->qcrs[i].buf);
            qemu_iovec_destroy(&acb->qcrs[i].qiov);
        }
    }

    g_free(acb->qcrs);
    qemu_aio_release(acb);
}

static bool quorum_sha256_compare(QuorumVoteValue *a, QuorumVoteValue *b)
{
    return !memcmp(a->h, b->h, HASH_LENGTH);
}

static bool quorum_64bits_compare(QuorumVoteValue *a, QuorumVoteValue *b)
{
    return a->l == b->l;
}

static QuorumAIOCB *quorum_aio_get(BDRVQuorumState *s,
                                   BlockDriverState *bs,
                                   QEMUIOVector *qiov,
                                   uint64_t sector_num,
                                   int nb_sectors,
                                   BlockDriverCompletionFunc *cb,
                                   void *opaque)
{
    QuorumAIOCB *acb = qemu_aio_get(&quorum_aiocb_info, bs, cb, opaque);
    int i;

    acb->common.bs->opaque = s;
    acb->sector_num = sector_num;
    acb->nb_sectors = nb_sectors;
    acb->qiov = qiov;
    acb->qcrs = g_new0(QuorumChildRequest, s->num_children);
    acb->count = 0;
    acb->success_count = 0;
    acb->votes.compare = quorum_sha256_compare;
    QLIST_INIT(&acb->votes.vote_list);
    acb->is_read = false;
    acb->vote_ret = 0;

    for (i = 0; i < s->num_children; i++) {
        acb->qcrs[i].buf = NULL;
        acb->qcrs[i].ret = 0;
        acb->qcrs[i].parent = acb;
    }

    return acb;
}

static void quorum_report_bad(QuorumAIOCB *acb, char *node_name, int ret)
{
    QObject *data;
    assert(node_name);
    data = qobject_from_jsonf("{ 'node-name': %s"
                              ", 'sector-num': %" PRId64
                              ", 'sectors-count': %d }",
                              node_name, acb->sector_num, acb->nb_sectors);
    if (ret < 0) {
        QDict *dict = qobject_to_qdict(data);
        qdict_put(dict, "error", qstring_from_str(strerror(-ret)));
    }
    monitor_protocol_event(QEVENT_QUORUM_REPORT_BAD, data);
    qobject_decref(data);
}

static void quorum_report_failure(QuorumAIOCB *acb)
{
    QObject *data;
    const char *reference = acb->common.bs->device_name[0] ?
                            acb->common.bs->device_name :
                            acb->common.bs->node_name;
    data = qobject_from_jsonf("{ 'reference': %s"
                              ", 'sector-num': %" PRId64
                              ", 'sectors-count': %d }",
                              reference, acb->sector_num, acb->nb_sectors);
    monitor_protocol_event(QEVENT_QUORUM_FAILURE, data);
    qobject_decref(data);
}

static int quorum_vote_error(QuorumAIOCB *acb);

static bool quorum_has_too_much_io_failed(QuorumAIOCB *acb)
{
    BDRVQuorumState *s = acb->common.bs->opaque;

    if (acb->success_count < s->threshold) {
        acb->vote_ret = quorum_vote_error(acb);
        quorum_report_failure(acb);
        return true;
    }

    return false;
}

static void quorum_aio_cb(void *opaque, int ret)
{
    QuorumChildRequest *sacb = opaque;
    QuorumAIOCB *acb = sacb->parent;
    BDRVQuorumState *s = acb->common.bs->opaque;

    sacb->ret = ret;
    acb->count++;
    if (ret == 0) {
        acb->success_count++;
    } else {
        quorum_report_bad(acb, sacb->aiocb->bs->node_name, ret);
    }
    assert(acb->count <= s->num_children);
    assert(acb->success_count <= s->num_children);
    if (acb->count < s->num_children) {
        return;
    }

    /* Do the vote on read */
    if (acb->is_read) {
        quorum_vote(acb);
    } else {
        quorum_has_too_much_io_failed(acb);
    }

    quorum_aio_finalize(acb);
}

static void quorum_report_bad_versions(BDRVQuorumState *s,
                                       QuorumAIOCB *acb,
                                       QuorumVoteValue *value)
{
    QuorumVoteVersion *version;
    QuorumVoteItem *item;

    QLIST_FOREACH(version, &acb->votes.vote_list, next) {
        if (acb->votes.compare(&version->value, value)) {
            continue;
        }
        QLIST_FOREACH(item, &version->items, next) {
            quorum_report_bad(acb, s->bs[item->index]->node_name, 0);
        }
    }
}

static void quorum_copy_qiov(QEMUIOVector *dest, QEMUIOVector *source)
{
    int i;
    assert(dest->niov == source->niov);
    assert(dest->size == source->size);
    for (i = 0; i < source->niov; i++) {
        assert(dest->iov[i].iov_len == source->iov[i].iov_len);
        memcpy(dest->iov[i].iov_base,
               source->iov[i].iov_base,
               source->iov[i].iov_len);
    }
}

static void quorum_count_vote(QuorumVotes *votes,
                              QuorumVoteValue *value,
                              int index)
{
    QuorumVoteVersion *v = NULL, *version = NULL;
    QuorumVoteItem *item;

    /* look if we have something with this hash */
    QLIST_FOREACH(v, &votes->vote_list, next) {
        if (votes->compare(&v->value, value)) {
            version = v;
            break;
        }
    }

    /* It's a version not yet in the list add it */
    if (!version) {
        version = g_new0(QuorumVoteVersion, 1);
        QLIST_INIT(&version->items);
        memcpy(&version->value, value, sizeof(version->value));
        version->index = index;
        version->vote_count = 0;
        QLIST_INSERT_HEAD(&votes->vote_list, version, next);
    }

    version->vote_count++;

    item = g_new0(QuorumVoteItem, 1);
    item->index = index;
    QLIST_INSERT_HEAD(&version->items, item, next);
}

static void quorum_free_vote_list(QuorumVotes *votes)
{
    QuorumVoteVersion *version, *next_version;
    QuorumVoteItem *item, *next_item;

    QLIST_FOREACH_SAFE(version, &votes->vote_list, next, next_version) {
        QLIST_REMOVE(version, next);
        QLIST_FOREACH_SAFE(item, &version->items, next, next_item) {
            QLIST_REMOVE(item, next);
            g_free(item);
        }
        g_free(version);
    }
}

static int quorum_compute_hash(QuorumAIOCB *acb, int i, QuorumVoteValue *hash)
{
    int j, ret;
    gnutls_hash_hd_t dig;
    QEMUIOVector *qiov = &acb->qcrs[i].qiov;

    ret = gnutls_hash_init(&dig, GNUTLS_DIG_SHA256);

    if (ret < 0) {
        return ret;
    }

    for (j = 0; j < qiov->niov; j++) {
        ret = gnutls_hash(dig, qiov->iov[j].iov_base, qiov->iov[j].iov_len);
        if (ret < 0) {
            break;
        }
    }

    gnutls_hash_deinit(dig, (void *) hash);
    return ret;
}

static QuorumVoteVersion *quorum_get_vote_winner(QuorumVotes *votes)
{
    int max = 0;
    QuorumVoteVersion *candidate, *winner = NULL;

    QLIST_FOREACH(candidate, &votes->vote_list, next) {
        if (candidate->vote_count > max) {
            max = candidate->vote_count;
            winner = candidate;
        }
    }

    return winner;
}

/* qemu_iovec_compare is handy for blkverify mode because it returns the first
 * differing byte location. Yet it is handcoded to compare vectors one byte
 * after another so it does not benefit from the libc SIMD optimizations.
 * quorum_iovec_compare is written for speed and should be used in the non
 * blkverify mode of quorum.
 */
static bool quorum_iovec_compare(QEMUIOVector *a, QEMUIOVector *b)
{
    int i;
    int result;

    assert(a->niov == b->niov);
    for (i = 0; i < a->niov; i++) {
        assert(a->iov[i].iov_len == b->iov[i].iov_len);
        result = memcmp(a->iov[i].iov_base,
                        b->iov[i].iov_base,
                        a->iov[i].iov_len);
        if (result) {
            return false;
        }
    }

    return true;
}

static void GCC_FMT_ATTR(2, 3) quorum_err(QuorumAIOCB *acb,
                                          const char *fmt, ...)
{
    va_list ap;

    va_start(ap, fmt);
    fprintf(stderr, "quorum: sector_num=%" PRId64 " nb_sectors=%d ",
            acb->sector_num, acb->nb_sectors);
    vfprintf(stderr, fmt, ap);
    fprintf(stderr, "\n");
    va_end(ap);
    exit(1);
}

static bool quorum_compare(QuorumAIOCB *acb,
                           QEMUIOVector *a,
                           QEMUIOVector *b)
{
    BDRVQuorumState *s = acb->common.bs->opaque;
    ssize_t offset;

    /* This driver will replace blkverify in this particular case */
    if (s->is_blkverify) {
        offset = qemu_iovec_compare(a, b);
        if (offset != -1) {
            quorum_err(acb, "contents mismatch in sector %" PRId64,
                       acb->sector_num +
                       (uint64_t)(offset / BDRV_SECTOR_SIZE));
        }
        return true;
    }

    return quorum_iovec_compare(a, b);
}

/* Do a vote to get the error code */
static int quorum_vote_error(QuorumAIOCB *acb)
{
    BDRVQuorumState *s = acb->common.bs->opaque;
    QuorumVoteVersion *winner = NULL;
    QuorumVotes error_votes;
    QuorumVoteValue result_value;
    int i, ret = 0;
    bool error = false;

    QLIST_INIT(&error_votes.vote_list);
    error_votes.compare = quorum_64bits_compare;

    for (i = 0; i < s->num_children; i++) {
        ret = acb->qcrs[i].ret;
        if (ret) {
            error = true;
            result_value.l = ret;
            quorum_count_vote(&error_votes, &result_value, i);
        }
    }

    if (error) {
        winner = quorum_get_vote_winner(&error_votes);
        ret = winner->value.l;
    }

    quorum_free_vote_list(&error_votes);

    return ret;
}

static void quorum_vote(QuorumAIOCB *acb)
{
    bool quorum = true;
    int i, j, ret;
    QuorumVoteValue hash;
    BDRVQuorumState *s = acb->common.bs->opaque;
    QuorumVoteVersion *winner;

    if (quorum_has_too_much_io_failed(acb)) {
        return;
    }

    /* get the index of the first successful read */
    for (i = 0; i < s->num_children; i++) {
        if (!acb->qcrs[i].ret) {
            break;
        }
    }

    assert(i < s->num_children);

    /* compare this read with all other successful reads stopping at quorum
     * failure
     */
    for (j = i + 1; j < s->num_children; j++) {
        if (acb->qcrs[j].ret) {
            continue;
        }
        quorum = quorum_compare(acb, &acb->qcrs[i].qiov, &acb->qcrs[j].qiov);
        if (!quorum) {
            break;
       }
    }

    /* Every successful read agrees */
    if (quorum) {
        quorum_copy_qiov(acb->qiov, &acb->qcrs[i].qiov);
        return;
    }

    /* compute hashes for each successful read, also store indexes */
    for (i = 0; i < s->num_children; i++) {
        if (acb->qcrs[i].ret) {
            continue;
        }
        ret = quorum_compute_hash(acb, i, &hash);
        /* if ever the hash computation failed */
        if (ret < 0) {
            acb->vote_ret = ret;
            goto free_exit;
        }
        quorum_count_vote(&acb->votes, &hash, i);
    }

    /* vote to select the most represented version */
    winner = quorum_get_vote_winner(&acb->votes);

    /* if the winner count is smaller than threshold the read fails */
    if (winner->vote_count < s->threshold) {
        quorum_report_failure(acb);
        acb->vote_ret = -EIO;
        goto free_exit;
    }

    /* we have a winner: copy it */
    quorum_copy_qiov(acb->qiov, &acb->qcrs[winner->index].qiov);

    /* some versions are bad print them */
    quorum_report_bad_versions(s, acb, &winner->value);

free_exit:
    /* free lists */
    quorum_free_vote_list(&acb->votes);
}

static BlockDriverAIOCB *quorum_aio_readv(BlockDriverState *bs,
                                         int64_t sector_num,
                                         QEMUIOVector *qiov,
                                         int nb_sectors,
                                         BlockDriverCompletionFunc *cb,
                                         void *opaque)
{
    BDRVQuorumState *s = bs->opaque;
    QuorumAIOCB *acb = quorum_aio_get(s, bs, qiov, sector_num,
                                      nb_sectors, cb, opaque);
    int i;

    acb->is_read = true;

    for (i = 0; i < s->num_children; i++) {
        acb->qcrs[i].buf = qemu_blockalign(s->bs[i], qiov->size);
        qemu_iovec_init(&acb->qcrs[i].qiov, qiov->niov);
        qemu_iovec_clone(&acb->qcrs[i].qiov, qiov, acb->qcrs[i].buf);
    }

    for (i = 0; i < s->num_children; i++) {
        bdrv_aio_readv(s->bs[i], sector_num, &acb->qcrs[i].qiov, nb_sectors,
                       quorum_aio_cb, &acb->qcrs[i]);
    }

    return &acb->common;
}

static BlockDriverAIOCB *quorum_aio_writev(BlockDriverState *bs,
                                          int64_t sector_num,
                                          QEMUIOVector *qiov,
                                          int nb_sectors,
                                          BlockDriverCompletionFunc *cb,
                                          void *opaque)
{
    BDRVQuorumState *s = bs->opaque;
    QuorumAIOCB *acb = quorum_aio_get(s, bs, qiov, sector_num, nb_sectors,
                                      cb, opaque);
    int i;

    for (i = 0; i < s->num_children; i++) {
        acb->qcrs[i].aiocb = bdrv_aio_writev(s->bs[i], sector_num, qiov,
                                             nb_sectors, &quorum_aio_cb,
                                             &acb->qcrs[i]);
    }

    return &acb->common;
}

static int64_t quorum_getlength(BlockDriverState *bs)
{
    BDRVQuorumState *s = bs->opaque;
    int64_t result;
    int i;

    /* check that all file have the same length */
    result = bdrv_getlength(s->bs[0]);
    if (result < 0) {
        return result;
    }
    for (i = 1; i < s->num_children; i++) {
        int64_t value = bdrv_getlength(s->bs[i]);
        if (value < 0) {
            return value;
        }
        if (value != result) {
            return -EIO;
        }
    }

    return result;
}

static void quorum_invalidate_cache(BlockDriverState *bs, Error **errp)
{
    BDRVQuorumState *s = bs->opaque;
    Error *local_err = NULL;
    int i;

    for (i = 0; i < s->num_children; i++) {
        bdrv_invalidate_cache(s->bs[i], &local_err);
        if (local_err) {
            error_propagate(errp, local_err);
            return;
        }
    }
}

static coroutine_fn int quorum_co_flush(BlockDriverState *bs)
{
    BDRVQuorumState *s = bs->opaque;
    QuorumVoteVersion *winner = NULL;
    QuorumVotes error_votes;
    QuorumVoteValue result_value;
    int i;
    int result = 0;

    QLIST_INIT(&error_votes.vote_list);
    error_votes.compare = quorum_64bits_compare;

    for (i = 0; i < s->num_children; i++) {
        result = bdrv_co_flush(s->bs[i]);
        result_value.l = result;
        quorum_count_vote(&error_votes, &result_value, i);
    }

    winner = quorum_get_vote_winner(&error_votes);
    result = winner->value.l;

    quorum_free_vote_list(&error_votes);

    return result;
}

static bool quorum_recurse_is_first_non_filter(BlockDriverState *bs,
                                               BlockDriverState *candidate)
{
    BDRVQuorumState *s = bs->opaque;
    int i;

    for (i = 0; i < s->num_children; i++) {
        bool perm = bdrv_recurse_is_first_non_filter(s->bs[i],
                                                     candidate);
        if (perm) {
            return true;
        }
    }

    return false;
}

static int quorum_valid_threshold(int threshold, int num_children, Error **errp)
{

    if (threshold < 1) {
        error_set(errp, QERR_INVALID_PARAMETER_VALUE,
                  "vote-threshold", "value >= 1");
        return -ERANGE;
    }

    if (threshold > num_children) {
        error_setg(errp, "threshold may not exceed children count");
        return -ERANGE;
    }

    return 0;
}

static QemuOptsList quorum_runtime_opts = {
    .name = "quorum",
    .head = QTAILQ_HEAD_INITIALIZER(quorum_runtime_opts.head),
    .desc = {
        {
            .name = QUORUM_OPT_VOTE_THRESHOLD,
            .type = QEMU_OPT_NUMBER,
            .help = "The number of vote needed for reaching quorum",
        },
        {
            .name = QUORUM_OPT_BLKVERIFY,
            .type = QEMU_OPT_BOOL,
            .help = "Trigger block verify mode if set",
        },
        { /* end of list */ }
    },
};

static int quorum_open(BlockDriverState *bs, QDict *options, int flags,
                       Error **errp)
{
    BDRVQuorumState *s = bs->opaque;
    Error *local_err = NULL;
    QemuOpts *opts;
    bool *opened;
    QDict *sub = NULL;
    QList *list = NULL;
    const QListEntry *lentry;
    int i;
    int ret = 0;

    qdict_flatten(options);
    qdict_extract_subqdict(options, &sub, "children.");
    qdict_array_split(sub, &list);

    if (qdict_size(sub)) {
        error_setg(&local_err, "Invalid option children.%s",
                   qdict_first(sub)->key);
        ret = -EINVAL;
        goto exit;
    }

    /* count how many different children are present */
    s->num_children = qlist_size(list);
    if (s->num_children < 2) {
        error_setg(&local_err,
                   "Number of provided children must be greater than 1");
        ret = -EINVAL;
        goto exit;
    }

    opts = qemu_opts_create(&quorum_runtime_opts, NULL, 0, &error_abort);
    qemu_opts_absorb_qdict(opts, options, &local_err);
    if (local_err) {
        ret = -EINVAL;
        goto exit;
    }

    s->threshold = qemu_opt_get_number(opts, QUORUM_OPT_VOTE_THRESHOLD, 0);

    /* and validate it against s->num_children */
    ret = quorum_valid_threshold(s->threshold, s->num_children, &local_err);
    if (ret < 0) {
        goto exit;
    }

    /* is the driver in blkverify mode */
    if (qemu_opt_get_bool(opts, QUORUM_OPT_BLKVERIFY, false) &&
        s->num_children == 2 && s->threshold == 2) {
        s->is_blkverify = true;
    } else if (qemu_opt_get_bool(opts, QUORUM_OPT_BLKVERIFY, false)) {
        fprintf(stderr, "blkverify mode is set by setting blkverify=on "
                "and using two files with vote_threshold=2\n");
    }

    /* allocate the children BlockDriverState array */
    s->bs = g_new0(BlockDriverState *, s->num_children);
    opened = g_new0(bool, s->num_children);

    for (i = 0, lentry = qlist_first(list); lentry;
         lentry = qlist_next(lentry), i++) {
        QDict *d;
        QString *string;

        switch (qobject_type(lentry->value))
        {
            /* List of options */
            case QTYPE_QDICT:
                d = qobject_to_qdict(lentry->value);
                QINCREF(d);
                ret = bdrv_open(&s->bs[i], NULL, NULL, d, flags, NULL,
                                &local_err);
                break;

            /* QMP reference */
            case QTYPE_QSTRING:
                string = qobject_to_qstring(lentry->value);
                ret = bdrv_open(&s->bs[i], NULL, qstring_get_str(string), NULL,
                                flags, NULL, &local_err);
                break;

            default:
                error_setg(&local_err, "Specification of child block device %i "
                           "is invalid", i);
                ret = -EINVAL;
        }

        if (ret < 0) {
            goto close_exit;
        }
        opened[i] = true;
    }

    g_free(opened);
    goto exit;

close_exit:
    /* cleanup on error */
    for (i = 0; i < s->num_children; i++) {
        if (!opened[i]) {
            continue;
        }
        bdrv_unref(s->bs[i]);
    }
    g_free(s->bs);
    g_free(opened);
exit:
    /* propagate error */
    if (local_err) {
        error_propagate(errp, local_err);
    }
    QDECREF(list);
    QDECREF(sub);
    return ret;
}

static void quorum_close(BlockDriverState *bs)
{
    BDRVQuorumState *s = bs->opaque;
    int i;

    for (i = 0; i < s->num_children; i++) {
        bdrv_unref(s->bs[i]);
    }

    g_free(s->bs);
}

static BlockDriver bdrv_quorum = {
    .format_name        = "quorum",
    .protocol_name      = "quorum",

    .instance_size      = sizeof(BDRVQuorumState),

    .bdrv_file_open     = quorum_open,
    .bdrv_close         = quorum_close,

    .bdrv_co_flush_to_disk = quorum_co_flush,

    .bdrv_getlength     = quorum_getlength,

    .bdrv_aio_readv     = quorum_aio_readv,
    .bdrv_aio_writev    = quorum_aio_writev,
    .bdrv_invalidate_cache = quorum_invalidate_cache,

    .is_filter           = true,
    .bdrv_recurse_is_first_non_filter = quorum_recurse_is_first_non_filter,
};

static void bdrv_quorum_init(void)
{
    bdrv_register(&bdrv_quorum);
}

block_init(bdrv_quorum_init);