Root/drivers/md/dm-snap-persistent.c

1/*
2 * Copyright (C) 2001-2002 Sistina Software (UK) Limited.
3 * Copyright (C) 2006-2008 Red Hat GmbH
4 *
5 * This file is released under the GPL.
6 */
7
8#include "dm-exception-store.h"
9
10#include <linux/mm.h>
11#include <linux/pagemap.h>
12#include <linux/vmalloc.h>
13#include <linux/export.h>
14#include <linux/slab.h>
15#include <linux/dm-io.h>
16
17#define DM_MSG_PREFIX "persistent snapshot"
18#define DM_CHUNK_SIZE_DEFAULT_SECTORS 32 /* 16KB */
19
20/*-----------------------------------------------------------------
21 * Persistent snapshots, by persistent we mean that the snapshot
22 * will survive a reboot.
23 *---------------------------------------------------------------*/
24
25/*
26 * We need to store a record of which parts of the origin have
27 * been copied to the snapshot device. The snapshot code
28 * requires that we copy exception chunks to chunk aligned areas
29 * of the COW store. It makes sense therefore, to store the
30 * metadata in chunk size blocks.
31 *
32 * There is no backward or forward compatibility implemented,
33 * snapshots with different disk versions than the kernel will
34 * not be usable. It is expected that "lvcreate" will blank out
35 * the start of a fresh COW device before calling the snapshot
36 * constructor.
37 *
38 * The first chunk of the COW device just contains the header.
39 * After this there is a chunk filled with exception metadata,
40 * followed by as many exception chunks as can fit in the
41 * metadata areas.
42 *
43 * All on disk structures are in little-endian format. The end
44 * of the exceptions info is indicated by an exception with a
45 * new_chunk of 0, which is invalid since it would point to the
46 * header chunk.
47 */
48
49/*
50 * Magic for persistent snapshots: "SnAp" - Feeble isn't it.
51 */
52#define SNAP_MAGIC 0x70416e53
53
54/*
55 * The on-disk version of the metadata.
56 */
57#define SNAPSHOT_DISK_VERSION 1
58
59#define NUM_SNAPSHOT_HDR_CHUNKS 1
60
61struct disk_header {
62    __le32 magic;
63
64    /*
65     * Is this snapshot valid. There is no way of recovering
66     * an invalid snapshot.
67     */
68    __le32 valid;
69
70    /*
71     * Simple, incrementing version. no backward
72     * compatibility.
73     */
74    __le32 version;
75
76    /* In sectors */
77    __le32 chunk_size;
78} __packed;
79
80struct disk_exception {
81    __le64 old_chunk;
82    __le64 new_chunk;
83} __packed;
84
85struct core_exception {
86    uint64_t old_chunk;
87    uint64_t new_chunk;
88};
89
90struct commit_callback {
91    void (*callback)(void *, int success);
92    void *context;
93};
94
95/*
96 * The top level structure for a persistent exception store.
97 */
98struct pstore {
99    struct dm_exception_store *store;
100    int version;
101    int valid;
102    uint32_t exceptions_per_area;
103
104    /*
105     * Now that we have an asynchronous kcopyd there is no
106     * need for large chunk sizes, so it wont hurt to have a
107     * whole chunks worth of metadata in memory at once.
108     */
109    void *area;
110
111    /*
112     * An area of zeros used to clear the next area.
113     */
114    void *zero_area;
115
116    /*
117     * An area used for header. The header can be written
118     * concurrently with metadata (when invalidating the snapshot),
119     * so it needs a separate buffer.
120     */
121    void *header_area;
122
123    /*
124     * Used to keep track of which metadata area the data in
125     * 'chunk' refers to.
126     */
127    chunk_t current_area;
128
129    /*
130     * The next free chunk for an exception.
131     *
132     * When creating exceptions, all the chunks here and above are
133     * free. It holds the next chunk to be allocated. On rare
134     * occasions (e.g. after a system crash) holes can be left in
135     * the exception store because chunks can be committed out of
136     * order.
137     *
138     * When merging exceptions, it does not necessarily mean all the
139     * chunks here and above are free. It holds the value it would
140     * have held if all chunks had been committed in order of
141     * allocation. Consequently the value may occasionally be
142     * slightly too low, but since it's only used for 'status' and
143     * it can never reach its minimum value too early this doesn't
144     * matter.
145     */
146
147    chunk_t next_free;
148
149    /*
150     * The index of next free exception in the current
151     * metadata area.
152     */
153    uint32_t current_committed;
154
155    atomic_t pending_count;
156    uint32_t callback_count;
157    struct commit_callback *callbacks;
158    struct dm_io_client *io_client;
159
160    struct workqueue_struct *metadata_wq;
161};
162
163static int alloc_area(struct pstore *ps)
164{
165    int r = -ENOMEM;
166    size_t len;
167
168    len = ps->store->chunk_size << SECTOR_SHIFT;
169
170    /*
171     * Allocate the chunk_size block of memory that will hold
172     * a single metadata area.
173     */
174    ps->area = vmalloc(len);
175    if (!ps->area)
176        goto err_area;
177
178    ps->zero_area = vzalloc(len);
179    if (!ps->zero_area)
180        goto err_zero_area;
181
182    ps->header_area = vmalloc(len);
183    if (!ps->header_area)
184        goto err_header_area;
185
186    return 0;
187
188err_header_area:
189    vfree(ps->zero_area);
190
191err_zero_area:
192    vfree(ps->area);
193
194err_area:
195    return r;
196}
197
198static void free_area(struct pstore *ps)
199{
200    if (ps->area)
201        vfree(ps->area);
202    ps->area = NULL;
203
204    if (ps->zero_area)
205        vfree(ps->zero_area);
206    ps->zero_area = NULL;
207
208    if (ps->header_area)
209        vfree(ps->header_area);
210    ps->header_area = NULL;
211}
212
213struct mdata_req {
214    struct dm_io_region *where;
215    struct dm_io_request *io_req;
216    struct work_struct work;
217    int result;
218};
219
220static void do_metadata(struct work_struct *work)
221{
222    struct mdata_req *req = container_of(work, struct mdata_req, work);
223
224    req->result = dm_io(req->io_req, 1, req->where, NULL);
225}
226
227/*
228 * Read or write a chunk aligned and sized block of data from a device.
229 */
230static int chunk_io(struct pstore *ps, void *area, chunk_t chunk, int rw,
231            int metadata)
232{
233    struct dm_io_region where = {
234        .bdev = dm_snap_cow(ps->store->snap)->bdev,
235        .sector = ps->store->chunk_size * chunk,
236        .count = ps->store->chunk_size,
237    };
238    struct dm_io_request io_req = {
239        .bi_rw = rw,
240        .mem.type = DM_IO_VMA,
241        .mem.ptr.vma = area,
242        .client = ps->io_client,
243        .notify.fn = NULL,
244    };
245    struct mdata_req req;
246
247    if (!metadata)
248        return dm_io(&io_req, 1, &where, NULL);
249
250    req.where = &where;
251    req.io_req = &io_req;
252
253    /*
254     * Issue the synchronous I/O from a different thread
255     * to avoid generic_make_request recursion.
256     */
257    INIT_WORK_ONSTACK(&req.work, do_metadata);
258    queue_work(ps->metadata_wq, &req.work);
259    flush_work(&req.work);
260
261    return req.result;
262}
263
264/*
265 * Convert a metadata area index to a chunk index.
266 */
267static chunk_t area_location(struct pstore *ps, chunk_t area)
268{
269    return NUM_SNAPSHOT_HDR_CHUNKS + ((ps->exceptions_per_area + 1) * area);
270}
271
272/*
273 * Read or write a metadata area. Remembering to skip the first
274 * chunk which holds the header.
275 */
276static int area_io(struct pstore *ps, int rw)
277{
278    int r;
279    chunk_t chunk;
280
281    chunk = area_location(ps, ps->current_area);
282
283    r = chunk_io(ps, ps->area, chunk, rw, 0);
284    if (r)
285        return r;
286
287    return 0;
288}
289
290static void zero_memory_area(struct pstore *ps)
291{
292    memset(ps->area, 0, ps->store->chunk_size << SECTOR_SHIFT);
293}
294
295static int zero_disk_area(struct pstore *ps, chunk_t area)
296{
297    return chunk_io(ps, ps->zero_area, area_location(ps, area), WRITE, 0);
298}
299
300static int read_header(struct pstore *ps, int *new_snapshot)
301{
302    int r;
303    struct disk_header *dh;
304    unsigned chunk_size;
305    int chunk_size_supplied = 1;
306    char *chunk_err;
307
308    /*
309     * Use default chunk size (or logical_block_size, if larger)
310     * if none supplied
311     */
312    if (!ps->store->chunk_size) {
313        ps->store->chunk_size = max(DM_CHUNK_SIZE_DEFAULT_SECTORS,
314            bdev_logical_block_size(dm_snap_cow(ps->store->snap)->
315                        bdev) >> 9);
316        ps->store->chunk_mask = ps->store->chunk_size - 1;
317        ps->store->chunk_shift = ffs(ps->store->chunk_size) - 1;
318        chunk_size_supplied = 0;
319    }
320
321    ps->io_client = dm_io_client_create();
322    if (IS_ERR(ps->io_client))
323        return PTR_ERR(ps->io_client);
324
325    r = alloc_area(ps);
326    if (r)
327        return r;
328
329    r = chunk_io(ps, ps->header_area, 0, READ, 1);
330    if (r)
331        goto bad;
332
333    dh = ps->header_area;
334
335    if (le32_to_cpu(dh->magic) == 0) {
336        *new_snapshot = 1;
337        return 0;
338    }
339
340    if (le32_to_cpu(dh->magic) != SNAP_MAGIC) {
341        DMWARN("Invalid or corrupt snapshot");
342        r = -ENXIO;
343        goto bad;
344    }
345
346    *new_snapshot = 0;
347    ps->valid = le32_to_cpu(dh->valid);
348    ps->version = le32_to_cpu(dh->version);
349    chunk_size = le32_to_cpu(dh->chunk_size);
350
351    if (ps->store->chunk_size == chunk_size)
352        return 0;
353
354    if (chunk_size_supplied)
355        DMWARN("chunk size %u in device metadata overrides "
356               "table chunk size of %u.",
357               chunk_size, ps->store->chunk_size);
358
359    /* We had a bogus chunk_size. Fix stuff up. */
360    free_area(ps);
361
362    r = dm_exception_store_set_chunk_size(ps->store, chunk_size,
363                          &chunk_err);
364    if (r) {
365        DMERR("invalid on-disk chunk size %u: %s.",
366              chunk_size, chunk_err);
367        return r;
368    }
369
370    r = alloc_area(ps);
371    return r;
372
373bad:
374    free_area(ps);
375    return r;
376}
377
378static int write_header(struct pstore *ps)
379{
380    struct disk_header *dh;
381
382    memset(ps->header_area, 0, ps->store->chunk_size << SECTOR_SHIFT);
383
384    dh = ps->header_area;
385    dh->magic = cpu_to_le32(SNAP_MAGIC);
386    dh->valid = cpu_to_le32(ps->valid);
387    dh->version = cpu_to_le32(ps->version);
388    dh->chunk_size = cpu_to_le32(ps->store->chunk_size);
389
390    return chunk_io(ps, ps->header_area, 0, WRITE, 1);
391}
392
393/*
394 * Access functions for the disk exceptions, these do the endian conversions.
395 */
396static struct disk_exception *get_exception(struct pstore *ps, uint32_t index)
397{
398    BUG_ON(index >= ps->exceptions_per_area);
399
400    return ((struct disk_exception *) ps->area) + index;
401}
402
403static void read_exception(struct pstore *ps,
404               uint32_t index, struct core_exception *result)
405{
406    struct disk_exception *de = get_exception(ps, index);
407
408    /* copy it */
409    result->old_chunk = le64_to_cpu(de->old_chunk);
410    result->new_chunk = le64_to_cpu(de->new_chunk);
411}
412
413static void write_exception(struct pstore *ps,
414                uint32_t index, struct core_exception *e)
415{
416    struct disk_exception *de = get_exception(ps, index);
417
418    /* copy it */
419    de->old_chunk = cpu_to_le64(e->old_chunk);
420    de->new_chunk = cpu_to_le64(e->new_chunk);
421}
422
423static void clear_exception(struct pstore *ps, uint32_t index)
424{
425    struct disk_exception *de = get_exception(ps, index);
426
427    /* clear it */
428    de->old_chunk = 0;
429    de->new_chunk = 0;
430}
431
432/*
433 * Registers the exceptions that are present in the current area.
434 * 'full' is filled in to indicate if the area has been
435 * filled.
436 */
437static int insert_exceptions(struct pstore *ps,
438                 int (*callback)(void *callback_context,
439                         chunk_t old, chunk_t new),
440                 void *callback_context,
441                 int *full)
442{
443    int r;
444    unsigned int i;
445    struct core_exception e;
446
447    /* presume the area is full */
448    *full = 1;
449
450    for (i = 0; i < ps->exceptions_per_area; i++) {
451        read_exception(ps, i, &e);
452
453        /*
454         * If the new_chunk is pointing at the start of
455         * the COW device, where the first metadata area
456         * is we know that we've hit the end of the
457         * exceptions. Therefore the area is not full.
458         */
459        if (e.new_chunk == 0LL) {
460            ps->current_committed = i;
461            *full = 0;
462            break;
463        }
464
465        /*
466         * Keep track of the start of the free chunks.
467         */
468        if (ps->next_free <= e.new_chunk)
469            ps->next_free = e.new_chunk + 1;
470
471        /*
472         * Otherwise we add the exception to the snapshot.
473         */
474        r = callback(callback_context, e.old_chunk, e.new_chunk);
475        if (r)
476            return r;
477    }
478
479    return 0;
480}
481
482static int read_exceptions(struct pstore *ps,
483               int (*callback)(void *callback_context, chunk_t old,
484                       chunk_t new),
485               void *callback_context)
486{
487    int r, full = 1;
488
489    /*
490     * Keeping reading chunks and inserting exceptions until
491     * we find a partially full area.
492     */
493    for (ps->current_area = 0; full; ps->current_area++) {
494        r = area_io(ps, READ);
495        if (r)
496            return r;
497
498        r = insert_exceptions(ps, callback, callback_context, &full);
499        if (r)
500            return r;
501    }
502
503    ps->current_area--;
504
505    return 0;
506}
507
508static struct pstore *get_info(struct dm_exception_store *store)
509{
510    return (struct pstore *) store->context;
511}
512
513static void persistent_usage(struct dm_exception_store *store,
514                 sector_t *total_sectors,
515                 sector_t *sectors_allocated,
516                 sector_t *metadata_sectors)
517{
518    struct pstore *ps = get_info(store);
519
520    *sectors_allocated = ps->next_free * store->chunk_size;
521    *total_sectors = get_dev_size(dm_snap_cow(store->snap)->bdev);
522
523    /*
524     * First chunk is the fixed header.
525     * Then there are (ps->current_area + 1) metadata chunks, each one
526     * separated from the next by ps->exceptions_per_area data chunks.
527     */
528    *metadata_sectors = (ps->current_area + 1 + NUM_SNAPSHOT_HDR_CHUNKS) *
529                store->chunk_size;
530}
531
532static void persistent_dtr(struct dm_exception_store *store)
533{
534    struct pstore *ps = get_info(store);
535
536    destroy_workqueue(ps->metadata_wq);
537
538    /* Created in read_header */
539    if (ps->io_client)
540        dm_io_client_destroy(ps->io_client);
541    free_area(ps);
542
543    /* Allocated in persistent_read_metadata */
544    if (ps->callbacks)
545        vfree(ps->callbacks);
546
547    kfree(ps);
548}
549
550static int persistent_read_metadata(struct dm_exception_store *store,
551                    int (*callback)(void *callback_context,
552                            chunk_t old, chunk_t new),
553                    void *callback_context)
554{
555    int r, uninitialized_var(new_snapshot);
556    struct pstore *ps = get_info(store);
557
558    /*
559     * Read the snapshot header.
560     */
561    r = read_header(ps, &new_snapshot);
562    if (r)
563        return r;
564
565    /*
566     * Now we know correct chunk_size, complete the initialisation.
567     */
568    ps->exceptions_per_area = (ps->store->chunk_size << SECTOR_SHIFT) /
569                  sizeof(struct disk_exception);
570    ps->callbacks = dm_vcalloc(ps->exceptions_per_area,
571                   sizeof(*ps->callbacks));
572    if (!ps->callbacks)
573        return -ENOMEM;
574
575    /*
576     * Do we need to setup a new snapshot ?
577     */
578    if (new_snapshot) {
579        r = write_header(ps);
580        if (r) {
581            DMWARN("write_header failed");
582            return r;
583        }
584
585        ps->current_area = 0;
586        zero_memory_area(ps);
587        r = zero_disk_area(ps, 0);
588        if (r)
589            DMWARN("zero_disk_area(0) failed");
590        return r;
591    }
592    /*
593     * Sanity checks.
594     */
595    if (ps->version != SNAPSHOT_DISK_VERSION) {
596        DMWARN("unable to handle snapshot disk version %d",
597               ps->version);
598        return -EINVAL;
599    }
600
601    /*
602     * Metadata are valid, but snapshot is invalidated
603     */
604    if (!ps->valid)
605        return 1;
606
607    /*
608     * Read the metadata.
609     */
610    r = read_exceptions(ps, callback, callback_context);
611
612    return r;
613}
614
615static int persistent_prepare_exception(struct dm_exception_store *store,
616                    struct dm_exception *e)
617{
618    struct pstore *ps = get_info(store);
619    uint32_t stride;
620    chunk_t next_free;
621    sector_t size = get_dev_size(dm_snap_cow(store->snap)->bdev);
622
623    /* Is there enough room ? */
624    if (size < ((ps->next_free + 1) * store->chunk_size))
625        return -ENOSPC;
626
627    e->new_chunk = ps->next_free;
628
629    /*
630     * Move onto the next free pending, making sure to take
631     * into account the location of the metadata chunks.
632     */
633    stride = (ps->exceptions_per_area + 1);
634    next_free = ++ps->next_free;
635    if (sector_div(next_free, stride) == 1)
636        ps->next_free++;
637
638    atomic_inc(&ps->pending_count);
639    return 0;
640}
641
642static void persistent_commit_exception(struct dm_exception_store *store,
643                    struct dm_exception *e,
644                    void (*callback) (void *, int success),
645                    void *callback_context)
646{
647    unsigned int i;
648    struct pstore *ps = get_info(store);
649    struct core_exception ce;
650    struct commit_callback *cb;
651
652    ce.old_chunk = e->old_chunk;
653    ce.new_chunk = e->new_chunk;
654    write_exception(ps, ps->current_committed++, &ce);
655
656    /*
657     * Add the callback to the back of the array. This code
658     * is the only place where the callback array is
659     * manipulated, and we know that it will never be called
660     * multiple times concurrently.
661     */
662    cb = ps->callbacks + ps->callback_count++;
663    cb->callback = callback;
664    cb->context = callback_context;
665
666    /*
667     * If there are exceptions in flight and we have not yet
668     * filled this metadata area there's nothing more to do.
669     */
670    if (!atomic_dec_and_test(&ps->pending_count) &&
671        (ps->current_committed != ps->exceptions_per_area))
672        return;
673
674    /*
675     * If we completely filled the current area, then wipe the next one.
676     */
677    if ((ps->current_committed == ps->exceptions_per_area) &&
678        zero_disk_area(ps, ps->current_area + 1))
679        ps->valid = 0;
680
681    /*
682     * Commit exceptions to disk.
683     */
684    if (ps->valid && area_io(ps, WRITE_FLUSH_FUA))
685        ps->valid = 0;
686
687    /*
688     * Advance to the next area if this one is full.
689     */
690    if (ps->current_committed == ps->exceptions_per_area) {
691        ps->current_committed = 0;
692        ps->current_area++;
693        zero_memory_area(ps);
694    }
695
696    for (i = 0; i < ps->callback_count; i++) {
697        cb = ps->callbacks + i;
698        cb->callback(cb->context, ps->valid);
699    }
700
701    ps->callback_count = 0;
702}
703
704static int persistent_prepare_merge(struct dm_exception_store *store,
705                    chunk_t *last_old_chunk,
706                    chunk_t *last_new_chunk)
707{
708    struct pstore *ps = get_info(store);
709    struct core_exception ce;
710    int nr_consecutive;
711    int r;
712
713    /*
714     * When current area is empty, move back to preceding area.
715     */
716    if (!ps->current_committed) {
717        /*
718         * Have we finished?
719         */
720        if (!ps->current_area)
721            return 0;
722
723        ps->current_area--;
724        r = area_io(ps, READ);
725        if (r < 0)
726            return r;
727        ps->current_committed = ps->exceptions_per_area;
728    }
729
730    read_exception(ps, ps->current_committed - 1, &ce);
731    *last_old_chunk = ce.old_chunk;
732    *last_new_chunk = ce.new_chunk;
733
734    /*
735     * Find number of consecutive chunks within the current area,
736     * working backwards.
737     */
738    for (nr_consecutive = 1; nr_consecutive < ps->current_committed;
739         nr_consecutive++) {
740        read_exception(ps, ps->current_committed - 1 - nr_consecutive,
741                   &ce);
742        if (ce.old_chunk != *last_old_chunk - nr_consecutive ||
743            ce.new_chunk != *last_new_chunk - nr_consecutive)
744            break;
745    }
746
747    return nr_consecutive;
748}
749
750static int persistent_commit_merge(struct dm_exception_store *store,
751                   int nr_merged)
752{
753    int r, i;
754    struct pstore *ps = get_info(store);
755
756    BUG_ON(nr_merged > ps->current_committed);
757
758    for (i = 0; i < nr_merged; i++)
759        clear_exception(ps, ps->current_committed - 1 - i);
760
761    r = area_io(ps, WRITE_FLUSH_FUA);
762    if (r < 0)
763        return r;
764
765    ps->current_committed -= nr_merged;
766
767    /*
768     * At this stage, only persistent_usage() uses ps->next_free, so
769     * we make no attempt to keep ps->next_free strictly accurate
770     * as exceptions may have been committed out-of-order originally.
771     * Once a snapshot has become merging, we set it to the value it
772     * would have held had all the exceptions been committed in order.
773     *
774     * ps->current_area does not get reduced by prepare_merge() until
775     * after commit_merge() has removed the nr_merged previous exceptions.
776     */
777    ps->next_free = area_location(ps, ps->current_area) +
778            ps->current_committed + 1;
779
780    return 0;
781}
782
783static void persistent_drop_snapshot(struct dm_exception_store *store)
784{
785    struct pstore *ps = get_info(store);
786
787    ps->valid = 0;
788    if (write_header(ps))
789        DMWARN("write header failed");
790}
791
792static int persistent_ctr(struct dm_exception_store *store,
793              unsigned argc, char **argv)
794{
795    struct pstore *ps;
796
797    /* allocate the pstore */
798    ps = kzalloc(sizeof(*ps), GFP_KERNEL);
799    if (!ps)
800        return -ENOMEM;
801
802    ps->store = store;
803    ps->valid = 1;
804    ps->version = SNAPSHOT_DISK_VERSION;
805    ps->area = NULL;
806    ps->zero_area = NULL;
807    ps->header_area = NULL;
808    ps->next_free = NUM_SNAPSHOT_HDR_CHUNKS + 1; /* header and 1st area */
809    ps->current_committed = 0;
810
811    ps->callback_count = 0;
812    atomic_set(&ps->pending_count, 0);
813    ps->callbacks = NULL;
814
815    ps->metadata_wq = alloc_workqueue("ksnaphd", WQ_MEM_RECLAIM, 0);
816    if (!ps->metadata_wq) {
817        kfree(ps);
818        DMERR("couldn't start header metadata update thread");
819        return -ENOMEM;
820    }
821
822    store->context = ps;
823
824    return 0;
825}
826
827static unsigned persistent_status(struct dm_exception_store *store,
828                  status_type_t status, char *result,
829                  unsigned maxlen)
830{
831    unsigned sz = 0;
832
833    switch (status) {
834    case STATUSTYPE_INFO:
835        break;
836    case STATUSTYPE_TABLE:
837        DMEMIT(" P %llu", (unsigned long long)store->chunk_size);
838    }
839
840    return sz;
841}
842
843static struct dm_exception_store_type _persistent_type = {
844    .name = "persistent",
845    .module = THIS_MODULE,
846    .ctr = persistent_ctr,
847    .dtr = persistent_dtr,
848    .read_metadata = persistent_read_metadata,
849    .prepare_exception = persistent_prepare_exception,
850    .commit_exception = persistent_commit_exception,
851    .prepare_merge = persistent_prepare_merge,
852    .commit_merge = persistent_commit_merge,
853    .drop_snapshot = persistent_drop_snapshot,
854    .usage = persistent_usage,
855    .status = persistent_status,
856};
857
858static struct dm_exception_store_type _persistent_compat_type = {
859    .name = "P",
860    .module = THIS_MODULE,
861    .ctr = persistent_ctr,
862    .dtr = persistent_dtr,
863    .read_metadata = persistent_read_metadata,
864    .prepare_exception = persistent_prepare_exception,
865    .commit_exception = persistent_commit_exception,
866    .prepare_merge = persistent_prepare_merge,
867    .commit_merge = persistent_commit_merge,
868    .drop_snapshot = persistent_drop_snapshot,
869    .usage = persistent_usage,
870    .status = persistent_status,
871};
872
873int dm_persistent_snapshot_init(void)
874{
875    int r;
876
877    r = dm_exception_store_type_register(&_persistent_type);
878    if (r) {
879        DMERR("Unable to register persistent exception store type");
880        return r;
881    }
882
883    r = dm_exception_store_type_register(&_persistent_compat_type);
884    if (r) {
885        DMERR("Unable to register old-style persistent exception "
886              "store type");
887        dm_exception_store_type_unregister(&_persistent_type);
888        return r;
889    }
890
891    return r;
892}
893
894void dm_persistent_snapshot_exit(void)
895{
896    dm_exception_store_type_unregister(&_persistent_type);
897    dm_exception_store_type_unregister(&_persistent_compat_type);
898}
899

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