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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}
1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Copyright (C) 2001-2002 Sistina Software (UK) Limited.
4 * Copyright (C) 2006-2008 Red Hat GmbH
5 *
6 * This file is released under the GPL.
7 */
8
9#include "dm-exception-store.h"
10
11#include <linux/ctype.h>
12#include <linux/mm.h>
13#include <linux/pagemap.h>
14#include <linux/vmalloc.h>
15#include <linux/export.h>
16#include <linux/slab.h>
17#include <linux/dm-io.h>
18#include <linux/dm-bufio.h>
19
20#define DM_MSG_PREFIX "persistent snapshot"
21#define DM_CHUNK_SIZE_DEFAULT_SECTORS 32U /* 16KB */
22
23#define DM_PREFETCH_CHUNKS 12
24
25/*
26 *---------------------------------------------------------------
27 * Persistent snapshots, by persistent we mean that the snapshot
28 * will survive a reboot.
29 *---------------------------------------------------------------
30 */
31
32/*
33 * We need to store a record of which parts of the origin have
34 * been copied to the snapshot device. The snapshot code
35 * requires that we copy exception chunks to chunk aligned areas
36 * of the COW store. It makes sense therefore, to store the
37 * metadata in chunk size blocks.
38 *
39 * There is no backward or forward compatibility implemented,
40 * snapshots with different disk versions than the kernel will
41 * not be usable. It is expected that "lvcreate" will blank out
42 * the start of a fresh COW device before calling the snapshot
43 * constructor.
44 *
45 * The first chunk of the COW device just contains the header.
46 * After this there is a chunk filled with exception metadata,
47 * followed by as many exception chunks as can fit in the
48 * metadata areas.
49 *
50 * All on disk structures are in little-endian format. The end
51 * of the exceptions info is indicated by an exception with a
52 * new_chunk of 0, which is invalid since it would point to the
53 * header chunk.
54 */
55
56/*
57 * Magic for persistent snapshots: "SnAp" - Feeble isn't it.
58 */
59#define SNAP_MAGIC 0x70416e53
60
61/*
62 * The on-disk version of the metadata.
63 */
64#define SNAPSHOT_DISK_VERSION 1
65
66#define NUM_SNAPSHOT_HDR_CHUNKS 1
67
68struct disk_header {
69 __le32 magic;
70
71 /*
72 * Is this snapshot valid. There is no way of recovering
73 * an invalid snapshot.
74 */
75 __le32 valid;
76
77 /*
78 * Simple, incrementing version. no backward
79 * compatibility.
80 */
81 __le32 version;
82
83 /* In sectors */
84 __le32 chunk_size;
85} __packed;
86
87struct disk_exception {
88 __le64 old_chunk;
89 __le64 new_chunk;
90} __packed;
91
92struct core_exception {
93 uint64_t old_chunk;
94 uint64_t new_chunk;
95};
96
97struct commit_callback {
98 void (*callback)(void *ref, int success);
99 void *context;
100};
101
102/*
103 * The top level structure for a persistent exception store.
104 */
105struct pstore {
106 struct dm_exception_store *store;
107 int version;
108 int valid;
109 uint32_t exceptions_per_area;
110
111 /*
112 * Now that we have an asynchronous kcopyd there is no
113 * need for large chunk sizes, so it wont hurt to have a
114 * whole chunks worth of metadata in memory at once.
115 */
116 void *area;
117
118 /*
119 * An area of zeros used to clear the next area.
120 */
121 void *zero_area;
122
123 /*
124 * An area used for header. The header can be written
125 * concurrently with metadata (when invalidating the snapshot),
126 * so it needs a separate buffer.
127 */
128 void *header_area;
129
130 /*
131 * Used to keep track of which metadata area the data in
132 * 'chunk' refers to.
133 */
134 chunk_t current_area;
135
136 /*
137 * The next free chunk for an exception.
138 *
139 * When creating exceptions, all the chunks here and above are
140 * free. It holds the next chunk to be allocated. On rare
141 * occasions (e.g. after a system crash) holes can be left in
142 * the exception store because chunks can be committed out of
143 * order.
144 *
145 * When merging exceptions, it does not necessarily mean all the
146 * chunks here and above are free. It holds the value it would
147 * have held if all chunks had been committed in order of
148 * allocation. Consequently the value may occasionally be
149 * slightly too low, but since it's only used for 'status' and
150 * it can never reach its minimum value too early this doesn't
151 * matter.
152 */
153
154 chunk_t next_free;
155
156 /*
157 * The index of next free exception in the current
158 * metadata area.
159 */
160 uint32_t current_committed;
161
162 atomic_t pending_count;
163 uint32_t callback_count;
164 struct commit_callback *callbacks;
165 struct dm_io_client *io_client;
166
167 struct workqueue_struct *metadata_wq;
168};
169
170static int alloc_area(struct pstore *ps)
171{
172 int r = -ENOMEM;
173 size_t len;
174
175 len = ps->store->chunk_size << SECTOR_SHIFT;
176
177 /*
178 * Allocate the chunk_size block of memory that will hold
179 * a single metadata area.
180 */
181 ps->area = vmalloc(len);
182 if (!ps->area)
183 goto err_area;
184
185 ps->zero_area = vzalloc(len);
186 if (!ps->zero_area)
187 goto err_zero_area;
188
189 ps->header_area = vmalloc(len);
190 if (!ps->header_area)
191 goto err_header_area;
192
193 return 0;
194
195err_header_area:
196 vfree(ps->zero_area);
197
198err_zero_area:
199 vfree(ps->area);
200
201err_area:
202 return r;
203}
204
205static void free_area(struct pstore *ps)
206{
207 vfree(ps->area);
208 ps->area = NULL;
209 vfree(ps->zero_area);
210 ps->zero_area = NULL;
211 vfree(ps->header_area);
212 ps->header_area = NULL;
213}
214
215struct mdata_req {
216 struct dm_io_region *where;
217 struct dm_io_request *io_req;
218 struct work_struct work;
219 int result;
220};
221
222static void do_metadata(struct work_struct *work)
223{
224 struct mdata_req *req = container_of(work, struct mdata_req, work);
225
226 req->result = dm_io(req->io_req, 1, req->where, NULL, IOPRIO_DEFAULT);
227}
228
229/*
230 * Read or write a chunk aligned and sized block of data from a device.
231 */
232static int chunk_io(struct pstore *ps, void *area, chunk_t chunk, blk_opf_t opf,
233 int metadata)
234{
235 struct dm_io_region where = {
236 .bdev = dm_snap_cow(ps->store->snap)->bdev,
237 .sector = ps->store->chunk_size * chunk,
238 .count = ps->store->chunk_size,
239 };
240 struct dm_io_request io_req = {
241 .bi_opf = opf,
242 .mem.type = DM_IO_VMA,
243 .mem.ptr.vma = area,
244 .client = ps->io_client,
245 .notify.fn = NULL,
246 };
247 struct mdata_req req;
248
249 if (!metadata)
250 return dm_io(&io_req, 1, &where, NULL, IOPRIO_DEFAULT);
251
252 req.where = &where;
253 req.io_req = &io_req;
254
255 /*
256 * Issue the synchronous I/O from a different thread
257 * to avoid submit_bio_noacct recursion.
258 */
259 INIT_WORK_ONSTACK(&req.work, do_metadata);
260 queue_work(ps->metadata_wq, &req.work);
261 flush_workqueue(ps->metadata_wq);
262 destroy_work_on_stack(&req.work);
263
264 return req.result;
265}
266
267/*
268 * Convert a metadata area index to a chunk index.
269 */
270static chunk_t area_location(struct pstore *ps, chunk_t area)
271{
272 return NUM_SNAPSHOT_HDR_CHUNKS + ((ps->exceptions_per_area + 1) * area);
273}
274
275static void skip_metadata(struct pstore *ps)
276{
277 uint32_t stride = ps->exceptions_per_area + 1;
278 chunk_t next_free = ps->next_free;
279
280 if (sector_div(next_free, stride) == NUM_SNAPSHOT_HDR_CHUNKS)
281 ps->next_free++;
282}
283
284/*
285 * Read or write a metadata area. Remembering to skip the first
286 * chunk which holds the header.
287 */
288static int area_io(struct pstore *ps, blk_opf_t opf)
289{
290 chunk_t chunk = area_location(ps, ps->current_area);
291
292 return chunk_io(ps, ps->area, chunk, opf, 0);
293}
294
295static void zero_memory_area(struct pstore *ps)
296{
297 memset(ps->area, 0, ps->store->chunk_size << SECTOR_SHIFT);
298}
299
300static int zero_disk_area(struct pstore *ps, chunk_t area)
301{
302 return chunk_io(ps, ps->zero_area, area_location(ps, area),
303 REQ_OP_WRITE, 0);
304}
305
306static int read_header(struct pstore *ps, int *new_snapshot)
307{
308 int r;
309 struct disk_header *dh;
310 unsigned int chunk_size;
311 int chunk_size_supplied = 1;
312 char *chunk_err;
313
314 /*
315 * Use default chunk size (or logical_block_size, if larger)
316 * if none supplied
317 */
318 if (!ps->store->chunk_size) {
319 ps->store->chunk_size = max(DM_CHUNK_SIZE_DEFAULT_SECTORS,
320 bdev_logical_block_size(dm_snap_cow(ps->store->snap)->
321 bdev) >> 9);
322 ps->store->chunk_mask = ps->store->chunk_size - 1;
323 ps->store->chunk_shift = __ffs(ps->store->chunk_size);
324 chunk_size_supplied = 0;
325 }
326
327 ps->io_client = dm_io_client_create();
328 if (IS_ERR(ps->io_client))
329 return PTR_ERR(ps->io_client);
330
331 r = alloc_area(ps);
332 if (r)
333 return r;
334
335 r = chunk_io(ps, ps->header_area, 0, REQ_OP_READ, 1);
336 if (r)
337 goto bad;
338
339 dh = ps->header_area;
340
341 if (le32_to_cpu(dh->magic) == 0) {
342 *new_snapshot = 1;
343 return 0;
344 }
345
346 if (le32_to_cpu(dh->magic) != SNAP_MAGIC) {
347 DMWARN("Invalid or corrupt snapshot");
348 r = -ENXIO;
349 goto bad;
350 }
351
352 *new_snapshot = 0;
353 ps->valid = le32_to_cpu(dh->valid);
354 ps->version = le32_to_cpu(dh->version);
355 chunk_size = le32_to_cpu(dh->chunk_size);
356
357 if (ps->store->chunk_size == chunk_size)
358 return 0;
359
360 if (chunk_size_supplied)
361 DMWARN("chunk size %u in device metadata overrides table chunk size of %u.",
362 chunk_size, ps->store->chunk_size);
363
364 /* We had a bogus chunk_size. Fix stuff up. */
365 free_area(ps);
366
367 r = dm_exception_store_set_chunk_size(ps->store, chunk_size,
368 &chunk_err);
369 if (r) {
370 DMERR("invalid on-disk chunk size %u: %s.",
371 chunk_size, chunk_err);
372 return r;
373 }
374
375 r = alloc_area(ps);
376 return r;
377
378bad:
379 free_area(ps);
380 return r;
381}
382
383static int write_header(struct pstore *ps)
384{
385 struct disk_header *dh;
386
387 memset(ps->header_area, 0, ps->store->chunk_size << SECTOR_SHIFT);
388
389 dh = ps->header_area;
390 dh->magic = cpu_to_le32(SNAP_MAGIC);
391 dh->valid = cpu_to_le32(ps->valid);
392 dh->version = cpu_to_le32(ps->version);
393 dh->chunk_size = cpu_to_le32(ps->store->chunk_size);
394
395 return chunk_io(ps, ps->header_area, 0, REQ_OP_WRITE, 1);
396}
397
398/*
399 * Access functions for the disk exceptions, these do the endian conversions.
400 */
401static struct disk_exception *get_exception(struct pstore *ps, void *ps_area,
402 uint32_t index)
403{
404 BUG_ON(index >= ps->exceptions_per_area);
405
406 return ((struct disk_exception *) ps_area) + index;
407}
408
409static void read_exception(struct pstore *ps, void *ps_area,
410 uint32_t index, struct core_exception *result)
411{
412 struct disk_exception *de = get_exception(ps, ps_area, index);
413
414 /* copy it */
415 result->old_chunk = le64_to_cpu(de->old_chunk);
416 result->new_chunk = le64_to_cpu(de->new_chunk);
417}
418
419static void write_exception(struct pstore *ps,
420 uint32_t index, struct core_exception *e)
421{
422 struct disk_exception *de = get_exception(ps, ps->area, index);
423
424 /* copy it */
425 de->old_chunk = cpu_to_le64(e->old_chunk);
426 de->new_chunk = cpu_to_le64(e->new_chunk);
427}
428
429static void clear_exception(struct pstore *ps, uint32_t index)
430{
431 struct disk_exception *de = get_exception(ps, ps->area, index);
432
433 /* clear it */
434 de->old_chunk = 0;
435 de->new_chunk = 0;
436}
437
438/*
439 * Registers the exceptions that are present in the current area.
440 * 'full' is filled in to indicate if the area has been
441 * filled.
442 */
443static int insert_exceptions(struct pstore *ps, void *ps_area,
444 int (*callback)(void *callback_context,
445 chunk_t old, chunk_t new),
446 void *callback_context,
447 int *full)
448{
449 int r;
450 unsigned int i;
451 struct core_exception e;
452
453 /* presume the area is full */
454 *full = 1;
455
456 for (i = 0; i < ps->exceptions_per_area; i++) {
457 read_exception(ps, ps_area, i, &e);
458
459 /*
460 * If the new_chunk is pointing at the start of
461 * the COW device, where the first metadata area
462 * is we know that we've hit the end of the
463 * exceptions. Therefore the area is not full.
464 */
465 if (e.new_chunk == 0LL) {
466 ps->current_committed = i;
467 *full = 0;
468 break;
469 }
470
471 /*
472 * Keep track of the start of the free chunks.
473 */
474 if (ps->next_free <= e.new_chunk)
475 ps->next_free = e.new_chunk + 1;
476
477 /*
478 * Otherwise we add the exception to the snapshot.
479 */
480 r = callback(callback_context, e.old_chunk, e.new_chunk);
481 if (r)
482 return r;
483 }
484
485 return 0;
486}
487
488static int read_exceptions(struct pstore *ps,
489 int (*callback)(void *callback_context, chunk_t old,
490 chunk_t new),
491 void *callback_context)
492{
493 int r, full = 1;
494 struct dm_bufio_client *client;
495 chunk_t prefetch_area = 0;
496
497 client = dm_bufio_client_create(dm_snap_cow(ps->store->snap)->bdev,
498 ps->store->chunk_size << SECTOR_SHIFT,
499 1, 0, NULL, NULL, 0);
500
501 if (IS_ERR(client))
502 return PTR_ERR(client);
503
504 /*
505 * Setup for one current buffer + desired readahead buffers.
506 */
507 dm_bufio_set_minimum_buffers(client, 1 + DM_PREFETCH_CHUNKS);
508
509 /*
510 * Keeping reading chunks and inserting exceptions until
511 * we find a partially full area.
512 */
513 for (ps->current_area = 0; full; ps->current_area++) {
514 struct dm_buffer *bp;
515 void *area;
516 chunk_t chunk;
517
518 if (unlikely(prefetch_area < ps->current_area))
519 prefetch_area = ps->current_area;
520
521 if (DM_PREFETCH_CHUNKS) {
522 do {
523 chunk_t pf_chunk = area_location(ps, prefetch_area);
524
525 if (unlikely(pf_chunk >= dm_bufio_get_device_size(client)))
526 break;
527 dm_bufio_prefetch(client, pf_chunk, 1);
528 prefetch_area++;
529 if (unlikely(!prefetch_area))
530 break;
531 } while (prefetch_area <= ps->current_area + DM_PREFETCH_CHUNKS);
532 }
533
534 chunk = area_location(ps, ps->current_area);
535
536 area = dm_bufio_read(client, chunk, &bp);
537 if (IS_ERR(area)) {
538 r = PTR_ERR(area);
539 goto ret_destroy_bufio;
540 }
541
542 r = insert_exceptions(ps, area, callback, callback_context,
543 &full);
544
545 if (!full)
546 memcpy(ps->area, area, ps->store->chunk_size << SECTOR_SHIFT);
547
548 dm_bufio_release(bp);
549
550 dm_bufio_forget(client, chunk);
551
552 if (unlikely(r))
553 goto ret_destroy_bufio;
554 }
555
556 ps->current_area--;
557
558 skip_metadata(ps);
559
560 r = 0;
561
562ret_destroy_bufio:
563 dm_bufio_client_destroy(client);
564
565 return r;
566}
567
568static struct pstore *get_info(struct dm_exception_store *store)
569{
570 return store->context;
571}
572
573static void persistent_usage(struct dm_exception_store *store,
574 sector_t *total_sectors,
575 sector_t *sectors_allocated,
576 sector_t *metadata_sectors)
577{
578 struct pstore *ps = get_info(store);
579
580 *sectors_allocated = ps->next_free * store->chunk_size;
581 *total_sectors = get_dev_size(dm_snap_cow(store->snap)->bdev);
582
583 /*
584 * First chunk is the fixed header.
585 * Then there are (ps->current_area + 1) metadata chunks, each one
586 * separated from the next by ps->exceptions_per_area data chunks.
587 */
588 *metadata_sectors = (ps->current_area + 1 + NUM_SNAPSHOT_HDR_CHUNKS) *
589 store->chunk_size;
590}
591
592static void persistent_dtr(struct dm_exception_store *store)
593{
594 struct pstore *ps = get_info(store);
595
596 destroy_workqueue(ps->metadata_wq);
597
598 /* Created in read_header */
599 if (ps->io_client)
600 dm_io_client_destroy(ps->io_client);
601 free_area(ps);
602
603 /* Allocated in persistent_read_metadata */
604 kvfree(ps->callbacks);
605
606 kfree(ps);
607}
608
609static int persistent_read_metadata(struct dm_exception_store *store,
610 int (*callback)(void *callback_context,
611 chunk_t old, chunk_t new),
612 void *callback_context)
613{
614 int r, new_snapshot;
615 struct pstore *ps = get_info(store);
616
617 /*
618 * Read the snapshot header.
619 */
620 r = read_header(ps, &new_snapshot);
621 if (r)
622 return r;
623
624 /*
625 * Now we know correct chunk_size, complete the initialisation.
626 */
627 ps->exceptions_per_area = (ps->store->chunk_size << SECTOR_SHIFT) /
628 sizeof(struct disk_exception);
629 ps->callbacks = kvcalloc(ps->exceptions_per_area,
630 sizeof(*ps->callbacks), GFP_KERNEL);
631 if (!ps->callbacks)
632 return -ENOMEM;
633
634 /*
635 * Do we need to setup a new snapshot ?
636 */
637 if (new_snapshot) {
638 r = write_header(ps);
639 if (r) {
640 DMWARN("write_header failed");
641 return r;
642 }
643
644 ps->current_area = 0;
645 zero_memory_area(ps);
646 r = zero_disk_area(ps, 0);
647 if (r)
648 DMWARN("zero_disk_area(0) failed");
649 return r;
650 }
651 /*
652 * Sanity checks.
653 */
654 if (ps->version != SNAPSHOT_DISK_VERSION) {
655 DMWARN("unable to handle snapshot disk version %d",
656 ps->version);
657 return -EINVAL;
658 }
659
660 /*
661 * Metadata are valid, but snapshot is invalidated
662 */
663 if (!ps->valid)
664 return 1;
665
666 /*
667 * Read the metadata.
668 */
669 r = read_exceptions(ps, callback, callback_context);
670
671 return r;
672}
673
674static int persistent_prepare_exception(struct dm_exception_store *store,
675 struct dm_exception *e)
676{
677 struct pstore *ps = get_info(store);
678 sector_t size = get_dev_size(dm_snap_cow(store->snap)->bdev);
679
680 /* Is there enough room ? */
681 if (size < ((ps->next_free + 1) * store->chunk_size))
682 return -ENOSPC;
683
684 e->new_chunk = ps->next_free;
685
686 /*
687 * Move onto the next free pending, making sure to take
688 * into account the location of the metadata chunks.
689 */
690 ps->next_free++;
691 skip_metadata(ps);
692
693 atomic_inc(&ps->pending_count);
694 return 0;
695}
696
697static void persistent_commit_exception(struct dm_exception_store *store,
698 struct dm_exception *e, int valid,
699 void (*callback)(void *, int success),
700 void *callback_context)
701{
702 unsigned int i;
703 struct pstore *ps = get_info(store);
704 struct core_exception ce;
705 struct commit_callback *cb;
706
707 if (!valid)
708 ps->valid = 0;
709
710 ce.old_chunk = e->old_chunk;
711 ce.new_chunk = e->new_chunk;
712 write_exception(ps, ps->current_committed++, &ce);
713
714 /*
715 * Add the callback to the back of the array. This code
716 * is the only place where the callback array is
717 * manipulated, and we know that it will never be called
718 * multiple times concurrently.
719 */
720 cb = ps->callbacks + ps->callback_count++;
721 cb->callback = callback;
722 cb->context = callback_context;
723
724 /*
725 * If there are exceptions in flight and we have not yet
726 * filled this metadata area there's nothing more to do.
727 */
728 if (!atomic_dec_and_test(&ps->pending_count) &&
729 (ps->current_committed != ps->exceptions_per_area))
730 return;
731
732 /*
733 * If we completely filled the current area, then wipe the next one.
734 */
735 if ((ps->current_committed == ps->exceptions_per_area) &&
736 zero_disk_area(ps, ps->current_area + 1))
737 ps->valid = 0;
738
739 /*
740 * Commit exceptions to disk.
741 */
742 if (ps->valid && area_io(ps, REQ_OP_WRITE | REQ_PREFLUSH | REQ_FUA |
743 REQ_SYNC))
744 ps->valid = 0;
745
746 /*
747 * Advance to the next area if this one is full.
748 */
749 if (ps->current_committed == ps->exceptions_per_area) {
750 ps->current_committed = 0;
751 ps->current_area++;
752 zero_memory_area(ps);
753 }
754
755 for (i = 0; i < ps->callback_count; i++) {
756 cb = ps->callbacks + i;
757 cb->callback(cb->context, ps->valid);
758 }
759
760 ps->callback_count = 0;
761}
762
763static int persistent_prepare_merge(struct dm_exception_store *store,
764 chunk_t *last_old_chunk,
765 chunk_t *last_new_chunk)
766{
767 struct pstore *ps = get_info(store);
768 struct core_exception ce;
769 int nr_consecutive;
770 int r;
771
772 /*
773 * When current area is empty, move back to preceding area.
774 */
775 if (!ps->current_committed) {
776 /*
777 * Have we finished?
778 */
779 if (!ps->current_area)
780 return 0;
781
782 ps->current_area--;
783 r = area_io(ps, REQ_OP_READ);
784 if (r < 0)
785 return r;
786 ps->current_committed = ps->exceptions_per_area;
787 }
788
789 read_exception(ps, ps->area, ps->current_committed - 1, &ce);
790 *last_old_chunk = ce.old_chunk;
791 *last_new_chunk = ce.new_chunk;
792
793 /*
794 * Find number of consecutive chunks within the current area,
795 * working backwards.
796 */
797 for (nr_consecutive = 1; nr_consecutive < ps->current_committed;
798 nr_consecutive++) {
799 read_exception(ps, ps->area,
800 ps->current_committed - 1 - nr_consecutive, &ce);
801 if (ce.old_chunk != *last_old_chunk - nr_consecutive ||
802 ce.new_chunk != *last_new_chunk - nr_consecutive)
803 break;
804 }
805
806 return nr_consecutive;
807}
808
809static int persistent_commit_merge(struct dm_exception_store *store,
810 int nr_merged)
811{
812 int r, i;
813 struct pstore *ps = get_info(store);
814
815 BUG_ON(nr_merged > ps->current_committed);
816
817 for (i = 0; i < nr_merged; i++)
818 clear_exception(ps, ps->current_committed - 1 - i);
819
820 r = area_io(ps, REQ_OP_WRITE | REQ_PREFLUSH | REQ_FUA);
821 if (r < 0)
822 return r;
823
824 ps->current_committed -= nr_merged;
825
826 /*
827 * At this stage, only persistent_usage() uses ps->next_free, so
828 * we make no attempt to keep ps->next_free strictly accurate
829 * as exceptions may have been committed out-of-order originally.
830 * Once a snapshot has become merging, we set it to the value it
831 * would have held had all the exceptions been committed in order.
832 *
833 * ps->current_area does not get reduced by prepare_merge() until
834 * after commit_merge() has removed the nr_merged previous exceptions.
835 */
836 ps->next_free = area_location(ps, ps->current_area) +
837 ps->current_committed + 1;
838
839 return 0;
840}
841
842static void persistent_drop_snapshot(struct dm_exception_store *store)
843{
844 struct pstore *ps = get_info(store);
845
846 ps->valid = 0;
847 if (write_header(ps))
848 DMWARN("write header failed");
849}
850
851static int persistent_ctr(struct dm_exception_store *store, char *options)
852{
853 struct pstore *ps;
854 int r;
855
856 /* allocate the pstore */
857 ps = kzalloc(sizeof(*ps), GFP_KERNEL);
858 if (!ps)
859 return -ENOMEM;
860
861 ps->store = store;
862 ps->valid = 1;
863 ps->version = SNAPSHOT_DISK_VERSION;
864 ps->area = NULL;
865 ps->zero_area = NULL;
866 ps->header_area = NULL;
867 ps->next_free = NUM_SNAPSHOT_HDR_CHUNKS + 1; /* header and 1st area */
868 ps->current_committed = 0;
869
870 ps->callback_count = 0;
871 atomic_set(&ps->pending_count, 0);
872 ps->callbacks = NULL;
873
874 ps->metadata_wq = alloc_workqueue("ksnaphd", WQ_MEM_RECLAIM, 0);
875 if (!ps->metadata_wq) {
876 DMERR("couldn't start header metadata update thread");
877 r = -ENOMEM;
878 goto err_workqueue;
879 }
880
881 if (options) {
882 char overflow = toupper(options[0]);
883
884 if (overflow == 'O')
885 store->userspace_supports_overflow = true;
886 else {
887 DMERR("Unsupported persistent store option: %s", options);
888 r = -EINVAL;
889 goto err_options;
890 }
891 }
892
893 store->context = ps;
894
895 return 0;
896
897err_options:
898 destroy_workqueue(ps->metadata_wq);
899err_workqueue:
900 kfree(ps);
901
902 return r;
903}
904
905static unsigned int persistent_status(struct dm_exception_store *store,
906 status_type_t status, char *result,
907 unsigned int maxlen)
908{
909 unsigned int sz = 0;
910
911 switch (status) {
912 case STATUSTYPE_INFO:
913 break;
914 case STATUSTYPE_TABLE:
915 DMEMIT(" %s %llu", store->userspace_supports_overflow ? "PO" : "P",
916 (unsigned long long)store->chunk_size);
917 break;
918 case STATUSTYPE_IMA:
919 *result = '\0';
920 break;
921 }
922
923 return sz;
924}
925
926static struct dm_exception_store_type _persistent_type = {
927 .name = "persistent",
928 .module = THIS_MODULE,
929 .ctr = persistent_ctr,
930 .dtr = persistent_dtr,
931 .read_metadata = persistent_read_metadata,
932 .prepare_exception = persistent_prepare_exception,
933 .commit_exception = persistent_commit_exception,
934 .prepare_merge = persistent_prepare_merge,
935 .commit_merge = persistent_commit_merge,
936 .drop_snapshot = persistent_drop_snapshot,
937 .usage = persistent_usage,
938 .status = persistent_status,
939};
940
941static struct dm_exception_store_type _persistent_compat_type = {
942 .name = "P",
943 .module = THIS_MODULE,
944 .ctr = persistent_ctr,
945 .dtr = persistent_dtr,
946 .read_metadata = persistent_read_metadata,
947 .prepare_exception = persistent_prepare_exception,
948 .commit_exception = persistent_commit_exception,
949 .prepare_merge = persistent_prepare_merge,
950 .commit_merge = persistent_commit_merge,
951 .drop_snapshot = persistent_drop_snapshot,
952 .usage = persistent_usage,
953 .status = persistent_status,
954};
955
956int dm_persistent_snapshot_init(void)
957{
958 int r;
959
960 r = dm_exception_store_type_register(&_persistent_type);
961 if (r) {
962 DMERR("Unable to register persistent exception store type");
963 return r;
964 }
965
966 r = dm_exception_store_type_register(&_persistent_compat_type);
967 if (r) {
968 DMERR("Unable to register old-style persistent exception store type");
969 dm_exception_store_type_unregister(&_persistent_type);
970 return r;
971 }
972
973 return r;
974}
975
976void dm_persistent_snapshot_exit(void)
977{
978 dm_exception_store_type_unregister(&_persistent_type);
979 dm_exception_store_type_unregister(&_persistent_compat_type);
980}