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