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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);
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);
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}
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 "dm-bufio.h"
18
19#define DM_MSG_PREFIX "persistent snapshot"
20#define DM_CHUNK_SIZE_DEFAULT_SECTORS 32 /* 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 generic_make_request 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, uninitialized_var(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, REQ_PREFLUSH | REQ_FUA))
745 ps->valid = 0;
746
747 /*
748 * Advance to the next area if this one is full.
749 */
750 if (ps->current_committed == ps->exceptions_per_area) {
751 ps->current_committed = 0;
752 ps->current_area++;
753 zero_memory_area(ps);
754 }
755
756 for (i = 0; i < ps->callback_count; i++) {
757 cb = ps->callbacks + i;
758 cb->callback(cb->context, ps->valid);
759 }
760
761 ps->callback_count = 0;
762}
763
764static int persistent_prepare_merge(struct dm_exception_store *store,
765 chunk_t *last_old_chunk,
766 chunk_t *last_new_chunk)
767{
768 struct pstore *ps = get_info(store);
769 struct core_exception ce;
770 int nr_consecutive;
771 int r;
772
773 /*
774 * When current area is empty, move back to preceding area.
775 */
776 if (!ps->current_committed) {
777 /*
778 * Have we finished?
779 */
780 if (!ps->current_area)
781 return 0;
782
783 ps->current_area--;
784 r = area_io(ps, REQ_OP_READ, 0);
785 if (r < 0)
786 return r;
787 ps->current_committed = ps->exceptions_per_area;
788 }
789
790 read_exception(ps, ps->area, ps->current_committed - 1, &ce);
791 *last_old_chunk = ce.old_chunk;
792 *last_new_chunk = ce.new_chunk;
793
794 /*
795 * Find number of consecutive chunks within the current area,
796 * working backwards.
797 */
798 for (nr_consecutive = 1; nr_consecutive < ps->current_committed;
799 nr_consecutive++) {
800 read_exception(ps, ps->area,
801 ps->current_committed - 1 - nr_consecutive, &ce);
802 if (ce.old_chunk != *last_old_chunk - nr_consecutive ||
803 ce.new_chunk != *last_new_chunk - nr_consecutive)
804 break;
805 }
806
807 return nr_consecutive;
808}
809
810static int persistent_commit_merge(struct dm_exception_store *store,
811 int nr_merged)
812{
813 int r, i;
814 struct pstore *ps = get_info(store);
815
816 BUG_ON(nr_merged > ps->current_committed);
817
818 for (i = 0; i < nr_merged; i++)
819 clear_exception(ps, ps->current_committed - 1 - i);
820
821 r = area_io(ps, REQ_OP_WRITE, REQ_PREFLUSH | REQ_FUA);
822 if (r < 0)
823 return r;
824
825 ps->current_committed -= nr_merged;
826
827 /*
828 * At this stage, only persistent_usage() uses ps->next_free, so
829 * we make no attempt to keep ps->next_free strictly accurate
830 * as exceptions may have been committed out-of-order originally.
831 * Once a snapshot has become merging, we set it to the value it
832 * would have held had all the exceptions been committed in order.
833 *
834 * ps->current_area does not get reduced by prepare_merge() until
835 * after commit_merge() has removed the nr_merged previous exceptions.
836 */
837 ps->next_free = area_location(ps, ps->current_area) +
838 ps->current_committed + 1;
839
840 return 0;
841}
842
843static void persistent_drop_snapshot(struct dm_exception_store *store)
844{
845 struct pstore *ps = get_info(store);
846
847 ps->valid = 0;
848 if (write_header(ps))
849 DMWARN("write header failed");
850}
851
852static int persistent_ctr(struct dm_exception_store *store, char *options)
853{
854 struct pstore *ps;
855 int r;
856
857 /* allocate the pstore */
858 ps = kzalloc(sizeof(*ps), GFP_KERNEL);
859 if (!ps)
860 return -ENOMEM;
861
862 ps->store = store;
863 ps->valid = 1;
864 ps->version = SNAPSHOT_DISK_VERSION;
865 ps->area = NULL;
866 ps->zero_area = NULL;
867 ps->header_area = NULL;
868 ps->next_free = NUM_SNAPSHOT_HDR_CHUNKS + 1; /* header and 1st area */
869 ps->current_committed = 0;
870
871 ps->callback_count = 0;
872 atomic_set(&ps->pending_count, 0);
873 ps->callbacks = NULL;
874
875 ps->metadata_wq = alloc_workqueue("ksnaphd", WQ_MEM_RECLAIM, 0);
876 if (!ps->metadata_wq) {
877 DMERR("couldn't start header metadata update thread");
878 r = -ENOMEM;
879 goto err_workqueue;
880 }
881
882 if (options) {
883 char overflow = toupper(options[0]);
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 persistent_status(struct dm_exception_store *store,
906 status_type_t status, char *result,
907 unsigned maxlen)
908{
909 unsigned 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 }
918
919 return sz;
920}
921
922static struct dm_exception_store_type _persistent_type = {
923 .name = "persistent",
924 .module = THIS_MODULE,
925 .ctr = persistent_ctr,
926 .dtr = persistent_dtr,
927 .read_metadata = persistent_read_metadata,
928 .prepare_exception = persistent_prepare_exception,
929 .commit_exception = persistent_commit_exception,
930 .prepare_merge = persistent_prepare_merge,
931 .commit_merge = persistent_commit_merge,
932 .drop_snapshot = persistent_drop_snapshot,
933 .usage = persistent_usage,
934 .status = persistent_status,
935};
936
937static struct dm_exception_store_type _persistent_compat_type = {
938 .name = "P",
939 .module = THIS_MODULE,
940 .ctr = persistent_ctr,
941 .dtr = persistent_dtr,
942 .read_metadata = persistent_read_metadata,
943 .prepare_exception = persistent_prepare_exception,
944 .commit_exception = persistent_commit_exception,
945 .prepare_merge = persistent_prepare_merge,
946 .commit_merge = persistent_commit_merge,
947 .drop_snapshot = persistent_drop_snapshot,
948 .usage = persistent_usage,
949 .status = persistent_status,
950};
951
952int dm_persistent_snapshot_init(void)
953{
954 int r;
955
956 r = dm_exception_store_type_register(&_persistent_type);
957 if (r) {
958 DMERR("Unable to register persistent exception store type");
959 return r;
960 }
961
962 r = dm_exception_store_type_register(&_persistent_compat_type);
963 if (r) {
964 DMERR("Unable to register old-style persistent exception "
965 "store type");
966 dm_exception_store_type_unregister(&_persistent_type);
967 return r;
968 }
969
970 return r;
971}
972
973void dm_persistent_snapshot_exit(void)
974{
975 dm_exception_store_type_unregister(&_persistent_type);
976 dm_exception_store_type_unregister(&_persistent_compat_type);
977}