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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/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, blk_opf_t opf,
230 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_opf = opf,
239 .mem.type = DM_IO_VMA,
240 .mem.ptr.vma = area,
241 .client = ps->io_client,
242 .notify.fn = NULL,
243 };
244 struct mdata_req req;
245
246 if (!metadata)
247 return dm_io(&io_req, 1, &where, NULL);
248
249 req.where = &where;
250 req.io_req = &io_req;
251
252 /*
253 * Issue the synchronous I/O from a different thread
254 * to avoid submit_bio_noacct recursion.
255 */
256 INIT_WORK_ONSTACK(&req.work, do_metadata);
257 queue_work(ps->metadata_wq, &req.work);
258 flush_workqueue(ps->metadata_wq);
259 destroy_work_on_stack(&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
272static void skip_metadata(struct pstore *ps)
273{
274 uint32_t stride = ps->exceptions_per_area + 1;
275 chunk_t next_free = ps->next_free;
276 if (sector_div(next_free, stride) == NUM_SNAPSHOT_HDR_CHUNKS)
277 ps->next_free++;
278}
279
280/*
281 * Read or write a metadata area. Remembering to skip the first
282 * chunk which holds the header.
283 */
284static int area_io(struct pstore *ps, blk_opf_t opf)
285{
286 chunk_t chunk = area_location(ps, ps->current_area);
287
288 return chunk_io(ps, ps->area, chunk, opf, 0);
289}
290
291static void zero_memory_area(struct pstore *ps)
292{
293 memset(ps->area, 0, ps->store->chunk_size << SECTOR_SHIFT);
294}
295
296static int zero_disk_area(struct pstore *ps, chunk_t area)
297{
298 return chunk_io(ps, ps->zero_area, area_location(ps, area),
299 REQ_OP_WRITE, 0);
300}
301
302static int read_header(struct pstore *ps, int *new_snapshot)
303{
304 int r;
305 struct disk_header *dh;
306 unsigned chunk_size;
307 int chunk_size_supplied = 1;
308 char *chunk_err;
309
310 /*
311 * Use default chunk size (or logical_block_size, if larger)
312 * if none supplied
313 */
314 if (!ps->store->chunk_size) {
315 ps->store->chunk_size = max(DM_CHUNK_SIZE_DEFAULT_SECTORS,
316 bdev_logical_block_size(dm_snap_cow(ps->store->snap)->
317 bdev) >> 9);
318 ps->store->chunk_mask = ps->store->chunk_size - 1;
319 ps->store->chunk_shift = __ffs(ps->store->chunk_size);
320 chunk_size_supplied = 0;
321 }
322
323 ps->io_client = dm_io_client_create();
324 if (IS_ERR(ps->io_client))
325 return PTR_ERR(ps->io_client);
326
327 r = alloc_area(ps);
328 if (r)
329 return r;
330
331 r = chunk_io(ps, ps->header_area, 0, REQ_OP_READ, 1);
332 if (r)
333 goto bad;
334
335 dh = ps->header_area;
336
337 if (le32_to_cpu(dh->magic) == 0) {
338 *new_snapshot = 1;
339 return 0;
340 }
341
342 if (le32_to_cpu(dh->magic) != SNAP_MAGIC) {
343 DMWARN("Invalid or corrupt snapshot");
344 r = -ENXIO;
345 goto bad;
346 }
347
348 *new_snapshot = 0;
349 ps->valid = le32_to_cpu(dh->valid);
350 ps->version = le32_to_cpu(dh->version);
351 chunk_size = le32_to_cpu(dh->chunk_size);
352
353 if (ps->store->chunk_size == chunk_size)
354 return 0;
355
356 if (chunk_size_supplied)
357 DMWARN("chunk size %u in device metadata overrides "
358 "table chunk size of %u.",
359 chunk_size, ps->store->chunk_size);
360
361 /* We had a bogus chunk_size. Fix stuff up. */
362 free_area(ps);
363
364 r = dm_exception_store_set_chunk_size(ps->store, chunk_size,
365 &chunk_err);
366 if (r) {
367 DMERR("invalid on-disk chunk size %u: %s.",
368 chunk_size, chunk_err);
369 return r;
370 }
371
372 r = alloc_area(ps);
373 return r;
374
375bad:
376 free_area(ps);
377 return r;
378}
379
380static int write_header(struct pstore *ps)
381{
382 struct disk_header *dh;
383
384 memset(ps->header_area, 0, ps->store->chunk_size << SECTOR_SHIFT);
385
386 dh = ps->header_area;
387 dh->magic = cpu_to_le32(SNAP_MAGIC);
388 dh->valid = cpu_to_le32(ps->valid);
389 dh->version = cpu_to_le32(ps->version);
390 dh->chunk_size = cpu_to_le32(ps->store->chunk_size);
391
392 return chunk_io(ps, ps->header_area, 0, REQ_OP_WRITE, 1);
393}
394
395/*
396 * Access functions for the disk exceptions, these do the endian conversions.
397 */
398static struct disk_exception *get_exception(struct pstore *ps, void *ps_area,
399 uint32_t index)
400{
401 BUG_ON(index >= ps->exceptions_per_area);
402
403 return ((struct disk_exception *) ps_area) + index;
404}
405
406static void read_exception(struct pstore *ps, void *ps_area,
407 uint32_t index, struct core_exception *result)
408{
409 struct disk_exception *de = get_exception(ps, ps_area, index);
410
411 /* copy it */
412 result->old_chunk = le64_to_cpu(de->old_chunk);
413 result->new_chunk = le64_to_cpu(de->new_chunk);
414}
415
416static void write_exception(struct pstore *ps,
417 uint32_t index, struct core_exception *e)
418{
419 struct disk_exception *de = get_exception(ps, ps->area, index);
420
421 /* copy it */
422 de->old_chunk = cpu_to_le64(e->old_chunk);
423 de->new_chunk = cpu_to_le64(e->new_chunk);
424}
425
426static void clear_exception(struct pstore *ps, uint32_t index)
427{
428 struct disk_exception *de = get_exception(ps, ps->area, index);
429
430 /* clear it */
431 de->old_chunk = 0;
432 de->new_chunk = 0;
433}
434
435/*
436 * Registers the exceptions that are present in the current area.
437 * 'full' is filled in to indicate if the area has been
438 * filled.
439 */
440static int insert_exceptions(struct pstore *ps, void *ps_area,
441 int (*callback)(void *callback_context,
442 chunk_t old, chunk_t new),
443 void *callback_context,
444 int *full)
445{
446 int r;
447 unsigned int i;
448 struct core_exception e;
449
450 /* presume the area is full */
451 *full = 1;
452
453 for (i = 0; i < ps->exceptions_per_area; i++) {
454 read_exception(ps, ps_area, i, &e);
455
456 /*
457 * If the new_chunk is pointing at the start of
458 * the COW device, where the first metadata area
459 * is we know that we've hit the end of the
460 * exceptions. Therefore the area is not full.
461 */
462 if (e.new_chunk == 0LL) {
463 ps->current_committed = i;
464 *full = 0;
465 break;
466 }
467
468 /*
469 * Keep track of the start of the free chunks.
470 */
471 if (ps->next_free <= e.new_chunk)
472 ps->next_free = e.new_chunk + 1;
473
474 /*
475 * Otherwise we add the exception to the snapshot.
476 */
477 r = callback(callback_context, e.old_chunk, e.new_chunk);
478 if (r)
479 return r;
480 }
481
482 return 0;
483}
484
485static int read_exceptions(struct pstore *ps,
486 int (*callback)(void *callback_context, chunk_t old,
487 chunk_t new),
488 void *callback_context)
489{
490 int r, full = 1;
491 struct dm_bufio_client *client;
492 chunk_t prefetch_area = 0;
493
494 client = dm_bufio_client_create(dm_snap_cow(ps->store->snap)->bdev,
495 ps->store->chunk_size << SECTOR_SHIFT,
496 1, 0, NULL, NULL, 0);
497
498 if (IS_ERR(client))
499 return PTR_ERR(client);
500
501 /*
502 * Setup for one current buffer + desired readahead buffers.
503 */
504 dm_bufio_set_minimum_buffers(client, 1 + DM_PREFETCH_CHUNKS);
505
506 /*
507 * Keeping reading chunks and inserting exceptions until
508 * we find a partially full area.
509 */
510 for (ps->current_area = 0; full; ps->current_area++) {
511 struct dm_buffer *bp;
512 void *area;
513 chunk_t chunk;
514
515 if (unlikely(prefetch_area < ps->current_area))
516 prefetch_area = ps->current_area;
517
518 if (DM_PREFETCH_CHUNKS) do {
519 chunk_t pf_chunk = area_location(ps, prefetch_area);
520 if (unlikely(pf_chunk >= dm_bufio_get_device_size(client)))
521 break;
522 dm_bufio_prefetch(client, pf_chunk, 1);
523 prefetch_area++;
524 if (unlikely(!prefetch_area))
525 break;
526 } while (prefetch_area <= ps->current_area + DM_PREFETCH_CHUNKS);
527
528 chunk = area_location(ps, ps->current_area);
529
530 area = dm_bufio_read(client, chunk, &bp);
531 if (IS_ERR(area)) {
532 r = PTR_ERR(area);
533 goto ret_destroy_bufio;
534 }
535
536 r = insert_exceptions(ps, area, callback, callback_context,
537 &full);
538
539 if (!full)
540 memcpy(ps->area, area, ps->store->chunk_size << SECTOR_SHIFT);
541
542 dm_bufio_release(bp);
543
544 dm_bufio_forget(client, chunk);
545
546 if (unlikely(r))
547 goto ret_destroy_bufio;
548 }
549
550 ps->current_area--;
551
552 skip_metadata(ps);
553
554 r = 0;
555
556ret_destroy_bufio:
557 dm_bufio_client_destroy(client);
558
559 return r;
560}
561
562static struct pstore *get_info(struct dm_exception_store *store)
563{
564 return (struct pstore *) store->context;
565}
566
567static void persistent_usage(struct dm_exception_store *store,
568 sector_t *total_sectors,
569 sector_t *sectors_allocated,
570 sector_t *metadata_sectors)
571{
572 struct pstore *ps = get_info(store);
573
574 *sectors_allocated = ps->next_free * store->chunk_size;
575 *total_sectors = get_dev_size(dm_snap_cow(store->snap)->bdev);
576
577 /*
578 * First chunk is the fixed header.
579 * Then there are (ps->current_area + 1) metadata chunks, each one
580 * separated from the next by ps->exceptions_per_area data chunks.
581 */
582 *metadata_sectors = (ps->current_area + 1 + NUM_SNAPSHOT_HDR_CHUNKS) *
583 store->chunk_size;
584}
585
586static void persistent_dtr(struct dm_exception_store *store)
587{
588 struct pstore *ps = get_info(store);
589
590 destroy_workqueue(ps->metadata_wq);
591
592 /* Created in read_header */
593 if (ps->io_client)
594 dm_io_client_destroy(ps->io_client);
595 free_area(ps);
596
597 /* Allocated in persistent_read_metadata */
598 kvfree(ps->callbacks);
599
600 kfree(ps);
601}
602
603static int persistent_read_metadata(struct dm_exception_store *store,
604 int (*callback)(void *callback_context,
605 chunk_t old, chunk_t new),
606 void *callback_context)
607{
608 int r, new_snapshot;
609 struct pstore *ps = get_info(store);
610
611 /*
612 * Read the snapshot header.
613 */
614 r = read_header(ps, &new_snapshot);
615 if (r)
616 return r;
617
618 /*
619 * Now we know correct chunk_size, complete the initialisation.
620 */
621 ps->exceptions_per_area = (ps->store->chunk_size << SECTOR_SHIFT) /
622 sizeof(struct disk_exception);
623 ps->callbacks = kvcalloc(ps->exceptions_per_area,
624 sizeof(*ps->callbacks), GFP_KERNEL);
625 if (!ps->callbacks)
626 return -ENOMEM;
627
628 /*
629 * Do we need to setup a new snapshot ?
630 */
631 if (new_snapshot) {
632 r = write_header(ps);
633 if (r) {
634 DMWARN("write_header failed");
635 return r;
636 }
637
638 ps->current_area = 0;
639 zero_memory_area(ps);
640 r = zero_disk_area(ps, 0);
641 if (r)
642 DMWARN("zero_disk_area(0) failed");
643 return r;
644 }
645 /*
646 * Sanity checks.
647 */
648 if (ps->version != SNAPSHOT_DISK_VERSION) {
649 DMWARN("unable to handle snapshot disk version %d",
650 ps->version);
651 return -EINVAL;
652 }
653
654 /*
655 * Metadata are valid, but snapshot is invalidated
656 */
657 if (!ps->valid)
658 return 1;
659
660 /*
661 * Read the metadata.
662 */
663 r = read_exceptions(ps, callback, callback_context);
664
665 return r;
666}
667
668static int persistent_prepare_exception(struct dm_exception_store *store,
669 struct dm_exception *e)
670{
671 struct pstore *ps = get_info(store);
672 sector_t size = get_dev_size(dm_snap_cow(store->snap)->bdev);
673
674 /* Is there enough room ? */
675 if (size < ((ps->next_free + 1) * store->chunk_size))
676 return -ENOSPC;
677
678 e->new_chunk = ps->next_free;
679
680 /*
681 * Move onto the next free pending, making sure to take
682 * into account the location of the metadata chunks.
683 */
684 ps->next_free++;
685 skip_metadata(ps);
686
687 atomic_inc(&ps->pending_count);
688 return 0;
689}
690
691static void persistent_commit_exception(struct dm_exception_store *store,
692 struct dm_exception *e, int valid,
693 void (*callback) (void *, int success),
694 void *callback_context)
695{
696 unsigned int i;
697 struct pstore *ps = get_info(store);
698 struct core_exception ce;
699 struct commit_callback *cb;
700
701 if (!valid)
702 ps->valid = 0;
703
704 ce.old_chunk = e->old_chunk;
705 ce.new_chunk = e->new_chunk;
706 write_exception(ps, ps->current_committed++, &ce);
707
708 /*
709 * Add the callback to the back of the array. This code
710 * is the only place where the callback array is
711 * manipulated, and we know that it will never be called
712 * multiple times concurrently.
713 */
714 cb = ps->callbacks + ps->callback_count++;
715 cb->callback = callback;
716 cb->context = callback_context;
717
718 /*
719 * If there are exceptions in flight and we have not yet
720 * filled this metadata area there's nothing more to do.
721 */
722 if (!atomic_dec_and_test(&ps->pending_count) &&
723 (ps->current_committed != ps->exceptions_per_area))
724 return;
725
726 /*
727 * If we completely filled the current area, then wipe the next one.
728 */
729 if ((ps->current_committed == ps->exceptions_per_area) &&
730 zero_disk_area(ps, ps->current_area + 1))
731 ps->valid = 0;
732
733 /*
734 * Commit exceptions to disk.
735 */
736 if (ps->valid && area_io(ps, REQ_OP_WRITE | REQ_PREFLUSH | REQ_FUA |
737 REQ_SYNC))
738 ps->valid = 0;
739
740 /*
741 * Advance to the next area if this one is full.
742 */
743 if (ps->current_committed == ps->exceptions_per_area) {
744 ps->current_committed = 0;
745 ps->current_area++;
746 zero_memory_area(ps);
747 }
748
749 for (i = 0; i < ps->callback_count; i++) {
750 cb = ps->callbacks + i;
751 cb->callback(cb->context, ps->valid);
752 }
753
754 ps->callback_count = 0;
755}
756
757static int persistent_prepare_merge(struct dm_exception_store *store,
758 chunk_t *last_old_chunk,
759 chunk_t *last_new_chunk)
760{
761 struct pstore *ps = get_info(store);
762 struct core_exception ce;
763 int nr_consecutive;
764 int r;
765
766 /*
767 * When current area is empty, move back to preceding area.
768 */
769 if (!ps->current_committed) {
770 /*
771 * Have we finished?
772 */
773 if (!ps->current_area)
774 return 0;
775
776 ps->current_area--;
777 r = area_io(ps, REQ_OP_READ);
778 if (r < 0)
779 return r;
780 ps->current_committed = ps->exceptions_per_area;
781 }
782
783 read_exception(ps, ps->area, ps->current_committed - 1, &ce);
784 *last_old_chunk = ce.old_chunk;
785 *last_new_chunk = ce.new_chunk;
786
787 /*
788 * Find number of consecutive chunks within the current area,
789 * working backwards.
790 */
791 for (nr_consecutive = 1; nr_consecutive < ps->current_committed;
792 nr_consecutive++) {
793 read_exception(ps, ps->area,
794 ps->current_committed - 1 - nr_consecutive, &ce);
795 if (ce.old_chunk != *last_old_chunk - nr_consecutive ||
796 ce.new_chunk != *last_new_chunk - nr_consecutive)
797 break;
798 }
799
800 return nr_consecutive;
801}
802
803static int persistent_commit_merge(struct dm_exception_store *store,
804 int nr_merged)
805{
806 int r, i;
807 struct pstore *ps = get_info(store);
808
809 BUG_ON(nr_merged > ps->current_committed);
810
811 for (i = 0; i < nr_merged; i++)
812 clear_exception(ps, ps->current_committed - 1 - i);
813
814 r = area_io(ps, REQ_OP_WRITE | REQ_PREFLUSH | REQ_FUA);
815 if (r < 0)
816 return r;
817
818 ps->current_committed -= nr_merged;
819
820 /*
821 * At this stage, only persistent_usage() uses ps->next_free, so
822 * we make no attempt to keep ps->next_free strictly accurate
823 * as exceptions may have been committed out-of-order originally.
824 * Once a snapshot has become merging, we set it to the value it
825 * would have held had all the exceptions been committed in order.
826 *
827 * ps->current_area does not get reduced by prepare_merge() until
828 * after commit_merge() has removed the nr_merged previous exceptions.
829 */
830 ps->next_free = area_location(ps, ps->current_area) +
831 ps->current_committed + 1;
832
833 return 0;
834}
835
836static void persistent_drop_snapshot(struct dm_exception_store *store)
837{
838 struct pstore *ps = get_info(store);
839
840 ps->valid = 0;
841 if (write_header(ps))
842 DMWARN("write header failed");
843}
844
845static int persistent_ctr(struct dm_exception_store *store, char *options)
846{
847 struct pstore *ps;
848 int r;
849
850 /* allocate the pstore */
851 ps = kzalloc(sizeof(*ps), GFP_KERNEL);
852 if (!ps)
853 return -ENOMEM;
854
855 ps->store = store;
856 ps->valid = 1;
857 ps->version = SNAPSHOT_DISK_VERSION;
858 ps->area = NULL;
859 ps->zero_area = NULL;
860 ps->header_area = NULL;
861 ps->next_free = NUM_SNAPSHOT_HDR_CHUNKS + 1; /* header and 1st area */
862 ps->current_committed = 0;
863
864 ps->callback_count = 0;
865 atomic_set(&ps->pending_count, 0);
866 ps->callbacks = NULL;
867
868 ps->metadata_wq = alloc_workqueue("ksnaphd", WQ_MEM_RECLAIM, 0);
869 if (!ps->metadata_wq) {
870 DMERR("couldn't start header metadata update thread");
871 r = -ENOMEM;
872 goto err_workqueue;
873 }
874
875 if (options) {
876 char overflow = toupper(options[0]);
877 if (overflow == 'O')
878 store->userspace_supports_overflow = true;
879 else {
880 DMERR("Unsupported persistent store option: %s", options);
881 r = -EINVAL;
882 goto err_options;
883 }
884 }
885
886 store->context = ps;
887
888 return 0;
889
890err_options:
891 destroy_workqueue(ps->metadata_wq);
892err_workqueue:
893 kfree(ps);
894
895 return r;
896}
897
898static unsigned persistent_status(struct dm_exception_store *store,
899 status_type_t status, char *result,
900 unsigned maxlen)
901{
902 unsigned sz = 0;
903
904 switch (status) {
905 case STATUSTYPE_INFO:
906 break;
907 case STATUSTYPE_TABLE:
908 DMEMIT(" %s %llu", store->userspace_supports_overflow ? "PO" : "P",
909 (unsigned long long)store->chunk_size);
910 break;
911 case STATUSTYPE_IMA:
912 *result = '\0';
913 break;
914 }
915
916 return sz;
917}
918
919static struct dm_exception_store_type _persistent_type = {
920 .name = "persistent",
921 .module = THIS_MODULE,
922 .ctr = persistent_ctr,
923 .dtr = persistent_dtr,
924 .read_metadata = persistent_read_metadata,
925 .prepare_exception = persistent_prepare_exception,
926 .commit_exception = persistent_commit_exception,
927 .prepare_merge = persistent_prepare_merge,
928 .commit_merge = persistent_commit_merge,
929 .drop_snapshot = persistent_drop_snapshot,
930 .usage = persistent_usage,
931 .status = persistent_status,
932};
933
934static struct dm_exception_store_type _persistent_compat_type = {
935 .name = "P",
936 .module = THIS_MODULE,
937 .ctr = persistent_ctr,
938 .dtr = persistent_dtr,
939 .read_metadata = persistent_read_metadata,
940 .prepare_exception = persistent_prepare_exception,
941 .commit_exception = persistent_commit_exception,
942 .prepare_merge = persistent_prepare_merge,
943 .commit_merge = persistent_commit_merge,
944 .drop_snapshot = persistent_drop_snapshot,
945 .usage = persistent_usage,
946 .status = persistent_status,
947};
948
949int dm_persistent_snapshot_init(void)
950{
951 int r;
952
953 r = dm_exception_store_type_register(&_persistent_type);
954 if (r) {
955 DMERR("Unable to register persistent exception store type");
956 return r;
957 }
958
959 r = dm_exception_store_type_register(&_persistent_compat_type);
960 if (r) {
961 DMERR("Unable to register old-style persistent exception "
962 "store type");
963 dm_exception_store_type_unregister(&_persistent_type);
964 return r;
965 }
966
967 return r;
968}
969
970void dm_persistent_snapshot_exit(void)
971{
972 dm_exception_store_type_unregister(&_persistent_type);
973 dm_exception_store_type_unregister(&_persistent_compat_type);
974}
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}