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}