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 rw,
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_rw = rw,
 
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 generic_make_request 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, int rw)
285{
286	int r;
287	chunk_t chunk;
288
289	chunk = area_location(ps, ps->current_area);
290
291	r = chunk_io(ps, ps->area, chunk, rw, 0);
292	if (r)
293		return r;
294
295	return 0;
296}
297
298static void zero_memory_area(struct pstore *ps)
299{
300	memset(ps->area, 0, ps->store->chunk_size << SECTOR_SHIFT);
301}
302
303static int zero_disk_area(struct pstore *ps, chunk_t area)
304{
305	return chunk_io(ps, ps->zero_area, area_location(ps, area), WRITE, 0);
 
306}
307
308static int read_header(struct pstore *ps, int *new_snapshot)
309{
310	int r;
311	struct disk_header *dh;
312	unsigned chunk_size;
313	int chunk_size_supplied = 1;
314	char *chunk_err;
315
316	/*
317	 * Use default chunk size (or logical_block_size, if larger)
318	 * if none supplied
319	 */
320	if (!ps->store->chunk_size) {
321		ps->store->chunk_size = max(DM_CHUNK_SIZE_DEFAULT_SECTORS,
322		    bdev_logical_block_size(dm_snap_cow(ps->store->snap)->
323					    bdev) >> 9);
324		ps->store->chunk_mask = ps->store->chunk_size - 1;
325		ps->store->chunk_shift = __ffs(ps->store->chunk_size);
326		chunk_size_supplied = 0;
327	}
328
329	ps->io_client = dm_io_client_create();
330	if (IS_ERR(ps->io_client))
331		return PTR_ERR(ps->io_client);
332
333	r = alloc_area(ps);
334	if (r)
335		return r;
336
337	r = chunk_io(ps, ps->header_area, 0, READ, 1);
338	if (r)
339		goto bad;
340
341	dh = ps->header_area;
342
343	if (le32_to_cpu(dh->magic) == 0) {
344		*new_snapshot = 1;
345		return 0;
346	}
347
348	if (le32_to_cpu(dh->magic) != SNAP_MAGIC) {
349		DMWARN("Invalid or corrupt snapshot");
350		r = -ENXIO;
351		goto bad;
352	}
353
354	*new_snapshot = 0;
355	ps->valid = le32_to_cpu(dh->valid);
356	ps->version = le32_to_cpu(dh->version);
357	chunk_size = le32_to_cpu(dh->chunk_size);
358
359	if (ps->store->chunk_size == chunk_size)
360		return 0;
361
362	if (chunk_size_supplied)
363		DMWARN("chunk size %u in device metadata overrides "
364		       "table chunk size of %u.",
365		       chunk_size, ps->store->chunk_size);
366
367	/* We had a bogus chunk_size. Fix stuff up. */
368	free_area(ps);
369
370	r = dm_exception_store_set_chunk_size(ps->store, chunk_size,
371					      &chunk_err);
372	if (r) {
373		DMERR("invalid on-disk chunk size %u: %s.",
374		      chunk_size, chunk_err);
375		return r;
376	}
377
378	r = alloc_area(ps);
379	return r;
380
381bad:
382	free_area(ps);
383	return r;
384}
385
386static int write_header(struct pstore *ps)
387{
388	struct disk_header *dh;
389
390	memset(ps->header_area, 0, ps->store->chunk_size << SECTOR_SHIFT);
391
392	dh = ps->header_area;
393	dh->magic = cpu_to_le32(SNAP_MAGIC);
394	dh->valid = cpu_to_le32(ps->valid);
395	dh->version = cpu_to_le32(ps->version);
396	dh->chunk_size = cpu_to_le32(ps->store->chunk_size);
397
398	return chunk_io(ps, ps->header_area, 0, WRITE, 1);
399}
400
401/*
402 * Access functions for the disk exceptions, these do the endian conversions.
403 */
404static struct disk_exception *get_exception(struct pstore *ps, void *ps_area,
405					    uint32_t index)
406{
407	BUG_ON(index >= ps->exceptions_per_area);
408
409	return ((struct disk_exception *) ps_area) + index;
410}
411
412static void read_exception(struct pstore *ps, void *ps_area,
413			   uint32_t index, struct core_exception *result)
414{
415	struct disk_exception *de = get_exception(ps, ps_area, index);
416
417	/* copy it */
418	result->old_chunk = le64_to_cpu(de->old_chunk);
419	result->new_chunk = le64_to_cpu(de->new_chunk);
420}
421
422static void write_exception(struct pstore *ps,
423			    uint32_t index, struct core_exception *e)
424{
425	struct disk_exception *de = get_exception(ps, ps->area, index);
426
427	/* copy it */
428	de->old_chunk = cpu_to_le64(e->old_chunk);
429	de->new_chunk = cpu_to_le64(e->new_chunk);
430}
431
432static void clear_exception(struct pstore *ps, uint32_t index)
433{
434	struct disk_exception *de = get_exception(ps, ps->area, index);
435
436	/* clear it */
437	de->old_chunk = 0;
438	de->new_chunk = 0;
439}
440
441/*
442 * Registers the exceptions that are present in the current area.
443 * 'full' is filled in to indicate if the area has been
444 * filled.
445 */
446static int insert_exceptions(struct pstore *ps, void *ps_area,
447			     int (*callback)(void *callback_context,
448					     chunk_t old, chunk_t new),
449			     void *callback_context,
450			     int *full)
451{
452	int r;
453	unsigned int i;
454	struct core_exception e;
455
456	/* presume the area is full */
457	*full = 1;
458
459	for (i = 0; i < ps->exceptions_per_area; i++) {
460		read_exception(ps, ps_area, i, &e);
461
462		/*
463		 * If the new_chunk is pointing at the start of
464		 * the COW device, where the first metadata area
465		 * is we know that we've hit the end of the
466		 * exceptions.  Therefore the area is not full.
467		 */
468		if (e.new_chunk == 0LL) {
469			ps->current_committed = i;
470			*full = 0;
471			break;
472		}
473
474		/*
475		 * Keep track of the start of the free chunks.
476		 */
477		if (ps->next_free <= e.new_chunk)
478			ps->next_free = e.new_chunk + 1;
479
480		/*
481		 * Otherwise we add the exception to the snapshot.
482		 */
483		r = callback(callback_context, e.old_chunk, e.new_chunk);
484		if (r)
485			return r;
486	}
487
488	return 0;
489}
490
491static int read_exceptions(struct pstore *ps,
492			   int (*callback)(void *callback_context, chunk_t old,
493					   chunk_t new),
494			   void *callback_context)
495{
496	int r, full = 1;
497	struct dm_bufio_client *client;
498	chunk_t prefetch_area = 0;
499
500	client = dm_bufio_client_create(dm_snap_cow(ps->store->snap)->bdev,
501					ps->store->chunk_size << SECTOR_SHIFT,
502					1, 0, NULL, NULL);
503
504	if (IS_ERR(client))
505		return PTR_ERR(client);
506
507	/*
508	 * Setup for one current buffer + desired readahead buffers.
509	 */
510	dm_bufio_set_minimum_buffers(client, 1 + DM_PREFETCH_CHUNKS);
511
512	/*
513	 * Keeping reading chunks and inserting exceptions until
514	 * we find a partially full area.
515	 */
516	for (ps->current_area = 0; full; ps->current_area++) {
517		struct dm_buffer *bp;
518		void *area;
519		chunk_t chunk;
520
521		if (unlikely(prefetch_area < ps->current_area))
522			prefetch_area = ps->current_area;
523
524		if (DM_PREFETCH_CHUNKS) do {
525			chunk_t pf_chunk = area_location(ps, prefetch_area);
526			if (unlikely(pf_chunk >= dm_bufio_get_device_size(client)))
527				break;
528			dm_bufio_prefetch(client, pf_chunk, 1);
529			prefetch_area++;
530			if (unlikely(!prefetch_area))
531				break;
532		} while (prefetch_area <= ps->current_area + DM_PREFETCH_CHUNKS);
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 (struct pstore *) 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	vfree(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, uninitialized_var(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 = dm_vcalloc(ps->exceptions_per_area,
630				   sizeof(*ps->callbacks));
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, WRITE_FLUSH_FUA))
 
743		ps->valid = 0;
744
745	/*
746	 * Advance to the next area if this one is full.
747	 */
748	if (ps->current_committed == ps->exceptions_per_area) {
749		ps->current_committed = 0;
750		ps->current_area++;
751		zero_memory_area(ps);
752	}
753
754	for (i = 0; i < ps->callback_count; i++) {
755		cb = ps->callbacks + i;
756		cb->callback(cb->context, ps->valid);
757	}
758
759	ps->callback_count = 0;
760}
761
762static int persistent_prepare_merge(struct dm_exception_store *store,
763				    chunk_t *last_old_chunk,
764				    chunk_t *last_new_chunk)
765{
766	struct pstore *ps = get_info(store);
767	struct core_exception ce;
768	int nr_consecutive;
769	int r;
770
771	/*
772	 * When current area is empty, move back to preceding area.
773	 */
774	if (!ps->current_committed) {
775		/*
776		 * Have we finished?
777		 */
778		if (!ps->current_area)
779			return 0;
780
781		ps->current_area--;
782		r = area_io(ps, READ);
783		if (r < 0)
784			return r;
785		ps->current_committed = ps->exceptions_per_area;
786	}
787
788	read_exception(ps, ps->area, ps->current_committed - 1, &ce);
789	*last_old_chunk = ce.old_chunk;
790	*last_new_chunk = ce.new_chunk;
791
792	/*
793	 * Find number of consecutive chunks within the current area,
794	 * working backwards.
795	 */
796	for (nr_consecutive = 1; nr_consecutive < ps->current_committed;
797	     nr_consecutive++) {
798		read_exception(ps, ps->area,
799			       ps->current_committed - 1 - nr_consecutive, &ce);
800		if (ce.old_chunk != *last_old_chunk - nr_consecutive ||
801		    ce.new_chunk != *last_new_chunk - nr_consecutive)
802			break;
803	}
804
805	return nr_consecutive;
806}
807
808static int persistent_commit_merge(struct dm_exception_store *store,
809				   int nr_merged)
810{
811	int r, i;
812	struct pstore *ps = get_info(store);
813
814	BUG_ON(nr_merged > ps->current_committed);
815
816	for (i = 0; i < nr_merged; i++)
817		clear_exception(ps, ps->current_committed - 1 - i);
818
819	r = area_io(ps, WRITE_FLUSH_FUA);
820	if (r < 0)
821		return r;
822
823	ps->current_committed -= nr_merged;
824
825	/*
826	 * At this stage, only persistent_usage() uses ps->next_free, so
827	 * we make no attempt to keep ps->next_free strictly accurate
828	 * as exceptions may have been committed out-of-order originally.
829	 * Once a snapshot has become merging, we set it to the value it
830	 * would have held had all the exceptions been committed in order.
831	 *
832	 * ps->current_area does not get reduced by prepare_merge() until
833	 * after commit_merge() has removed the nr_merged previous exceptions.
834	 */
835	ps->next_free = area_location(ps, ps->current_area) +
836			ps->current_committed + 1;
837
838	return 0;
839}
840
841static void persistent_drop_snapshot(struct dm_exception_store *store)
842{
843	struct pstore *ps = get_info(store);
844
845	ps->valid = 0;
846	if (write_header(ps))
847		DMWARN("write header failed");
848}
849
850static int persistent_ctr(struct dm_exception_store *store, char *options)
851{
852	struct pstore *ps;
853	int r;
854
855	/* allocate the pstore */
856	ps = kzalloc(sizeof(*ps), GFP_KERNEL);
857	if (!ps)
858		return -ENOMEM;
859
860	ps->store = store;
861	ps->valid = 1;
862	ps->version = SNAPSHOT_DISK_VERSION;
863	ps->area = NULL;
864	ps->zero_area = NULL;
865	ps->header_area = NULL;
866	ps->next_free = NUM_SNAPSHOT_HDR_CHUNKS + 1; /* header and 1st area */
867	ps->current_committed = 0;
868
869	ps->callback_count = 0;
870	atomic_set(&ps->pending_count, 0);
871	ps->callbacks = NULL;
872
873	ps->metadata_wq = alloc_workqueue("ksnaphd", WQ_MEM_RECLAIM, 0);
874	if (!ps->metadata_wq) {
875		DMERR("couldn't start header metadata update thread");
876		r = -ENOMEM;
877		goto err_workqueue;
878	}
879
880	if (options) {
881		char overflow = toupper(options[0]);
882		if (overflow == 'O')
883			store->userspace_supports_overflow = true;
884		else {
885			DMERR("Unsupported persistent store option: %s", options);
886			r = -EINVAL;
887			goto err_options;
888		}
889	}
890
891	store->context = ps;
892
893	return 0;
894
895err_options:
896	destroy_workqueue(ps->metadata_wq);
897err_workqueue:
898	kfree(ps);
899
900	return r;
901}
902
903static unsigned persistent_status(struct dm_exception_store *store,
904				  status_type_t status, char *result,
905				  unsigned maxlen)
906{
907	unsigned sz = 0;
908
909	switch (status) {
910	case STATUSTYPE_INFO:
911		break;
912	case STATUSTYPE_TABLE:
913		DMEMIT(" %s %llu", store->userspace_supports_overflow ? "PO" : "P",
914		       (unsigned long long)store->chunk_size);
915	}
916
917	return sz;
918}
919
920static struct dm_exception_store_type _persistent_type = {
921	.name = "persistent",
922	.module = THIS_MODULE,
923	.ctr = persistent_ctr,
924	.dtr = persistent_dtr,
925	.read_metadata = persistent_read_metadata,
926	.prepare_exception = persistent_prepare_exception,
927	.commit_exception = persistent_commit_exception,
928	.prepare_merge = persistent_prepare_merge,
929	.commit_merge = persistent_commit_merge,
930	.drop_snapshot = persistent_drop_snapshot,
931	.usage = persistent_usage,
932	.status = persistent_status,
933};
934
935static struct dm_exception_store_type _persistent_compat_type = {
936	.name = "P",
937	.module = THIS_MODULE,
938	.ctr = persistent_ctr,
939	.dtr = persistent_dtr,
940	.read_metadata = persistent_read_metadata,
941	.prepare_exception = persistent_prepare_exception,
942	.commit_exception = persistent_commit_exception,
943	.prepare_merge = persistent_prepare_merge,
944	.commit_merge = persistent_commit_merge,
945	.drop_snapshot = persistent_drop_snapshot,
946	.usage = persistent_usage,
947	.status = persistent_status,
948};
949
950int dm_persistent_snapshot_init(void)
951{
952	int r;
953
954	r = dm_exception_store_type_register(&_persistent_type);
955	if (r) {
956		DMERR("Unable to register persistent exception store type");
957		return r;
958	}
959
960	r = dm_exception_store_type_register(&_persistent_compat_type);
961	if (r) {
962		DMERR("Unable to register old-style persistent exception "
963		      "store type");
964		dm_exception_store_type_unregister(&_persistent_type);
965		return r;
966	}
967
968	return r;
969}
970
971void dm_persistent_snapshot_exit(void)
972{
973	dm_exception_store_type_unregister(&_persistent_type);
974	dm_exception_store_type_unregister(&_persistent_compat_type);
975}