xref: /openbmc/linux/drivers/md/dm-snap.c (revision 81d67439)
1 /*
2  * dm-snapshot.c
3  *
4  * Copyright (C) 2001-2002 Sistina Software (UK) Limited.
5  *
6  * This file is released under the GPL.
7  */
8 
9 #include <linux/blkdev.h>
10 #include <linux/device-mapper.h>
11 #include <linux/delay.h>
12 #include <linux/fs.h>
13 #include <linux/init.h>
14 #include <linux/kdev_t.h>
15 #include <linux/list.h>
16 #include <linux/mempool.h>
17 #include <linux/module.h>
18 #include <linux/slab.h>
19 #include <linux/vmalloc.h>
20 #include <linux/log2.h>
21 #include <linux/dm-kcopyd.h>
22 
23 #include "dm-exception-store.h"
24 
25 #define DM_MSG_PREFIX "snapshots"
26 
27 static const char dm_snapshot_merge_target_name[] = "snapshot-merge";
28 
29 #define dm_target_is_snapshot_merge(ti) \
30 	((ti)->type->name == dm_snapshot_merge_target_name)
31 
32 /*
33  * The percentage increment we will wake up users at
34  */
35 #define WAKE_UP_PERCENT 5
36 
37 /*
38  * kcopyd priority of snapshot operations
39  */
40 #define SNAPSHOT_COPY_PRIORITY 2
41 
42 /*
43  * The size of the mempool used to track chunks in use.
44  */
45 #define MIN_IOS 256
46 
47 #define DM_TRACKED_CHUNK_HASH_SIZE	16
48 #define DM_TRACKED_CHUNK_HASH(x)	((unsigned long)(x) & \
49 					 (DM_TRACKED_CHUNK_HASH_SIZE - 1))
50 
51 struct dm_exception_table {
52 	uint32_t hash_mask;
53 	unsigned hash_shift;
54 	struct list_head *table;
55 };
56 
57 struct dm_snapshot {
58 	struct rw_semaphore lock;
59 
60 	struct dm_dev *origin;
61 	struct dm_dev *cow;
62 
63 	struct dm_target *ti;
64 
65 	/* List of snapshots per Origin */
66 	struct list_head list;
67 
68 	/*
69 	 * You can't use a snapshot if this is 0 (e.g. if full).
70 	 * A snapshot-merge target never clears this.
71 	 */
72 	int valid;
73 
74 	/* Origin writes don't trigger exceptions until this is set */
75 	int active;
76 
77 	atomic_t pending_exceptions_count;
78 
79 	mempool_t *pending_pool;
80 
81 	struct dm_exception_table pending;
82 	struct dm_exception_table complete;
83 
84 	/*
85 	 * pe_lock protects all pending_exception operations and access
86 	 * as well as the snapshot_bios list.
87 	 */
88 	spinlock_t pe_lock;
89 
90 	/* Chunks with outstanding reads */
91 	spinlock_t tracked_chunk_lock;
92 	mempool_t *tracked_chunk_pool;
93 	struct hlist_head tracked_chunk_hash[DM_TRACKED_CHUNK_HASH_SIZE];
94 
95 	/* The on disk metadata handler */
96 	struct dm_exception_store *store;
97 
98 	struct dm_kcopyd_client *kcopyd_client;
99 
100 	/* Wait for events based on state_bits */
101 	unsigned long state_bits;
102 
103 	/* Range of chunks currently being merged. */
104 	chunk_t first_merging_chunk;
105 	int num_merging_chunks;
106 
107 	/*
108 	 * The merge operation failed if this flag is set.
109 	 * Failure modes are handled as follows:
110 	 * - I/O error reading the header
111 	 *   	=> don't load the target; abort.
112 	 * - Header does not have "valid" flag set
113 	 *   	=> use the origin; forget about the snapshot.
114 	 * - I/O error when reading exceptions
115 	 *   	=> don't load the target; abort.
116 	 *         (We can't use the intermediate origin state.)
117 	 * - I/O error while merging
118 	 *	=> stop merging; set merge_failed; process I/O normally.
119 	 */
120 	int merge_failed;
121 
122 	/*
123 	 * Incoming bios that overlap with chunks being merged must wait
124 	 * for them to be committed.
125 	 */
126 	struct bio_list bios_queued_during_merge;
127 };
128 
129 /*
130  * state_bits:
131  *   RUNNING_MERGE  - Merge operation is in progress.
132  *   SHUTDOWN_MERGE - Set to signal that merge needs to be stopped;
133  *                    cleared afterwards.
134  */
135 #define RUNNING_MERGE          0
136 #define SHUTDOWN_MERGE         1
137 
138 struct dm_dev *dm_snap_origin(struct dm_snapshot *s)
139 {
140 	return s->origin;
141 }
142 EXPORT_SYMBOL(dm_snap_origin);
143 
144 struct dm_dev *dm_snap_cow(struct dm_snapshot *s)
145 {
146 	return s->cow;
147 }
148 EXPORT_SYMBOL(dm_snap_cow);
149 
150 static sector_t chunk_to_sector(struct dm_exception_store *store,
151 				chunk_t chunk)
152 {
153 	return chunk << store->chunk_shift;
154 }
155 
156 static int bdev_equal(struct block_device *lhs, struct block_device *rhs)
157 {
158 	/*
159 	 * There is only ever one instance of a particular block
160 	 * device so we can compare pointers safely.
161 	 */
162 	return lhs == rhs;
163 }
164 
165 struct dm_snap_pending_exception {
166 	struct dm_exception e;
167 
168 	/*
169 	 * Origin buffers waiting for this to complete are held
170 	 * in a bio list
171 	 */
172 	struct bio_list origin_bios;
173 	struct bio_list snapshot_bios;
174 
175 	/* Pointer back to snapshot context */
176 	struct dm_snapshot *snap;
177 
178 	/*
179 	 * 1 indicates the exception has already been sent to
180 	 * kcopyd.
181 	 */
182 	int started;
183 };
184 
185 /*
186  * Hash table mapping origin volumes to lists of snapshots and
187  * a lock to protect it
188  */
189 static struct kmem_cache *exception_cache;
190 static struct kmem_cache *pending_cache;
191 
192 struct dm_snap_tracked_chunk {
193 	struct hlist_node node;
194 	chunk_t chunk;
195 };
196 
197 static struct kmem_cache *tracked_chunk_cache;
198 
199 static struct dm_snap_tracked_chunk *track_chunk(struct dm_snapshot *s,
200 						 chunk_t chunk)
201 {
202 	struct dm_snap_tracked_chunk *c = mempool_alloc(s->tracked_chunk_pool,
203 							GFP_NOIO);
204 	unsigned long flags;
205 
206 	c->chunk = chunk;
207 
208 	spin_lock_irqsave(&s->tracked_chunk_lock, flags);
209 	hlist_add_head(&c->node,
210 		       &s->tracked_chunk_hash[DM_TRACKED_CHUNK_HASH(chunk)]);
211 	spin_unlock_irqrestore(&s->tracked_chunk_lock, flags);
212 
213 	return c;
214 }
215 
216 static void stop_tracking_chunk(struct dm_snapshot *s,
217 				struct dm_snap_tracked_chunk *c)
218 {
219 	unsigned long flags;
220 
221 	spin_lock_irqsave(&s->tracked_chunk_lock, flags);
222 	hlist_del(&c->node);
223 	spin_unlock_irqrestore(&s->tracked_chunk_lock, flags);
224 
225 	mempool_free(c, s->tracked_chunk_pool);
226 }
227 
228 static int __chunk_is_tracked(struct dm_snapshot *s, chunk_t chunk)
229 {
230 	struct dm_snap_tracked_chunk *c;
231 	struct hlist_node *hn;
232 	int found = 0;
233 
234 	spin_lock_irq(&s->tracked_chunk_lock);
235 
236 	hlist_for_each_entry(c, hn,
237 	    &s->tracked_chunk_hash[DM_TRACKED_CHUNK_HASH(chunk)], node) {
238 		if (c->chunk == chunk) {
239 			found = 1;
240 			break;
241 		}
242 	}
243 
244 	spin_unlock_irq(&s->tracked_chunk_lock);
245 
246 	return found;
247 }
248 
249 /*
250  * This conflicting I/O is extremely improbable in the caller,
251  * so msleep(1) is sufficient and there is no need for a wait queue.
252  */
253 static void __check_for_conflicting_io(struct dm_snapshot *s, chunk_t chunk)
254 {
255 	while (__chunk_is_tracked(s, chunk))
256 		msleep(1);
257 }
258 
259 /*
260  * One of these per registered origin, held in the snapshot_origins hash
261  */
262 struct origin {
263 	/* The origin device */
264 	struct block_device *bdev;
265 
266 	struct list_head hash_list;
267 
268 	/* List of snapshots for this origin */
269 	struct list_head snapshots;
270 };
271 
272 /*
273  * Size of the hash table for origin volumes. If we make this
274  * the size of the minors list then it should be nearly perfect
275  */
276 #define ORIGIN_HASH_SIZE 256
277 #define ORIGIN_MASK      0xFF
278 static struct list_head *_origins;
279 static struct rw_semaphore _origins_lock;
280 
281 static DECLARE_WAIT_QUEUE_HEAD(_pending_exceptions_done);
282 static DEFINE_SPINLOCK(_pending_exceptions_done_spinlock);
283 static uint64_t _pending_exceptions_done_count;
284 
285 static int init_origin_hash(void)
286 {
287 	int i;
288 
289 	_origins = kmalloc(ORIGIN_HASH_SIZE * sizeof(struct list_head),
290 			   GFP_KERNEL);
291 	if (!_origins) {
292 		DMERR("unable to allocate memory");
293 		return -ENOMEM;
294 	}
295 
296 	for (i = 0; i < ORIGIN_HASH_SIZE; i++)
297 		INIT_LIST_HEAD(_origins + i);
298 	init_rwsem(&_origins_lock);
299 
300 	return 0;
301 }
302 
303 static void exit_origin_hash(void)
304 {
305 	kfree(_origins);
306 }
307 
308 static unsigned origin_hash(struct block_device *bdev)
309 {
310 	return bdev->bd_dev & ORIGIN_MASK;
311 }
312 
313 static struct origin *__lookup_origin(struct block_device *origin)
314 {
315 	struct list_head *ol;
316 	struct origin *o;
317 
318 	ol = &_origins[origin_hash(origin)];
319 	list_for_each_entry (o, ol, hash_list)
320 		if (bdev_equal(o->bdev, origin))
321 			return o;
322 
323 	return NULL;
324 }
325 
326 static void __insert_origin(struct origin *o)
327 {
328 	struct list_head *sl = &_origins[origin_hash(o->bdev)];
329 	list_add_tail(&o->hash_list, sl);
330 }
331 
332 /*
333  * _origins_lock must be held when calling this function.
334  * Returns number of snapshots registered using the supplied cow device, plus:
335  * snap_src - a snapshot suitable for use as a source of exception handover
336  * snap_dest - a snapshot capable of receiving exception handover.
337  * snap_merge - an existing snapshot-merge target linked to the same origin.
338  *   There can be at most one snapshot-merge target. The parameter is optional.
339  *
340  * Possible return values and states of snap_src and snap_dest.
341  *   0: NULL, NULL  - first new snapshot
342  *   1: snap_src, NULL - normal snapshot
343  *   2: snap_src, snap_dest  - waiting for handover
344  *   2: snap_src, NULL - handed over, waiting for old to be deleted
345  *   1: NULL, snap_dest - source got destroyed without handover
346  */
347 static int __find_snapshots_sharing_cow(struct dm_snapshot *snap,
348 					struct dm_snapshot **snap_src,
349 					struct dm_snapshot **snap_dest,
350 					struct dm_snapshot **snap_merge)
351 {
352 	struct dm_snapshot *s;
353 	struct origin *o;
354 	int count = 0;
355 	int active;
356 
357 	o = __lookup_origin(snap->origin->bdev);
358 	if (!o)
359 		goto out;
360 
361 	list_for_each_entry(s, &o->snapshots, list) {
362 		if (dm_target_is_snapshot_merge(s->ti) && snap_merge)
363 			*snap_merge = s;
364 		if (!bdev_equal(s->cow->bdev, snap->cow->bdev))
365 			continue;
366 
367 		down_read(&s->lock);
368 		active = s->active;
369 		up_read(&s->lock);
370 
371 		if (active) {
372 			if (snap_src)
373 				*snap_src = s;
374 		} else if (snap_dest)
375 			*snap_dest = s;
376 
377 		count++;
378 	}
379 
380 out:
381 	return count;
382 }
383 
384 /*
385  * On success, returns 1 if this snapshot is a handover destination,
386  * otherwise returns 0.
387  */
388 static int __validate_exception_handover(struct dm_snapshot *snap)
389 {
390 	struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
391 	struct dm_snapshot *snap_merge = NULL;
392 
393 	/* Does snapshot need exceptions handed over to it? */
394 	if ((__find_snapshots_sharing_cow(snap, &snap_src, &snap_dest,
395 					  &snap_merge) == 2) ||
396 	    snap_dest) {
397 		snap->ti->error = "Snapshot cow pairing for exception "
398 				  "table handover failed";
399 		return -EINVAL;
400 	}
401 
402 	/*
403 	 * If no snap_src was found, snap cannot become a handover
404 	 * destination.
405 	 */
406 	if (!snap_src)
407 		return 0;
408 
409 	/*
410 	 * Non-snapshot-merge handover?
411 	 */
412 	if (!dm_target_is_snapshot_merge(snap->ti))
413 		return 1;
414 
415 	/*
416 	 * Do not allow more than one merging snapshot.
417 	 */
418 	if (snap_merge) {
419 		snap->ti->error = "A snapshot is already merging.";
420 		return -EINVAL;
421 	}
422 
423 	if (!snap_src->store->type->prepare_merge ||
424 	    !snap_src->store->type->commit_merge) {
425 		snap->ti->error = "Snapshot exception store does not "
426 				  "support snapshot-merge.";
427 		return -EINVAL;
428 	}
429 
430 	return 1;
431 }
432 
433 static void __insert_snapshot(struct origin *o, struct dm_snapshot *s)
434 {
435 	struct dm_snapshot *l;
436 
437 	/* Sort the list according to chunk size, largest-first smallest-last */
438 	list_for_each_entry(l, &o->snapshots, list)
439 		if (l->store->chunk_size < s->store->chunk_size)
440 			break;
441 	list_add_tail(&s->list, &l->list);
442 }
443 
444 /*
445  * Make a note of the snapshot and its origin so we can look it
446  * up when the origin has a write on it.
447  *
448  * Also validate snapshot exception store handovers.
449  * On success, returns 1 if this registration is a handover destination,
450  * otherwise returns 0.
451  */
452 static int register_snapshot(struct dm_snapshot *snap)
453 {
454 	struct origin *o, *new_o = NULL;
455 	struct block_device *bdev = snap->origin->bdev;
456 	int r = 0;
457 
458 	new_o = kmalloc(sizeof(*new_o), GFP_KERNEL);
459 	if (!new_o)
460 		return -ENOMEM;
461 
462 	down_write(&_origins_lock);
463 
464 	r = __validate_exception_handover(snap);
465 	if (r < 0) {
466 		kfree(new_o);
467 		goto out;
468 	}
469 
470 	o = __lookup_origin(bdev);
471 	if (o)
472 		kfree(new_o);
473 	else {
474 		/* New origin */
475 		o = new_o;
476 
477 		/* Initialise the struct */
478 		INIT_LIST_HEAD(&o->snapshots);
479 		o->bdev = bdev;
480 
481 		__insert_origin(o);
482 	}
483 
484 	__insert_snapshot(o, snap);
485 
486 out:
487 	up_write(&_origins_lock);
488 
489 	return r;
490 }
491 
492 /*
493  * Move snapshot to correct place in list according to chunk size.
494  */
495 static void reregister_snapshot(struct dm_snapshot *s)
496 {
497 	struct block_device *bdev = s->origin->bdev;
498 
499 	down_write(&_origins_lock);
500 
501 	list_del(&s->list);
502 	__insert_snapshot(__lookup_origin(bdev), s);
503 
504 	up_write(&_origins_lock);
505 }
506 
507 static void unregister_snapshot(struct dm_snapshot *s)
508 {
509 	struct origin *o;
510 
511 	down_write(&_origins_lock);
512 	o = __lookup_origin(s->origin->bdev);
513 
514 	list_del(&s->list);
515 	if (o && list_empty(&o->snapshots)) {
516 		list_del(&o->hash_list);
517 		kfree(o);
518 	}
519 
520 	up_write(&_origins_lock);
521 }
522 
523 /*
524  * Implementation of the exception hash tables.
525  * The lowest hash_shift bits of the chunk number are ignored, allowing
526  * some consecutive chunks to be grouped together.
527  */
528 static int dm_exception_table_init(struct dm_exception_table *et,
529 				   uint32_t size, unsigned hash_shift)
530 {
531 	unsigned int i;
532 
533 	et->hash_shift = hash_shift;
534 	et->hash_mask = size - 1;
535 	et->table = dm_vcalloc(size, sizeof(struct list_head));
536 	if (!et->table)
537 		return -ENOMEM;
538 
539 	for (i = 0; i < size; i++)
540 		INIT_LIST_HEAD(et->table + i);
541 
542 	return 0;
543 }
544 
545 static void dm_exception_table_exit(struct dm_exception_table *et,
546 				    struct kmem_cache *mem)
547 {
548 	struct list_head *slot;
549 	struct dm_exception *ex, *next;
550 	int i, size;
551 
552 	size = et->hash_mask + 1;
553 	for (i = 0; i < size; i++) {
554 		slot = et->table + i;
555 
556 		list_for_each_entry_safe (ex, next, slot, hash_list)
557 			kmem_cache_free(mem, ex);
558 	}
559 
560 	vfree(et->table);
561 }
562 
563 static uint32_t exception_hash(struct dm_exception_table *et, chunk_t chunk)
564 {
565 	return (chunk >> et->hash_shift) & et->hash_mask;
566 }
567 
568 static void dm_remove_exception(struct dm_exception *e)
569 {
570 	list_del(&e->hash_list);
571 }
572 
573 /*
574  * Return the exception data for a sector, or NULL if not
575  * remapped.
576  */
577 static struct dm_exception *dm_lookup_exception(struct dm_exception_table *et,
578 						chunk_t chunk)
579 {
580 	struct list_head *slot;
581 	struct dm_exception *e;
582 
583 	slot = &et->table[exception_hash(et, chunk)];
584 	list_for_each_entry (e, slot, hash_list)
585 		if (chunk >= e->old_chunk &&
586 		    chunk <= e->old_chunk + dm_consecutive_chunk_count(e))
587 			return e;
588 
589 	return NULL;
590 }
591 
592 static struct dm_exception *alloc_completed_exception(void)
593 {
594 	struct dm_exception *e;
595 
596 	e = kmem_cache_alloc(exception_cache, GFP_NOIO);
597 	if (!e)
598 		e = kmem_cache_alloc(exception_cache, GFP_ATOMIC);
599 
600 	return e;
601 }
602 
603 static void free_completed_exception(struct dm_exception *e)
604 {
605 	kmem_cache_free(exception_cache, e);
606 }
607 
608 static struct dm_snap_pending_exception *alloc_pending_exception(struct dm_snapshot *s)
609 {
610 	struct dm_snap_pending_exception *pe = mempool_alloc(s->pending_pool,
611 							     GFP_NOIO);
612 
613 	atomic_inc(&s->pending_exceptions_count);
614 	pe->snap = s;
615 
616 	return pe;
617 }
618 
619 static void free_pending_exception(struct dm_snap_pending_exception *pe)
620 {
621 	struct dm_snapshot *s = pe->snap;
622 
623 	mempool_free(pe, s->pending_pool);
624 	smp_mb__before_atomic_dec();
625 	atomic_dec(&s->pending_exceptions_count);
626 }
627 
628 static void dm_insert_exception(struct dm_exception_table *eh,
629 				struct dm_exception *new_e)
630 {
631 	struct list_head *l;
632 	struct dm_exception *e = NULL;
633 
634 	l = &eh->table[exception_hash(eh, new_e->old_chunk)];
635 
636 	/* Add immediately if this table doesn't support consecutive chunks */
637 	if (!eh->hash_shift)
638 		goto out;
639 
640 	/* List is ordered by old_chunk */
641 	list_for_each_entry_reverse(e, l, hash_list) {
642 		/* Insert after an existing chunk? */
643 		if (new_e->old_chunk == (e->old_chunk +
644 					 dm_consecutive_chunk_count(e) + 1) &&
645 		    new_e->new_chunk == (dm_chunk_number(e->new_chunk) +
646 					 dm_consecutive_chunk_count(e) + 1)) {
647 			dm_consecutive_chunk_count_inc(e);
648 			free_completed_exception(new_e);
649 			return;
650 		}
651 
652 		/* Insert before an existing chunk? */
653 		if (new_e->old_chunk == (e->old_chunk - 1) &&
654 		    new_e->new_chunk == (dm_chunk_number(e->new_chunk) - 1)) {
655 			dm_consecutive_chunk_count_inc(e);
656 			e->old_chunk--;
657 			e->new_chunk--;
658 			free_completed_exception(new_e);
659 			return;
660 		}
661 
662 		if (new_e->old_chunk > e->old_chunk)
663 			break;
664 	}
665 
666 out:
667 	list_add(&new_e->hash_list, e ? &e->hash_list : l);
668 }
669 
670 /*
671  * Callback used by the exception stores to load exceptions when
672  * initialising.
673  */
674 static int dm_add_exception(void *context, chunk_t old, chunk_t new)
675 {
676 	struct dm_snapshot *s = context;
677 	struct dm_exception *e;
678 
679 	e = alloc_completed_exception();
680 	if (!e)
681 		return -ENOMEM;
682 
683 	e->old_chunk = old;
684 
685 	/* Consecutive_count is implicitly initialised to zero */
686 	e->new_chunk = new;
687 
688 	dm_insert_exception(&s->complete, e);
689 
690 	return 0;
691 }
692 
693 /*
694  * Return a minimum chunk size of all snapshots that have the specified origin.
695  * Return zero if the origin has no snapshots.
696  */
697 static sector_t __minimum_chunk_size(struct origin *o)
698 {
699 	struct dm_snapshot *snap;
700 	unsigned chunk_size = 0;
701 
702 	if (o)
703 		list_for_each_entry(snap, &o->snapshots, list)
704 			chunk_size = min_not_zero(chunk_size,
705 						  snap->store->chunk_size);
706 
707 	return chunk_size;
708 }
709 
710 /*
711  * Hard coded magic.
712  */
713 static int calc_max_buckets(void)
714 {
715 	/* use a fixed size of 2MB */
716 	unsigned long mem = 2 * 1024 * 1024;
717 	mem /= sizeof(struct list_head);
718 
719 	return mem;
720 }
721 
722 /*
723  * Allocate room for a suitable hash table.
724  */
725 static int init_hash_tables(struct dm_snapshot *s)
726 {
727 	sector_t hash_size, cow_dev_size, origin_dev_size, max_buckets;
728 
729 	/*
730 	 * Calculate based on the size of the original volume or
731 	 * the COW volume...
732 	 */
733 	cow_dev_size = get_dev_size(s->cow->bdev);
734 	origin_dev_size = get_dev_size(s->origin->bdev);
735 	max_buckets = calc_max_buckets();
736 
737 	hash_size = min(origin_dev_size, cow_dev_size) >> s->store->chunk_shift;
738 	hash_size = min(hash_size, max_buckets);
739 
740 	if (hash_size < 64)
741 		hash_size = 64;
742 	hash_size = rounddown_pow_of_two(hash_size);
743 	if (dm_exception_table_init(&s->complete, hash_size,
744 				    DM_CHUNK_CONSECUTIVE_BITS))
745 		return -ENOMEM;
746 
747 	/*
748 	 * Allocate hash table for in-flight exceptions
749 	 * Make this smaller than the real hash table
750 	 */
751 	hash_size >>= 3;
752 	if (hash_size < 64)
753 		hash_size = 64;
754 
755 	if (dm_exception_table_init(&s->pending, hash_size, 0)) {
756 		dm_exception_table_exit(&s->complete, exception_cache);
757 		return -ENOMEM;
758 	}
759 
760 	return 0;
761 }
762 
763 static void merge_shutdown(struct dm_snapshot *s)
764 {
765 	clear_bit_unlock(RUNNING_MERGE, &s->state_bits);
766 	smp_mb__after_clear_bit();
767 	wake_up_bit(&s->state_bits, RUNNING_MERGE);
768 }
769 
770 static struct bio *__release_queued_bios_after_merge(struct dm_snapshot *s)
771 {
772 	s->first_merging_chunk = 0;
773 	s->num_merging_chunks = 0;
774 
775 	return bio_list_get(&s->bios_queued_during_merge);
776 }
777 
778 /*
779  * Remove one chunk from the index of completed exceptions.
780  */
781 static int __remove_single_exception_chunk(struct dm_snapshot *s,
782 					   chunk_t old_chunk)
783 {
784 	struct dm_exception *e;
785 
786 	e = dm_lookup_exception(&s->complete, old_chunk);
787 	if (!e) {
788 		DMERR("Corruption detected: exception for block %llu is "
789 		      "on disk but not in memory",
790 		      (unsigned long long)old_chunk);
791 		return -EINVAL;
792 	}
793 
794 	/*
795 	 * If this is the only chunk using this exception, remove exception.
796 	 */
797 	if (!dm_consecutive_chunk_count(e)) {
798 		dm_remove_exception(e);
799 		free_completed_exception(e);
800 		return 0;
801 	}
802 
803 	/*
804 	 * The chunk may be either at the beginning or the end of a
805 	 * group of consecutive chunks - never in the middle.  We are
806 	 * removing chunks in the opposite order to that in which they
807 	 * were added, so this should always be true.
808 	 * Decrement the consecutive chunk counter and adjust the
809 	 * starting point if necessary.
810 	 */
811 	if (old_chunk == e->old_chunk) {
812 		e->old_chunk++;
813 		e->new_chunk++;
814 	} else if (old_chunk != e->old_chunk +
815 		   dm_consecutive_chunk_count(e)) {
816 		DMERR("Attempt to merge block %llu from the "
817 		      "middle of a chunk range [%llu - %llu]",
818 		      (unsigned long long)old_chunk,
819 		      (unsigned long long)e->old_chunk,
820 		      (unsigned long long)
821 		      e->old_chunk + dm_consecutive_chunk_count(e));
822 		return -EINVAL;
823 	}
824 
825 	dm_consecutive_chunk_count_dec(e);
826 
827 	return 0;
828 }
829 
830 static void flush_bios(struct bio *bio);
831 
832 static int remove_single_exception_chunk(struct dm_snapshot *s)
833 {
834 	struct bio *b = NULL;
835 	int r;
836 	chunk_t old_chunk = s->first_merging_chunk + s->num_merging_chunks - 1;
837 
838 	down_write(&s->lock);
839 
840 	/*
841 	 * Process chunks (and associated exceptions) in reverse order
842 	 * so that dm_consecutive_chunk_count_dec() accounting works.
843 	 */
844 	do {
845 		r = __remove_single_exception_chunk(s, old_chunk);
846 		if (r)
847 			goto out;
848 	} while (old_chunk-- > s->first_merging_chunk);
849 
850 	b = __release_queued_bios_after_merge(s);
851 
852 out:
853 	up_write(&s->lock);
854 	if (b)
855 		flush_bios(b);
856 
857 	return r;
858 }
859 
860 static int origin_write_extent(struct dm_snapshot *merging_snap,
861 			       sector_t sector, unsigned chunk_size);
862 
863 static void merge_callback(int read_err, unsigned long write_err,
864 			   void *context);
865 
866 static uint64_t read_pending_exceptions_done_count(void)
867 {
868 	uint64_t pending_exceptions_done;
869 
870 	spin_lock(&_pending_exceptions_done_spinlock);
871 	pending_exceptions_done = _pending_exceptions_done_count;
872 	spin_unlock(&_pending_exceptions_done_spinlock);
873 
874 	return pending_exceptions_done;
875 }
876 
877 static void increment_pending_exceptions_done_count(void)
878 {
879 	spin_lock(&_pending_exceptions_done_spinlock);
880 	_pending_exceptions_done_count++;
881 	spin_unlock(&_pending_exceptions_done_spinlock);
882 
883 	wake_up_all(&_pending_exceptions_done);
884 }
885 
886 static void snapshot_merge_next_chunks(struct dm_snapshot *s)
887 {
888 	int i, linear_chunks;
889 	chunk_t old_chunk, new_chunk;
890 	struct dm_io_region src, dest;
891 	sector_t io_size;
892 	uint64_t previous_count;
893 
894 	BUG_ON(!test_bit(RUNNING_MERGE, &s->state_bits));
895 	if (unlikely(test_bit(SHUTDOWN_MERGE, &s->state_bits)))
896 		goto shut;
897 
898 	/*
899 	 * valid flag never changes during merge, so no lock required.
900 	 */
901 	if (!s->valid) {
902 		DMERR("Snapshot is invalid: can't merge");
903 		goto shut;
904 	}
905 
906 	linear_chunks = s->store->type->prepare_merge(s->store, &old_chunk,
907 						      &new_chunk);
908 	if (linear_chunks <= 0) {
909 		if (linear_chunks < 0) {
910 			DMERR("Read error in exception store: "
911 			      "shutting down merge");
912 			down_write(&s->lock);
913 			s->merge_failed = 1;
914 			up_write(&s->lock);
915 		}
916 		goto shut;
917 	}
918 
919 	/* Adjust old_chunk and new_chunk to reflect start of linear region */
920 	old_chunk = old_chunk + 1 - linear_chunks;
921 	new_chunk = new_chunk + 1 - linear_chunks;
922 
923 	/*
924 	 * Use one (potentially large) I/O to copy all 'linear_chunks'
925 	 * from the exception store to the origin
926 	 */
927 	io_size = linear_chunks * s->store->chunk_size;
928 
929 	dest.bdev = s->origin->bdev;
930 	dest.sector = chunk_to_sector(s->store, old_chunk);
931 	dest.count = min(io_size, get_dev_size(dest.bdev) - dest.sector);
932 
933 	src.bdev = s->cow->bdev;
934 	src.sector = chunk_to_sector(s->store, new_chunk);
935 	src.count = dest.count;
936 
937 	/*
938 	 * Reallocate any exceptions needed in other snapshots then
939 	 * wait for the pending exceptions to complete.
940 	 * Each time any pending exception (globally on the system)
941 	 * completes we are woken and repeat the process to find out
942 	 * if we can proceed.  While this may not seem a particularly
943 	 * efficient algorithm, it is not expected to have any
944 	 * significant impact on performance.
945 	 */
946 	previous_count = read_pending_exceptions_done_count();
947 	while (origin_write_extent(s, dest.sector, io_size)) {
948 		wait_event(_pending_exceptions_done,
949 			   (read_pending_exceptions_done_count() !=
950 			    previous_count));
951 		/* Retry after the wait, until all exceptions are done. */
952 		previous_count = read_pending_exceptions_done_count();
953 	}
954 
955 	down_write(&s->lock);
956 	s->first_merging_chunk = old_chunk;
957 	s->num_merging_chunks = linear_chunks;
958 	up_write(&s->lock);
959 
960 	/* Wait until writes to all 'linear_chunks' drain */
961 	for (i = 0; i < linear_chunks; i++)
962 		__check_for_conflicting_io(s, old_chunk + i);
963 
964 	dm_kcopyd_copy(s->kcopyd_client, &src, 1, &dest, 0, merge_callback, s);
965 	return;
966 
967 shut:
968 	merge_shutdown(s);
969 }
970 
971 static void error_bios(struct bio *bio);
972 
973 static void merge_callback(int read_err, unsigned long write_err, void *context)
974 {
975 	struct dm_snapshot *s = context;
976 	struct bio *b = NULL;
977 
978 	if (read_err || write_err) {
979 		if (read_err)
980 			DMERR("Read error: shutting down merge.");
981 		else
982 			DMERR("Write error: shutting down merge.");
983 		goto shut;
984 	}
985 
986 	if (s->store->type->commit_merge(s->store,
987 					 s->num_merging_chunks) < 0) {
988 		DMERR("Write error in exception store: shutting down merge");
989 		goto shut;
990 	}
991 
992 	if (remove_single_exception_chunk(s) < 0)
993 		goto shut;
994 
995 	snapshot_merge_next_chunks(s);
996 
997 	return;
998 
999 shut:
1000 	down_write(&s->lock);
1001 	s->merge_failed = 1;
1002 	b = __release_queued_bios_after_merge(s);
1003 	up_write(&s->lock);
1004 	error_bios(b);
1005 
1006 	merge_shutdown(s);
1007 }
1008 
1009 static void start_merge(struct dm_snapshot *s)
1010 {
1011 	if (!test_and_set_bit(RUNNING_MERGE, &s->state_bits))
1012 		snapshot_merge_next_chunks(s);
1013 }
1014 
1015 static int wait_schedule(void *ptr)
1016 {
1017 	schedule();
1018 
1019 	return 0;
1020 }
1021 
1022 /*
1023  * Stop the merging process and wait until it finishes.
1024  */
1025 static void stop_merge(struct dm_snapshot *s)
1026 {
1027 	set_bit(SHUTDOWN_MERGE, &s->state_bits);
1028 	wait_on_bit(&s->state_bits, RUNNING_MERGE, wait_schedule,
1029 		    TASK_UNINTERRUPTIBLE);
1030 	clear_bit(SHUTDOWN_MERGE, &s->state_bits);
1031 }
1032 
1033 /*
1034  * Construct a snapshot mapping: <origin_dev> <COW-dev> <p/n> <chunk-size>
1035  */
1036 static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
1037 {
1038 	struct dm_snapshot *s;
1039 	int i;
1040 	int r = -EINVAL;
1041 	char *origin_path, *cow_path;
1042 	unsigned args_used, num_flush_requests = 1;
1043 	fmode_t origin_mode = FMODE_READ;
1044 
1045 	if (argc != 4) {
1046 		ti->error = "requires exactly 4 arguments";
1047 		r = -EINVAL;
1048 		goto bad;
1049 	}
1050 
1051 	if (dm_target_is_snapshot_merge(ti)) {
1052 		num_flush_requests = 2;
1053 		origin_mode = FMODE_WRITE;
1054 	}
1055 
1056 	s = kmalloc(sizeof(*s), GFP_KERNEL);
1057 	if (!s) {
1058 		ti->error = "Cannot allocate snapshot context private "
1059 		    "structure";
1060 		r = -ENOMEM;
1061 		goto bad;
1062 	}
1063 
1064 	origin_path = argv[0];
1065 	argv++;
1066 	argc--;
1067 
1068 	r = dm_get_device(ti, origin_path, origin_mode, &s->origin);
1069 	if (r) {
1070 		ti->error = "Cannot get origin device";
1071 		goto bad_origin;
1072 	}
1073 
1074 	cow_path = argv[0];
1075 	argv++;
1076 	argc--;
1077 
1078 	r = dm_get_device(ti, cow_path, dm_table_get_mode(ti->table), &s->cow);
1079 	if (r) {
1080 		ti->error = "Cannot get COW device";
1081 		goto bad_cow;
1082 	}
1083 
1084 	r = dm_exception_store_create(ti, argc, argv, s, &args_used, &s->store);
1085 	if (r) {
1086 		ti->error = "Couldn't create exception store";
1087 		r = -EINVAL;
1088 		goto bad_store;
1089 	}
1090 
1091 	argv += args_used;
1092 	argc -= args_used;
1093 
1094 	s->ti = ti;
1095 	s->valid = 1;
1096 	s->active = 0;
1097 	atomic_set(&s->pending_exceptions_count, 0);
1098 	init_rwsem(&s->lock);
1099 	INIT_LIST_HEAD(&s->list);
1100 	spin_lock_init(&s->pe_lock);
1101 	s->state_bits = 0;
1102 	s->merge_failed = 0;
1103 	s->first_merging_chunk = 0;
1104 	s->num_merging_chunks = 0;
1105 	bio_list_init(&s->bios_queued_during_merge);
1106 
1107 	/* Allocate hash table for COW data */
1108 	if (init_hash_tables(s)) {
1109 		ti->error = "Unable to allocate hash table space";
1110 		r = -ENOMEM;
1111 		goto bad_hash_tables;
1112 	}
1113 
1114 	s->kcopyd_client = dm_kcopyd_client_create();
1115 	if (IS_ERR(s->kcopyd_client)) {
1116 		r = PTR_ERR(s->kcopyd_client);
1117 		ti->error = "Could not create kcopyd client";
1118 		goto bad_kcopyd;
1119 	}
1120 
1121 	s->pending_pool = mempool_create_slab_pool(MIN_IOS, pending_cache);
1122 	if (!s->pending_pool) {
1123 		ti->error = "Could not allocate mempool for pending exceptions";
1124 		goto bad_pending_pool;
1125 	}
1126 
1127 	s->tracked_chunk_pool = mempool_create_slab_pool(MIN_IOS,
1128 							 tracked_chunk_cache);
1129 	if (!s->tracked_chunk_pool) {
1130 		ti->error = "Could not allocate tracked_chunk mempool for "
1131 			    "tracking reads";
1132 		goto bad_tracked_chunk_pool;
1133 	}
1134 
1135 	for (i = 0; i < DM_TRACKED_CHUNK_HASH_SIZE; i++)
1136 		INIT_HLIST_HEAD(&s->tracked_chunk_hash[i]);
1137 
1138 	spin_lock_init(&s->tracked_chunk_lock);
1139 
1140 	ti->private = s;
1141 	ti->num_flush_requests = num_flush_requests;
1142 
1143 	/* Add snapshot to the list of snapshots for this origin */
1144 	/* Exceptions aren't triggered till snapshot_resume() is called */
1145 	r = register_snapshot(s);
1146 	if (r == -ENOMEM) {
1147 		ti->error = "Snapshot origin struct allocation failed";
1148 		goto bad_load_and_register;
1149 	} else if (r < 0) {
1150 		/* invalid handover, register_snapshot has set ti->error */
1151 		goto bad_load_and_register;
1152 	}
1153 
1154 	/*
1155 	 * Metadata must only be loaded into one table at once, so skip this
1156 	 * if metadata will be handed over during resume.
1157 	 * Chunk size will be set during the handover - set it to zero to
1158 	 * ensure it's ignored.
1159 	 */
1160 	if (r > 0) {
1161 		s->store->chunk_size = 0;
1162 		return 0;
1163 	}
1164 
1165 	r = s->store->type->read_metadata(s->store, dm_add_exception,
1166 					  (void *)s);
1167 	if (r < 0) {
1168 		ti->error = "Failed to read snapshot metadata";
1169 		goto bad_read_metadata;
1170 	} else if (r > 0) {
1171 		s->valid = 0;
1172 		DMWARN("Snapshot is marked invalid.");
1173 	}
1174 
1175 	if (!s->store->chunk_size) {
1176 		ti->error = "Chunk size not set";
1177 		goto bad_read_metadata;
1178 	}
1179 	ti->split_io = s->store->chunk_size;
1180 
1181 	return 0;
1182 
1183 bad_read_metadata:
1184 	unregister_snapshot(s);
1185 
1186 bad_load_and_register:
1187 	mempool_destroy(s->tracked_chunk_pool);
1188 
1189 bad_tracked_chunk_pool:
1190 	mempool_destroy(s->pending_pool);
1191 
1192 bad_pending_pool:
1193 	dm_kcopyd_client_destroy(s->kcopyd_client);
1194 
1195 bad_kcopyd:
1196 	dm_exception_table_exit(&s->pending, pending_cache);
1197 	dm_exception_table_exit(&s->complete, exception_cache);
1198 
1199 bad_hash_tables:
1200 	dm_exception_store_destroy(s->store);
1201 
1202 bad_store:
1203 	dm_put_device(ti, s->cow);
1204 
1205 bad_cow:
1206 	dm_put_device(ti, s->origin);
1207 
1208 bad_origin:
1209 	kfree(s);
1210 
1211 bad:
1212 	return r;
1213 }
1214 
1215 static void __free_exceptions(struct dm_snapshot *s)
1216 {
1217 	dm_kcopyd_client_destroy(s->kcopyd_client);
1218 	s->kcopyd_client = NULL;
1219 
1220 	dm_exception_table_exit(&s->pending, pending_cache);
1221 	dm_exception_table_exit(&s->complete, exception_cache);
1222 }
1223 
1224 static void __handover_exceptions(struct dm_snapshot *snap_src,
1225 				  struct dm_snapshot *snap_dest)
1226 {
1227 	union {
1228 		struct dm_exception_table table_swap;
1229 		struct dm_exception_store *store_swap;
1230 	} u;
1231 
1232 	/*
1233 	 * Swap all snapshot context information between the two instances.
1234 	 */
1235 	u.table_swap = snap_dest->complete;
1236 	snap_dest->complete = snap_src->complete;
1237 	snap_src->complete = u.table_swap;
1238 
1239 	u.store_swap = snap_dest->store;
1240 	snap_dest->store = snap_src->store;
1241 	snap_src->store = u.store_swap;
1242 
1243 	snap_dest->store->snap = snap_dest;
1244 	snap_src->store->snap = snap_src;
1245 
1246 	snap_dest->ti->split_io = snap_dest->store->chunk_size;
1247 	snap_dest->valid = snap_src->valid;
1248 
1249 	/*
1250 	 * Set source invalid to ensure it receives no further I/O.
1251 	 */
1252 	snap_src->valid = 0;
1253 }
1254 
1255 static void snapshot_dtr(struct dm_target *ti)
1256 {
1257 #ifdef CONFIG_DM_DEBUG
1258 	int i;
1259 #endif
1260 	struct dm_snapshot *s = ti->private;
1261 	struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
1262 
1263 	down_read(&_origins_lock);
1264 	/* Check whether exception handover must be cancelled */
1265 	(void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL);
1266 	if (snap_src && snap_dest && (s == snap_src)) {
1267 		down_write(&snap_dest->lock);
1268 		snap_dest->valid = 0;
1269 		up_write(&snap_dest->lock);
1270 		DMERR("Cancelling snapshot handover.");
1271 	}
1272 	up_read(&_origins_lock);
1273 
1274 	if (dm_target_is_snapshot_merge(ti))
1275 		stop_merge(s);
1276 
1277 	/* Prevent further origin writes from using this snapshot. */
1278 	/* After this returns there can be no new kcopyd jobs. */
1279 	unregister_snapshot(s);
1280 
1281 	while (atomic_read(&s->pending_exceptions_count))
1282 		msleep(1);
1283 	/*
1284 	 * Ensure instructions in mempool_destroy aren't reordered
1285 	 * before atomic_read.
1286 	 */
1287 	smp_mb();
1288 
1289 #ifdef CONFIG_DM_DEBUG
1290 	for (i = 0; i < DM_TRACKED_CHUNK_HASH_SIZE; i++)
1291 		BUG_ON(!hlist_empty(&s->tracked_chunk_hash[i]));
1292 #endif
1293 
1294 	mempool_destroy(s->tracked_chunk_pool);
1295 
1296 	__free_exceptions(s);
1297 
1298 	mempool_destroy(s->pending_pool);
1299 
1300 	dm_exception_store_destroy(s->store);
1301 
1302 	dm_put_device(ti, s->cow);
1303 
1304 	dm_put_device(ti, s->origin);
1305 
1306 	kfree(s);
1307 }
1308 
1309 /*
1310  * Flush a list of buffers.
1311  */
1312 static void flush_bios(struct bio *bio)
1313 {
1314 	struct bio *n;
1315 
1316 	while (bio) {
1317 		n = bio->bi_next;
1318 		bio->bi_next = NULL;
1319 		generic_make_request(bio);
1320 		bio = n;
1321 	}
1322 }
1323 
1324 static int do_origin(struct dm_dev *origin, struct bio *bio);
1325 
1326 /*
1327  * Flush a list of buffers.
1328  */
1329 static void retry_origin_bios(struct dm_snapshot *s, struct bio *bio)
1330 {
1331 	struct bio *n;
1332 	int r;
1333 
1334 	while (bio) {
1335 		n = bio->bi_next;
1336 		bio->bi_next = NULL;
1337 		r = do_origin(s->origin, bio);
1338 		if (r == DM_MAPIO_REMAPPED)
1339 			generic_make_request(bio);
1340 		bio = n;
1341 	}
1342 }
1343 
1344 /*
1345  * Error a list of buffers.
1346  */
1347 static void error_bios(struct bio *bio)
1348 {
1349 	struct bio *n;
1350 
1351 	while (bio) {
1352 		n = bio->bi_next;
1353 		bio->bi_next = NULL;
1354 		bio_io_error(bio);
1355 		bio = n;
1356 	}
1357 }
1358 
1359 static void __invalidate_snapshot(struct dm_snapshot *s, int err)
1360 {
1361 	if (!s->valid)
1362 		return;
1363 
1364 	if (err == -EIO)
1365 		DMERR("Invalidating snapshot: Error reading/writing.");
1366 	else if (err == -ENOMEM)
1367 		DMERR("Invalidating snapshot: Unable to allocate exception.");
1368 
1369 	if (s->store->type->drop_snapshot)
1370 		s->store->type->drop_snapshot(s->store);
1371 
1372 	s->valid = 0;
1373 
1374 	dm_table_event(s->ti->table);
1375 }
1376 
1377 static void pending_complete(struct dm_snap_pending_exception *pe, int success)
1378 {
1379 	struct dm_exception *e;
1380 	struct dm_snapshot *s = pe->snap;
1381 	struct bio *origin_bios = NULL;
1382 	struct bio *snapshot_bios = NULL;
1383 	int error = 0;
1384 
1385 	if (!success) {
1386 		/* Read/write error - snapshot is unusable */
1387 		down_write(&s->lock);
1388 		__invalidate_snapshot(s, -EIO);
1389 		error = 1;
1390 		goto out;
1391 	}
1392 
1393 	e = alloc_completed_exception();
1394 	if (!e) {
1395 		down_write(&s->lock);
1396 		__invalidate_snapshot(s, -ENOMEM);
1397 		error = 1;
1398 		goto out;
1399 	}
1400 	*e = pe->e;
1401 
1402 	down_write(&s->lock);
1403 	if (!s->valid) {
1404 		free_completed_exception(e);
1405 		error = 1;
1406 		goto out;
1407 	}
1408 
1409 	/* Check for conflicting reads */
1410 	__check_for_conflicting_io(s, pe->e.old_chunk);
1411 
1412 	/*
1413 	 * Add a proper exception, and remove the
1414 	 * in-flight exception from the list.
1415 	 */
1416 	dm_insert_exception(&s->complete, e);
1417 
1418  out:
1419 	dm_remove_exception(&pe->e);
1420 	snapshot_bios = bio_list_get(&pe->snapshot_bios);
1421 	origin_bios = bio_list_get(&pe->origin_bios);
1422 	free_pending_exception(pe);
1423 
1424 	increment_pending_exceptions_done_count();
1425 
1426 	up_write(&s->lock);
1427 
1428 	/* Submit any pending write bios */
1429 	if (error)
1430 		error_bios(snapshot_bios);
1431 	else
1432 		flush_bios(snapshot_bios);
1433 
1434 	retry_origin_bios(s, origin_bios);
1435 }
1436 
1437 static void commit_callback(void *context, int success)
1438 {
1439 	struct dm_snap_pending_exception *pe = context;
1440 
1441 	pending_complete(pe, success);
1442 }
1443 
1444 /*
1445  * Called when the copy I/O has finished.  kcopyd actually runs
1446  * this code so don't block.
1447  */
1448 static void copy_callback(int read_err, unsigned long write_err, void *context)
1449 {
1450 	struct dm_snap_pending_exception *pe = context;
1451 	struct dm_snapshot *s = pe->snap;
1452 
1453 	if (read_err || write_err)
1454 		pending_complete(pe, 0);
1455 
1456 	else
1457 		/* Update the metadata if we are persistent */
1458 		s->store->type->commit_exception(s->store, &pe->e,
1459 						 commit_callback, pe);
1460 }
1461 
1462 /*
1463  * Dispatches the copy operation to kcopyd.
1464  */
1465 static void start_copy(struct dm_snap_pending_exception *pe)
1466 {
1467 	struct dm_snapshot *s = pe->snap;
1468 	struct dm_io_region src, dest;
1469 	struct block_device *bdev = s->origin->bdev;
1470 	sector_t dev_size;
1471 
1472 	dev_size = get_dev_size(bdev);
1473 
1474 	src.bdev = bdev;
1475 	src.sector = chunk_to_sector(s->store, pe->e.old_chunk);
1476 	src.count = min((sector_t)s->store->chunk_size, dev_size - src.sector);
1477 
1478 	dest.bdev = s->cow->bdev;
1479 	dest.sector = chunk_to_sector(s->store, pe->e.new_chunk);
1480 	dest.count = src.count;
1481 
1482 	/* Hand over to kcopyd */
1483 	dm_kcopyd_copy(s->kcopyd_client,
1484 		    &src, 1, &dest, 0, copy_callback, pe);
1485 }
1486 
1487 static struct dm_snap_pending_exception *
1488 __lookup_pending_exception(struct dm_snapshot *s, chunk_t chunk)
1489 {
1490 	struct dm_exception *e = dm_lookup_exception(&s->pending, chunk);
1491 
1492 	if (!e)
1493 		return NULL;
1494 
1495 	return container_of(e, struct dm_snap_pending_exception, e);
1496 }
1497 
1498 /*
1499  * Looks to see if this snapshot already has a pending exception
1500  * for this chunk, otherwise it allocates a new one and inserts
1501  * it into the pending table.
1502  *
1503  * NOTE: a write lock must be held on snap->lock before calling
1504  * this.
1505  */
1506 static struct dm_snap_pending_exception *
1507 __find_pending_exception(struct dm_snapshot *s,
1508 			 struct dm_snap_pending_exception *pe, chunk_t chunk)
1509 {
1510 	struct dm_snap_pending_exception *pe2;
1511 
1512 	pe2 = __lookup_pending_exception(s, chunk);
1513 	if (pe2) {
1514 		free_pending_exception(pe);
1515 		return pe2;
1516 	}
1517 
1518 	pe->e.old_chunk = chunk;
1519 	bio_list_init(&pe->origin_bios);
1520 	bio_list_init(&pe->snapshot_bios);
1521 	pe->started = 0;
1522 
1523 	if (s->store->type->prepare_exception(s->store, &pe->e)) {
1524 		free_pending_exception(pe);
1525 		return NULL;
1526 	}
1527 
1528 	dm_insert_exception(&s->pending, &pe->e);
1529 
1530 	return pe;
1531 }
1532 
1533 static void remap_exception(struct dm_snapshot *s, struct dm_exception *e,
1534 			    struct bio *bio, chunk_t chunk)
1535 {
1536 	bio->bi_bdev = s->cow->bdev;
1537 	bio->bi_sector = chunk_to_sector(s->store,
1538 					 dm_chunk_number(e->new_chunk) +
1539 					 (chunk - e->old_chunk)) +
1540 					 (bio->bi_sector &
1541 					  s->store->chunk_mask);
1542 }
1543 
1544 static int snapshot_map(struct dm_target *ti, struct bio *bio,
1545 			union map_info *map_context)
1546 {
1547 	struct dm_exception *e;
1548 	struct dm_snapshot *s = ti->private;
1549 	int r = DM_MAPIO_REMAPPED;
1550 	chunk_t chunk;
1551 	struct dm_snap_pending_exception *pe = NULL;
1552 
1553 	if (bio->bi_rw & REQ_FLUSH) {
1554 		bio->bi_bdev = s->cow->bdev;
1555 		return DM_MAPIO_REMAPPED;
1556 	}
1557 
1558 	chunk = sector_to_chunk(s->store, bio->bi_sector);
1559 
1560 	/* Full snapshots are not usable */
1561 	/* To get here the table must be live so s->active is always set. */
1562 	if (!s->valid)
1563 		return -EIO;
1564 
1565 	/* FIXME: should only take write lock if we need
1566 	 * to copy an exception */
1567 	down_write(&s->lock);
1568 
1569 	if (!s->valid) {
1570 		r = -EIO;
1571 		goto out_unlock;
1572 	}
1573 
1574 	/* If the block is already remapped - use that, else remap it */
1575 	e = dm_lookup_exception(&s->complete, chunk);
1576 	if (e) {
1577 		remap_exception(s, e, bio, chunk);
1578 		goto out_unlock;
1579 	}
1580 
1581 	/*
1582 	 * Write to snapshot - higher level takes care of RW/RO
1583 	 * flags so we should only get this if we are
1584 	 * writeable.
1585 	 */
1586 	if (bio_rw(bio) == WRITE) {
1587 		pe = __lookup_pending_exception(s, chunk);
1588 		if (!pe) {
1589 			up_write(&s->lock);
1590 			pe = alloc_pending_exception(s);
1591 			down_write(&s->lock);
1592 
1593 			if (!s->valid) {
1594 				free_pending_exception(pe);
1595 				r = -EIO;
1596 				goto out_unlock;
1597 			}
1598 
1599 			e = dm_lookup_exception(&s->complete, chunk);
1600 			if (e) {
1601 				free_pending_exception(pe);
1602 				remap_exception(s, e, bio, chunk);
1603 				goto out_unlock;
1604 			}
1605 
1606 			pe = __find_pending_exception(s, pe, chunk);
1607 			if (!pe) {
1608 				__invalidate_snapshot(s, -ENOMEM);
1609 				r = -EIO;
1610 				goto out_unlock;
1611 			}
1612 		}
1613 
1614 		remap_exception(s, &pe->e, bio, chunk);
1615 		bio_list_add(&pe->snapshot_bios, bio);
1616 
1617 		r = DM_MAPIO_SUBMITTED;
1618 
1619 		if (!pe->started) {
1620 			/* this is protected by snap->lock */
1621 			pe->started = 1;
1622 			up_write(&s->lock);
1623 			start_copy(pe);
1624 			goto out;
1625 		}
1626 	} else {
1627 		bio->bi_bdev = s->origin->bdev;
1628 		map_context->ptr = track_chunk(s, chunk);
1629 	}
1630 
1631  out_unlock:
1632 	up_write(&s->lock);
1633  out:
1634 	return r;
1635 }
1636 
1637 /*
1638  * A snapshot-merge target behaves like a combination of a snapshot
1639  * target and a snapshot-origin target.  It only generates new
1640  * exceptions in other snapshots and not in the one that is being
1641  * merged.
1642  *
1643  * For each chunk, if there is an existing exception, it is used to
1644  * redirect I/O to the cow device.  Otherwise I/O is sent to the origin,
1645  * which in turn might generate exceptions in other snapshots.
1646  * If merging is currently taking place on the chunk in question, the
1647  * I/O is deferred by adding it to s->bios_queued_during_merge.
1648  */
1649 static int snapshot_merge_map(struct dm_target *ti, struct bio *bio,
1650 			      union map_info *map_context)
1651 {
1652 	struct dm_exception *e;
1653 	struct dm_snapshot *s = ti->private;
1654 	int r = DM_MAPIO_REMAPPED;
1655 	chunk_t chunk;
1656 
1657 	if (bio->bi_rw & REQ_FLUSH) {
1658 		if (!map_context->target_request_nr)
1659 			bio->bi_bdev = s->origin->bdev;
1660 		else
1661 			bio->bi_bdev = s->cow->bdev;
1662 		map_context->ptr = NULL;
1663 		return DM_MAPIO_REMAPPED;
1664 	}
1665 
1666 	chunk = sector_to_chunk(s->store, bio->bi_sector);
1667 
1668 	down_write(&s->lock);
1669 
1670 	/* Full merging snapshots are redirected to the origin */
1671 	if (!s->valid)
1672 		goto redirect_to_origin;
1673 
1674 	/* If the block is already remapped - use that */
1675 	e = dm_lookup_exception(&s->complete, chunk);
1676 	if (e) {
1677 		/* Queue writes overlapping with chunks being merged */
1678 		if (bio_rw(bio) == WRITE &&
1679 		    chunk >= s->first_merging_chunk &&
1680 		    chunk < (s->first_merging_chunk +
1681 			     s->num_merging_chunks)) {
1682 			bio->bi_bdev = s->origin->bdev;
1683 			bio_list_add(&s->bios_queued_during_merge, bio);
1684 			r = DM_MAPIO_SUBMITTED;
1685 			goto out_unlock;
1686 		}
1687 
1688 		remap_exception(s, e, bio, chunk);
1689 
1690 		if (bio_rw(bio) == WRITE)
1691 			map_context->ptr = track_chunk(s, chunk);
1692 		goto out_unlock;
1693 	}
1694 
1695 redirect_to_origin:
1696 	bio->bi_bdev = s->origin->bdev;
1697 
1698 	if (bio_rw(bio) == WRITE) {
1699 		up_write(&s->lock);
1700 		return do_origin(s->origin, bio);
1701 	}
1702 
1703 out_unlock:
1704 	up_write(&s->lock);
1705 
1706 	return r;
1707 }
1708 
1709 static int snapshot_end_io(struct dm_target *ti, struct bio *bio,
1710 			   int error, union map_info *map_context)
1711 {
1712 	struct dm_snapshot *s = ti->private;
1713 	struct dm_snap_tracked_chunk *c = map_context->ptr;
1714 
1715 	if (c)
1716 		stop_tracking_chunk(s, c);
1717 
1718 	return 0;
1719 }
1720 
1721 static void snapshot_merge_presuspend(struct dm_target *ti)
1722 {
1723 	struct dm_snapshot *s = ti->private;
1724 
1725 	stop_merge(s);
1726 }
1727 
1728 static int snapshot_preresume(struct dm_target *ti)
1729 {
1730 	int r = 0;
1731 	struct dm_snapshot *s = ti->private;
1732 	struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
1733 
1734 	down_read(&_origins_lock);
1735 	(void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL);
1736 	if (snap_src && snap_dest) {
1737 		down_read(&snap_src->lock);
1738 		if (s == snap_src) {
1739 			DMERR("Unable to resume snapshot source until "
1740 			      "handover completes.");
1741 			r = -EINVAL;
1742 		} else if (!dm_suspended(snap_src->ti)) {
1743 			DMERR("Unable to perform snapshot handover until "
1744 			      "source is suspended.");
1745 			r = -EINVAL;
1746 		}
1747 		up_read(&snap_src->lock);
1748 	}
1749 	up_read(&_origins_lock);
1750 
1751 	return r;
1752 }
1753 
1754 static void snapshot_resume(struct dm_target *ti)
1755 {
1756 	struct dm_snapshot *s = ti->private;
1757 	struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
1758 
1759 	down_read(&_origins_lock);
1760 	(void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL);
1761 	if (snap_src && snap_dest) {
1762 		down_write(&snap_src->lock);
1763 		down_write_nested(&snap_dest->lock, SINGLE_DEPTH_NESTING);
1764 		__handover_exceptions(snap_src, snap_dest);
1765 		up_write(&snap_dest->lock);
1766 		up_write(&snap_src->lock);
1767 	}
1768 	up_read(&_origins_lock);
1769 
1770 	/* Now we have correct chunk size, reregister */
1771 	reregister_snapshot(s);
1772 
1773 	down_write(&s->lock);
1774 	s->active = 1;
1775 	up_write(&s->lock);
1776 }
1777 
1778 static sector_t get_origin_minimum_chunksize(struct block_device *bdev)
1779 {
1780 	sector_t min_chunksize;
1781 
1782 	down_read(&_origins_lock);
1783 	min_chunksize = __minimum_chunk_size(__lookup_origin(bdev));
1784 	up_read(&_origins_lock);
1785 
1786 	return min_chunksize;
1787 }
1788 
1789 static void snapshot_merge_resume(struct dm_target *ti)
1790 {
1791 	struct dm_snapshot *s = ti->private;
1792 
1793 	/*
1794 	 * Handover exceptions from existing snapshot.
1795 	 */
1796 	snapshot_resume(ti);
1797 
1798 	/*
1799 	 * snapshot-merge acts as an origin, so set ti->split_io
1800 	 */
1801 	ti->split_io = get_origin_minimum_chunksize(s->origin->bdev);
1802 
1803 	start_merge(s);
1804 }
1805 
1806 static int snapshot_status(struct dm_target *ti, status_type_t type,
1807 			   char *result, unsigned int maxlen)
1808 {
1809 	unsigned sz = 0;
1810 	struct dm_snapshot *snap = ti->private;
1811 
1812 	switch (type) {
1813 	case STATUSTYPE_INFO:
1814 
1815 		down_write(&snap->lock);
1816 
1817 		if (!snap->valid)
1818 			DMEMIT("Invalid");
1819 		else if (snap->merge_failed)
1820 			DMEMIT("Merge failed");
1821 		else {
1822 			if (snap->store->type->usage) {
1823 				sector_t total_sectors, sectors_allocated,
1824 					 metadata_sectors;
1825 				snap->store->type->usage(snap->store,
1826 							 &total_sectors,
1827 							 &sectors_allocated,
1828 							 &metadata_sectors);
1829 				DMEMIT("%llu/%llu %llu",
1830 				       (unsigned long long)sectors_allocated,
1831 				       (unsigned long long)total_sectors,
1832 				       (unsigned long long)metadata_sectors);
1833 			}
1834 			else
1835 				DMEMIT("Unknown");
1836 		}
1837 
1838 		up_write(&snap->lock);
1839 
1840 		break;
1841 
1842 	case STATUSTYPE_TABLE:
1843 		/*
1844 		 * kdevname returns a static pointer so we need
1845 		 * to make private copies if the output is to
1846 		 * make sense.
1847 		 */
1848 		DMEMIT("%s %s", snap->origin->name, snap->cow->name);
1849 		snap->store->type->status(snap->store, type, result + sz,
1850 					  maxlen - sz);
1851 		break;
1852 	}
1853 
1854 	return 0;
1855 }
1856 
1857 static int snapshot_iterate_devices(struct dm_target *ti,
1858 				    iterate_devices_callout_fn fn, void *data)
1859 {
1860 	struct dm_snapshot *snap = ti->private;
1861 	int r;
1862 
1863 	r = fn(ti, snap->origin, 0, ti->len, data);
1864 
1865 	if (!r)
1866 		r = fn(ti, snap->cow, 0, get_dev_size(snap->cow->bdev), data);
1867 
1868 	return r;
1869 }
1870 
1871 
1872 /*-----------------------------------------------------------------
1873  * Origin methods
1874  *---------------------------------------------------------------*/
1875 
1876 /*
1877  * If no exceptions need creating, DM_MAPIO_REMAPPED is returned and any
1878  * supplied bio was ignored.  The caller may submit it immediately.
1879  * (No remapping actually occurs as the origin is always a direct linear
1880  * map.)
1881  *
1882  * If further exceptions are required, DM_MAPIO_SUBMITTED is returned
1883  * and any supplied bio is added to a list to be submitted once all
1884  * the necessary exceptions exist.
1885  */
1886 static int __origin_write(struct list_head *snapshots, sector_t sector,
1887 			  struct bio *bio)
1888 {
1889 	int r = DM_MAPIO_REMAPPED;
1890 	struct dm_snapshot *snap;
1891 	struct dm_exception *e;
1892 	struct dm_snap_pending_exception *pe;
1893 	struct dm_snap_pending_exception *pe_to_start_now = NULL;
1894 	struct dm_snap_pending_exception *pe_to_start_last = NULL;
1895 	chunk_t chunk;
1896 
1897 	/* Do all the snapshots on this origin */
1898 	list_for_each_entry (snap, snapshots, list) {
1899 		/*
1900 		 * Don't make new exceptions in a merging snapshot
1901 		 * because it has effectively been deleted
1902 		 */
1903 		if (dm_target_is_snapshot_merge(snap->ti))
1904 			continue;
1905 
1906 		down_write(&snap->lock);
1907 
1908 		/* Only deal with valid and active snapshots */
1909 		if (!snap->valid || !snap->active)
1910 			goto next_snapshot;
1911 
1912 		/* Nothing to do if writing beyond end of snapshot */
1913 		if (sector >= dm_table_get_size(snap->ti->table))
1914 			goto next_snapshot;
1915 
1916 		/*
1917 		 * Remember, different snapshots can have
1918 		 * different chunk sizes.
1919 		 */
1920 		chunk = sector_to_chunk(snap->store, sector);
1921 
1922 		/*
1923 		 * Check exception table to see if block
1924 		 * is already remapped in this snapshot
1925 		 * and trigger an exception if not.
1926 		 */
1927 		e = dm_lookup_exception(&snap->complete, chunk);
1928 		if (e)
1929 			goto next_snapshot;
1930 
1931 		pe = __lookup_pending_exception(snap, chunk);
1932 		if (!pe) {
1933 			up_write(&snap->lock);
1934 			pe = alloc_pending_exception(snap);
1935 			down_write(&snap->lock);
1936 
1937 			if (!snap->valid) {
1938 				free_pending_exception(pe);
1939 				goto next_snapshot;
1940 			}
1941 
1942 			e = dm_lookup_exception(&snap->complete, chunk);
1943 			if (e) {
1944 				free_pending_exception(pe);
1945 				goto next_snapshot;
1946 			}
1947 
1948 			pe = __find_pending_exception(snap, pe, chunk);
1949 			if (!pe) {
1950 				__invalidate_snapshot(snap, -ENOMEM);
1951 				goto next_snapshot;
1952 			}
1953 		}
1954 
1955 		r = DM_MAPIO_SUBMITTED;
1956 
1957 		/*
1958 		 * If an origin bio was supplied, queue it to wait for the
1959 		 * completion of this exception, and start this one last,
1960 		 * at the end of the function.
1961 		 */
1962 		if (bio) {
1963 			bio_list_add(&pe->origin_bios, bio);
1964 			bio = NULL;
1965 
1966 			if (!pe->started) {
1967 				pe->started = 1;
1968 				pe_to_start_last = pe;
1969 			}
1970 		}
1971 
1972 		if (!pe->started) {
1973 			pe->started = 1;
1974 			pe_to_start_now = pe;
1975 		}
1976 
1977  next_snapshot:
1978 		up_write(&snap->lock);
1979 
1980 		if (pe_to_start_now) {
1981 			start_copy(pe_to_start_now);
1982 			pe_to_start_now = NULL;
1983 		}
1984 	}
1985 
1986 	/*
1987 	 * Submit the exception against which the bio is queued last,
1988 	 * to give the other exceptions a head start.
1989 	 */
1990 	if (pe_to_start_last)
1991 		start_copy(pe_to_start_last);
1992 
1993 	return r;
1994 }
1995 
1996 /*
1997  * Called on a write from the origin driver.
1998  */
1999 static int do_origin(struct dm_dev *origin, struct bio *bio)
2000 {
2001 	struct origin *o;
2002 	int r = DM_MAPIO_REMAPPED;
2003 
2004 	down_read(&_origins_lock);
2005 	o = __lookup_origin(origin->bdev);
2006 	if (o)
2007 		r = __origin_write(&o->snapshots, bio->bi_sector, bio);
2008 	up_read(&_origins_lock);
2009 
2010 	return r;
2011 }
2012 
2013 /*
2014  * Trigger exceptions in all non-merging snapshots.
2015  *
2016  * The chunk size of the merging snapshot may be larger than the chunk
2017  * size of some other snapshot so we may need to reallocate multiple
2018  * chunks in other snapshots.
2019  *
2020  * We scan all the overlapping exceptions in the other snapshots.
2021  * Returns 1 if anything was reallocated and must be waited for,
2022  * otherwise returns 0.
2023  *
2024  * size must be a multiple of merging_snap's chunk_size.
2025  */
2026 static int origin_write_extent(struct dm_snapshot *merging_snap,
2027 			       sector_t sector, unsigned size)
2028 {
2029 	int must_wait = 0;
2030 	sector_t n;
2031 	struct origin *o;
2032 
2033 	/*
2034 	 * The origin's __minimum_chunk_size() got stored in split_io
2035 	 * by snapshot_merge_resume().
2036 	 */
2037 	down_read(&_origins_lock);
2038 	o = __lookup_origin(merging_snap->origin->bdev);
2039 	for (n = 0; n < size; n += merging_snap->ti->split_io)
2040 		if (__origin_write(&o->snapshots, sector + n, NULL) ==
2041 		    DM_MAPIO_SUBMITTED)
2042 			must_wait = 1;
2043 	up_read(&_origins_lock);
2044 
2045 	return must_wait;
2046 }
2047 
2048 /*
2049  * Origin: maps a linear range of a device, with hooks for snapshotting.
2050  */
2051 
2052 /*
2053  * Construct an origin mapping: <dev_path>
2054  * The context for an origin is merely a 'struct dm_dev *'
2055  * pointing to the real device.
2056  */
2057 static int origin_ctr(struct dm_target *ti, unsigned int argc, char **argv)
2058 {
2059 	int r;
2060 	struct dm_dev *dev;
2061 
2062 	if (argc != 1) {
2063 		ti->error = "origin: incorrect number of arguments";
2064 		return -EINVAL;
2065 	}
2066 
2067 	r = dm_get_device(ti, argv[0], dm_table_get_mode(ti->table), &dev);
2068 	if (r) {
2069 		ti->error = "Cannot get target device";
2070 		return r;
2071 	}
2072 
2073 	ti->private = dev;
2074 	ti->num_flush_requests = 1;
2075 
2076 	return 0;
2077 }
2078 
2079 static void origin_dtr(struct dm_target *ti)
2080 {
2081 	struct dm_dev *dev = ti->private;
2082 	dm_put_device(ti, dev);
2083 }
2084 
2085 static int origin_map(struct dm_target *ti, struct bio *bio,
2086 		      union map_info *map_context)
2087 {
2088 	struct dm_dev *dev = ti->private;
2089 	bio->bi_bdev = dev->bdev;
2090 
2091 	if (bio->bi_rw & REQ_FLUSH)
2092 		return DM_MAPIO_REMAPPED;
2093 
2094 	/* Only tell snapshots if this is a write */
2095 	return (bio_rw(bio) == WRITE) ? do_origin(dev, bio) : DM_MAPIO_REMAPPED;
2096 }
2097 
2098 /*
2099  * Set the target "split_io" field to the minimum of all the snapshots'
2100  * chunk sizes.
2101  */
2102 static void origin_resume(struct dm_target *ti)
2103 {
2104 	struct dm_dev *dev = ti->private;
2105 
2106 	ti->split_io = get_origin_minimum_chunksize(dev->bdev);
2107 }
2108 
2109 static int origin_status(struct dm_target *ti, status_type_t type, char *result,
2110 			 unsigned int maxlen)
2111 {
2112 	struct dm_dev *dev = ti->private;
2113 
2114 	switch (type) {
2115 	case STATUSTYPE_INFO:
2116 		result[0] = '\0';
2117 		break;
2118 
2119 	case STATUSTYPE_TABLE:
2120 		snprintf(result, maxlen, "%s", dev->name);
2121 		break;
2122 	}
2123 
2124 	return 0;
2125 }
2126 
2127 static int origin_merge(struct dm_target *ti, struct bvec_merge_data *bvm,
2128 			struct bio_vec *biovec, int max_size)
2129 {
2130 	struct dm_dev *dev = ti->private;
2131 	struct request_queue *q = bdev_get_queue(dev->bdev);
2132 
2133 	if (!q->merge_bvec_fn)
2134 		return max_size;
2135 
2136 	bvm->bi_bdev = dev->bdev;
2137 	bvm->bi_sector = bvm->bi_sector;
2138 
2139 	return min(max_size, q->merge_bvec_fn(q, bvm, biovec));
2140 }
2141 
2142 static int origin_iterate_devices(struct dm_target *ti,
2143 				  iterate_devices_callout_fn fn, void *data)
2144 {
2145 	struct dm_dev *dev = ti->private;
2146 
2147 	return fn(ti, dev, 0, ti->len, data);
2148 }
2149 
2150 static struct target_type origin_target = {
2151 	.name    = "snapshot-origin",
2152 	.version = {1, 7, 1},
2153 	.module  = THIS_MODULE,
2154 	.ctr     = origin_ctr,
2155 	.dtr     = origin_dtr,
2156 	.map     = origin_map,
2157 	.resume  = origin_resume,
2158 	.status  = origin_status,
2159 	.merge	 = origin_merge,
2160 	.iterate_devices = origin_iterate_devices,
2161 };
2162 
2163 static struct target_type snapshot_target = {
2164 	.name    = "snapshot",
2165 	.version = {1, 10, 0},
2166 	.module  = THIS_MODULE,
2167 	.ctr     = snapshot_ctr,
2168 	.dtr     = snapshot_dtr,
2169 	.map     = snapshot_map,
2170 	.end_io  = snapshot_end_io,
2171 	.preresume  = snapshot_preresume,
2172 	.resume  = snapshot_resume,
2173 	.status  = snapshot_status,
2174 	.iterate_devices = snapshot_iterate_devices,
2175 };
2176 
2177 static struct target_type merge_target = {
2178 	.name    = dm_snapshot_merge_target_name,
2179 	.version = {1, 1, 0},
2180 	.module  = THIS_MODULE,
2181 	.ctr     = snapshot_ctr,
2182 	.dtr     = snapshot_dtr,
2183 	.map     = snapshot_merge_map,
2184 	.end_io  = snapshot_end_io,
2185 	.presuspend = snapshot_merge_presuspend,
2186 	.preresume  = snapshot_preresume,
2187 	.resume  = snapshot_merge_resume,
2188 	.status  = snapshot_status,
2189 	.iterate_devices = snapshot_iterate_devices,
2190 };
2191 
2192 static int __init dm_snapshot_init(void)
2193 {
2194 	int r;
2195 
2196 	r = dm_exception_store_init();
2197 	if (r) {
2198 		DMERR("Failed to initialize exception stores");
2199 		return r;
2200 	}
2201 
2202 	r = dm_register_target(&snapshot_target);
2203 	if (r < 0) {
2204 		DMERR("snapshot target register failed %d", r);
2205 		goto bad_register_snapshot_target;
2206 	}
2207 
2208 	r = dm_register_target(&origin_target);
2209 	if (r < 0) {
2210 		DMERR("Origin target register failed %d", r);
2211 		goto bad_register_origin_target;
2212 	}
2213 
2214 	r = dm_register_target(&merge_target);
2215 	if (r < 0) {
2216 		DMERR("Merge target register failed %d", r);
2217 		goto bad_register_merge_target;
2218 	}
2219 
2220 	r = init_origin_hash();
2221 	if (r) {
2222 		DMERR("init_origin_hash failed.");
2223 		goto bad_origin_hash;
2224 	}
2225 
2226 	exception_cache = KMEM_CACHE(dm_exception, 0);
2227 	if (!exception_cache) {
2228 		DMERR("Couldn't create exception cache.");
2229 		r = -ENOMEM;
2230 		goto bad_exception_cache;
2231 	}
2232 
2233 	pending_cache = KMEM_CACHE(dm_snap_pending_exception, 0);
2234 	if (!pending_cache) {
2235 		DMERR("Couldn't create pending cache.");
2236 		r = -ENOMEM;
2237 		goto bad_pending_cache;
2238 	}
2239 
2240 	tracked_chunk_cache = KMEM_CACHE(dm_snap_tracked_chunk, 0);
2241 	if (!tracked_chunk_cache) {
2242 		DMERR("Couldn't create cache to track chunks in use.");
2243 		r = -ENOMEM;
2244 		goto bad_tracked_chunk_cache;
2245 	}
2246 
2247 	return 0;
2248 
2249 bad_tracked_chunk_cache:
2250 	kmem_cache_destroy(pending_cache);
2251 bad_pending_cache:
2252 	kmem_cache_destroy(exception_cache);
2253 bad_exception_cache:
2254 	exit_origin_hash();
2255 bad_origin_hash:
2256 	dm_unregister_target(&merge_target);
2257 bad_register_merge_target:
2258 	dm_unregister_target(&origin_target);
2259 bad_register_origin_target:
2260 	dm_unregister_target(&snapshot_target);
2261 bad_register_snapshot_target:
2262 	dm_exception_store_exit();
2263 
2264 	return r;
2265 }
2266 
2267 static void __exit dm_snapshot_exit(void)
2268 {
2269 	dm_unregister_target(&snapshot_target);
2270 	dm_unregister_target(&origin_target);
2271 	dm_unregister_target(&merge_target);
2272 
2273 	exit_origin_hash();
2274 	kmem_cache_destroy(pending_cache);
2275 	kmem_cache_destroy(exception_cache);
2276 	kmem_cache_destroy(tracked_chunk_cache);
2277 
2278 	dm_exception_store_exit();
2279 }
2280 
2281 /* Module hooks */
2282 module_init(dm_snapshot_init);
2283 module_exit(dm_snapshot_exit);
2284 
2285 MODULE_DESCRIPTION(DM_NAME " snapshot target");
2286 MODULE_AUTHOR("Joe Thornber");
2287 MODULE_LICENSE("GPL");
2288