xref: /linux/drivers/md/dm-snap.c (revision 4f3c8320c78cdd11c8fdd23c33787407f719322e)
1 /*
2  * Copyright (C) 2001-2002 Sistina Software (UK) Limited.
3  *
4  * This file is released under the GPL.
5  */
6 
7 #include <linux/blkdev.h>
8 #include <linux/device-mapper.h>
9 #include <linux/delay.h>
10 #include <linux/fs.h>
11 #include <linux/init.h>
12 #include <linux/kdev_t.h>
13 #include <linux/list.h>
14 #include <linux/list_bl.h>
15 #include <linux/mempool.h>
16 #include <linux/module.h>
17 #include <linux/slab.h>
18 #include <linux/vmalloc.h>
19 #include <linux/log2.h>
20 #include <linux/dm-kcopyd.h>
21 
22 #include "dm.h"
23 
24 #include "dm-exception-store.h"
25 
26 #define DM_MSG_PREFIX "snapshots"
27 
28 static const char dm_snapshot_merge_target_name[] = "snapshot-merge";
29 
30 #define dm_target_is_snapshot_merge(ti) \
31 	((ti)->type->name == dm_snapshot_merge_target_name)
32 
33 /*
34  * The size of the mempool used to track chunks in use.
35  */
36 #define MIN_IOS 256
37 
38 #define DM_TRACKED_CHUNK_HASH_SIZE	16
39 #define DM_TRACKED_CHUNK_HASH(x)	((unsigned long)(x) & \
40 					 (DM_TRACKED_CHUNK_HASH_SIZE - 1))
41 
42 struct dm_exception_table {
43 	uint32_t hash_mask;
44 	unsigned hash_shift;
45 	struct hlist_bl_head *table;
46 };
47 
48 struct dm_snapshot {
49 	struct rw_semaphore lock;
50 
51 	struct dm_dev *origin;
52 	struct dm_dev *cow;
53 
54 	struct dm_target *ti;
55 
56 	/* List of snapshots per Origin */
57 	struct list_head list;
58 
59 	/*
60 	 * You can't use a snapshot if this is 0 (e.g. if full).
61 	 * A snapshot-merge target never clears this.
62 	 */
63 	int valid;
64 
65 	/*
66 	 * The snapshot overflowed because of a write to the snapshot device.
67 	 * We don't have to invalidate the snapshot in this case, but we need
68 	 * to prevent further writes.
69 	 */
70 	int snapshot_overflowed;
71 
72 	/* Origin writes don't trigger exceptions until this is set */
73 	int active;
74 
75 	atomic_t pending_exceptions_count;
76 
77 	spinlock_t pe_allocation_lock;
78 
79 	/* Protected by "pe_allocation_lock" */
80 	sector_t exception_start_sequence;
81 
82 	/* Protected by kcopyd single-threaded callback */
83 	sector_t exception_complete_sequence;
84 
85 	/*
86 	 * A list of pending exceptions that completed out of order.
87 	 * Protected by kcopyd single-threaded callback.
88 	 */
89 	struct rb_root out_of_order_tree;
90 
91 	mempool_t pending_pool;
92 
93 	struct dm_exception_table pending;
94 	struct dm_exception_table complete;
95 
96 	/*
97 	 * pe_lock protects all pending_exception operations and access
98 	 * as well as the snapshot_bios list.
99 	 */
100 	spinlock_t pe_lock;
101 
102 	/* Chunks with outstanding reads */
103 	spinlock_t tracked_chunk_lock;
104 	struct hlist_head tracked_chunk_hash[DM_TRACKED_CHUNK_HASH_SIZE];
105 
106 	/* The on disk metadata handler */
107 	struct dm_exception_store *store;
108 
109 	unsigned in_progress;
110 	struct wait_queue_head in_progress_wait;
111 
112 	struct dm_kcopyd_client *kcopyd_client;
113 
114 	/* Wait for events based on state_bits */
115 	unsigned long state_bits;
116 
117 	/* Range of chunks currently being merged. */
118 	chunk_t first_merging_chunk;
119 	int num_merging_chunks;
120 
121 	/*
122 	 * The merge operation failed if this flag is set.
123 	 * Failure modes are handled as follows:
124 	 * - I/O error reading the header
125 	 *   	=> don't load the target; abort.
126 	 * - Header does not have "valid" flag set
127 	 *   	=> use the origin; forget about the snapshot.
128 	 * - I/O error when reading exceptions
129 	 *   	=> don't load the target; abort.
130 	 *         (We can't use the intermediate origin state.)
131 	 * - I/O error while merging
132 	 *	=> stop merging; set merge_failed; process I/O normally.
133 	 */
134 	bool merge_failed:1;
135 
136 	bool discard_zeroes_cow:1;
137 	bool discard_passdown_origin:1;
138 
139 	/*
140 	 * Incoming bios that overlap with chunks being merged must wait
141 	 * for them to be committed.
142 	 */
143 	struct bio_list bios_queued_during_merge;
144 };
145 
146 /*
147  * state_bits:
148  *   RUNNING_MERGE  - Merge operation is in progress.
149  *   SHUTDOWN_MERGE - Set to signal that merge needs to be stopped;
150  *                    cleared afterwards.
151  */
152 #define RUNNING_MERGE          0
153 #define SHUTDOWN_MERGE         1
154 
155 /*
156  * Maximum number of chunks being copied on write.
157  *
158  * The value was decided experimentally as a trade-off between memory
159  * consumption, stalling the kernel's workqueues and maintaining a high enough
160  * throughput.
161  */
162 #define DEFAULT_COW_THRESHOLD 2048
163 
164 static unsigned cow_threshold = DEFAULT_COW_THRESHOLD;
165 module_param_named(snapshot_cow_threshold, cow_threshold, uint, 0644);
166 MODULE_PARM_DESC(snapshot_cow_threshold, "Maximum number of chunks being copied on write");
167 
168 DECLARE_DM_KCOPYD_THROTTLE_WITH_MODULE_PARM(snapshot_copy_throttle,
169 		"A percentage of time allocated for copy on write");
170 
171 struct dm_dev *dm_snap_origin(struct dm_snapshot *s)
172 {
173 	return s->origin;
174 }
175 EXPORT_SYMBOL(dm_snap_origin);
176 
177 struct dm_dev *dm_snap_cow(struct dm_snapshot *s)
178 {
179 	return s->cow;
180 }
181 EXPORT_SYMBOL(dm_snap_cow);
182 
183 static sector_t chunk_to_sector(struct dm_exception_store *store,
184 				chunk_t chunk)
185 {
186 	return chunk << store->chunk_shift;
187 }
188 
189 static int bdev_equal(struct block_device *lhs, struct block_device *rhs)
190 {
191 	/*
192 	 * There is only ever one instance of a particular block
193 	 * device so we can compare pointers safely.
194 	 */
195 	return lhs == rhs;
196 }
197 
198 struct dm_snap_pending_exception {
199 	struct dm_exception e;
200 
201 	/*
202 	 * Origin buffers waiting for this to complete are held
203 	 * in a bio list
204 	 */
205 	struct bio_list origin_bios;
206 	struct bio_list snapshot_bios;
207 
208 	/* Pointer back to snapshot context */
209 	struct dm_snapshot *snap;
210 
211 	/*
212 	 * 1 indicates the exception has already been sent to
213 	 * kcopyd.
214 	 */
215 	int started;
216 
217 	/* There was copying error. */
218 	int copy_error;
219 
220 	/* A sequence number, it is used for in-order completion. */
221 	sector_t exception_sequence;
222 
223 	struct rb_node out_of_order_node;
224 
225 	/*
226 	 * For writing a complete chunk, bypassing the copy.
227 	 */
228 	struct bio *full_bio;
229 	bio_end_io_t *full_bio_end_io;
230 };
231 
232 /*
233  * Hash table mapping origin volumes to lists of snapshots and
234  * a lock to protect it
235  */
236 static struct kmem_cache *exception_cache;
237 static struct kmem_cache *pending_cache;
238 
239 struct dm_snap_tracked_chunk {
240 	struct hlist_node node;
241 	chunk_t chunk;
242 };
243 
244 static void init_tracked_chunk(struct bio *bio)
245 {
246 	struct dm_snap_tracked_chunk *c = dm_per_bio_data(bio, sizeof(struct dm_snap_tracked_chunk));
247 	INIT_HLIST_NODE(&c->node);
248 }
249 
250 static bool is_bio_tracked(struct bio *bio)
251 {
252 	struct dm_snap_tracked_chunk *c = dm_per_bio_data(bio, sizeof(struct dm_snap_tracked_chunk));
253 	return !hlist_unhashed(&c->node);
254 }
255 
256 static void track_chunk(struct dm_snapshot *s, struct bio *bio, chunk_t chunk)
257 {
258 	struct dm_snap_tracked_chunk *c = dm_per_bio_data(bio, sizeof(struct dm_snap_tracked_chunk));
259 
260 	c->chunk = chunk;
261 
262 	spin_lock_irq(&s->tracked_chunk_lock);
263 	hlist_add_head(&c->node,
264 		       &s->tracked_chunk_hash[DM_TRACKED_CHUNK_HASH(chunk)]);
265 	spin_unlock_irq(&s->tracked_chunk_lock);
266 }
267 
268 static void stop_tracking_chunk(struct dm_snapshot *s, struct bio *bio)
269 {
270 	struct dm_snap_tracked_chunk *c = dm_per_bio_data(bio, sizeof(struct dm_snap_tracked_chunk));
271 	unsigned long flags;
272 
273 	spin_lock_irqsave(&s->tracked_chunk_lock, flags);
274 	hlist_del(&c->node);
275 	spin_unlock_irqrestore(&s->tracked_chunk_lock, flags);
276 }
277 
278 static int __chunk_is_tracked(struct dm_snapshot *s, chunk_t chunk)
279 {
280 	struct dm_snap_tracked_chunk *c;
281 	int found = 0;
282 
283 	spin_lock_irq(&s->tracked_chunk_lock);
284 
285 	hlist_for_each_entry(c,
286 	    &s->tracked_chunk_hash[DM_TRACKED_CHUNK_HASH(chunk)], node) {
287 		if (c->chunk == chunk) {
288 			found = 1;
289 			break;
290 		}
291 	}
292 
293 	spin_unlock_irq(&s->tracked_chunk_lock);
294 
295 	return found;
296 }
297 
298 /*
299  * This conflicting I/O is extremely improbable in the caller,
300  * so msleep(1) is sufficient and there is no need for a wait queue.
301  */
302 static void __check_for_conflicting_io(struct dm_snapshot *s, chunk_t chunk)
303 {
304 	while (__chunk_is_tracked(s, chunk))
305 		msleep(1);
306 }
307 
308 /*
309  * One of these per registered origin, held in the snapshot_origins hash
310  */
311 struct origin {
312 	/* The origin device */
313 	struct block_device *bdev;
314 
315 	struct list_head hash_list;
316 
317 	/* List of snapshots for this origin */
318 	struct list_head snapshots;
319 };
320 
321 /*
322  * This structure is allocated for each origin target
323  */
324 struct dm_origin {
325 	struct dm_dev *dev;
326 	struct dm_target *ti;
327 	unsigned split_boundary;
328 	struct list_head hash_list;
329 };
330 
331 /*
332  * Size of the hash table for origin volumes. If we make this
333  * the size of the minors list then it should be nearly perfect
334  */
335 #define ORIGIN_HASH_SIZE 256
336 #define ORIGIN_MASK      0xFF
337 static struct list_head *_origins;
338 static struct list_head *_dm_origins;
339 static struct rw_semaphore _origins_lock;
340 
341 static DECLARE_WAIT_QUEUE_HEAD(_pending_exceptions_done);
342 static DEFINE_SPINLOCK(_pending_exceptions_done_spinlock);
343 static uint64_t _pending_exceptions_done_count;
344 
345 static int init_origin_hash(void)
346 {
347 	int i;
348 
349 	_origins = kmalloc_array(ORIGIN_HASH_SIZE, sizeof(struct list_head),
350 				 GFP_KERNEL);
351 	if (!_origins) {
352 		DMERR("unable to allocate memory for _origins");
353 		return -ENOMEM;
354 	}
355 	for (i = 0; i < ORIGIN_HASH_SIZE; i++)
356 		INIT_LIST_HEAD(_origins + i);
357 
358 	_dm_origins = kmalloc_array(ORIGIN_HASH_SIZE,
359 				    sizeof(struct list_head),
360 				    GFP_KERNEL);
361 	if (!_dm_origins) {
362 		DMERR("unable to allocate memory for _dm_origins");
363 		kfree(_origins);
364 		return -ENOMEM;
365 	}
366 	for (i = 0; i < ORIGIN_HASH_SIZE; i++)
367 		INIT_LIST_HEAD(_dm_origins + i);
368 
369 	init_rwsem(&_origins_lock);
370 
371 	return 0;
372 }
373 
374 static void exit_origin_hash(void)
375 {
376 	kfree(_origins);
377 	kfree(_dm_origins);
378 }
379 
380 static unsigned origin_hash(struct block_device *bdev)
381 {
382 	return bdev->bd_dev & ORIGIN_MASK;
383 }
384 
385 static struct origin *__lookup_origin(struct block_device *origin)
386 {
387 	struct list_head *ol;
388 	struct origin *o;
389 
390 	ol = &_origins[origin_hash(origin)];
391 	list_for_each_entry (o, ol, hash_list)
392 		if (bdev_equal(o->bdev, origin))
393 			return o;
394 
395 	return NULL;
396 }
397 
398 static void __insert_origin(struct origin *o)
399 {
400 	struct list_head *sl = &_origins[origin_hash(o->bdev)];
401 	list_add_tail(&o->hash_list, sl);
402 }
403 
404 static struct dm_origin *__lookup_dm_origin(struct block_device *origin)
405 {
406 	struct list_head *ol;
407 	struct dm_origin *o;
408 
409 	ol = &_dm_origins[origin_hash(origin)];
410 	list_for_each_entry (o, ol, hash_list)
411 		if (bdev_equal(o->dev->bdev, origin))
412 			return o;
413 
414 	return NULL;
415 }
416 
417 static void __insert_dm_origin(struct dm_origin *o)
418 {
419 	struct list_head *sl = &_dm_origins[origin_hash(o->dev->bdev)];
420 	list_add_tail(&o->hash_list, sl);
421 }
422 
423 static void __remove_dm_origin(struct dm_origin *o)
424 {
425 	list_del(&o->hash_list);
426 }
427 
428 /*
429  * _origins_lock must be held when calling this function.
430  * Returns number of snapshots registered using the supplied cow device, plus:
431  * snap_src - a snapshot suitable for use as a source of exception handover
432  * snap_dest - a snapshot capable of receiving exception handover.
433  * snap_merge - an existing snapshot-merge target linked to the same origin.
434  *   There can be at most one snapshot-merge target. The parameter is optional.
435  *
436  * Possible return values and states of snap_src and snap_dest.
437  *   0: NULL, NULL  - first new snapshot
438  *   1: snap_src, NULL - normal snapshot
439  *   2: snap_src, snap_dest  - waiting for handover
440  *   2: snap_src, NULL - handed over, waiting for old to be deleted
441  *   1: NULL, snap_dest - source got destroyed without handover
442  */
443 static int __find_snapshots_sharing_cow(struct dm_snapshot *snap,
444 					struct dm_snapshot **snap_src,
445 					struct dm_snapshot **snap_dest,
446 					struct dm_snapshot **snap_merge)
447 {
448 	struct dm_snapshot *s;
449 	struct origin *o;
450 	int count = 0;
451 	int active;
452 
453 	o = __lookup_origin(snap->origin->bdev);
454 	if (!o)
455 		goto out;
456 
457 	list_for_each_entry(s, &o->snapshots, list) {
458 		if (dm_target_is_snapshot_merge(s->ti) && snap_merge)
459 			*snap_merge = s;
460 		if (!bdev_equal(s->cow->bdev, snap->cow->bdev))
461 			continue;
462 
463 		down_read(&s->lock);
464 		active = s->active;
465 		up_read(&s->lock);
466 
467 		if (active) {
468 			if (snap_src)
469 				*snap_src = s;
470 		} else if (snap_dest)
471 			*snap_dest = s;
472 
473 		count++;
474 	}
475 
476 out:
477 	return count;
478 }
479 
480 /*
481  * On success, returns 1 if this snapshot is a handover destination,
482  * otherwise returns 0.
483  */
484 static int __validate_exception_handover(struct dm_snapshot *snap)
485 {
486 	struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
487 	struct dm_snapshot *snap_merge = NULL;
488 
489 	/* Does snapshot need exceptions handed over to it? */
490 	if ((__find_snapshots_sharing_cow(snap, &snap_src, &snap_dest,
491 					  &snap_merge) == 2) ||
492 	    snap_dest) {
493 		snap->ti->error = "Snapshot cow pairing for exception "
494 				  "table handover failed";
495 		return -EINVAL;
496 	}
497 
498 	/*
499 	 * If no snap_src was found, snap cannot become a handover
500 	 * destination.
501 	 */
502 	if (!snap_src)
503 		return 0;
504 
505 	/*
506 	 * Non-snapshot-merge handover?
507 	 */
508 	if (!dm_target_is_snapshot_merge(snap->ti))
509 		return 1;
510 
511 	/*
512 	 * Do not allow more than one merging snapshot.
513 	 */
514 	if (snap_merge) {
515 		snap->ti->error = "A snapshot is already merging.";
516 		return -EINVAL;
517 	}
518 
519 	if (!snap_src->store->type->prepare_merge ||
520 	    !snap_src->store->type->commit_merge) {
521 		snap->ti->error = "Snapshot exception store does not "
522 				  "support snapshot-merge.";
523 		return -EINVAL;
524 	}
525 
526 	return 1;
527 }
528 
529 static void __insert_snapshot(struct origin *o, struct dm_snapshot *s)
530 {
531 	struct dm_snapshot *l;
532 
533 	/* Sort the list according to chunk size, largest-first smallest-last */
534 	list_for_each_entry(l, &o->snapshots, list)
535 		if (l->store->chunk_size < s->store->chunk_size)
536 			break;
537 	list_add_tail(&s->list, &l->list);
538 }
539 
540 /*
541  * Make a note of the snapshot and its origin so we can look it
542  * up when the origin has a write on it.
543  *
544  * Also validate snapshot exception store handovers.
545  * On success, returns 1 if this registration is a handover destination,
546  * otherwise returns 0.
547  */
548 static int register_snapshot(struct dm_snapshot *snap)
549 {
550 	struct origin *o, *new_o = NULL;
551 	struct block_device *bdev = snap->origin->bdev;
552 	int r = 0;
553 
554 	new_o = kmalloc(sizeof(*new_o), GFP_KERNEL);
555 	if (!new_o)
556 		return -ENOMEM;
557 
558 	down_write(&_origins_lock);
559 
560 	r = __validate_exception_handover(snap);
561 	if (r < 0) {
562 		kfree(new_o);
563 		goto out;
564 	}
565 
566 	o = __lookup_origin(bdev);
567 	if (o)
568 		kfree(new_o);
569 	else {
570 		/* New origin */
571 		o = new_o;
572 
573 		/* Initialise the struct */
574 		INIT_LIST_HEAD(&o->snapshots);
575 		o->bdev = bdev;
576 
577 		__insert_origin(o);
578 	}
579 
580 	__insert_snapshot(o, snap);
581 
582 out:
583 	up_write(&_origins_lock);
584 
585 	return r;
586 }
587 
588 /*
589  * Move snapshot to correct place in list according to chunk size.
590  */
591 static void reregister_snapshot(struct dm_snapshot *s)
592 {
593 	struct block_device *bdev = s->origin->bdev;
594 
595 	down_write(&_origins_lock);
596 
597 	list_del(&s->list);
598 	__insert_snapshot(__lookup_origin(bdev), s);
599 
600 	up_write(&_origins_lock);
601 }
602 
603 static void unregister_snapshot(struct dm_snapshot *s)
604 {
605 	struct origin *o;
606 
607 	down_write(&_origins_lock);
608 	o = __lookup_origin(s->origin->bdev);
609 
610 	list_del(&s->list);
611 	if (o && list_empty(&o->snapshots)) {
612 		list_del(&o->hash_list);
613 		kfree(o);
614 	}
615 
616 	up_write(&_origins_lock);
617 }
618 
619 /*
620  * Implementation of the exception hash tables.
621  * The lowest hash_shift bits of the chunk number are ignored, allowing
622  * some consecutive chunks to be grouped together.
623  */
624 static uint32_t exception_hash(struct dm_exception_table *et, chunk_t chunk);
625 
626 /* Lock to protect access to the completed and pending exception hash tables. */
627 struct dm_exception_table_lock {
628 	struct hlist_bl_head *complete_slot;
629 	struct hlist_bl_head *pending_slot;
630 };
631 
632 static void dm_exception_table_lock_init(struct dm_snapshot *s, chunk_t chunk,
633 					 struct dm_exception_table_lock *lock)
634 {
635 	struct dm_exception_table *complete = &s->complete;
636 	struct dm_exception_table *pending = &s->pending;
637 
638 	lock->complete_slot = &complete->table[exception_hash(complete, chunk)];
639 	lock->pending_slot = &pending->table[exception_hash(pending, chunk)];
640 }
641 
642 static void dm_exception_table_lock(struct dm_exception_table_lock *lock)
643 {
644 	hlist_bl_lock(lock->complete_slot);
645 	hlist_bl_lock(lock->pending_slot);
646 }
647 
648 static void dm_exception_table_unlock(struct dm_exception_table_lock *lock)
649 {
650 	hlist_bl_unlock(lock->pending_slot);
651 	hlist_bl_unlock(lock->complete_slot);
652 }
653 
654 static int dm_exception_table_init(struct dm_exception_table *et,
655 				   uint32_t size, unsigned hash_shift)
656 {
657 	unsigned int i;
658 
659 	et->hash_shift = hash_shift;
660 	et->hash_mask = size - 1;
661 	et->table = dm_vcalloc(size, sizeof(struct hlist_bl_head));
662 	if (!et->table)
663 		return -ENOMEM;
664 
665 	for (i = 0; i < size; i++)
666 		INIT_HLIST_BL_HEAD(et->table + i);
667 
668 	return 0;
669 }
670 
671 static void dm_exception_table_exit(struct dm_exception_table *et,
672 				    struct kmem_cache *mem)
673 {
674 	struct hlist_bl_head *slot;
675 	struct dm_exception *ex;
676 	struct hlist_bl_node *pos, *n;
677 	int i, size;
678 
679 	size = et->hash_mask + 1;
680 	for (i = 0; i < size; i++) {
681 		slot = et->table + i;
682 
683 		hlist_bl_for_each_entry_safe(ex, pos, n, slot, hash_list)
684 			kmem_cache_free(mem, ex);
685 	}
686 
687 	vfree(et->table);
688 }
689 
690 static uint32_t exception_hash(struct dm_exception_table *et, chunk_t chunk)
691 {
692 	return (chunk >> et->hash_shift) & et->hash_mask;
693 }
694 
695 static void dm_remove_exception(struct dm_exception *e)
696 {
697 	hlist_bl_del(&e->hash_list);
698 }
699 
700 /*
701  * Return the exception data for a sector, or NULL if not
702  * remapped.
703  */
704 static struct dm_exception *dm_lookup_exception(struct dm_exception_table *et,
705 						chunk_t chunk)
706 {
707 	struct hlist_bl_head *slot;
708 	struct hlist_bl_node *pos;
709 	struct dm_exception *e;
710 
711 	slot = &et->table[exception_hash(et, chunk)];
712 	hlist_bl_for_each_entry(e, pos, slot, hash_list)
713 		if (chunk >= e->old_chunk &&
714 		    chunk <= e->old_chunk + dm_consecutive_chunk_count(e))
715 			return e;
716 
717 	return NULL;
718 }
719 
720 static struct dm_exception *alloc_completed_exception(gfp_t gfp)
721 {
722 	struct dm_exception *e;
723 
724 	e = kmem_cache_alloc(exception_cache, gfp);
725 	if (!e && gfp == GFP_NOIO)
726 		e = kmem_cache_alloc(exception_cache, GFP_ATOMIC);
727 
728 	return e;
729 }
730 
731 static void free_completed_exception(struct dm_exception *e)
732 {
733 	kmem_cache_free(exception_cache, e);
734 }
735 
736 static struct dm_snap_pending_exception *alloc_pending_exception(struct dm_snapshot *s)
737 {
738 	struct dm_snap_pending_exception *pe = mempool_alloc(&s->pending_pool,
739 							     GFP_NOIO);
740 
741 	atomic_inc(&s->pending_exceptions_count);
742 	pe->snap = s;
743 
744 	return pe;
745 }
746 
747 static void free_pending_exception(struct dm_snap_pending_exception *pe)
748 {
749 	struct dm_snapshot *s = pe->snap;
750 
751 	mempool_free(pe, &s->pending_pool);
752 	smp_mb__before_atomic();
753 	atomic_dec(&s->pending_exceptions_count);
754 }
755 
756 static void dm_insert_exception(struct dm_exception_table *eh,
757 				struct dm_exception *new_e)
758 {
759 	struct hlist_bl_head *l;
760 	struct hlist_bl_node *pos;
761 	struct dm_exception *e = NULL;
762 
763 	l = &eh->table[exception_hash(eh, new_e->old_chunk)];
764 
765 	/* Add immediately if this table doesn't support consecutive chunks */
766 	if (!eh->hash_shift)
767 		goto out;
768 
769 	/* List is ordered by old_chunk */
770 	hlist_bl_for_each_entry(e, pos, l, hash_list) {
771 		/* Insert after an existing chunk? */
772 		if (new_e->old_chunk == (e->old_chunk +
773 					 dm_consecutive_chunk_count(e) + 1) &&
774 		    new_e->new_chunk == (dm_chunk_number(e->new_chunk) +
775 					 dm_consecutive_chunk_count(e) + 1)) {
776 			dm_consecutive_chunk_count_inc(e);
777 			free_completed_exception(new_e);
778 			return;
779 		}
780 
781 		/* Insert before an existing chunk? */
782 		if (new_e->old_chunk == (e->old_chunk - 1) &&
783 		    new_e->new_chunk == (dm_chunk_number(e->new_chunk) - 1)) {
784 			dm_consecutive_chunk_count_inc(e);
785 			e->old_chunk--;
786 			e->new_chunk--;
787 			free_completed_exception(new_e);
788 			return;
789 		}
790 
791 		if (new_e->old_chunk < e->old_chunk)
792 			break;
793 	}
794 
795 out:
796 	if (!e) {
797 		/*
798 		 * Either the table doesn't support consecutive chunks or slot
799 		 * l is empty.
800 		 */
801 		hlist_bl_add_head(&new_e->hash_list, l);
802 	} else if (new_e->old_chunk < e->old_chunk) {
803 		/* Add before an existing exception */
804 		hlist_bl_add_before(&new_e->hash_list, &e->hash_list);
805 	} else {
806 		/* Add to l's tail: e is the last exception in this slot */
807 		hlist_bl_add_behind(&new_e->hash_list, &e->hash_list);
808 	}
809 }
810 
811 /*
812  * Callback used by the exception stores to load exceptions when
813  * initialising.
814  */
815 static int dm_add_exception(void *context, chunk_t old, chunk_t new)
816 {
817 	struct dm_exception_table_lock lock;
818 	struct dm_snapshot *s = context;
819 	struct dm_exception *e;
820 
821 	e = alloc_completed_exception(GFP_KERNEL);
822 	if (!e)
823 		return -ENOMEM;
824 
825 	e->old_chunk = old;
826 
827 	/* Consecutive_count is implicitly initialised to zero */
828 	e->new_chunk = new;
829 
830 	/*
831 	 * Although there is no need to lock access to the exception tables
832 	 * here, if we don't then hlist_bl_add_head(), called by
833 	 * dm_insert_exception(), will complain about accessing the
834 	 * corresponding list without locking it first.
835 	 */
836 	dm_exception_table_lock_init(s, old, &lock);
837 
838 	dm_exception_table_lock(&lock);
839 	dm_insert_exception(&s->complete, e);
840 	dm_exception_table_unlock(&lock);
841 
842 	return 0;
843 }
844 
845 /*
846  * Return a minimum chunk size of all snapshots that have the specified origin.
847  * Return zero if the origin has no snapshots.
848  */
849 static uint32_t __minimum_chunk_size(struct origin *o)
850 {
851 	struct dm_snapshot *snap;
852 	unsigned chunk_size = 0;
853 
854 	if (o)
855 		list_for_each_entry(snap, &o->snapshots, list)
856 			chunk_size = min_not_zero(chunk_size,
857 						  snap->store->chunk_size);
858 
859 	return (uint32_t) chunk_size;
860 }
861 
862 /*
863  * Hard coded magic.
864  */
865 static int calc_max_buckets(void)
866 {
867 	/* use a fixed size of 2MB */
868 	unsigned long mem = 2 * 1024 * 1024;
869 	mem /= sizeof(struct hlist_bl_head);
870 
871 	return mem;
872 }
873 
874 /*
875  * Allocate room for a suitable hash table.
876  */
877 static int init_hash_tables(struct dm_snapshot *s)
878 {
879 	sector_t hash_size, cow_dev_size, max_buckets;
880 
881 	/*
882 	 * Calculate based on the size of the original volume or
883 	 * the COW volume...
884 	 */
885 	cow_dev_size = get_dev_size(s->cow->bdev);
886 	max_buckets = calc_max_buckets();
887 
888 	hash_size = cow_dev_size >> s->store->chunk_shift;
889 	hash_size = min(hash_size, max_buckets);
890 
891 	if (hash_size < 64)
892 		hash_size = 64;
893 	hash_size = rounddown_pow_of_two(hash_size);
894 	if (dm_exception_table_init(&s->complete, hash_size,
895 				    DM_CHUNK_CONSECUTIVE_BITS))
896 		return -ENOMEM;
897 
898 	/*
899 	 * Allocate hash table for in-flight exceptions
900 	 * Make this smaller than the real hash table
901 	 */
902 	hash_size >>= 3;
903 	if (hash_size < 64)
904 		hash_size = 64;
905 
906 	if (dm_exception_table_init(&s->pending, hash_size, 0)) {
907 		dm_exception_table_exit(&s->complete, exception_cache);
908 		return -ENOMEM;
909 	}
910 
911 	return 0;
912 }
913 
914 static void merge_shutdown(struct dm_snapshot *s)
915 {
916 	clear_bit_unlock(RUNNING_MERGE, &s->state_bits);
917 	smp_mb__after_atomic();
918 	wake_up_bit(&s->state_bits, RUNNING_MERGE);
919 }
920 
921 static struct bio *__release_queued_bios_after_merge(struct dm_snapshot *s)
922 {
923 	s->first_merging_chunk = 0;
924 	s->num_merging_chunks = 0;
925 
926 	return bio_list_get(&s->bios_queued_during_merge);
927 }
928 
929 /*
930  * Remove one chunk from the index of completed exceptions.
931  */
932 static int __remove_single_exception_chunk(struct dm_snapshot *s,
933 					   chunk_t old_chunk)
934 {
935 	struct dm_exception *e;
936 
937 	e = dm_lookup_exception(&s->complete, old_chunk);
938 	if (!e) {
939 		DMERR("Corruption detected: exception for block %llu is "
940 		      "on disk but not in memory",
941 		      (unsigned long long)old_chunk);
942 		return -EINVAL;
943 	}
944 
945 	/*
946 	 * If this is the only chunk using this exception, remove exception.
947 	 */
948 	if (!dm_consecutive_chunk_count(e)) {
949 		dm_remove_exception(e);
950 		free_completed_exception(e);
951 		return 0;
952 	}
953 
954 	/*
955 	 * The chunk may be either at the beginning or the end of a
956 	 * group of consecutive chunks - never in the middle.  We are
957 	 * removing chunks in the opposite order to that in which they
958 	 * were added, so this should always be true.
959 	 * Decrement the consecutive chunk counter and adjust the
960 	 * starting point if necessary.
961 	 */
962 	if (old_chunk == e->old_chunk) {
963 		e->old_chunk++;
964 		e->new_chunk++;
965 	} else if (old_chunk != e->old_chunk +
966 		   dm_consecutive_chunk_count(e)) {
967 		DMERR("Attempt to merge block %llu from the "
968 		      "middle of a chunk range [%llu - %llu]",
969 		      (unsigned long long)old_chunk,
970 		      (unsigned long long)e->old_chunk,
971 		      (unsigned long long)
972 		      e->old_chunk + dm_consecutive_chunk_count(e));
973 		return -EINVAL;
974 	}
975 
976 	dm_consecutive_chunk_count_dec(e);
977 
978 	return 0;
979 }
980 
981 static void flush_bios(struct bio *bio);
982 
983 static int remove_single_exception_chunk(struct dm_snapshot *s)
984 {
985 	struct bio *b = NULL;
986 	int r;
987 	chunk_t old_chunk = s->first_merging_chunk + s->num_merging_chunks - 1;
988 
989 	down_write(&s->lock);
990 
991 	/*
992 	 * Process chunks (and associated exceptions) in reverse order
993 	 * so that dm_consecutive_chunk_count_dec() accounting works.
994 	 */
995 	do {
996 		r = __remove_single_exception_chunk(s, old_chunk);
997 		if (r)
998 			goto out;
999 	} while (old_chunk-- > s->first_merging_chunk);
1000 
1001 	b = __release_queued_bios_after_merge(s);
1002 
1003 out:
1004 	up_write(&s->lock);
1005 	if (b)
1006 		flush_bios(b);
1007 
1008 	return r;
1009 }
1010 
1011 static int origin_write_extent(struct dm_snapshot *merging_snap,
1012 			       sector_t sector, unsigned chunk_size);
1013 
1014 static void merge_callback(int read_err, unsigned long write_err,
1015 			   void *context);
1016 
1017 static uint64_t read_pending_exceptions_done_count(void)
1018 {
1019 	uint64_t pending_exceptions_done;
1020 
1021 	spin_lock(&_pending_exceptions_done_spinlock);
1022 	pending_exceptions_done = _pending_exceptions_done_count;
1023 	spin_unlock(&_pending_exceptions_done_spinlock);
1024 
1025 	return pending_exceptions_done;
1026 }
1027 
1028 static void increment_pending_exceptions_done_count(void)
1029 {
1030 	spin_lock(&_pending_exceptions_done_spinlock);
1031 	_pending_exceptions_done_count++;
1032 	spin_unlock(&_pending_exceptions_done_spinlock);
1033 
1034 	wake_up_all(&_pending_exceptions_done);
1035 }
1036 
1037 static void snapshot_merge_next_chunks(struct dm_snapshot *s)
1038 {
1039 	int i, linear_chunks;
1040 	chunk_t old_chunk, new_chunk;
1041 	struct dm_io_region src, dest;
1042 	sector_t io_size;
1043 	uint64_t previous_count;
1044 
1045 	BUG_ON(!test_bit(RUNNING_MERGE, &s->state_bits));
1046 	if (unlikely(test_bit(SHUTDOWN_MERGE, &s->state_bits)))
1047 		goto shut;
1048 
1049 	/*
1050 	 * valid flag never changes during merge, so no lock required.
1051 	 */
1052 	if (!s->valid) {
1053 		DMERR("Snapshot is invalid: can't merge");
1054 		goto shut;
1055 	}
1056 
1057 	linear_chunks = s->store->type->prepare_merge(s->store, &old_chunk,
1058 						      &new_chunk);
1059 	if (linear_chunks <= 0) {
1060 		if (linear_chunks < 0) {
1061 			DMERR("Read error in exception store: "
1062 			      "shutting down merge");
1063 			down_write(&s->lock);
1064 			s->merge_failed = true;
1065 			up_write(&s->lock);
1066 		}
1067 		goto shut;
1068 	}
1069 
1070 	/* Adjust old_chunk and new_chunk to reflect start of linear region */
1071 	old_chunk = old_chunk + 1 - linear_chunks;
1072 	new_chunk = new_chunk + 1 - linear_chunks;
1073 
1074 	/*
1075 	 * Use one (potentially large) I/O to copy all 'linear_chunks'
1076 	 * from the exception store to the origin
1077 	 */
1078 	io_size = linear_chunks * s->store->chunk_size;
1079 
1080 	dest.bdev = s->origin->bdev;
1081 	dest.sector = chunk_to_sector(s->store, old_chunk);
1082 	dest.count = min(io_size, get_dev_size(dest.bdev) - dest.sector);
1083 
1084 	src.bdev = s->cow->bdev;
1085 	src.sector = chunk_to_sector(s->store, new_chunk);
1086 	src.count = dest.count;
1087 
1088 	/*
1089 	 * Reallocate any exceptions needed in other snapshots then
1090 	 * wait for the pending exceptions to complete.
1091 	 * Each time any pending exception (globally on the system)
1092 	 * completes we are woken and repeat the process to find out
1093 	 * if we can proceed.  While this may not seem a particularly
1094 	 * efficient algorithm, it is not expected to have any
1095 	 * significant impact on performance.
1096 	 */
1097 	previous_count = read_pending_exceptions_done_count();
1098 	while (origin_write_extent(s, dest.sector, io_size)) {
1099 		wait_event(_pending_exceptions_done,
1100 			   (read_pending_exceptions_done_count() !=
1101 			    previous_count));
1102 		/* Retry after the wait, until all exceptions are done. */
1103 		previous_count = read_pending_exceptions_done_count();
1104 	}
1105 
1106 	down_write(&s->lock);
1107 	s->first_merging_chunk = old_chunk;
1108 	s->num_merging_chunks = linear_chunks;
1109 	up_write(&s->lock);
1110 
1111 	/* Wait until writes to all 'linear_chunks' drain */
1112 	for (i = 0; i < linear_chunks; i++)
1113 		__check_for_conflicting_io(s, old_chunk + i);
1114 
1115 	dm_kcopyd_copy(s->kcopyd_client, &src, 1, &dest, 0, merge_callback, s);
1116 	return;
1117 
1118 shut:
1119 	merge_shutdown(s);
1120 }
1121 
1122 static void error_bios(struct bio *bio);
1123 
1124 static void merge_callback(int read_err, unsigned long write_err, void *context)
1125 {
1126 	struct dm_snapshot *s = context;
1127 	struct bio *b = NULL;
1128 
1129 	if (read_err || write_err) {
1130 		if (read_err)
1131 			DMERR("Read error: shutting down merge.");
1132 		else
1133 			DMERR("Write error: shutting down merge.");
1134 		goto shut;
1135 	}
1136 
1137 	if (s->store->type->commit_merge(s->store,
1138 					 s->num_merging_chunks) < 0) {
1139 		DMERR("Write error in exception store: shutting down merge");
1140 		goto shut;
1141 	}
1142 
1143 	if (remove_single_exception_chunk(s) < 0)
1144 		goto shut;
1145 
1146 	snapshot_merge_next_chunks(s);
1147 
1148 	return;
1149 
1150 shut:
1151 	down_write(&s->lock);
1152 	s->merge_failed = true;
1153 	b = __release_queued_bios_after_merge(s);
1154 	up_write(&s->lock);
1155 	error_bios(b);
1156 
1157 	merge_shutdown(s);
1158 }
1159 
1160 static void start_merge(struct dm_snapshot *s)
1161 {
1162 	if (!test_and_set_bit(RUNNING_MERGE, &s->state_bits))
1163 		snapshot_merge_next_chunks(s);
1164 }
1165 
1166 /*
1167  * Stop the merging process and wait until it finishes.
1168  */
1169 static void stop_merge(struct dm_snapshot *s)
1170 {
1171 	set_bit(SHUTDOWN_MERGE, &s->state_bits);
1172 	wait_on_bit(&s->state_bits, RUNNING_MERGE, TASK_UNINTERRUPTIBLE);
1173 	clear_bit(SHUTDOWN_MERGE, &s->state_bits);
1174 }
1175 
1176 static int parse_snapshot_features(struct dm_arg_set *as, struct dm_snapshot *s,
1177 				   struct dm_target *ti)
1178 {
1179 	int r;
1180 	unsigned argc;
1181 	const char *arg_name;
1182 
1183 	static const struct dm_arg _args[] = {
1184 		{0, 2, "Invalid number of feature arguments"},
1185 	};
1186 
1187 	/*
1188 	 * No feature arguments supplied.
1189 	 */
1190 	if (!as->argc)
1191 		return 0;
1192 
1193 	r = dm_read_arg_group(_args, as, &argc, &ti->error);
1194 	if (r)
1195 		return -EINVAL;
1196 
1197 	while (argc && !r) {
1198 		arg_name = dm_shift_arg(as);
1199 		argc--;
1200 
1201 		if (!strcasecmp(arg_name, "discard_zeroes_cow"))
1202 			s->discard_zeroes_cow = true;
1203 
1204 		else if (!strcasecmp(arg_name, "discard_passdown_origin"))
1205 			s->discard_passdown_origin = true;
1206 
1207 		else {
1208 			ti->error = "Unrecognised feature requested";
1209 			r = -EINVAL;
1210 			break;
1211 		}
1212 	}
1213 
1214 	if (!s->discard_zeroes_cow && s->discard_passdown_origin) {
1215 		/*
1216 		 * TODO: really these are disjoint.. but ti->num_discard_bios
1217 		 * and dm_bio_get_target_bio_nr() require rigid constraints.
1218 		 */
1219 		ti->error = "discard_passdown_origin feature depends on discard_zeroes_cow";
1220 		r = -EINVAL;
1221 	}
1222 
1223 	return r;
1224 }
1225 
1226 /*
1227  * Construct a snapshot mapping:
1228  * <origin_dev> <COW-dev> <p|po|n> <chunk-size> [<# feature args> [<arg>]*]
1229  */
1230 static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
1231 {
1232 	struct dm_snapshot *s;
1233 	struct dm_arg_set as;
1234 	int i;
1235 	int r = -EINVAL;
1236 	char *origin_path, *cow_path;
1237 	dev_t origin_dev, cow_dev;
1238 	unsigned args_used, num_flush_bios = 1;
1239 	fmode_t origin_mode = FMODE_READ;
1240 
1241 	if (argc < 4) {
1242 		ti->error = "requires 4 or more arguments";
1243 		r = -EINVAL;
1244 		goto bad;
1245 	}
1246 
1247 	if (dm_target_is_snapshot_merge(ti)) {
1248 		num_flush_bios = 2;
1249 		origin_mode = FMODE_WRITE;
1250 	}
1251 
1252 	s = kzalloc(sizeof(*s), GFP_KERNEL);
1253 	if (!s) {
1254 		ti->error = "Cannot allocate private snapshot structure";
1255 		r = -ENOMEM;
1256 		goto bad;
1257 	}
1258 
1259 	as.argc = argc;
1260 	as.argv = argv;
1261 	dm_consume_args(&as, 4);
1262 	r = parse_snapshot_features(&as, s, ti);
1263 	if (r)
1264 		goto bad_features;
1265 
1266 	origin_path = argv[0];
1267 	argv++;
1268 	argc--;
1269 
1270 	r = dm_get_device(ti, origin_path, origin_mode, &s->origin);
1271 	if (r) {
1272 		ti->error = "Cannot get origin device";
1273 		goto bad_origin;
1274 	}
1275 	origin_dev = s->origin->bdev->bd_dev;
1276 
1277 	cow_path = argv[0];
1278 	argv++;
1279 	argc--;
1280 
1281 	cow_dev = dm_get_dev_t(cow_path);
1282 	if (cow_dev && cow_dev == origin_dev) {
1283 		ti->error = "COW device cannot be the same as origin device";
1284 		r = -EINVAL;
1285 		goto bad_cow;
1286 	}
1287 
1288 	r = dm_get_device(ti, cow_path, dm_table_get_mode(ti->table), &s->cow);
1289 	if (r) {
1290 		ti->error = "Cannot get COW device";
1291 		goto bad_cow;
1292 	}
1293 
1294 	r = dm_exception_store_create(ti, argc, argv, s, &args_used, &s->store);
1295 	if (r) {
1296 		ti->error = "Couldn't create exception store";
1297 		r = -EINVAL;
1298 		goto bad_store;
1299 	}
1300 
1301 	argv += args_used;
1302 	argc -= args_used;
1303 
1304 	s->ti = ti;
1305 	s->valid = 1;
1306 	s->snapshot_overflowed = 0;
1307 	s->active = 0;
1308 	atomic_set(&s->pending_exceptions_count, 0);
1309 	spin_lock_init(&s->pe_allocation_lock);
1310 	s->exception_start_sequence = 0;
1311 	s->exception_complete_sequence = 0;
1312 	s->out_of_order_tree = RB_ROOT;
1313 	init_rwsem(&s->lock);
1314 	INIT_LIST_HEAD(&s->list);
1315 	spin_lock_init(&s->pe_lock);
1316 	s->state_bits = 0;
1317 	s->merge_failed = false;
1318 	s->first_merging_chunk = 0;
1319 	s->num_merging_chunks = 0;
1320 	bio_list_init(&s->bios_queued_during_merge);
1321 
1322 	/* Allocate hash table for COW data */
1323 	if (init_hash_tables(s)) {
1324 		ti->error = "Unable to allocate hash table space";
1325 		r = -ENOMEM;
1326 		goto bad_hash_tables;
1327 	}
1328 
1329 	init_waitqueue_head(&s->in_progress_wait);
1330 
1331 	s->kcopyd_client = dm_kcopyd_client_create(&dm_kcopyd_throttle);
1332 	if (IS_ERR(s->kcopyd_client)) {
1333 		r = PTR_ERR(s->kcopyd_client);
1334 		ti->error = "Could not create kcopyd client";
1335 		goto bad_kcopyd;
1336 	}
1337 
1338 	r = mempool_init_slab_pool(&s->pending_pool, MIN_IOS, pending_cache);
1339 	if (r) {
1340 		ti->error = "Could not allocate mempool for pending exceptions";
1341 		goto bad_pending_pool;
1342 	}
1343 
1344 	for (i = 0; i < DM_TRACKED_CHUNK_HASH_SIZE; i++)
1345 		INIT_HLIST_HEAD(&s->tracked_chunk_hash[i]);
1346 
1347 	spin_lock_init(&s->tracked_chunk_lock);
1348 
1349 	ti->private = s;
1350 	ti->num_flush_bios = num_flush_bios;
1351 	if (s->discard_zeroes_cow)
1352 		ti->num_discard_bios = (s->discard_passdown_origin ? 2 : 1);
1353 	ti->per_io_data_size = sizeof(struct dm_snap_tracked_chunk);
1354 
1355 	/* Add snapshot to the list of snapshots for this origin */
1356 	/* Exceptions aren't triggered till snapshot_resume() is called */
1357 	r = register_snapshot(s);
1358 	if (r == -ENOMEM) {
1359 		ti->error = "Snapshot origin struct allocation failed";
1360 		goto bad_load_and_register;
1361 	} else if (r < 0) {
1362 		/* invalid handover, register_snapshot has set ti->error */
1363 		goto bad_load_and_register;
1364 	}
1365 
1366 	/*
1367 	 * Metadata must only be loaded into one table at once, so skip this
1368 	 * if metadata will be handed over during resume.
1369 	 * Chunk size will be set during the handover - set it to zero to
1370 	 * ensure it's ignored.
1371 	 */
1372 	if (r > 0) {
1373 		s->store->chunk_size = 0;
1374 		return 0;
1375 	}
1376 
1377 	r = s->store->type->read_metadata(s->store, dm_add_exception,
1378 					  (void *)s);
1379 	if (r < 0) {
1380 		ti->error = "Failed to read snapshot metadata";
1381 		goto bad_read_metadata;
1382 	} else if (r > 0) {
1383 		s->valid = 0;
1384 		DMWARN("Snapshot is marked invalid.");
1385 	}
1386 
1387 	if (!s->store->chunk_size) {
1388 		ti->error = "Chunk size not set";
1389 		goto bad_read_metadata;
1390 	}
1391 
1392 	r = dm_set_target_max_io_len(ti, s->store->chunk_size);
1393 	if (r)
1394 		goto bad_read_metadata;
1395 
1396 	return 0;
1397 
1398 bad_read_metadata:
1399 	unregister_snapshot(s);
1400 bad_load_and_register:
1401 	mempool_exit(&s->pending_pool);
1402 bad_pending_pool:
1403 	dm_kcopyd_client_destroy(s->kcopyd_client);
1404 bad_kcopyd:
1405 	dm_exception_table_exit(&s->pending, pending_cache);
1406 	dm_exception_table_exit(&s->complete, exception_cache);
1407 bad_hash_tables:
1408 	dm_exception_store_destroy(s->store);
1409 bad_store:
1410 	dm_put_device(ti, s->cow);
1411 bad_cow:
1412 	dm_put_device(ti, s->origin);
1413 bad_origin:
1414 bad_features:
1415 	kfree(s);
1416 bad:
1417 	return r;
1418 }
1419 
1420 static void __free_exceptions(struct dm_snapshot *s)
1421 {
1422 	dm_kcopyd_client_destroy(s->kcopyd_client);
1423 	s->kcopyd_client = NULL;
1424 
1425 	dm_exception_table_exit(&s->pending, pending_cache);
1426 	dm_exception_table_exit(&s->complete, exception_cache);
1427 }
1428 
1429 static void __handover_exceptions(struct dm_snapshot *snap_src,
1430 				  struct dm_snapshot *snap_dest)
1431 {
1432 	union {
1433 		struct dm_exception_table table_swap;
1434 		struct dm_exception_store *store_swap;
1435 	} u;
1436 
1437 	/*
1438 	 * Swap all snapshot context information between the two instances.
1439 	 */
1440 	u.table_swap = snap_dest->complete;
1441 	snap_dest->complete = snap_src->complete;
1442 	snap_src->complete = u.table_swap;
1443 
1444 	u.store_swap = snap_dest->store;
1445 	snap_dest->store = snap_src->store;
1446 	snap_dest->store->userspace_supports_overflow = u.store_swap->userspace_supports_overflow;
1447 	snap_src->store = u.store_swap;
1448 
1449 	snap_dest->store->snap = snap_dest;
1450 	snap_src->store->snap = snap_src;
1451 
1452 	snap_dest->ti->max_io_len = snap_dest->store->chunk_size;
1453 	snap_dest->valid = snap_src->valid;
1454 	snap_dest->snapshot_overflowed = snap_src->snapshot_overflowed;
1455 
1456 	/*
1457 	 * Set source invalid to ensure it receives no further I/O.
1458 	 */
1459 	snap_src->valid = 0;
1460 }
1461 
1462 static void snapshot_dtr(struct dm_target *ti)
1463 {
1464 #ifdef CONFIG_DM_DEBUG
1465 	int i;
1466 #endif
1467 	struct dm_snapshot *s = ti->private;
1468 	struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
1469 
1470 	down_read(&_origins_lock);
1471 	/* Check whether exception handover must be cancelled */
1472 	(void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL);
1473 	if (snap_src && snap_dest && (s == snap_src)) {
1474 		down_write(&snap_dest->lock);
1475 		snap_dest->valid = 0;
1476 		up_write(&snap_dest->lock);
1477 		DMERR("Cancelling snapshot handover.");
1478 	}
1479 	up_read(&_origins_lock);
1480 
1481 	if (dm_target_is_snapshot_merge(ti))
1482 		stop_merge(s);
1483 
1484 	/* Prevent further origin writes from using this snapshot. */
1485 	/* After this returns there can be no new kcopyd jobs. */
1486 	unregister_snapshot(s);
1487 
1488 	while (atomic_read(&s->pending_exceptions_count))
1489 		msleep(1);
1490 	/*
1491 	 * Ensure instructions in mempool_exit aren't reordered
1492 	 * before atomic_read.
1493 	 */
1494 	smp_mb();
1495 
1496 #ifdef CONFIG_DM_DEBUG
1497 	for (i = 0; i < DM_TRACKED_CHUNK_HASH_SIZE; i++)
1498 		BUG_ON(!hlist_empty(&s->tracked_chunk_hash[i]));
1499 #endif
1500 
1501 	__free_exceptions(s);
1502 
1503 	mempool_exit(&s->pending_pool);
1504 
1505 	dm_exception_store_destroy(s->store);
1506 
1507 	dm_put_device(ti, s->cow);
1508 
1509 	dm_put_device(ti, s->origin);
1510 
1511 	WARN_ON(s->in_progress);
1512 
1513 	kfree(s);
1514 }
1515 
1516 static void account_start_copy(struct dm_snapshot *s)
1517 {
1518 	spin_lock(&s->in_progress_wait.lock);
1519 	s->in_progress++;
1520 	spin_unlock(&s->in_progress_wait.lock);
1521 }
1522 
1523 static void account_end_copy(struct dm_snapshot *s)
1524 {
1525 	spin_lock(&s->in_progress_wait.lock);
1526 	BUG_ON(!s->in_progress);
1527 	s->in_progress--;
1528 	if (likely(s->in_progress <= cow_threshold) &&
1529 	    unlikely(waitqueue_active(&s->in_progress_wait)))
1530 		wake_up_locked(&s->in_progress_wait);
1531 	spin_unlock(&s->in_progress_wait.lock);
1532 }
1533 
1534 static bool wait_for_in_progress(struct dm_snapshot *s, bool unlock_origins)
1535 {
1536 	if (unlikely(s->in_progress > cow_threshold)) {
1537 		spin_lock(&s->in_progress_wait.lock);
1538 		if (likely(s->in_progress > cow_threshold)) {
1539 			/*
1540 			 * NOTE: this throttle doesn't account for whether
1541 			 * the caller is servicing an IO that will trigger a COW
1542 			 * so excess throttling may result for chunks not required
1543 			 * to be COW'd.  But if cow_threshold was reached, extra
1544 			 * throttling is unlikely to negatively impact performance.
1545 			 */
1546 			DECLARE_WAITQUEUE(wait, current);
1547 			__add_wait_queue(&s->in_progress_wait, &wait);
1548 			__set_current_state(TASK_UNINTERRUPTIBLE);
1549 			spin_unlock(&s->in_progress_wait.lock);
1550 			if (unlock_origins)
1551 				up_read(&_origins_lock);
1552 			io_schedule();
1553 			remove_wait_queue(&s->in_progress_wait, &wait);
1554 			return false;
1555 		}
1556 		spin_unlock(&s->in_progress_wait.lock);
1557 	}
1558 	return true;
1559 }
1560 
1561 /*
1562  * Flush a list of buffers.
1563  */
1564 static void flush_bios(struct bio *bio)
1565 {
1566 	struct bio *n;
1567 
1568 	while (bio) {
1569 		n = bio->bi_next;
1570 		bio->bi_next = NULL;
1571 		submit_bio_noacct(bio);
1572 		bio = n;
1573 	}
1574 }
1575 
1576 static int do_origin(struct dm_dev *origin, struct bio *bio, bool limit);
1577 
1578 /*
1579  * Flush a list of buffers.
1580  */
1581 static void retry_origin_bios(struct dm_snapshot *s, struct bio *bio)
1582 {
1583 	struct bio *n;
1584 	int r;
1585 
1586 	while (bio) {
1587 		n = bio->bi_next;
1588 		bio->bi_next = NULL;
1589 		r = do_origin(s->origin, bio, false);
1590 		if (r == DM_MAPIO_REMAPPED)
1591 			submit_bio_noacct(bio);
1592 		bio = n;
1593 	}
1594 }
1595 
1596 /*
1597  * Error a list of buffers.
1598  */
1599 static void error_bios(struct bio *bio)
1600 {
1601 	struct bio *n;
1602 
1603 	while (bio) {
1604 		n = bio->bi_next;
1605 		bio->bi_next = NULL;
1606 		bio_io_error(bio);
1607 		bio = n;
1608 	}
1609 }
1610 
1611 static void __invalidate_snapshot(struct dm_snapshot *s, int err)
1612 {
1613 	if (!s->valid)
1614 		return;
1615 
1616 	if (err == -EIO)
1617 		DMERR("Invalidating snapshot: Error reading/writing.");
1618 	else if (err == -ENOMEM)
1619 		DMERR("Invalidating snapshot: Unable to allocate exception.");
1620 
1621 	if (s->store->type->drop_snapshot)
1622 		s->store->type->drop_snapshot(s->store);
1623 
1624 	s->valid = 0;
1625 
1626 	dm_table_event(s->ti->table);
1627 }
1628 
1629 static void invalidate_snapshot(struct dm_snapshot *s, int err)
1630 {
1631 	down_write(&s->lock);
1632 	__invalidate_snapshot(s, err);
1633 	up_write(&s->lock);
1634 }
1635 
1636 static void pending_complete(void *context, int success)
1637 {
1638 	struct dm_snap_pending_exception *pe = context;
1639 	struct dm_exception *e;
1640 	struct dm_snapshot *s = pe->snap;
1641 	struct bio *origin_bios = NULL;
1642 	struct bio *snapshot_bios = NULL;
1643 	struct bio *full_bio = NULL;
1644 	struct dm_exception_table_lock lock;
1645 	int error = 0;
1646 
1647 	dm_exception_table_lock_init(s, pe->e.old_chunk, &lock);
1648 
1649 	if (!success) {
1650 		/* Read/write error - snapshot is unusable */
1651 		invalidate_snapshot(s, -EIO);
1652 		error = 1;
1653 
1654 		dm_exception_table_lock(&lock);
1655 		goto out;
1656 	}
1657 
1658 	e = alloc_completed_exception(GFP_NOIO);
1659 	if (!e) {
1660 		invalidate_snapshot(s, -ENOMEM);
1661 		error = 1;
1662 
1663 		dm_exception_table_lock(&lock);
1664 		goto out;
1665 	}
1666 	*e = pe->e;
1667 
1668 	down_read(&s->lock);
1669 	dm_exception_table_lock(&lock);
1670 	if (!s->valid) {
1671 		up_read(&s->lock);
1672 		free_completed_exception(e);
1673 		error = 1;
1674 
1675 		goto out;
1676 	}
1677 
1678 	/*
1679 	 * Add a proper exception. After inserting the completed exception all
1680 	 * subsequent snapshot reads to this chunk will be redirected to the
1681 	 * COW device.  This ensures that we do not starve. Moreover, as long
1682 	 * as the pending exception exists, neither origin writes nor snapshot
1683 	 * merging can overwrite the chunk in origin.
1684 	 */
1685 	dm_insert_exception(&s->complete, e);
1686 	up_read(&s->lock);
1687 
1688 	/* Wait for conflicting reads to drain */
1689 	if (__chunk_is_tracked(s, pe->e.old_chunk)) {
1690 		dm_exception_table_unlock(&lock);
1691 		__check_for_conflicting_io(s, pe->e.old_chunk);
1692 		dm_exception_table_lock(&lock);
1693 	}
1694 
1695 out:
1696 	/* Remove the in-flight exception from the list */
1697 	dm_remove_exception(&pe->e);
1698 
1699 	dm_exception_table_unlock(&lock);
1700 
1701 	snapshot_bios = bio_list_get(&pe->snapshot_bios);
1702 	origin_bios = bio_list_get(&pe->origin_bios);
1703 	full_bio = pe->full_bio;
1704 	if (full_bio)
1705 		full_bio->bi_end_io = pe->full_bio_end_io;
1706 	increment_pending_exceptions_done_count();
1707 
1708 	/* Submit any pending write bios */
1709 	if (error) {
1710 		if (full_bio)
1711 			bio_io_error(full_bio);
1712 		error_bios(snapshot_bios);
1713 	} else {
1714 		if (full_bio)
1715 			bio_endio(full_bio);
1716 		flush_bios(snapshot_bios);
1717 	}
1718 
1719 	retry_origin_bios(s, origin_bios);
1720 
1721 	free_pending_exception(pe);
1722 }
1723 
1724 static void complete_exception(struct dm_snap_pending_exception *pe)
1725 {
1726 	struct dm_snapshot *s = pe->snap;
1727 
1728 	/* Update the metadata if we are persistent */
1729 	s->store->type->commit_exception(s->store, &pe->e, !pe->copy_error,
1730 					 pending_complete, pe);
1731 }
1732 
1733 /*
1734  * Called when the copy I/O has finished.  kcopyd actually runs
1735  * this code so don't block.
1736  */
1737 static void copy_callback(int read_err, unsigned long write_err, void *context)
1738 {
1739 	struct dm_snap_pending_exception *pe = context;
1740 	struct dm_snapshot *s = pe->snap;
1741 
1742 	pe->copy_error = read_err || write_err;
1743 
1744 	if (pe->exception_sequence == s->exception_complete_sequence) {
1745 		struct rb_node *next;
1746 
1747 		s->exception_complete_sequence++;
1748 		complete_exception(pe);
1749 
1750 		next = rb_first(&s->out_of_order_tree);
1751 		while (next) {
1752 			pe = rb_entry(next, struct dm_snap_pending_exception,
1753 					out_of_order_node);
1754 			if (pe->exception_sequence != s->exception_complete_sequence)
1755 				break;
1756 			next = rb_next(next);
1757 			s->exception_complete_sequence++;
1758 			rb_erase(&pe->out_of_order_node, &s->out_of_order_tree);
1759 			complete_exception(pe);
1760 			cond_resched();
1761 		}
1762 	} else {
1763 		struct rb_node *parent = NULL;
1764 		struct rb_node **p = &s->out_of_order_tree.rb_node;
1765 		struct dm_snap_pending_exception *pe2;
1766 
1767 		while (*p) {
1768 			pe2 = rb_entry(*p, struct dm_snap_pending_exception, out_of_order_node);
1769 			parent = *p;
1770 
1771 			BUG_ON(pe->exception_sequence == pe2->exception_sequence);
1772 			if (pe->exception_sequence < pe2->exception_sequence)
1773 				p = &((*p)->rb_left);
1774 			else
1775 				p = &((*p)->rb_right);
1776 		}
1777 
1778 		rb_link_node(&pe->out_of_order_node, parent, p);
1779 		rb_insert_color(&pe->out_of_order_node, &s->out_of_order_tree);
1780 	}
1781 	account_end_copy(s);
1782 }
1783 
1784 /*
1785  * Dispatches the copy operation to kcopyd.
1786  */
1787 static void start_copy(struct dm_snap_pending_exception *pe)
1788 {
1789 	struct dm_snapshot *s = pe->snap;
1790 	struct dm_io_region src, dest;
1791 	struct block_device *bdev = s->origin->bdev;
1792 	sector_t dev_size;
1793 
1794 	dev_size = get_dev_size(bdev);
1795 
1796 	src.bdev = bdev;
1797 	src.sector = chunk_to_sector(s->store, pe->e.old_chunk);
1798 	src.count = min((sector_t)s->store->chunk_size, dev_size - src.sector);
1799 
1800 	dest.bdev = s->cow->bdev;
1801 	dest.sector = chunk_to_sector(s->store, pe->e.new_chunk);
1802 	dest.count = src.count;
1803 
1804 	/* Hand over to kcopyd */
1805 	account_start_copy(s);
1806 	dm_kcopyd_copy(s->kcopyd_client, &src, 1, &dest, 0, copy_callback, pe);
1807 }
1808 
1809 static void full_bio_end_io(struct bio *bio)
1810 {
1811 	void *callback_data = bio->bi_private;
1812 
1813 	dm_kcopyd_do_callback(callback_data, 0, bio->bi_status ? 1 : 0);
1814 }
1815 
1816 static void start_full_bio(struct dm_snap_pending_exception *pe,
1817 			   struct bio *bio)
1818 {
1819 	struct dm_snapshot *s = pe->snap;
1820 	void *callback_data;
1821 
1822 	pe->full_bio = bio;
1823 	pe->full_bio_end_io = bio->bi_end_io;
1824 
1825 	account_start_copy(s);
1826 	callback_data = dm_kcopyd_prepare_callback(s->kcopyd_client,
1827 						   copy_callback, pe);
1828 
1829 	bio->bi_end_io = full_bio_end_io;
1830 	bio->bi_private = callback_data;
1831 
1832 	submit_bio_noacct(bio);
1833 }
1834 
1835 static struct dm_snap_pending_exception *
1836 __lookup_pending_exception(struct dm_snapshot *s, chunk_t chunk)
1837 {
1838 	struct dm_exception *e = dm_lookup_exception(&s->pending, chunk);
1839 
1840 	if (!e)
1841 		return NULL;
1842 
1843 	return container_of(e, struct dm_snap_pending_exception, e);
1844 }
1845 
1846 /*
1847  * Inserts a pending exception into the pending table.
1848  *
1849  * NOTE: a write lock must be held on the chunk's pending exception table slot
1850  * before calling this.
1851  */
1852 static struct dm_snap_pending_exception *
1853 __insert_pending_exception(struct dm_snapshot *s,
1854 			   struct dm_snap_pending_exception *pe, chunk_t chunk)
1855 {
1856 	pe->e.old_chunk = chunk;
1857 	bio_list_init(&pe->origin_bios);
1858 	bio_list_init(&pe->snapshot_bios);
1859 	pe->started = 0;
1860 	pe->full_bio = NULL;
1861 
1862 	spin_lock(&s->pe_allocation_lock);
1863 	if (s->store->type->prepare_exception(s->store, &pe->e)) {
1864 		spin_unlock(&s->pe_allocation_lock);
1865 		free_pending_exception(pe);
1866 		return NULL;
1867 	}
1868 
1869 	pe->exception_sequence = s->exception_start_sequence++;
1870 	spin_unlock(&s->pe_allocation_lock);
1871 
1872 	dm_insert_exception(&s->pending, &pe->e);
1873 
1874 	return pe;
1875 }
1876 
1877 /*
1878  * Looks to see if this snapshot already has a pending exception
1879  * for this chunk, otherwise it allocates a new one and inserts
1880  * it into the pending table.
1881  *
1882  * NOTE: a write lock must be held on the chunk's pending exception table slot
1883  * before calling this.
1884  */
1885 static struct dm_snap_pending_exception *
1886 __find_pending_exception(struct dm_snapshot *s,
1887 			 struct dm_snap_pending_exception *pe, chunk_t chunk)
1888 {
1889 	struct dm_snap_pending_exception *pe2;
1890 
1891 	pe2 = __lookup_pending_exception(s, chunk);
1892 	if (pe2) {
1893 		free_pending_exception(pe);
1894 		return pe2;
1895 	}
1896 
1897 	return __insert_pending_exception(s, pe, chunk);
1898 }
1899 
1900 static void remap_exception(struct dm_snapshot *s, struct dm_exception *e,
1901 			    struct bio *bio, chunk_t chunk)
1902 {
1903 	bio_set_dev(bio, s->cow->bdev);
1904 	bio->bi_iter.bi_sector =
1905 		chunk_to_sector(s->store, dm_chunk_number(e->new_chunk) +
1906 				(chunk - e->old_chunk)) +
1907 		(bio->bi_iter.bi_sector & s->store->chunk_mask);
1908 }
1909 
1910 static void zero_callback(int read_err, unsigned long write_err, void *context)
1911 {
1912 	struct bio *bio = context;
1913 	struct dm_snapshot *s = bio->bi_private;
1914 
1915 	account_end_copy(s);
1916 	bio->bi_status = write_err ? BLK_STS_IOERR : 0;
1917 	bio_endio(bio);
1918 }
1919 
1920 static void zero_exception(struct dm_snapshot *s, struct dm_exception *e,
1921 			   struct bio *bio, chunk_t chunk)
1922 {
1923 	struct dm_io_region dest;
1924 
1925 	dest.bdev = s->cow->bdev;
1926 	dest.sector = bio->bi_iter.bi_sector;
1927 	dest.count = s->store->chunk_size;
1928 
1929 	account_start_copy(s);
1930 	WARN_ON_ONCE(bio->bi_private);
1931 	bio->bi_private = s;
1932 	dm_kcopyd_zero(s->kcopyd_client, 1, &dest, 0, zero_callback, bio);
1933 }
1934 
1935 static bool io_overlaps_chunk(struct dm_snapshot *s, struct bio *bio)
1936 {
1937 	return bio->bi_iter.bi_size ==
1938 		(s->store->chunk_size << SECTOR_SHIFT);
1939 }
1940 
1941 static int snapshot_map(struct dm_target *ti, struct bio *bio)
1942 {
1943 	struct dm_exception *e;
1944 	struct dm_snapshot *s = ti->private;
1945 	int r = DM_MAPIO_REMAPPED;
1946 	chunk_t chunk;
1947 	struct dm_snap_pending_exception *pe = NULL;
1948 	struct dm_exception_table_lock lock;
1949 
1950 	init_tracked_chunk(bio);
1951 
1952 	if (bio->bi_opf & REQ_PREFLUSH) {
1953 		bio_set_dev(bio, s->cow->bdev);
1954 		return DM_MAPIO_REMAPPED;
1955 	}
1956 
1957 	chunk = sector_to_chunk(s->store, bio->bi_iter.bi_sector);
1958 	dm_exception_table_lock_init(s, chunk, &lock);
1959 
1960 	/* Full snapshots are not usable */
1961 	/* To get here the table must be live so s->active is always set. */
1962 	if (!s->valid)
1963 		return DM_MAPIO_KILL;
1964 
1965 	if (bio_data_dir(bio) == WRITE) {
1966 		while (unlikely(!wait_for_in_progress(s, false)))
1967 			; /* wait_for_in_progress() has slept */
1968 	}
1969 
1970 	down_read(&s->lock);
1971 	dm_exception_table_lock(&lock);
1972 
1973 	if (!s->valid || (unlikely(s->snapshot_overflowed) &&
1974 	    bio_data_dir(bio) == WRITE)) {
1975 		r = DM_MAPIO_KILL;
1976 		goto out_unlock;
1977 	}
1978 
1979 	if (unlikely(bio_op(bio) == REQ_OP_DISCARD)) {
1980 		if (s->discard_passdown_origin && dm_bio_get_target_bio_nr(bio)) {
1981 			/*
1982 			 * passdown discard to origin (without triggering
1983 			 * snapshot exceptions via do_origin; doing so would
1984 			 * defeat the goal of freeing space in origin that is
1985 			 * implied by the "discard_passdown_origin" feature)
1986 			 */
1987 			bio_set_dev(bio, s->origin->bdev);
1988 			track_chunk(s, bio, chunk);
1989 			goto out_unlock;
1990 		}
1991 		/* discard to snapshot (target_bio_nr == 0) zeroes exceptions */
1992 	}
1993 
1994 	/* If the block is already remapped - use that, else remap it */
1995 	e = dm_lookup_exception(&s->complete, chunk);
1996 	if (e) {
1997 		remap_exception(s, e, bio, chunk);
1998 		if (unlikely(bio_op(bio) == REQ_OP_DISCARD) &&
1999 		    io_overlaps_chunk(s, bio)) {
2000 			dm_exception_table_unlock(&lock);
2001 			up_read(&s->lock);
2002 			zero_exception(s, e, bio, chunk);
2003 			r = DM_MAPIO_SUBMITTED; /* discard is not issued */
2004 			goto out;
2005 		}
2006 		goto out_unlock;
2007 	}
2008 
2009 	if (unlikely(bio_op(bio) == REQ_OP_DISCARD)) {
2010 		/*
2011 		 * If no exception exists, complete discard immediately
2012 		 * otherwise it'll trigger copy-out.
2013 		 */
2014 		bio_endio(bio);
2015 		r = DM_MAPIO_SUBMITTED;
2016 		goto out_unlock;
2017 	}
2018 
2019 	/*
2020 	 * Write to snapshot - higher level takes care of RW/RO
2021 	 * flags so we should only get this if we are
2022 	 * writeable.
2023 	 */
2024 	if (bio_data_dir(bio) == WRITE) {
2025 		pe = __lookup_pending_exception(s, chunk);
2026 		if (!pe) {
2027 			dm_exception_table_unlock(&lock);
2028 			pe = alloc_pending_exception(s);
2029 			dm_exception_table_lock(&lock);
2030 
2031 			e = dm_lookup_exception(&s->complete, chunk);
2032 			if (e) {
2033 				free_pending_exception(pe);
2034 				remap_exception(s, e, bio, chunk);
2035 				goto out_unlock;
2036 			}
2037 
2038 			pe = __find_pending_exception(s, pe, chunk);
2039 			if (!pe) {
2040 				dm_exception_table_unlock(&lock);
2041 				up_read(&s->lock);
2042 
2043 				down_write(&s->lock);
2044 
2045 				if (s->store->userspace_supports_overflow) {
2046 					if (s->valid && !s->snapshot_overflowed) {
2047 						s->snapshot_overflowed = 1;
2048 						DMERR("Snapshot overflowed: Unable to allocate exception.");
2049 					}
2050 				} else
2051 					__invalidate_snapshot(s, -ENOMEM);
2052 				up_write(&s->lock);
2053 
2054 				r = DM_MAPIO_KILL;
2055 				goto out;
2056 			}
2057 		}
2058 
2059 		remap_exception(s, &pe->e, bio, chunk);
2060 
2061 		r = DM_MAPIO_SUBMITTED;
2062 
2063 		if (!pe->started && io_overlaps_chunk(s, bio)) {
2064 			pe->started = 1;
2065 
2066 			dm_exception_table_unlock(&lock);
2067 			up_read(&s->lock);
2068 
2069 			start_full_bio(pe, bio);
2070 			goto out;
2071 		}
2072 
2073 		bio_list_add(&pe->snapshot_bios, bio);
2074 
2075 		if (!pe->started) {
2076 			/* this is protected by the exception table lock */
2077 			pe->started = 1;
2078 
2079 			dm_exception_table_unlock(&lock);
2080 			up_read(&s->lock);
2081 
2082 			start_copy(pe);
2083 			goto out;
2084 		}
2085 	} else {
2086 		bio_set_dev(bio, s->origin->bdev);
2087 		track_chunk(s, bio, chunk);
2088 	}
2089 
2090 out_unlock:
2091 	dm_exception_table_unlock(&lock);
2092 	up_read(&s->lock);
2093 out:
2094 	return r;
2095 }
2096 
2097 /*
2098  * A snapshot-merge target behaves like a combination of a snapshot
2099  * target and a snapshot-origin target.  It only generates new
2100  * exceptions in other snapshots and not in the one that is being
2101  * merged.
2102  *
2103  * For each chunk, if there is an existing exception, it is used to
2104  * redirect I/O to the cow device.  Otherwise I/O is sent to the origin,
2105  * which in turn might generate exceptions in other snapshots.
2106  * If merging is currently taking place on the chunk in question, the
2107  * I/O is deferred by adding it to s->bios_queued_during_merge.
2108  */
2109 static int snapshot_merge_map(struct dm_target *ti, struct bio *bio)
2110 {
2111 	struct dm_exception *e;
2112 	struct dm_snapshot *s = ti->private;
2113 	int r = DM_MAPIO_REMAPPED;
2114 	chunk_t chunk;
2115 
2116 	init_tracked_chunk(bio);
2117 
2118 	if (bio->bi_opf & REQ_PREFLUSH) {
2119 		if (!dm_bio_get_target_bio_nr(bio))
2120 			bio_set_dev(bio, s->origin->bdev);
2121 		else
2122 			bio_set_dev(bio, s->cow->bdev);
2123 		return DM_MAPIO_REMAPPED;
2124 	}
2125 
2126 	if (unlikely(bio_op(bio) == REQ_OP_DISCARD)) {
2127 		/* Once merging, discards no longer effect change */
2128 		bio_endio(bio);
2129 		return DM_MAPIO_SUBMITTED;
2130 	}
2131 
2132 	chunk = sector_to_chunk(s->store, bio->bi_iter.bi_sector);
2133 
2134 	down_write(&s->lock);
2135 
2136 	/* Full merging snapshots are redirected to the origin */
2137 	if (!s->valid)
2138 		goto redirect_to_origin;
2139 
2140 	/* If the block is already remapped - use that */
2141 	e = dm_lookup_exception(&s->complete, chunk);
2142 	if (e) {
2143 		/* Queue writes overlapping with chunks being merged */
2144 		if (bio_data_dir(bio) == WRITE &&
2145 		    chunk >= s->first_merging_chunk &&
2146 		    chunk < (s->first_merging_chunk +
2147 			     s->num_merging_chunks)) {
2148 			bio_set_dev(bio, s->origin->bdev);
2149 			bio_list_add(&s->bios_queued_during_merge, bio);
2150 			r = DM_MAPIO_SUBMITTED;
2151 			goto out_unlock;
2152 		}
2153 
2154 		remap_exception(s, e, bio, chunk);
2155 
2156 		if (bio_data_dir(bio) == WRITE)
2157 			track_chunk(s, bio, chunk);
2158 		goto out_unlock;
2159 	}
2160 
2161 redirect_to_origin:
2162 	bio_set_dev(bio, s->origin->bdev);
2163 
2164 	if (bio_data_dir(bio) == WRITE) {
2165 		up_write(&s->lock);
2166 		return do_origin(s->origin, bio, false);
2167 	}
2168 
2169 out_unlock:
2170 	up_write(&s->lock);
2171 
2172 	return r;
2173 }
2174 
2175 static int snapshot_end_io(struct dm_target *ti, struct bio *bio,
2176 		blk_status_t *error)
2177 {
2178 	struct dm_snapshot *s = ti->private;
2179 
2180 	if (is_bio_tracked(bio))
2181 		stop_tracking_chunk(s, bio);
2182 
2183 	return DM_ENDIO_DONE;
2184 }
2185 
2186 static void snapshot_merge_presuspend(struct dm_target *ti)
2187 {
2188 	struct dm_snapshot *s = ti->private;
2189 
2190 	stop_merge(s);
2191 }
2192 
2193 static int snapshot_preresume(struct dm_target *ti)
2194 {
2195 	int r = 0;
2196 	struct dm_snapshot *s = ti->private;
2197 	struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
2198 
2199 	down_read(&_origins_lock);
2200 	(void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL);
2201 	if (snap_src && snap_dest) {
2202 		down_read(&snap_src->lock);
2203 		if (s == snap_src) {
2204 			DMERR("Unable to resume snapshot source until "
2205 			      "handover completes.");
2206 			r = -EINVAL;
2207 		} else if (!dm_suspended(snap_src->ti)) {
2208 			DMERR("Unable to perform snapshot handover until "
2209 			      "source is suspended.");
2210 			r = -EINVAL;
2211 		}
2212 		up_read(&snap_src->lock);
2213 	}
2214 	up_read(&_origins_lock);
2215 
2216 	return r;
2217 }
2218 
2219 static void snapshot_resume(struct dm_target *ti)
2220 {
2221 	struct dm_snapshot *s = ti->private;
2222 	struct dm_snapshot *snap_src = NULL, *snap_dest = NULL, *snap_merging = NULL;
2223 	struct dm_origin *o;
2224 	struct mapped_device *origin_md = NULL;
2225 	bool must_restart_merging = false;
2226 
2227 	down_read(&_origins_lock);
2228 
2229 	o = __lookup_dm_origin(s->origin->bdev);
2230 	if (o)
2231 		origin_md = dm_table_get_md(o->ti->table);
2232 	if (!origin_md) {
2233 		(void) __find_snapshots_sharing_cow(s, NULL, NULL, &snap_merging);
2234 		if (snap_merging)
2235 			origin_md = dm_table_get_md(snap_merging->ti->table);
2236 	}
2237 	if (origin_md == dm_table_get_md(ti->table))
2238 		origin_md = NULL;
2239 	if (origin_md) {
2240 		if (dm_hold(origin_md))
2241 			origin_md = NULL;
2242 	}
2243 
2244 	up_read(&_origins_lock);
2245 
2246 	if (origin_md) {
2247 		dm_internal_suspend_fast(origin_md);
2248 		if (snap_merging && test_bit(RUNNING_MERGE, &snap_merging->state_bits)) {
2249 			must_restart_merging = true;
2250 			stop_merge(snap_merging);
2251 		}
2252 	}
2253 
2254 	down_read(&_origins_lock);
2255 
2256 	(void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL);
2257 	if (snap_src && snap_dest) {
2258 		down_write(&snap_src->lock);
2259 		down_write_nested(&snap_dest->lock, SINGLE_DEPTH_NESTING);
2260 		__handover_exceptions(snap_src, snap_dest);
2261 		up_write(&snap_dest->lock);
2262 		up_write(&snap_src->lock);
2263 	}
2264 
2265 	up_read(&_origins_lock);
2266 
2267 	if (origin_md) {
2268 		if (must_restart_merging)
2269 			start_merge(snap_merging);
2270 		dm_internal_resume_fast(origin_md);
2271 		dm_put(origin_md);
2272 	}
2273 
2274 	/* Now we have correct chunk size, reregister */
2275 	reregister_snapshot(s);
2276 
2277 	down_write(&s->lock);
2278 	s->active = 1;
2279 	up_write(&s->lock);
2280 }
2281 
2282 static uint32_t get_origin_minimum_chunksize(struct block_device *bdev)
2283 {
2284 	uint32_t min_chunksize;
2285 
2286 	down_read(&_origins_lock);
2287 	min_chunksize = __minimum_chunk_size(__lookup_origin(bdev));
2288 	up_read(&_origins_lock);
2289 
2290 	return min_chunksize;
2291 }
2292 
2293 static void snapshot_merge_resume(struct dm_target *ti)
2294 {
2295 	struct dm_snapshot *s = ti->private;
2296 
2297 	/*
2298 	 * Handover exceptions from existing snapshot.
2299 	 */
2300 	snapshot_resume(ti);
2301 
2302 	/*
2303 	 * snapshot-merge acts as an origin, so set ti->max_io_len
2304 	 */
2305 	ti->max_io_len = get_origin_minimum_chunksize(s->origin->bdev);
2306 
2307 	start_merge(s);
2308 }
2309 
2310 static void snapshot_status(struct dm_target *ti, status_type_t type,
2311 			    unsigned status_flags, char *result, unsigned maxlen)
2312 {
2313 	unsigned sz = 0;
2314 	struct dm_snapshot *snap = ti->private;
2315 	unsigned num_features;
2316 
2317 	switch (type) {
2318 	case STATUSTYPE_INFO:
2319 
2320 		down_write(&snap->lock);
2321 
2322 		if (!snap->valid)
2323 			DMEMIT("Invalid");
2324 		else if (snap->merge_failed)
2325 			DMEMIT("Merge failed");
2326 		else if (snap->snapshot_overflowed)
2327 			DMEMIT("Overflow");
2328 		else {
2329 			if (snap->store->type->usage) {
2330 				sector_t total_sectors, sectors_allocated,
2331 					 metadata_sectors;
2332 				snap->store->type->usage(snap->store,
2333 							 &total_sectors,
2334 							 &sectors_allocated,
2335 							 &metadata_sectors);
2336 				DMEMIT("%llu/%llu %llu",
2337 				       (unsigned long long)sectors_allocated,
2338 				       (unsigned long long)total_sectors,
2339 				       (unsigned long long)metadata_sectors);
2340 			}
2341 			else
2342 				DMEMIT("Unknown");
2343 		}
2344 
2345 		up_write(&snap->lock);
2346 
2347 		break;
2348 
2349 	case STATUSTYPE_TABLE:
2350 		/*
2351 		 * kdevname returns a static pointer so we need
2352 		 * to make private copies if the output is to
2353 		 * make sense.
2354 		 */
2355 		DMEMIT("%s %s", snap->origin->name, snap->cow->name);
2356 		sz += snap->store->type->status(snap->store, type, result + sz,
2357 						maxlen - sz);
2358 		num_features = snap->discard_zeroes_cow + snap->discard_passdown_origin;
2359 		if (num_features) {
2360 			DMEMIT(" %u", num_features);
2361 			if (snap->discard_zeroes_cow)
2362 				DMEMIT(" discard_zeroes_cow");
2363 			if (snap->discard_passdown_origin)
2364 				DMEMIT(" discard_passdown_origin");
2365 		}
2366 		break;
2367 	}
2368 }
2369 
2370 static int snapshot_iterate_devices(struct dm_target *ti,
2371 				    iterate_devices_callout_fn fn, void *data)
2372 {
2373 	struct dm_snapshot *snap = ti->private;
2374 	int r;
2375 
2376 	r = fn(ti, snap->origin, 0, ti->len, data);
2377 
2378 	if (!r)
2379 		r = fn(ti, snap->cow, 0, get_dev_size(snap->cow->bdev), data);
2380 
2381 	return r;
2382 }
2383 
2384 static void snapshot_io_hints(struct dm_target *ti, struct queue_limits *limits)
2385 {
2386 	struct dm_snapshot *snap = ti->private;
2387 
2388 	if (snap->discard_zeroes_cow) {
2389 		struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
2390 
2391 		down_read(&_origins_lock);
2392 
2393 		(void) __find_snapshots_sharing_cow(snap, &snap_src, &snap_dest, NULL);
2394 		if (snap_src && snap_dest)
2395 			snap = snap_src;
2396 
2397 		/* All discards are split on chunk_size boundary */
2398 		limits->discard_granularity = snap->store->chunk_size;
2399 		limits->max_discard_sectors = snap->store->chunk_size;
2400 
2401 		up_read(&_origins_lock);
2402 	}
2403 }
2404 
2405 /*-----------------------------------------------------------------
2406  * Origin methods
2407  *---------------------------------------------------------------*/
2408 
2409 /*
2410  * If no exceptions need creating, DM_MAPIO_REMAPPED is returned and any
2411  * supplied bio was ignored.  The caller may submit it immediately.
2412  * (No remapping actually occurs as the origin is always a direct linear
2413  * map.)
2414  *
2415  * If further exceptions are required, DM_MAPIO_SUBMITTED is returned
2416  * and any supplied bio is added to a list to be submitted once all
2417  * the necessary exceptions exist.
2418  */
2419 static int __origin_write(struct list_head *snapshots, sector_t sector,
2420 			  struct bio *bio)
2421 {
2422 	int r = DM_MAPIO_REMAPPED;
2423 	struct dm_snapshot *snap;
2424 	struct dm_exception *e;
2425 	struct dm_snap_pending_exception *pe, *pe2;
2426 	struct dm_snap_pending_exception *pe_to_start_now = NULL;
2427 	struct dm_snap_pending_exception *pe_to_start_last = NULL;
2428 	struct dm_exception_table_lock lock;
2429 	chunk_t chunk;
2430 
2431 	/* Do all the snapshots on this origin */
2432 	list_for_each_entry (snap, snapshots, list) {
2433 		/*
2434 		 * Don't make new exceptions in a merging snapshot
2435 		 * because it has effectively been deleted
2436 		 */
2437 		if (dm_target_is_snapshot_merge(snap->ti))
2438 			continue;
2439 
2440 		/* Nothing to do if writing beyond end of snapshot */
2441 		if (sector >= dm_table_get_size(snap->ti->table))
2442 			continue;
2443 
2444 		/*
2445 		 * Remember, different snapshots can have
2446 		 * different chunk sizes.
2447 		 */
2448 		chunk = sector_to_chunk(snap->store, sector);
2449 		dm_exception_table_lock_init(snap, chunk, &lock);
2450 
2451 		down_read(&snap->lock);
2452 		dm_exception_table_lock(&lock);
2453 
2454 		/* Only deal with valid and active snapshots */
2455 		if (!snap->valid || !snap->active)
2456 			goto next_snapshot;
2457 
2458 		pe = __lookup_pending_exception(snap, chunk);
2459 		if (!pe) {
2460 			/*
2461 			 * Check exception table to see if block is already
2462 			 * remapped in this snapshot and trigger an exception
2463 			 * if not.
2464 			 */
2465 			e = dm_lookup_exception(&snap->complete, chunk);
2466 			if (e)
2467 				goto next_snapshot;
2468 
2469 			dm_exception_table_unlock(&lock);
2470 			pe = alloc_pending_exception(snap);
2471 			dm_exception_table_lock(&lock);
2472 
2473 			pe2 = __lookup_pending_exception(snap, chunk);
2474 
2475 			if (!pe2) {
2476 				e = dm_lookup_exception(&snap->complete, chunk);
2477 				if (e) {
2478 					free_pending_exception(pe);
2479 					goto next_snapshot;
2480 				}
2481 
2482 				pe = __insert_pending_exception(snap, pe, chunk);
2483 				if (!pe) {
2484 					dm_exception_table_unlock(&lock);
2485 					up_read(&snap->lock);
2486 
2487 					invalidate_snapshot(snap, -ENOMEM);
2488 					continue;
2489 				}
2490 			} else {
2491 				free_pending_exception(pe);
2492 				pe = pe2;
2493 			}
2494 		}
2495 
2496 		r = DM_MAPIO_SUBMITTED;
2497 
2498 		/*
2499 		 * If an origin bio was supplied, queue it to wait for the
2500 		 * completion of this exception, and start this one last,
2501 		 * at the end of the function.
2502 		 */
2503 		if (bio) {
2504 			bio_list_add(&pe->origin_bios, bio);
2505 			bio = NULL;
2506 
2507 			if (!pe->started) {
2508 				pe->started = 1;
2509 				pe_to_start_last = pe;
2510 			}
2511 		}
2512 
2513 		if (!pe->started) {
2514 			pe->started = 1;
2515 			pe_to_start_now = pe;
2516 		}
2517 
2518 next_snapshot:
2519 		dm_exception_table_unlock(&lock);
2520 		up_read(&snap->lock);
2521 
2522 		if (pe_to_start_now) {
2523 			start_copy(pe_to_start_now);
2524 			pe_to_start_now = NULL;
2525 		}
2526 	}
2527 
2528 	/*
2529 	 * Submit the exception against which the bio is queued last,
2530 	 * to give the other exceptions a head start.
2531 	 */
2532 	if (pe_to_start_last)
2533 		start_copy(pe_to_start_last);
2534 
2535 	return r;
2536 }
2537 
2538 /*
2539  * Called on a write from the origin driver.
2540  */
2541 static int do_origin(struct dm_dev *origin, struct bio *bio, bool limit)
2542 {
2543 	struct origin *o;
2544 	int r = DM_MAPIO_REMAPPED;
2545 
2546 again:
2547 	down_read(&_origins_lock);
2548 	o = __lookup_origin(origin->bdev);
2549 	if (o) {
2550 		if (limit) {
2551 			struct dm_snapshot *s;
2552 			list_for_each_entry(s, &o->snapshots, list)
2553 				if (unlikely(!wait_for_in_progress(s, true)))
2554 					goto again;
2555 		}
2556 
2557 		r = __origin_write(&o->snapshots, bio->bi_iter.bi_sector, bio);
2558 	}
2559 	up_read(&_origins_lock);
2560 
2561 	return r;
2562 }
2563 
2564 /*
2565  * Trigger exceptions in all non-merging snapshots.
2566  *
2567  * The chunk size of the merging snapshot may be larger than the chunk
2568  * size of some other snapshot so we may need to reallocate multiple
2569  * chunks in other snapshots.
2570  *
2571  * We scan all the overlapping exceptions in the other snapshots.
2572  * Returns 1 if anything was reallocated and must be waited for,
2573  * otherwise returns 0.
2574  *
2575  * size must be a multiple of merging_snap's chunk_size.
2576  */
2577 static int origin_write_extent(struct dm_snapshot *merging_snap,
2578 			       sector_t sector, unsigned size)
2579 {
2580 	int must_wait = 0;
2581 	sector_t n;
2582 	struct origin *o;
2583 
2584 	/*
2585 	 * The origin's __minimum_chunk_size() got stored in max_io_len
2586 	 * by snapshot_merge_resume().
2587 	 */
2588 	down_read(&_origins_lock);
2589 	o = __lookup_origin(merging_snap->origin->bdev);
2590 	for (n = 0; n < size; n += merging_snap->ti->max_io_len)
2591 		if (__origin_write(&o->snapshots, sector + n, NULL) ==
2592 		    DM_MAPIO_SUBMITTED)
2593 			must_wait = 1;
2594 	up_read(&_origins_lock);
2595 
2596 	return must_wait;
2597 }
2598 
2599 /*
2600  * Origin: maps a linear range of a device, with hooks for snapshotting.
2601  */
2602 
2603 /*
2604  * Construct an origin mapping: <dev_path>
2605  * The context for an origin is merely a 'struct dm_dev *'
2606  * pointing to the real device.
2607  */
2608 static int origin_ctr(struct dm_target *ti, unsigned int argc, char **argv)
2609 {
2610 	int r;
2611 	struct dm_origin *o;
2612 
2613 	if (argc != 1) {
2614 		ti->error = "origin: incorrect number of arguments";
2615 		return -EINVAL;
2616 	}
2617 
2618 	o = kmalloc(sizeof(struct dm_origin), GFP_KERNEL);
2619 	if (!o) {
2620 		ti->error = "Cannot allocate private origin structure";
2621 		r = -ENOMEM;
2622 		goto bad_alloc;
2623 	}
2624 
2625 	r = dm_get_device(ti, argv[0], dm_table_get_mode(ti->table), &o->dev);
2626 	if (r) {
2627 		ti->error = "Cannot get target device";
2628 		goto bad_open;
2629 	}
2630 
2631 	o->ti = ti;
2632 	ti->private = o;
2633 	ti->num_flush_bios = 1;
2634 
2635 	return 0;
2636 
2637 bad_open:
2638 	kfree(o);
2639 bad_alloc:
2640 	return r;
2641 }
2642 
2643 static void origin_dtr(struct dm_target *ti)
2644 {
2645 	struct dm_origin *o = ti->private;
2646 
2647 	dm_put_device(ti, o->dev);
2648 	kfree(o);
2649 }
2650 
2651 static int origin_map(struct dm_target *ti, struct bio *bio)
2652 {
2653 	struct dm_origin *o = ti->private;
2654 	unsigned available_sectors;
2655 
2656 	bio_set_dev(bio, o->dev->bdev);
2657 
2658 	if (unlikely(bio->bi_opf & REQ_PREFLUSH))
2659 		return DM_MAPIO_REMAPPED;
2660 
2661 	if (bio_data_dir(bio) != WRITE)
2662 		return DM_MAPIO_REMAPPED;
2663 
2664 	available_sectors = o->split_boundary -
2665 		((unsigned)bio->bi_iter.bi_sector & (o->split_boundary - 1));
2666 
2667 	if (bio_sectors(bio) > available_sectors)
2668 		dm_accept_partial_bio(bio, available_sectors);
2669 
2670 	/* Only tell snapshots if this is a write */
2671 	return do_origin(o->dev, bio, true);
2672 }
2673 
2674 /*
2675  * Set the target "max_io_len" field to the minimum of all the snapshots'
2676  * chunk sizes.
2677  */
2678 static void origin_resume(struct dm_target *ti)
2679 {
2680 	struct dm_origin *o = ti->private;
2681 
2682 	o->split_boundary = get_origin_minimum_chunksize(o->dev->bdev);
2683 
2684 	down_write(&_origins_lock);
2685 	__insert_dm_origin(o);
2686 	up_write(&_origins_lock);
2687 }
2688 
2689 static void origin_postsuspend(struct dm_target *ti)
2690 {
2691 	struct dm_origin *o = ti->private;
2692 
2693 	down_write(&_origins_lock);
2694 	__remove_dm_origin(o);
2695 	up_write(&_origins_lock);
2696 }
2697 
2698 static void origin_status(struct dm_target *ti, status_type_t type,
2699 			  unsigned status_flags, char *result, unsigned maxlen)
2700 {
2701 	struct dm_origin *o = ti->private;
2702 
2703 	switch (type) {
2704 	case STATUSTYPE_INFO:
2705 		result[0] = '\0';
2706 		break;
2707 
2708 	case STATUSTYPE_TABLE:
2709 		snprintf(result, maxlen, "%s", o->dev->name);
2710 		break;
2711 	}
2712 }
2713 
2714 static int origin_iterate_devices(struct dm_target *ti,
2715 				  iterate_devices_callout_fn fn, void *data)
2716 {
2717 	struct dm_origin *o = ti->private;
2718 
2719 	return fn(ti, o->dev, 0, ti->len, data);
2720 }
2721 
2722 static struct target_type origin_target = {
2723 	.name    = "snapshot-origin",
2724 	.version = {1, 9, 0},
2725 	.module  = THIS_MODULE,
2726 	.ctr     = origin_ctr,
2727 	.dtr     = origin_dtr,
2728 	.map     = origin_map,
2729 	.resume  = origin_resume,
2730 	.postsuspend = origin_postsuspend,
2731 	.status  = origin_status,
2732 	.iterate_devices = origin_iterate_devices,
2733 };
2734 
2735 static struct target_type snapshot_target = {
2736 	.name    = "snapshot",
2737 	.version = {1, 16, 0},
2738 	.module  = THIS_MODULE,
2739 	.ctr     = snapshot_ctr,
2740 	.dtr     = snapshot_dtr,
2741 	.map     = snapshot_map,
2742 	.end_io  = snapshot_end_io,
2743 	.preresume  = snapshot_preresume,
2744 	.resume  = snapshot_resume,
2745 	.status  = snapshot_status,
2746 	.iterate_devices = snapshot_iterate_devices,
2747 	.io_hints = snapshot_io_hints,
2748 };
2749 
2750 static struct target_type merge_target = {
2751 	.name    = dm_snapshot_merge_target_name,
2752 	.version = {1, 5, 0},
2753 	.module  = THIS_MODULE,
2754 	.ctr     = snapshot_ctr,
2755 	.dtr     = snapshot_dtr,
2756 	.map     = snapshot_merge_map,
2757 	.end_io  = snapshot_end_io,
2758 	.presuspend = snapshot_merge_presuspend,
2759 	.preresume  = snapshot_preresume,
2760 	.resume  = snapshot_merge_resume,
2761 	.status  = snapshot_status,
2762 	.iterate_devices = snapshot_iterate_devices,
2763 	.io_hints = snapshot_io_hints,
2764 };
2765 
2766 static int __init dm_snapshot_init(void)
2767 {
2768 	int r;
2769 
2770 	r = dm_exception_store_init();
2771 	if (r) {
2772 		DMERR("Failed to initialize exception stores");
2773 		return r;
2774 	}
2775 
2776 	r = init_origin_hash();
2777 	if (r) {
2778 		DMERR("init_origin_hash failed.");
2779 		goto bad_origin_hash;
2780 	}
2781 
2782 	exception_cache = KMEM_CACHE(dm_exception, 0);
2783 	if (!exception_cache) {
2784 		DMERR("Couldn't create exception cache.");
2785 		r = -ENOMEM;
2786 		goto bad_exception_cache;
2787 	}
2788 
2789 	pending_cache = KMEM_CACHE(dm_snap_pending_exception, 0);
2790 	if (!pending_cache) {
2791 		DMERR("Couldn't create pending cache.");
2792 		r = -ENOMEM;
2793 		goto bad_pending_cache;
2794 	}
2795 
2796 	r = dm_register_target(&snapshot_target);
2797 	if (r < 0) {
2798 		DMERR("snapshot target register failed %d", r);
2799 		goto bad_register_snapshot_target;
2800 	}
2801 
2802 	r = dm_register_target(&origin_target);
2803 	if (r < 0) {
2804 		DMERR("Origin target register failed %d", r);
2805 		goto bad_register_origin_target;
2806 	}
2807 
2808 	r = dm_register_target(&merge_target);
2809 	if (r < 0) {
2810 		DMERR("Merge target register failed %d", r);
2811 		goto bad_register_merge_target;
2812 	}
2813 
2814 	return 0;
2815 
2816 bad_register_merge_target:
2817 	dm_unregister_target(&origin_target);
2818 bad_register_origin_target:
2819 	dm_unregister_target(&snapshot_target);
2820 bad_register_snapshot_target:
2821 	kmem_cache_destroy(pending_cache);
2822 bad_pending_cache:
2823 	kmem_cache_destroy(exception_cache);
2824 bad_exception_cache:
2825 	exit_origin_hash();
2826 bad_origin_hash:
2827 	dm_exception_store_exit();
2828 
2829 	return r;
2830 }
2831 
2832 static void __exit dm_snapshot_exit(void)
2833 {
2834 	dm_unregister_target(&snapshot_target);
2835 	dm_unregister_target(&origin_target);
2836 	dm_unregister_target(&merge_target);
2837 
2838 	exit_origin_hash();
2839 	kmem_cache_destroy(pending_cache);
2840 	kmem_cache_destroy(exception_cache);
2841 
2842 	dm_exception_store_exit();
2843 }
2844 
2845 /* Module hooks */
2846 module_init(dm_snapshot_init);
2847 module_exit(dm_snapshot_exit);
2848 
2849 MODULE_DESCRIPTION(DM_NAME " snapshot target");
2850 MODULE_AUTHOR("Joe Thornber");
2851 MODULE_LICENSE("GPL");
2852 MODULE_ALIAS("dm-snapshot-origin");
2853 MODULE_ALIAS("dm-snapshot-merge");
2854