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dm snapshot: do not use map_context
[~shefty/rdma-dev.git] / drivers / md / dm-snap.c
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 size of the mempool used to track chunks in use.
34  */
35 #define MIN_IOS 256
36
37 #define DM_TRACKED_CHUNK_HASH_SIZE      16
38 #define DM_TRACKED_CHUNK_HASH(x)        ((unsigned long)(x) & \
39                                          (DM_TRACKED_CHUNK_HASH_SIZE - 1))
40
41 struct dm_exception_table {
42         uint32_t hash_mask;
43         unsigned hash_shift;
44         struct list_head *table;
45 };
46
47 struct dm_snapshot {
48         struct rw_semaphore lock;
49
50         struct dm_dev *origin;
51         struct dm_dev *cow;
52
53         struct dm_target *ti;
54
55         /* List of snapshots per Origin */
56         struct list_head list;
57
58         /*
59          * You can't use a snapshot if this is 0 (e.g. if full).
60          * A snapshot-merge target never clears this.
61          */
62         int valid;
63
64         /* Origin writes don't trigger exceptions until this is set */
65         int active;
66
67         atomic_t pending_exceptions_count;
68
69         mempool_t *pending_pool;
70
71         struct dm_exception_table pending;
72         struct dm_exception_table complete;
73
74         /*
75          * pe_lock protects all pending_exception operations and access
76          * as well as the snapshot_bios list.
77          */
78         spinlock_t pe_lock;
79
80         /* Chunks with outstanding reads */
81         spinlock_t tracked_chunk_lock;
82         struct hlist_head tracked_chunk_hash[DM_TRACKED_CHUNK_HASH_SIZE];
83
84         /* The on disk metadata handler */
85         struct dm_exception_store *store;
86
87         struct dm_kcopyd_client *kcopyd_client;
88
89         /* Wait for events based on state_bits */
90         unsigned long state_bits;
91
92         /* Range of chunks currently being merged. */
93         chunk_t first_merging_chunk;
94         int num_merging_chunks;
95
96         /*
97          * The merge operation failed if this flag is set.
98          * Failure modes are handled as follows:
99          * - I/O error reading the header
100          *      => don't load the target; abort.
101          * - Header does not have "valid" flag set
102          *      => use the origin; forget about the snapshot.
103          * - I/O error when reading exceptions
104          *      => don't load the target; abort.
105          *         (We can't use the intermediate origin state.)
106          * - I/O error while merging
107          *      => stop merging; set merge_failed; process I/O normally.
108          */
109         int merge_failed;
110
111         /*
112          * Incoming bios that overlap with chunks being merged must wait
113          * for them to be committed.
114          */
115         struct bio_list bios_queued_during_merge;
116 };
117
118 /*
119  * state_bits:
120  *   RUNNING_MERGE  - Merge operation is in progress.
121  *   SHUTDOWN_MERGE - Set to signal that merge needs to be stopped;
122  *                    cleared afterwards.
123  */
124 #define RUNNING_MERGE          0
125 #define SHUTDOWN_MERGE         1
126
127 struct dm_dev *dm_snap_origin(struct dm_snapshot *s)
128 {
129         return s->origin;
130 }
131 EXPORT_SYMBOL(dm_snap_origin);
132
133 struct dm_dev *dm_snap_cow(struct dm_snapshot *s)
134 {
135         return s->cow;
136 }
137 EXPORT_SYMBOL(dm_snap_cow);
138
139 static sector_t chunk_to_sector(struct dm_exception_store *store,
140                                 chunk_t chunk)
141 {
142         return chunk << store->chunk_shift;
143 }
144
145 static int bdev_equal(struct block_device *lhs, struct block_device *rhs)
146 {
147         /*
148          * There is only ever one instance of a particular block
149          * device so we can compare pointers safely.
150          */
151         return lhs == rhs;
152 }
153
154 struct dm_snap_pending_exception {
155         struct dm_exception e;
156
157         /*
158          * Origin buffers waiting for this to complete are held
159          * in a bio list
160          */
161         struct bio_list origin_bios;
162         struct bio_list snapshot_bios;
163
164         /* Pointer back to snapshot context */
165         struct dm_snapshot *snap;
166
167         /*
168          * 1 indicates the exception has already been sent to
169          * kcopyd.
170          */
171         int started;
172
173         /*
174          * For writing a complete chunk, bypassing the copy.
175          */
176         struct bio *full_bio;
177         bio_end_io_t *full_bio_end_io;
178         void *full_bio_private;
179 };
180
181 /*
182  * Hash table mapping origin volumes to lists of snapshots and
183  * a lock to protect it
184  */
185 static struct kmem_cache *exception_cache;
186 static struct kmem_cache *pending_cache;
187
188 struct dm_snap_tracked_chunk {
189         struct hlist_node node;
190         chunk_t chunk;
191 };
192
193 static void init_tracked_chunk(struct bio *bio)
194 {
195         struct dm_snap_tracked_chunk *c = dm_per_bio_data(bio, sizeof(struct dm_snap_tracked_chunk));
196         INIT_HLIST_NODE(&c->node);
197 }
198
199 static bool is_bio_tracked(struct bio *bio)
200 {
201         struct dm_snap_tracked_chunk *c = dm_per_bio_data(bio, sizeof(struct dm_snap_tracked_chunk));
202         return !hlist_unhashed(&c->node);
203 }
204
205 static void track_chunk(struct dm_snapshot *s, struct bio *bio, chunk_t chunk)
206 {
207         struct dm_snap_tracked_chunk *c = dm_per_bio_data(bio, sizeof(struct dm_snap_tracked_chunk));
208
209         c->chunk = chunk;
210
211         spin_lock_irq(&s->tracked_chunk_lock);
212         hlist_add_head(&c->node,
213                        &s->tracked_chunk_hash[DM_TRACKED_CHUNK_HASH(chunk)]);
214         spin_unlock_irq(&s->tracked_chunk_lock);
215 }
216
217 static void stop_tracking_chunk(struct dm_snapshot *s, struct bio *bio)
218 {
219         struct dm_snap_tracked_chunk *c = dm_per_bio_data(bio, sizeof(struct dm_snap_tracked_chunk));
220         unsigned long flags;
221
222         spin_lock_irqsave(&s->tracked_chunk_lock, flags);
223         hlist_del(&c->node);
224         spin_unlock_irqrestore(&s->tracked_chunk_lock, flags);
225 }
226
227 static int __chunk_is_tracked(struct dm_snapshot *s, chunk_t chunk)
228 {
229         struct dm_snap_tracked_chunk *c;
230         struct hlist_node *hn;
231         int found = 0;
232
233         spin_lock_irq(&s->tracked_chunk_lock);
234
235         hlist_for_each_entry(c, hn,
236             &s->tracked_chunk_hash[DM_TRACKED_CHUNK_HASH(chunk)], node) {
237                 if (c->chunk == chunk) {
238                         found = 1;
239                         break;
240                 }
241         }
242
243         spin_unlock_irq(&s->tracked_chunk_lock);
244
245         return found;
246 }
247
248 /*
249  * This conflicting I/O is extremely improbable in the caller,
250  * so msleep(1) is sufficient and there is no need for a wait queue.
251  */
252 static void __check_for_conflicting_io(struct dm_snapshot *s, chunk_t chunk)
253 {
254         while (__chunk_is_tracked(s, chunk))
255                 msleep(1);
256 }
257
258 /*
259  * One of these per registered origin, held in the snapshot_origins hash
260  */
261 struct origin {
262         /* The origin device */
263         struct block_device *bdev;
264
265         struct list_head hash_list;
266
267         /* List of snapshots for this origin */
268         struct list_head snapshots;
269 };
270
271 /*
272  * Size of the hash table for origin volumes. If we make this
273  * the size of the minors list then it should be nearly perfect
274  */
275 #define ORIGIN_HASH_SIZE 256
276 #define ORIGIN_MASK      0xFF
277 static struct list_head *_origins;
278 static struct rw_semaphore _origins_lock;
279
280 static DECLARE_WAIT_QUEUE_HEAD(_pending_exceptions_done);
281 static DEFINE_SPINLOCK(_pending_exceptions_done_spinlock);
282 static uint64_t _pending_exceptions_done_count;
283
284 static int init_origin_hash(void)
285 {
286         int i;
287
288         _origins = kmalloc(ORIGIN_HASH_SIZE * sizeof(struct list_head),
289                            GFP_KERNEL);
290         if (!_origins) {
291                 DMERR("unable to allocate memory");
292                 return -ENOMEM;
293         }
294
295         for (i = 0; i < ORIGIN_HASH_SIZE; i++)
296                 INIT_LIST_HEAD(_origins + i);
297         init_rwsem(&_origins_lock);
298
299         return 0;
300 }
301
302 static void exit_origin_hash(void)
303 {
304         kfree(_origins);
305 }
306
307 static unsigned origin_hash(struct block_device *bdev)
308 {
309         return bdev->bd_dev & ORIGIN_MASK;
310 }
311
312 static struct origin *__lookup_origin(struct block_device *origin)
313 {
314         struct list_head *ol;
315         struct origin *o;
316
317         ol = &_origins[origin_hash(origin)];
318         list_for_each_entry (o, ol, hash_list)
319                 if (bdev_equal(o->bdev, origin))
320                         return o;
321
322         return NULL;
323 }
324
325 static void __insert_origin(struct origin *o)
326 {
327         struct list_head *sl = &_origins[origin_hash(o->bdev)];
328         list_add_tail(&o->hash_list, sl);
329 }
330
331 /*
332  * _origins_lock must be held when calling this function.
333  * Returns number of snapshots registered using the supplied cow device, plus:
334  * snap_src - a snapshot suitable for use as a source of exception handover
335  * snap_dest - a snapshot capable of receiving exception handover.
336  * snap_merge - an existing snapshot-merge target linked to the same origin.
337  *   There can be at most one snapshot-merge target. The parameter is optional.
338  *
339  * Possible return values and states of snap_src and snap_dest.
340  *   0: NULL, NULL  - first new snapshot
341  *   1: snap_src, NULL - normal snapshot
342  *   2: snap_src, snap_dest  - waiting for handover
343  *   2: snap_src, NULL - handed over, waiting for old to be deleted
344  *   1: NULL, snap_dest - source got destroyed without handover
345  */
346 static int __find_snapshots_sharing_cow(struct dm_snapshot *snap,
347                                         struct dm_snapshot **snap_src,
348                                         struct dm_snapshot **snap_dest,
349                                         struct dm_snapshot **snap_merge)
350 {
351         struct dm_snapshot *s;
352         struct origin *o;
353         int count = 0;
354         int active;
355
356         o = __lookup_origin(snap->origin->bdev);
357         if (!o)
358                 goto out;
359
360         list_for_each_entry(s, &o->snapshots, list) {
361                 if (dm_target_is_snapshot_merge(s->ti) && snap_merge)
362                         *snap_merge = s;
363                 if (!bdev_equal(s->cow->bdev, snap->cow->bdev))
364                         continue;
365
366                 down_read(&s->lock);
367                 active = s->active;
368                 up_read(&s->lock);
369
370                 if (active) {
371                         if (snap_src)
372                                 *snap_src = s;
373                 } else if (snap_dest)
374                         *snap_dest = s;
375
376                 count++;
377         }
378
379 out:
380         return count;
381 }
382
383 /*
384  * On success, returns 1 if this snapshot is a handover destination,
385  * otherwise returns 0.
386  */
387 static int __validate_exception_handover(struct dm_snapshot *snap)
388 {
389         struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
390         struct dm_snapshot *snap_merge = NULL;
391
392         /* Does snapshot need exceptions handed over to it? */
393         if ((__find_snapshots_sharing_cow(snap, &snap_src, &snap_dest,
394                                           &snap_merge) == 2) ||
395             snap_dest) {
396                 snap->ti->error = "Snapshot cow pairing for exception "
397                                   "table handover failed";
398                 return -EINVAL;
399         }
400
401         /*
402          * If no snap_src was found, snap cannot become a handover
403          * destination.
404          */
405         if (!snap_src)
406                 return 0;
407
408         /*
409          * Non-snapshot-merge handover?
410          */
411         if (!dm_target_is_snapshot_merge(snap->ti))
412                 return 1;
413
414         /*
415          * Do not allow more than one merging snapshot.
416          */
417         if (snap_merge) {
418                 snap->ti->error = "A snapshot is already merging.";
419                 return -EINVAL;
420         }
421
422         if (!snap_src->store->type->prepare_merge ||
423             !snap_src->store->type->commit_merge) {
424                 snap->ti->error = "Snapshot exception store does not "
425                                   "support snapshot-merge.";
426                 return -EINVAL;
427         }
428
429         return 1;
430 }
431
432 static void __insert_snapshot(struct origin *o, struct dm_snapshot *s)
433 {
434         struct dm_snapshot *l;
435
436         /* Sort the list according to chunk size, largest-first smallest-last */
437         list_for_each_entry(l, &o->snapshots, list)
438                 if (l->store->chunk_size < s->store->chunk_size)
439                         break;
440         list_add_tail(&s->list, &l->list);
441 }
442
443 /*
444  * Make a note of the snapshot and its origin so we can look it
445  * up when the origin has a write on it.
446  *
447  * Also validate snapshot exception store handovers.
448  * On success, returns 1 if this registration is a handover destination,
449  * otherwise returns 0.
450  */
451 static int register_snapshot(struct dm_snapshot *snap)
452 {
453         struct origin *o, *new_o = NULL;
454         struct block_device *bdev = snap->origin->bdev;
455         int r = 0;
456
457         new_o = kmalloc(sizeof(*new_o), GFP_KERNEL);
458         if (!new_o)
459                 return -ENOMEM;
460
461         down_write(&_origins_lock);
462
463         r = __validate_exception_handover(snap);
464         if (r < 0) {
465                 kfree(new_o);
466                 goto out;
467         }
468
469         o = __lookup_origin(bdev);
470         if (o)
471                 kfree(new_o);
472         else {
473                 /* New origin */
474                 o = new_o;
475
476                 /* Initialise the struct */
477                 INIT_LIST_HEAD(&o->snapshots);
478                 o->bdev = bdev;
479
480                 __insert_origin(o);
481         }
482
483         __insert_snapshot(o, snap);
484
485 out:
486         up_write(&_origins_lock);
487
488         return r;
489 }
490
491 /*
492  * Move snapshot to correct place in list according to chunk size.
493  */
494 static void reregister_snapshot(struct dm_snapshot *s)
495 {
496         struct block_device *bdev = s->origin->bdev;
497
498         down_write(&_origins_lock);
499
500         list_del(&s->list);
501         __insert_snapshot(__lookup_origin(bdev), s);
502
503         up_write(&_origins_lock);
504 }
505
506 static void unregister_snapshot(struct dm_snapshot *s)
507 {
508         struct origin *o;
509
510         down_write(&_origins_lock);
511         o = __lookup_origin(s->origin->bdev);
512
513         list_del(&s->list);
514         if (o && list_empty(&o->snapshots)) {
515                 list_del(&o->hash_list);
516                 kfree(o);
517         }
518
519         up_write(&_origins_lock);
520 }
521
522 /*
523  * Implementation of the exception hash tables.
524  * The lowest hash_shift bits of the chunk number are ignored, allowing
525  * some consecutive chunks to be grouped together.
526  */
527 static int dm_exception_table_init(struct dm_exception_table *et,
528                                    uint32_t size, unsigned hash_shift)
529 {
530         unsigned int i;
531
532         et->hash_shift = hash_shift;
533         et->hash_mask = size - 1;
534         et->table = dm_vcalloc(size, sizeof(struct list_head));
535         if (!et->table)
536                 return -ENOMEM;
537
538         for (i = 0; i < size; i++)
539                 INIT_LIST_HEAD(et->table + i);
540
541         return 0;
542 }
543
544 static void dm_exception_table_exit(struct dm_exception_table *et,
545                                     struct kmem_cache *mem)
546 {
547         struct list_head *slot;
548         struct dm_exception *ex, *next;
549         int i, size;
550
551         size = et->hash_mask + 1;
552         for (i = 0; i < size; i++) {
553                 slot = et->table + i;
554
555                 list_for_each_entry_safe (ex, next, slot, hash_list)
556                         kmem_cache_free(mem, ex);
557         }
558
559         vfree(et->table);
560 }
561
562 static uint32_t exception_hash(struct dm_exception_table *et, chunk_t chunk)
563 {
564         return (chunk >> et->hash_shift) & et->hash_mask;
565 }
566
567 static void dm_remove_exception(struct dm_exception *e)
568 {
569         list_del(&e->hash_list);
570 }
571
572 /*
573  * Return the exception data for a sector, or NULL if not
574  * remapped.
575  */
576 static struct dm_exception *dm_lookup_exception(struct dm_exception_table *et,
577                                                 chunk_t chunk)
578 {
579         struct list_head *slot;
580         struct dm_exception *e;
581
582         slot = &et->table[exception_hash(et, chunk)];
583         list_for_each_entry (e, slot, hash_list)
584                 if (chunk >= e->old_chunk &&
585                     chunk <= e->old_chunk + dm_consecutive_chunk_count(e))
586                         return e;
587
588         return NULL;
589 }
590
591 static struct dm_exception *alloc_completed_exception(void)
592 {
593         struct dm_exception *e;
594
595         e = kmem_cache_alloc(exception_cache, GFP_NOIO);
596         if (!e)
597                 e = kmem_cache_alloc(exception_cache, GFP_ATOMIC);
598
599         return e;
600 }
601
602 static void free_completed_exception(struct dm_exception *e)
603 {
604         kmem_cache_free(exception_cache, e);
605 }
606
607 static struct dm_snap_pending_exception *alloc_pending_exception(struct dm_snapshot *s)
608 {
609         struct dm_snap_pending_exception *pe = mempool_alloc(s->pending_pool,
610                                                              GFP_NOIO);
611
612         atomic_inc(&s->pending_exceptions_count);
613         pe->snap = s;
614
615         return pe;
616 }
617
618 static void free_pending_exception(struct dm_snap_pending_exception *pe)
619 {
620         struct dm_snapshot *s = pe->snap;
621
622         mempool_free(pe, s->pending_pool);
623         smp_mb__before_atomic_dec();
624         atomic_dec(&s->pending_exceptions_count);
625 }
626
627 static void dm_insert_exception(struct dm_exception_table *eh,
628                                 struct dm_exception *new_e)
629 {
630         struct list_head *l;
631         struct dm_exception *e = NULL;
632
633         l = &eh->table[exception_hash(eh, new_e->old_chunk)];
634
635         /* Add immediately if this table doesn't support consecutive chunks */
636         if (!eh->hash_shift)
637                 goto out;
638
639         /* List is ordered by old_chunk */
640         list_for_each_entry_reverse(e, l, hash_list) {
641                 /* Insert after an existing chunk? */
642                 if (new_e->old_chunk == (e->old_chunk +
643                                          dm_consecutive_chunk_count(e) + 1) &&
644                     new_e->new_chunk == (dm_chunk_number(e->new_chunk) +
645                                          dm_consecutive_chunk_count(e) + 1)) {
646                         dm_consecutive_chunk_count_inc(e);
647                         free_completed_exception(new_e);
648                         return;
649                 }
650
651                 /* Insert before an existing chunk? */
652                 if (new_e->old_chunk == (e->old_chunk - 1) &&
653                     new_e->new_chunk == (dm_chunk_number(e->new_chunk) - 1)) {
654                         dm_consecutive_chunk_count_inc(e);
655                         e->old_chunk--;
656                         e->new_chunk--;
657                         free_completed_exception(new_e);
658                         return;
659                 }
660
661                 if (new_e->old_chunk > e->old_chunk)
662                         break;
663         }
664
665 out:
666         list_add(&new_e->hash_list, e ? &e->hash_list : l);
667 }
668
669 /*
670  * Callback used by the exception stores to load exceptions when
671  * initialising.
672  */
673 static int dm_add_exception(void *context, chunk_t old, chunk_t new)
674 {
675         struct dm_snapshot *s = context;
676         struct dm_exception *e;
677
678         e = alloc_completed_exception();
679         if (!e)
680                 return -ENOMEM;
681
682         e->old_chunk = old;
683
684         /* Consecutive_count is implicitly initialised to zero */
685         e->new_chunk = new;
686
687         dm_insert_exception(&s->complete, e);
688
689         return 0;
690 }
691
692 /*
693  * Return a minimum chunk size of all snapshots that have the specified origin.
694  * Return zero if the origin has no snapshots.
695  */
696 static uint32_t __minimum_chunk_size(struct origin *o)
697 {
698         struct dm_snapshot *snap;
699         unsigned chunk_size = 0;
700
701         if (o)
702                 list_for_each_entry(snap, &o->snapshots, list)
703                         chunk_size = min_not_zero(chunk_size,
704                                                   snap->store->chunk_size);
705
706         return (uint32_t) chunk_size;
707 }
708
709 /*
710  * Hard coded magic.
711  */
712 static int calc_max_buckets(void)
713 {
714         /* use a fixed size of 2MB */
715         unsigned long mem = 2 * 1024 * 1024;
716         mem /= sizeof(struct list_head);
717
718         return mem;
719 }
720
721 /*
722  * Allocate room for a suitable hash table.
723  */
724 static int init_hash_tables(struct dm_snapshot *s)
725 {
726         sector_t hash_size, cow_dev_size, origin_dev_size, max_buckets;
727
728         /*
729          * Calculate based on the size of the original volume or
730          * the COW volume...
731          */
732         cow_dev_size = get_dev_size(s->cow->bdev);
733         origin_dev_size = get_dev_size(s->origin->bdev);
734         max_buckets = calc_max_buckets();
735
736         hash_size = min(origin_dev_size, cow_dev_size) >> s->store->chunk_shift;
737         hash_size = min(hash_size, max_buckets);
738
739         if (hash_size < 64)
740                 hash_size = 64;
741         hash_size = rounddown_pow_of_two(hash_size);
742         if (dm_exception_table_init(&s->complete, hash_size,
743                                     DM_CHUNK_CONSECUTIVE_BITS))
744                 return -ENOMEM;
745
746         /*
747          * Allocate hash table for in-flight exceptions
748          * Make this smaller than the real hash table
749          */
750         hash_size >>= 3;
751         if (hash_size < 64)
752                 hash_size = 64;
753
754         if (dm_exception_table_init(&s->pending, hash_size, 0)) {
755                 dm_exception_table_exit(&s->complete, exception_cache);
756                 return -ENOMEM;
757         }
758
759         return 0;
760 }
761
762 static void merge_shutdown(struct dm_snapshot *s)
763 {
764         clear_bit_unlock(RUNNING_MERGE, &s->state_bits);
765         smp_mb__after_clear_bit();
766         wake_up_bit(&s->state_bits, RUNNING_MERGE);
767 }
768
769 static struct bio *__release_queued_bios_after_merge(struct dm_snapshot *s)
770 {
771         s->first_merging_chunk = 0;
772         s->num_merging_chunks = 0;
773
774         return bio_list_get(&s->bios_queued_during_merge);
775 }
776
777 /*
778  * Remove one chunk from the index of completed exceptions.
779  */
780 static int __remove_single_exception_chunk(struct dm_snapshot *s,
781                                            chunk_t old_chunk)
782 {
783         struct dm_exception *e;
784
785         e = dm_lookup_exception(&s->complete, old_chunk);
786         if (!e) {
787                 DMERR("Corruption detected: exception for block %llu is "
788                       "on disk but not in memory",
789                       (unsigned long long)old_chunk);
790                 return -EINVAL;
791         }
792
793         /*
794          * If this is the only chunk using this exception, remove exception.
795          */
796         if (!dm_consecutive_chunk_count(e)) {
797                 dm_remove_exception(e);
798                 free_completed_exception(e);
799                 return 0;
800         }
801
802         /*
803          * The chunk may be either at the beginning or the end of a
804          * group of consecutive chunks - never in the middle.  We are
805          * removing chunks in the opposite order to that in which they
806          * were added, so this should always be true.
807          * Decrement the consecutive chunk counter and adjust the
808          * starting point if necessary.
809          */
810         if (old_chunk == e->old_chunk) {
811                 e->old_chunk++;
812                 e->new_chunk++;
813         } else if (old_chunk != e->old_chunk +
814                    dm_consecutive_chunk_count(e)) {
815                 DMERR("Attempt to merge block %llu from the "
816                       "middle of a chunk range [%llu - %llu]",
817                       (unsigned long long)old_chunk,
818                       (unsigned long long)e->old_chunk,
819                       (unsigned long long)
820                       e->old_chunk + dm_consecutive_chunk_count(e));
821                 return -EINVAL;
822         }
823
824         dm_consecutive_chunk_count_dec(e);
825
826         return 0;
827 }
828
829 static void flush_bios(struct bio *bio);
830
831 static int remove_single_exception_chunk(struct dm_snapshot *s)
832 {
833         struct bio *b = NULL;
834         int r;
835         chunk_t old_chunk = s->first_merging_chunk + s->num_merging_chunks - 1;
836
837         down_write(&s->lock);
838
839         /*
840          * Process chunks (and associated exceptions) in reverse order
841          * so that dm_consecutive_chunk_count_dec() accounting works.
842          */
843         do {
844                 r = __remove_single_exception_chunk(s, old_chunk);
845                 if (r)
846                         goto out;
847         } while (old_chunk-- > s->first_merging_chunk);
848
849         b = __release_queued_bios_after_merge(s);
850
851 out:
852         up_write(&s->lock);
853         if (b)
854                 flush_bios(b);
855
856         return r;
857 }
858
859 static int origin_write_extent(struct dm_snapshot *merging_snap,
860                                sector_t sector, unsigned chunk_size);
861
862 static void merge_callback(int read_err, unsigned long write_err,
863                            void *context);
864
865 static uint64_t read_pending_exceptions_done_count(void)
866 {
867         uint64_t pending_exceptions_done;
868
869         spin_lock(&_pending_exceptions_done_spinlock);
870         pending_exceptions_done = _pending_exceptions_done_count;
871         spin_unlock(&_pending_exceptions_done_spinlock);
872
873         return pending_exceptions_done;
874 }
875
876 static void increment_pending_exceptions_done_count(void)
877 {
878         spin_lock(&_pending_exceptions_done_spinlock);
879         _pending_exceptions_done_count++;
880         spin_unlock(&_pending_exceptions_done_spinlock);
881
882         wake_up_all(&_pending_exceptions_done);
883 }
884
885 static void snapshot_merge_next_chunks(struct dm_snapshot *s)
886 {
887         int i, linear_chunks;
888         chunk_t old_chunk, new_chunk;
889         struct dm_io_region src, dest;
890         sector_t io_size;
891         uint64_t previous_count;
892
893         BUG_ON(!test_bit(RUNNING_MERGE, &s->state_bits));
894         if (unlikely(test_bit(SHUTDOWN_MERGE, &s->state_bits)))
895                 goto shut;
896
897         /*
898          * valid flag never changes during merge, so no lock required.
899          */
900         if (!s->valid) {
901                 DMERR("Snapshot is invalid: can't merge");
902                 goto shut;
903         }
904
905         linear_chunks = s->store->type->prepare_merge(s->store, &old_chunk,
906                                                       &new_chunk);
907         if (linear_chunks <= 0) {
908                 if (linear_chunks < 0) {
909                         DMERR("Read error in exception store: "
910                               "shutting down merge");
911                         down_write(&s->lock);
912                         s->merge_failed = 1;
913                         up_write(&s->lock);
914                 }
915                 goto shut;
916         }
917
918         /* Adjust old_chunk and new_chunk to reflect start of linear region */
919         old_chunk = old_chunk + 1 - linear_chunks;
920         new_chunk = new_chunk + 1 - linear_chunks;
921
922         /*
923          * Use one (potentially large) I/O to copy all 'linear_chunks'
924          * from the exception store to the origin
925          */
926         io_size = linear_chunks * s->store->chunk_size;
927
928         dest.bdev = s->origin->bdev;
929         dest.sector = chunk_to_sector(s->store, old_chunk);
930         dest.count = min(io_size, get_dev_size(dest.bdev) - dest.sector);
931
932         src.bdev = s->cow->bdev;
933         src.sector = chunk_to_sector(s->store, new_chunk);
934         src.count = dest.count;
935
936         /*
937          * Reallocate any exceptions needed in other snapshots then
938          * wait for the pending exceptions to complete.
939          * Each time any pending exception (globally on the system)
940          * completes we are woken and repeat the process to find out
941          * if we can proceed.  While this may not seem a particularly
942          * efficient algorithm, it is not expected to have any
943          * significant impact on performance.
944          */
945         previous_count = read_pending_exceptions_done_count();
946         while (origin_write_extent(s, dest.sector, io_size)) {
947                 wait_event(_pending_exceptions_done,
948                            (read_pending_exceptions_done_count() !=
949                             previous_count));
950                 /* Retry after the wait, until all exceptions are done. */
951                 previous_count = read_pending_exceptions_done_count();
952         }
953
954         down_write(&s->lock);
955         s->first_merging_chunk = old_chunk;
956         s->num_merging_chunks = linear_chunks;
957         up_write(&s->lock);
958
959         /* Wait until writes to all 'linear_chunks' drain */
960         for (i = 0; i < linear_chunks; i++)
961                 __check_for_conflicting_io(s, old_chunk + i);
962
963         dm_kcopyd_copy(s->kcopyd_client, &src, 1, &dest, 0, merge_callback, s);
964         return;
965
966 shut:
967         merge_shutdown(s);
968 }
969
970 static void error_bios(struct bio *bio);
971
972 static void merge_callback(int read_err, unsigned long write_err, void *context)
973 {
974         struct dm_snapshot *s = context;
975         struct bio *b = NULL;
976
977         if (read_err || write_err) {
978                 if (read_err)
979                         DMERR("Read error: shutting down merge.");
980                 else
981                         DMERR("Write error: shutting down merge.");
982                 goto shut;
983         }
984
985         if (s->store->type->commit_merge(s->store,
986                                          s->num_merging_chunks) < 0) {
987                 DMERR("Write error in exception store: shutting down merge");
988                 goto shut;
989         }
990
991         if (remove_single_exception_chunk(s) < 0)
992                 goto shut;
993
994         snapshot_merge_next_chunks(s);
995
996         return;
997
998 shut:
999         down_write(&s->lock);
1000         s->merge_failed = 1;
1001         b = __release_queued_bios_after_merge(s);
1002         up_write(&s->lock);
1003         error_bios(b);
1004
1005         merge_shutdown(s);
1006 }
1007
1008 static void start_merge(struct dm_snapshot *s)
1009 {
1010         if (!test_and_set_bit(RUNNING_MERGE, &s->state_bits))
1011                 snapshot_merge_next_chunks(s);
1012 }
1013
1014 static int wait_schedule(void *ptr)
1015 {
1016         schedule();
1017
1018         return 0;
1019 }
1020
1021 /*
1022  * Stop the merging process and wait until it finishes.
1023  */
1024 static void stop_merge(struct dm_snapshot *s)
1025 {
1026         set_bit(SHUTDOWN_MERGE, &s->state_bits);
1027         wait_on_bit(&s->state_bits, RUNNING_MERGE, wait_schedule,
1028                     TASK_UNINTERRUPTIBLE);
1029         clear_bit(SHUTDOWN_MERGE, &s->state_bits);
1030 }
1031
1032 /*
1033  * Construct a snapshot mapping: <origin_dev> <COW-dev> <p/n> <chunk-size>
1034  */
1035 static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
1036 {
1037         struct dm_snapshot *s;
1038         int i;
1039         int r = -EINVAL;
1040         char *origin_path, *cow_path;
1041         unsigned args_used, num_flush_requests = 1;
1042         fmode_t origin_mode = FMODE_READ;
1043
1044         if (argc != 4) {
1045                 ti->error = "requires exactly 4 arguments";
1046                 r = -EINVAL;
1047                 goto bad;
1048         }
1049
1050         if (dm_target_is_snapshot_merge(ti)) {
1051                 num_flush_requests = 2;
1052                 origin_mode = FMODE_WRITE;
1053         }
1054
1055         s = kmalloc(sizeof(*s), GFP_KERNEL);
1056         if (!s) {
1057                 ti->error = "Cannot allocate private snapshot structure";
1058                 r = -ENOMEM;
1059                 goto bad;
1060         }
1061
1062         origin_path = argv[0];
1063         argv++;
1064         argc--;
1065
1066         r = dm_get_device(ti, origin_path, origin_mode, &s->origin);
1067         if (r) {
1068                 ti->error = "Cannot get origin device";
1069                 goto bad_origin;
1070         }
1071
1072         cow_path = argv[0];
1073         argv++;
1074         argc--;
1075
1076         r = dm_get_device(ti, cow_path, dm_table_get_mode(ti->table), &s->cow);
1077         if (r) {
1078                 ti->error = "Cannot get COW device";
1079                 goto bad_cow;
1080         }
1081
1082         r = dm_exception_store_create(ti, argc, argv, s, &args_used, &s->store);
1083         if (r) {
1084                 ti->error = "Couldn't create exception store";
1085                 r = -EINVAL;
1086                 goto bad_store;
1087         }
1088
1089         argv += args_used;
1090         argc -= args_used;
1091
1092         s->ti = ti;
1093         s->valid = 1;
1094         s->active = 0;
1095         atomic_set(&s->pending_exceptions_count, 0);
1096         init_rwsem(&s->lock);
1097         INIT_LIST_HEAD(&s->list);
1098         spin_lock_init(&s->pe_lock);
1099         s->state_bits = 0;
1100         s->merge_failed = 0;
1101         s->first_merging_chunk = 0;
1102         s->num_merging_chunks = 0;
1103         bio_list_init(&s->bios_queued_during_merge);
1104
1105         /* Allocate hash table for COW data */
1106         if (init_hash_tables(s)) {
1107                 ti->error = "Unable to allocate hash table space";
1108                 r = -ENOMEM;
1109                 goto bad_hash_tables;
1110         }
1111
1112         s->kcopyd_client = dm_kcopyd_client_create();
1113         if (IS_ERR(s->kcopyd_client)) {
1114                 r = PTR_ERR(s->kcopyd_client);
1115                 ti->error = "Could not create kcopyd client";
1116                 goto bad_kcopyd;
1117         }
1118
1119         s->pending_pool = mempool_create_slab_pool(MIN_IOS, pending_cache);
1120         if (!s->pending_pool) {
1121                 ti->error = "Could not allocate mempool for pending exceptions";
1122                 goto bad_pending_pool;
1123         }
1124
1125         for (i = 0; i < DM_TRACKED_CHUNK_HASH_SIZE; i++)
1126                 INIT_HLIST_HEAD(&s->tracked_chunk_hash[i]);
1127
1128         spin_lock_init(&s->tracked_chunk_lock);
1129
1130         ti->private = s;
1131         ti->num_flush_requests = num_flush_requests;
1132         ti->per_bio_data_size = sizeof(struct dm_snap_tracked_chunk);
1133
1134         /* Add snapshot to the list of snapshots for this origin */
1135         /* Exceptions aren't triggered till snapshot_resume() is called */
1136         r = register_snapshot(s);
1137         if (r == -ENOMEM) {
1138                 ti->error = "Snapshot origin struct allocation failed";
1139                 goto bad_load_and_register;
1140         } else if (r < 0) {
1141                 /* invalid handover, register_snapshot has set ti->error */
1142                 goto bad_load_and_register;
1143         }
1144
1145         /*
1146          * Metadata must only be loaded into one table at once, so skip this
1147          * if metadata will be handed over during resume.
1148          * Chunk size will be set during the handover - set it to zero to
1149          * ensure it's ignored.
1150          */
1151         if (r > 0) {
1152                 s->store->chunk_size = 0;
1153                 return 0;
1154         }
1155
1156         r = s->store->type->read_metadata(s->store, dm_add_exception,
1157                                           (void *)s);
1158         if (r < 0) {
1159                 ti->error = "Failed to read snapshot metadata";
1160                 goto bad_read_metadata;
1161         } else if (r > 0) {
1162                 s->valid = 0;
1163                 DMWARN("Snapshot is marked invalid.");
1164         }
1165
1166         if (!s->store->chunk_size) {
1167                 ti->error = "Chunk size not set";
1168                 goto bad_read_metadata;
1169         }
1170
1171         r = dm_set_target_max_io_len(ti, s->store->chunk_size);
1172         if (r)
1173                 goto bad_read_metadata;
1174
1175         return 0;
1176
1177 bad_read_metadata:
1178         unregister_snapshot(s);
1179
1180 bad_load_and_register:
1181         mempool_destroy(s->pending_pool);
1182
1183 bad_pending_pool:
1184         dm_kcopyd_client_destroy(s->kcopyd_client);
1185
1186 bad_kcopyd:
1187         dm_exception_table_exit(&s->pending, pending_cache);
1188         dm_exception_table_exit(&s->complete, exception_cache);
1189
1190 bad_hash_tables:
1191         dm_exception_store_destroy(s->store);
1192
1193 bad_store:
1194         dm_put_device(ti, s->cow);
1195
1196 bad_cow:
1197         dm_put_device(ti, s->origin);
1198
1199 bad_origin:
1200         kfree(s);
1201
1202 bad:
1203         return r;
1204 }
1205
1206 static void __free_exceptions(struct dm_snapshot *s)
1207 {
1208         dm_kcopyd_client_destroy(s->kcopyd_client);
1209         s->kcopyd_client = NULL;
1210
1211         dm_exception_table_exit(&s->pending, pending_cache);
1212         dm_exception_table_exit(&s->complete, exception_cache);
1213 }
1214
1215 static void __handover_exceptions(struct dm_snapshot *snap_src,
1216                                   struct dm_snapshot *snap_dest)
1217 {
1218         union {
1219                 struct dm_exception_table table_swap;
1220                 struct dm_exception_store *store_swap;
1221         } u;
1222
1223         /*
1224          * Swap all snapshot context information between the two instances.
1225          */
1226         u.table_swap = snap_dest->complete;
1227         snap_dest->complete = snap_src->complete;
1228         snap_src->complete = u.table_swap;
1229
1230         u.store_swap = snap_dest->store;
1231         snap_dest->store = snap_src->store;
1232         snap_src->store = u.store_swap;
1233
1234         snap_dest->store->snap = snap_dest;
1235         snap_src->store->snap = snap_src;
1236
1237         snap_dest->ti->max_io_len = snap_dest->store->chunk_size;
1238         snap_dest->valid = snap_src->valid;
1239
1240         /*
1241          * Set source invalid to ensure it receives no further I/O.
1242          */
1243         snap_src->valid = 0;
1244 }
1245
1246 static void snapshot_dtr(struct dm_target *ti)
1247 {
1248 #ifdef CONFIG_DM_DEBUG
1249         int i;
1250 #endif
1251         struct dm_snapshot *s = ti->private;
1252         struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
1253
1254         down_read(&_origins_lock);
1255         /* Check whether exception handover must be cancelled */
1256         (void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL);
1257         if (snap_src && snap_dest && (s == snap_src)) {
1258                 down_write(&snap_dest->lock);
1259                 snap_dest->valid = 0;
1260                 up_write(&snap_dest->lock);
1261                 DMERR("Cancelling snapshot handover.");
1262         }
1263         up_read(&_origins_lock);
1264
1265         if (dm_target_is_snapshot_merge(ti))
1266                 stop_merge(s);
1267
1268         /* Prevent further origin writes from using this snapshot. */
1269         /* After this returns there can be no new kcopyd jobs. */
1270         unregister_snapshot(s);
1271
1272         while (atomic_read(&s->pending_exceptions_count))
1273                 msleep(1);
1274         /*
1275          * Ensure instructions in mempool_destroy aren't reordered
1276          * before atomic_read.
1277          */
1278         smp_mb();
1279
1280 #ifdef CONFIG_DM_DEBUG
1281         for (i = 0; i < DM_TRACKED_CHUNK_HASH_SIZE; i++)
1282                 BUG_ON(!hlist_empty(&s->tracked_chunk_hash[i]));
1283 #endif
1284
1285         __free_exceptions(s);
1286
1287         mempool_destroy(s->pending_pool);
1288
1289         dm_exception_store_destroy(s->store);
1290
1291         dm_put_device(ti, s->cow);
1292
1293         dm_put_device(ti, s->origin);
1294
1295         kfree(s);
1296 }
1297
1298 /*
1299  * Flush a list of buffers.
1300  */
1301 static void flush_bios(struct bio *bio)
1302 {
1303         struct bio *n;
1304
1305         while (bio) {
1306                 n = bio->bi_next;
1307                 bio->bi_next = NULL;
1308                 generic_make_request(bio);
1309                 bio = n;
1310         }
1311 }
1312
1313 static int do_origin(struct dm_dev *origin, struct bio *bio);
1314
1315 /*
1316  * Flush a list of buffers.
1317  */
1318 static void retry_origin_bios(struct dm_snapshot *s, struct bio *bio)
1319 {
1320         struct bio *n;
1321         int r;
1322
1323         while (bio) {
1324                 n = bio->bi_next;
1325                 bio->bi_next = NULL;
1326                 r = do_origin(s->origin, bio);
1327                 if (r == DM_MAPIO_REMAPPED)
1328                         generic_make_request(bio);
1329                 bio = n;
1330         }
1331 }
1332
1333 /*
1334  * Error a list of buffers.
1335  */
1336 static void error_bios(struct bio *bio)
1337 {
1338         struct bio *n;
1339
1340         while (bio) {
1341                 n = bio->bi_next;
1342                 bio->bi_next = NULL;
1343                 bio_io_error(bio);
1344                 bio = n;
1345         }
1346 }
1347
1348 static void __invalidate_snapshot(struct dm_snapshot *s, int err)
1349 {
1350         if (!s->valid)
1351                 return;
1352
1353         if (err == -EIO)
1354                 DMERR("Invalidating snapshot: Error reading/writing.");
1355         else if (err == -ENOMEM)
1356                 DMERR("Invalidating snapshot: Unable to allocate exception.");
1357
1358         if (s->store->type->drop_snapshot)
1359                 s->store->type->drop_snapshot(s->store);
1360
1361         s->valid = 0;
1362
1363         dm_table_event(s->ti->table);
1364 }
1365
1366 static void pending_complete(struct dm_snap_pending_exception *pe, int success)
1367 {
1368         struct dm_exception *e;
1369         struct dm_snapshot *s = pe->snap;
1370         struct bio *origin_bios = NULL;
1371         struct bio *snapshot_bios = NULL;
1372         struct bio *full_bio = NULL;
1373         int error = 0;
1374
1375         if (!success) {
1376                 /* Read/write error - snapshot is unusable */
1377                 down_write(&s->lock);
1378                 __invalidate_snapshot(s, -EIO);
1379                 error = 1;
1380                 goto out;
1381         }
1382
1383         e = alloc_completed_exception();
1384         if (!e) {
1385                 down_write(&s->lock);
1386                 __invalidate_snapshot(s, -ENOMEM);
1387                 error = 1;
1388                 goto out;
1389         }
1390         *e = pe->e;
1391
1392         down_write(&s->lock);
1393         if (!s->valid) {
1394                 free_completed_exception(e);
1395                 error = 1;
1396                 goto out;
1397         }
1398
1399         /* Check for conflicting reads */
1400         __check_for_conflicting_io(s, pe->e.old_chunk);
1401
1402         /*
1403          * Add a proper exception, and remove the
1404          * in-flight exception from the list.
1405          */
1406         dm_insert_exception(&s->complete, e);
1407
1408 out:
1409         dm_remove_exception(&pe->e);
1410         snapshot_bios = bio_list_get(&pe->snapshot_bios);
1411         origin_bios = bio_list_get(&pe->origin_bios);
1412         full_bio = pe->full_bio;
1413         if (full_bio) {
1414                 full_bio->bi_end_io = pe->full_bio_end_io;
1415                 full_bio->bi_private = pe->full_bio_private;
1416         }
1417         free_pending_exception(pe);
1418
1419         increment_pending_exceptions_done_count();
1420
1421         up_write(&s->lock);
1422
1423         /* Submit any pending write bios */
1424         if (error) {
1425                 if (full_bio)
1426                         bio_io_error(full_bio);
1427                 error_bios(snapshot_bios);
1428         } else {
1429                 if (full_bio)
1430                         bio_endio(full_bio, 0);
1431                 flush_bios(snapshot_bios);
1432         }
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, &src, 1, &dest, 0, copy_callback, pe);
1484 }
1485
1486 static void full_bio_end_io(struct bio *bio, int error)
1487 {
1488         void *callback_data = bio->bi_private;
1489
1490         dm_kcopyd_do_callback(callback_data, 0, error ? 1 : 0);
1491 }
1492
1493 static void start_full_bio(struct dm_snap_pending_exception *pe,
1494                            struct bio *bio)
1495 {
1496         struct dm_snapshot *s = pe->snap;
1497         void *callback_data;
1498
1499         pe->full_bio = bio;
1500         pe->full_bio_end_io = bio->bi_end_io;
1501         pe->full_bio_private = bio->bi_private;
1502
1503         callback_data = dm_kcopyd_prepare_callback(s->kcopyd_client,
1504                                                    copy_callback, pe);
1505
1506         bio->bi_end_io = full_bio_end_io;
1507         bio->bi_private = callback_data;
1508
1509         generic_make_request(bio);
1510 }
1511
1512 static struct dm_snap_pending_exception *
1513 __lookup_pending_exception(struct dm_snapshot *s, chunk_t chunk)
1514 {
1515         struct dm_exception *e = dm_lookup_exception(&s->pending, chunk);
1516
1517         if (!e)
1518                 return NULL;
1519
1520         return container_of(e, struct dm_snap_pending_exception, e);
1521 }
1522
1523 /*
1524  * Looks to see if this snapshot already has a pending exception
1525  * for this chunk, otherwise it allocates a new one and inserts
1526  * it into the pending table.
1527  *
1528  * NOTE: a write lock must be held on snap->lock before calling
1529  * this.
1530  */
1531 static struct dm_snap_pending_exception *
1532 __find_pending_exception(struct dm_snapshot *s,
1533                          struct dm_snap_pending_exception *pe, chunk_t chunk)
1534 {
1535         struct dm_snap_pending_exception *pe2;
1536
1537         pe2 = __lookup_pending_exception(s, chunk);
1538         if (pe2) {
1539                 free_pending_exception(pe);
1540                 return pe2;
1541         }
1542
1543         pe->e.old_chunk = chunk;
1544         bio_list_init(&pe->origin_bios);
1545         bio_list_init(&pe->snapshot_bios);
1546         pe->started = 0;
1547         pe->full_bio = NULL;
1548
1549         if (s->store->type->prepare_exception(s->store, &pe->e)) {
1550                 free_pending_exception(pe);
1551                 return NULL;
1552         }
1553
1554         dm_insert_exception(&s->pending, &pe->e);
1555
1556         return pe;
1557 }
1558
1559 static void remap_exception(struct dm_snapshot *s, struct dm_exception *e,
1560                             struct bio *bio, chunk_t chunk)
1561 {
1562         bio->bi_bdev = s->cow->bdev;
1563         bio->bi_sector = chunk_to_sector(s->store,
1564                                          dm_chunk_number(e->new_chunk) +
1565                                          (chunk - e->old_chunk)) +
1566                                          (bio->bi_sector &
1567                                           s->store->chunk_mask);
1568 }
1569
1570 static int snapshot_map(struct dm_target *ti, struct bio *bio,
1571                         union map_info *map_context)
1572 {
1573         struct dm_exception *e;
1574         struct dm_snapshot *s = ti->private;
1575         int r = DM_MAPIO_REMAPPED;
1576         chunk_t chunk;
1577         struct dm_snap_pending_exception *pe = NULL;
1578
1579         init_tracked_chunk(bio);
1580
1581         if (bio->bi_rw & REQ_FLUSH) {
1582                 bio->bi_bdev = s->cow->bdev;
1583                 return DM_MAPIO_REMAPPED;
1584         }
1585
1586         chunk = sector_to_chunk(s->store, bio->bi_sector);
1587
1588         /* Full snapshots are not usable */
1589         /* To get here the table must be live so s->active is always set. */
1590         if (!s->valid)
1591                 return -EIO;
1592
1593         /* FIXME: should only take write lock if we need
1594          * to copy an exception */
1595         down_write(&s->lock);
1596
1597         if (!s->valid) {
1598                 r = -EIO;
1599                 goto out_unlock;
1600         }
1601
1602         /* If the block is already remapped - use that, else remap it */
1603         e = dm_lookup_exception(&s->complete, chunk);
1604         if (e) {
1605                 remap_exception(s, e, bio, chunk);
1606                 goto out_unlock;
1607         }
1608
1609         /*
1610          * Write to snapshot - higher level takes care of RW/RO
1611          * flags so we should only get this if we are
1612          * writeable.
1613          */
1614         if (bio_rw(bio) == WRITE) {
1615                 pe = __lookup_pending_exception(s, chunk);
1616                 if (!pe) {
1617                         up_write(&s->lock);
1618                         pe = alloc_pending_exception(s);
1619                         down_write(&s->lock);
1620
1621                         if (!s->valid) {
1622                                 free_pending_exception(pe);
1623                                 r = -EIO;
1624                                 goto out_unlock;
1625                         }
1626
1627                         e = dm_lookup_exception(&s->complete, chunk);
1628                         if (e) {
1629                                 free_pending_exception(pe);
1630                                 remap_exception(s, e, bio, chunk);
1631                                 goto out_unlock;
1632                         }
1633
1634                         pe = __find_pending_exception(s, pe, chunk);
1635                         if (!pe) {
1636                                 __invalidate_snapshot(s, -ENOMEM);
1637                                 r = -EIO;
1638                                 goto out_unlock;
1639                         }
1640                 }
1641
1642                 remap_exception(s, &pe->e, bio, chunk);
1643
1644                 r = DM_MAPIO_SUBMITTED;
1645
1646                 if (!pe->started &&
1647                     bio->bi_size == (s->store->chunk_size << SECTOR_SHIFT)) {
1648                         pe->started = 1;
1649                         up_write(&s->lock);
1650                         start_full_bio(pe, bio);
1651                         goto out;
1652                 }
1653
1654                 bio_list_add(&pe->snapshot_bios, bio);
1655
1656                 if (!pe->started) {
1657                         /* this is protected by snap->lock */
1658                         pe->started = 1;
1659                         up_write(&s->lock);
1660                         start_copy(pe);
1661                         goto out;
1662                 }
1663         } else {
1664                 bio->bi_bdev = s->origin->bdev;
1665                 track_chunk(s, bio, chunk);
1666         }
1667
1668 out_unlock:
1669         up_write(&s->lock);
1670 out:
1671         return r;
1672 }
1673
1674 /*
1675  * A snapshot-merge target behaves like a combination of a snapshot
1676  * target and a snapshot-origin target.  It only generates new
1677  * exceptions in other snapshots and not in the one that is being
1678  * merged.
1679  *
1680  * For each chunk, if there is an existing exception, it is used to
1681  * redirect I/O to the cow device.  Otherwise I/O is sent to the origin,
1682  * which in turn might generate exceptions in other snapshots.
1683  * If merging is currently taking place on the chunk in question, the
1684  * I/O is deferred by adding it to s->bios_queued_during_merge.
1685  */
1686 static int snapshot_merge_map(struct dm_target *ti, struct bio *bio,
1687                               union map_info *map_context)
1688 {
1689         struct dm_exception *e;
1690         struct dm_snapshot *s = ti->private;
1691         int r = DM_MAPIO_REMAPPED;
1692         chunk_t chunk;
1693
1694         init_tracked_chunk(bio);
1695
1696         if (bio->bi_rw & REQ_FLUSH) {
1697                 if (!dm_bio_get_target_request_nr(bio))
1698                         bio->bi_bdev = s->origin->bdev;
1699                 else
1700                         bio->bi_bdev = s->cow->bdev;
1701                 return DM_MAPIO_REMAPPED;
1702         }
1703
1704         chunk = sector_to_chunk(s->store, bio->bi_sector);
1705
1706         down_write(&s->lock);
1707
1708         /* Full merging snapshots are redirected to the origin */
1709         if (!s->valid)
1710                 goto redirect_to_origin;
1711
1712         /* If the block is already remapped - use that */
1713         e = dm_lookup_exception(&s->complete, chunk);
1714         if (e) {
1715                 /* Queue writes overlapping with chunks being merged */
1716                 if (bio_rw(bio) == WRITE &&
1717                     chunk >= s->first_merging_chunk &&
1718                     chunk < (s->first_merging_chunk +
1719                              s->num_merging_chunks)) {
1720                         bio->bi_bdev = s->origin->bdev;
1721                         bio_list_add(&s->bios_queued_during_merge, bio);
1722                         r = DM_MAPIO_SUBMITTED;
1723                         goto out_unlock;
1724                 }
1725
1726                 remap_exception(s, e, bio, chunk);
1727
1728                 if (bio_rw(bio) == WRITE)
1729                         track_chunk(s, bio, chunk);
1730                 goto out_unlock;
1731         }
1732
1733 redirect_to_origin:
1734         bio->bi_bdev = s->origin->bdev;
1735
1736         if (bio_rw(bio) == WRITE) {
1737                 up_write(&s->lock);
1738                 return do_origin(s->origin, bio);
1739         }
1740
1741 out_unlock:
1742         up_write(&s->lock);
1743
1744         return r;
1745 }
1746
1747 static int snapshot_end_io(struct dm_target *ti, struct bio *bio,
1748                            int error, union map_info *map_context)
1749 {
1750         struct dm_snapshot *s = ti->private;
1751
1752         if (is_bio_tracked(bio))
1753                 stop_tracking_chunk(s, bio);
1754
1755         return 0;
1756 }
1757
1758 static void snapshot_merge_presuspend(struct dm_target *ti)
1759 {
1760         struct dm_snapshot *s = ti->private;
1761
1762         stop_merge(s);
1763 }
1764
1765 static int snapshot_preresume(struct dm_target *ti)
1766 {
1767         int r = 0;
1768         struct dm_snapshot *s = ti->private;
1769         struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
1770
1771         down_read(&_origins_lock);
1772         (void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL);
1773         if (snap_src && snap_dest) {
1774                 down_read(&snap_src->lock);
1775                 if (s == snap_src) {
1776                         DMERR("Unable to resume snapshot source until "
1777                               "handover completes.");
1778                         r = -EINVAL;
1779                 } else if (!dm_suspended(snap_src->ti)) {
1780                         DMERR("Unable to perform snapshot handover until "
1781                               "source is suspended.");
1782                         r = -EINVAL;
1783                 }
1784                 up_read(&snap_src->lock);
1785         }
1786         up_read(&_origins_lock);
1787
1788         return r;
1789 }
1790
1791 static void snapshot_resume(struct dm_target *ti)
1792 {
1793         struct dm_snapshot *s = ti->private;
1794         struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
1795
1796         down_read(&_origins_lock);
1797         (void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL);
1798         if (snap_src && snap_dest) {
1799                 down_write(&snap_src->lock);
1800                 down_write_nested(&snap_dest->lock, SINGLE_DEPTH_NESTING);
1801                 __handover_exceptions(snap_src, snap_dest);
1802                 up_write(&snap_dest->lock);
1803                 up_write(&snap_src->lock);
1804         }
1805         up_read(&_origins_lock);
1806
1807         /* Now we have correct chunk size, reregister */
1808         reregister_snapshot(s);
1809
1810         down_write(&s->lock);
1811         s->active = 1;
1812         up_write(&s->lock);
1813 }
1814
1815 static uint32_t get_origin_minimum_chunksize(struct block_device *bdev)
1816 {
1817         uint32_t min_chunksize;
1818
1819         down_read(&_origins_lock);
1820         min_chunksize = __minimum_chunk_size(__lookup_origin(bdev));
1821         up_read(&_origins_lock);
1822
1823         return min_chunksize;
1824 }
1825
1826 static void snapshot_merge_resume(struct dm_target *ti)
1827 {
1828         struct dm_snapshot *s = ti->private;
1829
1830         /*
1831          * Handover exceptions from existing snapshot.
1832          */
1833         snapshot_resume(ti);
1834
1835         /*
1836          * snapshot-merge acts as an origin, so set ti->max_io_len
1837          */
1838         ti->max_io_len = get_origin_minimum_chunksize(s->origin->bdev);
1839
1840         start_merge(s);
1841 }
1842
1843 static int snapshot_status(struct dm_target *ti, status_type_t type,
1844                            unsigned status_flags, char *result, unsigned maxlen)
1845 {
1846         unsigned sz = 0;
1847         struct dm_snapshot *snap = ti->private;
1848
1849         switch (type) {
1850         case STATUSTYPE_INFO:
1851
1852                 down_write(&snap->lock);
1853
1854                 if (!snap->valid)
1855                         DMEMIT("Invalid");
1856                 else if (snap->merge_failed)
1857                         DMEMIT("Merge failed");
1858                 else {
1859                         if (snap->store->type->usage) {
1860                                 sector_t total_sectors, sectors_allocated,
1861                                          metadata_sectors;
1862                                 snap->store->type->usage(snap->store,
1863                                                          &total_sectors,
1864                                                          &sectors_allocated,
1865                                                          &metadata_sectors);
1866                                 DMEMIT("%llu/%llu %llu",
1867                                        (unsigned long long)sectors_allocated,
1868                                        (unsigned long long)total_sectors,
1869                                        (unsigned long long)metadata_sectors);
1870                         }
1871                         else
1872                                 DMEMIT("Unknown");
1873                 }
1874
1875                 up_write(&snap->lock);
1876
1877                 break;
1878
1879         case STATUSTYPE_TABLE:
1880                 /*
1881                  * kdevname returns a static pointer so we need
1882                  * to make private copies if the output is to
1883                  * make sense.
1884                  */
1885                 DMEMIT("%s %s", snap->origin->name, snap->cow->name);
1886                 snap->store->type->status(snap->store, type, result + sz,
1887                                           maxlen - sz);
1888                 break;
1889         }
1890
1891         return 0;
1892 }
1893
1894 static int snapshot_iterate_devices(struct dm_target *ti,
1895                                     iterate_devices_callout_fn fn, void *data)
1896 {
1897         struct dm_snapshot *snap = ti->private;
1898         int r;
1899
1900         r = fn(ti, snap->origin, 0, ti->len, data);
1901
1902         if (!r)
1903                 r = fn(ti, snap->cow, 0, get_dev_size(snap->cow->bdev), data);
1904
1905         return r;
1906 }
1907
1908
1909 /*-----------------------------------------------------------------
1910  * Origin methods
1911  *---------------------------------------------------------------*/
1912
1913 /*
1914  * If no exceptions need creating, DM_MAPIO_REMAPPED is returned and any
1915  * supplied bio was ignored.  The caller may submit it immediately.
1916  * (No remapping actually occurs as the origin is always a direct linear
1917  * map.)
1918  *
1919  * If further exceptions are required, DM_MAPIO_SUBMITTED is returned
1920  * and any supplied bio is added to a list to be submitted once all
1921  * the necessary exceptions exist.
1922  */
1923 static int __origin_write(struct list_head *snapshots, sector_t sector,
1924                           struct bio *bio)
1925 {
1926         int r = DM_MAPIO_REMAPPED;
1927         struct dm_snapshot *snap;
1928         struct dm_exception *e;
1929         struct dm_snap_pending_exception *pe;
1930         struct dm_snap_pending_exception *pe_to_start_now = NULL;
1931         struct dm_snap_pending_exception *pe_to_start_last = NULL;
1932         chunk_t chunk;
1933
1934         /* Do all the snapshots on this origin */
1935         list_for_each_entry (snap, snapshots, list) {
1936                 /*
1937                  * Don't make new exceptions in a merging snapshot
1938                  * because it has effectively been deleted
1939                  */
1940                 if (dm_target_is_snapshot_merge(snap->ti))
1941                         continue;
1942
1943                 down_write(&snap->lock);
1944
1945                 /* Only deal with valid and active snapshots */
1946                 if (!snap->valid || !snap->active)
1947                         goto next_snapshot;
1948
1949                 /* Nothing to do if writing beyond end of snapshot */
1950                 if (sector >= dm_table_get_size(snap->ti->table))
1951                         goto next_snapshot;
1952
1953                 /*
1954                  * Remember, different snapshots can have
1955                  * different chunk sizes.
1956                  */
1957                 chunk = sector_to_chunk(snap->store, sector);
1958
1959                 /*
1960                  * Check exception table to see if block
1961                  * is already remapped in this snapshot
1962                  * and trigger an exception if not.
1963                  */
1964                 e = dm_lookup_exception(&snap->complete, chunk);
1965                 if (e)
1966                         goto next_snapshot;
1967
1968                 pe = __lookup_pending_exception(snap, chunk);
1969                 if (!pe) {
1970                         up_write(&snap->lock);
1971                         pe = alloc_pending_exception(snap);
1972                         down_write(&snap->lock);
1973
1974                         if (!snap->valid) {
1975                                 free_pending_exception(pe);
1976                                 goto next_snapshot;
1977                         }
1978
1979                         e = dm_lookup_exception(&snap->complete, chunk);
1980                         if (e) {
1981                                 free_pending_exception(pe);
1982                                 goto next_snapshot;
1983                         }
1984
1985                         pe = __find_pending_exception(snap, pe, chunk);
1986                         if (!pe) {
1987                                 __invalidate_snapshot(snap, -ENOMEM);
1988                                 goto next_snapshot;
1989                         }
1990                 }
1991
1992                 r = DM_MAPIO_SUBMITTED;
1993
1994                 /*
1995                  * If an origin bio was supplied, queue it to wait for the
1996                  * completion of this exception, and start this one last,
1997                  * at the end of the function.
1998                  */
1999                 if (bio) {
2000                         bio_list_add(&pe->origin_bios, bio);
2001                         bio = NULL;
2002
2003                         if (!pe->started) {
2004                                 pe->started = 1;
2005                                 pe_to_start_last = pe;
2006                         }
2007                 }
2008
2009                 if (!pe->started) {
2010                         pe->started = 1;
2011                         pe_to_start_now = pe;
2012                 }
2013
2014 next_snapshot:
2015                 up_write(&snap->lock);
2016
2017                 if (pe_to_start_now) {
2018                         start_copy(pe_to_start_now);
2019                         pe_to_start_now = NULL;
2020                 }
2021         }
2022
2023         /*
2024          * Submit the exception against which the bio is queued last,
2025          * to give the other exceptions a head start.
2026          */
2027         if (pe_to_start_last)
2028                 start_copy(pe_to_start_last);
2029
2030         return r;
2031 }
2032
2033 /*
2034  * Called on a write from the origin driver.
2035  */
2036 static int do_origin(struct dm_dev *origin, struct bio *bio)
2037 {
2038         struct origin *o;
2039         int r = DM_MAPIO_REMAPPED;
2040
2041         down_read(&_origins_lock);
2042         o = __lookup_origin(origin->bdev);
2043         if (o)
2044                 r = __origin_write(&o->snapshots, bio->bi_sector, bio);
2045         up_read(&_origins_lock);
2046
2047         return r;
2048 }
2049
2050 /*
2051  * Trigger exceptions in all non-merging snapshots.
2052  *
2053  * The chunk size of the merging snapshot may be larger than the chunk
2054  * size of some other snapshot so we may need to reallocate multiple
2055  * chunks in other snapshots.
2056  *
2057  * We scan all the overlapping exceptions in the other snapshots.
2058  * Returns 1 if anything was reallocated and must be waited for,
2059  * otherwise returns 0.
2060  *
2061  * size must be a multiple of merging_snap's chunk_size.
2062  */
2063 static int origin_write_extent(struct dm_snapshot *merging_snap,
2064                                sector_t sector, unsigned size)
2065 {
2066         int must_wait = 0;
2067         sector_t n;
2068         struct origin *o;
2069
2070         /*
2071          * The origin's __minimum_chunk_size() got stored in max_io_len
2072          * by snapshot_merge_resume().
2073          */
2074         down_read(&_origins_lock);
2075         o = __lookup_origin(merging_snap->origin->bdev);
2076         for (n = 0; n < size; n += merging_snap->ti->max_io_len)
2077                 if (__origin_write(&o->snapshots, sector + n, NULL) ==
2078                     DM_MAPIO_SUBMITTED)
2079                         must_wait = 1;
2080         up_read(&_origins_lock);
2081
2082         return must_wait;
2083 }
2084
2085 /*
2086  * Origin: maps a linear range of a device, with hooks for snapshotting.
2087  */
2088
2089 /*
2090  * Construct an origin mapping: <dev_path>
2091  * The context for an origin is merely a 'struct dm_dev *'
2092  * pointing to the real device.
2093  */
2094 static int origin_ctr(struct dm_target *ti, unsigned int argc, char **argv)
2095 {
2096         int r;
2097         struct dm_dev *dev;
2098
2099         if (argc != 1) {
2100                 ti->error = "origin: incorrect number of arguments";
2101                 return -EINVAL;
2102         }
2103
2104         r = dm_get_device(ti, argv[0], dm_table_get_mode(ti->table), &dev);
2105         if (r) {
2106                 ti->error = "Cannot get target device";
2107                 return r;
2108         }
2109
2110         ti->private = dev;
2111         ti->num_flush_requests = 1;
2112
2113         return 0;
2114 }
2115
2116 static void origin_dtr(struct dm_target *ti)
2117 {
2118         struct dm_dev *dev = ti->private;
2119         dm_put_device(ti, dev);
2120 }
2121
2122 static int origin_map(struct dm_target *ti, struct bio *bio,
2123                       union map_info *map_context)
2124 {
2125         struct dm_dev *dev = ti->private;
2126         bio->bi_bdev = dev->bdev;
2127
2128         if (bio->bi_rw & REQ_FLUSH)
2129                 return DM_MAPIO_REMAPPED;
2130
2131         /* Only tell snapshots if this is a write */
2132         return (bio_rw(bio) == WRITE) ? do_origin(dev, bio) : DM_MAPIO_REMAPPED;
2133 }
2134
2135 /*
2136  * Set the target "max_io_len" field to the minimum of all the snapshots'
2137  * chunk sizes.
2138  */
2139 static void origin_resume(struct dm_target *ti)
2140 {
2141         struct dm_dev *dev = ti->private;
2142
2143         ti->max_io_len = get_origin_minimum_chunksize(dev->bdev);
2144 }
2145
2146 static int origin_status(struct dm_target *ti, status_type_t type,
2147                          unsigned status_flags, char *result, unsigned maxlen)
2148 {
2149         struct dm_dev *dev = ti->private;
2150
2151         switch (type) {
2152         case STATUSTYPE_INFO:
2153                 result[0] = '\0';
2154                 break;
2155
2156         case STATUSTYPE_TABLE:
2157                 snprintf(result, maxlen, "%s", dev->name);
2158                 break;
2159         }
2160
2161         return 0;
2162 }
2163
2164 static int origin_merge(struct dm_target *ti, struct bvec_merge_data *bvm,
2165                         struct bio_vec *biovec, int max_size)
2166 {
2167         struct dm_dev *dev = ti->private;
2168         struct request_queue *q = bdev_get_queue(dev->bdev);
2169
2170         if (!q->merge_bvec_fn)
2171                 return max_size;
2172
2173         bvm->bi_bdev = dev->bdev;
2174
2175         return min(max_size, q->merge_bvec_fn(q, bvm, biovec));
2176 }
2177
2178 static int origin_iterate_devices(struct dm_target *ti,
2179                                   iterate_devices_callout_fn fn, void *data)
2180 {
2181         struct dm_dev *dev = ti->private;
2182
2183         return fn(ti, dev, 0, ti->len, data);
2184 }
2185
2186 static struct target_type origin_target = {
2187         .name    = "snapshot-origin",
2188         .version = {1, 8, 0},
2189         .module  = THIS_MODULE,
2190         .ctr     = origin_ctr,
2191         .dtr     = origin_dtr,
2192         .map     = origin_map,
2193         .resume  = origin_resume,
2194         .status  = origin_status,
2195         .merge   = origin_merge,
2196         .iterate_devices = origin_iterate_devices,
2197 };
2198
2199 static struct target_type snapshot_target = {
2200         .name    = "snapshot",
2201         .version = {1, 11, 0},
2202         .module  = THIS_MODULE,
2203         .ctr     = snapshot_ctr,
2204         .dtr     = snapshot_dtr,
2205         .map     = snapshot_map,
2206         .end_io  = snapshot_end_io,
2207         .preresume  = snapshot_preresume,
2208         .resume  = snapshot_resume,
2209         .status  = snapshot_status,
2210         .iterate_devices = snapshot_iterate_devices,
2211 };
2212
2213 static struct target_type merge_target = {
2214         .name    = dm_snapshot_merge_target_name,
2215         .version = {1, 2, 0},
2216         .module  = THIS_MODULE,
2217         .ctr     = snapshot_ctr,
2218         .dtr     = snapshot_dtr,
2219         .map     = snapshot_merge_map,
2220         .end_io  = snapshot_end_io,
2221         .presuspend = snapshot_merge_presuspend,
2222         .preresume  = snapshot_preresume,
2223         .resume  = snapshot_merge_resume,
2224         .status  = snapshot_status,
2225         .iterate_devices = snapshot_iterate_devices,
2226 };
2227
2228 static int __init dm_snapshot_init(void)
2229 {
2230         int r;
2231
2232         r = dm_exception_store_init();
2233         if (r) {
2234                 DMERR("Failed to initialize exception stores");
2235                 return r;
2236         }
2237
2238         r = dm_register_target(&snapshot_target);
2239         if (r < 0) {
2240                 DMERR("snapshot target register failed %d", r);
2241                 goto bad_register_snapshot_target;
2242         }
2243
2244         r = dm_register_target(&origin_target);
2245         if (r < 0) {
2246                 DMERR("Origin target register failed %d", r);
2247                 goto bad_register_origin_target;
2248         }
2249
2250         r = dm_register_target(&merge_target);
2251         if (r < 0) {
2252                 DMERR("Merge target register failed %d", r);
2253                 goto bad_register_merge_target;
2254         }
2255
2256         r = init_origin_hash();
2257         if (r) {
2258                 DMERR("init_origin_hash failed.");
2259                 goto bad_origin_hash;
2260         }
2261
2262         exception_cache = KMEM_CACHE(dm_exception, 0);
2263         if (!exception_cache) {
2264                 DMERR("Couldn't create exception cache.");
2265                 r = -ENOMEM;
2266                 goto bad_exception_cache;
2267         }
2268
2269         pending_cache = KMEM_CACHE(dm_snap_pending_exception, 0);
2270         if (!pending_cache) {
2271                 DMERR("Couldn't create pending cache.");
2272                 r = -ENOMEM;
2273                 goto bad_pending_cache;
2274         }
2275
2276         return 0;
2277
2278 bad_pending_cache:
2279         kmem_cache_destroy(exception_cache);
2280 bad_exception_cache:
2281         exit_origin_hash();
2282 bad_origin_hash:
2283         dm_unregister_target(&merge_target);
2284 bad_register_merge_target:
2285         dm_unregister_target(&origin_target);
2286 bad_register_origin_target:
2287         dm_unregister_target(&snapshot_target);
2288 bad_register_snapshot_target:
2289         dm_exception_store_exit();
2290
2291         return r;
2292 }
2293
2294 static void __exit dm_snapshot_exit(void)
2295 {
2296         dm_unregister_target(&snapshot_target);
2297         dm_unregister_target(&origin_target);
2298         dm_unregister_target(&merge_target);
2299
2300         exit_origin_hash();
2301         kmem_cache_destroy(pending_cache);
2302         kmem_cache_destroy(exception_cache);
2303
2304         dm_exception_store_exit();
2305 }
2306
2307 /* Module hooks */
2308 module_init(dm_snapshot_init);
2309 module_exit(dm_snapshot_exit);
2310
2311 MODULE_DESCRIPTION(DM_NAME " snapshot target");
2312 MODULE_AUTHOR("Joe Thornber");
2313 MODULE_LICENSE("GPL");