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1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Copyright (C) 2001-2002 Sistina Software (UK) Limited.
4 *
5 * This file is released under the GPL.
6 */
7
8#include <linux/blkdev.h>
9#include <linux/device-mapper.h>
10#include <linux/delay.h>
11#include <linux/fs.h>
12#include <linux/init.h>
13#include <linux/kdev_t.h>
14#include <linux/list.h>
15#include <linux/list_bl.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.h"
24
25#include "dm-exception-store.h"
26
27#define DM_MSG_PREFIX "snapshots"
28
29static const char dm_snapshot_merge_target_name[] = "snapshot-merge";
30
31#define dm_target_is_snapshot_merge(ti) \
32 ((ti)->type->name == dm_snapshot_merge_target_name)
33
34/*
35 * The size of the mempool used to track chunks in use.
36 */
37#define MIN_IOS 256
38
39#define DM_TRACKED_CHUNK_HASH_SIZE 16
40#define DM_TRACKED_CHUNK_HASH(x) ((unsigned long)(x) & \
41 (DM_TRACKED_CHUNK_HASH_SIZE - 1))
42
43struct dm_exception_table {
44 uint32_t hash_mask;
45 unsigned int hash_shift;
46 struct hlist_bl_head *table;
47};
48
49struct dm_snapshot {
50 struct rw_semaphore lock;
51
52 struct dm_dev *origin;
53 struct dm_dev *cow;
54
55 struct dm_target *ti;
56
57 /* List of snapshots per Origin */
58 struct list_head list;
59
60 /*
61 * You can't use a snapshot if this is 0 (e.g. if full).
62 * A snapshot-merge target never clears this.
63 */
64 int valid;
65
66 /*
67 * The snapshot overflowed because of a write to the snapshot device.
68 * We don't have to invalidate the snapshot in this case, but we need
69 * to prevent further writes.
70 */
71 int snapshot_overflowed;
72
73 /* Origin writes don't trigger exceptions until this is set */
74 int active;
75
76 atomic_t pending_exceptions_count;
77
78 spinlock_t pe_allocation_lock;
79
80 /* Protected by "pe_allocation_lock" */
81 sector_t exception_start_sequence;
82
83 /* Protected by kcopyd single-threaded callback */
84 sector_t exception_complete_sequence;
85
86 /*
87 * A list of pending exceptions that completed out of order.
88 * Protected by kcopyd single-threaded callback.
89 */
90 struct rb_root out_of_order_tree;
91
92 mempool_t pending_pool;
93
94 struct dm_exception_table pending;
95 struct dm_exception_table complete;
96
97 /*
98 * pe_lock protects all pending_exception operations and access
99 * as well as the snapshot_bios list.
100 */
101 spinlock_t pe_lock;
102
103 /* Chunks with outstanding reads */
104 spinlock_t tracked_chunk_lock;
105 struct hlist_head tracked_chunk_hash[DM_TRACKED_CHUNK_HASH_SIZE];
106
107 /* The on disk metadata handler */
108 struct dm_exception_store *store;
109
110 unsigned int in_progress;
111 struct wait_queue_head in_progress_wait;
112
113 struct dm_kcopyd_client *kcopyd_client;
114
115 /* Wait for events based on state_bits */
116 unsigned long state_bits;
117
118 /* Range of chunks currently being merged. */
119 chunk_t first_merging_chunk;
120 int num_merging_chunks;
121
122 /*
123 * The merge operation failed if this flag is set.
124 * Failure modes are handled as follows:
125 * - I/O error reading the header
126 * => don't load the target; abort.
127 * - Header does not have "valid" flag set
128 * => use the origin; forget about the snapshot.
129 * - I/O error when reading exceptions
130 * => don't load the target; abort.
131 * (We can't use the intermediate origin state.)
132 * - I/O error while merging
133 * => stop merging; set merge_failed; process I/O normally.
134 */
135 bool merge_failed:1;
136
137 bool discard_zeroes_cow:1;
138 bool discard_passdown_origin:1;
139
140 /*
141 * Incoming bios that overlap with chunks being merged must wait
142 * for them to be committed.
143 */
144 struct bio_list bios_queued_during_merge;
145};
146
147/*
148 * state_bits:
149 * RUNNING_MERGE - Merge operation is in progress.
150 * SHUTDOWN_MERGE - Set to signal that merge needs to be stopped;
151 * cleared afterwards.
152 */
153#define RUNNING_MERGE 0
154#define SHUTDOWN_MERGE 1
155
156/*
157 * Maximum number of chunks being copied on write.
158 *
159 * The value was decided experimentally as a trade-off between memory
160 * consumption, stalling the kernel's workqueues and maintaining a high enough
161 * throughput.
162 */
163#define DEFAULT_COW_THRESHOLD 2048
164
165static unsigned int cow_threshold = DEFAULT_COW_THRESHOLD;
166module_param_named(snapshot_cow_threshold, cow_threshold, uint, 0644);
167MODULE_PARM_DESC(snapshot_cow_threshold, "Maximum number of chunks being copied on write");
168
169DECLARE_DM_KCOPYD_THROTTLE_WITH_MODULE_PARM(snapshot_copy_throttle,
170 "A percentage of time allocated for copy on write");
171
172struct dm_dev *dm_snap_origin(struct dm_snapshot *s)
173{
174 return s->origin;
175}
176EXPORT_SYMBOL(dm_snap_origin);
177
178struct dm_dev *dm_snap_cow(struct dm_snapshot *s)
179{
180 return s->cow;
181}
182EXPORT_SYMBOL(dm_snap_cow);
183
184static sector_t chunk_to_sector(struct dm_exception_store *store,
185 chunk_t chunk)
186{
187 return chunk << store->chunk_shift;
188}
189
190static int bdev_equal(struct block_device *lhs, struct block_device *rhs)
191{
192 /*
193 * There is only ever one instance of a particular block
194 * device so we can compare pointers safely.
195 */
196 return lhs == rhs;
197}
198
199struct dm_snap_pending_exception {
200 struct dm_exception e;
201
202 /*
203 * Origin buffers waiting for this to complete are held
204 * in a bio list
205 */
206 struct bio_list origin_bios;
207 struct bio_list snapshot_bios;
208
209 /* Pointer back to snapshot context */
210 struct dm_snapshot *snap;
211
212 /*
213 * 1 indicates the exception has already been sent to
214 * kcopyd.
215 */
216 int started;
217
218 /* There was copying error. */
219 int copy_error;
220
221 /* A sequence number, it is used for in-order completion. */
222 sector_t exception_sequence;
223
224 struct rb_node out_of_order_node;
225
226 /*
227 * For writing a complete chunk, bypassing the copy.
228 */
229 struct bio *full_bio;
230 bio_end_io_t *full_bio_end_io;
231};
232
233/*
234 * Hash table mapping origin volumes to lists of snapshots and
235 * a lock to protect it
236 */
237static struct kmem_cache *exception_cache;
238static struct kmem_cache *pending_cache;
239
240struct dm_snap_tracked_chunk {
241 struct hlist_node node;
242 chunk_t chunk;
243};
244
245static void init_tracked_chunk(struct bio *bio)
246{
247 struct dm_snap_tracked_chunk *c = dm_per_bio_data(bio, sizeof(struct dm_snap_tracked_chunk));
248
249 INIT_HLIST_NODE(&c->node);
250}
251
252static bool is_bio_tracked(struct bio *bio)
253{
254 struct dm_snap_tracked_chunk *c = dm_per_bio_data(bio, sizeof(struct dm_snap_tracked_chunk));
255
256 return !hlist_unhashed(&c->node);
257}
258
259static void track_chunk(struct dm_snapshot *s, struct bio *bio, chunk_t chunk)
260{
261 struct dm_snap_tracked_chunk *c = dm_per_bio_data(bio, sizeof(struct dm_snap_tracked_chunk));
262
263 c->chunk = chunk;
264
265 spin_lock_irq(&s->tracked_chunk_lock);
266 hlist_add_head(&c->node,
267 &s->tracked_chunk_hash[DM_TRACKED_CHUNK_HASH(chunk)]);
268 spin_unlock_irq(&s->tracked_chunk_lock);
269}
270
271static void stop_tracking_chunk(struct dm_snapshot *s, struct bio *bio)
272{
273 struct dm_snap_tracked_chunk *c = dm_per_bio_data(bio, sizeof(struct dm_snap_tracked_chunk));
274 unsigned long flags;
275
276 spin_lock_irqsave(&s->tracked_chunk_lock, flags);
277 hlist_del(&c->node);
278 spin_unlock_irqrestore(&s->tracked_chunk_lock, flags);
279}
280
281static int __chunk_is_tracked(struct dm_snapshot *s, chunk_t chunk)
282{
283 struct dm_snap_tracked_chunk *c;
284 int found = 0;
285
286 spin_lock_irq(&s->tracked_chunk_lock);
287
288 hlist_for_each_entry(c,
289 &s->tracked_chunk_hash[DM_TRACKED_CHUNK_HASH(chunk)], node) {
290 if (c->chunk == chunk) {
291 found = 1;
292 break;
293 }
294 }
295
296 spin_unlock_irq(&s->tracked_chunk_lock);
297
298 return found;
299}
300
301/*
302 * This conflicting I/O is extremely improbable in the caller,
303 * so fsleep(1000) is sufficient and there is no need for a wait queue.
304 */
305static void __check_for_conflicting_io(struct dm_snapshot *s, chunk_t chunk)
306{
307 while (__chunk_is_tracked(s, chunk))
308 fsleep(1000);
309}
310
311/*
312 * One of these per registered origin, held in the snapshot_origins hash
313 */
314struct origin {
315 /* The origin device */
316 struct block_device *bdev;
317
318 struct list_head hash_list;
319
320 /* List of snapshots for this origin */
321 struct list_head snapshots;
322};
323
324/*
325 * This structure is allocated for each origin target
326 */
327struct dm_origin {
328 struct dm_dev *dev;
329 struct dm_target *ti;
330 unsigned int split_boundary;
331 struct list_head hash_list;
332};
333
334/*
335 * Size of the hash table for origin volumes. If we make this
336 * the size of the minors list then it should be nearly perfect
337 */
338#define ORIGIN_HASH_SIZE 256
339#define ORIGIN_MASK 0xFF
340static struct list_head *_origins;
341static struct list_head *_dm_origins;
342static struct rw_semaphore _origins_lock;
343
344static DECLARE_WAIT_QUEUE_HEAD(_pending_exceptions_done);
345static DEFINE_SPINLOCK(_pending_exceptions_done_spinlock);
346static uint64_t _pending_exceptions_done_count;
347
348static int init_origin_hash(void)
349{
350 int i;
351
352 _origins = kmalloc_array(ORIGIN_HASH_SIZE, sizeof(struct list_head),
353 GFP_KERNEL);
354 if (!_origins) {
355 DMERR("unable to allocate memory for _origins");
356 return -ENOMEM;
357 }
358 for (i = 0; i < ORIGIN_HASH_SIZE; i++)
359 INIT_LIST_HEAD(_origins + i);
360
361 _dm_origins = kmalloc_array(ORIGIN_HASH_SIZE,
362 sizeof(struct list_head),
363 GFP_KERNEL);
364 if (!_dm_origins) {
365 DMERR("unable to allocate memory for _dm_origins");
366 kfree(_origins);
367 return -ENOMEM;
368 }
369 for (i = 0; i < ORIGIN_HASH_SIZE; i++)
370 INIT_LIST_HEAD(_dm_origins + i);
371
372 init_rwsem(&_origins_lock);
373
374 return 0;
375}
376
377static void exit_origin_hash(void)
378{
379 kfree(_origins);
380 kfree(_dm_origins);
381}
382
383static unsigned int origin_hash(struct block_device *bdev)
384{
385 return bdev->bd_dev & ORIGIN_MASK;
386}
387
388static struct origin *__lookup_origin(struct block_device *origin)
389{
390 struct list_head *ol;
391 struct origin *o;
392
393 ol = &_origins[origin_hash(origin)];
394 list_for_each_entry(o, ol, hash_list)
395 if (bdev_equal(o->bdev, origin))
396 return o;
397
398 return NULL;
399}
400
401static void __insert_origin(struct origin *o)
402{
403 struct list_head *sl = &_origins[origin_hash(o->bdev)];
404
405 list_add_tail(&o->hash_list, sl);
406}
407
408static struct dm_origin *__lookup_dm_origin(struct block_device *origin)
409{
410 struct list_head *ol;
411 struct dm_origin *o;
412
413 ol = &_dm_origins[origin_hash(origin)];
414 list_for_each_entry(o, ol, hash_list)
415 if (bdev_equal(o->dev->bdev, origin))
416 return o;
417
418 return NULL;
419}
420
421static void __insert_dm_origin(struct dm_origin *o)
422{
423 struct list_head *sl = &_dm_origins[origin_hash(o->dev->bdev)];
424
425 list_add_tail(&o->hash_list, sl);
426}
427
428static void __remove_dm_origin(struct dm_origin *o)
429{
430 list_del(&o->hash_list);
431}
432
433/*
434 * _origins_lock must be held when calling this function.
435 * Returns number of snapshots registered using the supplied cow device, plus:
436 * snap_src - a snapshot suitable for use as a source of exception handover
437 * snap_dest - a snapshot capable of receiving exception handover.
438 * snap_merge - an existing snapshot-merge target linked to the same origin.
439 * There can be at most one snapshot-merge target. The parameter is optional.
440 *
441 * Possible return values and states of snap_src and snap_dest.
442 * 0: NULL, NULL - first new snapshot
443 * 1: snap_src, NULL - normal snapshot
444 * 2: snap_src, snap_dest - waiting for handover
445 * 2: snap_src, NULL - handed over, waiting for old to be deleted
446 * 1: NULL, snap_dest - source got destroyed without handover
447 */
448static int __find_snapshots_sharing_cow(struct dm_snapshot *snap,
449 struct dm_snapshot **snap_src,
450 struct dm_snapshot **snap_dest,
451 struct dm_snapshot **snap_merge)
452{
453 struct dm_snapshot *s;
454 struct origin *o;
455 int count = 0;
456 int active;
457
458 o = __lookup_origin(snap->origin->bdev);
459 if (!o)
460 goto out;
461
462 list_for_each_entry(s, &o->snapshots, list) {
463 if (dm_target_is_snapshot_merge(s->ti) && snap_merge)
464 *snap_merge = s;
465 if (!bdev_equal(s->cow->bdev, snap->cow->bdev))
466 continue;
467
468 down_read(&s->lock);
469 active = s->active;
470 up_read(&s->lock);
471
472 if (active) {
473 if (snap_src)
474 *snap_src = s;
475 } else if (snap_dest)
476 *snap_dest = s;
477
478 count++;
479 }
480
481out:
482 return count;
483}
484
485/*
486 * On success, returns 1 if this snapshot is a handover destination,
487 * otherwise returns 0.
488 */
489static int __validate_exception_handover(struct dm_snapshot *snap)
490{
491 struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
492 struct dm_snapshot *snap_merge = NULL;
493
494 /* Does snapshot need exceptions handed over to it? */
495 if ((__find_snapshots_sharing_cow(snap, &snap_src, &snap_dest,
496 &snap_merge) == 2) ||
497 snap_dest) {
498 snap->ti->error = "Snapshot cow pairing for exception table handover failed";
499 return -EINVAL;
500 }
501
502 /*
503 * If no snap_src was found, snap cannot become a handover
504 * destination.
505 */
506 if (!snap_src)
507 return 0;
508
509 /*
510 * Non-snapshot-merge handover?
511 */
512 if (!dm_target_is_snapshot_merge(snap->ti))
513 return 1;
514
515 /*
516 * Do not allow more than one merging snapshot.
517 */
518 if (snap_merge) {
519 snap->ti->error = "A snapshot is already merging.";
520 return -EINVAL;
521 }
522
523 if (!snap_src->store->type->prepare_merge ||
524 !snap_src->store->type->commit_merge) {
525 snap->ti->error = "Snapshot exception store does not support snapshot-merge.";
526 return -EINVAL;
527 }
528
529 return 1;
530}
531
532static void __insert_snapshot(struct origin *o, struct dm_snapshot *s)
533{
534 struct dm_snapshot *l;
535
536 /* Sort the list according to chunk size, largest-first smallest-last */
537 list_for_each_entry(l, &o->snapshots, list)
538 if (l->store->chunk_size < s->store->chunk_size)
539 break;
540 list_add_tail(&s->list, &l->list);
541}
542
543/*
544 * Make a note of the snapshot and its origin so we can look it
545 * up when the origin has a write on it.
546 *
547 * Also validate snapshot exception store handovers.
548 * On success, returns 1 if this registration is a handover destination,
549 * otherwise returns 0.
550 */
551static int register_snapshot(struct dm_snapshot *snap)
552{
553 struct origin *o, *new_o = NULL;
554 struct block_device *bdev = snap->origin->bdev;
555 int r = 0;
556
557 new_o = kmalloc(sizeof(*new_o), GFP_KERNEL);
558 if (!new_o)
559 return -ENOMEM;
560
561 down_write(&_origins_lock);
562
563 r = __validate_exception_handover(snap);
564 if (r < 0) {
565 kfree(new_o);
566 goto out;
567 }
568
569 o = __lookup_origin(bdev);
570 if (o)
571 kfree(new_o);
572 else {
573 /* New origin */
574 o = new_o;
575
576 /* Initialise the struct */
577 INIT_LIST_HEAD(&o->snapshots);
578 o->bdev = bdev;
579
580 __insert_origin(o);
581 }
582
583 __insert_snapshot(o, snap);
584
585out:
586 up_write(&_origins_lock);
587
588 return r;
589}
590
591/*
592 * Move snapshot to correct place in list according to chunk size.
593 */
594static void reregister_snapshot(struct dm_snapshot *s)
595{
596 struct block_device *bdev = s->origin->bdev;
597
598 down_write(&_origins_lock);
599
600 list_del(&s->list);
601 __insert_snapshot(__lookup_origin(bdev), s);
602
603 up_write(&_origins_lock);
604}
605
606static void unregister_snapshot(struct dm_snapshot *s)
607{
608 struct origin *o;
609
610 down_write(&_origins_lock);
611 o = __lookup_origin(s->origin->bdev);
612
613 list_del(&s->list);
614 if (o && list_empty(&o->snapshots)) {
615 list_del(&o->hash_list);
616 kfree(o);
617 }
618
619 up_write(&_origins_lock);
620}
621
622/*
623 * Implementation of the exception hash tables.
624 * The lowest hash_shift bits of the chunk number are ignored, allowing
625 * some consecutive chunks to be grouped together.
626 */
627static uint32_t exception_hash(struct dm_exception_table *et, chunk_t chunk);
628
629/* Lock to protect access to the completed and pending exception hash tables. */
630struct dm_exception_table_lock {
631 struct hlist_bl_head *complete_slot;
632 struct hlist_bl_head *pending_slot;
633};
634
635static void dm_exception_table_lock_init(struct dm_snapshot *s, chunk_t chunk,
636 struct dm_exception_table_lock *lock)
637{
638 struct dm_exception_table *complete = &s->complete;
639 struct dm_exception_table *pending = &s->pending;
640
641 lock->complete_slot = &complete->table[exception_hash(complete, chunk)];
642 lock->pending_slot = &pending->table[exception_hash(pending, chunk)];
643}
644
645static void dm_exception_table_lock(struct dm_exception_table_lock *lock)
646{
647 hlist_bl_lock(lock->complete_slot);
648 hlist_bl_lock(lock->pending_slot);
649}
650
651static void dm_exception_table_unlock(struct dm_exception_table_lock *lock)
652{
653 hlist_bl_unlock(lock->pending_slot);
654 hlist_bl_unlock(lock->complete_slot);
655}
656
657static int dm_exception_table_init(struct dm_exception_table *et,
658 uint32_t size, unsigned int hash_shift)
659{
660 unsigned int i;
661
662 et->hash_shift = hash_shift;
663 et->hash_mask = size - 1;
664 et->table = kvmalloc_array(size, sizeof(struct hlist_bl_head),
665 GFP_KERNEL);
666 if (!et->table)
667 return -ENOMEM;
668
669 for (i = 0; i < size; i++)
670 INIT_HLIST_BL_HEAD(et->table + i);
671
672 return 0;
673}
674
675static void dm_exception_table_exit(struct dm_exception_table *et,
676 struct kmem_cache *mem)
677{
678 struct hlist_bl_head *slot;
679 struct dm_exception *ex;
680 struct hlist_bl_node *pos, *n;
681 int i, size;
682
683 size = et->hash_mask + 1;
684 for (i = 0; i < size; i++) {
685 slot = et->table + i;
686
687 hlist_bl_for_each_entry_safe(ex, pos, n, slot, hash_list)
688 kmem_cache_free(mem, ex);
689 }
690
691 kvfree(et->table);
692}
693
694static uint32_t exception_hash(struct dm_exception_table *et, chunk_t chunk)
695{
696 return (chunk >> et->hash_shift) & et->hash_mask;
697}
698
699static void dm_remove_exception(struct dm_exception *e)
700{
701 hlist_bl_del(&e->hash_list);
702}
703
704/*
705 * Return the exception data for a sector, or NULL if not
706 * remapped.
707 */
708static struct dm_exception *dm_lookup_exception(struct dm_exception_table *et,
709 chunk_t chunk)
710{
711 struct hlist_bl_head *slot;
712 struct hlist_bl_node *pos;
713 struct dm_exception *e;
714
715 slot = &et->table[exception_hash(et, chunk)];
716 hlist_bl_for_each_entry(e, pos, slot, hash_list)
717 if (chunk >= e->old_chunk &&
718 chunk <= e->old_chunk + dm_consecutive_chunk_count(e))
719 return e;
720
721 return NULL;
722}
723
724static struct dm_exception *alloc_completed_exception(gfp_t gfp)
725{
726 struct dm_exception *e;
727
728 e = kmem_cache_alloc(exception_cache, gfp);
729 if (!e && gfp == GFP_NOIO)
730 e = kmem_cache_alloc(exception_cache, GFP_ATOMIC);
731
732 return e;
733}
734
735static void free_completed_exception(struct dm_exception *e)
736{
737 kmem_cache_free(exception_cache, e);
738}
739
740static struct dm_snap_pending_exception *alloc_pending_exception(struct dm_snapshot *s)
741{
742 struct dm_snap_pending_exception *pe = mempool_alloc(&s->pending_pool,
743 GFP_NOIO);
744
745 atomic_inc(&s->pending_exceptions_count);
746 pe->snap = s;
747
748 return pe;
749}
750
751static void free_pending_exception(struct dm_snap_pending_exception *pe)
752{
753 struct dm_snapshot *s = pe->snap;
754
755 mempool_free(pe, &s->pending_pool);
756 smp_mb__before_atomic();
757 atomic_dec(&s->pending_exceptions_count);
758}
759
760static void dm_insert_exception(struct dm_exception_table *eh,
761 struct dm_exception *new_e)
762{
763 struct hlist_bl_head *l;
764 struct hlist_bl_node *pos;
765 struct dm_exception *e = NULL;
766
767 l = &eh->table[exception_hash(eh, new_e->old_chunk)];
768
769 /* Add immediately if this table doesn't support consecutive chunks */
770 if (!eh->hash_shift)
771 goto out;
772
773 /* List is ordered by old_chunk */
774 hlist_bl_for_each_entry(e, pos, l, hash_list) {
775 /* Insert after an existing chunk? */
776 if (new_e->old_chunk == (e->old_chunk +
777 dm_consecutive_chunk_count(e) + 1) &&
778 new_e->new_chunk == (dm_chunk_number(e->new_chunk) +
779 dm_consecutive_chunk_count(e) + 1)) {
780 dm_consecutive_chunk_count_inc(e);
781 free_completed_exception(new_e);
782 return;
783 }
784
785 /* Insert before an existing chunk? */
786 if (new_e->old_chunk == (e->old_chunk - 1) &&
787 new_e->new_chunk == (dm_chunk_number(e->new_chunk) - 1)) {
788 dm_consecutive_chunk_count_inc(e);
789 e->old_chunk--;
790 e->new_chunk--;
791 free_completed_exception(new_e);
792 return;
793 }
794
795 if (new_e->old_chunk < e->old_chunk)
796 break;
797 }
798
799out:
800 if (!e) {
801 /*
802 * Either the table doesn't support consecutive chunks or slot
803 * l is empty.
804 */
805 hlist_bl_add_head(&new_e->hash_list, l);
806 } else if (new_e->old_chunk < e->old_chunk) {
807 /* Add before an existing exception */
808 hlist_bl_add_before(&new_e->hash_list, &e->hash_list);
809 } else {
810 /* Add to l's tail: e is the last exception in this slot */
811 hlist_bl_add_behind(&new_e->hash_list, &e->hash_list);
812 }
813}
814
815/*
816 * Callback used by the exception stores to load exceptions when
817 * initialising.
818 */
819static int dm_add_exception(void *context, chunk_t old, chunk_t new)
820{
821 struct dm_exception_table_lock lock;
822 struct dm_snapshot *s = context;
823 struct dm_exception *e;
824
825 e = alloc_completed_exception(GFP_KERNEL);
826 if (!e)
827 return -ENOMEM;
828
829 e->old_chunk = old;
830
831 /* Consecutive_count is implicitly initialised to zero */
832 e->new_chunk = new;
833
834 /*
835 * Although there is no need to lock access to the exception tables
836 * here, if we don't then hlist_bl_add_head(), called by
837 * dm_insert_exception(), will complain about accessing the
838 * corresponding list without locking it first.
839 */
840 dm_exception_table_lock_init(s, old, &lock);
841
842 dm_exception_table_lock(&lock);
843 dm_insert_exception(&s->complete, e);
844 dm_exception_table_unlock(&lock);
845
846 return 0;
847}
848
849/*
850 * Return a minimum chunk size of all snapshots that have the specified origin.
851 * Return zero if the origin has no snapshots.
852 */
853static uint32_t __minimum_chunk_size(struct origin *o)
854{
855 struct dm_snapshot *snap;
856 unsigned int chunk_size = rounddown_pow_of_two(UINT_MAX);
857
858 if (o)
859 list_for_each_entry(snap, &o->snapshots, list)
860 chunk_size = min_not_zero(chunk_size,
861 snap->store->chunk_size);
862
863 return (uint32_t) chunk_size;
864}
865
866/*
867 * Hard coded magic.
868 */
869static int calc_max_buckets(void)
870{
871 /* use a fixed size of 2MB */
872 unsigned long mem = 2 * 1024 * 1024;
873
874 mem /= sizeof(struct hlist_bl_head);
875
876 return mem;
877}
878
879/*
880 * Allocate room for a suitable hash table.
881 */
882static int init_hash_tables(struct dm_snapshot *s)
883{
884 sector_t hash_size, cow_dev_size, max_buckets;
885
886 /*
887 * Calculate based on the size of the original volume or
888 * the COW volume...
889 */
890 cow_dev_size = get_dev_size(s->cow->bdev);
891 max_buckets = calc_max_buckets();
892
893 hash_size = cow_dev_size >> s->store->chunk_shift;
894 hash_size = min(hash_size, max_buckets);
895
896 if (hash_size < 64)
897 hash_size = 64;
898 hash_size = rounddown_pow_of_two(hash_size);
899 if (dm_exception_table_init(&s->complete, hash_size,
900 DM_CHUNK_CONSECUTIVE_BITS))
901 return -ENOMEM;
902
903 /*
904 * Allocate hash table for in-flight exceptions
905 * Make this smaller than the real hash table
906 */
907 hash_size >>= 3;
908 if (hash_size < 64)
909 hash_size = 64;
910
911 if (dm_exception_table_init(&s->pending, hash_size, 0)) {
912 dm_exception_table_exit(&s->complete, exception_cache);
913 return -ENOMEM;
914 }
915
916 return 0;
917}
918
919static void merge_shutdown(struct dm_snapshot *s)
920{
921 clear_bit_unlock(RUNNING_MERGE, &s->state_bits);
922 smp_mb__after_atomic();
923 wake_up_bit(&s->state_bits, RUNNING_MERGE);
924}
925
926static struct bio *__release_queued_bios_after_merge(struct dm_snapshot *s)
927{
928 s->first_merging_chunk = 0;
929 s->num_merging_chunks = 0;
930
931 return bio_list_get(&s->bios_queued_during_merge);
932}
933
934/*
935 * Remove one chunk from the index of completed exceptions.
936 */
937static int __remove_single_exception_chunk(struct dm_snapshot *s,
938 chunk_t old_chunk)
939{
940 struct dm_exception *e;
941
942 e = dm_lookup_exception(&s->complete, old_chunk);
943 if (!e) {
944 DMERR("Corruption detected: exception for block %llu is on disk but not in memory",
945 (unsigned long long)old_chunk);
946 return -EINVAL;
947 }
948
949 /*
950 * If this is the only chunk using this exception, remove exception.
951 */
952 if (!dm_consecutive_chunk_count(e)) {
953 dm_remove_exception(e);
954 free_completed_exception(e);
955 return 0;
956 }
957
958 /*
959 * The chunk may be either at the beginning or the end of a
960 * group of consecutive chunks - never in the middle. We are
961 * removing chunks in the opposite order to that in which they
962 * were added, so this should always be true.
963 * Decrement the consecutive chunk counter and adjust the
964 * starting point if necessary.
965 */
966 if (old_chunk == e->old_chunk) {
967 e->old_chunk++;
968 e->new_chunk++;
969 } else if (old_chunk != e->old_chunk +
970 dm_consecutive_chunk_count(e)) {
971 DMERR("Attempt to merge block %llu from the middle of a chunk range [%llu - %llu]",
972 (unsigned long long)old_chunk,
973 (unsigned long long)e->old_chunk,
974 (unsigned long long)
975 e->old_chunk + dm_consecutive_chunk_count(e));
976 return -EINVAL;
977 }
978
979 dm_consecutive_chunk_count_dec(e);
980
981 return 0;
982}
983
984static void flush_bios(struct bio *bio);
985
986static int remove_single_exception_chunk(struct dm_snapshot *s)
987{
988 struct bio *b = NULL;
989 int r;
990 chunk_t old_chunk = s->first_merging_chunk + s->num_merging_chunks - 1;
991
992 down_write(&s->lock);
993
994 /*
995 * Process chunks (and associated exceptions) in reverse order
996 * so that dm_consecutive_chunk_count_dec() accounting works.
997 */
998 do {
999 r = __remove_single_exception_chunk(s, old_chunk);
1000 if (r)
1001 goto out;
1002 } while (old_chunk-- > s->first_merging_chunk);
1003
1004 b = __release_queued_bios_after_merge(s);
1005
1006out:
1007 up_write(&s->lock);
1008 if (b)
1009 flush_bios(b);
1010
1011 return r;
1012}
1013
1014static int origin_write_extent(struct dm_snapshot *merging_snap,
1015 sector_t sector, unsigned int chunk_size);
1016
1017static void merge_callback(int read_err, unsigned long write_err,
1018 void *context);
1019
1020static uint64_t read_pending_exceptions_done_count(void)
1021{
1022 uint64_t pending_exceptions_done;
1023
1024 spin_lock(&_pending_exceptions_done_spinlock);
1025 pending_exceptions_done = _pending_exceptions_done_count;
1026 spin_unlock(&_pending_exceptions_done_spinlock);
1027
1028 return pending_exceptions_done;
1029}
1030
1031static void increment_pending_exceptions_done_count(void)
1032{
1033 spin_lock(&_pending_exceptions_done_spinlock);
1034 _pending_exceptions_done_count++;
1035 spin_unlock(&_pending_exceptions_done_spinlock);
1036
1037 wake_up_all(&_pending_exceptions_done);
1038}
1039
1040static void snapshot_merge_next_chunks(struct dm_snapshot *s)
1041{
1042 int i, linear_chunks;
1043 chunk_t old_chunk, new_chunk;
1044 struct dm_io_region src, dest;
1045 sector_t io_size;
1046 uint64_t previous_count;
1047
1048 BUG_ON(!test_bit(RUNNING_MERGE, &s->state_bits));
1049 if (unlikely(test_bit(SHUTDOWN_MERGE, &s->state_bits)))
1050 goto shut;
1051
1052 /*
1053 * valid flag never changes during merge, so no lock required.
1054 */
1055 if (!s->valid) {
1056 DMERR("Snapshot is invalid: can't merge");
1057 goto shut;
1058 }
1059
1060 linear_chunks = s->store->type->prepare_merge(s->store, &old_chunk,
1061 &new_chunk);
1062 if (linear_chunks <= 0) {
1063 if (linear_chunks < 0) {
1064 DMERR("Read error in exception store: shutting down merge");
1065 down_write(&s->lock);
1066 s->merge_failed = true;
1067 up_write(&s->lock);
1068 }
1069 goto shut;
1070 }
1071
1072 /* Adjust old_chunk and new_chunk to reflect start of linear region */
1073 old_chunk = old_chunk + 1 - linear_chunks;
1074 new_chunk = new_chunk + 1 - linear_chunks;
1075
1076 /*
1077 * Use one (potentially large) I/O to copy all 'linear_chunks'
1078 * from the exception store to the origin
1079 */
1080 io_size = linear_chunks * s->store->chunk_size;
1081
1082 dest.bdev = s->origin->bdev;
1083 dest.sector = chunk_to_sector(s->store, old_chunk);
1084 dest.count = min(io_size, get_dev_size(dest.bdev) - dest.sector);
1085
1086 src.bdev = s->cow->bdev;
1087 src.sector = chunk_to_sector(s->store, new_chunk);
1088 src.count = dest.count;
1089
1090 /*
1091 * Reallocate any exceptions needed in other snapshots then
1092 * wait for the pending exceptions to complete.
1093 * Each time any pending exception (globally on the system)
1094 * completes we are woken and repeat the process to find out
1095 * if we can proceed. While this may not seem a particularly
1096 * efficient algorithm, it is not expected to have any
1097 * significant impact on performance.
1098 */
1099 previous_count = read_pending_exceptions_done_count();
1100 while (origin_write_extent(s, dest.sector, io_size)) {
1101 wait_event(_pending_exceptions_done,
1102 (read_pending_exceptions_done_count() !=
1103 previous_count));
1104 /* Retry after the wait, until all exceptions are done. */
1105 previous_count = read_pending_exceptions_done_count();
1106 }
1107
1108 down_write(&s->lock);
1109 s->first_merging_chunk = old_chunk;
1110 s->num_merging_chunks = linear_chunks;
1111 up_write(&s->lock);
1112
1113 /* Wait until writes to all 'linear_chunks' drain */
1114 for (i = 0; i < linear_chunks; i++)
1115 __check_for_conflicting_io(s, old_chunk + i);
1116
1117 dm_kcopyd_copy(s->kcopyd_client, &src, 1, &dest, 0, merge_callback, s);
1118 return;
1119
1120shut:
1121 merge_shutdown(s);
1122}
1123
1124static void error_bios(struct bio *bio);
1125
1126static void merge_callback(int read_err, unsigned long write_err, void *context)
1127{
1128 struct dm_snapshot *s = context;
1129 struct bio *b = NULL;
1130
1131 if (read_err || write_err) {
1132 if (read_err)
1133 DMERR("Read error: shutting down merge.");
1134 else
1135 DMERR("Write error: shutting down merge.");
1136 goto shut;
1137 }
1138
1139 if (blkdev_issue_flush(s->origin->bdev) < 0) {
1140 DMERR("Flush after merge failed: shutting down merge");
1141 goto shut;
1142 }
1143
1144 if (s->store->type->commit_merge(s->store,
1145 s->num_merging_chunks) < 0) {
1146 DMERR("Write error in exception store: shutting down merge");
1147 goto shut;
1148 }
1149
1150 if (remove_single_exception_chunk(s) < 0)
1151 goto shut;
1152
1153 snapshot_merge_next_chunks(s);
1154
1155 return;
1156
1157shut:
1158 down_write(&s->lock);
1159 s->merge_failed = true;
1160 b = __release_queued_bios_after_merge(s);
1161 up_write(&s->lock);
1162 error_bios(b);
1163
1164 merge_shutdown(s);
1165}
1166
1167static void start_merge(struct dm_snapshot *s)
1168{
1169 if (!test_and_set_bit(RUNNING_MERGE, &s->state_bits))
1170 snapshot_merge_next_chunks(s);
1171}
1172
1173/*
1174 * Stop the merging process and wait until it finishes.
1175 */
1176static void stop_merge(struct dm_snapshot *s)
1177{
1178 set_bit(SHUTDOWN_MERGE, &s->state_bits);
1179 wait_on_bit(&s->state_bits, RUNNING_MERGE, TASK_UNINTERRUPTIBLE);
1180 clear_bit(SHUTDOWN_MERGE, &s->state_bits);
1181}
1182
1183static int parse_snapshot_features(struct dm_arg_set *as, struct dm_snapshot *s,
1184 struct dm_target *ti)
1185{
1186 int r;
1187 unsigned int argc;
1188 const char *arg_name;
1189
1190 static const struct dm_arg _args[] = {
1191 {0, 2, "Invalid number of feature arguments"},
1192 };
1193
1194 /*
1195 * No feature arguments supplied.
1196 */
1197 if (!as->argc)
1198 return 0;
1199
1200 r = dm_read_arg_group(_args, as, &argc, &ti->error);
1201 if (r)
1202 return -EINVAL;
1203
1204 while (argc && !r) {
1205 arg_name = dm_shift_arg(as);
1206 argc--;
1207
1208 if (!strcasecmp(arg_name, "discard_zeroes_cow"))
1209 s->discard_zeroes_cow = true;
1210
1211 else if (!strcasecmp(arg_name, "discard_passdown_origin"))
1212 s->discard_passdown_origin = true;
1213
1214 else {
1215 ti->error = "Unrecognised feature requested";
1216 r = -EINVAL;
1217 break;
1218 }
1219 }
1220
1221 if (!s->discard_zeroes_cow && s->discard_passdown_origin) {
1222 /*
1223 * TODO: really these are disjoint.. but ti->num_discard_bios
1224 * and dm_bio_get_target_bio_nr() require rigid constraints.
1225 */
1226 ti->error = "discard_passdown_origin feature depends on discard_zeroes_cow";
1227 r = -EINVAL;
1228 }
1229
1230 return r;
1231}
1232
1233/*
1234 * Construct a snapshot mapping:
1235 * <origin_dev> <COW-dev> <p|po|n> <chunk-size> [<# feature args> [<arg>]*]
1236 */
1237static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
1238{
1239 struct dm_snapshot *s;
1240 struct dm_arg_set as;
1241 int i;
1242 int r = -EINVAL;
1243 char *origin_path, *cow_path;
1244 unsigned int args_used, num_flush_bios = 1;
1245 blk_mode_t origin_mode = BLK_OPEN_READ;
1246
1247 if (argc < 4) {
1248 ti->error = "requires 4 or more arguments";
1249 r = -EINVAL;
1250 goto bad;
1251 }
1252
1253 if (dm_target_is_snapshot_merge(ti)) {
1254 num_flush_bios = 2;
1255 origin_mode = BLK_OPEN_WRITE;
1256 }
1257
1258 s = kzalloc(sizeof(*s), GFP_KERNEL);
1259 if (!s) {
1260 ti->error = "Cannot allocate private snapshot structure";
1261 r = -ENOMEM;
1262 goto bad;
1263 }
1264
1265 as.argc = argc;
1266 as.argv = argv;
1267 dm_consume_args(&as, 4);
1268 r = parse_snapshot_features(&as, s, ti);
1269 if (r)
1270 goto bad_features;
1271
1272 origin_path = argv[0];
1273 argv++;
1274 argc--;
1275
1276 r = dm_get_device(ti, origin_path, origin_mode, &s->origin);
1277 if (r) {
1278 ti->error = "Cannot get origin device";
1279 goto bad_origin;
1280 }
1281
1282 cow_path = argv[0];
1283 argv++;
1284 argc--;
1285
1286 r = dm_get_device(ti, cow_path, dm_table_get_mode(ti->table), &s->cow);
1287 if (r) {
1288 ti->error = "Cannot get COW device";
1289 goto bad_cow;
1290 }
1291 if (s->cow->bdev && s->cow->bdev == s->origin->bdev) {
1292 ti->error = "COW device cannot be the same as origin device";
1293 r = -EINVAL;
1294 goto bad_store;
1295 }
1296
1297 r = dm_exception_store_create(ti, argc, argv, s, &args_used, &s->store);
1298 if (r) {
1299 ti->error = "Couldn't create exception store";
1300 r = -EINVAL;
1301 goto bad_store;
1302 }
1303
1304 argv += args_used;
1305 argc -= args_used;
1306
1307 s->ti = ti;
1308 s->valid = 1;
1309 s->snapshot_overflowed = 0;
1310 s->active = 0;
1311 atomic_set(&s->pending_exceptions_count, 0);
1312 spin_lock_init(&s->pe_allocation_lock);
1313 s->exception_start_sequence = 0;
1314 s->exception_complete_sequence = 0;
1315 s->out_of_order_tree = RB_ROOT;
1316 init_rwsem(&s->lock);
1317 INIT_LIST_HEAD(&s->list);
1318 spin_lock_init(&s->pe_lock);
1319 s->state_bits = 0;
1320 s->merge_failed = false;
1321 s->first_merging_chunk = 0;
1322 s->num_merging_chunks = 0;
1323 bio_list_init(&s->bios_queued_during_merge);
1324
1325 /* Allocate hash table for COW data */
1326 if (init_hash_tables(s)) {
1327 ti->error = "Unable to allocate hash table space";
1328 r = -ENOMEM;
1329 goto bad_hash_tables;
1330 }
1331
1332 init_waitqueue_head(&s->in_progress_wait);
1333
1334 s->kcopyd_client = dm_kcopyd_client_create(&dm_kcopyd_throttle);
1335 if (IS_ERR(s->kcopyd_client)) {
1336 r = PTR_ERR(s->kcopyd_client);
1337 ti->error = "Could not create kcopyd client";
1338 goto bad_kcopyd;
1339 }
1340
1341 r = mempool_init_slab_pool(&s->pending_pool, MIN_IOS, pending_cache);
1342 if (r) {
1343 ti->error = "Could not allocate mempool for pending exceptions";
1344 goto bad_pending_pool;
1345 }
1346
1347 for (i = 0; i < DM_TRACKED_CHUNK_HASH_SIZE; i++)
1348 INIT_HLIST_HEAD(&s->tracked_chunk_hash[i]);
1349
1350 spin_lock_init(&s->tracked_chunk_lock);
1351
1352 ti->private = s;
1353 ti->num_flush_bios = num_flush_bios;
1354 if (s->discard_zeroes_cow)
1355 ti->num_discard_bios = (s->discard_passdown_origin ? 2 : 1);
1356 ti->per_io_data_size = sizeof(struct dm_snap_tracked_chunk);
1357
1358 /* Add snapshot to the list of snapshots for this origin */
1359 /* Exceptions aren't triggered till snapshot_resume() is called */
1360 r = register_snapshot(s);
1361 if (r == -ENOMEM) {
1362 ti->error = "Snapshot origin struct allocation failed";
1363 goto bad_load_and_register;
1364 } else if (r < 0) {
1365 /* invalid handover, register_snapshot has set ti->error */
1366 goto bad_load_and_register;
1367 }
1368
1369 /*
1370 * Metadata must only be loaded into one table at once, so skip this
1371 * if metadata will be handed over during resume.
1372 * Chunk size will be set during the handover - set it to zero to
1373 * ensure it's ignored.
1374 */
1375 if (r > 0) {
1376 s->store->chunk_size = 0;
1377 return 0;
1378 }
1379
1380 r = s->store->type->read_metadata(s->store, dm_add_exception,
1381 (void *)s);
1382 if (r < 0) {
1383 ti->error = "Failed to read snapshot metadata";
1384 goto bad_read_metadata;
1385 } else if (r > 0) {
1386 s->valid = 0;
1387 DMWARN("Snapshot is marked invalid.");
1388 }
1389
1390 if (!s->store->chunk_size) {
1391 ti->error = "Chunk size not set";
1392 r = -EINVAL;
1393 goto bad_read_metadata;
1394 }
1395
1396 r = dm_set_target_max_io_len(ti, s->store->chunk_size);
1397 if (r)
1398 goto bad_read_metadata;
1399
1400 return 0;
1401
1402bad_read_metadata:
1403 unregister_snapshot(s);
1404bad_load_and_register:
1405 mempool_exit(&s->pending_pool);
1406bad_pending_pool:
1407 dm_kcopyd_client_destroy(s->kcopyd_client);
1408bad_kcopyd:
1409 dm_exception_table_exit(&s->pending, pending_cache);
1410 dm_exception_table_exit(&s->complete, exception_cache);
1411bad_hash_tables:
1412 dm_exception_store_destroy(s->store);
1413bad_store:
1414 dm_put_device(ti, s->cow);
1415bad_cow:
1416 dm_put_device(ti, s->origin);
1417bad_origin:
1418bad_features:
1419 kfree(s);
1420bad:
1421 return r;
1422}
1423
1424static void __free_exceptions(struct dm_snapshot *s)
1425{
1426 dm_kcopyd_client_destroy(s->kcopyd_client);
1427 s->kcopyd_client = NULL;
1428
1429 dm_exception_table_exit(&s->pending, pending_cache);
1430 dm_exception_table_exit(&s->complete, exception_cache);
1431}
1432
1433static void __handover_exceptions(struct dm_snapshot *snap_src,
1434 struct dm_snapshot *snap_dest)
1435{
1436 union {
1437 struct dm_exception_table table_swap;
1438 struct dm_exception_store *store_swap;
1439 } u;
1440
1441 /*
1442 * Swap all snapshot context information between the two instances.
1443 */
1444 u.table_swap = snap_dest->complete;
1445 snap_dest->complete = snap_src->complete;
1446 snap_src->complete = u.table_swap;
1447
1448 u.store_swap = snap_dest->store;
1449 snap_dest->store = snap_src->store;
1450 snap_dest->store->userspace_supports_overflow = u.store_swap->userspace_supports_overflow;
1451 snap_src->store = u.store_swap;
1452
1453 snap_dest->store->snap = snap_dest;
1454 snap_src->store->snap = snap_src;
1455
1456 snap_dest->ti->max_io_len = snap_dest->store->chunk_size;
1457 snap_dest->valid = snap_src->valid;
1458 snap_dest->snapshot_overflowed = snap_src->snapshot_overflowed;
1459
1460 /*
1461 * Set source invalid to ensure it receives no further I/O.
1462 */
1463 snap_src->valid = 0;
1464}
1465
1466static void snapshot_dtr(struct dm_target *ti)
1467{
1468#ifdef CONFIG_DM_DEBUG
1469 int i;
1470#endif
1471 struct dm_snapshot *s = ti->private;
1472 struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
1473
1474 down_read(&_origins_lock);
1475 /* Check whether exception handover must be cancelled */
1476 (void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL);
1477 if (snap_src && snap_dest && (s == snap_src)) {
1478 down_write(&snap_dest->lock);
1479 snap_dest->valid = 0;
1480 up_write(&snap_dest->lock);
1481 DMERR("Cancelling snapshot handover.");
1482 }
1483 up_read(&_origins_lock);
1484
1485 if (dm_target_is_snapshot_merge(ti))
1486 stop_merge(s);
1487
1488 /* Prevent further origin writes from using this snapshot. */
1489 /* After this returns there can be no new kcopyd jobs. */
1490 unregister_snapshot(s);
1491
1492 while (atomic_read(&s->pending_exceptions_count))
1493 fsleep(1000);
1494 /*
1495 * Ensure instructions in mempool_exit aren't reordered
1496 * before atomic_read.
1497 */
1498 smp_mb();
1499
1500#ifdef CONFIG_DM_DEBUG
1501 for (i = 0; i < DM_TRACKED_CHUNK_HASH_SIZE; i++)
1502 BUG_ON(!hlist_empty(&s->tracked_chunk_hash[i]));
1503#endif
1504
1505 __free_exceptions(s);
1506
1507 mempool_exit(&s->pending_pool);
1508
1509 dm_exception_store_destroy(s->store);
1510
1511 dm_put_device(ti, s->cow);
1512
1513 dm_put_device(ti, s->origin);
1514
1515 WARN_ON(s->in_progress);
1516
1517 kfree(s);
1518}
1519
1520static void account_start_copy(struct dm_snapshot *s)
1521{
1522 spin_lock(&s->in_progress_wait.lock);
1523 s->in_progress++;
1524 spin_unlock(&s->in_progress_wait.lock);
1525}
1526
1527static void account_end_copy(struct dm_snapshot *s)
1528{
1529 spin_lock(&s->in_progress_wait.lock);
1530 BUG_ON(!s->in_progress);
1531 s->in_progress--;
1532 if (likely(s->in_progress <= cow_threshold) &&
1533 unlikely(waitqueue_active(&s->in_progress_wait)))
1534 wake_up_locked(&s->in_progress_wait);
1535 spin_unlock(&s->in_progress_wait.lock);
1536}
1537
1538static bool wait_for_in_progress(struct dm_snapshot *s, bool unlock_origins)
1539{
1540 if (unlikely(s->in_progress > cow_threshold)) {
1541 spin_lock(&s->in_progress_wait.lock);
1542 if (likely(s->in_progress > cow_threshold)) {
1543 /*
1544 * NOTE: this throttle doesn't account for whether
1545 * the caller is servicing an IO that will trigger a COW
1546 * so excess throttling may result for chunks not required
1547 * to be COW'd. But if cow_threshold was reached, extra
1548 * throttling is unlikely to negatively impact performance.
1549 */
1550 DECLARE_WAITQUEUE(wait, current);
1551
1552 __add_wait_queue(&s->in_progress_wait, &wait);
1553 __set_current_state(TASK_UNINTERRUPTIBLE);
1554 spin_unlock(&s->in_progress_wait.lock);
1555 if (unlock_origins)
1556 up_read(&_origins_lock);
1557 io_schedule();
1558 remove_wait_queue(&s->in_progress_wait, &wait);
1559 return false;
1560 }
1561 spin_unlock(&s->in_progress_wait.lock);
1562 }
1563 return true;
1564}
1565
1566/*
1567 * Flush a list of buffers.
1568 */
1569static void flush_bios(struct bio *bio)
1570{
1571 struct bio *n;
1572
1573 while (bio) {
1574 n = bio->bi_next;
1575 bio->bi_next = NULL;
1576 submit_bio_noacct(bio);
1577 bio = n;
1578 }
1579}
1580
1581static int do_origin(struct dm_dev *origin, struct bio *bio, bool limit);
1582
1583/*
1584 * Flush a list of buffers.
1585 */
1586static void retry_origin_bios(struct dm_snapshot *s, struct bio *bio)
1587{
1588 struct bio *n;
1589 int r;
1590
1591 while (bio) {
1592 n = bio->bi_next;
1593 bio->bi_next = NULL;
1594 r = do_origin(s->origin, bio, false);
1595 if (r == DM_MAPIO_REMAPPED)
1596 submit_bio_noacct(bio);
1597 bio = n;
1598 }
1599}
1600
1601/*
1602 * Error a list of buffers.
1603 */
1604static void error_bios(struct bio *bio)
1605{
1606 struct bio *n;
1607
1608 while (bio) {
1609 n = bio->bi_next;
1610 bio->bi_next = NULL;
1611 bio_io_error(bio);
1612 bio = n;
1613 }
1614}
1615
1616static void __invalidate_snapshot(struct dm_snapshot *s, int err)
1617{
1618 if (!s->valid)
1619 return;
1620
1621 if (err == -EIO)
1622 DMERR("Invalidating snapshot: Error reading/writing.");
1623 else if (err == -ENOMEM)
1624 DMERR("Invalidating snapshot: Unable to allocate exception.");
1625
1626 if (s->store->type->drop_snapshot)
1627 s->store->type->drop_snapshot(s->store);
1628
1629 s->valid = 0;
1630
1631 dm_table_event(s->ti->table);
1632}
1633
1634static void invalidate_snapshot(struct dm_snapshot *s, int err)
1635{
1636 down_write(&s->lock);
1637 __invalidate_snapshot(s, err);
1638 up_write(&s->lock);
1639}
1640
1641static void pending_complete(void *context, int success)
1642{
1643 struct dm_snap_pending_exception *pe = context;
1644 struct dm_exception *e;
1645 struct dm_snapshot *s = pe->snap;
1646 struct bio *origin_bios = NULL;
1647 struct bio *snapshot_bios = NULL;
1648 struct bio *full_bio = NULL;
1649 struct dm_exception_table_lock lock;
1650 int error = 0;
1651
1652 dm_exception_table_lock_init(s, pe->e.old_chunk, &lock);
1653
1654 if (!success) {
1655 /* Read/write error - snapshot is unusable */
1656 invalidate_snapshot(s, -EIO);
1657 error = 1;
1658
1659 dm_exception_table_lock(&lock);
1660 goto out;
1661 }
1662
1663 e = alloc_completed_exception(GFP_NOIO);
1664 if (!e) {
1665 invalidate_snapshot(s, -ENOMEM);
1666 error = 1;
1667
1668 dm_exception_table_lock(&lock);
1669 goto out;
1670 }
1671 *e = pe->e;
1672
1673 down_read(&s->lock);
1674 dm_exception_table_lock(&lock);
1675 if (!s->valid) {
1676 up_read(&s->lock);
1677 free_completed_exception(e);
1678 error = 1;
1679
1680 goto out;
1681 }
1682
1683 /*
1684 * Add a proper exception. After inserting the completed exception all
1685 * subsequent snapshot reads to this chunk will be redirected to the
1686 * COW device. This ensures that we do not starve. Moreover, as long
1687 * as the pending exception exists, neither origin writes nor snapshot
1688 * merging can overwrite the chunk in origin.
1689 */
1690 dm_insert_exception(&s->complete, e);
1691 up_read(&s->lock);
1692
1693 /* Wait for conflicting reads to drain */
1694 if (__chunk_is_tracked(s, pe->e.old_chunk)) {
1695 dm_exception_table_unlock(&lock);
1696 __check_for_conflicting_io(s, pe->e.old_chunk);
1697 dm_exception_table_lock(&lock);
1698 }
1699
1700out:
1701 /* Remove the in-flight exception from the list */
1702 dm_remove_exception(&pe->e);
1703
1704 dm_exception_table_unlock(&lock);
1705
1706 snapshot_bios = bio_list_get(&pe->snapshot_bios);
1707 origin_bios = bio_list_get(&pe->origin_bios);
1708 full_bio = pe->full_bio;
1709 if (full_bio)
1710 full_bio->bi_end_io = pe->full_bio_end_io;
1711 increment_pending_exceptions_done_count();
1712
1713 /* Submit any pending write bios */
1714 if (error) {
1715 if (full_bio)
1716 bio_io_error(full_bio);
1717 error_bios(snapshot_bios);
1718 } else {
1719 if (full_bio)
1720 bio_endio(full_bio);
1721 flush_bios(snapshot_bios);
1722 }
1723
1724 retry_origin_bios(s, origin_bios);
1725
1726 free_pending_exception(pe);
1727}
1728
1729static void complete_exception(struct dm_snap_pending_exception *pe)
1730{
1731 struct dm_snapshot *s = pe->snap;
1732
1733 /* Update the metadata if we are persistent */
1734 s->store->type->commit_exception(s->store, &pe->e, !pe->copy_error,
1735 pending_complete, pe);
1736}
1737
1738/*
1739 * Called when the copy I/O has finished. kcopyd actually runs
1740 * this code so don't block.
1741 */
1742static void copy_callback(int read_err, unsigned long write_err, void *context)
1743{
1744 struct dm_snap_pending_exception *pe = context;
1745 struct dm_snapshot *s = pe->snap;
1746
1747 pe->copy_error = read_err || write_err;
1748
1749 if (pe->exception_sequence == s->exception_complete_sequence) {
1750 struct rb_node *next;
1751
1752 s->exception_complete_sequence++;
1753 complete_exception(pe);
1754
1755 next = rb_first(&s->out_of_order_tree);
1756 while (next) {
1757 pe = rb_entry(next, struct dm_snap_pending_exception,
1758 out_of_order_node);
1759 if (pe->exception_sequence != s->exception_complete_sequence)
1760 break;
1761 next = rb_next(next);
1762 s->exception_complete_sequence++;
1763 rb_erase(&pe->out_of_order_node, &s->out_of_order_tree);
1764 complete_exception(pe);
1765 cond_resched();
1766 }
1767 } else {
1768 struct rb_node *parent = NULL;
1769 struct rb_node **p = &s->out_of_order_tree.rb_node;
1770 struct dm_snap_pending_exception *pe2;
1771
1772 while (*p) {
1773 pe2 = rb_entry(*p, struct dm_snap_pending_exception, out_of_order_node);
1774 parent = *p;
1775
1776 BUG_ON(pe->exception_sequence == pe2->exception_sequence);
1777 if (pe->exception_sequence < pe2->exception_sequence)
1778 p = &((*p)->rb_left);
1779 else
1780 p = &((*p)->rb_right);
1781 }
1782
1783 rb_link_node(&pe->out_of_order_node, parent, p);
1784 rb_insert_color(&pe->out_of_order_node, &s->out_of_order_tree);
1785 }
1786 account_end_copy(s);
1787}
1788
1789/*
1790 * Dispatches the copy operation to kcopyd.
1791 */
1792static void start_copy(struct dm_snap_pending_exception *pe)
1793{
1794 struct dm_snapshot *s = pe->snap;
1795 struct dm_io_region src, dest;
1796 struct block_device *bdev = s->origin->bdev;
1797 sector_t dev_size;
1798
1799 dev_size = get_dev_size(bdev);
1800
1801 src.bdev = bdev;
1802 src.sector = chunk_to_sector(s->store, pe->e.old_chunk);
1803 src.count = min((sector_t)s->store->chunk_size, dev_size - src.sector);
1804
1805 dest.bdev = s->cow->bdev;
1806 dest.sector = chunk_to_sector(s->store, pe->e.new_chunk);
1807 dest.count = src.count;
1808
1809 /* Hand over to kcopyd */
1810 account_start_copy(s);
1811 dm_kcopyd_copy(s->kcopyd_client, &src, 1, &dest, 0, copy_callback, pe);
1812}
1813
1814static void full_bio_end_io(struct bio *bio)
1815{
1816 void *callback_data = bio->bi_private;
1817
1818 dm_kcopyd_do_callback(callback_data, 0, bio->bi_status ? 1 : 0);
1819}
1820
1821static void start_full_bio(struct dm_snap_pending_exception *pe,
1822 struct bio *bio)
1823{
1824 struct dm_snapshot *s = pe->snap;
1825 void *callback_data;
1826
1827 pe->full_bio = bio;
1828 pe->full_bio_end_io = bio->bi_end_io;
1829
1830 account_start_copy(s);
1831 callback_data = dm_kcopyd_prepare_callback(s->kcopyd_client,
1832 copy_callback, pe);
1833
1834 bio->bi_end_io = full_bio_end_io;
1835 bio->bi_private = callback_data;
1836
1837 submit_bio_noacct(bio);
1838}
1839
1840static struct dm_snap_pending_exception *
1841__lookup_pending_exception(struct dm_snapshot *s, chunk_t chunk)
1842{
1843 struct dm_exception *e = dm_lookup_exception(&s->pending, chunk);
1844
1845 if (!e)
1846 return NULL;
1847
1848 return container_of(e, struct dm_snap_pending_exception, e);
1849}
1850
1851/*
1852 * Inserts a pending exception into the pending table.
1853 *
1854 * NOTE: a write lock must be held on the chunk's pending exception table slot
1855 * before calling this.
1856 */
1857static struct dm_snap_pending_exception *
1858__insert_pending_exception(struct dm_snapshot *s,
1859 struct dm_snap_pending_exception *pe, chunk_t chunk)
1860{
1861 pe->e.old_chunk = chunk;
1862 bio_list_init(&pe->origin_bios);
1863 bio_list_init(&pe->snapshot_bios);
1864 pe->started = 0;
1865 pe->full_bio = NULL;
1866
1867 spin_lock(&s->pe_allocation_lock);
1868 if (s->store->type->prepare_exception(s->store, &pe->e)) {
1869 spin_unlock(&s->pe_allocation_lock);
1870 free_pending_exception(pe);
1871 return NULL;
1872 }
1873
1874 pe->exception_sequence = s->exception_start_sequence++;
1875 spin_unlock(&s->pe_allocation_lock);
1876
1877 dm_insert_exception(&s->pending, &pe->e);
1878
1879 return pe;
1880}
1881
1882/*
1883 * Looks to see if this snapshot already has a pending exception
1884 * for this chunk, otherwise it allocates a new one and inserts
1885 * it into the pending table.
1886 *
1887 * NOTE: a write lock must be held on the chunk's pending exception table slot
1888 * before calling this.
1889 */
1890static struct dm_snap_pending_exception *
1891__find_pending_exception(struct dm_snapshot *s,
1892 struct dm_snap_pending_exception *pe, chunk_t chunk)
1893{
1894 struct dm_snap_pending_exception *pe2;
1895
1896 pe2 = __lookup_pending_exception(s, chunk);
1897 if (pe2) {
1898 free_pending_exception(pe);
1899 return pe2;
1900 }
1901
1902 return __insert_pending_exception(s, pe, chunk);
1903}
1904
1905static void remap_exception(struct dm_snapshot *s, struct dm_exception *e,
1906 struct bio *bio, chunk_t chunk)
1907{
1908 bio_set_dev(bio, s->cow->bdev);
1909 bio->bi_iter.bi_sector =
1910 chunk_to_sector(s->store, dm_chunk_number(e->new_chunk) +
1911 (chunk - e->old_chunk)) +
1912 (bio->bi_iter.bi_sector & s->store->chunk_mask);
1913}
1914
1915static void zero_callback(int read_err, unsigned long write_err, void *context)
1916{
1917 struct bio *bio = context;
1918 struct dm_snapshot *s = bio->bi_private;
1919
1920 account_end_copy(s);
1921 bio->bi_status = write_err ? BLK_STS_IOERR : 0;
1922 bio_endio(bio);
1923}
1924
1925static void zero_exception(struct dm_snapshot *s, struct dm_exception *e,
1926 struct bio *bio, chunk_t chunk)
1927{
1928 struct dm_io_region dest;
1929
1930 dest.bdev = s->cow->bdev;
1931 dest.sector = bio->bi_iter.bi_sector;
1932 dest.count = s->store->chunk_size;
1933
1934 account_start_copy(s);
1935 WARN_ON_ONCE(bio->bi_private);
1936 bio->bi_private = s;
1937 dm_kcopyd_zero(s->kcopyd_client, 1, &dest, 0, zero_callback, bio);
1938}
1939
1940static bool io_overlaps_chunk(struct dm_snapshot *s, struct bio *bio)
1941{
1942 return bio->bi_iter.bi_size ==
1943 (s->store->chunk_size << SECTOR_SHIFT);
1944}
1945
1946static int snapshot_map(struct dm_target *ti, struct bio *bio)
1947{
1948 struct dm_exception *e;
1949 struct dm_snapshot *s = ti->private;
1950 int r = DM_MAPIO_REMAPPED;
1951 chunk_t chunk;
1952 struct dm_snap_pending_exception *pe = NULL;
1953 struct dm_exception_table_lock lock;
1954
1955 init_tracked_chunk(bio);
1956
1957 if (bio->bi_opf & REQ_PREFLUSH) {
1958 bio_set_dev(bio, s->cow->bdev);
1959 return DM_MAPIO_REMAPPED;
1960 }
1961
1962 chunk = sector_to_chunk(s->store, bio->bi_iter.bi_sector);
1963 dm_exception_table_lock_init(s, chunk, &lock);
1964
1965 /* Full snapshots are not usable */
1966 /* To get here the table must be live so s->active is always set. */
1967 if (!s->valid)
1968 return DM_MAPIO_KILL;
1969
1970 if (bio_data_dir(bio) == WRITE) {
1971 while (unlikely(!wait_for_in_progress(s, false)))
1972 ; /* wait_for_in_progress() has slept */
1973 }
1974
1975 down_read(&s->lock);
1976 dm_exception_table_lock(&lock);
1977
1978 if (!s->valid || (unlikely(s->snapshot_overflowed) &&
1979 bio_data_dir(bio) == WRITE)) {
1980 r = DM_MAPIO_KILL;
1981 goto out_unlock;
1982 }
1983
1984 if (unlikely(bio_op(bio) == REQ_OP_DISCARD)) {
1985 if (s->discard_passdown_origin && dm_bio_get_target_bio_nr(bio)) {
1986 /*
1987 * passdown discard to origin (without triggering
1988 * snapshot exceptions via do_origin; doing so would
1989 * defeat the goal of freeing space in origin that is
1990 * implied by the "discard_passdown_origin" feature)
1991 */
1992 bio_set_dev(bio, s->origin->bdev);
1993 track_chunk(s, bio, chunk);
1994 goto out_unlock;
1995 }
1996 /* discard to snapshot (target_bio_nr == 0) zeroes exceptions */
1997 }
1998
1999 /* If the block is already remapped - use that, else remap it */
2000 e = dm_lookup_exception(&s->complete, chunk);
2001 if (e) {
2002 remap_exception(s, e, bio, chunk);
2003 if (unlikely(bio_op(bio) == REQ_OP_DISCARD) &&
2004 io_overlaps_chunk(s, bio)) {
2005 dm_exception_table_unlock(&lock);
2006 up_read(&s->lock);
2007 zero_exception(s, e, bio, chunk);
2008 r = DM_MAPIO_SUBMITTED; /* discard is not issued */
2009 goto out;
2010 }
2011 goto out_unlock;
2012 }
2013
2014 if (unlikely(bio_op(bio) == REQ_OP_DISCARD)) {
2015 /*
2016 * If no exception exists, complete discard immediately
2017 * otherwise it'll trigger copy-out.
2018 */
2019 bio_endio(bio);
2020 r = DM_MAPIO_SUBMITTED;
2021 goto out_unlock;
2022 }
2023
2024 /*
2025 * Write to snapshot - higher level takes care of RW/RO
2026 * flags so we should only get this if we are
2027 * writable.
2028 */
2029 if (bio_data_dir(bio) == WRITE) {
2030 pe = __lookup_pending_exception(s, chunk);
2031 if (!pe) {
2032 dm_exception_table_unlock(&lock);
2033 pe = alloc_pending_exception(s);
2034 dm_exception_table_lock(&lock);
2035
2036 e = dm_lookup_exception(&s->complete, chunk);
2037 if (e) {
2038 free_pending_exception(pe);
2039 remap_exception(s, e, bio, chunk);
2040 goto out_unlock;
2041 }
2042
2043 pe = __find_pending_exception(s, pe, chunk);
2044 if (!pe) {
2045 dm_exception_table_unlock(&lock);
2046 up_read(&s->lock);
2047
2048 down_write(&s->lock);
2049
2050 if (s->store->userspace_supports_overflow) {
2051 if (s->valid && !s->snapshot_overflowed) {
2052 s->snapshot_overflowed = 1;
2053 DMERR("Snapshot overflowed: Unable to allocate exception.");
2054 }
2055 } else
2056 __invalidate_snapshot(s, -ENOMEM);
2057 up_write(&s->lock);
2058
2059 r = DM_MAPIO_KILL;
2060 goto out;
2061 }
2062 }
2063
2064 remap_exception(s, &pe->e, bio, chunk);
2065
2066 r = DM_MAPIO_SUBMITTED;
2067
2068 if (!pe->started && io_overlaps_chunk(s, bio)) {
2069 pe->started = 1;
2070
2071 dm_exception_table_unlock(&lock);
2072 up_read(&s->lock);
2073
2074 start_full_bio(pe, bio);
2075 goto out;
2076 }
2077
2078 bio_list_add(&pe->snapshot_bios, bio);
2079
2080 if (!pe->started) {
2081 /* this is protected by the exception table lock */
2082 pe->started = 1;
2083
2084 dm_exception_table_unlock(&lock);
2085 up_read(&s->lock);
2086
2087 start_copy(pe);
2088 goto out;
2089 }
2090 } else {
2091 bio_set_dev(bio, s->origin->bdev);
2092 track_chunk(s, bio, chunk);
2093 }
2094
2095out_unlock:
2096 dm_exception_table_unlock(&lock);
2097 up_read(&s->lock);
2098out:
2099 return r;
2100}
2101
2102/*
2103 * A snapshot-merge target behaves like a combination of a snapshot
2104 * target and a snapshot-origin target. It only generates new
2105 * exceptions in other snapshots and not in the one that is being
2106 * merged.
2107 *
2108 * For each chunk, if there is an existing exception, it is used to
2109 * redirect I/O to the cow device. Otherwise I/O is sent to the origin,
2110 * which in turn might generate exceptions in other snapshots.
2111 * If merging is currently taking place on the chunk in question, the
2112 * I/O is deferred by adding it to s->bios_queued_during_merge.
2113 */
2114static int snapshot_merge_map(struct dm_target *ti, struct bio *bio)
2115{
2116 struct dm_exception *e;
2117 struct dm_snapshot *s = ti->private;
2118 int r = DM_MAPIO_REMAPPED;
2119 chunk_t chunk;
2120
2121 init_tracked_chunk(bio);
2122
2123 if (bio->bi_opf & REQ_PREFLUSH) {
2124 if (!dm_bio_get_target_bio_nr(bio))
2125 bio_set_dev(bio, s->origin->bdev);
2126 else
2127 bio_set_dev(bio, s->cow->bdev);
2128 return DM_MAPIO_REMAPPED;
2129 }
2130
2131 if (unlikely(bio_op(bio) == REQ_OP_DISCARD)) {
2132 /* Once merging, discards no longer effect change */
2133 bio_endio(bio);
2134 return DM_MAPIO_SUBMITTED;
2135 }
2136
2137 chunk = sector_to_chunk(s->store, bio->bi_iter.bi_sector);
2138
2139 down_write(&s->lock);
2140
2141 /* Full merging snapshots are redirected to the origin */
2142 if (!s->valid)
2143 goto redirect_to_origin;
2144
2145 /* If the block is already remapped - use that */
2146 e = dm_lookup_exception(&s->complete, chunk);
2147 if (e) {
2148 /* Queue writes overlapping with chunks being merged */
2149 if (bio_data_dir(bio) == WRITE &&
2150 chunk >= s->first_merging_chunk &&
2151 chunk < (s->first_merging_chunk +
2152 s->num_merging_chunks)) {
2153 bio_set_dev(bio, s->origin->bdev);
2154 bio_list_add(&s->bios_queued_during_merge, bio);
2155 r = DM_MAPIO_SUBMITTED;
2156 goto out_unlock;
2157 }
2158
2159 remap_exception(s, e, bio, chunk);
2160
2161 if (bio_data_dir(bio) == WRITE)
2162 track_chunk(s, bio, chunk);
2163 goto out_unlock;
2164 }
2165
2166redirect_to_origin:
2167 bio_set_dev(bio, s->origin->bdev);
2168
2169 if (bio_data_dir(bio) == WRITE) {
2170 up_write(&s->lock);
2171 return do_origin(s->origin, bio, false);
2172 }
2173
2174out_unlock:
2175 up_write(&s->lock);
2176
2177 return r;
2178}
2179
2180static int snapshot_end_io(struct dm_target *ti, struct bio *bio,
2181 blk_status_t *error)
2182{
2183 struct dm_snapshot *s = ti->private;
2184
2185 if (is_bio_tracked(bio))
2186 stop_tracking_chunk(s, bio);
2187
2188 return DM_ENDIO_DONE;
2189}
2190
2191static void snapshot_merge_presuspend(struct dm_target *ti)
2192{
2193 struct dm_snapshot *s = ti->private;
2194
2195 stop_merge(s);
2196}
2197
2198static int snapshot_preresume(struct dm_target *ti)
2199{
2200 int r = 0;
2201 struct dm_snapshot *s = ti->private;
2202 struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
2203
2204 down_read(&_origins_lock);
2205 (void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL);
2206 if (snap_src && snap_dest) {
2207 down_read(&snap_src->lock);
2208 if (s == snap_src) {
2209 DMERR("Unable to resume snapshot source until handover completes.");
2210 r = -EINVAL;
2211 } else if (!dm_suspended(snap_src->ti)) {
2212 DMERR("Unable to perform snapshot handover until source is suspended.");
2213 r = -EINVAL;
2214 }
2215 up_read(&snap_src->lock);
2216 }
2217 up_read(&_origins_lock);
2218
2219 return r;
2220}
2221
2222static void snapshot_resume(struct dm_target *ti)
2223{
2224 struct dm_snapshot *s = ti->private;
2225 struct dm_snapshot *snap_src = NULL, *snap_dest = NULL, *snap_merging = NULL;
2226 struct dm_origin *o;
2227 struct mapped_device *origin_md = NULL;
2228 bool must_restart_merging = false;
2229
2230 down_read(&_origins_lock);
2231
2232 o = __lookup_dm_origin(s->origin->bdev);
2233 if (o)
2234 origin_md = dm_table_get_md(o->ti->table);
2235 if (!origin_md) {
2236 (void) __find_snapshots_sharing_cow(s, NULL, NULL, &snap_merging);
2237 if (snap_merging)
2238 origin_md = dm_table_get_md(snap_merging->ti->table);
2239 }
2240 if (origin_md == dm_table_get_md(ti->table))
2241 origin_md = NULL;
2242 if (origin_md) {
2243 if (dm_hold(origin_md))
2244 origin_md = NULL;
2245 }
2246
2247 up_read(&_origins_lock);
2248
2249 if (origin_md) {
2250 dm_internal_suspend_fast(origin_md);
2251 if (snap_merging && test_bit(RUNNING_MERGE, &snap_merging->state_bits)) {
2252 must_restart_merging = true;
2253 stop_merge(snap_merging);
2254 }
2255 }
2256
2257 down_read(&_origins_lock);
2258
2259 (void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL);
2260 if (snap_src && snap_dest) {
2261 down_write(&snap_src->lock);
2262 down_write_nested(&snap_dest->lock, SINGLE_DEPTH_NESTING);
2263 __handover_exceptions(snap_src, snap_dest);
2264 up_write(&snap_dest->lock);
2265 up_write(&snap_src->lock);
2266 }
2267
2268 up_read(&_origins_lock);
2269
2270 if (origin_md) {
2271 if (must_restart_merging)
2272 start_merge(snap_merging);
2273 dm_internal_resume_fast(origin_md);
2274 dm_put(origin_md);
2275 }
2276
2277 /* Now we have correct chunk size, reregister */
2278 reregister_snapshot(s);
2279
2280 down_write(&s->lock);
2281 s->active = 1;
2282 up_write(&s->lock);
2283}
2284
2285static uint32_t get_origin_minimum_chunksize(struct block_device *bdev)
2286{
2287 uint32_t min_chunksize;
2288
2289 down_read(&_origins_lock);
2290 min_chunksize = __minimum_chunk_size(__lookup_origin(bdev));
2291 up_read(&_origins_lock);
2292
2293 return min_chunksize;
2294}
2295
2296static void snapshot_merge_resume(struct dm_target *ti)
2297{
2298 struct dm_snapshot *s = ti->private;
2299
2300 /*
2301 * Handover exceptions from existing snapshot.
2302 */
2303 snapshot_resume(ti);
2304
2305 /*
2306 * snapshot-merge acts as an origin, so set ti->max_io_len
2307 */
2308 ti->max_io_len = get_origin_minimum_chunksize(s->origin->bdev);
2309
2310 start_merge(s);
2311}
2312
2313static void snapshot_status(struct dm_target *ti, status_type_t type,
2314 unsigned int status_flags, char *result, unsigned int maxlen)
2315{
2316 unsigned int sz = 0;
2317 struct dm_snapshot *snap = ti->private;
2318 unsigned int num_features;
2319
2320 switch (type) {
2321 case STATUSTYPE_INFO:
2322
2323 down_write(&snap->lock);
2324
2325 if (!snap->valid)
2326 DMEMIT("Invalid");
2327 else if (snap->merge_failed)
2328 DMEMIT("Merge failed");
2329 else if (snap->snapshot_overflowed)
2330 DMEMIT("Overflow");
2331 else {
2332 if (snap->store->type->usage) {
2333 sector_t total_sectors, sectors_allocated,
2334 metadata_sectors;
2335 snap->store->type->usage(snap->store,
2336 &total_sectors,
2337 §ors_allocated,
2338 &metadata_sectors);
2339 DMEMIT("%llu/%llu %llu",
2340 (unsigned long long)sectors_allocated,
2341 (unsigned long long)total_sectors,
2342 (unsigned long long)metadata_sectors);
2343 } else
2344 DMEMIT("Unknown");
2345 }
2346
2347 up_write(&snap->lock);
2348
2349 break;
2350
2351 case STATUSTYPE_TABLE:
2352 /*
2353 * kdevname returns a static pointer so we need
2354 * to make private copies if the output is to
2355 * make sense.
2356 */
2357 DMEMIT("%s %s", snap->origin->name, snap->cow->name);
2358 sz += snap->store->type->status(snap->store, type, result + sz,
2359 maxlen - sz);
2360 num_features = snap->discard_zeroes_cow + snap->discard_passdown_origin;
2361 if (num_features) {
2362 DMEMIT(" %u", num_features);
2363 if (snap->discard_zeroes_cow)
2364 DMEMIT(" discard_zeroes_cow");
2365 if (snap->discard_passdown_origin)
2366 DMEMIT(" discard_passdown_origin");
2367 }
2368 break;
2369
2370 case STATUSTYPE_IMA:
2371 DMEMIT_TARGET_NAME_VERSION(ti->type);
2372 DMEMIT(",snap_origin_name=%s", snap->origin->name);
2373 DMEMIT(",snap_cow_name=%s", snap->cow->name);
2374 DMEMIT(",snap_valid=%c", snap->valid ? 'y' : 'n');
2375 DMEMIT(",snap_merge_failed=%c", snap->merge_failed ? 'y' : 'n');
2376 DMEMIT(",snapshot_overflowed=%c", snap->snapshot_overflowed ? 'y' : 'n');
2377 DMEMIT(";");
2378 break;
2379 }
2380}
2381
2382static int snapshot_iterate_devices(struct dm_target *ti,
2383 iterate_devices_callout_fn fn, void *data)
2384{
2385 struct dm_snapshot *snap = ti->private;
2386 int r;
2387
2388 r = fn(ti, snap->origin, 0, ti->len, data);
2389
2390 if (!r)
2391 r = fn(ti, snap->cow, 0, get_dev_size(snap->cow->bdev), data);
2392
2393 return r;
2394}
2395
2396static void snapshot_io_hints(struct dm_target *ti, struct queue_limits *limits)
2397{
2398 struct dm_snapshot *snap = ti->private;
2399
2400 if (snap->discard_zeroes_cow) {
2401 struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
2402
2403 down_read(&_origins_lock);
2404
2405 (void) __find_snapshots_sharing_cow(snap, &snap_src, &snap_dest, NULL);
2406 if (snap_src && snap_dest)
2407 snap = snap_src;
2408
2409 /* All discards are split on chunk_size boundary */
2410 limits->discard_granularity = snap->store->chunk_size;
2411 limits->max_discard_sectors = snap->store->chunk_size;
2412
2413 up_read(&_origins_lock);
2414 }
2415}
2416
2417/*
2418 *---------------------------------------------------------------
2419 * Origin methods
2420 *---------------------------------------------------------------
2421 */
2422/*
2423 * If no exceptions need creating, DM_MAPIO_REMAPPED is returned and any
2424 * supplied bio was ignored. The caller may submit it immediately.
2425 * (No remapping actually occurs as the origin is always a direct linear
2426 * map.)
2427 *
2428 * If further exceptions are required, DM_MAPIO_SUBMITTED is returned
2429 * and any supplied bio is added to a list to be submitted once all
2430 * the necessary exceptions exist.
2431 */
2432static int __origin_write(struct list_head *snapshots, sector_t sector,
2433 struct bio *bio)
2434{
2435 int r = DM_MAPIO_REMAPPED;
2436 struct dm_snapshot *snap;
2437 struct dm_exception *e;
2438 struct dm_snap_pending_exception *pe, *pe2;
2439 struct dm_snap_pending_exception *pe_to_start_now = NULL;
2440 struct dm_snap_pending_exception *pe_to_start_last = NULL;
2441 struct dm_exception_table_lock lock;
2442 chunk_t chunk;
2443
2444 /* Do all the snapshots on this origin */
2445 list_for_each_entry(snap, snapshots, list) {
2446 /*
2447 * Don't make new exceptions in a merging snapshot
2448 * because it has effectively been deleted
2449 */
2450 if (dm_target_is_snapshot_merge(snap->ti))
2451 continue;
2452
2453 /* Nothing to do if writing beyond end of snapshot */
2454 if (sector >= dm_table_get_size(snap->ti->table))
2455 continue;
2456
2457 /*
2458 * Remember, different snapshots can have
2459 * different chunk sizes.
2460 */
2461 chunk = sector_to_chunk(snap->store, sector);
2462 dm_exception_table_lock_init(snap, chunk, &lock);
2463
2464 down_read(&snap->lock);
2465 dm_exception_table_lock(&lock);
2466
2467 /* Only deal with valid and active snapshots */
2468 if (!snap->valid || !snap->active)
2469 goto next_snapshot;
2470
2471 pe = __lookup_pending_exception(snap, chunk);
2472 if (!pe) {
2473 /*
2474 * Check exception table to see if block is already
2475 * remapped in this snapshot and trigger an exception
2476 * if not.
2477 */
2478 e = dm_lookup_exception(&snap->complete, chunk);
2479 if (e)
2480 goto next_snapshot;
2481
2482 dm_exception_table_unlock(&lock);
2483 pe = alloc_pending_exception(snap);
2484 dm_exception_table_lock(&lock);
2485
2486 pe2 = __lookup_pending_exception(snap, chunk);
2487
2488 if (!pe2) {
2489 e = dm_lookup_exception(&snap->complete, chunk);
2490 if (e) {
2491 free_pending_exception(pe);
2492 goto next_snapshot;
2493 }
2494
2495 pe = __insert_pending_exception(snap, pe, chunk);
2496 if (!pe) {
2497 dm_exception_table_unlock(&lock);
2498 up_read(&snap->lock);
2499
2500 invalidate_snapshot(snap, -ENOMEM);
2501 continue;
2502 }
2503 } else {
2504 free_pending_exception(pe);
2505 pe = pe2;
2506 }
2507 }
2508
2509 r = DM_MAPIO_SUBMITTED;
2510
2511 /*
2512 * If an origin bio was supplied, queue it to wait for the
2513 * completion of this exception, and start this one last,
2514 * at the end of the function.
2515 */
2516 if (bio) {
2517 bio_list_add(&pe->origin_bios, bio);
2518 bio = NULL;
2519
2520 if (!pe->started) {
2521 pe->started = 1;
2522 pe_to_start_last = pe;
2523 }
2524 }
2525
2526 if (!pe->started) {
2527 pe->started = 1;
2528 pe_to_start_now = pe;
2529 }
2530
2531next_snapshot:
2532 dm_exception_table_unlock(&lock);
2533 up_read(&snap->lock);
2534
2535 if (pe_to_start_now) {
2536 start_copy(pe_to_start_now);
2537 pe_to_start_now = NULL;
2538 }
2539 }
2540
2541 /*
2542 * Submit the exception against which the bio is queued last,
2543 * to give the other exceptions a head start.
2544 */
2545 if (pe_to_start_last)
2546 start_copy(pe_to_start_last);
2547
2548 return r;
2549}
2550
2551/*
2552 * Called on a write from the origin driver.
2553 */
2554static int do_origin(struct dm_dev *origin, struct bio *bio, bool limit)
2555{
2556 struct origin *o;
2557 int r = DM_MAPIO_REMAPPED;
2558
2559again:
2560 down_read(&_origins_lock);
2561 o = __lookup_origin(origin->bdev);
2562 if (o) {
2563 if (limit) {
2564 struct dm_snapshot *s;
2565
2566 list_for_each_entry(s, &o->snapshots, list)
2567 if (unlikely(!wait_for_in_progress(s, true)))
2568 goto again;
2569 }
2570
2571 r = __origin_write(&o->snapshots, bio->bi_iter.bi_sector, bio);
2572 }
2573 up_read(&_origins_lock);
2574
2575 return r;
2576}
2577
2578/*
2579 * Trigger exceptions in all non-merging snapshots.
2580 *
2581 * The chunk size of the merging snapshot may be larger than the chunk
2582 * size of some other snapshot so we may need to reallocate multiple
2583 * chunks in other snapshots.
2584 *
2585 * We scan all the overlapping exceptions in the other snapshots.
2586 * Returns 1 if anything was reallocated and must be waited for,
2587 * otherwise returns 0.
2588 *
2589 * size must be a multiple of merging_snap's chunk_size.
2590 */
2591static int origin_write_extent(struct dm_snapshot *merging_snap,
2592 sector_t sector, unsigned int size)
2593{
2594 int must_wait = 0;
2595 sector_t n;
2596 struct origin *o;
2597
2598 /*
2599 * The origin's __minimum_chunk_size() got stored in max_io_len
2600 * by snapshot_merge_resume().
2601 */
2602 down_read(&_origins_lock);
2603 o = __lookup_origin(merging_snap->origin->bdev);
2604 for (n = 0; n < size; n += merging_snap->ti->max_io_len)
2605 if (__origin_write(&o->snapshots, sector + n, NULL) ==
2606 DM_MAPIO_SUBMITTED)
2607 must_wait = 1;
2608 up_read(&_origins_lock);
2609
2610 return must_wait;
2611}
2612
2613/*
2614 * Origin: maps a linear range of a device, with hooks for snapshotting.
2615 */
2616
2617/*
2618 * Construct an origin mapping: <dev_path>
2619 * The context for an origin is merely a 'struct dm_dev *'
2620 * pointing to the real device.
2621 */
2622static int origin_ctr(struct dm_target *ti, unsigned int argc, char **argv)
2623{
2624 int r;
2625 struct dm_origin *o;
2626
2627 if (argc != 1) {
2628 ti->error = "origin: incorrect number of arguments";
2629 return -EINVAL;
2630 }
2631
2632 o = kmalloc(sizeof(struct dm_origin), GFP_KERNEL);
2633 if (!o) {
2634 ti->error = "Cannot allocate private origin structure";
2635 r = -ENOMEM;
2636 goto bad_alloc;
2637 }
2638
2639 r = dm_get_device(ti, argv[0], dm_table_get_mode(ti->table), &o->dev);
2640 if (r) {
2641 ti->error = "Cannot get target device";
2642 goto bad_open;
2643 }
2644
2645 o->ti = ti;
2646 ti->private = o;
2647 ti->num_flush_bios = 1;
2648
2649 return 0;
2650
2651bad_open:
2652 kfree(o);
2653bad_alloc:
2654 return r;
2655}
2656
2657static void origin_dtr(struct dm_target *ti)
2658{
2659 struct dm_origin *o = ti->private;
2660
2661 dm_put_device(ti, o->dev);
2662 kfree(o);
2663}
2664
2665static int origin_map(struct dm_target *ti, struct bio *bio)
2666{
2667 struct dm_origin *o = ti->private;
2668 unsigned int available_sectors;
2669
2670 bio_set_dev(bio, o->dev->bdev);
2671
2672 if (unlikely(bio->bi_opf & REQ_PREFLUSH))
2673 return DM_MAPIO_REMAPPED;
2674
2675 if (bio_data_dir(bio) != WRITE)
2676 return DM_MAPIO_REMAPPED;
2677
2678 available_sectors = o->split_boundary -
2679 ((unsigned int)bio->bi_iter.bi_sector & (o->split_boundary - 1));
2680
2681 if (bio_sectors(bio) > available_sectors)
2682 dm_accept_partial_bio(bio, available_sectors);
2683
2684 /* Only tell snapshots if this is a write */
2685 return do_origin(o->dev, bio, true);
2686}
2687
2688/*
2689 * Set the target "max_io_len" field to the minimum of all the snapshots'
2690 * chunk sizes.
2691 */
2692static void origin_resume(struct dm_target *ti)
2693{
2694 struct dm_origin *o = ti->private;
2695
2696 o->split_boundary = get_origin_minimum_chunksize(o->dev->bdev);
2697
2698 down_write(&_origins_lock);
2699 __insert_dm_origin(o);
2700 up_write(&_origins_lock);
2701}
2702
2703static void origin_postsuspend(struct dm_target *ti)
2704{
2705 struct dm_origin *o = ti->private;
2706
2707 down_write(&_origins_lock);
2708 __remove_dm_origin(o);
2709 up_write(&_origins_lock);
2710}
2711
2712static void origin_status(struct dm_target *ti, status_type_t type,
2713 unsigned int status_flags, char *result, unsigned int maxlen)
2714{
2715 struct dm_origin *o = ti->private;
2716
2717 switch (type) {
2718 case STATUSTYPE_INFO:
2719 result[0] = '\0';
2720 break;
2721
2722 case STATUSTYPE_TABLE:
2723 snprintf(result, maxlen, "%s", o->dev->name);
2724 break;
2725 case STATUSTYPE_IMA:
2726 result[0] = '\0';
2727 break;
2728 }
2729}
2730
2731static int origin_iterate_devices(struct dm_target *ti,
2732 iterate_devices_callout_fn fn, void *data)
2733{
2734 struct dm_origin *o = ti->private;
2735
2736 return fn(ti, o->dev, 0, ti->len, data);
2737}
2738
2739static struct target_type origin_target = {
2740 .name = "snapshot-origin",
2741 .version = {1, 9, 0},
2742 .module = THIS_MODULE,
2743 .ctr = origin_ctr,
2744 .dtr = origin_dtr,
2745 .map = origin_map,
2746 .resume = origin_resume,
2747 .postsuspend = origin_postsuspend,
2748 .status = origin_status,
2749 .iterate_devices = origin_iterate_devices,
2750};
2751
2752static struct target_type snapshot_target = {
2753 .name = "snapshot",
2754 .version = {1, 16, 0},
2755 .module = THIS_MODULE,
2756 .ctr = snapshot_ctr,
2757 .dtr = snapshot_dtr,
2758 .map = snapshot_map,
2759 .end_io = snapshot_end_io,
2760 .preresume = snapshot_preresume,
2761 .resume = snapshot_resume,
2762 .status = snapshot_status,
2763 .iterate_devices = snapshot_iterate_devices,
2764 .io_hints = snapshot_io_hints,
2765};
2766
2767static struct target_type merge_target = {
2768 .name = dm_snapshot_merge_target_name,
2769 .version = {1, 5, 0},
2770 .module = THIS_MODULE,
2771 .ctr = snapshot_ctr,
2772 .dtr = snapshot_dtr,
2773 .map = snapshot_merge_map,
2774 .end_io = snapshot_end_io,
2775 .presuspend = snapshot_merge_presuspend,
2776 .preresume = snapshot_preresume,
2777 .resume = snapshot_merge_resume,
2778 .status = snapshot_status,
2779 .iterate_devices = snapshot_iterate_devices,
2780 .io_hints = snapshot_io_hints,
2781};
2782
2783static int __init dm_snapshot_init(void)
2784{
2785 int r;
2786
2787 r = dm_exception_store_init();
2788 if (r) {
2789 DMERR("Failed to initialize exception stores");
2790 return r;
2791 }
2792
2793 r = init_origin_hash();
2794 if (r) {
2795 DMERR("init_origin_hash failed.");
2796 goto bad_origin_hash;
2797 }
2798
2799 exception_cache = KMEM_CACHE(dm_exception, 0);
2800 if (!exception_cache) {
2801 DMERR("Couldn't create exception cache.");
2802 r = -ENOMEM;
2803 goto bad_exception_cache;
2804 }
2805
2806 pending_cache = KMEM_CACHE(dm_snap_pending_exception, 0);
2807 if (!pending_cache) {
2808 DMERR("Couldn't create pending cache.");
2809 r = -ENOMEM;
2810 goto bad_pending_cache;
2811 }
2812
2813 r = dm_register_target(&snapshot_target);
2814 if (r < 0)
2815 goto bad_register_snapshot_target;
2816
2817 r = dm_register_target(&origin_target);
2818 if (r < 0)
2819 goto bad_register_origin_target;
2820
2821 r = dm_register_target(&merge_target);
2822 if (r < 0)
2823 goto bad_register_merge_target;
2824
2825 return 0;
2826
2827bad_register_merge_target:
2828 dm_unregister_target(&origin_target);
2829bad_register_origin_target:
2830 dm_unregister_target(&snapshot_target);
2831bad_register_snapshot_target:
2832 kmem_cache_destroy(pending_cache);
2833bad_pending_cache:
2834 kmem_cache_destroy(exception_cache);
2835bad_exception_cache:
2836 exit_origin_hash();
2837bad_origin_hash:
2838 dm_exception_store_exit();
2839
2840 return r;
2841}
2842
2843static void __exit dm_snapshot_exit(void)
2844{
2845 dm_unregister_target(&snapshot_target);
2846 dm_unregister_target(&origin_target);
2847 dm_unregister_target(&merge_target);
2848
2849 exit_origin_hash();
2850 kmem_cache_destroy(pending_cache);
2851 kmem_cache_destroy(exception_cache);
2852
2853 dm_exception_store_exit();
2854}
2855
2856/* Module hooks */
2857module_init(dm_snapshot_init);
2858module_exit(dm_snapshot_exit);
2859
2860MODULE_DESCRIPTION(DM_NAME " snapshot target");
2861MODULE_AUTHOR("Joe Thornber");
2862MODULE_LICENSE("GPL");
2863MODULE_ALIAS("dm-snapshot-origin");
2864MODULE_ALIAS("dm-snapshot-merge");
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
27static 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
41struct dm_exception_table {
42 uint32_t hash_mask;
43 unsigned hash_shift;
44 struct list_head *table;
45};
46
47struct 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 /* Protected by "lock" */
70 sector_t exception_start_sequence;
71
72 /* Protected by kcopyd single-threaded callback */
73 sector_t exception_complete_sequence;
74
75 /*
76 * A list of pending exceptions that completed out of order.
77 * Protected by kcopyd single-threaded callback.
78 */
79 struct list_head out_of_order_list;
80
81 mempool_t *pending_pool;
82
83 struct dm_exception_table pending;
84 struct dm_exception_table complete;
85
86 /*
87 * pe_lock protects all pending_exception operations and access
88 * as well as the snapshot_bios list.
89 */
90 spinlock_t pe_lock;
91
92 /* Chunks with outstanding reads */
93 spinlock_t tracked_chunk_lock;
94 struct hlist_head tracked_chunk_hash[DM_TRACKED_CHUNK_HASH_SIZE];
95
96 /* The on disk metadata handler */
97 struct dm_exception_store *store;
98
99 struct dm_kcopyd_client *kcopyd_client;
100
101 /* Wait for events based on state_bits */
102 unsigned long state_bits;
103
104 /* Range of chunks currently being merged. */
105 chunk_t first_merging_chunk;
106 int num_merging_chunks;
107
108 /*
109 * The merge operation failed if this flag is set.
110 * Failure modes are handled as follows:
111 * - I/O error reading the header
112 * => don't load the target; abort.
113 * - Header does not have "valid" flag set
114 * => use the origin; forget about the snapshot.
115 * - I/O error when reading exceptions
116 * => don't load the target; abort.
117 * (We can't use the intermediate origin state.)
118 * - I/O error while merging
119 * => stop merging; set merge_failed; process I/O normally.
120 */
121 int merge_failed;
122
123 /*
124 * Incoming bios that overlap with chunks being merged must wait
125 * for them to be committed.
126 */
127 struct bio_list bios_queued_during_merge;
128};
129
130/*
131 * state_bits:
132 * RUNNING_MERGE - Merge operation is in progress.
133 * SHUTDOWN_MERGE - Set to signal that merge needs to be stopped;
134 * cleared afterwards.
135 */
136#define RUNNING_MERGE 0
137#define SHUTDOWN_MERGE 1
138
139DECLARE_DM_KCOPYD_THROTTLE_WITH_MODULE_PARM(snapshot_copy_throttle,
140 "A percentage of time allocated for copy on write");
141
142struct dm_dev *dm_snap_origin(struct dm_snapshot *s)
143{
144 return s->origin;
145}
146EXPORT_SYMBOL(dm_snap_origin);
147
148struct dm_dev *dm_snap_cow(struct dm_snapshot *s)
149{
150 return s->cow;
151}
152EXPORT_SYMBOL(dm_snap_cow);
153
154static sector_t chunk_to_sector(struct dm_exception_store *store,
155 chunk_t chunk)
156{
157 return chunk << store->chunk_shift;
158}
159
160static int bdev_equal(struct block_device *lhs, struct block_device *rhs)
161{
162 /*
163 * There is only ever one instance of a particular block
164 * device so we can compare pointers safely.
165 */
166 return lhs == rhs;
167}
168
169struct dm_snap_pending_exception {
170 struct dm_exception e;
171
172 /*
173 * Origin buffers waiting for this to complete are held
174 * in a bio list
175 */
176 struct bio_list origin_bios;
177 struct bio_list snapshot_bios;
178
179 /* Pointer back to snapshot context */
180 struct dm_snapshot *snap;
181
182 /*
183 * 1 indicates the exception has already been sent to
184 * kcopyd.
185 */
186 int started;
187
188 /* There was copying error. */
189 int copy_error;
190
191 /* A sequence number, it is used for in-order completion. */
192 sector_t exception_sequence;
193
194 struct list_head out_of_order_entry;
195
196 /*
197 * For writing a complete chunk, bypassing the copy.
198 */
199 struct bio *full_bio;
200 bio_end_io_t *full_bio_end_io;
201 void *full_bio_private;
202};
203
204/*
205 * Hash table mapping origin volumes to lists of snapshots and
206 * a lock to protect it
207 */
208static struct kmem_cache *exception_cache;
209static struct kmem_cache *pending_cache;
210
211struct dm_snap_tracked_chunk {
212 struct hlist_node node;
213 chunk_t chunk;
214};
215
216static void init_tracked_chunk(struct bio *bio)
217{
218 struct dm_snap_tracked_chunk *c = dm_per_bio_data(bio, sizeof(struct dm_snap_tracked_chunk));
219 INIT_HLIST_NODE(&c->node);
220}
221
222static bool is_bio_tracked(struct bio *bio)
223{
224 struct dm_snap_tracked_chunk *c = dm_per_bio_data(bio, sizeof(struct dm_snap_tracked_chunk));
225 return !hlist_unhashed(&c->node);
226}
227
228static void track_chunk(struct dm_snapshot *s, struct bio *bio, chunk_t chunk)
229{
230 struct dm_snap_tracked_chunk *c = dm_per_bio_data(bio, sizeof(struct dm_snap_tracked_chunk));
231
232 c->chunk = chunk;
233
234 spin_lock_irq(&s->tracked_chunk_lock);
235 hlist_add_head(&c->node,
236 &s->tracked_chunk_hash[DM_TRACKED_CHUNK_HASH(chunk)]);
237 spin_unlock_irq(&s->tracked_chunk_lock);
238}
239
240static void stop_tracking_chunk(struct dm_snapshot *s, struct bio *bio)
241{
242 struct dm_snap_tracked_chunk *c = dm_per_bio_data(bio, sizeof(struct dm_snap_tracked_chunk));
243 unsigned long flags;
244
245 spin_lock_irqsave(&s->tracked_chunk_lock, flags);
246 hlist_del(&c->node);
247 spin_unlock_irqrestore(&s->tracked_chunk_lock, flags);
248}
249
250static int __chunk_is_tracked(struct dm_snapshot *s, chunk_t chunk)
251{
252 struct dm_snap_tracked_chunk *c;
253 int found = 0;
254
255 spin_lock_irq(&s->tracked_chunk_lock);
256
257 hlist_for_each_entry(c,
258 &s->tracked_chunk_hash[DM_TRACKED_CHUNK_HASH(chunk)], node) {
259 if (c->chunk == chunk) {
260 found = 1;
261 break;
262 }
263 }
264
265 spin_unlock_irq(&s->tracked_chunk_lock);
266
267 return found;
268}
269
270/*
271 * This conflicting I/O is extremely improbable in the caller,
272 * so msleep(1) is sufficient and there is no need for a wait queue.
273 */
274static void __check_for_conflicting_io(struct dm_snapshot *s, chunk_t chunk)
275{
276 while (__chunk_is_tracked(s, chunk))
277 msleep(1);
278}
279
280/*
281 * One of these per registered origin, held in the snapshot_origins hash
282 */
283struct origin {
284 /* The origin device */
285 struct block_device *bdev;
286
287 struct list_head hash_list;
288
289 /* List of snapshots for this origin */
290 struct list_head snapshots;
291};
292
293/*
294 * Size of the hash table for origin volumes. If we make this
295 * the size of the minors list then it should be nearly perfect
296 */
297#define ORIGIN_HASH_SIZE 256
298#define ORIGIN_MASK 0xFF
299static struct list_head *_origins;
300static struct rw_semaphore _origins_lock;
301
302static DECLARE_WAIT_QUEUE_HEAD(_pending_exceptions_done);
303static DEFINE_SPINLOCK(_pending_exceptions_done_spinlock);
304static uint64_t _pending_exceptions_done_count;
305
306static int init_origin_hash(void)
307{
308 int i;
309
310 _origins = kmalloc(ORIGIN_HASH_SIZE * sizeof(struct list_head),
311 GFP_KERNEL);
312 if (!_origins) {
313 DMERR("unable to allocate memory");
314 return -ENOMEM;
315 }
316
317 for (i = 0; i < ORIGIN_HASH_SIZE; i++)
318 INIT_LIST_HEAD(_origins + i);
319 init_rwsem(&_origins_lock);
320
321 return 0;
322}
323
324static void exit_origin_hash(void)
325{
326 kfree(_origins);
327}
328
329static unsigned origin_hash(struct block_device *bdev)
330{
331 return bdev->bd_dev & ORIGIN_MASK;
332}
333
334static struct origin *__lookup_origin(struct block_device *origin)
335{
336 struct list_head *ol;
337 struct origin *o;
338
339 ol = &_origins[origin_hash(origin)];
340 list_for_each_entry (o, ol, hash_list)
341 if (bdev_equal(o->bdev, origin))
342 return o;
343
344 return NULL;
345}
346
347static void __insert_origin(struct origin *o)
348{
349 struct list_head *sl = &_origins[origin_hash(o->bdev)];
350 list_add_tail(&o->hash_list, sl);
351}
352
353/*
354 * _origins_lock must be held when calling this function.
355 * Returns number of snapshots registered using the supplied cow device, plus:
356 * snap_src - a snapshot suitable for use as a source of exception handover
357 * snap_dest - a snapshot capable of receiving exception handover.
358 * snap_merge - an existing snapshot-merge target linked to the same origin.
359 * There can be at most one snapshot-merge target. The parameter is optional.
360 *
361 * Possible return values and states of snap_src and snap_dest.
362 * 0: NULL, NULL - first new snapshot
363 * 1: snap_src, NULL - normal snapshot
364 * 2: snap_src, snap_dest - waiting for handover
365 * 2: snap_src, NULL - handed over, waiting for old to be deleted
366 * 1: NULL, snap_dest - source got destroyed without handover
367 */
368static int __find_snapshots_sharing_cow(struct dm_snapshot *snap,
369 struct dm_snapshot **snap_src,
370 struct dm_snapshot **snap_dest,
371 struct dm_snapshot **snap_merge)
372{
373 struct dm_snapshot *s;
374 struct origin *o;
375 int count = 0;
376 int active;
377
378 o = __lookup_origin(snap->origin->bdev);
379 if (!o)
380 goto out;
381
382 list_for_each_entry(s, &o->snapshots, list) {
383 if (dm_target_is_snapshot_merge(s->ti) && snap_merge)
384 *snap_merge = s;
385 if (!bdev_equal(s->cow->bdev, snap->cow->bdev))
386 continue;
387
388 down_read(&s->lock);
389 active = s->active;
390 up_read(&s->lock);
391
392 if (active) {
393 if (snap_src)
394 *snap_src = s;
395 } else if (snap_dest)
396 *snap_dest = s;
397
398 count++;
399 }
400
401out:
402 return count;
403}
404
405/*
406 * On success, returns 1 if this snapshot is a handover destination,
407 * otherwise returns 0.
408 */
409static int __validate_exception_handover(struct dm_snapshot *snap)
410{
411 struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
412 struct dm_snapshot *snap_merge = NULL;
413
414 /* Does snapshot need exceptions handed over to it? */
415 if ((__find_snapshots_sharing_cow(snap, &snap_src, &snap_dest,
416 &snap_merge) == 2) ||
417 snap_dest) {
418 snap->ti->error = "Snapshot cow pairing for exception "
419 "table handover failed";
420 return -EINVAL;
421 }
422
423 /*
424 * If no snap_src was found, snap cannot become a handover
425 * destination.
426 */
427 if (!snap_src)
428 return 0;
429
430 /*
431 * Non-snapshot-merge handover?
432 */
433 if (!dm_target_is_snapshot_merge(snap->ti))
434 return 1;
435
436 /*
437 * Do not allow more than one merging snapshot.
438 */
439 if (snap_merge) {
440 snap->ti->error = "A snapshot is already merging.";
441 return -EINVAL;
442 }
443
444 if (!snap_src->store->type->prepare_merge ||
445 !snap_src->store->type->commit_merge) {
446 snap->ti->error = "Snapshot exception store does not "
447 "support snapshot-merge.";
448 return -EINVAL;
449 }
450
451 return 1;
452}
453
454static void __insert_snapshot(struct origin *o, struct dm_snapshot *s)
455{
456 struct dm_snapshot *l;
457
458 /* Sort the list according to chunk size, largest-first smallest-last */
459 list_for_each_entry(l, &o->snapshots, list)
460 if (l->store->chunk_size < s->store->chunk_size)
461 break;
462 list_add_tail(&s->list, &l->list);
463}
464
465/*
466 * Make a note of the snapshot and its origin so we can look it
467 * up when the origin has a write on it.
468 *
469 * Also validate snapshot exception store handovers.
470 * On success, returns 1 if this registration is a handover destination,
471 * otherwise returns 0.
472 */
473static int register_snapshot(struct dm_snapshot *snap)
474{
475 struct origin *o, *new_o = NULL;
476 struct block_device *bdev = snap->origin->bdev;
477 int r = 0;
478
479 new_o = kmalloc(sizeof(*new_o), GFP_KERNEL);
480 if (!new_o)
481 return -ENOMEM;
482
483 down_write(&_origins_lock);
484
485 r = __validate_exception_handover(snap);
486 if (r < 0) {
487 kfree(new_o);
488 goto out;
489 }
490
491 o = __lookup_origin(bdev);
492 if (o)
493 kfree(new_o);
494 else {
495 /* New origin */
496 o = new_o;
497
498 /* Initialise the struct */
499 INIT_LIST_HEAD(&o->snapshots);
500 o->bdev = bdev;
501
502 __insert_origin(o);
503 }
504
505 __insert_snapshot(o, snap);
506
507out:
508 up_write(&_origins_lock);
509
510 return r;
511}
512
513/*
514 * Move snapshot to correct place in list according to chunk size.
515 */
516static void reregister_snapshot(struct dm_snapshot *s)
517{
518 struct block_device *bdev = s->origin->bdev;
519
520 down_write(&_origins_lock);
521
522 list_del(&s->list);
523 __insert_snapshot(__lookup_origin(bdev), s);
524
525 up_write(&_origins_lock);
526}
527
528static void unregister_snapshot(struct dm_snapshot *s)
529{
530 struct origin *o;
531
532 down_write(&_origins_lock);
533 o = __lookup_origin(s->origin->bdev);
534
535 list_del(&s->list);
536 if (o && list_empty(&o->snapshots)) {
537 list_del(&o->hash_list);
538 kfree(o);
539 }
540
541 up_write(&_origins_lock);
542}
543
544/*
545 * Implementation of the exception hash tables.
546 * The lowest hash_shift bits of the chunk number are ignored, allowing
547 * some consecutive chunks to be grouped together.
548 */
549static int dm_exception_table_init(struct dm_exception_table *et,
550 uint32_t size, unsigned hash_shift)
551{
552 unsigned int i;
553
554 et->hash_shift = hash_shift;
555 et->hash_mask = size - 1;
556 et->table = dm_vcalloc(size, sizeof(struct list_head));
557 if (!et->table)
558 return -ENOMEM;
559
560 for (i = 0; i < size; i++)
561 INIT_LIST_HEAD(et->table + i);
562
563 return 0;
564}
565
566static void dm_exception_table_exit(struct dm_exception_table *et,
567 struct kmem_cache *mem)
568{
569 struct list_head *slot;
570 struct dm_exception *ex, *next;
571 int i, size;
572
573 size = et->hash_mask + 1;
574 for (i = 0; i < size; i++) {
575 slot = et->table + i;
576
577 list_for_each_entry_safe (ex, next, slot, hash_list)
578 kmem_cache_free(mem, ex);
579 }
580
581 vfree(et->table);
582}
583
584static uint32_t exception_hash(struct dm_exception_table *et, chunk_t chunk)
585{
586 return (chunk >> et->hash_shift) & et->hash_mask;
587}
588
589static void dm_remove_exception(struct dm_exception *e)
590{
591 list_del(&e->hash_list);
592}
593
594/*
595 * Return the exception data for a sector, or NULL if not
596 * remapped.
597 */
598static struct dm_exception *dm_lookup_exception(struct dm_exception_table *et,
599 chunk_t chunk)
600{
601 struct list_head *slot;
602 struct dm_exception *e;
603
604 slot = &et->table[exception_hash(et, chunk)];
605 list_for_each_entry (e, slot, hash_list)
606 if (chunk >= e->old_chunk &&
607 chunk <= e->old_chunk + dm_consecutive_chunk_count(e))
608 return e;
609
610 return NULL;
611}
612
613static struct dm_exception *alloc_completed_exception(gfp_t gfp)
614{
615 struct dm_exception *e;
616
617 e = kmem_cache_alloc(exception_cache, gfp);
618 if (!e && gfp == GFP_NOIO)
619 e = kmem_cache_alloc(exception_cache, GFP_ATOMIC);
620
621 return e;
622}
623
624static void free_completed_exception(struct dm_exception *e)
625{
626 kmem_cache_free(exception_cache, e);
627}
628
629static struct dm_snap_pending_exception *alloc_pending_exception(struct dm_snapshot *s)
630{
631 struct dm_snap_pending_exception *pe = mempool_alloc(s->pending_pool,
632 GFP_NOIO);
633
634 atomic_inc(&s->pending_exceptions_count);
635 pe->snap = s;
636
637 return pe;
638}
639
640static void free_pending_exception(struct dm_snap_pending_exception *pe)
641{
642 struct dm_snapshot *s = pe->snap;
643
644 mempool_free(pe, s->pending_pool);
645 smp_mb__before_atomic_dec();
646 atomic_dec(&s->pending_exceptions_count);
647}
648
649static void dm_insert_exception(struct dm_exception_table *eh,
650 struct dm_exception *new_e)
651{
652 struct list_head *l;
653 struct dm_exception *e = NULL;
654
655 l = &eh->table[exception_hash(eh, new_e->old_chunk)];
656
657 /* Add immediately if this table doesn't support consecutive chunks */
658 if (!eh->hash_shift)
659 goto out;
660
661 /* List is ordered by old_chunk */
662 list_for_each_entry_reverse(e, l, hash_list) {
663 /* Insert after an existing chunk? */
664 if (new_e->old_chunk == (e->old_chunk +
665 dm_consecutive_chunk_count(e) + 1) &&
666 new_e->new_chunk == (dm_chunk_number(e->new_chunk) +
667 dm_consecutive_chunk_count(e) + 1)) {
668 dm_consecutive_chunk_count_inc(e);
669 free_completed_exception(new_e);
670 return;
671 }
672
673 /* Insert before an existing chunk? */
674 if (new_e->old_chunk == (e->old_chunk - 1) &&
675 new_e->new_chunk == (dm_chunk_number(e->new_chunk) - 1)) {
676 dm_consecutive_chunk_count_inc(e);
677 e->old_chunk--;
678 e->new_chunk--;
679 free_completed_exception(new_e);
680 return;
681 }
682
683 if (new_e->old_chunk > e->old_chunk)
684 break;
685 }
686
687out:
688 list_add(&new_e->hash_list, e ? &e->hash_list : l);
689}
690
691/*
692 * Callback used by the exception stores to load exceptions when
693 * initialising.
694 */
695static int dm_add_exception(void *context, chunk_t old, chunk_t new)
696{
697 struct dm_snapshot *s = context;
698 struct dm_exception *e;
699
700 e = alloc_completed_exception(GFP_KERNEL);
701 if (!e)
702 return -ENOMEM;
703
704 e->old_chunk = old;
705
706 /* Consecutive_count is implicitly initialised to zero */
707 e->new_chunk = new;
708
709 dm_insert_exception(&s->complete, e);
710
711 return 0;
712}
713
714/*
715 * Return a minimum chunk size of all snapshots that have the specified origin.
716 * Return zero if the origin has no snapshots.
717 */
718static uint32_t __minimum_chunk_size(struct origin *o)
719{
720 struct dm_snapshot *snap;
721 unsigned chunk_size = 0;
722
723 if (o)
724 list_for_each_entry(snap, &o->snapshots, list)
725 chunk_size = min_not_zero(chunk_size,
726 snap->store->chunk_size);
727
728 return (uint32_t) chunk_size;
729}
730
731/*
732 * Hard coded magic.
733 */
734static int calc_max_buckets(void)
735{
736 /* use a fixed size of 2MB */
737 unsigned long mem = 2 * 1024 * 1024;
738 mem /= sizeof(struct list_head);
739
740 return mem;
741}
742
743/*
744 * Allocate room for a suitable hash table.
745 */
746static int init_hash_tables(struct dm_snapshot *s)
747{
748 sector_t hash_size, cow_dev_size, max_buckets;
749
750 /*
751 * Calculate based on the size of the original volume or
752 * the COW volume...
753 */
754 cow_dev_size = get_dev_size(s->cow->bdev);
755 max_buckets = calc_max_buckets();
756
757 hash_size = cow_dev_size >> s->store->chunk_shift;
758 hash_size = min(hash_size, max_buckets);
759
760 if (hash_size < 64)
761 hash_size = 64;
762 hash_size = rounddown_pow_of_two(hash_size);
763 if (dm_exception_table_init(&s->complete, hash_size,
764 DM_CHUNK_CONSECUTIVE_BITS))
765 return -ENOMEM;
766
767 /*
768 * Allocate hash table for in-flight exceptions
769 * Make this smaller than the real hash table
770 */
771 hash_size >>= 3;
772 if (hash_size < 64)
773 hash_size = 64;
774
775 if (dm_exception_table_init(&s->pending, hash_size, 0)) {
776 dm_exception_table_exit(&s->complete, exception_cache);
777 return -ENOMEM;
778 }
779
780 return 0;
781}
782
783static void merge_shutdown(struct dm_snapshot *s)
784{
785 clear_bit_unlock(RUNNING_MERGE, &s->state_bits);
786 smp_mb__after_clear_bit();
787 wake_up_bit(&s->state_bits, RUNNING_MERGE);
788}
789
790static struct bio *__release_queued_bios_after_merge(struct dm_snapshot *s)
791{
792 s->first_merging_chunk = 0;
793 s->num_merging_chunks = 0;
794
795 return bio_list_get(&s->bios_queued_during_merge);
796}
797
798/*
799 * Remove one chunk from the index of completed exceptions.
800 */
801static int __remove_single_exception_chunk(struct dm_snapshot *s,
802 chunk_t old_chunk)
803{
804 struct dm_exception *e;
805
806 e = dm_lookup_exception(&s->complete, old_chunk);
807 if (!e) {
808 DMERR("Corruption detected: exception for block %llu is "
809 "on disk but not in memory",
810 (unsigned long long)old_chunk);
811 return -EINVAL;
812 }
813
814 /*
815 * If this is the only chunk using this exception, remove exception.
816 */
817 if (!dm_consecutive_chunk_count(e)) {
818 dm_remove_exception(e);
819 free_completed_exception(e);
820 return 0;
821 }
822
823 /*
824 * The chunk may be either at the beginning or the end of a
825 * group of consecutive chunks - never in the middle. We are
826 * removing chunks in the opposite order to that in which they
827 * were added, so this should always be true.
828 * Decrement the consecutive chunk counter and adjust the
829 * starting point if necessary.
830 */
831 if (old_chunk == e->old_chunk) {
832 e->old_chunk++;
833 e->new_chunk++;
834 } else if (old_chunk != e->old_chunk +
835 dm_consecutive_chunk_count(e)) {
836 DMERR("Attempt to merge block %llu from the "
837 "middle of a chunk range [%llu - %llu]",
838 (unsigned long long)old_chunk,
839 (unsigned long long)e->old_chunk,
840 (unsigned long long)
841 e->old_chunk + dm_consecutive_chunk_count(e));
842 return -EINVAL;
843 }
844
845 dm_consecutive_chunk_count_dec(e);
846
847 return 0;
848}
849
850static void flush_bios(struct bio *bio);
851
852static int remove_single_exception_chunk(struct dm_snapshot *s)
853{
854 struct bio *b = NULL;
855 int r;
856 chunk_t old_chunk = s->first_merging_chunk + s->num_merging_chunks - 1;
857
858 down_write(&s->lock);
859
860 /*
861 * Process chunks (and associated exceptions) in reverse order
862 * so that dm_consecutive_chunk_count_dec() accounting works.
863 */
864 do {
865 r = __remove_single_exception_chunk(s, old_chunk);
866 if (r)
867 goto out;
868 } while (old_chunk-- > s->first_merging_chunk);
869
870 b = __release_queued_bios_after_merge(s);
871
872out:
873 up_write(&s->lock);
874 if (b)
875 flush_bios(b);
876
877 return r;
878}
879
880static int origin_write_extent(struct dm_snapshot *merging_snap,
881 sector_t sector, unsigned chunk_size);
882
883static void merge_callback(int read_err, unsigned long write_err,
884 void *context);
885
886static uint64_t read_pending_exceptions_done_count(void)
887{
888 uint64_t pending_exceptions_done;
889
890 spin_lock(&_pending_exceptions_done_spinlock);
891 pending_exceptions_done = _pending_exceptions_done_count;
892 spin_unlock(&_pending_exceptions_done_spinlock);
893
894 return pending_exceptions_done;
895}
896
897static void increment_pending_exceptions_done_count(void)
898{
899 spin_lock(&_pending_exceptions_done_spinlock);
900 _pending_exceptions_done_count++;
901 spin_unlock(&_pending_exceptions_done_spinlock);
902
903 wake_up_all(&_pending_exceptions_done);
904}
905
906static void snapshot_merge_next_chunks(struct dm_snapshot *s)
907{
908 int i, linear_chunks;
909 chunk_t old_chunk, new_chunk;
910 struct dm_io_region src, dest;
911 sector_t io_size;
912 uint64_t previous_count;
913
914 BUG_ON(!test_bit(RUNNING_MERGE, &s->state_bits));
915 if (unlikely(test_bit(SHUTDOWN_MERGE, &s->state_bits)))
916 goto shut;
917
918 /*
919 * valid flag never changes during merge, so no lock required.
920 */
921 if (!s->valid) {
922 DMERR("Snapshot is invalid: can't merge");
923 goto shut;
924 }
925
926 linear_chunks = s->store->type->prepare_merge(s->store, &old_chunk,
927 &new_chunk);
928 if (linear_chunks <= 0) {
929 if (linear_chunks < 0) {
930 DMERR("Read error in exception store: "
931 "shutting down merge");
932 down_write(&s->lock);
933 s->merge_failed = 1;
934 up_write(&s->lock);
935 }
936 goto shut;
937 }
938
939 /* Adjust old_chunk and new_chunk to reflect start of linear region */
940 old_chunk = old_chunk + 1 - linear_chunks;
941 new_chunk = new_chunk + 1 - linear_chunks;
942
943 /*
944 * Use one (potentially large) I/O to copy all 'linear_chunks'
945 * from the exception store to the origin
946 */
947 io_size = linear_chunks * s->store->chunk_size;
948
949 dest.bdev = s->origin->bdev;
950 dest.sector = chunk_to_sector(s->store, old_chunk);
951 dest.count = min(io_size, get_dev_size(dest.bdev) - dest.sector);
952
953 src.bdev = s->cow->bdev;
954 src.sector = chunk_to_sector(s->store, new_chunk);
955 src.count = dest.count;
956
957 /*
958 * Reallocate any exceptions needed in other snapshots then
959 * wait for the pending exceptions to complete.
960 * Each time any pending exception (globally on the system)
961 * completes we are woken and repeat the process to find out
962 * if we can proceed. While this may not seem a particularly
963 * efficient algorithm, it is not expected to have any
964 * significant impact on performance.
965 */
966 previous_count = read_pending_exceptions_done_count();
967 while (origin_write_extent(s, dest.sector, io_size)) {
968 wait_event(_pending_exceptions_done,
969 (read_pending_exceptions_done_count() !=
970 previous_count));
971 /* Retry after the wait, until all exceptions are done. */
972 previous_count = read_pending_exceptions_done_count();
973 }
974
975 down_write(&s->lock);
976 s->first_merging_chunk = old_chunk;
977 s->num_merging_chunks = linear_chunks;
978 up_write(&s->lock);
979
980 /* Wait until writes to all 'linear_chunks' drain */
981 for (i = 0; i < linear_chunks; i++)
982 __check_for_conflicting_io(s, old_chunk + i);
983
984 dm_kcopyd_copy(s->kcopyd_client, &src, 1, &dest, 0, merge_callback, s);
985 return;
986
987shut:
988 merge_shutdown(s);
989}
990
991static void error_bios(struct bio *bio);
992
993static void merge_callback(int read_err, unsigned long write_err, void *context)
994{
995 struct dm_snapshot *s = context;
996 struct bio *b = NULL;
997
998 if (read_err || write_err) {
999 if (read_err)
1000 DMERR("Read error: shutting down merge.");
1001 else
1002 DMERR("Write error: shutting down merge.");
1003 goto shut;
1004 }
1005
1006 if (s->store->type->commit_merge(s->store,
1007 s->num_merging_chunks) < 0) {
1008 DMERR("Write error in exception store: shutting down merge");
1009 goto shut;
1010 }
1011
1012 if (remove_single_exception_chunk(s) < 0)
1013 goto shut;
1014
1015 snapshot_merge_next_chunks(s);
1016
1017 return;
1018
1019shut:
1020 down_write(&s->lock);
1021 s->merge_failed = 1;
1022 b = __release_queued_bios_after_merge(s);
1023 up_write(&s->lock);
1024 error_bios(b);
1025
1026 merge_shutdown(s);
1027}
1028
1029static void start_merge(struct dm_snapshot *s)
1030{
1031 if (!test_and_set_bit(RUNNING_MERGE, &s->state_bits))
1032 snapshot_merge_next_chunks(s);
1033}
1034
1035static int wait_schedule(void *ptr)
1036{
1037 schedule();
1038
1039 return 0;
1040}
1041
1042/*
1043 * Stop the merging process and wait until it finishes.
1044 */
1045static void stop_merge(struct dm_snapshot *s)
1046{
1047 set_bit(SHUTDOWN_MERGE, &s->state_bits);
1048 wait_on_bit(&s->state_bits, RUNNING_MERGE, wait_schedule,
1049 TASK_UNINTERRUPTIBLE);
1050 clear_bit(SHUTDOWN_MERGE, &s->state_bits);
1051}
1052
1053/*
1054 * Construct a snapshot mapping: <origin_dev> <COW-dev> <p/n> <chunk-size>
1055 */
1056static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
1057{
1058 struct dm_snapshot *s;
1059 int i;
1060 int r = -EINVAL;
1061 char *origin_path, *cow_path;
1062 unsigned args_used, num_flush_bios = 1;
1063 fmode_t origin_mode = FMODE_READ;
1064
1065 if (argc != 4) {
1066 ti->error = "requires exactly 4 arguments";
1067 r = -EINVAL;
1068 goto bad;
1069 }
1070
1071 if (dm_target_is_snapshot_merge(ti)) {
1072 num_flush_bios = 2;
1073 origin_mode = FMODE_WRITE;
1074 }
1075
1076 s = kmalloc(sizeof(*s), GFP_KERNEL);
1077 if (!s) {
1078 ti->error = "Cannot allocate private snapshot structure";
1079 r = -ENOMEM;
1080 goto bad;
1081 }
1082
1083 origin_path = argv[0];
1084 argv++;
1085 argc--;
1086
1087 r = dm_get_device(ti, origin_path, origin_mode, &s->origin);
1088 if (r) {
1089 ti->error = "Cannot get origin device";
1090 goto bad_origin;
1091 }
1092
1093 cow_path = argv[0];
1094 argv++;
1095 argc--;
1096
1097 r = dm_get_device(ti, cow_path, dm_table_get_mode(ti->table), &s->cow);
1098 if (r) {
1099 ti->error = "Cannot get COW device";
1100 goto bad_cow;
1101 }
1102
1103 r = dm_exception_store_create(ti, argc, argv, s, &args_used, &s->store);
1104 if (r) {
1105 ti->error = "Couldn't create exception store";
1106 r = -EINVAL;
1107 goto bad_store;
1108 }
1109
1110 argv += args_used;
1111 argc -= args_used;
1112
1113 s->ti = ti;
1114 s->valid = 1;
1115 s->active = 0;
1116 atomic_set(&s->pending_exceptions_count, 0);
1117 s->exception_start_sequence = 0;
1118 s->exception_complete_sequence = 0;
1119 INIT_LIST_HEAD(&s->out_of_order_list);
1120 init_rwsem(&s->lock);
1121 INIT_LIST_HEAD(&s->list);
1122 spin_lock_init(&s->pe_lock);
1123 s->state_bits = 0;
1124 s->merge_failed = 0;
1125 s->first_merging_chunk = 0;
1126 s->num_merging_chunks = 0;
1127 bio_list_init(&s->bios_queued_during_merge);
1128
1129 /* Allocate hash table for COW data */
1130 if (init_hash_tables(s)) {
1131 ti->error = "Unable to allocate hash table space";
1132 r = -ENOMEM;
1133 goto bad_hash_tables;
1134 }
1135
1136 s->kcopyd_client = dm_kcopyd_client_create(&dm_kcopyd_throttle);
1137 if (IS_ERR(s->kcopyd_client)) {
1138 r = PTR_ERR(s->kcopyd_client);
1139 ti->error = "Could not create kcopyd client";
1140 goto bad_kcopyd;
1141 }
1142
1143 s->pending_pool = mempool_create_slab_pool(MIN_IOS, pending_cache);
1144 if (!s->pending_pool) {
1145 ti->error = "Could not allocate mempool for pending exceptions";
1146 r = -ENOMEM;
1147 goto bad_pending_pool;
1148 }
1149
1150 for (i = 0; i < DM_TRACKED_CHUNK_HASH_SIZE; i++)
1151 INIT_HLIST_HEAD(&s->tracked_chunk_hash[i]);
1152
1153 spin_lock_init(&s->tracked_chunk_lock);
1154
1155 ti->private = s;
1156 ti->num_flush_bios = num_flush_bios;
1157 ti->per_bio_data_size = sizeof(struct dm_snap_tracked_chunk);
1158
1159 /* Add snapshot to the list of snapshots for this origin */
1160 /* Exceptions aren't triggered till snapshot_resume() is called */
1161 r = register_snapshot(s);
1162 if (r == -ENOMEM) {
1163 ti->error = "Snapshot origin struct allocation failed";
1164 goto bad_load_and_register;
1165 } else if (r < 0) {
1166 /* invalid handover, register_snapshot has set ti->error */
1167 goto bad_load_and_register;
1168 }
1169
1170 /*
1171 * Metadata must only be loaded into one table at once, so skip this
1172 * if metadata will be handed over during resume.
1173 * Chunk size will be set during the handover - set it to zero to
1174 * ensure it's ignored.
1175 */
1176 if (r > 0) {
1177 s->store->chunk_size = 0;
1178 return 0;
1179 }
1180
1181 r = s->store->type->read_metadata(s->store, dm_add_exception,
1182 (void *)s);
1183 if (r < 0) {
1184 ti->error = "Failed to read snapshot metadata";
1185 goto bad_read_metadata;
1186 } else if (r > 0) {
1187 s->valid = 0;
1188 DMWARN("Snapshot is marked invalid.");
1189 }
1190
1191 if (!s->store->chunk_size) {
1192 ti->error = "Chunk size not set";
1193 goto bad_read_metadata;
1194 }
1195
1196 r = dm_set_target_max_io_len(ti, s->store->chunk_size);
1197 if (r)
1198 goto bad_read_metadata;
1199
1200 return 0;
1201
1202bad_read_metadata:
1203 unregister_snapshot(s);
1204
1205bad_load_and_register:
1206 mempool_destroy(s->pending_pool);
1207
1208bad_pending_pool:
1209 dm_kcopyd_client_destroy(s->kcopyd_client);
1210
1211bad_kcopyd:
1212 dm_exception_table_exit(&s->pending, pending_cache);
1213 dm_exception_table_exit(&s->complete, exception_cache);
1214
1215bad_hash_tables:
1216 dm_exception_store_destroy(s->store);
1217
1218bad_store:
1219 dm_put_device(ti, s->cow);
1220
1221bad_cow:
1222 dm_put_device(ti, s->origin);
1223
1224bad_origin:
1225 kfree(s);
1226
1227bad:
1228 return r;
1229}
1230
1231static void __free_exceptions(struct dm_snapshot *s)
1232{
1233 dm_kcopyd_client_destroy(s->kcopyd_client);
1234 s->kcopyd_client = NULL;
1235
1236 dm_exception_table_exit(&s->pending, pending_cache);
1237 dm_exception_table_exit(&s->complete, exception_cache);
1238}
1239
1240static void __handover_exceptions(struct dm_snapshot *snap_src,
1241 struct dm_snapshot *snap_dest)
1242{
1243 union {
1244 struct dm_exception_table table_swap;
1245 struct dm_exception_store *store_swap;
1246 } u;
1247
1248 /*
1249 * Swap all snapshot context information between the two instances.
1250 */
1251 u.table_swap = snap_dest->complete;
1252 snap_dest->complete = snap_src->complete;
1253 snap_src->complete = u.table_swap;
1254
1255 u.store_swap = snap_dest->store;
1256 snap_dest->store = snap_src->store;
1257 snap_src->store = u.store_swap;
1258
1259 snap_dest->store->snap = snap_dest;
1260 snap_src->store->snap = snap_src;
1261
1262 snap_dest->ti->max_io_len = snap_dest->store->chunk_size;
1263 snap_dest->valid = snap_src->valid;
1264
1265 /*
1266 * Set source invalid to ensure it receives no further I/O.
1267 */
1268 snap_src->valid = 0;
1269}
1270
1271static void snapshot_dtr(struct dm_target *ti)
1272{
1273#ifdef CONFIG_DM_DEBUG
1274 int i;
1275#endif
1276 struct dm_snapshot *s = ti->private;
1277 struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
1278
1279 down_read(&_origins_lock);
1280 /* Check whether exception handover must be cancelled */
1281 (void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL);
1282 if (snap_src && snap_dest && (s == snap_src)) {
1283 down_write(&snap_dest->lock);
1284 snap_dest->valid = 0;
1285 up_write(&snap_dest->lock);
1286 DMERR("Cancelling snapshot handover.");
1287 }
1288 up_read(&_origins_lock);
1289
1290 if (dm_target_is_snapshot_merge(ti))
1291 stop_merge(s);
1292
1293 /* Prevent further origin writes from using this snapshot. */
1294 /* After this returns there can be no new kcopyd jobs. */
1295 unregister_snapshot(s);
1296
1297 while (atomic_read(&s->pending_exceptions_count))
1298 msleep(1);
1299 /*
1300 * Ensure instructions in mempool_destroy aren't reordered
1301 * before atomic_read.
1302 */
1303 smp_mb();
1304
1305#ifdef CONFIG_DM_DEBUG
1306 for (i = 0; i < DM_TRACKED_CHUNK_HASH_SIZE; i++)
1307 BUG_ON(!hlist_empty(&s->tracked_chunk_hash[i]));
1308#endif
1309
1310 __free_exceptions(s);
1311
1312 mempool_destroy(s->pending_pool);
1313
1314 dm_exception_store_destroy(s->store);
1315
1316 dm_put_device(ti, s->cow);
1317
1318 dm_put_device(ti, s->origin);
1319
1320 kfree(s);
1321}
1322
1323/*
1324 * Flush a list of buffers.
1325 */
1326static void flush_bios(struct bio *bio)
1327{
1328 struct bio *n;
1329
1330 while (bio) {
1331 n = bio->bi_next;
1332 bio->bi_next = NULL;
1333 generic_make_request(bio);
1334 bio = n;
1335 }
1336}
1337
1338static int do_origin(struct dm_dev *origin, struct bio *bio);
1339
1340/*
1341 * Flush a list of buffers.
1342 */
1343static void retry_origin_bios(struct dm_snapshot *s, struct bio *bio)
1344{
1345 struct bio *n;
1346 int r;
1347
1348 while (bio) {
1349 n = bio->bi_next;
1350 bio->bi_next = NULL;
1351 r = do_origin(s->origin, bio);
1352 if (r == DM_MAPIO_REMAPPED)
1353 generic_make_request(bio);
1354 bio = n;
1355 }
1356}
1357
1358/*
1359 * Error a list of buffers.
1360 */
1361static void error_bios(struct bio *bio)
1362{
1363 struct bio *n;
1364
1365 while (bio) {
1366 n = bio->bi_next;
1367 bio->bi_next = NULL;
1368 bio_io_error(bio);
1369 bio = n;
1370 }
1371}
1372
1373static void __invalidate_snapshot(struct dm_snapshot *s, int err)
1374{
1375 if (!s->valid)
1376 return;
1377
1378 if (err == -EIO)
1379 DMERR("Invalidating snapshot: Error reading/writing.");
1380 else if (err == -ENOMEM)
1381 DMERR("Invalidating snapshot: Unable to allocate exception.");
1382
1383 if (s->store->type->drop_snapshot)
1384 s->store->type->drop_snapshot(s->store);
1385
1386 s->valid = 0;
1387
1388 dm_table_event(s->ti->table);
1389}
1390
1391static void pending_complete(struct dm_snap_pending_exception *pe, int success)
1392{
1393 struct dm_exception *e;
1394 struct dm_snapshot *s = pe->snap;
1395 struct bio *origin_bios = NULL;
1396 struct bio *snapshot_bios = NULL;
1397 struct bio *full_bio = NULL;
1398 int error = 0;
1399
1400 if (!success) {
1401 /* Read/write error - snapshot is unusable */
1402 down_write(&s->lock);
1403 __invalidate_snapshot(s, -EIO);
1404 error = 1;
1405 goto out;
1406 }
1407
1408 e = alloc_completed_exception(GFP_NOIO);
1409 if (!e) {
1410 down_write(&s->lock);
1411 __invalidate_snapshot(s, -ENOMEM);
1412 error = 1;
1413 goto out;
1414 }
1415 *e = pe->e;
1416
1417 down_write(&s->lock);
1418 if (!s->valid) {
1419 free_completed_exception(e);
1420 error = 1;
1421 goto out;
1422 }
1423
1424 /* Check for conflicting reads */
1425 __check_for_conflicting_io(s, pe->e.old_chunk);
1426
1427 /*
1428 * Add a proper exception, and remove the
1429 * in-flight exception from the list.
1430 */
1431 dm_insert_exception(&s->complete, e);
1432
1433out:
1434 dm_remove_exception(&pe->e);
1435 snapshot_bios = bio_list_get(&pe->snapshot_bios);
1436 origin_bios = bio_list_get(&pe->origin_bios);
1437 full_bio = pe->full_bio;
1438 if (full_bio) {
1439 full_bio->bi_end_io = pe->full_bio_end_io;
1440 full_bio->bi_private = pe->full_bio_private;
1441 atomic_inc(&full_bio->bi_remaining);
1442 }
1443 free_pending_exception(pe);
1444
1445 increment_pending_exceptions_done_count();
1446
1447 up_write(&s->lock);
1448
1449 /* Submit any pending write bios */
1450 if (error) {
1451 if (full_bio)
1452 bio_io_error(full_bio);
1453 error_bios(snapshot_bios);
1454 } else {
1455 if (full_bio)
1456 bio_endio(full_bio, 0);
1457 flush_bios(snapshot_bios);
1458 }
1459
1460 retry_origin_bios(s, origin_bios);
1461}
1462
1463static void commit_callback(void *context, int success)
1464{
1465 struct dm_snap_pending_exception *pe = context;
1466
1467 pending_complete(pe, success);
1468}
1469
1470static void complete_exception(struct dm_snap_pending_exception *pe)
1471{
1472 struct dm_snapshot *s = pe->snap;
1473
1474 if (unlikely(pe->copy_error))
1475 pending_complete(pe, 0);
1476
1477 else
1478 /* Update the metadata if we are persistent */
1479 s->store->type->commit_exception(s->store, &pe->e,
1480 commit_callback, pe);
1481}
1482
1483/*
1484 * Called when the copy I/O has finished. kcopyd actually runs
1485 * this code so don't block.
1486 */
1487static void copy_callback(int read_err, unsigned long write_err, void *context)
1488{
1489 struct dm_snap_pending_exception *pe = context;
1490 struct dm_snapshot *s = pe->snap;
1491
1492 pe->copy_error = read_err || write_err;
1493
1494 if (pe->exception_sequence == s->exception_complete_sequence) {
1495 s->exception_complete_sequence++;
1496 complete_exception(pe);
1497
1498 while (!list_empty(&s->out_of_order_list)) {
1499 pe = list_entry(s->out_of_order_list.next,
1500 struct dm_snap_pending_exception, out_of_order_entry);
1501 if (pe->exception_sequence != s->exception_complete_sequence)
1502 break;
1503 s->exception_complete_sequence++;
1504 list_del(&pe->out_of_order_entry);
1505 complete_exception(pe);
1506 }
1507 } else {
1508 struct list_head *lh;
1509 struct dm_snap_pending_exception *pe2;
1510
1511 list_for_each_prev(lh, &s->out_of_order_list) {
1512 pe2 = list_entry(lh, struct dm_snap_pending_exception, out_of_order_entry);
1513 if (pe2->exception_sequence < pe->exception_sequence)
1514 break;
1515 }
1516 list_add(&pe->out_of_order_entry, lh);
1517 }
1518}
1519
1520/*
1521 * Dispatches the copy operation to kcopyd.
1522 */
1523static void start_copy(struct dm_snap_pending_exception *pe)
1524{
1525 struct dm_snapshot *s = pe->snap;
1526 struct dm_io_region src, dest;
1527 struct block_device *bdev = s->origin->bdev;
1528 sector_t dev_size;
1529
1530 dev_size = get_dev_size(bdev);
1531
1532 src.bdev = bdev;
1533 src.sector = chunk_to_sector(s->store, pe->e.old_chunk);
1534 src.count = min((sector_t)s->store->chunk_size, dev_size - src.sector);
1535
1536 dest.bdev = s->cow->bdev;
1537 dest.sector = chunk_to_sector(s->store, pe->e.new_chunk);
1538 dest.count = src.count;
1539
1540 /* Hand over to kcopyd */
1541 dm_kcopyd_copy(s->kcopyd_client, &src, 1, &dest, 0, copy_callback, pe);
1542}
1543
1544static void full_bio_end_io(struct bio *bio, int error)
1545{
1546 void *callback_data = bio->bi_private;
1547
1548 dm_kcopyd_do_callback(callback_data, 0, error ? 1 : 0);
1549}
1550
1551static void start_full_bio(struct dm_snap_pending_exception *pe,
1552 struct bio *bio)
1553{
1554 struct dm_snapshot *s = pe->snap;
1555 void *callback_data;
1556
1557 pe->full_bio = bio;
1558 pe->full_bio_end_io = bio->bi_end_io;
1559 pe->full_bio_private = bio->bi_private;
1560
1561 callback_data = dm_kcopyd_prepare_callback(s->kcopyd_client,
1562 copy_callback, pe);
1563
1564 bio->bi_end_io = full_bio_end_io;
1565 bio->bi_private = callback_data;
1566
1567 generic_make_request(bio);
1568}
1569
1570static struct dm_snap_pending_exception *
1571__lookup_pending_exception(struct dm_snapshot *s, chunk_t chunk)
1572{
1573 struct dm_exception *e = dm_lookup_exception(&s->pending, chunk);
1574
1575 if (!e)
1576 return NULL;
1577
1578 return container_of(e, struct dm_snap_pending_exception, e);
1579}
1580
1581/*
1582 * Looks to see if this snapshot already has a pending exception
1583 * for this chunk, otherwise it allocates a new one and inserts
1584 * it into the pending table.
1585 *
1586 * NOTE: a write lock must be held on snap->lock before calling
1587 * this.
1588 */
1589static struct dm_snap_pending_exception *
1590__find_pending_exception(struct dm_snapshot *s,
1591 struct dm_snap_pending_exception *pe, chunk_t chunk)
1592{
1593 struct dm_snap_pending_exception *pe2;
1594
1595 pe2 = __lookup_pending_exception(s, chunk);
1596 if (pe2) {
1597 free_pending_exception(pe);
1598 return pe2;
1599 }
1600
1601 pe->e.old_chunk = chunk;
1602 bio_list_init(&pe->origin_bios);
1603 bio_list_init(&pe->snapshot_bios);
1604 pe->started = 0;
1605 pe->full_bio = NULL;
1606
1607 if (s->store->type->prepare_exception(s->store, &pe->e)) {
1608 free_pending_exception(pe);
1609 return NULL;
1610 }
1611
1612 pe->exception_sequence = s->exception_start_sequence++;
1613
1614 dm_insert_exception(&s->pending, &pe->e);
1615
1616 return pe;
1617}
1618
1619static void remap_exception(struct dm_snapshot *s, struct dm_exception *e,
1620 struct bio *bio, chunk_t chunk)
1621{
1622 bio->bi_bdev = s->cow->bdev;
1623 bio->bi_iter.bi_sector =
1624 chunk_to_sector(s->store, dm_chunk_number(e->new_chunk) +
1625 (chunk - e->old_chunk)) +
1626 (bio->bi_iter.bi_sector & s->store->chunk_mask);
1627}
1628
1629static int snapshot_map(struct dm_target *ti, struct bio *bio)
1630{
1631 struct dm_exception *e;
1632 struct dm_snapshot *s = ti->private;
1633 int r = DM_MAPIO_REMAPPED;
1634 chunk_t chunk;
1635 struct dm_snap_pending_exception *pe = NULL;
1636
1637 init_tracked_chunk(bio);
1638
1639 if (bio->bi_rw & REQ_FLUSH) {
1640 bio->bi_bdev = s->cow->bdev;
1641 return DM_MAPIO_REMAPPED;
1642 }
1643
1644 chunk = sector_to_chunk(s->store, bio->bi_iter.bi_sector);
1645
1646 /* Full snapshots are not usable */
1647 /* To get here the table must be live so s->active is always set. */
1648 if (!s->valid)
1649 return -EIO;
1650
1651 /* FIXME: should only take write lock if we need
1652 * to copy an exception */
1653 down_write(&s->lock);
1654
1655 if (!s->valid) {
1656 r = -EIO;
1657 goto out_unlock;
1658 }
1659
1660 /* If the block is already remapped - use that, else remap it */
1661 e = dm_lookup_exception(&s->complete, chunk);
1662 if (e) {
1663 remap_exception(s, e, bio, chunk);
1664 goto out_unlock;
1665 }
1666
1667 /*
1668 * Write to snapshot - higher level takes care of RW/RO
1669 * flags so we should only get this if we are
1670 * writeable.
1671 */
1672 if (bio_rw(bio) == WRITE) {
1673 pe = __lookup_pending_exception(s, chunk);
1674 if (!pe) {
1675 up_write(&s->lock);
1676 pe = alloc_pending_exception(s);
1677 down_write(&s->lock);
1678
1679 if (!s->valid) {
1680 free_pending_exception(pe);
1681 r = -EIO;
1682 goto out_unlock;
1683 }
1684
1685 e = dm_lookup_exception(&s->complete, chunk);
1686 if (e) {
1687 free_pending_exception(pe);
1688 remap_exception(s, e, bio, chunk);
1689 goto out_unlock;
1690 }
1691
1692 pe = __find_pending_exception(s, pe, chunk);
1693 if (!pe) {
1694 __invalidate_snapshot(s, -ENOMEM);
1695 r = -EIO;
1696 goto out_unlock;
1697 }
1698 }
1699
1700 remap_exception(s, &pe->e, bio, chunk);
1701
1702 r = DM_MAPIO_SUBMITTED;
1703
1704 if (!pe->started &&
1705 bio->bi_iter.bi_size ==
1706 (s->store->chunk_size << SECTOR_SHIFT)) {
1707 pe->started = 1;
1708 up_write(&s->lock);
1709 start_full_bio(pe, bio);
1710 goto out;
1711 }
1712
1713 bio_list_add(&pe->snapshot_bios, bio);
1714
1715 if (!pe->started) {
1716 /* this is protected by snap->lock */
1717 pe->started = 1;
1718 up_write(&s->lock);
1719 start_copy(pe);
1720 goto out;
1721 }
1722 } else {
1723 bio->bi_bdev = s->origin->bdev;
1724 track_chunk(s, bio, chunk);
1725 }
1726
1727out_unlock:
1728 up_write(&s->lock);
1729out:
1730 return r;
1731}
1732
1733/*
1734 * A snapshot-merge target behaves like a combination of a snapshot
1735 * target and a snapshot-origin target. It only generates new
1736 * exceptions in other snapshots and not in the one that is being
1737 * merged.
1738 *
1739 * For each chunk, if there is an existing exception, it is used to
1740 * redirect I/O to the cow device. Otherwise I/O is sent to the origin,
1741 * which in turn might generate exceptions in other snapshots.
1742 * If merging is currently taking place on the chunk in question, the
1743 * I/O is deferred by adding it to s->bios_queued_during_merge.
1744 */
1745static int snapshot_merge_map(struct dm_target *ti, struct bio *bio)
1746{
1747 struct dm_exception *e;
1748 struct dm_snapshot *s = ti->private;
1749 int r = DM_MAPIO_REMAPPED;
1750 chunk_t chunk;
1751
1752 init_tracked_chunk(bio);
1753
1754 if (bio->bi_rw & REQ_FLUSH) {
1755 if (!dm_bio_get_target_bio_nr(bio))
1756 bio->bi_bdev = s->origin->bdev;
1757 else
1758 bio->bi_bdev = s->cow->bdev;
1759 return DM_MAPIO_REMAPPED;
1760 }
1761
1762 chunk = sector_to_chunk(s->store, bio->bi_iter.bi_sector);
1763
1764 down_write(&s->lock);
1765
1766 /* Full merging snapshots are redirected to the origin */
1767 if (!s->valid)
1768 goto redirect_to_origin;
1769
1770 /* If the block is already remapped - use that */
1771 e = dm_lookup_exception(&s->complete, chunk);
1772 if (e) {
1773 /* Queue writes overlapping with chunks being merged */
1774 if (bio_rw(bio) == WRITE &&
1775 chunk >= s->first_merging_chunk &&
1776 chunk < (s->first_merging_chunk +
1777 s->num_merging_chunks)) {
1778 bio->bi_bdev = s->origin->bdev;
1779 bio_list_add(&s->bios_queued_during_merge, bio);
1780 r = DM_MAPIO_SUBMITTED;
1781 goto out_unlock;
1782 }
1783
1784 remap_exception(s, e, bio, chunk);
1785
1786 if (bio_rw(bio) == WRITE)
1787 track_chunk(s, bio, chunk);
1788 goto out_unlock;
1789 }
1790
1791redirect_to_origin:
1792 bio->bi_bdev = s->origin->bdev;
1793
1794 if (bio_rw(bio) == WRITE) {
1795 up_write(&s->lock);
1796 return do_origin(s->origin, bio);
1797 }
1798
1799out_unlock:
1800 up_write(&s->lock);
1801
1802 return r;
1803}
1804
1805static int snapshot_end_io(struct dm_target *ti, struct bio *bio, int error)
1806{
1807 struct dm_snapshot *s = ti->private;
1808
1809 if (is_bio_tracked(bio))
1810 stop_tracking_chunk(s, bio);
1811
1812 return 0;
1813}
1814
1815static void snapshot_merge_presuspend(struct dm_target *ti)
1816{
1817 struct dm_snapshot *s = ti->private;
1818
1819 stop_merge(s);
1820}
1821
1822static int snapshot_preresume(struct dm_target *ti)
1823{
1824 int r = 0;
1825 struct dm_snapshot *s = ti->private;
1826 struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
1827
1828 down_read(&_origins_lock);
1829 (void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL);
1830 if (snap_src && snap_dest) {
1831 down_read(&snap_src->lock);
1832 if (s == snap_src) {
1833 DMERR("Unable to resume snapshot source until "
1834 "handover completes.");
1835 r = -EINVAL;
1836 } else if (!dm_suspended(snap_src->ti)) {
1837 DMERR("Unable to perform snapshot handover until "
1838 "source is suspended.");
1839 r = -EINVAL;
1840 }
1841 up_read(&snap_src->lock);
1842 }
1843 up_read(&_origins_lock);
1844
1845 return r;
1846}
1847
1848static void snapshot_resume(struct dm_target *ti)
1849{
1850 struct dm_snapshot *s = ti->private;
1851 struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
1852
1853 down_read(&_origins_lock);
1854 (void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL);
1855 if (snap_src && snap_dest) {
1856 down_write(&snap_src->lock);
1857 down_write_nested(&snap_dest->lock, SINGLE_DEPTH_NESTING);
1858 __handover_exceptions(snap_src, snap_dest);
1859 up_write(&snap_dest->lock);
1860 up_write(&snap_src->lock);
1861 }
1862 up_read(&_origins_lock);
1863
1864 /* Now we have correct chunk size, reregister */
1865 reregister_snapshot(s);
1866
1867 down_write(&s->lock);
1868 s->active = 1;
1869 up_write(&s->lock);
1870}
1871
1872static uint32_t get_origin_minimum_chunksize(struct block_device *bdev)
1873{
1874 uint32_t min_chunksize;
1875
1876 down_read(&_origins_lock);
1877 min_chunksize = __minimum_chunk_size(__lookup_origin(bdev));
1878 up_read(&_origins_lock);
1879
1880 return min_chunksize;
1881}
1882
1883static void snapshot_merge_resume(struct dm_target *ti)
1884{
1885 struct dm_snapshot *s = ti->private;
1886
1887 /*
1888 * Handover exceptions from existing snapshot.
1889 */
1890 snapshot_resume(ti);
1891
1892 /*
1893 * snapshot-merge acts as an origin, so set ti->max_io_len
1894 */
1895 ti->max_io_len = get_origin_minimum_chunksize(s->origin->bdev);
1896
1897 start_merge(s);
1898}
1899
1900static void snapshot_status(struct dm_target *ti, status_type_t type,
1901 unsigned status_flags, char *result, unsigned maxlen)
1902{
1903 unsigned sz = 0;
1904 struct dm_snapshot *snap = ti->private;
1905
1906 switch (type) {
1907 case STATUSTYPE_INFO:
1908
1909 down_write(&snap->lock);
1910
1911 if (!snap->valid)
1912 DMEMIT("Invalid");
1913 else if (snap->merge_failed)
1914 DMEMIT("Merge failed");
1915 else {
1916 if (snap->store->type->usage) {
1917 sector_t total_sectors, sectors_allocated,
1918 metadata_sectors;
1919 snap->store->type->usage(snap->store,
1920 &total_sectors,
1921 §ors_allocated,
1922 &metadata_sectors);
1923 DMEMIT("%llu/%llu %llu",
1924 (unsigned long long)sectors_allocated,
1925 (unsigned long long)total_sectors,
1926 (unsigned long long)metadata_sectors);
1927 }
1928 else
1929 DMEMIT("Unknown");
1930 }
1931
1932 up_write(&snap->lock);
1933
1934 break;
1935
1936 case STATUSTYPE_TABLE:
1937 /*
1938 * kdevname returns a static pointer so we need
1939 * to make private copies if the output is to
1940 * make sense.
1941 */
1942 DMEMIT("%s %s", snap->origin->name, snap->cow->name);
1943 snap->store->type->status(snap->store, type, result + sz,
1944 maxlen - sz);
1945 break;
1946 }
1947}
1948
1949static int snapshot_iterate_devices(struct dm_target *ti,
1950 iterate_devices_callout_fn fn, void *data)
1951{
1952 struct dm_snapshot *snap = ti->private;
1953 int r;
1954
1955 r = fn(ti, snap->origin, 0, ti->len, data);
1956
1957 if (!r)
1958 r = fn(ti, snap->cow, 0, get_dev_size(snap->cow->bdev), data);
1959
1960 return r;
1961}
1962
1963
1964/*-----------------------------------------------------------------
1965 * Origin methods
1966 *---------------------------------------------------------------*/
1967
1968/*
1969 * If no exceptions need creating, DM_MAPIO_REMAPPED is returned and any
1970 * supplied bio was ignored. The caller may submit it immediately.
1971 * (No remapping actually occurs as the origin is always a direct linear
1972 * map.)
1973 *
1974 * If further exceptions are required, DM_MAPIO_SUBMITTED is returned
1975 * and any supplied bio is added to a list to be submitted once all
1976 * the necessary exceptions exist.
1977 */
1978static int __origin_write(struct list_head *snapshots, sector_t sector,
1979 struct bio *bio)
1980{
1981 int r = DM_MAPIO_REMAPPED;
1982 struct dm_snapshot *snap;
1983 struct dm_exception *e;
1984 struct dm_snap_pending_exception *pe;
1985 struct dm_snap_pending_exception *pe_to_start_now = NULL;
1986 struct dm_snap_pending_exception *pe_to_start_last = NULL;
1987 chunk_t chunk;
1988
1989 /* Do all the snapshots on this origin */
1990 list_for_each_entry (snap, snapshots, list) {
1991 /*
1992 * Don't make new exceptions in a merging snapshot
1993 * because it has effectively been deleted
1994 */
1995 if (dm_target_is_snapshot_merge(snap->ti))
1996 continue;
1997
1998 down_write(&snap->lock);
1999
2000 /* Only deal with valid and active snapshots */
2001 if (!snap->valid || !snap->active)
2002 goto next_snapshot;
2003
2004 /* Nothing to do if writing beyond end of snapshot */
2005 if (sector >= dm_table_get_size(snap->ti->table))
2006 goto next_snapshot;
2007
2008 /*
2009 * Remember, different snapshots can have
2010 * different chunk sizes.
2011 */
2012 chunk = sector_to_chunk(snap->store, sector);
2013
2014 /*
2015 * Check exception table to see if block
2016 * is already remapped in this snapshot
2017 * and trigger an exception if not.
2018 */
2019 e = dm_lookup_exception(&snap->complete, chunk);
2020 if (e)
2021 goto next_snapshot;
2022
2023 pe = __lookup_pending_exception(snap, chunk);
2024 if (!pe) {
2025 up_write(&snap->lock);
2026 pe = alloc_pending_exception(snap);
2027 down_write(&snap->lock);
2028
2029 if (!snap->valid) {
2030 free_pending_exception(pe);
2031 goto next_snapshot;
2032 }
2033
2034 e = dm_lookup_exception(&snap->complete, chunk);
2035 if (e) {
2036 free_pending_exception(pe);
2037 goto next_snapshot;
2038 }
2039
2040 pe = __find_pending_exception(snap, pe, chunk);
2041 if (!pe) {
2042 __invalidate_snapshot(snap, -ENOMEM);
2043 goto next_snapshot;
2044 }
2045 }
2046
2047 r = DM_MAPIO_SUBMITTED;
2048
2049 /*
2050 * If an origin bio was supplied, queue it to wait for the
2051 * completion of this exception, and start this one last,
2052 * at the end of the function.
2053 */
2054 if (bio) {
2055 bio_list_add(&pe->origin_bios, bio);
2056 bio = NULL;
2057
2058 if (!pe->started) {
2059 pe->started = 1;
2060 pe_to_start_last = pe;
2061 }
2062 }
2063
2064 if (!pe->started) {
2065 pe->started = 1;
2066 pe_to_start_now = pe;
2067 }
2068
2069next_snapshot:
2070 up_write(&snap->lock);
2071
2072 if (pe_to_start_now) {
2073 start_copy(pe_to_start_now);
2074 pe_to_start_now = NULL;
2075 }
2076 }
2077
2078 /*
2079 * Submit the exception against which the bio is queued last,
2080 * to give the other exceptions a head start.
2081 */
2082 if (pe_to_start_last)
2083 start_copy(pe_to_start_last);
2084
2085 return r;
2086}
2087
2088/*
2089 * Called on a write from the origin driver.
2090 */
2091static int do_origin(struct dm_dev *origin, struct bio *bio)
2092{
2093 struct origin *o;
2094 int r = DM_MAPIO_REMAPPED;
2095
2096 down_read(&_origins_lock);
2097 o = __lookup_origin(origin->bdev);
2098 if (o)
2099 r = __origin_write(&o->snapshots, bio->bi_iter.bi_sector, bio);
2100 up_read(&_origins_lock);
2101
2102 return r;
2103}
2104
2105/*
2106 * Trigger exceptions in all non-merging snapshots.
2107 *
2108 * The chunk size of the merging snapshot may be larger than the chunk
2109 * size of some other snapshot so we may need to reallocate multiple
2110 * chunks in other snapshots.
2111 *
2112 * We scan all the overlapping exceptions in the other snapshots.
2113 * Returns 1 if anything was reallocated and must be waited for,
2114 * otherwise returns 0.
2115 *
2116 * size must be a multiple of merging_snap's chunk_size.
2117 */
2118static int origin_write_extent(struct dm_snapshot *merging_snap,
2119 sector_t sector, unsigned size)
2120{
2121 int must_wait = 0;
2122 sector_t n;
2123 struct origin *o;
2124
2125 /*
2126 * The origin's __minimum_chunk_size() got stored in max_io_len
2127 * by snapshot_merge_resume().
2128 */
2129 down_read(&_origins_lock);
2130 o = __lookup_origin(merging_snap->origin->bdev);
2131 for (n = 0; n < size; n += merging_snap->ti->max_io_len)
2132 if (__origin_write(&o->snapshots, sector + n, NULL) ==
2133 DM_MAPIO_SUBMITTED)
2134 must_wait = 1;
2135 up_read(&_origins_lock);
2136
2137 return must_wait;
2138}
2139
2140/*
2141 * Origin: maps a linear range of a device, with hooks for snapshotting.
2142 */
2143
2144/*
2145 * Construct an origin mapping: <dev_path>
2146 * The context for an origin is merely a 'struct dm_dev *'
2147 * pointing to the real device.
2148 */
2149static int origin_ctr(struct dm_target *ti, unsigned int argc, char **argv)
2150{
2151 int r;
2152 struct dm_dev *dev;
2153
2154 if (argc != 1) {
2155 ti->error = "origin: incorrect number of arguments";
2156 return -EINVAL;
2157 }
2158
2159 r = dm_get_device(ti, argv[0], dm_table_get_mode(ti->table), &dev);
2160 if (r) {
2161 ti->error = "Cannot get target device";
2162 return r;
2163 }
2164
2165 ti->private = dev;
2166 ti->num_flush_bios = 1;
2167
2168 return 0;
2169}
2170
2171static void origin_dtr(struct dm_target *ti)
2172{
2173 struct dm_dev *dev = ti->private;
2174 dm_put_device(ti, dev);
2175}
2176
2177static int origin_map(struct dm_target *ti, struct bio *bio)
2178{
2179 struct dm_dev *dev = ti->private;
2180 bio->bi_bdev = dev->bdev;
2181
2182 if (bio->bi_rw & REQ_FLUSH)
2183 return DM_MAPIO_REMAPPED;
2184
2185 /* Only tell snapshots if this is a write */
2186 return (bio_rw(bio) == WRITE) ? do_origin(dev, bio) : DM_MAPIO_REMAPPED;
2187}
2188
2189/*
2190 * Set the target "max_io_len" field to the minimum of all the snapshots'
2191 * chunk sizes.
2192 */
2193static void origin_resume(struct dm_target *ti)
2194{
2195 struct dm_dev *dev = ti->private;
2196
2197 ti->max_io_len = get_origin_minimum_chunksize(dev->bdev);
2198}
2199
2200static void origin_status(struct dm_target *ti, status_type_t type,
2201 unsigned status_flags, char *result, unsigned maxlen)
2202{
2203 struct dm_dev *dev = ti->private;
2204
2205 switch (type) {
2206 case STATUSTYPE_INFO:
2207 result[0] = '\0';
2208 break;
2209
2210 case STATUSTYPE_TABLE:
2211 snprintf(result, maxlen, "%s", dev->name);
2212 break;
2213 }
2214}
2215
2216static int origin_merge(struct dm_target *ti, struct bvec_merge_data *bvm,
2217 struct bio_vec *biovec, int max_size)
2218{
2219 struct dm_dev *dev = ti->private;
2220 struct request_queue *q = bdev_get_queue(dev->bdev);
2221
2222 if (!q->merge_bvec_fn)
2223 return max_size;
2224
2225 bvm->bi_bdev = dev->bdev;
2226
2227 return min(max_size, q->merge_bvec_fn(q, bvm, biovec));
2228}
2229
2230static int origin_iterate_devices(struct dm_target *ti,
2231 iterate_devices_callout_fn fn, void *data)
2232{
2233 struct dm_dev *dev = ti->private;
2234
2235 return fn(ti, dev, 0, ti->len, data);
2236}
2237
2238static struct target_type origin_target = {
2239 .name = "snapshot-origin",
2240 .version = {1, 8, 1},
2241 .module = THIS_MODULE,
2242 .ctr = origin_ctr,
2243 .dtr = origin_dtr,
2244 .map = origin_map,
2245 .resume = origin_resume,
2246 .status = origin_status,
2247 .merge = origin_merge,
2248 .iterate_devices = origin_iterate_devices,
2249};
2250
2251static struct target_type snapshot_target = {
2252 .name = "snapshot",
2253 .version = {1, 12, 0},
2254 .module = THIS_MODULE,
2255 .ctr = snapshot_ctr,
2256 .dtr = snapshot_dtr,
2257 .map = snapshot_map,
2258 .end_io = snapshot_end_io,
2259 .preresume = snapshot_preresume,
2260 .resume = snapshot_resume,
2261 .status = snapshot_status,
2262 .iterate_devices = snapshot_iterate_devices,
2263};
2264
2265static struct target_type merge_target = {
2266 .name = dm_snapshot_merge_target_name,
2267 .version = {1, 2, 0},
2268 .module = THIS_MODULE,
2269 .ctr = snapshot_ctr,
2270 .dtr = snapshot_dtr,
2271 .map = snapshot_merge_map,
2272 .end_io = snapshot_end_io,
2273 .presuspend = snapshot_merge_presuspend,
2274 .preresume = snapshot_preresume,
2275 .resume = snapshot_merge_resume,
2276 .status = snapshot_status,
2277 .iterate_devices = snapshot_iterate_devices,
2278};
2279
2280static int __init dm_snapshot_init(void)
2281{
2282 int r;
2283
2284 r = dm_exception_store_init();
2285 if (r) {
2286 DMERR("Failed to initialize exception stores");
2287 return r;
2288 }
2289
2290 r = dm_register_target(&snapshot_target);
2291 if (r < 0) {
2292 DMERR("snapshot target register failed %d", r);
2293 goto bad_register_snapshot_target;
2294 }
2295
2296 r = dm_register_target(&origin_target);
2297 if (r < 0) {
2298 DMERR("Origin target register failed %d", r);
2299 goto bad_register_origin_target;
2300 }
2301
2302 r = dm_register_target(&merge_target);
2303 if (r < 0) {
2304 DMERR("Merge target register failed %d", r);
2305 goto bad_register_merge_target;
2306 }
2307
2308 r = init_origin_hash();
2309 if (r) {
2310 DMERR("init_origin_hash failed.");
2311 goto bad_origin_hash;
2312 }
2313
2314 exception_cache = KMEM_CACHE(dm_exception, 0);
2315 if (!exception_cache) {
2316 DMERR("Couldn't create exception cache.");
2317 r = -ENOMEM;
2318 goto bad_exception_cache;
2319 }
2320
2321 pending_cache = KMEM_CACHE(dm_snap_pending_exception, 0);
2322 if (!pending_cache) {
2323 DMERR("Couldn't create pending cache.");
2324 r = -ENOMEM;
2325 goto bad_pending_cache;
2326 }
2327
2328 return 0;
2329
2330bad_pending_cache:
2331 kmem_cache_destroy(exception_cache);
2332bad_exception_cache:
2333 exit_origin_hash();
2334bad_origin_hash:
2335 dm_unregister_target(&merge_target);
2336bad_register_merge_target:
2337 dm_unregister_target(&origin_target);
2338bad_register_origin_target:
2339 dm_unregister_target(&snapshot_target);
2340bad_register_snapshot_target:
2341 dm_exception_store_exit();
2342
2343 return r;
2344}
2345
2346static void __exit dm_snapshot_exit(void)
2347{
2348 dm_unregister_target(&snapshot_target);
2349 dm_unregister_target(&origin_target);
2350 dm_unregister_target(&merge_target);
2351
2352 exit_origin_hash();
2353 kmem_cache_destroy(pending_cache);
2354 kmem_cache_destroy(exception_cache);
2355
2356 dm_exception_store_exit();
2357}
2358
2359/* Module hooks */
2360module_init(dm_snapshot_init);
2361module_exit(dm_snapshot_exit);
2362
2363MODULE_DESCRIPTION(DM_NAME " snapshot target");
2364MODULE_AUTHOR("Joe Thornber");
2365MODULE_LICENSE("GPL");
2366MODULE_ALIAS("dm-snapshot-origin");
2367MODULE_ALIAS("dm-snapshot-merge");