| Author | Tokens | Token Proportion | Commits | Commit Proportion |
|---|---|---|---|---|
| Mikulas Patocka | 3851 | 33.77% | 50 | 32.05% |
| Alasdair G. Kergon | 3565 | 31.27% | 21 | 13.46% |
| Mike Snitzer | 2155 | 18.90% | 16 | 10.26% |
| Nikos Tsironis | 770 | 6.75% | 5 | 3.21% |
| Milan Broz | 286 | 2.51% | 3 | 1.92% |
| Jonathan E Brassow | 229 | 2.01% | 17 | 10.90% |
| David Jeffery | 126 | 1.11% | 1 | 0.64% |
| Christoph Hellwig | 95 | 0.83% | 10 | 6.41% |
| Tushar Sugandhi | 79 | 0.69% | 1 | 0.64% |
| monty_pavel@sina.com | 65 | 0.57% | 1 | 0.64% |
| Heinz Mauelshagen | 40 | 0.35% | 8 | 5.13% |
| Kent Overstreet | 25 | 0.22% | 3 | 1.92% |
| Mark McLoughlin | 22 | 0.19% | 1 | 0.64% |
| Andrew Morton | 20 | 0.18% | 2 | 1.28% |
| Akilesh Kailash | 12 | 0.11% | 1 | 0.64% |
| Kiyoshi Ueda | 12 | 0.11% | 3 | 1.92% |
| Lars Marowsky-Bree | 11 | 0.10% | 1 | 0.64% |
| Christoph Lameter | 6 | 0.05% | 1 | 0.64% |
| Tejun Heo | 6 | 0.05% | 1 | 0.64% |
| Matthew Wilcox | 4 | 0.04% | 1 | 0.64% |
| Kees Cook | 4 | 0.04% | 1 | 0.64% |
| Alan Cox | 3 | 0.03% | 1 | 0.64% |
| Jens Axboe | 3 | 0.03% | 1 | 0.64% |
| Vignesh Babu | 3 | 0.03% | 1 | 0.64% |
| zhengbin | 3 | 0.03% | 1 | 0.64% |
| Michael Christie | 3 | 0.03% | 1 | 0.64% |
| Peter Zijlstra | 2 | 0.02% | 1 | 0.64% |
| Kevin Corry | 1 | 0.01% | 1 | 0.64% |
| Zhang Jiaming | 1 | 0.01% | 1 | 0.64% |
| Total | 11402 | 156 |
// SPDX-License-Identifier: GPL-2.0-only /* * Copyright (C) 2001-2002 Sistina Software (UK) Limited. * * This file is released under the GPL. */ #include <linux/blkdev.h> #include <linux/device-mapper.h> #include <linux/delay.h> #include <linux/fs.h> #include <linux/init.h> #include <linux/kdev_t.h> #include <linux/list.h> #include <linux/list_bl.h> #include <linux/mempool.h> #include <linux/module.h> #include <linux/slab.h> #include <linux/vmalloc.h> #include <linux/log2.h> #include <linux/dm-kcopyd.h> #include "dm.h" #include "dm-exception-store.h" #define DM_MSG_PREFIX "snapshots" static const char dm_snapshot_merge_target_name[] = "snapshot-merge"; #define dm_target_is_snapshot_merge(ti) \ ((ti)->type->name == dm_snapshot_merge_target_name) /* * The size of the mempool used to track chunks in use. */ #define MIN_IOS 256 #define DM_TRACKED_CHUNK_HASH_SIZE 16 #define DM_TRACKED_CHUNK_HASH(x) ((unsigned long)(x) & \ (DM_TRACKED_CHUNK_HASH_SIZE - 1)) struct dm_exception_table { uint32_t hash_mask; unsigned int hash_shift; struct hlist_bl_head *table; }; struct dm_snapshot { struct rw_semaphore lock; struct dm_dev *origin; struct dm_dev *cow; struct dm_target *ti; /* List of snapshots per Origin */ struct list_head list; /* * You can't use a snapshot if this is 0 (e.g. if full). * A snapshot-merge target never clears this. */ int valid; /* * The snapshot overflowed because of a write to the snapshot device. * We don't have to invalidate the snapshot in this case, but we need * to prevent further writes. */ int snapshot_overflowed; /* Origin writes don't trigger exceptions until this is set */ int active; atomic_t pending_exceptions_count; spinlock_t pe_allocation_lock; /* Protected by "pe_allocation_lock" */ sector_t exception_start_sequence; /* Protected by kcopyd single-threaded callback */ sector_t exception_complete_sequence; /* * A list of pending exceptions that completed out of order. * Protected by kcopyd single-threaded callback. */ struct rb_root out_of_order_tree; mempool_t pending_pool; struct dm_exception_table pending; struct dm_exception_table complete; /* * pe_lock protects all pending_exception operations and access * as well as the snapshot_bios list. */ spinlock_t pe_lock; /* Chunks with outstanding reads */ spinlock_t tracked_chunk_lock; struct hlist_head tracked_chunk_hash[DM_TRACKED_CHUNK_HASH_SIZE]; /* The on disk metadata handler */ struct dm_exception_store *store; unsigned int in_progress; struct wait_queue_head in_progress_wait; struct dm_kcopyd_client *kcopyd_client; /* Wait for events based on state_bits */ unsigned long state_bits; /* Range of chunks currently being merged. */ chunk_t first_merging_chunk; int num_merging_chunks; /* * The merge operation failed if this flag is set. * Failure modes are handled as follows: * - I/O error reading the header * => don't load the target; abort. * - Header does not have "valid" flag set * => use the origin; forget about the snapshot. * - I/O error when reading exceptions * => don't load the target; abort. * (We can't use the intermediate origin state.) * - I/O error while merging * => stop merging; set merge_failed; process I/O normally. */ bool merge_failed:1; bool discard_zeroes_cow:1; bool discard_passdown_origin:1; /* * Incoming bios that overlap with chunks being merged must wait * for them to be committed. */ struct bio_list bios_queued_during_merge; }; /* * state_bits: * RUNNING_MERGE - Merge operation is in progress. * SHUTDOWN_MERGE - Set to signal that merge needs to be stopped; * cleared afterwards. */ #define RUNNING_MERGE 0 #define SHUTDOWN_MERGE 1 /* * Maximum number of chunks being copied on write. * * The value was decided experimentally as a trade-off between memory * consumption, stalling the kernel's workqueues and maintaining a high enough * throughput. */ #define DEFAULT_COW_THRESHOLD 2048 static unsigned int cow_threshold = DEFAULT_COW_THRESHOLD; module_param_named(snapshot_cow_threshold, cow_threshold, uint, 0644); MODULE_PARM_DESC(snapshot_cow_threshold, "Maximum number of chunks being copied on write"); DECLARE_DM_KCOPYD_THROTTLE_WITH_MODULE_PARM(snapshot_copy_throttle, "A percentage of time allocated for copy on write"); struct dm_dev *dm_snap_origin(struct dm_snapshot *s) { return s->origin; } EXPORT_SYMBOL(dm_snap_origin); struct dm_dev *dm_snap_cow(struct dm_snapshot *s) { return s->cow; } EXPORT_SYMBOL(dm_snap_cow); static sector_t chunk_to_sector(struct dm_exception_store *store, chunk_t chunk) { return chunk << store->chunk_shift; } static int bdev_equal(struct block_device *lhs, struct block_device *rhs) { /* * There is only ever one instance of a particular block * device so we can compare pointers safely. */ return lhs == rhs; } struct dm_snap_pending_exception { struct dm_exception e; /* * Origin buffers waiting for this to complete are held * in a bio list */ struct bio_list origin_bios; struct bio_list snapshot_bios; /* Pointer back to snapshot context */ struct dm_snapshot *snap; /* * 1 indicates the exception has already been sent to * kcopyd. */ int started; /* There was copying error. */ int copy_error; /* A sequence number, it is used for in-order completion. */ sector_t exception_sequence; struct rb_node out_of_order_node; /* * For writing a complete chunk, bypassing the copy. */ struct bio *full_bio; bio_end_io_t *full_bio_end_io; }; /* * Hash table mapping origin volumes to lists of snapshots and * a lock to protect it */ static struct kmem_cache *exception_cache; static struct kmem_cache *pending_cache; struct dm_snap_tracked_chunk { struct hlist_node node; chunk_t chunk; }; static void init_tracked_chunk(struct bio *bio) { struct dm_snap_tracked_chunk *c = dm_per_bio_data(bio, sizeof(struct dm_snap_tracked_chunk)); INIT_HLIST_NODE(&c->node); } static bool is_bio_tracked(struct bio *bio) { struct dm_snap_tracked_chunk *c = dm_per_bio_data(bio, sizeof(struct dm_snap_tracked_chunk)); return !hlist_unhashed(&c->node); } static void track_chunk(struct dm_snapshot *s, struct bio *bio, chunk_t chunk) { struct dm_snap_tracked_chunk *c = dm_per_bio_data(bio, sizeof(struct dm_snap_tracked_chunk)); c->chunk = chunk; spin_lock_irq(&s->tracked_chunk_lock); hlist_add_head(&c->node, &s->tracked_chunk_hash[DM_TRACKED_CHUNK_HASH(chunk)]); spin_unlock_irq(&s->tracked_chunk_lock); } static void stop_tracking_chunk(struct dm_snapshot *s, struct bio *bio) { struct dm_snap_tracked_chunk *c = dm_per_bio_data(bio, sizeof(struct dm_snap_tracked_chunk)); unsigned long flags; spin_lock_irqsave(&s->tracked_chunk_lock, flags); hlist_del(&c->node); spin_unlock_irqrestore(&s->tracked_chunk_lock, flags); } static int __chunk_is_tracked(struct dm_snapshot *s, chunk_t chunk) { struct dm_snap_tracked_chunk *c; int found = 0; spin_lock_irq(&s->tracked_chunk_lock); hlist_for_each_entry(c, &s->tracked_chunk_hash[DM_TRACKED_CHUNK_HASH(chunk)], node) { if (c->chunk == chunk) { found = 1; break; } } spin_unlock_irq(&s->tracked_chunk_lock); return found; } /* * This conflicting I/O is extremely improbable in the caller, * so fsleep(1000) is sufficient and there is no need for a wait queue. */ static void __check_for_conflicting_io(struct dm_snapshot *s, chunk_t chunk) { while (__chunk_is_tracked(s, chunk)) fsleep(1000); } /* * One of these per registered origin, held in the snapshot_origins hash */ struct origin { /* The origin device */ struct block_device *bdev; struct list_head hash_list; /* List of snapshots for this origin */ struct list_head snapshots; }; /* * This structure is allocated for each origin target */ struct dm_origin { struct dm_dev *dev; struct dm_target *ti; unsigned int split_boundary; struct list_head hash_list; }; /* * Size of the hash table for origin volumes. If we make this * the size of the minors list then it should be nearly perfect */ #define ORIGIN_HASH_SIZE 256 #define ORIGIN_MASK 0xFF static struct list_head *_origins; static struct list_head *_dm_origins; static struct rw_semaphore _origins_lock; static DECLARE_WAIT_QUEUE_HEAD(_pending_exceptions_done); static DEFINE_SPINLOCK(_pending_exceptions_done_spinlock); static uint64_t _pending_exceptions_done_count; static int init_origin_hash(void) { int i; _origins = kmalloc_array(ORIGIN_HASH_SIZE, sizeof(struct list_head), GFP_KERNEL); if (!_origins) { DMERR("unable to allocate memory for _origins"); return -ENOMEM; } for (i = 0; i < ORIGIN_HASH_SIZE; i++) INIT_LIST_HEAD(_origins + i); _dm_origins = kmalloc_array(ORIGIN_HASH_SIZE, sizeof(struct list_head), GFP_KERNEL); if (!_dm_origins) { DMERR("unable to allocate memory for _dm_origins"); kfree(_origins); return -ENOMEM; } for (i = 0; i < ORIGIN_HASH_SIZE; i++) INIT_LIST_HEAD(_dm_origins + i); init_rwsem(&_origins_lock); return 0; } static void exit_origin_hash(void) { kfree(_origins); kfree(_dm_origins); } static unsigned int origin_hash(struct block_device *bdev) { return bdev->bd_dev & ORIGIN_MASK; } static struct origin *__lookup_origin(struct block_device *origin) { struct list_head *ol; struct origin *o; ol = &_origins[origin_hash(origin)]; list_for_each_entry(o, ol, hash_list) if (bdev_equal(o->bdev, origin)) return o; return NULL; } static void __insert_origin(struct origin *o) { struct list_head *sl = &_origins[origin_hash(o->bdev)]; list_add_tail(&o->hash_list, sl); } static struct dm_origin *__lookup_dm_origin(struct block_device *origin) { struct list_head *ol; struct dm_origin *o; ol = &_dm_origins[origin_hash(origin)]; list_for_each_entry(o, ol, hash_list) if (bdev_equal(o->dev->bdev, origin)) return o; return NULL; } static void __insert_dm_origin(struct dm_origin *o) { struct list_head *sl = &_dm_origins[origin_hash(o->dev->bdev)]; list_add_tail(&o->hash_list, sl); } static void __remove_dm_origin(struct dm_origin *o) { list_del(&o->hash_list); } /* * _origins_lock must be held when calling this function. * Returns number of snapshots registered using the supplied cow device, plus: * snap_src - a snapshot suitable for use as a source of exception handover * snap_dest - a snapshot capable of receiving exception handover. * snap_merge - an existing snapshot-merge target linked to the same origin. * There can be at most one snapshot-merge target. The parameter is optional. * * Possible return values and states of snap_src and snap_dest. * 0: NULL, NULL - first new snapshot * 1: snap_src, NULL - normal snapshot * 2: snap_src, snap_dest - waiting for handover * 2: snap_src, NULL - handed over, waiting for old to be deleted * 1: NULL, snap_dest - source got destroyed without handover */ static int __find_snapshots_sharing_cow(struct dm_snapshot *snap, struct dm_snapshot **snap_src, struct dm_snapshot **snap_dest, struct dm_snapshot **snap_merge) { struct dm_snapshot *s; struct origin *o; int count = 0; int active; o = __lookup_origin(snap->origin->bdev); if (!o) goto out; list_for_each_entry(s, &o->snapshots, list) { if (dm_target_is_snapshot_merge(s->ti) && snap_merge) *snap_merge = s; if (!bdev_equal(s->cow->bdev, snap->cow->bdev)) continue; down_read(&s->lock); active = s->active; up_read(&s->lock); if (active) { if (snap_src) *snap_src = s; } else if (snap_dest) *snap_dest = s; count++; } out: return count; } /* * On success, returns 1 if this snapshot is a handover destination, * otherwise returns 0. */ static int __validate_exception_handover(struct dm_snapshot *snap) { struct dm_snapshot *snap_src = NULL, *snap_dest = NULL; struct dm_snapshot *snap_merge = NULL; /* Does snapshot need exceptions handed over to it? */ if ((__find_snapshots_sharing_cow(snap, &snap_src, &snap_dest, &snap_merge) == 2) || snap_dest) { snap->ti->error = "Snapshot cow pairing for exception table handover failed"; return -EINVAL; } /* * If no snap_src was found, snap cannot become a handover * destination. */ if (!snap_src) return 0; /* * Non-snapshot-merge handover? */ if (!dm_target_is_snapshot_merge(snap->ti)) return 1; /* * Do not allow more than one merging snapshot. */ if (snap_merge) { snap->ti->error = "A snapshot is already merging."; return -EINVAL; } if (!snap_src->store->type->prepare_merge || !snap_src->store->type->commit_merge) { snap->ti->error = "Snapshot exception store does not support snapshot-merge."; return -EINVAL; } return 1; } static void __insert_snapshot(struct origin *o, struct dm_snapshot *s) { struct dm_snapshot *l; /* Sort the list according to chunk size, largest-first smallest-last */ list_for_each_entry(l, &o->snapshots, list) if (l->store->chunk_size < s->store->chunk_size) break; list_add_tail(&s->list, &l->list); } /* * Make a note of the snapshot and its origin so we can look it * up when the origin has a write on it. * * Also validate snapshot exception store handovers. * On success, returns 1 if this registration is a handover destination, * otherwise returns 0. */ static int register_snapshot(struct dm_snapshot *snap) { struct origin *o, *new_o = NULL; struct block_device *bdev = snap->origin->bdev; int r = 0; new_o = kmalloc(sizeof(*new_o), GFP_KERNEL); if (!new_o) return -ENOMEM; down_write(&_origins_lock); r = __validate_exception_handover(snap); if (r < 0) { kfree(new_o); goto out; } o = __lookup_origin(bdev); if (o) kfree(new_o); else { /* New origin */ o = new_o; /* Initialise the struct */ INIT_LIST_HEAD(&o->snapshots); o->bdev = bdev; __insert_origin(o); } __insert_snapshot(o, snap); out: up_write(&_origins_lock); return r; } /* * Move snapshot to correct place in list according to chunk size. */ static void reregister_snapshot(struct dm_snapshot *s) { struct block_device *bdev = s->origin->bdev; down_write(&_origins_lock); list_del(&s->list); __insert_snapshot(__lookup_origin(bdev), s); up_write(&_origins_lock); } static void unregister_snapshot(struct dm_snapshot *s) { struct origin *o; down_write(&_origins_lock); o = __lookup_origin(s->origin->bdev); list_del(&s->list); if (o && list_empty(&o->snapshots)) { list_del(&o->hash_list); kfree(o); } up_write(&_origins_lock); } /* * Implementation of the exception hash tables. * The lowest hash_shift bits of the chunk number are ignored, allowing * some consecutive chunks to be grouped together. */ static uint32_t exception_hash(struct dm_exception_table *et, chunk_t chunk); /* Lock to protect access to the completed and pending exception hash tables. */ struct dm_exception_table_lock { struct hlist_bl_head *complete_slot; struct hlist_bl_head *pending_slot; }; static void dm_exception_table_lock_init(struct dm_snapshot *s, chunk_t chunk, struct dm_exception_table_lock *lock) { struct dm_exception_table *complete = &s->complete; struct dm_exception_table *pending = &s->pending; lock->complete_slot = &complete->table[exception_hash(complete, chunk)]; lock->pending_slot = &pending->table[exception_hash(pending, chunk)]; } static void dm_exception_table_lock(struct dm_exception_table_lock *lock) { hlist_bl_lock(lock->complete_slot); hlist_bl_lock(lock->pending_slot); } static void dm_exception_table_unlock(struct dm_exception_table_lock *lock) { hlist_bl_unlock(lock->pending_slot); hlist_bl_unlock(lock->complete_slot); } static int dm_exception_table_init(struct dm_exception_table *et, uint32_t size, unsigned int hash_shift) { unsigned int i; et->hash_shift = hash_shift; et->hash_mask = size - 1; et->table = kvmalloc_array(size, sizeof(struct hlist_bl_head), GFP_KERNEL); if (!et->table) return -ENOMEM; for (i = 0; i < size; i++) INIT_HLIST_BL_HEAD(et->table + i); return 0; } static void dm_exception_table_exit(struct dm_exception_table *et, struct kmem_cache *mem) { struct hlist_bl_head *slot; struct dm_exception *ex; struct hlist_bl_node *pos, *n; int i, size; size = et->hash_mask + 1; for (i = 0; i < size; i++) { slot = et->table + i; hlist_bl_for_each_entry_safe(ex, pos, n, slot, hash_list) { kmem_cache_free(mem, ex); cond_resched(); } } kvfree(et->table); } static uint32_t exception_hash(struct dm_exception_table *et, chunk_t chunk) { return (chunk >> et->hash_shift) & et->hash_mask; } static void dm_remove_exception(struct dm_exception *e) { hlist_bl_del(&e->hash_list); } /* * Return the exception data for a sector, or NULL if not * remapped. */ static struct dm_exception *dm_lookup_exception(struct dm_exception_table *et, chunk_t chunk) { struct hlist_bl_head *slot; struct hlist_bl_node *pos; struct dm_exception *e; slot = &et->table[exception_hash(et, chunk)]; hlist_bl_for_each_entry(e, pos, slot, hash_list) if (chunk >= e->old_chunk && chunk <= e->old_chunk + dm_consecutive_chunk_count(e)) return e; return NULL; } static struct dm_exception *alloc_completed_exception(gfp_t gfp) { struct dm_exception *e; e = kmem_cache_alloc(exception_cache, gfp); if (!e && gfp == GFP_NOIO) e = kmem_cache_alloc(exception_cache, GFP_ATOMIC); return e; } static void free_completed_exception(struct dm_exception *e) { kmem_cache_free(exception_cache, e); } static struct dm_snap_pending_exception *alloc_pending_exception(struct dm_snapshot *s) { struct dm_snap_pending_exception *pe = mempool_alloc(&s->pending_pool, GFP_NOIO); atomic_inc(&s->pending_exceptions_count); pe->snap = s; return pe; } static void free_pending_exception(struct dm_snap_pending_exception *pe) { struct dm_snapshot *s = pe->snap; mempool_free(pe, &s->pending_pool); smp_mb__before_atomic(); atomic_dec(&s->pending_exceptions_count); } static void dm_insert_exception(struct dm_exception_table *eh, struct dm_exception *new_e) { struct hlist_bl_head *l; struct hlist_bl_node *pos; struct dm_exception *e = NULL; l = &eh->table[exception_hash(eh, new_e->old_chunk)]; /* Add immediately if this table doesn't support consecutive chunks */ if (!eh->hash_shift) goto out; /* List is ordered by old_chunk */ hlist_bl_for_each_entry(e, pos, l, hash_list) { /* Insert after an existing chunk? */ if (new_e->old_chunk == (e->old_chunk + dm_consecutive_chunk_count(e) + 1) && new_e->new_chunk == (dm_chunk_number(e->new_chunk) + dm_consecutive_chunk_count(e) + 1)) { dm_consecutive_chunk_count_inc(e); free_completed_exception(new_e); return; } /* Insert before an existing chunk? */ if (new_e->old_chunk == (e->old_chunk - 1) && new_e->new_chunk == (dm_chunk_number(e->new_chunk) - 1)) { dm_consecutive_chunk_count_inc(e); e->old_chunk--; e->new_chunk--; free_completed_exception(new_e); return; } if (new_e->old_chunk < e->old_chunk) break; } out: if (!e) { /* * Either the table doesn't support consecutive chunks or slot * l is empty. */ hlist_bl_add_head(&new_e->hash_list, l); } else if (new_e->old_chunk < e->old_chunk) { /* Add before an existing exception */ hlist_bl_add_before(&new_e->hash_list, &e->hash_list); } else { /* Add to l's tail: e is the last exception in this slot */ hlist_bl_add_behind(&new_e->hash_list, &e->hash_list); } } /* * Callback used by the exception stores to load exceptions when * initialising. */ static int dm_add_exception(void *context, chunk_t old, chunk_t new) { struct dm_exception_table_lock lock; struct dm_snapshot *s = context; struct dm_exception *e; e = alloc_completed_exception(GFP_KERNEL); if (!e) return -ENOMEM; e->old_chunk = old; /* Consecutive_count is implicitly initialised to zero */ e->new_chunk = new; /* * Although there is no need to lock access to the exception tables * here, if we don't then hlist_bl_add_head(), called by * dm_insert_exception(), will complain about accessing the * corresponding list without locking it first. */ dm_exception_table_lock_init(s, old, &lock); dm_exception_table_lock(&lock); dm_insert_exception(&s->complete, e); dm_exception_table_unlock(&lock); return 0; } /* * Return a minimum chunk size of all snapshots that have the specified origin. * Return zero if the origin has no snapshots. */ static uint32_t __minimum_chunk_size(struct origin *o) { struct dm_snapshot *snap; unsigned int chunk_size = rounddown_pow_of_two(UINT_MAX); if (o) list_for_each_entry(snap, &o->snapshots, list) chunk_size = min_not_zero(chunk_size, snap->store->chunk_size); return (uint32_t) chunk_size; } /* * Hard coded magic. */ static int calc_max_buckets(void) { /* use a fixed size of 2MB */ unsigned long mem = 2 * 1024 * 1024; mem /= sizeof(struct hlist_bl_head); return mem; } /* * Allocate room for a suitable hash table. */ static int init_hash_tables(struct dm_snapshot *s) { sector_t hash_size, cow_dev_size, max_buckets; /* * Calculate based on the size of the original volume or * the COW volume... */ cow_dev_size = get_dev_size(s->cow->bdev); max_buckets = calc_max_buckets(); hash_size = cow_dev_size >> s->store->chunk_shift; hash_size = min(hash_size, max_buckets); if (hash_size < 64) hash_size = 64; hash_size = rounddown_pow_of_two(hash_size); if (dm_exception_table_init(&s->complete, hash_size, DM_CHUNK_CONSECUTIVE_BITS)) return -ENOMEM; /* * Allocate hash table for in-flight exceptions * Make this smaller than the real hash table */ hash_size >>= 3; if (hash_size < 64) hash_size = 64; if (dm_exception_table_init(&s->pending, hash_size, 0)) { dm_exception_table_exit(&s->complete, exception_cache); return -ENOMEM; } return 0; } static void merge_shutdown(struct dm_snapshot *s) { clear_bit_unlock(RUNNING_MERGE, &s->state_bits); smp_mb__after_atomic(); wake_up_bit(&s->state_bits, RUNNING_MERGE); } static struct bio *__release_queued_bios_after_merge(struct dm_snapshot *s) { s->first_merging_chunk = 0; s->num_merging_chunks = 0; return bio_list_get(&s->bios_queued_during_merge); } /* * Remove one chunk from the index of completed exceptions. */ static int __remove_single_exception_chunk(struct dm_snapshot *s, chunk_t old_chunk) { struct dm_exception *e; e = dm_lookup_exception(&s->complete, old_chunk); if (!e) { DMERR("Corruption detected: exception for block %llu is on disk but not in memory", (unsigned long long)old_chunk); return -EINVAL; } /* * If this is the only chunk using this exception, remove exception. */ if (!dm_consecutive_chunk_count(e)) { dm_remove_exception(e); free_completed_exception(e); return 0; } /* * The chunk may be either at the beginning or the end of a * group of consecutive chunks - never in the middle. We are * removing chunks in the opposite order to that in which they * were added, so this should always be true. * Decrement the consecutive chunk counter and adjust the * starting point if necessary. */ if (old_chunk == e->old_chunk) { e->old_chunk++; e->new_chunk++; } else if (old_chunk != e->old_chunk + dm_consecutive_chunk_count(e)) { DMERR("Attempt to merge block %llu from the middle of a chunk range [%llu - %llu]", (unsigned long long)old_chunk, (unsigned long long)e->old_chunk, (unsigned long long) e->old_chunk + dm_consecutive_chunk_count(e)); return -EINVAL; } dm_consecutive_chunk_count_dec(e); return 0; } static void flush_bios(struct bio *bio); static int remove_single_exception_chunk(struct dm_snapshot *s) { struct bio *b = NULL; int r; chunk_t old_chunk = s->first_merging_chunk + s->num_merging_chunks - 1; down_write(&s->lock); /* * Process chunks (and associated exceptions) in reverse order * so that dm_consecutive_chunk_count_dec() accounting works. */ do { r = __remove_single_exception_chunk(s, old_chunk); if (r) goto out; } while (old_chunk-- > s->first_merging_chunk); b = __release_queued_bios_after_merge(s); out: up_write(&s->lock); if (b) flush_bios(b); return r; } static int origin_write_extent(struct dm_snapshot *merging_snap, sector_t sector, unsigned int chunk_size); static void merge_callback(int read_err, unsigned long write_err, void *context); static uint64_t read_pending_exceptions_done_count(void) { uint64_t pending_exceptions_done; spin_lock(&_pending_exceptions_done_spinlock); pending_exceptions_done = _pending_exceptions_done_count; spin_unlock(&_pending_exceptions_done_spinlock); return pending_exceptions_done; } static void increment_pending_exceptions_done_count(void) { spin_lock(&_pending_exceptions_done_spinlock); _pending_exceptions_done_count++; spin_unlock(&_pending_exceptions_done_spinlock); wake_up_all(&_pending_exceptions_done); } static void snapshot_merge_next_chunks(struct dm_snapshot *s) { int i, linear_chunks; chunk_t old_chunk, new_chunk; struct dm_io_region src, dest; sector_t io_size; uint64_t previous_count; BUG_ON(!test_bit(RUNNING_MERGE, &s->state_bits)); if (unlikely(test_bit(SHUTDOWN_MERGE, &s->state_bits))) goto shut; /* * valid flag never changes during merge, so no lock required. */ if (!s->valid) { DMERR("Snapshot is invalid: can't merge"); goto shut; } linear_chunks = s->store->type->prepare_merge(s->store, &old_chunk, &new_chunk); if (linear_chunks <= 0) { if (linear_chunks < 0) { DMERR("Read error in exception store: shutting down merge"); down_write(&s->lock); s->merge_failed = true; up_write(&s->lock); } goto shut; } /* Adjust old_chunk and new_chunk to reflect start of linear region */ old_chunk = old_chunk + 1 - linear_chunks; new_chunk = new_chunk + 1 - linear_chunks; /* * Use one (potentially large) I/O to copy all 'linear_chunks' * from the exception store to the origin */ io_size = linear_chunks * s->store->chunk_size; dest.bdev = s->origin->bdev; dest.sector = chunk_to_sector(s->store, old_chunk); dest.count = min(io_size, get_dev_size(dest.bdev) - dest.sector); src.bdev = s->cow->bdev; src.sector = chunk_to_sector(s->store, new_chunk); src.count = dest.count; /* * Reallocate any exceptions needed in other snapshots then * wait for the pending exceptions to complete. * Each time any pending exception (globally on the system) * completes we are woken and repeat the process to find out * if we can proceed. While this may not seem a particularly * efficient algorithm, it is not expected to have any * significant impact on performance. */ previous_count = read_pending_exceptions_done_count(); while (origin_write_extent(s, dest.sector, io_size)) { wait_event(_pending_exceptions_done, (read_pending_exceptions_done_count() != previous_count)); /* Retry after the wait, until all exceptions are done. */ previous_count = read_pending_exceptions_done_count(); } down_write(&s->lock); s->first_merging_chunk = old_chunk; s->num_merging_chunks = linear_chunks; up_write(&s->lock); /* Wait until writes to all 'linear_chunks' drain */ for (i = 0; i < linear_chunks; i++) __check_for_conflicting_io(s, old_chunk + i); dm_kcopyd_copy(s->kcopyd_client, &src, 1, &dest, 0, merge_callback, s); return; shut: merge_shutdown(s); } static void error_bios(struct bio *bio); static void merge_callback(int read_err, unsigned long write_err, void *context) { struct dm_snapshot *s = context; struct bio *b = NULL; if (read_err || write_err) { if (read_err) DMERR("Read error: shutting down merge."); else DMERR("Write error: shutting down merge."); goto shut; } if (blkdev_issue_flush(s->origin->bdev) < 0) { DMERR("Flush after merge failed: shutting down merge"); goto shut; } if (s->store->type->commit_merge(s->store, s->num_merging_chunks) < 0) { DMERR("Write error in exception store: shutting down merge"); goto shut; } if (remove_single_exception_chunk(s) < 0) goto shut; snapshot_merge_next_chunks(s); return; shut: down_write(&s->lock); s->merge_failed = true; b = __release_queued_bios_after_merge(s); up_write(&s->lock); error_bios(b); merge_shutdown(s); } static void start_merge(struct dm_snapshot *s) { if (!test_and_set_bit(RUNNING_MERGE, &s->state_bits)) snapshot_merge_next_chunks(s); } /* * Stop the merging process and wait until it finishes. */ static void stop_merge(struct dm_snapshot *s) { set_bit(SHUTDOWN_MERGE, &s->state_bits); wait_on_bit(&s->state_bits, RUNNING_MERGE, TASK_UNINTERRUPTIBLE); clear_bit(SHUTDOWN_MERGE, &s->state_bits); } static int parse_snapshot_features(struct dm_arg_set *as, struct dm_snapshot *s, struct dm_target *ti) { int r; unsigned int argc; const char *arg_name; static const struct dm_arg _args[] = { {0, 2, "Invalid number of feature arguments"}, }; /* * No feature arguments supplied. */ if (!as->argc) return 0; r = dm_read_arg_group(_args, as, &argc, &ti->error); if (r) return -EINVAL; while (argc && !r) { arg_name = dm_shift_arg(as); argc--; if (!strcasecmp(arg_name, "discard_zeroes_cow")) s->discard_zeroes_cow = true; else if (!strcasecmp(arg_name, "discard_passdown_origin")) s->discard_passdown_origin = true; else { ti->error = "Unrecognised feature requested"; r = -EINVAL; break; } } if (!s->discard_zeroes_cow && s->discard_passdown_origin) { /* * TODO: really these are disjoint.. but ti->num_discard_bios * and dm_bio_get_target_bio_nr() require rigid constraints. */ ti->error = "discard_passdown_origin feature depends on discard_zeroes_cow"; r = -EINVAL; } return r; } /* * Construct a snapshot mapping: * <origin_dev> <COW-dev> <p|po|n> <chunk-size> [<# feature args> [<arg>]*] */ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv) { struct dm_snapshot *s; struct dm_arg_set as; int i; int r = -EINVAL; char *origin_path, *cow_path; unsigned int args_used, num_flush_bios = 1; blk_mode_t origin_mode = BLK_OPEN_READ; if (argc < 4) { ti->error = "requires 4 or more arguments"; r = -EINVAL; goto bad; } if (dm_target_is_snapshot_merge(ti)) { num_flush_bios = 2; origin_mode = BLK_OPEN_WRITE; } s = kzalloc(sizeof(*s), GFP_KERNEL); if (!s) { ti->error = "Cannot allocate private snapshot structure"; r = -ENOMEM; goto bad; } as.argc = argc; as.argv = argv; dm_consume_args(&as, 4); r = parse_snapshot_features(&as, s, ti); if (r) goto bad_features; origin_path = argv[0]; argv++; argc--; r = dm_get_device(ti, origin_path, origin_mode, &s->origin); if (r) { ti->error = "Cannot get origin device"; goto bad_origin; } cow_path = argv[0]; argv++; argc--; r = dm_get_device(ti, cow_path, dm_table_get_mode(ti->table), &s->cow); if (r) { ti->error = "Cannot get COW device"; goto bad_cow; } if (s->cow->bdev && s->cow->bdev == s->origin->bdev) { ti->error = "COW device cannot be the same as origin device"; r = -EINVAL; goto bad_store; } r = dm_exception_store_create(ti, argc, argv, s, &args_used, &s->store); if (r) { ti->error = "Couldn't create exception store"; r = -EINVAL; goto bad_store; } argv += args_used; argc -= args_used; s->ti = ti; s->valid = 1; s->snapshot_overflowed = 0; s->active = 0; atomic_set(&s->pending_exceptions_count, 0); spin_lock_init(&s->pe_allocation_lock); s->exception_start_sequence = 0; s->exception_complete_sequence = 0; s->out_of_order_tree = RB_ROOT; init_rwsem(&s->lock); INIT_LIST_HEAD(&s->list); spin_lock_init(&s->pe_lock); s->state_bits = 0; s->merge_failed = false; s->first_merging_chunk = 0; s->num_merging_chunks = 0; bio_list_init(&s->bios_queued_during_merge); /* Allocate hash table for COW data */ if (init_hash_tables(s)) { ti->error = "Unable to allocate hash table space"; r = -ENOMEM; goto bad_hash_tables; } init_waitqueue_head(&s->in_progress_wait); s->kcopyd_client = dm_kcopyd_client_create(&dm_kcopyd_throttle); if (IS_ERR(s->kcopyd_client)) { r = PTR_ERR(s->kcopyd_client); ti->error = "Could not create kcopyd client"; goto bad_kcopyd; } r = mempool_init_slab_pool(&s->pending_pool, MIN_IOS, pending_cache); if (r) { ti->error = "Could not allocate mempool for pending exceptions"; goto bad_pending_pool; } for (i = 0; i < DM_TRACKED_CHUNK_HASH_SIZE; i++) INIT_HLIST_HEAD(&s->tracked_chunk_hash[i]); spin_lock_init(&s->tracked_chunk_lock); ti->private = s; ti->num_flush_bios = num_flush_bios; if (s->discard_zeroes_cow) ti->num_discard_bios = (s->discard_passdown_origin ? 2 : 1); ti->per_io_data_size = sizeof(struct dm_snap_tracked_chunk); /* Add snapshot to the list of snapshots for this origin */ /* Exceptions aren't triggered till snapshot_resume() is called */ r = register_snapshot(s); if (r == -ENOMEM) { ti->error = "Snapshot origin struct allocation failed"; goto bad_load_and_register; } else if (r < 0) { /* invalid handover, register_snapshot has set ti->error */ goto bad_load_and_register; } /* * Metadata must only be loaded into one table at once, so skip this * if metadata will be handed over during resume. * Chunk size will be set during the handover - set it to zero to * ensure it's ignored. */ if (r > 0) { s->store->chunk_size = 0; return 0; } r = s->store->type->read_metadata(s->store, dm_add_exception, (void *)s); if (r < 0) { ti->error = "Failed to read snapshot metadata"; goto bad_read_metadata; } else if (r > 0) { s->valid = 0; DMWARN("Snapshot is marked invalid."); } if (!s->store->chunk_size) { ti->error = "Chunk size not set"; r = -EINVAL; goto bad_read_metadata; } r = dm_set_target_max_io_len(ti, s->store->chunk_size); if (r) goto bad_read_metadata; return 0; bad_read_metadata: unregister_snapshot(s); bad_load_and_register: mempool_exit(&s->pending_pool); bad_pending_pool: dm_kcopyd_client_destroy(s->kcopyd_client); bad_kcopyd: dm_exception_table_exit(&s->pending, pending_cache); dm_exception_table_exit(&s->complete, exception_cache); bad_hash_tables: dm_exception_store_destroy(s->store); bad_store: dm_put_device(ti, s->cow); bad_cow: dm_put_device(ti, s->origin); bad_origin: bad_features: kfree(s); bad: return r; } static void __free_exceptions(struct dm_snapshot *s) { dm_kcopyd_client_destroy(s->kcopyd_client); s->kcopyd_client = NULL; dm_exception_table_exit(&s->pending, pending_cache); dm_exception_table_exit(&s->complete, exception_cache); } static void __handover_exceptions(struct dm_snapshot *snap_src, struct dm_snapshot *snap_dest) { union { struct dm_exception_table table_swap; struct dm_exception_store *store_swap; } u; /* * Swap all snapshot context information between the two instances. */ u.table_swap = snap_dest->complete; snap_dest->complete = snap_src->complete; snap_src->complete = u.table_swap; u.store_swap = snap_dest->store; snap_dest->store = snap_src->store; snap_dest->store->userspace_supports_overflow = u.store_swap->userspace_supports_overflow; snap_src->store = u.store_swap; snap_dest->store->snap = snap_dest; snap_src->store->snap = snap_src; snap_dest->ti->max_io_len = snap_dest->store->chunk_size; snap_dest->valid = snap_src->valid; snap_dest->snapshot_overflowed = snap_src->snapshot_overflowed; /* * Set source invalid to ensure it receives no further I/O. */ snap_src->valid = 0; } static void snapshot_dtr(struct dm_target *ti) { #ifdef CONFIG_DM_DEBUG int i; #endif struct dm_snapshot *s = ti->private; struct dm_snapshot *snap_src = NULL, *snap_dest = NULL; down_read(&_origins_lock); /* Check whether exception handover must be cancelled */ (void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL); if (snap_src && snap_dest && (s == snap_src)) { down_write(&snap_dest->lock); snap_dest->valid = 0; up_write(&snap_dest->lock); DMERR("Cancelling snapshot handover."); } up_read(&_origins_lock); if (dm_target_is_snapshot_merge(ti)) stop_merge(s); /* Prevent further origin writes from using this snapshot. */ /* After this returns there can be no new kcopyd jobs. */ unregister_snapshot(s); while (atomic_read(&s->pending_exceptions_count)) fsleep(1000); /* * Ensure instructions in mempool_exit aren't reordered * before atomic_read. */ smp_mb(); #ifdef CONFIG_DM_DEBUG for (i = 0; i < DM_TRACKED_CHUNK_HASH_SIZE; i++) BUG_ON(!hlist_empty(&s->tracked_chunk_hash[i])); #endif __free_exceptions(s); mempool_exit(&s->pending_pool); dm_exception_store_destroy(s->store); dm_put_device(ti, s->cow); dm_put_device(ti, s->origin); WARN_ON(s->in_progress); kfree(s); } static void account_start_copy(struct dm_snapshot *s) { spin_lock(&s->in_progress_wait.lock); s->in_progress++; spin_unlock(&s->in_progress_wait.lock); } static void account_end_copy(struct dm_snapshot *s) { spin_lock(&s->in_progress_wait.lock); BUG_ON(!s->in_progress); s->in_progress--; if (likely(s->in_progress <= cow_threshold) && unlikely(waitqueue_active(&s->in_progress_wait))) wake_up_locked(&s->in_progress_wait); spin_unlock(&s->in_progress_wait.lock); } static bool wait_for_in_progress(struct dm_snapshot *s, bool unlock_origins) { if (unlikely(s->in_progress > cow_threshold)) { spin_lock(&s->in_progress_wait.lock); if (likely(s->in_progress > cow_threshold)) { /* * NOTE: this throttle doesn't account for whether * the caller is servicing an IO that will trigger a COW * so excess throttling may result for chunks not required * to be COW'd. But if cow_threshold was reached, extra * throttling is unlikely to negatively impact performance. */ DECLARE_WAITQUEUE(wait, current); __add_wait_queue(&s->in_progress_wait, &wait); __set_current_state(TASK_UNINTERRUPTIBLE); spin_unlock(&s->in_progress_wait.lock); if (unlock_origins) up_read(&_origins_lock); io_schedule(); remove_wait_queue(&s->in_progress_wait, &wait); return false; } spin_unlock(&s->in_progress_wait.lock); } return true; } /* * Flush a list of buffers. */ static void flush_bios(struct bio *bio) { struct bio *n; while (bio) { n = bio->bi_next; bio->bi_next = NULL; submit_bio_noacct(bio); bio = n; } } static int do_origin(struct dm_dev *origin, struct bio *bio, bool limit); /* * Flush a list of buffers. */ static void retry_origin_bios(struct dm_snapshot *s, struct bio *bio) { struct bio *n; int r; while (bio) { n = bio->bi_next; bio->bi_next = NULL; r = do_origin(s->origin, bio, false); if (r == DM_MAPIO_REMAPPED) submit_bio_noacct(bio); bio = n; } } /* * Error a list of buffers. */ static void error_bios(struct bio *bio) { struct bio *n; while (bio) { n = bio->bi_next; bio->bi_next = NULL; bio_io_error(bio); bio = n; } } static void __invalidate_snapshot(struct dm_snapshot *s, int err) { if (!s->valid) return; if (err == -EIO) DMERR("Invalidating snapshot: Error reading/writing."); else if (err == -ENOMEM) DMERR("Invalidating snapshot: Unable to allocate exception."); if (s->store->type->drop_snapshot) s->store->type->drop_snapshot(s->store); s->valid = 0; dm_table_event(s->ti->table); } static void invalidate_snapshot(struct dm_snapshot *s, int err) { down_write(&s->lock); __invalidate_snapshot(s, err); up_write(&s->lock); } static void pending_complete(void *context, int success) { struct dm_snap_pending_exception *pe = context; struct dm_exception *e; struct dm_snapshot *s = pe->snap; struct bio *origin_bios = NULL; struct bio *snapshot_bios = NULL; struct bio *full_bio = NULL; struct dm_exception_table_lock lock; int error = 0; dm_exception_table_lock_init(s, pe->e.old_chunk, &lock); if (!success) { /* Read/write error - snapshot is unusable */ invalidate_snapshot(s, -EIO); error = 1; dm_exception_table_lock(&lock); goto out; } e = alloc_completed_exception(GFP_NOIO); if (!e) { invalidate_snapshot(s, -ENOMEM); error = 1; dm_exception_table_lock(&lock); goto out; } *e = pe->e; down_read(&s->lock); dm_exception_table_lock(&lock); if (!s->valid) { up_read(&s->lock); free_completed_exception(e); error = 1; goto out; } /* * Add a proper exception. After inserting the completed exception all * subsequent snapshot reads to this chunk will be redirected to the * COW device. This ensures that we do not starve. Moreover, as long * as the pending exception exists, neither origin writes nor snapshot * merging can overwrite the chunk in origin. */ dm_insert_exception(&s->complete, e); up_read(&s->lock); /* Wait for conflicting reads to drain */ if (__chunk_is_tracked(s, pe->e.old_chunk)) { dm_exception_table_unlock(&lock); __check_for_conflicting_io(s, pe->e.old_chunk); dm_exception_table_lock(&lock); } out: /* Remove the in-flight exception from the list */ dm_remove_exception(&pe->e); dm_exception_table_unlock(&lock); snapshot_bios = bio_list_get(&pe->snapshot_bios); origin_bios = bio_list_get(&pe->origin_bios); full_bio = pe->full_bio; if (full_bio) full_bio->bi_end_io = pe->full_bio_end_io; increment_pending_exceptions_done_count(); /* Submit any pending write bios */ if (error) { if (full_bio) bio_io_error(full_bio); error_bios(snapshot_bios); } else { if (full_bio) bio_endio(full_bio); flush_bios(snapshot_bios); } retry_origin_bios(s, origin_bios); free_pending_exception(pe); } static void complete_exception(struct dm_snap_pending_exception *pe) { struct dm_snapshot *s = pe->snap; /* Update the metadata if we are persistent */ s->store->type->commit_exception(s->store, &pe->e, !pe->copy_error, pending_complete, pe); } /* * Called when the copy I/O has finished. kcopyd actually runs * this code so don't block. */ static void copy_callback(int read_err, unsigned long write_err, void *context) { struct dm_snap_pending_exception *pe = context; struct dm_snapshot *s = pe->snap; pe->copy_error = read_err || write_err; if (pe->exception_sequence == s->exception_complete_sequence) { struct rb_node *next; s->exception_complete_sequence++; complete_exception(pe); next = rb_first(&s->out_of_order_tree); while (next) { pe = rb_entry(next, struct dm_snap_pending_exception, out_of_order_node); if (pe->exception_sequence != s->exception_complete_sequence) break; next = rb_next(next); s->exception_complete_sequence++; rb_erase(&pe->out_of_order_node, &s->out_of_order_tree); complete_exception(pe); cond_resched(); } } else { struct rb_node *parent = NULL; struct rb_node **p = &s->out_of_order_tree.rb_node; struct dm_snap_pending_exception *pe2; while (*p) { pe2 = rb_entry(*p, struct dm_snap_pending_exception, out_of_order_node); parent = *p; BUG_ON(pe->exception_sequence == pe2->exception_sequence); if (pe->exception_sequence < pe2->exception_sequence) p = &((*p)->rb_left); else p = &((*p)->rb_right); } rb_link_node(&pe->out_of_order_node, parent, p); rb_insert_color(&pe->out_of_order_node, &s->out_of_order_tree); } account_end_copy(s); } /* * Dispatches the copy operation to kcopyd. */ static void start_copy(struct dm_snap_pending_exception *pe) { struct dm_snapshot *s = pe->snap; struct dm_io_region src, dest; struct block_device *bdev = s->origin->bdev; sector_t dev_size; dev_size = get_dev_size(bdev); src.bdev = bdev; src.sector = chunk_to_sector(s->store, pe->e.old_chunk); src.count = min((sector_t)s->store->chunk_size, dev_size - src.sector); dest.bdev = s->cow->bdev; dest.sector = chunk_to_sector(s->store, pe->e.new_chunk); dest.count = src.count; /* Hand over to kcopyd */ account_start_copy(s); dm_kcopyd_copy(s->kcopyd_client, &src, 1, &dest, 0, copy_callback, pe); } static void full_bio_end_io(struct bio *bio) { void *callback_data = bio->bi_private; dm_kcopyd_do_callback(callback_data, 0, bio->bi_status ? 1 : 0); } static void start_full_bio(struct dm_snap_pending_exception *pe, struct bio *bio) { struct dm_snapshot *s = pe->snap; void *callback_data; pe->full_bio = bio; pe->full_bio_end_io = bio->bi_end_io; account_start_copy(s); callback_data = dm_kcopyd_prepare_callback(s->kcopyd_client, copy_callback, pe); bio->bi_end_io = full_bio_end_io; bio->bi_private = callback_data; submit_bio_noacct(bio); } static struct dm_snap_pending_exception * __lookup_pending_exception(struct dm_snapshot *s, chunk_t chunk) { struct dm_exception *e = dm_lookup_exception(&s->pending, chunk); if (!e) return NULL; return container_of(e, struct dm_snap_pending_exception, e); } /* * Inserts a pending exception into the pending table. * * NOTE: a write lock must be held on the chunk's pending exception table slot * before calling this. */ static struct dm_snap_pending_exception * __insert_pending_exception(struct dm_snapshot *s, struct dm_snap_pending_exception *pe, chunk_t chunk) { pe->e.old_chunk = chunk; bio_list_init(&pe->origin_bios); bio_list_init(&pe->snapshot_bios); pe->started = 0; pe->full_bio = NULL; spin_lock(&s->pe_allocation_lock); if (s->store->type->prepare_exception(s->store, &pe->e)) { spin_unlock(&s->pe_allocation_lock); free_pending_exception(pe); return NULL; } pe->exception_sequence = s->exception_start_sequence++; spin_unlock(&s->pe_allocation_lock); dm_insert_exception(&s->pending, &pe->e); return pe; } /* * Looks to see if this snapshot already has a pending exception * for this chunk, otherwise it allocates a new one and inserts * it into the pending table. * * NOTE: a write lock must be held on the chunk's pending exception table slot * before calling this. */ static struct dm_snap_pending_exception * __find_pending_exception(struct dm_snapshot *s, struct dm_snap_pending_exception *pe, chunk_t chunk) { struct dm_snap_pending_exception *pe2; pe2 = __lookup_pending_exception(s, chunk); if (pe2) { free_pending_exception(pe); return pe2; } return __insert_pending_exception(s, pe, chunk); } static void remap_exception(struct dm_snapshot *s, struct dm_exception *e, struct bio *bio, chunk_t chunk) { bio_set_dev(bio, s->cow->bdev); bio->bi_iter.bi_sector = chunk_to_sector(s->store, dm_chunk_number(e->new_chunk) + (chunk - e->old_chunk)) + (bio->bi_iter.bi_sector & s->store->chunk_mask); } static void zero_callback(int read_err, unsigned long write_err, void *context) { struct bio *bio = context; struct dm_snapshot *s = bio->bi_private; account_end_copy(s); bio->bi_status = write_err ? BLK_STS_IOERR : 0; bio_endio(bio); } static void zero_exception(struct dm_snapshot *s, struct dm_exception *e, struct bio *bio, chunk_t chunk) { struct dm_io_region dest; dest.bdev = s->cow->bdev; dest.sector = bio->bi_iter.bi_sector; dest.count = s->store->chunk_size; account_start_copy(s); WARN_ON_ONCE(bio->bi_private); bio->bi_private = s; dm_kcopyd_zero(s->kcopyd_client, 1, &dest, 0, zero_callback, bio); } static bool io_overlaps_chunk(struct dm_snapshot *s, struct bio *bio) { return bio->bi_iter.bi_size == (s->store->chunk_size << SECTOR_SHIFT); } static int snapshot_map(struct dm_target *ti, struct bio *bio) { struct dm_exception *e; struct dm_snapshot *s = ti->private; int r = DM_MAPIO_REMAPPED; chunk_t chunk; struct dm_snap_pending_exception *pe = NULL; struct dm_exception_table_lock lock; init_tracked_chunk(bio); if (bio->bi_opf & REQ_PREFLUSH) { bio_set_dev(bio, s->cow->bdev); return DM_MAPIO_REMAPPED; } chunk = sector_to_chunk(s->store, bio->bi_iter.bi_sector); dm_exception_table_lock_init(s, chunk, &lock); /* Full snapshots are not usable */ /* To get here the table must be live so s->active is always set. */ if (!s->valid) return DM_MAPIO_KILL; if (bio_data_dir(bio) == WRITE) { while (unlikely(!wait_for_in_progress(s, false))) ; /* wait_for_in_progress() has slept */ } down_read(&s->lock); dm_exception_table_lock(&lock); if (!s->valid || (unlikely(s->snapshot_overflowed) && bio_data_dir(bio) == WRITE)) { r = DM_MAPIO_KILL; goto out_unlock; } if (unlikely(bio_op(bio) == REQ_OP_DISCARD)) { if (s->discard_passdown_origin && dm_bio_get_target_bio_nr(bio)) { /* * passdown discard to origin (without triggering * snapshot exceptions via do_origin; doing so would * defeat the goal of freeing space in origin that is * implied by the "discard_passdown_origin" feature) */ bio_set_dev(bio, s->origin->bdev); track_chunk(s, bio, chunk); goto out_unlock; } /* discard to snapshot (target_bio_nr == 0) zeroes exceptions */ } /* If the block is already remapped - use that, else remap it */ e = dm_lookup_exception(&s->complete, chunk); if (e) { remap_exception(s, e, bio, chunk); if (unlikely(bio_op(bio) == REQ_OP_DISCARD) && io_overlaps_chunk(s, bio)) { dm_exception_table_unlock(&lock); up_read(&s->lock); zero_exception(s, e, bio, chunk); r = DM_MAPIO_SUBMITTED; /* discard is not issued */ goto out; } goto out_unlock; } if (unlikely(bio_op(bio) == REQ_OP_DISCARD)) { /* * If no exception exists, complete discard immediately * otherwise it'll trigger copy-out. */ bio_endio(bio); r = DM_MAPIO_SUBMITTED; goto out_unlock; } /* * Write to snapshot - higher level takes care of RW/RO * flags so we should only get this if we are * writable. */ if (bio_data_dir(bio) == WRITE) { pe = __lookup_pending_exception(s, chunk); if (!pe) { dm_exception_table_unlock(&lock); pe = alloc_pending_exception(s); dm_exception_table_lock(&lock); e = dm_lookup_exception(&s->complete, chunk); if (e) { free_pending_exception(pe); remap_exception(s, e, bio, chunk); goto out_unlock; } pe = __find_pending_exception(s, pe, chunk); if (!pe) { dm_exception_table_unlock(&lock); up_read(&s->lock); down_write(&s->lock); if (s->store->userspace_supports_overflow) { if (s->valid && !s->snapshot_overflowed) { s->snapshot_overflowed = 1; DMERR("Snapshot overflowed: Unable to allocate exception."); } } else __invalidate_snapshot(s, -ENOMEM); up_write(&s->lock); r = DM_MAPIO_KILL; goto out; } } remap_exception(s, &pe->e, bio, chunk); r = DM_MAPIO_SUBMITTED; if (!pe->started && io_overlaps_chunk(s, bio)) { pe->started = 1; dm_exception_table_unlock(&lock); up_read(&s->lock); start_full_bio(pe, bio); goto out; } bio_list_add(&pe->snapshot_bios, bio); if (!pe->started) { /* this is protected by the exception table lock */ pe->started = 1; dm_exception_table_unlock(&lock); up_read(&s->lock); start_copy(pe); goto out; } } else { bio_set_dev(bio, s->origin->bdev); track_chunk(s, bio, chunk); } out_unlock: dm_exception_table_unlock(&lock); up_read(&s->lock); out: return r; } /* * A snapshot-merge target behaves like a combination of a snapshot * target and a snapshot-origin target. It only generates new * exceptions in other snapshots and not in the one that is being * merged. * * For each chunk, if there is an existing exception, it is used to * redirect I/O to the cow device. Otherwise I/O is sent to the origin, * which in turn might generate exceptions in other snapshots. * If merging is currently taking place on the chunk in question, the * I/O is deferred by adding it to s->bios_queued_during_merge. */ static int snapshot_merge_map(struct dm_target *ti, struct bio *bio) { struct dm_exception *e; struct dm_snapshot *s = ti->private; int r = DM_MAPIO_REMAPPED; chunk_t chunk; init_tracked_chunk(bio); if (bio->bi_opf & REQ_PREFLUSH) { if (!dm_bio_get_target_bio_nr(bio)) bio_set_dev(bio, s->origin->bdev); else bio_set_dev(bio, s->cow->bdev); return DM_MAPIO_REMAPPED; } if (unlikely(bio_op(bio) == REQ_OP_DISCARD)) { /* Once merging, discards no longer effect change */ bio_endio(bio); return DM_MAPIO_SUBMITTED; } chunk = sector_to_chunk(s->store, bio->bi_iter.bi_sector); down_write(&s->lock); /* Full merging snapshots are redirected to the origin */ if (!s->valid) goto redirect_to_origin; /* If the block is already remapped - use that */ e = dm_lookup_exception(&s->complete, chunk); if (e) { /* Queue writes overlapping with chunks being merged */ if (bio_data_dir(bio) == WRITE && chunk >= s->first_merging_chunk && chunk < (s->first_merging_chunk + s->num_merging_chunks)) { bio_set_dev(bio, s->origin->bdev); bio_list_add(&s->bios_queued_during_merge, bio); r = DM_MAPIO_SUBMITTED; goto out_unlock; } remap_exception(s, e, bio, chunk); if (bio_data_dir(bio) == WRITE) track_chunk(s, bio, chunk); goto out_unlock; } redirect_to_origin: bio_set_dev(bio, s->origin->bdev); if (bio_data_dir(bio) == WRITE) { up_write(&s->lock); return do_origin(s->origin, bio, false); } out_unlock: up_write(&s->lock); return r; } static int snapshot_end_io(struct dm_target *ti, struct bio *bio, blk_status_t *error) { struct dm_snapshot *s = ti->private; if (is_bio_tracked(bio)) stop_tracking_chunk(s, bio); return DM_ENDIO_DONE; } static void snapshot_merge_presuspend(struct dm_target *ti) { struct dm_snapshot *s = ti->private; stop_merge(s); } static int snapshot_preresume(struct dm_target *ti) { int r = 0; struct dm_snapshot *s = ti->private; struct dm_snapshot *snap_src = NULL, *snap_dest = NULL; down_read(&_origins_lock); (void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL); if (snap_src && snap_dest) { down_read(&snap_src->lock); if (s == snap_src) { DMERR("Unable to resume snapshot source until handover completes."); r = -EINVAL; } else if (!dm_suspended(snap_src->ti)) { DMERR("Unable to perform snapshot handover until source is suspended."); r = -EINVAL; } up_read(&snap_src->lock); } up_read(&_origins_lock); return r; } static void snapshot_resume(struct dm_target *ti) { struct dm_snapshot *s = ti->private; struct dm_snapshot *snap_src = NULL, *snap_dest = NULL, *snap_merging = NULL; struct dm_origin *o; struct mapped_device *origin_md = NULL; bool must_restart_merging = false; down_read(&_origins_lock); o = __lookup_dm_origin(s->origin->bdev); if (o) origin_md = dm_table_get_md(o->ti->table); if (!origin_md) { (void) __find_snapshots_sharing_cow(s, NULL, NULL, &snap_merging); if (snap_merging) origin_md = dm_table_get_md(snap_merging->ti->table); } if (origin_md == dm_table_get_md(ti->table)) origin_md = NULL; if (origin_md) { if (dm_hold(origin_md)) origin_md = NULL; } up_read(&_origins_lock); if (origin_md) { dm_internal_suspend_fast(origin_md); if (snap_merging && test_bit(RUNNING_MERGE, &snap_merging->state_bits)) { must_restart_merging = true; stop_merge(snap_merging); } } down_read(&_origins_lock); (void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL); if (snap_src && snap_dest) { down_write(&snap_src->lock); down_write_nested(&snap_dest->lock, SINGLE_DEPTH_NESTING); __handover_exceptions(snap_src, snap_dest); up_write(&snap_dest->lock); up_write(&snap_src->lock); } up_read(&_origins_lock); if (origin_md) { if (must_restart_merging) start_merge(snap_merging); dm_internal_resume_fast(origin_md); dm_put(origin_md); } /* Now we have correct chunk size, reregister */ reregister_snapshot(s); down_write(&s->lock); s->active = 1; up_write(&s->lock); } static uint32_t get_origin_minimum_chunksize(struct block_device *bdev) { uint32_t min_chunksize; down_read(&_origins_lock); min_chunksize = __minimum_chunk_size(__lookup_origin(bdev)); up_read(&_origins_lock); return min_chunksize; } static void snapshot_merge_resume(struct dm_target *ti) { struct dm_snapshot *s = ti->private; /* * Handover exceptions from existing snapshot. */ snapshot_resume(ti); /* * snapshot-merge acts as an origin, so set ti->max_io_len */ ti->max_io_len = get_origin_minimum_chunksize(s->origin->bdev); start_merge(s); } static void snapshot_status(struct dm_target *ti, status_type_t type, unsigned int status_flags, char *result, unsigned int maxlen) { unsigned int sz = 0; struct dm_snapshot *snap = ti->private; unsigned int num_features; switch (type) { case STATUSTYPE_INFO: down_write(&snap->lock); if (!snap->valid) DMEMIT("Invalid"); else if (snap->merge_failed) DMEMIT("Merge failed"); else if (snap->snapshot_overflowed) DMEMIT("Overflow"); else { if (snap->store->type->usage) { sector_t total_sectors, sectors_allocated, metadata_sectors; snap->store->type->usage(snap->store, &total_sectors, §ors_allocated, &metadata_sectors); DMEMIT("%llu/%llu %llu", (unsigned long long)sectors_allocated, (unsigned long long)total_sectors, (unsigned long long)metadata_sectors); } else DMEMIT("Unknown"); } up_write(&snap->lock); break; case STATUSTYPE_TABLE: /* * kdevname returns a static pointer so we need * to make private copies if the output is to * make sense. */ DMEMIT("%s %s", snap->origin->name, snap->cow->name); sz += snap->store->type->status(snap->store, type, result + sz, maxlen - sz); num_features = snap->discard_zeroes_cow + snap->discard_passdown_origin; if (num_features) { DMEMIT(" %u", num_features); if (snap->discard_zeroes_cow) DMEMIT(" discard_zeroes_cow"); if (snap->discard_passdown_origin) DMEMIT(" discard_passdown_origin"); } break; case STATUSTYPE_IMA: DMEMIT_TARGET_NAME_VERSION(ti->type); DMEMIT(",snap_origin_name=%s", snap->origin->name); DMEMIT(",snap_cow_name=%s", snap->cow->name); DMEMIT(",snap_valid=%c", snap->valid ? 'y' : 'n'); DMEMIT(",snap_merge_failed=%c", snap->merge_failed ? 'y' : 'n'); DMEMIT(",snapshot_overflowed=%c", snap->snapshot_overflowed ? 'y' : 'n'); DMEMIT(";"); break; } } static int snapshot_iterate_devices(struct dm_target *ti, iterate_devices_callout_fn fn, void *data) { struct dm_snapshot *snap = ti->private; int r; r = fn(ti, snap->origin, 0, ti->len, data); if (!r) r = fn(ti, snap->cow, 0, get_dev_size(snap->cow->bdev), data); return r; } static void snapshot_io_hints(struct dm_target *ti, struct queue_limits *limits) { struct dm_snapshot *snap = ti->private; if (snap->discard_zeroes_cow) { struct dm_snapshot *snap_src = NULL, *snap_dest = NULL; down_read(&_origins_lock); (void) __find_snapshots_sharing_cow(snap, &snap_src, &snap_dest, NULL); if (snap_src && snap_dest) snap = snap_src; /* All discards are split on chunk_size boundary */ limits->discard_granularity = snap->store->chunk_size; limits->max_hw_discard_sectors = snap->store->chunk_size; up_read(&_origins_lock); } } /* *--------------------------------------------------------------- * Origin methods *--------------------------------------------------------------- */ /* * If no exceptions need creating, DM_MAPIO_REMAPPED is returned and any * supplied bio was ignored. The caller may submit it immediately. * (No remapping actually occurs as the origin is always a direct linear * map.) * * If further exceptions are required, DM_MAPIO_SUBMITTED is returned * and any supplied bio is added to a list to be submitted once all * the necessary exceptions exist. */ static int __origin_write(struct list_head *snapshots, sector_t sector, struct bio *bio) { int r = DM_MAPIO_REMAPPED; struct dm_snapshot *snap; struct dm_exception *e; struct dm_snap_pending_exception *pe, *pe2; struct dm_snap_pending_exception *pe_to_start_now = NULL; struct dm_snap_pending_exception *pe_to_start_last = NULL; struct dm_exception_table_lock lock; chunk_t chunk; /* Do all the snapshots on this origin */ list_for_each_entry(snap, snapshots, list) { /* * Don't make new exceptions in a merging snapshot * because it has effectively been deleted */ if (dm_target_is_snapshot_merge(snap->ti)) continue; /* Nothing to do if writing beyond end of snapshot */ if (sector >= dm_table_get_size(snap->ti->table)) continue; /* * Remember, different snapshots can have * different chunk sizes. */ chunk = sector_to_chunk(snap->store, sector); dm_exception_table_lock_init(snap, chunk, &lock); down_read(&snap->lock); dm_exception_table_lock(&lock); /* Only deal with valid and active snapshots */ if (!snap->valid || !snap->active) goto next_snapshot; pe = __lookup_pending_exception(snap, chunk); if (!pe) { /* * Check exception table to see if block is already * remapped in this snapshot and trigger an exception * if not. */ e = dm_lookup_exception(&snap->complete, chunk); if (e) goto next_snapshot; dm_exception_table_unlock(&lock); pe = alloc_pending_exception(snap); dm_exception_table_lock(&lock); pe2 = __lookup_pending_exception(snap, chunk); if (!pe2) { e = dm_lookup_exception(&snap->complete, chunk); if (e) { free_pending_exception(pe); goto next_snapshot; } pe = __insert_pending_exception(snap, pe, chunk); if (!pe) { dm_exception_table_unlock(&lock); up_read(&snap->lock); invalidate_snapshot(snap, -ENOMEM); continue; } } else { free_pending_exception(pe); pe = pe2; } } r = DM_MAPIO_SUBMITTED; /* * If an origin bio was supplied, queue it to wait for the * completion of this exception, and start this one last, * at the end of the function. */ if (bio) { bio_list_add(&pe->origin_bios, bio); bio = NULL; if (!pe->started) { pe->started = 1; pe_to_start_last = pe; } } if (!pe->started) { pe->started = 1; pe_to_start_now = pe; } next_snapshot: dm_exception_table_unlock(&lock); up_read(&snap->lock); if (pe_to_start_now) { start_copy(pe_to_start_now); pe_to_start_now = NULL; } } /* * Submit the exception against which the bio is queued last, * to give the other exceptions a head start. */ if (pe_to_start_last) start_copy(pe_to_start_last); return r; } /* * Called on a write from the origin driver. */ static int do_origin(struct dm_dev *origin, struct bio *bio, bool limit) { struct origin *o; int r = DM_MAPIO_REMAPPED; again: down_read(&_origins_lock); o = __lookup_origin(origin->bdev); if (o) { if (limit) { struct dm_snapshot *s; list_for_each_entry(s, &o->snapshots, list) if (unlikely(!wait_for_in_progress(s, true))) goto again; } r = __origin_write(&o->snapshots, bio->bi_iter.bi_sector, bio); } up_read(&_origins_lock); return r; } /* * Trigger exceptions in all non-merging snapshots. * * The chunk size of the merging snapshot may be larger than the chunk * size of some other snapshot so we may need to reallocate multiple * chunks in other snapshots. * * We scan all the overlapping exceptions in the other snapshots. * Returns 1 if anything was reallocated and must be waited for, * otherwise returns 0. * * size must be a multiple of merging_snap's chunk_size. */ static int origin_write_extent(struct dm_snapshot *merging_snap, sector_t sector, unsigned int size) { int must_wait = 0; sector_t n; struct origin *o; /* * The origin's __minimum_chunk_size() got stored in max_io_len * by snapshot_merge_resume(). */ down_read(&_origins_lock); o = __lookup_origin(merging_snap->origin->bdev); for (n = 0; n < size; n += merging_snap->ti->max_io_len) if (__origin_write(&o->snapshots, sector + n, NULL) == DM_MAPIO_SUBMITTED) must_wait = 1; up_read(&_origins_lock); return must_wait; } /* * Origin: maps a linear range of a device, with hooks for snapshotting. */ /* * Construct an origin mapping: <dev_path> * The context for an origin is merely a 'struct dm_dev *' * pointing to the real device. */ static int origin_ctr(struct dm_target *ti, unsigned int argc, char **argv) { int r; struct dm_origin *o; if (argc != 1) { ti->error = "origin: incorrect number of arguments"; return -EINVAL; } o = kmalloc(sizeof(struct dm_origin), GFP_KERNEL); if (!o) { ti->error = "Cannot allocate private origin structure"; r = -ENOMEM; goto bad_alloc; } r = dm_get_device(ti, argv[0], dm_table_get_mode(ti->table), &o->dev); if (r) { ti->error = "Cannot get target device"; goto bad_open; } o->ti = ti; ti->private = o; ti->num_flush_bios = 1; return 0; bad_open: kfree(o); bad_alloc: return r; } static void origin_dtr(struct dm_target *ti) { struct dm_origin *o = ti->private; dm_put_device(ti, o->dev); kfree(o); } static int origin_map(struct dm_target *ti, struct bio *bio) { struct dm_origin *o = ti->private; unsigned int available_sectors; bio_set_dev(bio, o->dev->bdev); if (unlikely(bio->bi_opf & REQ_PREFLUSH)) return DM_MAPIO_REMAPPED; if (bio_data_dir(bio) != WRITE) return DM_MAPIO_REMAPPED; available_sectors = o->split_boundary - ((unsigned int)bio->bi_iter.bi_sector & (o->split_boundary - 1)); if (bio_sectors(bio) > available_sectors) dm_accept_partial_bio(bio, available_sectors); /* Only tell snapshots if this is a write */ return do_origin(o->dev, bio, true); } /* * Set the target "max_io_len" field to the minimum of all the snapshots' * chunk sizes. */ static void origin_resume(struct dm_target *ti) { struct dm_origin *o = ti->private; o->split_boundary = get_origin_minimum_chunksize(o->dev->bdev); down_write(&_origins_lock); __insert_dm_origin(o); up_write(&_origins_lock); } static void origin_postsuspend(struct dm_target *ti) { struct dm_origin *o = ti->private; down_write(&_origins_lock); __remove_dm_origin(o); up_write(&_origins_lock); } static void origin_status(struct dm_target *ti, status_type_t type, unsigned int status_flags, char *result, unsigned int maxlen) { struct dm_origin *o = ti->private; switch (type) { case STATUSTYPE_INFO: result[0] = '\0'; break; case STATUSTYPE_TABLE: snprintf(result, maxlen, "%s", o->dev->name); break; case STATUSTYPE_IMA: result[0] = '\0'; break; } } static int origin_iterate_devices(struct dm_target *ti, iterate_devices_callout_fn fn, void *data) { struct dm_origin *o = ti->private; return fn(ti, o->dev, 0, ti->len, data); } static struct target_type origin_target = { .name = "snapshot-origin", .version = {1, 9, 0}, .module = THIS_MODULE, .ctr = origin_ctr, .dtr = origin_dtr, .map = origin_map, .resume = origin_resume, .postsuspend = origin_postsuspend, .status = origin_status, .iterate_devices = origin_iterate_devices, }; static struct target_type snapshot_target = { .name = "snapshot", .version = {1, 16, 0}, .module = THIS_MODULE, .ctr = snapshot_ctr, .dtr = snapshot_dtr, .map = snapshot_map, .end_io = snapshot_end_io, .preresume = snapshot_preresume, .resume = snapshot_resume, .status = snapshot_status, .iterate_devices = snapshot_iterate_devices, .io_hints = snapshot_io_hints, }; static struct target_type merge_target = { .name = dm_snapshot_merge_target_name, .version = {1, 5, 0}, .module = THIS_MODULE, .ctr = snapshot_ctr, .dtr = snapshot_dtr, .map = snapshot_merge_map, .end_io = snapshot_end_io, .presuspend = snapshot_merge_presuspend, .preresume = snapshot_preresume, .resume = snapshot_merge_resume, .status = snapshot_status, .iterate_devices = snapshot_iterate_devices, .io_hints = snapshot_io_hints, }; static int __init dm_snapshot_init(void) { int r; r = dm_exception_store_init(); if (r) { DMERR("Failed to initialize exception stores"); return r; } r = init_origin_hash(); if (r) { DMERR("init_origin_hash failed."); goto bad_origin_hash; } exception_cache = KMEM_CACHE(dm_exception, 0); if (!exception_cache) { DMERR("Couldn't create exception cache."); r = -ENOMEM; goto bad_exception_cache; } pending_cache = KMEM_CACHE(dm_snap_pending_exception, 0); if (!pending_cache) { DMERR("Couldn't create pending cache."); r = -ENOMEM; goto bad_pending_cache; } r = dm_register_target(&snapshot_target); if (r < 0) goto bad_register_snapshot_target; r = dm_register_target(&origin_target); if (r < 0) goto bad_register_origin_target; r = dm_register_target(&merge_target); if (r < 0) goto bad_register_merge_target; return 0; bad_register_merge_target: dm_unregister_target(&origin_target); bad_register_origin_target: dm_unregister_target(&snapshot_target); bad_register_snapshot_target: kmem_cache_destroy(pending_cache); bad_pending_cache: kmem_cache_destroy(exception_cache); bad_exception_cache: exit_origin_hash(); bad_origin_hash: dm_exception_store_exit(); return r; } static void __exit dm_snapshot_exit(void) { dm_unregister_target(&snapshot_target); dm_unregister_target(&origin_target); dm_unregister_target(&merge_target); exit_origin_hash(); kmem_cache_destroy(pending_cache); kmem_cache_destroy(exception_cache); dm_exception_store_exit(); } /* Module hooks */ module_init(dm_snapshot_init); module_exit(dm_snapshot_exit); MODULE_DESCRIPTION(DM_NAME " snapshot target"); MODULE_AUTHOR("Joe Thornber"); MODULE_LICENSE("GPL"); MODULE_ALIAS("dm-snapshot-origin"); MODULE_ALIAS("dm-snapshot-merge");
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