/* * dm-snapshot.c * * 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/mempool.h> #include <linux/module.h> #include <linux/slab.h> #include <linux/vmalloc.h> #include <linux/log2.h> #include <linux/dm-kcopyd.h> #include <linux/workqueue.h> #include "dm-exception-store.h" #define DM_MSG_PREFIX "snapshots" /* * The percentage increment we will wake up users at */ #define WAKE_UP_PERCENT 5 /* * kcopyd priority of snapshot operations */ #define SNAPSHOT_COPY_PRIORITY 2 /* * Reserve 1MB for each snapshot initially (with minimum of 1 page). */ #define SNAPSHOT_PAGES (((1UL << 20) >> PAGE_SHIFT) ? : 1) /* * 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 exception_table { uint32_t hash_mask; unsigned hash_shift; struct list_head *table; }; struct dm_snapshot { struct rw_semaphore lock; struct dm_dev *origin; /* List of snapshots per Origin */ struct list_head list; /* You can't use a snapshot if this is 0 (e.g. if full) */ int valid; /* Origin writes don't trigger exceptions until this is set */ int active; mempool_t *pending_pool; atomic_t pending_exceptions_count; struct exception_table pending; struct exception_table complete; /* * pe_lock protects all pending_exception operations and access * as well as the snapshot_bios list. */ spinlock_t pe_lock; /* The on disk metadata handler */ struct dm_exception_store *store; struct dm_kcopyd_client *kcopyd_client; /* Queue of snapshot writes for ksnapd to flush */ struct bio_list queued_bios; struct work_struct queued_bios_work; /* Chunks with outstanding reads */ mempool_t *tracked_chunk_pool; spinlock_t tracked_chunk_lock; struct hlist_head tracked_chunk_hash[DM_TRACKED_CHUNK_HASH_SIZE]; }; static struct workqueue_struct *ksnapd; static void flush_queued_bios(struct work_struct *work); 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_snap_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; /* * Short-term queue of pending exceptions prior to submission. */ struct list_head list; /* * The primary pending_exception is the one that holds * the ref_count and the list of origin_bios for a * group of pending_exceptions. It is always last to get freed. * These fields get set up when writing to the origin. */ struct dm_snap_pending_exception *primary_pe; /* * Number of pending_exceptions processing this chunk. * When this drops to zero we must complete the origin bios. * If incrementing or decrementing this, hold pe->snap->lock for * the sibling concerned and not pe->primary_pe->snap->lock unless * they are the same. */ atomic_t ref_count; /* Pointer back to snapshot context */ struct dm_snapshot *snap; /* * 1 indicates the exception has already been sent to * kcopyd. */ int started; }; /* * 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 struct kmem_cache *tracked_chunk_cache; static struct dm_snap_tracked_chunk *track_chunk(struct dm_snapshot *s, chunk_t chunk) { struct dm_snap_tracked_chunk *c = mempool_alloc(s->tracked_chunk_pool, GFP_NOIO); unsigned long flags; c->chunk = chunk; spin_lock_irqsave(&s->tracked_chunk_lock, flags); hlist_add_head(&c->node, &s->tracked_chunk_hash[DM_TRACKED_CHUNK_HASH(chunk)]); spin_unlock_irqrestore(&s->tracked_chunk_lock, flags); return c; } static void stop_tracking_chunk(struct dm_snapshot *s, struct dm_snap_tracked_chunk *c) { unsigned long flags; spin_lock_irqsave(&s->tracked_chunk_lock, flags); hlist_del(&c->node); spin_unlock_irqrestore(&s->tracked_chunk_lock, flags); mempool_free(c, s->tracked_chunk_pool); } static int __chunk_is_tracked(struct dm_snapshot *s, chunk_t chunk) { struct dm_snap_tracked_chunk *c; struct hlist_node *hn; int found = 0; spin_lock_irq(&s->tracked_chunk_lock); hlist_for_each_entry(c, hn, &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; } /* * 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; }; /* * 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 rw_semaphore _origins_lock; static int init_origin_hash(void) { int i; _origins = kmalloc(ORIGIN_HASH_SIZE * sizeof(struct list_head), GFP_KERNEL); if (!_origins) { DMERR("unable to allocate memory"); return -ENOMEM; } for (i = 0; i < ORIGIN_HASH_SIZE; i++) INIT_LIST_HEAD(_origins + i); init_rwsem(&_origins_lock); return 0; } static void exit_origin_hash(void) { kfree(_origins); } static unsigned 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); } /* * Make a note of the snapshot and its origin so we can look it * up when the origin has a write on it. */ static int register_snapshot(struct dm_snapshot *snap) { struct origin *o, *new_o; struct block_device *bdev = snap->origin->bdev; new_o = kmalloc(sizeof(*new_o), GFP_KERNEL); if (!new_o) return -ENOMEM; down_write(&_origins_lock); 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); } list_add_tail(&snap->list, &o->snapshots); up_write(&_origins_lock); return 0; } 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 (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 int init_exception_table(struct exception_table *et, uint32_t size, unsigned hash_shift) { unsigned int i; et->hash_shift = hash_shift; et->hash_mask = size - 1; et->table = dm_vcalloc(size, sizeof(struct list_head)); if (!et->table) return -ENOMEM; for (i = 0; i < size; i++) INIT_LIST_HEAD(et->table + i); return 0; } static void exit_exception_table(struct exception_table *et, struct kmem_cache *mem) { struct list_head *slot; struct dm_snap_exception *ex, *next; int i, size; size = et->hash_mask + 1; for (i = 0; i < size; i++) { slot = et->table + i; list_for_each_entry_safe (ex, next, slot, hash_list) kmem_cache_free(mem, ex); } vfree(et->table); } static uint32_t exception_hash(struct exception_table *et, chunk_t chunk) { return (chunk >> et->hash_shift) & et->hash_mask; } static void insert_exception(struct exception_table *eh, struct dm_snap_exception *e) { struct list_head *l = &eh->table[exception_hash(eh, e->old_chunk)]; list_add(&e->hash_list, l); } static void remove_exception(struct dm_snap_exception *e) { list_del(&e->hash_list); } /* * Return the exception data for a sector, or NULL if not * remapped. */ static struct dm_snap_exception *lookup_exception(struct exception_table *et, chunk_t chunk) { struct list_head *slot; struct dm_snap_exception *e; slot = &et->table[exception_hash(et, chunk)]; list_for_each_entry (e, slot, hash_list) if (chunk >= e->old_chunk && chunk <= e->old_chunk + dm_consecutive_chunk_count(e)) return e; return NULL; } static struct dm_snap_exception *alloc_exception(void) { struct dm_snap_exception *e; e = kmem_cache_alloc(exception_cache, GFP_NOIO); if (!e) e = kmem_cache_alloc(exception_cache, GFP_ATOMIC); return e; } static void free_exception(struct dm_snap_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_dec(); atomic_dec(&s->pending_exceptions_count); } static void insert_completed_exception(struct dm_snapshot *s, struct dm_snap_exception *new_e) { struct exception_table *eh = &s->complete; struct list_head *l; struct dm_snap_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 */ list_for_each_entry_reverse(e, 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_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_exception(new_e); return; } if (new_e->old_chunk > e->old_chunk) break; } out: list_add(&new_e->hash_list, e ? &e->hash_list : l); } /* * 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_snapshot *s = context; struct dm_snap_exception *e; e = alloc_exception(); if (!e) return -ENOMEM; e->old_chunk = old; /* Consecutive_count is implicitly initialised to zero */ e->new_chunk = new; insert_completed_exception(s, e); return 0; } /* * Hard coded magic. */ static int calc_max_buckets(void) { /* use a fixed size of 2MB */ unsigned long mem = 2 * 1024 * 1024; mem /= sizeof(struct list_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, origin_dev_size, max_buckets; /* * Calculate based on the size of the original volume or * the COW volume... */ cow_dev_size = get_dev_size(s->store->cow->bdev); origin_dev_size = get_dev_size(s->origin->bdev); max_buckets = calc_max_buckets(); hash_size = min(origin_dev_size, cow_dev_size) >> s->store->chunk_shift; hash_size = min(hash_size, max_buckets); hash_size = rounddown_pow_of_two(hash_size); if (init_exception_table(&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 (init_exception_table(&s->pending, hash_size, 0)) { exit_exception_table(&s->complete, exception_cache); return -ENOMEM; } return 0; } /* * Construct a snapshot mapping: <origin_dev> <COW-dev> <p/n> <chunk-size> */ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv) { struct dm_snapshot *s; int i; int r = -EINVAL; char *origin_path; struct dm_exception_store *store; unsigned args_used; if (argc != 4) { ti->error = "requires exactly 4 arguments"; r = -EINVAL; goto bad_args; } origin_path = argv[0]; argv++; argc--; r = dm_exception_store_create(ti, argc, argv, &args_used, &store); if (r) { ti->error = "Couldn't create exception store"; r = -EINVAL; goto bad_args; } argv += args_used; argc -= args_used; s = kmalloc(sizeof(*s), GFP_KERNEL); if (!s) { ti->error = "Cannot allocate snapshot context private " "structure"; r = -ENOMEM; goto bad_snap; } r = dm_get_device(ti, origin_path, 0, ti->len, FMODE_READ, &s->origin); if (r) { ti->error = "Cannot get origin device"; goto bad_origin; } s->store = store; s->valid = 1; s->active = 0; atomic_set(&s->pending_exceptions_count, 0); init_rwsem(&s->lock); spin_lock_init(&s->pe_lock); /* 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; } r = dm_kcopyd_client_create(SNAPSHOT_PAGES, &s->kcopyd_client); if (r) { ti->error = "Could not create kcopyd client"; goto bad_kcopyd; } s->pending_pool = mempool_create_slab_pool(MIN_IOS, pending_cache); if (!s->pending_pool) { ti->error = "Could not allocate mempool for pending exceptions"; goto bad_pending_pool; } s->tracked_chunk_pool = mempool_create_slab_pool(MIN_IOS, tracked_chunk_cache); if (!s->tracked_chunk_pool) { ti->error = "Could not allocate tracked_chunk mempool for " "tracking reads"; goto bad_tracked_chunk_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); /* Metadata must only be loaded into one table at once */ 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_load_and_register; } else if (r > 0) { s->valid = 0; DMWARN("Snapshot is marked invalid."); } bio_list_init(&s->queued_bios); INIT_WORK(&s->queued_bios_work, flush_queued_bios); /* Add snapshot to the list of snapshots for this origin */ /* Exceptions aren't triggered till snapshot_resume() is called */ if (register_snapshot(s)) { r = -EINVAL; ti->error = "Cannot register snapshot origin"; goto bad_load_and_register; } ti->private = s; ti->split_io = s->store->chunk_size; ti->num_flush_requests = 1; return 0; bad_load_and_register: mempool_destroy(s->tracked_chunk_pool); bad_tracked_chunk_pool: mempool_destroy(s->pending_pool); bad_pending_pool: dm_kcopyd_client_destroy(s->kcopyd_client); bad_kcopyd: exit_exception_table(&s->pending, pending_cache); exit_exception_table(&s->complete, exception_cache); bad_hash_tables: dm_put_device(ti, s->origin); bad_origin: kfree(s); bad_snap: dm_exception_store_destroy(store); bad_args: return r; } static void __free_exceptions(struct dm_snapshot *s) { dm_kcopyd_client_destroy(s->kcopyd_client); s->kcopyd_client = NULL; exit_exception_table(&s->pending, pending_cache); exit_exception_table(&s->complete, exception_cache); } static void snapshot_dtr(struct dm_target *ti) { #ifdef CONFIG_DM_DEBUG int i; #endif struct dm_snapshot *s = ti->private; flush_workqueue(ksnapd); /* 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)) msleep(1); /* * Ensure instructions in mempool_destroy 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 mempool_destroy(s->tracked_chunk_pool); __free_exceptions(s); mempool_destroy(s->pending_pool); dm_put_device(ti, s->origin); dm_exception_store_destroy(s->store); kfree(s); } /* * 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; generic_make_request(bio); bio = n; } } static void flush_queued_bios(struct work_struct *work) { struct dm_snapshot *s = container_of(work, struct dm_snapshot, queued_bios_work); struct bio *queued_bios; unsigned long flags; spin_lock_irqsave(&s->pe_lock, flags); queued_bios = bio_list_get(&s->queued_bios); spin_unlock_irqrestore(&s->pe_lock, flags); flush_bios(queued_bios); } /* * 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->store->ti->table); } static void get_pending_exception(struct dm_snap_pending_exception *pe) { atomic_inc(&pe->ref_count); } static struct bio *put_pending_exception(struct dm_snap_pending_exception *pe) { struct dm_snap_pending_exception *primary_pe; struct bio *origin_bios = NULL; primary_pe = pe->primary_pe; /* * If this pe is involved in a write to the origin and * it is the last sibling to complete then release * the bios for the original write to the origin. */ if (primary_pe && atomic_dec_and_test(&primary_pe->ref_count)) { origin_bios = bio_list_get(&primary_pe->origin_bios); free_pending_exception(primary_pe); } /* * Free the pe if it's not linked to an origin write or if * it's not itself a primary pe. */ if (!primary_pe || primary_pe != pe) free_pending_exception(pe); return origin_bios; } static void pending_complete(struct dm_snap_pending_exception *pe, int success) { struct dm_snap_exception *e; struct dm_snapshot *s = pe->snap; struct bio *origin_bios = NULL; struct bio *snapshot_bios = NULL; int error = 0; if (!success) { /* Read/write error - snapshot is unusable */ down_write(&s->lock); __invalidate_snapshot(s, -EIO); error = 1; goto out; } e = alloc_exception(); if (!e) { down_write(&s->lock); __invalidate_snapshot(s, -ENOMEM); error = 1; goto out; } *e = pe->e; down_write(&s->lock); if (!s->valid) { free_exception(e); error = 1; goto out; } /* * Check for conflicting reads. This is extremely improbable, * so msleep(1) is sufficient and there is no need for a wait queue. */ while (__chunk_is_tracked(s, pe->e.old_chunk)) msleep(1); /* * Add a proper exception, and remove the * in-flight exception from the list. */ insert_completed_exception(s, e); out: remove_exception(&pe->e); snapshot_bios = bio_list_get(&pe->snapshot_bios); origin_bios = put_pending_exception(pe); up_write(&s->lock); /* Submit any pending write bios */ if (error) error_bios(snapshot_bios); else flush_bios(snapshot_bios); flush_bios(origin_bios); } static void commit_callback(void *context, int success) { struct dm_snap_pending_exception *pe = context; pending_complete(pe, success); } /* * 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; if (read_err || write_err) pending_complete(pe, 0); else /* Update the metadata if we are persistent */ s->store->type->commit_exception(s->store, &pe->e, commit_callback, pe); } /* * 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(s->store->chunk_size, dev_size - src.sector); dest.bdev = s->store->cow->bdev; dest.sector = chunk_to_sector(s->store, pe->e.new_chunk); dest.count = src.count; /* Hand over to kcopyd */ dm_kcopyd_copy(s->kcopyd_client, &src, 1, &dest, 0, copy_callback, pe); } static struct dm_snap_pending_exception * __lookup_pending_exception(struct dm_snapshot *s, chunk_t chunk) { struct dm_snap_exception *e = lookup_exception(&s->pending, chunk); if (!e) return NULL; return container_of(e, struct dm_snap_pending_exception, e); } /* * 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 snap->lock 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; } pe->e.old_chunk = chunk; bio_list_init(&pe->origin_bios); bio_list_init(&pe->snapshot_bios); pe->primary_pe = NULL; atomic_set(&pe->ref_count, 0); pe->started = 0; if (s->store->type->prepare_exception(s->store, &pe->e)) { free_pending_exception(pe); return NULL; } get_pending_exception(pe); insert_exception(&s->pending, &pe->e); return pe; } static void remap_exception(struct dm_snapshot *s, struct dm_snap_exception *e, struct bio *bio, chunk_t chunk) { bio->bi_bdev = s->store->cow->bdev; bio->bi_sector = chunk_to_sector(s->store, dm_chunk_number(e->new_chunk) + (chunk - e->old_chunk)) + (bio->bi_sector & s->store->chunk_mask); } static int snapshot_map(struct dm_target *ti, struct bio *bio, union map_info *map_context) { struct dm_snap_exception *e; struct dm_snapshot *s = ti->private; int r = DM_MAPIO_REMAPPED; chunk_t chunk; struct dm_snap_pending_exception *pe = NULL; if (unlikely(bio_empty_barrier(bio))) { bio->bi_bdev = s->store->cow->bdev; return DM_MAPIO_REMAPPED; } chunk = sector_to_chunk(s->store, bio->bi_sector); /* Full snapshots are not usable */ /* To get here the table must be live so s->active is always set. */ if (!s->valid) return -EIO; /* FIXME: should only take write lock if we need * to copy an exception */ down_write(&s->lock); if (!s->valid) { r = -EIO; goto out_unlock; } /* If the block is already remapped - use that, else remap it */ e = lookup_exception(&s->complete, chunk); if (e) { remap_exception(s, e, bio, chunk); goto out_unlock; } /* * Write to snapshot - higher level takes care of RW/RO * flags so we should only get this if we are * writeable. */ if (bio_rw(bio) == WRITE) { pe = __lookup_pending_exception(s, chunk); if (!pe) { up_write(&s->lock); pe = alloc_pending_exception(s); down_write(&s->lock); if (!s->valid) { free_pending_exception(pe); r = -EIO; goto out_unlock; } e = 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) { __invalidate_snapshot(s, -ENOMEM); r = -EIO; goto out_unlock; } } remap_exception(s, &pe->e, bio, chunk); bio_list_add(&pe->snapshot_bios, bio); r = DM_MAPIO_SUBMITTED; if (!pe->started) { /* this is protected by snap->lock */ pe->started = 1; up_write(&s->lock); start_copy(pe); goto out; } } else { bio->bi_bdev = s->origin->bdev; map_context->ptr = track_chunk(s, chunk); } out_unlock: up_write(&s->lock); out: return r; } static int snapshot_end_io(struct dm_target *ti, struct bio *bio, int error, union map_info *map_context) { struct dm_snapshot *s = ti->private; struct dm_snap_tracked_chunk *c = map_context->ptr; if (c) stop_tracking_chunk(s, c); return 0; } static void snapshot_resume(struct dm_target *ti) { struct dm_snapshot *s = ti->private; down_write(&s->lock); s->active = 1; up_write(&s->lock); } static int snapshot_status(struct dm_target *ti, status_type_t type, char *result, unsigned int maxlen) { unsigned sz = 0; struct dm_snapshot *snap = ti->private; switch (type) { case STATUSTYPE_INFO: if (!snap->valid) DMEMIT("Invalid"); else { if (snap->store->type->fraction_full) { sector_t numerator, denominator; snap->store->type->fraction_full(snap->store, &numerator, &denominator); DMEMIT("%llu/%llu", (unsigned long long)numerator, (unsigned long long)denominator); } else DMEMIT("Unknown"); } 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", snap->origin->name); snap->store->type->status(snap->store, type, result + sz, maxlen - sz); break; } return 0; } static int snapshot_iterate_devices(struct dm_target *ti, iterate_devices_callout_fn fn, void *data) { struct dm_snapshot *snap = ti->private; return fn(ti, snap->origin, 0, ti->len, data); } /*----------------------------------------------------------------- * Origin methods *---------------------------------------------------------------*/ static int __origin_write(struct list_head *snapshots, struct bio *bio) { int r = DM_MAPIO_REMAPPED, first = 0; struct dm_snapshot *snap; struct dm_snap_exception *e; struct dm_snap_pending_exception *pe, *next_pe, *primary_pe = NULL; chunk_t chunk; LIST_HEAD(pe_queue); /* Do all the snapshots on this origin */ list_for_each_entry (snap, snapshots, list) { down_write(&snap->lock); /* Only deal with valid and active snapshots */ if (!snap->valid || !snap->active) goto next_snapshot; /* Nothing to do if writing beyond end of snapshot */ if (bio->bi_sector >= dm_table_get_size(snap->store->ti->table)) goto next_snapshot; /* * Remember, different snapshots can have * different chunk sizes. */ chunk = sector_to_chunk(snap->store, bio->bi_sector); /* * Check exception table to see if block * is already remapped in this snapshot * and trigger an exception if not. * * ref_count is initialised to 1 so pending_complete() * won't destroy the primary_pe while we're inside this loop. */ e = lookup_exception(&snap->complete, chunk); if (e) goto next_snapshot; pe = __lookup_pending_exception(snap, chunk); if (!pe) { up_write(&snap->lock); pe = alloc_pending_exception(snap); down_write(&snap->lock); if (!snap->valid) { free_pending_exception(pe); goto next_snapshot; } e = lookup_exception(&snap->complete, chunk); if (e) { free_pending_exception(pe); goto next_snapshot; } pe = __find_pending_exception(snap, pe, chunk); if (!pe) { __invalidate_snapshot(snap, -ENOMEM); goto next_snapshot; } } if (!primary_pe) { /* * Either every pe here has same * primary_pe or none has one yet. */ if (pe->primary_pe) primary_pe = pe->primary_pe; else { primary_pe = pe; first = 1; } bio_list_add(&primary_pe->origin_bios, bio); r = DM_MAPIO_SUBMITTED; } if (!pe->primary_pe) { pe->primary_pe = primary_pe; get_pending_exception(primary_pe); } if (!pe->started) { pe->started = 1; list_add_tail(&pe->list, &pe_queue); } next_snapshot: up_write(&snap->lock); } if (!primary_pe) return r; /* * If this is the first time we're processing this chunk and * ref_count is now 1 it means all the pending exceptions * got completed while we were in the loop above, so it falls to * us here to remove the primary_pe and submit any origin_bios. */ if (first && atomic_dec_and_test(&primary_pe->ref_count)) { flush_bios(bio_list_get(&primary_pe->origin_bios)); free_pending_exception(primary_pe); /* If we got here, pe_queue is necessarily empty. */ return r; } /* * Now that we have a complete pe list we can start the copying. */ list_for_each_entry_safe(pe, next_pe, &pe_queue, list) start_copy(pe); return r; } /* * Called on a write from the origin driver. */ static int do_origin(struct dm_dev *origin, struct bio *bio) { struct origin *o; int r = DM_MAPIO_REMAPPED; down_read(&_origins_lock); o = __lookup_origin(origin->bdev); if (o) r = __origin_write(&o->snapshots, bio); up_read(&_origins_lock); return r; } /* * 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_dev *dev; if (argc != 1) { ti->error = "origin: incorrect number of arguments"; return -EINVAL; } r = dm_get_device(ti, argv[0], 0, ti->len, dm_table_get_mode(ti->table), &dev); if (r) { ti->error = "Cannot get target device"; return r; } ti->private = dev; ti->num_flush_requests = 1; return 0; } static void origin_dtr(struct dm_target *ti) { struct dm_dev *dev = ti->private; dm_put_device(ti, dev); } static int origin_map(struct dm_target *ti, struct bio *bio, union map_info *map_context) { struct dm_dev *dev = ti->private; bio->bi_bdev = dev->bdev; if (unlikely(bio_empty_barrier(bio))) return DM_MAPIO_REMAPPED; /* Only tell snapshots if this is a write */ return (bio_rw(bio) == WRITE) ? do_origin(dev, bio) : DM_MAPIO_REMAPPED; } #define min_not_zero(l, r) (l == 0) ? r : ((r == 0) ? l : min(l, r)) /* * Set the target "split_io" field to the minimum of all the snapshots' * chunk sizes. */ static void origin_resume(struct dm_target *ti) { struct dm_dev *dev = ti->private; struct dm_snapshot *snap; struct origin *o; chunk_t chunk_size = 0; down_read(&_origins_lock); o = __lookup_origin(dev->bdev); if (o) list_for_each_entry (snap, &o->snapshots, list) chunk_size = min_not_zero(chunk_size, snap->store->chunk_size); up_read(&_origins_lock); ti->split_io = chunk_size; } static int origin_status(struct dm_target *ti, status_type_t type, char *result, unsigned int maxlen) { struct dm_dev *dev = ti->private; switch (type) { case STATUSTYPE_INFO: result[0] = '\0'; break; case STATUSTYPE_TABLE: snprintf(result, maxlen, "%s", dev->name); break; } return 0; } static int origin_iterate_devices(struct dm_target *ti, iterate_devices_callout_fn fn, void *data) { struct dm_dev *dev = ti->private; return fn(ti, dev, 0, ti->len, data); } static struct target_type origin_target = { .name = "snapshot-origin", .version = {1, 7, 0}, .module = THIS_MODULE, .ctr = origin_ctr, .dtr = origin_dtr, .map = origin_map, .resume = origin_resume, .status = origin_status, .iterate_devices = origin_iterate_devices, }; static struct target_type snapshot_target = { .name = "snapshot", .version = {1, 7, 0}, .module = THIS_MODULE, .ctr = snapshot_ctr, .dtr = snapshot_dtr, .map = snapshot_map, .end_io = snapshot_end_io, .resume = snapshot_resume, .status = snapshot_status, .iterate_devices = snapshot_iterate_devices, }; 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 = dm_register_target(&snapshot_target); if (r) { DMERR("snapshot target register failed %d", r); return r; } r = dm_register_target(&origin_target); if (r < 0) { DMERR("Origin target register failed %d", r); goto bad1; } r = init_origin_hash(); if (r) { DMERR("init_origin_hash failed."); goto bad2; } exception_cache = KMEM_CACHE(dm_snap_exception, 0); if (!exception_cache) { DMERR("Couldn't create exception cache."); r = -ENOMEM; goto bad3; } pending_cache = KMEM_CACHE(dm_snap_pending_exception, 0); if (!pending_cache) { DMERR("Couldn't create pending cache."); r = -ENOMEM; goto bad4; } tracked_chunk_cache = KMEM_CACHE(dm_snap_tracked_chunk, 0); if (!tracked_chunk_cache) { DMERR("Couldn't create cache to track chunks in use."); r = -ENOMEM; goto bad5; } ksnapd = create_singlethread_workqueue("ksnapd"); if (!ksnapd) { DMERR("Failed to create ksnapd workqueue."); r = -ENOMEM; goto bad_pending_pool; } return 0; bad_pending_pool: kmem_cache_destroy(tracked_chunk_cache); bad5: kmem_cache_destroy(pending_cache); bad4: kmem_cache_destroy(exception_cache); bad3: exit_origin_hash(); bad2: dm_unregister_target(&origin_target); bad1: dm_unregister_target(&snapshot_target); return r; } static void __exit dm_snapshot_exit(void) { destroy_workqueue(ksnapd); dm_unregister_target(&snapshot_target); dm_unregister_target(&origin_target); exit_origin_hash(); kmem_cache_destroy(pending_cache); kmem_cache_destroy(exception_cache); kmem_cache_destroy(tracked_chunk_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");