1 files changed, 1208 insertions, 0 deletions

diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
new file mode 100644
index 000000000000..7e691ab9a748
--- /dev/null
+++ b/drivers/md/dm-snap.c
@@ -0,0 +1,1208 @@
+/*
+ * dm-snapshot.c
+ *
+ * Copyright (C) 2001-2002 Sistina Software (UK) Limited.
+ *
+ * This file is released under the GPL.
+ */
+
+#include <linux/blkdev.h>
+#include <linux/config.h>
+#include <linux/ctype.h>
+#include <linux/device-mapper.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 "dm-snap.h"
+#include "dm-bio-list.h"
+#include "kcopyd.h"
+
+/*
+ * The percentage increment we will wake up users at
+ */
+#define WAKE_UP_PERCENT 5
+
+/*
+ * kcopyd priority of snapshot operations
+ */
+#define SNAPSHOT_COPY_PRIORITY 2
+
+/*
+ * Each snapshot reserves this many pages for io
+ */
+#define SNAPSHOT_PAGES 256
+
+struct pending_exception {
+        struct 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;
+
+        /*
+         * Other pending_exceptions that are processing this
+         * chunk.  When this list is empty, we know we can
+         * complete the origins.
+         */
+        struct list_head siblings;
+
+        /* 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 kmem_cache_t *exception_cache;
+static kmem_cache_t *pending_cache;
+static mempool_t *pending_pool;
+
+/*
+ * 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("Device mapper: Snapshot: 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 inline 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);
+}
+
+/*
+ * 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;
+        struct block_device *bdev = snap->origin->bdev;
+
+        down_write(&_origins_lock);
+        o = __lookup_origin(bdev);
+
+        if (!o) {
+                /* New origin */
+                o = kmalloc(sizeof(*o), GFP_KERNEL);
+                if (!o) {
+                        up_write(&_origins_lock);
+                        return -ENOMEM;
+                }
+
+                /* 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.
+ */
+static int init_exception_table(struct exception_table *et, uint32_t size)
+{
+        unsigned int i;
+
+        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, kmem_cache_t *mem)
+{
+        struct list_head *slot;
+        struct 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 inline uint32_t exception_hash(struct exception_table *et, chunk_t chunk)
+{
+        return chunk & et->hash_mask;
+}
+
+static void insert_exception(struct exception_table *eh, struct exception *e)
+{
+        struct list_head *l = &eh->table[exception_hash(eh, e->old_chunk)];
+        list_add(&e->hash_list, l);
+}
+
+static inline void remove_exception(struct exception *e)
+{
+        list_del(&e->hash_list);
+}
+
+/*
+ * Return the exception data for a sector, or NULL if not
+ * remapped.
+ */
+static struct exception *lookup_exception(struct exception_table *et,
+                                          chunk_t chunk)
+{
+        struct list_head *slot;
+        struct exception *e;
+
+        slot = &et->table[exception_hash(et, chunk)];
+        list_for_each_entry (e, slot, hash_list)
+                if (e->old_chunk == chunk)
+                        return e;
+
+        return NULL;
+}
+
+static inline struct exception *alloc_exception(void)
+{
+        struct exception *e;
+
+        e = kmem_cache_alloc(exception_cache, GFP_NOIO);
+        if (!e)
+                e = kmem_cache_alloc(exception_cache, GFP_ATOMIC);
+
+        return e;
+}
+
+static inline void free_exception(struct exception *e)
+{
+        kmem_cache_free(exception_cache, e);
+}
+
+static inline struct pending_exception *alloc_pending_exception(void)
+{
+        return mempool_alloc(pending_pool, GFP_NOIO);
+}
+
+static inline void free_pending_exception(struct pending_exception *pe)
+{
+        mempool_free(pe, pending_pool);
+}
+
+int dm_add_exception(struct dm_snapshot *s, chunk_t old, chunk_t new)
+{
+        struct exception *e;
+
+        e = alloc_exception();
+        if (!e)
+                return -ENOMEM;
+
+        e->old_chunk = old;
+        e->new_chunk = new;
+        insert_exception(&s->complete, 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;
+}
+
+/*
+ * Rounds a number down to a power of 2.
+ */
+static inline uint32_t round_down(uint32_t n)
+{
+        while (n & (n - 1))
+                n &= (n - 1);
+        return n;
+}
+
+/*
+ * 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->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->chunk_shift;
+        hash_size = min(hash_size, max_buckets);
+
+        /* Round it down to a power of 2 */
+        hash_size = round_down(hash_size);
+        if (init_exception_table(&s->complete, hash_size))
+                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)) {
+                exit_exception_table(&s->complete, exception_cache);
+                return -ENOMEM;
+        }
+
+        return 0;
+}
+
+/*
+ * Round a number up to the nearest 'size' boundary.  size must
+ * be a power of 2.
+ */
+static inline ulong round_up(ulong n, ulong size)
+{
+        size--;
+        return (n + size) & ~size;
+}
+
+/*
+ * 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;
+        unsigned long chunk_size;
+        int r = -EINVAL;
+        char persistent;
+        char *origin_path;
+        char *cow_path;
+        char *value;
+        int blocksize;
+
+        if (argc < 4) {
+                ti->error = "dm-snapshot: requires exactly 4 arguments";
+                r = -EINVAL;
+                goto bad1;
+        }
+
+        origin_path = argv[0];
+        cow_path = argv[1];
+        persistent = toupper(*argv[2]);
+
+        if (persistent != 'P' && persistent != 'N') {
+                ti->error = "Persistent flag is not P or N";
+                r = -EINVAL;
+                goto bad1;
+        }
+
+        chunk_size = simple_strtoul(argv[3], &value, 10);
+        if (chunk_size == 0 || value == NULL) {
+                ti->error = "Invalid chunk size";
+                r = -EINVAL;
+                goto bad1;
+        }
+
+        s = kmalloc(sizeof(*s), GFP_KERNEL);
+        if (s == NULL) {
+                ti->error = "Cannot allocate snapshot context private "
+                    "structure";
+                r = -ENOMEM;
+                goto bad1;
+        }
+
+        r = dm_get_device(ti, origin_path, 0, ti->len, FMODE_READ, &s->origin);
+        if (r) {
+                ti->error = "Cannot get origin device";
+                goto bad2;
+        }
+
+        r = dm_get_device(ti, cow_path, 0, 0,
+                          FMODE_READ | FMODE_WRITE, &s->cow);
+        if (r) {
+                dm_put_device(ti, s->origin);
+                ti->error = "Cannot get COW device";
+                goto bad2;
+        }
+
+        /*
+         * Chunk size must be multiple of page size.  Silently
+         * round up if it's not.
+         */
+        chunk_size = round_up(chunk_size, PAGE_SIZE >> 9);
+
+        /* Validate the chunk size against the device block size */
+        blocksize = s->cow->bdev->bd_disk->queue->hardsect_size;
+        if (chunk_size % (blocksize >> 9)) {
+                ti->error = "Chunk size is not a multiple of device blocksize";
+                r = -EINVAL;
+                goto bad3;
+        }
+
+        /* Check chunk_size is a power of 2 */
+        if (chunk_size & (chunk_size - 1)) {
+                ti->error = "Chunk size is not a power of 2";
+                r = -EINVAL;
+                goto bad3;
+        }
+
+        s->chunk_size = chunk_size;
+        s->chunk_mask = chunk_size - 1;
+        s->type = persistent;
+        s->chunk_shift = ffs(chunk_size) - 1;
+
+        s->valid = 1;
+        s->have_metadata = 0;
+        s->last_percent = 0;
+        init_rwsem(&s->lock);
+        s->table = ti->table;
+
+        /* Allocate hash table for COW data */
+        if (init_hash_tables(s)) {
+                ti->error = "Unable to allocate hash table space";
+                r = -ENOMEM;
+                goto bad3;
+        }
+
+        /*
+         * Check the persistent flag - done here because we need the iobuf
+         * to check the LV header
+         */
+        s->store.snap = s;
+
+        if (persistent == 'P')
+                r = dm_create_persistent(&s->store, chunk_size);
+        else
+                r = dm_create_transient(&s->store, s, blocksize);
+
+        if (r) {
+                ti->error = "Couldn't create exception store";
+                r = -EINVAL;
+                goto bad4;
+        }
+
+        r = kcopyd_client_create(SNAPSHOT_PAGES, &s->kcopyd_client);
+        if (r) {
+                ti->error = "Could not create kcopyd client";
+                goto bad5;
+        }
+
+        /* Add snapshot to the list of snapshots for this origin */
+        if (register_snapshot(s)) {
+                r = -EINVAL;
+                ti->error = "Cannot register snapshot origin";
+                goto bad6;
+        }
+
+        ti->private = s;
+        ti->split_io = chunk_size;
+
+        return 0;
+
+ bad6:
+        kcopyd_client_destroy(s->kcopyd_client);
+
+ bad5:
+        s->store.destroy(&s->store);
+
+ bad4:
+        exit_exception_table(&s->pending, pending_cache);
+        exit_exception_table(&s->complete, exception_cache);
+
+ bad3:
+        dm_put_device(ti, s->cow);
+        dm_put_device(ti, s->origin);
+
+ bad2:
+        kfree(s);
+
+ bad1:
+        return r;
+}
+
+static void snapshot_dtr(struct dm_target *ti)
+{
+        struct dm_snapshot *s = (struct dm_snapshot *) ti->private;
+
+        unregister_snapshot(s);
+
+        exit_exception_table(&s->pending, pending_cache);
+        exit_exception_table(&s->complete, exception_cache);
+
+        /* Deallocate memory used */
+        s->store.destroy(&s->store);
+
+        dm_put_device(ti, s->origin);
+        dm_put_device(ti, s->cow);
+        kcopyd_client_destroy(s->kcopyd_client);
+        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;
+        }
+}
+
+/*
+ * 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->bi_size);
+                bio = n;
+        }
+}
+
+static struct bio *__flush_bios(struct pending_exception *pe)
+{
+        struct pending_exception *sibling;
+
+        if (list_empty(&pe->siblings))
+                return bio_list_get(&pe->origin_bios);
+
+        sibling = list_entry(pe->siblings.next,
+                             struct pending_exception, siblings);
+
+        list_del(&pe->siblings);
+
+        /* This is fine as long as kcopyd is single-threaded. If kcopyd
+         * becomes multi-threaded, we'll need some locking here.
+         */
+        bio_list_merge(&sibling->origin_bios, &pe->origin_bios);
+
+        return NULL;
+}
+
+static void pending_complete(struct pending_exception *pe, int success)
+{
+        struct exception *e;
+        struct dm_snapshot *s = pe->snap;
+        struct bio *flush = NULL;
+
+        if (success) {
+                e = alloc_exception();
+                if (!e) {
+                        DMWARN("Unable to allocate exception.");
+                        down_write(&s->lock);
+                        s->store.drop_snapshot(&s->store);
+                        s->valid = 0;
+                        flush = __flush_bios(pe);
+                        up_write(&s->lock);
+
+                        error_bios(bio_list_get(&pe->snapshot_bios));
+                        goto out;
+                }
+                *e = pe->e;
+
+                /*
+                 * Add a proper exception, and remove the
+                 * in-flight exception from the list.
+                 */
+                down_write(&s->lock);
+                insert_exception(&s->complete, e);
+                remove_exception(&pe->e);
+                flush = __flush_bios(pe);
+
+                /* Submit any pending write bios */
+                up_write(&s->lock);
+
+                flush_bios(bio_list_get(&pe->snapshot_bios));
+        } else {
+                /* Read/write error - snapshot is unusable */
+                down_write(&s->lock);
+                if (s->valid)
+                        DMERR("Error reading/writing snapshot");
+                s->store.drop_snapshot(&s->store);
+                s->valid = 0;
+                remove_exception(&pe->e);
+                flush = __flush_bios(pe);
+                up_write(&s->lock);
+
+                error_bios(bio_list_get(&pe->snapshot_bios));
+
+                dm_table_event(s->table);
+        }
+
+ out:
+        free_pending_exception(pe);
+
+        if (flush)
+                flush_bios(flush);
+}
+
+static void commit_callback(void *context, int success)
+{
+        struct pending_exception *pe = (struct pending_exception *) 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 int write_err, void *context)
+{
+        struct pending_exception *pe = (struct pending_exception *) 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.commit_exception(&s->store, &pe->e, commit_callback,
+                                          pe);
+}
+
+/*
+ * Dispatches the copy operation to kcopyd.
+ */
+static inline void start_copy(struct pending_exception *pe)
+{
+        struct dm_snapshot *s = pe->snap;
+        struct 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, pe->e.old_chunk);
+        src.count = min(s->chunk_size, dev_size - src.sector);
+
+        dest.bdev = s->cow->bdev;
+        dest.sector = chunk_to_sector(s, pe->e.new_chunk);
+        dest.count = src.count;
+
+        /* Hand over to kcopyd */
+        kcopyd_copy(s->kcopyd_client,
+                    &src, 1, &dest, 0, copy_callback, 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 snap->lock before calling
+ * this.
+ */
+static struct pending_exception *
+__find_pending_exception(struct dm_snapshot *s, struct bio *bio)
+{
+        struct exception *e;
+        struct pending_exception *pe;
+        chunk_t chunk = sector_to_chunk(s, bio->bi_sector);
+
+        /*
+         * Is there a pending exception for this already ?
+         */
+        e = lookup_exception(&s->pending, chunk);
+        if (e) {
+                /* cast the exception to a pending exception */
+                pe = container_of(e, struct pending_exception, e);
+
+        } else {
+                /*
+                 * Create a new pending exception, we don't want
+                 * to hold the lock while we do this.
+                 */
+                up_write(&s->lock);
+                pe = alloc_pending_exception();
+                down_write(&s->lock);
+
+                e = lookup_exception(&s->pending, chunk);
+                if (e) {
+                        free_pending_exception(pe);
+                        pe = container_of(e, struct pending_exception, e);
+                } else {
+                        pe->e.old_chunk = chunk;
+                        bio_list_init(&pe->origin_bios);
+                        bio_list_init(&pe->snapshot_bios);
+                        INIT_LIST_HEAD(&pe->siblings);
+                        pe->snap = s;
+                        pe->started = 0;
+
+                        if (s->store.prepare_exception(&s->store, &pe->e)) {
+                                free_pending_exception(pe);
+                                s->valid = 0;
+                                return NULL;
+                        }
+
+                        insert_exception(&s->pending, &pe->e);
+                }
+        }
+
+        return pe;
+}
+
+static inline void remap_exception(struct dm_snapshot *s, struct exception *e,
+                                   struct bio *bio)
+{
+        bio->bi_bdev = s->cow->bdev;
+        bio->bi_sector = chunk_to_sector(s, e->new_chunk) +
+                (bio->bi_sector & s->chunk_mask);
+}
+
+static int snapshot_map(struct dm_target *ti, struct bio *bio,
+                        union map_info *map_context)
+{
+        struct exception *e;
+        struct dm_snapshot *s = (struct dm_snapshot *) ti->private;
+        int r = 1;
+        chunk_t chunk;
+        struct pending_exception *pe;
+
+        chunk = sector_to_chunk(s, bio->bi_sector);
+
+        /* Full snapshots are not usable */
+        if (!s->valid)
+                return -1;
+
+        /*
+         * 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) {
+
+                /* FIXME: should only take write lock if we need
+                 * to copy an exception */
+                down_write(&s->lock);
+
+                /* If the block is already remapped - use that, else remap it */
+                e = lookup_exception(&s->complete, chunk);
+                if (e) {
+                        remap_exception(s, e, bio);
+                        up_write(&s->lock);
+
+                } else {
+                        pe = __find_pending_exception(s, bio);
+
+                        if (!pe) {
+                                if (s->store.drop_snapshot)
+                                        s->store.drop_snapshot(&s->store);
+                                s->valid = 0;
+                                r = -EIO;
+                                up_write(&s->lock);
+                        } else {
+                                remap_exception(s, &pe->e, bio);
+                                bio_list_add(&pe->snapshot_bios, bio);
+
+                                if (!pe->started) {
+                                        /* this is protected by snap->lock */
+                                        pe->started = 1;
+                                        up_write(&s->lock);
+                                        start_copy(pe);
+                                } else
+                                        up_write(&s->lock);
+                                r = 0;
+                        }
+                }
+
+        } else {
+                /*
+                 * FIXME: this read path scares me because we
+                 * always use the origin when we have a pending
+                 * exception.  However I can't think of a
+                 * situation where this is wrong - ejt.
+                 */
+
+                /* Do reads */
+                down_read(&s->lock);
+
+                /* See if it it has been remapped */
+                e = lookup_exception(&s->complete, chunk);
+                if (e)
+                        remap_exception(s, e, bio);
+                else
+                        bio->bi_bdev = s->origin->bdev;
+
+                up_read(&s->lock);
+        }
+
+        return r;
+}
+
+static void snapshot_resume(struct dm_target *ti)
+{
+        struct dm_snapshot *s = (struct dm_snapshot *) ti->private;
+
+        if (s->have_metadata)
+                return;
+
+        if (s->store.read_metadata(&s->store)) {
+                down_write(&s->lock);
+                s->valid = 0;
+                up_write(&s->lock);
+        }
+
+        s->have_metadata = 1;
+}
+
+static int snapshot_status(struct dm_target *ti, status_type_t type,
+                           char *result, unsigned int maxlen)
+{
+        struct dm_snapshot *snap = (struct dm_snapshot *) ti->private;
+
+        switch (type) {
+        case STATUSTYPE_INFO:
+                if (!snap->valid)
+                        snprintf(result, maxlen, "Invalid");
+                else {
+                        if (snap->store.fraction_full) {
+                                sector_t numerator, denominator;
+                                snap->store.fraction_full(&snap->store,
+                                                          &numerator,
+                                                          &denominator);
+                                snprintf(result, maxlen,
+                                         SECTOR_FORMAT "/" SECTOR_FORMAT,
+                                         numerator, denominator);
+                        }
+                        else
+                                snprintf(result, maxlen, "Unknown");
+                }
+                break;
+
+        case STATUSTYPE_TABLE:
+                /*
+                 * kdevname returns a static pointer so we need
+                 * to make private copies if the output is to
+                 * make sense.
+                 */
+                snprintf(result, maxlen, "%s %s %c " SECTOR_FORMAT,
+                         snap->origin->name, snap->cow->name,
+                         snap->type, snap->chunk_size);
+                break;
+        }
+
+        return 0;
+}
+
+/*-----------------------------------------------------------------
+ * Origin methods
+ *---------------------------------------------------------------*/
+static void list_merge(struct list_head *l1, struct list_head *l2)
+{
+        struct list_head *l1_n, *l2_p;
+
+        l1_n = l1->next;
+        l2_p = l2->prev;
+
+        l1->next = l2;
+        l2->prev = l1;
+
+        l2_p->next = l1_n;
+        l1_n->prev = l2_p;
+}
+
+static int __origin_write(struct list_head *snapshots, struct bio *bio)
+{
+        int r = 1, first = 1;
+        struct dm_snapshot *snap;
+        struct exception *e;
+        struct pending_exception *pe, *last = NULL;
+        chunk_t chunk;
+
+        /* Do all the snapshots on this origin */
+        list_for_each_entry (snap, snapshots, list) {
+
+                /* Only deal with valid snapshots */
+                if (!snap->valid)
+                        continue;
+
+                down_write(&snap->lock);
+
+                /*
+                 * Remember, different snapshots can have
+                 * different chunk sizes.
+                 */
+                chunk = sector_to_chunk(snap, bio->bi_sector);
+
+                /*
+                 * Check exception table to see if block
+                 * is already remapped in this snapshot
+                 * and trigger an exception if not.
+                 */
+                e = lookup_exception(&snap->complete, chunk);
+                if (!e) {
+                        pe = __find_pending_exception(snap, bio);
+                        if (!pe) {
+                                snap->store.drop_snapshot(&snap->store);
+                                snap->valid = 0;
+
+                        } else {
+                                if (last)
+                                        list_merge(&pe->siblings,
+                                                   &last->siblings);
+
+                                last = pe;
+                                r = 0;
+                        }
+                }
+
+                up_write(&snap->lock);
+        }
+
+        /*
+         * Now that we have a complete pe list we can start the copying.
+         */
+        if (last) {
+                pe = last;
+                do {
+                        down_write(&pe->snap->lock);
+                        if (first)
+                                bio_list_add(&pe->origin_bios, bio);
+                        if (!pe->started) {
+                                pe->started = 1;
+                                up_write(&pe->snap->lock);
+                                start_copy(pe);
+                        } else
+                                up_write(&pe->snap->lock);
+                        first = 0;
+                        pe = list_entry(pe->siblings.next,
+                                        struct pending_exception, siblings);
+
+                } while (pe != last);
+        }
+
+        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 = 1;
+
+        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 = "dm-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;
+        return 0;
+}
+
+static void origin_dtr(struct dm_target *ti)
+{
+        struct dm_dev *dev = (struct dm_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 = (struct dm_dev *) ti->private;
+        bio->bi_bdev = dev->bdev;
+
+        /* Only tell snapshots if this is a write */
+        return (bio_rw(bio) == WRITE) ? do_origin(dev, bio) : 1;
+}
+
+#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 = (struct dm_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->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 = (struct dm_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 struct target_type origin_target = {
+        .name    = "snapshot-origin",
+        .version = {1, 0, 1},
+        .module  = THIS_MODULE,
+        .ctr     = origin_ctr,
+        .dtr     = origin_dtr,
+        .map     = origin_map,
+        .resume  = origin_resume,
+        .status  = origin_status,
+};
+
+static struct target_type snapshot_target = {
+        .name    = "snapshot",
+        .version = {1, 0, 1},
+        .module  = THIS_MODULE,
+        .ctr     = snapshot_ctr,
+        .dtr     = snapshot_dtr,
+        .map     = snapshot_map,
+        .resume  = snapshot_resume,
+        .status  = snapshot_status,
+};
+
+static int __init dm_snapshot_init(void)
+{
+        int 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("Device mapper: Origin: register failed %d\n", r);
+                goto bad1;
+        }
+
+        r = init_origin_hash();
+        if (r) {
+                DMERR("init_origin_hash failed.");
+                goto bad2;
+        }
+
+        exception_cache = kmem_cache_create("dm-snapshot-ex",
+                                            sizeof(struct exception),
+                                            __alignof__(struct exception),
+                                            0, NULL, NULL);
+        if (!exception_cache) {
+                DMERR("Couldn't create exception cache.");
+                r = -ENOMEM;
+                goto bad3;
+        }
+
+        pending_cache =
+            kmem_cache_create("dm-snapshot-in",
+                              sizeof(struct pending_exception),
+                              __alignof__(struct pending_exception),
+                              0, NULL, NULL);
+        if (!pending_cache) {
+                DMERR("Couldn't create pending cache.");
+                r = -ENOMEM;
+                goto bad4;
+        }
+
+        pending_pool = mempool_create(128, mempool_alloc_slab,
+                                      mempool_free_slab, pending_cache);
+        if (!pending_pool) {
+                DMERR("Couldn't create pending pool.");
+                r = -ENOMEM;
+                goto bad5;
+        }
+
+        return 0;
+
+      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)
+{
+        int r;
+
+        r = dm_unregister_target(&snapshot_target);
+        if (r)
+                DMERR("snapshot unregister failed %d", r);
+
+        r = dm_unregister_target(&origin_target);
+        if (r)
+                DMERR("origin unregister failed %d", r);
+
+        exit_origin_hash();
+        mempool_destroy(pending_pool);
+        kmem_cache_destroy(pending_cache);
+        kmem_cache_destroy(exception_cache);
+}
+
+/* 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");