dm snapshot: split out exception store implementations

Move the existing snapshot exception store implementations out into
separate files.  Later patches will place these behind a new
interface in preparation for alternative implementations.

Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 19 insertions, 730 deletions

diff --git a/drivers/md/dm-exception-store.c b/drivers/md/dm-exception-store.c
index c5c9a2652315..74777e0f80df 100644
--- a/drivers/md/dm-exception-store.c
+++ b/drivers/md/dm-exception-store.c
@@ -1,757 +1,46 @@
 /*
- * dm-exception-store.c
- *
  * Copyright (C) 2001-2002 Sistina Software (UK) Limited.
- * Copyright (C) 2006 Red Hat GmbH
+ * Copyright (C) 2006-2008 Red Hat GmbH
  *
  * This file is released under the GPL.
  */
 
 #include "dm-exception-store.h"
-#include "dm-snap.h"
 
 #include <linux/mm.h>
 #include <linux/pagemap.h>
 #include <linux/vmalloc.h>
 #include <linux/slab.h>
-#include <linux/dm-io.h>
-#include <linux/dm-kcopyd.h>
-
-#define DM_MSG_PREFIX "snapshots"
-#define DM_CHUNK_SIZE_DEFAULT_SECTORS 32        /* 16KB */
-
-/*-----------------------------------------------------------------
- * Persistent snapshots, by persistent we mean that the snapshot
- * will survive a reboot.
- *---------------------------------------------------------------*/
-
-/*
- * We need to store a record of which parts of the origin have
- * been copied to the snapshot device.  The snapshot code
- * requires that we copy exception chunks to chunk aligned areas
- * of the COW store.  It makes sense therefore, to store the
- * metadata in chunk size blocks.
- *
- * There is no backward or forward compatibility implemented,
- * snapshots with different disk versions than the kernel will
- * not be usable.  It is expected that "lvcreate" will blank out
- * the start of a fresh COW device before calling the snapshot
- * constructor.
- *
- * The first chunk of the COW device just contains the header.
- * After this there is a chunk filled with exception metadata,
- * followed by as many exception chunks as can fit in the
- * metadata areas.
- *
- * All on disk structures are in little-endian format.  The end
- * of the exceptions info is indicated by an exception with a
- * new_chunk of 0, which is invalid since it would point to the
- * header chunk.
- */
-
-/*
- * Magic for persistent snapshots: "SnAp" - Feeble isn't it.
- */
-#define SNAP_MAGIC 0x70416e53
-
-/*
- * The on-disk version of the metadata.
- */
-#define SNAPSHOT_DISK_VERSION 1
-
-struct disk_header {
-        uint32_t magic;
-
-        /*
-         * Is this snapshot valid.  There is no way of recovering
-         * an invalid snapshot.
-         */
-        uint32_t valid;
-
-        /*
-         * Simple, incrementing version. no backward
-         * compatibility.
-         */
-        uint32_t version;
-
-        /* In sectors */
-        uint32_t chunk_size;
-};
-
-struct disk_exception {
-        uint64_t old_chunk;
-        uint64_t new_chunk;
-};
-
-struct commit_callback {
-        void (*callback)(void *, int success);
-        void *context;
-};
-
-/*
- * The top level structure for a persistent exception store.
- */
-struct pstore {
-        struct dm_snapshot *snap;       /* up pointer to my snapshot */
-        int version;
-        int valid;
-        uint32_t exceptions_per_area;
-
-        /*
-         * Now that we have an asynchronous kcopyd there is no
-         * need for large chunk sizes, so it wont hurt to have a
-         * whole chunks worth of metadata in memory at once.
-         */
-        void *area;
-
-        /*
-         * An area of zeros used to clear the next area.
-         */
-        void *zero_area;
-
-        /*
-         * Used to keep track of which metadata area the data in
-         * 'chunk' refers to.
-         */
-        chunk_t current_area;
-
-        /*
-         * The next free chunk for an exception.
-         */
-        chunk_t next_free;
-
-        /*
-         * The index of next free exception in the current
-         * metadata area.
-         */
-        uint32_t current_committed;
-
-        atomic_t pending_count;
-        uint32_t callback_count;
-        struct commit_callback *callbacks;
-        struct dm_io_client *io_client;
-
-        struct workqueue_struct *metadata_wq;
-};
-
-static unsigned sectors_to_pages(unsigned sectors)
-{
-        return DIV_ROUND_UP(sectors, PAGE_SIZE >> 9);
-}
-
-static int alloc_area(struct pstore *ps)
-{
-        int r = -ENOMEM;
-        size_t len;
-
-        len = ps->snap->chunk_size << SECTOR_SHIFT;
-
-        /*
-         * Allocate the chunk_size block of memory that will hold
-         * a single metadata area.
-         */
-        ps->area = vmalloc(len);
-        if (!ps->area)
-                return r;
-
-        ps->zero_area = vmalloc(len);
-        if (!ps->zero_area) {
-                vfree(ps->area);
-                return r;
-        }
-        memset(ps->zero_area, 0, len);
-
-        return 0;
-}
-
-static void free_area(struct pstore *ps)
-{
-        vfree(ps->area);
-        ps->area = NULL;
-        vfree(ps->zero_area);
-        ps->zero_area = NULL;
-}
-
-struct mdata_req {
-        struct dm_io_region *where;
-        struct dm_io_request *io_req;
-        struct work_struct work;
-        int result;
-};
-
-static void do_metadata(struct work_struct *work)
-{
-        struct mdata_req *req = container_of(work, struct mdata_req, work);
-
-        req->result = dm_io(req->io_req, 1, req->where, NULL);
-}
-
-/*
- * Read or write a chunk aligned and sized block of data from a device.
- */
-static int chunk_io(struct pstore *ps, chunk_t chunk, int rw, int metadata)
-{
-        struct dm_io_region where = {
-                .bdev = ps->snap->cow->bdev,
-                .sector = ps->snap->chunk_size * chunk,
-                .count = ps->snap->chunk_size,
-        };
-        struct dm_io_request io_req = {
-                .bi_rw = rw,
-                .mem.type = DM_IO_VMA,
-                .mem.ptr.vma = ps->area,
-                .client = ps->io_client,
-                .notify.fn = NULL,
-        };
-        struct mdata_req req;
-
-        if (!metadata)
-                return dm_io(&io_req, 1, &where, NULL);
-
-        req.where = &where;
-        req.io_req = &io_req;
-
-        /*
-         * Issue the synchronous I/O from a different thread
-         * to avoid generic_make_request recursion.
-         */
-        INIT_WORK(&req.work, do_metadata);
-        queue_work(ps->metadata_wq, &req.work);
-        flush_workqueue(ps->metadata_wq);
-
-        return req.result;
-}
-
-/*
- * Convert a metadata area index to a chunk index.
- */
-static chunk_t area_location(struct pstore *ps, chunk_t area)
-{
-        return 1 + ((ps->exceptions_per_area + 1) * area);
-}
-
-/*
- * Read or write a metadata area.  Remembering to skip the first
- * chunk which holds the header.
- */
-static int area_io(struct pstore *ps, int rw)
-{
-        int r;
-        chunk_t chunk;
-
-        chunk = area_location(ps, ps->current_area);
-
-        r = chunk_io(ps, chunk, rw, 0);
-        if (r)
-                return r;
-
-        return 0;
-}
-
-static void zero_memory_area(struct pstore *ps)
-{
-        memset(ps->area, 0, ps->snap->chunk_size << SECTOR_SHIFT);
-}
-
-static int zero_disk_area(struct pstore *ps, chunk_t area)
-{
-        struct dm_io_region where = {
-                .bdev = ps->snap->cow->bdev,
-                .sector = ps->snap->chunk_size * area_location(ps, area),
-                .count = ps->snap->chunk_size,
-        };
-        struct dm_io_request io_req = {
-                .bi_rw = WRITE,
-                .mem.type = DM_IO_VMA,
-                .mem.ptr.vma = ps->zero_area,
-                .client = ps->io_client,
-                .notify.fn = NULL,
-        };
-
-        return dm_io(&io_req, 1, &where, NULL);
-}
-
-static int read_header(struct pstore *ps, int *new_snapshot)
-{
-        int r;
-        struct disk_header *dh;
-        chunk_t chunk_size;
-        int chunk_size_supplied = 1;
-
-        /*
-         * Use default chunk size (or hardsect_size, if larger) if none supplied
-         */
-        if (!ps->snap->chunk_size) {
-                ps->snap->chunk_size = max(DM_CHUNK_SIZE_DEFAULT_SECTORS,
-                    bdev_hardsect_size(ps->snap->cow->bdev) >> 9);
-                ps->snap->chunk_mask = ps->snap->chunk_size - 1;
-                ps->snap->chunk_shift = ffs(ps->snap->chunk_size) - 1;
-                chunk_size_supplied = 0;
-        }
-
-        ps->io_client = dm_io_client_create(sectors_to_pages(ps->snap->
-                                                             chunk_size));
-        if (IS_ERR(ps->io_client))
-                return PTR_ERR(ps->io_client);
-
-        r = alloc_area(ps);
-        if (r)
-                return r;
-
-        r = chunk_io(ps, 0, READ, 1);
-        if (r)
-                goto bad;
-
-        dh = (struct disk_header *) ps->area;
-
-        if (le32_to_cpu(dh->magic) == 0) {
-                *new_snapshot = 1;
-                return 0;
-        }
-
-        if (le32_to_cpu(dh->magic) != SNAP_MAGIC) {
-                DMWARN("Invalid or corrupt snapshot");
-                r = -ENXIO;
-                goto bad;
-        }
-
-        *new_snapshot = 0;
-        ps->valid = le32_to_cpu(dh->valid);
-        ps->version = le32_to_cpu(dh->version);
-        chunk_size = le32_to_cpu(dh->chunk_size);
-
-        if (!chunk_size_supplied || ps->snap->chunk_size == chunk_size)
-                return 0;
-
-        DMWARN("chunk size %llu in device metadata overrides "
-               "table chunk size of %llu.",
-               (unsigned long long)chunk_size,
-               (unsigned long long)ps->snap->chunk_size);
-
-        /* We had a bogus chunk_size. Fix stuff up. */
-        free_area(ps);
-
-        ps->snap->chunk_size = chunk_size;
-        ps->snap->chunk_mask = chunk_size - 1;
-        ps->snap->chunk_shift = ffs(chunk_size) - 1;
-
-        r = dm_io_client_resize(sectors_to_pages(ps->snap->chunk_size),
-                                ps->io_client);
-        if (r)
-                return r;
-
-        r = alloc_area(ps);
-        return r;
-
-bad:
-        free_area(ps);
-        return r;
-}
-
-static int write_header(struct pstore *ps)
-{
-        struct disk_header *dh;
-
-        memset(ps->area, 0, ps->snap->chunk_size << SECTOR_SHIFT);
-
-        dh = (struct disk_header *) ps->area;
-        dh->magic = cpu_to_le32(SNAP_MAGIC);
-        dh->valid = cpu_to_le32(ps->valid);
-        dh->version = cpu_to_le32(ps->version);
-        dh->chunk_size = cpu_to_le32(ps->snap->chunk_size);
-
-        return chunk_io(ps, 0, WRITE, 1);
-}
-
-/*
- * Access functions for the disk exceptions, these do the endian conversions.
- */
-static struct disk_exception *get_exception(struct pstore *ps, uint32_t index)
-{
-        BUG_ON(index >= ps->exceptions_per_area);
-
-        return ((struct disk_exception *) ps->area) + index;
-}
+#include <linux/device-mapper.h>
 
-static void read_exception(struct pstore *ps,
-                           uint32_t index, struct disk_exception *result)
-{
-        struct disk_exception *e = get_exception(ps, index);
-
-        /* copy it */
-        result->old_chunk = le64_to_cpu(e->old_chunk);
-        result->new_chunk = le64_to_cpu(e->new_chunk);
-}
-
-static void write_exception(struct pstore *ps,
-                            uint32_t index, struct disk_exception *de)
-{
-        struct disk_exception *e = get_exception(ps, index);
-
-        /* copy it */
-        e->old_chunk = cpu_to_le64(de->old_chunk);
-        e->new_chunk = cpu_to_le64(de->new_chunk);
-}
+#define DM_MSG_PREFIX "snapshot exception stores"
 
-/*
- * Registers the exceptions that are present in the current area.
- * 'full' is filled in to indicate if the area has been
- * filled.
- */
-static int insert_exceptions(struct pstore *ps, int *full)
+int dm_exception_store_init(void)
 {
         int r;
-        unsigned int i;
-        struct disk_exception de;
-
-        /* presume the area is full */
-        *full = 1;
-
-        for (i = 0; i < ps->exceptions_per_area; i++) {
-                read_exception(ps, i, &de);
-
-                /*
-                 * If the new_chunk is pointing at the start of
-                 * the COW device, where the first metadata area
-                 * is we know that we've hit the end of the
-                 * exceptions.  Therefore the area is not full.
-                 */
-                if (de.new_chunk == 0LL) {
-                        ps->current_committed = i;
-                        *full = 0;
-                        break;
-                }
-
-                /*
-                 * Keep track of the start of the free chunks.
-                 */
-                if (ps->next_free <= de.new_chunk)
-                        ps->next_free = de.new_chunk + 1;
-
-                /*
-                 * Otherwise we add the exception to the snapshot.
-                 */
-                r = dm_add_exception(ps->snap, de.old_chunk, de.new_chunk);
-                if (r)
-                        return r;
-        }
-
-        return 0;
-}
-
-static int read_exceptions(struct pstore *ps)
-{
-        int r, full = 1;
-
-        /*
-         * Keeping reading chunks and inserting exceptions until
-         * we find a partially full area.
-         */
-        for (ps->current_area = 0; full; ps->current_area++) {
-                r = area_io(ps, READ);
-                if (r)
-                        return r;
 
-                r = insert_exceptions(ps, &full);
-                if (r)
-                        return r;
+        r = dm_transient_snapshot_init();
+        if (r) {
+                DMERR("Unable to register transient exception store type.");
+                goto transient_fail;
         }
 
-        ps->current_area--;
-
-        return 0;
-}
-
-static struct pstore *get_info(struct dm_exception_store *store)
-{
-        return (struct pstore *) store->context;
-}
-
-static void persistent_fraction_full(struct dm_exception_store *store,
-                                     sector_t *numerator, sector_t *denominator)
-{
-        *numerator = get_info(store)->next_free * store->snap->chunk_size;
-        *denominator = get_dev_size(store->snap->cow->bdev);
-}
-
-static void persistent_destroy(struct dm_exception_store *store)
-{
-        struct pstore *ps = get_info(store);
-
-        destroy_workqueue(ps->metadata_wq);
-        dm_io_client_destroy(ps->io_client);
-        vfree(ps->callbacks);
-        free_area(ps);
-        kfree(ps);
-}
-
-static int persistent_read_metadata(struct dm_exception_store *store)
-{
-        int r, uninitialized_var(new_snapshot);
-        struct pstore *ps = get_info(store);
-
-        /*
-         * Read the snapshot header.
-         */
-        r = read_header(ps, &new_snapshot);
-        if (r)
-                return r;
-
-        /*
-         * Now we know correct chunk_size, complete the initialisation.
-         */
-        ps->exceptions_per_area = (ps->snap->chunk_size << SECTOR_SHIFT) /
-                                  sizeof(struct disk_exception);
-        ps->callbacks = dm_vcalloc(ps->exceptions_per_area,
-                        sizeof(*ps->callbacks));
-        if (!ps->callbacks)
-                return -ENOMEM;
-
-        /*
-         * Do we need to setup a new snapshot ?
-         */
-        if (new_snapshot) {
-                r = write_header(ps);
-                if (r) {
-                        DMWARN("write_header failed");
-                        return r;
-                }
-
-                ps->current_area = 0;
-                zero_memory_area(ps);
-                r = zero_disk_area(ps, 0);
-                if (r) {
-                        DMWARN("zero_disk_area(0) failed");
-                        return r;
-                }
-        } else {
-                /*
-                 * Sanity checks.
-                 */
-                if (ps->version != SNAPSHOT_DISK_VERSION) {
-                        DMWARN("unable to handle snapshot disk version %d",
-                               ps->version);
-                        return -EINVAL;
-                }
-
-                /*
-                 * Metadata are valid, but snapshot is invalidated
-                 */
-                if (!ps->valid)
-                        return 1;
-
-                /*
-                 * Read the metadata.
-                 */
-                r = read_exceptions(ps);
-                if (r)
-                        return r;
+        r = dm_persistent_snapshot_init();
+        if (r) {
+                DMERR("Unable to register persistent exception store type");
+                goto persistent_fail;
         }
 
         return 0;
-}
-
-static int persistent_prepare(struct dm_exception_store *store,
-                              struct dm_snap_exception *e)
-{
-        struct pstore *ps = get_info(store);
-        uint32_t stride;
-        chunk_t next_free;
-        sector_t size = get_dev_size(store->snap->cow->bdev);
-
-        /* Is there enough room ? */
-        if (size < ((ps->next_free + 1) * store->snap->chunk_size))
-                return -ENOSPC;
 
-        e->new_chunk = ps->next_free;
-
-        /*
-         * Move onto the next free pending, making sure to take
-         * into account the location of the metadata chunks.
-         */
-        stride = (ps->exceptions_per_area + 1);
-        next_free = ++ps->next_free;
-        if (sector_div(next_free, stride) == 1)
-                ps->next_free++;
-
-        atomic_inc(&ps->pending_count);
-        return 0;
-}
-
-static void persistent_commit(struct dm_exception_store *store,
-                              struct dm_snap_exception *e,
-                              void (*callback) (void *, int success),
-                              void *callback_context)
-{
-        unsigned int i;
-        struct pstore *ps = get_info(store);
-        struct disk_exception de;
-        struct commit_callback *cb;
-
-        de.old_chunk = e->old_chunk;
-        de.new_chunk = e->new_chunk;
-        write_exception(ps, ps->current_committed++, &de);
-
-        /*
-         * Add the callback to the back of the array.  This code
-         * is the only place where the callback array is
-         * manipulated, and we know that it will never be called
-         * multiple times concurrently.
-         */
-        cb = ps->callbacks + ps->callback_count++;
-        cb->callback = callback;
-        cb->context = callback_context;
-
-        /*
-         * If there are exceptions in flight and we have not yet
-         * filled this metadata area there's nothing more to do.
-         */
-        if (!atomic_dec_and_test(&ps->pending_count) &&
-            (ps->current_committed != ps->exceptions_per_area))
-                return;
-
-        /*
-         * If we completely filled the current area, then wipe the next one.
-         */
-        if ((ps->current_committed == ps->exceptions_per_area) &&
-             zero_disk_area(ps, ps->current_area + 1))
-                ps->valid = 0;
-
-        /*
-         * Commit exceptions to disk.
-         */
-        if (ps->valid && area_io(ps, WRITE))
-                ps->valid = 0;
-
-        /*
-         * Advance to the next area if this one is full.
-         */
-        if (ps->current_committed == ps->exceptions_per_area) {
-                ps->current_committed = 0;
-                ps->current_area++;
-                zero_memory_area(ps);
-        }
-
-        for (i = 0; i < ps->callback_count; i++) {
-                cb = ps->callbacks + i;
-                cb->callback(cb->context, ps->valid);
-        }
-
-        ps->callback_count = 0;
-}
-
-static void persistent_drop(struct dm_exception_store *store)
-{
-        struct pstore *ps = get_info(store);
-
-        ps->valid = 0;
-        if (write_header(ps))
-                DMWARN("write header failed");
-}
-
-int dm_create_persistent(struct dm_exception_store *store)
-{
-        struct pstore *ps;
-
-        /* allocate the pstore */
-        ps = kmalloc(sizeof(*ps), GFP_KERNEL);
-        if (!ps)
-                return -ENOMEM;
-
-        ps->snap = store->snap;
-        ps->valid = 1;
-        ps->version = SNAPSHOT_DISK_VERSION;
-        ps->area = NULL;
-        ps->next_free = 2;      /* skipping the header and first area */
-        ps->current_committed = 0;
-
-        ps->callback_count = 0;
-        atomic_set(&ps->pending_count, 0);
-        ps->callbacks = NULL;
-
-        ps->metadata_wq = create_singlethread_workqueue("ksnaphd");
-        if (!ps->metadata_wq) {
-                kfree(ps);
-                DMERR("couldn't start header metadata update thread");
-                return -ENOMEM;
-        }
-
-        store->destroy = persistent_destroy;
-        store->read_metadata = persistent_read_metadata;
-        store->prepare_exception = persistent_prepare;
-        store->commit_exception = persistent_commit;
-        store->drop_snapshot = persistent_drop;
-        store->fraction_full = persistent_fraction_full;
-        store->context = ps;
-
-        return 0;
-}
-
-/*-----------------------------------------------------------------
- * Implementation of the store for non-persistent snapshots.
- *---------------------------------------------------------------*/
-struct transient_c {
-        sector_t next_free;
-};
-
-static void transient_destroy(struct dm_exception_store *store)
-{
-        kfree(store->context);
-}
-
-static int transient_read_metadata(struct dm_exception_store *store)
-{
-        return 0;
-}
-
-static int transient_prepare(struct dm_exception_store *store,
-                             struct dm_snap_exception *e)
-{
-        struct transient_c *tc = (struct transient_c *) store->context;
-        sector_t size = get_dev_size(store->snap->cow->bdev);
-
-        if (size < (tc->next_free + store->snap->chunk_size))
-                return -1;
-
-        e->new_chunk = sector_to_chunk(store->snap, tc->next_free);
-        tc->next_free += store->snap->chunk_size;
-
-        return 0;
-}
-
-static void transient_commit(struct dm_exception_store *store,
-                             struct dm_snap_exception *e,
-                             void (*callback) (void *, int success),
-                             void *callback_context)
-{
-        /* Just succeed */
-        callback(callback_context, 1);
-}
-
-static void transient_fraction_full(struct dm_exception_store *store,
-                                    sector_t *numerator, sector_t *denominator)
-{
-        *numerator = ((struct transient_c *) store->context)->next_free;
-        *denominator = get_dev_size(store->snap->cow->bdev);
+persistent_fail:
+        dm_persistent_snapshot_exit();
+transient_fail:
+        return r;
 }
 
-int dm_create_transient(struct dm_exception_store *store)
+void dm_exception_store_exit(void)
 {
-        struct transient_c *tc;
-
-        store->destroy = transient_destroy;
-        store->read_metadata = transient_read_metadata;
-        store->prepare_exception = transient_prepare;
-        store->commit_exception = transient_commit;
-        store->drop_snapshot = NULL;
-        store->fraction_full = transient_fraction_full;
-
-        tc = kmalloc(sizeof(struct transient_c), GFP_KERNEL);
-        if (!tc)
-                return -ENOMEM;
-
-        tc->next_free = 0;
-        store->context = tc;
-
-        return 0;
+        dm_persistent_snapshot_exit();
+        dm_transient_snapshot_exit();
 }