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>
diff --git a/drivers/md/dm-snap-persistent.c b/drivers/md/dm-snap-persistent.c
new file mode 100644
index 0000000..57c946c
--- /dev/null
+++ b/drivers/md/dm-snap-persistent.c
@@ -0,0 +1,694 @@
+/*
+ * Copyright (C) 2001-2002 Sistina Software (UK) Limited.
+ * 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>
+
+#define DM_MSG_PREFIX "persistent snapshot"
+#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;
+}
+
+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);
+}
+
+/*
+ * 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 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;
+ }
+
+ 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;
+ }
+
+ 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;
+}
+
+int dm_persistent_snapshot_init(void)
+{
+ return 0;
+}
+
+void dm_persistent_snapshot_exit(void)
+{
+}