1 files changed, 648 insertions, 0 deletions
diff --git a/drivers/md/dm-exception-store.c b/drivers/md/dm-exception-store.c
new file mode 100644
index 000000000000..17212b4201a1
--- /dev/null
+++ b/drivers/md/dm-exception-store.c
@@ -0,0 +1,648 @@
+/*
+ * dm-snapshot.c
+ *
+ * Copyright (C) 2001-2002 Sistina Software (UK) Limited.
+ *
+ * This file is released under the GPL.
+ */
+
+#include "dm.h"
+#include "dm-snap.h"
+#include "dm-io.h"
+#include "kcopyd.h"
+
+#include <linux/mm.h>
+#include <linux/pagemap.h>
+#include <linux/vmalloc.h>
+#include <linux/slab.h>
+
+/*-----------------------------------------------------------------
+ * 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 chunk_size;
+	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;
+
+	/*
+	 * Used to keep track of which metadata area the data in
+	 * 'chunk' refers to.
+	 */
+	uint32_t current_area;
+
+	/*
+	 * The next free chunk for an exception.
+	 */
+	uint32_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;
+};
+
+static inline unsigned int sectors_to_pages(unsigned int sectors)
+{
+	return sectors / (PAGE_SIZE >> 9);
+}
+
+static int alloc_area(struct pstore *ps)
+{
+	int r = -ENOMEM;
+	size_t len;
+
+	len = ps->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;
+
+	return 0;
+}
+
+static void free_area(struct pstore *ps)
+{
+	vfree(ps->area);
+}
+
+/*
+ * Read or write a chunk aligned and sized block of data from a device.
+ */
+static int chunk_io(struct pstore *ps, uint32_t chunk, int rw)
+{
+	struct io_region where;
+	unsigned long bits;
+
+	where.bdev = ps->snap->cow->bdev;
+	where.sector = ps->chunk_size * chunk;
+	where.count = ps->chunk_size;
+
+	return dm_io_sync_vm(1, &where, rw, ps->area, &bits);
+}
+
+/*
+ * Read or write a metadata area.  Remembering to skip the first
+ * chunk which holds the header.
+ */
+static int area_io(struct pstore *ps, uint32_t area, int rw)
+{
+	int r;
+	uint32_t chunk;
+
+	/* convert a metadata area index to a chunk index */
+	chunk = 1 + ((ps->exceptions_per_area + 1) * area);
+
+	r = chunk_io(ps, chunk, rw);
+	if (r)
+		return r;
+
+	ps->current_area = area;
+	return 0;
+}
+
+static int zero_area(struct pstore *ps, uint32_t area)
+{
+	memset(ps->area, 0, ps->chunk_size << SECTOR_SHIFT);
+	return area_io(ps, area, WRITE);
+}
+
+static int read_header(struct pstore *ps, int *new_snapshot)
+{
+	int r;
+	struct disk_header *dh;
+
+	r = chunk_io(ps, 0, READ);
+	if (r)
+		return r;
+
+	dh = (struct disk_header *) ps->area;
+
+	if (le32_to_cpu(dh->magic) == 0) {
+		*new_snapshot = 1;
+
+	} else if (le32_to_cpu(dh->magic) == SNAP_MAGIC) {
+		*new_snapshot = 0;
+		ps->valid = le32_to_cpu(dh->valid);
+		ps->version = le32_to_cpu(dh->version);
+		ps->chunk_size = le32_to_cpu(dh->chunk_size);
+
+	} else {
+		DMWARN("Invalid/corrupt snapshot");
+		r = -ENXIO;
+	}
+
+	return r;
+}
+
+static int write_header(struct pstore *ps)
+{
+	struct disk_header *dh;
+
+	memset(ps->area, 0, ps->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->chunk_size);
+
+	return chunk_io(ps, 0, WRITE);
+}
+
+/*
+ * Access functions for the disk exceptions, these do the endian conversions.
+ */
+static struct disk_exception *get_exception(struct pstore *ps, uint32_t index)
+{
+	if (index >= ps->exceptions_per_area)
+		return NULL;
+
+	return ((struct disk_exception *) ps->area) + index;
+}
+
+static int read_exception(struct pstore *ps,
+			  uint32_t index, struct disk_exception *result)
+{
+	struct disk_exception *e;
+
+	e = get_exception(ps, index);
+	if (!e)
+		return -EINVAL;
+
+	/* copy it */
+	result->old_chunk = le64_to_cpu(e->old_chunk);
+	result->new_chunk = le64_to_cpu(e->new_chunk);
+
+	return 0;
+}
+
+static int write_exception(struct pstore *ps,
+			   uint32_t index, struct disk_exception *de)
+{
+	struct disk_exception *e;
+
+	e = get_exception(ps, index);
+	if (!e)
+		return -EINVAL;
+
+	/* copy it */
+	e->old_chunk = cpu_to_le64(de->old_chunk);
+	e->new_chunk = cpu_to_le64(de->new_chunk);
+
+	return 0;
+}
+
+/*
+ * 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++) {
+		r = read_exception(ps, i, &de);
+
+		if (r)
+			return r;
+
+		/*
+		 * 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)
+{
+	uint32_t area;
+	int r, full = 1;
+
+	/*
+	 * Keeping reading chunks and inserting exceptions until
+	 * we find a partially full area.
+	 */
+	for (area = 0; full; area++) {
+		r = area_io(ps, area, READ);
+		if (r)
+			return r;
+
+		r = insert_exceptions(ps, &full);
+		if (r)
+			return r;
+	}
+
+	return 0;
+}
+
+static inline struct pstore *get_info(struct exception_store *store)
+{
+	return (struct pstore *) store->context;
+}
+
+static void persistent_fraction_full(struct 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 exception_store *store)
+{
+	struct pstore *ps = get_info(store);
+
+	dm_io_put(sectors_to_pages(ps->chunk_size));
+	vfree(ps->callbacks);
+	free_area(ps);
+	kfree(ps);
+}
+
+static int persistent_read_metadata(struct exception_store *store)
+{
+	int r, new_snapshot;
+	struct pstore *ps = get_info(store);
+
+	/*
+	 * Read the snapshot header.
+	 */
+	r = read_header(ps, &new_snapshot);
+	if (r)
+		return r;
+
+	/*
+	 * Do we need to setup a new snapshot ?
+	 */
+	if (new_snapshot) {
+		r = write_header(ps);
+		if (r) {
+			DMWARN("write_header failed");
+			return r;
+		}
+
+		r = zero_area(ps, 0);
+		if (r) {
+			DMWARN("zero_area(0) failed");
+			return r;
+		}
+
+	} else {
+		/*
+		 * Sanity checks.
+		 */
+		if (!ps->valid) {
+			DMWARN("snapshot is marked invalid");
+			return -EINVAL;
+		}
+
+		if (ps->version != SNAPSHOT_DISK_VERSION) {
+			DMWARN("unable to handle snapshot disk version %d",
+			       ps->version);
+			return -EINVAL;
+		}
+
+		/*
+		 * Read the metadata.
+		 */
+		r = read_exceptions(ps);
+		if (r)
+			return r;
+	}
+
+	return 0;
+}
+
+static int persistent_prepare(struct exception_store *store,
+			      struct exception *e)
+{
+	struct pstore *ps = get_info(store);
+	uint32_t stride;
+	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);
+	if ((++ps->next_free % stride) == 1)
+		ps->next_free++;
+
+	atomic_inc(&ps->pending_count);
+	return 0;
+}
+
+static void persistent_commit(struct exception_store *store,
+			      struct exception *e,
+			      void (*callback) (void *, int success),
+			      void *callback_context)
+{
+	int r;
+	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 no more exceptions in flight, or we have
+	 * filled this metadata area we commit the exceptions to
+	 * disk.
+	 */
+	if (atomic_dec_and_test(&ps->pending_count) ||
+	    (ps->current_committed == ps->exceptions_per_area)) {
+		r = area_io(ps, ps->current_area, WRITE);
+		if (r)
+			ps->valid = 0;
+
+		for (i = 0; i < ps->callback_count; i++) {
+			cb = ps->callbacks + i;
+			cb->callback(cb->context, r == 0 ? 1 : 0);
+		}
+
+		ps->callback_count = 0;
+	}
+
+	/*
+	 * Have we completely filled the current area ?
+	 */
+	if (ps->current_committed == ps->exceptions_per_area) {
+		ps->current_committed = 0;
+		r = zero_area(ps, ps->current_area + 1);
+		if (r)
+			ps->valid = 0;
+	}
+}
+
+static void persistent_drop(struct 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 exception_store *store, uint32_t chunk_size)
+{
+	int r;
+	struct pstore *ps;
+
+	r = dm_io_get(sectors_to_pages(chunk_size));
+	if (r)
+		return r;
+
+	/* allocate the pstore */
+	ps = kmalloc(sizeof(*ps), GFP_KERNEL);
+	if (!ps) {
+		r = -ENOMEM;
+		goto bad;
+	}
+
+	ps->snap = store->snap;
+	ps->valid = 1;
+	ps->version = SNAPSHOT_DISK_VERSION;
+	ps->chunk_size = chunk_size;
+	ps->exceptions_per_area = (chunk_size << SECTOR_SHIFT) /
+	    sizeof(struct disk_exception);
+	ps->next_free = 2;	/* skipping the header and first area */
+	ps->current_committed = 0;
+
+	r = alloc_area(ps);
+	if (r)
+		goto bad;
+
+	/*
+	 * Allocate space for all the callbacks.
+	 */
+	ps->callback_count = 0;
+	atomic_set(&ps->pending_count, 0);
+	ps->callbacks = dm_vcalloc(ps->exceptions_per_area,
+				   sizeof(*ps->callbacks));
+
+	if (!ps->callbacks) {
+		r = -ENOMEM;
+		goto bad;
+	}
+
+	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;
+
+      bad:
+	dm_io_put(sectors_to_pages(chunk_size));
+	if (ps) {
+		if (ps->area)
+			free_area(ps);
+
+		kfree(ps);
+	}
+	return r;
+}
+
+/*-----------------------------------------------------------------
+ * Implementation of the store for non-persistent snapshots.
+ *---------------------------------------------------------------*/
+struct transient_c {
+	sector_t next_free;
+};
+
+static void transient_destroy(struct exception_store *store)
+{
+	kfree(store->context);
+}
+
+static int transient_read_metadata(struct exception_store *store)
+{
+	return 0;
+}
+
+static int transient_prepare(struct exception_store *store, struct 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 exception_store *store,
+		      struct exception *e,
+		      void (*callback) (void *, int success),
+		      void *callback_context)
+{
+	/* Just succeed */
+	callback(callback_context, 1);
+}
+
+static void transient_fraction_full(struct 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);
+}
+
+int dm_create_transient(struct exception_store *store,
+			struct dm_snapshot *s, int blocksize)
+{
+	struct transient_c *tc;
+
+	memset(store, 0, sizeof(*store));
+	store->destroy = transient_destroy;
+	store->read_metadata = transient_read_metadata;
+	store->prepare_exception = transient_prepare;
+	store->commit_exception = transient_commit;
+	store->fraction_full = transient_fraction_full;
+	store->snap = s;
+
+	tc = kmalloc(sizeof(struct transient_c), GFP_KERNEL);
+	if (!tc)
+		return -ENOMEM;
+
+	tc->next_free = 0;
+	store->context = tc;
+
+	return 0;
+}