dm-exception-store.c

linux 内核源代码

	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)
{
	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 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);

	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 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;

	/*
	 * 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;
		}

		r = zero_area(ps, 0);
		if (r) {
			DMWARN("zero_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 exception_store *store,
			      struct dm_snap_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 dm_snap_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;

		/*
		 * 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;
		}

		for (i = 0; i < ps->callback_count; i++) {
			cb = ps->callbacks + i;
			cb->callback(cb->context, r == 0 ? 1 : 0);
		}

		ps->callback_count = 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)
{
	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 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 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 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 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 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;
}