dm exception store: split set_chunk_size

Break the function set_chunk_size to two functions in preparation for
the fix in the following patch.

Cc: stable@kernel.org
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

drivers/md/dm-exception-store.c

@@ -171,6 +171,14 @@ static int set_chunk_size(struct dm_exception_store *store,
 	 */
 	chunk_size_ulong = round_up(chunk_size_ulong, PAGE_SIZE >> 9);
 
+	return dm_exception_store_set_chunk_size(store, chunk_size_ulong,
+						 error);
+}
+
+int dm_exception_store_set_chunk_size(struct dm_exception_store *store,
+				      unsigned long chunk_size_ulong,
+				      char **error)
+{
 	/* Check chunk_size is a power of 2 */
 	if (!is_power_of_2(chunk_size_ulong)) {
 		*error = "Chunk size is not a power of 2";

drivers/md/dm-exception-store.h

@@ -168,6 +168,10 @@ static inline chunk_t sector_to_chunk(struct dm_exception_store *store,
 int dm_exception_store_type_register(struct dm_exception_store_type *type);
 int dm_exception_store_type_unregister(struct dm_exception_store_type *type);
 
+int dm_exception_store_set_chunk_size(struct dm_exception_store *store,
+				      unsigned long chunk_size_ulong,
+				      char **error);
+
 int dm_exception_store_create(struct dm_target *ti, int argc, char **argv,
 			      unsigned *args_used,
 			      struct dm_exception_store **store);