I would like to use 'filestore_omap_backend' and 'keyvaluestore_backend' to separate. They now use the valid options leveldb and rocksdb, but in the future, keyvaluestore will has more backend filestore omap,can't support. Then 'osd_keyvaluedb' has two meaning, one is filestore omap backend, another is keyvaluestore backend. It will confuse users while they think filestore and keyvaluestore are different object store. So I think it will be more clear to use two different options.