__lookup_origin
min_chunksize = __minimum_chunk_size(__lookup_origin(bdev));
o = __lookup_origin(origin->bdev);
o = __lookup_origin(merging_snap->origin->bdev);
o = __lookup_origin(snap->origin->bdev);
o = __lookup_origin(bdev);
__insert_snapshot(__lookup_origin(bdev), s);
o = __lookup_origin(s->origin->bdev);