refactor work for filer write handler
refactor work for filer write handler

chrislusf/seaweedfs,hxiaodon/seaweedfs,chrislusf/seaweedfs,k85169336/seaweedfs,hxiaodon/seaweedfs,chrislusf/seaweedfs,chrislusf/seaweedfs,k85169336/seaweedfs