Improve refreshNodes in DFSAdmin to support hdfs federation

In hdfs federated cluster, we find the dfsadmin command "hdfs dfsadmin -refreshNodes" can only refresh the nameservice (or namenode) which configured in fs.defaultFS. The other nameservices configured in hdfs-site.xml can't be refreshed unless changing the fs.defaultFS value and run this command again. I think we need additional parameters as following to give a convenient way:
[-a] fresh all namenodes configured in hdfs-site.xml.
[-ns <nameserviceId>] specify a nameservice to refresh.
[host:ipc_port] specify a nn to refresh.

please give your opinions. Thanks!