// filerExportOutputFile = cmdFilerExport.Flag.String("output", "", "the output file. If empty, only list out the directory tree")
filerExportSourceStore=cmdFilerExport.Flag.String("sourceStore","","the source store name in filer.toml")
filerExportTargetStore=cmdFilerExport.Flag.String("targetStore","","the target store name in filer.toml, or \"notification\" to export all files to message queue")
dir=cmdFilerExport.Flag.String("dir","/","only process files under this directory")
dirListLimit=cmdFilerExport.Flag.Int("dirListLimit",100000,"limit directory list size")