* change interfaces of FileSystem

* updt interfaces and posix_file_system

* updt posix_file_system

* updt filesystem interfaces

* remove Status

* updt filesystem interfaces

* resolve conflict

* un-unploaded conflicts

* fix bug in record_kernel, replace LOG with PLOG

* replace createdir with createdirifnotexist in snapshot

* remove createdirifnotexist

* updt .gitignore

* remove predict output

* roll back

* fix bug

* fix for review