flags for open() and creat() include platform specific and also platform version specific options. 

protocol should try to translate only those flags which are valid on the client side. (client side does not necessarily mean 'the machine on which mount-point exists').

for example, a client running linux-2.6.20 will omit O_CLOEXEC flag, even if the server runs linux-2.6.30. 

protocol untranslate should untranslate only those flags which are valid on the server side. (server side does not necessarily mean 'the machine on which storage/posix exists').

for example, a server running linux-2.4.9 will omit O_DIRECT flag, even if the client runs linux-2.6.0

NOTE: this might lead to omitting of multiple flags for open(), creat().