Actually no... the application makes all calls using utf-8, and is expected to provide it in a well-formed manner so that the system call layer could convert it to utf-16. In the reverse route, where utf-16 is read by the system call layer and then converted to utf-8 (getdents(2) and friends), it is expected that file names be in well-formed utf-16. For a file-system volume to have ill-formed utf-16 name entries would make for an interesting case... have not encountered that yet, but will certainly look into that.