What is our story for ACL's on Unix, where file system supports it?

Mono.Posix (what we point at for API for Unix primitives) does not support them. Do we need to offer support for them somewhere?

Whereever that support lies, do we need to add extension methods (like this) to allow objects to be created with the ACL applied? If not, what is the story for folks porting Windows code using ACL's to Linux?

This assumes we do not want to attempt to overload types like DirectorySecurity, which were designed with Windows in mind, to accommodate Unix.