pub fn mount<P1, P2, P3, P4>( source: Option<&P1>, target: &P2, fstype: Option<&P3>, flags: MsFlags, data: Option<&P4>) -> Result<(), Errno> where P1: NixPath + ?Sized, P2: NixPath + ?Sized, P3: NixPath + ?Sized, P4: NixPath + ?Sized,