2.1.9 64-bit file ID
A 64-bit value that uniquely identifies a file within a given volume. This identifier is generated and stored by the file system. The identifier SHOULD<10> be unique to the volume and stable until the file is deleted.
For file systems that do not support a 64-bit file ID, this field MUST be set to 0, and MUST be ignored.
For files for which a unique 64-bit file ID cannot be established, this field MUST be set to 0xffffffffffffffff, and MUST be ignored.