On input, RequestLength is the length (in octets) of the Descriptor that should be returned. If this value is less than the ...

On input, RequestLength is the length (in octets) of the Descriptor that should be returned. If this value is less than the actual length of the Descriptor, only the requested length will be returned. If it is more than the actual length, the actual length is returned. On output, this parameter is the length, in octets, of the Buffer being returned. If the requested Descriptor does not exist, the contents of this parameter are undefined.