Vchan.Locationval to_offset : offset -> intto_offset x converts x to bytes
val to_length : t -> intto_length t gives the maximum number of available bytes at t
val to_order : t -> intto_order t gives the 'order' which is shared via the metadata page and used to uniquely identify the location
val of_order : int -> (t, [> `Msg of string ]) Stdlib.resultof_order x parses the order