+class offset_device : string -> int64 -> int64 -> device ->
+ object
+ method name : string
+ method read : int64 -> int -> string
+ method read_bitstring : int64 -> int -> string * int * int
+ method size : int64
+ end
+ (** A concrete device which maps a linear part of an underlying device.
+
+ [new offset_device name start size dev] creates a new
+ device which maps bytes from [start] to [start+size-1]
+ of the underlying device [dev] (ie. in this device they
+ appear as bytes [0] to [size-1]).
+
+ Useful for things like partitions.
+ *)
+