Description

   The mrd_position(3mrd) routine provides access to the SCSI
   Position to Element command. For the robot specified by the
   robot_name, the routine will attempt to position the specified
   transport to the specified element. The transport and element
   addresses are zero based. On subsystems that support inverting a
   cartridge during a move, the cartridge_side argument can be used
   to indicate that the transport should be inverted to invert a
   cartridge.

   The robot will be opened and the arguments to the function
   verified that they are appropriate. The element address and
   type will be checked that they are within the valid range of
   elements on the robot. The cartridge_side argument will be
   verified that it is either the value one (1) or two (2). All
   pointer arguments, except transport, are checked to verify they
   are not NULL pointers.

   Many robot subsystems support an absolute transport address of
   zero for the Position to Element command so that the robot can
   select the appropriate transport if multiple are available. This
   routines allows the default transport address to be specified by
   using a NULL pointer for the transport string.