Description

   The mrd_unload(3mrd) function is a specialized interface to the
   SCSI Move Medium command (or DSA equivalent). For the robot
   specified by robot_name, the routine will attempt to move the
   cartridge in the specified drive to the specified slot. Element
   addresses are zero based.

   The robot will be opened and the arguments to the function will
   be verified to make sure they are safe and appropriate. The drive
   and slot address will be verified they are within the valid range
   of those elements on the robot.

   The volume_tag argument can be used to perform cartridge volume
   tag verification before the move. If the cartridge volume tag at
   the port doesn't match that specified by this argument, then mrd_
   unload(3mrd) will fail with the status MRD_STATUS_CART_INVALID.
   If volume_tag argument is a NULL pointer, an empty string or
   used on a robot without vision support this argument is silently
   ignored and the volume tag check will not be made.

   The DLT libraries (TL82X and TL81X families) require the host
   issue a SCSI Unload command before a cartridge may be removed
   from the drive. The function mrd_unload(3mrd), does not offer
   this feature. Thus, the calling program must do this itself. The
   example below shows how this can be done on Digital UNIX.