This routine performs a SCSI Prevent/Allow Media Removal. It is
    used by mrd_lock(3mrd). The robot_info argument is the address of
    a robot_info_t that has been opened by mrd_startup(3mrd).

    When a lock value of one (1) is specified media removal is
    prevented. When the value zero (0) is used, media removal is
    allowed. If other values for lock are used, the routine will
    create a status which corresponds to an illegal request.

    This routine uses the dev_status_t structure for handing errors.
    The dev_status_t structure includes the code, os_status, and SCSI
    error fields. The following describes how to decode errors with
    the dev_status_t structure.

    SCSI Errors

    SCSI errors are indicated when the value of the valid field of
    the SCSI error is not equal to 0. The key, asc, and ascq fields
    provide additional information to help determine the cause of the
    error.

    The code usually maps the Additional Sense Code and Additional
    Sense Code Qualifier (ASC/ASCQ) values to an MRD error. The asc
    and ascq values are copied from the request sense data returned
    by the target.

    The Additional Sense Code (asc) indicates further information
    related to the error or exception condition reported in the sense
    key field. The Additional Sense Code Qualifier (ascq) indicates
    detailed information related to the additional sense code. For
    more information, consult the SCSI-2 Specification.

    Operating System Errors

    Operating system errors are indicated when the value of the valid
    field of the SCSI error is equal to 0 and the value of the os_
    status field is not equal to 0. This result is most likely caused
    by an operating system error, and probably has a mapped error in
    MRD.

    MRD Errors

    MRD errors are indicated when the value of the os_status field is
    0, and the value of the valid field of the SCSI error is 0. This
    result is most likely caused when MRD encounters its own failure.