I was reading about file system stack and found a source code and i am trying to understand what it is actually doing

it is finding the device object of \device\harddisk0\partition0 and then it sends a IRP_MJ_PNP request to it and builds the IRP using IoBuildSynchronousFsdRequest, sets the minorfunc to IRP_MN_QUERY_DEVICE_RELATIONS and QueryDeviceRelations.Type to TargetDeviceRelation

now can someone explain what does this actually do? whats the purpose of IRP_MN_QUERY_DEVICE_RELATIONS regarding the partition0 device object and whats the deal with this TargetDeviceRelation? where can i read more about this?

    KeInitializeEvent( &event, NotificationEvent, FALSE );

    irp = IoBuildSynchronousFsdRequest( IRP_MJ_PNP,
                                        DeviceObject,
                                        NULL,
                                        0,
                                        NULL,
                                        &event,
                                        &ioStatusBlock );

    if (irp == NULL) {
        status = STATUS_INSUFFICIENT_RESOURCES;
        goto End;
    }

    irpStack = IoGetNextIrpStackLocation( irp );
    irpStack->MinorFunction = IRP_MN_QUERY_DEVICE_RELATIONS;
    irpStack->Parameters.QueryDeviceRelations.Type = TargetDeviceRelation;

    irp->IoStatus.Status = STATUS_NOT_SUPPORTED ;


    status = IoCallDriver( DeviceObject, irp );

    if (status == STATUS_PENDING) {

        KeWaitForSingleObject( &event, Executive, KernelMode, FALSE, NULL );
        status = ioStatusBlock.Status;}