All FlexRIO Host VIs are found in the following LLB:

C:\Program Files\National Instruments\LabVIEW\vi.lib\FlexRIO\FlexRIO_HostInterface.llb

NI recommends using the System Configuration API in all cases where you are querying an attribute.

Caution The Host VIs provide low-level access to the FlexRIO device. Improper use of these VIs can damage the FlexRIO and put it in an unrecoverable state.