NVMe Management Interface (NVMe-MI) support

This libnvme project also includes support for the NVMe Management Interface (NVMe-MI), currently over a Management Component Transport (MCTP) protocol link. This MCTP link will typically use i2c/SMBus as the hardware transport, enabling out-of-band management and control over NVMe devices using a simple SMBus interface.

The MI interface is compiled into a separate shared object, libnvme-mi.so.

Most of the MI API is transport-agnostic, except for the endpoint constructor functions. Once an endpoint object (nvme_mi_ep_t) is created, the generic functions can be used to manage it.

MCTP Transport

The MI API is generally transport-agnostic, but the only currently-supported transport is MCTP, using the kernel AF_MCTP socket interface.

MCTP endpoints are addressed by a (network-id, endpoint-id) pair. Endpoint IDs (EIDs) are defined by the MCTP standard as an 8-bit value. Since the address space is somewhat limited, the Linux AF_MCTP support allows for separate MCTP “networks”, which provide separate address spaces. These networks each have a unique unsigned int as their ID.

The default Network ID is 1; unless you have configured otherwise, MCTP endpoints will appear on this network.

If compiled with D-Bus support, libnvme-mi can query the system MCTP daemon (“mctpd”) to find attached NVMe devices, via the nvme_mi_scan_mctp() function. Calling this will establish a nvme_root_t object, populated with the results of that scan. Use the nvme_mi_for_each_endpoint macro to iterate through the scanned endpoints.

Note that the MCTP daemon is provided separately, as part of the MCTP userspace tools, at https://github.com/CodeConstruct/mctp . mctpd is responsible for discovery and enumeration for MCTP endpoints on the system, and will query each for its protocol capabilities during enumeration. Consequently, NVMe-MI endpoints will need to report support for NVMe-MI-over-MCTP (protocol 0x4) in their supported protocols list (ie., as returned by the MCTP Get Message Type Support command) in order to be discovered.