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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.
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