54 lines
2.7 KiB
ReStructuredText
54 lines
2.7 KiB
ReStructuredText
NVMe Management Interface (NVMe-MI) support
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===========================================
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This libnvme project also includes support for the NVMe Management Interface
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(NVMe-MI), currently over a Management Component Transport (MCTP)
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protocol link. This MCTP link will typically use i2c/SMBus as the
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hardware transport, enabling out-of-band management and control over NVMe
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devices using a simple SMBus interface.
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The MI interface is compiled into a separate shared object, ``libnvme-mi.so``.
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Most of the MI API is transport-agnostic, except for the endpoint constructor
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functions. Once an endpoint object (``nvme_mi_ep_t``) is created, the generic
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functions can be used to manage it.
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When endpoints are created (through one of the transport-specific functions,
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like ``nvme_mi_open_mctp()``), the endpoint hardware will be probed to
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see if any device-specific workarounds ("quirks") are required. This is
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implemented as an Identify Controller command, requesting a small amount of
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data on controller ID 0.
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To suppress this probe, the ``LIBNVME_MI_PROBE_ENABLED`` environment var can be
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set. Values of ``0``, ``false`` and ``disabled`` will disable the probe, and no
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quirks will be applied. Other values, or an unset environment variable, will
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enable the probe.
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MCTP Transport
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--------------
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The MI API is generally transport-agnostic, but the only currently-supported
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transport is MCTP, using the kernel ``AF_MCTP`` socket interface.
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MCTP endpoints are addressed by a (network-id, endpoint-id) pair. Endpoint
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IDs (EIDs) are defined by the MCTP standard as an 8-bit value. Since the
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address space is somewhat limited, the Linux `AF_MCTP` support allows for
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separate MCTP "networks", which provide separate address spaces. These networks
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each have a unique ``unsigned int`` as their ID.
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The default Network ID is 1; unless you have configured otherwise, MCTP
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endpoints will appear on this network.
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If compiled with D-Bus support, ``libnvme-mi`` can query the system MCTP daemon
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("``mctpd``") to find attached NVMe devices, via the ``nvme_mi_scan_mctp()``
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function. Calling this will establish a ``nvme_root_t`` object, populated
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with the results of that scan. Use the ``nvme_mi_for_each_endpoint`` macro
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to iterate through the scanned endpoints.
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Note that the MCTP daemon is provided separately, as part of the MCTP userspace
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tools, at https://github.com/CodeConstruct/mctp . ``mctpd`` is responsible for
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discovery and enumeration for MCTP endpoints on the system, and will query
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each for its protocol capabilities during enumeration. Consequently, NVMe-MI
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endpoints will need to report support for NVMe-MI-over-MCTP (protocol 0x4) in
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their supported protocols list (ie., as returned by the MCTP Get Message Type
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Support command) in order to be discovered.
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