designs/mctp/mctp-userspace.md

1 # OpenBMC platform communication channel: MCTP & PLDM in userspace
5 Please refer to the [MCTP Overview](mctp.md) document for general MCTP design
8 This document describes a userspace implementation of MCTP infrastructure,
9 allowing a straightforward mechanism of supporting MCTP messaging within an
14 The MCTP core specification just provides the packetisation, routing and
16 hardware binding of the MCTP transport.
18 For OpenBMC, we would introduce a MCTP daemon, which implements the transport
21 complete MCTP messages. This daemon is responsible for the packetisation and
22 routing of MCTP messages from external endpoints, and handling the forwarding
24 handling local MCTP-stack configuration, like local EID assignments.
28 1.  the core MCTP stack
30 2.  one or more binding implementations (eg, MCTP-over-serial), which interact
35 The proposed implementation here is to produce an MCTP "library" which provides
50 The reason for a library is to allow the same MCTP implementation to be used in
67 over the MCTP channel, and connect to the central daemon over a UNIX domain
68 socket. Each of these would register with the MCTP daemon to receive MCTP
69 messages of a certain type, and would transmit MCTP messages of that same type.
78 MCTP implementation without requiring major structural changes to handler
83 MCTP is intended to be an optional component of OpenBMC. Platforms using OpenBMC
88 MCTP handlers (ie, clients of the demultiplexer) connect using a unix-domain
98 MCTP messages should be forwarded to the client. Types must be greater than
101 Subsequent messages sent over the socket are MCTP messages sent/received by the
102 demultiplexer, that match the specified MCTP message type. Clients should use
112 outgoing MCTP message. For messages going to the demux daemon, this indicates
115 The rest of the message data is the complete MCTP message, including MCTP
119 for the tag field in individual MCTP packets.
123 In terms of an MCTP daemon structure, an alternative is to have the MCTP
127 possible functionality that is available over MCTP, which may be quite a
131 significant modifications if/when MCTP protocol support is moved to the kernel.
134 as a socket-based interface. However, an alternative here would be to pass MCTP
141 For the core MCTP library, we are able to run tests there in complete isolation
142 (I have already been able to run a prototype MCTP stack through the afl fuzzer)
145 For MCTP hardware bindings, we would develop channel-specific tests that would
148 For the OpenBMC MCTP daemon implementation, testing models would depend on the