At a high-level, code in this repository belongs to one of the following three components.
This is a library which deals with the encoding and decoding of PLDM messages. It should be possible to use this library by projects other than OpenBMC, and hence certain constraints apply to it:
- keeping it light weight
- implementation in C
- minimal dynamic memory allocations
- endian-safe
- no OpenBMC specific dependencies
Source files are named according to the PLDM Type, for eg base.[h/c], fru.[h/c], etc.
Given a PLDM command "foo", the library will provide the following API: For the Requester function:
encode_foo_req() - encode a foo request
decode_foo_resp() - decode a response to foo
For the Responder function:
decode_foo_req() - decode a foo request
encode_foo_resp() - encode a response to foo
The library also provides API to pack and unpack PLDM headers.
This library provides handlers for incoming PLDM request messages. It provides for a registration as well as a plug-in mechanism. The library is implemented in modern C++, and handles OpenBMC's platform specifics.
The handlers are of the form
Response handler(Request payload, size_t payloadLen)
Source files are named according to the PLDM Type, for eg base.[hpp/cpp], fru.[hpp/cpp], etc.
This is the PLDM daemon application that deals with various aspects of the requester and responder functions, as explained at https://github.com/openbmc/docs/blob/master/designs/pldm-stack.md.
The PLDM daemon provides a registration API for dynamically linked and dynamically loaded responder libraries so that they can register handlers for PLDM commands. The registration API is as follows:
void registerHandler(
uint8_t pldmType, uint8_t pldmCommand,
void(*func_ptr)(const pldm_msg_payload* request, pldm_msg* response));
The handler has to prepare a PLDM response message and write the same to an output argument.
The PLDM daemon will expect each of the responder libraries to implement a
method that it can invoke to perform the registration. The implementation of
this method would call registerHandler to register various handlers. The
signature of this method is:
void registerHandlers()
For standard PLDM types, libpldmresponder must place this method in appropriate
namespaces, for eg pldm::base::registerHandlers.
Consider hosting libpldm above in a repo of its own, probably even outside the OpenBMC project? A separate repo would enable something like git submodule.
This section documents important code flow paths.
a) PLDM daemon receives PLDM request message from underlying transport (MCTP).
b) PLDM daemon routes message to message handler, based on the PLDM command.
c) Message handler decodes request payload into various field(s) of the request message. It can make use of a decode_foo_req() API, and doesn't have to perform deserialization of the request payload by itself.
d) Message handler works with the request field(s) and generates response field(s).
e) Message handler prepares a response message. It can make use of an encode_foo_resp() API, and doesn't have to perform the serialization of the response field(s) by itself.
f) The PLDM daemon sends the response message prepared at step e) to the remote PLDM device.
a) A BMC PLDM requester app prepares a PLDM request message. There would be several requester apps (based on functionality/PLDM remote device). Each of them needn't bother with the serialization of request field(s), and can instead make use of an encode_foo_req() API.
b) BMC requester app requests PLDM daemon to send the request message to remote PLDM device.
c) Once the PLDM daemon receives a corresponding response message, it notifies the requester app.
d) The requester app has to work with the response field(s). It can make use of a decode_foo_resp() API to deserialize the response message.