Entity manager configuration files are JSON documents and can be validated with a JSON schema. This document provides an overview of the general structure of an entity manager configuration file.
An entity manager configuration file consists of one or more entity manager configurations. This provides flexibility for system designers - the configuration data for an entire platform or set of platforms can be expressed in a single file, or can be organized into several smaller files. Thus, the top most schema describes a single object or an array of objects.
To remain consistent with the OpenBMC CPP source code file name guidelines, entity manager configuration file and schema file names must be lower_snake_case.
At its core entity manager simply exports objects onto DBus when a specific event occurs. As such, an entity manager configuration provides a syntax for describing the dbus interfaces to export, the object paths on which to add the interfaces and the event that should trigger the export. This is accomplished with four properties.
The type property identifies the type of the configuration. When exported, configuration data will be instantiated as grandchildren of /xyz/openbmc_project/inventory/system/<Type>. For a comprehensive list of supported types, consult the schema (global.json).
The name property identifies the name of the configuration. When exported, configuration data will be instantiated as children of /xyz/openbmc_project/inventory/system/<Type>/<Name>. Additionally, any DBus interfaces listed in openbmc-dbus.json will be added on /xyz/openbmc_project/inventory/system/<Type>/<Name>.
The probe property describes the event which will cause entity manager to export the configuration to DBus, making it available to other applications.
The exposes property describes the configuration data at its most specific level. The exposes property is an array of heterogeneous configuration data. Each exposes element has its own schema which is outlined by the subschemas in the schemas directory. Each schema must require a type and name (not to be confused with the Type and Name properties of the parent JSON object) property since entity manager will construct the Dbus interface name and object path based on those properties:
/xyz/openbmc_project/inventory/system/Board/RiserCard1/<Name>: xyz.openbmc_project.Configuration.<Type>: <remaining properties defined by exposes subschema>
New subschema for the exposes property must be added to the schema directory, and then referenced from global.json at /definitions/EMExposesElement. Exposes element subschema must require a type and name property (the validator will fail otherwise) and should explicitly enumerate all properties and use additionalProperties so mistakes can be found during validation.
To export new interfaces on the configuration parent object e.g.: /xyz/openbmc_project/inventory/system/Board/RiserCard1 add additional subschema to openbmc-dbus.json.