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Entity Manager DBus API

The Entity Manager is in charge of inventory management by scanning JSON files and representing the data on DBus in a meaningful way. For more information on the internal structure of the Entity Manager, please refer to the README of the Entity Manager. This file documents a consumers usage of the entity manager, and is not a description of the internal workings.

DBus Object

Object Paths

Entities: /xyz/openbmc_project/Inventory/Item/{Entity Type}/{Entity Name}

Entities are top level json objects that describe a piece of hardware. They are groups of configurations with few properties of their own, they are a container type for most pratical purposes.

Devices: /xyz/openbmc_project/Inventory/Item/{Entity Type}/{Entity Name}/{Configuration}

Configurations are components that are exposed when an entity is added to the "global" system configuration. An example would be a TMP75 sensor that is exposed when the front panel is detected.

Example:

/xyz/openbmc_project/Inventory/Item/Board/Intel_Front_Panel/Front_Panel_Temp

Interfaces

xyz.openbmc_project.{InventoryType}

See upstream types

  • BMC
  • Board
  • Chassis
  • CPU
  • ...

These types closely align with Redfish types.

Entity objects describe pieces of physical hardware.

Properties

unsigned int num_children: Number of configurations under this entity.

std::string name: name of the inventory item

xyz.openbmc_project.Configuration

Configuration objects describe components owned by the Entity.

Properties

Properties will contain all non-objects (simple types) exposed by the JSON.

Example:

path: /xyz/openbmc_project/Inventory/Item/Board/Intel_Front_Panel/Front_Panel_Temp
Interface: xyz.openbmc_project.Configuration
    string name = "front panel temp"
    string address = "0x4D"
    string "bus" = "1"

xyz.openbmc_project.Device.{Object}.{index}

{Object}s are members of the parent device that were originally described as dictionaries. This allows for creating more complex types, while still being able to get a picture of the entire system when doing a get managed objects method call. Array objects will be indexed zero based.

Properties

All members of the dictonary.

Example:

path: /xyz/openbmc_project/Inventory/Item/Board/Intel_Front_Panel/Front_Panel_Temp
Interface: xyz.openbmc_project.Device.threshold.0
    string direction = "greater than"
    int value = 55

JSON Requirements

JSON syntax requirements

Based on the above DBus object, there is an implicit requirement that device objects may not have more than one level deep of dictionary or list of dictionary. It is possible to extend in the future to allow nearly infinite levels deep of dictonary with extending the xyz.openbmc_project.Device.{Object} to allow xyz.openbmc_project.Device.{Object}.{SubObject}.{SubObject} but that complexity will be avoided until proven needed.

Example:

Legal:

exposes :
[
    {
        "name" : "front panel temp",
        "property": {"key: "value"}
    }
]

Not Legal:

exposes :
[
    {
        "name" : "front panel temp",
        "property": {
            "key": {
                "key2": "value"
            }
        }
    }
]