1# Entity Manager 2 3Entity manager is a design for managing physical system components, and mapping 4them to software resources within the BMC. Said resources are designed to allow 5the flexible adjustment of the system at runtime, as well as the reduction in 6the number of independent system configurations one needs to create. 7 8## Definitions 9 10### Entity 11 12A server component that is physically separate, detectable through some means, 13and can be added or removed from a given OpenBMC system. Said component can, and 14likely does contain multiple sub-components, but the component itself as a whole 15is referred to as an entity. 16 17Note, this term is needed because most other terms that could've been used 18(Component, Field Replaceable Unit, or Assembly) are already overloaded in the 19industry, and have a distinct definition already, which is a subset of what an 20entity encompasses. 21 22### Exposes 23 24A particular feature of an Entity. An Entity generally will have multiple 25Exposes records for the various features that component supports. Some examples 26of features include, LM75 sensors, PID control parameters, or CPU information. 27 28### Probe 29 30A set of rules for detecting a given entity. Said rules generally take the form 31of a D-Bus interface definition. 32 33## Goals 34 35Entity manager has the following goals (unless you can think of better ones): 36 371. Minimize the time and debugging required to "port" OpenBMC to new systems 382. Reduce the amount of code that is different between platforms 393. Create system level maintainability in the long term, across hundreds of 40 platforms and components, such that components interoperate as much as 41 physically possible. 42 43## Implementation 44 45A full BMC setup using Entity Manager consists of a few parts: 46 471. **A detection daemon** This is something that can be used to detect 48 components at runtime. The most common of these, fru-device, is included in 49 the Entity-Manager repo, and scans all available I2C buses for IPMI FRU 50 EEPROM devices. Other examples of detection daemons include: 51 **[peci-pcie](https://github.com/openbmc/peci-pcie):** A daemon that utilizes 52 the CPU bus to read in a list of PCIe devices from the processor. 53 **[smbios-mdr](https://github.com/openbmc/smbios-mdr):** A daemon that 54 utilizes the x86 SMBIOS table specification to detect the available systems 55 dependencies from BIOS. 56 57 In many cases, the existing detection daemons are sufficient for a single 58 system, but in cases where there is a superseding inventory control system in 59 place (such as in a large datacenter) they can be replaced with application 60 specific daemons that speak the protocol information of their controller, and 61 expose the inventory information, such that failing devices can be detected 62 more readily, and system configurations can be "verified" rather than 63 detected. 64 652. **An entity manager configuration file** Entity manager configuration files 66 are located in the ./configurations directory in the entity manager 67 repository, and include one file per device supported. Entities are detected 68 based on the "Probe" key in the json file. The intention is that this folder 69 contains all hardware configurations that OpenBMC supports, to allows an easy 70 answer to "Is X device supported". An EM configuration contains a number of 71 Exposes records that specify the specific features that this Entity supports. 72 Once a component is detected, entity manager will publish these Exposes 73 records to D-Bus. 74 753. **A reactor** The reactors are things that take the entity manager 76 configurations, and use them to execute and enable the features that they 77 describe. One example of this is dbus-sensors, which contains a suite of 78 applications that input the Exposes records for sensor devices, then connect 79 to the filesystem to create the sensors and scan loops to scan sensors for 80 those devices. Other examples of reactors could include: CPU management 81 daemons and Hot swap backplane management daemons, or drive daemons. 82 83**note:** In some cases, a given daemon could be both a detection daemon and a 84reactor when architectures are multi-tiered. An example of this might include a 85hot swap backplane daemon, which both reacts to the hot swap being detected, and 86also creates detection records of what drives are present. 87 88## Requirements 89 901. Entity manager shall support the dynamic discovery of hardware at runtime, 91 using inventory interfaces. The types of devices include, but are not limited 92 to hard drives, hot swap backplanes, baseboards, power supplies, CPUs, and 93 PCIe Add-in-cards. 94 952. Entity manager shall support the ability to add or remove support for 96 particular devices in a given binary image. By default, entity manager will 97 support all available and known working devices for all platforms. 98 993. Entity manager shall provide data to D-Bus about a particular device such 100 that other daemons can create instances of the features being exposed. 101 1024. Entity manager shall support multiple detection runs, and shall do the 103 minimal number of changes necessary when new components are detected or no 104 longer detected. Some examples of re-detection events might include host 105 power on, drive plug/unplug, PSU plug/unplug. 106 1075. Entity manager shall have exactly one configuration file per supported device 108 model. In some cases this will cause duplicated information between files, 109 but the ability to list and see all supported device models in a single 110 place, as well as maintenance when devices do differ in the future is 111 determined to be more important than duplication of configuration files. 112 113### Explicitly out of scope 114 1151. Entity manager shall not directly participate in the detection of devices, 116 and instead will rely on other D-Bus applications to publish interfaces that 117 can be detected. 1182. Entity manager shall not directly participate in management of any specific 119 device. This is requirement is intended to intentionally limit the size and 120 feature set of entity manager, to ensure it remains small, and effective to 121 all users. 122 123### Entity Manager Compatible Software 124 125**bmcweb** A webserver implementation that uses the inventory information from 126entity-manager to produce a Redfish compliant REST API. **intel-ipmi-oem** An 127implementation of the IPMI SDR, FRU, and Storage commands that utilize Entity 128Manager as the source of information. 129 130## Additional Documentation 131 1321. **[Entity Manager DBus API](https://github.com/openbmc/entity-manager/blob/master/docs/entity_manager_dbus_api.md)** 1332. **[My First Sensor Example](https://github.com/openbmc/entity-manager/blob/master/docs/my_first_sensors.md)** 1343. **[Configuration File Schema](https://github.com/openbmc/entity-manager/tree/master/schemas)** 135