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Phosphor State Manager Documentation

This repository contains the software responsible for tracking and controlling the state of different objects within OpenBMC. This currently includes the BMC, Chassis, Host, and Hypervisor. The most critical feature of phosphor-state-manager (PSM) software is its support for requests to power on and off the system by the user.

This software also enforces any restore policy (i.e. auto power on system after a system power event or bmc reset) and ensures its states are updated correctly in situations where the BMC is rebooted and the chassis or host are in on/running states.

This repository also provides a command line tool, obmcutil, which provides basic command line support to query and control phosphor-state-manager applications running within an OpenBMC system. This tool itself runs within an OpenBMC system and utilizes D-Bus APIs. These D-Bus APIs are used for development and debug and are not intended for end users.

As with all OpenBMC applications, interfaces and properties within phosphor-state-manager are D-Bus interfaces. These interfaces are then used by external interface protocols, such as Redfish and IPMI, to report and control state to/by the end user.

State Tracking and Control

phosphor-state-manager makes extensive use of systemd. There is a writeup here with an overview of systemd and its use by OpenBMC.

phosphor-state-manager monitors for systemd targets to complete as a trigger to updating the its corresponding D-Bus property. When using PSM, a user must ensure all generic services installed within the PSM targets complete successfully in order to have PSM properly report states.

phosphor-state-manager follows some basics design guidelines in its implementation and use of systemd:

  • Keep the different objects as independent as possible (host, chassis, bmc)
  • Use systemd targets for everything and keep the code within PSM minimal
  • Ensure it can support required external interfaces, but don't necessarily create 1x1 mappings otherwise every external interface will end up with its own special chassis or host state request
  • If something like a hard power off can be done by just turning off the chassis, don't provide a command in the host to do the same thing

phosphor-state-manager implements states and state requests as defined in phosphor-dbus-interfaces for each object it supports.

  • bmc: The BMC has very minimal states. It is NotReady when first started and Ready once all services within the default.target have executed. It is Quiesced when a critical service has entered the failed state. The only state change request you can make of the BMC is for it to reboot itself.
    • CurrentBMCState: NotReady, Ready, Quiesced
    • RequestedBMCTransition: Reboot
    • Monitored systemd targets: multi-user.target and [email protected]
  • chassis: The chassis represents the physical hardware in which the system is contained. It usually has the power supplies, fans, and other hardware associated with it. It can be either On, Off, or in a fail state. A BrownOut state indicates there is not enough chassis power to fully power on and UninterruptiblePowerSupply indicates the chassis is running on a UPS.
  • host: The host represents the software running on the system. In most cases this is an operating system of some sort. The host can be Off, Running, TransitioningToRunning, TransitioningToOff, Quiesced(error condition), or in DiagnosticMode(collecting diagnostic data for a failure)
  • hypervisor: The hypervisor is an optional package systems can install which tracks the state of the hypervisor on the system. This state manager object implements a limited subset of the host D-Bus interface.
    • CurrentHostState: Standby, TransitionToRunning, Running, Off, Quiesced
    • RequestedHostTransition: On

As noted above, PSM provides a command line tool, obmcutil, which takes a state parameter. This will use D-Bus commands to retrieve the above states and present them to the user. It also provides other commands which will send the appropriate D-Bus commands to the above properties to power on/off the chassis and host (see obmcutil --help within an OpenBMC system).

The above objects also implement other D-Bus objects like power on hours, boot progress, reboot attempts, and operating system status. These D-Bus objects are also defined out in the phosphor-dbus-interfaces repository.

Restore Policy on Power Events

The RestorePolicy defines the behavior the user wants when the BMC is reset. If the chassis or host is on/running then this service will not run. If they are off then the RestorePolicy will be read and executed by PSM code.

The PowerRestoreDelay property within the interface defines a maximum time the service will wait for the BMC to enter the Ready state before issuing the power on request, this allows host to be powered on as early as the BMC is ready.

Only Allow System Boot When BMC Ready

There is an optional only-allow-boot-when-bmc-ready feature which can be enabled within PSM that will not allow chassis or host operations (other then Off requests) if the BMC is not in a Ready state. Care should be taken to ensure PowerRestoreDelay is set to a suitable value to ensure the BMC reaches Ready before the power restore function requests the power on.

BMC Reset with Host and/or Chassis On

In situations where the BMC is reset and the chassis and host are on and running, its critical that the BMC software do two things:

  • Never impact the state of the system (causing a power off of a running system is very bad)
  • Ensure the BMC, Chassis, and Host states accurately represent the state of the system.

Note that some of this logic is provided via service files in system-specific meta layers. That is because the logic to determine if the chassis is on or if the host is running can vary from system to system. The requirement to create the files defined below and ensure the common targets go active is a must for anyone wishing to enable this feature.

phosphor-state-manager discovers state vs. trying to cache and save states. This ensure it's always getting the most accurate state information. It discovers the chassis state by checking the pgood value from the power application. If it determines that power is on then it will do the following:

  • Create a file called /run/openbmc/chassis@0-on
    • The presence of this file tells the services to alter their behavior because the chassis is already powered on
  • Start the [email protected]
    • The majority of services in this target will "fake start" due to the file being present. They will report to systemd that they started and ran successfully but they actually do nothing. This is what you would want in this case. Power is already on so you don't want to run the services to turn power on. You do want to get the [email protected] in the Active state though so that the chassis object within PSM will correctly report that the chassis is On
  • Start a service to check if the host is on

The chassis@0-on file is removed once the [email protected] becomes active (i.e. all service have been successfully started which are wanted or required by this target).

The logic to check if the host is on sends a command to the host, and if a response is received then similar logic to chassis is done:

  • Create a file called /run/openbmc/host@0-on
  • Start the [email protected]
    • Similar to above, most services will not run due to the file being created and their service files implementing a "ConditionPathExists=!/run/openbmc/host@0-request"

The host@0-on file is removed once the [email protected] and [email protected] become active (i.e. all service have been successfully started which are wanted or required by these targets).

Building the Code

To build this package, do the following steps:

  1. meson setup build
  2. ninja -C build

To clean the repository again run rm -rf build.