Goal & motivation
The Component Framework is one of the key foundations for Fuchsia's usermode runtime environment. The original incarnation of components dates back to the inception of the Fuchsia OS and the initial commits in 2016. The framework has steadily evolved since then.
Last updated: May 2021
A high-level diagram of the system's component topology is shown below:
- v2 components are shown in blue boxes.
- v1 components are shown in red boxes.
- Boxes with dashed lines represent components that are only present on some build configurations.
In addition, all unit tests with generated manifests are v2 components.
Components v1 vs. v2
Components v1 is largely comprised of:
appmgr, a program that manages the runtime environment for v1 components.
appmgrimplements the root of the v1 components tree, as well as some foundational services such as the Components v1 ELF runner and Loader service.
, a component that manages the so-called
sysmgris launched by
.cmxfile format for v1 component manifests.
Components v1 development reached its peak in 2018. In 2019, Fuchsia team began developing Component Framework v2.
Components v2 is largely comprised of:
- Component manager, a program that manages the runtime
environment for v2 components. Component manager is now responsible for
appmgrhas become a v2 component itself, which serves as the parent of all v1 components still present in the system.
.cmlfile format for v2 component manifests.
In addition, both Components v1 and v2 use
cmc (component manifest
compiler), a build-time host tool that processes all formats of component
Component manager launches
appmgr, itself a v2 component, in order to manage
v1 components. All v1 components on the system run under
appmgr. Users may
continue developing and maintaining v1 components while v2 migrations take place
at their own pace.
Build configurations that use the Session Framework also
session_manager component. All v1-backed capabilities the session
needs are routed to the
Use this terminology when talking about the state of migrating a component and its tests from v1 to v2.
|The component||Tests that exercise it|
"root_presenter is partially migrated but its tests are not migrated."
"stash and its tests are fully migrated."
"basemgr is a partially migrated component with partially migrated tests. Specifically, ..."
"setui_service was prototyped to v2 and it exposed some missing dependencies."
How to help
Last updated: May 2021
Picking a task
Components v2 migrations are happening throughout the system. Any component that
still has at least one
.cmx file is a migration candidate. However there is
currently additional focus on:
- The stack of Software Delivery components and associated tests, including the package cache and package resolver.
- The Netstack2 components, including migration of Netemul and associated tests to Test Runner Framework.
- The Bluetooth components and associated tests.
- Components under sysmgr that are critical to system functionality but each have a smaller footprint than the ones above, tracked here.
- Scaling migrations by creating and expanding a self-service guide.
- Exploratory work with migrating wlan and Thread/Weave components.
Doing a task
Component migrations may take multiple incremental steps to complete due to dependencies between other components that have not been migrated yet. For example, a component and its tests can be migrated separately. For more details on the incremental stages, see terminology.
The final step for migrating a component from v1 to v2 typically involves
.cmx files with equivalent
For detailed instructions on migrating a component and its tests, see the
self-service migration guide.
Completing a task
Send code reviews to owners of the directories with the component definitions that you're changing, and to people listed below who volunteered to help with these migrations:
New volunteer? Please add yourself to the list!
- 504575: [http-client] Migrate to Components v2
- 504523: [soundplayer] transition to CFv2
- 489757: [device_settings] Migrate to CFv2
Reach out for questions or for status updates: