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.
Presently there are two revisions of the Component Framework that exist on Fuchsia, which are referred to as Components v1 and Components v2.
Components v1 is largely comprised of:
appmgr
, a program that manages the runtime environment for v1 components. appmgr
implements the root of the v1 components tree, as well as some foundational services such as the Components v1 ELF runner and Loader service.sysmgr
, a component that manages the so-called "sys"
realm. sysmgr
is launched by appmgr
..cmx
file format for v1 component manifests.fuchsia.sys.*
FIDL library.Components v1 development reached its peak in 2018. In 2019, Fuchsia team began developing Component Framework v2.
Components v2 is largely comprised of:
appmgr
. appmgr
has become a v2 component itself, which serves as the parent of all v1 components still present in the system..cml
file format for v2 component manifests.fuchsia.sys2.*
FIDL library.In addition, both Components v1 and v2 use cmc
(component manifest compiler), a build-time host tool that processes all formats of component manifest files.
The nature of migrations is that they may take a long time and happen in incremental steps. The final step for migrating a component from v1 to v2 typically involves replacing a .cmx
file with a .cml
file.
Last updated: January 2021
A high-level diagram of the system's component topology is shown below:
Component manager is one of the initial processes that are started in the system boot sequence. The system startup sequence then launches a number of low-level system components that deal with various responsibilities, including in no particular order:
In addition, Component manager launches appmgr
, itself a v2 component, in order to manage all remaining v1 components in a dedicated sub-realm. As the migration continues, typically components will move from the v1 sub-realm to elsewhere in the component instance topology.
Note: component_manager_sfw
is currently included in build configurations that use the Session Framework. This second instance of the component_manager
facilitates interoperability between v2 components (required under Session Framework) and legacy v1 components. Once all v1 components have been migrated to v2, the session_manager
will become a direct descendent of the root component_manager
, and component_manager_sfw
can be removed.
Last updated: January 2021
Components v2 migrations are happening throughout the system. However there is currently additional focus on: