The purpose of this document is to provide short definitions for a collection of technical terms used in the Fuchsia source tree.
The Application Manager (AppMgr) is responsible for launching applications and managing the namespaces in which those applications run. It is the first process started in the
fuchsia job by the DevMgr.
A Channel is the fundamental IPC primitive provided by Magenta. It is a bidirectional, datagram-like transport that can transfer small messages including Handles.
A Device Host (DevHost) is a process containing one or more device drivers. They are created by the Device Manager, as needed, to provide isolation between drivers for stability and security.
The Device Manager (DevMgr) is responsible for enumerating, loading, and managing the lifecycle of device drivers, as well as low level system tasks (providing filesystem servers for the boot filesystem, launching AppMgr, and so on).
The Driver Development Kit is the documentation, APIs, and ABIs necessary to build Magenta Device Drivers. Device drivers are implemented as ELF shared libraries loaded by Magenta's Device Manager.
The Fuchsia Archive Format is a container for files to be used by Magenta and Fuchsia. It will replace Magenta's older BootFS container and be used in Fuchsia Packages.
The Fuchsia Interface Definition Language (FIDL) is a language for defining protocols for use over Channels. FIDL is programming language agnostic and has bindings for many popular languages, including C, C++, Dart, Go, and Rust. This approach lets system components written in a variety of languages interact seamlessly.
Flutter is a functional-reactive user interface framework optimized for Fuchsia and is used by many system components. Flutter also runs on a variety of other platform, including Android and iOS. Fuchsia itself does not require you to use any particular language or user interface framework.
GN is a meta-build system which generates build files so that Fuchsia can be built with Ninja. GN is fast and comes with solid tools to manage and explore dependencies. GN files, named
BUILD.gn, are located all over the repository.
The “file descriptor” of the Magenta kernel. A Handle is how a userspace process refers to a kernel object. They can be passed to other processes over Channels.
Launchpad is a library provided by Magenta that provides the functionality to create and start new processes (including loading ELF binaries, passing initial RPC messages needed by runtime init, etc). It is a low-level library and over time it is expected that few pieces of code will make direct use of it.
Little Kernel (LK) is the embedded kernel that formed the core of the Magenta Kernel. LK is more microcontroller-centric and lacks support for MMUs, userspace, system calls -- features that Magenta added.
Magenta is the microkernel and lowest level userspace components (driver runtime environment, core drivers, libc, etc) at the core of Fuchsia. In a traditional monolithic kernel, many of the userspace components of Magenta would be part of the kernel itself.
Fuchsia's standard C library (libc) is based on Musl Libc.
MX is an abbreviation of “Magenta” used in Magenta C APIs/ABIs (
MX_EVENT_SIGNALED, etc) and libraries (mxio, mxtl, etc).
mxio is the Magenta IO Library. It provides the implementation of posix-style open(), close(), read(), write(), select(), poll(), etc, against the RemoteIO RPC protocol. These APIs are return-not-supported stubs in libc, and linking against libmxio overrides these stubs with functional implementations.
Ninja is the build system executing Fuchsia builds. It is a small build system with a strong emphasis on speed. Unlike other systems, Ninja files are not supposed to be manually written but should be generated by more featureful systems, such as GN in Fuchsia.
RemoteIO is the Magenta RPC protocol used between mxio (open/close/read/write/ioctl) and filesystems, device drivers, etc. As part of FIDL v2, it will become a set of FIDL Interfaces (File, Directory, Device, ...) allowing easier interoperability, and more flexible asynchronous IO for clients or servers.
A service is an implementation of a FIDL interface. Components can offer their creator a set of services, which the creator can either use directly or offer to other components.
Services can also be obtained by interface name from a Namespace, which lets the component that created the namespace pick the implementation of the interface. Long-running services, such as Mozart, are typically obtained through a Namespace, which lets many clients connect to a common implementation.
The VDSO is a Virtual Shared Library -- it is provided by the Magenta kernel and does not appear in the filesystem or a package. It provides the Magenta System Call API/ABI to userspace processes in the form of an ELF library that's “always there.” In the Fuchsia SDK and Magenta DDK it exists as
libmagenta.so for the purpose of having something to pass to the linker representing the VDSO.
A Virtual Memory Address Range is a Magenta Kernel Object that controls where and how VMOs may be mapped into the address space of a process.
A Virtual Memory Object is a Magenta Kernel Object that represents a collection of pages (or the potential for pages) which may be read, written, mapped into the address space of a process, or shared with another process by passing a Handle over a Channel.