It is expected that a GN build configuration include exactly one board GNI file, and one product GNI file. In fx this pair is the primary argument to the
fx set command.
In a Fuchsia GN build configuration the board is always included first. The board starts the definition of three dependency lists that are then augmented by the imported product (and later, optional GN inclusions). Those list are Base, Cache and Universe respectively, and are defined below.
A board defines the architecture that the build produces for, as well as key features of the device upon which the build is intended to run. This configuration includes what drivers are included, and may also influence device specific kernel parameters.
The available boards can be listed using
A product defines the software configuration that a build will produce. Most critically, a product typically defines the kinds of user experiences that are provided for, such as what kind of graphical shell the user might observe, whether or not multimedia support is included, and so on.
The available products can be listed using
Boards define, and products augment three lists of dependencies, Base, Cache and Universe. These dependencies are GN labels that ultimately contribute packages to various system artifacts, such as disk images and signed package metadata, as well as various development artifacts such as host tools and tests.
base dependency list contributes packages to disk images and system updates as well as the package repository. A package included by the
base dependency set takes precedence over a duplicate membership in the
cache dependency set. Base packages in a system configuration are considered system and security critical. They are updated as an atomic unit and are never evicted at runtime regardless of resource pressure.
cache dependency list contributes packages that are pre-cached in the disk image artifacts of the build, and will also be made available in the package repository. These packages are not added to the system updates, but would instead be updated ephemerally. Cached packages can also be evicted from running systems in order to free resources based on runtime resource demands.
universe dependency list contributes packages to the package repository only. These packages will be available for runtime caching and updating, but are not found in system update images nor are they pre-cached in any disk images. All members of
cache are inherently also members of
There are many more than below, but the following three particularly important configurations to be familiar with:
bringupis a minimal feature set product that is focused on being very simple and very lean. It exists to provide fast builds and small images (primarily used in a netboot rather than paved fashion), and is great for working on very low-level facilities, such as the Zircon kernel or board-specific drivers and configurations. It lacks most network capabilities, and therefore is not able to add new software at runtime or upgrade itself.
coreis a minimal feature set that can install additional software (such as items added to the “universe” dependency set). It is the starting point for all higher-level product configurations. It has common network capabilities and can update a system over-the-air.
workstationis a basis for a general purpose development environment, good for working on UI, media and many other high-level features. This is also the best environment for enthusiasts to play with and explore.