bringup product is the most minimal viable target for development. It is
a minimal feature set product that is focused on being very simple and very lean.
Note that the name
bringup build should not imply “only used during bringup of
a new platform”, the name is historical.
The bringup product serves at least these purposes:
- Bringup: When a new platform is not running Fuchsia yet (
coreproduct configuration or higher) because all the pieces necessary to run are not completed/work-reliable, for instance networking, storage or configurations needed for fx device discovery and package management.
- Kernel and low level driver development: Developing facilities that need to
be working to even try a
coreproduct requires a bringup build. This applies to kernel development and drivers like networking and storage that are needed in
core. Note that higher level drivers like audio also can benefit from bringup builds, when the drivers needed for core are not ready yet.
A bringup build has these basic features:
- Has serial output enabled: This includes debug logging from drivers (for instance via zxlogf). This must guarantee that developers bringing up new platforms are able to printf debug as needed.
- Is RAM loadable: It must be possible to load into RAM a bringup build in
order of preference:
- For those platforms that support 'fastboot boot' it must be possible to implement RAM booting a ZBI directly from the bootloader (for example using the bootshim mechanism).
- For those platforms that do not support 'fastboot boot' it must be possible to boot using an existing zedboot (for instance loaded in a bootable USB stick or previously flashed) with a mechanism like netsvc (used for netbooting) or overnet (for instance over serial).
- For those platforms that do not support 'fastboot boot' (for instance when there is no control over the bootloader) it must also be possible to implement RAM booting a ZBI directly from the bootloader (for example by creating a bootshim for the specific bootloader).
- Does not have dependencies on drivers not available in early bringup: Examples of drivers available in early bringup include interrupt controllers and serial port. Examples of drivers not available in early bringup include networking and storage.
- Has minimum dependencies on Fuchsia at large, in that it:
- Has workflows driven over a serial link.
- Allows for everything needed in the build to be loaded alongside the kernel (i.e. in bootfs).
- Does not depend on Fuchsia features like paving that require storage.
- Does not support fx commands such as fx serve and fx shell. As a result, bringup builds are not able to add new software at runtime or upgrade themselves.
- Allows for easy inclusion of additional drivers or binaries: It must be possible to include additional binaries and drivers in the bringup build. For instance through inclusion into bootfs via GN to add a driver in development to the build.
Note that these features do not prevent the possible expansion of the bringup build minimal configuration to other more complete configurations that allow for improved workflows.