RFC-0081: fastboot boot

RFC-0081: fastboot boot
Status	Accepted
Areas	General
Description	Replace Zedboot based netbooting flows with fastboot boot
Gerrit change	498344
Authors	andresoportus@google.com
Reviewers	amituttam@ boetger@google.com bradenkell@google.com cpu@google.com curtisgalloway@google.com dpursell@google.com raggi@google.com tkilbourn@google.com travisg@google.com alizhang@google.com
Date submitted (year-month-day)	2021-03-09
Date reviewed (year-month-day)	2021-03-25

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Summary

This document proposes deprecating RAM loading via Zedboot's netsvc. Instead, it proposes replacing the netsvc based RAM loading flows with flows based on fastboot boot.

Motivation

Without netsvc RAM loading we can avoid the duplication of this functionality between Zedboot and bootloaders. This RFC is inline with RFC Deprecate Zedboot-based paving for provisioning devices, converging around the use of fastboot instead of Zedboot, allowing for the eventual deprecation and removal of Zedboot.

Background

Netsvc RAM loading is commonly used for bringup workflows using Zedboot. However bootloaders supporting fastboot boot already provide this functionality, e.g. RAM loading a build deployed to a device via the network, and also provide RAM loading via USB. Zedboot was initially developed as a simple networking alternative to using bootloaders because UEFI bootloaders vary in quality and in some fastboot would not be reliable enough. This is less of a problem for targets currently supported by Fuchsia with good enough support or support in the works (e.g. https://fxbug.dev/42137791). Platforms where fastboot is not available have the backup option of flashing Fuchsia to a USB device and booting from it.

Design

Fastboot is a mature mechansim and in use in Android devices. Bootloaders that support Fuchsia MUST follow the fastboot protocol.

Implementation

Bootloaders will need to be updated for example, Gigaboot will need to be modified to implement fastboot boot https://fxbug.dev/42137791.
fx scripts will need to be updated to redirect fx netboot users to fastboot boot (we likely want to wrap these flows in an fx/ffx helper command to make it as straightforward as possible).
Infra will need to be transitioned to fastboot https://fxbug.dev/42124288.
Zedboot deprecation as described in RFC Deprecate Zedboot-based paving for provisioning devices.

Backwards Compatibility

Once fx scripts are updated and Zedboot is removed, there will be no backward compatibility with netsvc.

Security and Privacy considerations

fastboot boot will be supported in unlocked "dev" bootloaders. fastboot boot support for locked bootloaders and unlocked "prod" bootloaders is under consideration but not defined in this RFC.

Documentation

Documentation for developer workflows will need to be updated to reflect the new fasboot boot based flows.

Drawbacks, alternatives, and unknowns

A drawback is that this creates a commitment to support fastboot in other Fuchsia bootloaders besides those that already support it. This means, as new boards are brought up in Fuchsia, fastboot support is required during early bringup. This includes support for fastboot boot on Gigaboot bootloaders used on Intel NUCs (https://fxbug.dev/42137791) and on coreboot based systems like Pixelbooks.

Prior art and references

Fastboot is a mature mechansim and in use in Android devices.