| # `cros_evaluate_seed` |
| |
| This directory is for code to evaluate field trial state early in boot on |
| ChromeOS. All code here will be used in a single program, `evaluate_seed`. It is |
| not for general use in ash (or lacros). |
| |
| ## `evaluate_seed` |
| |
| The executable `evaluate_seed` is a minimal program (budget: 2MiB of disk space |
| for the executable itself) used early in ChromeOS boot to determine which group |
| each early-boot experiment should be in, as well as any parameters for the |
| experiment. It lives here so that it is trivial to keep the code in sync between |
| ChromeOS's platform layer and chrome. |
| |
| It will be built alongside ash. |
| |
| It will be executed primarily by `featured`, which lives in |
| `//platform2/featured/`. |
| |
| `evaluate_seed` will write a serialized version of the computed state to stdout, |
| along with a representation of the seed used for computation (for purposes of |
| determining whether the seed can be marked as "safe"). |
| |
| ## Seed usage |
| |
| When the device starts up, `featured` will exec `evaluate_seed`, which will by |
| default use whatever the latest seed in `/home/chronos/Local State` is. The |
| state computed by `evaluate_seed` will be cached in a tmpfs until the next |
| reboot, so even if ash later downloads and applies different seeds, |
| `evaluate_seed` will not re-evaluate the seed until the next device reboot. |
| |
| For disaster recovery, featured will determine whether to use the safe (or null) |
| seed, and pass that information along with the value of the safe seed to use |
| along to `evaluate_seed`. |
