[NiLuJe]

@yifanlu: linkjail is ran @rc3, before otaup, at which point we can safely compare the *.bin file against the whitelist, and switch keys if needed via a bind mount. It'll be unmounted @rc5 once the update is finished and the framework restarts.

Basically, we have an open window between the 'Update Your Kindle' click and otaup, and the switch is made during that window. We switch back to default keys when the framework restarts (or when the Kindle reboots, since it's a bind mount).