Add a torrc option and descriptor line to opt-in as a FallbackDir
This needs:
- a proposal and a design
- a patch to dir-spec.txt
- a patch to the tor man page
- a tor code patch
- an updateFallbackDirs.py code patch
- a wiki update to [[doc/UpdatingFallbackDirectoryMirrors]]
Here's a quick sketch of a design:
- Relay operators set
OfferFallbackDir 1
to offer their relay as a potential FallbackDir. - Relays with this option set put
offer-fallback-dir
in their descriptors - updateFallbackDirs.py loads relay fingerprints with
offer-fallback-dir
, and from the legacy offer list - updateFallbackDirs.py does stability checks, and generates the fallback list