[TOPIC 15/17] Reachability checks

["James Ramsay" <james@jramsay.com.au>]

1. Jonathan N: seed the idea that it would be nice to hint the ref that 
your commit might be reachable from to help the server avoid iterating 
over all refs. Also, any strategies for speeding up reachability checks?

2. Demitr: reachability by user, or would you consider open to everyone?

3. Stolee: we don’t do branch level security, but we do tailor ref 
list to default, favorites and those you’ve pushed. There is also a 
full endpoint.

4. Brian: security model we have to have is that we assume everyone has 
read to everything. There are too many ways to attack. Useful for 
performance reasons, but not sure reachability checks provide much 
benefit. Don’t think it’s difficult to automate.

5. Demitr: what about security issues

6. Stolee: we’d say find another way.

7. Terry: we have a mono repo, easier to test everything. JGit goes down 
to object level.

8. Peff: Git doesn’t go down to that level, doesn’t validate haves.

9. Jonathan: two lessons, no one except Gerrit cares strongly about 
this; second if we like the model by branch permissions, worth making it 
work well in Git to prevent distance between JGit and Git.

10. Terry: can remove a branch very quickly and prevent new people 
getting it

11. Peff: don’t deny its usefulness, but the performance implication 
is concerning. Trying to keep objects private from determined attackers. 
But pushing a malicious commit to Linux, a user can see it, and won’t 
understand reachability doesn’t imply endorsement.

12. Jonathan: if Git has an easy cheap way to do it, people would use 
it.

13. Peff: have flirted with it, but might have to open 50GB of 
packfiles, or bitmap has corner cases. There are some obvious ways to 
improve, but a lot of work. V2 spec says you’re not allowed to check 
reachability.

14. Jonathan N: nah, it says you don't advertise a capability describing 
whether it is checking reachability.

15. Peff: submodule, but then the commit disappears and becomes 
unreachable. How do you handle?

16. Jonathan N: encourage folks to do fast forward only updates. In 
hooks instead of the git layer

17. Peff: you might not know what ref has reachability to that commit. I 
like the hint thing, if it’s just a hint.