[PATCH v3] Babel: Replace internal route selection by bird's nest

[dxld at darkboxed.org]

HI,

On Sat, Feb 11, 2023 at 02:22:13PM +0100, Maria Matejka wrote:
> > I'm still trying to find a convincing argument for why the bad case can
> > never happen though. Can you think of a codepath that calls rt_notify with
> > one of our own routes outside of us calling into rte_update*? I'm having a
> > hard time reading the rt-table code, it just has so many twists and turns
> > :)
> 
> This is definitely possible, think about this case:
> 
> protocol babel { preference 150; ... }
> protocol static { preference 200; ... }
> 
> $ show route
> X/Y via A, preference 200, protocol static [*]
> X/Y via B, preference 150, protocol babel
> 
> When Babel imports the route, it gets back (rt_notify) the static route
> which is best.
> 
> Then the admin requests "disable static1" and Babel gets (rt_notify) its own
> route without doing anything.

Ah, of course. That makes sense. I'll have to dig deeper into the object
lifetimes then and keep the code more defensive for now.

> And you should also be aware that in BIRD 3, you never get rt_notify while
> calling rte_update(); route updates are always asynchronous and you get them
> always in a clean context.

Interesting. I'll have to look at that. Speaking of bird v3, is it
intentional that the branch for that isn't public? At least I couldn't find
it when I last checked.

Thanks,
--Daniel