After a suggestion by Santiago, I added the direct list pointer into
events and the events are now using this value to check whether the
route is active or not. Also the whole trick with sentinel node unioned
with event list is now gone.
For debugging, there is also an internal circular buffer to store what
has been recently happening in event code before e.g. a crash happened.
By default, this debug is off and must be manually enabled in
lib/event.c as it eats quite some time and space.
In some specific configurations, it was possible to send BIRD into an
infinite loop of recursive next hop resolution. This was caused by route
priority inversion.
To prevent priority inversions affecting other next hops, we simply
refuse to resolve any next hop if the best route for the matching prefix
is recursive or any other route with the same preference is recursive.
Next hop resolution doesn't change route priority, therefore it is
perfectly OK to resolve BGP next hops e.g. by an OSPF route, yet if the
same (or covering) prefix is also announced by iBGP, by retraction of
the OSPF route we would get a possible priority inversion.
By this, the requesting channels do the timers in their own loops,
avoiding unnecessary synchronization when the central timer went off.
This is of course less effective for now, yet it allows to easily
implement selective reloads in future.
Instead of synchronous notifications, we use the asynchronous export
framework to notify flowspec src route updates. This allows us to
invoke flowspec revalidation without locking collisions.
Instead of synchronous notifications, we use the asynchronous export
framework to notify also hostcache updates. This allows us to do the
hostcache update and the subsequent next hop update notification without
locking collisions.
We can't free the network structures before the export has been cleaned
up, therefore it makes more sense to request prune only after export
cleanup. This change also reduces prune calls on table shutdown.
