There is no reak callback scheduler and previous behavior causes
bad things during hard congestion (like BGP hold timeouts).
Smart callback scheduler is still missing, but main loop was
changed such that it first processes all tx callbacks (which
are fast enough) (but max 4* per socket) + rx callbacks for CLI,
and in the second phase it processes one rx callback per
socket up to four sockets (as rx callback can be slow when
there are too many protocols, because route redistribution
is done synchronously inside rx callback). If there is event
callback ready, second phase is skipped in 90% of iterations
(to speed up CLI during congestion).
This also fixes bug that timer->recurrent was not cleared
in tm_new() and unexpected recurrence of startup timer
in BGP confused state machine and caused crash.
If other side of a socket is sending data faster than
BIRD is processing, BIRD does not schedule any other
callbacks (events, timers, rx/tx callbacks).
Under specific circumstances there might be two mixed-up
netlink sessions (one for scan, the other for route change
request). This patch separates netlink scans and requests
to two fds (and seq counters).
This should fix http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=428865
KRF_INSTALLED flag was not cleared during reconfiguration
that lead to not removing routes during reconfigure when
export rules changed.
We also should not try to remove routes we didi not installed,
on Linux this leads to warnings (as kernel checks route source
field and do not allow to remove non-bird routes) but we should
not rely on it.
