In multithreaded environment, we need to pass messages between workers.
This is done by queuing events to their respective queues. The
double-linked list is not really useful for that as it needs locking
everywhere.
This commit rewrites the event subsystem to use a single-linked list
where events are enqueued by a single atomic instruction and the queue
is processed after atomically moving the whole queue aside.
There were more conflicts that I'd like to see, most notably in route
export. If a bisect identifies this commit with something related, it
may be simply true that this commit introduces that bug. Let's hope it
doesn't happen.
The invalid routes were filtered out before they could ever get
exported, yet some of the routines need them available, e.g. for
display or import reload.
Now the invalid routes are properly exported and dropped in channel
export routines instead.
Introduced by 13ef5e53dd, the CLI was not
properly cleaned up when the command finished, causing BIRD to not parse
any other command after "show route".
For BGP LLGR purposes, there was an API allowing a protocol to directly
modify their stale routes in table before flushing them. This API was
called by the table prune routine which violates the future locking
requirements.
Instead of this, BGP now requests a special route export and reimports
these routes into the table, allowing for asynchronous execution without
locking the table on export.
Until now, we were marking routes as REF_STALE and REF_DISCARD to
cleanup old routes after route refresh. This needed a synchronous route
table walk at both beginning and the end of route refresh routine,
marking the routes by the flags.
We avoid these walks by using a stale counter. Every route contains:
u8 stale_cycle;
Every import hook contains:
u8 stale_set;
u8 stale_valid;
u8 stale_pruned;
u8 stale_pruning;
In base_state, stale_set == stale_valid == stale_pruned == stale_pruning
and all routes' stale_cycle also have the same value.
The route refresh looks like follows:
+ ----------- + --------- + ----------- + ------------- + ------------ +
| | stale_set | stale_valid | stale_pruning | stale_pruned |
| Base | x | x | x | x |
| Begin | x+1 | x | x | x |
... now routes are being inserted with stale_cycle == (x+1)
| End | x+1 | x+1 | x | x |
... now table pruning routine is scheduled
| Prune begin | x+1 | x+1 | x+1 | x |
... now routes with stale_cycle not between stale_set and stale_valid
are deleted
| Prune end | x+1 | x+1 | x+1 | x+1 |
+ ----------- + --------- + ----------- + ------------- + ------------ +
The pruning routine is asynchronous and may have high latency in
high-load environments. Therefore, multiple route refresh requests may
happen before the pruning routine starts, leading to this situation:
| Prune begin | x+k | x+k | x -> x+k | x |
... or even
| Prune begin | x+k+1 | x+k | x -> x+k | x |
... if the prune event starts while another route refresh is running.
In such a case, the pruning routine still deletes routes not fitting
between stale_set and and stale_valid, effectively pruning the remnants
of all unpruned route refreshes from before:
| Prune end | x+k | x+k | x+k | x+k |
In extremely rare cases, there may happen too many route refreshes
before any route prune routine finishes. If the difference between
stale_valid and stale_pruned becomes more than 128 when requesting for
another route refresh, the routine walks the table synchronously and
resets all the stale values to a base state, while logging a warning.
Until now, if export table was enabled, Nest was storing exactly the
route before rt_notify() was called on it. This was quite sloppy and
spooky and it also wasn't reflecting the changes BGP does before
sending. And as BGP is storing the routes to be sent anyway, we are
simply keeping the already-sent routes in there to better rule out
unneeded reexports.
Some of the route attributes (IGP metric, preference) make no sense in
BGP, therefore these will be probably replaced by something sensible.
Also the nexthop shown in the short output is the BGP nexthop.
For loops allow to iterate over elements in compound data like BGP paths
or community lists. The syntax is:
for [ <type> ] <variable> in <expr> do <command-body>
When f_line is done, we have to pop the stack frame. The old code just
removed nominal number of args/vars. Change it to use stored ventry value
modified by number of returned values. This allows to allocate variables
on a stack frame during execution of f_lines instead of just at start.
But we need to know the number of returned values for a f_line. It is 1
for term, 0 for cmd. Store that to f_line during linearization.
Passing protocol to preexport was in fact a historical relic from the
old times when channels weren't a thing. Refactoring that to match
current extensibility needs.
In the multithreaded environment, it is not supposed that anybody
traverses the routing table as the CLI show-route was doing. Now the
routing table traversal is gone and CLI won't hold the table locked
while computing filters.
Added an option for export filter to allow for prefiltering based on the
prefix. Routes outside the given prefix are completely ignored. Config
is simple:
export in <net> <filter>;
There were quite a lot of conflicts in flowspec validation code which
ultimately led to some code being a bit rewritten, not only adapted from
this or that branch, yet it is still in a limit of a merge.
Validation is called internally from route table at the same place where
nexthop resolution is done. Also accounting for rte->sender semantics
change (not a channel but the import hook instead).
Use timer (configurable as 'gc period') to schedule routing table
GC/pruning to ensure that prune is done on time but not too often.
Randomize GC timers to avoid concentration of GC events from different
tables in one loop cycle.
Fix a bug that caused minimum inter-GC interval be 5 us instead of 5 s.
Make default 'gc period' adaptive based on number of routing tables,
from 10 s for small setups to 600 s for large ones.
In marge multi-table RS setup, the patch improved time of flushing
a downed peer from 20-30 min to <2 min and removed 40s latencies.
