sd-event: add ability to ratelimit event sources

Let's a concept of "rate limiting" to event sources: if specific event
sources fire too often in some time interval temporarily take them
offline, and take them back online once the interval passed.

This is a simple scheme of avoiding starvation of event sources if some
event source fires too often.

This introduces the new conceptual states of "offline" and "online" for
event sources: an event source is "online" only when enabled *and* not
ratelimited, and offline in all other cases. An event source that is
online hence has its fds registered in the epoll, its signals in the
signalfd and so on.

1 files changed, 3 insertions, 0 deletions

diff --git a/src/systemd/sd-event.h b/src/systemd/sd-event.h
index 937c9bd460..2ae2a0da48 100644
--- a/src/systemd/sd-event.h
+++ b/src/systemd/sd-event.h
@@ -162,6 +162,9 @@ int sd_event_source_get_floating(sd_event_source *s);
 int sd_event_source_set_floating(sd_event_source *s, int b);
 int sd_event_source_get_exit_on_failure(sd_event_source *s);
 int sd_event_source_set_exit_on_failure(sd_event_source *s, int b);
+int sd_event_source_set_ratelimit(sd_event_source *s, uint64_t interval_usec, unsigned burst);
+int sd_event_source_get_ratelimit(sd_event_source *s, uint64_t *ret_interval_usec, unsigned *ret_burst);
+int sd_event_source_is_ratelimited(sd_event_source *s);
 
 /* Define helpers so that __attribute__((cleanup(sd_event_unrefp))) and similar may be used. */
 _SD_DEFINE_POINTER_CLEANUP_FUNC(sd_event, sd_event_unref);