ratbagd: set up a simple exit-on-idle

ratbagd is not something that needs stay around forever just because we
configured a mouse once. We have DBus activation and we don't store anything
anyway, so we might as well exit after a period of inactivity (20 min).

There's a slight race condition where if something comes in at exactly the
20min mark, we may shut down anyway and the messages get lost. This is too
narrow to worry about.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>

ratbagd/ratbagd.c

@@ -489,6 +489,26 @@ exit:
 	return r;
 }
 
+static int on_timeout_cb(sd_event_source *s, uint64_t usec, void *userdata)
+{
+	log_info("Exiting after idle\n");
+	sd_event_exit(sd_event_source_get_event(s), 0);
+	return 0;
+}
+
+static int before_idle_cb(sd_event_source *s, void *userdata)
+{
+	struct ratbagd *ctx = userdata;
+	uint64_t usec;
+
+	sd_event_now(sd_event_source_get_event(s), CLOCK_MONOTONIC, &usec);
+#define min2us(us_) (us_ * 1000000 * 60)
+	usec += min2us(20);
+	sd_event_source_set_time(ctx->timeout_source, usec);
+
+	return 0;
+}
+
 static int sighandler(sd_event_source *source,
 		      const struct signalfd_siginfo *si,
 		      void *userdata)
@@ -502,18 +522,6 @@ static int ratbagd_run(struct ratbagd *ctx)
 {
 	int r;
 
-	/*
-	 * TODO: We should support exit-on-idle and bus-activation. Note that
-	 *       we don't store any state on our own, hence, all we have to do
-	 *       is to make sure we advertise device add/remove events via the
-	 *       bus (in case there is a listener).
-	 *       To track such events, we should store devices we already
-	 *       advertised in /run/ratbagd/devices/ and read it out on
-	 *       activation.
-	 *       Note that this feature requires udev-activation, which might
-	 *       not be possible, yet.
-	 */
-
 	r = ratbagd_run_enumerate(ctx);
 	if (r < 0)
 		return r;
@@ -524,6 +532,24 @@ static int ratbagd_run(struct ratbagd *ctx)
 	sigprocmask(SIG_BLOCK, &sigset, NULL);
 	sd_event_add_signal(ctx->event, NULL, SIGINT, sighandler, NULL);
 
+	/* exit-on-idle: we set up a timer to simply exit. Since we don't
+	 * store anything, it doesn't matter and we can just restart next
+	 * time someone wants us.
+	 *
+	 * since we don't want to monitor every single dbus call, we just
+	 * set up a post source that gets called before we go idle. That
+	 * resets the timer, so as long as something is happening, ratbagd
+	 * won't exit.
+	 */
+	sd_event_add_time(ctx->event,
+			  &ctx->timeout_source,
+			  CLOCK_MONOTONIC,
+			  -1, /* infinite, see before_idle_cb */
+			  min2us(1), /* accuracy doesn't matter */
+			  on_timeout_cb,
+			  ctx);
+	sd_event_add_post(ctx->event, NULL, before_idle_cb, ctx);
+
 	return sd_event_loop(ctx->event);
 }
 

ratbagd/ratbagd.h

@@ -208,6 +208,7 @@ struct ratbagd {
 	sd_event *event;
 	struct ratbag *lib_ctx;
 	struct udev_monitor *monitor;
+	sd_event_source *timeout_source;
 	sd_event_source *monitor_source;
 	sd_bus *bus;