[PATCH libinput v2] evdev: Log evdev event queue overflows

[Derek Foreman]

Log a message when the kernel event queue overflows and events are dropped.
After 10 messages logging stops to avoid flooding the logs if the condition
is persistent.
---
 src/evdev.c | 11 +++++++++++
 src/evdev.h |  4 ++++
 2 files changed, 15 insertions(+)

diff --git a/src/evdev.c b/src/evdev.c
index 1b4ce10..9026f5c 100644
--- a/src/evdev.c
+++ b/src/evdev.c
@@ -924,6 +924,17 @@ evdev_device_dispatch(void *data)
 		rc = libevdev_next_event(device->evdev,
 					 LIBEVDEV_READ_FLAG_NORMAL, &ev);
 		if (rc == LIBEVDEV_READ_STATUS_SYNC) {
+			if (device->syn_drops_received < 10) {
+				device->syn_drops_received++;
+				log_info(libinput, "SYN_DROPPED event from "
+					 "\"%s\" - some input events have "
+					 "been lost.\n", device->devname);
+				if (device->syn_drops_received == 10)
+					log_info(libinput, "No longer logging "
+						 "SYN_DROPPED events for "
+						 "\"%s\"\n", device->devname);
+			}
+
 			/* send one more sync event so we handle all
 			   currently pending events before we sync up
 			   to the current state */
diff --git a/src/evdev.h b/src/evdev.h
index c0d6577..9e84623 100644
--- a/src/evdev.h
+++ b/src/evdev.h
@@ -135,6 +135,10 @@ struct evdev_device {
 		/* Checks if buttons are down and commits the setting */
 		void (*change_to_left_handed)(struct evdev_device *device);
 	} buttons;
+
+	/* The number of times libevdev processes a SYN_DROPPED, so we can
+	 * stop logging them to avoid flooding the logs. */
+	int syn_drops_received;
 };
 
 #define EVDEV_UNHANDLED_DEVICE ((struct evdev_device *) 1)
-- 
2.1.1