[PATCH libinput] evdev: recover from a lost button count

[Peter Hutterer]

If the kernel sends us a button press for a button that is thought to be down
we have lost track of the state of the button. Ignore the button press event,
in the hope that the next release makes things right again.

A release event may be masked if another process grabs the device for some
period of time, e.g. libinput debug-events --grab.

https://bugs.freedesktop.org/show_bug.cgi?id=101796

Signed-off-by: Peter Hutterer <peter.hutterer at who-t.net>
---
 src/evdev.c         | 20 ++++++++++----------
 test/test-pointer.c | 35 +++++++++++++++++++++++++++++++++++
 2 files changed, 45 insertions(+), 10 deletions(-)

diff --git a/src/evdev.c b/src/evdev.c
index 24bfad07..bd1725c0 100644
--- a/src/evdev.c
+++ b/src/evdev.c
@@ -836,16 +836,16 @@ fallback_process_key(struct fallback_dispatch *dispatch,
 	type = get_key_type(e->code);
 
 	/* Ignore key release events from the kernel for keys that libinput
-	 * never got a pressed event for. */
-	if (e->value == 0) {
-		switch (type) {
-		case EVDEV_KEY_TYPE_NONE:
-			break;
-		case EVDEV_KEY_TYPE_KEY:
-		case EVDEV_KEY_TYPE_BUTTON:
-			if (!hw_is_key_down(dispatch, e->code))
-				return;
-		}
+	 * never got a pressed event for or key presses for keys that we
+	 * think are still down */
+	switch (type) {
+	case EVDEV_KEY_TYPE_NONE:
+		break;
+	case EVDEV_KEY_TYPE_KEY:
+	case EVDEV_KEY_TYPE_BUTTON:
+		if ((e->value && hw_is_key_down(dispatch, e->code)) ||
+		    (e->value == 0 && !hw_is_key_down(dispatch, e->code)))
+			return;
 	}
 
 	hw_set_key_down(dispatch, e->code, e->value);
diff --git a/test/test-pointer.c b/test/test-pointer.c
index e09f8f8a..2f03195a 100644
--- a/test/test-pointer.c
+++ b/test/test-pointer.c
@@ -490,6 +490,40 @@ START_TEST(pointer_button_has_no_button)
 }
 END_TEST
 
+START_TEST(pointer_recover_from_lost_button_count)
+{
+	struct litest_device *dev = litest_current_device();
+	struct libinput *li = dev->libinput;
+	struct libevdev *evdev = dev->evdev;
+
+	disable_button_scrolling(dev);
+
+	litest_drain_events(dev->libinput);
+
+	litest_button_click(dev, BTN_LEFT, 1);
+
+	litest_assert_button_event(li,
+				   BTN_LEFT,
+				   LIBINPUT_BUTTON_STATE_PRESSED);
+
+	/* Grab for the release to make libinput lose count */
+	libevdev_grab(evdev, LIBEVDEV_GRAB);
+	litest_button_click(dev, BTN_LEFT, 0);
+	libevdev_grab(evdev, LIBEVDEV_UNGRAB);
+
+	litest_assert_empty_queue(li);
+
+	litest_button_click(dev, BTN_LEFT, 1);
+	litest_assert_empty_queue(li);
+
+	litest_button_click(dev, BTN_LEFT, 0);
+	litest_assert_button_event(li,
+				   BTN_LEFT,
+				   LIBINPUT_BUTTON_STATE_RELEASED);
+	litest_assert_empty_queue(li);
+}
+END_TEST
+
 static inline double
 wheel_click_count(struct litest_device *dev, int which)
 {
@@ -2088,6 +2122,7 @@ litest_setup_tests_pointer(void)
 	litest_add_no_device("pointer:button", pointer_button_auto_release);
 	litest_add_no_device("pointer:button", pointer_seat_button_count);
 	litest_add_for_device("pointer:button", pointer_button_has_no_button, LITEST_KEYBOARD);
+	litest_add("pointer:button", pointer_recover_from_lost_button_count, LITEST_BUTTON, LITEST_CLICKPAD);
 	litest_add("pointer:scroll", pointer_scroll_wheel, LITEST_WHEEL, LITEST_TABLET);
 	litest_add("pointer:scroll", pointer_scroll_button, LITEST_RELATIVE|LITEST_BUTTON, LITEST_ANY);
 	litest_add("pointer:scroll", pointer_scroll_button_noscroll, LITEST_ABSOLUTE|LITEST_BUTTON, LITEST_RELATIVE);
-- 
2.13.3