eis: Expose eis_event_ref()

This makes handling prolonged synchronization sequences easier, as one
doesn't have to work around only being allowed to hold one reference.

Part-of: <https://gitlab.freedesktop.org/libinput/libei/-/merge_requests/340>

src/libeis-event.c

@@ -118,9 +118,8 @@ eis_event_new_for_device(struct eis_device *device)
 	return e;
 }
 
-/* this one is not public */
+_public_
 OBJECT_IMPLEMENT_REF(eis_event);
-
 _public_
 OBJECT_IMPLEMENT_UNREF_CLEANUP(eis_event);
 _public_

src/libeis-event.h

@@ -83,6 +83,3 @@ eis_event_new_for_device(struct eis_device *device);
 
 struct eis *
 eis_event_get_context(struct eis_event *event);
-
-struct eis_event*
-eis_event_ref(struct eis_event *event);

src/libeis.h

@@ -674,13 +674,24 @@ struct eis_event *
 eis_peek_event(struct eis *eis);
 
 /**
- * Release resources associated with this event. This function always
- * returns NULL.
+ * Increase the refcount of this struct by one. Use eis_event_unref() to decrease
+ * the refcount. This function always returns the same event that the reference
+ * was added to.
  *
- * The caller cannot increase the refcount of an event. Events should be
- * considered transient data and not be held longer than required.
- * eis_event_unref() is provided for consistency (as opposed to, say,
- * eis_event_free()).
+ * Events should be considered transient data and not be held longer than
+ * required.
+ */
+struct eis_event *
+eis_event_ref(struct eis_event *event);
+
+/**
+ * Decrease the refcount of this struct by one. When the refcount reaches
+ * zero, all allocated resources for this struct are released.
+ *
+ * Events should be considered transient data and not be held longer than
+ * required.
+ *
+ * @return always NULL
  */
 struct eis_event *
 eis_event_unref(struct eis_event *event);