+/*
+ * askappend can return four values:
+ *
+ * - 2 means overwrite the log file
+ * - 1 means append to the log file
+ * - 0 means cancel logging for this session
+ * - -1 means please wait.
+ */
+int askappend(void *frontend, Filename filename,
+ void (*callback)(void *ctx, int result), void *ctx);