- * buffer buf_ptr buf_end
- * +-------------------+-----------+
- * |/ / / / / / / / / /| |
- * write buffer: | / to be flushed / | |
- * |/ / / / / / / / / /| |
- * +-------------------+-----------+
+ * buf_ptr_max
+ * buffer (buf_ptr) buf_end
+ * +-----------------------+--------------+
+ * |/ / / / / / / / / / / /| |
+ * write buffer: | / / to be flushed / / | |
+ * |/ / / / / / / / / / / /| |
+ * +-----------------------+--------------+
+ * buf_ptr can be in this
+ * due to a backward seek