* @param cls closure
* @param offset offset to read from; it is possible
* that the caller might need to go backwards
- * a bit at times
+ * a bit at times; set to UINT64_MAX to tell
+ * the reader that we won't be reading for a while
+ * (used to close the file descriptor but NOT fully
+ * clean up the reader's state); in this case,
+ * a value of '0' for max should be ignored
* @param max maximum number of bytes that should be
* copied to buf; readers are not allowed
* to provide less data unless there is an error;