Don't say that a return value is returned.
*
* \return Zero or a negative error code. If the underlying call to readv(2)
* returned zero (indicating an end of file condition) or failed for some
- * reason other than \p EAGAIN, a negative return value is returned.
+ * reason other than \p EAGAIN, a negative error code is returned.
*
* In any case, \a num_bytes contains the number of bytes that have been
* successfully read from \a fd (zero if the first readv() call failed with