diff --git a/include/linux/ethtool.h b/include/linux/ethtool.h
index c8e3e7e39c6b..0a114d05f68d 100644
--- a/include/linux/ethtool.h
+++ b/include/linux/ethtool.h
@@ -183,6 +183,9 @@ static inline u32 ethtool_rxfh_indir_default(u32 index, u32 n_rx_rings)
  * hold the RTNL lock.
  *
  * See the structures used by these operations for further documentation.
+ * Note that for all operations using a structure ending with a zero-
+ * length array, the array is allocated separately in the kernel and
+ * is passed to the driver as an additional parameter.
  *
  * See &struct net_device and &struct net_device_ops for documentation
  * of the generic netdev features interface.