ethdev: document xstats API assumption

[dpdk.git] / lib / librte_ethdev / rte_ethdev.h

diff --git a/lib/librte_ethdev/rte_ethdev.h b/lib/librte_ethdev/rte_ethdev.h
index aa991da..42803e3 100644 (file)
--- a/lib/librte_ethdev/rte_ethdev.h
+++ b/lib/librte_ethdev/rte_ethdev.h
@@ -2014,6 +2014,15 @@ int rte_eth_stats_reset(uint16_t port_id);
 /**
  * Retrieve names of extended statistics of an Ethernet device.
  *
+ * There is an assumption that 'xstat_names' and 'xstats' arrays are matched
+ * by array index:
+ *  xstats_names[i].name => xstats[i].value
+ *
+ * And the array index is same with id field of 'struct rte_eth_xstat':
+ *  xstats[i].id == i
+ *
+ * This assumption makes key-value pair matching less flexible but simpler.
+ *
  * @param port_id
  *   The port identifier of the Ethernet device.
  * @param xstats_names
@@ -2038,13 +2047,20 @@ int rte_eth_xstats_get_names(uint16_t port_id,
 /**
  * Retrieve extended statistics of an Ethernet device.
  *
+ * There is an assumption that 'xstat_names' and 'xstats' arrays are matched
+ * by array index:
+ *  xstats_names[i].name => xstats[i].value
+ *
+ * And the array index is same with id field of 'struct rte_eth_xstat':
+ *  xstats[i].id == i
+ *
+ * This assumption makes key-value pair matching less flexible but simpler.
+ *
  * @param port_id
  *   The port identifier of the Ethernet device.
  * @param xstats
  *   A pointer to a table of structure of type *rte_eth_xstat*
- *   to be filled with device statistics ids and values: id is the
- *   index of the name string in xstats_names (see rte_eth_xstats_get_names()),
- *   and value is the statistic counter.
+ *   to be filled with device statistics ids and values.
  *   This parameter can be set to NULL if n is 0.
  * @param n
  *   The size of the xstats array (number of elements).