ethtool: add interface to read RMON stats

Most devices maintain RMON (RFC 2819) stats - particularly
the "histogram" of packets received by size. Unlike other
RFCs which duplicate IEEE stats, the short/oversized frame
counters in RMON don't seem to match IEEE stats 1-to-1 either,
so expose those, too. Do not expose basic packet, CRC errors
etc - those are already otherwise covered.

Because standard defines packet ranges only up to 1518, and
everything above that should theoretically be "oversized"
- devices often create their own ranges.

Going beyond what the RFC defines - expose the "histogram"
in the Tx direction (assume for now that the ranges will
be the same).

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/ethtool_netlink.h

@@ -700,6 +700,7 @@ enum {
 	ETHTOOL_STATS_ETH_PHY,
 	ETHTOOL_STATS_ETH_MAC,
 	ETHTOOL_STATS_ETH_CTRL,
+	ETHTOOL_STATS_RMON,
 
 	/* add new constants above here */
 	__ETHTOOL_STATS_CNT
@@ -714,6 +715,13 @@ enum {
 
 	ETHTOOL_A_STATS_GRP_STAT,		/* nest */
 
+	ETHTOOL_A_STATS_GRP_HIST_RX,		/* nest */
+	ETHTOOL_A_STATS_GRP_HIST_TX,		/* nest */
+
+	ETHTOOL_A_STATS_GRP_HIST_BKT_LOW,	/* u32 */
+	ETHTOOL_A_STATS_GRP_HIST_BKT_HI,	/* u32 */
+	ETHTOOL_A_STATS_GRP_HIST_VAL,		/* u64 */
+
 	/* add new constants above here */
 	__ETHTOOL_A_STATS_GRP_CNT,
 	ETHTOOL_A_STATS_GRP_MAX = (__ETHTOOL_A_STATS_CNT - 1)
@@ -793,6 +801,21 @@ enum {
 	ETHTOOL_A_STATS_ETH_CTRL_MAX = (__ETHTOOL_A_STATS_ETH_CTRL_CNT - 1)
 };
 
+enum {
+	/* etherStatsUndersizePkts */
+	ETHTOOL_A_STATS_RMON_UNDERSIZE,
+	/* etherStatsOversizePkts */
+	ETHTOOL_A_STATS_RMON_OVERSIZE,
+	/* etherStatsFragments */
+	ETHTOOL_A_STATS_RMON_FRAG,
+	/* etherStatsJabbers */
+	ETHTOOL_A_STATS_RMON_JABBER,
+
+	/* add new constants above here */
+	__ETHTOOL_A_STATS_RMON_CNT,
+	ETHTOOL_A_STATS_RMON_MAX = (__ETHTOOL_A_STATS_RMON_CNT - 1)
+};
+
 /* generic netlink info */
 #define ETHTOOL_GENL_NAME "ethtool"
 #define ETHTOOL_GENL_VERSION 1