docs: net: include the new ethtool pause stats in the stats doc

Tell people that there now is an interface for querying pause frames.
A little bit of restructuring is needed given this is a first source
of such statistics.
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/statistics.rst

@@ -4,16 +4,23 @@
 Interface statistics
 ====================
 
+Overview
+========
+
 This document is a guide to Linux network interface statistics.
 
-There are two main sources of interface statistics in Linux:
+There are three main sources of interface statistics in Linux:
 
  - standard interface statistics based on
-   :c:type:`struct rtnl_link_stats64 <rtnl_link_stats64>`; and
+   :c:type:`struct rtnl_link_stats64 <rtnl_link_stats64>`;
+ - protocol-specific statistics; and
  - driver-defined statistics available via ethtool.
 
-There are multiple interfaces to reach the former. Most commonly used
-is the `ip` command from `iproute2`::
+Standard interface statistics
+-----------------------------
+
+There are multiple interfaces to reach the standard statistics.
+Most commonly used is the `ip` command from `iproute2`::
 
   $ ip -s -s link show dev ens4u1u1
   6: ens4u1u1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
@@ -34,7 +41,26 @@ If `-s` is specified once the detailed errors won't be shown.
 
 `ip` supports JSON formatting via the `-j` option.
 
-Ethtool statistics can be dumped using `ethtool -S $ifc`, e.g.::
+Protocol-specific statistics
+----------------------------
+
+Some of the interfaces used for configuring devices are also able
+to report related statistics. For example ethtool interface used
+to configure pause frames can report corresponding hardware counters::
+
+  $ ethtool --include-statistics -a eth0
+  Pause parameters for eth0:
+  Autonegotiate:	on
+  RX:			on
+  TX:			on
+  Statistics:
+    tx_pause_frames: 1
+    rx_pause_frames: 1
+
+Driver-defined statistics
+-------------------------
+
+Driver-defined ethtool statistics can be dumped using `ethtool -S $ifc`, e.g.::
 
   $ ethtool -S ens4u1u1
   NIC statistics:
@@ -94,6 +120,17 @@ Identifiers via `ETHTOOL_GSTRINGS` with `string_set` set to `ETH_SS_STATS`,
 and values via `ETHTOOL_GSTATS`. User space should use `ETHTOOL_GDRVINFO`
 to retrieve the number of statistics (`.n_stats`).
 
+ethtool-netlink
+---------------
+
+Ethtool netlink is a replacement for the older IOCTL interface.
+
+Protocol-related statistics can be requested in get commands by setting
+the `ETHTOOL_FLAG_STATS` flag in `ETHTOOL_A_HEADER_FLAGS`. Currently
+statistics are supported in the following commands:
+
+  - `ETHTOOL_MSG_PAUSE_GET`
+
 debugfs
 -------
 
@@ -130,3 +167,13 @@ user space trying to read them.
 
 Statistics must persist across routine operations like bringing the interface
 down and up.
+
+Kernel-internal data structures
+-------------------------------
+
+The following structures are internal to the kernel, their members are
+translated to netlink attributes when dumped. Drivers must not overwrite
+the statistics they don't report with 0.
+
+.. kernel-doc:: include/linux/ethtool.h
+    :identifiers: ethtool_pause_stats