.. SPDX-License-Identifier: GPL-2.0

====================
Interface statistics
====================

Overview
========

This document is a guide to Linux network interface statistics.

There are three main sources of interface statistics in Linux:

 - standard interface statistics based on
   :c:type:`struct rtnl_link_stats64 <rtnl_link_stats64>`;
 - protocol-specific statistics; and
 - driver-defined statistics available via ethtool.

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
    link/ether 48:2a:e3:4c:b1:d1 brd ff:ff:ff:ff:ff:ff
    RX: bytes  packets  errors  dropped overrun mcast
    74327665117 69016965 0       0       0       0
    RX errors: length   crc     frame   fifo    missed
               0        0       0       0       0
    TX: bytes  packets  errors  dropped carrier collsns
    21405556176 44608960 0       0       0       0
    TX errors: aborted  fifo   window heartbeat transns
               0        0       0       0       128
    altname enp58s0u1u1

Note that `-s` has been specified twice to see all members of
:c:type:`struct rtnl_link_stats64 <rtnl_link_stats64>`.
If `-s` is specified once the detailed errors won't be shown.

`ip` supports JSON formatting via the `-j` option.

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:
     tx_single_collisions: 0
     tx_multi_collisions: 0

uAPIs
=====

procfs
------

The historical `/proc/net/dev` text interface gives access to the list
of interfaces as well as their statistics.

Note that even though this interface is using
:c:type:`struct rtnl_link_stats64 <rtnl_link_stats64>`
internally it combines some of the fields.

sysfs
-----

Each device directory in sysfs contains a `statistics` directory (e.g.
`/sys/class/net/lo/statistics/`) with files corresponding to
members of :c:type:`struct rtnl_link_stats64 <rtnl_link_stats64>`.

This simple interface is convenient especially in constrained/embedded
environments without access to tools. However, it's inefficient when
reading multiple stats as it internally performs a full dump of
:c:type:`struct rtnl_link_stats64 <rtnl_link_stats64>`
and reports only the stat corresponding to the accessed file.

Sysfs files are documented in
`Documentation/ABI/testing/sysfs-class-net-statistics`.


netlink
-------

`rtnetlink` (`NETLINK_ROUTE`) is the preferred method of accessing
:c:type:`struct rtnl_link_stats64 <rtnl_link_stats64>` stats.

Statistics are reported both in the responses to link information
requests (`RTM_GETLINK`) and statistic requests (`RTM_GETSTATS`,
when `IFLA_STATS_LINK_64` bit is set in the `.filter_mask` of the request).

ethtool
-------

Ethtool IOCTL interface allows drivers to report implementation
specific statistics. Historically it has also been used to report
statistics for which other APIs did not exist, like per-device-queue
statistics, or standard-based statistics (e.g. RFC 2863).

Statistics and their string identifiers are retrieved separately.
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
-------

Some drivers expose extra statistics via `debugfs`.

struct rtnl_link_stats64
========================

.. kernel-doc:: include/uapi/linux/if_link.h
    :identifiers: rtnl_link_stats64

Notes for driver authors
========================

Drivers should report all statistics which have a matching member in
:c:type:`struct rtnl_link_stats64 <rtnl_link_stats64>` exclusively
via `.ndo_get_stats64`. Reporting such standard stats via ethtool
or debugfs will not be accepted.

Drivers must ensure best possible compliance with
:c:type:`struct rtnl_link_stats64 <rtnl_link_stats64>`.
Please note for example that detailed error statistics must be
added into the general `rx_error` / `tx_error` counters.

The `.ndo_get_stats64` callback can not sleep because of accesses
via `/proc/net/dev`. If driver may sleep when retrieving the statistics
from the device it should do so periodically asynchronously and only return
a recent copy from `.ndo_get_stats64`. Ethtool interrupt coalescing interface
allows setting the frequency of refreshing statistics, if needed.

Retrieving ethtool statistics is a multi-syscall process, drivers are advised
to keep the number of statistics constant to avoid race conditions with
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.

- ethtool_pause_stats()