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![Jakub Kicinski](/assets/img/avatar_default.png)
The ethtool-nl family does a good job exposing various protocol related and IEEE/IETF statistics which used to get dumped under ethtool -S, with creative names. Queue stats don't have a netlink API, yet, and remain a lion's share of ethtool -S output for new drivers. Not only is that bad because the names differ driver to driver but it's also bug-prone. Intuitively drivers try to report only the stats for active queues, but querying ethtool stats involves multiple system calls, and the number of stats is read separately from the stats themselves. Worse still when user space asks for values of the stats, it doesn't inform the kernel how big the buffer is. If number of stats increases in the meantime kernel will overflow user buffer. Add a netlink API for dumping queue stats. Queue information is exposed via the netdev-genl family, so add the stats there. Support per-queue and sum-for-device dumps. Latter will be useful when subsequent patches add more interesting common stats than just bytes and packets. The API does not currently distinguish between HW and SW stats. The expectation is that the source of the stats will either not matter much (good packets) or be obvious (skb alloc errors). Acked-by: Stanislav Fomichev <sdf@google.com> Reviewed-by: Amritha Nambiar <amritha.nambiar@intel.com> Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com> Link: https://lore.kernel.org/r/20240306195509.1502746-2-kuba@kernel.org Signed-off-by: Jakub Kicinski <kuba@kernel.org>
237 lines
7.8 KiB
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237 lines
7.8 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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====================
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Interface statistics
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====================
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Overview
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========
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This document is a guide to Linux network interface statistics.
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There are three main sources of interface statistics in Linux:
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- standard interface statistics based on
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:c:type:`struct rtnl_link_stats64 <rtnl_link_stats64>`;
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- protocol-specific statistics; and
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- driver-defined statistics available via ethtool.
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Standard interface statistics
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-----------------------------
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There are multiple interfaces to reach the standard statistics.
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Most commonly used is the `ip` command from `iproute2`::
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$ ip -s -s link show dev ens4u1u1
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6: ens4u1u1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
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link/ether 48:2a:e3:4c:b1:d1 brd ff:ff:ff:ff:ff:ff
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RX: bytes packets errors dropped overrun mcast
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74327665117 69016965 0 0 0 0
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RX errors: length crc frame fifo missed
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0 0 0 0 0
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TX: bytes packets errors dropped carrier collsns
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21405556176 44608960 0 0 0 0
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TX errors: aborted fifo window heartbeat transns
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0 0 0 0 128
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altname enp58s0u1u1
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Note that `-s` has been specified twice to see all members of
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:c:type:`struct rtnl_link_stats64 <rtnl_link_stats64>`.
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If `-s` is specified once the detailed errors won't be shown.
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`ip` supports JSON formatting via the `-j` option.
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Queue statistics
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~~~~~~~~~~~~~~~~
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Queue statistics are accessible via the netdev netlink family.
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Currently no widely distributed CLI exists to access those statistics.
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Kernel development tools (ynl) can be used to experiment with them,
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see `Documentation/userspace-api/netlink/intro-specs.rst`.
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Protocol-specific statistics
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----------------------------
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Protocol-specific statistics are exposed via relevant interfaces,
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the same interfaces as are used to configure them.
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ethtool
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~~~~~~~
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Ethtool exposes common low-level statistics.
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All the standard statistics are expected to be maintained
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by the device, not the driver (as opposed to driver-defined stats
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described in the next section which mix software and hardware stats).
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For devices which contain unmanaged
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switches (e.g. legacy SR-IOV or multi-host NICs) the events counted
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may not pertain exclusively to the packets destined to
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the local host interface. In other words the events may
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be counted at the network port (MAC/PHY blocks) without separation
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for different host side (PCIe) devices. Such ambiguity must not
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be present when internal switch is managed by Linux (so called
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switchdev mode for NICs).
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Standard ethtool statistics can be accessed via the interfaces used
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for configuration. For example ethtool interface used
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to configure pause frames can report corresponding hardware counters::
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$ ethtool --include-statistics -a eth0
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Pause parameters for eth0:
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Autonegotiate: on
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RX: on
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TX: on
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Statistics:
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tx_pause_frames: 1
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rx_pause_frames: 1
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General Ethernet statistics not associated with any particular
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functionality are exposed via ``ethtool -S $ifc`` by specifying
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the ``--groups`` parameter::
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$ ethtool -S eth0 --groups eth-phy eth-mac eth-ctrl rmon
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Stats for eth0:
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eth-phy-SymbolErrorDuringCarrier: 0
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eth-mac-FramesTransmittedOK: 1
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eth-mac-FrameTooLongErrors: 1
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eth-ctrl-MACControlFramesTransmitted: 1
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eth-ctrl-MACControlFramesReceived: 0
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eth-ctrl-UnsupportedOpcodesReceived: 1
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rmon-etherStatsUndersizePkts: 1
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rmon-etherStatsJabbers: 0
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rmon-rx-etherStatsPkts64Octets: 1
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rmon-rx-etherStatsPkts65to127Octets: 0
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rmon-rx-etherStatsPkts128to255Octets: 0
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rmon-tx-etherStatsPkts64Octets: 2
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rmon-tx-etherStatsPkts65to127Octets: 3
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rmon-tx-etherStatsPkts128to255Octets: 0
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Driver-defined statistics
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-------------------------
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Driver-defined ethtool statistics can be dumped using `ethtool -S $ifc`, e.g.::
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$ ethtool -S ens4u1u1
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NIC statistics:
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tx_single_collisions: 0
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tx_multi_collisions: 0
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uAPIs
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=====
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procfs
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------
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The historical `/proc/net/dev` text interface gives access to the list
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of interfaces as well as their statistics.
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Note that even though this interface is using
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:c:type:`struct rtnl_link_stats64 <rtnl_link_stats64>`
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internally it combines some of the fields.
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sysfs
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-----
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Each device directory in sysfs contains a `statistics` directory (e.g.
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`/sys/class/net/lo/statistics/`) with files corresponding to
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members of :c:type:`struct rtnl_link_stats64 <rtnl_link_stats64>`.
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This simple interface is convenient especially in constrained/embedded
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environments without access to tools. However, it's inefficient when
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reading multiple stats as it internally performs a full dump of
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:c:type:`struct rtnl_link_stats64 <rtnl_link_stats64>`
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and reports only the stat corresponding to the accessed file.
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Sysfs files are documented in
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`Documentation/ABI/testing/sysfs-class-net-statistics`.
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netlink
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-------
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`rtnetlink` (`NETLINK_ROUTE`) is the preferred method of accessing
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:c:type:`struct rtnl_link_stats64 <rtnl_link_stats64>` stats.
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Statistics are reported both in the responses to link information
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requests (`RTM_GETLINK`) and statistic requests (`RTM_GETSTATS`,
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when `IFLA_STATS_LINK_64` bit is set in the `.filter_mask` of the request).
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netdev (netlink)
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~~~~~~~~~~~~~~~~
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`netdev` generic netlink family allows accessing page pool and per queue
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statistics.
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ethtool
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-------
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Ethtool IOCTL interface allows drivers to report implementation
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specific statistics. Historically it has also been used to report
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statistics for which other APIs did not exist, like per-device-queue
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statistics, or standard-based statistics (e.g. RFC 2863).
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Statistics and their string identifiers are retrieved separately.
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Identifiers via `ETHTOOL_GSTRINGS` with `string_set` set to `ETH_SS_STATS`,
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and values via `ETHTOOL_GSTATS`. User space should use `ETHTOOL_GDRVINFO`
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to retrieve the number of statistics (`.n_stats`).
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ethtool-netlink
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---------------
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Ethtool netlink is a replacement for the older IOCTL interface.
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Protocol-related statistics can be requested in get commands by setting
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the `ETHTOOL_FLAG_STATS` flag in `ETHTOOL_A_HEADER_FLAGS`. Currently
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statistics are supported in the following commands:
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- `ETHTOOL_MSG_PAUSE_GET`
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- `ETHTOOL_MSG_FEC_GET`
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- `ETHTOOL_MSG_MM_GET`
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debugfs
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-------
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Some drivers expose extra statistics via `debugfs`.
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struct rtnl_link_stats64
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========================
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.. kernel-doc:: include/uapi/linux/if_link.h
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:identifiers: rtnl_link_stats64
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Notes for driver authors
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========================
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Drivers should report all statistics which have a matching member in
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:c:type:`struct rtnl_link_stats64 <rtnl_link_stats64>` exclusively
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via `.ndo_get_stats64`. Reporting such standard stats via ethtool
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or debugfs will not be accepted.
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Drivers must ensure best possible compliance with
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:c:type:`struct rtnl_link_stats64 <rtnl_link_stats64>`.
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Please note for example that detailed error statistics must be
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added into the general `rx_error` / `tx_error` counters.
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The `.ndo_get_stats64` callback can not sleep because of accesses
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via `/proc/net/dev`. If driver may sleep when retrieving the statistics
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from the device it should do so periodically asynchronously and only return
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a recent copy from `.ndo_get_stats64`. Ethtool interrupt coalescing interface
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allows setting the frequency of refreshing statistics, if needed.
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Retrieving ethtool statistics is a multi-syscall process, drivers are advised
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to keep the number of statistics constant to avoid race conditions with
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user space trying to read them.
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Statistics must persist across routine operations like bringing the interface
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down and up.
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Kernel-internal data structures
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-------------------------------
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The following structures are internal to the kernel, their members are
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translated to netlink attributes when dumped. Drivers must not overwrite
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the statistics they don't report with 0.
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- ethtool_pause_stats()
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- ethtool_fec_stats()
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