Netlink interface for ethtool

Basic information

Netlink interface for ethtool uses generic netlink family ethtool (userspace application should use macros ETHTOOL_GENL_NAME and ETHTOOL_GENL_VERSION defined in <linux/ethtool_netlink.h> uapi header). This family does not use a specific header, all information in requests and replies is passed using netlink attributes.

The ethtool netlink interface uses extended ACK for error and warning reporting, userspace application developers are encouraged to make these messages available to user in a suitable way.

Requests can be divided into three categories: “get” (retrieving information), “set” (setting parameters) and “action” (invoking an action).

All “set” and “action” type requests require admin privileges (CAP_NET_ADMIN in the namespace). Most “get” type requests are allowed for anyone but there are exceptions (where the response contains sensitive information). In some cases, the request as such is allowed for anyone but unprivileged users have attributes with sensitive information (e.g. wake-on-lan password) omitted.

Conventions

Attributes which represent a boolean value usually use NLA_U8 type so that we can distinguish three states: “on”, “off” and “not present” (meaning the information is not available in “get” requests or value is not to be changed in “set” requests). For these attributes, the “true” value should be passed as number 1 but any non-zero value should be understood as “true” by recipient. In the tables below, “bool” denotes NLA_U8 attributes interpreted in this way.

In the message structure descriptions below, if an attribute name is suffixed with “+”, parent nest can contain multiple attributes of the same type. This implements an array of entries.

Request header

Each request or reply message contains a nested attribute with common header. Structure of this header is

ETHTOOL_A_HEADER_DEV_INDEX	u32	device ifindex
ETHTOOL_A_HEADER_DEV_NAME	string	device name
ETHTOOL_A_HEADER_FLAGS	u32	flags common for all requests

ETHTOOL_A_HEADER_DEV_INDEX and ETHTOOL_A_HEADER_DEV_NAME identify the device message relates to. One of them is sufficient in requests, if both are used, they must identify the same device. Some requests, e.g. global string sets, do not require device identification. Most GET requests also allow dump requests without device identification to query the same information for all devices providing it (each device in a separate message).

ETHTOOL_A_HEADER_FLAGS is a bitmap of request flags common for all request types. The interpretation of these flags is the same for all request types but the flags may not apply to requests. Recognized flags are:

ETHTOOL_FLAG_COMPACT_BITSETS	use compact format bitsets in reply
ETHTOOL_FLAG_OMIT_REPLY	omit optional reply (_SET and _ACT)

New request flags should follow the general idea that if the flag is not set, the behaviour is backward compatible, i.e. requests from old clients not aware of the flag should be interpreted the way the client expects. A client must not set flags it does not understand.

Bit sets

For short bitmaps of (reasonably) fixed length, standard NLA_BITFIELD32 type is used. For arbitrary length bitmaps, ethtool netlink uses a nested attribute with contents of one of two forms: compact (two binary bitmaps representing bit values and mask of affected bits) and bit-by-bit (list of bits identified by either index or name).

Verbose (bit-by-bit) bitsets allow sending symbolic names for bits together with their values which saves a round trip (when the bitset is passed in a request) or at least a second request (when the bitset is in a reply). This is useful for one shot applications like traditional ethtool command. On the other hand, long running applications like ethtool monitor (displaying notifications) or network management daemons may prefer fetching the names only once and using compact form to save message size. Notifications from ethtool netlink interface always use compact form for bitsets.

A bitset can represent either a value/mask pair (ETHTOOL_A_BITSET_NOMASK not set) or a single bitmap (ETHTOOL_A_BITSET_NOMASK set). In requests modifying a bitmap, the former changes the bit set in mask to values set in value and preserves the rest; the latter sets the bits set in the bitmap and clears the rest.

Compact form: nested (bitset) atrribute contents:

ETHTOOL_A_BITSET_NOMASK	flag	no mask, only a list
ETHTOOL_A_BITSET_SIZE	u32	number of significant bits
ETHTOOL_A_BITSET_VALUE	binary	bitmap of bit values
ETHTOOL_A_BITSET_MASK	binary	bitmap of valid bits

Value and mask must have length at least ETHTOOL_A_BITSET_SIZE bits rounded up to a multiple of 32 bits. They consist of 32-bit words in host byte order, words ordered from least significant to most significant (i.e. the same way as bitmaps are passed with ioctl interface).

For compact form, ETHTOOL_A_BITSET_SIZE and ETHTOOL_A_BITSET_VALUE are mandatory. ETHTOOL_A_BITSET_MASK attribute is mandatory if ETHTOOL_A_BITSET_NOMASK is not set (bitset represents a value/mask pair); if ETHTOOL_A_BITSET_NOMASK is not set, ETHTOOL_A_BITSET_MASK is not allowed (bitset represents a single bitmap.

Kernel bit set length may differ from userspace length if older application is used on newer kernel or vice versa. If userspace bitmap is longer, an error is issued only if the request actually tries to set values of some bits not recognized by kernel.

Bit-by-bit form: nested (bitset) attribute contents:

ETHTOOL_A_BITSET_NOMASK			flag	no mask, only a list
ETHTOOL_A_BITSET_SIZE			u32	number of significant bits
ETHTOOL_A_BITSET_BITS			nested	array of bits
	ETHTOOL_A_BITSET_BITS_BIT+		nested	one bit
		ETHTOOL_A_BITSET_BIT_INDEX	u32	bit index (0 for LSB)
		ETHTOOL_A_BITSET_BIT_NAME	string	bit name
		ETHTOOL_A_BITSET_BIT_VALUE	flag	present if bit is set

Bit size is optional for bit-by-bit form. ETHTOOL_A_BITSET_BITS nest can only contain ETHTOOL_A_BITSET_BITS_BIT attributes but there can be an arbitrary number of them. A bit may be identified by its index or by its name. When used in requests, listed bits are set to 0 or 1 according to ETHTOOL_A_BITSET_BIT_VALUE, the rest is preserved. A request fails if index exceeds kernel bit length or if name is not recognized.

When ETHTOOL_A_BITSET_NOMASK flag is present, bitset is interpreted as a simple bitmap. ETHTOOL_A_BITSET_BIT_VALUE attributes are not used in such case. Such bitset represents a bitmap with listed bits set and the rest zero.

In requests, application can use either form. Form used by kernel in reply is determined by ETHTOOL_FLAG_COMPACT_BITSETS flag in flags field of request header. Semantics of value and mask depends on the attribute.

List of message types

All constants identifying message types use ETHTOOL_CMD_ prefix and suffix according to message purpose:

_GET	userspace request to retrieve data
_SET	userspace request to set data
_ACT	userspace request to perform an action
_GET_REPLY	kernel reply to a GET request
_SET_REPLY	kernel reply to a SET request
_ACT_REPLY	kernel reply to an ACT request
_NTF	kernel notification

Userspace to kernel:

ETHTOOL_MSG_STRSET_GET	get string set
ETHTOOL_MSG_LINKINFO_GET	get link settings
ETHTOOL_MSG_LINKINFO_SET	set link settings
ETHTOOL_MSG_LINKMODES_GET	get link modes info
ETHTOOL_MSG_LINKMODES_SET	set link modes info
ETHTOOL_MSG_LINKSTATE_GET	get link state
ETHTOOL_MSG_DEBUG_GET	get debugging settings
ETHTOOL_MSG_DEBUG_SET	set debugging settings
ETHTOOL_MSG_WOL_GET	get wake-on-lan settings
ETHTOOL_MSG_WOL_SET	set wake-on-lan settings

Kernel to userspace:

ETHTOOL_MSG_STRSET_GET_REPLY	string set contents
ETHTOOL_MSG_LINKINFO_GET_REPLY	link settings
ETHTOOL_MSG_LINKINFO_NTF	link settings notification
ETHTOOL_MSG_LINKMODES_GET_REPLY	link modes info
ETHTOOL_MSG_LINKMODES_NTF	link modes notification
ETHTOOL_MSG_LINKSTATE_GET_REPLY	link state info
ETHTOOL_MSG_DEBUG_GET_REPLY	debugging settings
ETHTOOL_MSG_DEBUG_NTF	debugging settings notification
ETHTOOL_MSG_WOL_GET_REPLY	wake-on-lan settings
ETHTOOL_MSG_WOL_NTF	wake-on-lan settings notification

GET requests are sent by userspace applications to retrieve device information. They usually do not contain any message specific attributes. Kernel replies with corresponding “GET_REPLY” message. For most types, GET request with NLM_F_DUMP and no device identification can be used to query the information for all devices supporting the request.

If the data can be also modified, corresponding SET message with the same layout as corresponding GET_REPLY is used to request changes. Only attributes where a change is requested are included in such request (also, not all attributes may be changed). Replies to most SET request consist only of error code and extack; if kernel provides additional data, it is sent in the form of corresponding SET_REPLY message which can be suppressed by setting ETHTOOL_FLAG_OMIT_REPLY flag in request header.

Data modification also triggers sending a NTF message with a notification. These usually bear only a subset of attributes which was affected by the change. The same notification is issued if the data is modified using other means (mostly ioctl ethtool interface). Unlike notifications from ethtool netlink code which are only sent if something actually changed, notifications triggered by ioctl interface may be sent even if the request did not actually change any data.

ACT messages request kernel (driver) to perform a specific action. If some information is reported by kernel (which can be suppressed by setting ETHTOOL_FLAG_OMIT_REPLY flag in request header), the reply takes form of an ACT_REPLY message. Performing an action also triggers a notification (NTF message).

Later sections describe the format and semantics of these messages.

STRSET_GET

Requests contents of a string set as provided by ioctl commands ETHTOOL_GSSET_INFO and ETHTOOL_GSTRINGS. String sets are not user writeable so that the corresponding STRSET_SET message is only used in kernel replies. There are two types of string sets: global (independent of a device, e.g. device feature names) and device specific (e.g. device private flags).

Request contents:

ETHTOOL_A_STRSET_HEADER			nested	request header
ETHTOOL_A_STRSET_STRINGSETS			nested	string set to request
	ETHTOOL_A_STRINGSETS_STRINGSET+		nested	one string set
		ETHTOOL_A_STRINGSET_ID	u32	set id

Kernel response contents:

ETHTOOL_A_STRSET_HEADER					nested	reply header
ETHTOOL_A_STRSET_STRINGSETS					nested	array of string sets
	ETHTOOL_A_STRINGSETS_STRINGSET+				nested	one string set
		ETHTOOL_A_STRINGSET_ID			u32	set id
		ETHTOOL_A_STRINGSET_COUNT			u32	number of strings
		ETHTOOL_A_STRINGSET_STRINGS			nested	array of strings
			ETHTOOL_A_STRINGS_STRING+		nested	one string
				ETHTOOL_A_STRING_INDEX	u32	string index
				ETHTOOL_A_STRING_VALUE	string	string value
ETHTOOL_A_STRSET_COUNTS_ONLY					flag	return only counts

Device identification in request header is optional. Depending on its presence a and NLM_F_DUMP flag, there are three type of STRSET_GET requests:

• no NLM_F_DUMP, no device: get “global” stringsets

• no NLM_F_DUMP, with device: get string sets related to the device

• NLM_F_DUMP, no device: get device related string sets for all devices

If there is no ETHTOOL_A_STRSET_STRINGSETS array, all string sets of requested type are returned, otherwise only those specified in the request. Flag ETHTOOL_A_STRSET_COUNTS_ONLY tells kernel to only return string counts of the sets, not the actual strings.

LINKINFO_GET

Requests link settings as provided by ETHTOOL_GLINKSETTINGS except for link modes and autonegotiation related information. The request does not use any attributes.

Request contents:

ETHTOOL_A_LINKINFO_HEADER

nested

request header

Kernel response contents:

ETHTOOL_A_LINKINFO_HEADER	nested	reply header
ETHTOOL_A_LINKINFO_PORT	u8	physical port
ETHTOOL_A_LINKINFO_PHYADDR	u8	phy MDIO address
ETHTOOL_A_LINKINFO_TP_MDIX	u8	MDI(-X) status
ETHTOOL_A_LINKINFO_TP_MDIX_CTRL	u8	MDI(-X) control
ETHTOOL_A_LINKINFO_TRANSCEIVER	u8	transceiver

Attributes and their values have the same meaning as matching members of the corresponding ioctl structures.

LINKINFO_GET allows dump requests (kernel returns reply message for all devices supporting the request).

LINKINFO_SET

LINKINFO_SET request allows setting some of the attributes reported by LINKINFO_GET.

Request contents:

ETHTOOL_A_LINKINFO_HEADER	nested	request header
ETHTOOL_A_LINKINFO_PORT	u8	physical port
ETHTOOL_A_LINKINFO_PHYADDR	u8	phy MDIO address
ETHTOOL_A_LINKINFO_TP_MDIX_CTRL	u8	MDI(-X) control

MDI(-X) status and transceiver cannot be set, request with the corresponding attributes is rejected.

LINKMODES_GET

Requests link modes (supported, advertised and peer advertised) and related information (autonegotiation status, link speed and duplex) as provided by ETHTOOL_GLINKSETTINGS. The request does not use any attributes.

Request contents:

ETHTOOL_A_LINKMODES_HEADER

nested

request header

Kernel response contents:

ETHTOOL_A_LINKMODES_HEADER	nested	reply header
ETHTOOL_A_LINKMODES_AUTONEG	u8	autonegotiation status
ETHTOOL_A_LINKMODES_OURS	bitset	advertised link modes
ETHTOOL_A_LINKMODES_PEER	bitset	partner link modes
ETHTOOL_A_LINKMODES_SPEED	u32	link speed (Mb/s)
ETHTOOL_A_LINKMODES_DUPLEX	u8	duplex mode

For ETHTOOL_A_LINKMODES_OURS, value represents advertised modes and mask represents supported modes. ETHTOOL_A_LINKMODES_PEER in the reply is a bit list.

LINKMODES_GET allows dump requests (kernel returns reply messages for all devices supporting the request).

LINKMODES_SET

Request contents:

ETHTOOL_A_LINKMODES_HEADER	nested	request header
ETHTOOL_A_LINKMODES_AUTONEG	u8	autonegotiation status
ETHTOOL_A_LINKMODES_OURS	bitset	advertised link modes
ETHTOOL_A_LINKMODES_PEER	bitset	partner link modes
ETHTOOL_A_LINKMODES_SPEED	u32	link speed (Mb/s)
ETHTOOL_A_LINKMODES_DUPLEX	u8	duplex mode

ETHTOOL_A_LINKMODES_OURS bit set allows setting advertised link modes. If autonegotiation is on (either set now or kept from before), advertised modes are not changed (no ETHTOOL_A_LINKMODES_OURS attribute) and at least one of speed and duplex is specified, kernel adjusts advertised modes to all supported modes matching speed, duplex or both (whatever is specified). This autoselection is done on ethtool side with ioctl interface, netlink interface is supposed to allow requesting changes without knowing what exactly kernel supports.

LINKSTATE_GET

Requests link state information. At the moment, only link up/down flag (as provided by ETHTOOL_GLINK ioctl command) is provided but some future extensions are planned (e.g. link down reason). This request does not have any attributes.

Request contents:

ETHTOOL_A_LINKSTATE_HEADER

nested

request header

Kernel response contents:

ETHTOOL_A_LINKSTATE_HEADER	nested	reply header
ETHTOOL_A_LINKSTATE_LINK	bool	link state (up/down)

For most NIC drivers, the value of ETHTOOL_A_LINKSTATE_LINK returns carrier flag provided by netif_carrier_ok() but there are drivers which define their own handler.

LINKSTATE_GET allows dump requests (kernel returns reply messages for all devices supporting the request).

DEBUG_GET

Requests debugging settings of a device. At the moment, only message mask is provided.

Request contents:

ETHTOOL_A_DEBUG_HEADER

nested

request header

Kernel response contents:

ETHTOOL_A_DEBUG_HEADER	nested	reply header
ETHTOOL_A_DEBUG_MSGMASK	bitset	message mask

The message mask (ETHTOOL_A_DEBUG_MSGMASK) is equal to message level as provided by ETHTOOL_GMSGLVL and set by ETHTOOL_SMSGLVL in ioctl interface. While it is called message level there for historical reasons, most drivers and almost all newer drivers use it as a mask of enabled message classes (represented by NETIF_MSG_* constants); therefore netlink interface follows its actual use in practice.

DEBUG_GET allows dump requests (kernel returns reply messages for all devices supporting the request).

DEBUG_SET

Set or update debugging settings of a device. At the moment, only message mask is supported.

Request contents:

ETHTOOL_A_DEBUG_HEADER	nested	request header
ETHTOOL_A_DEBUG_MSGMASK	bitset	message mask

ETHTOOL_A_DEBUG_MSGMASK bit set allows setting or modifying mask of enabled debugging message types for the device.

WOL_GET

Query device wake-on-lan settings. Unlike most “GET” type requests, ETHTOOL_MSG_WOL_GET requires (netns) CAP_NET_ADMIN privileges as it (potentially) provides SecureOn(tm) password which is confidential.

Request contents:

ETHTOOL_A_WOL_HEADER

nested

request header

Kernel response contents:

ETHTOOL_A_WOL_HEADER	nested	reply header
ETHTOOL_A_WOL_MODES	bitset	mask of enabled WoL modes
ETHTOOL_A_WOL_SOPASS	binary	SecureOn(tm) password

In reply, ETHTOOL_A_WOL_MODES mask consists of modes supported by the device, value of modes which are enabled. ETHTOOL_A_WOL_SOPASS is only included in reply if WAKE_MAGICSECURE mode is supported.

WOL_SET

Set or update wake-on-lan settings.

Request contents:

ETHTOOL_A_WOL_HEADER	nested	request header
ETHTOOL_A_WOL_MODES	bitset	enabled WoL modes
ETHTOOL_A_WOL_SOPASS	binary	SecureOn(tm) password

ETHTOOL_A_WOL_SOPASS is only allowed for devices supporting WAKE_MAGICSECURE mode.

Request translation

The following table maps ioctl commands to netlink commands providing their functionality. Entries with “n/a” in right column are commands which do not have their netlink replacement yet.

ioctl command	netlink command
ETHTOOL_GSET	ETHTOOL_MSG_LINKINFO_GET ETHTOOL_MSG_LINKMODES_GET
ETHTOOL_SSET	ETHTOOL_MSG_LINKINFO_SET ETHTOOL_MSG_LINKMODES_SET
ETHTOOL_GDRVINFO	n/a
ETHTOOL_GREGS	n/a
ETHTOOL_GWOL	ETHTOOL_MSG_WOL_GET
ETHTOOL_SWOL	ETHTOOL_MSG_WOL_SET
ETHTOOL_GMSGLVL	ETHTOOL_MSG_DEBUG_GET
ETHTOOL_SMSGLVL	ETHTOOL_MSG_DEBUG_SET
ETHTOOL_NWAY_RST	n/a
ETHTOOL_GLINK	ETHTOOL_MSG_LINKSTATE_GET
ETHTOOL_GEEPROM	n/a
ETHTOOL_SEEPROM	n/a
ETHTOOL_GCOALESCE	n/a
ETHTOOL_SCOALESCE	n/a
ETHTOOL_GRINGPARAM	n/a
ETHTOOL_SRINGPARAM	n/a
ETHTOOL_GPAUSEPARAM	n/a
ETHTOOL_SPAUSEPARAM	n/a
ETHTOOL_GRXCSUM	n/a
ETHTOOL_SRXCSUM	n/a
ETHTOOL_GTXCSUM	n/a
ETHTOOL_STXCSUM	n/a
ETHTOOL_GSG	n/a
ETHTOOL_SSG	n/a
ETHTOOL_TEST	n/a
ETHTOOL_GSTRINGS	ETHTOOL_MSG_STRSET_GET
ETHTOOL_PHYS_ID	n/a
ETHTOOL_GSTATS	n/a
ETHTOOL_GTSO	n/a
ETHTOOL_STSO	n/a
ETHTOOL_GPERMADDR	rtnetlink RTM_GETLINK
ETHTOOL_GUFO	n/a
ETHTOOL_SUFO	n/a
ETHTOOL_GGSO	n/a
ETHTOOL_SGSO	n/a
ETHTOOL_GFLAGS	n/a
ETHTOOL_SFLAGS	n/a
ETHTOOL_GPFLAGS	n/a
ETHTOOL_SPFLAGS	n/a
ETHTOOL_GRXFH	n/a
ETHTOOL_SRXFH	n/a
ETHTOOL_GGRO	n/a
ETHTOOL_SGRO	n/a
ETHTOOL_GRXRINGS	n/a
ETHTOOL_GRXCLSRLCNT	n/a
ETHTOOL_GRXCLSRULE	n/a
ETHTOOL_GRXCLSRLALL	n/a
ETHTOOL_SRXCLSRLDEL	n/a
ETHTOOL_SRXCLSRLINS	n/a
ETHTOOL_FLASHDEV	n/a
ETHTOOL_RESET	n/a
ETHTOOL_SRXNTUPLE	n/a
ETHTOOL_GRXNTUPLE	n/a
ETHTOOL_GSSET_INFO	ETHTOOL_MSG_STRSET_GET
ETHTOOL_GRXFHINDIR	n/a
ETHTOOL_SRXFHINDIR	n/a
ETHTOOL_GFEATURES	n/a
ETHTOOL_SFEATURES	n/a
ETHTOOL_GCHANNELS	n/a
ETHTOOL_SCHANNELS	n/a
ETHTOOL_SET_DUMP	n/a
ETHTOOL_GET_DUMP_FLAG	n/a
ETHTOOL_GET_DUMP_DATA	n/a
ETHTOOL_GET_TS_INFO	n/a
ETHTOOL_GMODULEINFO	n/a
ETHTOOL_GMODULEEEPROM	n/a
ETHTOOL_GEEE	n/a
ETHTOOL_SEEE	n/a
ETHTOOL_GRSSH	n/a
ETHTOOL_SRSSH	n/a
ETHTOOL_GTUNABLE	n/a
ETHTOOL_STUNABLE	n/a
ETHTOOL_GPHYSTATS	n/a
ETHTOOL_PERQUEUE	n/a
ETHTOOL_GLINKSETTINGS	ETHTOOL_MSG_LINKINFO_GET ETHTOOL_MSG_LINKMODES_GET
ETHTOOL_SLINKSETTINGS	ETHTOOL_MSG_LINKINFO_SET ETHTOOL_MSG_LINKMODES_SET
ETHTOOL_PHY_GTUNABLE	n/a
ETHTOOL_PHY_STUNABLE	n/a
ETHTOOL_GFECPARAM	n/a
ETHTOOL_SFECPARAM	n/a