ethtool: add LinkModeUpdate and Client.UpdateLinkMode

client.go

@@ -99,6 +99,14 @@ type LinkMode struct {
 	Duplex        Duplex
 }
 
+// LinkModeUpdate contains an update to the link mode information
+// for an Ethernet interface.
+type LinkModeUpdate struct {
+	SpeedMegabits *int
+	Ours, Peer    []AdvertisedLinkMode
+	Duplex        *Duplex
+}
+
 // A Duplex is the link duplex type for a LinkMode structure.
 type Duplex int
 
@@ -131,6 +139,13 @@ func (c *Client) LinkMode(ifi Interface) (*LinkMode, error) {
 	return c.c.LinkMode(ifi)
 }
 
+// UpdateLinkMode updates link mode information for the specified Interface.
+//
+// Specifically, the interface is brought to agreement with the non-nil fields of lmu.
+func (c *Client) UpdateLinkMode(ifi Interface, lmu *LinkModeUpdate) error {
+	return c.c.UpdateLinkMode(ifi, lmu)
+}
+
 // LinkState contains link state information for an Ethernet interface.
 type LinkState struct {
 	Interface Interface

client_linux.go

@@ -147,6 +147,35 @@ func (c *client) linkMode(flags netlink.HeaderFlags, ifi Interface) ([]*LinkMode
 	return parseLinkModes(msgs)
 }
 
+// UpdateLinkMode updates link mode information for a single ethtool-supported interface.
+func (c *client) UpdateLinkMode(ifi Interface, lmu *LinkModeUpdate) error {
+	_, err := c.get(
+		unix.ETHTOOL_A_LINKMODES_HEADER,
+		unix.ETHTOOL_MSG_LINKMODES_SET,
+		netlink.Acknowledge,
+		ifi,
+		lmu.encode,
+	)
+	return err
+}
+
+// encode packs LinkModeUpdate data into the appropriate netlink attributes for the
+// encoder.
+func (lmu *LinkModeUpdate) encode(ae *netlink.AttributeEncoder) {
+	if lmu.SpeedMegabits != nil {
+		ae.Uint32(unix.ETHTOOL_A_LINKMODES_SPEED, uint32(*lmu.SpeedMegabits))
+	}
+	if lmu.Ours != nil {
+		ae.Nested(unix.ETHTOOL_A_LINKMODES_OURS, packALMs(lmu.Ours))
+	}
+	if lmu.Peer != nil {
+		ae.Nested(unix.ETHTOOL_A_LINKMODES_PEER, packALMs(lmu.Peer))
+	}
+	if lmu.Duplex != nil {
+		ae.Uint8(unix.ETHTOOL_A_LINKMODES_DUPLEX, uint8(*lmu.Duplex))
+	}
+}
+
 // LinkStates fetches link state data for all ethtool-supported links.
 func (c *client) LinkStates() ([]*LinkState, error) {
 	return c.linkState(netlink.Dump, Interface{})
@@ -562,6 +591,34 @@ func parseInterface(ifi *Interface) func(*netlink.AttributeDecoder) error {
 	}
 }
 
+// packALMBitset encodes given AdvertisedLinkModes as a compact bitset.
+func packALMBitset(alms []AdvertisedLinkMode) func() ([]byte, error) {
+	return func() ([]byte, error) {
+		// Calculate the number of words necessary for the bitset, then
+		// multiply by 4 for bytes.
+		b := make([]byte, ((len(linkModes)+31)/32)*4)
+
+		for _, alm := range alms {
+			byteIndex := alm.Index / 8
+			bitIndex := alm.Index % 8
+			b[byteIndex] |= 1 << bitIndex
+		}
+
+		return b, nil
+	}
+}
+
+// packALMs encodes given AdvertisedLinkModes.
+func packALMs(alms []AdvertisedLinkMode) func(*netlink.AttributeEncoder) error {
+	return func(nae *netlink.AttributeEncoder) error {
+		fn := packALMBitset(alms)
+		nae.Uint32(unix.ETHTOOL_A_BITSET_SIZE, uint32(len(alms)))
+		nae.Do(unix.ETHTOOL_A_BITSET_VALUE, fn)
+		nae.Do(unix.ETHTOOL_A_BITSET_MASK, fn)
+		return nil
+	}
+}
+
 func panicf(format string, a ...interface{}) {
 	panic(fmt.Sprintf(format, a...))
 }

client_linux_test.go

@@ -758,18 +758,8 @@ func encodeLinkMode(t *testing.T, lm LinkMode) genetlink.Message {
 
 			ae.Uint32(unix.ETHTOOL_A_LINKMODES_SPEED, uint32(lm.SpeedMegabits))
 
-			packALMs := func(typ uint16, alms []AdvertisedLinkMode) {
-				ae.Nested(typ, func(nae *netlink.AttributeEncoder) error {
-					fn := packALMBitset(alms)
-					nae.Uint32(unix.ETHTOOL_A_BITSET_SIZE, uint32(len(linkModes)))
-					nae.Do(unix.ETHTOOL_A_BITSET_VALUE, fn)
-					nae.Do(unix.ETHTOOL_A_BITSET_MASK, fn)
-					return nil
-				})
-			}
-
-			packALMs(unix.ETHTOOL_A_LINKMODES_OURS, lm.Ours)
-			packALMs(unix.ETHTOOL_A_LINKMODES_PEER, lm.Peer)
+			ae.Nested(unix.ETHTOOL_A_LINKMODES_OURS, packALMs(lm.Ours))
+			ae.Nested(unix.ETHTOOL_A_LINKMODES_PEER, packALMs(lm.Peer))
 
 			ae.Uint8(unix.ETHTOOL_A_LINKMODES_DUPLEX, uint8(lm.Duplex))
 		}),
@@ -814,22 +804,6 @@ func encodeWOL(t *testing.T, wol WakeOnLAN) genetlink.Message {
 	}
 }
 
-func packALMBitset(alms []AdvertisedLinkMode) func() ([]byte, error) {
-	return func() ([]byte, error) {
-		// Calculate the number of words necessary for the bitset, then
-		// multiply by 4 for bytes.
-		b := make([]byte, ((len(linkModes)+31)/32)*4)
-
-		for _, alm := range alms {
-			byteIndex := alm.Index / 8
-			bitIndex := alm.Index % 8
-			b[byteIndex] |= 1 << bitIndex
-		}
-
-		return b, nil
-	}
-}
-
 func encode(t *testing.T, fn func(ae *netlink.AttributeEncoder)) []byte {
 	t.Helper()