unix: add IoctlGetEthtoolTsInfo on Linux

The function fetches ethtool timestamping and PHC association for a
network interface. Its primary usage is to query the mapping between
the interface and its corresponding PTP clock number in /dev/ptp𝑛.

Change-Id: Id09466b3b43056c628593d4d2e05d77ec8d8082b
GitHub-Last-Rev: 3743a3a6504e6926031b8f2ece331078ae543b25
GitHub-Pull-Request: golang/sys#222
Reviewed-on: https://go-review.googlesource.com/c/sys/+/619335
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Auto-Submit: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>

unix/ioctl_linux.go

@@ -58,6 +58,21 @@ func IoctlGetEthtoolDrvinfo(fd int, ifname string) (*EthtoolDrvinfo, error) {
 	return &value, err
 }
 
+// IoctlGetEthtoolTsInfo fetches ethtool timestamping and PHC
+// association for the network device specified by ifname.
+func IoctlGetEthtoolTsInfo(fd int, ifname string) (*EthtoolTsInfo, error) {
+	ifr, err := NewIfreq(ifname)
+	if err != nil {
+		return nil, err
+	}
+
+	value := EthtoolTsInfo{Cmd: ETHTOOL_GET_TS_INFO}
+	ifrd := ifr.withData(unsafe.Pointer(&value))
+
+	err = ioctlIfreqData(fd, SIOCETHTOOL, &ifrd)
+	return &value, err
+}
+
 // IoctlGetWatchdogInfo fetches information about a watchdog device from the
 // Linux watchdog API. For more information, see:
 // https://www.kernel.org/doc/html/latest/watchdog/watchdog-api.html.