open-nomad/client/fingerprint/network_linux.go

// Copyright (c) HashiCorp, Inc.
// SPDX-License-Identifier: MPL-2.0

package fingerprint

import (
	"fmt"
	"os"
	"os/exec"
	"regexp"
	"strconv"
	"strings"
)

// linkSpeedSys parses link speed in Mb/s from /sys.
func (f *NetworkFingerprint) linkSpeedSys(device string) int {
	path := fmt.Sprintf("/sys/class/net/%s/speed", device)

	// Read contents of the device/speed file
	content, err := os.ReadFile(path)
	if err != nil {
		f.logger.Debug("unable to read link speed", "path", path, "device", device)
		return 0
	}

	lines := strings.Split(string(content), "\n")
	mbs, err := strconv.Atoi(lines[0])
	if err != nil || mbs <= 0 {
		f.logger.Debug("unable to parse link speed", "path", path, "device", device)
		return 0
	}

	return mbs
}

// linkSpeed returns link speed in Mb/s, or 0 when unable to determine it.
func (f *NetworkFingerprint) linkSpeed(device string) int {
	// Use LookPath to find the ethtool in the systems $PATH
	// If it's not found or otherwise errors, LookPath returns and empty string
	// and an error we can ignore for our purposes
	ethtoolPath, _ := exec.LookPath("ethtool")
	if ethtoolPath != "" {
		if speed := f.linkSpeedEthtool(ethtoolPath, device); speed > 0 {
			return speed
		}
	}

	// Fall back on checking a system file for link speed.
	return f.linkSpeedSys(device)
}

// linkSpeedEthtool determines link speed in Mb/s with 'ethtool'.
func (f *NetworkFingerprint) linkSpeedEthtool(path, device string) int {
	outBytes, err := exec.Command(path, device).Output()
	if err != nil {
		f.logger.Warn("error calling ethtool", "error", err, "path", path, "device", device)
		return 0
	}

	output := strings.TrimSpace(string(outBytes))
	re := regexp.MustCompile("Speed: [0-9]+[a-zA-Z]+/s")
	m := re.FindString(output)
	if m == "" {
		// no matches found, output may be in a different format
		f.logger.Warn("unable to parse speed", "path", path, "device", device)
		return 0
	}

	// Split and trim the Mb/s unit from the string output
	args := strings.Split(m, ": ")
	raw := strings.TrimSuffix(args[1], "Mb/s")

	// convert to Mb/s
	mbs, err := strconv.Atoi(raw)
	if err != nil || mbs <= 0 {
		f.logger.Warn("unable to parse Mb/s", "path", path, "device", device)
		return 0
	}

	return mbs
}