Enhance device index detection with sysfs-based approach

Improves network interface device index detection reliability by:
- Adding a primary method that reads device index directly from sysfs
- Maintaining the name-based parsing as a fallback mechanism
- Adding logging to indicate which method was used

This makes the interface detection more robust across different system configurations where sysfs information is available, reducing reliance on interface naming conventions.

Author: John Lam

pkg/eni-manager/network/manager.go

@@ -267,8 +267,14 @@ func (m *Manager) getPCIAddressForInterface(ifaceName string) (string, error) {
 }
 
 func (m *Manager) getDeviceIndexForInterface(ifaceName string) (int, error) {
-	// Try to extract device index from interface name
-	// This is a simplified approach - in practice, this would use more sophisticated mapping
+	// Method 1: Try to read device index from sysfs (most reliable)
+	if deviceIndex, err := m.getDeviceIndexFromSysfs(ifaceName); err == nil {
+		log.Printf("Device index for %s from sysfs: %d", ifaceName, deviceIndex)
+		return deviceIndex, nil
+	}
+
+	// Method 2: Fallback to interface name parsing
+	log.Printf("Sysfs unavailable for %s, using name-based calculation", ifaceName)
 
 	// For eth interfaces (eth0, eth1, etc.)
 	if strings.HasPrefix(ifaceName, "eth") {
@@ -290,6 +296,25 @@ func (m *Manager) getDeviceIndexForInterface(ifaceName string) (int, error) {
 	return 0, fmt.Errorf("could not determine device index for interface %s", ifaceName)
 }
 
+// getDeviceIndexFromSysfs reads the device index directly from sysfs
+func (m *Manager) getDeviceIndexFromSysfs(ifaceName string) (int, error) {
+	// Try multiple sysfs paths for device index
+	paths := []string{
+		fmt.Sprintf("/sys/class/net/%s/device/device_index", ifaceName),
+		fmt.Sprintf("/sys/class/net/%s/dev_id", ifaceName),
+	}
+
+	for _, path := range paths {
+		if data, err := os.ReadFile(path); err == nil {
+			if deviceIndex, err := strconv.Atoi(strings.TrimSpace(string(data))); err == nil {
+				return deviceIndex, nil
+			}
+		}
+	}
+
+	return 0, fmt.Errorf("device index not found in sysfs for interface %s", ifaceName)
+}
+
 func (m *Manager) bringUpInterfaceWithIP(ifaceName string) error {
 	cmd := exec.Command("ip", "link", "set", "dev", ifaceName, "up")
 	output, err := cmd.CombinedOutput()