func findPairInterfaceOfContainerInterface(e exec.Interface, containerPid int, containerInterfaceName string) (string, error) {
nsenterPath, err := e.LookPath("nsenter")
if err != nil {
return "", err
}
ethtoolPath, err := e.LookPath("ethtool")
if err != nil {
return "", err
}
// Get container's interface index
output, err := e.Command(nsenterPath, "-t", fmt.Sprintf("%d", containerPid), "-n", "-F", "--", ethtoolPath, "--statistics", containerInterfaceName).CombinedOutput()
if err != nil {
return "", fmt.Errorf("Unable to query interface %s of container %d: %v", containerInterfaceName, containerPid, err)
}
// look for peer_ifindex
match := ethtoolOutputRegex.FindSubmatch(output)
if match == nil {
return "", fmt.Errorf("No peer_ifindex in interface statistics for %s of container %d", containerInterfaceName, containerPid)
}
peerIfIndex, err := strconv.Atoi(string(match[1]))
if err != nil { // seems impossible (\d+ not numeric)
return "", fmt.Errorf("peer_ifindex wasn't numeric: %s: %v", match[1], err)
}
iface, err := net.InterfaceByIndex(peerIfIndex)
if err != nil {
return "", err
}
return iface.Name, nil
}
