def get_device_mac(run_command_fn, dev_name, netns_name=None):
    """Find device MAC address"""
    if netns_name:
        command_prefix = 'ip netns exec %s ' % netns_name
    else:
        command_prefix = ''
    output, _ = run_command_fn('%scat /sys/class/net/%s/address' % (
        command_prefix, dev_name))
    return output[0]
