def METHOD_NAME(block_device):
    # Given a block device returns the partition's device node of a root fs
    # partition. It looks for a partition with the root fs guuid. Returns
    # None if no root fs is found.
    root_guuid = '0fc63daf-8483-4772-8e79-3d69d8477de4'
    process = subprocess.run(['lsblk', block_device, '-lno', 'NAME'],
                             capture_output=True, check=True)
    for ln in process.stdout.decode().split():
        part = '/dev/' + ln
        if part == block_device:
            continue
        process = subprocess.run(['blkid', '-p', part],
                                 capture_output=True, check=True)
        result = process.stdout.decode().replace(part + ': ', '')
        tokens = result.replace('"', '').split(' ')
        data = {i.split('=')[0]: i.split('=')[1] for i in tokens}
        entry_type = data.get('PART_ENTRY_TYPE', None)
        if entry_type == root_guuid:
          return part
        label = data.get('LABEL', None)
        if label == 'root':
          return part
    return None