def _convert_to(maybe_device, convert_to):
    '''
    Convert a device name, UUID or LABEL to a device name, UUID or
    LABEL.

    Return the fs_spec required for fstab.

    '''

    # Fast path. If we already have the information required, we can
    # save one blkid call
    if not convert_to or \
       (convert_to == 'device' and maybe_device.startswith('/')) or \
       maybe_device.startswith('{}='.format(convert_to.upper())):
        return maybe_device

    # Get the device information
    if maybe_device.startswith('/'):
        blkid = __salt__['disk.blkid'](maybe_device)
    else:
        blkid = __salt__['disk.blkid'](token=maybe_device)

    result = None
    if len(blkid) == 1:
        if convert_to == 'device':
            result = list(blkid.keys())[0]
        else:
            key = convert_to.upper()
            result = '{}={}'.format(key, list(blkid.values())[0][key])

    return result
Convert a device name, UUID or LABEL to a device name, UUID or
    LABEL.

    Return the fs_spec required for fstab.