Return the information which subsystems are mounted where.
    @return a generator of tuples (subsystem, mountpoint)

def _find_cgroup_mounts():
    """
    Return the information which subsystems are mounted where.
    @return a generator of tuples (subsystem, mountpoint)
    """
    try:
        with open('/proc/mounts', 'rt') as mountsFile:
            for mount in mountsFile:
                mount = mount.split(' ')
                if mount[2] == 'cgroup':
                    mountpoint = mount[1]
                    options = mount[3]
                    for option in options.split(','):
                        if option in ALL_KNOWN_SUBSYSTEMS:
                            yield (option, mountpoint)
    except IOError:
        logging.exception('Cannot read /proc/mounts')