Show in which disk the chunks are allocated.

    CLI Example:

    .. code-block:: bash

        salt '*' btrfs.usage /your/mountpoint

def usage(path):
    '''
    Show in which disk the chunks are allocated.

    CLI Example:

    .. code-block:: bash

        salt '*' btrfs.usage /your/mountpoint
    '''
    out = __salt__['cmd.run_all']("btrfs filesystem usage {0}".format(path))
    salt.utils.fsutils._verify_run(out)

    ret = {}
    for section in out['stdout'].split("\n\n"):
        if section.startswith("Overall:\n"):
            ret['overall'] = _usage_overall(section)
        elif section.startswith("Unallocated:\n"):
            ret['unallocated'] = _usage_unallocated(section)
        else:
            ret.update(_usage_specific(section))

    return ret