Function run_with 

pub unsafe extern "C" fn run_with(
    ls: *mut custom_labels_labelset_t,
    labels: *mut custom_labels_label_t,
    n: c_int,
    cb: Option<unsafe extern "C" fn(arg1: *mut c_void) -> *mut c_void>,
    data: *mut c_void,
    out: *mut *mut c_void,
) -> c_int

Run the supplied callback function (passing it the supplied data pointer) with the supplied set of N labels applied, then re-set the old values. Optionally, if out is non-NULL, write the return value of the callback into out.