Function sioul_colord_checksums 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn sioul_colord_checksums(
    output: *const c_char,
    out: *mut u8,
    capacity: usize,
) -> isize

colord’s checksums of the profiles it keeps for the output X11 names output (“eDP-1”), for cpp/screencolours.cpp: one per line in out, cut to capacity bytes, their whole length returned (more than capacity: asked again with room enough); 0, none (colord does not know the output); -1, colord did not answer. Read by sioul_sync::colord, on a connection of Sioul’s own (sioul_sync::bus), never Qt’s.

Safety

output is null or a C string; out has room for capacity bytes.