Function vsyslog 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn vsyslog(
    priority: c_int,
    message: *const c_char,
    ap: VaList<'_>,
)

See https://www.man7.org/linux/man-pages/man3/vsyslog.3.html.

Non-POSIX, 4.3BSD-Reno.