rate_limiter: add a safety comment
@@ -343,6 +343,7 @@ impl RateLimiter {
let timer_fd = TimerFd::new()?;
// Note: vmm_sys_util::TimerFd::new() open the fd w/o O_NONBLOCK. We manually add this flag
// so that `Self::event_handler` won't be blocked with `vmm_sys_util::TimerFd::wait()`.
+ // SAFETY: FFI calls.
let ret = unsafe {
let fd = timer_fd.as_raw_fd();
let mut flags = libc::fcntl(fd, libc::F_GETFL);
