pub fn sys_fill_exact(
buf: &mut [MaybeUninit<u8>],
sys_fill: impl Fn(&mut [MaybeUninit<u8>]) -> ssize_t,
) -> Result<(), Error>pub fn sys_fill_exact(
buf: &mut [MaybeUninit<u8>],
sys_fill: impl Fn(&mut [MaybeUninit<u8>]) -> ssize_t,
) -> Result<(), Error>