Function default_read_vectored 

#[doc(hidden)]
pub fn default_read_vectored<F>(
    read: F,
    bufs: &mut [IoSliceMut<'_>],
) -> Result<usize>
where
    F: FnOnce(&mut [u8]) -> Result<usize>,

🔬This is a nightly-only experimental API. (core_io_internals)