pub fn copy<R: ?Sized, W: ?Sized>(reader: &mut R, writer: &mut W) -> Result<u64>
where
    R: Read,
    W: Write,
{
    cfg_if::cfg_if! {
        if #[cfg(any(target_os = "linux", target_os = "android"))] {
            crate::sys::kernel_copy::copy_spec(reader, writer)
        } else {
            generic_copy(reader, writer)
        }
    }