nix::convert_ioctl_res!

macro_rules! convert_ioctl_res {
    ($w:expr) => (
        {
            let res = $w;
            if res < 0 {
                return Err($crate::Error::Sys($crate::errno::Errno::last()))
            }
            Ok(res) // res may contain useful information for user
        }
    );
}

Convert raw ioctl return value to a Nix result