Function drop 

pub fn drop(mode: Mode) -> Result<(), Errno>

Destructively change mode, preventing the process from returning. This function will set Real, Effective, and Saved values to the desired Mode. This prevents the process from changing their mode

Examples

user::drop(user::Mode::Real).unwrap();
// This will only fail if we were SetUID.
if user::USER.real != user::USER.effective {
    user::set(user::Mode::Effective).expect_err("Cannot return!");
}