/// Wait for process to change state.
///
/// # Examples
///
/// ```
/// let pid = unsafe { nc::fork() };
///
/// match pid {
/// Err(errno) => {
/// eprintln!("fork() error: {}", nc::strerror(errno));
/// unsafe { nc::exit(1) };
/// }
/// Ok(0) => println!("[child] pid is: {}", unsafe { nc::getpid() }),
/// Ok(pid) => {
/// let mut status = 0;
/// let ret = unsafe { nc::waitpid(pid, &mut status, 0) };
/// assert!(ret.is_ok());
/// let exited_pid = ret.unwrap();
/// assert_eq!(exited_pid, pid);
/// }
/// }
/// ```
pub unsafe fn waitpid(pid: pid_t, status: &mut i32, options: i32) -> Result<pid_t, Errno> {
let pid = pid as usize;
let status_ptr = status as *mut i32 as usize;
let options = options as usize;
syscall3(SYS_WAITPID, pid, status_ptr, options).map(|ret| ret as pid_t)
}