Function killpg 

#[unsafe(no_mangle)]
pub extern "C" fn killpg(pgrp: pid_t, sig: c_int) -> c_int

See https://pubs.opengroup.org/onlinepubs/9799919799/functions/killpg.html.

Sends the signali specified by sig to the process group specified by pgrp.

Upon success, returns 0. Upon failure, returns -1 and sets errno to indicate the error. No signal is sent if failed.