PIDFD_NONBLOCK
BUILD_BUG_ON(PIDFD_STALE == PIDFD_NONBLOCK);
if (flags & ~(PIDFD_NONBLOCK | PIDFD_THREAD))
#ifndef PIDFD_NONBLOCK
pidfd = sys_pidfd_open(getpid(), PIDFD_NONBLOCK);
pidfd = sys_pidfd_open(pid, PIDFD_NONBLOCK);