FD_PIDFS_ROOT
if (fd == FD_PIDFS_ROOT) {
#ifndef FD_PIDFS_ROOT
pidfd = open_by_handle_at(FD_PIDFS_ROOT, fh, 0);
pidfd = open_by_handle_at(FD_PIDFS_ROOT, fh, O_CLOEXEC);
pidfd = open_by_handle_at(FD_PIDFS_ROOT, fh, O_NONBLOCK);