MNT_NONBUSY
fflag |= MNT_NONBUSY;
if ((fflag & MNT_FORCE) != 0 && (fflag & MNT_NONBUSY) != 0)
if (flags & MNT_NONBUSY) {
MNT_FORCE | MNT_SNAPSHOT | MNT_NONBUSY | \
error = unmount(fsid_str, MNT_NONBUSY | MNT_BYFSID);