CS_DRAIN
if ((flags & CS_DRAIN) != 0)
if ((flags & CS_DRAIN) == 0 && c->c_lock != NULL) {
if ((flags & CS_DRAIN) == 0)
if ((flags & CS_DRAIN) != 0) {
rv = _callout_stop_safe(&hpts->co, CS_DRAIN);
#define callout_drain(c) _callout_stop_safe(c, CS_DRAIN)