rw_tryrdlock
if (rw_tryrdlock(&rdcp->rwlock) == 0) {
ret = rw_tryrdlock(&imc->l);
if (rw_tryrdlock(&mod_unload_lock) != 0) {
int rw_tryrdlock(rwlock_t *);
int rw_tryrdlock(lwp_rwlock_t *);
rv = rw_tryrdlock(&rwlp->rw_lock);