DTRACE_HASHPREV
ASSERT(*nextp == NULL && *(DTRACE_HASHPREV(hash, new)) == NULL);
prevp = DTRACE_HASHPREV(hash, bucket->dthb_chain);
dtrace_probe_t **prevp = DTRACE_HASHPREV(hash, probe);
*(DTRACE_HASHPREV(hash, *nextp)) = *prevp;