tqhash_prev
prsm = tqhash_prev(rack->r_ctl.tqh, rsm);
prev = tqhash_prev(rack->r_ctl.tqh, rsm);
prev = tqhash_prev(rack->r_ctl.tqh, rsm);
prev = tqhash_prev(rack->r_ctl.tqh, rsm);
hs->rsm_max = tqhash_prev(hs, rsm);
tqhash_prev(struct tailq_hash *hs, struct rack_sendmap *rsm);
(var) = tqhash_prev((head), (var)))