CIRC_SPACE
if (CIRC_SPACE(head, tail, DRM_CRC_ENTRIES_NR) < 1) {
space = CIRC_SPACE(ctb->tail, ctb->head, ctb->size) - ctb->resv_space;
space = CIRC_SPACE(ctb->tail, head, ctb->size);
CIRC_SPACE(ce->parallel.guc.wqi_tail, ce->parallel.guc.wqi_head, WQ_SIZE)