il_get_cmd_idx
idx = il_get_cmd_idx(q, q->write_ptr, 0);
i = il_get_cmd_idx(q, q->read_ptr, 0);
idx = il_get_cmd_idx(q, q->write_ptr, cmd->flags & CMD_SIZE_HUGE);
cmd_idx = il_get_cmd_idx(&txq->q, idx, huge);