TMS320F280039C: 如何在使用中断收发的时候获取到接收报文的长度

Part Number: TMS320F280039C

__interrupt void INT_myCAN0_1_ISR_TXRX(void)
{
uint32_t status;

status = CAN_getInterruptCause(CANA_BASE);
if( (status>>16) == 1)
{
CAN_clearInterruptStatus(CANA_BASE, 1);
}
else if( (status>>16) == 2)
{
CAN_readMessage(CANA_BASE,2,data);
CAN_clearInterruptStatus(CANA_BASE, 2);
}
else{}
CAN_clearGlobalInterruptStatus(CANA_BASE, CAN_GLOBAL_INT_CANINT1);
Interrupt_clearACKGroup(INTERRUPT_ACK_GROUP9);
}

UDS服务需要判断接收的报文是不是8字节长度，readmessage  api中只能收到数据，请问下报文长度如何获取？