获得ToS字节的BSD(或可移植的)方法是什么(比如从linux获取IP_RECVTOS)?

What is the right (portable, stable) way to get the ToS byte of a received packet? I'm doing UDP with recvmsg() and on linux I can get the ToS if I setsockopt() IP_RECVTOS/IPV6_RECVTCLASS, but IP_RECVTOS doesn't seem to be available on my BSD systems. What is the right way to do this?What is the right (portable, stable) way to get