socket编程急问

ringfree

用两块网卡接收组播包,主要程序如下：
  m_sock = socket (AF_INET, SOCK_RAW, IPPROTO_IP);
   
  localaddr.sin_addr.s_addr = INADDR_ANY;
  localaddr.sin_family = AF_INET;
  localaddr.sin_port = htons(0);
  bind(m_sock, (PSOCKADDR)&localaddr, sizeof(localaddr));  
  
  ipmr.imr_multiaddr.s_addr = GROUP_ADDR;
  ipmr.imr_interface.s_addr = INADDR_ANY;
  setsockopt(ospf_sock,IPPROTO_IP,IP_ADD_MEMBERSHIP,(char *)&ipmr,sizeof(ipmr)
);

结果socket只能接收到一块默认网卡上的数据包，用sniffer监测发现其实两块网卡上都有
数据到达。请教如何修改才能在同一socket中收到两块网卡上的数据包？急用，谢谢！