多网卡情况下如何判断是哪个网卡接收到的数据包

发布于 2021-08-25 16:48:01 浏览：1941 订阅该版

在多网卡情况下，不同网卡有不同的地址。
在socket中使用udp协议监听了一个端口,监听的地址为0.0.0.0表示任意网卡都可以接收到数据。现在的问题是，接收数据包我可以用(recvfrom)获取到发送方的ip地址和端口。但是我不知道是从哪个网卡接收到的。
查询了linux头文件
```c
#include <sys/socket.h>
ssize_t recvmsg(int socket, struct msghdr *message, int flags);
```
可以拿到本地接收端地址，但是这个函数在rtt中好像没有实现

连lwip中也只有
```c
int lwip_sendmsg(int s, const struct msghdr *message, int flags);
```

**没有找到recvmsg函数**

代码如下
```c
void task_udp(void *p)
{
    int err = 0;
    int sockfd = 0;
    struct sockaddr_in bindAddr = {0};
    struct sockaddr_in destAddr = {0};
    struct sockaddr_in sourceAddr = {0};
    int udp_tick = 0;
    int len = 0;
    char addr_str[128];
    struct timeval tv;
    
    char * rx_buffer = malloc(UDP_BUF_SIZE);
    char * tx_buffer = malloc(UDP_BUF_SIZE);
    while(1)
    {
        sockfd = socket(AF_INET,SOCK_DGRAM,IPPROTO_IP);
        LOG_D("socket created :%d",sockfd);

bindAddr.sin_family = AF_INET;
        bindAddr.sin_port = htons(UDP_BIND_PORT);
        bindAddr.sin_addr.s_addr = htonl(IPADDR_ANY);
        err = bind(sockfd, (struct sockaddr *)&bindAddr, sizeof(bindAddr));
        if (err < 0)
        {
            LOG_D( "Failed to bind socket. Error %d", errno);
        }
        LOG_D( "socket bind :%d",ntohs(bindAddr.sin_port));

destAddr.sin_family = AF_INET;
        destAddr.sin_port = htons(UDP_SEND_PORT);
        // destAddr.sin_addr.s_addr = inet_addr(MULTICAST_IPV4_ADDR);
        destAddr.sin_addr.s_addr = inet_addr("255.255.255.255"); //htonl(IPADDR_BROADCAST);  
        
        int mode = 0;
        ioctlsocket(sockfd, FIONBIO, &mode);

/* Set recv timeout of this fd as per config */
        tv.tv_sec = 10;
        tv.tv_usec = 0;
        setsockopt(sockfd, SOL_SOCKET, SO_RCVTIMEO, (const char*)&tv, sizeof(tv));

/* Set send timeout of this fd as per config */
        tv.tv_sec = 3;
        tv.tv_usec = 0;
        setsockopt(sockfd, SOL_SOCKET, SO_SNDTIMEO, (const char*)&tv, sizeof(tv));
        
        const int opt = 1;
        setsockopt(sockfd, SOL_SOCKET, SO_BROADCAST, (char *)&opt, sizeof(opt));

// this is also a listening socket, so add it to the multicast
        // group for listening...
        // socket_add_ipv4_multicast_group(sockfd, true);

socklen_t socklen = sizeof(sourceAddr);
        while(1)
        {
            //len = recv(sockfd, rx_buffer, 1024-1, 0);
            len = recvfrom(sockfd, rx_buffer, UDP_BUF_SIZE-1, 0,(struct sockaddr *)&sourceAddr,&socklen);
            // Error occured during receiving
            if (len > 0)
            {
                inet_ntoa_r(((struct sockaddr_in *)&sourceAddr)->sin_addr.s_addr, addr_str, sizeof(addr_str) - 1);
                rx_buffer[len] = 0;
                LOG_D( "recvfrom from %s : %d , %d bytes", addr_str,ntohs(sourceAddr.sin_port) , len);
                LOG_D( "%s", rx_buffer);
							
								len = udpfind_json_process(rx_buffer,UDP_BUF_SIZE,board_ip_str_get(),board_mac_str_get() , board_unique_id_str()  );
								LOG_D( "send %d bytes", len);
								int err = sendto(sockfd,rx_buffer, len, 0,(struct sockaddr *)&destAddr,sizeof(destAddr));
								if (err < 0) 
								{
										LOG_D( "Error occured during sending: errno %d", errno);
										break;
								}
            }else
            {
                if(!(errno == EINTR || errno == EWOULDBLOCK || errno == EAGAIN))
                {
                    //  LOG_E("net recv err :%d",rc);
                    LOG_D( "recvfrom failed: errno %d", errno);
                    break;
                }
            }
            
            //vTaskDelay(100 / portTICK_RATE_MS);
        }
        if (sockfd != -1) {
            LOG_D( "Shutting down socket and restarting...");
            shutdown(sockfd, 0);
            closesocket(sockfd);
        }
    }
    free(rx_buffer);
    free(tx_buffer);
}
```