c - 没有连接到网络（AF_ROUTE）时没有这样的过程（3）

Question

当我连接到网络时，我可以向struct rt_msghdr*内核发送 a 并接收相应的路由。但是，当我断开与网络的连接并尝试发送相同的路由消息头时，套接字send()以errno = ESRCH (3) No such process.

通用代码：（在 MacOS 上测试）

int sd = create_socket(AF_ROUTE, IPPROTO_RAW, AF_UNSPEC);

memset(&buffer[0], 0, buffer.size());
struct rt_msghdr* rmh = (struct rt_msghdr*)(&buffer[0]);
rmh->rtm_msglen       = sizeof(struct rt_msghdr) + sizeof(struct sockaddr_in);
rmh->rtm_version      = RTM_VERSION;
rmh->rtm_type         = RTM_GET;
rmh->rtm_addrs        = RTA_DST;
rmh->rtm_pid          = getpid();
rmh->rtm_seq          = 1;
struct sockaddr_in* sa_in = (struct sockaddr_in*)(rmh + 1);
sa_in->sin_len            = sizeof(struct sockaddr_in);
sa_in->sin_family         = AF_INET;

int status;
if ((status = send(sd, rmh, rmh->rtm_msglen, 0) < 0) {
    rmh->rtm_msglen =
        sizeof(struct rt_msghdr) + sizeof(struct sockaddr_in6);
    struct sockaddr_in6* sa_in6 = (struct sockaddr_in6*)(rmh + 1);
    memset(sa_in6, 0, sizeof(struct sockaddr_in6));
    sa_in6->sin6_len    = sizeof(struct sockaddr_in6);
    sa_in6->sin6_family = AF_INET6;
    if ((status = send(sd, rmh, rmh->rtm_msglen, 0) < 0) {
        // process errno
        // * issue happens here when not connected to a network
    }
}

// receive kernel response(s)
// process responses

close(sd);

我验证了在标题中正确设置了进程 ID (pid)。netstat -nr 在未连接到网络时返回默认路由而不会出现问题。我无法理解为什么此代码依赖于网络连接。

结果来自netstat -nr：

# with a network connection (Internet)
Destination        Gateway     Flags          Refs      Use   Netif Expire
default            X.X.X.X     UGSc           58        0     en1

# without a network connection (Internet6)
Destination        Gateway            Flags         Netif Expire
default            fe80::%utun0       UGcI          utun0 

标签： cnetworkingroutesbsd