Linux 网络选项 setsockopt 设置

函数原型

#include
/**
 * @brief 设置与某个套接字关联的选项
 * 
 * @param fd 套接字
 * @param level：选项所在的协议层，支持SOLSOCKET、IPPROTOTCP、IPPROTOIP和IPPROTOIPV6
 * 		一般选择SOLSOCKET
 * @param optname：需设置的选项，而有部分选项需在listen/connect调用前设置才有效
 * @param optval：指针，指向存放选项值的缓冲区
 * @param optlen：长度
 * @return int: 0 返回设置成功，-1 设置失败，errno 出错原因
 */
extern int setsockopt (int fd, int level, int optname,
		       const void *optval, socklen_t optlen);
		       
extern int getsockopt (int fd, int level, int optname,
		       void *restrict optval,
		       socklen_t *restrict optlen);
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linux 5.10 内核系统调用声明

// net/socket.c
SYSCALL_DEFINE5(setsockopt, int, fd, int, level, int, optname,
		char __user *, optval, int, optlen)
{
	return __sys_setsockopt(fd, level, optname, optval, optlen);
}
// net/socket.c line:2096
int __sys_setsockopt(int fd, int level, int optname, char __user *user_optval,
		int optlen)
{
	...
	if (level == SOL_SOCKET && !sock_use_custom_sol_socket(sock))
		err = sock_setsockopt(sock, level, optname, optval, optlen);
	else if (unlikely(!sock->ops->setsockopt))
		err = -EOPNOTSUPP;
	else
		err = sock->ops->setsockopt(sock, level, optname, optval,
					    optlen);
}
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optname选项设置, 可以参考 man 7 socket

// net/core/sock.c line:823
int sock_setsockopt(struct socket *sock, int level, int optname,
		    sockptr_t optval, unsigned int optlen)
{
	...
	if (optname == SO_BINDTODEVICE)
		return sock_setbindtodevice(sk, optval, optlen);
	...
	switch (optname) {
	case SO_DEBUG:
		if (val && !capable(CAP_NET_ADMIN))
			ret = -EACCES;
		else
			sock_valbool_flag(sk, SOCK_DBG, valbool);
		break;
	case SO_REUSEADDR: // 允许重用本地地址
		sk->sk_reuse = (valbool ? SK_CAN_REUSE : SK_NO_REUSE);
		break;
	case SO_REUSEPORT:  // 允许重用本地端口
		sk->sk_reuseport = valbool;
		break;
	case SO_TYPE:
	case SO_PROTOCOL:
	case SO_DOMAIN:
	case SO_ERROR:
		ret = -ENOPROTOOPT;
		break;
	case SO_DONTROUTE: // 不查找路由　
		sock_valbool_flag(sk, SOCK_LOCALROUTE, valbool);
		sk_dst_reset(sk);
		break;
	case SO_BROADCAST: // 允许发送广播数据
		sock_valbool_flag(sk, SOCK_BROADCAST, valbool);
		break;
	...
	case SO_KEEPALIVE: // 保持连接
		if (sk->sk_prot->keepalive)
			sk->sk_prot->keepalive(sk, valbool);
		sock_valbool_flag(sk, SOCK_KEEPOPEN, valbool);
		break;

	case SO_OOBINLINE: // 带外数据放入正常数据流
		sock_valbool_flag(sk, SOCK_URGINLINE, valbool);
		break;

	case SO_NO_CHECK:
		sk->sk_no_check_tx = valbool;
		break;

	case SO_PRIORITY:
		if ((val >= 0 && val <= 6) ||
		    ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN))
			sk->sk_priority = val;
		else
			ret = -EPERM;
		break;
	....
	case SO_RCVTIMEO_OLD:
	case SO_RCVTIMEO_NEW:
		ret = sock_set_timeout(&sk->sk_rcvtimeo, optval,
				       optlen, optname == SO_RCVTIMEO_OLD);
		break;

	case SO_SNDTIMEO_OLD:
	case SO_SNDTIMEO_NEW:
		ret = sock_set_timeout(&sk->sk_sndtimeo, optval,
				       optlen, optname == SO_SNDTIMEO_OLD);
		break;

	case SO_ATTACH_FILTER: {
		struct sock_fprog fprog;

		ret = copy_bpf_fprog_from_user(&fprog, optval, optlen);
		if (!ret)
			ret = sk_attach_filter(&fprog, sk);
		break;
	}
	...
	case SO_INCOMING_CPU:
		WRITE_ONCE(sk->sk_incoming_cpu, val);
		break;

	case SO_CNX_ADVICE:
		if (val == 1)
			dst_negative_advice(sk);
		break;

	case SO_ZEROCOPY:
		...
		break;
	...

	default:
		ret = -ENOPROTOOPT;
		break;
	}
	release_sock(sk);
	return ret;
}
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绑定指定网卡

参考setsockopt 的 SO_BINDTODEVICE 套接口选项

sockfd = socket(AF_INET, SOCK_STREAM, 0);
struct ifreq interface;
// 网卡名称
strncpy(interface.ifr_name, "wlp3s0", IFNAMSIZ);
if (setsockopt(sockfd, SOL_SOCKET, SO_BINDTODEVICE, (char *)&interface, sizeof(interface)) < 0) {
    perror("wlp3s0-client:SO_BINDTODEVICE failed");
    return -1;
}
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