用户层获取XFRM_MSG_GETSA的C代码

以下是获取XFRM_MSG_GETSA消息的C代码示例：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <linux/xfrm.h>

int main(int argc, char **argv)
{
    int sockfd;
    struct xfrm_usersa_info info;
    struct sockaddr_nl nladdr;
    struct msghdr msg;
    struct iovec iov;
    char buf[4096];
    int len;

    memset(&info, 0, sizeof(info));
    info.family = AF_INET;
    info.sel.family = AF_INET;
    info.sel.saddr = inet_addr("192.168.1.1");
    info.sel.prefixlen_s = 32;
    info.sel.daddr = inet_addr("192.168.2.1");
    info.sel.prefixlen_d = 32;
    info.lft.soft_byte_limit = 1024;
    info.lft.hard_byte_limit = 2048;
    info.lft.soft_packet_limit = 100;
    info.lft.hard_packet_limit = 200;
    info.lft.soft_add_expires_seconds = 60;
    info.lft.hard_add_expires_seconds = 120;
    info.lft.soft_use_expires_seconds = 180;
    info.lft.hard_use_expires_seconds = 360;

    sockfd = socket(AF_NETLINK, SOCK_RAW, NETLINK_XFRM);
    if (sockfd < 0) {
        perror("socket");
        exit(1);
    }

    memset(&nladdr, 0, sizeof(nladdr));
    nladdr.nl_family = AF_NETLINK;

    memset(&msg, 0, sizeof(msg));
    msg.msg_name = &nladdr;
    msg.msg_namelen = sizeof(nladdr);

    memset(&iov, 0, sizeof(iov));
    iov.iov_base = &info;
    iov.iov_len = sizeof(info);

    memset(buf, 0, sizeof(buf));
    msg.msg_iov = &iov;
    msg.msg_iovlen = 1;
    msg.msg_control = buf;
    msg.msg_controllen = sizeof(buf);

    if (sendmsg(sockfd, &msg, 0) < 0) {
        perror("sendmsg");
        exit(1);
    }

    memset(&msg, 0, sizeof(msg));
    msg.msg_name = &nladdr;
    msg.msg_namelen = sizeof(nladdr);

    memset(&iov, 0, sizeof(iov));
    iov.iov_base = buf;
    iov.iov_len = sizeof(buf);

    msg.msg_iov = &iov;
    msg.msg_iovlen = 1;

    if ((len = recvmsg(sockfd, &msg, 0)) < 0) {
        perror("recvmsg");
        exit(1);
    }

    close(sockfd);

    return 0;
}

该代码创建一个AF_NETLINK套接字，发送XFRM_MSG_GETSA消息，接收回复消息并关闭套接字。在发送消息时，需要填写xfrm_usersa_info结构体，该结构体包含了需要获取的SA的信息，如源地址、目的地址、生存时间等。在接收回复消息时，可以从msg_iov中获取回复消息的数据