NETLINK_XFRM用户层获取SA的C代码

以下是NETLINK_XFRM用户层获取SA的C代码示例：

#include <linux/xfrm.h>
#include <linux/netlink.h>
#include <linux/socket.h>
#include <linux/rtnetlink.h>

int main() {
    struct sockaddr_nl nladdr;
    struct nlmsghdr *nlh;
    struct msghdr msg;
    struct iovec iov;
    int sock_fd, len;
    char buffer[4096];
    struct {
        struct nlmsghdr nlh;
        struct xfrm_userpolicy_info up;
    } req;

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

    sock_fd = socket(PF_NETLINK, SOCK_RAW, NETLINK_XFRM);
    if (sock_fd < 0) {
        perror("socket");
        return -1;
    }

    if (bind(sock_fd, (struct sockaddr *)&nladdr, sizeof(nladdr)) < 0) {
        perror("bind");
        close(sock_fd);
        return -1;
    }

    memset(&req, 0, sizeof(req));
    req.nlh.nlmsg_len = NLMSG_LENGTH(sizeof(req.up));
    req.nlh.nlmsg_flags = NLM_F_REQUEST | NLM_F_DUMP;
    req.nlh.nlmsg_type = XFRM_MSG_GETPOLICY;
    req.up.sel.family = AF_INET;
    req.up.sel.sport = htons(1234);
    req.up.sel.dport = htons(5678);

    nlh = &req.nlh;

    iov.iov_base = (void *)nlh;
    iov.iov_len = nlh->nlmsg_len;
    memset(&msg, 0, sizeof(msg));
    msg.msg_name = &nladdr;
    msg.msg_namelen = sizeof(nladdr);
    msg.msg_iov = &iov;
    msg.msg_iovlen = 1;

    if (sendmsg(sock_fd, &msg, 0) < 0) {
        perror("sendmsg");
        close(sock_fd);
        return -1;
    }

    do {
        len = recv(sock_fd, buffer, sizeof(buffer), 0);
        if (len < 0) {
            perror("recv");
            close(sock_fd);
            return -1;
        }

        for (nlh = (struct nlmsghdr *)buffer; NLMSG_OK(nlh, len);
             nlh = NLMSG_NEXT(nlh, len)) {
            if (nlh->nlmsg_type == NLMSG_DONE) {
                close(sock_fd);
                return 0;
            } else if (nlh->nlmsg_type == NLMSG_ERROR) {
                perror("NLMSG_ERROR");
                close(sock_fd);
                return -1;
            } else if (nlh->nlmsg_type == XFRM_MSG_NEWSA) {
                struct xfrm_usersa_info *usa = NLMSG_DATA(nlh);
                printf("New SA: spi=%u\n", usa->id.proto.spi);
            } else if (nlh->nlmsg_type == XFRM_MSG_DELSA) {
                struct xfrm_usersa_info *usa = NLMSG_DATA(nlh);
                printf("Deleted SA: spi=%u\n", usa->id.proto.spi);
            }
        }
    } while (1);

    close(sock_fd);
    return 0;
}

该示例代码通过NETLINK_XFRM套接字通信协议，向内核发送XFRM_MSG_GETPOLICY消息来获取安全策略，然后接收内核返回的消息并解析其中的安全关联信息。在接收到消息时，根据消息类型来处理安全关联信息，可以获取到新建或删除的安全关联的SPI