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

#define MAX_PAYLOAD 1024
#define MYPROTO NETLINK_USERSOCK
#define MY_GROUP    27


int main(void)
{
    int sock_fd;
    struct sockaddr_nl addr;
    struct nlmsghdr *nlh;
    struct iovec iov;
    struct msghdr msg;
    char buffer[MAX_PAYLOAD];


    /* 1. Create netlink socket */
    sock_fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_USERSOCK);
    if (sock_fd < 0) {
        perror("socket");
        return -1;
    }

    memset(&addr, 0, sizeof(addr));
    addr.nl_family = AF_NETLINK;
    addr.nl_pid = getpid();
    addr.nl_groups = 1 << (MY_GROUP - 1);  

    // (Group is 1-based, sets bit (group-1) for subscription)

    /* 2. Bind the socket */
    if (bind(sock_fd, (struct sockaddr *)&addr, sizeof(addr)) < 0) {
        perror("bind");
        close(sock_fd);
        return -1;
    }


    while (1) {
        /* 3. Prepare to receive messages in a loop */
        memset(buffer, 0, sizeof(buffer));
        nlh = (struct nlmsghdr *)buffer;
        iov.iov_base = (void *)nlh;
        iov.iov_len = MAX_PAYLOAD;

        memset(&msg, 0, sizeof(msg));
        msg.msg_name = (void *)&addr;
        msg.msg_namelen = sizeof(addr);
        msg.msg_iov = &iov;
        msg.msg_iovlen = 1;

        printf("Waiting for kernel broadcast...\n");
        if (recvmsg(sock_fd, &msg, 0) < 0) {
            perror("recvmsg");
            break;
        }

        printf("Received kernel message: \"%s\"\n", (char *)NLMSG_DATA(nlh));
    }

    close(sock_fd);
    return 0;
}