#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/netlink.h>
#include <net/sock.h>
#include <linux/skbuff.h>

#define NETLINK_USER_CUSTOM 31

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Leo");
MODULE_DESCRIPTION("Netlink message logger for custom protocol");

static struct sock *nl_sk = NULL;

static void netlink_recv_msg(struct sk_buff *skb)
{
    struct nlmsghdr *nlh;
    char *payload;

    if (!skb)
        return;

    nlh = nlmsg_hdr(skb);
    payload = (char *)nlmsg_data(nlh);

    pr_info("[netlink_logger] Received netlink msg: %s\n", payload);
}

static int __init netlink_logger_init(void)
{
    struct netlink_kernel_cfg cfg = {
        .input = netlink_recv_msg,
    };

    nl_sk = netlink_kernel_create(&init_net, NETLINK_USER_CUSTOM, &cfg);
    if (!nl_sk) {
        pr_err("[netlink_logger] Failed to create netlink socket\n");
        return -ENOMEM;
    }

    pr_info("[netlink_logger] Netlink logger module loaded (protocol: %d)\n", NETLINK_USER_CUSTOM);
    return 0;
}

static void __exit netlink_logger_exit(void)
{
    if (nl_sk)
        netlink_kernel_release(nl_sk);
    pr_info("[netlink_logger] Module unloaded\n");
}

module_init(netlink_logger_init);
module_exit(netlink_logger_exit);