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

#define NETLINK_TESTPROTO (30)

static struct sock *my_nl_sock;


static void nl_test_recv(struct sk_buff *skb)
{
	
struct nlmsghdr *nlh;
int pid;
struct sk_buff *skb_out;
int msg_size;
char *msg="Hello from kernel";
int res;

printk(KERN_INFO "Entering: %s\n", __FUNCTION__);

msg_size=strlen(msg);

nlh=(struct nlmsghdr*)skb->data;
printk(KERN_INFO "Netlink received msg payload:%s\n",(char*)nlmsg_data(nlh));
pid = nlh->nlmsg_pid; /*pid of sending process */

skb_out = nlmsg_new(msg_size,0);

if(!skb_out)
{

    printk(KERN_ERR "Failed to allocate new skb\n");
    return;

} 
nlh=nlmsg_put(skb_out,0,0,NLMSG_DONE,msg_size,0);  
NETLINK_CB(skb_out).dst_group = 0; /* not in mcast group */
strncpy(nlmsg_data(nlh),msg,msg_size);

res=nlmsg_unicast(my_nl_sock,skb_out,pid);

if(res<0)
    printk(KERN_INFO "Error while sending bak to user\n");

}

static struct netlink_kernel_cfg nl_cfg = {
	.groups = 0,
	.input = nl_test_recv,
};

static int nl_test_init(void)
{	

	my_nl_sock = netlink_kernel_create(&init_net, NETLINK_TESTPROTO, &nl_cfg);
	
	if (!my_nl_sock) {
        	printk(KERN_ERR "%s: receive handler registration failed\n", __func__);
        	return -ENOMEM;
	}

	printk(KERN_INFO "Hello :)\n");
	return 0;
}

static void nl_test_exit(void)
{
	if (my_nl_sock)
		netlink_kernel_release(my_nl_sock);

	printk(KERN_INFO "Goodbye :(\n");
}

module_init(nl_test_init);
module_exit(nl_test_exit);

MODULE_AUTHOR("Mario Huettel <mario.huettel@gmx.net>");
MODULE_LICENSE("GPL v2");
MODULE_DESCRIPTION("Netlink communication test");