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/* https://cirosantilli.com/linux-kernel-module-cheat#netlink-sockets */

#include <linux/delay.h> /* usleep_range */

#include <linux/module.h>

#include <linux/netlink.h>

#include <linux/skbuff.h>

#include <net/sock.h>

#include <lkmc/netlink.h>

struct sock *nl_sk = NULL;

static u32 count;

static u32 sleep;

module_param(sleep, int, S_IRUSR | S_IWUSR);

static void callback(struct sk_buff *skb)

{

char readbuf[9];

size_t readbuflen;

int pid;

int res;

struct nlmsghdr *nlh;

struct sk_buff *skb_out;

nlh = (struct nlmsghdr *)skb->data;

pr_info("kernel received: %s\n", (char *)nlmsg_data(nlh));

if (sleep)

usleep_range(1000000, 1000001);

readbuflen = snprintf(readbuf, sizeof(readbuf), "%x", count);

count++;

pid = nlh->nlmsg_pid;

skb_out = nlmsg_new(readbuflen, 0);

if (!skb_out) {

pr_err("nlmsg_new\n");

return;

}

nlh = nlmsg_put(skb_out, 0, 0, NLMSG_DONE, readbuflen, 0);

NETLINK_CB(skb_out).dst_group = 0;

strncpy(nlmsg_data(nlh), readbuf, readbuflen);

res = nlmsg_unicast(nl_sk, skb_out, pid);

if (res < 0)

pr_info("nlmsg_unicast\n");

}

static int myinit(void)

{

struct netlink_kernel_cfg cfg = {

.input = callback,

};

nl_sk = netlink_kernel_create(&init_net, NETLINK_USER, &cfg);

if (!nl_sk) {

pr_err("netlink_kernel_create\n");

return -10;

}

return 0;

}

static void myexit(void)

{

netlink_kernel_release(nl_sk);

}

module_init(myinit);

module_exit(myexit);

MODULE_LICENSE("GPL");