linux-kernel/netlink/tiny-to-kernel/netlink-tiny-tk.c

   1 /*
   2  * netlink-tiny-tk: Wait for a netlink message from user-space, when it
   3  * arraives print the process ID of the process which sent the message.
   4  *
   5  * Luiz Fernando N. Capitulino
   6  * <lcapitulino@gmail.com>
   7  */
   8 #include <linux/kernel.h>
   9 #include <linux/module.h>
  10 #include <linux/init.h>
  11 #include <linux/mutex.h>
  12 #include <linux/net.h>
  13 #include <linux/skbuff.h>
  14 #include <linux/netlink.h>
  15 #include <net/sock.h>
  16
  17 #define NETLINK_TINY_TK 20   // always check whether this is safe
  18 #define LOG_PREFIX "KNETLINK_TINY_TK: "
  19
  20 static struct sock *nl;
  21 static DEFINE_MUTEX(netlink_tiny_tk_mutex);
  22
  23 static void netlink_tiny_tk_input(struct sk_buff *skb)
  24 {
  25         struct nlmsghdr *nlh;
  26
  27         mutex_lock(&netlink_tiny_tk_mutex);
  28
  29         if (skb->len < sizeof(*nlh))
  30                 return;
  31
  32         nlh = nlmsg_hdr(skb);
  33         printk(LOG_PREFIX "message from: %d\n", nlh->nlmsg_pid);
  34
  35         mutex_unlock(&netlink_tiny_tk_mutex);
  36 }
  37
  38 static int __init netlink_tiny_tk_init(void)
  39 {
  40         nl = netlink_kernel_create(&init_net, NETLINK_TINY_TK, 10,
  41                                    netlink_tiny_tk_input, NULL, THIS_MODULE);
  42         if (!nl) {
  43                 printk(KERN_ERR LOG_PREFIX "cannot create socket\n");
  44                 return -EINVAL;
  45         }
  46
  47         return 0;
  48 }
  49
  50 static void __exit netlink_tiny_tk_exit(void)
  51 {
  52         sock_release(nl->sk_socket);
  53 }
  54
  55 module_init(netlink_tiny_tk_init);
  56 module_exit(netlink_tiny_tk_exit);
  57
  58 MODULE_LICENSE("GPL");
  59 MODULE_AUTHOR("Luiz Capitulino <lcapitulino@gmail.com>");
  60 MODULE_DESCRIPTION("Netlink (to kernel) example module");