linux-kernel/netlink/tiny-to-user/netlink-tiny-tu.c

   1 /*
   2  * netlink-tiny-tu: Send a netlink message to user-space after
   3  * NETLINK_TINY_DELAY seconds the module has been loaded.
   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/string.h>
  12 #include <linux/mutex.h>
  13 #include <linux/net.h>
  14 #include <linux/skbuff.h>
  15 #include <linux/netlink.h>
  16 #include <linux/timer.h>
  17 #include <net/sock.h>
  18
  19 #define NETLINK_TINY_TU 20   // always check whether this is safe
  20 #define TINY_TY_GRP      1
  21 #define LOG_PREFIX "KNETLINK_TINY_TU: "
  22 #define NETLINK_TINY_DELAY (HZ * 7)  // seven seconds
  23
  24 #define UNUSED(x)  (x = x)
  25
  26 static struct sock *nl;
  27 static struct timer_list netlink_tiny_timer;
  28
  29 static int send_message(const char *message)
  30 {
  31         size_t len;
  32         struct sk_buff *skb;
  33         struct nlmsghdr *nlh;
  34
  35         len = NLMSG_SPACE(strlen(message) + 1);
  36         skb = alloc_skb(len, GFP_ATOMIC);
  37         if (!skb) {
  38                 printk(KERN_ERR LOG_PREFIX "cannot allocate memory\n");
  39                 return -ENOMEM;
  40         }
  41
  42         nlh = NLMSG_PUT(skb, 0, 0, 0, len - sizeof(*nlh));
  43         strcpy(NLMSG_DATA(nlh), message);
  44
  45         NETLINK_CB(skb).pid = 0;      /* from kernel */
  46         NETLINK_CB(skb).dst_group = TINY_TY_GRP;  /* group */
  47
  48         netlink_broadcast(nl, skb, 0, TINY_TY_GRP, GFP_ATOMIC);
  49
  50         return 0;
  51
  52 nlmsg_failure:
  53         kfree_skb(skb);
  54         return -EINVAL;
  55 }
  56
  57 static void netlink_tiny_timer_handler(unsigned long data)
  58 {
  59         int err;
  60
  61         UNUSED(data);
  62
  63         err = send_message("Hello, world!");
  64         if (err)
  65                 printk(KERN_ERR LOG_PREFIX "could not send message\n");
  66
  67         printk(LOG_PREFIX "message sent!");
  68 }
  69
  70 static void __init netlink_tiny_timer_init(void)
  71 {
  72         init_timer(&netlink_tiny_timer);
  73         netlink_tiny_timer.function = netlink_tiny_timer_handler;
  74         netlink_tiny_timer.expires = jiffies + NETLINK_TINY_DELAY;
  75         add_timer(&netlink_tiny_timer);
  76 }
  77
  78 static int __init netlink_tiny_tu_init(void)
  79 {
  80         nl = netlink_kernel_create(&init_net, NETLINK_TINY_TU, TINY_TY_GRP,
  81                                    NULL, NULL, THIS_MODULE);
  82         if (!nl) {
  83                 printk(KERN_ERR LOG_PREFIX "cannot create socket\n");
  84                 return -EINVAL;
  85         }
  86
  87         netlink_tiny_timer_init();
  88
  89         return 0;
  90 }
  91
  92 static void __exit netlink_tiny_tu_exit(void)
  93 {
  94         sock_release(nl->sk_socket);
  95 }
  96
  97 module_init(netlink_tiny_tu_init);
  98 module_exit(netlink_tiny_tu_exit);
  99
 100 MODULE_LICENSE("GPL");
 101 MODULE_AUTHOR("Luiz Capitulino <lcapitulino@gmail.com>");
 102 MODULE_DESCRIPTION("Netlink (to user-space) example module");