linux-kernel/netlink/echo/netlink-echo.c

   1 /*
   2  * netlink-echo: Receives a string from user-space and echoes it back.
   3  * It's just yet another netlink usage example.
   4  *
   5  * FIXME: I don't whether it's ok to call netlink_unicast() from
   6  * netlink_echo_input().
   7  *
   8  * Luiz Fernando N. Capitulino
   9  * <lcapitulino@gmail.com>
  10  */
  11 #include <linux/kernel.h>
  12 #include <linux/module.h>
  13 #include <linux/init.h>
  14 #include <linux/string.h>
  15 #include <linux/mutex.h>
  16 #include <linux/net.h>
  17 #include <linux/skbuff.h>
  18 #include <linux/netlink.h>
  19 #include <net/sock.h>
  20
  21 #define NETLINK_ECHO 20   // always check whether this is safe
  22
  23 static struct sock *nl;
  24 static DEFINE_MUTEX(netlink_echo_mutex);
  25
  26 static void send_packet(int pid, const char *message)
  27 {
  28         size_t len;
  29         struct sk_buff *skb;
  30         struct nlmsghdr *nlh;
  31
  32         len = NLMSG_SPACE(strlen(message) + 1);
  33         skb = alloc_skb(len, GFP_ATOMIC);
  34         if (!skb) {
  35                 printk(KERN_ERR "[netlink_echo]: cannot allocate memory\n");
  36                 return;
  37         }
  38
  39         nlh = NLMSG_PUT(skb, 0, 0, 0, len - sizeof(*nlh));
  40         strcpy(NLMSG_DATA(nlh), message);
  41
  42         NETLINK_CB(skb).pid = 0;      /* from kernel */
  43         NETLINK_CB(skb).dst_group = 0;  /* unicast */
  44         netlink_unicast(nl, skb, pid, GFP_ATOMIC);
  45
  46         return;
  47
  48 nlmsg_failure:
  49         kfree_skb(skb);
  50 }
  51
  52 static void netlink_echo_input(struct sk_buff *skb)
  53 {
  54         char *msg;
  55         struct nlmsghdr *nlh;
  56
  57         mutex_lock(&netlink_echo_mutex);
  58
  59         if (skb->len < sizeof(*nlh))
  60                 return;
  61
  62         nlh = nlmsg_hdr(skb);
  63         msg = NLMSG_DATA(nlh);
  64         send_packet(nlh->nlmsg_pid, msg);
  65
  66         mutex_unlock(&netlink_echo_mutex);
  67 }
  68
  69 static int __init netlink_echo_init(void)
  70 {
  71         nl = netlink_kernel_create(&init_net, NETLINK_ECHO, 0,
  72                                    netlink_echo_input, NULL, THIS_MODULE);
  73         if (!nl) {
  74                 printk(KERN_ERR "[netlink_echo]: cannot create socket\n");
  75                 return -EINVAL;
  76         }
  77
  78         return 0;
  79 }
  80
  81 static void __exit netlink_echo_exit(void)
  82 {
  83         sock_release(nl->sk_socket);
  84 }
  85
  86 module_init(netlink_echo_init);
  87 module_exit(netlink_echo_exit);
  88
  89 MODULE_LICENSE("GPL");
  90 MODULE_AUTHOR("Luiz Capitulino <lcapitulino@gmail.com>");
  91 MODULE_DESCRIPTION("Netlink example module");