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

   1 /*
   2  * tk-test: send a netlink message to the kernel w/o any payload.
   3  *
   4  * This requires the netlink-tiny-tk kernel module. It will read
   5  * the netlink message and print this process' ID in the kernel
   6  * ring buffer.
   7  *
   8  * Luiz Fernando N. Capitulino
   9  * <lcapitulino@gmail.com>
  10  */
  11 #include <stdio.h>
  12 #include <string.h>
  13 #include <stdlib.h>
  14 #include <unistd.h>
  15 #include <sys/types.h>
  16 #include <sys/socket.h>
  17 #include <linux/netlink.h>
  18
  19 #define NETLINK_TEST 20 // from netlink-tiny-tk.c
  20
  21 int main(void)
  22 {
  23         ssize_t bytes;
  24         int err, sock_fd;
  25         struct iovec iov;
  26         struct msghdr msg;
  27         struct nlmsghdr nlhdr;
  28         struct sockaddr_nl sa, nladdr;
  29
  30         /*
  31          * Create the netlink socket and bind it to a port
  32          * (which is our pid).
  33          *
  34          * Data structure used: struct sockaddr_nl sa
  35          */
  36
  37         sock_fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_TEST);
  38         if (sock_fd < 0) {
  39                 perror("socket()");
  40                 exit(1);
  41         }
  42
  43         memset(&sa, 0, sizeof(sa));
  44         sa.nl_family = AF_NETLINK;
  45         sa.nl_pid = getpid(); // self pid
  46
  47         err = bind(sock_fd, (struct sockaddr *) &sa, sizeof(sa));
  48         if (err) {
  49                 perror("bind()");
  50                 exit(1);
  51         }
  52
  53         /*
  54          * Send a netlink message to the kernel
  55          *
  56          * Fill the required structures and send a netlink
  57          * message to the kernel using sendmsg().
  58          *
  59          * Data structures used:
  60          *
  61          *   struct nlmsghdr nlhdr: netlink header
  62          *   struct iovec iov: payload (?)
  63          *   struct msghdr msg: required by sendmsg()
  64          */
  65
  66         memset(&nlhdr, 0, sizeof(nlhdr));
  67         nlhdr.nlmsg_len = sizeof(nlhdr);
  68         nlhdr.nlmsg_pid = getpid();
  69
  70         iov.iov_base = (void *) &nlhdr;
  71         iov.iov_len  = nlhdr.nlmsg_len;
  72
  73         memset(&nladdr, 0, sizeof(nladdr));
  74         nladdr.nl_family = AF_NETLINK;
  75
  76         memset(&msg, 0, sizeof(msg));
  77         msg.msg_name = (void *) &(nladdr);
  78         msg.msg_namelen = sizeof(nladdr);
  79         msg.msg_iov = &iov;
  80         msg.msg_iovlen = 1;
  81
  82         bytes = sendmsg(sock_fd, &msg, 0);
  83         if (bytes < 0) {
  84                 perror("sendmsg()");
  85                 exit(1);
  86         }
  87
  88         close(sock_fd);
  89
  90         printf("Message sent! My pid: %d\n", getpid());
  91
  92         return 0;
  93 }