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

   1 /*
   2  * tu-test: Read a netlink message from the kernel.
   3  *
   4  * This program requires the netlink-tiny-tu kernel module. It sends a
   5  * netlink message to user-space.
   6  *
   7  * Luiz Fernando N. Capitulino
   8  * <lcapitulino@gmail.com>
   9  */
  10 #include <stdio.h>
  11 #include <string.h>
  12 #include <stdlib.h>
  13 #include <unistd.h>
  14 #include <sys/types.h>
  15 #include <sys/socket.h>
  16 #include <linux/netlink.h>
  17
  18 #define MSG_MAX_SIZE    512
  19 #define NETLINK_TINY_TU 20 // from netlink-tiny-tu.c
  20
  21 /* create_socket(): Create a netlink socket and bind it.
  22  * Return a file-descriptor on success, -1 otherwise. */
  23 static int create_socket(void)
  24 {
  25         int err, fd;
  26         struct sockaddr_nl sa;
  27
  28         fd = socket(PF_NETLINK, SOCK_RAW, NETLINK_TINY_TU);
  29         if (fd < 0)
  30                 return -1;
  31
  32         memset(&sa, 0, sizeof(sa));
  33         sa.nl_family = AF_NETLINK;
  34         sa.nl_pid = getpid(); // self pid
  35         sa.nl_groups = 1;     // group
  36
  37         err = bind(fd, (struct sockaddr *) &sa, sizeof(sa));
  38         if (err)
  39                 return -1;
  40
  41         return fd;
  42 }
  43
  44 /* read_message(): Read a netlink message from 'sock_fd'
  45  * and return it. */
  46 static struct nlmsghdr *read_message(int sock_fd, size_t len)
  47 {
  48         ssize_t bytes;
  49         struct iovec iov;
  50         struct msghdr msg;
  51         struct nlmsghdr *nlhdr;
  52         struct sockaddr_nl nladdr;
  53
  54         len = NLMSG_SPACE(len);
  55         nlhdr = malloc(len);
  56         if (!nlhdr)
  57                 return NULL;
  58
  59         memset(nlhdr, 0, len);
  60         iov.iov_base = (void *) nlhdr;
  61         iov.iov_len  = len;
  62
  63         memset(&nladdr, 0, sizeof(nladdr));
  64
  65         memset(&msg, 0, sizeof(msg));
  66         msg.msg_name = (void *) &(nladdr);
  67         msg.msg_namelen = sizeof(nladdr);
  68         msg.msg_iov = &iov;
  69         msg.msg_iovlen = 1;
  70
  71         bytes = recvmsg(sock_fd, &msg, 0);
  72         if (bytes < 0) {
  73                 free(nlhdr);
  74                 return NULL;
  75         }
  76
  77         return nlhdr;
  78 }
  79
  80 int main(int argc, char *argv[])
  81 {
  82         int sock_fd;
  83         struct nlmsghdr *msg;
  84
  85         sock_fd = create_socket();
  86         if (sock_fd < 0) {
  87                 perror("create_socket()");
  88                 exit(1);
  89         }
  90
  91         msg = read_message(sock_fd, MSG_MAX_SIZE);
  92         if (!msg) {
  93                 perror("read_message()");
  94                 exit(1);
  95         }
  96
  97         printf("%s\n", (char *) NLMSG_DATA(msg));
  98
  99         free(msg);
 100         close(sock_fd);
 101
 102         return 0;
 103 }