IOCTL returns No such device

I have written a code to create and set the properties of VLAN interface. I am able to set the IP address, however the I am facing problem in setting the gateway address and reading the device flags. Please have a look at code and suggest what could be wrong.

I am getting error in the function generic_ioctrlcall.

/**
* Create socket function
*/
int create_socket() 
{

  int sockfd = 0;

  sockfd = socket(AF_INET, SOCK_DGRAM, 0);
  if(sockfd == -1){
    fprintf(stderr, "Could not get socket.\n");
    return -1;
  }

  return sockfd;

}

/**
* Generic ioctrlcall to reduce code size
*/
int generic_ioctrlcall(int sockfd, u_long *flags, struct ifreq *ifr) {

  if (ioctl(sockfd, (long unsigned int)flags, &ifr) < 0) {
    fprintf(stderr, "ioctl: %s\n", (char *)flags);
    return -1;
  }
  return 1;
}

/**
* Set route with metric 100
*/
int set_route(int sockfd, char *gateway_addr,  struct sockaddr_in *addr) {

  struct rtentry route;
  int err = 0;
  memset(&route, 0, sizeof(route));
  addr = (struct sockaddr_in*) &route.rt_gateway;
  addr->sin_family = AF_INET;
  addr->sin_addr.s_addr = inet_addr(gateway_addr);
  addr = (struct sockaddr_in*) &route.rt_dst;
  addr->sin_family = AF_INET;
  addr->sin_addr.s_addr = inet_addr("0.0.0.0");
  addr = (struct sockaddr_in*) &route.rt_genmask;
  addr->sin_family = AF_INET;
  addr->sin_addr.s_addr = inet_addr("0.0.0.0");
  route.rt_flags = RTF_UP | RTF_GATEWAY;
  route.rt_metric = 100;

  if ((err = ioctl(sockfd, SIOCADDRT, &route)) < 0) {
    fprintf(stderr, "ioctl: %s\n", (char *)flags);
    return -1;
  }
  return 1;

}

/**
* Set ip function
*/
int set_ip(char *iface_name, char *ip_addr, char *gateway_addr)
{
  if(!iface_name)
    return -1;

  struct ifreq ifr;
  struct sockaddr_in sin;
  int sockfd = create_socket();

  sin.sin_family = AF_INET;

  // Convert IP from numbers and dots to binary notation
  inet_aton(ip_addr,&sin.sin_addr.s_addr);

  /* get interface name */
  strncpy(ifr.ifr_name, iface_name, IFNAMSIZ);

  /* Read interface flags */
  generic_ioctrlcall(sockfd, (u_long *)"SIOCGIFFLAGS", &ifr);

  /*
  * Expected in <net/if.h> according to
  * "UNIX Network Programming".
  */
  #ifdef ifr_flags
  # define IRFFLAGS       ifr_flags
  #else   /* Present on kFreeBSD */
  # define IRFFLAGS       ifr_flagshigh
  #endif

  // If interface is down, bring it up
  if (ifr.IRFFLAGS | ~(IFF_UP)) {
    ifr.IRFFLAGS |= IFF_UP;
    generic_ioctrlcall(sockfd, (u_long *)"SIOCSIFFLAGS", &ifr);
  }

  // Set route
  set_route(sockfd, gateway_addr,  &sin);

  memcpy(&ifr.ifr_addr, &sin, sizeof(struct sockaddr)); 

  // Set interface address
  if (ioctl(sockfd, SIOCSIFADDR, &ifr) < 0) {
    fprintf(stderr, "Cannot set IP address. ");
    perror(ifr.ifr_name);
    return -1;
  }             
  #undef IRFFLAGS

  return 0;
}

Solution

Many problems here. The proximate cause of your difficulty is that the second argument to ioctl is a long integer, not a pointer to a character string.

generic_ioctrlcall(sockfd, (u_long *)"SIOCGIFFLAGS", &ifr);

does not create a pointer to the integer value of SIOCGIFFLAGS which is presumably what you intended. Other issues:

(1) Since ioctl takes a long integer as the second argument, why did you want to pass a pointer to an integer? Just pass the integer as argument.

(2) If you do wish to pass a pointer to an integer, you would need to do something like this:

u_long ioctl_arg = SIOCGIFFLAGS;
generic_ioctrlcall(sockfd, &ioctl_arg, &ifr);

(3) You cannot convert a pointed-to integer to an integer simply by casting it. You need to dereference the pointer. That is:

Change:
    if (ioctl(sockfd, (long unsigned int)flags, &ifr) < 0) {
to:
    if (ioctl(sockfd, *flags, &ifr) < 0) {

(4) on an ioctl failure, you should be printing out errno (or, better yet, its text translation) after the failure in order to figure out what went wrong:

if (ioctl(sockfd, *flags, &ifr) < 0) {
    fprintf(stderr, "ioctl: flags %ld errno %d/%s\n", *flags, errno, strerror(errno));

And by the way, it seems unlikely that the errno from any of your generic_ioctl calls would be ENODEV (No such device) -- as your title implies. It seems much more likely that the errno would be EINVAL since the chances of your pointer-to-character-string forming a valid ioctl integer argument are very slim.