Assign ipv6 address using ioctl - networking

Question

I'm trying to assign an IPv6 address to an interface using ioctl, but in vain. Here's the code I used:
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stddef.h>
#include <net/if.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <linux/sockios.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#define IFNAME "eth1"
#define HOST "fec2::22"
#define ifreq_offsetof(x) offsetof(struct ifreq, x)
int main(int argc, char **argv) {
struct ifreq ifr;
struct sockaddr_in6 sai;
int sockfd; /* socket fd we use to manipulate stuff with */
int selector;
unsigned char mask;
char *p;
/* Create a channel to the NET kernel. */
sockfd = socket(AF_INET6, SOCK_DGRAM, 0);
if (sockfd == -1) {
printf("Bad fd\n");
return -1;
}
/* get interface name */
strncpy(ifr.ifr_name, IFNAME, IFNAMSIZ);
memset(&sai, 0, sizeof(struct sockaddr));
sai.sin6_family = AF_INET6;
sai.sin6_port = 0;
//if(inet_aton(HOST, &sai.sin_addr.s_addr) == 0) {
if(inet_pton(AF_INET6, HOST, (void *)&sai.sin6_addr) <= 0) {
//&((struct sockaddr_in*)&sa)->sin_addr
printf("Bad address\n");
return -1;
}
p = (char *) &sai;
memcpy( (((char *)&ifr + ifreq_offsetof(ifr_addr) )),
p, sizeof(struct sockaddr));
int ret = ioctl(sockfd, SIOCSIFADDR, &ifr);
printf("ret: %d\terrno: %d\n", ret, errno);
ioctl(sockfd, SIOCGIFFLAGS, &ifr);
printf("ret: %d\terrno: %d\n", ret, errno);
ifr.ifr_flags |= IFF_UP | IFF_RUNNING;
// ifr.ifr_flags &= ~selector; // unset something
ioctl(sockfd, SIOCSIFFLAGS, &ifr);
printf("ret: %d\terrno: %d\n", ret, errno);
close(sockfd);
return 0;
}
The ioctl calls fail saying ENODEV. When the family of the socket is changed to sockfd = socket(AF_INET, SOCK_DGRAM, 0);, the calls fail again saying EINVAL.
I was able to assign an IPv4 address to the interface with the above code by using
sockaddr_in in lieu of sockaddr_in6.
Is it not possible to assign IPv6 address using ioctl?

Answer 1

Drawing inspiration from the linux implementation of 'ifconfig' command, I was able to set the IPv6 address on an interface. Here's the code for it:
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stddef.h>
#include <net/if.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <linux/sockios.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#if __GLIBC__ >=2 && __GLIBC_MINOR >= 1
#include <netpacket/packet.h>
#include <net/ethernet.h>
#else
#include <asm/types.h>
#include <linux/if_ether.h>
#endif
#define IFNAME "eth0"
#define HOST "fec2::22"
#define ifreq_offsetof(x) offsetof(struct ifreq, x)
struct in6_ifreq {
struct in6_addr ifr6_addr;
__u32 ifr6_prefixlen;
unsigned int ifr6_ifindex;
};
int main(int argc, char **argv) {
struct ifreq ifr;
struct sockaddr_in6 sai;
int sockfd;
struct in6_ifreq ifr6;
sockfd = socket(AF_INET6, SOCK_DGRAM, IPPROTO_IP);
if (sockfd == -1) {
printf("Bad fd\n");
return -1;
}
/* get interface name */
strncpy(ifr.ifr_name, IFNAME, IFNAMSIZ);
memset(&sai, 0, sizeof(struct sockaddr));
sai.sin6_family = AF_INET6;
sai.sin6_port = 0;
if(inet_pton(AF_INET6, HOST, (void *)&sai.sin6_addr) <= 0) {
printf("Bad address\n");
return -1;
}
memcpy((char *) &ifr6.ifr6_addr, (char *) &sai.sin6_addr,
sizeof(struct in6_addr));
if (ioctl(sockfd, SIOGIFINDEX, &ifr) < 0) {
perror("SIOGIFINDEX");
}
ifr6.ifr6_ifindex = ifr.ifr_ifindex;
ifr6.ifr6_prefixlen = 64;
if (ioctl(sockfd, SIOCSIFADDR, &ifr6) < 0) {
perror("SIOCSIFADDR");
}
ifr.ifr_flags |= IFF_UP | IFF_RUNNING;
int ret = ioctl(sockfd, SIOCSIFFLAGS, &ifr);
printf("ret: %d\terrno: %d\n", ret, errno);
close(sockfd);
return 0;
}

Answer 2

Based off of #maddy's answer I made a more compact version that is a little easier to adapt. The trick is the struct in6_ifreq structure that has to be passed to the ioctl.
#include <stdint.h>
#include <string.h>
#include <sys/ioctl.h>
#include <net/if.h>
#include <netinet/in.h>
#define IFNAME "eth0"
#define HOST "2001::22"
struct in6_ifreq {
struct in6_addr addr;
uint32_t prefixlen;
unsigned int ifindex;
};
int main(int argc, char **argv) {
struct ifreq ifr;
struct in6_ifreq ifr6;
int sockfd;
int err;
// Create IPv6 socket to perform the ioctl operations on
sockfd = socket(AF_INET6, SOCK_DGRAM, IPPROTO_IP);
// Copy the interface name to the ifreq struct
strncpy(ifr.ifr_name, IFNAME, IFNAMSIZ);
// Get the ifrindex of the interface
err = ioctl(sockfd, SIOGIFINDEX, &ifr);
// Prepare the in6_ifreq struct and set the address to the interface
inet_pton(AF_INET6, HOST, &ifr6.addr);
ifr6.ifindex = ifr.ifr_ifindex;
ifr6.prefixlen = 64;
err = ioctl(sockfd, SIOCSIFADDR, &ifr6);
close(sockfd);
return 0;
}
I left off all error checking for readability but the commands should be checked for errors.