setsockopt() get EBADF in mmaped netlink - sockets

Question

Im trying to use memory map I/O netlink to transfer bulk packets from kernel to user space, and I followed a guide document from Patrick McHardy 1. However, when I try to setup the shared ring buffer in user space by using:
setsockopt(sock_fd, SOL_NETLINK, NETLINK_RX_RING, &req, sizeof(req));
setsockopt(sock_fd, SOL_NETLINK, NETLINK_TX_RING, &req, sizeof(req));
Both functions return -1, and the errno is 1, which means the descriptor is invalid. Im confused about that because I also referred to many other source codes and they can setup the ring successfully.
My code is almost the same as Patrick's 1:
int sock_fd = -1;
sock_fd = socket(PF_NETLINK, SOCK_RAW, NETLINK_DECODE);
if (sock_fd < 0)
return -1;
bind(sock_fd, (struct sockaddr *)&src_addr, sizeof(src_addr));
/* init the mmap buffer */
unsigned int block_size = 16 * getpagesize();
struct nl_mmap_req req = {
.nm_block_size = block_size,
.nm_block_nr = 64,
.nm_frame_size = 16384,
.nm_frame_nr = 64 * block_size / 16384,
};
/* Configure ring parameters */
if (setsockopt(sock_fd, SOL_NETLINK, NETLINK_RX_RING, &req, sizeof(req)) < 0){
if(errno > 0)
printf("%d\n", errno);
}
if (setsockopt(sock_fd, SOL_NETLINK, NETLINK_TX_RING, &req, sizeof(req)) < 0){
if(errno > 0)
printf("%d", errno);
exit(1);
}
This code is built in Ubuntu 14.04, and kernel version is 3.13.0-74-generic.
Anyone idea about it? Thanks a lot.