Program to collect survey details of WiFi interface using Netlink Protocol Library

/*
* main_survey.c
*
*  Created on: Nov 3, 2016
*      Author: k_mathews
*/


#include <netlink/netlink.h>
#include <netlink/socket.h>
#include <netlink/genl/genl.h>
#include <netlink/genl/ctrl.h>
#include <netlink/genl/family.h>
#include <net/if.h>
#include <linux/nl80211.h>

static int expectedId;

static int error_handler(struct sockaddr_nl *nla, struct nlmsgerr *err,
void *arg)
{
	printf("Error in callback\n");
	return 1;

}

static int nlCallback(struct nl_msg* msg, void* arg)
{
	printf("Callback Received\n");
	struct nlattr *tb[NL80211_ATTR_MAX + 1];
	struct genlmsghdr *gnlh = nlmsg_data(nlmsg_hdr(msg));
	struct nlattr *sinfo[NL80211_SURVEY_INFO_MAX + 1];
	char dev[20];

	static struct nla_policy survey_policy[NL80211_SURVEY_INFO_MAX + 1] = {
		[NL80211_SURVEY_INFO_FREQUENCY] = { .type = NLA_U32 },
		[NL80211_SURVEY_INFO_NOISE] = { .type = NLA_U8 },
	};

	nla_parse(tb, NL80211_ATTR_MAX, genlmsg_attrdata(gnlh, 0),
	genlmsg_attrlen(gnlh, 0), NULL);

	if_indextoname(nla_get_u32(tb[NL80211_ATTR_IFINDEX]), dev);
	printf("Survey data from %s\n", dev);

	if (!tb[NL80211_ATTR_SURVEY_INFO]) {
		fprintf(stderr, "survey data missing!\n");
		return NL_SKIP;
	}

	if (nla_parse_nested(sinfo, NL80211_SURVEY_INFO_MAX,
		tb[NL80211_ATTR_SURVEY_INFO],
		survey_policy)) {
			fprintf(stderr, "failed to parse nested attributes!\n");
			return NL_SKIP;
		}
	if (sinfo[NL80211_SURVEY_INFO_FREQUENCY])
	printf("\tfrequency:\t\t\t%u MHz%s\n",
	nla_get_u32(sinfo[NL80211_SURVEY_INFO_FREQUENCY]),
	sinfo[NL80211_SURVEY_INFO_IN_USE] ? " [in use]" : "");
	if (sinfo[NL80211_SURVEY_INFO_NOISE])
	printf("\tnoise:\t\t\t\t%d dBm\n",
	(int8_t)nla_get_u8(sinfo[NL80211_SURVEY_INFO_NOISE]));
	if (sinfo[NL80211_SURVEY_INFO_CHANNEL_TIME])
	printf("\tchannel active time:\t\t%llu ms\n",
	(unsigned long long)nla_get_u64(sinfo[NL80211_SURVEY_INFO_CHANNEL_TIME]));
	if (sinfo[NL80211_SURVEY_INFO_CHANNEL_TIME_BUSY])
	printf("\tchannel busy time:\t\t%llu ms\n",
	(unsigned long long)nla_get_u64(sinfo[NL80211_SURVEY_INFO_CHANNEL_TIME_BUSY]));
	if (sinfo[NL80211_SURVEY_INFO_CHANNEL_TIME_EXT_BUSY])
	printf("\textension channel busy time:\t%llu ms\n",
	(unsigned long long)nla_get_u64(sinfo[NL80211_SURVEY_INFO_CHANNEL_TIME_EXT_BUSY]));
	if (sinfo[NL80211_SURVEY_INFO_CHANNEL_TIME_RX])
	printf("\tchannel receive time:\t\t%llu ms\n",
	(unsigned long long)nla_get_u64(sinfo[NL80211_SURVEY_INFO_CHANNEL_TIME_RX]));
	if (sinfo[NL80211_SURVEY_INFO_CHANNEL_TIME_TX])
	printf("\tchannel transmit time:\t\t%llu ms\n",
	(unsigned long long)nla_get_u64(sinfo[NL80211_SURVEY_INFO_CHANNEL_TIME_TX]));
	return NL_SKIP;
}



int main(int argc, char** argv){
	int ret;

	//allocate socket
	struct nl_sock* sk = nl_socket_alloc();
	if (!sk) {
		printf("Failed to allocate netlink socket.\n");

	}
	/*
	* connect to generic netlink
	* genl_connect(sk); wiil bind the socket
	*
	*/
	if (genl_connect(sk)) {
		printf("Failed to connect to generic netlink.\n");
		goto out_handle_destroy;
	}


	//find the nl80211 driver ID
	expectedId = genl_ctrl_resolve(sk, "nl80211");

	// callback identifier
	struct nl_cb *cb = nl_cb_alloc(NL_CB_DEFAULT);

	//allocate a message
	struct nl_msg* msg = nlmsg_alloc();



	const enum nl80211_commands cmd = NL80211_CMD_GET_SURVEY;


	/*
	* Change the interface name here
	* */
	int ifIndex = if_nametoindex("mon0");

	/** setup the message
	* NLM_F_DUMP: Flag to dump the survey details
	***/
	genlmsg_put(msg, 0, 0, expectedId, 0, NLM_F_DUMP, cmd, 0);

	//add message attributes
	nla_put_u32(msg, NL80211_ATTR_IFINDEX, ifIndex);


	//
	/*attach a callback
	*				(another way to attach callback)
	* nl_socket_modify_cb(sk, NL_CB_VALID, NL_CB_CUSTOM,
	  nlCallback2, NULL);
	*/
	nl_socket_set_cb(sk,cb);
	nl_cb_set(cb, NL_CB_VALID, NL_CB_CUSTOM, nlCallback, NULL);
	nl_cb_err(cb, NL_CB_CUSTOM, error_handler, NULL);



	//send the messge (this frees it)
	ret = nl_send_auto_complete(sk, msg);
	//block for message to return
	nl_recvmsgs_default(sk);
	return 0;

	nla_put_failure:
	 nlmsg_free(msg);
	return 1;
	out_handle_destroy:
	 nl_socket_free(sk);
}