问题
I am sending single SSID and frequency to libnl for scanning, but i got multiple scan result along with my requested SSID and frequency,But i need single scan result (only for requested SSID), how to achieve this. Kindly help me , i am sending my code also.This code will run.
Compile: gcc -g -o scan scantesthandler.c -L /usr/lib/i386-linux-gnu/libnl.so -lnl
Run with debug log: NLCB=debug ./scan
#include<assert.h>
#include<errno.h>
#include<ifaddrs.h>
#include<netdb.h>
#include<stddef.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#include <sys/socket.h>
#include <asm/types.h>
#include <linux/rtnetlink.h>
#include <netlink/netlink.h>
#include <netlink/msg.h>
#include <netlink/cache.h>
#include <netlink/socket.h>
#include <netlink/genl/genl.h>
#include <netlink/genl/ctrl.h>
#include <stdlib.h>
#include <netlink/genl/genl.h>
#include <netlink/genl/ctrl.h>
#include <netlink/route/link.h>
#include <linux/nl80211.h>
static int expectedId;
static int ifIndex;
struct wpa_scan_res
{
unsigned char bssid[6];
int freq;
};
static int error_handler(struct sockaddr_nl *nla, struct nlmsgerr *err, void *arg)
{
int *ret = arg;
*ret = err->error;
return NL_SKIP;
}
static int finish_handler(struct nl_msg *msg, void *arg)
{
int *ret = arg;
*ret = 0;
return NL_SKIP;
}
static int ack_handler(struct nl_msg *msg, void *arg)
{
int *err = arg;
*err = 0;
return NL_STOP;
}
static int bss_info_handler(struct nl_msg *msg, void *arg)
{
printf("\nFunction: %s, Line: %d\n",__FUNCTION__,__LINE__);
struct nlattr *tb[NL80211_ATTR_MAX + 1];
struct genlmsghdr *gnlh = nlmsg_data(nlmsg_hdr(msg));
struct nlattr *bss[NL80211_BSS_MAX + 1];
static struct nla_policy bss_policy[NL80211_BSS_MAX + 1] = {
[NL80211_BSS_BSSID] = { .type = NLA_UNSPEC },
[NL80211_BSS_FREQUENCY] = { .type = NLA_U32 },
[NL80211_BSS_TSF] = { .type = NLA_U64 },
[NL80211_BSS_BEACON_INTERVAL] = { .type = NLA_U16 },
[NL80211_BSS_CAPABILITY] = { .type = NLA_U16 },
[NL80211_BSS_INFORMATION_ELEMENTS] = { .type = NLA_UNSPEC },
[NL80211_BSS_SIGNAL_MBM] = { .type = NLA_U32 },
[NL80211_BSS_SIGNAL_UNSPEC] = { .type = NLA_U8 },
[NL80211_BSS_STATUS] = { .type = NLA_U32 },
[NL80211_BSS_SEEN_MS_AGO] = { .type = NLA_U32 },
[NL80211_BSS_BEACON_IES] = { .type = NLA_UNSPEC },
};
struct wpa_scan_res *r = NULL;
r = (struct wpa_scan_res*)malloc(sizeof(struct wpa_scan_res));
nla_parse(tb, NL80211_ATTR_MAX, genlmsg_attrdata(gnlh, 0),
genlmsg_attrlen(gnlh, 0), NULL);
if (!tb[NL80211_ATTR_BSS])
return NL_SKIP;
if (nla_parse_nested(bss, NL80211_BSS_MAX, tb[NL80211_ATTR_BSS],
bss_policy))
return NL_SKIP;
if (bss[NL80211_BSS_BSSID])
memcpy(r->bssid, nla_data(bss[NL80211_BSS_BSSID]),6);
if (bss[NL80211_BSS_FREQUENCY])
r->freq = nla_get_u32(bss[NL80211_BSS_FREQUENCY]);
printf("\nFrequency: %d ,BSSID: %2x:%2x:%2x:%2x:%2x:%2x",r->freq,r->bssid[0],r->bssid[1],r->bssid[2],r->bssid[3],r->bssid[4],r->bssid[5]);
return NL_SKIP;
}
static struct nl_msg* nl80211_scan_common(uint8_t cmd, int expectedId)
{
const char* ssid = "amitssid";
int ret;
struct nl_msg *msg;
int err;
size_t i;
int flags = 0,ifIndex;
msg = nlmsg_alloc();
if (!msg)
return NULL;
// setup the message
if(NULL==genlmsg_put(msg, 0, 0, expectedId, 0, flags, cmd, 0))
{
printf("\nError return genlMsg_put\n");
}
else
{
printf("\nSuccess genlMsg_put\n");
}
ifIndex = if_nametoindex("wlan1");
if(nla_put_u32(msg, NL80211_ATTR_IFINDEX, ifIndex) < 0)
{
goto fail;
}
struct nl_msg *ssids = nlmsg_alloc();
if(nla_put(ssids, 1,strlen(ssid) ,ssid) <0)
{
nlmsg_free(ssids);
goto fail;
}
err = nla_put_nested(msg, NL80211_ATTR_SCAN_SSIDS,ssids);
nlmsg_free(ssids);
if (err < 0)
goto fail;
struct nl_msg *freqs = nlmsg_alloc();
if( nla_put_u32(freqs,1 ,2437) < 0) //amitssid
{
printf("\nnla_put_fail\n");
goto fail;
}
else
{
printf("\nnla_put_u32 pass\n");
}
//add message attributes
if(nla_put_nested(msg, NL80211_FREQUENCY_ATTR_FREQ,freqs) < 0)
{
printf("\nnla_put_nested failing:\n");
}
else
{
printf("\nnla_put_nested pass\n");
}
nlmsg_free(freqs);
if (err < 0)
goto fail;
return msg;
nla_put_failure:
printf("\nnla_put_failure\n");
nlmsg_free(msg);
return NULL;
fail:
nlmsg_free(msg);
return NULL;
}
int main(int argc, char** argv)
{
struct nl_msg *msg= NULL;
int ret = -1;
struct nl_cb *cb = NULL;
int err = -ENOMEM;
int returnvalue,getret;
int ifIndex, callbackret=-1;
struct nl_sock* sk = (void*)nl_handle_alloc();
if(sk == NULL)
{
printf("\nmemory error\n");
return;
}
cb = nl_cb_alloc(NL_CB_CUSTOM);
if(cb == NULL)
{
printf("\nfailed to allocate netlink callback\n");
}
enum nl80211_commands cmd;
if(genl_connect((void*)sk))
{
printf("\nConnected failed\n");
return;
}
//find the nl80211 driverID
expectedId = genl_ctrl_resolve((void*)sk, "nl80211");
if(expectedId < 0)
{
printf("\nnegative error code returned\n");
return;
}
else
{
printf("\ngenl_ctrl_resolve returned:%d\n",expectedId);
}
msg = nl80211_scan_common(NL80211_CMD_TRIGGER_SCAN, expectedId);
if (!msg)
{
printf("\nmsgbal:\n");
return -1;
}
err = nl_send_auto_complete((void*)sk, msg);
if (err < 0)
goto out;
else
{
printf("\nSent successfully\n");
}
err = 1;
nl_cb_err(cb,NL_CB_CUSTOM,error_handler,&err);
nl_cb_set(cb,NL_CB_FINISH,NL_CB_CUSTOM,finish_handler,&err);
nl_cb_set(cb,NL_CB_ACK,NL_CB_CUSTOM,ack_handler,&err);
callbackret = nl_cb_set(cb,NL_CB_VALID,NL_CB_CUSTOM,bss_info_handler,&err);
if(callbackret < 0)
{
printf("\n*************CallbackRet failed:***************** %d\n",callbackret);
}
else
{
printf("\n*************CallbackRet pass:***************** %d\n",callbackret);
}
returnvalue=nl_recvmsgs((void*)sk,cb);
printf("\n returnval:%d\n",returnvalue);
nlmsg_free(msg);
msg = NULL;
msg = nlmsg_alloc();
if (!msg)
return -1;
if(NULL==genlmsg_put(msg, 0, 0, expectedId, 0, NLM_F_DUMP, NL80211_CMD_GET_SCAN, 0))
{
printf("\nError return genlMsg_put\n");
}
else
{
printf("\nSuccess genlMsg_put\n");
}
ifIndex = if_nametoindex("wlan1");
printf("\nGet Scaninterface returned :%d\n",ifIndex);
nla_put_u32(msg,NL80211_ATTR_IFINDEX,ifIndex);
err = nl_send_auto_complete((void*)sk,msg);
if(err < 0) goto out;
err = 1;
getret= nl_recvmsgs((void*)sk,cb);
printf("\nGt Scan resultreturn:%d\n",getret);
out:
nlmsg_free(msg);
return err;
nla_put_failure:
printf("\nnla_put_failure\n");
nlmsg_free(msg);
return err;
}
You can just copy and paste this code on your system and run it.
回答1:
As far as I know (and have seen) the scan command and result is dependent upon the vendor's device driver. One thing for certain there is no option to scan for a specific ssid; instead what you can do is to get all the scan result and loop through to check whether the ssid is in the list or not (wpa_supplicant uses this mechanism to match network configuration with scan result).
Now for the frequency, it should be possible to scan only a certain channel if the device driver has that functionality. But generally scan command scans all channel and returns the SSID (think your network-manager; it shows all the available SSID found for a scan command. which is essentially posted by device driver via cfg80211).
来源：https://stackoverflow.com/questions/23760780/how-to-send-single-channel-scan-request-to-libnl-and-receive-single-channel-sca