[PATCH] cfg80211: allow scanning on specified frequencies when using wext-compatibility

[PATCH] cfg80211: allow scanning on specified frequencies when using wext-compatibility

[Holger Schurig]

Handles the case when SIOCSIWSCAN specified iw_scan_req.num_channels and
iw_scan_req.channels[].

Signed-off-by: Holger Schurig <hs4233@mail.mn-solutions.de>

Index: linux-wl/net/wireless/scan.c
===================================================================
--- linux-wl.orig/net/wireless/scan.c	2009-09-09 10:38:58.000000000 +0200
+++ linux-wl/net/wireless/scan.c	2009-09-09 11:59:39.000000000 +0200
@@ -607,6 +607,9 @@ int cfg80211_wext_siwscan(struct net_dev
 	if (!netif_running(dev))
 		return -ENETDOWN;
 
+	if (wrqu->data.length == sizeof(struct iw_scan_req))
+		wreq = (struct iw_scan_req *)extra;
+
 	rdev = cfg80211_get_dev_from_ifindex(dev_net(dev), dev->ifindex);
 
 	if (IS_ERR(rdev))
@@ -619,9 +622,14 @@ int cfg80211_wext_siwscan(struct net_dev
 
 	wiphy = &rdev->wiphy;
 
-	for (band = 0; band < IEEE80211_NUM_BANDS; band++)
-		if (wiphy->bands[band])
-			n_channels += wiphy->bands[band]->n_channels;
+	/* Determine number of channels, needed to allocate creq */
+	if (wreq && wreq->num_channels)
+		n_channels = wreq->num_channels;
+	else {
+		for (band = 0; band < IEEE80211_NUM_BANDS; band++)
+			if (wiphy->bands[band])
+				n_channels += wiphy->bands[band]->n_channels;
+	}
 
 	creq = kzalloc(sizeof(*creq) + sizeof(struct cfg80211_ssid) +
 		       n_channels * sizeof(void *),
@@ -638,22 +646,41 @@ int cfg80211_wext_siwscan(struct net_dev
 	creq->n_channels = n_channels;
 	creq->n_ssids = 1;
 
-	/* all channels */
+	/* translate "Scan on frequencies" request */
 	i = 0;
 	for (band = 0; band < IEEE80211_NUM_BANDS; band++) {
 		int j;
 		if (!wiphy->bands[band])
 			continue;
 		for (j = 0; j < wiphy->bands[band]->n_channels; j++) {
+
+			/* If we have a wireless request structure and the
+			 * wireless request specifies frequencies, then search
+			 * for the matching hardware channel.
+			 */
+			if (wreq && wreq->num_channels) {
+				int k;
+				int wiphy_freq = wiphy->bands[band]->channels[j].center_freq;
+				for (k = 0; k < wreq->num_channels; k++) {
+					int wext_freq = wreq->channel_list[k].m / 100000;
+					if (wext_freq == wiphy_freq)
+						goto wext_freq_found;
+				}
+				goto wext_freq_not_found;
+			}
+
+		wext_freq_found:
 			creq->channels[i] = &wiphy->bands[band]->channels[j];
 			i++;
+		wext_freq_not_found: ;
 		}
 	}
 
-	/* translate scan request */
-	if (wrqu->data.length == sizeof(struct iw_scan_req)) {
-		wreq = (struct iw_scan_req *)extra;
+	/* Set real number of channels specified in creq->channels[] */
+	creq->n_channels = i;
 
+	/* translate "Scan for SSID" request */
+	if (wreq) {
 		if (wrqu->data.flags & IW_SCAN_THIS_ESSID) {
 			if (wreq->essid_len > IEEE80211_MAX_SSID_LEN)
 				return -EINVAL;

Re: [PATCH] cfg80211: allow scanning on specified frequencies when using wext-compatibility

[Johannes Berg]

[-- Attachment #1: Type: text/plain, Size: 900 bytes --]

On Wed, 2009-09-09 at 13:09 +0200, Holger Schurig wrote:
> Handles the case when SIOCSIWSCAN specified iw_scan_req.num_channels and
> iw_scan_req.channels[].

> +
> +			/* If we have a wireless request structure and the
> +			 * wireless request specifies frequencies, then search
> +			 * for the matching hardware channel.
> +			 */
> +			if (wreq && wreq->num_channels) {
> +				int k;
> +				int wiphy_freq = wiphy->bands[band]->channels[j].center_freq;
> +				for (k = 0; k < wreq->num_channels; k++) {
> +					int wext_freq = wreq->channel_list[k].m / 100000;
> +					if (wext_freq == wiphy_freq)
> +						goto wext_freq_found;
> +				}
> +				goto wext_freq_not_found;

This is a bit weird -- this way you don't report errors if the user
specified frequencies that don't exist. Also, are you sure that it has
to be a frequency as opposed to a channel number?

johannes

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Re: [PATCH] cfg80211: allow scanning on specified frequencies when using wext-compatibility

[Holger Schurig]

> This is a bit weird -- this way you don't report errors if the
> user specified frequencies that don't exist.

Couldn't / shouldn't this done in user-space, e.g. after checking
IWRANGE.


> Also, are you sure that it has to be a frequency as opposed to
> a channel number?

I'm not totally sure, because there's nowhere any documentation
about the exact meanings of fields in "struct iw_freq". My patch
for wpa_supplicant's driver_wext.c only put's a frequency there:

+        req.channel_list[i].m = params->freqs[i] * 100000;
+        req.channel_list[i].e = 1;
+        req.channel_list[i].i = i;
+        req.channel_list[i].flags = 0;

But now that you bring this into my mind, I should have looked
at another consumer of "struct iw_freq", e.g. I should use
cfg80211_wext_freq() like cfg80211_wext_siwfreq() ?!?

I'll prepare some patch.

-- 
http://www.holgerschurig.de

Re: [PATCH] cfg80211: allow scanning on specified frequencies when using wext-compatibility

[Holger Schurig]

> This is a bit weird -- this way you don't report errors if the
> user specified frequencies that don't exist.

The old code did this:

Loop over all bands
   Loop over all channels
      Stick channel to scan request

I simply added this:

Loop over all bands
   Loop over all channels
      If scan-request hasn't this channel freq: continue
      Stick channel to scan request


Now, if I want to report an -EINVAL for every possibly invalid 
scan-request channel, I'd have to do this:


If scan-request has freqs:
   Loop over all scan-request freqs
      Loop over all bands
         Loop over all channels
            search for freq
   if found:
       Stick channel to scan request
   else:
       err = -EINVAL
else:
   Loop over all bands
      Loop over all channels
         Stick channel to scan request

This is considerable code-bloat for such a seldom-used function.


I'd rather do it like this:


Loop over all bands
   Loop over all channels
      If scan-request hasn't this channel freq: continue
      Stick channel to scan request
if no channels:
   err = -EINVAL

That's a compromise :-)

-- 
http://www.holgerschurig.de

Re: [PATCH] cfg80211: allow scanning on specified frequencies when using wext-compatibility

[Johannes Berg]

[-- Attachment #1: Type: text/plain, Size: 1074 bytes --]

On Fri, 2009-09-11 at 09:52 +0200, Holger Schurig wrote:

> Now, if I want to report an -EINVAL for every possibly invalid 
> scan-request channel, I'd have to do this:
> 
> 
> If scan-request has freqs:
>    Loop over all scan-request freqs
>       Loop over all bands
>          Loop over all channels
>             search for freq
>    if found:
>        Stick channel to scan request
>    else:
>        err = -EINVAL
> else:
>    Loop over all bands
>       Loop over all channels
>          Stick channel to scan request
> 
> This is considerable code-bloat for such a seldom-used function.

Doesn't seem that bad considering that the inner loop is already in an
existing function.

> I'd rather do it like this:
> 
> 
> Loop over all bands
>    Loop over all channels
>       If scan-request hasn't this channel freq: continue
>       Stick channel to scan request
> if no channels:
>    err = -EINVAL
> 
> That's a compromise :-)

I guess. I'd still prefer the other way, but it's wext, so I don't
really care :)

johannes


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