Subject: Re: [PATCH RFC] mac80211: Filter scan results
From: Marcel Holtmann <holtmann@linux.intel.com>
To: Johannes Berg <johannes@sipsolutions.net>
Cc: Samuel Ortiz <samuel@sortiz.org>,
	John Linville <linville@tuxdriver.com>,
	Reinette Chatre <reinette.chatre@intel.com>,
	linux-wireless@vger.kernel.org
In-Reply-To: <1233760201.3992.20.camel@johannes.local>
References: <20090204150857.GA5069@sortiz.org>
	 (sfid-20090204_160640_465532_8378EED5)  <1233760201.3992.20.camel@johannes.local>
Content-Type: text/plain
Date: Thu, 05 Feb 2009 00:18:16 +0100
Message-Id: <1233789496.5559.10.camel@californication> (sfid-20090205_001826_760057_B8FFA6E5)
Mime-Version: 1.0
Sender: linux-wireless-owner@vger.kernel.org

Hi Johannes,

> > In very dense environment, the scan result buffer can get really large, mostly
> > due to the addition of proprietary IEs. iwlist fails, typically warning about:
> > "print_scanning_info: Allocation failed". wpa_supplicant fails as well, after
> > reallocating the scan result buffer several times, up to 132 Kbytes:
> > 	[snip]
> > 	Scan results did not fit - trying larger buffer (131072 bytes)
> > 	ioctl[SIOCGIWSCAN]: Argument list too long
> > 
> > By adding a mac80211 module parameter, we can filter the scan results and keep
> > only the ones userspace currently worries about, i.e. WPA1, WPA2, WMM and WPS.
> > 
> > To activate this feature, 1 has to be written to
> > /sys/module/mac80211/parameters/ieee80211_scan_ie_filter
> 
> Module parameter, hard-coded filter, just to work around wext crap. Eww.
> NACK.

we are perfectly aware that this is ugly and trust me, that nobody of us
wants to do it. However we do have these setups and they happen in real
life. I have been in a couple of locations where I ran into this problem
and in that cases there is no way for me to establish any kind of WiFi
connection at all, because the buffers are just too small. And that is
with a laptop. Then just think about a mobile phone running mac80211
where the memory is limited.

So WEXT is crap and everybody agrees, but until we can use cfg80211 for
scanning, we need something to make this work. So if this patch is not
acceptable, then do we get scanning support via cfg80211 for 2.6.30? You
were always marking your patches as development/RFC.

> Go for
> http://johannes.sipsolutions.net/patches/kernel/all/LATEST/028-cfg80211-scan.patch

Return a 404 btw.

Regards

Marcel