Date: Tue, 11 Feb 2014 17:33:29 +1100
From: James Cameron <quozl@laptop.org>
To: linux-wireless@vger.kernel.org
Subject: libertas: probe responses with zero length SSID cause scan result
 loss
Message-ID: <20140211063329.GO5487@us.netrek.org> (sfid-20140211_073348_895055_E1BA8EBF)
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Sender: linux-wireless-owner@vger.kernel.org

G'day,

I'd appreciate a sanity check, as I'm not sure what I am doing.

We saw for years that scan results for an OLPC XO-1 laptop would be
unreliable in large groups.  APs would not be easily found.  We
presumed other causes until recently.

Using monitor mode on another computer, and "iwlist eth0 scan" on the
XO-1, I found probe responses from an AP, and ACKs from the host to
the AP, but the output omitted the AP.

Further, the AP would be missing if there was a probe response from
another XO-1 running mesh, and an ACK from the host to that XO-1.

Enabling debugging, lbs_ret_scan was reporting "scan response: invalid
IE fmt" because the probe response had a zero length SSID IE.

Is a zero length SSID IE valid?  (We can't change the wireless firmware
at this stage.)

Background data and dmesg fragments:
http://dev.laptop.org/ticket/12757

Patch being tested (lacks signoff and any review):
http://dev.laptop.org/git/olpc-kernel/commit/?h=x86-3.3&id=e98f01abce522fb70a3852b23b62205244ef69b8

-- 
James Cameron
http://quozl.linux.org.au/