linux-kernel - Re: attempt to scan fails (device busy) if essid/ssid was changed recently

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Date:	Tue, 07 Apr 2009 15:51:29 +0300
From:	Maxim Levitsky <maximlevitsky@...il.com>
To:	Johannes Berg <johannes@...solutions.net>
Cc:	linux-wireless <linux-wireless@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: attempt to scan fails (device busy) if essid/ssid was changed
 recently

On Tue, 2009-04-07 at 10:18 +0200, Johannes Berg wrote:
> On Tue, 2009-04-07 at 03:00 +0300, Maxim Levitsky wrote:
> 
> > I noticed that always first attempt at scan fails when NM asks for scan.
> > I also noticed that this happens with quite recent kernels (I think
> > 2,6.28) didn't have this behavior.
> 
> I'm pretty sure it did.
I am sure that on older kernel there was no -EBUSY error returned to
userspace. It probably just stalled the client.


> 
> > Looking a bit deeper I discovered that each time NM disconnects from a
> > networks it sets random ssid/essid to the card (using wireless
> > extensions)
> 
> This forces a scan
> 
> > After that scan fails for some time.
> > 
> > as a NM free example you can run 
> > 
> > iwconfig wlan0 essid dummy
> > iwlist scan
> 
> and then this fails with EBUSY.
Thanks for explanation.
Since NM has its reasons to clear essid (to prevent unwanted
association), then what can be  done to prevent this (and still use
wireless extensions, since nl80211 support isn't yet mature)?


Best regards,
	Maxim Levitsky

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