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

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Date:	Tue, 07 Apr 2009 16:04:57 +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 14:56 +0200, Johannes Berg wrote:
> On Tue, 2009-04-07 at 15:51 +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.
> 
> Can't imagine it did, maybe it just dropped the request though without
> indicating an error.
Very likely.

> 
> > > > 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)?
> 
> Nothing. Wext sucks, news at 11, yadda.
Thanks.
Everything understood.


Best regards,
	Maxim Levitsky

> 
> johannes

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