netdev - Re: rfkill vs. interface up

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Date:	Thu, 21 May 2009 11:39:49 -0400
From:	Dan Williams <dcbw@...hat.com>
To:	Johannes Berg <johannes@...solutions.net>
Cc:	linux-wireless <linux-wireless@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>
Subject: Re: rfkill vs. interface up

On Tue, 2009-05-19 at 14:32 +0200, Johannes Berg wrote:
> Hi,
> 
> More thoughts on rfkill ...
> 
> So we were thinking it would be sensible to just force interfaces down
> on rfkill, which is of course possible, and then reject attempts to set
> the interface UP while killed.
> 
> There's just one problem with that -- when you un-rfkill, does the
> kernel set interfaces UP again?
> 
> If not -- how would we possibly handle 'iwconfig .. txpower off'? We're
> mostly handling it like rfkill now afaict, but 'iwconfig .. txpower on'
> wouldn't be able to do anything properly.
> 
> If yes -- how do we know which interfaces to set UP? However we turn it,
> userspace can then not disable an interface regardless of rfkill state,
> which gets really confusing.
> 
> Therefore, I don't think we can simply set interfaces down on rfkill
> with the current scheme.
> 
> On the other hand, the interfaces really are dysfunctional in rfkill and
> we really need more integration.
> 
> 
> I'm happy to give up on 'iwconfig wlan0 txpower on/off' entirely, simply
> refuse supporting it (return -EINVAL if txpower.disabled) and then use
> the first scheme where rfkill forces the interface down but userspace is
> responsible for enabling it again. This is asymmetric, but I don't see
> what else to do.

That proposal sounds fine to me from a userspace perspective.  Sane
implementations don't assume the interface is IFF_UP when they configure
the device anyway (since it's not necessarily up at boot time or after
hibernate for example), and since you need a reconfigure after rfkill,
this seems reasonable.

You wouldn't have to give up on txpower either, you could simply map
'txpower off' to SW-rfkill, and 'txpower on' to un-SW-rfkill, where of
course the interface would be !IFF_UP after 'txpower on' just like
flipping the killswitch would.

Dan


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