Message-ID: <1399467968.10517.39.camel@jlt4.sipsolutions.net> (sfid-20140507_150621_493870_0EEB72CC)
Subject: Re: [PATCH v5] mac80211: implement multi-vif in-place reservations
From: Johannes Berg <johannes@sipsolutions.net>
To: Luca Coelho <luca@coelho.fi>
Cc: Michal Kazior <michal.kazior@tieto.com>,
	linux-wireless <linux-wireless@vger.kernel.org>,
	Simon Wunderlich <sw@simonwunderlich.de>
Date: Wed, 07 May 2014 15:06:08 +0200
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On Wed, 2014-05-07 at 15:53 +0300, Luca Coelho wrote:

> > > >  new chanctx3
> > > >  switch vif2 chanctx1->chanctx3
> > > >  switch_transaction(chanctx1, chanctx2, vif1)
> > > 
> > > Couldn't this potentially break the combinations temporarily again?
> > 
> > I don't see why? You had a spare channel context to start with,
> > otherwise you'd never have accepted this situation. Therefore, you can
> > use the spare one before actually doing the proposed
> > switch_vif_chanctx().
> 
> It's not about the spare, it's about having this temporarily:
> 
> chanctx3-vif2
> chanctx1-vif1
> 
> Can we be sure that chanctx1 with vif1 is compatible with chanctx3 with
> vif2? We only check chanctx2 with vif1 and chanctx3 with vif2, which is
> our final goal.
> 
> I'm not sure this is even possible, but it was something like this I had
> in mind.

Oh, I get it, you're thinking that there might be a situation where
those vif types are maybe not supported with different channels?

But in your example you're going from this situation:

chanctx1: vif1, vif2

to

chanctx2: vif1
chanctx3: vif2


The intermediate step that I proposed would give you

chanctx1: vif1
chanctx3: vif2

Which isn't really any different? Maybe you could construct a more
difficult via situation though where it actually does end up with a
conflict - or can we prove that can't happen?

johannes