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From: Luca Coelho <luca@coelho.fi>
To: Johannes Berg <johannes@sipsolutions.net>
Cc: Michal Kazior <michal.kazior@tieto.com>,
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Date: Wed, 07 May 2014 12:40:57 +0300
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Subject: Re: [PATCH v5] mac80211: implement multi-vif in-place reservations
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On Wed, 2014-05-07 at 10:07 +0200, Johannes Berg wrote:
> On Wed, 2014-05-07 at 08:05 +0200, Michal Kazior wrote:
> 
> > Hmm... Now that I think about the atomic swap - it actually becomes a
> > little bit of an issue in some cases.
> > 
> > For one you might need to overcommit number of chanctx since swapping
> > requires both chanctx (old and new) to exist but that's the least of
> > the eproblem. If you have more than one interface you end up with
> > temporarily breaking interface combinations from driver point of view
> > while switching (first swap breaks it, last swap fixes it). Driver
> > won't know whether given swap is first/last unless we somehow pass it
> > through the switch_vif_chanctx(). IOW we actually need a "chanctx
> > transaction" (sort of a start-stop) that can batch up a couple of
> > chanctx switches for different vifs as an atomic op.
> 
> Hmmm. Don't you already have that problem? Or you don't because you'd do
> 
> for_each_affected_vif: unassign
> del chanctx [optional depending on reservation]
> add chanctx [ditto]
> for_each_affected_vif: assign
> 
> right now?
> 
> I suppose a sort of transaction API, if designed the right way, would
> also work somehow - Luca?

Yeah, I think this is a good idea.  If we have an atomic transaction API
towards the driver, we can solve the problems of switching several vifs
at once.

--
Luca.