From: Michal Sojka <sojkam1@fel.cvut.cz>
To: Johannes Berg <johannes@sipsolutions.net>,
	linux-wireless@vger.kernel.org
Cc: bernd.lehmann@volkswagen.de, s.sander@nordsys.de,
	wireless-regdb@lists.infradead.org, ath9k-devel@lists.ath9k.org,
	ath9k-devel@qca.qualcomm.com,
	Jan =?utf-8?Q?Kaisrl=C3=ADk?= <kaisrja1@fel.cvut.cz>,
	Jouni Malinen <j@w1.fi>
Subject: Re: [PATCH v2 5/8] cfg80211: Add support for OCB-only channels
In-Reply-To: <1448613238.2531.12.camel@sipsolutions.net>
References: <1448303241-27747-1-git-send-email-sojkam1@fel.cvut.cz> <1448303241-27747-6-git-send-email-sojkam1@fel.cvut.cz> <1448613238.2531.12.camel@sipsolutions.net>
Date: Fri, 27 Nov 2015 09:59:09 +0100
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MIME-Version: 1.0
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Sender: linux-wireless-owner@vger.kernel.org

On Fri, Nov 27 2015, Johannes Berg wrote:
> On Mon, 2015-11-23 at 19:27 +0100, Michal Sojka wrote:
>
>>  #define NL80211_RRF_PASSIVE_SCAN	NL80211_RRF_NO_IR
>> diff --git a/net/wireless/chan.c b/net/wireless/chan.c
>> index 59cabc9..b1ab77a 100644
>> --- a/net/wireless/chan.c
>> +++ b/net/wireless/chan.c
>> @@ -804,7 +804,8 @@ static bool _cfg80211_reg_can_beacon(struct wiphy
>> *wiphy,
>>  {
>>  	bool res;
>>  	u32 prohibited_flags = IEEE80211_CHAN_DISABLED |
>> -			       IEEE80211_CHAN_RADAR;
>> +			       IEEE80211_CHAN_RADAR |
>> +			       IEEE80211_CHAN_OCB_ONLY;
>
> So ... for the kernel, I don't *like* this approach, because it
> requires touching every single driver, and every single person who
> writes code in the future must be aware of the special handling for
> this flag.
>
> For userspace, however, this approach is simply impossible. Consider an
> older version of wpa_supplicant, that queries the channel list and
> isn't aware of the OCB_ONLY flag. This version would take the channel
> list and build a scan request with it, only to get the scan rejected
> since some channels it picked were only usable for OCB, as far as I can
> tell.
>
> I think the solution to this would be to redefine the CHAN_DISABLED
> flag to mean "channel disabled for non-ocb mode" and add a
> CHAN_OCB_ENABLED flag.
>
> Then code that knows about OCB would simply not test CHAN_DISABLED, but
> would instead test CHAN_OCB_ENABLED instead - and if that's clear OCB
> would not be permitted.
>
> However, this would have the side effect of enabling OCB *only* on OCB
> channels, which might not be a good idea, for testing purposes one
> might want to use the regular 2.4 or 5 GHz channels? If so, OCB could
> still be made to do something like
>
> 	ocb_usable = (flags & OCB_ENABLED) || !(flags & DISABLED);
>
> or we could even make the channel list internally maintain a
> CHAN_OCB_USABLE flag that essentially encodes the logic above.
>
> In any case, this would collapse the patch down to modifying only OCB
> code and nothing else, which is nice, and would keep existing userspace
> working since it would just see disabled channels while ignoring the
> OCB flag.

Yes, this makes perfect sense. I'll rework the patch.

-Michal