Re: [RFC v3 7/7] mac80211: reuse channels for channel contexts

[Michal Kazior <michal.kazior@tieto.com>]

Johannes Berg wrote:
> On Tue, 2012-06-26 at 14:37 +0200, Michal Kazior wrote:
>
>> +static enum nl80211_channel_type
>> +ieee80211_calc_chantype(struct ieee80211_local *local,
>> +			struct ieee80211_chanctx *ctx)
>> +{
>> +	struct ieee80211_chanctx_conf *conf = &ctx->conf;
>> +	struct ieee80211_sub_if_data *sdata;
>> +	enum nl80211_channel_type chantype = NL80211_CHAN_NO_HT;
>> +	enum nl80211_channel_type compat;
>> +
>> +	lockdep_assert_held(&local->chanctx_mtx);
>> +
>> +	rcu_read_lock();
>> +	list_for_each_entry_rcu(sdata, &local->interfaces, list) {
>> +		if (!ieee80211_sdata_running(sdata))
>> +			continue;
>> +		if (sdata->vif.chanctx_conf != conf)
>> +			continue;
>> +
>> +		BUG_ON(!ieee80211_channel_types_are_compatible(
>> +				conf->channel_type, chantype, &compat));
>
> Please no BUG_ON, maybe only WARN_ON_ONCE even?

Okay. I guess returning NL80211_CHAN_NO_HT in such case is okay.


>> +		chantype = compat;
>> +	}
>> +	rcu_read_unlock();
>> +
>> +	return chantype;
>> +}
>
> I don't think I understand this, wouldn't it need some per-vif requested
> channel type to work correctly? I don't see any chantype values coming
> from the sdata here, so I don't think this could work?
>
> If say vif1 needs ht40+ and vif2 ht20, the channel context will be set
> to ht40+, but then if vif1 goes away and you don't know anything about
> vif2 at all, then how can this work? The way I see it, your code here
> doesn't really do anything, except recalculate that ht40+ is compatible
> with ht40+, or something like that? I guess I'm a bit confused, it seems
> to me that this cannot work even in theory unless you have per-vif data.

It seems I must've had a mind-derp. I was planning on using 
sdata->vif.bss_conf.channel_type which should be ok, right?


>>   static void
>>   ieee80211_unassign_vif_chanctx(struct ieee80211_sub_if_data *sdata,
>>   			       struct ieee80211_chanctx *ctx)
>> @@ -248,6 +302,8 @@ ieee80211_unassign_vif_chanctx(struct ieee80211_sub_if_data *sdata,
>>
>>   	drv_unassign_vif_chanctx(sdata->local, sdata, ctx);
>>
>> +	ieee80211_recalc_chanctx_chantype(sdata->local, ctx);
>> +
>>   	ctx->refcount--;
>>   	sdata->vif.chanctx_conf = NULL;
>
> And then shouldn't you recalc *after* setting chanctx_conf = NULL so you
> skip this vif?

You're absolutely right.


-- 
Pozdrawiam / Best regards, Michal Kazior.