Re: [RFC] mac80211: Support on-channel scan option.

[Ben Greear <greearb@candelatech.com>]

On 04/01/2012 02:11 PM, Johannes Berg wrote:
> On Sun, 2012-04-01 at 13:53 -0700, Ben Greear wrote:
>> On 04/01/2012 01:49 PM, Johannes Berg wrote:
>>> On Sun, 2012-04-01 at 13:45 -0700, Ben Greear wrote:
>>>> On 04/01/2012 11:45 AM, Johannes Berg wrote:
>>>>> On Sat, 2012-03-31 at 15:30 -0700, greearb@candelatech.com wrote:
>>>>>
>>>>>
>>>>>>     static int __ieee80211_start_scan(struct ieee80211_sub_if_data *sdata,
>>>>>>     				  struct cfg80211_scan_request *req)
>>>>>> @@ -438,6 +461,33 @@ static int __ieee80211_start_scan(struct ieee80211_sub_if_data *sdata,
>>>>>>     	local->scan_req = req;
>>>>>>     	local->scan_sdata = sdata;
>>>>>>
>>>>>> +	/* If we are scanning only on the current channel, then
>>>>>> +	 * we do not need to stop normal activities
>>>>>> +	 */
>>>>>> +	if ((req->n_channels == 1)&&
>>>>>> +	    (req->channels[0]->center_freq ==
>>>>>> +	     local->hw.conf.channel->center_freq)) {
>>>>> ...
>>>>>> +		return 0;
>>>>>> +	}
>>>>>> +
>>>>>>     	if (local->ops->hw_scan)
>>>>>>     		__set_bit(SCAN_HW_SCANNING,&local->scanning);
>>>>>
>>>>> Clearly, you're joking.
>>>>
>>>> That is worthless feedback and gives me no idea what you
>>>> think should be fixed about it.
>>>>
>>>> If you hate the entire idea of optimizing scanning on channel,
>>>> just say so plainly.
>>>
>>> I did quote only the relevant pieces -- you're completely ignoring hw
>>> scan. Why should I care about this patch then?
>>
>> Well, I was hoping that a simple scan-on-channel wouldn't need to
>> care about the hw-scan logic.
>
> So you thought about it, but didn't document it? This bothers me quite a
> bit -- why should I have to always do the thinking again?

You know more about this stuff than I do.  You could have replaced the
original snide response with a 2-line note that I need to
do this only for sw-scan NICs and saved us all some trouble.

If you had added another 2 lines to explain why, as you did below,
then maybe I and anyone else reading the email would have learned
something as well.

>> But, I can change it so that the optimized scan-on-channel only
>> is supported on NICs that do software-scan?
>
> In any case, yes, you'll have to do that. Think about how scanning
> works, and consider that devices may very well chose to filter by BSSID
> when associated etc.

OK, it's easy enough to only enable this for sw-scan NICs.  I'll
fix up the patch and repost when I get a chance to test it more
thoroughly.

Thanks,
Ben

-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com