Re: [PATCH v2 2/6] mac80211: Support getting sta_info stats via ethtool.

[Ben Greear <greearb@candelatech.com>]

On 04/17/2012 09:00 PM, Johannes Berg wrote:
> On Tue, 2012-04-17 at 20:46 -0700, Ben Greear wrote:
>
>>>> +	rcu_read_lock();
>>>> +	list_for_each_entry_rcu(sta,&local->sta_list, list) {
>>>
>>> This doesn't seem right -- shouldn't it look up the BSSID or something
>>> and only work on managed interfaces? What if there really are two
>>> stations on this interface -- then it'll just overwrite it and return a
>>> random station's data? That's useless.
>>
>> Well, its weird at least.
>>
>> But, if there are multiple stations, like for APs??, then it will
>> add the station's stats together.  Perhaps not horribly useful, but better
>> than nothing.
>
> Oh, right, it's adding, I missed that. But is that really useful?

It provides a summary for AP, and precise stats for managed station
mode (excepting TDLS where it may return sums, it seems).

I could just return all zeros for non managed
station interfaces, but I *have* to return some value, so it seems
little loss to just add the station stats together.

>> For managed interface, I *think* they don't have more than one station, right?
>
> You can't rely on it. Typically they will, but with TDLS there might be
> multiple.
>
>> And, as for the underlying driver stats and survey stats (in later patches),
>> that is only probed once.  I guess if you somehow had two
>> stations on different channels on the same network device,
>> the survey stats would be a bit dodgy, but it does return
>> the freq for the stats in question, so at least you know
>> what you are getting.
>
> A single netdev is always going to be on a single channel. Actually, I
> take that back, I think TDLS can work out of channel too, but we don't
> support that right now.

So, based on your response, a sum still seems most useful to me.  The ethtool
API gives no way to request any subset of stats, so all I can key off of
is the netdev.

I have some plans percolating to add some new ethtool API to get subsets
of stats, but that is likely a ways off, and of course it may not be
accepted regardless.

Thanks,
Ben


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