Re: Connection issues with BW Tracking in mac80211

[Krishna Chaitanya <chaitanya.mgit@gmail.com>]

On Wed, Mar 11, 2015 at 10:05 PM, Krishna Chaitanya
<chaitanya.mgit@gmail.com> wrote:
> On Wed, Mar 11, 2015 at 9:50 PM, Johannes Berg
> <johannes@sipsolutions.net> wrote:
>> On Wed, 2015-03-11 at 21:45 +0530, Krishna Chaitanya wrote:
>>
>>> I did some experiments on this and found the root cause.
>>>
>>> We are using 5GHz in WORLD Mode, so only passive scan is allowed.
>>> So when connecting the very first time, the mac80211 MLME sees that
>>> there are no probe_resp ies (only beacon_ies are present) and it sends
>>> a directed probe and updates the probe_resp ies. (and also the "ies").
>>>
>>> But when config is changed and we get disconnected, beacon_ies are updated
>>> with the new config, but the probe_resp ies are not.
>>> cfg80211_bss_update assigns
>>> probe_resp ies to "ies' and mac80211 updates its bss info based on the
>>> probe_resp
>>> ies which have old config causing the issue.
>>>
>>> Solution:
>>>
>>> 1) Make the directed probe mandatory.
>>> 2) As you suggested maintain timestamps for probe_resp_ies and beacon_ies
>>> and use the latest.
>>>
>>> Any takes?
>>
>> What's the operational problem here? I don't really see it. Are you
>> afraid users will reconfigure their APs often enough for this to be an
>> issue?
> Use case point of view, i understand that this doesn't happen often.
> But from functional point of view, it can still happen and even
> after disconnect mac80211 will not allow connection.
>
> Also solution: would be to flush scan results up on disconnection.
Johannes,

Assuming that this problem needs to be solved in spite of
low probability of the occurrence. What do you think is the
best way, which has low impact on other features out of these?

1.  Make the directed probe mandatory:
         a. Check for successful probe resp without depending on proberesp_ies.
         b. remove the proberesp_ies from the auth_data to trigger
directed probe.

2. Timestamps for proberesp and beacons and update the latest one to "ies".

3. while update "ies" check only for beacon as its supposed to have latest
information (This will trigger #1 automatically).

As a quick and minimal impact solution i am thinking 1-b.

Regards,
Chaitanya T K.