Re: [PATCH] mac80211: add support for userspace to handle auth frames on adhoc ifaces

[Nicolas Cavallari <Nicolas.Cavallari@lri.fr>]

On 14/06/2012 13:24, Johannes Berg wrote:
> On Thu, 2012-06-14 at 10:00 +0200, Nicolas Cavallari wrote:
> 
>> I just have a question here : when auth frames are not delivered to
>> userspace, mac80211 will respond to them, and also uses them to detect
>> node reboot. If you register for auth frames, mac80211 will still send
>> auth frames as soon as a new station is seen, which might be confusing
>> for user space. Is that ok to do this ? Or should userspace have more
>> control over how mac80211 sends auth frames ?
> 
> Please read the code. If userspace registers for them, mac80211 will
> never do anything with the frame.

I didn't say the contrary. But if you read ieee80211_ibss_finish_sta(),
you see that mac80211 sends auth frames to each discovered station, even
if userspace want to handle auth frames. This seems strange to be able
to receive and handle auth frames from userspace while mac80211 sends
them behind userspace's back.

> 
>> There is also another thing to consider if you want to send auth frames
>> from userspace, as CMD_FRAME requires a frequency, which in IBSS mode,
>> can change anytime without userspace being notified. If you only have to
>> answer to received auth frames, this is easier as you can reuse the
>> frequency given by nl80211 when receiving the auth frame. But if you
>> want to send a auth frame independently, how do you get the frequency to
>> use ?
> 
> You check the BSS info, that's trivial.

There is no GET_BSS from userspace. when merging IBSS, only the new
BSSID is notified. The only way to get this info from userspace would be
to dump the scan result and check the "we joined that ibss" flag, and
this isn't race-free. That, or using fixed_freq.