On 05/22/2018 04:28 PM, Johannes Berg wrote:
On Tue, 2018-05-22 at 16:25 -0500, Denis Kenzior wrote:
Hi Johannes,
But in theory, I think you could've received the beacon with hidden SSID
*before* the scan, yet it might be present in the scan results if the
new scan caused the probe response to be associated with that scan.
Right, your explanation was helpful, thanks. It still seems completely
weird and redundant that we get two separate entries though. The second
entry with the probe response data still carries the beacon info (as you
point out). Should the pure-beacon one be filtered?
I'm not sure. It still indicates that a hidden SSID was found, and in
general even a real SSID on the same BSSID doesn't indicate that this
was the only hidden SSID ...
Right, but you still get that info conveyed through the Beacon IEs
elements on the second/third/etc entry. So it still seems redundant to
include the pure beacon one?
Also, given that you have to ask for the SSID you want specifically,
what practical purpose does it serve to know that this wasn't the only
hidden SSID? I mean you can see that hidden SSIDs are out there, run an
active scan for the ones you can use. If none are there, you can just
ignore that bssid...
Right, so thinking out loud here. Would it be useful to tell GET SCAN
to only return entries with actual probe response data? Combined with
the flush flag it seems like a much better fit for the cases you point out.
I don't really see much point in doing filtering in the kernel. It
wouldn't doesn't hurt, but just trades off more kernel code for less
transferred data - and that's mostly in this particular corner case, so
not really an efficiency problem?
Fair enough. It was more motivated by 'make the API a bit more readable
/ accessible / user friendly'.
And if it wasn't a hidden SSID, then you probably do want to know about
the non-hidden SSIDs that you picked up along the way. In fact, this
will become crucial with OCE, since that results in cases where you
don't even send a probe request if you've picked up certain things
during the scan passively.
Right. In our case we only scan passively unless we detect a hidden
ssid and have provisioned hidden ssids. Then we issue an active scan
for just those...
Regards,
-Denis
