Hi Johannes,
On 10/8/19 10:52 AM, Johannes Berg wrote:
Hi,
You could have two interfaces, one which is scanning right now, right?
And then theoretically you don't care about the other one - it *should*
be OK to remove/re-add (with new MAC address) the one that *isn't*
scanning, right?
Actually, I don't think you can? Unless I'm missing something? All the
scan state is stored on struct ieee80211_local, so if that struct is
allocated per phy as you point out below, then what you suggest is
currently not possible?
?
The scan_req struct contains a reference to which interface is scanning,
so it should very well be possible to have
phy0:
wlan0: IFF_UP & scanning
wlan1: IFF_UP & change MAC address all the time
just like it's possible to change the MAC address when wlan1 *isn't*
IFF_UP even if wlan0 is scanning, right?
Indeed. But that is not what you were suggesting earlier with just
checking local->scanning. So if scan_req contains a wdev, then yes it
should be possible to compare the scan_req->wdev to the interface being
changed.
But we don't have that granularity here for anything - you're just
checking "sdata->local->something", and by going from sdata to local
you've now checked the whole NIC, not just a single interface on that
NIC.
Right. But that seems to be a limitation of mac80211 actually. We
can't run two scans concurrently on different interfaces. This is
rather unintuitive given that scan requests require an ifindex/wdev.
Can this be changed / fixed in mac80211 actually? I would expect that
if a card supports p2p and station simultaneously, then it can scan / go
offchannel on two interfaces simultaneously? Or not? What can iwlwifi
do for example?
No, this typically cannot be fixed, and it doesn't really make sense.
The NIC cannot possibly do two scans at a time since it has only a
single radio resource :-)
So why is the scan request not per phy then? And should mac address
even affect the ongoing scan? Can we simply change it with the scan
ongoing?
Given the above, I'm not sure I see anything wrong? The switch/case can
probably be gotten rid of, but it actually makes things clear that only
station/p2p_device and adhoc are handled specially.
I just don't think they *should* be handled specially.
Fair enough.
Given your code now, you can have
phy0:
wlan0: STATION, IFF_UP & something is doing remain-on-channel
wlan1: STATION, IFF_UP
--> cannot change wlan1 MAC address
phy0:
wlan0: STATION, IFF_UP & something is doing remain-on-channel
wlan1: AP, IFF_UP
--> *can* change wlan1 MAC address
This doesn't really make much sense?
Agreed.
Regards,
-Denis
