wpa_supplicant cannot authenticate connection on prism2 radios if interface names do not match

Thomas Richter thor
Tue Mar 17 09:00:56 PDT 2015

Hi Dan,

did you get this?


>>> sorry to ask again, probably the issue got lost over the weekend. I
>>> reported yesterday the following weird problem for wpa_supplicant
>>> failing on prism2 wireless cards under some conditions related to udev.
>>> Typically, the prism2 driver creates paired devices, wifi0 (raw radio,
>>> as I understand it) and wlan0 (the established connection). For reasons
>>> unclear to me, wpa_supplicant seems to depend matched names, i.e. if
>>> wlanX is there, and it is a hostap (prism2) managed device, it also
>>> expects wifiX there, with the same X.
>> I would consider it a bug that the supplicant has to depend on the
>> matched names.  However, if the driver provides no mechanism to
>> determine the sibling from the other interface, then obviously the bug
>> in the supplicant could not be fixed until the driver exposes that kind
>> of information.
> Well, the information on the pairing is actually available in the sysfs
> filing system. Thus,
> /sys/class/net/wlan0/device/
> contains two directories, namely the two network interfaces the device
> manages.
>> I don't happen to have a PCMCIA-capable laptop usable at the moment so I
>> can't plug in a prism2 card to check, but is there anything
>> in /sys/class/net/wlanX or its sub-directories that would link the
>> sibling interfaces together?
> Yes, see above.
>> If so, then perhaps the supplicant could
>> be modified to use that information and solve the problem.  If not, then
>> the driver needs some modification to advertise those.  MAC address
>> matching could work too, but that seems pretty fragile.
> Hmm. I wonder why that is more fragile than above? It's probably harder
> to do.
> Anyhow, whatever the fix is, please let me know if I can try anything here.
> BTW, you do not necessarily need PCMCIA to test this, it "only" needs
> the hostap kernel driver. In this particular case, it is even a mini-PCI
> card, but I have the same chip in a PCMCIA card.
> Greetings,
>     Thomas
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