[systemd-devel] udev breaks hostap linkage of raw/user interfaces, causing wpa_supplicant problems

Greg KH greg at kroah.com
Mon Mar 16 01:54:42 PDT 2015

On Mon, Mar 16, 2015 at 09:32:17AM +0100, Thomas Richter wrote:
> Am 16.03.2015 um 09:04 schrieb Greg KH:
> > On Mon, Mar 16, 2015 at 08:26:00AM +0100, Thomas Richter wrote:
> >> Hi folks,
> >>
> >>> udev seems to create a problem here with the hostap (prism2) kernel
> >>> driver. Unlike many wifi devices, the hostap device driver always
> >>> creates paired interfaces, a raw interface (wifiX) and a network
> >>> interface (wlanX) that represents the configured network.
> >>>
> >>> Unfortunately, udev (or hostap?) does not seem to be aware of this
> >>> linkage, and hence, if you have two wifi radios in your system, may
> >>> rename the second (wlanX) without the first (wifiX), and hence causing a
> >>> name mismatch between the two.
> >>>
> >>> In general, this is not a problem, however, wpa_supplicant seems to
> >>> depend on the linkage of the names. Hence, if wifiX does not match
> >>> wlanX, wpa_supplicant will be unable to provide a WPA2 connection over a
> >>> hostap driven wifi connection.
> >>>
> >>> Even worse, the complete procedure is completely untransparent to the
> >>> user, i.e. neither wpa_supplicant (nor network-manager, depending on
> >>> wpa_supplicant) nor network-manager provide a useful error message.
> >>>
> >>> Any chance of fixing this problem? Is this "only" a configuration issue?
> >>> Is this an issue of hostap? Is this an issue of wpa_supplicant?
> >>>
> >>> Either way, it took me several hours of figuring out what was wrong....
> >>
> >> One day passed, no useful pointers. Folks, sorry to say, but it is
> >> unacceptable if udev *breaks* the prism wifi.
> > 
> > A Sunday passed, and you are upset that no one fixed a problem for an
> > obsolete kernel driver?  What kind of free software support are you used
> > to?
> > 
> > Anyway, which exact kernel driver is this?  Is it prism2_usb?  Or
> > something else?
> It's regular PCI based prism2, thank you. I'm not expecting *you* to fix
> things in prism2, for sure. This is not the hostap mailing list.

Which exact kernel driver is this?  I don't see a prism2 PCI driver in
the latest kernel source tree, but I'm probably looking in the wrong
place.  Pointers to it would be appreciated so we can see exactly what
is different about it's user/kernel interfaces that is causing problems

> But look, if udev can take a working kernel driver (and prism2 surely
> is), and breaks its interfaces, then apparently something changed in the
> interface from back then when prism2 was written and working, to now,
> where it no longer is.

When did things break?  What previous version of udev worked properly?
What changed on your system that caused this problem to show up?  Did
you upgrade the kernel?  Whole system?  Something else?  What distro is
this?  We need a bit more information here please.


greg k-h

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