Re: RFC: mac80211/ath9k: allow scanning single channel if other VIF is associated.

[Ben Greear <greearb@candelatech.com>]

On 09/15/2010 02:04 PM, Luis R. Rodriguez wrote:
> On Wed, Sep 15, 2010 at 1:31 PM, Jouni Malinen<j@w1.fi>  wrote:
>> On Tue, Sep 14, 2010 at 10:30:04PM -0700, Ben Greear wrote:
>>> I think for the multi-VIF scenario, it should scan the single associated
>>> channel by default, but it would be nice to allow full scans on demand.
>>> (I would very much like to work with standard wpa_supplicant, but if hacking it
>>> is the only way, then I can attempt that.)
>>
>> "Standard wpa_supplicant" needs to become more aware of multiple users
>> of the same radio, so it is certainly fine to add changes there. For
>> example, a mechanism for noticing that interfaces are sharing a radio
>> would be useful. With that, it should also be possible to share the BSS
>> table and scan results (and requests!) within wpa_supplicant.
>
> Depending on how this is implementing, sharing of the physical radio
> may require some kernel synchronization between the different
> interfaces using the same radio. It may also be possible to share the
> same radio between an 802.11 device and a wimax device, for example.
> Long ago we thought up of a frequency broker [1] but never really
> wrote it as we have had no usage case for it yet. If we implement the
> frequency broker we could also technically add a scheduler to sharing
> the same radio between separate interfaces / technologies, this could
> just be done in userspace as well, although I am not sure if the
> timing considerations for doing it in userspace would suffice.

At least for my use, I hope to be able to fully utilize the bandwidth for
a particular channel, and emulate as close as possible a bunch of wireless
devices sharing an AP or set of APs.  So, I don't want to be switching off the main
channel for any significant amount of time.  I think as long as you stick
to the main channel, there are no significant scheduling issues with
the hardware, but I could be wrong about that.

Also, I want to be able to run one supplicant per interface, so while
wpa_supplicant could become clever if it manages multiple devices, I
want them to be able to run independently as well.

As for figuring out what hardware a VIF belongs to, you can deduce this
by following links in sysfs to find it's phyX device.  It is a pain
when the phyX changes name due to module reload or something, but it can still
be dealt with.

Thanks,
Ben

-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com