On 02/24/2015 02:11 AM, Johannes Berg wrote:
On Mon, 2015-02-23 at 09:43 -0800, Ben Greear wrote:
This seems a bit strange - don't we already tag packets with the
frequency? Why would you need the channel change separately? What does
that even mean? Depending on how you use this it could entirely break
off-channel operation, for example.
I was thinking about passive scans. In that case, we would not always get a packet transmitted
when the channel changes?
Ah, well, ok. However, hwsim doesn't actually really have a concept of
the 'current channel', for example in the offchannel code it just
temporarily listens on two channels ... so that's not very good for a
more realistic implementation :)
I was thinking user-space would mimic a real radio that can only listen on
one channel at once (can any real radios actually listen on two channels at once?)
No, real radios cannot do that (not really anyway - I guess if it was
VHT80 it's really already listening on 4 channels but ...)
So, if we are off-channel, and pkt arrives for the 'main' channel, then
a real radio should drop it, right?
Yes.
Of course, if user-space does not care, then it can simply ignore the channel-change
logic so I think this would be backwards compat with existing hwsim user-space apps.
Sure. But given the murky concept of channel change, and not going to PS
for off-channel in hwsim etc. I think this would need a bit more design
rather than just exposing the mac80211 channel change. Additionally,
with chanctx support that won't even be invoked for example.
We could push more and more of this to user-space and let it decide whether and
how to forward or accept frames for particular radios.
But, to do that, we need the low-level settings sent to user-space
(such as current channel). Encryption keys could be a future enhancement
here, so that we can do 'hardware' encryption in hwsim (and handle encrypt/decrypt
logic however we want in user-space).
For in-kernel testing (ie, no user-space hwsim tool), then other methods can be used,
or we can just ignore the trickier details. My interest is primarily in user-space
hwsim tool at the moment.
Thanks,
Ben
--
Ben Greear <greearb@xxxxxxxxxxxxxxx>
Candela Technologies Inc http://www.candelatech.com
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