Virtual Interface for P2P operations

Johannes Berg johannes
Fri Jul 22 10:17:22 PDT 2011

On Fri, 2011-07-22 at 09:51 -0700, Henry Ptasinski wrote:

> > Some drivers/devices would like to
> >
> >     use a separate MAC address
> To make sure we've all got the same understanding:
> The P2P spec talks about 3 types of addresses a device can have:
> 	WLAN address - for traditional connections
> 	P2P Device address - for P2P discovery and GO negotiation
> 	P2P Interface address - for messages sent within a P2P group
> The P2P device address can be either: the globally administered MAC 
> address, or the globally administered MAC address with the locally 
> administered address bit set.

Right. I'm more talking about configuration interfaces though.

> For concurrent WLAN and P2P operation, the spec requires that the WLAN 
> and P2P Interface addresses be distinct.

Yeah. Right now we'll use the globally administered address for WLAN,
and another address for the P2P Interface.

> For simultaneous P2P membership in multiple groups, the spec requires 
> that the P2P Interface address used in each group be different.

Yup. Different netdevs for the different P2P interfaces for this.

> The WLAN address and P2P Device address never change for a device (I think).

The WLAN address can be changed manually, but typically wouldn't. Then
the Device address would follow, currently, I think.

> > wpa_supplicant calls this the WPA_IF_P2P_GROUP but I think the term "P2P device interface" would be more appropriate here.
> Is this the P2P Device address or the P2P Interface address?  "P2P 
> device interface" is going to be a problematic name I think.

Well, again, I'm more thinking of configuration interfaces, not
addresses. Since it wouldn't be a netdev, it wouldn't directly have an
address, though we'd actually give it an address -- this would be the
Device address. But you're right, calling it "interface" is probably bad
idea since it's not a netdev. Maybe actually just call it "P2P Device".

> Does wpa_supplicant understand multiple simultaneous P2P groups?  Is 
> wpa_supplicant handling discovery and the GO negotiation, or is that 
> done somewhere else?

Yes and yes.

> The WPS and the 4-way handshake happens with the P2P Interface address.

Right, and in terms of APIs it happens on the netdev. The issue at hand
is that currently in nl80211, WLAN == P2P Device, and we use the WLAN
MAC as the P2P Device MAC, and also use the WLAN netdev for the P2P APIs
for public action, discovery, etc.

> > WoP2P anyone?
> Shudder.



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