[PATCH] wpa_supplicant/hostapd: add an option to only advertise FTM responder

[Otcheretianski, Andrei]

> On Mon, Dec 05, 2022 at 04:43:36PM +0200, Andrei Otcheretianski wrote:
> > When configuring FTM responder, wpa_supplicant/hostapd configures the
> > driver to operate as a responder. However, it is possible that it is
> > only needed to advertise the FTM responder capabilties, but not
> > configure the driver to operate as a responder (e.g. when a usespace
> > daemon operates as a responder). Add an option to only advertise the
> > FTM responder capabilities without configuring the driver.
> 
> How would a user know when to use the new ftm_responder_capab_only
> vs.
> the old ftm_responder_capab configuration parameter? What happens if
> ftp_responder_capab_only=1 is used and there is no userspace daemon to
> process the operations? Is this something that could be handled
> automatically? It would seem to be much more convenient to not add this
> new configuration parameter at all and instead determine the FTM
> responder location between the driver and that separate userspace daemon
> automatically so that it does not matter whether hostapd/wpa_supplicant
> requests the driver to process the requests.

I understand your concern about having multiple similar configurations which may be confusing for the user.
Actually, after looking at the code again, it looks that if the driver doesn't publish WPA_DRIVER_FLAGS_FTM_RESPONDER while regular ftm_responder configuration flag is set, hostapd will publish ext. capability bit but will not attempt to configure the responder (without failing).
I'm not sure if this is the intended behavior, but if it is, it can be used to achieve what we want.
However, for drivers that do support FTM_RESPONDER, there is no way to signal to hostapd that the responder shouldn't be started.
Automatically coordinating FTM responder location between the drivers and external daemon sounds quite complicated and will require more kernel API's and driver changes.

Andrei
> 
> --
> Jouni Malinen                                            PGP id EFC895FA