Re: [RFC PATCH 1/1] supplicant: request ACS if channel==0

Hi Dan,

On Fri, May 27, 2016 at 12:07:09PM -0500, Dan Williams wrote:
On Fri, 2016-05-27 at 18:12 +0200, Ulrich Ölmann wrote:
By analogy to wpa_supplicant.conf Automatic Channel Selection (ACS)
is coded as
"channel=0" within a connection. wpa_supplicant then needs to know if
it shall
look out for a channel in the 2.4 GHz or the 5 GHz band. This
information is
passed over via a sample frequency from the respective band.

Definitely good to do and thanks for the patch.  Given that the ACS
support isn't yet in a released supplicant, does this patch cause
problems with older supplicants that don't have ACS support?

it probably will - I have to look into that.

I think this patch will change the behavior a bit for older
supplicants, so that for AdHoc/APs that leave band/frequency undefined
will now no longer send the NM-determined frequency to the supplicant.
 act_stage2_config() calls ensure_hotspot_frequency() to set a fixed
frequency, and that gets passed
to nm_supplicant_config_add_setting_wireless().  But since channel is
still undefined, that random fixed_freq will get overwritten either
with FIVE_GHZ_SAMPLE_FREQ/TWO_GHZ_SAMPLE_FREQ or will remain at 0 if
the connection specifies no band.

We could use the supplicant's global capabilities
(see wpas_dbus_getter_global_capabilities()) to add an ACS flag when
the supplicant has ACS compiled in, which NM could then read and use to
enable the new ACS behavior?

Hopefully I will have time to look into this and prepare a v2 next week.

Thanks for your suggestions

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