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

[Dan Williams <dcbw redhat com>]

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?

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?

Dan

> Signed-off-by: Ulrich Ölmann <u oelmann pengutronix de>
> ---
>  src/supplicant-manager/nm-supplicant-config.c      | 37
> ++++++++++++++++++----
>  .../nm-supplicant-settings-verify.c                |  1 +
>  2 files changed, 31 insertions(+), 7 deletions(-)
>
> diff --git a/src/supplicant-manager/nm-supplicant-config.c
> b/src/supplicant-manager/nm-supplicant-config.c
> index 5ce8bb31968a..e16353a98583 100644
> --- a/src/supplicant-manager/nm-supplicant-config.c
> +++ b/src/supplicant-manager/nm-supplicant-config.c
> @@ -381,6 +381,9 @@ wifi_freqs_to_string (gboolean bg_band)
>       return str;
>  }
>  
> +#define TWO_GHZ_SAMPLE_FREQ  2412
> +#define FIVE_GHZ_SAMPLE_FREQ 5280
> +
>  gboolean
>  nm_supplicant_config_add_setting_wireless (NMSupplicantConfig *
> self,
>                                             NMSettingWireless *
> setting,
> @@ -428,12 +431,34 @@ nm_supplicant_config_add_setting_wireless
> (NMSupplicantConfig * self,
>                       return FALSE;
>       }
>  
> -     if ((is_adhoc || is_ap) && fixed_freq) {
> -             gs_free char *str_freq = NULL;
> +     band = nm_setting_wireless_get_band (setting);
> +     channel = nm_setting_wireless_get_channel (setting);
> +     if (is_adhoc || is_ap) {
> +             /* By analogy to wpa_supplicant.conf Automatic
> Channel Selection (ACS)
> +              * is coded as "channel=0" within the connection -
> wpa_supplicant then
> +              * needs the option "acs=1" and a sample frequency
> which points the ACS
> +              * heuristic to the desired band.
> +              */
> +             if (!channel) {
> +                     if (!nm_supplicant_config_add_option (self,
> "acs", "1", -1, FALSE, error))
> +                             return FALSE;
>  
> -             str_freq = g_strdup_printf ("%u", fixed_freq);
> -             if (!nm_supplicant_config_add_option (self,
> "frequency", str_freq, -1, FALSE, error))
> -                     return FALSE;
> +                     fixed_freq = 0;
> +                     if (band) {
> +                             if (!strcmp (band, "a"))
> +                                     fixed_freq =
> FIVE_GHZ_SAMPLE_FREQ;
> +                             else if (!strcmp (band, "bg"))
> +                                     fixed_freq =
> TWO_GHZ_SAMPLE_FREQ;
> +                     }
> +             }
> +
> +             if (fixed_freq) {
> +                     gs_free char *str_freq = NULL;
> +
> +                     str_freq = g_strdup_printf ("%u",
> fixed_freq);
> +                     if (!nm_supplicant_config_add_option (self,
> "frequency", str_freq, -1, FALSE, error))
> +                             return FALSE;
> +             }
>       }
>  
>       /* Except for Ad-Hoc and Hotspot, request that the driver
> probe for the
> @@ -453,8 +478,6 @@ nm_supplicant_config_add_setting_wireless
> (NMSupplicantConfig * self,
>                       return FALSE;
>       }
>  
> -     band = nm_setting_wireless_get_band (setting);
> -     channel = nm_setting_wireless_get_channel (setting);
>       if (band) {
>               if (channel) {
>                       guint32 freq;
> diff --git a/src/supplicant-manager/nm-supplicant-settings-verify.c
> b/src/supplicant-manager/nm-supplicant-settings-verify.c
> index bb046f9361d9..4e7ebcd1d7d0 100644
> --- a/src/supplicant-manager/nm-supplicant-settings-verify.c
> +++ b/src/supplicant-manager/nm-supplicant-settings-verify.c
> @@ -93,6 +93,7 @@ static const struct Opt opt_table[] = {
>       { "bssid",              TYPE_KEYWORD, 0, 0, FALSE,  NULL },
>       { "scan_ssid",          TYPE_INT,     0, 1, FALSE,  NULL },
>       { "mode",               TYPE_INT,     0, 2, FALSE,  NULL },
> +     { "acs",                TYPE_INT,     0, 1, FALSE,  NULL },
>       { "frequency",          TYPE_INT,     2412, 5825,
> FALSE,  NULL },
>       { "auth_alg",           TYPE_KEYWORD, 0, 0,
> FALSE,  auth_alg_allowed },
>       { "psk",                TYPE_BYTES,   0, 0, FALSE,  NULL },