[RFC] Allow active scanning while associated with custom world regulatory domain

Commit Message

Blaise Gassend Feb. 5, 2014, 10:20 a.m. UTC

An alternative proposal that just came to mind:

It appears that only world regulatory domains actually have
IEEE80211_CHAN_PASSIVE_SCAN set. Given that this is the case, why not
allow beacon hints to work no matter what the regulatory domain is?

The only case where you have IEEE80211_CHAN_PASSIVE_SCAN on a
non-world regulatory domain is when you have merged a world regulatory
domain into a country IE regulatory domain. In that case, continuing
to use beacon hints to remove IEEE80211_CHAN_PASSIVE_SCAN seems
legitimate, since that flag was set by the world regulatory domain
side of the merge.


On Wed, Feb 5, 2014 at 2:12 AM, Blaise Gassend <[e-mail]> wrote:
> Hi Folks,
>
> I have noticed that with the ath9k boards I use, I am unable to do
> active scanning while associated.
>
> I have tracked down the problem to the following causes:
>
> 1. The ath9k driver has a custom regulatory domain. It is a world
> regulatory domain that has passive scanning
> (IEEE80211_CHAN_PASSIVE_SCAN) on most (all?) of the 5GHz band.
>
> 2. When I associate, that world regulatory domain is merged with the
> country IE regulatory domain to determine what the actual regulatory
> domain should be. As part of this merge, the channel flags are ORed
> together, so most of the 5GHz band ends up having
> IEEE80211_CHAN_PASSIVE_SCAN.
>
> 3. When I am associated to an AP with a non-world regulatory domain,
> regulatory hints are disabled so there is no mechanism to clear
> IEEE80211_CHAN_PASSIVE_SCAN (as there was when I was unassociated and
> operating on the driver's world regulatory domain).
>
> This is particularly annoying if you are on a hidden SSID and you are
> trying to use multiple interfaces, or if you are trying to do
> background scanning to roam to a different BSS, as it is now
> impossible to send out the probe requests you need to see BSSes for
> your SSID.
>
> I'd be interested in comments on the patch below. It is based on the
> assumption that drivers may need to set a custom regulatory domain to
> prevent access to certain channels (if the hardware isn't calibrated
> for that channel, for instance), but that a driver never needs to
> restrict passive scanning beyond what is allowed by the country IE
> regulatory domain.
>
> So, are there cases where IEEE80211_CHAN_PASSIVE_SCAN is set in
> orig_flags, but not for the country IE regulatory domain and where we
> actually do want to prevent active scanning after we associate? Any
> other flaws in the proposal below?
>
> Best regards,
> Blaise Gassend
>
> Signed-off-by: Blaise Gassend <[e-mail]>
> diff --git a/modules/backports-20131025/net/wireless/reg.c
> b/modules/backports-20131025/net/wireless/reg.c
> --- a/modules/backports-20131025/net/wireless/reg.c
> +++ b/modules/backports-20131025/net/wireless/reg.c
> @@ -837,8 +837,6 @@ static void handle_channel(struct wiphy
>
>         request_wiphy = wiphy_idx_to_wiphy(lr->wiphy_idx);
>
> -       flags = chan->orig_flags;
> -
>         reg_rule = freq_reg_info(wiphy, MHZ_TO_KHZ(chan->center_freq));
>         if (IS_ERR(reg_rule)) {
>                 /*
> @@ -892,7 +890,16 @@ static void handle_channel(struct wiphy
>         chan->dfs_state = NL80211_DFS_USABLE;
>         chan->dfs_state_entered = jiffies;
>
> -       chan->beacon_found = false;
> +        /*
> +         * Clear IEEE80211_CHAN_PASSIVE_SCAN from the driver's flags to
> +         * allow the associated country IE to permit active scanning on
> +         * frequencies that only allow passive scanning according to the
> +         * driver's world regulatory domain. Prior to association, beacon
> +         * hints would enable active scanning on these channels.
> +         */
> +        flags = chan->orig_flags & ~IEEE80211_CHAN_PASSIVE_SCAN;
> +
> +        chan->beacon_found = false;
>         chan->flags = flags | bw_flags | map_regdom_flags(reg_rule->flags);
>         chan->max_antenna_gain =
>                 min_t(int, chan->orig_mag,
--
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Patch

diff --git a/modules/backports-20131025/net/wireless/reg.c
b/modules/backports-20131025/net/wireless/reg.c
--- a/modules/backports-20131025/net/wireless/reg.c
+++ b/modules/backports-20131025/net/wireless/reg.c
@@ -1058,9 +1058,6 @@  static void handle_reg_beacon(struct wip

        chan->beacon_found = true;

-       if (!reg_is_world_roaming(wiphy))
-               return;
-
        if (wiphy->flags & WIPHY_FLAG_DISABLE_BEACON_HINTS)
                return;