On 25 March 2014 08:59, Luca Coelho <luca@xxxxxxxxx> wrote:
> On Fri, 2014-03-21 at 14:47 +0100, Michal Kazior wrote:
>> Do not allocate more channel contexts than a
>> driver is capable for currently matching interface
>> combination.
>>
>> This allows the ieee80211_vif_reserve_chanctx() to
>> act as a guard against breaking interface
>> combinations.
>>
>> Signed-off-by: Michal Kazior <michal.kazior@xxxxxxxxx>
>> ---
>
> [...]
>> @@ -745,13 +764,16 @@ int ieee80211_vif_reserve_chanctx(struct ieee80211_sub_if_data *sdata,
>> * context, reserve our current context
>> */
>> new_ctx = curr_ctx;
>> - } else {
>> + } else if (ieee80211_can_create_new_chanctx(local)) {
>> /* create a new context and reserve it */
>> new_ctx = ieee80211_new_chanctx(local, chandef, mode);
>> if (IS_ERR(new_ctx)) {
>> ret = PTR_ERR(new_ctx);
>> goto out;
>> }
>> + } else {
>> + ret = -EBUSY;
>> + goto out;
>
> I'm not sure about this whole allowed channels counting thing. Does it
> really matter what is the total number of allowed channels? I think the
> actual combinations is what should be checked here.
>
> Let's say the driver supports these combinations:
>
> 1. num_different_channels = 2; limits max 2 APs;
> 2. num_different_channels = 1; limits 1 AP, 1 STA;
>
> Then you're running on a single-channel with 1 AP and 1 STA. The STA
> gets a CSA to move to a new channel. If you only consider the
> max_num_channels you calculated, you will think that it is okay to
> switch, but it is not, because you cannot have 1 AP and 1 STA on
> different channels.
>
> Or am I missing something?
Yes. You're missing the fact, that ieee80211_max_num_channels() uses
current iftype set to narrow down matching combinations.
In the above example you provided ieee80211_max_num_channels() returns 1.
Michał
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