On Tue, 2014-03-25 at 09:37 +0100, Michal Kazior wrote:
> 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.
Exactly, that's what I was missing. :)
--
Luca.
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