Re: [RFC v3 12/13] cfg80211: add channel checking for iface combinations

[Johannes Berg <johannes@sipsolutions.net>]

On Tue, 2012-06-26 at 15:44 +0200, Michal Kazior wrote:
> Johannes Berg wrote:
> > On Tue, 2012-06-26 at 14:30 +0200, Michal Kazior wrote:
> >
> >> +#define CFG80211_MAX_NUM_DIFFERENT_CHANNELS 10
> >
> > Might make sense to put this into cfg80211.h, since e.g. hwsim could
> > support this many channels?
> >
> >> +		cfg80211_get_chan_state(rdev, wdev_iter, &ch, &chmode);
> >> +
> >> +		switch (chmode) {
> >> +		case CHAN_MODE_UNDEFINED:
> >> +			break;
> >> +		case CHAN_MODE_SHARED:
> >> +			for (i = 0; i < CFG80211_MAX_NUM_DIFFERENT_CHANNELS; i++)
> >> +				if (!used_channels[i] || used_channels[i] == ch)
> >> +					break;
> >> +
> >> +			BUG_ON(i == CFG80211_MAX_NUM_DIFFERENT_CHANNELS);
> >
> > I'd prefer not to use BUG_ON(), maybe WARN_ON() and return some error?
> > It seems it could actually happen with buggy drivers that suddenly go
> > above their num_different_channels by switching around themselves or
> > something?
> 
> Hmm.. Now that I think of it we could probably hit the BUG_ON normally. 
> Suppose a driver supports num_different_channels == 
> CFG80211_MAX_NUM_DIFFERENT_CHANNELS. If cfg80211_can_use_iftype_chan is 
> called with another different channel we will hit the BUG_ON, no?
> 
> I think we should either do a WARN_ON_ONCE here, or nothing actually. 
> And return -EBUSY of course.

Good point, this seems like it could happen.

johannes