d80211: RFC: divide by zero when hw->maxssi not set

d80211: RFC: divide by zero when hw->maxssi not set

[David Kimdon]

Hi,

commit 448bf25bc9e3d70a211fdf235426472089371c43 added
ieee80211_get_wireless_stats in net/d80211/ieee80211_ioctl.c.  At
present we get a divide by zero (oops) if the low level driver does
not set the new hw->maxssi field.  Perhaps:

- reject registration of devices which do not set maxssi
- do not attempt to report link quality for drivers which do not 
  set maxssi
- other ideas? 

-David

Re: d80211: RFC: divide by zero when hw->maxssi not set

[Michael Wu]

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On Friday 17 November 2006 18:51, David Kimdon wrote:
> - reject registration of devices which do not set maxssi
> - do not attempt to report link quality for drivers which do not
>   set maxssi
> - other ideas?
>
I've noticed that too. p54 didn't get a driver update when maxssi was added. I 
don't mind adding a dummy maxssi just to make sure we don't divide by zero. 
In fact, I'm going to come up with a patch for p54 to do that soon.

-Michael Wu

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Re: d80211: RFC: divide by zero when hw->maxssi not set

[Dan Williams]

On Fri, 2006-11-17 at 15:51 -0800, David Kimdon wrote:
> Hi,
> 
> commit 448bf25bc9e3d70a211fdf235426472089371c43 added
> ieee80211_get_wireless_stats in net/d80211/ieee80211_ioctl.c.  At
> present we get a divide by zero (oops) if the low level driver does
> not set the new hw->maxssi field.  Perhaps:
> 
> - reject registration of devices which do not set maxssi
> - do not attempt to report link quality for drivers which do not 
>   set maxssi
> - other ideas? 

#1 could be too draconian, but has the benefit of making driver writers
put _something_ there.  Either way, it's pretty obvious to anyone that
the driver is broken for quality reporting.  But at least #1 forces the
issue to making quality somewhat work.

Dan

> -David
> -
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Re: d80211: RFC: divide by zero when hw->maxssi not set

[Ingo Oeser]

Hi there,

Dan Williams schrieb:
> On Fri, 2006-11-17 at 15:51 -0800, David Kimdon wrote:
> > commit 448bf25bc9e3d70a211fdf235426472089371c43 added
> > ieee80211_get_wireless_stats in net/d80211/ieee80211_ioctl.c.  At
> > present we get a divide by zero (oops) if the low level driver does
> > not set the new hw->maxssi field.  Perhaps:
> > 
> > - reject registration of devices which do not set maxssi

> #1 could be too draconian, but has the benefit of making driver writers
> put _something_ there.  Either way, it's pretty obvious to anyone that
> the driver is broken for quality reporting.  But at least #1 forces the
> issue to making quality somewhat work.

Looks like a perfect cancdidate for -EINVAL and WARN_ON() at registration.
BUG_ON() is also ok, until that stuff is widely deployed.

That's much better than dummy values, because it doesn't make
people think "Hmm, it works somehow, but I don't know why 
(and I don't care why)".


Regards

Ingo Oeser