Re: [PATCH/RFC] pci: dynids.use_driver_data considered harmful

[Milton Miller]

On Aug 17, 2008, at 2:06 PM, Jean Delvare wrote:
> On Fri, 15 Aug 2008 23:22:59 -0700, Greg KH wrote:
> > On Fri, Aug 15, 2008 at 12:15:01PM -0700, Jesse Barnes wrote:
> > > On Friday, August 15, 2008 11:55 am Jean Delvare wrote:
> > > > In fact we can do even better than that. We could accept from
> > > > user-space only driver_data values which at least one device ID 
> > > > entry in
> > > > the driver already uses. That should be fairly easy to implement, 
> > > > and
> > > > would offer a level of safety an order of magnitude above what we 
> > > > have
> > > > at the moment... And it works both ways: if 0 is not a valid data 
> > > > for
> > > > some driver, that would force the user to provide a non-zero (and
> > > > valid) data value. And it guarantees that the user can't ask for
> > > > something the driver doesn't expect, so drivers don't even need 
> > > > extra
> > > > checks. And no need for a use_driver_data flag either.
> > >
> > > Meaning a driver audit of the usage?  Yeah that would be great.

Thanks Jean for doing this.  Sometimes things move quickly after a long 
stall.  I thought about proposing a similar patch and therefore have to 
say Ack.

> > > > The only drawback is that it prevents the user from passing a "new"
> > > > data value even if it would be valid. But honestly, I don't expect 
> > > > that
> > > > case to happen frequently... if ever at all. So I'd say the benefits
> > > > totally outweight the drawback.

There are a few drivers that could benefit, mainly ones that I 
identified as using flags.  For example, the radeon driver uses 
different fields of the data to specify crt controller, video output 
device, etc.   I'm fine with deferring a flag for such drivers until 
someone audits a driver and wants the support.

> > > > If the interested people agree with the idea, I'll look into
> > > > implementing it.
> > >
> > > Well the audit would show if user supplied "new" values are needed; 
> > > otherwise
> > > the approach sounds good to me.
> >
> > That sounds reasonable, and should work properly.
> >
> > No objection from me.

so, if anyone asks,

Concept-Acked-By: Milton Miller <miltonm@xxxxxxx>

milton

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