RE: [PATCH v6 13/14] platform/x86: wmi: create character devices when requested by drivers

[Mario.Limonciello]

> -----Original Message-----
> From: Pali RohÃr [mailto:pali.rohar@xxxxxxxxx]
> Sent: Tuesday, October 10, 2017 2:12 PM
> To: Limonciello, Mario <Mario_Limonciello@xxxxxxxx>
> Cc: dvhart@xxxxxxxxxxxxx; Andy Shevchenko <andy.shevchenko@xxxxxxxxx>;
> LKML <linux-kernel@xxxxxxxxxxxxxxx>; platform-driver-x86@xxxxxxxxxxxxxxx;
> Andy Lutomirski <luto@xxxxxxxxxx>; quasisec@xxxxxxxxxx; rjw@xxxxxxxxxxxxx;
> mjg59@xxxxxxxxxx; hch@xxxxxx; Greg KH <greg@xxxxxxxxx>
> Subject: Re: [PATCH v6 13/14] platform/x86: wmi: create character devices when
> requested by drivers
> 
> On Monday 09 October 2017 17:51:51 Mario Limonciello wrote:
> > +	/* make sure we're not calling a higher instance than exists*/
> > +	if (_IOC_NR(cmd) > wblock->gblock.instance_count - 1)
> > +		return -EINVAL;
> 
> Is this condition really working? instance_count is unsigned, cmd is
> also unsigned... and when instance_count is zero, then IIRC error would
> not be thrown.
> 

But instance count can't be zero.  MOF would fall apart with a zero instance count.
If a broken BIOS was shipped with an instance count of zero bigger problems would
have happened.