RE: [PATCH v6 14/14] platform/x86: dell-smbios-wmi: introduce userspace interface

[Mario.Limonciello]

> -----Original Message-----
> From: Greg KH [mailto:greg@xxxxxxxxx]
> Sent: Tuesday, October 10, 2017 8:59 AM
> 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;
> pali.rohar@xxxxxxxxx; rjw@xxxxxxxxxxxxx; mjg59@xxxxxxxxxx; hch@xxxxxx
> Subject: Re: [PATCH v6 14/14] platform/x86: dell-smbios-wmi: introduce
> userspace interface
> 
> On Mon, Oct 09, 2017 at 05:51:52PM -0500, Mario Limonciello wrote:
> > +	ret = device_create_file(&wdev->dev, &priv->req_buf_size_attr);
> > +	if (ret)
> > +		goto fail_create_sysfs;
> 
> Why isn't the "WMI core" creating this sysfs file?  Why have per-driver
> sysfs files, making all of the different apis totally different?  It's a
> "common" attribute that they are all going to have to provide, right?
> 
I hadn't really thought about that.  I suppose it's entirely reasonable
to have a way that all WMI ioctls for future drivers will advertise the size
of their expected buffer the same way.

So this does beg a question to others on this distribution who have worked
on WMI drivers- do you know of any WM**/ methods with multiple instances 
that use different buffer sizes, or is it reasonable to expect that the buffer size 
is consistent between instances?

Even in advanced MOF designs I haven't seen it, but this makes me
wonder if an attribute should be created for every instance to be future proof.
(For example $GUID/required_buffer_size/instance0, 
$GUID/required_buffer_size/instance1 etc)

> That way you also don't race with userspace :)
> 
> thanks,
> 
> greg k-h