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Subject: RE: RFC: WMI Enhancements
Thread-Topic: RFC: WMI Enhancements
Thread-Index: AQHSs+HFfWGz3Na/pUazu2XvXvLesqHDPEIAgACGNAD//7EgQA==
Date: Thu, 13 Apr 2017 15:55:01 +0000
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> -----Original Message-----
> From: Andy Lutomirski [mailto:luto@kernel.org]
> Sent: Thursday, April 13, 2017 10:33 AM
> To: Michał Kępień <kernel@kempniu.pl>
> Cc: Darren Hart <dvhart@infradead.org>; Rafael Wysocki <rjw@rjwysocki.net>;
> Len Brown <len.brown@intel.com>; Pali Rohár <pali.rohar@gmail.com>; Corentin
> Chary <corentin.chary@gmail.com>; Limonciello, Mario
> <Mario_Limonciello@Dell.com>; Andy Lutomirski <luto@kernel.org>; Andy
> Shevchenko <andriy.shevchenko@linux.intel.com>; LKML <linux-
> kernel@vger.kernel.org>; platform-driver-x86@vger.kernel.org; linux-
> pm@vger.kernel.org
> Subject: Re: RFC: WMI Enhancements
> 
> On Thu, Apr 13, 2017 at 12:32 AM, Michał Kępień <kernel@kempniu.pl> wrote:
> >> Hi All,
> >>
> >> There are a few parallel efforts involving the Windows Management
> >> Instrumentation (WMI)[1] and dependent/related drivers. I'd like to
> >> have a round of discussion among those of you that have been involved
> >> in this space before we decide on a direction.
> >>
> >> The WMI support in the kernel today fairly narrowly supports a
> >> handful of systems. Andy L. has a work-in-progress series [2] which
> >> converts wmi into a platform device and a proper bus, providing
> >> devices for dependent drivers to bind to, and a mechanism for sibling devices to
> communicate with each other.
> >> I've reviewed the series and feel like the approach is sound, I plan
> >> to carry this series forward and merge it (with Andy L's permission).
> >>
> >> Are there any objections to this?
> >
> > Back in January 2016, I sent Andy a few minor comments about this
> > series.  A year later, I offered to iron out the remaining issues and
> > resubmit the series in Andy's name when I find the time.  Sadly,
> > things have changed a bit for me since that time and it is unlikely
> > that I will be able to deliver, for which I am sorry.
> >
> > However, browsing Andy's branch I see that most issues have been
> > resolved, though I think some of my remarks [1] have either been
> > missed or silently refuted :)
> >
> > Anyway, I also like this approach and I think this series is a
> > valuable cleanup.
> 
> Me too :)
> 
> >> In Windows, applications interact with WMI more or less directly. We
> >> don't do this in Linux currently, although it has been discussed in
> >> the past [3]. Some vendors will work around this by performing
> >> SMI/SMM, which is inefficient at best. Exposing WMI methods to
> >> userspace would bring parity to WMI for Linux and Windows.
> >>
> >> There are two principal concerns I'd appreciate your thoughts on:
> >>
> >> a) As an undiscoverable interface (you need to know the method
> >> signatures ahead of time), universally exposing every WMI "device" to
> >> userspace seems like "a bad idea" from a security and stability
> >> perspective. While access would certainly be privileged, it seems
> >> more prudent to make this exposure opt-in. We also handle some of
> >> this with kernel drivers and exposing those "devices" to userspace
> >> would enable userspace and the kernel to fight over control. So - if
> >> we expose WMI devices to userspace, I believe this should be done on
> >> a case by case basis, opting in, and not by default as part of the
> >> WMI driver (although it can provide the mechanism for a sub-driver to use), and
> possibly a devmode to do so by default.
> 
> I agree.  I don't want too see gnome-whatever-widget talking directly to WMI and
> confusing the kernel driver for the same thing.

So there are plenty of other things that can be done by WMI that don't
really make sense to live in the kernel, particularly on what Dell exposes via
WMI.

If the desire of this group ends up being to not expose WMI by default,
I'd like to at least propose it be exposed for the GUID's Dell is using.

Perhaps as part of changing dell-smbios to use WMI, also extend it's
functionality to userspace.

> 
> >> Secondarily, Andy L created a simple driver to expose the MOF buffer
> >> [2] to userspace which could be consumed by a userspace tool to
> >> create sources for an interface to the exposed WMI methods.
> >
> > +1 for the idea, it makes figuring out what the firmware actually
> > exposes through WMI a bit easier.  After skimming through the driver's
> > code, I would only recommend to review the included headers
> > (linux/input/sparse-keymap.h, linux/dmi.h and acpi/video.h all seem
> > redundant to me).
> >
> > What we still need, though, is an open source version of wmiofck.exe.
> > I am unaware of anything like that existing and installing the Windows
> > Driver Kit just to run one command which spits out a single *.h file
> > is not something I would describe as convenient (been there).
> 
> I haven't tried to see whether they do what's needed, but there's OpenWBEM and
> OpenPegasus.
> 
> Anyway, if such a tool exists, it would be handy to expose the binary MOF data to
> userspace so the tool could be used to help get WMI working on new platforms.