linux-kernel - Re: RFC: WMI Enhancements

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Date:   Mon, 8 May 2017 08:47:25 -0700
From:   Darren Hart <dvhart@...radead.org>
To:     Mario.Limonciello@...l.com
Cc:     luto@...nel.org, pali.rohar@...il.com, rjw@...ysocki.net,
        len.brown@...el.com, corentin.chary@...il.com,
        andriy.shevchenko@...ux.intel.com, linux-kernel@...r.kernel.org,
        platform-driver-x86@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: RFC: WMI Enhancements

On Mon, May 08, 2017 at 03:36:31PM +0000, Mario.Limonciello@...l.com wrote:
> > -----Original Message-----
> > From: Darren Hart [mailto:dvhart@...radead.org]
> > Sent: Monday, May 8, 2017 10:29 AM
> > To: Andy Lutomirski <luto@...nel.org>
> > Cc: Limonciello, Mario <Mario_Limonciello@...l.com>; Pali Rohár
> > <pali.rohar@...il.com>; Rafael J. Wysocki <rjw@...ysocki.net>; Len Brown
> > <len.brown@...el.com>; Corentin Chary <corentin.chary@...il.com>; Andy
> > Shevchenko <andriy.shevchenko@...ux.intel.com>; linux-kernel@...r.kernel.org;
> > platform-driver-x86@...r.kernel.org; linux-pm@...r.kernel.org
> > Subject: Re: RFC: WMI Enhancements
> > 
> > On Fri, May 05, 2017 at 06:25:08PM -0700, Andy Lutomirski wrote:
> > > On Fri, May 5, 2017 at 5:51 PM,  <Mario.Limonciello@...l.com> wrote:
> > > >> -----Original Message-----
> > > >> From: Darren Hart [mailto:dvhart@...radead.org]
> > > >> Sent: Friday, May 5, 2017 6:45 PM
> > > >> To: Limonciello, Mario <Mario_Limonciello@...l.com>
> > > >> Cc: pali.rohar@...il.com; rjw@...ysocki.net; luto@...capital.net;
> > > >> len.brown@...el.com; corentin.chary@...il.com; luto@...nel.org;
> > > >> andriy.shevchenko@...ux.intel.com; linux-kernel@...r.kernel.org; platform-
> > > >> driver-x86@...r.kernel.org; linux-pm@...r.kernel.org
> > > >> Subject: Re: RFC: WMI Enhancements
> > >
> > >
> > > > I meant that to say that at least for now Andy's wmi-mof driver should still be
> > merged.
> > > > If something is going to build on top of this to do WBEM tools, they'll need that
> > MOF
> > > > data once someone figures out how to nicely deconstruct it.
> > > >
> > >
> > > The thing I don't like about my own driver is that, as a WMI device
> > > driver, it can be loaded before the rest of the bus finishes probing.
> > > So user programs that are notified asynchronously that the wmi-mof
> > > driver is loaded and try to use future functionality (ioctl to issue a
> > > MOF-based method call?) might end up doing so before the rest of the
> > > bus is probed.
> > >
> > > This could be addressed by always exposing the wmi-mof device last
> > > (sort of -- it can be a module) or perhaps by moving MOF functionality
> > > to the core driver.  Or maybe it's not really a problem.
> > 
> > Thanks Andy, I'll keep that in mind and see if I can come up with something to
> > address it while working on WMI this week.
> > 
> > The other problem with wmi-mof is that there will be no immediate open source
> > consumers of the interface, and none on the horizon. We can't even test it to
> > any meaningful degree on Linux. I suspect this will be met with stiff
> > resistance.
> 
> Well FWIW I did a quick PoC check with the binary that I got out of it to make 
> sure it matched what was supposed to be.  I brought it over to a Win10 box and 
> decompiled using the mofcmp tool and those crazy arguments I mentioned and 
> it was correct.
> 
> I'd argue that even if there is no open source tools available today, not making 
> the data available to userspace makes it difficult to even attempt to start 
> to reverse engineer.
> 
> Kernel config with default of "N" perhaps for wmi-mof?

All true. There is a precedent we're working against on this. I'll include it in
my leveling-up thread today or tomorrow.

> > 
> > >
> > > Also, isn't there a way to ask Microsoft to document this?  Are you
> > > supposed to "ask a question" on this forum, perhaps:
> > >
> > > https://msdn.microsoft.com/en-us/library/gg134029.aspx
> > >
> > > I'm guessing the Samba team knows how to do this, too.
> > >
> 
> Microsoft treats this as an "intermediary" format.  I'm not convinced
> that anyone other than MS knows anything about it today.
> 
> I agree asking them to document it is probably the right way to go.
> 

Mario, you are most likely in a better position to do that than I am. Would you
take that on?

-- 
Darren Hart
VMware Open Source Technology Center