linux-kernel - Re: [PATCH v3 4/8] platform/x86: wmi: create character devices when requested by drivers

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Date:   Sat, 30 Sep 2017 10:12:05 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Darren Hart <dvhart@...radead.org>
Cc:     Mario Limonciello <mario.limonciello@...l.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        platform-driver-x86@...r.kernel.org,
        Andy Lutomirski <luto@...nel.org>, quasisec@...gle.com,
        pali.rohar@...il.com, Rafael Wysocki <rjw@...ysocki.net>,
        Matthew Garrett <mjg59@...gle.com>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v3 4/8] platform/x86: wmi: create character devices when
 requested by drivers

On Fri, Sep 29, 2017 at 06:52:28PM -0700, Darren Hart wrote:
> 
> On Wed, Sep 27, 2017 at 11:02:16PM -0500, Mario Limonciello wrote:
> > For WMI operations that are only Set or Query read or write sysfs
> > attributes created by WMI vendor drivers make sense.
> > 
> > For other WMI operations that are run on Method, there needs to be a
> > way to guarantee to userspace that the results from the method call
> > belong to the data request to the method call.  Sysfs attributes don't
> > work well in this scenario because two userspace processes may be
> > competing at reading/writing an attribute and step on each other's
> > data.
> > 
> > When a WMI vendor driver declares a set of functions in a
> > file_operations object the WMI bus driver will create a character
> > device that maps to those file operations.
> > 
> > That character device will correspond to this path:
> > /dev/wmi/$driver
> > 
> > This policy is selected as one driver may map and use multiple
> > GUIDs and it would be better to only expose a single character
> > device.
> > 
> > The WMI vendor drivers will be responsible for managing access to
> > this character device and proper locking on it.
> > 
> > When a WMI vendor driver is unloaded the WMI bus driver will clean
> > up the character device.
> > 
> > Signed-off-by: Mario Limonciello <mario.limonciello@...l.com>
> > ---
> >  drivers/platform/x86/wmi.c | 98 +++++++++++++++++++++++++++++++++++++++++++---
> >  include/linux/wmi.h        |  1 +
> >  2 files changed, 94 insertions(+), 5 deletions(-)
> 
> +Greg, Rafael, Matthew, and Christoph
> 
> You each provided feedback regarding the method of exposing WMI methods
> to userspace. This and subsequent patches from Mario lay some of the
> core groundwork.
> 
> They implement an implicit whitelist as only drivers requesting the char
> dev will see it created.
> 
> https://lkml.org/lkml/2017/9/28/8

If you want patchs reviewed, it's best to actually cc: us on the patch
itself :(