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    SubjectRE: [PATCH v3 4/8] platform/x86: wmi: create character devices when requested by drivers
    Date
    > -----Original Message-----
    > From: Greg KH [mailto:greg@kroah.com]
    > Sent: Tuesday, October 3, 2017 4:24 AM
    > To: Limonciello, Mario <Mario_Limonciello@Dell.com>
    > Cc: dvhart@infradead.org; Andy Shevchenko <andy.shevchenko@gmail.com>;
    > LKML <linux-kernel@vger.kernel.org>; platform-driver-x86@vger.kernel.org;
    > Andy Lutomirski <luto@kernel.org>; quasisec@google.com;
    > pali.rohar@gmail.com
    > Subject: Re: [PATCH v3 4/8] platform/x86: wmi: create character devices when
    > requested by drivers
    >
    > 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@dell.com>
    > > ---
    > > drivers/platform/x86/wmi.c | 98
    > +++++++++++++++++++++++++++++++++++++++++++---
    > > include/linux/wmi.h | 1 +
    > > 2 files changed, 94 insertions(+), 5 deletions(-)
    > >
    > > diff --git a/drivers/platform/x86/wmi.c b/drivers/platform/x86/wmi.c
    > > index 4d73a87c2ddf..17399df87948 100644
    > > --- a/drivers/platform/x86/wmi.c
    > > +++ b/drivers/platform/x86/wmi.c
    > > @@ -34,7 +34,9 @@
    > > #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
    > >
    > > #include <linux/acpi.h>
    > > +#include <linux/cdev.h>
    > > #include <linux/device.h>
    > > +#include <linux/idr.h>
    > > #include <linux/init.h>
    > > #include <linux/kernel.h>
    > > #include <linux/list.h>
    > > @@ -50,6 +52,9 @@ MODULE_AUTHOR("Carlos Corbacho");
    > > MODULE_DESCRIPTION("ACPI-WMI Mapping Driver");
    > > MODULE_LICENSE("GPL");
    > >
    > > +#define WMI_MAX_DEVS MINORMASK
    > > +static DEFINE_IDR(wmi_idr);
    >
    > You never free the idr's memory when you unload the module :(

    Whoops thanks, will fix. ☹
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