linux-kernel - Re: [PATCH 06/12] platform/x86: dell-wmi-smbios: Add a sysfs interface for SMBIOS tokens

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Date:   Wed, 27 Sep 2017 11:55:14 -0700
From:   Darren Hart <dvhart@...radead.org>
To:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Andy Lutomirski <luto@...capital.net>
Cc:     Mario Limonciello <Mario.Limonciello@...l.com>,
        Pali Rohár <pali.rohar@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Platform Driver <platform-driver-x86@...r.kernel.org>,
        quasisec@...gle.com
Subject: Re: [PATCH 06/12] platform/x86: dell-wmi-smbios: Add a sysfs
 interface for SMBIOS tokens

On Wed, Sep 27, 2017 at 09:31:47PM +0300, Andy Shevchenko wrote:
> On Wed, Sep 27, 2017 at 9:27 PM,  <Mario.Limonciello@...l.com> wrote:
> 
> >> > > > Darren, Andy, any comments? I'm not quite sure if such API is suitable
> >> > > > for long term in kernel.
> >> > >
> >> > > I would try to avoid sysfs interfaces for some particular devices.
> >> > > Besides we are creating a character device. Would it be suitable there?
> >> >
> >> > If the character device having 2 different ioctls for different needs is
> >> > acceptable I'm happy to adjust the series to do this instead.
> >>
> >> One piece of feedback I had re the char device was to see if we could avoid the
> >> need for the IOCTL altogether, I'd like to have that discussion before we add
> >> another.
> >
> > My original design was sysfs files for everything but it was raised by several folks
> > that you run into the potential of two userspace processes stomping on each
> > other's data when they run the ACPI call.  That's why I need to have a mutex to
> > protect and make sure that userspace calls get the right results.
> >
> 
> >> > > > Basically tokens are list of tuples <id, location, value> with
> >> > > > possibility to active them, right?
> >> > > >
> >> >
> >> > I didn't add a way to activate them through this, it was only for
> >> > reading purpose.  Activating them should be possible through the
> >> > SMBIOS calling interface though.
> >> >
> >>
> >> These are read-only as I understood it, and only with the right privileges.
> >> Sysfs seemed appropriate for this to me.
> >
> > Andy S was against having this data as another sysfs file.   From a userspace
> > perspective I think it's simpler to just parse a sysfs file with read only static
> > data as root.  With the current ioctl based solution it requires userspace to run
> > an ioctl to determine how many tokens exist, then allocate a chunk of memory
> > big enough to hold all the token data and then run another ioctl to get all the tokens.
> >
> > Andy S, given this change between v1 and v2 what do you feel is better?
> 
> I have no strong opinion on this. That's why I recommended to listen to Andy L.

+Andy Lutomirski

Andy L, any preference on your part regarding exporting these tokens via sysfs
or through an additional IOCTL in the chardev?

-- 
Darren Hart
VMware Open Source Technology Center