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

[Andy Lutomirski]

On 09/27/2017 11:55 AM, Darren Hart wrote:
> On Wed, Sep 27, 2017 at 09:31:47PM +0300, Andy Shevchenko wrote:
> > On Wed, Sep 27, 2017 at 9:27 PM,  <Mario.Limonciello@xxxxxxxx> 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?

Not really.  If this is indeed static data that is potentially useful 
for scripts and such, than sysfs is kind of nice.