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

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Message-ID: <CAHp75VfURDc-FPfnsO93B_P5sEz9EzxjuPjHLKArmB39ABMp1w@mail.gmail.com>
Date:   Wed, 27 Sep 2017 21:31:47 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Mario Limonciello <Mario.Limonciello@...l.com>
Cc:     "dvhart@...radead.org" <dvhart@...radead.org>,
        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 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.

-- 
With Best Regards,
Andy Shevchenko