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

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Message-ID: <3a5a8de9-0a5b-45ad-73c6-6b3ebfdd5ebb@kernel.org>
Date:   Wed, 27 Sep 2017 12:49:04 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Darren Hart <dvhart@...radead.org>,
        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 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@...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?
> 

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