linux-kernel - Re: [PATCH 1/3] sysfs: Fix is_visible() support for binary attributes

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Date:	Wed, 09 Sep 2015 06:30:42 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Emilio López <emilio.lopez@...labora.co.uk>,
	Greg KH <gregkh@...uxfoundation.org>
CC:	olof@...om.net, kgene@...nel.org, k.kozlowski@...sung.com,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-samsung-soc@...r.kernel.org
Subject: Re: [PATCH 1/3] sysfs: Fix is_visible() support for binary attributes

On 09/09/2015 06:14 AM, Emilio López wrote:
> On 09/09/15 01:12, Guenter Roeck wrote:
>> On 09/08/2015 08:58 PM, Greg KH wrote:
>>> On Tue, Sep 08, 2015 at 06:10:16PM -0700, Guenter Roeck wrote:
>>>> Hi Emilio,
>>>>
>>>> On 09/08/2015 05:51 PM, Emilio López wrote:
>>>>> Hi Greg & Guenter,
>>>>>
>>>> [ ... ]
>>>>>>>>
>>>>>>>> Unless I am missing something, this is not explained anywhere,
>>>>>>>> but it is
>>>>>>>> not entirely trivial to understand. I think it should be documented.
>>>>>
>>>>> I agree. I couldn't find any mention of what this int was supposed
>>>>> to be by looking at Documentation/ (is_visible is not even mentioned
>>>>> :/) or include/linux/sysfs.h. Once we settle on something I'll
>>>>> document it before sending a v2.
>>>>>
>>>> In the include file ? No strong preference, though.
>>>>
>>>>> By the way, I wrote a quick coccinelle script to match is_visible()
>>>>> users which reference the index (included below), and it found
>>>>> references to drivers which do not seem to use any binary
>>>>> attributes, so I believe changing the index meaning shouldn't be an
>>>>> issue.
>>>>>
>>>> Good.
>>>>
>>>>>>> I agree, make i the number of the bin attribute and that should solve
>>>>>>> this issue.
>>>>>>>
>>>>>> No, that would conflict with the "normal" use of is_visible for
>>>>>> non-binary
>>>>>> attributes, and make the index all but useless, since the
>>>>>> is_visible function
>>>>>> would have to search through all the attributes anyway to figure
>>>>>> out which one
>>>>>> is being checked.
>>>>>
>>>>> Yeah, using the same indexes would be somewhat pointless, although
>>>>> not many seem to be using it anyway (only 14 files matched). Others
>>>>> seem to be comparing the attr* instead. An alternative would be to
>>>>> use negative indexes for binary attributes and positive indexes for
>>>>> normal attributes.
>>>>>
>>>> ... and I probably wrote or reviewed a significant percentage of
>>>> those ;-).
>>>>
>>>> Using negative numbers for binary attributes is an interesting idea.
>>>> Kind of unusual, though. Greg, any thoughts on that ?
>>>
>>> Ick, no, that's a mess, maybe we just could drop the index alltogether?
>>>
>>
>> No, please don't. Having to manually compare dozens of index pointers
>> would be
>> even more of a mess.
>
> So, what about keeping it the way it is in the patch, and documenting it thoroughly? Otherwise, we could introduce another "is_bin_visible" function to do this same thing but just on binary attributes, but I'd rather not add a new function pointer if possible.
>

I would prefer to keep and document it.

Guenter

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