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

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Date:	Tue, 08 Sep 2015 21:12:37 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Greg KH <gregkh@...uxfoundation.org>
CC:	Emilio López <emilio.lopez@...labora.co.uk>,
	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 09/08/2015 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.

Guenter


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