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

["Emilio López" <emilio.lopez@collabora.co.uk>]

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.

Cheers,
Emilio