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

[Guenter Roeck]

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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