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

[Greg KH]

On Wed, Sep 09, 2015 at 10:14:46AM -0300, 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.

is_bin_visiable makes sense to me instead of trying to overload the
index number in some crazy way.  There's no issue with adding another
function pointer.

thanks,

greg k-h