Re: [RFC] DT_WHT

[Rical Jasan <ricaljasan at pacific dot net>]

On 03/04/2018 05:50 PM, Ben Hutchings wrote:
> On Thu, 2018-03-01 at 15:02 -0800, Rical Jasan wrote:
>> On 03/01/2018 08:24 AM, Ben Hutchings wrote:
>>> On Wed, 2018-02-21 at 02:16 -0800, Rical Jasan wrote:
>>>> There is one undocumented DT_* macro in manual/filesys.texi: DT_WHT.  It
>>>> is defined in dirent/dirent.h and appears to be used once in io/fts.c:
>>>>
>>>> #if defined FTS_WHITEOUT && 0
>>>>                 if (dp->d_type == DT_WHT)
>>>>                         p->fts_flags |= FTS_ISW;
>>>> #endif
>>>>
>>>> For an entry in the manual, I was thinking something along the lines of:
>>>>
>>>> "This macro is obsolete and has no effect.  It was used to..."
>>>>
>>>> but I'm not sure what to say about what it was used for.
>>>
>>> [...]
>>>> Lastly, I can't find a reference to it in any of the standards I've
>>>> managed to obtain so far (not to say that's exhaustive at all).  Is this
>>>> also BSD?
>>>
>>> Some Linux filesystems support white-out directory entries for use with
>>> union filesystems.  At least the coda and xfs implementations of
>>> getdents() appear to be capable of setting d_type to DT_WHT.
>>
>> The code as-is isn't used, though.  Other "#if ... 0" blocks also use
>> some apparently whiteout-related macros that aren't defined anywhere.
>>
>> Do you think instead of removing the unused code it should be changed to
>> actually do something?
> 
> I have no opinion on that code, but it sounded like you proposed to
> remove the macro definition too.  I wanted to point out that the macro
> is meaningful and may be useful to applications.

It's a complete NOOP, though, so why should we provide it?

Rical