bug#16133: 24.3; copy-file fails on chmod when copying to FAT filesystem

[Josh]

On Sat, Dec 14, 2013 at 12:57 PM, Eli Zaretskii <eliz@gnu.org> wrote:
>> From: Josh <josh@foxtail.org>
>> Date: Sat, 14 Dec 2013 12:46:59 -0800
>> Cc: Paul Eggert <eggert@cs.ucla.edu>, Artem Chuprina <ran@lasgalen.net>,
>>       16133@debbugs.gnu.org
>>
>> On Sat, Dec 14, 2013 at 12:19 PM, Glenn Morris <rgm@gnu.org> wrote:
>> > I don't know how we tidy this up for the future though.
>> > Add yet another optional argument "error-if-permissions-fail"? Yuck.
>>
>> It might be reasonable to error only when the existing
>> PRESERVE-UID-GID argument was non-nil.
>
> That argument has nothing to do with mode bits, which is what this bug
> is about.

That argument being nil indicates that the user doesn't care about
preserving UID and GID.  Are there cases when the user would care
about preserving mode bits but not UID and GID?