Re: [PATCH v12 04/15] exfat: Implement fileattr_get for case sensitivity

[David Timber <dxdt@dev.snart.me>]

On 4/30/26 03:07, Chuck Lever wrote:
> From: Chuck Lever <chuck.lever@oracle.com>
>
> Report exFAT's case sensitivity behavior via the FS_XFLAG_CASEFOLD
> flag. exFAT is always case-insensitive (using an upcase table for
> comparison) and always preserves case at rest.
Not necessarily "always".

Link: https://github.com/exfatprogs/exfatprogs/issues/313

The specs(SD spec part 2 and MS spec) leave it up to the formatter
implementation on how the volume should behave. The observed behaviour
is that it is quite flexible: you can pretty much use any artitrary
up-case table to make an exFAT volume behave completely different and
major implementations including Linux and Windows kernel honour the
table no matter what. So exFAT is not so "binary"(folding vs. not
folding) when it comes to case folding behaviour.

NTFS also has a similar up-case table feature. Although it's usually
unused, if an up-case table exists in the volume, the implementation
probably has to honour it(although this is not written down in any spec,
this should be the expectation).

At the end of the day, it wouldn't matter much because no sane formatter
would produce a volume with some weird version up-case table. But if
that attribute plays a important role in some system that has some level
of impact, I suggest considering another attribute, say "unknown" or "it
depends".

Davo