Re: filename and normalization (was gcc identifiers)

["H. Peter Anvin" <hpa@xxxxxxxxx>]

Followup to:  <Pine.LNX.4.44js.0212040855170.13309-100000@xxxxxxxx>
By author:    Jungshik Shin <jshin@xxxxxxxxxxx>
In newsgroup: linux.utf8
> >
> > Yes.  Filenames are byte sequences, period, full stop.  Any attempt at
> > normalization would violate SUS/POSIX.
> 
>   All right. That's what the *current* SUS/POSIX says. However, that
> is hardly a solace to a user who'd be puzzled that two visually
> identical and cannonically equivalent filenames are treated differently.
> 
> For instance, U+00D6(Latin Capital Letter O with diaresis) should look
> identical and be treated identically with U+004F foll. by U+0308. That's
> what users expect.  I don't know what's the best way to resolve
> this conflict. It may be time to consider seriously this particular
> aspect of SUS/POSIX.  I'm wondering how MacOS X (well, it's not 100%
> SUS/POSIX compliant, but nonetheless it's Unix) works in this area. It
> uses NFD. That is, 'U+00D6' is stored as 'U+004F U+0308' and both are
> treated idnetically.
> 

There *is* no way to solve this problem.  You have the same kind of
problem with U+0041 LATIN CAPTIAL LETTER A versus U+0391 GREEK CAPITAL
LETTER ALPHA.  However, if you attempt normalizations you *will*
introduce security holes in the system (as have been amply shown by
Windows, even though *its* normalizations are even much simpler.)

The only possible answer is to make sure a decoded representation is
available to the user (ls -b or somesuch.)  Attempting
canonicalization is doomed to failure, if nothing else when the next
version of Unicode comes out, and you already have files that are
encoded with a different set of normalizations.  Now your files cannot
be accessed!  Oops!

	-hpa
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