Re: UTF-8 and case-insensitivity

[H. Peter Anvin]

Followup to:  <16434.41376.453823.260362@xxxxxxxxx>
By author:    tridge@xxxxxxxxx
In newsgroup: linux.dev.kernel
> 
>  > I don't know how Windows does it, so maybe this thing is hardcoded, and 
>  > you don't even want "true" case insensitivity. 
> 
> NTFS has a 128k table on disk, created at mkfs time and indexed by the
> UCS2 character.

So you're hosed if anyone uses characters outside the UCS-2 character
set...

> The interesting thing about this table is that it doesn't seem to
> vary between different locales as one might expect. I have checked 3
> locales so far (Swedish, Japanese and English) and all have the same
> 128k table. I should check a few more locales to see if it really is
> the same everywhere. Contact me off-list if you have a NTFS
> filesystem created in a different locale and would be willing to run
> a test program against it to see if the table is different from the
> one we have in Samba.

There is a "standard" table, which is published by the Unicode
consortium.  However, the "standard" table isn't what you want in
certain locales, e.g. Turkish.

> There is stuff in the charset handling of every locale that does vary
> in windows, but it isn't the case table, its the "valid characters"
> map used to determine what characters are allowed when converting
> strings into legacy multi-byte encodings. Even I don't think that the
> kernel will ever have to deal with that crap unless someone is foolish
> enough to port Samba into the kernel (several people have actually
> done that despite the insanity of the idea, but they all did an
> absolutely terrible job of it and certainly didn't take care to get
> all the charset handling right).
> 
> > How "correct" is Windows?
> 
> from my rather limited point of view I always have to assume that
> windows is "correct", unless I can show that its behaviour leads to
> data loss, a security hole or something equally extreme.

Well, we don't want to support a bunch of hacks to make it behave like
Windows if what Windows does doesn't make sense.  If so you should use
a metalayer where you canonicalize the filenames and don't store
"Makefile" on the disk; store "makefile" and keep the "real" filename
stashed elsewhere, perhaps an EA.

	-hpa

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