[Debburn-devel] Character sets in UDF

[Peter Samuelson]

[Florent Rougon]
> I'm not sure what you mean with "If you know the encoding". If you're
> talking about my files: yes, sure, I know the encoding. But if you're
> talking about a random UDF filesystem burnt to DVD, I don't know if
> it's possible, and that's a big part of my question.

There _is_ metadata for each filename's encoding, a byte that is either
0x08 or 0x16.  The spec is not explicit about what the bytes mean, but
from context - particularly the mention of the Unicode byte-order mark
0xfeff / 0xfffe - I gather that 8 means ASCII and 16 means UCS-2BE.  I
just checked the Linux kernel source, and it agrees with me, for both
reading and writing.

Note also that for _writing_ filenames, having a target encoding
(UCS-2BE) is not enough, you also need to specify a normalization form.
The UDF errata document DCN-2157 recommends Normalization Form C (NFC).
Almost everyone on Linux uses NFC already, so that should not be a
problem.

It's possible that some OSes now use UTF-16BE instead of UCS-2BE, but
that only matters if your filenames include Unicode characters with
codepoints higher than 0xffff, which is rare.  The Linux UDF driver
(the only driver whose source code I have handy) uses UCS-2BE.
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