[RFC v2] Unicode/UTF-8 support for XFS

[Olaf Weber]

On 26-09-14 19:04, Jeremy Allison wrote:
> On Fri, Sep 26, 2014 at 09:56:05AM -0700, Christoph Hellwig wrote:
>>
>> My take on this is:
>>
>>   - I think we'll have to prevent non-utf8 file names for any cases where
>>     we use utf8 normalization.  If you do not use utf8 normalization
>>     it's plain old Unix everything is allowed.
>>
>>   - I think utf8 normalization vs not should be mkfs option, to make sure
>>     everyone including kernel and repair knows what sort of filesystem
>>     deal with.
>>
>>   - case insensitive matching for utf8 normalized filesystems should be
>>     a runtime decision.  mount time for now, but Samba people would be
>>     extremly happy to allow per-operation or per-process CI matching.
>>     But that is another totally different discusion I'd like to keep
>>     separate, I just want to make sure the disk format allows for it for
>>     now.
>
> Actually, I'm so eager for case-insensitive matching I'd
> take "at format time", as with ZFS :-) :-).

My argument against "mount time case-insensitivity" and for "mkfs time 
case-insensitivity" is related to switching from the case-sensitive domain 
to the case-insensitive one.

For case-sensitive, from "README" to "readme" there are 64 different 
possible filenames.  Let's say you create 63 out of these 64. Now remount 
the filesystem case-insensitive, and try to open by the 64th version of 
"readme". It is not an exact match for any of the 63 candidate files, and a 
case-insensitive match to all 63 candidate files. Which of these 63 files 
should be opened, and why that one in particular?

> Having CI matching can speed up Samba operations by a
> factor of 10 on large directories (warning, number made
> up, depending on the number of entries per dir :-).

I really want that to be true, but the proof of the pudding...

Olaf

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