linux-kernel - Re: exfat upcase table for code points above U+FFFF (Was: Re: [PATCH] staging: exfat: add exfat filesystem code to staging)

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Message-ID: <20200427154913.GR13035@sasha-vm>
Date:   Mon, 27 Apr 2020 11:49:13 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     Pali Rohár <pali@...nel.org>
Cc:     Valdis Klētnieks <valdis.kletnieks@...edu>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        devel@...verdev.osuosl.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Sasha Levin <alexander.levin@...rosoft.com>,
        Christoph Hellwig <hch@...radead.org>
Subject: Re: exfat upcase table for code points above U+FFFF (Was: Re:
 [PATCH] staging: exfat: add exfat filesystem code to staging)

On Tue, Apr 21, 2020 at 11:30:45PM +0200, Pali Rohár wrote:
>On Thursday 13 February 2020 16:18:47 Sasha Levin wrote:
>> On Thu, Feb 13, 2020 at 01:06:56AM +0100, Pali Rohár wrote:
>> > In released exFAT specification is not written how are Unicode code
>> > points above U+FFFF represented in exFAT upcase table. Normally in
>> > UTF-16 are Unicode code points above U+FFFF represented by surrogate
>> > pairs but compression format of exFAT upcase table is not clear how to
>> > do it there.
>> >
>> > Are you able to send question about this problem to relevant MS people?
>> >
>> > New Linux implementation of exfat which is waiting on mailing list just
>> > do not support Unicode code points above U+FFFF in exFAT upcase table.
>>
>> Sure, I'll forward this question on. I'll see if I can get someone from
>> their team who could be available to answer questions such as these in
>> the future - Microsoft is interested in maintaining compatiblity between
>> Linux and Windows exFAT implementations.
>
>Hello Sasha! Have you got any answer from exfat MS team about upcase
>table for Unicode code points above U+FFFF?

Sorry for taking so long. This is my understanding from the Windows
folks: Windows filesystems just don't support variable encoding length,
and expect UCS-2 strings.

-- 
Thanks,
Sasha