From: Matthew Wilcox <willy@infradead.org>
To: lampahome <pahome.chen@mirlab.org>
Cc: linux-fsdevel@vger.kernel.org
Subject: Re: why do we need utf8 normalization when compare name?
Date: Mon, 2 Mar 2020 04:54:32 -0800 [thread overview]
Message-ID: <20200302125432.GP29971@bombadil.infradead.org> (raw)
In-Reply-To: <CAB3eZfv4VSj6_XBBdHK12iX_RakhvXnTCFAmQfwogR34uySo3Q@mail.gmail.com>
On Mon, Mar 02, 2020 at 05:00:24PM +0800, lampahome wrote:
> According to case insensitive since kernel 5.2, d_compare will
> transform string into normalized form and then compare.
>
> But why do we need this normalization function? Could we just compare
> by utf8 string?
Have you read https://en.wikipedia.org/wiki/Unicode_equivalence ?
We need to decide whether a user with a case-insensitive filesystem
who looks up a file with the name U+00E5 (lower case "a" with ring)
should find a file which is named U+00C5 (upper case "A" with ring)
or U+212B (Angstrom sign).
Then there's the question of whether e-acute is stored as U+00E9
or U+0065 followed by U+0301, and both of those will need to be found
by a user search for U+00C9 or a user searching for U+0045 U+0301.
So yes, normalisation needs to be done.
next prev parent reply other threads:[~2020-03-02 12:54 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-02 9:00 why do we need utf8 normalization when compare name? lampahome
2020-03-02 10:37 ` Aleksa Sarai
2020-03-02 10:47 ` Aleksa Sarai
2020-03-03 1:48 ` lampahome
[not found] ` <20200303070928.aawxoyeq77wnc3ts@yavin>
2020-03-03 10:13 ` lampahome
2020-03-03 17:22 ` Theodore Y. Ts'o
2020-03-02 12:54 ` Matthew Wilcox [this message]
2020-03-02 15:28 ` Al Viro
2020-03-02 17:14 ` Matthew Wilcox
2020-03-02 18:12 ` Theodore Y. Ts'o
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