linux-kernel - Re: [PATCH v2 1/6] fs: Add case sensitivity info to file

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Message-ID: <20251211234152.GA460739@google.com>
Date: Thu, 11 Dec 2025 23:41:52 +0000
From: Eric Biggers <ebiggers@...nel.org>
To: Chuck Lever <cel@...nel.org>
Cc: Al Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>,
	linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
	linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	hirofumi@...l.parknet.co.jp,
	almaz.alexandrovich@...agon-software.com, tytso@....edu,
	adilger.kernel@...ger.ca, Volker.Lendecke@...net.de,
	Chuck Lever <chuck.lever@...cle.com>
Subject: Re: [PATCH v2 1/6] fs: Add case sensitivity info to file_kattr

On Thu, Dec 11, 2025 at 10:21:11AM -0500, Chuck Lever wrote:
> +/* Values stored in the low-order byte */
> +enum fileattr_case_folding {
> +	/* Code points are compared directly with no case folding. */
> +	FILEATTR_CASEFOLD_NONE = 0,
> +
> +	/* ASCII case-insensitive: A-Z are treated as a-z. */
> +	FILEATTR_CASEFOLD_ASCII,
> +
> +	/* Unicode case-insensitive matching. */
> +	FILEATTR_CASEFOLD_UNICODE,
> +};

What does "Unicode case-insensitive matching" mean?  There are many
different things it could mean: there are multiple types of Unicode
normalization, Unicode case-folding, NTFS's upper case table, etc.
There are also multiple versions of each.

I see you're proposing that ext4, fat, and ntfs3 all set
FILEATTR_CASEFOLD_UNICODE, at least in some cases.

That seems odd, since they don't do the matching the same way.

- Eric