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From: "Theodore Y. Ts'o" <tytso@mit.edu>
To: "Pali Rohár" <pali.rohar@gmail.com>
Cc: Jan Kara <jack@suse.cz>,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-ntfs-dev@lists.sourceforge.net, linux-cifs@vger.kernel.org,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Luis de Bethencourt <luisbg@kernel.org>,
	Salah Triki <salah.triki@gmail.com>,
	Steve French <sfrench@samba.org>,
	OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	David Sterba <dsterba@suse.com>,
	Dave Kleikamp <shaggy@kernel.org>,
	Anton Altaparmakov <anton@tuxera.com>, Jan Kara <jack@suse.com>,
	Eric Sandeen <sandeen@redhat.com>,
	Namjae Jeon <linkinjeon@gmail.com>, Pavel Machek <pavel@ucw.cz>,
	Christoph Hellwig <hch@infradead.org>
Subject: Re: Unification of filesystem encoding options
Date: Tue, 7 Jan 2020 15:03:01 -0500
Message-ID: <20200107200301.GE3619@mit.edu> (raw)
In-Reply-To: <20200107173842.ciskn4ahuhiklycm@pali>

On Tue, Jan 07, 2020 at 06:38:42PM +0100, Pali Rohár wrote:
> Adding support for case-insensitivity into UTF-8 NLS encoding would mean
> to create completely new kernel NLS API (which would support variable
> length encodings) and rewrite all NLS filesystems to use this new API.
> Also all existing NLS encodings would be needed to port into this new
> API.
> 
> It is really something which have a value? Just because of UTF-8?
> 
> For me it looks like better option would be to remove UTF-8 NLS encoding
> as it is broken. Some filesystems already do not use NLS API for their
> UTF-8 support (e.g. vfat, udf or newly prepared exfat). And others could
> be modified/extended/fixed in similar way.

You didn't mention ext4 and f2fs, which is using the Unicode code in
fs/unicode for its case-folding and normalization support.  Ext4 and
f2fs only supports utf-8, so using the NLS API would have added no
value --- and it as you pointed out, the NLS API doesn't support
variable length encoding anyway.  In contrast the fs/unicode functions
have support for full Unicode case folding and normalization, and
currently has the latest Unicode 12.1 tables (released May 2019).

What I'd suggest is to create a new API, enhancing the functions in
fs/unicode, to support those file systems that need to deal with
UTF-16 and UTF-32 for their on-disk directory format, and that we
assume that for the most part, userspace *will* be using a UTF-8
encoding for the user<->kernel interface.  We can keep the existing
NLS interface and mount options for legacy support, but in my opinion
it's not worth the effort to try to do anything else.

					- Ted

  reply index

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-02 21:18 Pali Rohár
2020-01-07 13:32 ` Jan Kara
2020-01-07 17:38   ` Pali Rohár
2020-01-07 20:03     ` Theodore Y. Ts'o [this message]
2020-01-07 20:37       ` Pali Rohár
2020-01-08  7:13         ` OGAWA Hirofumi
2020-01-08  7:00     ` OGAWA Hirofumi

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