linux-kernel - Re: [PATCH v5 4/4] fs: unicode: Add utf8 module and a unicode layer

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Date:   Mon, 29 Mar 2021 22:47:52 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Gabriel Krisman Bertazi <krisman@...labora.com>
Cc:     Shreeya Patel <shreeya.patel@...labora.com>, tytso@....edu,
        adilger.kernel@...ger.ca, jaegeuk@...nel.org, chao@...nel.org,
        drosen@...gle.com, yuchao0@...wei.com, linux-ext4@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-fsdevel@...r.kernel.org, kernel@...labora.com,
        andre.almeida@...labora.com
Subject: Re: [PATCH v5 4/4] fs: unicode: Add utf8 module and a unicode layer

On Mon, Mar 29, 2021 at 10:16:57PM -0400, Gabriel Krisman Bertazi wrote:
> Eric Biggers <ebiggers@...nel.org> writes:
> 
> > On Tue, Mar 30, 2021 at 02:12:40AM +0530, Shreeya Patel wrote:
> >> diff --git a/fs/unicode/Kconfig b/fs/unicode/Kconfig
> >> index 2c27b9a5cd6c..ad4b837f2eb2 100644
> >> --- a/fs/unicode/Kconfig
> >> +++ b/fs/unicode/Kconfig
> >> @@ -2,13 +2,26 @@
> >>  #
> >>  # UTF-8 normalization
> >>  #
> >> +# CONFIG_UNICODE will be automatically enabled if CONFIG_UNICODE_UTF8
> >> +# is enabled. This config option adds the unicode subsystem layer which loads
> >> +# the UTF-8 module whenever any filesystem needs it.
> >>  config UNICODE
> >> -	bool "UTF-8 normalization and casefolding support"
> >> +	bool
> >> +
> >> +# utf8data.h_shipped has a large database table which is an auto-generated
> >> +# decodification trie for the unicode normalization functions and it is not
> >> +# necessary to carry this large table in the kernel.
> >> +# Enabling UNICODE_UTF8 option will allow UTF-8 encoding to be built as a
> >> +# module and this module will be loaded by the unicode subsystem layer only
> >> +# when any filesystem needs it.
> >> +config UNICODE_UTF8
> >> +	tristate "UTF-8 module"
> >>  	help
> >>  	  Say Y here to enable UTF-8 NFD normalization and NFD+CF casefolding
> >>  	  support.
> >> +	select UNICODE
> >
> > This seems problematic; it allows users to set CONFIG_EXT4_FS=y (or
> > CONFIG_F2FS_FS=y) but then CONFIG_UNICODE_UTF8=m.  Then the filesystem won't
> > work if the modules are located on the filesystem itself.
> 
> Hi Eric,
> 
> Isn't this a user problem?  If the modules required to boot are on the
> filesystem itself, you are in trouble.  But, if that is the case, your
> rootfs is case-insensitive and you gotta have utf8 as built-in or have
> it in an early userspace.
> 

We could make it the user's problem, but that seems rather unfriendly.
Especially because the utf8 module would be needed if the filesystem has the
casefold feature at all, regardless of whether any casefolded directories are
needed at boot time or not.  (Unless there is a plan to change that?)

- Eric