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 22:16:57 -0400
From:   Gabriel Krisman Bertazi <krisman@...labora.com>
To:     Eric Biggers <ebiggers@...nel.org>
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

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.

> I think it should work analogously to CONFIG_FS_ENCRYPTION and
> CONFIG_FS_ENCRYPTION_ALGS.  That is, CONFIG_UNICODE should be a user-selectable
> bool, and then the tristate symbols CONFIG_EXT4_FS and CONFIG_F2FS_FS should
> select the tristate symbol CONFIG_UNICODE_UTF8 if CONFIG_UNICODE.





-- 
Gabriel Krisman Bertazi