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Subject: Re: [f2fs-dev] [PATCH v4 2/3] f2fs: include charset encoding
 information in the superblock
To:     Daniel Rosenberg <drosen@google.com>,
        Jaegeuk Kim <jaegeuk@kernel.org>, Chao Yu <yuchao0@huawei.com>,
        Jonathan Corbet <corbet@lwn.net>,
        linux-f2fs-devel@lists.sourceforge.net
Cc:     linux-doc@vger.kernel.org, linux-api@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        kernel-team@android.com
References: <20190723230529.251659-1-drosen@google.com>
 <20190723230529.251659-3-drosen@google.com>
From:   Chao Yu <chao@kernel.org>
Message-ID: <af60ce55-1a29-d8da-81e4-77c880f4a0d0@kernel.org>
Date:   Sun, 28 Jul 2019 08:45:51 +0800
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On 2019-7-24 7:05, Daniel Rosenberg via Linux-f2fs-devel wrote:
> Add charset encoding to f2fs to support casefolding. It is modeled after
> the same feature introduced in commit c83ad55eaa91 ("ext4: include charset
> encoding information in the superblock")
> 
> Currently this is not compatible with encryption, similar to the current
> ext4 imlpementation. This will change in the future.
> 
> From the ext4 patch:
> """
> The s_encoding field stores a magic number indicating the encoding
> format and version used globally by file and directory names in the
> filesystem.  The s_encoding_flags defines policies for using the charset
> encoding, like how to handle invalid sequences.  The magic number is
> mapped to the exact charset table, but the mapping is specific to ext4.
> Since we don't have any commitment to support old encodings, the only
> encoding I am supporting right now is utf8-12.1.0.
> 
> The current implementation prevents the user from enabling encoding and
> per-directory encryption on the same filesystem at the same time.  The
> incompatibility between these features lies in how we do efficient
> directory searches when we cannot be sure the encryption of the user
> provided fname will match the actual hash stored in the disk without
> decrypting every directory entry, because of normalization cases.  My
> quickest solution is to simply block the concurrent use of these
> features for now, and enable it later, once we have a better solution.
> """
> 
> Signed-off-by: Daniel Rosenberg <drosen@google.com>

Reviewed-by: Chao Yu <yuchao0@huawei.com>

Thanks,