linux-ext4 - Re: [PATCH 4/8] vfs: Fold casefolding into vfs

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Message-ID: <20191203074154.GA216261@architecture4>
Date:   Tue, 3 Dec 2019 15:41:54 +0800
From:   Gao Xiang <gaoxiang25@...wei.com>
To:     Daniel Rosenberg <drosen@...gle.com>
CC:     Theodore Ts'o <tytso@....edu>, <linux-ext4@...r.kernel.org>,
        Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <chao@...nel.org>,
        <linux-f2fs-devel@...ts.sourceforge.net>,
        Eric Biggers <ebiggers@...nel.org>,
        <linux-fscrypt@...r.kernel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Jonathan Corbet <corbet@....net>, <linux-doc@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
        Gabriel Krisman Bertazi <krisman@...labora.com>,
        <kernel-team@...roid.com>
Subject: Re: [PATCH 4/8] vfs: Fold casefolding into vfs

On Mon, Dec 02, 2019 at 09:10:45PM -0800, Daniel Rosenberg wrote:
> Ext4 and F2fs are both using casefolding, and they, along with any other
> filesystem that adds the feature, will be using identical dentry_ops.
> Additionally, those dentry ops interfere with the dentry_ops required
> for fscrypt once we add support for casefolding and encryption.
> Moving this into the vfs removes code duplication as well as the
> complication with encryption.
> 
> Currently this is pretty close to just moving the existing f2fs/ext4
> code up a level into the vfs, although there is a lot of room for
> improvement now.
> 
> Signed-off-by: Daniel Rosenberg <drosen@...gle.com>

I'm afraid that such vfs modification is unneeded.

Just a quick glance it seems just can be replaced by introducing some
.d_cmp, .d_hash helpers (or with little modification) and most non-Android
emulated storage files are not casefolded (even in Android).

"those dentry ops interfere with the dentry_ops required for fscrypt",
I don't think it's a real diffculty and it could be done with some
better approach instead.

Thanks,
Gao Xiang