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Date:   Tue, 17 Nov 2020 10:36:06 -0800
From:   Eric Biggers <ebiggers@kernel.org>
To:     Daniel Rosenberg <drosen@google.com>
Cc:     kernel-team@android.com, "Theodore Y . Ts'o" <tytso@mit.edu>,
        Richard Weinberger <richard@nod.at>,
        linux-kernel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net,
        linux-fscrypt@vger.kernel.org,
        Andreas Dilger <adilger.kernel@dilger.ca>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        linux-mtd@lists.infradead.org, linux-fsdevel@vger.kernel.org,
        Jaegeuk Kim <jaegeuk@kernel.org>, linux-ext4@vger.kernel.org,
        Gabriel Krisman Bertazi <krisman@collabora.com>
Subject: Re: [f2fs-dev] [PATCH v2 1/3] libfs: Add generic function for
 setting dentry_ops
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 <20201117040315.28548-2-drosen@google.com>
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On Tue, Nov 17, 2020 at 10:16:49AM -0800, Eric Biggers wrote:
> 
> Here's a suggestion which I think explains it a lot better.  It's still possible
> I'm misunderstanding something, though, so please check it carefully:
> 
> /**
>  * generic_set_encrypted_ci_d_ops - helper for setting d_ops for given dentry
>  * @dentry:	dentry to set ops on
>  *
>  * Casefolded directories need d_hash and d_compare set, so that the dentries
>  * contained in them are handled case-insensitively.  Note that these operations
>  * are needed on the parent directory rather than on the dentries in it, and the
>  * casefolding flag can be enabled on an empty directory later but the
>  * dentry_operations can't be changed later.  As a result, if the filesystem has
>  * casefolding support enabled at all, we have to give all dentries the
>  * casefolding operations even if their inode doesn't have the casefolding flag
>  * currently (and thus the casefolding ops would be no-ops for now).
>  *
>  * Encryption works differently in that the only dentry operation it needs is
>  * d_revalidate, which it only needs on dentries that have the no-key name flag.
>  * The no-key flag can't be set "later", so we don't have to worry about that.
>  *
>  * Finally, to maximize compatibility with overlayfs (which isn't compatible
>  * with certain dentry operations) and to avoid taking an unnecessary
>  * performance hit, we use custom dentry_operations for each possible
>  * combination rather always installing all operations.
>  */

Last line in my suggestion has a typo: "rather" => "rather than".

- Eric