Re: [f2fs-dev] [PATCH v2 1/3] libfs: Add generic function for setting dentry_ops

[Eric Biggers]

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