linux-kernel - Re: [PATCH v8 6/8] libfs: Add generic function for setting dentry

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Message-ID: <20200307054115.GC1069@sol.localdomain>
Date:   Fri, 6 Mar 2020 21:41:15 -0800
From:   Eric Biggers <ebiggers@...nel.org>
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,
        linux-fscrypt@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Richard Weinberger <richard@....at>,
        linux-mtd@...ts.infradead.org,
        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 v8 6/8] libfs: Add generic function for setting dentry_ops

On Fri, Mar 06, 2020 at 06:36:09PM -0800, Daniel Rosenberg wrote:
> This adds a function to set dentry operations at lookup time that will
> work for both encrypted files and casefolded filenames.
> 
> A filesystem that supports both features simultaneously can use this
> function during lookup preperations to set up its dentry operations once
> fscrypt no longer does that itself.
> 
> Signed-off-by: Daniel Rosenberg <drosen@...gle.com>
> ---
>  fs/libfs.c         | 50 ++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/fs.h |  2 ++
>  2 files changed, 52 insertions(+)
> 
> diff --git a/fs/libfs.c b/fs/libfs.c
> index 0eaa63a9ae037..bdda03c8ece9e 100644
> --- a/fs/libfs.c
> +++ b/fs/libfs.c
> @@ -1474,4 +1474,54 @@ int generic_ci_d_hash(const struct dentry *dentry, struct qstr *str)
>  	return ret;
>  }
>  EXPORT_SYMBOL(generic_ci_d_hash);
> +
> +static const struct dentry_operations generic_ci_dentry_ops = {
> +	.d_hash = generic_ci_d_hash,
> +	.d_compare = generic_ci_d_compare,
> +};
> +#endif
> +
> +#ifdef CONFIG_FS_ENCRYPTION
> +static const struct dentry_operations generic_encrypted_dentry_ops = {
> +	.d_revalidate = fscrypt_d_revalidate,
> +};
> +#endif
> +
> +#if IS_ENABLED(CONFIG_UNICODE) && IS_ENABLED(CONFIG_FS_ENCRYPTION)
> +static const struct dentry_operations generic_encrypted_ci_dentry_ops = {
> +	.d_hash = generic_ci_d_hash,
> +	.d_compare = generic_ci_d_compare,
> +	.d_revalidate = fscrypt_d_revalidate,
> +};
> +#endif
> +
> +/**
> + * generic_set_encrypted_ci_d_ops - helper for setting d_ops for given dentry
> + * @dir:	parent of dentry whose ops to set
> + * @dentry:	dentry to set ops on
> + *
> + * This function sets the dentry ops for the given dentry to handle both
> + * casefolding and encryption of the dentry name.
> + */
> +void generic_set_encrypted_ci_d_ops(struct inode *dir, struct dentry *dentry)
> +{
> +#ifdef CONFIG_FS_ENCRYPTION
> +	if (dentry->d_flags & DCACHE_ENCRYPTED_NAME) {
> +#ifdef CONFIG_UNICODE
> +		if (dir->i_sb->s_encoding) {
> +			d_set_d_op(dentry, &generic_encrypted_ci_dentry_ops);
> +			return;
> +		}
>  #endif
> +		d_set_d_op(dentry, &generic_encrypted_dentry_ops);
> +		return;
> +	}
> +#endif
> +#ifdef CONFIG_UNICODE
> +	if (dir->i_sb->s_encoding) {
> +		d_set_d_op(dentry, &generic_ci_dentry_ops);
> +		return;
> +	}
> +#endif
> +}
> +EXPORT_SYMBOL(generic_set_encrypted_ci_d_ops);

What's wrong with using dentry->d_sb?  Then the 'dir' parameter wouldn't be
needed.

Also, can you please document why the dentry_operations for casefolding are set
per-filesystem while the dentry_operations for encryption are set per-dentry,
despite both features actually being per-directory things?

- Eric