Re: [PATCH v8 6/8] libfs: Add generic function for setting dentry_ops

Eric Biggers
2020-03-07T05:41:22Z

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@google.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