Re: [PATCH 1/2] fs/dcache: add d_compare() helper support

[Jeff Layton <jlayton@kernel.org>]

On Mon, 2022-05-16 at 20:20 +0800, Xiubo Li wrote:
> Signed-off-by: Xiubo Li <xiubli@redhat.com>
> ---
>  fs/dcache.c            | 15 +++++++++++++++
>  include/linux/dcache.h |  2 ++
>  2 files changed, 17 insertions(+)
> 
> diff --git a/fs/dcache.c b/fs/dcache.c
> index 93f4f5ee07bf..95a72f92a94b 100644
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -2262,6 +2262,21 @@ static inline bool d_same_name(const struct dentry *dentry,
>  				       name) == 0;
>  }
>  
> +/**
> + * d_compare - compare dentry name with case-exact name
> + * @parent: parent dentry
> + * @dentry: the negative dentry that was passed to the parent's lookup func
> + * @name:   the case-exact name to be associated with the returned dentry
> + *
> + * Return: 0 if names are same, or 1
> + */
> +bool d_compare(const struct dentry *parent, const struct dentry *dentry,
> +	       const struct qstr *name)
> +{
> +	return !d_same_name(dentry, parent, name);
> +}
> +EXPORT_SYMBOL(d_compare);
> +
>  /**
>   * __d_lookup_rcu - search for a dentry (racy, store-free)
>   * @parent: parent dentry
> diff --git a/include/linux/dcache.h b/include/linux/dcache.h
> index f5bba51480b2..444b2230e5c3 100644
> --- a/include/linux/dcache.h
> +++ b/include/linux/dcache.h
> @@ -233,6 +233,8 @@ extern struct dentry * d_alloc_parallel(struct dentry *, const struct qstr *,
>  					wait_queue_head_t *);
>  extern struct dentry * d_splice_alias(struct inode *, struct dentry *);
>  extern struct dentry * d_add_ci(struct dentry *, struct inode *, struct qstr *);
> +extern bool d_compare(const struct dentry *parent, const struct dentry *dentry,
> +		      const struct qstr *name);
>  extern struct dentry * d_exact_alias(struct dentry *, struct inode *);
>  extern struct dentry *d_find_any_alias(struct inode *inode);
>  extern struct dentry * d_obtain_alias(struct inode *);

I wonder if we ought to just un-inline and export d_same_name instead?
Still, this is less disruptive and the dcache code is hugely performance
sensitive. It's possible that inlining that function makes a difference.

Reviewed-by: Jeff Layton <jlayton@kernel.org>