Re: [PATCH 2/3] hlist-bl: add hlist_bl_fake()

[Kent Overstreet <kent.overstreet@gmail.com>]

On Tue, Apr 06, 2021 at 10:33:42PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> in preparation for switching the VFS inode cache over the hlist_bl
> lists, we nee dto be able to fake a list node that looks like it is
> hased for correct operation of filesystems that don't directly use
> the VFS indoe cache.
> 
> Signed-off-by: Dave Chinner <dchinner@redhat.com>

Reviewed-by: Kent Overstreet <kent.overstreet@gmail.com>

> ---
>  include/linux/list_bl.h | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/include/linux/list_bl.h b/include/linux/list_bl.h
> index ae1b541446c9..8ee2bf5af131 100644
> --- a/include/linux/list_bl.h
> +++ b/include/linux/list_bl.h
> @@ -143,6 +143,28 @@ static inline void hlist_bl_del_init(struct hlist_bl_node *n)
>  	}
>  }
>  
> +/**
> + * hlist_bl_add_fake - create a fake list consisting of a single headless node
> + * @n: Node to make a fake list out of
> + *
> + * This makes @n appear to be its own predecessor on a headless hlist.
> + * The point of this is to allow things like hlist_bl_del() to work correctly
> + * in cases where there is no list.
> + */
> +static inline void hlist_bl_add_fake(struct hlist_bl_node *n)
> +{
> +	n->pprev = &n->next;
> +}
> +
> +/**
> + * hlist_fake: Is this node a fake hlist_bl?
> + * @h: Node to check for being a self-referential fake hlist.
> + */
> +static inline bool hlist_bl_fake(struct hlist_bl_node *n)
> +{
> +	return n->pprev == &n->next;
> +}
> +
>  static inline void hlist_bl_lock(struct hlist_bl_head *b)
>  {
>  	bit_spin_lock(0, (unsigned long *)b);
> -- 
> 2.31.0
>