linux-kernel - Re: [PATCH 01/13] list.h: add list_pop and list_pop

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Message-ID: <20190627204842.GR5171@magnolia>
Date:   Thu, 27 Jun 2019 13:48:42 -0700
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Damien Le Moal <Damien.LeMoal@....com>,
        Andreas Gruenbacher <agruenba@...hat.com>,
        linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 01/13] list.h: add list_pop and list_pop_entry helpers

On Thu, Jun 27, 2019 at 12:48:24PM +0200, Christoph Hellwig wrote:
> We have a very common pattern where we want to delete the first entry
> from a list and return it as the properly typed container structure.
> 
> Add two helpers to implement this behavior.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>

LGTM,
Reviewed-by: Darrick J. Wong <darrick.wong@...cle.com>

--D

> ---
>  include/linux/list.h | 33 +++++++++++++++++++++++++++++++++
>  1 file changed, 33 insertions(+)
> 
> diff --git a/include/linux/list.h b/include/linux/list.h
> index e951228db4b2..ba6e27d2235a 100644
> --- a/include/linux/list.h
> +++ b/include/linux/list.h
> @@ -500,6 +500,39 @@ static inline void list_splice_tail_init(struct list_head *list,
>  	pos__ != head__ ? list_entry(pos__, type, member) : NULL; \
>  })
>  
> +/**
> + * list_pop - delete the first entry from a list and return it
> + * @list:	the list to take the element from.
> + *
> + * Return the list entry after @list.  If @list is empty return NULL.
> + */
> +static inline struct list_head *list_pop(struct list_head *list)
> +{
> +	struct list_head *pos = READ_ONCE(list->next);
> +
> +	if (pos == list)
> +		return NULL;
> +	list_del(pos);
> +	return pos;
> +}
> +
> +/**
> + * list_pop_entry - delete the first entry from a list and return the
> + *			containing structure
> + * @list:	the list to take the element from.
> + * @type:	the type of the struct this is embedded in.
> + * @member:	the name of the list_head within the struct.
> + *
> + * Return the containing structure for the list entry after @list.  If @list
> + * is empty return NULL.
> + */
> +#define list_pop_entry(list, type, member)			\
> +({								\
> +	struct list_head *pos__ = list_pop(list);		\
> +								\
> +	pos__ ? list_entry(pos__, type, member) : NULL;		\
> +})
> +
>  /**
>   * list_next_entry - get the next element in list
>   * @pos:	the type * to cursor
> -- 
> 2.20.1
>