linux-kernel - Re: [PATCH 01/12] list.h: add a list

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Date:   Mon, 24 Jun 2019 07:53:25 -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 01/12] list.h: add a list_pop helper

On Mon, Jun 24, 2019 at 07:52:42AM +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 a list_pop helper to implement this behavior.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  include/linux/list.h | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/include/linux/list.h b/include/linux/list.h
> index e951228db4b2..e07a5f54cc9d 100644
> --- a/include/linux/list.h
> +++ b/include/linux/list.h
> @@ -500,6 +500,28 @@ 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.
> + * @type:	the type of the struct this is embedded in.
> + * @member:	the name of the list_head within the struct.
> + *
> + * Note that if the list is empty, it returns NULL.
> + */
> +#define list_pop(list, type, member) 				\

Unnecessary space after the ')' here, though I can fix that up if I
merge this version of the series...

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

--D


> +({								\
> +	struct list_head *head__ = (list);			\
> +	struct list_head *pos__ = READ_ONCE(head__->next);	\
> +	type *entry__ = NULL;					\
> +								\
> +	if (pos__ != head__) {					\
> +		entry__ = list_entry(pos__, type, member);	\
> +		list_del(pos__);				\
> +	}							\
> +								\
> +	entry__;						\
> +})
> +
>  /**
>   * list_next_entry - get the next element in list
>   * @pos:	the type * to cursor
> -- 
> 2.20.1
>