Re: [PATCH 01/12] list.h: add a list_pop helper

Darrick J. Wong
2019-06-24T14:54:08Z

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@lst.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@oracle.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
>