On Thu, May 28, 2015 at 04:35:27PM -0400, Dan Streetman wrote:
> Add list_last_or_null_rcu(), to simplify getting the last entry from a
> rcu-protected list. The standard list_last_entry() can't be used as it
> is not rcu-protected; the list may be modified concurrently. And the
> ->prev pointer can't be used, as only the ->next pointers are protected
> by rcu.
>
> This simply iterates forward through the entire list, to get to the last
> entry. If the list is empty, it returns NULL.
>
> Signed-off-by: Dan Streetman <ddstr...@ieee.org>
The list iteration functions are macros because they introduce a loop
with attached loop block. For this, is there any reason not to make it
an inline function instead of a macro?
> include/linux/rculist.h | 21 +++++++++++++++++++++
> 1 file changed, 21 insertions(+)
>
> diff --git a/include/linux/rculist.h b/include/linux/rculist.h
> index a18b16f..954fde5 100644
> --- a/include/linux/rculist.h
> +++ b/include/linux/rculist.h
> @@ -293,6 +293,27 @@ static inline void list_splice_init_rcu(struct list_head
> *list,
> })
>
> /**
> + * list_last_or_null_rcu - get the last element from a list
> + * @ptr: the list head 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.
> + *
> + * This primitive may safely run concurrently with the _rcu list-mutation
> + * primitives such as list_add_rcu() as long as it's guarded by
> rcu_read_lock().
> + */
> +#define list_last_or_null_rcu(ptr, type, member) \
> +({ \
> + struct list_head *__ptr = (ptr); \
> + struct list_head *__last = __ptr; \
> + struct list_head *__entry = list_next_rcu(__ptr); \
> + for (; __entry != __ptr; __entry = list_next_rcu(__entry)) \
> + __last = __entry; \
> + likely(__ptr != __last) ? list_entry_rcu(__last, type, member) : NULL; \
> +})
> +
> +/**
> * list_for_each_entry_rcu - iterate over rcu list of given type
> * @pos: the type * to use as a loop cursor.
> * @head: the head for your list.
> --
> 2.1.0
>
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