On Thu, May 28, 2015 at 4:39 PM, <j...@joshtriplett.org> wrote:
> 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?
true, there's no reason i can see not to make it inline, let me send
an updated patch.
>
>> 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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