Hi Oleg,
Sorry for my late response!
On 11/16/2013 01:12 AM, Oleg Nesterov wrote:
> On 11/15, Oleg Nesterov wrote:
>>
>> But probably list_last_entry() makes sense in the "else" branch,
>> athough this is minor.
>>
>>
>> Off-topic. Not sure this really makes sense, but I was thinking about
>>
>> list_get_first(pos, head, member) \
>> ((pos) = list_first_entry(head, typeof(*pos), member))
>>
>> and list_get_first() last of course. The obvious advantage is that
>> compared to
>>
>> tr = list_last_entry(sdp->sd_ail1_list, struct gfs2_trans, tr_list);
>>
>> above you do not need to type "struct gfs2_trans",
>>
>> list_get_last(tr, sdp->sd_ail1_list, tr_list);
>>
>> looks a bit better.
>
> And list.h can use it too.
>
> So how about the patch below? I can't decide whether it cleanups or
> uglfies the code, I do not trust my taste ;) But to me it looks a
> bit better this way.
I personally think this is better for GFS2 case if I understood correctly,
and it can make the existing list helper a bit neat per my taste :)
The current list_first_entry() works fine consider a common pattern below:
while (!list_empty(ptr)) {
struct dummy *p = list_first_entry(ptr, struct dummy, member);
....
}
But I'm not sure if we can find out more external use cases can get
benefits with list_get_first/last...
Thanks,
-Jeff
>
> Oleg.
> --
>
> diff --git a/include/linux/list.h b/include/linux/list.h
> index ef95941..f52aba8 100644
> --- a/include/linux/list.h
> +++ b/include/linux/list.h
> @@ -372,6 +372,12 @@ static inline void list_splice_tail_init(struct list_head *list,
> #define list_last_entry(ptr, type, member) \
> list_entry((ptr)->prev, type, member)
>
> +#define list_get_first(pos, head, member) \
> + ((pos) = list_first_entry(head, typeof(*(pos)), member))
> +
> +#define list_get_last(pos, head, member) \
> + ((pos) = list_last_entry(head, typeof(*(pos)), member))
> +
> /**
> * list_first_entry_or_null - get the first element from a list
> * @ptr: the list head to take the element from.
> @@ -443,7 +449,7 @@ static inline void list_splice_tail_init(struct list_head *list,
> * @member: the name of the list_struct within the struct.
> */
> #define list_for_each_entry(pos, head, member) \
> - for (pos = list_first_entry(head, typeof(*pos), member); \
> + for (list_get_first(pos, head, member); \
> &pos->member != (head); \
> pos = list_next_entry(pos, member))
>
> @@ -454,7 +460,7 @@ static inline void list_splice_tail_init(struct list_head *list,
> * @member: the name of the list_struct within the struct.
> */
> #define list_for_each_entry_reverse(pos, head, member) \
> - for (pos = list_last_entry(head, typeof(*pos), member); \
> + for (list_get_last(pos, head, member); \
> &pos->member != (head); \
> pos = list_prev_entry(pos, member))
>
> @@ -517,7 +523,7 @@ static inline void list_splice_tail_init(struct list_head *list,
> * @member: the name of the list_struct within the struct.
> */
> #define list_for_each_entry_safe(pos, n, head, member) \
> - for (pos = list_first_entry(head, typeof(*pos), member), \
> + for (list_get_first(pos, head, member), \
> n = list_next_entry(pos, member); \
> &pos->member != (head); \
> pos = n, n = list_next_entry(n, member))
> @@ -564,7 +570,7 @@ static inline void list_splice_tail_init(struct list_head *list,
> * of list entry.
> */
> #define list_for_each_entry_safe_reverse(pos, n, head, member) \
> - for (pos = list_last_entry(head, typeof(*pos), member), \
> + for (list_get_last(pos, head, member), \
> n = list_prev_entry(pos, member); \
> &pos->member != (head); \
> pos = n, n = list_prev_entry(n, member))
>
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