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Date: Fri, 15 Nov 2013 18:12:59 +0100 From: Oleg Nesterov <oleg@...hat.com> To: Jeff Liu <jeff.liu@...cle.com> Cc: linux-kernel@...r.kernel.org, akpm@...ux-foundation.org, "xfs@....sgi.com" <xfs@....sgi.com>, cluster-devel@...hat.com, linux-mtd@...ts.infradead.org, jfs-discussion@...ts.sourceforge.net, jiri@...nulli.us, gregkh@...uxfoundation.org Subject: introduce list_get_first/last (Was: [PATCH 3/6] gfs2: simplify current_tail() via list_last_entry_or_null()) 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. 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)) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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