linux-kernel - [PATCH 1/2] list: add while_list_drain

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Date:	Tue, 4 Jun 2013 22:03:41 -0400
From:	Jörn Engel <joern@...fs.org>
To:	Arne Jansen <sensille@....net>
Cc:	Chris Mason <clmason@...ionio.com>,
	Christoph Hellwig <hch@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-btrfs@...r.kernel.org" <linux-btrfs@...r.kernel.org>
Subject: [PATCH 1/2] list: add while_list_drain_entry

I have seen a lot of boilerplate code that either follows the pattern of
	while (!list_empty(head)) {
		pos = list_entry(head->next, struct foo, list);
		list_del(pos->list);
		...
	}
or some variant thereof.

With this patch in, people can use
	while_list_drain_entry(pos, head, list) {
		...
	}

The patch also adds a while_list_drain variant, even though I have
only found a single user for that one so far.

Signed-off-by: Joern Engel <joern@...fs.org>
---
 include/linux/list.h |   18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/include/linux/list.h b/include/linux/list.h
index 6a1f8df..ab39c7d 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -557,6 +557,24 @@ static inline void list_splice_tail_init(struct list_head *list,
 #define list_safe_reset_next(pos, n, member)				\
 	n = list_entry(pos->member.next, typeof(*pos), member)
 
+/**
+ * while_list_drain - removes an entry from the list until it is empty
+ * @pos:	the &struct list_head to use as a loop cursor.
+ * @head:	the head of your list.
+ */
+#define while_list_drain(pos, head) \
+	while (list_empty(head) ? 0 : (pos = (head)->next, list_del(pos), 1))
+
+/**
+ * while_list_drain_entry - removes an entry from the list until it is empty
+ * @pos:	the type * to use as loop cursor.
+ * @head:	the head of your list.
+ * @member:	the name of the list_struct within the struct
+ */
+#define while_list_drain_entry(pos, head, member) \
+	while (list_empty(head) && (pos = list_first_entry((head), \
+		typeof(*pos), member), list_del((head)->next), 1))
+
 /*
  * Double linked lists with a single pointer list head.
  * Mostly useful for hash tables where the two pointer list head is
-- 
1.7.10.4

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