linux-kernel - [PATCH v4 2/3] llist: add a safe version of llist_for_each

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Message-ID: <1355395179-55724-2-git-send-email-roger.pau@citrix.com>
Date:	Thu, 13 Dec 2012 11:39:38 +0100
From:	Roger Pau Monne <roger.pau@...rix.com>
To:	<linux-kernel@...r.kernel.org>
CC:	Roger Pau Monne <roger.pau@...rix.com>,
	Huang Ying <ying.huang@...el.com>,
	Konrad Rzeszutek Wilk <konrad@...nel.org>
Subject: [PATCH v4 2/3] llist: add a safe version of llist_for_each_entry

Signed-off-by: Roger Pau Monné <roger.pau@...rix.com>
Cc: Huang Ying <ying.huang@...el.com>
Cc: Konrad Rzeszutek Wilk <konrad@...nel.org>
---
Changes since v3:
 * Change n to use type *, to keep the same semantics as
   list_for_each_entry_safe.
Changes since v2:
 * Allow to pass a NULL node as the first entry of deleted list
   entries.
---
 include/linux/llist.h |   29 +++++++++++++++++++++++++++++
 1 files changed, 29 insertions(+), 0 deletions(-)

diff --git a/include/linux/llist.h b/include/linux/llist.h
index a5199f6..f551ac4 100644
--- a/include/linux/llist.h
+++ b/include/linux/llist.h
@@ -125,6 +125,35 @@ static inline void init_llist_head(struct llist_head *list)
 	     (pos) = llist_entry((pos)->member.next, typeof(*(pos)), member))
 
 /**
+ * llist_for_each_entry_safe - safely iterate over some deleted entries of
+ *                             lock-less list of given type
+ * @pos:	the type * to use as a loop cursor.
+ * @n:		another type * to use as temporary storage
+ * @node:	the fist entry of deleted list entries.
+ * @member:	the name of the llist_node with the struct.
+ *
+ * In general, some entries of the lock-less list can be traversed
+ * safely only after being removed from list, so start with an entry
+ * instead of list head.
+ *
+ * If being used on entries deleted from lock-less list directly, the
+ * traverse order is from the newest to the oldest added entry.  If
+ * you want to traverse from the oldest to the newest, you must
+ * reverse the order by yourself before traversing.
+ *
+ * n is used to store a reference to the next item llist_node, so
+ * pos can be freed while iterating.
+ */
+#define llist_for_each_entry_safe(pos, n, node, member)		\
+	for ((pos) = llist_entry((node), typeof(*(pos)), member),	\
+	     (n) = llist_entry(((&(pos)->member != NULL) ?		\
+	         (pos)->member.next : NULL), typeof(*(pos)), member);	\
+	     &(pos)->member != NULL;					\
+	     (pos) = n,							\
+	     (n) = llist_entry(((&(pos)->member != NULL) ?		\
+	         (pos)->member.next : NULL), typeof(*(pos)), member))
+
+/**
  * llist_empty - tests whether a lock-less list is empty
  * @head:	the list to test
  *
-- 
1.7.7.5 (Apple Git-26)

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