linux-kernel - [PATCH 01/12] list.h: add a list

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Message-Id: <20190624055253.31183-2-hch@lst.de>
Date:   Mon, 24 Jun 2019 07:52:42 +0200
From:   Christoph Hellwig <hch@....de>
To:     "Darrick J . Wong" <darrick.wong@...cle.com>
Cc:     Damien Le Moal <Damien.LeMoal@....com>,
        Andreas Gruenbacher <agruenba@...hat.com>,
        linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 01/12] list.h: add a list_pop helper

We have a very common pattern where we want to delete the first entry
from a list and return it as the properly typed container structure.

Add a list_pop helper to implement this behavior.

Signed-off-by: Christoph Hellwig <hch@....de>
---
 include/linux/list.h | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/include/linux/list.h b/include/linux/list.h
index e951228db4b2..e07a5f54cc9d 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -500,6 +500,28 @@ static inline void list_splice_tail_init(struct list_head *list,
 	pos__ != head__ ? list_entry(pos__, type, member) : NULL; \
 })
 
+/**
+ * list_pop - delete the first entry from a list and return it
+ * @list:	the list 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.
+ */
+#define list_pop(list, type, member) 				\
+({								\
+	struct list_head *head__ = (list);			\
+	struct list_head *pos__ = READ_ONCE(head__->next);	\
+	type *entry__ = NULL;					\
+								\
+	if (pos__ != head__) {					\
+		entry__ = list_entry(pos__, type, member);	\
+		list_del(pos__);				\
+	}							\
+								\
+	entry__;						\
+})
+
 /**
  * list_next_entry - get the next element in list
  * @pos:	the type * to cursor
-- 
2.20.1