[PATCH 01/12] list.h: add a list_pop helper

Christoph Hellwig
2019-06-24T05:53:04Z

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@lst.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