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Subject[PATCH 01/12] list.h: add list_pop and list_pop_entry helpers
Date
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 two helpers to implement this behavior.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
include/linux/list.h | 33 +++++++++++++++++++++++++++++++++
1 file changed, 33 insertions(+)

diff --git a/include/linux/list.h b/include/linux/list.h
index 85c92555e31f..d3b00267446a 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -514,6 +514,39 @@ 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.
+ *
+ * Return the list entry after @list. If @list is empty return NULL.
+ */
+static inline struct list_head *list_pop(struct list_head *list)
+{
+ struct list_head *pos = READ_ONCE(list->next);
+
+ if (pos == list)
+ return NULL;
+ list_del(pos);
+ return pos;
+}
+
+/**
+ * list_pop_entry - delete the first entry from a list and return the
+ * containing structure
+ * @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.
+ *
+ * Return the containing structure for the list entry after @list. If @list
+ * is empty return NULL.
+ */
+#define list_pop_entry(list, type, member) \
+({ \
+ struct list_head *pos__ = list_pop(list); \
+ \
+ pos__ ? list_entry(pos__, type, member) : NULL; \
+})
+
/**
* list_next_entry - get the next element in list
* @pos: the type * to cursor
--
2.20.1
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