[PATCH 06/11] maple_tree: Introduce mas_replace_entry() to directly replace an entry

[Peng Zhang <zhangpeng.00@bytedance.com>]

If mas has located a specific entry, it may be need to replace this
entry, so introduce mas_replace_entry() to do this. mas_replace_entry()
will be more efficient than mas_store*() because it doesn't do many
unnecessary checks.

This function should be inline, but more functions need to be moved to
the header file, so I didn't do it for the time being.

Signed-off-by: Peng Zhang <zhangpeng.00@bytedance.com>
---
 include/linux/maple_tree.h |  1 +
 lib/maple_tree.c           | 25 +++++++++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/include/linux/maple_tree.h b/include/linux/maple_tree.h
index 229fe78e4c89..a05e9827d761 100644
--- a/include/linux/maple_tree.h
+++ b/include/linux/maple_tree.h
@@ -462,6 +462,7 @@ struct ma_wr_state {
 
 void *mas_walk(struct ma_state *mas);
 void *mas_store(struct ma_state *mas, void *entry);
+void mas_replace_entry(struct ma_state *mas, void *entry);
 void *mas_erase(struct ma_state *mas);
 int mas_store_gfp(struct ma_state *mas, void *entry, gfp_t gfp);
 void mas_store_prealloc(struct ma_state *mas, void *entry);
diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index efac6761ae37..d58572666a00 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -5600,6 +5600,31 @@ void *mas_store(struct ma_state *mas, void *entry)
 }
 EXPORT_SYMBOL_GPL(mas_store);
 
+/**
+ * mas_replace_entry() - Replace an entry that already exists in the maple tree
+ * @mas: The maple state
+ * @entry: The entry to store
+ *
+ * Please note that mas must already locate an existing entry, and the new entry
+ * must not be NULL. If these two points cannot be guaranteed, please use
+ * mas_store*() instead, otherwise it will cause an internal error in the maple
+ * tree. This function does not need to allocate memory, so it must succeed.
+ */
+void mas_replace_entry(struct ma_state *mas, void *entry)
+{
+	void __rcu **slots;
+
+#ifdef CONFIG_DEBUG_MAPLE_TREE
+	MAS_WARN_ON(mas, !mte_is_leaf(mas->node));
+	MAS_WARN_ON(mas, !entry);
+	MAS_WARN_ON(mas, mas->offset >= mt_slots[mte_node_type(mas->node)]);
+#endif
+
+	slots = ma_slots(mte_to_node(mas->node), mte_node_type(mas->node));
+	rcu_assign_pointer(slots[mas->offset], entry);
+}
+EXPORT_SYMBOL_GPL(mas_replace_entry);
+
 /**
  * mas_store_gfp() - Store a value into the tree.
  * @mas: The maple state
-- 
2.20.1