[PATCH 3/4] lib/xarray: introduce a new helper xas_get_order

[Kairui Song <ryncsn@gmail.com>]

From: Kairui Song <kasong@tencent.com>

It can be used after xas_load to check the order of loaded entries.
Compared to xa_get_order, it saves an XA_STATE and avoid a rewalk.

Signed-off-by: Kairui Song <kasong@tencent.com>
---
 include/linux/xarray.h |  6 ++++++
 lib/xarray.c           | 49 ++++++++++++++++++++++++++----------------
 2 files changed, 37 insertions(+), 18 deletions(-)

diff --git a/include/linux/xarray.h b/include/linux/xarray.h
index cb571dfcf4b1..d9d479334c9e 100644
--- a/include/linux/xarray.h
+++ b/include/linux/xarray.h
@@ -1548,6 +1548,7 @@ void xas_create_range(struct xa_state *);
 
 #ifdef CONFIG_XARRAY_MULTI
 int xa_get_order(struct xarray *, unsigned long index);
+int xas_get_order(struct xa_state *xas);
 void xas_split(struct xa_state *, void *entry, unsigned int order);
 void xas_split_alloc(struct xa_state *, void *entry, unsigned int order, gfp_t);
 #else
@@ -1556,6 +1557,11 @@ static inline int xa_get_order(struct xarray *xa, unsigned long index)
 	return 0;
 }
 
+static inline int xas_get_order(struct xa_state *xas)
+{
+	return 0;
+}
+
 static inline void xas_split(struct xa_state *xas, void *entry,
 		unsigned int order)
 {
diff --git a/lib/xarray.c b/lib/xarray.c
index 39f07bfc4dcc..88fbea481e1b 100644
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -1750,39 +1750,52 @@ void *xa_store_range(struct xarray *xa, unsigned long first,
 EXPORT_SYMBOL(xa_store_range);
 
 /**
- * xa_get_order() - Get the order of an entry.
- * @xa: XArray.
- * @index: Index of the entry.
+ * xas_get_order() - Get the order of an loaded entry after xas_load.
+ * @xas: XArray operation state.
+ *
+ * Called after xas_load, the xas should not be in an error state.
  *
  * Return: A number between 0 and 63 indicating the order of the entry.
  */
-int xa_get_order(struct xarray *xa, unsigned long index)
+int xas_get_order(struct xa_state *xas)
 {
-	XA_STATE(xas, xa, index);
-	void *entry;
 	int order = 0;
 
-	rcu_read_lock();
-	entry = xas_load(&xas);
-
-	if (!entry)
-		goto unlock;
-
-	if (!xas.xa_node)
-		goto unlock;
+	if (!xas->xa_node)
+		return 0;
 
 	for (;;) {
-		unsigned int slot = xas.xa_offset + (1 << order);
+		unsigned int slot = xas->xa_offset + (1 << order);
 
 		if (slot >= XA_CHUNK_SIZE)
 			break;
-		if (!xa_is_sibling(xas.xa_node->slots[slot]))
+		if (!xa_is_sibling(xas->xa_node->slots[slot]))
 			break;
 		order++;
 	}
 
-	order += xas.xa_node->shift;
-unlock:
+	order += xas->xa_node->shift;
+	return order;
+}
+EXPORT_SYMBOL(xas_get_order);
+
+/**
+ * xa_get_order() - Get the order of an entry.
+ * @xa: XArray.
+ * @index: Index of the entry.
+ *
+ * Return: A number between 0 and 63 indicating the order of the entry.
+ */
+int xa_get_order(struct xarray *xa, unsigned long index)
+{
+	XA_STATE(xas, xa, index);
+	int order = 0;
+	void *entry;
+
+	rcu_read_lock();
+	entry = xas_load(&xas);
+	if (entry)
+		order = xas_get_order(&xas);
 	rcu_read_unlock();
 
 	return order;
-- 
2.43.0