XArray: Add xas_advance()

Add a new helper function to help iterate over multi-index entries.
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>

include/linux/xarray.h

@@ -1580,6 +1580,24 @@ static inline void xas_set(struct xa_state *xas, unsigned long index)
 	xas->xa_node = XAS_RESTART;
 }
 
+/**
+ * xas_advance() - Skip over sibling entries.
+ * @xas: XArray operation state.
+ * @index: Index of last sibling entry.
+ *
+ * Move the operation state to refer to the last sibling entry.
+ * This is useful for loops that normally want to see sibling
+ * entries but sometimes want to skip them.  Use xas_set() if you
+ * want to move to an index which is not part of this entry.
+ */
+static inline void xas_advance(struct xa_state *xas, unsigned long index)
+{
+	unsigned char shift = xas_is_node(xas) ? xas->xa_node->shift : 0;
+
+	xas->xa_index = index;
+	xas->xa_offset = (index >> shift) & XA_CHUNK_MASK;
+}
+
 /**
  * xas_set_order() - Set up XArray operation state for a multislot entry.
  * @xas: XArray operation state.

lib/xarray.c

@@ -157,7 +157,7 @@ static void xas_move_index(struct xa_state *xas, unsigned long offset)
 	xas->xa_index += offset << shift;
 }
 
-static void xas_advance(struct xa_state *xas)
+static void xas_next_offset(struct xa_state *xas)
 {
 	xas->xa_offset++;
 	xas_move_index(xas, xas->xa_offset);
@@ -1250,7 +1250,7 @@ void *xas_find(struct xa_state *xas, unsigned long max)
 		xas->xa_offset = ((xas->xa_index - 1) & XA_CHUNK_MASK) + 1;
 	}
 
-	xas_advance(xas);
+	xas_next_offset(xas);
 
 	while (xas->xa_node && (xas->xa_index <= max)) {
 		if (unlikely(xas->xa_offset == XA_CHUNK_SIZE)) {
@@ -1268,7 +1268,7 @@ void *xas_find(struct xa_state *xas, unsigned long max)
 		if (entry && !xa_is_sibling(entry))
 			return entry;
 
-		xas_advance(xas);
+		xas_next_offset(xas);
 	}
 
 	if (!xas->xa_node)