XArray: Add xa_for_each_range

This function supports iterating over a range of an array.  Also add
documentation links for xa_for_each_start().

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

1 files changed, 32 insertions, 5 deletions

diff --git a/include/linux/xarray.h b/include/linux/xarray.h
index 736afd3aa56f..f73e1775ded0 100644
--- a/include/linux/xarray.h
+++ b/include/linux/xarray.h
@@ -417,6 +417,36 @@ static inline bool xa_marked(const struct xarray *xa, xa_mark_t mark)
 }
 
 /**
+ * xa_for_each_range() - Iterate over a portion of an XArray.
+ * @xa: XArray.
+ * @index: Index of @entry.
+ * @entry: Entry retrieved from array.
+ * @start: First index to retrieve from array.
+ * @last: Last index to retrieve from array.
+ *
+ * During the iteration, @entry will have the value of the entry stored
+ * in @xa at @index.  You may modify @index during the iteration if you
+ * want to skip or reprocess indices.  It is safe to modify the array
+ * during the iteration.  At the end of the iteration, @entry will be set
+ * to NULL and @index will have a value less than or equal to max.
+ *
+ * xa_for_each_range() is O(n.log(n)) while xas_for_each() is O(n).  You have
+ * to handle your own locking with xas_for_each(), and if you have to unlock
+ * after each iteration, it will also end up being O(n.log(n)).
+ * xa_for_each_range() will spin if it hits a retry entry; if you intend to
+ * see retry entries, you should use the xas_for_each() iterator instead.
+ * The xas_for_each() iterator will expand into more inline code than
+ * xa_for_each_range().
+ *
+ * Context: Any context.  Takes and releases the RCU lock.
+ */
+#define xa_for_each_range(xa, index, entry, start, last)		\
+	for (index = start,						\
+	     entry = xa_find(xa, &index, last, XA_PRESENT);		\
+	     entry;							\
+	     entry = xa_find_after(xa, &index, last, XA_PRESENT))
+
+/**
  * xa_for_each_start() - Iterate over a portion of an XArray.
  * @xa: XArray.
  * @index: Index of @entry.
@@ -439,11 +469,8 @@ static inline bool xa_marked(const struct xarray *xa, xa_mark_t mark)
  *
  * Context: Any context.  Takes and releases the RCU lock.
  */
-#define xa_for_each_start(xa, index, entry, start)			\
-	for (index = start,						\
-	     entry = xa_find(xa, &index, ULONG_MAX, XA_PRESENT);	\
-	     entry;							\
-	     entry = xa_find_after(xa, &index, ULONG_MAX, XA_PRESENT))
+#define xa_for_each_start(xa, index, entry, start) \
+	xa_for_each_range(xa, index, entry, start, ULONG_MAX)
 
 /**
  * xa_for_each() - Iterate over present entries in an XArray.