XArray: Change xa_for_each iterator

There were three problems with this API:
1. It took too many arguments; almost all users wanted to iterate over
every element in the array rather than a subset.
2. It required that 'index' be initialised before use, and there's no
realistic way to make GCC catch that.
3. 'index' and 'entry' were the opposite way round from every other
member of the XArray APIs.

So split it into three different APIs:

xa_for_each(xa, index, entry)
xa_for_each_start(xa, index, entry, start)
xa_for_each_marked(xa, index, entry, filter)

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

1 files changed, 65 insertions, 13 deletions

diff --git a/include/linux/xarray.h b/include/linux/xarray.h
index 4cf3cd128689..3d0ce8b267e3 100644
--- a/include/linux/xarray.h
+++ b/include/linux/xarray.h
@@ -359,20 +359,45 @@ static inline bool xa_marked(const struct xarray *xa, xa_mark_t mark)
 }
 
 /**
- * xa_for_each() - Iterate over a portion of an XArray.
+ * xa_for_each_start() - 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.
+ *
+ * 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_start() 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_start() 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_start().
+ *
+ * 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))
+
+/**
+ * xa_for_each() - Iterate over present entries in an XArray.
+ * @xa: XArray.
  * @index: Index of @entry.
- * @max: Maximum index to retrieve from array.
- * @filter: Selection criterion.
+ * @entry: Entry retrieved from array.
  *
- * Initialise @index to the lowest index you want to retrieve from the
- * array.  During the iteration, @entry will have the value of the entry
- * stored in @xa at @index.  The iteration will skip all entries in the
- * array which do not match @filter.  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.
+ * 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() 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
@@ -383,9 +408,36 @@ 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(xa, entry, index, max, filter) \
-	for (entry = xa_find(xa, &index, max, filter); entry; \
-	     entry = xa_find_after(xa, &index, max, filter))
+#define xa_for_each(xa, index, entry) \
+	xa_for_each_start(xa, index, entry, 0)
+
+/**
+ * xa_for_each_marked() - Iterate over marked entries in an XArray.
+ * @xa: XArray.
+ * @index: Index of @entry.
+ * @entry: Entry retrieved from array.
+ * @filter: Selection criterion.
+ *
+ * During the iteration, @entry will have the value of the entry stored
+ * in @xa at @index.  The iteration will skip all entries in the array
+ * which do not match @filter.  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_marked() is O(n.log(n)) while xas_for_each_marked() 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_marked() will spin if it hits a retry entry; if you intend to
+ * see retry entries, you should use the xas_for_each_marked() iterator
+ * instead.  The xas_for_each_marked() iterator will expand into more inline
+ * code than xa_for_each_marked().
+ *
+ * Context: Any context.  Takes and releases the RCU lock.
+ */
+#define xa_for_each_marked(xa, index, entry, filter) \
+	for (index = 0, entry = xa_find(xa, &index, ULONG_MAX, filter); \
+	     entry; entry = xa_find_after(xa, &index, ULONG_MAX, filter))
 
 #define xa_trylock(xa)		spin_trylock(&(xa)->xa_lock)
 #define xa_lock(xa)		spin_lock(&(xa)->xa_lock)