xfs: add a xfs_group_next_range helper

Add a helper to iterate over iterate over all groups, which can be used
as a simple while loop:

	struct xfs_group		*xg = NULL;

	while ((xg = xfs_group_next_range(mp, xg, 0, MAX_GROUP))) {
		...
	}

This will be wrapped by the realtime group code first, and eventually
replace the for_each_rtgroup_from and for_each_rtgroup_range helpers.

Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Darrick J. Wong <[email protected]>
Signed-off-by: Darrick J. Wong <[email protected]>

Author: Christoph Hellwig

fs/xfs/libxfs/xfs_group.c

@@ -87,6 +87,32 @@ xfs_group_grab(
 	return xg;
 }
 
+/*
+ * Iterate to the next group.  To start the iteration at @start_index, a %NULL
+ * @xg is passed, else the previous group returned from this function.  The
+ * caller should break out of the loop when this returns %NULL.  If the caller
+ * wants to break out of a loop that did not finish it needs to release the
+ * active reference to @xg using xfs_group_rele() itself.
+ */
+struct xfs_group *
+xfs_group_next_range(
+	struct xfs_mount	*mp,
+	struct xfs_group	*xg,
+	uint32_t		start_index,
+	uint32_t		end_index,
+	enum xfs_group_type	type)
+{
+	uint32_t		index = start_index;
+
+	if (xg) {
+		index = xg->xg_gno + 1;
+		xfs_group_rele(xg);
+	}
+	if (index > end_index)
+		return NULL;
+	return xfs_group_grab(mp, index, type);
+}
+
 /*
  * Find the next group after @xg, or the first group if @xg is NULL.
  */

fs/xfs/libxfs/xfs_group.h

@@ -20,6 +20,9 @@ void xfs_group_put(struct xfs_group *xg);
 
 struct xfs_group *xfs_group_grab(struct xfs_mount *mp, uint32_t index,
 		enum xfs_group_type type);
+struct xfs_group *xfs_group_next_range(struct xfs_mount *mp,
+		struct xfs_group *xg, uint32_t start_index, uint32_t end_index,
+		enum xfs_group_type type);
 struct xfs_group *xfs_group_grab_next_mark(struct xfs_mount *mp,
 		struct xfs_group *xg, xa_mark_t mark, enum xfs_group_type type);
 void xfs_group_rele(struct xfs_group *xg);