xfs: fold perag loop iteration logic into helper function

Fold the loop iteration logic into a helper in preparation for
further fixups. No functional change in this patch.
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>

fs/xfs/libxfs/xfs_ag.h

@@ -124,12 +124,22 @@ void xfs_perag_put(struct xfs_perag *pag);
  * for_each_perag_from() because they terminate at sb_agcount where there are
  * no perag structures in tree beyond end_agno.
  */
+static inline struct xfs_perag *
+xfs_perag_next(
+	struct xfs_perag	*pag,
+	xfs_agnumber_t		*next_agno)
+{
+	struct xfs_mount	*mp = pag->pag_mount;
+
+	*next_agno = pag->pag_agno + 1;
+	xfs_perag_put(pag);
+	return xfs_perag_get(mp, *next_agno);
+}
+
 #define for_each_perag_range(mp, next_agno, end_agno, pag) \
 	for ((pag) = xfs_perag_get((mp), (next_agno)); \
 		(pag) != NULL && (next_agno) <= (end_agno); \
-		(next_agno) = (pag)->pag_agno + 1, \
-		xfs_perag_put(pag), \
-		(pag) = xfs_perag_get((mp), (next_agno)))
+		(pag) = xfs_perag_next((pag), &(next_agno)))
 
 #define for_each_perag_from(mp, next_agno, pag) \
 	for_each_perag_range((mp), (next_agno), (mp)->m_sb.sb_agcount, (pag))