xfs: make the start pointer passed to btree alloc_block functions const

The @start pointer passed to each per-AG btree type's ->alloc_block
function isn't supposed to be modified, since it's a hint about the
location of the btree block being split that is to be fed to the
allocator, so mark the parameter const.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

fs/xfs/libxfs/xfs_alloc_btree.c

@@ -51,7 +51,7 @@ xfs_allocbt_set_root(
 STATIC int
 xfs_allocbt_alloc_block(
 	struct xfs_btree_cur		*cur,
-	union xfs_btree_ptr	*start,
+	const union xfs_btree_ptr	*start,
 	union xfs_btree_ptr		*new,
 	int				*stat)
 {

fs/xfs/libxfs/xfs_bmap_btree.c

@@ -194,7 +194,7 @@ xfs_bmbt_update_cursor(
 STATIC int
 xfs_bmbt_alloc_block(
 	struct xfs_btree_cur		*cur,
-	union xfs_btree_ptr	*start,
+	const union xfs_btree_ptr	*start,
 	union xfs_btree_ptr		*new,
 	int				*stat)
 {

fs/xfs/libxfs/xfs_btree.h

@@ -110,7 +110,7 @@ struct xfs_btree_ops {
 
 	/* block allocation / freeing */
 	int	(*alloc_block)(struct xfs_btree_cur *cur,
-			       union xfs_btree_ptr *start_bno,
+			       const union xfs_btree_ptr *start_bno,
 			       union xfs_btree_ptr *new_bno,
 			       int *stat);
 	int	(*free_block)(struct xfs_btree_cur *cur, struct xfs_buf *bp);

fs/xfs/libxfs/xfs_btree_staging.c

@@ -60,7 +60,7 @@ xfs_btree_fakeroot_dup_cursor(
 STATIC int
 xfs_btree_fakeroot_alloc_block(
 	struct xfs_btree_cur		*cur,
-	union xfs_btree_ptr	*start_bno,
+	const union xfs_btree_ptr	*start_bno,
 	union xfs_btree_ptr		*new_bno,
 	int				*stat)
 {

fs/xfs/libxfs/xfs_ialloc_btree.c

@@ -89,7 +89,7 @@ xfs_inobt_mod_blockcount(
 STATIC int
 __xfs_inobt_alloc_block(
 	struct xfs_btree_cur		*cur,
-	union xfs_btree_ptr	*start,
+	const union xfs_btree_ptr	*start,
 	union xfs_btree_ptr		*new,
 	int				*stat,
 	enum xfs_ag_resv_type		resv)
@@ -128,7 +128,7 @@ __xfs_inobt_alloc_block(
 STATIC int
 xfs_inobt_alloc_block(
 	struct xfs_btree_cur		*cur,
-	union xfs_btree_ptr	*start,
+	const union xfs_btree_ptr	*start,
 	union xfs_btree_ptr		*new,
 	int				*stat)
 {
@@ -138,7 +138,7 @@ xfs_inobt_alloc_block(
 STATIC int
 xfs_finobt_alloc_block(
 	struct xfs_btree_cur		*cur,
-	union xfs_btree_ptr	*start,
+	const union xfs_btree_ptr	*start,
 	union xfs_btree_ptr		*new,
 	int				*stat)
 {

fs/xfs/libxfs/xfs_refcount_btree.c

@@ -52,7 +52,7 @@ xfs_refcountbt_set_root(
 STATIC int
 xfs_refcountbt_alloc_block(
 	struct xfs_btree_cur		*cur,
-	union xfs_btree_ptr	*start,
+	const union xfs_btree_ptr	*start,
 	union xfs_btree_ptr		*new,
 	int				*stat)
 {

fs/xfs/libxfs/xfs_rmap_btree.c

@@ -77,7 +77,7 @@ xfs_rmapbt_set_root(
 STATIC int
 xfs_rmapbt_alloc_block(
 	struct xfs_btree_cur		*cur,
-	union xfs_btree_ptr	*start,
+	const union xfs_btree_ptr	*start,
 	union xfs_btree_ptr		*new,
 	int				*stat)
 {