xfs: add a xfs_btree_init_ptr_from_cur

Inode-rooted btrees don't need to initialize the root pointer in the
->init_ptr_from_cur method as the root is found by the
xfs_btree_get_iroot method later.  Make ->init_ptr_from_cur option
for inode rooted btrees by providing a helper that does the right
thing for the given btree type and also documents the semantics.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>

fs/xfs/libxfs/xfs_bmap_btree.c

@@ -369,14 +369,6 @@ xfs_bmbt_init_rec_from_cur(
 	xfs_bmbt_disk_set_all(&rec->bmbt, &cur->bc_rec.b);
 }
 
-STATIC void
-xfs_bmbt_init_ptr_from_cur(
-	struct xfs_btree_cur	*cur,
-	union xfs_btree_ptr	*ptr)
-{
-	ptr->l = 0;
-}
-
 STATIC int64_t
 xfs_bmbt_key_diff(
 	struct xfs_btree_cur		*cur,
@@ -544,7 +536,6 @@ const struct xfs_btree_ops xfs_bmbt_ops = {
 	.init_key_from_rec	= xfs_bmbt_init_key_from_rec,
 	.init_high_key_from_rec	= xfs_bmbt_init_high_key_from_rec,
 	.init_rec_from_cur	= xfs_bmbt_init_rec_from_cur,
-	.init_ptr_from_cur	= xfs_bmbt_init_ptr_from_cur,
 	.key_diff		= xfs_bmbt_key_diff,
 	.diff_two_keys		= xfs_bmbt_diff_two_keys,
 	.buf_ops		= &xfs_bmbt_buf_ops,

fs/xfs/libxfs/xfs_btree.c

@@ -1881,6 +1881,25 @@ xfs_lookup_get_search_key(
 	return xfs_btree_key_addr(cur, keyno, block);
 }
 
+/*
+ * Initialize a pointer to the root block.
+ */
+void
+xfs_btree_init_ptr_from_cur(
+	struct xfs_btree_cur	*cur,
+	union xfs_btree_ptr	*ptr)
+{
+	if (cur->bc_ops->type == XFS_BTREE_TYPE_INODE) {
+		/*
+		 * Inode-rooted btrees call xfs_btree_get_iroot to find the root
+		 * in xfs_btree_lookup_get_block and don't need a pointer here.
+		 */
+		ptr->l = 0;
+	} else {
+		cur->bc_ops->init_ptr_from_cur(cur, ptr);
+	}
+}
+
 /*
  * Lookup the record.  The cursor is made to point to it, based on dir.
  * stat is set to 0 if can't find any such record, 1 for success.
@@ -1911,7 +1930,7 @@ xfs_btree_lookup(
 	keyno = 0;
 
 	/* initialise start pointer from cursor */
-	cur->bc_ops->init_ptr_from_cur(cur, &ptr);
+	xfs_btree_init_ptr_from_cur(cur, &ptr);
 	pp = &ptr;
 
 	/*
@@ -3121,7 +3140,7 @@ xfs_btree_new_root(
 	XFS_BTREE_STATS_INC(cur, newroot);
 
 	/* initialise our start point from the cursor */
-	cur->bc_ops->init_ptr_from_cur(cur, &rptr);
+	xfs_btree_init_ptr_from_cur(cur, &rptr);
 
 	/* Allocate the new block. If we can't do it, we're toast. Give up. */
 	error = xfs_btree_alloc_block(cur, &rptr, &lptr, stat);
@@ -4430,7 +4449,7 @@ xfs_btree_visit_blocks(
 	struct xfs_btree_block		*block = NULL;
 	int				error = 0;
 
-	cur->bc_ops->init_ptr_from_cur(cur, &lptr);
+	xfs_btree_init_ptr_from_cur(cur, &lptr);
 
 	/* for each level */
 	for (level = cur->bc_nlevels - 1; level >= 0; level--) {
@@ -4852,7 +4871,7 @@ xfs_btree_overlapped_query_range(
 
 	/* Load the root of the btree. */
 	level = cur->bc_nlevels - 1;
-	cur->bc_ops->init_ptr_from_cur(cur, &ptr);
+	xfs_btree_init_ptr_from_cur(cur, &ptr);
 	error = xfs_btree_lookup_get_block(cur, level, &ptr, &block);
 	if (error)
 		return error;

fs/xfs/libxfs/xfs_btree.h

@@ -714,6 +714,8 @@ void xfs_btree_copy_ptrs(struct xfs_btree_cur *cur,
 void xfs_btree_copy_keys(struct xfs_btree_cur *cur,
 		union xfs_btree_key *dst_key,
 		const union xfs_btree_key *src_key, int numkeys);
+void xfs_btree_init_ptr_from_cur(struct xfs_btree_cur *cur,
+		union xfs_btree_ptr *ptr);
 
 static inline struct xfs_btree_cur *
 xfs_btree_alloc_cursor(

fs/xfs/libxfs/xfs_btree_staging.c

@@ -225,7 +225,6 @@ xfs_btree_stage_ifakeroot(
 	memcpy(nops, cur->bc_ops, sizeof(struct xfs_btree_ops));
 	nops->alloc_block = xfs_btree_fakeroot_alloc_block;
 	nops->free_block = xfs_btree_fakeroot_free_block;
-	nops->init_ptr_from_cur = xfs_btree_fakeroot_init_ptr_from_cur;
 	nops->dup_cursor = xfs_btree_fakeroot_dup_cursor;
 
 	cur->bc_ino.ifake = ifake;

fs/xfs/scrub/btree.c

@@ -733,7 +733,7 @@ xchk_btree(
 	 * error codes for us.
 	 */
 	level = cur->bc_nlevels - 1;
-	cur->bc_ops->init_ptr_from_cur(cur, &ptr);
+	xfs_btree_init_ptr_from_cur(cur, &ptr);
 	if (!xchk_btree_ptr_ok(bs, cur->bc_nlevels, &ptr))
 		goto out;
 	error = xchk_btree_get_block(bs, level, &ptr, &block, &bp);