[XFS] add helpers for addressing entities inside a btree block

Add new helpers in xfs_btree.c to find the record, key and block pointer
entries inside a btree block. To implement this genericly the
->get_maxrecs methods and two new xfs_btree_ops entries for the key and
record sizes are used. Also add a big comment describing how the
addressing inside a btree block works.

Note that these helpers are unused until users are introduced in the next
patches and this patch will thus cause some harmless compiler warnings.

SGI-PV: 985583

SGI-Modid: xfs-linux-melb:xfs-kern:32189a

Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
Signed-off-by: Bill O'Donnell <billodo@sgi.com>
Signed-off-by: David Chinner <david@fromorbit.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/fs/xfs/xfs_btree.h b/fs/xfs/xfs_btree.h
index 5398cd0..593f82b 100644
--- a/fs/xfs/xfs_btree.h
+++ b/fs/xfs/xfs_btree.h
@@ -180,6 +180,10 @@ do {    \
 #define	XFS_BTREE_MAXLEVELS	8	/* max of all btrees */
 
 struct xfs_btree_ops {
+	/* size of the key and record structures */
+	size_t	key_len;
+	size_t	rec_len;
+
 	/* cursor operations */
 	struct xfs_btree_cur *(*dup_cursor)(struct xfs_btree_cur *);
 
@@ -497,6 +501,15 @@ xfs_btree_setbuf(
 	int			lev,	/* level in btree */
 	struct xfs_buf		*bp);	/* new buffer to set */
 
+
+/*
+ * Helpers.
+ */
+static inline int xfs_btree_get_level(struct xfs_btree_block *block)
+{
+	return be16_to_cpu(block->bb_level);
+}
+
 #endif	/* __KERNEL__ */