nilfs2: introduce check flag to btree node buffer

nilfs_btree_get_block() now may return untested buffer due to
read-ahead.  This adds a new flag for buffer heads so that the btree
code can check whether the buffer is already verified or not.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

fs/nilfs2/page.h

@@ -34,11 +34,13 @@ enum {
 	BH_NILFS_Allocated = BH_PrivateStart,
 	BH_NILFS_Node,
 	BH_NILFS_Volatile,
+	BH_NILFS_Checked,
 };
 
 BUFFER_FNS(NILFS_Allocated, nilfs_allocated)	/* nilfs private buffers */
 BUFFER_FNS(NILFS_Node, nilfs_node)		/* nilfs node buffers */
 BUFFER_FNS(NILFS_Volatile, nilfs_volatile)
+BUFFER_FNS(NILFS_Checked, nilfs_checked)	/* buffer is verified */
 
 
 void nilfs_mark_buffer_dirty(struct buffer_head *bh);