ocfs2: Validate metadata only when it's read from disk.

Add an optional validation hook to ocfs2_read_blocks().  Now the
validation function is only called when a block was actually read off of
disk.  It is not called when the buffer was in cache.

We add a buffer state bit BH_NeedsValidate to flag these buffers.  It
must always be one higher than the last JBD2 buffer state bit.

The dinode, dirblock, extent_block, and xattr_block validators are
lifted to this scheme directly.  The group_descriptor validator needs to
be split into two pieces.  The first part only needs the gd buffer and
is passed to ocfs2_read_block().  The second part requires the dinode as
well, and is called every time.  It's only 3 compares, so it's tiny.
This also allows us to clean up the non-fatal gd check used by resize.c.
It now has no magic argument.

Signed-off-by: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>
diff --git a/fs/ocfs2/resize.c b/fs/ocfs2/resize.c
index 252baff..867de3e 100644
--- a/fs/ocfs2/resize.c
+++ b/fs/ocfs2/resize.c
@@ -394,7 +394,7 @@
 		(struct ocfs2_group_desc *)group_bh->b_data;
 	u16 cl_bpc = le16_to_cpu(di->id2.i_chain.cl_bpc);
 
-	ret = ocfs2_validate_group_descriptor(inode->i_sb, di, group_bh, 1);
+	ret = ocfs2_check_group_descriptor(inode->i_sb, di, group_bh);
 	if (ret)
 		goto out;