[XFS] Fix up sparse warnings.

These are mostly locking annotations, marking things static, casts where
needed and declaring stuff in header files.

SGI-PV: 971186
SGI-Modid: xfs-linux-melb:xfs-kern:30002a

Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
diff --git a/fs/xfs/xfs_buf_item.h b/fs/xfs/xfs_buf_item.h
index d7e1361..5a41c34 100644
--- a/fs/xfs/xfs_buf_item.h
+++ b/fs/xfs/xfs_buf_item.h
@@ -18,6 +18,8 @@
 #ifndef	__XFS_BUF_ITEM_H__
 #define	__XFS_BUF_ITEM_H__
 
+extern kmem_zone_t	*xfs_buf_item_zone;
+
 /*
  * This is the structure used to lay out a buf log item in the
  * log.  The data map describes which 128 byte chunks of the buffer