NFSv4.1: Add an initialisation callback for pNFS

Ensure that we always get a layout before setting up the i/o request.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/include/linux/nfs_page.h b/include/linux/nfs_page.h
index d378f08..9ac2dd1 100644
--- a/include/linux/nfs_page.h
+++ b/include/linux/nfs_page.h
@@ -57,6 +57,7 @@
 
 struct nfs_pageio_descriptor;
 struct nfs_pageio_ops {
+	void	(*pg_init)(struct nfs_pageio_descriptor *, struct nfs_page *);
 	bool	(*pg_test)(struct nfs_pageio_descriptor *, struct nfs_page *, struct nfs_page *);
 	int	(*pg_doio)(struct nfs_pageio_descriptor *);
 };