pnfs: Add layout driver flag PNFS_LAYOUTGET_ON_OPEN

Driver can set flag to allow LAYOUTGET to be sent with OPEN.

Signed-off-by: Fred Isaman <fred.isaman@gmail.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
diff --git a/fs/nfs/pnfs.h b/fs/nfs/pnfs.h
index daf6cbf..f71a55f 100644
--- a/fs/nfs/pnfs.h
+++ b/fs/nfs/pnfs.h
@@ -110,6 +110,7 @@
 	PNFS_LAYOUTRET_ON_SETATTR	= 1 << 0,
 	PNFS_LAYOUTRET_ON_ERROR		= 1 << 1,
 	PNFS_READ_WHOLE_PAGE		= 1 << 2,
+	PNFS_LAYOUTGET_ON_OPEN		= 1 << 3,
 };
 
 struct nfs4_deviceid_node;