NFSv4.1 send layoutreturn to fence disconnected data server

Let the MDS know that you are redirecting I/O from pNFS to MDS.
Signed-off-by: Andy Adamson <andros@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/nfs4filelayout.c

@@ -186,6 +186,8 @@ static int filelayout_async_handle_error(struct rpc_task *task,
 	case -EPIPE:
 		dprintk("%s DS connection error %d\n", __func__,
 			task->tk_status);
+		if (!filelayout_test_devid_invalid(devid))
+			_pnfs_return_layout(state->inode);
 		filelayout_mark_devid_invalid(devid);
 		rpc_wake_up(&tbl->slot_tbl_waitq);
 		/* fall through */

fs/nfs/pnfs.c

@@ -692,6 +692,7 @@ _pnfs_return_layout(struct inode *ino)
 	dprintk("<-- %s status: %d\n", __func__, status);
 	return status;
 }
+EXPORT_SYMBOL_GPL(_pnfs_return_layout);
 
 bool pnfs_roc(struct inode *ino)
 {