pnfs: support for non-rpc layout drivers

Non-rpc layout driver such as for objects and blocks
implement their own I/O path and error handling logic.
Therefore bypass NFS-based error handling for these layout drivers.

[fix lseg ref-count bugs, and null de-refs]
[Fall out from: non-rpc layout drivers]
Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
[get rid of PNFS_USE_RPC_CODE]
[get rid of __nfs4_write_done_cb]
[revert useless change in nfs4_write_done_cb]
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
diff --git a/include/linux/nfs_xdr.h b/include/linux/nfs_xdr.h
index 7e371f7..7c8ff09 100644
--- a/include/linux/nfs_xdr.h
+++ b/include/linux/nfs_xdr.h
@@ -1087,6 +1087,7 @@
 	const struct rpc_call_ops *mds_ops;
 	int (*read_done_cb) (struct rpc_task *task, struct nfs_read_data *data);
 	__u64			mds_offset;
+	int			pnfs_error;
 	struct page		*page_array[NFS_PAGEVEC_SIZE];
 };
 
@@ -1112,6 +1113,7 @@
 	unsigned long		timestamp;	/* For lease renewal */
 #endif
 	__u64			mds_offset;	/* Filelayout dense stripe */
+	int			pnfs_error;
 	struct page		*page_array[NFS_PAGEVEC_SIZE];
 };