NFS: merge _full and _partial write rpc_ops

Decouple nfs_pgio_header and nfs_write_data, and have (possibly
multiple) nfs_write_datas each take a refcount on nfs_pgio_header.

For the moment keeps nfs_write_header as a way to preallocate a single
nfs_write_data with the nfs_pgio_header.  The code doesn't need this,
and would be prettier without, but given the amount of churn I am
already introducing I didn't want to play with tuning new mempools.

This also fixes bug in pnfs_ld_handle_write_error.  In the case of
desc->pg_bsize < PAGE_CACHE_SIZE, the pages list was empty, causing
replay attempt to do nothing.

Signed-off-by: Fred Isaman <iisaman@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/include/linux/nfs_xdr.h b/include/linux/nfs_xdr.h
index 1648621..0d17db7 100644
--- a/include/linux/nfs_xdr.h
+++ b/include/linux/nfs_xdr.h
@@ -1192,6 +1192,8 @@
 	NFS_IOHDR_ERROR = 0,
 	NFS_IOHDR_EOF,
 	NFS_IOHDR_REDO,
+	NFS_IOHDR_NEED_COMMIT,
+	NFS_IOHDR_NEED_RESCHED,
 };
 
 struct nfs_pgio_header {