NFSv4.1: implement generic pnfs layer write switch

Signed-off-by: Andy Adamson <andros@citi.umich.edu>
Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
Signed-off-by: Dean Hildebrand <dhildeb@us.ibm.com>
Signed-off-by: Fred Isaman <iisaman@citi.umich.edu>
Signed-off-by: J. Bruce Fields <bfields@fieldses.org>
Signed-off-by: Mike Sager <sager@netapp.com>
Signed-off-by: Ricardo Labiaga <Ricardo.Labiaga@netapp.com>
Signed-off-by: Tao Guo <guotao@nrchpc.ac.cn>
Signed-off-by: Andy Adamson <andros@netapp.com>
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
Signed-off-by: Fred Isaman <iisaman@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 49c4784..df99c5b 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -873,6 +873,10 @@
 	data->res.verf    = &data->verf;
 	nfs_fattr_init(&data->fattr);
 
+	if (data->lseg &&
+	    (pnfs_try_to_write_data(data, call_ops, how) == PNFS_ATTEMPTED))
+		return 0;
+
 	return nfs_initiate_write(data, NFS_CLIENT(inode), call_ops, how);
 }