pNFS/files: Fall back to I/O through the MDS on non-fatal layout errors

Only report the error when the server is returning a fatal error, such
as ESTALE, EIO, etc...
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

fs/nfs/filelayout/filelayout.c

@@ -839,7 +839,12 @@ fl_pnfs_update_layout(struct inode *ino,
 
 	lseg = pnfs_update_layout(ino, ctx, pos, count, iomode, strict_iomode,
 				  gfp_flags);
-	if (IS_ERR_OR_NULL(lseg))
+	if (IS_ERR(lseg)) {
+		/* Fall back to MDS on recoverable errors */
+		if (!nfs_error_is_fatal_on_server(PTR_ERR(lseg)))
+			lseg = NULL;
+		goto out;
+	} else if (!lseg)
 		goto out;
 
 	lo = NFS_I(ino)->layout;