diff --git a/common.h b/common.h
index d99daaf..e6e8f85 100644
--- a/common.h
+++ b/common.h
@@ -99,6 +99,12 @@
     const char* device2;      // alternative device to try if fs_type
                               // == "ext4" or "vfat" and mounting
                               // 'device' fails
+
+    long long length;         // (ext4 partition only) when
+                              // formatting, size to use for the
+                              // partition.  0 or negative number
+                              // means to format all but the last
+                              // (that much).
 } Volume;
 
 #endif  // RECOVERY_COMMON_H