mkuserimg.sh: ensure the extra size is larger than 80MB

diff --git a/ext4_utils/mkuserimg.sh b/ext4_utils/mkuserimg.sh
index 0435215..2643e2b 100755 (executable)
--- a/ext4_utils/mkuserimg.sh
+++ b/ext4_utils/mkuserimg.sh
@@ -48,7 +48,10 @@ if [ -z $SIZE ]; then
   echo "Need size of filesystem"
   exit 2
 elif [ 0 -eq 0$SIZE ]; then
-  SIZE=$((`du -sm $SRC_DIR | cut -f1`*11/10))M
+  s=$(du -sm $SRC_DIR | cut -f1)
+  e=$(($s / 10))
+  [ $e -lt 80 ] && e=80
+  SIZE=$(($s + $e))M
 fi
 
 if [ -n "$FC" ]; then