modules/microvm-host: improve update-microvm behaviour

modules/microvm-host.nix

@@ -90,17 +90,26 @@
             if [ -e booted ]; then
               nix store diff-closures $(readlink booted) $NEW
             else
-              echo "NOT BOOTED?"
+              echo "NOT BOOTED? Run:"
+              echo systemctl start microvm@$NAME
             fi
-            if [ "$(readlink current)" != $NEW ]; then
+
+            CHANGED=no
+            if ! [ -e current ]; then
+              ln -s $NEW current
+              CHANGED=yes
+            elif [ "$(readlink current)" != $NEW ]; then
               rm -f old
               mv current old
               ln -s $NEW current
+              CHANGED=yes
             fi
           fi
 
-          echo Run at your own peril:
-          echo systemctl restart microvm@$NAME
+          if [ "$CHANGED" = "yes" ]; then
+            echo Run at your own peril:
+            echo systemctl restart microvm@$NAME
+          fi
           echo
         done
       ''