Switch to qcow2 in the interactive VM.

lib/interactive-vm.nix

@@ -30,6 +30,7 @@ let
       disko.devices = cfg_.disko.devices;
     };
     testMode = true;
+    imageFormat = "qcow2";
   };
   rootDisk = {
     name = "root";
@@ -79,8 +80,8 @@ in
     trap 'rm -rf "$tmp"' EXIT
     ${lib.concatMapStringsSep "\n" (disk: ''
       ${pkgs.qemu}/bin/qemu-img create -f qcow2 \
-      -b ${diskoImages}/${disk.name}.raw \
-      -F raw "$tmp"/${disk.name}.qcow2
+      -b ${diskoImages}/${disk.name}.qcow2 \
+      -F qcow2 "$tmp"/${disk.name}.qcow2
     '') disks}
     set +f
     ${vm}/bin/run-*-vm

lib/make-disk-image.nix

@@ -8,6 +8,7 @@
 , copyNixStore ? true
 , testMode ? false
 , extraConfig ? { }
+, imageFormat ? "raw"
 }:
 let
   vmTools = pkgs.vmTools.override {
@@ -39,7 +40,7 @@ let
     findutils
   ] ++ nixosConfig.config.disko.extraDependencies;
   preVM = ''
-    ${lib.concatMapStringsSep "\n" (disk: "truncate -s ${disk.imageSize} ${disk.name}.raw") (lib.attrValues nixosConfig.config.disko.devices.disk)}
+    ${lib.concatMapStringsSep "\n" (disk: "${pkgs.qemu}/bin/qemu-img create -f ${imageFormat} ${disk.name}.${imageFormat} ${disk.imageSize}") (lib.attrValues nixosConfig.config.disko.devices.disk)}
     # This makes disko work, when canTouchEfiVariables is set to true.
     # Technically these boot entries will no be persisted this way, but
     # in most cases this is OK, because we can rely on the standard location for UEFI executables.
@@ -48,7 +49,7 @@ let
   postVM = ''
     # shellcheck disable=SC2154
     mkdir -p "$out"
-    ${lib.concatMapStringsSep "\n" (disk: "mv ${disk.name}.raw \"$out\"/${disk.name}.raw") (lib.attrValues nixosConfig.config.disko.devices.disk)}
+    ${lib.concatMapStringsSep "\n" (disk: "mv ${disk.name}.${imageFormat} \"$out\"/${disk.name}.${imageFormat}") (lib.attrValues nixosConfig.config.disko.devices.disk)}
     ${extraPostVM}
   '';
 
@@ -96,7 +97,7 @@ let
     "-drive if=pflash,format=raw,unit=1,file=efivars.fd"
   ] ++ builtins.map
     (disk:
-      "-drive file=${disk.name}.raw,if=virtio,cache=unsafe,werror=report,format=raw"
+      "-drive file=${disk.name}.${imageFormat},if=virtio,cache=unsafe,werror=report,format=${imageFormat}"
     )
     (lib.attrValues nixosConfig.config.disko.devices.disk));
 in

lib/types/disk.nix

@@ -20,7 +20,7 @@
       type = lib.types.strMatching "[0-9]+[KMGTP]?";
       description = ''
         size of the image if the makeDiskImages function from diksoLib is used.
-        is used as an argument to truncate -s
+        is used as an argument to "qemu-img create ..."
       '';
       default = "2G";
     };