Disable copy-on-write for qcow2 images. quickemu-project/quickemu#1228

Also, disable unsupported lazy_refcounts for non-qcow2 images

src/config.rs

@@ -317,12 +317,16 @@ pub enum PreAlloc {
     Full,
 }
 impl PreAlloc {
-    pub fn qemu_arg(&self) -> &'static str {
+    pub fn qemu_arg(&self, is_qcow2: bool) -> &'static str {
         match self {
-            Self::Off => "lazy_refcounts=on,preallocation=off",
-            Self::Metadata => "lazy_refcounts=on,preallocation=metadata",
-            Self::Falloc => "lazy_refcounts=on,preallocation=falloc",
-            Self::Full => "lazy_refcounts=on,preallocation=full",
+            Self::Off if is_qcow2 => "lazy_refcounts=on,preallocation=off,nocow=on",
+            Self::Off => "preallocation=off",
+            Self::Metadata if is_qcow2 => "lazy_refcounts=on,preallocation=metadata,nocow=on",
+            Self::Metadata => "preallocation=metadata",
+            Self::Falloc if is_qcow2 => "lazy_refcounts=on,preallocation=falloc,nocow=on",
+            Self::Falloc => "preallocation=falloc",
+            Self::Full if is_qcow2 => "lazy_refcounts=on,preallocation=full,nocow=on",
+            Self::Full => "preallocation=full"
         }
     }
 }

src/qemu_args/images.rs

@@ -19,7 +19,7 @@ pub fn image_args(vm_dir: &Path, images: Option<Vec<Image>>, disks: Vec<DiskImag
             let disk_format = disk_format(&disk.path.to_string_lossy(), &disk.preallocation)?;
             let size = disk.size.unwrap_or(guest_os.disk_size());
             let creation = Command::new(&qemu_img)
-                .args(["create", "-q", "-f", disk_format, "-o", disk.preallocation.qemu_arg()])
+                .args(["create", "-q", "-f", disk_format, "-o", disk.preallocation.qemu_arg(disk_format == "qcow2")])
                 .arg(&disk.path)
                 .arg(size.to_string())
                 .output().map_err(|e| anyhow!("Could not launch qemu-img to create disk image {}: {}", &disk.path.display(), e))?;