runtime-rs: Map and propagate block discard to CH sparse disks

Add the Cloud Hypervisor disk sparse option to the local DiskConfig
model and keep its default aligned with upstream. Map
BlockConfigModern.discard_unmap to DiskConfig.sparse so block devices
that request discard/unmap explicitly expose sparse discard support
through the CH API.

Signed-off-by: Alex Lyn <alex.lyn@antgroup.com>

src/runtime-rs/crates/hypervisor/ch-config/src/lib.rs

@@ -123,7 +123,7 @@ pub enum ImageType {
     Unknown,
 }
 
-#[derive(Clone, Debug, PartialEq, Eq, Deserialize, Serialize, Default)]
+#[derive(Clone, Debug, PartialEq, Eq, Deserialize, Serialize)]
 pub struct DiskConfig {
     pub path: Option<PathBuf>,
     #[serde(default)]
@@ -148,10 +148,37 @@ pub struct DiskConfig {
     pub disable_io_uring: bool,
     #[serde(default)]
     pub pci_segment: u16,
+    #[serde(default = "default_diskconfig_sparse")]
+    pub sparse: bool,
     #[serde(default)]
     pub image_type: ImageType,
 }
 
+pub fn default_diskconfig_sparse() -> bool {
+    true
+}
+
+impl Default for DiskConfig {
+    fn default() -> Self {
+        Self {
+            path: None,
+            readonly: false,
+            direct: false,
+            iommu: false,
+            num_queues: 0,
+            queue_size: 0,
+            vhost_user: false,
+            vhost_socket: None,
+            rate_limiter_config: None,
+            id: None,
+            disable_io_uring: false,
+            pci_segment: 0,
+            sparse: default_diskconfig_sparse(),
+            image_type: ImageType::default(),
+        }
+    }
+}
+
 #[derive(Clone, Debug, PartialEq, Eq, Deserialize, Serialize, Default)]
 pub struct FsConfig {
     pub tag: String,

src/runtime-rs/crates/hypervisor/src/ch/inner_device.rs

@@ -522,6 +522,7 @@ impl TryFrom<BlockConfigModern> for DiskConfig {
             readonly: blkcfg.is_readonly,
             num_queues: blkcfg.num_queues,
             queue_size: blkcfg.queue_size as u16,
+            sparse: blkcfg.discard_unmap,
             image_type: ImageType::Raw,
             ..Default::default()
         };