kata-deploy: Set block_device_driver to virtio-blk for EROFS

The EROFS multi-layer rootfs implementation in runtime-rs only supports
virtio-blk block devices, but the default QEMU block_device_driver is
virtio-scsi.

When kata-deploy configures a Rust shim with the erofs snapshotter,
generate a drop-in config file that overrides the block device driver to
virtio-blk.

Signed-off-by: Fabiano Fidêncio <ffidencio@nvidia.com>

tools/packaging/kata-deploy/binary/src/artifacts/install.rs

@@ -71,6 +71,30 @@ fn get_hypervisor_name(shim: &str) -> Result<&str> {
     }
 }
 
+/// Return the correct virtio-blk driver name for the current architecture.
+///
+/// runtime-rs only accepts the fully-qualified variants (`virtio-blk-pci`,
+/// `virtio-blk-ccw`, …); plain `"virtio-blk"` is rejected at config load time.
+fn erofs_virtio_blk_driver() -> &'static str {
+    match std::env::consts::ARCH {
+        "s390x" => "virtio-blk-ccw",
+        _ => "virtio-blk-pci",
+    }
+}
+
+/// Look up the snapshotter assigned to a shim from the mapping string.
+/// The mapping format is "shim1:snapshotter1,shim2:snapshotter2".
+fn get_snapshotter_for_shim<'a>(mapping: &'a str, shim: &str) -> Option<&'a str> {
+    mapping.split(',').find_map(|entry| {
+        let parts: Vec<&str> = entry.split(':').collect();
+        if parts.len() == 2 && parts[0].trim() == shim {
+            Some(parts[1].trim())
+        } else {
+            None
+        }
+    })
+}
+
 pub async fn install_artifacts(config: &Config, container_runtime: &str) -> Result<()> {
     info!("copying kata artifacts onto host");
 
@@ -618,6 +642,22 @@ async fn configure_shim_config(config: &Config, shim: &str, container_runtime: &
         configure_experimental_force_guest_pull(&kata_config_file).await?;
     }
 
+    if utils::is_rust_shim(shim) {
+        if let Some(ref mapping) = config.snapshotter_handler_mapping_for_arch {
+            if get_snapshotter_for_shim(mapping, shim) == Some("erofs") {
+                let hypervisor_name = get_hypervisor_name(shim)?;
+                let blk_driver = erofs_virtio_blk_driver();
+                let content = format!(
+                    "# EROFS snapshotter requires a virtio-blk block device driver\n\
+                     # Generated by kata-deploy\n\n\
+                     [hypervisor.{hypervisor_name}]\n\
+                     block_device_driver = \"{blk_driver}\"\n"
+                );
+                write_drop_in_file(&config_d_dir, "25-erofs-block-driver.toml", &content)?;
+            }
+        }
+    }
+
     Ok(())
 }
 
@@ -1095,6 +1135,28 @@ mod tests {
         );
     }
 
+    #[rstest]
+    #[case(
+        "qemu-coco-dev-runtime-rs:erofs",
+        "qemu-coco-dev-runtime-rs",
+        Some("erofs")
+    )]
+    #[case(
+        "qemu:nydus,qemu-coco-dev-runtime-rs:erofs",
+        "qemu-coco-dev-runtime-rs",
+        Some("erofs")
+    )]
+    #[case("qemu:nydus,qemu-coco-dev-runtime-rs:erofs", "qemu", Some("nydus"))]
+    #[case("qemu:nydus", "qemu-coco-dev-runtime-rs", None)]
+    #[case("", "qemu-coco-dev-runtime-rs", None)]
+    fn test_get_snapshotter_for_shim(
+        #[case] mapping: &str,
+        #[case] shim: &str,
+        #[case] expected: Option<&str>,
+    ) {
+        assert_eq!(get_snapshotter_for_shim(mapping, shim), expected);
+    }
+
     #[test]
     fn test_copy_artifacts_overwrites_existing_files() {
         use std::fs;