devices: set CacheType::Unsafe for macOS raw disks

Signed-off-by: Jan Noha <[email protected]>

Author: nohajc

src/devices/src/virtio/block/device.rs

@@ -51,6 +51,18 @@ pub enum CacheType {
     Writeback,
 }
 
+impl CacheType {
+    /// Picks the appropriate cache type based on disk image or device path.
+    /// Special files like `/dev/rdisk*` on macOS do not support flush/sync.
+    pub fn auto(_path: &str) -> CacheType {
+        #[cfg(target_os = "macos")]
+        if _path.starts_with("/dev/rdisk") {
+            return CacheType::Unsafe;
+        }
+        CacheType::Writeback
+    }
+}
+
 /// Helper object for setting up all `Block` fields derived from its backing file.
 pub(crate) struct DiskProperties {
     cache_type: CacheType,

src/libkrun/src/lib.rs

@@ -509,7 +509,7 @@ pub unsafe extern "C" fn krun_add_disk(
             let cfg = ctx_cfg.get_mut();
             let block_device_config = BlockDeviceConfig {
                 block_id: block_id.to_string(),
-                cache_type: CacheType::Writeback,
+                cache_type: CacheType::auto(disk_path),
                 disk_image_path: disk_path.to_string(),
                 disk_image_format: ImageType::Raw,
                 is_disk_read_only: read_only,
@@ -556,7 +556,7 @@ pub unsafe extern "C" fn krun_add_disk2(
             let cfg = ctx_cfg.get_mut();
             let block_device_config = BlockDeviceConfig {
                 block_id: block_id.to_string(),
-                cache_type: CacheType::Writeback,
+                cache_type: CacheType::auto(disk_path),
                 disk_image_path: disk_path.to_string(),
                 disk_image_format: format,
                 is_disk_read_only: read_only,
@@ -583,7 +583,7 @@ pub unsafe extern "C" fn krun_set_root_disk(ctx_id: u32, c_disk_path: *const c_c
             let cfg = ctx_cfg.get_mut();
             let block_device_config = BlockDeviceConfig {
                 block_id: "root".to_string(),
-                cache_type: CacheType::Writeback,
+                cache_type: CacheType::auto(disk_path),
                 disk_image_path: disk_path.to_string(),
                 disk_image_format: ImageType::Raw,
                 is_disk_read_only: false,
@@ -610,7 +610,7 @@ pub unsafe extern "C" fn krun_set_data_disk(ctx_id: u32, c_disk_path: *const c_c
             let cfg = ctx_cfg.get_mut();
             let block_device_config = BlockDeviceConfig {
                 block_id: "data".to_string(),
-                cache_type: CacheType::Writeback,
+                cache_type: CacheType::auto(disk_path),
                 disk_image_path: disk_path.to_string(),
                 disk_image_format: ImageType::Raw,
                 is_disk_read_only: false,