virtio-block: enable relaxed sync by default on macOS

On macOS, std::fs::File::flush() uses F_FULLFSYNC, which syncs the
buffers to the drive and asks the drive to wait for flushing all the
data to the permanent storage. In contrast, Apple
Virtualization.Framework only issues an fsync(), which doesn't ask the
drive to flush its buffered data.

When on macOS, tell imago to use relaxed sync to match the behavior of
Virtualization.Framework by default.

Related to containers/podman#27216

Signed-off-by: Jake Correnti <[email protected]>

Author: jakecorrenti

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

@@ -18,9 +18,10 @@ use std::result;
 use std::sync::Arc;
 use std::thread::JoinHandle;
 
-use imago::file::File as ImagoFile;
-use imago::qcow2::Qcow2;
-use imago::SyncFormatAccess;
+use imago::{
+    file::File as ImagoFile, qcow2::Qcow2, raw::Raw, DynStorage, Storage, StorageOpenOptions,
+    SyncFormatAccess,
+};
 use log::{error, warn};
 use utils::eventfd::{EventFd, EFD_NONBLOCK};
 use virtio_bindings::{
@@ -64,14 +65,14 @@ impl CacheType {
 /// Helper object for setting up all `Block` fields derived from its backing file.
 pub(crate) struct DiskProperties {
     cache_type: CacheType,
-    pub(crate) file: Arc<SyncFormatAccess<ImagoFile>>,
+    pub(crate) file: Arc<SyncFormatAccess<Box<dyn DynStorage>>>,
     nsectors: u64,
     image_id: Vec<u8>,
 }
 
 impl DiskProperties {
     pub fn new(
-        disk_image: Arc<SyncFormatAccess<ImagoFile>>,
+        disk_image: Arc<SyncFormatAccess<Box<dyn DynStorage>>>,
         disk_image_id: Vec<u8>,
         cache_type: CacheType,
     ) -> io::Result<Self> {
@@ -94,7 +95,7 @@ impl DiskProperties {
         })
     }
 
-    pub fn file(&self) -> &SyncFormatAccess<ImagoFile> {
+    pub fn file(&self) -> &SyncFormatAccess<Box<dyn DynStorage>> {
         self.file.as_ref()
     }
 
@@ -176,7 +177,7 @@ pub struct Block {
     // Host file and properties.
     disk: Option<DiskProperties>,
     cache_type: CacheType,
-    disk_image: Arc<SyncFormatAccess<ImagoFile>>,
+    disk_image: Arc<SyncFormatAccess<Box<dyn DynStorage>>>,
     disk_image_id: Vec<u8>,
     worker_thread: Option<JoinHandle<()>>,
     worker_stopfd: EventFd,
@@ -215,18 +216,32 @@ impl Block {
 
         let disk_image_id = DiskProperties::build_disk_image_id(&disk_image);
 
+        let file_opts = StorageOpenOptions::new()
+            .write(!is_disk_read_only)
+            .filename(disk_image_path);
+        #[cfg(target_os = "macos")]
+        let file_opts = file_opts.relaxed_sync(true);
+        let file = ImagoFile::open_sync(file_opts)?;
+
         let disk_image = match disk_image_format {
             ImageType::Qcow2 => {
-                let mut qcow_disk_image =
-                    Qcow2::<ImagoFile>::open_path_sync(disk_image_path, !is_disk_read_only)?;
-                qcow_disk_image.open_implicit_dependencies_sync()?;
-                SyncFormatAccess::new(qcow_disk_image)?
+                let mut qcow2 =
+                    Qcow2::<Box<dyn DynStorage>, Arc<imago::FormatAccess<_>>>::open_image_sync(
+                        Box::new(file),
+                        !is_disk_read_only,
+                    )?;
+                qcow2.open_implicit_dependencies_sync()?;
+                SyncFormatAccess::new(qcow2)?
             }
             ImageType::Raw => {
-                let raw = imago::raw::Raw::open_path_sync(disk_image_path, !is_disk_read_only)?;
+                let raw = Raw::<Box<dyn DynStorage>>::open_image_sync(
+                    Box::new(file),
+                    !is_disk_read_only,
+                )?;
                 SyncFormatAccess::new(raw)?
             }
         };
+
         let disk_image = Arc::new(disk_image);
 
         let disk_properties =