vmm: DeviceConfig: Store path as Option<PathBuf>

Relax DeviceConfig::path from PathBuf to Option<PathBuf> in preparation
to accept an externally-opened vfio cdev FD. The parser and OpenAPI spec
still enforces that `path` is set, so callers see no behavior change.

Signed-off-by: Bo Chen <bchen@crusoe.ai>
Assisted-by: Claude:Opus-4.7

vmm/src/config.rs

@@ -2442,7 +2442,7 @@ impl DeviceConfig {
             .unwrap_or_default();
         Ok(DeviceConfig {
             pci_common,
-            path,
+            path: Some(path),
             x_nv_gpudirect_clique,
             x_exclude_mmap_bars,
         })
@@ -3312,9 +3312,11 @@ impl VmConfig {
         if let Some(devices) = &self.devices {
             let mut device_paths = BTreeSet::new();
             for device in devices {
-                if !device_paths.insert(device.path.to_string_lossy()) {
+                if let Some(path) = device.path.as_deref()
+                    && !device_paths.insert(path.to_string_lossy())
+                {
                     return Err(ValidationError::DuplicateDevicePath(
-                        device.path.to_string_lossy().to_string(),
+                        path.to_string_lossy().to_string(),
                     ));
                 }
 
@@ -4719,7 +4721,7 @@ id=\"{id}\",pci_segment={pci_segment},queue_sizes={queue_sizes}"
     fn device_fixture() -> DeviceConfig {
         DeviceConfig {
             pci_common: PciDeviceCommonConfig::default(),
-            path: PathBuf::from("/path/to/device"),
+            path: Some(PathBuf::from("/path/to/device")),
             x_nv_gpudirect_clique: None,
             x_exclude_mmap_bars: Vec::new(),
         }
@@ -6073,11 +6075,11 @@ id=\"{id}\",pci_segment={pci_segment},queue_sizes={queue_sizes}"
         let mut still_valid_config = valid_config.clone();
         still_valid_config.devices = Some(vec![
             DeviceConfig {
-                path: "/device1".into(),
+                path: Some("/device1".into()),
                 ..device_fixture()
             },
             DeviceConfig {
-                path: "/device2".into(),
+                path: Some("/device2".into()),
                 ..device_fixture()
             },
         ]);
@@ -6086,11 +6088,11 @@ id=\"{id}\",pci_segment={pci_segment},queue_sizes={queue_sizes}"
         let mut invalid_config = valid_config.clone();
         invalid_config.devices = Some(vec![
             DeviceConfig {
-                path: "/device1".into(),
+                path: Some("/device1".into()),
                 ..device_fixture()
             },
             DeviceConfig {
-                path: "/device1".into(),
+                path: Some("/device1".into()),
                 ..device_fixture()
             },
         ]);

vmm/src/device_manager.rs

@@ -3976,9 +3976,13 @@ impl DeviceManager {
             vfio_ops
         };
 
-        let vfio_device =
-            VfioDevice::new(&device_cfg.path, Arc::clone(&vfio_ops) as Arc<dyn VfioOps>)
-                .map_err(DeviceManagerError::VfioCreate)?;
+        // The CLI parser and OpenAPI spec enforce that `path` is set
+        let device_path = device_cfg
+            .path
+            .as_deref()
+            .expect("DeviceConfig::parse enforces a path");
+        let vfio_device = VfioDevice::new(device_path, Arc::clone(&vfio_ops) as Arc<dyn VfioOps>)
+            .map_err(DeviceManagerError::VfioCreate)?;
 
         if needs_dma_mapping {
             // Register DMA mapping in IOMMU.
@@ -4063,7 +4067,7 @@ impl DeviceManager {
                 .iter()
                 .map(|bar| *bar as u8)
                 .collect(),
-            device_cfg.path.clone(),
+            device_path.to_path_buf(),
         )
         .map_err(DeviceManagerError::VfioPciCreate)?;
 

vmm/src/vm_config.rs

@@ -758,7 +758,8 @@ impl ApplyLandlock for DebugConsoleConfig {
 pub struct DeviceConfig {
     #[serde(flatten)]
     pub pci_common: PciDeviceCommonConfig,
-    pub path: PathBuf,
+    #[serde(default)]
+    pub path: Option<PathBuf>,
     #[serde(default)]
     pub x_nv_gpudirect_clique: Option<u8>,
     #[serde(default)]
@@ -767,7 +768,11 @@ pub struct DeviceConfig {
 
 impl ApplyLandlock for DeviceConfig {
     fn apply_landlock(&self, landlock: &mut Landlock) -> LandlockResult<()> {
-        let device_path = fs::read_link(self.path.as_path()).map_err(LandlockError::OpenPath)?;
+        let path = self
+            .path
+            .as_deref()
+            .expect("DeviceConfig::parse and OpenAPI spec enforce a path");
+        let device_path = fs::read_link(path).map_err(LandlockError::OpenPath)?;
         let iommu_group = device_path.file_name();
         let iommu_group_str = iommu_group
             .ok_or(LandlockError::InvalidPath)?