WCOW: restore support for client-mounted roots with process-isolated containers

internal/hcsoci/resources_wcow.go

@@ -34,18 +34,26 @@ func allocateWindowsResources(ctx context.Context, coi *createOptionsInternal, r
 		coi.Spec.Root = &specs.Root{}
 	}
 
-	if coi.Spec.Root.Path == "" && (coi.HostingSystem != nil || coi.Spec.Windows.HyperV == nil) {
-		log.G(ctx).Debug("hcsshim::allocateWindowsResources mounting storage")
-		mountedLayers, closer, err := layers.MountWCOWLayers(ctx, coi.actualID, coi.HostingSystem, coi.WCOWLayers)
-		if err != nil {
-			return errors.Wrap(err, "failed to mount container storage")
-		}
-		coi.Spec.Root.Path = mountedLayers.RootFS
-		coi.mountedWCOWLayers = mountedLayers
-		// If this is the pause container in a hypervisor-isolated pod, we can skip cleanup of
-		// layers, as that happens automatically when the UVM is terminated.
-		if !isSandbox || coi.HostingSystem == nil {
-			r.SetLayers(closer)
+	if coi.HostingSystem != nil || coi.Spec.Windows.HyperV == nil {
+		if coi.Spec.Root.Path == "" {
+			log.G(ctx).Debug("hcsshim::allocateWindowsResources mounting storage")
+			mountedLayers, closer, err := layers.MountWCOWLayers(ctx, coi.actualID, coi.HostingSystem, coi.WCOWLayers)
+			if err != nil {
+				return errors.Wrap(err, "failed to mount container storage")
+			}
+			coi.Spec.Root.Path = mountedLayers.RootFS
+			coi.mountedWCOWLayers = mountedLayers
+			// If this is the pause container in a hypervisor-isolated pod, we can skip cleanup of
+			// layers, as that happens automatically when the UVM is terminated.
+			if !isSandbox || coi.HostingSystem == nil {
+				r.SetLayers(closer)
+			}
+		} else {
+			l, err := layers.MakeMountedWCOWLayers(ctx, coi.WCOWLayers, coi.Spec.Root.Path)
+			if err != nil {
+				return errors.Wrap(err, "failed to use pre-mounted container storage")
+			}
+			coi.mountedWCOWLayers = l
 		}
 	}
 

internal/layers/wcow_mount.go

@@ -49,6 +49,44 @@ func MountWCOWLayers(ctx context.Context, containerID string, vm *uvm.UtilityVM,
 	}
 }
 
+// MakeMountedWCOWLayers creates a MountedWCOWLayers structure from wl, like
+// [MountWCOWLayers], without actually mounting anything.
+func MakeMountedWCOWLayers(ctx context.Context, wl WCOWLayers, mountPath string) (*MountedWCOWLayers, error) {
+	switch l := wl.(type) {
+	case *wcowWCIFSLayers:
+		layersWithID := []MountedWCOWLayer{}
+		for _, l := range l.layerPaths {
+			layerID, err := wclayer.LayerID(ctx, l)
+			if err != nil {
+				return nil, err
+			}
+			layersWithID = append(layersWithID, MountedWCOWLayer{
+				LayerID:     layerID.String(),
+				MountedPath: l,
+			})
+		}
+
+		return &MountedWCOWLayers{
+			RootFS:            mountPath,
+			MountedLayerPaths: layersWithID,
+		}, nil
+	case *wcowForkedCIMLayers, *wcowBlockCIMLayers:
+		layerID, err := cimlayer.LayerID(mountPath)
+		if err != nil {
+			return nil, err
+		}
+		return &MountedWCOWLayers{
+			RootFS: mountPath,
+			MountedLayerPaths: []MountedWCOWLayer{{
+				LayerID:     layerID,
+				MountedPath: mountPath,
+			}},
+		}, nil
+	default:
+		return nil, fmt.Errorf("invalid layer type %T", wl)
+	}
+}
+
 // Represents a single layer that is mounted and ready to use. Depending on the type of
 // layers each individual layer may or may not be mounted. However, HCS still needs paths
 // of individual layers and a unique ID for each layer.