Add a Windows section for Linux oci on LCOW

When creating a default OCI spec on Windows that is targeting the LCOW
platform it needs to contain a Windows section as well. This adds the
Windows section by default. It also protects against this case for all
OCI creation that doesnt use the OCI package in the runhcs-shim.

Signed-off-by: Justin Terry (VM) <juterry@microsoft.com>

oci/spec.go

@@ -19,6 +19,7 @@ package oci
 import (
 	"context"
 	"path/filepath"
+	"runtime"
 
 	"github.com/containerd/containerd/namespaces"
 	"github.com/containerd/containerd/platforms"
@@ -51,24 +52,32 @@ func GenerateSpec(ctx context.Context, client Client, c *containers.Container, o
 // GenerateSpecWithPlatform will generate a default spec from the provided image
 // for use as a containerd container in the platform requested.
 func GenerateSpecWithPlatform(ctx context.Context, client Client, platform string, c *containers.Container, opts ...SpecOpts) (*Spec, error) {
-	plat, err := platforms.Parse(platform)
-	if err != nil {
-		return nil, err
-	}
-
 	var s Spec
-	if plat.OS == "windows" {
-		err = populateDefaultWindowsSpec(ctx, &s, c.ID)
-	} else {
-		err = populateDefaultUnixSpec(ctx, &s, c.ID)
-	}
-	if err != nil {
+	if err := generateDefaultSpecWithPlatform(ctx, platform, c.ID, &s); err != nil {
 		return nil, err
 	}
 
 	return &s, ApplyOpts(ctx, client, c, &s, opts...)
 }
 
+func generateDefaultSpecWithPlatform(ctx context.Context, platform, id string, s *Spec) error {
+	plat, err := platforms.Parse(platform)
+	if err != nil {
+		return err
+	}
+
+	if plat.OS == "windows" {
+		err = populateDefaultWindowsSpec(ctx, s, id)
+	} else {
+		err = populateDefaultUnixSpec(ctx, s, id)
+		if err == nil && runtime.GOOS == "windows" {
+			// To run LCOW we have a Linux and Windows section. Add an empty one now.
+			s.Windows = &specs.Windows{}
+		}
+	}
+	return err
+}
+
 // ApplyOpts applys the options to the given spec, injecting data from the
 // context, client and container instance.
 func ApplyOpts(ctx context.Context, client Client, c *containers.Container, s *Spec, opts ...SpecOpts) error {

oci/spec_opts.go

@@ -23,7 +23,6 @@ import (
 	"io/ioutil"
 	"os"
 	"path/filepath"
-	"runtime"
 	"strconv"
 	"strings"
 
@@ -91,10 +90,7 @@ func setCapabilities(s *Spec) {
 // Use as the first option to clear the spec, then apply options afterwards.
 func WithDefaultSpec() SpecOpts {
 	return func(ctx context.Context, _ Client, c *containers.Container, s *Spec) error {
-		if runtime.GOOS == "windows" {
-			return populateDefaultWindowsSpec(ctx, s, c.ID)
-		}
-		return populateDefaultUnixSpec(ctx, s, c.ID)
+		return generateDefaultSpecWithPlatform(ctx, platforms.DefaultString(), c.ID, s)
 	}
 }
 
@@ -104,15 +100,7 @@ func WithDefaultSpec() SpecOpts {
 // Use as the first option to clear the spec, then apply options afterwards.
 func WithDefaultSpecForPlatform(platform string) SpecOpts {
 	return func(ctx context.Context, _ Client, c *containers.Container, s *Spec) error {
-		plat, err := platforms.Parse(platform)
-		if err != nil {
-			return err
-		}
-
-		if plat.OS == "windows" {
-			return populateDefaultWindowsSpec(ctx, s, c.ID)
-		}
-		return populateDefaultUnixSpec(ctx, s, c.ID)
+		return generateDefaultSpecWithPlatform(ctx, platform, c.ID, s)
 	}
 }
 

oci/spec_test.go

@@ -73,6 +73,44 @@ func TestGenerateSpec(t *testing.T) {
 	}
 }
 
+func TestGenerateSpecWithPlatform(t *testing.T) {
+	t.Parallel()
+
+	ctx := namespaces.WithNamespace(context.Background(), "testing")
+	platforms := []string{"windows/amd64", "linux/amd64"}
+	for _, p := range platforms {
+		t.Logf("Testing platform: %s", p)
+		s, err := GenerateSpecWithPlatform(ctx, nil, p, &containers.Container{ID: t.Name()})
+		if err != nil {
+			t.Fatalf("failed to generate spec: %v", err)
+		}
+
+		if s.Root == nil {
+			t.Fatal("expected non nil Root section.")
+		}
+		if s.Process == nil {
+			t.Fatal("expected non nil Process section.")
+		}
+		if p == "windows/amd64" {
+			if s.Linux != nil {
+				t.Fatal("expected nil Linux section")
+			}
+			if s.Windows == nil {
+				t.Fatal("expected non nil Windows section")
+			}
+		} else {
+			if s.Linux == nil {
+				t.Fatal("expected non nil Linux section")
+			}
+			if runtime.GOOS == "windows" && s.Windows == nil {
+				t.Fatal("expected non nil Windows section for LCOW")
+			} else if runtime.GOOS != "windows" && s.Windows != nil {
+				t.Fatal("expected nil Windows section")
+			}
+		}
+	}
+}
+
 func TestSpecWithTTY(t *testing.T) {
 	t.Parallel()
 

runtime/v2/runhcs/service.go

@@ -314,6 +314,14 @@ func writeMountsToConfig(bundle string, mounts []*containerd_types.Mount) error
 		return errors.Wrap(err, "failed to seek to 0 in config.json")
 	}
 
+	// If we are creating LCOW make sure that spec.Windows is filled out before
+	// appending layer folders.
+	if m.Type == "lcow-layer" && spec.Windows == nil {
+		spec.Windows = &oci.Windows{
+			HyperV: &oci.WindowsHyperV{},
+		}
+	}
+
 	// Append the parents
 	spec.Windows.LayerFolders = append(spec.Windows.LayerFolders, parentLayerPaths...)
 	// Append the scratch