LCOW: Add environment variable to enable

Signed-off-by: John Howard <jhoward@microsoft.com>

cmd/dockerd/daemon.go

@@ -40,6 +40,7 @@ import (
 	"github.com/docker/docker/pkg/pidfile"
 	"github.com/docker/docker/pkg/plugingetter"
 	"github.com/docker/docker/pkg/signal"
+	"github.com/docker/docker/pkg/system"
 	"github.com/docker/docker/plugin"
 	"github.com/docker/docker/registry"
 	"github.com/docker/docker/runconfig"
@@ -210,6 +211,10 @@ func (cli *DaemonCli) start(opts *daemonOptions) (err error) {
 		logrus.Fatalf("Error creating middlewares: %v", err)
 	}
 
+	if system.LCOWSupported() {
+		logrus.Warnln("LCOW support is enabled - this feature is incomplete")
+	}
+
 	d, err := daemon.NewDaemon(cli.Config, registryService, containerdRemote, pluginStore)
 	if err != nil {
 		return fmt.Errorf("Error starting daemon: %v", err)

distribution/config.go

@@ -14,6 +14,7 @@ import (
 	"github.com/docker/docker/image"
 	"github.com/docker/docker/layer"
 	"github.com/docker/docker/pkg/progress"
+	"github.com/docker/docker/pkg/system"
 	refstore "github.com/docker/docker/reference"
 	"github.com/docker/docker/registry"
 	"github.com/docker/libtrust"
@@ -143,8 +144,8 @@ func (s *imageConfigStore) RootFSFromConfig(c []byte) (*image.RootFS, error) {
 	}
 
 	// fail immediately on Windows when downloading a non-Windows image
-	// and vice versa
-	if runtime.GOOS == "windows" && unmarshalledConfig.OS == "linux" {
+	// and vice versa. Exception on Windows if Linux Containers are enabled.
+	if runtime.GOOS == "windows" && unmarshalledConfig.OS == "linux" && !system.LCOWSupported() {
 		return nil, fmt.Errorf("image operating system %q cannot be used on this platform", unmarshalledConfig.OS)
 	} else if runtime.GOOS != "windows" && unmarshalledConfig.OS == "windows" {
 		return nil, fmt.Errorf("image operating system %q cannot be used on this platform", unmarshalledConfig.OS)

pkg/system/chtimes.go

@@ -2,26 +2,9 @@ package system
 
 import (
 	"os"
-	"syscall"
 	"time"
-	"unsafe"
 )
 
-var (
-	maxTime time.Time
-)
-
-func init() {
-	if unsafe.Sizeof(syscall.Timespec{}.Nsec) == 8 {
-		// This is a 64 bit timespec
-		// os.Chtimes limits time to the following
-		maxTime = time.Unix(0, 1<<63-1)
-	} else {
-		// This is a 32 bit timespec
-		maxTime = time.Unix(1<<31-1, 0)
-	}
-}
-
 // Chtimes changes the access time and modified time of a file at the given path
 func Chtimes(name string, atime time.Time, mtime time.Time) error {
 	unixMinTime := time.Unix(0, 0)

pkg/system/init.go

@@ -0,0 +1,22 @@
+package system
+
+import (
+	"syscall"
+	"time"
+	"unsafe"
+)
+
+// Used by chtimes
+var maxTime time.Time
+
+func init() {
+	// chtimes initialization
+	if unsafe.Sizeof(syscall.Timespec{}.Nsec) == 8 {
+		// This is a 64 bit timespec
+		// os.Chtimes limits time to the following
+		maxTime = time.Unix(0, 1<<63-1)
+	} else {
+		// This is a 32 bit timespec
+		maxTime = time.Unix(1<<31-1, 0)
+	}
+}

pkg/system/init_windows.go

@@ -0,0 +1,17 @@
+package system
+
+import "os"
+
+// LCOWSupported determines if Linux Containers on Windows are supported.
+// Note: This feature is in development (06/17) and enabled through an
+// environment variable. At a future time, it will be enabled based
+// on build number. @jhowardmsft
+var lcowSupported = false
+
+func init() {
+	// LCOW initialization
+	if os.Getenv("LCOW_SUPPORTED") != "" {
+		lcowSupported = true
+	}
+
+}

pkg/system/lcow.go

@@ -0,0 +1,6 @@
+package system
+
+// LCOWSupported returns true if Linux containers on Windows are supported.
+func LCOWSupported() bool {
+	return lcowSupported
+}