create newBuildKit function separately in daemon_unix.go and daemon_windows.go for cross platform build

Signed-off-by: Anda Xu <anda.xu@docker.com>

cmd/dockerd/daemon.go

@@ -284,17 +284,7 @@ func newRouterOptions(config *config.Config, d *daemon.Daemon) (routerOptions, e
 	if err != nil {
 		return opts, err
 	}
-	cgroupParent := "docker"
-	useSystemd := daemon.UsingSystemd(config)
-	if useSystemd {
-		cgroupParent = "system.slice"
-	}
-	if config.CgroupParent != "" {
-		cgroupParent = config.CgroupParent
-	}
-	if useSystemd {
-		cgroupParent = cgroupParent + ":" + "docker" + ":"
-	}
+	cgroupParent := newCgroupParent(config)
 	bk, err := buildkit.New(buildkit.Opt{
 		SessionManager:      sm,
 		Root:                filepath.Join(config.Root, "buildkit"),

cmd/dockerd/daemon_unix.go

@@ -13,6 +13,7 @@ import (
 	"github.com/containerd/containerd/runtime/v1/linux"
 	"github.com/docker/docker/cmd/dockerd/hack"
 	"github.com/docker/docker/daemon"
+	"github.com/docker/docker/daemon/config"
 	"github.com/docker/docker/libcontainerd/supervisor"
 	"github.com/docker/libnetwork/portallocator"
 	"golang.org/x/sys/unix"
@@ -107,3 +108,18 @@ func wrapListeners(proto string, ls []net.Listener) []net.Listener {
 	}
 	return ls
 }
+
+func newCgroupParent(config *config.Config) string {
+	cgroupParent := "docker"
+	useSystemd := daemon.UsingSystemd(config)
+	if useSystemd {
+		cgroupParent = "system.slice"
+	}
+	if config.CgroupParent != "" {
+		cgroupParent = config.CgroupParent
+	}
+	if useSystemd {
+		cgroupParent = cgroupParent + ":" + "docker" + ":"
+	}
+	return cgroupParent
+}

cmd/dockerd/daemon_windows.go

@@ -6,6 +6,7 @@ import (
 	"os"
 	"path/filepath"
 
+	"github.com/docker/docker/daemon/config"
 	"github.com/docker/docker/libcontainerd/supervisor"
 	"github.com/sirupsen/logrus"
 	"golang.org/x/sys/windows"
@@ -83,3 +84,7 @@ func allocateDaemonPort(addr string) error {
 func wrapListeners(proto string, ls []net.Listener) []net.Listener {
 	return ls
 }
+
+func newCgroupParent(config *config.Config) string {
+	return ""
+}