cmd: dockerd: make systemd specific cgroups tweaks build-time optional

When running under systemd, we have to do some tweaks for systemd's
non standard cgroups setups. This isn't required if we'll never be running
in such an environment (eg. there're many distros free of such Lennartisms).

Therefore make it possible to opt out at build time by settings the
'no_systemd' tag.

changes v2: fixed danling import
            renamed 'nosystemd' tag to 'no_systemd'

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>

cmd/dockerd/daemon_nosystemd_unix.go

@@ -0,0 +1,15 @@
+// +build no_systemd
+
+package main
+
+import (
+	"github.com/docker/docker/daemon/config"
+)
+
+func newCgroupParent(config *config.Config) string {
+	cgroupParent := "docker"
+	if config.CgroupParent != "" {
+		cgroupParent = config.CgroupParent
+	}
+	return cgroupParent
+}

cmd/dockerd/daemon_systemd_unix.go

@@ -0,0 +1,23 @@
+// +build linux,!no_systemd
+
+package main
+
+import (
+	"github.com/docker/docker/daemon"
+	"github.com/docker/docker/daemon/config"
+)
+
+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_unix.go

@@ -13,7 +13,6 @@ import (
 	"time"
 
 	"github.com/containerd/containerd/runtime/v1/linux"
-	"github.com/docker/docker/daemon"
 	"github.com/docker/docker/daemon/config"
 	"github.com/docker/docker/libcontainerd/supervisor"
 	"github.com/docker/docker/libnetwork/portallocator"
@@ -121,21 +120,6 @@ func allocateDaemonPort(addr string) error {
 	return nil
 }
 
-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
-}
-
 func (cli *DaemonCli) initContainerD(ctx context.Context) (func(time.Duration) error, error) {
 	var waitForShutdown func(time.Duration) error
 	if cli.Config.ContainerdAddr == "" {