Test for systemd cgroupdriver memory setting

This is a test case for issue https://github.com/moby/moby/issues/35123,
making sure we can set container's memory limit when using
`native.cgroupdriver=systemd`.

[v2: skip if no systemd present]
[v3: add --iptables=false to avoid flaky tests with t.Parallel()]
[v4: rebase after PR#36507 merge]

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

integration/system/cgroupdriver_systemd_test.go

@@ -0,0 +1,64 @@
+package system
+
+import (
+	"context"
+	"os"
+	"testing"
+
+	"github.com/docker/docker/api/types"
+	"github.com/docker/docker/api/types/container"
+	"github.com/docker/docker/integration-cli/daemon"
+
+	"github.com/gotestyourself/gotestyourself/assert"
+)
+
+// hasSystemd checks whether the host was booted with systemd as its init
+// system. Stolen from
+// https://github.com/coreos/go-systemd/blob/176f85496f4e/util/util.go#L68
+func hasSystemd() bool {
+	fi, err := os.Lstat("/run/systemd/system")
+	if err != nil {
+		return false
+	}
+	return fi.IsDir()
+}
+
+// TestCgroupDriverSystemdMemoryLimit checks that container
+// memory limit can be set when using systemd cgroupdriver.
+//  https://github.com/moby/moby/issues/35123
+func TestCgroupDriverSystemdMemoryLimit(t *testing.T) {
+	t.Parallel()
+
+	if !hasSystemd() {
+		t.Skip("systemd not available")
+	}
+
+	d := daemon.New(t, "docker", "dockerd", daemon.Config{})
+	client, err := d.NewClient()
+	assert.NilError(t, err)
+	d.StartWithBusybox(t, "--exec-opt", "native.cgroupdriver=systemd", "--iptables=false")
+	defer d.Stop(t)
+
+	const mem = 64 * 1024 * 1024 // 64 MB
+	cfg := container.Config{
+		Image: "busybox",
+		Cmd:   []string{"top"},
+	}
+	hostcfg := container.HostConfig{
+		Resources: container.Resources{
+			Memory: mem,
+		},
+	}
+
+	ctx := context.Background()
+	ctr, err := client.ContainerCreate(ctx, &cfg, &hostcfg, nil, "")
+	assert.NilError(t, err)
+	defer client.ContainerRemove(ctx, ctr.ID, types.ContainerRemoveOptions{Force: true})
+
+	err = client.ContainerStart(ctx, ctr.ID, types.ContainerStartOptions{})
+	assert.NilError(t, err)
+
+	s, err := client.ContainerInspect(ctx, ctr.ID)
+	assert.NilError(t, err)
+	assert.Equal(t, s.HostConfig.Memory, mem)
+}