notify: simplify usage

Instead of passing the whole map of paths, pass the path to the memory
controller which these functions actually require.

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

libcontainer/container_linux.go

@@ -655,7 +655,7 @@ func (c *linuxContainer) NotifyOOM() (<-chan struct{}, error) {
 		}
 		return notifyOnOOMV2(path)
 	}
-	return notifyOnOOM(c.cgroupManager.GetPaths())
+	return notifyOnOOM(c.cgroupManager.GetPaths()["memory"])
 }
 
 func (c *linuxContainer) NotifyMemoryPressure(level PressureLevel) (<-chan struct{}, error) {
@@ -663,7 +663,7 @@ func (c *linuxContainer) NotifyMemoryPressure(level PressureLevel) (<-chan struc
 	if c.config.RootlessCgroups {
 		logrus.Warn("getting memory pressure notifications may fail if you don't have the full access to cgroups")
 	}
-	return notifyMemoryPressure(c.cgroupManager.GetPaths(), level)
+	return notifyMemoryPressure(c.cgroupManager.GetPaths()["memory"], level)
 }
 
 var criuFeatures *criurpc.CriuFeatures

libcontainer/notify_linux.go

@@ -3,6 +3,7 @@
 package libcontainer
 
 import (
+	"errors"
 	"fmt"
 	"io/ioutil"
 	"os"
@@ -11,8 +12,6 @@ import (
 	"golang.org/x/sys/unix"
 )
 
-const oomCgroupName = "memory"
-
 type PressureLevel uint
 
 const (
@@ -66,19 +65,17 @@ func registerMemoryEvent(cgDir string, evName string, arg string) (<-chan struct
 
 // notifyOnOOM returns channel on which you can expect event about OOM,
 // if process died without OOM this channel will be closed.
-func notifyOnOOM(paths map[string]string) (<-chan struct{}, error) {
-	dir := paths[oomCgroupName]
+func notifyOnOOM(dir string) (<-chan struct{}, error) {
 	if dir == "" {
-		return nil, fmt.Errorf("path %q missing", oomCgroupName)
+		return nil, errors.New("memory controller missing")
 	}
 
 	return registerMemoryEvent(dir, "memory.oom_control", "")
 }
 
-func notifyMemoryPressure(paths map[string]string, level PressureLevel) (<-chan struct{}, error) {
-	dir := paths[oomCgroupName]
+func notifyMemoryPressure(dir string, level PressureLevel) (<-chan struct{}, error) {
 	if dir == "" {
-		return nil, fmt.Errorf("path %q missing", oomCgroupName)
+		return nil, errors.New("memory controller missing")
 	}
 
 	if level > CriticalPressure {

libcontainer/notify_linux_test.go

@@ -14,7 +14,7 @@ import (
 	"golang.org/x/sys/unix"
 )
 
-type notifyFunc func(paths map[string]string) (<-chan struct{}, error)
+type notifyFunc func(path string) (<-chan struct{}, error)
 
 func testMemoryNotification(t *testing.T, evName string, notify notifyFunc, targ string) {
 	memoryPath, err := ioutil.TempDir("", "testmemnotification-"+evName)
@@ -29,10 +29,7 @@ func testMemoryNotification(t *testing.T, evName string, notify notifyFunc, targ
 	if err := ioutil.WriteFile(eventPath, []byte{}, 0700); err != nil {
 		t.Fatal(err)
 	}
-	paths := map[string]string{
-		"memory": memoryPath,
-	}
-	ch, err := notify(paths)
+	ch, err := notify(memoryPath)
 	if err != nil {
 		t.Fatal("expected no error, got:", err)
 	}
@@ -102,8 +99,8 @@ func testMemoryNotification(t *testing.T, evName string, notify notifyFunc, targ
 }
 
 func TestNotifyOnOOM(t *testing.T) {
-	f := func(paths map[string]string) (<-chan struct{}, error) {
-		return notifyOnOOM(paths)
+	f := func(path string) (<-chan struct{}, error) {
+		return notifyOnOOM(path)
 	}
 
 	testMemoryNotification(t, "memory.oom_control", f, "")
@@ -117,8 +114,8 @@ func TestNotifyMemoryPressure(t *testing.T) {
 	}
 
 	for level, arg := range tests {
-		f := func(paths map[string]string) (<-chan struct{}, error) {
-			return notifyMemoryPressure(paths, level)
+		f := func(path string) (<-chan struct{}, error) {
+			return notifyMemoryPressure(path, level)
 		}
 
 		testMemoryNotification(t, "memory.pressure_level", f, arg)