don't fail when subsystem not mounted

cgroups/fs/apply_raw.go

@@ -275,6 +275,11 @@ func (raw *data) join(subsystem string) (string, error) {
 }
 
 func writeFile(dir, file, data string) error {
+	// Normally dir should not be empty, one case is that cgroup subsystem
+	// is not mounted, we will get empty dir, and we want it fail here.
+	if dir == "" {
+		return fmt.Errorf("no such directory for %s.", file)
+	}
 	return ioutil.WriteFile(filepath.Join(dir, file), []byte(data), 0700)
 }
 

cgroups/fs/cpu.go

@@ -17,7 +17,7 @@ func (s *CpuGroup) Apply(d *data) error {
 	// We always want to join the cpu group, to allow fair cpu scheduling
 	// on a container basis
 	dir, err := d.join("cpu")
-	if err != nil {
+	if err != nil && !cgroups.IsNotFound(err) {
 		return err
 	}
 

cgroups/fs/cpuset.go

@@ -16,7 +16,7 @@ type CpusetGroup struct {
 
 func (s *CpusetGroup) Apply(d *data) error {
 	dir, err := d.path("cpuset")
-	if err != nil {
+	if err != nil && !cgroups.IsNotFound(err) {
 		return err
 	}
 
@@ -48,6 +48,11 @@ func (s *CpusetGroup) GetStats(path string, stats *cgroups.Stats) error {
 }
 
 func (s *CpusetGroup) ApplyDir(dir string, cgroup *configs.Cgroup, pid int) error {
+	// This might happen if we have no cpuset cgroup mounted.
+	// Just do nothing and don't fail.
+	if dir == "" {
+		return nil
+	}
 	if err := s.ensureParent(dir); err != nil {
 		return err
 	}

cgroups/fs/devices.go

@@ -11,6 +11,8 @@ type DevicesGroup struct {
 func (s *DevicesGroup) Apply(d *data) error {
 	dir, err := d.join("devices")
 	if err != nil {
+		// We will return error even it's `not found` error, devices
+		// cgroup is hard requirement for container's security.
 		return err
 	}
 

cgroups/fs/memory.go

@@ -16,8 +16,7 @@ type MemoryGroup struct {
 
 func (s *MemoryGroup) Apply(d *data) error {
 	dir, err := d.join("memory")
-	// only return an error for memory if it was specified
-	if err != nil && (d.c.Memory != 0 || d.c.MemoryReservation != 0 || d.c.MemorySwap != 0) {
+	if err != nil && !cgroups.IsNotFound(err) {
 		return err
 	}
 	defer func() {

cgroups/systemd/apply_systemd.go

@@ -256,6 +256,11 @@ func (m *Manager) GetPaths() map[string]string {
 }
 
 func writeFile(dir, file, data string) error {
+	// Normally dir should not be empty, one case is that cgroup subsystem
+	// is not mounted, we will get empty dir, and we want it fail here.
+	if dir == "" {
+		return fmt.Errorf("no such directory for %s.", file)
+	}
 	return ioutil.WriteFile(filepath.Join(dir, file), []byte(data), 0700)
 }
 
@@ -276,24 +281,24 @@ func join(c *configs.Cgroup, subsystem string, pid int) (string, error) {
 
 func joinCpu(c *configs.Cgroup, pid int) error {
 	path, err := getSubsystemPath(c, "cpu")
-	if err != nil {
+	if err != nil && !cgroups.IsNotFound(err) {
 		return err
 	}
 	if c.CpuQuota != 0 {
-		if err = ioutil.WriteFile(filepath.Join(path, "cpu.cfs_quota_us"), []byte(strconv.FormatInt(c.CpuQuota, 10)), 0700); err != nil {
+		if err = writeFile(path, "cpu.cfs_quota_us", strconv.FormatInt(c.CpuQuota, 10)); err != nil {
 			return err
 		}
 	}
 	if c.CpuPeriod != 0 {
-		if err = ioutil.WriteFile(filepath.Join(path, "cpu.cfs_period_us"), []byte(strconv.FormatInt(c.CpuPeriod, 10)), 0700); err != nil {
+		if err = writeFile(path, "cpu.cfs_period_us", strconv.FormatInt(c.CpuPeriod, 10)); err != nil {
 			return err
 		}
 	}
 	return nil
 }
 
 func joinFreezer(c *configs.Cgroup, pid int) error {
-	if _, err := join(c, "freezer", pid); err != nil {
+	if _, err := join(c, "freezer", pid); err != nil && !cgroups.IsNotFound(err) {
 		return err
 	}
 
@@ -393,6 +398,8 @@ func getUnitName(c *configs.Cgroup) string {
 // This happens at least for v208 when any sibling unit is started.
 func joinDevices(c *configs.Cgroup, pid int) error {
 	path, err := join(c, "devices", pid)
+	// Even if it's `not found` error, we'll return err because devices cgroup
+	// is hard requirement for container security.
 	if err != nil {
 		return err
 	}
@@ -420,19 +427,19 @@ func joinMemory(c *configs.Cgroup, pid int) error {
 	}
 
 	path, err := getSubsystemPath(c, "memory")
-	if err != nil {
+	if err != nil && !cgroups.IsNotFound(err) {
 		return err
 	}
 
-	return ioutil.WriteFile(filepath.Join(path, "memory.memsw.limit_in_bytes"), []byte(strconv.FormatInt(memorySwap, 10)), 0700)
+	return writeFile(path, "memory.memsw.limit_in_bytes", strconv.FormatInt(memorySwap, 10))
 }
 
 // systemd does not atm set up the cpuset controller, so we must manually
 // join it. Additionally that is a very finicky controller where each
 // level must have a full setup as the default for a new directory is "no cpus"
 func joinCpuset(c *configs.Cgroup, pid int) error {
 	path, err := getSubsystemPath(c, "cpuset")
-	if err != nil {
+	if err != nil && !cgroups.IsNotFound(err) {
 		return err
 	}