cgroups: only return path when subsystem really mounted

If cgroup patch doesn't exist, there is no point we do the Set.

Signed-off-by: Qiang Huang <h.huangqiang@huawei.com>

cgroups/fs/apply_raw.go

@@ -229,6 +229,12 @@ func (raw *data) parent(subsystem string) (string, error) {
 }
 
 func (raw *data) path(subsystem string) (string, error) {
+	_, err := cgroups.FindCgroupMountpoint(subsystem)
+	// If we didn't mount the subsystem, there is no point we make the path.
+	if err != nil {
+		return "", err
+	}
+
 	// If the cgroup name/path is absolute do not look relative to the cgroup of the init process.
 	if filepath.IsAbs(raw.cgroup) {
 		path := filepath.Join(raw.root, subsystem, raw.cgroup)

cgroups/fs/blkio.go

@@ -17,8 +17,12 @@ type BlkioGroup struct {
 
 func (s *BlkioGroup) Apply(d *data) error {
 	dir, err := d.join("blkio")
-	if err != nil && !cgroups.IsNotFound(err) {
-		return err
+	if err != nil {
+		if cgroups.IsNotFound(err) {
+			return nil
+		} else {
+			return err
+		}
 	}
 
 	if err := s.Set(dir, d.c); err != nil {

cgroups/fs/cpu.go

@@ -18,7 +18,11 @@ func (s *CpuGroup) Apply(d *data) error {
 	// on a container basis
 	dir, err := d.join("cpu")
 	if err != nil {
-		return err
+		if cgroups.IsNotFound(err) {
+			return nil
+		} else {
+			return err
+		}
 	}
 
 	if err := s.Set(dir, d.c); err != nil {

cgroups/fs/cpuset.go

@@ -17,7 +17,11 @@ type CpusetGroup struct {
 func (s *CpusetGroup) Apply(d *data) error {
 	dir, err := d.path("cpuset")
 	if err != nil {
-		return err
+		if cgroups.IsNotFound(err) {
+			return nil
+		} else {
+			return err
+		}
 	}
 	return s.ApplyDir(dir, d.c, d.pid)
 }

cgroups/fs/devices.go

@@ -11,7 +11,11 @@ type DevicesGroup struct {
 func (s *DevicesGroup) Apply(d *data) error {
 	dir, err := d.join("devices")
 	if err != nil {
-		return err
+		if cgroups.IsNotFound(err) {
+			return nil
+		} else {
+			return err
+		}
 	}
 
 	if err := s.Set(dir, d.c); err != nil {

cgroups/fs/freezer.go

@@ -13,8 +13,12 @@ type FreezerGroup struct {
 
 func (s *FreezerGroup) Apply(d *data) error {
 	dir, err := d.join("freezer")
-	if err != nil && !cgroups.IsNotFound(err) {
-		return err
+	if err != nil {
+		if cgroups.IsNotFound(err) {
+			return nil
+		} else {
+			return err
+		}
 	}
 
 	if err := s.Set(dir, d.c); err != nil {

cgroups/fs/memory.go

@@ -16,9 +16,12 @@ 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) {
-		return err
+	if err != nil {
+		if cgroups.IsNotFound(err) {
+			return nil
+		} else {
+			return err
+		}
 	}
 	defer func() {
 		if err != nil {