Add support for CgroupsPath field

Fixes #396

Signed-off-by: Kenfe-Mickael Laventure <mickael.laventure@gmail.com>

libcontainer/cgroups/fs/apply_raw.go

@@ -14,7 +14,6 @@ import (
 
 	"github.com/opencontainers/runc/libcontainer/cgroups"
 	"github.com/opencontainers/runc/libcontainer/configs"
-	libcontainerUtils "github.com/opencontainers/runc/libcontainer/utils"
 )
 
 var (
@@ -96,8 +95,7 @@ func getCgroupRoot() (string, error) {
 
 type cgroupData struct {
 	root      string
-	parent string
-	name   string
+	innerPath string
 	config    *configs.Cgroup
 	pid       int
 }
@@ -274,13 +272,18 @@ func getCgroupData(c *configs.Cgroup, pid int) (*cgroupData, error) {
 		return nil, err
 	}
 
-	// Clean the parent slice path.
-	c.Parent = libcontainerUtils.CleanPath(c.Parent)
+	if (c.Name != "" || c.Parent != "") && c.Path != "" {
+		return nil, fmt.Errorf("cgroup: either Path or Name and Parent should be used")
+	}
+
+	innerPath := c.Path
+	if innerPath == "" {
+		innerPath = filepath.Join(c.Parent, c.Name)
+	}
 
 	return &cgroupData{
 		root:      root,
-		parent: c.Parent,
-		name:   c.Name,
+		innerPath: c.Path,
 		config:    c,
 		pid:       pid,
 	}, nil
@@ -310,11 +313,10 @@ func (raw *cgroupData) path(subsystem string) (string, error) {
 		return "", err
 	}
 
-	cgPath := filepath.Join(raw.parent, raw.name)
 	// If the cgroup name/path is absolute do not look relative to the cgroup of the init process.
-	if filepath.IsAbs(cgPath) {
+	if filepath.IsAbs(raw.innerPath) {
 		// Sometimes subsystems can be mounted togethger as 'cpu,cpuacct'.
-		return filepath.Join(raw.root, filepath.Base(mnt), cgPath), nil
+		return filepath.Join(raw.root, filepath.Base(mnt), raw.innerPath), nil
 	}
 
 	parentPath, err := raw.parentPath(subsystem, mnt, root)
@@ -322,7 +324,7 @@ func (raw *cgroupData) path(subsystem string) (string, error) {
 		return "", err
 	}
 
-	return filepath.Join(parentPath, cgPath), nil
+	return filepath.Join(parentPath, raw.innerPath), nil
 }
 
 func (raw *cgroupData) join(subsystem string) (string, error) {

libcontainer/configs/cgroup_unix.go

@@ -11,15 +11,22 @@ const (
 )
 
 type Cgroup struct {
-	Name string `json:"name"`
+	// Deprecated, use Path instead
+	Name string `json:"name,omitempty"`
 
-	// name of parent cgroup or slice
-	Parent string `json:"parent"`
+	// name of parent of cgroup or slice
+	// Deprecated, use Path instead
+	Parent string `json:"parent,omitempty"`
+
+	// Path specifies the path to cgroups that are created and/or joined by the container.
+	// The path is assumed to be relative to the host system cgroup mountpoint.
+	Path string `json:"path"`
 
 	// ScopePrefix decribes prefix for the scope name
 	ScopePrefix string `json:"scope_prefix"`
 
-	// Paths represent the cgroups paths to join
+	// Paths represent the absolute cgroups paths to join.
+	// This takes precedence over Path.
 	Paths map[string]string
 
 	// Resources contains various cgroups settings to apply

libcontainer/integration/template_test.go

@@ -46,8 +46,7 @@ func newTemplateConfig(rootfs string) *configs.Config {
 			{Type: configs.NEWNET},
 		}),
 		Cgroups: &configs.Cgroup{
-			Name:   "test",
-			Parent: "integration",
+			Path: "integration/test",
 			Resources: &configs.Resources{
 				MemorySwappiness: -1,
 				AllowAllDevices:  false,

spec.go

@@ -18,6 +18,7 @@ import (
 	"github.com/opencontainers/runc/libcontainer/cgroups"
 	"github.com/opencontainers/runc/libcontainer/configs"
 	"github.com/opencontainers/runc/libcontainer/seccomp"
+	libcontainerUtils "github.com/opencontainers/runc/libcontainer/utils"
 	"github.com/opencontainers/specs"
 )
 
@@ -326,13 +327,22 @@ func createLibcontainerMount(cwd string, m specs.Mount) *configs.Mount {
 }
 
 func createCgroupConfig(name string, spec *specs.LinuxSpec) (*configs.Cgroup, error) {
-	myCgroupPath, err := cgroups.GetThisCgroupDir("devices")
+	var (
+		err          error
+		myCgroupPath string
+	)
+
+	if spec.Linux.CgroupsPath != nil {
+		myCgroupPath = libcontainerUtils.CleanPath(*spec.Linux.CgroupsPath)
+	} else {
+		myCgroupPath, err = cgroups.GetThisCgroupDir("devices")
 		if err != nil {
 			return nil, err
 		}
+	}
+
 	c := &configs.Cgroup{
-		Name:      name,
-		Parent:    myCgroupPath,
+		Path:      filepath.Join(myCgroupPath, name),
 		Resources: &configs.Resources{},
 	}
 	c.Resources.AllowedDevices = allowedDevices