utils: export ParseCgroupFile()

paths.go

@@ -39,7 +39,7 @@ func StaticPath(path string) Path {
 // NestedPath will nest the cgroups based on the calling processes cgroup
 // placing its child processes inside its own path
 func NestedPath(suffix string) Path {
-	paths, err := parseCgroupFile("/proc/self/cgroup")
+	paths, err := ParseCgroupFile("/proc/self/cgroup")
 	if err != nil {
 		return errorPath(err)
 	}
@@ -50,7 +50,7 @@ func NestedPath(suffix string) Path {
 // This is commonly used for the Load function to restore an existing container
 func PidPath(pid int) Path {
 	p := fmt.Sprintf("/proc/%d/cgroup", pid)
-	paths, err := parseCgroupFile(p)
+	paths, err := ParseCgroupFile(p)
 	if err != nil {
 		return errorPath(errors.Wrapf(err, "parse cgroup file %s", p))
 	}

paths_test.go

@@ -41,7 +41,7 @@ func TestSelfPath(t *testing.T) {
 	} else if err != nil {
 		t.Fatal(err)
 	}
-	paths, err := parseCgroupFile("/proc/self/cgroup")
+	paths, err := ParseCgroupFile("/proc/self/cgroup")
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -63,7 +63,7 @@ func TestPidPath(t *testing.T) {
 	} else if err != nil {
 		t.Fatal(err)
 	}
-	paths, err := parseCgroupFile("/proc/self/cgroup")
+	paths, err := ParseCgroupFile("/proc/self/cgroup")
 	if err != nil {
 		t.Fatal(err)
 	}

utils.go

@@ -285,7 +285,16 @@ func parseKV(raw string) (string, uint64, error) {
 	}
 }
 
-func parseCgroupFile(path string) (map[string]string, error) {
+// ParseCgroupFile parses the given cgroup file, typically /proc/self/cgroup
+// or /proc/<pid>/cgroup, into a map of subsystems to cgroup paths, e.g.
+//   "cpu": "/user.slice/user-1000.slice"
+//   "pids": "/user.slice/user-1000.slice"
+// etc.
+//
+// Note that for cgroup v2 unified hierarchy, there are no per-controller
+// cgroup paths, so the resulting map will have a single element where the key
+// is empty string ("") and the value is the cgroup path the <pid> is in.
+func ParseCgroupFile(path string) (map[string]string, error) {
 	f, err := os.Open(path)
 	if err != nil {
 		return nil, err