Libcontainer fs.GetStats() will not look for cgroups relative to the …

…cgroup of init process if the parent

in cgroups.Cgroup is absolute. This is required to get stats of other containers while running inside a docker container.

Docker-DCO-1.1-Signed-off-by: Vishnu Kannan <vishnuk@google.com> (github: vishh)

cgroups/fs/apply_raw.go

@@ -150,6 +150,10 @@ func (raw *data) parent(subsystem string) (string, error) {
 }
 
 func (raw *data) path(subsystem string) (string, error) {
+	// If the cgroup name/path is absolute do not look relative to the cgroup of the init process.
+	if filepath.IsAbs(raw.cgroup) {
+		return filepath.Join(raw.root, subsystem, raw.cgroup), nil
+	}
 	parent, err := raw.parent(subsystem)
 	if err != nil {
 		return "", err

cgroups/fs/utils_test.go

@@ -5,6 +5,8 @@ import (
 	"os"
 	"path/filepath"
 	"testing"
+
+	"github.com/docker/libcontainer/cgroups"
 )
 
 const (
@@ -66,3 +68,20 @@ func TestGetCgroupParamsInt(t *testing.T) {
 		t.Fatal("Expecting error, got none")
 	}
 }
+
+func TestAbsolutePathHandling(t *testing.T) {
+	testCgroup := cgroups.Cgroup{
+		Name:   "bar",
+		Parent: "/foo",
+	}
+	cgroupData := data{
+		root:   "/sys/fs/cgroup",
+		cgroup: "/foo/bar",
+		c:      &testCgroup,
+		pid:    1,
+	}
+	expectedPath := filepath.Join(cgroupData.root, "cpu", testCgroup.Parent, testCgroup.Name)
+	if path, err := cgroupData.path("cpu"); path != expectedPath || err != nil {
+		t.Fatalf("expected path %s but got %s %s", expectedPath, path, err)
+	}
+}