Merge pull request #1372 from cloudfoundry-incubator/cpuset-mount-root

Handle container creation when cgroups have already been mounted in another location

libcontainer/cgroups/fs/cpuset.go

@@ -57,10 +57,11 @@ func (s *CpusetGroup) ApplyDir(dir string, cgroup *configs.Cgroup, pid int) erro
 	if dir == "" {
 		return nil
 	}
-	root, err := getCgroupRoot()
+	mountInfo, err := ioutil.ReadFile("/proc/self/mountinfo")
 	if err != nil {
 		return err
 	}
+	root := filepath.Dir(cgroups.GetClosestMountpointAncestor(dir, string(mountInfo)))
 	// 'ensureParent' start with parent because we don't want to
 	// explicitly inherit from parent, it could conflict with
 	// 'cpuset.cpu_exclusive'.

libcontainer/cgroups/utils.go

@@ -66,6 +66,21 @@ func isSubsystemAvailable(subsystem string) bool {
 	return avail
 }
 
+func GetClosestMountpointAncestor(dir, mountinfo string) string {
+	deepestMountPoint := ""
+	for _, mountInfoEntry := range strings.Split(mountinfo, "\n") {
+		mountInfoParts := strings.Fields(mountInfoEntry)
+		if len(mountInfoParts) < 5 {
+			continue
+		}
+		mountPoint := mountInfoParts[4]
+		if strings.HasPrefix(mountPoint, deepestMountPoint) && strings.HasPrefix(dir, mountPoint) {
+			deepestMountPoint = mountPoint
+		}
+	}
+	return deepestMountPoint
+}
+
 func FindCgroupMountpointDir() (string, error) {
 	f, err := os.Open("/proc/self/mountinfo")
 	if err != nil {

libcontainer/cgroups/utils_test.go

@@ -300,3 +300,34 @@ func TestIgnoreCgroup2Mount(t *testing.T) {
 		}
 	}
 }
+
+const fakeMountInfo = ` 18 24 0:17 / /sys rw,nosuid,nodev,noexec,relatime - sysfs sysfs rw
+100 99 1:31 / /foo/bar rw,relatime - fake fake rw,fake
+100 99 1:31 / /foo/bar/baz2 rw,relatime - fake fake rw,fake
+100 99 1:31 / /foo/bar/baz rw,relatime - fake fake rw,fake
+100 99 1:31 / /foo/bar/bazza rw,relatime - fake fake rw,fake
+100 99 1:31 / /foo/bar/baz3 rw,relatime - fake fake rw,fake
+100 99 1:31 / /foo rw,relatime - fake fake rw,fake
+100 99 1:31 / /unrelated rw,relatime - fake fake rw,fake
+100 99 1:31 / / rw,relatime - fake fake rw,fake
+`
+
+func TestGetClosestMountpointAncestor(t *testing.T) {
+	testCases := []struct {
+		input      string
+		mountinfos string
+		output     string
+	}{
+		{input: "/foo/bar/baz/a/b/c", mountinfos: fakeMountInfo, output: "/foo/bar/baz"},
+		{input: "/foo/bar/baz", mountinfos: fakeMountInfo, output: "/foo/bar/baz"},
+		{input: "/foo/bar/bazza", mountinfos: fakeMountInfo, output: "/foo/bar/bazza"},
+		{input: "/a/b/c/d", mountinfos: fakeMountInfo, output: "/"},
+	}
+
+	for _, c := range testCases {
+		mountpoint := GetClosestMountpointAncestor(c.input, c.mountinfos)
+		if mountpoint != c.output {
+			t.Errorf("expected %s, got %s", c.output, mountpoint)
+		}
+	}
+}