Merge pull request #1872 from masters-of-cats/better-find-cgroup-mountpoint

Respect container's cgroup path

libcontainer/cgroups/utils.go

@@ -22,31 +22,41 @@ const (
 )
 
 // https://www.kernel.org/doc/Documentation/cgroup-v1/cgroups.txt
-func FindCgroupMountpoint(subsystem string) (string, error) {
-	mnt, _, err := FindCgroupMountpointAndRoot(subsystem)
+func FindCgroupMountpoint(cgroupPath, subsystem string) (string, error) {
+	mnt, _, err := FindCgroupMountpointAndRoot(cgroupPath, subsystem)
 	return mnt, err
 }
 
-func FindCgroupMountpointAndRoot(subsystem string) (string, string, error) {
+func FindCgroupMountpointAndRoot(cgroupPath, subsystem string) (string, string, error) {
 	// We are not using mount.GetMounts() because it's super-inefficient,
 	// parsing it directly sped up x10 times because of not using Sscanf.
 	// It was one of two major performance drawbacks in container start.
 	if !isSubsystemAvailable(subsystem) {
 		return "", "", NewNotFoundError(subsystem)
 	}
+
 	f, err := os.Open("/proc/self/mountinfo")
 	if err != nil {
 		return "", "", err
 	}
 	defer f.Close()
 
-	scanner := bufio.NewScanner(f)
+	return findCgroupMountpointAndRootFromReader(f, cgroupPath, subsystem)
+}
+
+func findCgroupMountpointAndRootFromReader(reader io.Reader, cgroupPath, subsystem string) (string, string, error) {
+	scanner := bufio.NewScanner(reader)
 	for scanner.Scan() {
 		txt := scanner.Text()
-		fields := strings.Split(txt, " ")
-		for _, opt := range strings.Split(fields[len(fields)-1], ",") {
-			if opt == subsystem {
-				return fields[4], fields[3], nil
+		fields := strings.Fields(txt)
+		if len(fields) < 5 {
+			continue
+		}
+		if strings.HasPrefix(fields[4], cgroupPath) {
+			for _, opt := range strings.Split(fields[len(fields)-1], ",") {
+				if opt == subsystem {
+					return fields[4], fields[3], nil
+				}
 			}
 		}
 	}
@@ -257,7 +267,7 @@ func GetInitCgroupPath(subsystem string) (string, error) {
 }
 
 func getCgroupPathHelper(subsystem, cgroup string) (string, error) {
-	mnt, root, err := FindCgroupMountpointAndRoot(subsystem)
+	mnt, root, err := FindCgroupMountpointAndRoot("", subsystem)
 	if err != nil {
 		return "", err
 	}