// checks if the required cgroups subsystems are mounted.
// As of now, only 'cpu' and 'memory' are required.
func validateSystemRequirements(mountUtil mount.Interface) error {
	const (
		cgroupMountType = "cgroup"
		localErr        = "system validation failed"
	)
	mountPoints, err := mountUtil.List()
	if err != nil {
		return fmt.Errorf("%s - %v", localErr, err)
	}
	expectedCgroups := sets.NewString("cpu", "cpuacct", "cpuset", "memory")
	for _, mountPoint := range mountPoints {
		if mountPoint.Type == cgroupMountType {
			for _, opt := range mountPoint.Opts {
				if expectedCgroups.Has(opt) {
					expectedCgroups.Delete(opt)
				}
			}
		}
	}

	if expectedCgroups.Len() > 0 {
		return fmt.Errorf("%s - Following Cgroup subsystem not mounted: %v", localErr, expectedCgroups.List())
	}
	return nil
}

// utility to mount a disk based filesystem
func diskSetUp(manager diskManager, b iscsiDiskBuilder, volPath string, mounter mount.Interface) error {
	globalPDPath := manager.MakeGlobalPDName(*b.iscsiDisk)
	// TODO: handle failed mounts here.
	notMnt, err := mounter.IsLikelyNotMountPoint(volPath)

	if err != nil && !os.IsNotExist(err) {
		glog.Errorf("cannot validate mountpoint: %s", volPath)
		return err
	}
	if !notMnt {
		return nil
	}
	if err := manager.AttachDisk(b); err != nil {
		glog.Errorf("failed to attach disk")
		return err
	}

	if err := os.MkdirAll(volPath, 0750); err != nil {
		glog.Errorf("failed to mkdir:%s", volPath)
		return err
	}
	// Perform a bind mount to the full path to allow duplicate mounts of the same disk.
	options := []string{"bind"}
	if b.readOnly {
		options = append(options, "ro")
	}
	err = mounter.Mount(globalPDPath, volPath, "", options)
	if err != nil {
		glog.Errorf("failed to bind mount:%s", globalPDPath)
		return err
	}
	return nil
}

// getDevicePrefixRefCount: given a prefix of device path, find its reference count from /proc/mounts
// returns the reference count to the device and error code
// for services like iscsi construct multiple device paths with the same prefix pattern.
// this function aggregates all references to a service based on the prefix pattern
// More specifically, this prefix semantics is to aggregate disk paths that belong to the same iSCSI target/iqn pair.
// an iSCSI target could expose multiple LUNs through the same IQN, and Linux iSCSI initiator creates disk paths that start the same prefix but end with different LUN number
// When we decide whether it is time to logout a target, we have to see if none of the LUNs are used any more.
// That's where the prefix based ref count kicks in. If we only count the disks using exact match, we could log other disks out.
func getDevicePrefixRefCount(mounter mount.Interface, deviceNamePrefix string) (int, error) {
	mps, err := mounter.List()
	if err != nil {
		return -1, err
	}

	// Find the number of references to the device.
	refCount := 0
	for i := range mps {
		if strings.HasPrefix(mps[i].Device, deviceNamePrefix) {
			refCount++
		}
	}
	return refCount, nil
}

// utility to tear down a disk based filesystem
func diskTearDown(manager diskManager, c iscsiDiskCleaner, volPath string, mounter mount.Interface) error {
	notMnt, err := mounter.IsLikelyNotMountPoint(volPath)
	if err != nil {
		glog.Errorf("cannot validate mountpoint %s", volPath)
		return err
	}
	if notMnt {
		return os.Remove(volPath)
	}

	refs, err := mount.GetMountRefs(mounter, volPath)
	if err != nil {
		glog.Errorf("failed to get reference count %s", volPath)
		return err
	}
	if err := mounter.Unmount(volPath); err != nil {
		glog.Errorf("failed to unmount %s", volPath)
		return err
	}
	// If len(refs) is 1, then all bind mounts have been removed, and the
	// remaining reference is the global mount. It is safe to detach.
	if len(refs) == 1 {
		mntPath := refs[0]
		if err := manager.DetachDisk(c, mntPath); err != nil {
			glog.Errorf("failed to detach disk from %s", mntPath)
			return err
		}
	}

	notMnt, mntErr := mounter.IsLikelyNotMountPoint(volPath)
	if mntErr != nil {
		glog.Errorf("IsLikelyNotMountPoint check failed: %v", mntErr)
		return err
	}
	if notMnt {
		if err := os.Remove(volPath); err != nil {
			return err
		}
	}
	return nil

}