rootfs_linux.go
func remountReadonly(path string) error {
	for i := 0; i < 5; i++ {
		if err := syscall.Mount("", path, "", syscall.MS_REMOUNT|syscall.MS_RDONLY, ""); err != nil && !os.IsNotExist(err) {
			switch err {
			case syscall.EINVAL:
				// Probably not a mountpoint, use bind-mount
				if err := syscall.Mount(path, path, "", syscall.MS_BIND, ""); err != nil {
					return err
				}
				return syscall.Mount(path, path, "", syscall.MS_BIND|syscall.MS_REMOUNT|syscall.MS_RDONLY|syscall.MS_REC|defaultMountFlags, "")
			case syscall.EBUSY:
				time.Sleep(100 * time.Millisecond)
				continue
			default:
				return err
			}
		}
		return nil
	}
	return fmt.Errorf("unable to mount %s as readonly max retries reached", path)
}
func remountReadonly(path string) error {
	for i := 0; i < 5; i++ {
		if err := syscall.Mount("", path, "", syscall.MS_REMOUNT|syscall.MS_RDONLY, ""); err != nil && !os.IsNotExist(err) {
			switch err {
			case syscall.EINVAL:
				// Probably not a mountpoint, use bind-mount
				if err := syscall.Mount(path, path, "", syscall.MS_BIND, ""); err != nil {
					return err
				}
				return syscall.Mount(path, path, "", syscall.MS_BIND|syscall.MS_REMOUNT|syscall.MS_RDONLY|syscall.MS_REC|defaultMountFlags, "")
			case syscall.EBUSY:
				time.Sleep(100 * time.Millisecond)
				continue
			default:
				return err
			}
		}
		return nil
	}
	return fmt.Errorf("unable to mount %s as readonly max retries reached", path)
}
// remountReadonly will bind over the top of an existing path and ensure that it is read-only.